€¦ · ii minister for mines the hon. george cash, jp, mlc director general k. r. perry director,...

DEPARTMENT OF MINERALS AND ENERGY

GEOLOGICAL SURVEY OF WESTERN AUSTRALIA

RECORD1995/3

COMPILATION OF SHRIMP U–Pb ZIRCONGEOCHRONOLOGY DATA, 1994

by D.R. NELSON

GEOLOGICAL SURVEY OF WESTERN AUSTRALIA

Record 1995/3

COMPILATION OF SHRIMP U–Pb ZIRCONGEOCHRONOLOGY DATA, 1994

by

D. R. Nelson

Perth 1995

ii

MINISTER FOR MINESThe Hon. George Cash, JP, MLC

DIRECTOR GENERALK. R. Perry

DIRECTOR, GEOLOGICAL SURVEY OF WESTERN AUSTRALIAPietro Guj

National Library of Australia Card Number and ISBN 0 7309 6503 1

Reprinted in 1997 with corrected locations for samples 83691, 83676A, 83700A, 83662.

Copies available from:

Mining Information CentreDepartment of Minerals and Energy100 Plain StreetEAST PERTH, WESTERN AUSTRALIA 6004Telephone (08) 9222 3459

Contents

Introduction ................................................................................................................................................................ 1Analytical details .............................................................................................................................................. 3Analytical errors ............................................................................................................................................... 3Abbreviations used ........................................................................................................................................... 3

Acknowledgements .................................................................................................................................................... 4

COLLIER 1:250 000 map sheet91591: porphyritic rhyolite, Tangadee ........................................................................................................................ 5112107: granodiorite, Jillawarra Sub-basin ................................................................................................................ 9

Albany–Fraser Orogen83691: biotite monzogranite gneiss, north of Young River ...................................................................................... 1283701A: biotite monzogranite gneiss, Young River ................................................................................................. 1583702: biotite tonalite gneiss, south of Young River ............................................................................................... 1983696A: biotite monzogranite gneiss, Powell Point ................................................................................................ 2383690: biotite granodiorite gneiss, Bald Rock ......................................................................................................... 2683658: hornblende–biotite granodiorite gneiss, Dalyup Creek ................................................................................ 3083649: granite pegmatite, Lake Gidong headland .................................................................................................... 3383651: biotite–hornblende monzogranite gneiss, Lake Gidong headland ............................................................... 3783652: biotite–hornblende granodiorite gneiss, Lake Gidong headland .................................................................. 4183666: garnet–biotite monzogranite gneiss, Ten Mile Rocks .................................................................................. 4583676A: hornblende syenogranite gneiss, Mount Andrew ...................................................................................... 4983700A: hornblende–biotite syenogranite gneiss, Coramup Hill Quarry ................................................................ 5383697: biotite monzogranite gneiss, Mount Burdett ................................................................................................ 5683659: recrystallized leucogranite, Observatory Point ............................................................................................ 5983657A: porphyritic biotite monzogranite, Esperance Harbour jetty ...................................................................... 6383662: biotite–hornblende monzogranite gneiss, Poison Creek .............................................................................. 6783667: porphyritic biotite granite, Balladonia Rock ................................................................................................ 7183663: granodiorite gneiss, Israelite Bay ................................................................................................................. 75112128: muscovite–biotite–sillimanite paragneiss, Point Malcolm ......................................................................... 78112163: rhyolite, Bandalup ...................................................................................................................................... 82

Eastern Goldfields112110: felsic volcanic rock, Nelson’s Fleet ............................................................................................................ 85112147: porphyritic dacite, Yindi Woolshed ............................................................................................................ 89100710: felsic tuff, Reidy Swamp ............................................................................................................................ 92100726: felsic tuff, Bulong townsite ........................................................................................................................ 96112112: K-feldspar volcanic rock, Jump Up Dam ................................................................................................... 99100758: felsic volcanic breccia, Perkolilli ............................................................................................................. 104104958: dacite, Ballarat – Last Chance .................................................................................................................. 109104964: biotite granodiorite gneiss, Fifty-Mile Tank ............................................................................................. 114104951: porphyry, Black Rabbit Dam .................................................................................................................... 118104975: rhyodacite porphyry, Burton Dam ............................................................................................................ 123112159: porphyritic dacite, Royal Arthur ............................................................................................................... 128104967: quartz–feldspar porphyry, Four Mile Hill ................................................................................................ 132112179: orthogneiss, north of Barret Well ............................................................................................................. 136104970: dacite breccia, Wild Dog Dam ................................................................................................................. 141104963: biotite rhyolite, Penneshaw Formation ..................................................................................................... 146104949C: metatrachyte, Steeple Hill ...................................................................................................................... 150112114: felsic volcanic rock, Ghost Rocks ............................................................................................................ 154104973: metadacite porphyry, east of Liberty Bore ............................................................................................... 158104979: metadacite breccia, Maggies Dam ........................................................................................................... 162104940A: porphyritic metadacite, Bulong Anticline ............................................................................................. 165112151: felsic volcanic rock, north-northeast of Pinjin ......................................................................................... 169101348: biotite monzogranite, Brady Well ............................................................................................................. 17293901: granodiorite, Scotia – Split Rock ............................................................................................................... 176101381: monzogranite, Cement Well – Barber Well .............................................................................................. 17998267: biotite monzogranite, Snot Rocks .............................................................................................................. 18298256: biotite syenogranite, Siberia Battery .......................................................................................................... 185

Paterson Orogen104932: garnet–biotite–muscovite syenogranite gneiss, Sundowner drillhole ...................................................... 188104934: biotite syenogranite gneiss (Green Pygmy) ............................................................................................. 192

iv

112379: biotite monzogranite (augen) gneiss, Split Rock ...................................................................................... 195112397: coarse-grained porphyritic biotite monzogranite (augen) gneiss, Watrara Inlier ..................................... 199104989: muscovite quartzite, Fingoon Quartzite ................................................................................................... 202111854: biotite–muscovite granodiorite gneiss, Poonemerlarra Creek west .......................................................... 205104937: coarse-grained biotite monzogranite, Mount Crofton .............................................................................. 209104938: pegmatite, Coondegoon ............................................................................................................................ 212112341: micromonzogranite (meta-aplite) dyke, Rudall airstrip ........................................................................... 216104980: monzogranite gneiss, Graphite Valley ...................................................................................................... 219112106: foliated monzogranite, Minyari ................................................................................................................ 222111843: biotite–muscovite monzogranite gneiss, Poynton Creek .......................................................................... 226112310: granodiorite gneiss, Dunn Creek west ...................................................................................................... 230113002: granodiorite gneiss, Cotton Creek ............................................................................................................ 234104981: biotite–muscovite monzogranite gneiss, southern part of Graphite Valley .............................................. 237110056: biotite–hornblende granodiorite gneiss, Rooney Creek ........................................................................... 240

Reference ................................................................................................................................................................ 244

Figures

1. Approximate locations of samples for which geochronology data are given in this report ............................. 22. Concordia plot for sample 91591: porphyritic rhyolite, Tangadee ................................................................... 83. Concordia plot for sample 112107: granodiorite, Jillawarra Sub-basin ......................................................... 114. Concordia plot for sample 83691: biotite monzogranite gneiss, north of Young River ................................. 135. Concordia plot for sample 83701A: biotite monzogranite gneiss, Young River ............................................ 166. Concordia plot for sample 83702: biotite tonalite gneiss, south of Young River ........................................... 207. Concordia plot for sample 83696A: biotite monzogranite gneiss, Powell Point ............................................ 248. Concordia plot for sample 83690: biotite granodiorite gneiss, Bald Rock ..................................................... 279. Concordia plot for sample 83658: hornblende–biotite granodiorite gneiss, Dalyup Creek ........................... 31

10. Concordia plot for sample 83649: granite pegmatite, Lake Gidong headland ............................................... 3411. Concordia plot for sample 83651: biotite–hornblende monzogranite gneiss, Lake Gidong headland ........... 3812. Concordia plot for sample 83652: biotite–hornblende granodiorite gneiss, Lake Gidong headland ............. 4213. Concordia plot for sample 83666: garnet–biotite monzogranite gneiss, Ten Mile Rocks .............................. 4614. Concordia plot for sample 83676A: hornblende syenogranite gneiss, Mount Andrew .................................. 5015. Concordia plot for sample 83700A: hornblende-biotite syenogranite gneiss, Coramup Hill Quarry ............ 5416. Concordia plot for sample 83697: biotite monzogranite gneiss, Mount Burdett ............................................ 5717. Concordia plot for sample 83659: recrystallized leucogranite, Observatory Point ........................................ 6018. Concordia plot for sample 83657A: porphyritic biotite monzogranite, Esperance Harbour jetty .................. 6419. Concordia plot for sample 83662: biotite–hornblende monzogranite gneiss, Poison Creek .......................... 6820. Concordia plot for sample 83667: porphyritic biotite granite, Balladonia Rock ............................................ 7221. Concordia plot for sample 83663: granodiorite gneiss, Israelite Bay ............................................................. 7622. Concordia plot for sample 112128: muscovite–biotite–sillimanite paragneiss, Point Malcolm .................... 7923. Concordia plot for sample 112163: rhyolite, Bandalup .................................................................................. 8324. Concordia plot for sample 112110: felsic volcanic rock, Nelson’s Fleet ....................................................... 8825. Concordia plot for sample 112147: porphyritic dacite, Yindi Woolshed ........................................................ 9026. Concordia plot for sample 100710: felsic tuff, Reidy Swamp........................................................................ 9327. Concordia plot for sample 100726: felsic tuff, Bulong townsite .................................................................... 9728. Concordia plot for sample 112112: K-feldspar volcanic rock, Jump Up Dam ............................................. 10029. Concordia plot for sample 100758: felsic volcanic breccia, Perkolilli ......................................................... 10530. Concordia plot for sample 104958: dacite, Ballarat – Last Chance ............................................................. 11131. Concordia plot for sample 104964: biotite granodiorite gneiss, Fifty-Mile Tank ........................................ 11732. Concordia plot for sample 104951: porphyry, Black Rabbit Dam ............................................................... 11933. Concordia plot for sample 104975: rhyodacite porphyry, Burton Dam ....................................................... 12534. Concordia plot for sample 112159: porphyritic dacite, Royal Arthur .......................................................... 12935. Concordia plot for sample 104967: quartz–feldspar porphyry, Four Mile Hill ............................................ 13436. Concordia plot for sample 112179: orthogneiss, north of Barret Well ......................................................... 13737. Concordia plot for sample 104970: dacite breccia, Wild Dog Dam ............................................................. 14338. Concordia plot for sample 104963: biotite rhyolite, Penneshaw Formation ................................................ 14839. Concordia plot for sample 104949C: metatrachyte, Steeple Hill ................................................................. 15240. Concordia plot for sample 112114: felsic volcanic rock, Ghost Rocks ........................................................ 15641. Concordia plot for sample 104973: metadacite porphyry, east of Liberty Bore ........................................... 16042. Concordia plot for sample 104979: metadacite breccia, Maggies Dam ....................................................... 16343. Concordia plot for sample 104940A: porphyritic metadacite, Bulong Anticline ......................................... 16644. Concordia plot for sample 112151: felsic volcanic rock, north-northeast of Pinjin ..................................... 170

v

45. Concordia plot for sample 101348: biotite monzogranite, Brady Well ........................................................ 17346. Concordia plot for sample 93901: granodiorite, Scotia – Split Rock ........................................................... 17747. Concordia plot for sample 101381: monzogranite, Cement Well – Barber Well ......................................... 18048. Concordia plot for sample 98267: biotite monzogranite, Snot Rocks .......................................................... 18349. Concordia plot for sample 98256: biotite syenogranite, Siberia Battery ...................................................... 18650. Concordia plot for sample 104932: garnet–biotite–muscovite syenogranite gneiss,

Sundowner drillhole ...................................................................................................................................... 18951. Concordia plot for sample 104934: biotite syenogranite gneiss (Green Pygmy) ......................................... 19352. Concordia plot for sample 112379: biotite monzogranite (augen) gneiss, Split Rock ................................. 19653. Concordia plot for sample 112397: coarse-grained porphyritic biotite monzogranite (augen) gneiss,

Watrara Inlier ................................................................................................................................................ 20054. Concordia plot for sample 104989: muscovite quartzite, Fingoon Quartzite ............................................... 20355. Concordia plot for sample 111854: biotite–muscovite granodiorite gneiss, Poonemerlarra Creek west ..... 20756. Concordia plot for sample 104937: coarse-grained biotite monzogranite, Mount Crofton .......................... 21057. Concordia plot for sample 104938: pegmatite, Coondegoon ....................................................................... 21358. Concordia plot for sample 112341: micromonzogranite (meta-aplite) dyke, Rudall airstrip ....................... 21759. Concordia plot for sample 104980: monzogranite gneiss, Graphite Valley ................................................. 22060. Concordia plot for sample 112106: foliated monzogranite, Minyari ........................................................... 22461. Concordia plot for sample 111843: biotite–muscovite monzogranite gneiss, Poynton Creek ..................... 22862. Concordia plot for sample 112310: granodiorite gneiss, Dunn Creek west ................................................. 23163. Concordia plot for sample 113002: granodiorite gneiss, Cotton Creek ........................................................ 23564. Concordia plot for sample 104981: biotite–muscovite monzogranite gneiss, southern part of

Graphite Valley ............................................................................................................................................. 23865. Concordia plot for sample 110056: biotite–hornblende granodiorite gneiss, Rooney Creek ....................... 241

Tables

1. Ion microprobe analytical results for sample 91591: porphyritic rhyolite, Tangadee ...................................... 72. Ion microprobe analytical results for sample 112107: granodiorite, Jillawarra Sub-basin ............................ 103. Ion microprobe analytical results for sample 83691: biotite monzogranite, north of Young River ............... 144. Ion microprobe analytical results for sample 83701A: biotite monzogranite, Young River .......................... 175. Ion microprobe analytical results for sample 83702: biotite tonalite gneiss, south of Young River .............. 216. Ion microprobe analytical results for sample 83696A: biotite monzogranite gneiss, Powell Point ............... 257. Ion microprobe analytical results for sample 83690: biotite granodiorite gneiss, Bald Rock ........................ 288. Ion microprobe analytical results for sample 83658: hornblende–biotite granodiorite gneiss,

Dalyup Creek .................................................................................................................................................. 329. Ion microprobe analytical results for sample 83649: granite pegmatite, Lake Gidong headland .................. 35

10. Ion microprobe analytical results for sample 83651: biotite–hornblende monzogranite gneiss,Lake Gidong headland .................................................................................................................................... 39

11. Ion microprobe analytical results for sample 83652: biotite–hornblende granodiorite gneiss,Lake Gidong headland .................................................................................................................................... 43

12. Ion microprobe analytical results for sample 83666: garnet–biotite monzogranite gneiss,Ten Mile Rocks ............................................................................................................................................... 47

13. Ion microprobe analytical results for sample 83676A: hornblende syenogranite gneiss, Mount Andrew ..... 5114. Ion microprobe analytical results for sample 83700A: hornblende–biotite syenogranite gneiss,

Coramup Hill Quarry ...................................................................................................................................... 5515. Ion microprobe analytical results for sample 83697: biotite monzogranite gneiss, Mount Burdett ............... 5816. Ion microprobe analytical results for sample 83659: recrystallized leucogranite, Observatory Point ........... 6117. Ion microprobe analytical results for sample 83657A: porphyritic biotite monzogranite,

Esperance Harbour jetty .................................................................................................................................. 6518. Ion microprobe analytical results for sample 83662: biotite–hornblende monzogranite gneiss,

Poison Creek ................................................................................................................................................... 6919. Ion microprobe analytical results for sample 83667: porphyritic biotite granite, Balladonia Rock ............... 7320. Ion microprobe analytical results for sample 83663: granodiorite gneiss, Israelite Bay ................................ 7721. Ion microprobe analytical results for sample 112128: muscovite–biotite–sillimanite paragneiss,

Point Malcolm ................................................................................................................................................. 8022. Ion microprobe analytical results for sample 112163: rhyolite, Bandalup ..................................................... 8423. Ion microprobe analytical results for sample 112110: felsic volcanic rock, Nelson’s Fleet ........................... 8724. Ion microprobe analytical results for sample 112147: porphyritic dacite, Yindi Woolshed ........................... 9125. Ion microprobe analytical results for sample 100710: felsic tuff, Reidy Swamp ........................................... 9426. Ion microprobe analytical results for sample 100726: felsic tuff, Bulong townsite ....................................... 9827. Ion microprobe analytical results for sample 112112: K-feldspar volcanic rock, Jump Up Dam ................ 10228. Ion microprobe analytical results for sample 100758: felsic volcanic breccia, Perkolilli ............................ 106

vi

29. Ion microprobe analytical results for sample 104958: dacite, Ballarat – Last Chance ................................ 11230. Ion microprobe analytical results for sample 104964: biotite granodiorite gneiss, Fifty-Mile Tank ........... 11631. Ion microprobe analytical results for sample 104951: porphyry, Black Rabbit Dam .................................. 12032. Ion microprobe analytical results for sample 104975: rhyodacite porphyry, Burton Dam .......................... 12633. Ion microprobe analytical results for sample 112159: porphyritic dacite, Royal Arthur ............................. 13034. Ion microprobe analytical results for sample 104967: quartz–feldspar porphyry, Four Mile Hill ............... 13535. Ion microprobe analytical results for sample 112179: orthogneiss, north of Barret Well ............................ 13836. Ion microprobe analytical results for sample 104970: dacite breccia, Wild Dog Dam ................................ 14437. Ion microprobe analytical results for sample 104963: biotite rhyolite, Penneshaw Formation ................... 14938. Ion microprobe analytical results for sample 104949C: metatrachyte, Steeple Hill .................................... 15339. Ion microprobe analytical results for sample 112114: felsic volcanic rock, Ghost Rocks ........................... 15740. Ion microprobe analytical results for sample 104973: metadacite porphyry, east of Liberty Bore .............. 16141. Ion microprobe analytical results for sample 104979: metadacite breccia, Maggies Dam .......................... 16442. Ion microprobe analytical results for sample 104940A: porphyritic metadacite, Bulong Anticline ............ 16843. Ion microprobe analytical results for sample 112151: felsic volcanic rock, north-northeast of Pinjin ........ 17144. Ion microprobe analytical results for sample 101348: biotite monzogranite, Brady Well ........................... 17445. Ion microprobe analytical results for sample 93901: granodiorite, Scotia – Split Rock .............................. 17846. Ion microprobe analytical results for sample 101381: monzogranite, Cement Well – Barber Well ............ 18147. Ion microprobe analytical results for sample 98267: biotite monzogranite, Snot Rocks ............................. 18448. Ion microprobe analytical results for sample 98256: biotite syenogranite, Siberia Battery ......................... 18749. Ion microprobe analytical results for sample 104932: garnet-biotite–muscovite syenogranite gneiss,

Sundowner drillhole ...................................................................................................................................... 19050. Ion microprobe analytical results for sample 104934: biotite syenogranite gneiss (Green Pygmy) ............ 19451. Ion microprobe analytical results for sample 112379: biotite monzogranite (augen) gneiss, Split Rock .... 19752. Ion microprobe analytical results for sample 112397: coarse-grained porphyritic biotite monzogranite

(augen) gneiss, Watrara Inlier ....................................................................................................................... 20153. Ion microprobe analytical results for sample 104989: muscovite quartzite, Fingoon Quartzite .................. 20454. Ion microprobe analytical results for sample 111854: biotite–muscovite granodiorite gneiss,

Poonemerlarra Creek west ............................................................................................................................ 20855. Ion microprobe analytical results for sample 104937: coarse-grained biotite monzogranite,

Mount Crofton .............................................................................................................................................. 21156. Ion microprobe analytical results for sample 104938: pegmatite, Coondegoon .......................................... 21457. Ion microprobe analytical results for sample 112341: micromonzogranite (meta-aplite) dyke,

Rudall airstrip ............................................................................................................................................... 21858. Ion microprobe analytical results for sample 104980: monzogranite gneiss, Graphite Valley .................... 22159. Ion microprobe analytical results for sample 112106: foliated monzogranite, Minyari ............................... 22560. Ion microprobe analytical results for sample 111843: biotite–muscovite granodiorite gneiss,

Poynton Creek ............................................................................................................................................... 22961. Ion microprobe analytical results for sample 112310: granodiorite gneiss, Dunn Creek west .................... 23262. Ion microprobe analytical results for sample 113002: granodiorite gneiss, Cotton Creek ........................... 23663. Ion microprobe analytical results for sample 104981: biotite–muscovite granodiorite gneiss,

southern part of Graphite Valley ................................................................................................................... 23964. Ion microprobe analytical results for sample 110056: biotite–hornblende granodiorite gneiss,

Rooney Creek ............................................................................................................................................... 242

1

Compilation of SHRIMP U–Pb zircongeochronology data, 1994

by

D. R. Nelson

Introduction

In December 1993, a Sensitive High-Resolution Ion MicroProbe (SHRIMP) facility

was commissioned in Western Australia. This instrument is jointly managed and

operated by geoscientists from Curtin University of Technology, the University of

Western Australia and the Geological Survey of Western Australia (GSWA), and will

be largely devoted to the dating of rocks from Western Australia by the U–Pb zircon

method.

This Record is the first in a series of GSWA publications intended to make high-

precision geochronology data on rocks from Western Australia available within twelve

months of their acquisition on the Perth SHRIMP. The localities of the geochronology

samples reported here are shown in Figure 1. The results presented here from the

Eastern Goldfields, obtained between December 1993 and December 1994, form part

of the detailed mapping program undertaken by GSWA geologists in the Eastern

Goldfields over the last ten years. This Record also documents previously unpublished

geochronological results from the Albany–Fraser Orogen (19 samples), the Rudall

Complex (4 samples), and the Bangemall Basin (2 samples), obtained on SHRIMP-1

at the Australian National University (ANU) during the period 1991 to 1993. These

results were obtained as part of a collaborative study with Allen Nutman of the

Research School of Earth Sciences at the ANU. The advice and assistance of Ian

Williams and Bill Compston in this work is gratefully acknowledged.

This Record describes the samples analysed and the analytical results obtained,

and contains some limited discussion of their interpretation. The broader geological

implications of the data presented here will be published elsewhere.

2

Figure 1. Approximate locations of samples for which geochronology data are givenin this report

20 o

114 o 122 o

114 o 122 o

28 o

36 o

o

20 o

28

112106104937

104932104934

112379

112397

112310

111854

110056

104980104981

104938111843

113002

91591

112114

112159

101381

101348

112112112179

112151104973

9825698267104951

93901

104970 104979

100710104967104958

100758

100726

104975112147

104949C112110104940A

104964

10496383676A

83666

83667

83663112128

8369783690

83701A 83691

83658

8365283651

83649 83659

83657A

8370283700A

83696A83662

112163

DN16 3.03.95

400 km

112341,

104989,

112107

3

Analytical details

Unless otherwise indicated, zircons were extracted from about 500 g of sample using

conventional heavy-liquid and magnetic techniques.

In most cases, similar and generally low 204Pb counts were measured on both

standards and unknown samples. Common-Pb corrections have therefore been applied

using the 204Pb correction method and assuming the isotopic composition of Broken

Hill common-Pb. Where this is inapplicable, common-Pb compositions have been

determined using the method of Cumming and Richards (1975). No hydride or excess204Pb corrections were made.

Analyses are listed in the tables in the order in which they were obtained. All

sample numbers are GSWA sample numbers.

Analytical errors

Errors given on individual analyses are based on counting statistics and are at the 1σlevel unless otherwise indicated; those given on pooled analyses are at tσ or 95%

confidence.

A chi-squared test has been applied to grouped analyses. Chi-squared values for

grouped analyses of less than or equal to unity indicate that all scatter about the

weighted mean value determined for the grouped analyses can be accounted for by

analytical sources of error alone. A chi-squared value greater than unity for grouped

analyses indicates that the scatter about the mean value is greater than that attributed

to analytical error and that other (‘geological’) sources of error are present within the

grouped population.

Abbreviations used

(a) Pb*/U = (radiogenic 206Pb)/238U

(b) f206% = 100 × (common 206Pb/total 206Pb)

(c) % concordance = 100 × (206Pb)/238U age)/(207Pb/206Pb age)

4

Acknowledgements

Sample preparation was competently undertaken by John Williams and technical staff

of the GSWA Carlisle Laboratories. Will Libby and John Lewis (GSWA) carried out

many of the petrographic descriptions given in this report. The Perth Consortium

SHRIMP is maintained by Allen Kennedy (Curtin University of Technology). The

GSWA dating program in the Albany–Fraser Orogen benefited from close

collaboration with John Thevissen and David Pearcy of PNC Exploration. Bruce

Harvey (CRA Exploration) provided logistic support and allowed access to drillcore

samples for the dating work undertaken on the Rudall Complex. Thanks are also due

to Ian Garsed (MIM Exploration), Greg Hall (Placer Pacific), David Harley (Western

Mining Corporation), Kevin Johnson (Central Norseman Gold Corporation),

Mike Joyce (Aberfoyle Resources), Peter Kitto (Norgold, Bottle Creek mine),

Bryan Smith and Chris Ringrose (Aztec Mining Company), Paul Roberts (Pasminco),

Ray Twist, John Bunting, and Bob Baxter (North Exploration), Greg Steemson

(Metana Minerals), and Karl Swensson (Poseidon) for allowing access to drillcore for

geochronology sampling in the Eastern Goldfields.

5

91591: porphyritic rhyolite, Tangadee

Location and sampling

COLLIER* (SG 50-4) 118°47’53"E 24°36’38"S

Sampled on 28 May 1988

About 4.2 km bearing 165° from Beggs Hill Telecom Tower, and about 20 km

southwest of Tangadee Homestead. The sample is from the easternmost outcrop of a

number of flow-banded rhyolite occurrences, intercalated with conglomeratic rocks of

the Coobarra Formation.

Tectonic unit/relations

This sample is of a rhyolite within the Coobarra Formation of the Bangemall Group.

Petrographic description

The phenocrysts in this sample were originally β-quartz and sanidine, but these have

been replaced in most cases by α-quartz and microcline respectively, although some

sanidine phenocrysts have been pseudomorphed by intergrowths of microcline and

quartz, and others include rosettes of chlorite. The phenocrysts are commonly

between 0.5 and 1.0 mm across, but may be up to 2 mm across. Some are perfectly

euhedral, the quartz forming bipyramids and the sanidine forming tabular crystals, but

others have strong resorption embayments or are rounded.

The groundmass is essentially a structureless intergrowth of very fine-grained to

cryptocrystalline quartz and microcline, with varying amounts of scattered sericite,

chlorite or biotite.

Irregularly-shaped amygdales, generally less than 1 mm across, infilled with

quartz and microcline, are sparsely distributed throughout the rock, and these

amygdales may also contain chlorite, carbonate or needles of ilmenorutile. Rare

spherulites and thin quartz veins are also present in the groundmass. The groundmass

* Capitalized names refer to standard map sheets.

6

shows no relict igneous textures (counting spherulites and amygdales as structures)

and has probably resulted from devitrification of a glass. GSWA Petrology Report

Number 625.

Zircon morphology

Most of the zircons extracted from this sample are dark, subhedral to anhedral, and

lack obvious internal structure.

Analytical details

This sample was analysed on 26 February 1992 on SHRIMP-1. The counter deadtime

was 20 ns. Analyses were carried out using five-scan data acquisition. Eight analyses

of the SL-13 standard were obtained during the entire session. The Pb*/U calibration

was stationary during the analysis time with an error of 2.32 (1σ%).

Results

Twelve analyses were obtained from 12 zircons. Results are given in Table 1 and

shown on a concordia plot in Figure 2.

Interpretation

Six analyses (5.1, 7.1, 8.1, 10.1, 11.1, and 12.1) have 207Pb/206Pb ratios close to a

single value with little excess scatter (chi-squared = 1.58) indicating an age of

1795 ± 13 Ma. This age is within error of the age obtained for sample 112107 (see

below) and it is likely that these zircons are xenocrysts derived from the granodiorite.

Two analyses (1.1 and 4.1) have higher 207Pb/206Pb ratios and three analyses (3.1, 6.1,

and 9.1) have lower 207Pb/206Pb ratios. Analyses 3.1 and 9.1 have 207Pb/206Pb ratios

corresponding to an age of 1638 ± 14 Ma (chi-squared = 5.27). Although this may

give the time of rhyolite emplacement, a more conservative interpretation of these

results is that this date provides the maximum age for emplacement of the rhyolite, as

there is a possibility that these zircons are also xenocrystic in origin. Alternatively, the

lower 207Pb/206Pb ratios of these analyses compared to the main population may be

7

Table 1. Ion microprobe analytical results for sample 91591: porphyritic rhyolite, Tangadee

Grain U Th Pb ƒ206% 207Pb/206Pb ±1σ 208Pb/206Pb ±1σ 206Pb/238U ±1σ 207Pb/235U ±1σ % 207Pb/206Pb ±1σ.spot (ppm) (ppm) (ppm) concordance Age

1.1 345 43 154 0.07 0.14506 0.00069 0.03402 0.00087 0.4405 0.0104 8.81 0.22 103 2 288 82.1 1 197 827 449 0.05 0.10752 0.00033 0.20080 0.00082 0.3321 0.0077 4.92 0.12 105 1 758 63.1 1 484 687 430 0.25 0.09992 0.00041 0.15220 0.00093 0.2664 0.0062 3.67 0.09 94 1 623 84.1 717 59 270 0.06 0.12360 0.00047 0.02329 0.00066 0.3804 0.0089 6.48 0.16 103 2 009 75.1 434 112 145 0.15 0.11084 0.00066 0.07954 0.00123 0.3252 0.0076 4.97 0.12 100 1 813 116.1 1 143 590 392 0.05 0.10473 0.00032 0.15082 0.00071 0.3171 0.0074 4.58 0.11 104 1 710 67.1 556 217 193 0.02 0.11024 0.00047 0.11352 0.00089 0.3301 0.0077 5.02 0.12 102 1 803 88.1 620 195 201 0.02 0.10952 0.00046 0.09187 0.00081 0.3142 0.0074 4.74 0.12 98 1 791 89.1 1 180 1 360 434 0.20 0.10150 0.00040 0.31961 0.00117 0.2983 0.0069 4.17 0.10 102 1 652 7

10.1 123 83 46 0.02 0.11034 0.00095 0.19207 0.00227 0.3321 0.0080 5.05 0.13 102 1 805 1611.1 616 277 211 0.06 0.10871 0.00048 0.13061 0.00099 0.3201 0.0075 4.80 0.12 101 1 778 812.1 320 321 131 0.05 0.10961 0.00069 0.29784 0.00199 0.3381 0.0080 5.11 0.13 105 1 793 11

8

due to loss of radiogenic Pb. The preferred interpretation of these results is that the

date of 1638 ± 14 Ma from analyses 3.1 and 9.1 represents a maximum age for

emplacement of the rhyolite.

Figure 2. Concordia plot for sample 91591: porphyritic rhyolite, Tangadee

9

112107: granodiorite, Jillawarra Sub-basin


COLLIER (SG 50-4) AMG Zone 51 672470E 7275185N

Geopeko drillhole CD-1, located near the Cadabra prospect; Tray 23, 275.9 m depth,

8 m of 1/2 core.


The granodiorite is believed to form a basement on which conglomeratic sediments of

the Coobarra Formation of the Bangemall Group were deposited, in the Coobarra

Dome area.


The sample is a coarse-grained granodiorite with grains of weakly sericitized

plagioclase (35–40% by volume; vol.%), up to 6 mm in length, and grains of weakly

perthitic feldspar (15–20 vol.%), locally with ‘swapped rims’ where two alkali

feldspar grains are adjacent to each other. Poikilitic biotite flakes up to 5 mm long

enclose feldspars, opaque oxides, and altered pyroxene. The fresh pyroxene in this

rock is orthopyroxene (4 vol.% of the rock), but it is commonly altered to fibrous

clays and actinolite, all as grains commonly 0.4 to 2 mm in size, and is locally

enclosed in poikilitic magnetite grains, together with apatite and zircon. The quartz,

comprising 30 vol.% of the rock, is anhedral with zones of fluid inclusions and

undulose extinction. Myrmekite is common between plagioclase and alkali feldspar.

The alkali feldspar is mostly orthoclase with some areas of microcline twinning, with

exsolution on a fine scale. Veins of chlorite and sericite are common.

Zircon morphology

This sample yielded zircons which are clear, light brown, subhedral to anhedral, up to

150 × 450 µm, and lack obvious internal structure.

10

Table 2. Ion microprobe analytical results for sample 122107: granodiorite, Jillawarra Sub-basin


1.1 352 504 154 0.18 0.10848 0.00078 0.41796 0.00258 0.3306 0.0078 4.95 0.13 104 1 774 132.1 119 235 57 0.13 0.10910 0.00153 0.58199 0.00562 0.3288 0.0080 4.95 0.15 103 1 784 263.1 289 121 104 0.05 0.11084 0.00083 0.12043 0.00170 0.3402 0.0081 5.20 0.13 104 1 813 144.1 147 279 71 0.34 0.11024 0.00182 0.56090 0.00571 0.3312 0.0080 5.03 0.16 102 1 803 305.1 371 933 194 0.01 0.11031 0.00059 0.74199 0.00328 0.3267 0.0077 4.97 0.12 101 1 805 106.1 248 401 110 0.04 0.11004 0.00081 0.47429 0.00314 0.3251 0.0078 4.93 0.13 101 1 800 137.1 105 126 42 0.43 0.10868 0.00186 0.34591 0.00519 0.3165 0.0079 4.74 0.15 100 1 778 318.1 171 376 88 0.02 0.11078 0.00084 0.64979 0.00429 0.3395 0.0082 5.19 0.14 104 1 812 149.1 108 179 49 0.33 0.10851 0.00182 0.46389 0.00563 0.3344 0.0082 5.00 0.16 105 1 775 31

10.1 132 165 57 0.18 0.10923 0.00153 0.35760 0.00431 0.3372 0.0082 5.08 0.15 105 1 787 2511.1 148 242 69 0.02 0.11038 0.00108 0.48382 0.00399 0.3388 0.0082 5.16 0.14 104 1 806 1812.1 119 66 44 0.23 0.10892 0.00153 0.16260 0.00347 0.3373 0.0082 5.07 0.15 105 1 781 2613.1 744 1 330 348 0.33 0.10678 0.00060 0.53606 0.00208 0.3277 0.0077 4.82 0.12 105 1 745 1014.1 164 341 81 0.12 0.11085 0.00137 0.61331 0.00485 0.3335 0.0080 5.10 0.14 102 1 813 221.2 344 485 154 0.09 0.11010 0.00064 0.41538 0.00234 0.3398 0.0080 5.16 0.13 105 1 801 11

15.1 92 107 39 0.13 0.10870 0.00172 0.34422 0.00477 0.3409 0.0083 5.11 0.16 106 1 778 2916.1 379 930 206 -0.01 0.10937 0.00059 0.71525 0.00292 0.3452 0.0081 5.21 0.13 107 1 789 10

11

Analytical details


was 20 ns. Analyses were carried out using five-scan data acquisition. Eight analyses


was stationary during the analysis time with an error of 2.32 (1σ%).

Results

Seventeen analyses were obtained from 16 zircons. Results are given in Table 2 and


Interpretation

Apart from analysis 13.1, which has a lower 207Pb/206Pb ratio and has probably lost

some radiogenic Pb, all analyses plot within error of concordia and have 207Pb/206Pb

ratios within error of a mean value (chi-squared = 0.64) indicating an age of

1797 ± 8 Ma. This is interpreted as the time of granite crystallization.

Figure 3. Concordia plot for sample 112107: granodiorite, Jillawarra Sub-basin

12

83691: biotite monzogranite gneiss,north of Young River


RAVENSTHORPE (SI 51-5) 120°51’E 33°27’S

Sampled on 20 March 1991

North of Young River.


This sample is of an orthogneiss within the Biranup Complex of the Albany–Fraser

Orogen. This rock is derived from a medium- and even-grained monzogranite with

tightly-folded pegmatite veins. A foliation has developed parallel to the axial planes of

these folds. The sample, taken from a homogeneous part of the rock, is moderately

foliated and partially recrystallized to amphibolite facies.


The sample consists of large igneous grains of microcline, oligoclase, and quartz, with

abundant recrystallized quartz and lesser amounts of biotite, myrmekite, calcite, and

feldspar that have formed a fine-grained intergranular mosaic. Muscovite, opaques,

sphene, apatite, and zircon are accessory minerals. GSWA Petrology Report Number

1604.

Zircon morphology

This sample contains zircons that are colourless to light green-brown, euhedral to

rounded, and equant to elongate, averaging 70 × 250 µm. Some grains are elliptical in

shape and multifaceted. Euhedral igneous zonation is also apparent in some zircons.

Rims and cores can be distinguished in many cases.

13

Analytical details

This sample was analysed on 23 and 24 February 1992 on SHRIMP-1. The counterdeadtime was 20 ns. Analyses were carried out using five-scan data acquisition.Fifteen analyses of the SL-13 standard were obtained during the entire session. ThePb*/U calibration was stationary during the analysis time with an error of 2.42 (1σ%).

Results

Fourteen analyses were obtained from 14 zircons. Results are given in Table 3 andshown on a concordia plot in Figure 4.

Interpretation

Twelve of the analyses have 207Pb/206Pb ratios close to a single value with littleexcess scatter (chi-squared = 2.34), corresponding to an age of 2631 ± 8 Ma, which isinterpreted as the time of crystallization of the granite protolith of the orthogneiss.Two analyses (9.1 and 14.1) have lower 207Pb/206Pb ratios than those of the mainpopulation and indicate some radiogenic Pb loss.

Figure 4. Concordia plot for sample 83691: biotite monzogranite gneiss, north ofYoung River

14

Table 3. Ion microprobe analytical results for sample 83691: biotite monzogranite gneiss, north of Young River


1.1 241 150 134 0.20 0.17515 0.00119 0.16537 0.00225 0.4809 0.0120 11.61 0.31 97 2 607 112.1 892 2 081 659 0.03 0.17799 0.00052 0.64478 0.00188 0.4695 0.0115 11.52 0.29 94 2 634 53.1 256 134 139 0.11 0.17822 0.00106 0.14655 0.00178 0.4749 0.0118 11.67 0.31 95 2 636 104.1 324 270 183 0.09 0.17637 0.00108 0.21518 0.00219 0.4713 0.0117 11.46 0.30 95 2 619 105.1 779 1 258 515 0.05 0.17814 0.00055 0.45391 0.00159 0.4692 0.0115 11.53 0.29 94 2 636 56.1 255 114 134 0.08 0.17804 0.00150 0.12301 0.00298 0.4687 0.0117 11.51 0.31 94 2 635 147.1 329 165 170 0.15 0.17575 0.00087 0.08892 0.00131 0.4723 0.0117 11.44 0.30 95 2 613 88.1 243 152 134 0.27 0.17533 0.00120 0.17152 0.00230 0.4702 0.0117 11.37 0.30 95 2 609 119.1 848 138 415 0.06 0.17404 0.00052 0.04424 0.00059 0.4663 0.0114 11.19 0.28 95 2 597 5

10.1 280 103 140 -0.02 0.17652 0.00095 0.08870 0.00134 0.4597 0.0114 11.19 0.29 93 2 620 911.1 410 130 222 0.04 0.17921 0.00076 0.08924 0.00109 0.4946 0.0122 12.22 0.31 98 2 646 712.1 84 127 57 0.58 0.17466 0.00242 0.41361 0.00623 0.4876 0.0129 11.74 0.37 98 2 603 2313.1 406 108 213 0.09 0.17920 0.00076 0.07406 0.00100 0.4851 0.0119 11.99 0.31 96 2 646 714.1 565 204 188 1.10 0.16294 0.00141 0.11080 0.00295 0.2933 0.0072 6.59 0.18 67 2 486 15

15

83701A: monzogranite gneiss, Young River




Young River.



Orogen. This rock comprises heterogeneous, grey, biotite-rich tonalitic gneiss, and a

younger phase of coarse, even-grained leucocratic monzogranite gneiss with biotite

clots (?after former orthopyroxene and/or garnet). The sample is of the leucocratic

monzogranite gneiss phase.


The sample consists of a coarse-grained, moderately foliated, granoblastic assemblage

of quartz, oligoclase, microcline, and biotite with accessory apatite, opaque oxides,

muscovite, hornblende, and zircon. GSWA Petrology Report Number 1604.

Zircon morphology

The zircons recovered from this sample are dark green-brown, subhedral, and

elongate, averaging 100 × 350 µm. Most are strongly metamict and are extensively

cracked. A few have colourless, structureless, radially cracked rims.

Analytical details

This sample was analysed on 28 and 29 February, 1992 on SHRIMP-1. The counter

deadtime was 20 ns. Analyses were carried out using five-scan data acquisition.

16

Eleven analyses of the SL-13 standard were obtained during the entire session. The

Pb*/U calibration was stationary during the analysis time with an error of 2.27 (1σ%).

Results

Ten analyses were obtained from 10 zircons. Results are given in Table 4 and shown

on a concordia plot in Figure 5.

Interpretation

No consistent differences were apparent in 207Pb/206Pb ratios determined on rim or

core zircon. Five analyses (1.1, 3.1, 5.1, 7.1, and 9.1) have 207Pb/206Pb ages close to a

single value with little excess scatter (chi-squared = 1.49) and corresponding to an age

Figure 5. Concordia plot for sample 83701A: monzogranite gneiss, Young River

17

Table 4. Ion microprobe analytical results for sample 83701A: monzogranite gneiss, Young River


1.1 61 28 37 1.55 0.17497 0.00324 0.10657 0.0068 0.52834 0.0133 12.75 0.42 105 2 606 312.1 254 387 146 0.32 0.17789 0.00092 0.12422 0.0016 0.50551 0.0118 12.40 0.30 100 2 633 93.1 3 341 1 227 1754 0.03 0.17203 0.00021 0.10285 0.0003 0.47802 0.0109 11.34 0.26 98 2 577 24.1 305 370 171 0.61 0.17622 0.00104 0.13442 0.0021 0.48806 0.0114 11.86 0.29 98 2 618 105.1 353 431 191 0.80 0.17285 0.00106 0.10705 0.0021 0.47847 0.0111 11.40 0.28 97 2 585 106.1 972 566 556 0.48 0.17652 0.00055 0.18626 0.0011 0.48025 0.0110 11.69 0.27 96 2 620 57.1 371 1 080 194 2.32 0.16888 0.00152 0.23237 0.0034 0.40448 0.0094 9.42 0.24 86 2 547 158.1 413 174 214 0.14 0.17561 0.00068 0.06264 0.0009 0.48500 0.0112 11.74 0.28 98 2 612 69.1 478 849 197 1.69 0.17276 0.00136 0.20360 0.0030 0.33004 0.0076 7.86 0.20 71 2 585 13

10.1 2 031 184 1059 0.04 0.18047 0.00028 0.02477 0.0003 0.50222 0.0115 12.50 0.29 99 2 657 3

18

of 2577 ± 9 Ma. The remaining five analyses have higher 207Pb/206Pb ratios than the

main population, but do not form a coherent group. One possible interpretation of

these results is that all of the analyses are of metamorphically disturbed zones. If this

is the case, then the best estimate of the minimum age of crystallization of the granite

protolith of the gneiss is 2657 ± 3 Ma, as indicated by analysis 10.1. The preferred

interpretation of these results is that the date of 2577 ± 9 Ma indicated by the main

population of analyses represents a minimum age of crystallization for the granite

protolith of this orthogneiss.

19

83702: biotite tonalite gneiss,south of Young River



Sampled on 18 April 1991

South of Young River.



Orogen. This rock represents the main tonalitic phase of a heterogeneous granitoid

gneiss that includes the monzogranitic phase represented by sample 83701A.


The sample is coarse-grained, moderately foliated and granoblastic, and consists of

quartz, calcic oligoclase, biotite, minor opaques, and apatite, with accessory

microcline, muscovite, allanite, and zircon. GSWA Petrology Report Number 1604.

Zircon morphology

The zircons recovered from this sample are dark green-brown, subhedral and

elongate, averaging 75 × 350 µm. Most have euhedral igneous zoning and are highly

metamict. Many (e.g. grain 6) have colourless, structureless, multifaceted, and

radially cracked rims.

Analytical details

This sample was analysed on 28 and 29 February 1992 on SHRIMP-1. The counter


20


Pb*/U calibration was stationary during the analysis time with an error of 2.27 (1σ%).

Results

Eleven analyses were obtained from 10 zircons. Results are given in Table 5 and


Interpretation

The analyses do not form a single coherent population and it is not possible to derive

a precise crystallization age. A date of 2639 ± 37 Ma, obtained by pooling the three

most concordant 207Pb/206Pb analyses (3.1, 4.1, and 6.2; chi-squared = 6.45), is

Figure 6. Concordia plot for sample 83702: biotite tonalite gneiss, south of Young River

21

Table 5. Ion microprobe analytical results for sample 83702: biotite tonalite gneiss, south of Young River


1.1 517 55 191 0.09 0.14920 0.00064 0.02781 0.00082 0.3638 0.0084 7.48 0.18 86 2 337 72.1 337 96 193 5.52 0.16796 0.00245 0.15038 0.00551 0.4255 0.0099 9.85 0.29 90 2 537 243.1 620 116 320 0.04 0.17975 0.00049 0.05203 0.00051 0.4857 0.0112 12.04 0.28 96 2 651 54.1 982 197 501 0.00 0.17805 0.00040 0.05472 0.00043 0.4809 0.0110 11.81 0.28 96 2 635 45.1 225 212 75 0.55 0.15532 0.00142 0.10189 0.00276 0.3031 0.0071 6.49 0.17 71 2 405 166.1 73 101 20 0.32 0.07668 0.00369 0.40047 0.01004 0.2157 0.0053 2.28 0.13 113 1 113 967.1 500 97 225 0.22 0.16970 0.00071 0.04761 0.00110 0.4269 0.0099 9.99 0.24 90 2 555 78.1 476 126 197 0.27 0.16534 0.00084 0.07716 0.00150 0.3837 0.0089 8.75 0.21 83 2 511 99.1 679 578 152 5.11 0.12051 0.00282 0.25394 0.00660 0.1617 0.0037 2.69 0.09 49 1 964 42

10.1 149 140 71 0.27 0.17124 0.00125 0.17665 0.00242 0.4067 0.0096 9.60 0.25 86 2 570 126.2 162 100 89 0.18 0.17526 0.00117 0.16007 0.00218 0.4779 0.0113 11.55 0.29 97 2 609 11

22

considered to represent a minimum age for crystallization of the granite protolith of

this gneiss. The much younger 207Pb/206Pb age of analysis 6.1, on the rim of a grain

with an Archaean-age core, suggests that this sample was metamorphosed during the

middle Proterozoic.

23

83696A: biotite monzogranite gneiss, Powell Point




North of Powell Point.



Orogen. This rock was taken from a coarse, even-grained, biotite-rich monzogranite

containing scattered K-feldspar phenocrysts. The sample is coarse-grained, with a

granoblastic metamorphic texture.


The sample consists of quartz, oligoclase, microcline, and biotite, with lesser

magnetite, and abundant accessory apatite, sphene, and zircon, and a trace of

metamict allanite. GSWA Petrology Report Number 1604.

Zircon morphology

The zircons recovered from this sample are colourless to dark brown, subhedral to

anhedral, and equant to elongate, with a wide range of sizes up to 150 × 600 µm.

Euhedral igneous zonation is common.

Analytical details


deadtime was 5 ns. Analyses were carried out using five-scan data acquisition. Fifteen

analyses of the SL-13 standard were obtained during the entire session. The Pb*/U

calibration was stationary during the analysis time with an error of 2.42 (1σ%).

24

Results

Fourteen analyses were obtained from 14 zircons. Results are given in Table 6 and


Interpretation

Thirteen of the analyses scatter about a mean 207Pb/206Pb ratio (chi-squared = 8.62)

corresponding to a date of 2595 ± 11 Ma, which is interpreted as the minimum age of

primary crystallization of the granite. Analysis 8.1, which is more discordant and

clearly older than the other analyses, may be of a xenocrystic zircon.

Figure 7. Concordia plot for sample 83696A: biotite monzogranite gneiss, Powell Point

25

Table 6. Ion microprobe analytical results for sample 83696A: biotite monzogranite gneiss, Powell Point


1.1 417 546 250 0.04 0.17536 0.00073 0.37347 0.00189 0.4487 0.0110 10.85 0.28 92 2 609 72.1 788 212 399 0.22 0.17405 0.00059 0.09096 0.00094 0.4612 0.0112 11.07 0.28 94 2 597 63.1 450 272 222 0.36 0.17293 0.00109 0.19233 0.00225 0.4156 0.0102 9.91 0.26 87 2 586 114.1 385 233 207 0.18 0.17472 0.00093 0.18335 0.00185 0.4582 0.0113 11.04 0.29 93 2 603 95.1 460 400 273 0.18 0.17575 0.00076 0.25104 0.00162 0.4805 0.0118 11.64 0.30 97 2 613 76.1 802 110 389 0.04 0.17293 0.00049 0.03776 0.00057 0.4649 0.0113 11.09 0.28 95 2 586 57.1 144 136 84 -0.13 0.18003 0.00431 0.26771 0.00983 0.4686 0.0120 11.63 0.43 93 2 653 408.1 680 531 309 0.18 0.18345 0.00088 0.25402 0.00185 0.3645 0.0089 9.22 0.24 75 2 684 89.1 474 286 261 0.13 0.17527 0.00068 0.17655 0.00123 0.4715 0.0116 11.39 0.29 95 2 609 6

10.1 291 207 158 0.01 0.17534 0.00079 0.18397 0.00139 0.4641 0.0115 11.22 0.29 94 2 609 811.1 874 123 424 0.19 0.17428 0.00053 0.04522 0.00079 0.4592 0.0112 11.04 0.27 94 2 599 512.1 1 185 769 570 0.20 0.17089 0.00048 0.18377 0.00094 0.4099 0.0100 9.66 0.24 86 2 566 513.1 759 1 068 490 0.04 0.17676 0.00050 0.40484 0.00136 0.4730 0.0115 11.53 0.29 95 2 623 514.1 998 65 465 0.00 0.17209 0.00044 0.01802 0.00022 0.4555 0.0111 10.81 0.27 94 2 578 4

26

83690: biotite granodiorite gneiss, Bald Rock




Near Bald Rock.



Orogen. This rock is a homogeneous portion of a heterogeneous, pegmatite-banded

gneiss, largely derived from a medium, even-grained granodiorite. It is coarse grained,

granoblastic, moderately foliated, and was metamorphosed at medium grade.


This sample is composed of quartz, oligoclase, minor microcline, and biotite, with

accessory muscovite, apatite, and rare zircon. GSWA Petrology Report Number 1604.

Zircon morphology

The zircons from this sample are colourless to dark brown, subhedral, equant to

elongate, and have euhedral igneous zonation. A few grains (e.g. grains 6, 10, and 16)

are clear, equant, and lack igneous zonation. Grain 10 is small (approximately 100 µm

in diameter) and rounded, and has a partially intact rim. Grain 15 is considerably

larger (approximately 400 µm long) than most of the other grains from this sample

(average length 250 µm), and is dark and strongly metamict with an unzoned core

surrounded by a corroded rim.

27

Analytical details


was 20 ns. Analyses were carried out using five-scan data acquisition. Seven analyses


was stationary during the analysis time with an error on Pb*/U of 2.97 (1σ%).

Results

Nineteen analyses were obtained from 16 zircons. Results are given in Table 7 and

shown on a concordia diagram in Figure 8.

Figure 8. Concordia plot for sample 83690: biotite granodiorite gneiss, Bald Rock

28

Table 7. Ion microprobe analytical results for sample 83690: biotite granodiorite gneiss, Bald Rock


1.1 494 573 92 0.028 0.08659 0.00225 0.25297 0.00542 0.1481 0.0044 1.769 0.074 66 1 351 502.1 489 614 76 0.006 0.08548 0.00121 0.15539 0.00286 0.1427 0.0043 1.681 0.058 65 1 326 273.1 428 492 92 0.014 0.08405 0.00157 0.23249 0.00383 0.1814 0.0054 2.103 0.078 83 1 294 364.1 506 365 111 0.017 0.08165 0.00160 0.13304 0.00372 0.1985 0.0059 2.234 0.084 94 1 237 385.1 325 587 71 0.001 0.08657 0.00103 0.16347 0.00248 0.2012 0.0060 2.402 0.081 87 1 351 236.1 237 133 83 0.004 0.10248 0.00116 0.16031 0.00267 0.3192 0.0096 4.511 0.151 107 1 670 217.1 419 440 96 0.002 0.08423 0.00083 0.13905 0.00195 0.2156 0.0064 2.504 0.082 97 1 298 198.1 205 167 52 0.005 0.08310 0.00158 0.22008 0.00398 0.2222 0.0067 2.546 0.096 102 1 272 379.1 434 187 101 0.004 0.08454 0.00106 0.12646 0.00244 0.2201 0.0066 2.566 0.087 98 1 305 24

10.1 126 77 80 0.001 0.18364 0.00145 0.17107 0.00285 0.5403 0.0166 13.681 0.446 104 2 686 1311.1 299 252 68 0.005 0.08283 0.00128 0.12064 0.00294 0.2166 0.0065 2.473 0.088 100 1 265 3012.1 276 176 69 0.003 0.08387 0.00097 0.20666 0.00254 0.2242 0.0067 2.593 0.087 101 1 289 2213.1 263 370 46 0.012 0.08342 0.00232 0.19344 0.00555 0.1533 0.0046 1.763 0.077 72 1 279 5414.1 357 998 63 0.027 0.08618 0.00278 0.30034 0.00679 0.1356 0.0041 1.611 0.075 61 1 342 6215.1 155 18 89 0.005 0.19860 0.00141 0.03148 0.00238 0.5333 0.0162 14.605 0.469 98 2 815 1216.1 260 601 75 0.009 0.10163 0.00153 0.22379 0.00371 0.2476 0.0074 3.469 0.122 86 1 654 288.2 219 175 61 0.000 0.08433 0.00075 0.23091 0.00230 0.2446 0.0074 2.844 0.092 108 1 300 178.3 398 191 97 0.003 0.08402 0.00076 0.13840 0.00177 0.2290 0.0068 2.653 0.086 103 1 293 18

12.2 434 632 66 0.026 0.08293 0.00274 0.29458 0.00667 0.1187 0.0036 1.357 0.064 57 1 268 64

29

Interpretation

Fifteen analyses have 207Pb/206Pb ratios within error of a single value (chi-squared =

0.86) corresponding to an age of 1299 ± 14 Ma, which is interpreted as the time of

crystallization of the granite protolith of the gneiss. Many of the analyses in this main

group are highly discordant, indicating the recent loss of a substantial proportion of

accumulated radiogenic Pb. Analyses obtained from four zircons indicate the presence

of xenocrystic zircon. Analyses 10.1 and 15.1, both of cores, gave Archaean zircon-

crystallization ages, whereas analyses 6.1 and 16.1 indicate middle Proterozoic ages.

30

83658: hornblende–biotite granodiorite gneiss,Dalyup Creek


ESPERANCE – MONDRAIN ISLAND (SI 51-6, 10) 121°35’E 33°43’S


Dalyup Creek, north side of Highway 1.



Orogen. This rock preserves a relict porphyritic texture that has been moderately

foliated and folded at amphibolite facies metamorphic grade.


The sample consists of alternating leucocratic layers of oligoclase (An27), orthoclase,

and quartz, and melanocratic layers rich in biotite and hornblende. Accessory minerals

include zircon, sphene, magnetite, apatite, and metamict allanite. GSWA Petrology

Report Number 1556.

Zircon morphology

The zircons from this sample are light brown with abundant opaque inclusions,

euhedral to subhedral, equant to elongate, generally large (ranging in size up to 300 ×

600 µm), and have euhedral igneous zonation. No rims or cores were identified.

Analytical details


deadtime was 22 ns. Analyses were carried out using five-scan data acquisition for

analyses 1.1, 2.1, and 3.1 and six scans for all other analyses. Thirteen analyses of the

31

SL-13 standard were obtained during the entire session. The Pb*/U calibration was

mobile during the analysis time so the Pb*/U of unknown samples has been corrected

using bracketing standard analyses, with an error on Pb*/U for the entire session of

2.19 (1σ%).

Results

Thirteen analyses were obtained from 12 individual zircons. Results are given in Table

8 and shown on a concordia plot in Figure 9.

Interpretation

All analyses form a single coherent population falling within error of concordia and

defining a 207Pb/206Pb age of 1692 ± 22 Ma (chi-squared = 0.96). This is interpreted

as the age of crystallization of the granodiorite precursor to the gneiss.

Figure 9. Concordia plot for sample 83658: hornblende–biotite granodiorite gneiss,Dalyup Creek

32

Table 8. Ion microprobe analytical results for sample 83658: hornblende–biotite granodiorite gneiss, Dalyup Creek


1.1 131 105 44 0.56 0.09980 0.00258 0.21826 0.00624 0.2905 0.0068 4.00 0.15 101 1 620 482.1 55 82 18 1.06 0.10301 0.00461 0.27782 0.01145 0.2725 0.0069 3.87 0.21 93 1 679 833.1 200 128 64 0.04 0.10464 0.00150 0.19031 0.00356 0.2851 0.0065 4.11 0.12 95 1 708 264.1 124 121 44 0.09 0.10400 0.00150 0.27701 0.00417 0.2958 0.0068 4.24 0.12 98 1 697 275.1 155 207 55 0.32 0.10471 0.00176 0.26217 0.00448 0.2980 0.0068 4.30 0.13 98 1 709 316.1 180 152 53 1.38 0.09866 0.00233 0.06279 0.00512 0.2823 0.0064 3.84 0.13 100 1 599 447.1 44 31 14 0.15 0.10748 0.00281 0.21023 0.00684 0.2792 0.0070 4.14 0.16 90 1 757 488.1 155 167 53 0.09 0.10437 0.00139 0.28990 0.00388 0.2867 0.0066 4.12 0.12 95 1 703 259.1 114 143 40 0.37 0.10461 0.00196 0.32331 0.00539 0.2843 0.0066 4.10 0.13 94 1 708 341.2 146 128 51 0.55 0.10247 0.00240 0.24030 0.00587 0.2977 0.0069 4.21 0.15 101 1 669 43

10.1 84 69 29 0.11 0.10548 0.00192 0.23328 0.00494 0.2955 0.0070 4.30 0.14 97 1 723 3311.1 37 24 12 0.43 0.10103 0.00466 0.17878 0.01090 0.2829 0.0074 3.94 0.22 98 1 643 8612.1 121 109 43 0.39 0.10222 0.00171 0.24075 0.00437 0.3015 0.0069 4.25 0.13 102 1 665 31

33

83649: granite pegmatite, Lake Gidong headland




Headland south of Lake Gidong.


This sample is from a pegmatite dyke within the Biranup Complex of the Albany–

Fraser Orogen. This folded pegmatite dyke intrudes monzogranite gneiss and

granodioritic gneiss (represented by samples 83651 and 83652 respectively) and a

metagabbro dyke.


The sample consists mainly of plagioclase (oligoclase), quartz, and orthoclase, with

accessory biotite, muscovite, Fe-oxides, sulfides, zircon, and rare apatite. GSWA

Petrology Report Number 1556.

Zircon morphology

The zircons recovered from this sample are dark brown, subhedral and elongate to

equant, ranging in size up to 300 × 500 µm. Most grains are extensively cracked and

have opaque inclusions. Euhedral cores and rims with igneous zoning can be

distinguished in many grains.

Analytical details

This sample was analysed on 28 January 1991 on SHRIMP-1. The counter deadtime

was 22 ns. Analyses were carried out using six-scan data acquisition. Six analyses of

the SL-13 standard were obtained during the entire session. The Pb*/U calibration was

34

stationary during the analysis time with an error for the analysis period of this sample

of 2.80 (1σ%).

Results

A total of 16 analyses were obtained from 14 zircons. Results are given in Table 9 and


Figure 10. Concordia plot for sample 83649: granite pegmatite, Lake Gidong headland

35

Table 9. Ion microprobe analytical results for sample 83649: granite pegmatite, Lake Gidong headland


1.1 838 328 247 0.19 0.10154 0.00060 0.11989 0.00128 0.2792 0.0079 3.909 0.115 96 1 652 112.1 715 596 245 0.10 0.10195 0.00063 0.23048 0.00163 0.2978 0.0084 4.187 0.124 101 1 660 113.1 1 770 20 350 0.33 0.08068 0.00048 0.00230 0.00091 0.2099 0.0059 2.334 0.069 101 1 214 124.1 171 6 033 1.04 0.08361 0.00312 0.01885 0.00689 0.1978 0.0057 2.280 0.113 91 1 283 735.1 1 161 32 243 1.39 0.07898 0.00109 0.01272 0.00239 0.2114 0.0059 2.302 0.075 106 1 172 275.2 224 13 876 0.49 0.10018 0.00156 0.16655 0.00363 0.3077 0.0088 4.250 0.145 106 1 627 296.1 1 288 110 257 0.06 0.07937 0.00041 0.02365 0.00064 0.2098 0.0059 2.296 0.067 104 1 181 107.1 122 5 25 0.60 0.07824 0.00234 -0.00017 0.00480 0.2139 0.0061 2.308 0.101 108 1 153 598.1 104 9 18 1.21 0.07611 0.00599 -0.00370 0.01349 0.1822 0.0053 1.912 0.167 98 1 098 1589.1 1 903 31 260 0.63 0.07331 0.00073 0.00232 0.00152 0.1442 0.0040 1.457 0.045 85 1 023 20

10.1 1 374 21 270 0.01 0.07922 0.00035 0.00441 0.00037 0.2110 0.0059 2.305 0.067 105 1 178 911.1 2 616 27 571 11.43 0.07432 0.00243 0.00401 0.00559 0.1557 0.0044 1.596 0.073 89 1 050 6610.2 1 703 20 347 0.04 0.07978 0.00035 0.00275 0.00042 0.2188 0.0061 2.407 0.070 107 1 192 912.1 3 271 31 378 0.34 0.06435 0.00049 0.00188 0.00098 0.1243 0.0035 1.102 0.033 100 753 1613.1 1 341 9 265 0.02 0.07959 0.00037 0.00221 0.00035 0.2124 0.0060 2.331 0.068 105 1 187 914.1 5 084 99 738 3.63 0.06425 0.00098 0.01384 0.00223 0.1363 0.0038 1.207 0.041 110 750 32

36

Interpretation

Three analyses of cores (1.1, 2.1, and 5.2) have 207Pb/206Pb ages within error of a

mean value (chi-squared = 0.50) of 1654 ± 28 Ma. This age is similar to those

obtained for the monzogranite and granodioritic gneiss (represented by samples 83651

and 83652 respectively; see below), which the pegmatite dyke intrudes. The main

population, consisting of ten analyses of rim zircon, has a mean 207Pb/206Pb age of

1187 ± 12 Ma (chi-squared = 1.48). This is interpreted as the crystallization age of the

pegmatite dyke. Three analyses (9.1, 12.1, and 14.1) have younger 207Pb/206Pb ages,

which may be the result of non-zero age-loss of radiogenic Pb.

37

83651: biotite–hornblende monzogranite gneiss,Lake Gidong headland







Orogen. This pegmatite-banded gneiss is intimately associated with the more

homogeneous biotite–hornblende granodiorite gneiss (see 83652 below). Both gneiss

phases are highly deformed and are cut by deformed to relatively undeformed

pegmatite dykes (such as that represented by 83649).


The principal minerals in this sample are hornblende, biotite, plagioclase (about

An25), quartz, orthoclase, and minor (and perhaps secondary) muscovite. Accessory

minerals include titanite, magnetite (secondary), apatite, and zircon. GSWA Petrology

Report Number 1556.

Zircon morphology

Most of the zircons extracted from this sample are light brown, subhedral, and

elongate, averaging 150 × 350 µm, and have pronounced igneous zoning. A few

grains have dark cores.

38

Analytical details


deadtime was 22 ns. Analyses were carried out using six-scan data acquisition.

Thirteen analyses of the SL-13 standard were obtained during the entire session. The

Pb*/U calibration was mobile during the analysis time so the Pb*/U of the unknown

samples has been corrected using bracketing standard analyses, with an error on

Pb*/U of standard analyses for the entire session of 2.19 (1σ%).

Results

Sixteen analyses were made of 16 zircons. Results are given in Table 10 and shown on

a concordia plot in Figure 11.

Figure 11. Concordia plot for sample 83651: biotite–hornblende monzogranite gneiss,Lake Gidong headland

39

Table 10. Ion microprobe analytical results for sample 83651: biotite–hornblende monzogranite gneiss, Lake Gidong headland


1.1 34 32 11 1.798 0.08742 0.00638 0.24395 0.01567 0.2578 0.0068 3.107 0.251 108 1 370 1412.1 240 113 76 0.618 0.10038 0.00148 0.17049 0.00346 0.2831 0.0064 3.918 0.111 99 1 631 273.1 247 301 73 0.127 0.10274 0.00113 0.33547 0.00342 0.2390 0.0053 3.385 0.088 83 1 674 204.1 5 328 2 183 984 0.093 0.08117 0.00023 0.12407 0.00053 0.1776 0.0039 1.987 0.045 86 1 226 65.1 623 319 162 0.292 0.09750 0.00075 0.14789 0.00172 0.2399 0.0053 3.225 0.078 88 1 577 146.1 161 224 61 -0.001 0.10290 0.00096 0.41141 0.00383 0.2900 0.0066 4.115 0.105 98 1 677 177.1 348 433 102 0.392 0.10260 0.00119 0.22235 0.00298 0.2539 0.0056 3.592 0.095 87 1 672 218.1 213 63 60 0.245 0.10227 0.00149 0.08848 0.00306 0.2736 0.0062 3.858 0.109 94 1 666 279.1 192 81 56 0.189 0.09925 0.00123 0.09541 0.00252 0.2843 0.0064 3.890 0.105 100 1 610 23

10.1 829 504 258 0.073 0.10143 0.00052 0.15857 0.00118 0.2862 0.0063 4.002 0.093 98 1 650 911.1 750 1 024 259 0.220 0.10079 0.00063 0.34203 0.00191 0.2754 0.0061 3.827 0.091 96 1 639 1212.1 250 350 50 0.841 0.10137 0.00255 0.23342 0.00617 0.1684 0.0038 2.354 0.084 61 1 649 4713.1 324 228 105 0.196 0.10212 0.00102 0.18973 0.00245 0.2893 0.0065 4.073 0.104 98 1 663 1814.1 1 188 955 418 0.046 0.10351 0.00039 0.22263 0.00104 0.3078 0.0068 4.392 0.100 102 1 688 715.1 585 604 215 0.029 0.10417 0.00053 0.29145 0.00165 0.3050 0.0068 4.381 0.102 101 1 700 916.1 498 1 260 182 2.423 0.10350 0.00190 0.41764 0.00490 0.2604 0.0058 3.716 0.113 88 1 688 34

40

Interpretation

The main population, excluding analyses 4.1 and 5.1, which have significantly lower207Pb/206Pb ratios, has a pooled 207Pb/206Pb age of 1671 ± 16 Ma (chi-squared =

3.04). This is interpreted as the age of crystallization of the granitic protolith of the

gneiss. The younger 207Pb/206Pb ages of analyses 4.1 and 5.1 may reflect disturbance

of the U–Pb systems of these zircons (or, in the case of 4.1, possibly crystallization of

newly formed zircon) during the event associated with the intrusion of the

granodiorite pegmatite dyke (83649).

41

83652: biotite–hornblende granodiorite gneiss,Lake Gidong headland







Orogen. This is the main rock type at this locality and along the coast as far as Butty

Head, 40 km to the east. It is intimately associated with the monzogranite gneiss

(represented by 83651); both rock types contain remnants of amphibolite dykes.


The principal minerals in this sample are oligoclase (about An25), quartz, orthoclase,

hornblende, and biotite. Accessory minerals present are zircon, apatite, titanite,

magnetite, and allanite. GSWA Petrology Report Number 1556.

Zircon morphology

Relatively few zircons were obtained from this sample. Most are colourless to dark

brown, anhedral (with distinctly rounded terminations), and elongate, ranging in size

up to 150 × 450 µm. Some grains (e.g. grain 5) have distinguishable cores and rims.

Analytical details


deadtime was 22 ns. Analyses were carried out using seven-scan data acquisition for

analyses 1.1, 2.1, 3.1, 4.1, 1.2, 5.1, 6.1, and 2.2, and six-scan acquisition for the

42

remaining analyses. Thirteen analyses of the SL-13 standard were obtained during the

entire session. The Pb*/U calibration was stationary during the analysis time with an

error for the entire session of 2.02 (1σ%).

Results



Figure 12. Concordia plot for sample 83652: biotite–hornblende granodiorite gneiss,Lake Gidong headland

43

Table 11. Ion microprobe analytical results for sample 83652: biotite–hornblende granodiorite gneiss, Lake Gidong headland


1.1 198 217 71 3.02 0.09163 0.00278 0.31833 0.00678 0.2707 0.0057 3.42 0.13 106 1 460 582.1 96 19 27 0.06 0.10416 0.00247 0.06024 0.00537 0.2805 0.0061 4.03 0.14 94 1 700 443.1 182 38 51 0.55 0.09714 0.00144 0.07670 0.00309 0.2750 0.0057 3.68 0.10 100 1 570 284.1 86 99 28 2.20 0.09747 0.00360 0.30814 0.00882 0.2489 0.0054 3.35 0.15 91 1 576 691.2 81 20 21 0.84 0.10192 0.00268 0.05880 0.00578 0.2563 0.0056 3.60 0.13 89 1 659 495.1 300 122 85 3.37 0.08596 0.00276 0.24388 0.00659 0.2236 0.0046 2.65 0.11 97 1 337 626.1 105 39 35 0.79 0.10288 0.00236 0.10029 0.00525 0.3117 0.0068 4.42 0.15 104 1 677 422.2 230 53 64 0.11 0.10006 0.00091 0.06280 0.00170 0.2775 0.0058 3.83 0.09 97 1 625 176.2 144 44 44 0.26 0.10196 0.00125 0.07687 0.00252 0.2978 0.0063 4.19 0.11 101 1 660 233.2 91 17 26 1.27 0.09991 0.00282 0.08119 0.00625 0.2716 0.0058 3.74 0.14 95 1 622 521.3 74 40 22 4.49 0.09880 0.00638 0.16621 0.01483 0.2397 0.0054 3.27 0.23 86 1 602 1214.2 194 215 69 0.66 0.10144 0.00142 0.29811 0.00366 0.2910 0.0061 4.07 0.11 100 1 651 26

44

Interpretation

The main population of ten analyses (excluding analyses 1.1 and 5.1, which have

significantly lower 207Pb/206Pb ratios) has a pooled 207Pb/206Pb age of 1634 ± 26 Ma

(chi-squared = 1.19), interpreted as the age of crystallization of the granitic protolith

of the gneiss. Analysis 1.1 has probably lost some radiogenic Pb. The younger207Pb/206Pb age of analysis 5.1, the only analysis of rim zircon, may date new zircon

growth that may have occurred during the event associated with intrusion of the

granodiorite pegmatite dyke (83649). The dates obtained for the monzogranite gneiss

(83651) and this sample, from the same locality, agree within their assigned analytical

error.

45

83666: garnet–biotite monzogranite gneiss,Ten Mile Rocks


NORSEMAN (SI 51-2) 122°39’E 32°06’S


North of Ten Mile Rocks.



Orogen. This rock is a strongly deformed and recrystallized porphyritic monzogranite.


The sample consists of a granoblastic assemblage of quartz, oligoclase, biotite, and

garnet, with lesser microcline and sphene. Accessory minerals include opaques,

apatite, zircon, clinozoisite, and metamict allanite. GSWA Petrology Report Number

1604.

Zircon morphology

Most of the zircons obtained from this sample are colourless to light brown,

subhedral, equant to elongate, averaging 75 × 250 µm in size, and contain abundant

fluid inclusions. Igneous zonation is apparent in most grains.

Analytical details


deadtime was 5 ns. Analyses were carried out using five-scan data acquisition. Fifteen


46

calibration was stationary during the analysis period with an error for the entire

session of 2.42 (1σ%).

Results

Sixteen analyses were obtained from 16 zircons. Results are given in Table 12 and


Interpretation

The main population (excluding analysis 15.1) has a pooled 207Pb/206Pb age of

1670 ± 15 Ma (chi-squared = 2.23), interpreted as the age of crystallization of the

Figure 13. Concordia plot for sample 83666: garnet–biotite monzogranite gneiss, TenMile Rocks

47

Table 12. Ion microprobe analytical results for sample 83666: garnet–biotite monzogranite gneiss, Ten Mile Rocks


1.1 386 162 118 0.25 0.10073 0.00104 0.11891 0.00227 0.2898 0.0071 4.02 0.11 100 1 638 192.1 228 86 74 0.14 0.10243 0.00102 0.11161 0.00214 0.3100 0.0077 4.38 0.12 104 1 669 183.1 158 126 54 0.48 0.10078 0.00189 0.22993 0.00463 0.2910 0.0073 4.04 0.13 101 1 639 354.1 449 179 137 0.17 0.10380 0.00081 0.11429 0.00169 0.2901 0.0071 4.15 0.11 97 1 693 145.1 269 110 82 0.02 0.10448 0.00078 0.12190 0.00153 0.2889 0.0071 4.16 0.11 96 1 705 146.1 297 134 95 0.03 0.10426 0.00081 0.13406 0.00172 0.2989 0.0074 4.30 0.11 99 1 701 147.1 268 117 82 0.16 0.10347 0.00103 0.12958 0.00225 0.2871 0.0071 4.10 0.11 96 1 687 188.1 280 118 87 0.32 0.10016 0.00122 0.11925 0.00268 0.2927 0.0072 4.04 0.12 102 1 627 239.1 157 60 48 0.45 0.09913 0.00172 0.10615 0.00378 0.2911 0.0073 3.98 0.13 102 1 608 32

10.1 408 172 124 0.06 0.10127 0.00073 0.12157 0.00155 0.2878 0.0070 4.02 0.11 99 1 648 1311.1 365 151 113 0.10 0.10156 0.00093 0.12233 0.00197 0.2916 0.0072 4.08 0.11 100 1 653 1712.1 360 180 111 0.15 0.10237 0.00086 0.14675 0.00192 0.2867 0.0070 4.05 0.11 97 1 668 1613.1 291 131 92 0.15 0.10391 0.00111 0.13007 0.00242 0.2958 0.0073 4.24 0.12 99 1 695 2014.1 433 294 137 0.11 0.10158 0.00080 0.20164 0.00197 0.2797 0.0069 3.92 0.10 96 1 653 1515.1 556 126 122 0.04 0.08883 0.00073 0.07443 0.00142 0.2197 0.0054 2.69 0.07 91 1 401 1616.1 224 105 71 0.33 0.10181 0.00148 0.13212 0.00329 0.2939 0.0073 4.13 0.13 100 1 657 27

48

granite protolith of the gneiss. Analysis 15.1 is from a morphologically similar zircon

to those of the main zircon population; however, it has a slightly higher U

concentration and lower Th/U than those of the main zircon population. Its lower206Pb/238U and 207Pb/206Pb ages are probably due to mid-Proterozoic disturbance.

49

83676A: hornblende syenogranite gneiss,Mount Andrew


NORSEMAN (SI 51-2) 122°55’E 32°32’S


North of Mount Andrew.



Orogen. This rock is derived from an even-grained syenogranite that was foliated,

isoclinally folded, and then recrystallized at granulite facies. Partial melting formed

pegmatite patches during the peak of metamorphism, and biotite clots probably

formed from garnet during retrogression to amphibolite facies. The sample is a

coarse-grained, granoblastic, moderately foliated gneissic granite.


This sample is composed of quartz, microcline, lesser oligoclase, and dark green-

brown hornblende, with minor intergrown biotite. Accessory minerals include zircon,

sphene, opaques, and apatite. GSWA Petrology Report Number 1604.

Zircon morphology

The zircons from this sample are dark green-brown to colourless, subhedral, equant to

elongate, averaging 75 × 200 µm in size, and display internal euhedral igneous

zonation. Grain 7 possesses a colourless, structureless, euhedrally zoned rim.

50

Analytical details




Pb*/U calibration was stationary during the analysis time with an error for the entire


Results

Seventeen analyses were obtained from 16 individual zircons. Results are given in

Table 13 and shown on a concordia plot in Figure 14.

Figure 14. Concordia plot for sample 83676A: hornblende syenogranite gneiss, MountAndrew

51

Table 13. Ion microprobe analytical results for sample 83676A: hornblende syenogranite gneiss, Mount Andrew


1.1 368 250 120 0.06 0.10447 0.00086 0.20383 0.00212 0.2881 0.0067 4.15 0.11 96 1 705 152.1 340 292 108 0.18 0.10238 0.00101 0.20472 0.00247 0.2800 0.0065 3.95 0.10 95 1 668 183.1 358 221 110 0.38 0.10182 0.00118 0.19294 0.00281 0.2727 0.0064 3.83 0.10 94 1 658 214.1 245 401 64 0.50 0.10378 0.00165 0.15158 0.00377 0.2385 0.0056 3.41 0.10 81 1 693 295.1 294 242 97 0.17 0.10480 0.00089 0.18227 0.00210 0.2955 0.0069 4.27 0.11 98 1 711 166.1 276 221 87 0.03 0.10466 0.00072 0.17958 0.00172 0.2853 0.0067 4.12 0.10 95 1 708 137.1 857 62 160 0.05 0.08000 0.00049 0.01385 0.00069 0.1982 0.0045 2.19 0.05 97 1 197 128.1 290 183 97 -0.03 0.10465 0.00079 0.18129 0.00188 0.3036 0.0071 4.38 0.11 100 1 708 149.1 340 224 97 0.81 0.09935 0.00136 0.19246 0.00326 0.2507 0.0058 3.43 0.10 89 1 612 26

10.1 202 101 62 0.03 0.10504 0.00136 0.14186 0.00303 0.2838 0.0067 4.11 0.12 94 1 715 2411.1 181 112 59 0.46 0.10182 0.00153 0.16563 0.00355 0.2940 0.0070 4.13 0.12 100 1 658 2812.1 355 232 117 0.20 0.10657 0.00092 0.18952 0.00219 0.2944 0.0068 4.33 0.11 96 1 741 1613.1 264 179 89 0.17 0.10267 0.00088 0.18308 0.00210 0.3020 0.0071 4.27 0.11 102 1 673 1614.1 227 137 65 0.03 0.09851 0.00075 0.13378 0.00159 0.2705 0.0063 3.67 0.09 97 1 596 1415.1 348 263 115 0.20 0.10357 0.00076 0.20881 0.00191 0.2912 0.0068 4.16 0.10 98 1 689 147.2 861 42 164 0.10 0.07899 0.00049 0.01267 0.00074 0.2025 0.0046 2.21 0.05 101 1 172 12

16.1 187 83 58 0.07 0.10062 0.00118 0.13039 0.00259 0.2917 0.0069 4.05 0.11 101 1 636 22

52

Interpretation

With the exception of the two rim analyses (7.1 and 7.2), all analyses have similar207Pb/206Pb ratios but have suffered various degrees of recent radiogenic-Pb loss. The

13 analyses of the main population have 207Pb/206Pb ratios defining a single value

with little excess scatter (chi-squared = 2.32) and corresponding to an age of

1695 ± 16 Ma. This is interpreted as the time of crystallization of the granite protolith

of the gneiss. Analyses 9.1 and 14.1 have 207Pb/206Pb ratios (chi-squared = 0.23) that

are statistically lower than those of the main population and indicating an age of

1600 ± 12 Ma. These zircons probably belong to the main population but experienced

some radiogenic-Pb loss during the middle Proterozoic. Analyses 7.1 and 7.2, made of

a zircon rim, indicate significantly lower Th/U than the other analyses of zircons from

this sample. The mean 207Pb/206Pb age of 1184 ± 12 Ma (chi-squared = 1.42)

determined from these two analyses may date the time of metamorphic zircon growth.

53

83700A: hornblende–biotite syenogranite gneiss,Coramup Hill Quarry




Coramup Hill Quarry.


An orthogneiss from within the Biranup Complex of the Albany–Fraser Orogen, this

rock is derived from even-grained syenogranite and pegmatite veins that were

strongly deformed and recrystallized during prograde granulite facies metamorphism,

followed by retrogression to amphibolite facies.


The sample, which is free of pegmatite veins, consists of strongly foliated microcline

and quartz, with minor hornblende, biotite, oligoclase, and opaque oxides, and

accessory apatite and zircon. GSWA Petrology Report Number 1604.

Zircon morphology

The zircons extracted from this sample are colourless to dark yellow-brown, subhedral

and equant to elongate, averaging 75 × 200 µm. Many have euhedral igneous zonation

and silicate inclusions. Rims can be distinguished on some grains but no analyses of

zircon rims were obtained.

Analytical details

This sample was analysed on 6 and 7 March 1992 on SHRIMP-1. The counter

deadtime was 20 ns. Analyses were undertaken using five-scan data acquisition. Ten


54

calibration was stationary during the analysis time with a calculated error for the

entire session of 1.96 (1σ%).

Results

Fourteen analyses were obtained from 13 zircons. Results are given in Table 14 and


Interpretation

All analyses have 207Pb/206Pb ratios within error of a single value (chi-squared = 0.70)

corresponding to an age of 1283 ± 13 Ma, which is interpreted as the age of

crystallization of the granitoid protolith of the gneiss.

Figure 15. Concordia plot for sample 83700A: hornblende–biotite syenogranite gneiss,Coramup Hill Quarry

55

Table 14. Ion microprobe analytical results for sample 83700A: hornblende–biotite syenogranite gneiss, Coramup Hill Quarry


1.1 267 253 66 0.32 0.08449 0.0012 0.23900 0.00332 0.2144 0.0043 2.498 0.066 96 1 304 282.1 273 323 59 0.39 0.08403 0.0013 0.16259 0.00314 0.1983 0.0040 2.298 0.062 90 1 293 303.1 399 231 93 0.56 0.08174 0.0013 0.19157 0.00314 0.2085 0.0042 2.349 0.063 99 1 239 314.1 515 376 131 0.13 0.08414 0.0007 0.21359 0.00192 0.2260 0.0045 2.621 0.059 101 1 296 165.1 418 343 99 0.23 0.08373 0.0009 0.16649 0.00222 0.2177 0.0043 2.513 0.060 99 1 286 216.1 772 731 181 5.04 0.08246 0.0027 0.48138 0.00674 0.1517 0.0030 1.725 0.069 72 1 256 647.1 269 170 65 0.06 0.08461 0.0010 0.16555 0.00247 0.2252 0.0046 2.628 0.065 100 1 307 237.2 685 748 177 0.17 0.08401 0.0007 0.26817 0.00191 0.2212 0.0044 2.562 0.057 100 1 293 158.1 369 206 90 0.29 0.08246 0.0010 0.15770 0.00237 0.2254 0.0045 2.563 0.063 104 1 257 239.1 254 133 64 0.40 0.08297 0.0013 0.16280 0.00307 0.2301 0.0047 2.632 0.071 105 1 269 30

10.1 236 234 58 1.36 0.08387 0.0024 0.24968 0.00581 0.2043 0.0041 2.362 0.087 93 1 290 5511.1 278 240 65 1.15 0.08325 0.0019 0.25377 0.00477 0.1967 0.0040 2.259 0.073 91 1 275 4512.1 388 252 87 0.66 0.08438 0.0013 0.18610 0.00317 0.1995 0.0040 2.321 0.062 90 1 301 3013.1 641 409 129 0.66 0.08170 0.0011 0.19065 0.00278 0.1802 0.0036 2.030 0.052 86 1 238 27

56

83697: biotite monzogranite gneiss, Mount Burdett




Mount Burdett.



Orogen. This rock is from a large (2 × 0.5 km) lens of relatively little-deformed and

partly recrystallized, very coarse, even-grained monzogranite, enclosed by

mylonitized monzogranite.


The sample consists of large augen of perthitic microcline and less abundant

oligoclase, up to 6 mm in diameter, in a fine-grained mosaic of quartz, plagioclase,

microcline, and biotite. Minor opaques and granular sphene commonly form coronas

around cores of fresh ilmenite. Accessory minerals include apatite, zircon, chlorite,

and muscovite. GSWA Petrology Report Number 1604.

Zircon morphology

The zircons from this sample are colourless, euhedral, elongate grains with an average

size of 75 × 150 µm, and contain igneous zonation and abundant silicate inclusions.

Analytical details


deadtime was 20 ns. Analyses were carried out using five-scan data acquisition. Ten


calibration was stationary during analysis time with a calculated error for the entire


57

Results

Thirteen analyses were made of 13 zircons. Results are given in Table 15 and shown


Interpretation

All analyses plot within error of concordia and have 207Pb/206Pb ratios almost within

error of a single value (chi-squared = 1.11) indicating an age of 1299 ± 18 Ma. This is

interpreted as the time of crystallization of the granitoid precursor to the gneiss.

Figure 16. Concordia plot for sample 83697: biotite monzogranite gneiss, MountBurdett

58

Table 15. Ion microprobe analytical results for sample 83697: biotite monzogranite gneiss, Mount Burdett


1.1 121 63 29 0.82 0.07955 0.0025 0.14096 0.00578 0.2230 0.0047 2.446 0.096 109 1 186 612.1 211 119 52 0.46 0.08257 0.0017 0.16427 0.00398 0.2269 0.0046 2.584 0.079 105 1 259 393.1 430 223 105 0.31 0.08432 0.0009 0.15627 0.00221 0.2250 0.0045 2.615 0.063 101 1 300 214.1 170 79 39 0.29 0.08432 0.0018 0.14144 0.00414 0.2164 0.0045 2.516 0.079 97 1 300 415.1 197 98 49 0.21 0.08680 0.0015 0.13350 0.00338 0.2360 0.0048 2.824 0.079 101 1 356 336.1 290 155 70 0.65 0.08514 0.0014 0.14917 0.00327 0.2240 0.0045 2.630 0.072 99 1 319 327.1 211 103 51 0.35 0.08297 0.0013 0.14176 0.00299 0.2273 0.0046 2.601 0.070 104 1 268 308.1 253 120 62 0.32 0.08322 0.0013 0.14535 0.00308 0.2285 0.0046 2.622 0.071 104 1 274 319.1 153 93 38 0.26 0.08450 0.0017 0.18013 0.00417 0.2264 0.0047 2.638 0.081 101 1 304 39

10.1 239 114 57 0.25 0.08273 0.0011 0.13855 0.00262 0.2270 0.0046 2.589 0.066 104 1 263 2611.1 244 124 60 0.30 0.08403 0.0014 0.15011 0.00321 0.2300 0.0047 2.664 0.073 103 1 293 3112.1 318 168 76 0.07 0.08535 0.0008 0.15934 0.00192 0.2241 0.0045 2.637 0.061 98 1 323 1813.1 327 163 80 0.08 0.08490 0.0009 0.15876 0.00223 0.2270 0.0046 2.657 0.064 100 1 313 21

59

83659: recrystallized leucogranite, Observatory Point




Observatory Point.


This sample is of a charnokite within the Biranup Complex of the Albany–Fraser

Orogen. This rock is a weakly deformed, even-grained leucogranite recrystallized

under granulite facies conditions.


This sample comprises perthitic alkali feldspar, oligoclase, and quartz, with accessory

biotite, heavily oxidized hypersthene, garnet, zircon, apatite, and magnetite.

Secondary accessory minerals include chlorite after biotite, and opaque oxides after

mafic minerals. GSWA Petrology Report Number 1556.

Zircon morphology

The zircons from this sample are colourless to light pink, subhedral and equant to

elongate, and average 60 × 120 µm in size. Euhedral igneous zonation is present in a

few grains. Rims or cores could not be distinguished.

Analytical details


deadtime was 22 ns. Analyses were carried out using seven-scan data acquisition for

analyses 1.1 and 2.1 and six-scan acquisition for the remaining analyses. Thirteen


60

calibration was stationary during the analysis time with a calculated error on Pb*/U

for the entire session of 2.02 (1σ%).

Results

Fifteen analyses were made of 15 individual zircons. Results are given in Table 16 and


Interpretation

With the exception of analysis 12.1, which has a slightly but statistically significantly

lower 207Pb/ 206Pb ratio, the analyses form a single coherent population (chi-squared

Figure 17. Concordia plot for sample 83659: recrystallized leucogranite, ObservatoryPoint

61

Table 16. Ion microprobe analytical results for sample 83659: recrystallized leucogranite, Observatory Point


1.1 353 291 92 0.91 0.08312 0.00134 0.22744 0.00333 0.2234 0.0046 2.561 0.071 102 1 272 322.1 389 211 96 0.27 0.08438 0.00081 0.16006 0.00196 0.2279 0.0047 2.652 0.063 102 1 301 193.1 417 267 101 0.41 0.08462 0.00106 0.18432 0.00261 0.2178 0.0045 2.542 0.065 97 1 307 244.1 807 289 170 1.27 0.08393 0.00121 0.10110 0.00276 0.1978 0.0040 2.289 0.060 90 1 291 285.1 534 397 138 0.15 0.08468 0.00066 0.21501 0.00179 0.2291 0.0047 2.675 0.061 102 1 308 156.1 403 210 98 0.12 0.08421 0.00079 0.15094 0.00190 0.2289 0.0047 2.657 0.063 102 1 297 187.1 1 006 618 263 0.06 0.08604 0.00042 0.18001 0.00110 0.2394 0.0049 2.840 0.061 103 1 339 98.1 671 259 150 1.03 0.08204 0.00112 0.10179 0.00255 0.2110 0.0043 2.387 0.062 99 1 246 279.1 160 91 38 0.46 0.08290 0.00206 0.15950 0.00490 0.2180 0.0046 2.491 0.086 100 1 267 49

10.1 446 377 123 0.02 0.08543 0.00058 0.25130 0.00183 0.2386 0.0049 2.811 0.063 104 1 325 1311.1 1 511 1 173 165 4.53 0.08394 0.00237 0.26232 0.00567 0.0819 0.0017 0.948 0.035 39 1 291 5512.1 1 840 177 400 0.09 0.08198 0.00035 0.02794 0.00060 0.2270 0.0046 2.566 0.055 106 1 245 813.1 570 357 154 0.94 0.08526 0.00101 0.19127 0.00244 0.2385 0.0049 2.804 0.070 104 1 321 2314.1 196 150 61 3.96 0.08515 0.00361 0.24768 0.00861 0.2376 0.0050 2.789 0.138 104 1 319 8215.1 613 327 156 0.03 0.08494 0.00044 0.15517 0.00109 0.2385 0.0049 2.793 0.060 105 1 314 10

62

= 1.38) with a 207Pb/206Pb age of 1288 ± 12 Ma. This is interpreted as the

crystallization age of the leucogranite. The granite probably crystallized during or

shortly following the peak of metamorphism, and this date may therefore also provide

an estimate of the time of granulite-facies metamorphism. The slightly lower207Pb/206Pb age of analysis 12.1 may be the result of some post-crystallization

disturbance of the U–Pb system in this zircon because it has relatively high U and Th

contents.

63

83657A: porphyritic biotite monzogranite,Esperance Harbour jetty




Wireless Hill. The sample was taken from the Esperance Harbour jetty but was

quarried from Wireless Hill.


This sample is of a granite within the Nornalup Complex of the Albany–Fraser

Orogen.


This monzogranite is composed of microcline, oligoclase (about An25), quartz, and

biotite, with accessory amounts of zircon, apatite, magnetite, and scarce secondary

muscovite. GSWA Petrology Report Number 1556.

Zircon morphology

The zircons recovered from this sample are light green-brown, subhedral, equant to

elongate, ranging in size up to 100 × 600 µm, and contain pronounced euhedral

igneous zoning. Rims and cores are distinguishable in some grains but no analyses of

rims were obtained.

Analytical details




64

Pb*/U calibration was mobile during the analysis time so Pb*/U of unknowns has

been corrected using bracketing standard analyses, with a calculated error on Pb*/U

for the entire session of 2.19 (1σ%).

Results

Twelve analyses were obtained from 12 individual zircons. Results are given in


Figure 18. Concordia plot for sample 83657A: porphyritic biotite monzogranite,Esperance Harbour jetty

65

Table 17. Ion microprobe analytical results for sample 83657A: porphyritic biotite monzogranite, Esperance Harbour jetty


1.1 1 396 2 041 369 0.03 0.08071 0.00041 0.42116 0.00180 0.2043 0.0045 2.274 0.053 99 1 214 102.1 217 152 43 1.22 0.07817 0.00283 0.22265 0.00692 0.1707 0.0038 1.840 0.083 88 1 151 723.1 305 445 47 0.66 0.07749 0.00199 0.42244 0.00579 0.1166 0.0026 1.246 0.045 63 1 134 514.1 1 915 391 371 0.24 0.07936 0.00042 0.07441 0.00088 0.1936 0.0043 2.118 0.049 97 1 181 105.1 9 248 2 629 1 796 0.13 0.07209 0.00016 0.08228 0.00034 0.1946 0.0043 1.935 0.043 116 989 46.1 1 914 178 356 0.02 0.07992 0.00034 0.02614 0.00052 0.1956 0.0043 2.155 0.049 96 1 195 87.1 782 271 142 0.16 0.08061 0.00069 0.11928 0.00157 0.1753 0.0039 1.949 0.048 86 1 212 178.1 1 940 1 352 331 0.37 0.07366 0.00055 0.21526 0.00147 0.1521 0.0033 1.544 0.037 88 1 032 159.1 2 455 790 392 0.68 0.07533 0.00056 0.05595 0.00124 0.1602 0.0035 1.663 0.040 89 1 077 15

10.1 2 402 750 463 0.09 0.07717 0.00030 0.09255 0.00064 0.1908 0.0042 2.031 0.046 100 1 125 811.1 3 773 936 713 0.24 0.07647 0.00030 0.07658 0.00064 0.1890 0.0041 1.992 0.045 101 1 107 812.1 2 462 1 679 498 0.13 0.07562 0.00036 0.19566 0.00097 0.1841 0.0040 1.920 0.044 100 1 085 9

66

Interpretation

The 207Pb/206Pb ages do not form a single coherent population but fall along

concordia, suggesting non-zero age disturbance of the U–Pb systems in these zircons.

Treating the analyses as a single population, but excluding analysis 5.1 because of its

substantially lower 207Pb/206Pb ratio, produces an estimate of the minimum age of

crystallization of the monzogranite of 1138 ± 38 Ma (chi-squared = 23.72). The high

U and Th contents of these zircons (in particular, grain 5) may provide some

explanation for the observed spread in 207Pb/206Pb, because the radiation damage

resulting from decay of U and Th will render these zircons more susceptible to later

disturbance.

67

83662: biotite–hornblende monzogranite gneiss,Poison Creek


MALCOLM – CAPE ARID (SI 51-7, 11) 123°20’E 33°54’S


Poison Creek, west side of estuary.


This sample is of an orthogneiss within the Nornalup Complex of the Albany–Fraser

Orogen. This rock is a moderately foliated and recrystallized coarse, even-grained

monzogranite with scattered K-feldspar phenocrysts.


The sample has been metamorphosed to amphibolite facies, and comprises

microcline, andesine–oligoclase (An30), quartz, biotite, and subordinate

ferrohastingsitic hornblende. Zircon, metamict allanite, apatite, titanite, and magnetite

are common primary accessory minerals. Secondary accessory minerals include

epidote, carbonate, and chlorite. GSWA Petrology Report Number 1556.

Zircon morphology

The zircons from this sample are light brown with abundant opaque inclusions. They

are euhedral, equant to elongate, and average 150 × 250 µm, but range in size up to

200 × 500 µm, with obvious euhedral igneous zonation. Rims or cores could not be

discerned.

68

Analytical details




Pb*/U calibration was stationary during the analysis time with a calculated error for

the entire session of 2.02 (1σ%).

Results

Thirteen analyses were obtained from 13 individual zircons. Results are given in


Figure 19. Concordia plot for sample 83662: biotite–hornblende monzogranite gneiss,Poison Creek

69

Table 18. Ion microprobe analytical results for sample 83662: biotite–hornblende monzogranite gneiss, Poison Creek


1.1 2 250 998 513 0.05 0.08261 0.00029 0.12783 0.00067 0.2184 0.0044 2.488 0.052 101 1 260 72.1 866 312 212 0.33 0.08657 0.00073 0.10617 0.00163 0.2354 0.0048 2.810 0.065 101 1 351 163.1 714 292 220 5.05 0.08438 0.00247 0.20928 0.00582 0.2352 0.0048 2.737 0.103 105 1 301 574.1 835 87 193 1.49 0.08220 0.00132 0.09750 0.00302 0.2162 0.0044 2.451 0.067 101 1 250 315.1 593 417 132 1.92 0.08684 0.00177 0.24438 0.00432 0.1821 0.0037 2.181 0.067 79 1 357 396.1 620 400 184 2.71 0.08341 0.00188 0.22800 0.00450 0.2405 0.0049 2.765 0.089 109 1 279 447.1 1 632 756 421 0.54 0.08599 0.00058 0.15286 0.00138 0.2372 0.0048 2.812 0.062 103 1 338 138.1 764 526 197 0.23 0.08516 0.00069 0.19951 0.00178 0.2311 0.0047 2.713 0.062 102 1 319 169.1 424 247 113 2.76 0.08702 0.00249 0.23392 0.00596 0.2154 0.0045 2.584 0.097 92 1 361 55

10.1 2 118 567 516 0.02 0.08540 0.00028 0.07881 0.00051 0.2433 0.0049 2.865 0.060 106 1 325 611.1 669 314 175 0.78 0.08457 0.00106 0.14609 0.00248 0.2403 0.0049 2.802 0.071 106 1 306 2412.1 2 064 1 105 527 0.37 0.08659 0.00050 0.16661 0.00120 0.2336 0.0047 2.789 0.061 100 1 351 1113.1 4 273 2 728 1 217 0.23 0.08376 0.00028 0.19148 0.00074 0.2576 0.0052 2.975 0.062 115 1 287 7

70

Interpretation

Apart from analyses 1.1 and 13.1, which have significantly lower 207Pb/206Pb ratios,

the analyses form a single coherent population plotting near to concordia with little

excess scatter (chi-squared = 1.62) and indicate a 207Pb/206Pb age of 1330 ± 14 Ma.

Analyses 1.1 and 13.1 have high U and Th concentrations and their lower 207Pb/206Pb

ratios may reflect some disturbance of their U–Pb systems.

71

83667: porphyritic biotite granite, Balladonia Rock


BALLADONIA (SI 51-3) 123°52’E 32°27’S


Balladonia Rock.


This sample is of a granite within the Nornalup Complex of the Albany–Fraser

Orogen. It is a uniform coarse-grained porphyritic granite with an early foliation,

parallel to the alignment of feldspar phenocrysts, that is patchily overprinted by a

more pronounced cataclastic foliation.


The sample consists of a coarse-grained assemblage of microcline, quartz, oligoclase,

and minor biotite. Accessory minerals include monazite, zircon, opaques, apatite and

sphene. There is some minor alteration of the feldspars to sericite, but the sample is

unmetamorphosed. GSWA Petrology Report Number 1604.

Zircon morphology

Abundant monazite and relatively few zircons were recovered from this sample. The

zircons are dark brown and euhedral, equant to elongate, averaging 75 × 150 µm.

Most are broken and irregular in shape. Rims and cores can be clearly seen in a few

grains.

Analytical details


deadtime was 20 ns. Analyses were carried out using five-scan data acquisition. Five

72




Results

Fourteen analyses were obtained from 14 individual zircons. Results are given in


Interpretation

It was not always possible to analyse rims and cores separately and a few analyses

may have included both rim and core material. The 207Pb/206Pb ages do not form a

single coherent population but fall along concordia into two groups. Nine analyses

Figure 20. Concordia plot for sample 83667: porphyritic biotite granite, Balladonia Rock

73

Table 19. Ion microprobe analytical results for sample 83667: porphyritic biotite granite, Balladonia Rock


1.1 1 123 663 173 8.71 0.08861 0.00322 0.16561 0.00751 0.1075 0.0030 1.313 0.063 47 1 396 702.1 1 114 224 218 0.84 0.08095 0.00078 0.06465 0.00172 0.1929 0.0053 2.154 0.065 93 1 220 193.1 694 1 128 192 1.68 0.08299 0.00154 0.50724 0.00423 0.1932 0.0053 2.211 0.077 90 1 269 364.1 6 485 704 1 385 0.73 0.07674 0.00029 0.03389 0.00062 0.2175 0.0059 2.301 0.064 114 1 114 75.1 146 317 49 7.87 0.09518 0.00720 0.82526 0.01924 0.1712 0.0049 2.247 0.189 67 1 532 1436.1 1 626 3 185 467 2.80 0.07809 0.00120 0.66501 0.00338 0.1787 0.0049 1.924 0.063 92 1 149 307.1 633 179 142 4.74 0.08807 0.00242 0.13393 0.00561 0.1819 0.0050 2.209 0.091 78 1 384 538.1 1 338 202 261 1.21 0.07939 0.00083 0.04619 0.00185 0.1924 0.0053 2.106 0.064 96 1 182 219.1 523 687 135 1.71 0.08532 0.00157 0.41778 0.00419 0.1903 0.0052 2.239 0.078 85 1 323 36

10.1 474 1 932 197 1.84 0.08378 0.00178 1.22609 0.00680 0.2012 0.0055 2.324 0.085 92 1 288 4111.1 421 808 131 4.00 0.07934 0.00262 0.64183 0.00711 0.1900 0.0052 2.079 0.095 95 1 181 6512.1 535 871 134 14.02 0.09594 0.00538 0.64034 0.01342 0.1191 0.0033 1.575 0.103 47 1 547 10513.1 2 108 648 404 1.65 0.07885 0.00089 0.07866 0.00204 0.1812 0.0049 1.970 0.061 92 1 168 2214.1 1 140 190 236 1.55 0.08201 0.00100 0.05810 0.00224 0.1994 0.0054 2.255 0.071 94 1 246 24

74

(analyses 1.1, 3.1, 5.1, 7.1, 9.1, 10.1, 11.1, 12.1, and 14.1) are almost within error of a

single mean 207Pb/206Pb value (chi-squared = 2.36) corresponding to an imprecise

date of 1285 ± 57 Ma. These analysis sites had U contents between 146 and

1140 ppm. The remaining five analyses, obtained on irregular zircon fragments and a

single zircon rim, indicate typically higher U contents of 1114 to 6485 ppm and define

a date of 1135 ± 56 Ma (chi-squared = 7.26). The favoured interpretation of these data

is that the younger date of 1135 ± 56 Ma provides the time of granite crystallization

and the older date of 1285 ± 57 Ma represents the average crystallization age of a

population of zircon xenocrysts. An alternative interpretation, that the 1285 ± 57 Ma

date corresponds to the time of granite crystallization and the younger date

corresponds to the time of metamorphic disturbance, is considered less plausible

because the granite is unmetamorphosed.

75

83663: granodiorite gneiss, Israelite Bay




Israelite Bay.


This sample is of an orthogneiss within the Nornalup Complex of the Albany–Fraser

Orogen. This rock has an augen structure derived by deformation and recrystallization

of a primary porphyritic texture.


The sample consists of andesine (An32–36), quartz, microcline, biotite, and traces of

garnet occurring along fractures in plagioclase, with accessory zircon and apatite.

GSWA Petrology Report Number 1556.

Zircon morphology

Most of the zircons extracted from this sample are clear to light brown, subhedral and

equant to elongate, ranging in size up to 100 × 550 µm. Many have fluid and mineral

inclusions.

Analytical details




Pb*/U calibration was stationary during the analysis time with a calculated error for

the entire session of 2.02 (1σ%).

76

Results



Interpretation

All analyses plot within error of concordia and have 207Pb/206Pb ages within error of a

single value (chi-squared = 0.66) corresponding to an age of 1314 ± 21 Ma, which is

interpreted as the age of crystallization of the granodiorite protolith of the gneiss.

Figure 21. Concordia plot for sample 83663: granodiorite gneiss, Israelite Bay

77

Table 20. Ion microprobe analytical results for sample 83663: granodiorite gneiss, Israelite Bay


1.1 155 146 42 0.527 0.08308 0.00218 0.26975 0.00573 0.2269 0.0046 2.599 0.092 104 1 271 512.1 172 123 42 0.480 0.08411 0.00240 0.20628 0.00585 0.2168 0.0044 2.514 0.093 98 1 295 553.1 82 153 25 0.405 0.08448 0.00372 0.55077 0.01147 0.2175 0.0046 2.534 0.129 97 1 304 864.1 277 100 69 0.038 0.08499 0.00151 0.11191 0.00342 0.2405 0.0048 2.819 0.080 106 1 315 355.1 223 130 56 0.187 0.08634 0.00157 0.18095 0.00385 0.2271 0.0046 2.703 0.078 98 1 346 356.1 243 77 56 0.335 0.08661 0.00156 0.09956 0.00347 0.2233 0.0045 2.667 0.076 96 1 352 357.1 203 172 55 0.258 0.08308 0.00144 0.25417 0.00392 0.2318 0.0047 2.655 0.075 106 1 271 348.1 194 45 43 0.404 0.08428 0.00157 0.06670 0.00334 0.2214 0.0045 2.573 0.075 99 1 299 369.1 123 145 35 0.297 0.08291 0.00172 0.35881 0.00543 0.2295 0.0047 2.623 0.081 105 1 267 40

10.1 80 79 22 -0.202 0.09021 0.00601 0.30483 0.01452 0.2295 0.0050 2.854 0.207 93 1 430 12711.1 111 84 30 0.522 0.08366 0.00264 0.22880 0.00663 0.2332 0.0048 2.690 0.107 105 1 285 6212.1 398 93 92 0.028 0.08558 0.00072 0.06845 0.00132 0.2318 0.0046 2.735 0.061 101 1 329 16

78

112128: muscovite–biotite–sillimanite paragneiss,Point Malcolm



Sampled on 23 November 1991

Sampled from outcrop along the beach about 6 km southwest of Point Malcolm.


This sample is of a strongly foliated paragneiss within the eastern part of the

Albany–Fraser Orogen. The paragneiss contains boudins, up to 2 m long and 20 cm

wide, of quartzite.


This sample is a foliated, medium- to coarse-grained assemblage of quartz, muscovite,

biotite, and andesine (An30–40) with minor sillimanite and accessory zircon. GSWA


Zircon morphology

Zircons with a wide range of different morphologies were recovered from this sample.

Most are small, with an average size of 60 × 60 µm, clear and rounded, and show

evidence of abrasion caused during transport as detrital grains.

Analytical details


deadtime was 20 ns. Analyses were carried out using six-scan data acquisition. Ten


79



Results

Eighteen analyses were obtained from 18 zircons. Results are given in Table 21 and


Interpretation

The analyses fall into five age groups. Zircons of the youngest group, comprising ten

analyses, have 207Pb/206Pb ratios that are within error of a single value with little

excess scatter (chi-squared = 1.72), indicating an age of 1560 ± 40 Ma. This date sets

Figure 22. Concordia plot for sample 112128: muscovite–biotite–sillimanite paragneiss,Point Malcolm

80

Table 21. Ion microprobe analytical results for sample 112128: muscovite–biotite–sillimanite paragneiss, Point Malcolm


1.1 272 385 105 6.10 0.10453 0.00472 0.49801 0.01172 0.2383 0.0050 3.435 0.179 81 1 706 832.1 218 298 74 0.67 0.09438 0.00178 0.40661 0.00519 0.2572 0.0053 3.347 0.099 97 1 516 363.1 284 159 84 2.74 0.09289 0.00320 0.19925 0.00754 0.2440 0.0050 3.125 0.132 95 1 486 654.1 784 92 298 0.34 0.12531 0.00071 0.03412 0.00131 0.3768 0.0075 6.510 0.140 101 2 033 105.1 192 207 66 0.72 0.09479 0.00177 0.33994 0.00497 0.2721 0.0057 3.557 0.105 102 1 524 356.1 517 134 179 1.75 0.10816 0.00152 0.07125 0.00336 0.3202 0.0065 4.775 0.124 101 1 769 267.1 569 96 148 2.81 0.09166 0.00220 0.05957 0.00498 0.2373 0.0048 2.998 0.100 94 1 460 468.1 196 165 125 0.47 0.18907 0.00159 0.25016 0.00341 0.5084 0.0107 13.254 0.313 97 2 734 149.1 149 141 58 0.92 0.10693 0.00231 0.26573 0.00571 0.3180 0.0067 4.688 0.150 102 1 748 40

10.1 293 529 118 3.35 0.09997 0.00305 0.55535 0.00808 0.2598 0.0053 3.580 0.139 92 1 623 5711.1 307 117 108 1.05 0.11205 0.00153 0.12569 0.00340 0.3194 0.0065 4.935 0.128 97 1 833 2512.1 288 316 98 0.84 0.09686 0.00172 0.34396 0.00457 0.2681 0.0055 3.581 0.103 98 1 565 3314.1 418 636 161 0.34 0.09864 0.00099 0.46733 0.00327 0.2819 0.0057 3.834 0.091 100 1 599 1915.1 604 52 195 0.28 0.11091 0.00078 0.02437 0.00140 0.3267 0.0065 4.995 0.110 100 1 814 1316.1 135 121 52 0.19 0.11111 0.00157 0.25913 0.00408 0.3248 0.0070 4.976 0.135 100 1 818 2617.1 408 178 180 0.31 0.13588 0.00098 0.13067 0.00198 0.4010 0.0081 7.512 0.168 100 2 175 1318.1 282 118 117 15.88 0.09401 0.00700 0.18089 0.01631 0.2308 0.0050 2.991 0.240 89 1 508 14119.1 357 357 125 5.73 0.09612 0.00375 0.32567 0.00902 0.2411 0.0049 3.196 0.148 90 1 550 73

81

a limit on the earliest time of deposition of the sediments that formed the protolith of

the paragneiss. Zircons of the second group, comprising five analyses (6.1, 9.1, 11.1,

15.1, and 16.1), form a discrete population (chi-squared = 1.39) with a 207Pb/206Pb

age of 1807 ± 35 Ma. Three analyses (4.1,17.1, and 8.1) have early Proterozoic or late

Archaean 207Pb/206Pb ages (2033 ± 10 Ma, 2175 ± 13 Ma, and 2734 ± 14 Ma).

82

112163: rhyolite, Bandalup


RAVENSTHORPE (SI 51-5) AMG Zone 51, 256400E 6271100N

Sampled on 15 December 1992


This sample is of a felsic volcanic unit within the Ravensthorpe greenstone belt, on

the southern margin of the Yilgarn Craton.


A fine-grained, moderately orientated mosaic of quartz and feldspar with abundant

small flakes of biotite and grains of epidote. Schlieren of biotite suggest the

orientation defines the original flow-banding. Numerous phenocrysts of quartz, up to

3 mm across, have recrystallized. Less abundant ‘ghosts’ of feldspar phenocrysts are

mostly microcline. A zone of coarser epidote with abundant muscovite may be a pre-

metamorphic vein. Minor muscovite and accessory apatite and sphene are present, as

are a number of large, fresh zircons, up to 0.15 mm across. The original rock was

probably a rhyodacite to rhyolite that has undergone low-grade metamorphism.

GSWA Petrology Report Number 1624.

Zircon morphology

The zircons recovered from this sample are light brown to dark brown, euhedral,

(typically 100 × 300 µm), with little or no obvious internal structure.

Analytical details

This sample was analysed on 31 October 1994. The counter deadtime was 36 ns.

Eight analyses of the CZ-3 standard were obtained during the analysis session. The

83

Pb*/U calibration was stationary during the analysis session and the calibration error

was 3.23 (1σ%).

Results

Twenty-three analyses from 23 zircons were obtained. Results are given in Table 22

and shown on a concordia plot in Figure 23.

Interpretation

All 23 analyses have 207Pb/206Pb ratios within error of a single mean value (chi-

squared = 0.92) and define an age of 2958 ± 4 Ma. This is interpreted as the time of

emplacement of the rhyolite.

Figure 23. Concordia plot for sample 112163: rhyolite, Bandalup

84

Table 22. Ion microprobe analytical results for sample 112163: rhyolite, Bandalup


1.1 93 34 62 1.583 0.21519 0.00148 0.08791 0.00292 0.5612 0.0183 16.652 0.570 98 2 945 112.1 105 119 55 1.176 0.21705 0.00145 0.14921 0.00287 0.4320 0.0141 12.930 0.442 78 2 959 113.1 150 87 99 0.557 0.21720 0.00092 0.15507 0.00168 0.5481 0.0179 16.414 0.548 95 2 960 74.1 182 112 125 0.576 0.21594 0.00097 0.16429 0.00180 0.5704 0.0186 16.984 0.569 99 2 951 75.1 60 23 40 1.145 0.21676 0.00192 0.10192 0.00370 0.5643 0.0187 16.866 0.597 98 2 957 146.1 156 93 101 0.626 0.21570 0.00102 0.14962 0.00189 0.5410 0.0177 16.090 0.541 95 2 949 87.1 66 23 43 1.388 0.21344 0.00216 0.08715 0.00425 0.5570 0.0185 16.391 0.590 97 2 932 168.1 83 31 54 1.220 0.21520 0.00159 0.09604 0.00305 0.5599 0.0184 16.613 0.575 97 2 945 129.1 84 58 55 1.015 0.21802 0.00151 0.15764 0.00298 0.5367 0.0177 16.133 0.556 93 2 966 11

10.1 85 36 58 0.826 0.21561 0.00146 0.11343 0.00276 0.5812 0.0191 17.277 0.594 100 2 948 1111.1 123 81 83 0.820 0.21556 0.00120 0.16386 0.00230 0.5526 0.0181 16.424 0.557 96 2 948 912.1 112 49 76 0.647 0.21737 0.00111 0.12132 0.00200 0.5752 0.0188 17.238 0.582 99 2 961 813.1 102 46 69 0.711 0.21765 0.00127 0.12135 0.00233 0.5770 0.0189 17.315 0.590 99 2 963 914.1 181 108 123 0.416 0.21810 0.00086 0.16024 0.00153 0.5647 0.0184 16.983 0.566 97 2 967 615.1 116 98 61 1.172 0.21616 0.00154 0.10997 0.00297 0.4426 0.0145 13.190 0.454 80 2 952 1116.1 160 90 108 0.507 0.21722 0.00088 0.14956 0.00158 0.5668 0.0185 16.976 0.566 98 2 960 617.1 95 43 65 0.611 0.21680 0.00123 0.12295 0.00224 0.5841 0.0192 17.460 0.594 100 2 957 918.1 122 67 83 0.696 0.21642 0.00108 0.14430 0.00200 0.5670 0.0185 16.919 0.570 98 2 954 819.1 96 66 59 1.240 0.21489 0.00158 0.10449 0.00311 0.5162 0.0169 15.296 0.528 91 2 943 1220.1 100 53 69 0.761 0.21905 0.00121 0.14128 0.00224 0.5766 0.0189 17.416 0.591 99 2 974 921.1 84 92 59 0.916 0.21908 0.00146 0.20172 0.00295 0.5642 0.0186 17.043 0.586 97 2 974 1122.1 81 33 54 0.715 0.21802 0.00142 0.11166 0.00264 0.5742 0.0189 17.260 0.593 99 2 966 1123.1 88 36 61 1.126 0.21719 0.00153 0.10825 0.00293 0.5882 0.0194 17.613 0.607 101 2 960 11

85

112110: felsic volcanic rock, Nelson’s Fleet


WIDGIEMOOLTHA (SH 51-14) AMG Zone 51, 385130E 6535670N


Sampled from Aztec Mining’s Kalgoorlie core yards. Aztec Mining drillhole

NFD-003, 168–169 m.


This sample is of a felsic volcanic unit within the Black Flag Group of the Kalgoorlie

Terrane.


The sample consists of medium to coarse grains of albitized plagioclase and quartz set

in a fine-grained, sheared matrix of quartz, feldspar, biotite, chlorite, and streamers of

sericite/muscovite. A few of the quartz grains are bipyramids suggesting that they are

of igneous origin. They are set in a fine, probably primary, groundmass. Thus the rock

may be a porphyry (or perhaps, but less probably, a tuff). Chlorite and biotite are both

abundant, but distinct. Lack of intergrowth suggests that the chlorite grew

independently of biotite and is not an alteration product of biotite. Accessory minerals

include apatite, opaques, and tourmaline. Broken zircon grains, 0.014 mm in size, are

present. The rock has clearly been metamorphosed and has been intensely sheared.

Some phases (muscovite/sericite, chlorite) are probably totally metamorphic; others

(biotite) have been mechanically disrupted and perhaps recrystallized; and others

(plagioclase) may only have been mechanically disturbed around grain margins,

although they have apparently been altered. The rock is a carbonated sericitic

feldspar-phyric quartzofeldspathic rock or metaporphyry. GSWA Petrology Report

Number 1596.

86

Zircon morphology

Most zircons are 60–350 µm long, clear to light brown, euhedral to anhedral, and

irregular in shape. Some are strongly zoned and many contain inclusions.

Analytical details

Heavy minerals were isolated from about 1 kg of sample using conventional heavy-

liquid and magnetic techniques.

This sample was analysed on 7 and 8 December 1993. The counter deadtime was

26 ns. Nine analyses of the SL-13 standard were obtained during the session. The Pb*/

U calibration was mobile during the analysis time so the analyses were processed

using bracketing standards. The calibration error for analyses 1.1 to 9.1 was

determined to be 3.50 (1σ%). For analyses 10.1 to 24.1, the calibration error was 5.65

(1σ%).

Results

Twenty-four analyses were obtained from 24 zircons. Results are given in Table 23


Interpretation

Measured 207Pb/206Pb ratios of all 24 analyses form a single population (chi-squared

= 0.78) indicating an age of 2681 ± 5 Ma. This is interpreted as the time of

emplacement of the volcanic rock.

87

Table 23. Ion microprobe analytical results for sample 112110: felsic volcanic rock, Nelson’s Fleet


1.1 93 45 52 1.89 0.18316 0.00185 0.13685 0.00394 0.4639 0.0165 11.71 0.45 92 2 682 172.1 104 76 63 1.50 0.18322 0.00157 0.20427 0.00339 0.4829 0.0171 12.20 0.46 95 2 682 143.1 102 64 62 1.55 0.18044 0.00150 0.17172 0.00324 0.5010 0.0177 12.46 0.47 99 2 657 144.1 111 78 68 1.26 0.18423 0.00142 0.19101 0.00304 0.4980 0.0176 12.65 0.47 97 2 691 135.1 71 38 42 1.02 0.18345 0.00166 0.14902 0.00343 0.5050 0.0180 12.77 0.48 98 2 684 156.1 92 47 55 1.87 0.18197 0.00179 0.13827 0.00383 0.4950 0.0176 12.42 0.47 97 2 671 167.1 79 33 46 2.11 0.18423 0.00217 0.11887 0.00463 0.4803 0.0171 12.20 0.47 94 2 691 198.1 94 61 57 1.38 0.18343 0.00160 0.18321 0.00343 0.4898 0.0174 12.39 0.47 96 2 684 149.1 74 42 43 1.41 0.18228 0.00164 0.14814 0.00345 0.4830 0.0172 12.14 0.46 95 2 674 15

10.1 66 41 40 1.67 0.18436 0.00196 0.17331 0.00421 0.4935 0.0281 12.54 0.74 96 2 693 1811.1 96 70 59 1.38 0.18200 0.00158 0.20122 0.00344 0.4913 0.0279 12.33 0.72 96 2 671 1412.1 103 47 61 1.19 0.18242 0.00147 0.12184 0.00303 0.5100 0.0289 12.83 0.75 99 2 675 1313.1 111 82 71 1.25 0.18274 0.00136 0.20081 0.00292 0.5193 0.0295 13.09 0.76 101 2 678 1214.1 123 68 78 1.08 0.18359 0.00126 0.15426 0.00262 0.5316 0.0301 13.46 0.78 102 2 686 1115.1 88 47 55 1.10 0.18380 0.00150 0.14483 0.00310 0.5253 0.0298 13.31 0.78 101 2 688 1316.1 70 38 43 1.84 0.18094 0.00206 0.14207 0.00439 0.5124 0.0291 12.78 0.76 100 2 662 1917.1 78 41 51 1.43 0.18284 0.00179 0.13727 0.00377 0.5569 0.0317 14.04 0.83 107 2 679 1618.1 141 84 95 0.87 0.18327 0.00105 0.15896 0.00213 0.5656 0.0321 14.29 0.82 108 2 683 919.1 60 32 41 2.11 0.18013 0.00233 0.14346 0.00501 0.5589 0.0318 13.88 0.83 108 2 654 2120.1 57 35 38 0.50 0.18648 0.00157 0.17062 0.00314 0.5706 0.0325 14.67 0.86 107 2 711 1421.1 131 95 94 0.88 0.18241 0.00109 0.20106 0.00230 0.5886 0.0334 14.80 0.85 112 2 675 1022.1 91 49 64 1.60 0.18092 0.00163 0.14243 0.00345 0.5866 0.0333 14.63 0.86 112 2 661 1523.1 191 215 142 0.73 0.18446 0.00095 0.30994 0.00217 0.5657 0.0320 14.39 0.83 107 2 693 924.1 71 40 50 1.94 0.18133 0.00212 0.15296 0.00456 0.5748 0.0327 14.37 0.86 110 2 665 19

88

Figure 24. Concordia plot for sample 112110: felsic volcanic rock, Nelson’s Fleet

89

112147: porphyritic dacite, Yindi Woolshed


KURNALPI (SH 51-10) AMG Zone 51, 455600E 6615400N

Sampled on 27 June 1992

The sample is from a well-exposed outcrop of a porphyritic dacitic volcanic rock with

obvious quartz and feldspar phenocrysts.


This sample is of a felsic volcanic unit within the Mulgabbie Domain of the Kurnalpi

Terrane.


This rock is composed of subhedral phenocrysts and aggregates of oligoclase up to

3 mm across, in a flow-banded, very fine-grained quartzofeldspathic groundmass

containing minor muscovite and biotite. Larger secondary muscovite flakes and

carbonate are present, with accessory opaques, zircon, and apatite. Carbonate is

present in two phases: early formed small crystals of ankerite, from which iron has

exsolved, and later formed, clear patches of calcite. Original biotite forms small

ragged olive-green flakes, which have been partially altered to chlorite. The more

common red-brown biotite is of metamorphic origin and indicates medium-grade, or

greenschist/amphibolite-transition facies metamorphism. Zircons are small

(20–70 µm), fresh, and unzoned. GSWA Petrology Report Number 1608.

Zircon morphology

Most zircons are 60–200 µm long, clear and colourless, anhedral to irregular, and

rounded. They are unzoned and contain some inclusions.

Analytical details



90

This sample was analysed on 8 and 9 December 1993. The counter deadtime was

26 ns. Six analyses of the SL-13 standard were obtained during the analysis of this

sample but standards analysed during the dating of another sample (112110), analysed

earlier in the same session, also indicate trends. The Pb*/U calibration was mobile

during the analysis time so analyses were processed using bracketing standards. The

Pb*/U calibration error was determined to be 5.65 (1σ%) for all unknown samples.

Results

Twenty-five analyses were obtained from 24 zircons. Results are given in Table 24


Interpretation

Measured 207Pb/206Pb ratios of all 25 analyses form a single population within the

assigned analytical errors (chi-squared = 0.97) indicating an interpreted time of

emplacement of the volcanic rock at 2673 ± 7 Ma.

Figure 25. Concordia plot for sample 112147: porphyritic dacite, Yindi Woolshed

91

Table 24. Ion microprobe analytical results for sample 112147: porphyritic dacite, Yindi Woolshed


1.1 66 51 47 1.88 0.17838 0.00217 0.20364 0.00479 0.5582 0.0318 13.73 0.82 108 2 638 202.1 101 77 68 1.31 0.18261 0.00158 0.20599 0.00342 0.5420 0.0308 13.65 0.80 104 2 677 143.1 81 57 51 2.29 0.18168 0.00225 0.19275 0.00496 0.4985 0.0283 12.49 0.75 98 2 668 214.1 77 40 51 2.20 0.17931 0.00217 0.13608 0.00468 0.5416 0.0308 13.39 0.80 105 2 647 205.1 73 52 44 3.01 0.18109 0.00262 0.18646 0.00580 0.4733 0.0270 11.82 0.71 94 2 663 246.1 72 52 45 1.30 0.18009 0.00180 0.19872 0.00388 0.5089 0.0290 12.64 0.75 100 2 654 177.1 79 57 51 0.99 0.18209 0.00162 0.18913 0.00342 0.5287 0.0301 13.27 0.78 102 2 672 158.1 79 63 51 1.08 0.18405 0.00176 0.22348 0.00385 0.5194 0.0295 13.18 0.78 100 2 690 169.1 60 39 40 2.66 0.17822 0.00265 0.17007 0.00583 0.5353 0.0305 13.15 0.80 105 2 636 25

10.1 72 52 48 2.09 0.18272 0.00237 0.19914 0.00520 0.5183 0.0295 13.06 0.78 101 2 678 2111.1 105 86 72 0.58 0.18531 0.00126 0.22356 0.00267 0.5503 0.0312 14.06 0.82 105 2 701 1112.1 77 44 47 2.01 0.18466 0.00229 0.15573 0.00493 0.4966 0.0283 12.64 0.76 96 2 695 2113.1 69 56 47 2.13 0.18227 0.00226 0.22625 0.00503 0.5267 0.0300 13.24 0.79 102 2 674 2114.1 97 76 60 1.86 0.18264 0.00189 0.21105 0.00416 0.4901 0.0278 12.34 0.73 96 2 677 1715.1 68 53 43 1.75 0.18339 0.00209 0.19820 0.00455 0.5049 0.0288 12.77 0.76 98 2 684 1916.1 58 37 33 1.08 0.18296 0.00218 0.17680 0.00462 0.4701 0.0268 11.86 0.71 93 2 680 2017.1 72 51 43 1.93 0.18176 0.00211 0.18771 0.00459 0.4770 0.0272 11.95 0.71 94 2 669 1918.1 53 35 31 2.12 0.18434 0.00264 0.18035 0.00576 0.4631 0.0265 11.77 0.71 91 2 692 2419.1 78 59 51 0.99 0.18435 0.00175 0.20343 0.00374 0.5332 0.0303 13.55 0.80 102 2 692 1620.1 106 96 67 1.57 0.18215 0.00172 0.22879 0.00378 0.4969 0.0282 12.48 0.73 97 2 673 1621.1 72 60 46 1.15 0.17955 0.00191 0.22200 0.00417 0.5126 0.0292 12.69 0.75 101 2 649 1822.1 45 26 29 1.76 0.18335 0.00314 0.15786 0.00681 0.5268 0.0302 13.32 0.82 102 2 683 2823.1 92 70 66 0.65 0.18019 0.00138 0.20310 0.00289 0.5859 0.0333 14.56 0.85 112 2 655 1324.1 70 48 51 0.47 0.18286 0.00176 0.18878 0.00365 0.6102 0.0348 15.39 0.91 115 2 679 161.2 54 35 42 2.64 0.18108 0.00298 0.17019 0.00652 0.6137 0.0350 15.32 0.94 116 2 663 27

92

100710: felsic tuff, Reidy Swamp





This sample is of a felsic volcanic unit within the Kanowna Domain of the Kurnalpi

Terrane. It is from a well-exposed outcrop of porphyry and occurs adjacent to rocks

that contain unequivocal volcaniclastic textures, suggesting that it was also probably

volcanic in origin. It is closely associated with basalts.


Not available.

Zircon morphology

Most zircons are 200–400 µm long, light brown to dark brown, euhedral, and strongly

zoned. Many have inclusions.

Analytical details



This sample was analysed on 18 and 19 February 1994. The counter deadtime

was 26 ns. Twelve analyses of the SL-13 standard were obtained. The Pb*/U

calibration was mobile during the early stages of the analysis time so the first five

unknown samples (first group of two and second group of three analyses) were

processed using the Pb*/U calibration determined from bracketing standards. The

93

remaining unknown samples were processed as one group. The Pb*/U calibration

error was 3.69 (1σ%) for all analyses of unknown samples.

Results

Thirty-seven analyses were obtained from 37 zircons. Results are given in Table 25


Interpretation

Measured 207Pb/206Pb ratios of 26 analyses form a single population with little excess

scatter (chi-squared = 2.16) and correspond to an interpreted time of emplacement of

the volcanic unit at 2683 ± 3 Ma. A further eleven analyses, characterized by higher U

concentrations, have lower 207Pb/206Pb ages. These are interpreted to be of disturbed

zones of zircons from the main 2683 Ma population.

Figure 26. Concordia plot for sample 100710: felsic tuff, Reidy Swamp

94

Table 25. Ion microprobe analytical results for sample 100710: felsic tuff, Reidy Swamp


1.1 569 341 313 0.021 0.17364 0.00030 0.16307 0.00050 0.4775 0.0176 11.43 0.43 97 2 593 32.1 1 449 742 578 0.014 0.12608 0.00017 0.14134 0.00033 0.3656 0.0135 6.36 0.24 98 2 044 23.1 351 251 211 0.002 0.18371 0.00035 0.19311 0.00060 0.5082 0.0188 12.87 0.48 99 2 687 34.1 161 75 93 0.202 0.18360 0.00059 0.12486 0.00099 0.5123 0.0190 12.97 0.49 99 2 686 55.1 1 869 845 673 0.041 0.12095 0.00015 0.12445 0.00028 0.3357 0.0124 5.60 0.21 95 1 970 26.1 448 283 243 0.251 0.17257 0.00037 0.17150 0.00071 0.4641 0.0171 11.04 0.41 95 2 583 47.1 179 61 104 0.035 0.18398 0.00051 0.09214 0.00064 0.5250 0.0194 13.32 0.50 101 2 689 58.1 181 88 105 0.036 0.18224 0.00052 0.13025 0.00077 0.5140 0.0190 12.91 0.48 100 2 673 59.1 268 212 163 0.015 0.18204 0.00040 0.21235 0.00073 0.5070 0.0187 12.73 0.47 99 2 672 4

10.1 98 38 57 0.243 0.18336 0.00082 0.10846 0.00137 0.5216 0.0194 13.19 0.50 101 2 684 711.1 364 182 215 0.034 0.18410 0.00035 0.13476 0.00052 0.5193 0.0192 13.18 0.49 100 2 690 312.1 199 105 114 0.047 0.18155 0.00051 0.14061 0.00080 0.5020 0.0186 12.57 0.47 98 2 667 513.1 333 126 190 0.360 0.18217 0.00047 0.10203 0.00081 0.5106 0.0189 12.82 0.48 99 2 673 414.1 259 120 154 0.018 0.18391 0.00043 0.12730 0.00062 0.5255 0.0194 13.33 0.50 101 2 688 415.1 2 615 1 994 1 107 0.007 0.13497 0.00013 0.20891 0.00028 0.3658 0.0135 6.81 0.25 93 2 164 216.1 535 212 299 0.013 0.18175 0.00028 0.10611 0.00036 0.5053 0.0187 12.66 0.47 99 2 669 317.1 494 247 259 0.013 0.16515 0.00028 0.13271 0.00043 0.4699 0.0174 10.70 0.40 99 2 509 318.1 473 392 292 0.018 0.18360 0.00030 0.22662 0.00057 0.5084 0.0188 12.87 0.48 99 2 686 319.1 163 65 90 0.148 0.18321 0.00059 0.10786 0.00092 0.4954 0.0183 12.51 0.47 97 2 682 520.1 139 63 83 0.244 0.18223 0.00067 0.12174 0.00115 0.5252 0.0195 13.20 0.50 102 2 673 621.1 492 220 282 0.036 0.18008 0.00031 0.12092 0.00043 0.5110 0.0189 12.69 0.47 100 2 654 322.1 322 141 178 0.030 0.17888 0.00039 0.11901 0.00055 0.4952 0.0183 12.21 0.46 98 2 643 423.1 141 50 83 0.528 0.18291 0.00081 0.10022 0.00146 0.5261 0.0195 13.27 0.50 102 2 679 724.1 262 204 156 0.019 0.18308 0.00044 0.20867 0.00080 0.4975 0.0184 12.56 0.47 97 2 681 425.1 284 222 173 0.100 0.18293 0.00045 0.21173 0.00084 0.5055 0.0187 12.75 0.48 98 2 680 426.1 252 92 145 0.086 0.18470 0.00046 0.09885 0.00066 0.5177 0.0191 13.18 0.49 100 2 696 427.1 333 215 197 0.186 0.18343 0.00043 0.17273 0.00078 0.5047 0.0187 12.77 0.48 98 2 684 428.1 361 233 211 0.041 0.17882 0.00036 0.17165 0.00062 0.5021 0.0186 12.38 0.46 99 2 642 329.1 258 106 147 0.028 0.18379 0.00044 0.10945 0.00058 0.5111 0.0189 12.95 0.48 99 2 687 430.1 302 134 177 0.083 0.18313 0.00041 0.11858 0.00061 0.5216 0.0193 13.17 0.49 101 2 681 4

95

Table 25. (continued)


31.1 240 129 139 0.154 0.18232 0.00049 0.14593 0.00084 0.5052 0.0187 12.70 0.48 99 2 674 432.1 296 133 172 0.241 0.18242 0.00047 0.12336 0.00080 0.5138 0.0190 12.92 0.48 100 2 675 433.1 184 123 111 0.149 0.18381 0.00058 0.18239 0.00106 0.5091 0.0188 12.90 0.48 99 2 688 534.1 269 135 151 0.128 0.18323 0.00046 0.13622 0.00075 0.4930 0.0182 12.46 0.47 96 2 682 435.1 256 102 147 0.029 0.18296 0.00043 0.10827 0.00059 0.5144 0.0190 12.98 0.48 100 2 680 436.1 274 182 153 0.052 0.18314 0.00045 0.18054 0.00077 0.4733 0.0175 11.95 0.45 93 2 682 437.1 267 122 145 0.122 0.18295 0.00047 0.12097 0.00074 0.4837 0.0179 12.20 0.46 95 2 680 4

96

100726: felsic tuff, Bulong townsite




Sampling locality is about 5 km southeast of Bulong townsite, about 20–30 m from

the contact with ultramafic rocks of the Bulong Complex.


This sample is of a felsic volcanic unit interbedded with mafic lavas of the Bulong

Complex, in the Kanowna Domain of the Kurnalpi Terrane. The sample is from a

felsic volcaniclastic unit containing tuffaceous zones and cognate clasts.


Not available.

Zircon morphology

Most zircons are 200–400 µm long, colourless to light brown, euhedral to irregular in

shape, and strongly zoned.

Analytical details



This sample was analysed on 4 and 5 February 1994. The counter deadtime was

26 ns. Thirteen analyses of the SL-13 standard were obtained but standard analysis 3

was deleted as an outlier. The Pb*/U calibration was unstable and changed

97

unsystematically. The Pb*/U calibration error was 4.48 (1σ%) for all analyses of

unknown samples.

Results

Thirty-one analyses were obtained from 31 zircons. Results are given in Table 26 and


Interpretation

Measured 207Pb/206Pb ratios of 30 analyses form a single population with a little

excess scatter (chi-squared = 2.62), indicating the volcanic unit was emplaced at

2705 ± 4 Ma. One analysis (8.1) has a significantly lower 207Pb/206Pb ratio and is

interpreted to be of a disturbed zone of a zircon originally belonging to the main

population.

Figure 27. Concordia plot for sample 100726: felsic tuff, Bulong townsite

98

Table 26. Ion microprobe analytical results for sample 100726: felsic tuff, Bulong townsite


1.1 193 163 155 0.295 0.18607 0.00081 0.22487 0.00165 0.6540 0.0294 16.78 0.77 120 2 708 72.1 710 665 575 0.125 0.18690 0.00038 0.24679 0.00076 0.6530 0.0293 16.83 0.76 119 2 715 33.1 324 222 231 0.071 0.18678 0.00060 0.17926 0.00106 0.6065 0.0272 15.62 0.71 113 2 714 54.1 183 110 131 0.135 0.18497 0.00085 0.15837 0.00154 0.6171 0.0277 15.74 0.72 115 2 698 85.1 272 222 200 0.047 0.18621 0.00071 0.21660 0.00135 0.6077 0.0273 15.60 0.71 113 2 709 66.1 393 185 258 0.144 0.18687 0.00060 0.12491 0.00099 0.5798 0.0260 14.94 0.68 109 2 715 57.1 636 360 424 0.088 0.18579 0.00047 0.14859 0.00078 0.5796 0.0260 14.85 0.67 109 2 705 48.1 453 257 294 0.154 0.17727 0.00055 0.14559 0.00098 0.5675 0.0254 13.87 0.63 110 2 628 59.1 471 315 317 0.085 0.18475 0.00052 0.16749 0.00090 0.5767 0.0259 14.69 0.67 109 2 696 5

10.1 288 181 194 0.160 0.18770 0.00078 0.16425 0.00141 0.5758 0.0258 14.90 0.68 108 2 722 711.1 173 86 111 0.399 0.18510 0.00125 0.12468 0.00228 0.5608 0.0252 14.31 0.66 106 2 699 1112.1 139 92 87 0.571 0.18398 0.00152 0.14693 0.00304 0.5360 0.0241 13.60 0.64 103 2 689 1413.1 189 128 125 0.113 0.18486 0.00097 0.17360 0.00175 0.5634 0.0253 14.36 0.66 107 2 697 914.1 246 141 156 0.104 0.18669 0.00091 0.15066 0.00157 0.5510 0.0248 14.18 0.65 104 2 713 815.1 178 63 109 -0.013 0.18594 0.00103 0.09530 0.00157 0.5553 0.0250 14.24 0.65 105 2 707 916.1 511 324 326 0.275 0.18354 0.00070 0.14531 0.00127 0.5516 0.0247 13.96 0.63 105 2 685 617.1 277 191 165 0.011 0.18660 0.00084 0.14735 0.00126 0.5182 0.0233 13.33 0.61 99 2 712 718.1 124 83 77 0.889 0.18344 0.00207 0.11382 0.00416 0.5370 0.0242 13.58 0.65 103 2 684 1919.1 783 730 551 0.735 0.18340 0.00077 0.24470 0.00168 0.5593 0.0251 14.14 0.64 107 2 684 720.1 670 302 403 0.060 0.18613 0.00059 0.11719 0.00092 0.5352 0.0240 13.74 0.62 102 2 708 521.1 278 319 164 0.757 0.18570 0.00133 0.19101 0.00277 0.4869 0.0219 12.47 0.58 95 2 704 1222.1 263 137 152 0.206 0.18263 0.00108 0.13215 0.00193 0.5094 0.0229 12.83 0.59 99 2 677 1023.1 128 63 74 0.630 0.18392 0.00247 0.10922 0.00490 0.5089 0.0230 12.90 0.63 99 2 689 2224.1 255 91 148 0.155 0.18635 0.00106 0.09370 0.00169 0.5248 0.0236 13.48 0.62 100 2 710 925.1 317 169 190 0.148 0.18384 0.00097 0.12956 0.00169 0.5270 0.0237 13.36 0.61 102 2 688 926.1 150 111 94 0.738 0.18236 0.00184 0.17351 0.00375 0.5214 0.0235 13.11 0.62 101 2 674 1727.1 128 49 76 0.160 0.18560 0.00171 0.10264 0.00287 0.5370 0.0242 13.74 0.65 102 2 704 1528.1 193 237 137 0.103 0.18574 0.00129 0.30714 0.00292 0.5506 0.0248 14.10 0.65 105 2 705 1229.1 116 54 69 0.433 0.18775 0.00208 0.12167 0.00398 0.5174 0.0234 13.39 0.64 99 2 723 1830.1 332 298 215 0.086 0.18404 0.00092 0.23803 0.00181 0.5275 0.0237 13.39 0.61 102 2 690 831.1 300 159 177 0.097 0.18825 0.00106 0.14025 0.00180 0.5134 0.0231 13.33 0.61 98 2 727 9

99

112112: K-feldspar volcanic rock, Jump Up Dam


EDJUDINA (SH 51-6) AMG Zone 51, 412300E 6710100N


Sampling locality is about 2 km southeast of Jump Up Dam.


This sample is of a felsic volcanic unit within the Kurnalpi Domain of the Kurnalpi

Terrane. The sample is a fine- to medium grained, banded, quartzofeldspathic rock,

possibly a felsic volcanic unit, from a 20 m-thick horizon interleaved with tholeiitic

basalt.


This is a carbonated porphyritic rhyodacite with a remarkably large amount of

K-feldspar. The apparent proportion of K-feldspar is probably enhanced by

saussuritization and carbonatization of plagioclase, and the dismemberment of

plagioclase during late-magmatic flow. Phenocrysts of all three major minerals —

quartz, plagioclase, and K-feldspar — are abundant. Opaques, now mainly leucoxene,

are abundant. Chlorite with low birefringence, but apparently in part prograde, is a

common accessory. Zircon was not found in a brief traverse of the thin section. A flow

structure is very strong throughout the sample, but is probably late magmatic rather

than metamorphic because all three major phenocryst minerals are still represented in

the phenocryst assemblage. If deformation occurred in the solid state, differential

fragmentation could be expected to have left one of the phases poorly represented. In

particular, quartz seems to have survived with little disruption. The presence of a few

subhedral quartz grains suggests that the rock crystallized as a porphyry and is not a

sheared granite. GSWA Petrology Report Number 1596.

Zircon morphology

Most zircons are 75–400 µm long, colourless to dark brown, euhedral, weakly to

strongly zoned, and a few have rare inclusions.

100

Analytical details



This sample was analysed on 16 and 17 March 1994. The counter deadtime was

36 ns. Thirteen analyses of the CZ-3 standard were obtained. The Pb*/U calibration

was stable with a calibration error of 2.22 (1σ%).

Results

Forty-three analyses were obtained from 40 zircons. Results are given in Table 27 and


Figure 28. Concordia plot for sample 112112: K-feldspar volcanic rock, Jump Up Dam

101

Interpretation

Measured 207Pb/206Pb ratios of 41 analyses on 38 zircons form a single population

with a little excess scatter (chi-squared = 2.50), indicating an interpreted time of

emplacement of the volcanic rock at 2684 ± 3 Ma. Analysis 14.1, which has a207Pb/206Pb age of 2730 ± 13 Ma, is interpreted to be of a xenocrystic zircon. Analysis

11.1, with a lower 207Pb/206Pb age of 2558 ± 4 Ma, has a significantly higher U

concentration and is interpreted to be of a disturbed zone of a zircon originally

belonging to the main population.

102

Table 27. Ion microprobe analytical results for sample 112112: K-feldspar volcanic rock, Jump Up Dam


1.1 242 144 146 0.082 0.18234 0.00053 0.16070 0.00096 0.5199 0.0116 13.07 0.30 101 2 674 52.1 80 36 47 0.267 0.18366 0.00100 0.11524 0.00180 0.5234 0.0119 13.25 0.32 101 2 686 93.1 91 33 52 0.212 0.18233 0.00102 0.09768 0.00185 0.5131 0.0116 12.90 0.31 100 2 674 94.1 169 94 100 0.120 0.18295 0.00065 0.14844 0.00117 0.5123 0.0115 12.92 0.30 100 2 680 65.1 488 342 297 0.010 0.18454 0.00034 0.19168 0.00061 0.5137 0.0114 13.07 0.29 99 2 694 36.1 142 78 85 0.123 0.18301 0.00071 0.14956 0.00127 0.5224 0.0117 13.18 0.31 101 2 680 67.1 169 88 99 0.201 0.18343 0.00070 0.13866 0.00126 0.5129 0.0115 12.97 0.30 99 2 684 68.1 111 49 64 0.114 0.18307 0.00077 0.11854 0.00130 0.5115 0.0115 12.91 0.30 99 2 681 79.1 85 29 50 0.383 0.18109 0.00113 0.08937 0.00211 0.5343 0.0121 13.34 0.32 104 2 663 10

10.1 121 42 70 1.055 0.18447 0.00130 0.10353 0.00264 0.5053 0.0114 12.85 0.31 98 2 693 1211.1 476 259 222 0.073 0.17002 0.00037 0.13733 0.00063 0.4133 0.0092 9.69 0.22 87 2 558 412.1 119 47 66 0.536 0.18434 0.00106 0.10024 0.00200 0.4946 0.0111 12.57 0.30 96 2 692 913.1 114 60 69 0.766 0.18119 0.00109 0.14023 0.00222 0.5173 0.0117 12.92 0.31 101 2 664 1014.1 78 29 45 0.695 0.18859 0.00152 0.10353 0.00301 0.5091 0.0116 13.24 0.33 97 2 730 1315.1 127 58 73 0.356 0.18256 0.00085 0.12970 0.00159 0.5058 0.0114 12.73 0.30 99 2 676 816.1 231 91 132 1.232 0.18392 0.00089 0.11334 0.00182 0.4929 0.0110 12.50 0.29 96 2 689 817.1 102 32 55 0.213 0.18572 0.00092 0.08672 0.00155 0.4910 0.0111 12.57 0.30 95 2 705 818.1 154 59 89 1.283 0.18306 0.00111 0.09940 0.00227 0.5006 0.0112 12.64 0.30 98 2 681 1019.1 106 47 62 1.049 0.18052 0.00135 0.11127 0.00276 0.5051 0.0114 12.57 0.31 99 2 658 1220.1 110 37 63 0.157 0.18566 0.00095 0.09221 0.00164 0.5208 0.0118 13.33 0.32 100 2 704 821.1 105 37 61 0.264 0.18416 0.00111 0.09611 0.00206 0.5184 0.0117 13.16 0.32 100 2 691 1022.1 119 58 66 1.454 0.18036 0.00145 0.10764 0.00304 0.4803 0.0108 11.94 0.30 95 2 656 1323.1 126 47 73 0.232 0.18259 0.00090 0.10169 0.00161 0.5193 0.0117 13.08 0.31 101 2 677 824.1 137 70 82 0.275 0.18455 0.00087 0.13958 0.00160 0.5183 0.0117 13.19 0.31 100 2 694 825.1 115 43 67 0.455 0.18358 0.00100 0.09682 0.00185 0.5206 0.0118 13.18 0.31 101 2 686 926.1 186 104 111 0.470 0.18352 0.00081 0.15300 0.00159 0.5112 0.0115 12.93 0.30 99 2 685 727.1 141 65 83 0.240 0.18367 0.00083 0.12401 0.00148 0.5170 0.0116 13.09 0.31 100 2 686 728.1 85 35 50 0.373 0.18402 0.00115 0.11272 0.00212 0.5251 0.0119 13.32 0.32 101 2 689 1029.1 177 91 104 0.307 0.18157 0.00073 0.13581 0.00135 0.5149 0.0116 12.89 0.30 100 2 667 730.1 221 87 129 0.183 0.18375 0.00059 0.10561 0.00097 0.5232 0.0117 13.26 0.30 101 2 687 531.1 147 53 79 0.607 0.18114 0.00097 0.10392 0.00187 0.4780 0.0107 11.94 0.28 95 2 663 9

103



32.1 100 55 61 0.237 0.18230 0.00101 0.14924 0.00188 0.5313 0.0120 13.35 0.32 103 2 674 933.1 307 159 182 0.268 0.18314 0.00060 0.14185 0.00111 0.5149 0.0115 13.00 0.30 100 2 682 534.1 195 93 112 0.606 0.18022 0.00091 0.12666 0.00177 0.5017 0.0113 12.47 0.29 99 2 655 81.2 401 279 245 0.099 0.18418 0.00034 0.19002 0.00061 0.5138 0.0114 13.05 0.29 99 2 691 31.3 266 163 162 0.186 0.18401 0.00043 0.16752 0.00078 0.5201 0.0116 13.20 0.30 100 2 689 4

35.1 212 72 121 0.982 0.18126 0.00073 0.09182 0.00146 0.5029 0.0112 12.57 0.29 99 2 664 736.1 95 46 58 0.393 0.18364 0.00094 0.13454 0.00183 0.5300 0.0119 13.42 0.32 102 2 686 937.1 124 45 72 0.146 0.18380 0.00065 0.09627 0.00103 0.5279 0.0118 13.38 0.31 102 2 687 638.1 142 69 85 1.036 0.18424 0.00089 0.13133 0.00182 0.5105 0.0114 12.97 0.30 99 2 691 839.1 109 49 65 0.887 0.18375 0.00105 0.12657 0.00213 0.5164 0.0116 13.08 0.31 100 2 687 940.1 94 42 56 0.381 0.18545 0.00093 0.12373 0.00174 0.5174 0.0117 13.23 0.31 99 2 702 87.2 113 40 64 0.320 0.18223 0.00092 0.09235 0.00165 0.5070 0.0114 12.74 0.30 99 2 673 8

104

100758: felsic volcanic breccia, Perkolilli




Sampling locality is about 1 km northeast of Harry Dam.


This sample is of a felsic volcanic rock within the Black Flag Group of the Kalgoorlie

Terrane, near the interpreted Kalgoorlie–Kurnalpi terrane boundary. It is from a felsic

volcaniclastic breccia containing clasts of black aphanitic blocks and quartz–feldspar

porphyry.


Not available.

Zircon morphology

Most zircons are 50–100 µm long, light brown to dark brown, irregular shaped, and

unzoned to strongly zoned. Some zircons contain inclusions.

Analytical details



This sample was analysed on 2 March and 7–8 March 1994 in two separate

batches. The counter deadtime was 36 ns. The SL-13 standard was used. Batch 1

consisted of two standards and three unknown samples. Background counts were high

during the analysis of this batch. The Pb*/U calibration error on two standards was

105

1.12 (1σ%). Unknown samples were processed assuming a calibration error of

2.5 (1σ%). Batch 2 consisted of 12 standards and 37 unknown samples. The Pb*/U

calibration error on the 12 standards was 4.62 (1σ%).

Results

Forty analyses were obtained from 36 zircons. Results are given in Table 28 and


Figure 29. Concordia plot for sample 100758: felsic volcanic breccia, Perkolilli

106

Table 28. Ion microprobe analytical results for sample 100758: felsic volcanic breccia, Perkolilli


1.1 155 76 91 0.596 0.18551 0.00151 0.12768 0.00311 0.5116 0.0131 13.09 0.36 99 2 703 132.1 149 53 85 0.545 0.18023 0.00128 0.09194 0.00248 0.5153 0.0132 12.80 0.35 101 2 655 123.1 121 72 72 0.575 0.18253 0.00153 0.15555 0.00316 0.5108 0.0132 12.85 0.36 99 2 676 144.1 135 51 74 0.323 0.18277 0.00106 0.09655 0.00199 0.4963 0.0230 12.51 0.59 97 2 678 105.1 119 53 68 2.092 0.18026 0.00174 0.09011 0.00369 0.4865 0.0225 12.09 0.59 96 2 655 166.1 124 59 73 0.275 0.18329 0.00109 0.12431 0.00211 0.5158 0.0239 13.04 0.62 100 2 683 107.1 134 46 74 1.777 0.18662 0.00205 0.09656 0.00432 0.4702 0.0218 12.10 0.59 92 2 713 188.1 161 63 94 0.041 0.18156 0.00058 0.10263 0.00083 0.5313 0.0246 13.30 0.62 103 2 667 59.1 158 87 96 0.194 0.18158 0.00069 0.14636 0.00127 0.5303 0.0245 13.28 0.62 103 2 667 6

10.1 142 64 83 0.228 0.18269 0.00072 0.10018 0.00123 0.5281 0.0244 13.30 0.62 102 2 677 711.1 158 64 98 1.405 0.18395 0.00114 0.11753 0.00238 0.5298 0.0245 13.44 0.64 102 2 689 1012.1 164 113 103 0.289 0.18361 0.00076 0.18327 0.00151 0.5275 0.0244 13.35 0.63 102 2 686 713.1 147 134 80 1.304 0.18076 0.00113 0.11160 0.00236 0.4702 0.0217 11.72 0.56 93 2 660 1014.1 148 65 88 0.461 0.18250 0.00085 0.11600 0.00166 0.5235 0.0242 13.17 0.62 101 2 676 815.1 202 118 98 1.527 0.18063 0.00111 0.08914 0.00230 0.4236 0.0196 10.55 0.50 86 2 659 1016.1 95 41 56 0.455 0.18143 0.00110 0.11154 0.00211 0.5163 0.0239 12.92 0.61 101 2 666 1017.1 133 68 82 0.306 0.18223 0.00082 0.13615 0.00154 0.5349 0.0247 13.44 0.63 103 2 673 718.1 149 51 88 0.309 0.18225 0.00084 0.08944 0.00152 0.5333 0.0247 13.40 0.63 103 2 673 819.1 167 69 101 0.255 0.18355 0.00073 0.10782 0.00130 0.5434 0.0251 13.75 0.64 104 2 685 720.1 144 77 80 0.738 0.18465 0.00100 0.10723 0.00196 0.4902 0.0227 12.48 0.59 95 2 695 921.1 147 71 89 1.433 0.18225 0.00118 0.12171 0.00247 0.5117 0.0237 12.86 0.61 100 2 673 1122.1 166 112 105 0.089 0.18552 0.00069 0.18474 0.00129 0.5339 0.0247 13.66 0.64 102 2 703 622.2 156 54 90 0.146 0.18317 0.00076 0.09268 0.00119 0.5203 0.0241 13.14 0.62 101 2 682 723.1 163 60 95 0.443 0.18290 0.00091 0.09397 0.00171 0.5227 0.0242 13.18 0.62 101 2 679 823.2 131 77 81 0.453 0.18209 0.00111 0.15453 0.00225 0.5262 0.0243 13.21 0.63 102 2 672 101.2 130 64 80 0.810 0.18132 0.00095 0.12725 0.00193 0.5297 0.0245 13.24 0.62 103 2 665 94.2 178 109 109 0.290 0.18193 0.00062 0.16034 0.00117 0.5275 0.0244 13.23 0.62 102 2 671 6

24.1 165 103 109 0.133 0.18293 0.00052 0.15506 0.00093 0.5706 0.0264 14.39 0.67 109 2 680 525.1 152 69 100 1.122 0.18303 0.00086 0.12990 0.00177 0.5610 0.0259 14.16 0.67 107 2 681 826.1 79 35 49 1.445 0.18246 0.00133 0.10281 0.00276 0.5361 0.0248 13.49 0.64 103 2 675 1227.1 177 116 119 0.143 0.18228 0.00052 0.17801 0.00097 0.5724 0.0264 14.39 0.67 109 2 674 5

107



28.1 184 62 116 0.127 0.18288 0.00050 0.09142 0.00077 0.5722 0.0264 14.43 0.67 109 2 679 429.1 172 68 109 0.493 0.18162 0.00064 0.10084 0.00121 0.5632 0.0260 14.10 0.66 108 2 668 630.1 165 99 112 0.271 0.18313 0.00068 0.16724 0.00130 0.5789 0.0268 14.62 0.68 110 2 681 631.1 169 81 113 0.445 0.18172 0.00076 0.13152 0.00146 0.5837 0.0270 14.62 0.69 111 2 669 732.1 191 111 114 0.756 0.18203 0.00076 0.08767 0.00146 0.5352 0.0247 13.43 0.63 103 2 671 733.1 178 76 114 0.217 0.18087 0.00054 0.11585 0.00095 0.5692 0.0263 14.20 0.66 109 2 661 534.1 134 72 90 0.143 0.18189 0.00062 0.14874 0.00111 0.5833 0.0270 14.63 0.68 111 2 670 635.1 161 54 100 0.067 0.18279 0.00056 0.09164 0.00090 0.5650 0.0261 14.24 0.66 108 2 678 536.1 171 107 111 0.394 0.18307 0.00065 0.16800 0.00129 0.5505 0.0254 13.90 0.65 105 2 681 6

108

Interpretation

Measured 207Pb/206Pb ratios of 36 analyses on 32 zircons form a single population

(chi-squared = 1.05) indicating an interpreted time of emplacement of the volcanic

rock at 2675 ± 3 Ma. Analyses 7.1, 20.1, and 22.1 have 207Pb/206Pb ratios within error

of a single value (chi-squared = 0.38) corresponding to an age of 2701 ± 20 Ma. These

analyses are interpreted to be of xenocrysts. Analysis 33.1, with a 207Pb/206Pb age of

2661 ± 5 Ma, is considered to be of a disturbed zone of a zircon belonging to the main

population.

109

104958: dacite, Ballarat – Last Chance



Core sampled on 14 August 1990

Geopeko drillhole DK-8, 93.6–95 m. Drillhole located on eastern side of ultramafic–

felsic contact.


This sample is from a felsic volcanic unit interbedded with the komatiite unit of the

Kalgoorlie Terrane.


The sample consists of very abundant, largely euhedral albite phenocrysts plus rare,

partly adsorbed quartz, and a few lithic clasts set in a quartz–sericite–carbonate

matrix. The sericite and carbonate are presumably after original groundmass feldspar.

Very small aggregates of powdery Ti-rich grains are abundant and there may be a few

small grains of apatite. The rock has undergone low grade metamorphism. Matrix

feldspars have been sericitized and carbonatized. Feldspar phenocrysts are heavily

dusted with alteration products as well as partially replaced with carbonate, and

possibly albitized. The extremely abundant quasi-euhedral plagioclase phenocrysts

indicate an igneous origin for the rock. However, recrystallization of the matrix would

make any textural evidence of a tuff difficult to recognize. The only indication of a

possible tuffaceous origin is the presence of what may be sparse lithic fragments. If

the rock were a tuff with a significant sedimentary component, evidence of bedding

would be expected. This was probably a lava flow or a very proximal tuff with little

exogenous material. The difficulty in determining the composition of the plagioclase

(oligoclase or albite) does not allow the composition of the rock to be determined

(dacite or albite rhyolite respectively). GSWA Petrology Report Number 1578.

110

Zircon morphology

Most zircons from this sample are 200–500 µm long, light brown to dark brown,

euhedral, and strongly zoned. Some zircons contain inclusions. Cores and rims are

discernible in the majority of grains, but most analyses are of cores.

Analytical details



This sample was analysed on 2 and 3 May 1994. The counter deadtime was 36 ns.

The primary beam was stable at 1.8 nA for the entire analysis session. Ten analyses of

the CZ-3 standard were obtained. The Pb*/U calibration was stationary for the entire

20 hour session, with a Pb*/U calibration error of 3.74 (1σ%). For unknown sample

18.1, the 254UO peak was not measured so a 254UO/238U value, determined by

averaging all unknown samples analysed, was assumed for this analysis. Some slight

undercounting of 204Pb on standard analyses, probably due to drifting off the 204Pb

peak or high background counts, was noted. However, this problem does not

significantly affect the final results. The relatively imprecise date obtained for this

sample is due to the very low U contents of the zircons (15–55 ppm) and slightly low

sensitivity during the analysis session.

Results

Thirty-seven analyses were obtained from 28 zircons. Results are given in Table 29


Interpretation

Measured 207Pb/206Pb ratios of 34 analyses define a single population with little

excess scatter (chi-squared = 2.47) indicating an interpreted time of emplacement of

the volcanic rock at 2709 ± 11 Ma. A further three analyses, with similar unusually

low U concentrations, may represent xenocrysts.

111

Figure 30. Concordia plot for sample 104958: dacite, Ballarat – Last Chance

112

Table 29. Ion microprobe analytical results for sample 104958: dacite, Ballarat – Last Chance


2.1 41 30 29 2.18 0.19784 0.00494 0.22002 0.01082 0.5478 0.0221 14.94 0.75 100 2 808 413.1 51 53 34 1.00 0.19031 0.00367 0.29238 0.00824 0.5112 0.0203 13.41 0.62 97 2 745 324.1 77 62 54 0.60 0.19926 0.00255 0.24512 0.00544 0.5510 0.0214 15.14 0.64 100 2 820 215.1 62 33 39 0.13 0.19251 0.00206 0.16136 0.00378 0.5333 0.0209 14.16 0.59 100 2 764 186.1 50 24 33 1.07 0.19264 0.00354 0.16973 0.00744 0.5494 0.0218 14.59 0.67 102 2 765 307.1 56 34 39 1.29 0.20291 0.00317 0.21982 0.00675 0.5475 0.0215 15.32 0.67 99 2 850 258.1 29 16 19 1.35 0.18621 0.00549 0.15250 0.01189 0.5438 0.0225 13.96 0.75 103 2 709 499.1 53 47 37 0.09 0.19052 0.00231 0.26288 0.00498 0.5554 0.0217 14.59 0.62 104 2 747 20

10.1 113 79 75 1.05 0.18832 0.00190 0.21233 0.00405 0.5367 0.0205 13.94 0.57 102 2 728 1711.1 36 24 23 0.81 0.19662 0.00333 0.21070 0.00701 0.5041 0.0202 13.67 0.62 94 2 798 2812.1 145 75 89 0.16 0.18900 0.00107 0.14982 0.00185 0.5319 0.0202 13.86 0.54 101 2 733 913.1 75 39 46 0.73 0.18356 0.00195 0.14718 0.00390 0.5204 0.0201 13.17 0.54 101 2 685 1814.1 109 47 64 0.26 0.18798 0.00143 0.12388 0.00252 0.5167 0.0198 13.39 0.54 99 2 725 1315.1 62 32 39 0.48 0.18589 0.00282 0.15662 0.00569 0.5348 0.0212 13.71 0.61 102 2 706 2516.1 33 21 22 1.29 0.18923 0.00397 0.18548 0.00846 0.5370 0.0215 14.01 0.67 101 2 735 3517.1 176 177 113 0.32 0.18932 0.00155 0.28179 0.00338 0.5030 0.0191 13.13 0.52 96 2 736 1318.1 131 38 85 0.87 0.20801 0.00157 0.15399 0.00310 0.5397 0.0205 15.48 0.61 96 2 890 1219.1 107 76 68 0.82 0.18323 0.00200 0.19231 0.00422 0.5255 0.0201 13.28 0.55 101 2 682 1820.1 52 40 32 1.13 0.18134 0.00264 0.19621 0.00569 0.5028 0.0195 12.57 0.54 99 2 665 2421.1 81 47 48 0.60 0.18558 0.00175 0.15986 0.00351 0.4979 0.0191 12.74 0.52 96 2 703 1622.1 79 43 46 0.69 0.18567 0.00192 0.15340 0.00389 0.4907 0.0188 12.56 0.51 95 2 704 1723.1 46 43 30 1.24 0.18486 0.00314 0.23884 0.00695 0.5028 0.0196 12.82 0.57 97 2 697 2824.1 55 36 33 0.67 0.18637 0.00228 0.18079 0.00472 0.5008 0.0193 12.87 0.54 97 2 710 20

25.156 12 31 1.00 0.18307 0.00265 0.05283 0.00534 0.5022 0.0194 12.68 0.54 98 2 681 2426.1 69 74 48 3.19 0.17871 0.00332 0.27096 0.00758 0.5088 0.0196 12.54 0.56 100 2 641 3127.1 59 28 35 1.10 0.18373 0.00239 0.11967 0.00489 0.5033 0.0194 12.75 0.54 98 2 687 2128.1 62 39 38 1.28 0.18356 0.00249 0.17047 0.00531 0.5021 0.0193 12.71 0.54 98 2 685 225.2 83 64 51 0.88 0.18641 0.00191 0.20563 0.00407 0.4917 0.0188 12.64 0.52 95 2 711 17

12.2 124 69 71 0.69 0.18437 0.00150 0.14901 0.00301 0.4886 0.0186 12.42 0.49 95 2 693 1315.2 48 25 28 1.27 0.18381 0.00305 0.13731 0.00645 0.4882 0.0190 12.37 0.55 95 2 688 2717.2 83 79 56 0.86 0.18142 0.00232 0.25898 0.00514 0.5302 0.0205 13.26 0.56 103 2 666 21

113



14.2 103 41 59 0.90 0.18080 0.00168 0.10477 0.00331 0.5042 0.0192 12.57 0.51 99 2 660 1513.2 67 34 40 1.33 0.18438 0.00240 0.13500 0.00502 0.4993 0.0192 12.69 0.53 97 2 693 221.2 51 27 30 0.72 0.18592 0.00215 0.14129 0.00425 0.5037 0.0195 12.91 0.54 97 2 706 193.2 38 34 25 3.44 0.17921 0.00469 0.21885 0.01055 0.4913 0.0193 12.14 0.61 97 2 646 43

20.2 55 41 35 1.03 0.18490 0.00257 0.20382 0.00546 0.5204 0.0203 13.27 0.57 100 2 697 2325.2 47 9 26 1.52 0.18330 0.00314 0.05334 0.00646 0.4979 0.0193 12.58 0.56 97 2 683 28

114

104964: biotite granodiorite gneiss, Fifty-Mile Tank


WIDGIEMOOLTHA (SH 51-14) AMG Zone 51, 370500E 6473200N

Sampled on 31 October 1990

Blast site closest to tank.


This sample is of an orthogneiss from the Pioneer Dome. It is a grey tonalitic gneiss,

free of obvious dykes and veins, but may contain patches of more mafic composition.


This rock is a granofelsic medium-grade biotite granodiorite gneiss. The principal

minerals in this sample are quartz, plagioclase (An16), and microcline with well-

orientated intragranular grains of biotite. Some patches are rich in microcline, perhaps

representing pre-deformational and pre-crystallization K-feldspar phenocrysts.

Accessory and secondary minerals include mainly unorientated and irregular grains of

muscovite. There is a small amount of chlorite, apparently after biotite. Scattered

small grains of apatite are common. Several very small (7 × 30 µm) rod-shaped grains

may be zircon. The basic texture of the rock is metamorphic. The felsic minerals are

granoblastic, commonly with 120° grain-boundary intersections. The biotite is

strongly orientated, commonly without regard for felsic grain boundaries, indicating

much stronger deformation than that indicated by the quartzofeldspathic texture.

Metamorphic grade has clearly been high enough for the crystallization of quartz and

feldspar to keep pace with substantial deformation. The modest calcium content of the

plagioclase together with the absence of epidote provides very little constraint on the

metamorphic grade. The grade is probably above greenschist facies, in the

epidote–amphibolite facies or higher. It could be much higher, as the texture (a very

poor indicator of grade) is appropriate for upper amphibolite facies. The rock is a

biotite granodiorite gneiss, with evidence of strong deformation in the well-orientated

biotite and thorough recrystallization in the granoblastic texture of the quartz and

feldspar. GSWA Petrology Report Number 1578.

115

Zircon morphology

Very few zircons were recovered from the large amount of sample processed.

Most grains are pale yellow, euhedral to rounded or irregular fragments, typically

50 × 150 µm, and are metamict. Some contain internal euhedral zoning and a few are

internally structureless.

Analytical details



This sample was analysed on 17 November 1993. The counter deadtime was

26 ns. Seven analyses of the SL-13 standard were obtained. The Pb*/U calibration

error was 2.90 (1σ%). Only 11 analyses of unknown zircons were obtained. Cumming

and Richards (1975) common-Pb was assumed for all analyses.

Results

Eleven analyses were made of 11 zircons. Results are given in Table 30 and shown on

a concordia plot in Figure 31.

Interpretation

All zircons analysed have high U contents and many have high common-Pb contents.

The relatively high metamorphic grade of this rock, the low zircon yield, the absence

of a dominant zircon population with a single age, and the metamict state of the

zircons make these analytical results difficult to interpret. Four analyses of two

zircons (4.2, 4.3, 5.1, 5.2) have 207Pb/206Pb ratios belonging to a single population

(chi-squared = 0.65) and indicating an age of 2664 ± 5 Ma. This age may relate either

to the time of crystallization of the granitoid precursor to the gneiss or (more

probably) to metamorphic resetting of the these high-U zircons. Analyses 3.1 and 6.1

have analytically indistinguishable 207Pb/206Pb ratios (chi-squared = 0.08) indicating

an age of 2887 ± 4 Ma. These, and grain 2, which has an older 207Pb/206Pb age, may

be xenocrysts or may have been inherited from the source region of the granitoid

precursor to the gneiss. The younger analyses (i.e. 4.1, 4.5) are of very high-U zones

and probably date post-crystallization disturbance events.

116

Table 30. Ion microprobe analytical results for sample 104964: biotite granodiorite gneiss, Fifty-Mile Tank


1.1 469 130 253 1.949 0.19111 0.00168 0.07294 0.00348 0.4646 0.0136 12.242 0.387 89 2 752 142.1 4 093 1 878 1 667 14.869 0.26812 0.00268 0.42962 0.00608 0.1935 0.0056 7.152 0.229 35 3 295 163.1 459 307 295 1.772 0.20796 0.00154 0.18339 0.00326 0.5077 0.0149 14.557 0.453 92 2 890 124.1 5 305 2 270 2 398 0.313 0.16887 0.00033 0.11600 0.00059 0.4045 0.0117 9.419 0.276 86 2 546 34.2 1 756 240 843 1.024 0.18144 0.00074 0.03129 0.00141 0.4439 0.0129 11.105 0.332 89 2 666 74.3 2 187 235 1 063 0.209 0.18114 0.00044 0.03220 0.00060 0.4623 0.0134 11.547 0.340 92 2 663 44.4 1 469 153 686 0.588 0.18442 0.00064 0.03018 0.00112 0.4380 0.0127 11.138 0.331 87 2 693 65.1 2 863 223 1 511 0.081 0.18155 0.00032 0.02186 0.00034 0.5087 0.0148 12.733 0.373 99 2 667 35.2 2 918 184 1 494 0.069 0.18083 0.00033 0.02042 0.00031 0.4945 0.0144 12.329 0.362 97 2 661 36.1 1 645 56 343 5.940 0.20701 0.00240 0.09589 0.00525 0.1543 0.0045 4.404 0.144 32 2 882 194.5 4 742 286 876 0.944 0.12145 0.00062 0.03237 0.00128 0.1798 0.0052 3.011 0.091 54 1 978 9

117

Figure 31. Concordia plot for sample 104964: biotite granodiorite gneiss, Fifty-MileTank

118

104951: porphyry, Black Rabbit Dam


KALGOORLIE (SH 51-9) AMG Zone 51, 295800E 6640900N

Sampled on 7 August 1990


This sample is from a felsic porphyry that has intruded the lower basalt unit at the

base of the Kalgoorlie Terrane stratigraphy. The porphyry may be related to the

Siberia Monzogranite.


The sample consists of partially altered coarse-grained plagioclase set in a matrix of

well-foliated biotite, fine-grained granular quartz and feldspar, and scattered fine

grains of sericite/muscovite. Irregular medium-grained magnetite has been partially

hematized. The biotite foliation, in particular, indicates substantial metamorphic

recrystallization, yet the plagioclase phenocrysts are undeformed. The presence of

biotite rather than chlorite may indicate a greenschist facies metamorphic grade.

However, this depends on whether the chlorite is primary, or is secondary after biotite.

The heavy dusting of plagioclase, and extensive oxidation of biotite, and of magnetite

to hematite, indicate post-metamorphic alteration, possibly due to weathering but

probably in part hydrothermal in origin. The clear distinction between plagioclase

phenocrysts and the biotite–quartzofeldspathic groundmass suggests an

uncomplicated porphyry precursor, either a lava or a subvolcanic shallow intrusion. In

either case, the rock was probably emplaced close to the source of volcanic activity.

The sample is a porphyroclastic metadacite. GSWA Petrology Report Number 1578.

Zircon morphology

Abundant clear or light yellow-brown to dark brown euhedral zircons, most between

150 and 350 µm long and displaying magmatic zoning, were recovered from this

sample. A few zircons are equant, 150–400 µm in diameter, clear, and cracked, and

several grains are rounded or elliptical (approximately 300–450 µm in diameter) and

clear.

119

Analytical details

Heavy minera ls were isolated from about 1 kg of sample using conventional heavy-


This sample was analysed on 26 May 1994. The counter deadtime was 36 ns.

Twelve analyses of the CZ-3 standard were obtained. The Pb*/U calibration did not

move systematically and the calibration error, based on the standard analyses, was

4.59 (1σ%). Most zircons have extremely low U concentrations. A few rounded, clear

zircons have extremely low U contents and were not analysed.

Results

Forty-three analyses were made on 31 zircons. Results are given in Table 31 and


Figure 32. Concordia plot for sample 104951: porphyry, Black Rabbit Dam

120

Table 31. Ion microprobe analytical results for sample 104951: porphyry, Black Rabbit Dam


1.1 131 117 69 0.18 0.18236 0.00143 0.21508 0.00286 0.4344 0.0202 10.92 0.53 87 2 675 132.1 156 117 88 0.20 0.18379 0.00129 0.19921 0.00251 0.4703 0.0218 11.92 0.57 92 2 687 123.1 94 52 52 0.48 0.18014 0.00206 0.13681 0.00396 0.4818 0.0226 11.97 0.59 96 2 654 194.1 503 17 241 0.06 0.17637 0.00064 0.00864 0.00062 0.4691 0.0216 11.41 0.53 95 2 619 65.1 85 63 47 0.32 0.18394 0.00190 0.17119 0.00366 0.4709 0.0221 11.94 0.59 93 2 689 176.1 145 83 81 0.21 0.17990 0.00129 0.14839 0.00235 0.4838 0.0225 12.00 0.57 96 2 652 127.1 220 157 121 0.84 0.18151 0.00153 0.18937 0.00323 0.4529 0.0209 11.33 0.54 90 2 667 148.1 78 138 35 0.84 0.17382 0.00302 0.12410 0.00626 0.3919 0.0184 9.39 0.49 82 2 595 299.1 56 30 31 0.79 0.18204 0.00325 0.13405 0.00674 0.4804 0.0227 12.06 0.63 95 2 672 30

10.1 121 60 62 0.50 0.17886 0.00210 0.13805 0.00410 0.4457 0.0209 10.99 0.55 90 2 642 1911.1 49 29 30 0.77 0.17964 0.00362 0.15188 0.00722 0.5208 0.0255 12.90 0.71 102 2 650 3312.1 103 48 61 0.65 0.17823 0.00274 0.11813 0.00541 0.5182 0.0246 12.73 0.66 102 2 636 2613.1 85 60 55 0.31 0.18363 0.00265 0.18445 0.00529 0.5472 0.0263 13.85 0.72 105 2 686 2414.1 58 32 36 1.16 0.18027 0.00372 0.13789 0.00771 0.5304 0.0258 13.18 0.73 103 2 655 3415.1 203 149 124 0.42 0.18088 0.00151 0.17876 0.00301 0.5149 0.0240 12.84 0.62 101 2 661 1416.1 48 24 29 0.83 0.18092 0.00395 0.12818 0.00809 0.5335 0.0262 13.31 0.75 104 2 661 3617.1 86 124 48 1.29 0.17566 0.00313 0.13147 0.00650 0.4739 0.0225 11.48 0.61 96 2 612 3018.1 81 158 37 1.11 0.17912 0.00381 0.17328 0.00810 0.3822 0.0183 9.44 0.52 79 2 645 3519.1 60 31 37 1.20 0.17166 0.00406 0.12040 0.00844 0.5252 0.0255 12.43 0.70 106 2 574 4020.1 89 75 51 0.40 0.18299 0.00226 0.15068 0.00433 0.4932 0.0233 12.44 0.63 96 2 680 2021.1 54 31 34 0.57 0.18237 0.00332 0.14929 0.00671 0.5312 0.0256 13.36 0.72 103 2 675 3022.1 80 48 49 0.47 0.18326 0.00255 0.16068 0.00515 0.5177 0.0246 13.08 0.67 100 2 683 2322.2 53 34 35 1.10 0.17470 0.00417 0.16697 0.00901 0.5475 0.0265 13.19 0.75 108 2 603 4023.1 136 164 64 1.53 0.17916 0.00311 0.16727 0.00671 0.3840 0.0180 9.49 0.49 79 2 645 2923.2 109 160 39 1.13 0.17740 0.00358 0.16058 0.00757 0.3018 0.0142 7.38 0.40 65 2 629 3424.1 61 36 37 0.57 0.17718 0.00289 0.15473 0.00587 0.5248 0.0251 12.82 0.67 104 2 627 2725.1 254 208 102 3.36 0.10047 0.00323 0.21546 0.00760 0.3170 0.0147 4.39 0.26 109 1 633 6026.1 57 25 35 0.80 0.17910 0.00315 0.10707 0.00624 0.5427 0.0259 13.40 0.71 106 2 645 2927.1 121 110 68 0.55 0.17928 0.00214 0.25872 0.00469 0.4457 0.0209 11.02 0.55 90 2 646 2027.2 137 137 81 0.58 0.18093 0.00206 0.26866 0.00458 0.4659 0.0218 11.62 0.58 93 2 661 1927.3 232 287 127 1.74 0.18342 0.00239 0.28727 0.00543 0.4102 0.0191 10.37 0.52 83 2 684 22

121



27.4 160 126 73 1.00 0.17808 0.00230 0.20566 0.00495 0.3710 0.0173 9.11 0.45 77 2 635 2127.5 105 73 63 0.40 0.18218 0.00183 0.17718 0.00355 0.5067 0.0238 12.73 0.63 99 2 673 1728.1 144 103 78 0.93 0.18170 0.00210 0.18471 0.00443 0.4473 0.0208 11.21 0.55 89 2 668 1928.2 116 90 70 0.13 0.18243 0.00191 0.21456 0.00399 0.5040 0.0236 12.68 0.62 98 2 675 1729.1 51 26 29 0.72 0.18028 0.00340 0.13429 0.00701 0.4999 0.0240 12.43 0.67 98 2 655 3129.2 55 32 34 0.38 0.18084 0.00300 0.16141 0.00610 0.5311 0.0254 13.24 0.70 103 2 661 2730.1 84 106 44 0.45 0.18391 0.00238 0.12825 0.00471 0.4561 0.0214 11.57 0.58 90 2 688 2130.2 50 100 27 2.06 0.17628 0.00475 0.15195 0.01038 0.4420 0.0211 10.74 0.62 90 2 618 4513.2 42 21 25 0.51 0.18097 0.00338 0.13402 0.00678 0.5286 0.0255 13.19 0.71 103 2 662 3111.2 101 70 59 0.47 0.17973 0.00184 0.17766 0.00371 0.4975 0.0233 12.33 0.61 98 2 650 172.2 134 92 78 0.64 0.18082 0.00177 0.16459 0.00357 0.4913 0.0229 12.25 0.60 97 2 660 16

31.1 179 173 108 0.65 0.17928 0.00152 0.24306 0.00331 0.4809 0.0223 11.89 0.57 96 2 646 14

122

Interpretation

Forty analyses of 28 zircons have measured 207Pb/206Pb ratios belonging to a single

population (chi-squared = 0.92) indicating an interpreted crystallization age for this

porphyry of 2658 ± 6 Ma. Analysis 4.1 has a lower 207Pb/206Pb ratio and 2.1 has a

higher 207Pb/206Pb ratio, and both fall statistically outside the main population.

Analysis 25.1, of an irregular-shaped grain, indicates a concordant age of

1633 ± 60 Ma.

123

104975: rhyodacite porphyry, Burton Dam





This sample is of a recrystallized porphyritic rhyodacite within a greenstone belt

consisting mainly of ultramafic rocks and basalts, to the west of the Jacko

Monzogranite of the Mulgabbie Pluton.


This sample consists of quartz and altered feldspar phenocrysts set in a sericitic,

feldspathic (perhaps quartzofeldspathic) groundmass. There is some quartz in the

groundmass but it is unclear whether it is a major component. Some of the feldspar is

K-feldspar but it is not clear whether this is the dominant feldspar or even whether it

is a major part of the feldspathic suite. Biotite is sparsely disseminated as extremely

fine grains, but is commonly aggregated together in clumps, probably after a former

mafic mineral or Fe-oxide. Opaques are common, some of which are magnetite.

Medium-sized rod-like grains of apatite are common. The feldspars have been

severely altered and a foliation has developed in the rock, although it is not clear how

much of the latter is due to metamorphism and how much to flowage during

emplacement. Secondary temperatures were high enough for the formation of biotite

(i.e. greenschist facies). The rock is an acid porphyry, probably rich in feldspar, which

is probably dominated by microcline. Inhomogeneities (especially wisps of material

rich in biotite, but also feldspar aggregates) may be lithic clasts, but these may also be

replaced phenocrysts (respectively mafic and felsic). GSWA Petrology Report

Number 1578.

124

Zircon morphology

Abundant transparent to light green-brown euhedral zircons, most between

250–450 µm across and with magmatic zoning, were recovered from this sample.

Analytical details



This sample was analysed on 4 and 5 July 1994. The counter deadtime was 36 ns.

Twelve analyses of the CZ-3 standard were obtained. The Pb*/U calibration was

stationary during the analysis session with a Pb*/U calibration error of 1.31 (1σ%).

Measured 204Pb counts on unknown samples were low, but consistently higher than

those measured on the standard (204Pb on standard analyses averaging <1.0 ppb,

compared to approximately 20 ppb on unknown samples), so Cumming and Richards

(1975) 2700 Ma common-Pb was assumed.

Results

Forty-eight analyses were obtained from 43 zircons. Results are given in Table 32 and


Interpretation

Most zircons have low U concentrations. A few (1.1, 7.1, and 33.1) with significantly

higher U contents, which are morphologically indistinguishable from the others, have

consistently lower 207Pb/206Pb ratios and are interpreted to represent disturbed

members of the main population. Five analyses of these ‘disturbed’ zircons (2.1, 11.1,

12.1, 14.1, and 17.1) have 207Pb/206Pb ratios within error of a single mean value (chi-

squared = 0.64), indicating an age of 2650 ± 6 Ma. This is interpreted as the time of a

metamorphic disturbance of these grains of high U content. Thirty-three analyses of

28 typically low-U zircons have 207Pb/206Pb ratios almost within error of a single

mean value (chi-squared = 1.83) indicating an interpreted crystallization age for this

125

volcanic rock of 2706 ± 3 Ma. Analyses 15.1 and 36.1 have higher 207Pb/206Pb ratios

and are interpreted to be of xenocrysts.

Figure 33. Concordia plot for sample 104975: rhyodacite porphyry, Burton Dam

126

Table 32. Ion microprobe analytical results for sample 104975: rhyodacite porphyry, Burton Dam


1.1 1 200 390 527 0.74 0.14533 0.00043 0.08893 0.00088 0.4031 0.0053 8.08 0.11 95 2 292 52.1 649 299 363 0.17 0.17949 0.00043 0.12013 0.00072 0.4974 0.0066 12.31 0.17 98 2 648 43.1 145 70 88 1.21 0.18474 0.00149 0.13765 0.00306 0.5153 0.0071 13.13 0.22 99 2 696 134.1 83 24 48 0.04 0.18546 0.00110 0.07838 0.00160 0.5299 0.0075 13.55 0.22 101 2 702 107.1 649 179 345 0.28 0.17713 0.00044 0.07388 0.00071 0.4896 0.0065 11.96 0.17 98 2 626 48.1 107 29 60 0.18 0.18538 0.00117 0.07409 0.00199 0.5115 0.0072 13.07 0.21 99 2 702 109.1 334 92 183 0.04 0.18712 0.00055 0.07592 0.00071 0.5033 0.0068 12.98 0.18 97 2 717 5

10.1 791 328 413 0.51 0.16591 0.00059 0.11016 0.00113 0.4680 0.0062 10.71 0.15 98 2 517 611.1 349 162 199 1.02 0.17879 0.00083 0.12860 0.00170 0.4910 0.0066 12.10 0.18 97 2 642 812.1 503 233 281 0.19 0.17974 0.00049 0.12579 0.00083 0.4943 0.0066 12.25 0.17 98 2 650 513.1 249 114 144 0.04 0.18663 0.00062 0.12879 0.00092 0.5095 0.0069 13.11 0.19 98 2 713 514.1 359 200 200 0.66 0.18057 0.00076 0.15739 0.00154 0.4740 0.0064 11.80 0.17 94 2 658 715.1 858 681 622 0.05 0.18835 0.00049 0.21723 0.00090 0.5982 0.0080 15.53 0.22 111 2 728 416.1 509 115 280 0.08 0.18652 0.00046 0.06159 0.00058 0.5105 0.0068 13.13 0.18 98 2 712 417.1 675 192 358 0.20 0.17985 0.00046 0.07371 0.00071 0.4877 0.0065 12.09 0.17 97 2 652 418.1 444 159 237 0.23 0.18155 0.00054 0.09853 0.00089 0.4813 0.0064 12.05 0.17 95 2 667 519.1 318 118 181 0.40 0.18633 0.00072 0.10243 0.00129 0.5052 0.0068 12.98 0.19 97 2 710 620.1 180 83 107 0.26 0.18445 0.00087 0.12408 0.00156 0.5248 0.0072 13.35 0.20 101 2 693 820.2 230 109 126 0.08 0.18502 0.00076 0.12826 0.00131 0.4841 0.0066 12.35 0.18 94 2 698 721.1 182 85 108 0.29 0.18504 0.00090 0.12636 0.00160 0.5219 0.0072 13.32 0.20 100 2 699 821.2 76 25 43 0.49 0.18624 0.00179 0.08945 0.00343 0.5039 0.0073 12.94 0.24 97 2 709 1622.1 274 120 157 0.69 0.18434 0.00088 0.11812 0.00171 0.5008 0.0068 12.73 0.19 97 2 692 823.1 207 92 116 0.35 0.18664 0.00087 0.11967 0.00156 0.4957 0.0068 12.76 0.19 96 2 713 824.1 173 68 99 0.03 0.18636 0.00080 0.10906 0.00123 0.5161 0.0071 13.26 0.20 99 2 710 725.1 430 135 240 0.01 0.18648 0.00046 0.08617 0.00058 0.5102 0.0068 13.12 0.18 98 2 711 426.1 246 62 135 0.05 0.18521 0.00064 0.06729 0.00078 0.5086 0.0069 12.99 0.19 98 2 700 627.1 265 72 156 1.05 0.18722 0.00098 0.07999 0.00192 0.5193 0.0070 13.41 0.20 99 2 718 928.1 456 104 256 0.19 0.18714 0.00050 0.06342 0.00072 0.5175 0.0069 13.35 0.19 99 2 717 429.1 100 36 58 0.40 0.18618 0.00131 0.09919 0.00234 0.5174 0.0074 13.28 0.22 99 2 709 1230.1 288 66 159 0.04 0.18649 0.00061 0.06347 0.00083 0.5145 0.0069 13.23 0.19 99 2 711 5

127



30.2 400 98 215 0.05 0.18577 0.00054 0.06669 0.00064 0.4989 0.0067 12.78 0.18 96 2 705 531.1 216 98 125 0.02 0.18430 0.00066 0.12762 0.00100 0.5134 0.0070 13.05 0.19 99 2 692 632.1 90 37 51 0.11 0.18561 0.00119 0.11340 0.00193 0.5088 0.0073 13.02 0.21 98 2 704 1133.1 578 476 322 0.81 0.15870 0.00061 0.22181 0.00135 0.4565 0.0061 9.99 0.14 99 2 442 634.1 201 81 115 0.12 0.18548 0.00077 0.11059 0.00121 0.5088 0.0070 13.01 0.19 98 2 702 735.1 484 151 274 0.16 0.18495 0.00048 0.08395 0.00069 0.5164 0.0069 13.17 0.18 99 2 698 436.1 93 29 57 3.02 0.21023 0.00329 0.11140 0.00697 0.4861 0.0070 14.09 0.32 88 2 907 2537.1 226 104 133 0.74 0.18531 0.00101 0.12972 0.00197 0.5075 0.0069 12.97 0.20 98 2 701 938.1 94 26 54 0.07 0.18621 0.00120 0.07628 0.00182 0.5212 0.0075 13.38 0.22 100 2 709 1139.1 165 63 100 0.04 0.18543 0.00079 0.10443 0.00116 0.5446 0.0076 13.93 0.21 104 2 702 739.2 191 63 108 0.02 0.18677 0.00078 0.09086 0.00107 0.5111 0.0070 13.16 0.20 98 2 714 740.1 283 77 162 0.48 0.18354 0.00080 0.07365 0.00139 0.5222 0.0071 13.22 0.20 101 2 685 741.1 559 200 319 0.47 0.18271 0.00058 0.09741 0.00105 0.5097 0.0068 12.84 0.18 99 2 678 542.1 297 129 170 0.71 0.18345 0.00100 0.11870 0.00195 0.5008 0.0068 12.67 0.19 97 2 684 943.1 225 105 135 0.78 0.18560 0.00123 0.13030 0.00245 0.5164 0.0071 13.22 0.21 99 2 704 1143.2 162 49 94 0.28 0.18780 0.00112 0.09143 0.00194 0.5223 0.0073 13.52 0.21 99 2 723 10

128

112159: porphyritic dacite, Royal Arthur


LEONORA (SH 51-1) AMG Zone 51, 318200E 6854200N


MIM Exploration drillhole WTB-86, 232–235 m.


This sample is of a dacite from a belt of felsic extrusive rocks that hosts the Teutonic

mine.


This sample consists of a fine-grained quartzofeldspathic groundmass with abundant

chlorite and microphenocrysts of plagioclase. Larger, euhedral phenocrysts of

plagioclase, up to 4 mm across, and a few quartz phenocrysts, up to 2 mm across,

together make up about 40% of the rock. Accessory carbonate and rutile are also

present. The phenocrysts of calcic oligoclase are distinctive in that small blebs of

quartz are common as inclusions in the rims of the grains. This appears to be a growth

feature, and in extreme cases the phenocryst is internally vermicular. The groundmass

contains a meshwork of small irregular veins of chlorite, possibly a late-stage cooling

phenomenon of an extrusive rock. The rock is only lightly metamorphosed and no

zircons were observed in the thin section described. GSWA Petrology Report Number

1615.

Zircon morphology

Abundant light brown euhedral to anhedral zircons, most between 150 and 300 µm

long, and with magmatic zoning, were recovered from this sample.

Analytical details



129

This sample was analysed on 6 and 7 July 1994. The counter deadtime was 36 ns.

Twelve analyses of the CZ-3 standard were obtained. The Pb*/U calibration was

stationary during the analysis session with a calibration error of 2.88 (1σ%).

Results

Forty-five analyses of 45 zircons were obtained. Results are given in Table 33 and


Interpretation

Forty-two samples have 207Pb/206Pb ratios belonging to single population with little

excess scatter (chi-squared = 1.28) and indicating an interpreted extrusion age for this

volcanic rock of 2692 ± 4 Ma. Analyses 31.1 and 42.1 have lower 207Pb/206Pb and

fall statistically outside the main population. These analyses probably reflect some

post-crystallization disturbance of these zircons. Analysis 30.1 has a significantly

higher 207Pb/206Pb ratio, suggesting that this grain may be a xenocryst.

Figure 34. Concordia plot for sample 112159: porphyritic dacite, Royal Arthur

130

Table 33. Ion microprobe analytical results for sample 112159: porphyritic dacite, Royal Arthur


1.1 136 70 76 0.19 0.18654 0.00109 0.14366 0.00198 0.4830 0.0141 12.42 0.38 94 2 712 102.1 50 30 30 0.71 0.18505 0.00228 0.16202 0.00466 0.4944 0.0148 12.61 0.43 96 2 699 203.1 68 61 42 0.77 0.18006 0.00213 0.23854 0.00467 0.4968 0.0148 12.34 0.41 98 2 653 204.1 141 106 84 0.30 0.18527 0.00122 0.21154 0.00251 0.4946 0.0145 12.63 0.39 96 2 701 115.1 139 72 79 0.45 0.18415 0.00115 0.13901 0.00217 0.4941 0.0144 12.55 0.38 96 2 691 106.1 64 35 36 0.37 0.18434 0.00192 0.15622 0.00383 0.4757 0.0142 12.09 0.40 93 2 692 177.1 62 34 37 0.63 0.18093 0.00181 0.14347 0.00358 0.5057 0.0150 12.62 0.41 99 2 661 178.1 215 129 125 0.20 0.18289 0.00085 0.15823 0.00156 0.5014 0.0146 12.64 0.38 98 2 679 89.1 156 85 88 0.32 0.18324 0.00112 0.14910 0.00212 0.4881 0.0143 12.33 0.38 96 2 682 10

10.1 82 30 45 0.49 0.18342 0.00158 0.09476 0.00284 0.4889 0.0145 12.36 0.39 96 2 684 1411.1 141 79 84 0.12 0.18549 0.00109 0.15326 0.00201 0.5135 0.0150 13.13 0.40 99 2 703 1012.1 68 48 42 0.92 0.18570 0.00240 0.19940 0.00507 0.5004 0.0150 12.81 0.44 97 2 704 2113.1 75 42 43 0.63 0.18609 0.00201 0.15900 0.00406 0.4926 0.0146 12.64 0.42 95 2 708 1814.1 83 63 49 0.80 0.18231 0.00181 0.20629 0.00388 0.4838 0.0143 12.16 0.39 95 2 674 1615.1 286 370 194 0.21 0.18381 0.00074 0.35801 0.00179 0.5067 0.0147 12.84 0.38 98 2 688 716.1 105 75 64 0.36 0.18382 0.00126 0.19134 0.00252 0.5056 0.0148 12.81 0.40 98 2 688 1117.1 70 36 43 0.47 0.18697 0.00190 0.13980 0.00378 0.5272 0.0157 13.59 0.44 101 2 716 1718.1 57 30 34 0.96 0.18311 0.00234 0.13900 0.00474 0.5021 0.0151 12.68 0.43 98 2 681 2119.1 43 21 25 1.32 0.18293 0.00301 0.12978 0.00622 0.4971 0.0151 12.54 0.46 97 2 680 2720.1 67 38 41 0.50 0.18550 0.00195 0.15580 0.00392 0.5147 0.0154 13.16 0.43 99 2 703 1721.1 142 85 85 0.26 0.18628 0.00114 0.16353 0.00213 0.5102 0.0150 13.10 0.40 98 2 710 1022.1 56 30 32 0.75 0.18646 0.00235 0.14637 0.00480 0.4928 0.0149 12.67 0.43 95 2 711 2123.1 90 50 53 0.43 0.18597 0.00153 0.15005 0.00298 0.5071 0.0150 13.00 0.41 98 2 707 1424.1 211 130 126 0.34 0.18475 0.00101 0.17024 0.00193 0.5072 0.0148 12.92 0.39 98 2 696 925.1 127 64 76 0.46 0.18399 0.00121 0.13865 0.00230 0.5165 0.0152 13.10 0.40 100 2 689 1126.1 155 78 91 0.34 0.18245 0.00110 0.13515 0.00206 0.5134 0.0150 12.91 0.39 100 2 675 1027.1 99 74 63 0.30 0.18586 0.00133 0.20409 0.00267 0.5262 0.0155 13.49 0.42 101 2 706 1228.1 146 68 86 0.29 0.18537 0.00113 0.12696 0.00205 0.5157 0.0151 13.18 0.40 99 2 702 1029.1 84 67 56 0.55 0.18340 0.00156 0.21362 0.00327 0.5408 0.0160 13.68 0.44 104 2 684 1430.1 167 138 108 0.25 0.19047 0.00099 0.23464 0.00201 0.5233 0.0153 13.74 0.42 99 2 746 9

131



31.1 125 58 69 0.36 0.17808 0.00128 0.12436 0.00233 0.4882 0.0143 11.99 0.37 97 2 635 1232.1 131 64 75 0.19 0.18643 0.00111 0.13662 0.00195 0.4985 0.0146 12.81 0.39 96 2 711 1033.1 145 111 88 0.44 0.18142 0.00120 0.20751 0.00248 0.5020 0.0147 12.56 0.39 98 2 666 1134.1 43 23 26 0.67 0.18340 0.00244 0.13804 0.00491 0.5253 0.0160 13.28 0.46 101 2 684 2235.1 90 45 55 0.36 0.18561 0.00140 0.13859 0.00257 0.5373 0.0159 13.75 0.43 103 2 704 1236.1 61 39 38 0.64 0.18564 0.00209 0.17814 0.00428 0.5216 0.0157 13.35 0.45 100 2 704 1937.1 134 87 81 0.38 0.18296 0.00127 0.17766 0.00254 0.5092 0.0149 12.85 0.40 99 2 680 1238.1 77 36 48 0.61 0.18750 0.00191 0.13094 0.00378 0.5351 0.0159 13.83 0.45 102 2 720 1739.1 83 57 51 0.44 0.18132 0.00167 0.18926 0.00341 0.5137 0.0153 12.84 0.41 100 2 665 1540.1 183 116 108 0.27 0.18388 0.00106 0.17515 0.00207 0.5005 0.0146 12.69 0.39 97 2 688 1041.1 252 320 167 0.24 0.18492 0.00090 0.34875 0.00215 0.4975 0.0145 12.69 0.38 97 2 697 842.1 275 306 189 0.08 0.18162 0.00067 0.31049 0.00152 0.5321 0.0155 13.33 0.40 103 2 668 643.1 144 139 96 0.23 0.18473 0.00111 0.26350 0.00239 0.5292 0.0155 13.48 0.41 102 2 696 1044.1 162 97 97 0.28 0.18352 0.00108 0.16382 0.00202 0.5151 0.0151 13.03 0.40 100 2 685 1045.1 88 42 53 0.45 0.18480 0.00149 0.13495 0.00282 0.5275 0.0156 13.44 0.43 101 2 696 13

132

104967: quartz–feldspar porphyry, Four Mile Hill




Sampled south of the Kanowna–Kurnalpi road, from the northern tip of the hill east of

Four Mile Hill.


This sample is of a porphyry within the Boorara Domain of the Kalgoorlie Terrane. It

is closely associated with rocks that have textures suggesting volcanogenic

autobrecciation has occurred.


The rock is dominated by coarse-grained quartz phenocrysts (many of which are

bipyramidal, establishing their igneous origin). The matrix contains quartz and/or

feldspar and sericite. Closer inspection shows ghost phenocrysts, replaced by material

similar to the matrix though richer in sericite, or psuedomorphed by an aggregate of

fine quartz. The different types of replacement may represent the different response of

two different feldspars or even feldspars and mafic minerals. In any case, the original

rock was a quartz–feldspar porphyry, probably dacitic in composition. The alteration

of the feldspar phenocrysts indicates that the present groundmass cannot be

considered to be the original igneous groundmass. The texture of the rock has been

substantially altered and it may be heavily silicified. Apparent finely zoned but

relatively coarse (for a rock of this type), stubby zircon grains about 0.05 mm across

appear to be associated with bundles of opaque titanian minerals and with ‘ghost’

phenocrysts. It is not clear whether the stubby zircon grains are inherently stubby or

appear to be so due to preferred orientation. Euhedral holes in the rock are similar in

shape to the bipyramidal quartz and in part are bordered by columnar quartz,

elongated normal to the former grain contact. This is a phenomenon commonly

associated with sulfide minerals. The rock gives an initial appearance of being little-

altered, but examination of the matrix indicates that previous phenocrysts have been

133

destroyed and the remaining traces almost erased. Therefore the matrix itself is totally

metamorphic in origin. The mineral assemblage and very fine grain size suggest

hydrothermal alteration at low grade, but grade-diagnostic minerals are not present.

Inhomogeneities in the groundmass suggest an initially fragmental rock, but this

cannot be established. If fragmental, it is a proximal deposit. GSWA Petrology Report

Number 1578.

Zircon morphology

Abundant light yellow-green irregular-shaped, cracked zircons, most between

150–300 µm, some displaying magmatic zoning, were recovered from this sample.

Analytical details



This sample was analysed on 13 and 14 July 1994. The counter deadtime was

36 ns. Twelve analyses of the CZ-3 standard were made during the entire session. The

Pb*/U calibration curve was mobile during the period covered by standard analyses 3

and 6. For the remaining standard analyses 1–3 and 6–12 (i.e. 10 standard analyses),

the calibration error was 1.90 (1σ%). For standards 3 and 4, the calibration error was

5.15 (1σ%). For standards 4 and 5, the error was 2.15 (1σ%) and for standards 5 and

6, the error was 4.66 (1σ%). The sample was analysed during standard analyses 4 to

12.

Results

Twenty-eight analyses were obtained from 28 zircons. Results are given in Table 34


134

Interpretation

Twenty-one analyses have 207Pb/206Pb ratios belonging to a single population with

minor excess scatter (chi-squared = 2.97) indicating an interpreted crystallization age

for this porphyry of 2613 ± 11 Ma. Analyses 3.1, 7.1, 8.1, 9.1, and 14.1 have207Pb/206Pb ratios belonging to a single population with some excess scatter (chi-

squared = 3.96) and indicating an age of 2530 ± 38 Ma. Two analyses (5.1 and 10.1)

have 207Pb/206Pb ratios belonging to a single population with some excess scatter

(chi-squared = 4.53) and indicating an age of 2427 ± 31 Ma. The zircons belonging to

these two populations have probably undergone some post-crystallization disturbance.

Figure 35. Concordia plot for sample 104967: quartz–feldspar porphyry, Four Mile Hill

135

Table 34. Ion microprobe analytical results for sample 104967: quartz–feldspar porphyry, Four Mile Hill


1.1 187 125 82 0.342 0.18978 0.00214 0.15473 0.00392 0.3752 0.0085 9.818 0.262 75 2 740 192.1 179 122 102 0.653 0.17158 0.00165 0.16838 0.00337 0.4856 0.0228 11.489 0.564 99 2 573 163.1 111 53 57 0.473 0.16928 0.00175 0.10895 0.00332 0.4578 0.0215 10.685 0.527 95 2 551 174.1 208 102 102 1.198 0.18125 0.00206 0.10372 0.00418 0.4263 0.0200 10.654 0.528 86 2 664 195.1 160 113 92 0.222 0.15866 0.00122 0.15980 0.00241 0.5053 0.0099 11.055 0.243 108 2 441 136.1 177 109 96 1.398 0.17010 0.00201 0.10733 0.00417 0.4679 0.0092 10.973 0.266 97 2 559 207.1 110 39 64 -0.002 0.17014 0.00104 0.08596 0.00120 0.5432 0.0108 12.743 0.274 109 2 559 108.1 157 124 78 1.268 0.16470 0.00187 0.08772 0.00380 0.4418 0.0086 10.032 0.239 94 2 504 199.1 181 118 106 0.139 0.16531 0.00092 0.14878 0.00164 0.5148 0.0100 11.734 0.245 107 2 511 9

10.1 146 72 69 2.371 0.15220 0.00238 0.06506 0.00505 0.4127 0.0081 8.660 0.230 94 2 371 2711.1 136 43 77 0.271 0.17263 0.00135 0.08111 0.00222 0.5191 0.0102 12.357 0.271 104 2 583 1312.1 135 87 76 0.754 0.17637 0.00159 0.15240 0.00321 0.4825 0.0095 11.733 0.265 97 2 619 1513.1 170 60 94 0.516 0.17630 0.00137 0.08513 0.00254 0.5008 0.0098 12.173 0.267 100 2 618 1314.1 242 349 99 7.986 0.15860 0.00431 0.08193 0.00951 0.2885 0.0057 6.310 0.224 67 2 441 4615.1 134 57 77 0.257 0.17357 0.00128 0.10455 0.00231 0.5156 0.0101 12.340 0.269 103 2 592 1216.1 126 61 64 2.968 0.17908 0.00269 0.10416 0.00573 0.4135 0.0081 10.210 0.267 84 2 644 2517.1 183 102 97 1.718 0.17542 0.00180 0.12247 0.00378 0.4448 0.0086 10.757 0.248 91 2 610 1718.1 171 97 102 0.132 0.17686 0.00103 0.14726 0.00188 0.5223 0.0101 12.737 0.267 103 2 624 1019.1 121 53 66 0.333 0.17700 0.00126 0.08840 0.00219 0.4971 0.0097 12.131 0.262 99 2 625 1220.1 126 66 68 1.220 0.17028 0.00189 0.08694 0.00383 0.4765 0.0093 11.188 0.265 98 2 560 1921.1 146 48 83 0.178 0.17556 0.00114 0.07647 0.00186 0.5229 0.0102 12.656 0.269 104 2 611 1122.1 86 33 50 0.142 0.17551 0.00162 0.09589 0.00286 0.5358 0.0107 12.966 0.298 106 2 611 1523.1 175 123 93 1.972 0.17577 0.00242 0.15402 0.00518 0.4348 0.0085 10.538 0.266 89 2 613 2324.1 159 64 92 0.131 0.17670 0.00093 0.10111 0.00148 0.5253 0.0102 12.798 0.265 104 2 622 925.1 145 60 81 0.797 0.17892 0.00142 0.09790 0.00275 0.4939 0.0096 12.185 0.266 98 2 643 1326.1 121 49 69 0.138 0.17582 0.00113 0.08350 0.00180 0.5287 0.0103 12.818 0.273 105 2 614 1127.1 201 205 106 1.975 0.17271 0.00192 0.12927 0.00407 0.4395 0.0085 10.466 0.246 91 2 584 1928.1 116 79 62 1.638 0.17886 0.00221 0.09271 0.00455 0.4631 0.0090 11.421 0.278 93 2 642 21

136

112179: orthogneiss, north of Barret Well


EDJUDINA (SH 51-6) AMG Zone 51, 471700E 6722650N


The sample is from a large area of well-exposed pavement.


This sample is of an orthogneiss from the high-deformation zone along the eastern

margin of the exposed greenstones of the Eastern Goldfields. The sample is from the

foliated mafic (melanocratic) phase of the gneiss at this location. The sample has a

very thin pegmatite band through it but is otherwise an almost pure dark phase.

Foliation is ‘wispy’ in appearance and folded into open to tight folds. The foliation

has been overprinted by a high-temperature event that has resulted in extensive

recrystallization.


Not available.

Zircon morphology

Abundant light yellow euhedral zircons, most between 150 and 250 µm long and with

magmatic zoning, were recovered from this sample.

Analytical details



137

Analysed on 22 and 23 July 1994. The counter deadtime was 36 ns. Ten analyses

of the CZ-3 standard were obtained for the entire session. The Pb*/U calibration was

mobile during the period covered by standards 4 and 5, with a total error for all ten

standards of 4.9 (1σ%), so the analyses were processed in three batches. For standards

1–4, the calibration error was 1.51 (1σ%). For standards 4–5, the calibration error was

2.80 (1σ%). For standards 5–10, the calibration error was 1.50 (1σ%). Measured204Pb is commonly low (204Pb <5.0 ppb) and similar for both standards and unknown

samples, with the exception of analysis 9.1, which has a measured 204Pb of 48.0 ppb.

Broken Hill common-Pb was assumed for all analyses except analysis 9.1, for which

Cumming and Richards (1975) common-Pb at 2570 Ma was used.

Results

Thirty-eight analyses were obtained from 38 zircons. Results are given in Table 35


Figure 36. Concordia plot for sample 112179: orthogneiss, north of Barret Well

138

Table 35. Ion microprobe analytical results for sample 112179: orthogneiss, north of Barret Well


1.1 338 182 205 0.298 0.18297 0.00080 0.15112 0.00146 0.5227 0.0082 13.19 0.22 101 2 680 72.1 667 392 382 0.116 0.18301 0.00052 0.16552 0.00090 0.4914 0.0076 12.40 0.20 96 2 680 53.1 818 519 472 0.111 0.18282 0.00046 0.17259 0.00082 0.4928 0.0076 12.42 0.20 96 2 679 44.1 570 342 328 0.143 0.18281 0.00053 0.16779 0.00093 0.4937 0.0076 12.44 0.20 97 2 679 55.1 467 234 261 0.180 0.18263 0.00062 0.13763 0.00104 0.4887 0.0076 12.31 0.20 96 2 677 66.1 563 359 315 0.181 0.17549 0.00056 0.17313 0.00104 0.4793 0.0074 11.60 0.19 97 2 611 57.1 769 361 368 0.118 0.17051 0.00046 0.13231 0.00076 0.4251 0.0065 9.99 0.16 89 2 563 48.1 508 326 296 0.086 0.18238 0.00060 0.17768 0.00105 0.4954 0.0077 12.46 0.20 97 2 675 59.1 932 670 514 0.421 0.17012 0.00059 0.20586 0.00122 0.4591 0.0071 10.77 0.17 95 2 559 6

10.1 578 385 342 0.090 0.18458 0.00053 0.18628 0.00095 0.5001 0.0078 12.73 0.21 97 2 695 511.1 493 296 298 0.061 0.18316 0.00053 0.17005 0.00091 0.5180 0.0146 13.08 0.37 100 2 682 512.1 282 144 167 0.149 0.18193 0.00077 0.14223 0.00133 0.5177 0.0146 12.99 0.38 101 2 671 713.1 730 412 394 0.134 0.17568 0.00046 0.15414 0.00080 0.4694 0.0132 11.37 0.32 95 2 613 414.1 340 194 203 0.129 0.18258 0.00064 0.15881 0.00110 0.5157 0.0145 12.98 0.37 100 2 676 615.1 515 435 333 0.071 0.18226 0.00047 0.23728 0.00093 0.5283 0.0081 13.28 0.21 102 2 674 416.1 365 209 216 0.091 0.18252 0.00058 0.15805 0.00098 0.5129 0.0079 12.91 0.21 100 2 676 517.1 497 341 293 0.062 0.18305 0.00046 0.18859 0.00082 0.4976 0.0076 12.56 0.20 97 2 681 418.1 211 99 118 0.255 0.18089 0.00079 0.12459 0.00139 0.4919 0.0076 12.27 0.20 97 2 661 719.1 575 377 336 0.106 0.18248 0.00041 0.17821 0.00073 0.4971 0.0076 12.51 0.20 97 2 676 420.1 386 235 226 0.082 0.18258 0.00050 0.16763 0.00088 0.5036 0.0077 12.68 0.20 98 2 676 521.1 731 506 431 0.040 0.18498 0.00034 0.18805 0.00058 0.4974 0.0075 12.69 0.20 96 2 698 322.1 722 491 420 0.043 0.18208 0.00035 0.18620 0.00060 0.4927 0.0075 12.37 0.19 97 2 672 323.1 211 91 118 0.165 0.18207 0.00071 0.12033 0.00115 0.4967 0.0077 12.47 0.21 97 2 672 624.1 720 492 416 0.049 0.18199 0.00033 0.18648 0.00059 0.4894 0.0074 12.28 0.19 96 2 671 325.1 236 125 133 0.177 0.18168 0.00071 0.14356 0.00126 0.4926 0.0076 12.34 0.20 97 2 668 626.1 320 138 166 0.063 0.17481 0.00051 0.12178 0.00078 0.4648 0.0071 11.20 0.18 94 2 604 527.1 237 116 133 0.093 0.18236 0.00061 0.13384 0.00098 0.4947 0.0076 12.44 0.20 97 2 674 628.1 798 506 468 0.048 0.18233 0.00033 0.17313 0.00056 0.5021 0.0076 12.62 0.20 98 2 674 329.1 340 177 194 0.043 0.18246 0.00051 0.14213 0.00081 0.4996 0.0077 12.57 0.20 98 2 675 530.1 535 317 309 0.046 0.18344 0.00040 0.16384 0.00065 0.4971 0.0076 12.57 0.20 97 2 684 4

139



31.1 611 300 339 0.048 0.18216 0.00041 0.13250 0.00064 0.4898 0.0075 12.30 0.19 96 2 673 432.1 537 333 318 0.055 0.18308 0.00042 0.17024 0.00071 0.5068 0.0077 12.79 0.20 99 2 681 433.1 447 278 258 0.070 0.18132 0.00050 0.17012 0.00087 0.4945 0.0076 12.36 0.20 97 2 665 534.1 321 172 186 0.109 0.18217 0.00058 0.14675 0.00098 0.5036 0.0077 12.65 0.20 98 2 673 535.1 401 225 228 0.104 0.18241 0.00050 0.15542 0.00085 0.4924 0.0075 12.38 0.20 96 2 675 536.1 543 330 309 0.069 0.18253 0.00044 0.16294 0.00074 0.4892 0.0074 12.31 0.19 96 2 676 437.1 589 341 343 0.058 0.18464 0.00040 0.15950 0.00064 0.5027 0.0077 12.80 0.20 97 2 695 438.1 451 283 265 0.045 0.18255 0.00047 0.16904 0.00078 0.5042 0.0077 12.69 0.20 98 2 676 4

140

Interpretation

Thirty analyses have 207Pb/206Pb ratios belonging to a single population (chi-squared

= 1.02) indicating an interpreted intrusion age for the granite precursor to this gneiss

of 2675 ± 2 Ma. Analyses 10.1, 21.1, and 37.1 have 207Pb/206Pb ratios defining a

single population (chi-squared = 0.23) and indicating an age of 2696 ± 8 Ma. These

zircons are interpreted to be xenocrysts. Three analyses (6.1, 13.1, and 26.1) have207Pb/206Pb ratios belonging to a single population (chi-squared = 0.66) and indicating

an age of 2609 ± 11 Ma (95% confidence). The analyses belonging to this population

may be derived from the pegmatite phase or may have undergone some post-

crystallization disturbance. Two analyses (7.1 and 9.1) have 207Pb/206Pb ratios

belonging to a single population (chi-squared = 0.19) and indicating an age of

2561 ± 4 Ma. The zircons of this population have probably undergone some post-

crystallization disturbance.

141

104970: dacite breccia, Wild Dog Dam





This sample is of a felsic volcanic rock within the Gindalbie Domain.


The principal identified primary minerals in this sample are quartz and plagioclase,

both of which occur as phenocrysts and in the matrix. K-feldspar may be present but

was not identified. Epidote and sericite are also abundant. The plagioclase

composition is difficult to determine but appears to be albite; however, minerals that

commonly replace anorthite are present in abundance, thus the primary plagioclase

probably was more calcic. The matrix is texturally heterogeneous. One xenolith was

easy to identify whereas others are less obvious. These relationships confirm the field

identification of this sample as a volcaniclastic rock. Furthermore, phenocrysts tend

perhaps to be more irregular in shape in this sample than in more typical ex-

vitrophyric porphyries. Irregularly distributed masses of fine to powdery grains have

very low anomalous birefringence and seem to be composed of clinozoisitic epidote,

but may contain minerals in the grossular–hydrogrossular–vesuvianite group. There

may be two minerals in this category of fine, high-relief materials, and the powdery

ones are possibly titanium rich. The matrix also contains abundant irregular sericite,

in parts closely associated with epidote. Biotite, mostly dark brown but in part bright

green, is a common fine-grained accessory. Zircons may be present in grains

measuring 0.06 × 0.03 mm. The groundmass texture has been substantially

recrystallized, obscuring the fragmental nature of the rock. Mineralogically, it would

appear that original intermediate plagioclase (oligoclase to andesine) has been

degraded to Fe-poor epidote and albite as a result of greenschist facies metamorphism.

There is no evidence of dynamic metamorphism. This is a fragmental dacite porphyry,

142

either an intrusive breccia, agglomerate, flow breccia or lapilli tuff. In any case, it

originated near the volcanic source. GSWA Petrology Report Number 1578.

Zircon morphology

Three different zircon morphologies can be recognized. Morphological type 1 consists

of long, thin, euhedral grains (typically approximately 300 × 50 µm) with fine igneous

zonation. Type 2 consists of more equant grains (typically approximately 350 ×

100 µm) with rounded terminations and a complex internal structure, and with

indistinct internal igneous zonation and, in many cases, thin rims. Type 3 are stubby,

rounded grains (typically approximately 200 × 200 µm, but with a wide size range)

with either igneous zonation or no obvious internal structure. Many zircons have

transitional morphologies and could not be confidently assigned to these three

morphology types.

Analytical details

This sample was analysed on 18 and 19 August 1994. The counter deadtime was

36 ns. Twelve analyses of the CZ-3 standard were obtained. The Pb*/U calibration was

stationary during the analysis session with a calibration error of 2.14 (1σ%).

Results

Forty-one analyses of 41 zircons were obtained. Results are given in Table 36 and


Interpretation

Based on 207Pb/206Pb ratios, all analyses can be placed into five distinct groups. These

groups do not correspond closely with the groups distinguished on the basis of zircon

morphology. Zircons of group 1, which consists of nine analyses (7.1, 8.1, 14.1, 21.1,

30.1, 31.1, 36.1, 40.1, and 42.1), have 207Pb/206Pb ratios belonging to a single

population with some excess scatter (chi-squared = 2.92) indicating an age of 2761 ±

4 Ma. Zircons of group 2, which consists of ten analyses (1.1, 5.1, 9.1, 14.1, 18.1,

143

22.1, 25.1, 31.1, 33.1, and 37.1), have 207Pb/206Pb ratios belonging to a single

population with some excess scatter (chi-squared = 3.44) and indicating an age of

2737 ± 6 Ma. These two populations are interpreted to comprise xenocrystic zircons.

Zircons of group 3, which consists of 16 analyses (2.1, 3.1, 4.1, 11.1, 12.1, 13.1, 17.1,

20.1, 22.1, 25.1, 27.1, 28.1, 29.1, 37.1, 39.1, and 41.1), have 207Pb/206Pb ratios

belonging to a single population with some excess scatter (chi-squared = 3.51)

indicating an age of 2709 ± 4 Ma. This population is interpreted to indicate the time of

deposition of the felsic breccia. Zircons of group 4, which consists of five analyses

(16.1, 18.1, 24.1, 33.1, and 35.1), have 207Pb/206Pb ratios belonging to a single

population with some excess scatter (chi-squared = 5.84) and indicating an age of

2668 ± 13 Ma. Group 5 comprises one analysis (6.1) that has a 207Pb/206Pb age of

2564 ± 3 Ma (1σ error). Groups 4 and 5 are characterized by comparatively high U

and Th contents (427–753 and 105–359 ppm respectively) and are interpreted to have

been disturbed by post-emplacement processes.

Figure 37. Concordia plot for sample 104970: dacite breccia, Wild Dog Dam

144

Table 36. Ion microprobe analytical results for sample 104970: dacite breccia, Wild Dog Dam


1.1 344 53 191 0.208 0.18839 0.00038 0.04129 0.00051 0.5213 0.0112 13.54 0.30 99 2 728 32.1 258 334 164 0.408 0.18467 0.00045 0.27363 0.00099 0.5011 0.0108 12.76 0.28 97 2 695 43.1 149 88 90 0.618 0.18532 0.00067 0.16745 0.00132 0.5091 0.0110 13.01 0.29 98 2 701 64.1 265 129 153 0.430 0.18467 0.00047 0.15398 0.00089 0.4955 0.0106 12.62 0.28 96 2 695 45.1 324 55 183 0.122 0.19037 0.00038 0.05934 0.00048 0.5229 0.0112 13.72 0.30 99 2 745 36.1 602 400 329 0.092 0.17068 0.00026 0.18600 0.00049 0.4664 0.0100 10.98 0.24 96 2 564 37.1 258 38 140 0.043 0.19161 0.00040 0.04172 0.00040 0.5127 0.0110 13.54 0.30 97 2 756 38.1 591 142 329 0.032 0.19216 0.00032 0.06567 0.00034 0.5132 0.0110 13.60 0.30 97 2 761 39.1 263 49 142 0.079 0.18925 0.00042 0.05183 0.00047 0.5054 0.0109 13.19 0.29 96 2 736 4

11.1 342 296 212 0.049 0.18551 0.00034 0.23894 0.00065 0.5052 0.0109 12.92 0.28 98 2 703 312.1 386 54 202 0.096 0.18667 0.00052 0.04793 0.00060 0.4918 0.0106 12.66 0.28 95 2 713 513.1 563 118 297 0.091 0.18663 0.00040 0.05807 0.00050 0.4908 0.0106 12.63 0.28 95 2 713 414.1 462 72 256 0.095 0.19349 0.00047 0.05250 0.00055 0.5155 0.0111 13.75 0.30 97 2 772 415.1 140 10 79 0.545 0.19119 0.00110 0.04163 0.00187 0.5198 0.0114 13.70 0.32 98 2 752 916.1 427 359 233 0.268 0.18226 0.00056 0.20939 0.00111 0.4510 0.0097 11.33 0.25 90 2 674 517.1 285 161 176 0.435 0.18682 0.00078 0.20210 0.00157 0.5082 0.0110 13.09 0.30 98 2 714 718.1 753 314 396 0.627 0.18340 0.00052 0.10434 0.00099 0.4646 0.0100 11.75 0.26 92 2 684 519.1 310 52 170 0.185 0.19055 0.00062 0.04526 0.00080 0.5123 0.0111 13.46 0.30 97 2 747 520.1 142 60 82 0.368 0.18615 0.00108 0.11281 0.00197 0.5109 0.0112 13.11 0.31 98 2 708 1021.1 563 128 313 0.163 0.19163 0.00047 0.06477 0.00063 0.5112 0.0110 13.51 0.30 97 2 756 422.1 370 137 204 0.158 0.18598 0.00058 0.10181 0.00087 0.4948 0.0107 12.69 0.28 96 2 707 523.1 369 60 199 0.096 0.19056 0.00056 0.04204 0.00062 0.5073 0.0110 13.33 0.30 96 2 747 524.1 628 151 336 0.063 0.18057 0.00038 0.06652 0.00044 0.4970 0.0107 12.37 0.27 98 2 658 325.1 223 118 127 0.208 0.18509 0.00087 0.14303 0.00149 0.4935 0.0107 12.59 0.29 96 2 699 826.1 408 104 213 0.270 0.18841 0.00086 0.06897 0.00136 0.4775 0.0103 12.40 0.28 92 2 728 827.1 418 351 209 0.022 0.18613 0.00067 0.22790 0.00126 0.4108 0.0089 10.54 0.24 82 2 708 628.1 362 86 192 0.105 0.18714 0.00036 0.07134 0.00047 0.4887 0.0105 12.61 0.27 94 2 717 329.1 564 154 304 0.030 0.18713 0.00026 0.07736 0.00029 0.4946 0.0106 12.76 0.28 95 2 717 230.1 355 22 198 0.052 0.19318 0.00032 0.01641 0.00026 0.5354 0.0115 14.26 0.31 100 2 769 331.1 257 30 139 0.104 0.19206 0.00041 0.03308 0.00045 0.5090 0.0109 13.48 0.29 96 2 760 3

145



32.1 457 181 265 0.127 0.18841 0.00045 0.11430 0.00067 0.5144 0.0111 13.36 0.29 98 2 728 433.1 606 105 319 0.131 0.18248 0.00041 0.05219 0.00053 0.4942 0.0106 12.43 0.27 97 2 676 434.1 467 77 248 0.074 0.18911 0.00050 0.05154 0.00056 0.4962 0.0107 12.94 0.28 95 2 734 435.1 561 110 284 0.333 0.18088 0.00042 0.06006 0.00068 0.4692 0.0101 11.70 0.26 93 2 661 436.1 334 59 202 0.101 0.19236 0.00046 0.04939 0.00055 0.5642 0.0121 14.96 0.33 104 2 762 437.1 236 119 143 0.140 0.18509 0.00056 0.13719 0.00091 0.5302 0.0114 13.53 0.30 102 2 699 538.1 252 54 145 0.215 0.19040 0.00057 0.09413 0.00088 0.5182 0.0112 13.60 0.30 98 2 746 539.1 194 83 114 0.137 0.18620 0.00066 0.11786 0.00103 0.5232 0.0113 13.43 0.30 100 2 709 640.1 311 40 178 0.094 0.19167 0.00048 0.03540 0.00052 0.5420 0.0117 14.32 0.32 101 2 757 441.1 394 340 254 0.105 0.18591 0.00042 0.23744 0.00083 0.5237 0.0113 13.42 0.29 100 2 706 442.1 375 65 211 0.082 0.19143 0.00043 0.04728 0.00047 0.5257 0.0113 13.87 0.30 99 2 755 4

146

104963: biotite rhyolite, Penneshaw Formation


NORSEMAN (SH 51-2) AMG Zone 51, 388552.30E 6430238.39N


Central Norseman drillhole PE-6, grab samples from the interval 2489–2510 ft.


This sample is of a felsic volcanic rock within the Penneshaw Formation.


This sample consists of medium- to coarse-grained quartz grains and polygranular

quartz masses together with medium-grained secondary biotite set in a recrystallized,

texturally heterogeneous matrix dominated by microcline but including quartz,

plagioclase, sericite, and biotite. The rock is studded with medium-grained sulfide

grains, probably pyrite. Inclusions in biotite with pleochroic haloes may be zircon. A

cross section of a discrete zircon grain was 0.04 mm across. Small apatite grains are

common. Carbonate and chlorite are rare. Sericite is abundant, mainly scattered

throughout the matrix. However, in one aggregate (possible clast) of discrete medium-

grained feldspar, aggregates of sericite alternate with clean grains of microcline,

suggesting that the sericite has been derived from plagioclase. The rock has been

strongly metamorphosed at low grade. The feldspars in the matrix are commonly of

medium grain size but appear smaller because of their irregular shape and because

they are speckled with fine-grained quartz and sericite. This is similar to textures

attributed to devitrification. Matrix microcline is polygonal and decussate. Sieve-

textured microcline grades locally but commonly into a microgranular texture. The

mineral assemblage does not distinguish between the upper part of low metamorphic

grade (the greenschist facies) and the lower part of middle metamorphic grade (lower

part of amphibolite facies). Some quartz grains have bipyramidal faces, suggesting

primary volcanic crystallization. The heterogeneous texture suggests a breccia, but the

limited compositional range suggests that everything was derived from the same

eruption. The dominance of microcline suggests a rhyolitic composition, which

147

supports both an explosive origin and the origin of the matrix by devitrification of a

glass. Thus the rock is of low to middle metamorphic grade, is a metamorphosed

rhyolitic glassy lapilli tuff, and probably originated near a volcanic vent. This sample

is a metamorphosed devitrified biotite rhyolitic vitrophyre. GSWA Petrology Report

Number 1578.

Zircon morphology

Zircons with a wide range of morphologies were recovered from this sample. Some

are large (approximately 100 × 400 µm) euhedral grains with euhedral igneous

zoning, but most consist of smaller (approximately 100 µm diameter) irregular

fragments with either igneous zoning or no obvious internal structure.

Analytical details


36 ns. Eight analyses of the CZ-3 standard were obtained. The Pb*/U calibration error

determined from these eight standard analyses was 3.78 (1σ%).

Results

Twenty-eight analyses of 28 zircons were obtained. Results are given in Table 37 and


Interpretation

Based on 207Pb/206Pb ratios, all analyses can be placed into four groups. These groups

do not correspond closely with zircon morphology characteristics. Group 1 consists of

two analyses (16.1 and 22.1) with 207Pb/206Pb ratios that may be grouped into a single

population (chi-squared = 12.61) indicating an age of 3106 ± 13 Ma. Group 2 consists

of ten analyses (1.1, 2.1, 4.1, 5.1, 11.1, 21.1, 23.1, 26.1, 27.1, and 29.1) that have207Pb/206Pb ratios belonging to a single population with some excess scatter (chi-

squared = 2.49) and indicating an age of 2977 ± 9 Ma. Zircons belonging to these two

populations are interpreted as xenocrysts. Group 3 consists of 14 analyses (3.1, 7.1,

148

8.1, 9.1, 10.1, 12.1, 13.1, 14.1, 15.1, 17.1, 18.1, 19.1, 20.1, and 28.1) that have207Pb/206Pb ratios belonging to single population (chi-squared = 0.91) indicating an

age of 2930 ± 4 Ma. This population is interpreted to indicate the time of deposition of

the rhyolite. Group 4 consists of two analyses (6.1 and 25.1) that have 207Pb/206Pb

ratios belonging to a single population with some excess scatter (chi-squared = 4.13)

and indicating an age of 2866 ± 13 Ma. Group 4 zircons are characterized by

comparatively high U and Th contents and these results are interpreted to be analyses

of sites that have been disturbed by post-emplacement processes.

Figure 38. Concordia plot for sample 104963: biotite rhyolite, Penneshaw Formation

149

Table 37. Ion microprobe analytical results for sample 104963: biotite rhyolite, Penneshaw Formation


1.1 606 418 426 0.122 0.21789 0.00109 0.17717 0.00175 0.584 0.022 17.53 0.69 100 2 965 82.1 508 220 358 0.330 0.21951 0.00099 0.10894 0.00157 0.610 0.023 18.45 0.72 103 2 977 73.1 749 447 543 0.746 0.21368 0.00095 0.16153 0.00183 0.598 0.023 17.61 0.68 103 2 934 74.1 484 177 328 0.376 0.21900 0.00105 0.09797 0.00168 0.590 0.023 17.82 0.70 101 2 973 85.1 299 175 200 0.306 0.22150 0.00114 0.15633 0.00194 0.558 0.021 17.05 0.67 96 2 992 86.1 474 209 274 0.372 0.20656 0.00091 0.12491 0.00158 0.498 0.019 14.19 0.55 91 2 879 77.1 768 325 469 0.128 0.21304 0.00060 0.11357 0.00088 0.533 0.020 15.66 0.60 94 2 929 58.1 493 241 320 0.233 0.21225 0.00080 0.12765 0.00128 0.558 0.021 16.33 0.63 98 2 923 69.1 320 132 208 0.345 0.21594 0.00112 0.11088 0.00190 0.563 0.022 16.76 0.66 98 2 951 8

10.1 548 338 346 0.197 0.21301 0.00079 0.16516 0.00132 0.530 0.020 15.55 0.60 94 2 929 611.1 551 48 341 0.178 0.22042 0.00078 0.02535 0.00093 0.574 0.022 17.45 0.67 98 2 984 612.1 303 117 196 0.489 0.21274 0.00123 0.09723 0.00207 0.566 0.022 16.61 0.66 99 2 927 913.1 352 140 229 0.519 0.21365 0.00122 0.10261 0.00214 0.566 0.022 16.66 0.66 99 2 933 914.1 483 218 328 0.394 0.21392 0.00097 0.11650 0.00165 0.584 0.022 17.23 0.67 101 2 935 715.1 629 344 420 0.167 0.21360 0.00073 0.15070 0.00115 0.566 0.022 16.67 0.64 99 2 933 516.1 502 74 339 0.251 0.24135 0.00094 0.03786 0.00121 0.609 0.023 20.26 0.79 98 3 129 617.1 321 108 205 0.219 0.21162 0.00107 0.08925 0.00165 0.566 0.022 16.53 0.65 99 2 918 818.1 429 169 273 0.334 0.21308 0.00099 0.10265 0.00155 0.555 0.021 16.31 0.64 97 2 929 719.1 391 146 249 0.285 0.21216 0.00099 0.09885 0.00153 0.560 0.021 16.37 0.64 98 2 922 820.1 355 139 224 0.438 0.21367 0.00123 0.10212 0.00215 0.549 0.021 16.19 0.64 96 2 934 921.1 640 319 438 0.272 0.21739 0.00078 0.12976 0.00127 0.586 0.022 17.56 0.68 100 2 961 622.1 1 486 25 971 0.066 0.23715 0.00047 0.00519 0.00036 0.610 0.023 19.96 0.76 99 3 101 323.1 464 238 295 0.267 0.21801 0.00094 0.13688 0.00153 0.541 0.021 16.25 0.63 94 2 966 725.1 569 312 321 0.269 0.20335 0.00093 0.13865 0.00158 0.484 0.018 13.58 0.53 89 2 853 726.1 419 189 276 0.245 0.22210 0.00104 0.12103 0.00168 0.565 0.022 17.31 0.68 96 2 996 827.1 266 118 175 0.470 0.22083 0.00139 0.11707 0.00238 0.563 0.022 17.13 0.68 96 2 987 1028.1 335 125 213 0.508 0.21338 0.00125 0.09767 0.00216 0.554 0.021 16.30 0.64 97 2 931 929.1 449 265 321 0.349 0.22041 0.00099 0.15310 0.00174 0.598 0.023 18.17 0.71 101 2 984 7

150

104949C: metatrachyte, Steeple Hill



Sampled on 19 June 1990

Placer Pacific drillhole KD-2, interval 232.5–233.5 m.


This sample is of a felsic volcanic rock within the Kurnalpi Domain.


The principal identified primary minerals in this sample are feldspar (optic figures

suggest plagioclase), sericite, and well-oriented platy opaque materials. The platy

opaques are white in reflected light, suggesting ilmenite or, more probably,

brookite/pseudobrookite. Chlorite is present but is not obviously an important

member of the general matrix. Quartz grains of medium grain size are sparsely

scattered through the rock. Sulfides, present in more-equant and larger grains, and

dusky-green tourmaline are accessory minerals. The rock has been thoroughly

metamorphosed at low grade, leading to the feldspar–sericite–chlorite assemblage.

The thorough penetrative deformation is shown mainly by the good orientation of

platy opaques. Both feldspar and sericite are not strongly foliated. Better lineation

may be developed normal to the thin section. The feldspars have been reworked at

very low grade, indicating that plagioclase must now be very sodic. The possibility

that this is a mafic plagioclase-bearing rock (metabasalt, dolerite or anorthosite)

seems eliminated by the lack of epidote or other anorthite-substitute mineral (e.g.

calcite). On the same basis, andesine is a dubious candidate. This leaves the

possibility that the rock is an albite or albite–K-feldspar trachyte, if the precursor is

fine-grained, or syenite if it is coarse-grained. The tightly packed medium- to coarse-

grained feldspars suggest deformation of a coarse-grained rock. However, the

continuation of the foliation defined by platy opaques through these grains suggests

that the packed feldspar grains are post- or late-syndeformational. The patchy

feldspars are probably deformed ‘snowflake’ devitrified patches. Thus, this is more

151

probably a metavolcanic rock rather than a phyllonitic granitic rock. The rock has

clearly been metamorphosed to low grade and seems to have been derived from an

acid feldspathic rock of low quartz content — a Na(–K) trachyte. GSWA Petrology

Report Number 1578.

Zircon morphology

The zircons recovered from this sample have various morphologies but are commonly

large equant to elongate grains (150 × 350 µm), with rounded terminations and

internal igneous zoning.

Analytical details


36 ns. Eight analyses of the CZ-3 standard were obtained. The Pb*/U calibration error

changed following instrument adjustment prior to the analysis of the sixth standard, so

the standards were processed in two batches. The calibration error for batch 1,

consisting of standards 1–5, was 2.41 (1σ%). For batch 2, consisting of standards 6–8,

the calibration error was 0.261 (1σ%). A calibration error of 1.5 (1σ%) was assumed

for batch 2 analyses of unknown samples (19.1–27.1).

Results

Twenty-seven analyses of 27 zircons were obtained. Results are given in Table 38 and


Interpretation

Twenty-six analyses have 207Pb/206Pb ratios belonging to a single population (chi-

squared = 0.63) indicating an age of 2699 ± 4 Ma. This is interpreted as the time of

emplacement of the trachyte. Analysis 6.1 has a lower 207Pb/206Pb age and is

interpreted to be from a site that has been disturbed by post-emplacement processes.

152

Figure 39. Concordia plot for sample 104949C: metatrachyte, Steeple Hill

153

Table 38. Ion microprobe analytical results for sample 104949C: metatrachyte, Steeple Hill


1.1 67 41 40 0.691 0.18505 0.00206 0.16527 0.00420 0.4996 0.0128 12.75 0.37 97 2 699 182.1 136 49 77 0.386 0.18577 0.00129 0.09305 0.00235 0.5059 0.0126 12.96 0.35 98 2 705 113.1 166 44 92 0.205 0.18490 0.00101 0.07410 0.00162 0.5114 0.0126 13.04 0.34 99 2 697 94.1 46 11 26 0.833 0.18441 0.00297 0.05928 0.00594 0.5202 0.0136 13.23 0.43 100 2 693 275.1 117 49 68 0.493 0.18395 0.00140 0.11225 0.00263 0.5132 0.0128 13.02 0.35 99 2 689 136.1 466 287 255 0.236 0.16491 0.00056 0.15640 0.00106 0.4774 0.0116 10.85 0.27 100 2 507 67.1 62 18 37 0.766 0.18232 0.00243 0.07744 0.00481 0.5345 0.0138 13.44 0.41 103 2 674 228.1 226 88 131 0.291 0.18464 0.00091 0.10662 0.00157 0.5153 0.0127 13.12 0.34 99 2 695 89.1 95 27 54 0.846 0.18630 0.00195 0.07408 0.00381 0.5165 0.0131 13.27 0.38 99 2 710 17

10.1 223 99 132 0.389 0.18470 0.00100 0.11801 0.00183 0.5207 0.0128 13.26 0.34 100 2 696 911.1 339 122 197 0.184 0.18319 0.00078 0.09514 0.00128 0.5254 0.0129 13.27 0.34 101 2 682 712.1 106 30 62 0.440 0.18752 0.00165 0.07901 0.00296 0.5279 0.0134 13.65 0.38 100 2 721 1413.1 118 39 71 0.655 0.18517 0.00160 0.08337 0.00297 0.5411 0.0137 13.82 0.38 103 2 700 1414.1 187 92 115 0.254 0.18460 0.00110 0.13056 0.00201 0.5408 0.0134 13.76 0.36 103 2 695 1015.1 146 59 87 0.141 0.18712 0.00124 0.10689 0.00207 0.5344 0.0134 13.79 0.37 102 2 717 1116.1 104 26 61 0.385 0.18650 0.00193 0.07030 0.00360 0.5342 0.0137 13.74 0.40 102 2 712 1717.1 117 30 71 0.412 0.18527 0.00165 0.06749 0.00293 0.5580 0.0142 14.25 0.40 106 2 701 1518.1 251 59 155 0.237 0.18546 0.00097 0.06166 0.00152 0.5699 0.0141 14.57 0.38 108 2 702 919.1 68 19 39 0.478 0.18421 0.00264 0.07668 0.00491 0.5301 0.0105 13.46 0.35 102 2 691 2420.1 263 68 135 0.056 0.18609 0.00097 0.07355 0.00141 0.4718 0.0076 12.10 0.21 92 2 708 921.1 130 38 63 0.278 0.18562 0.00197 0.07834 0.00352 0.4420 0.0075 11.31 0.24 87 2 704 1722.1 245 40 124 0.127 0.18500 0.00108 0.04428 0.00155 0.4755 0.0077 12.13 0.22 93 2 698 1023.1 133 70 73 0.246 0.18526 0.00179 0.14907 0.00346 0.4772 0.0081 12.19 0.25 93 2 700 1624.1 332 249 197 0.046 0.18576 0.00089 0.20569 0.00168 0.4941 0.0079 12.66 0.22 96 2 705 825.1 177 77 87 0.404 0.18526 0.00190 0.11693 0.00360 0.4319 0.0072 11.03 0.23 86 2 701 1726.1 160 66 81 0.391 0.18592 0.00210 0.10830 0.00407 0.4489 0.0077 11.51 0.25 88 2 706 1927.1 58 16 27 0.417 0.18635 0.00542 0.08925 0.01132 0.4184 0.0086 10.75 0.40 83 2 710 48

154

112114: felsic volcanic rock, Ghost Rocks





This sample is of a felsic volcanic rock near the base of the exposed stratigraphy of

the Kalgoorlie Terrane in the Menzies Domain.


The sample consists of well-defined medium to coarse grains of quartz and feldspar

and abundant muscovite set in a recrystallized quartzofeldspathic groundmass of fine

to medium grain size. Carbonate is common, ranging from wisps and small discrete

grains to irregular porphyroblasts. There is a small amount of very fine-grained, well-

oriented biotite and some chlorite, probably after biotite. The feldspar appears to be

mainly plagioclase with a substantial amount of intergrown microcline, but

identification is difficult. There is a small amount of secondary epidote with

secondary chlorite and carbonate. Accessory minerals include apatite and very minor

accessory opaques and sphene. The single quartz bipyramid implies that the quartz

phenocrysts crystallized in a fine-grained matrix, and that the rock is therefore a

(felsic to intermediate) porphyry. The rock is well metamorphosed, the matrix has

become coarser grained during metamorphism, and the feldspar crystals have either

grown as porphyroblasts or been substantially recrystallized. One quartz phenocryst

seems to be a well-formed bipyramid. The metamorphic grade cannot be determined

but probably lies in the range of middle greenschist to lower amphibolite facies. The

rock is a felsic to intermediate porphyry. GSWA Petrology Report Number 1596.

155

Zircon morphology

The zircons recovered from this sample are euhedral, elongate (typically 100 ×

350 µm), and have internal igneous zoning.

Analytical details

This sample was analysed on 9 September 1994. The counter deadtime was 36 ns.

Seven analyses of the CZ-3 standard were obtained during the analysis. The Pb*/U

calibration error was mobile after standard 4 and the standards were processed in three

batches. The calibration error for batch 1, consisting of standards 1–4, was

0.768 (1σ%). For batch 2, consisting of standards 4 and 5, the calibration error was

1.12 (1σ%). For batch 3, consisting of standards 5, 6, and 7, the calibration error was

0.677 (1σ%). A calibration error of 1.5 (1σ%) was assumed for all analyses of

unknown samples. Compared to the standard, high 204Pb counts were measured on the

unknown samples. Common-Pb corrections were therefore applied using the 204Pb

correction method and 2700 Ma common-Pb, determined using the method of

Cumming and Richards (1975).

Results

Twenty analyses were obtained from 18 zircons. Results are given in Table 39 and


Interpretation

Although some analyses are discordant, 19 analyses have 207Pb/206Pb ratios belonging

to a single population (chi-squared = 1.48), indicating an age of 2691 ± 6 Ma. This is

interpreted as the time of emplacement of the volcanic rock. Analysis 2.1 indicates a

higher 207Pb/206Pb age and zircon 2 may be a xenocryst.

156

Figure 40. Concordia plot for sample 112114: felsic volcanic rock, Ghost Rocks

157

Table 39. Ion microprobe analytical results for sample 112114: felsic volcanic rock, Ghost Rocks


1.1 136 60 81 1.219 0.18134 0.00126 0.11174 0.00255 0.5119 0.0080 12.798 0.228 100 2 665 122.1 485 167 266 0.587 0.19543 0.00055 0.10331 0.00100 0.4805 0.0073 12.948 0.204 91 2 788 53.1 173 176 105 2.212 0.18412 0.00144 0.20534 0.00313 0.4699 0.0073 11.930 0.217 92 2 690 134.1 188 133 108 2.089 0.18530 0.00135 0.15678 0.00285 0.4622 0.0071 11.809 0.211 91 2 701 125.1 152 105 97 4.757 0.18236 0.00220 0.16328 0.00482 0.4695 0.0073 11.804 0.247 93 2 674 206.1 200 75 110 0.416 0.18498 0.00076 0.09713 0.00132 0.4909 0.0076 12.521 0.206 95 2 698 77.1 233 149 141 0.364 0.18389 0.00066 0.17163 0.00127 0.5131 0.0079 13.010 0.211 99 2 688 68.1 156 40 87 0.133 0.18443 0.00074 0.07203 0.00110 0.5168 0.0080 13.142 0.217 100 2 693 79.1 173 178 86 0.397 0.18367 0.00090 0.20066 0.00181 0.4146 0.0064 10.500 0.176 83 2 686 8

10.1 177 108 92 5.415 0.18219 0.00254 0.13500 0.00556 0.3824 0.0060 9.607 0.214 78 2 673 238.2 217 58 121 0.340 0.18482 0.00073 0.07419 0.00122 0.5101 0.0079 12.998 0.213 99 2 697 78.3 169 52 91 0.294 0.18592 0.00078 0.08141 0.00128 0.4864 0.0075 12.469 0.206 94 2 706 7

11.1 177 131 105 3.698 0.18164 0.00190 0.16168 0.00413 0.4507 0.0070 11.287 0.223 90 2 668 1712.1 214 204 120 4.396 0.18577 0.00195 0.13135 0.00421 0.4249 0.0066 10.882 0.215 84 2 705 1713.1 155 112 91 3.624 0.18178 0.00196 0.14214 0.00425 0.4539 0.0071 11.377 0.228 90 2 669 1814.1 231 131 134 1.127 0.18440 0.00099 0.10433 0.00198 0.5034 0.0078 12.800 0.217 98 2 693 915.1 186 182 79 1.745 0.18045 0.00147 0.14977 0.00308 0.3468 0.0054 8.630 0.158 72 2 657 1316.1 195 116 113 0.896 0.18361 0.00104 0.16624 0.00210 0.4821 0.0075 12.204 0.209 94 2 686 917.1 195 87 88 0.950 0.18300 0.00111 0.10208 0.00217 0.3932 0.0061 9.921 0.171 80 2 680 1018.1 94 51 54 0.739 0.18577 0.00140 0.15430 0.00278 0.4793 0.0077 12.277 0.228 93 2 705 12

158

104973: metadacite porphyry, east of Liberty Bore





This sample is of a felsic volcanic rock within the Edjudina Domain.


The principal minerals identified in this sample are plagioclase, quartz, and very

abundant, but very fine-grained, biotite and opaque minerals. Muscovite/sericite is

clearly secondary but abundant. The medium- to coarse-grained plagioclase grains are

neither abundant or particularly euhedral. They are largely confined to non-foliated

eyes in the strongly microfoliated rock and appear to be relict phenocrysts. The

plagioclase is probably calcitic albite, about An9. K-feldspar was not identified.

Minute opaques are very abundant in the foliated fine-grained matrix but not in the

plagioclase ‘phenocrysts’ or in the non-foliated zones enclosing phenocrysts. Biotite is

abundant but is very fine-grained, and is almost the sole record of the foliation.

Carbonate is abundant, and is commonly associated with finely granular limonite,

suggesting it is Fe-carbonate. Less abundant accessories are difficult to find because

of the strong relief and colour contrasts among major minerals in the matrix.

Muscovite is clearly micropoikiloblastic and carbonate is probably secondary. Biotite

was probably in the primary rock but may have been recrystallized. There is no reason

to place metamorphism above the upper part of the greenschist facies (the ‘biotite’

zone). Deformation is equivocal. Much of the foliation in this rock may be flow

foliation in which biotite has crystallized in a glassy (vitrophyric) medium. Some of

the porphyritic plagioclase (especially a single, very flat tablet) may also have

crystallized at the same time. Aggregates of glomerophenocrysts in an early-

crystallized halo may have been deformed at this time. The crystalline halo is invoked

to account for the bleached zone around some of the non-foliated knots. It is possible

that the quartzofeldspathic component of the matrix may have subsequently

devitrified at subsolidus temperatures, to be later modified by metamorphism. The

159

simplest interpretation is that the rock is a metamorphically foliated dacite porphyry.

Alternatively, the rock may have been foliated by primary flow and the resulting

texture modified slightly by metamorphism. GSWA Petrology Report Number 1578.

Zircon morphology

The zircons recovered from this sample are dark and highly metamict, euhedral,

elongate (typically 100 × 300 µm), and have internal igneous zoning.

Analytical details

This sample was analysed on 13 and 14 September 1994. The counter deadtime was

36 ns. Five analyses of the CZ-3 standard were obtained during the analysis of this

sample. The Pb*/U calibration was stationary with a calibration error of 2.70 (1σ%).

Compared to the standard, high 204Pb counts were measured on most unknown

samples. Common-Pb corrections were therefore applied using the 204Pb correction

method and 2700 Ma common-Pb, determined using the method of Cumming and

Richards (1975). For analyses 2.1, 8.1, and 17.1, 204Pb counts were similar to that

measured on the standard, and Broken Hill common-Pb was assumed.

Results

Seventeen analyses were carried out on 17 zircons. Results are given in Table 40 and


Interpretation

Although some analyses are discordant, sixteen analyses have 207Pb/206Pb ratios

belonging to a single population with little excess scatter (chi-squared = 1.17)

indicating an age of 2708 ± 6 Ma. This is interpreted as the time of emplacement of

the volcanic rock. Analysis 3.1 has a higher 207Pb/206Pb age and zircon 3 may be a

xenocryst.

160

Figure 41. Concordia plot for sample 104973: metadacite porphyry, east of Liberty Bore

161

Table 40. Ion microprobe analytical results for sample 104973: metadacite porphyry, east of Liberty Bore


1.1 284 100 149 2.024 0.18641 0.00140 0.29132 0.00313 0.3877 0.0106 9.964 0.291 78 2 711 122.1 149 54 86 0.193 0.18711 0.00092 0.09969 0.00151 0.5172 0.0142 13.343 0.380 99 2 717 83.1 272 113 181 6.515 0.19509 0.00232 0.46182 0.00538 0.3899 0.0107 10.487 0.327 76 2 786 194.1 372 85 146 3.153 0.18410 0.00161 0.38720 0.00372 0.2646 0.0072 6.716 0.199 56 2 690 145.1 406 126 181 3.487 0.18705 0.00167 0.40705 0.00387 0.2940 0.0080 7.582 0.225 61 2 716 156.1 368 353 163 3.798 0.18752 0.00180 0.38001 0.00413 0.2932 0.0080 7.580 0.227 61 2 721 167.1 236 69 137 1.826 0.18787 0.00128 0.20859 0.00276 0.4543 0.0124 11.767 0.340 89 2 724 118.1 170 70 93 0.352 0.18573 0.00084 0.12592 0.00152 0.4798 0.0131 12.288 0.347 93 2 705 79.1 563 119 148 3.546 0.19016 0.00165 0.38747 0.00379 0.1744 0.0047 4.572 0.135 38 2 744 14

10.1 182 84 112 1.734 0.18577 0.00132 0.22104 0.00285 0.4803 0.0131 12.303 0.357 93 2 705 1211.1 315 105 132 3.044 0.18740 0.00154 0.34651 0.00350 0.2911 0.0079 7.521 0.221 61 2 720 1412.1 241 110 139 2.521 0.18518 0.00145 0.29561 0.00325 0.4172 0.0114 10.653 0.312 83 2 700 1313.1 341 401 120 2.377 0.18452 0.00162 0.33981 0.00370 0.2492 0.0068 6.340 0.188 53 2 694 1514.1 302 93 150 2.820 0.18591 0.00147 0.34913 0.00335 0.3457 0.0094 8.862 0.259 71 2 706 1315.1 334 98 137 2.032 0.18545 0.00130 0.29462 0.00290 0.3014 0.0082 7.706 0.223 63 2 702 1216.1 162 75 71 0.601 0.18414 0.00104 0.11314 0.00199 0.3868 0.0105 9.820 0.280 78 2 690 917.1 167 85 78 0.393 0.18550 0.00086 0.11136 0.00156 0.4159 0.0113 10.636 0.300 83 2 703 8

162

104979: metadacite breccia, Maggies Dam


KURNALPI (SH 51-10) AMG Zone 51, 388900E 6640300NSampled on 14 May 1991


This sample is of a felsic volcanic rock within the Gindalbie Domain.


This rock consists of plagioclase phenocrysts in various stages of alteration, andseriate secondary biotite set in a fine-grained to cryptocrystalline matrix withidentifiable quartz, plagioclase, epidote, and biotite. There may be some microcline.Interspersed with these elements are lithic clasts, some of which are obvious andothers merely suggested by ill-defined textures. Many of the fragments identifiable aslithic clasts seem to be rich in quartz, and some have a strong foliation defined byinclusions superposed on a fine-grained granoblastic background, resembling abanded iron-formation (BIF)-related chert. Idiomorphic apatite is rare. The primarylithologic character has been obscured by metamorphic recrystallization, comprisingsaussuritic clouding, biotite recrystallization, and probable intense recrystallization ofthe matrix. These metamorphic effects were developed at low grade. The sample is aweakly metamorphosed breccia, largely volcanic, and of probable daciticcomposition, perhaps towards a rhyodacite composition. It may contain clasts of rockof supracrustal origin (such as chert, BIF). It probably originated near the volcanicsource. GSWA Petrology Report Number 1578.

Zircon morphology

The zircons recovered from this sample are small (typically 50 × 100 µm), subhedralor rounded, dark, and structureless.

Analytical details

This sample was analysed on 13 and 14 September 1994. The counter deadtime was36 ns. Eight analyses of the CZ-3 standard were obtained during the analysis. ThePb*/U calibration error was mobile during the analysis session and the unknown

163

samples were processed in six batches, using bracketing standards. The calibration

error for batch 1, consisting of standards 1 and 2, was 5.64 (1σ%). For batch 2

(standards 2 and 3), the calibration error was 2.80 (1σ%). For batch 3 (standards 3 and

4), the calibration error was 5.56 (1σ%). For batch 4 (standards 4 and 5), the

calibration error was 4.95 (1σ%). For batch 5 (standards 6 and 7), the calibration error

was 1.32 (1σ%). A minimum calibration error of 1.5 (1σ%) was assumed for analyses

of unknown samples.

Results

Seventeen analyses were made of 17 zircons. Results are given in Table 41 and shown


Interpretation

All analyses have 207Pb/206Pb ratios belonging to a single population (chi-squared =

0.45) indicating an age of 2681 ± 5 Ma. This is interpreted as the time of emplacement

of the volcanic rock.

Figure 42. Concordia plot for sample 104979: metadacite breccia, Maggies Dam

164

Table 41. Ion microprobe analytical results for sample 104979: metadacite breccia, Maggies Dam


1.1 128 99 80 0.164 0.18311 0.00112 0.21723 0.00223 0.5162 0.0293 13.033 0.754 100 2 681 102.1 139 77 81 0.247 0.18252 0.00142 0.15666 0.00276 0.5044 0.0287 12.693 0.740 98 2 676 133.1 128 71 72 0.174 0.18147 0.00126 0.15517 0.00224 0.4888 0.0142 12.231 0.376 96 2 666 114.1 70 35 39 0.322 0.18173 0.00219 0.13393 0.00431 0.4899 0.0146 12.275 0.412 96 2 669 205.1 125 71 71 0.269 0.18361 0.00136 0.15119 0.00253 0.4940 0.0143 12.505 0.386 96 2 686 126.1 141 87 80 0.141 0.18405 0.00130 0.16988 0.00241 0.4860 0.0273 12.333 0.708 95 2 690 127.1 234 215 151 0.147 0.18335 0.00092 0.25495 0.00192 0.5191 0.0290 13.122 0.745 100 2 683 88.1 112 64 75 0.173 0.18300 0.00162 0.16121 0.00303 0.5741 0.0289 14.485 0.757 109 2 680 159.1 133 81 95 0.226 0.18343 0.00153 0.17000 0.00284 0.6082 0.0306 15.383 0.801 114 2 684 14

10.1 124 57 72 0.177 0.18378 0.00191 0.12776 0.00346 0.5097 0.0257 12.916 0.681 99 2 687 1711.1 80 39 48 0.319 0.18194 0.00163 0.13845 0.00312 0.5209 0.0080 13.067 0.244 101 2 671 1512.1 86 48 53 0.467 0.18215 0.00156 0.15504 0.00308 0.5286 0.0080 13.275 0.243 102 2 673 1413.1 107 64 60 0.125 0.18424 0.00101 0.16288 0.00176 0.4782 0.0069 12.147 0.195 94 2 691 914.1 108 63 66 0.259 0.18225 0.00117 0.16318 0.00218 0.5256 0.0146 13.209 0.387 102 2 673 1115.1 126 76 77 0.191 0.18410 0.00103 0.16504 0.00186 0.5230 0.0144 13.276 0.383 101 2 690 916.1 129 69 79 0.178 0.18337 0.00104 0.15327 0.00191 0.5275 0.0145 13.335 0.385 102 2 684 917.1 144 116 92 0.185 0.18232 0.00095 0.22335 0.00191 0.5210 0.0143 13.098 0.375 101 2 674 9

165

104940A: porphyritic metadacite, Bulong Anticline


KURNALPI (SH 51-10) 121°04’E 30°58’S

Sampled on 19 July 1990

Sampled from Western Mining Corporation’s (WMC) Kalgoorlie coreyard. WMC’s

drillhole YDD-1, 53.1–54.6 m, between Dart and Teddy Dams.


This sample is of a felsic volcanic rock within the Bulong Anticline of the Gindalbie

Domain.


In the phaneritic assemblage in this sample, small plagioclase phenocrysts and biotite

are dominant with quartz, carbonate, and chlorite subordinate. Individual minerals

cannot be identified within the dominantly quartzofeldspathic groundmass. Magnetite

and apatite are common accessories. Zircon is sparse. Flow structure between

phenocrysts may be either an affect of primary flow or of metamorphic deformation.

In any case, deformation has not been so intense as to seriously disrupt the euhedral

plagioclase phenocrysts. The biotite was probably in the primary assemblage, but it

has been recrystallized. Chlorite may be of two types, a light-coloured, well-formed

and possibly primary (in the metamorphic phase) variety, and a darker, very irregular

variety that is a late phase, probably after the main metamorphism. Epidote, probably

associated with the main metamorphism, is common, but not abundant. An

unidentified colourless mineral of moderate relief and low second-order interference

colours may be scapolite, which would also be metamorphic. While the unidentified

mineral may actually be muscovite, the habit is unusual for a mica. The rock is a

quartz-poor porphyritic dacite, metamorphosed probably to upper greenschist facies

(biotite and chlorite co-exist). Carbonate is well crystallized and may belong to the

metamorphic phase. GSWA Petrology Report Number 1578.

166

Zircon morphology

The zircons recovered from this sample are clear, euhedral, elongate (typically 100 ×

350 µm), and have strong internal igneous zoning. Apatite inclusions are common.

Analytical details

This sample was analysed on 6 and 7 October 1994. The counter deadtime was 36 ns.

Six analyses of the CZ-3 standard were obtained during the analysis. The Pb*/U

calibration was stable during the analysis session and the calibration error was

2.14 (1σ%). Compared to the standard, slightly higher 204Pb counts were measured on

unknown samples. Common-Pb corrections were therefore applied using the 204Pb

correction method and using 2700 Ma common-Pb, determined using the method of

Cumming and Richards (1975). However, essentially identical results are produced if

the Broken Hill common-Pb composition is used.

Figure 43. Concordia plot for sample 104940A: porphyritic metadacite, Bulong Anticline

167

Results

Twenty-three analyses were obtained from 19 zircons. Results are given in Table 42


Interpretation

All analyses have 207Pb/206Pb ratios belonging to a single population (chi-squared =

0.91) indicating an age of 2672 ± 12 Ma. This is interpreted as the time of

emplacement of the volcanic rock.

168

Table 42. Ion microprobe analytical results for sample 104940A: porphyritic metadacite, Bulong Anticline


1.1 70 25 46 3.394 0.17781 0.00366 0.08973 0.00780 0.5298 0.0125 12.988 0.431 104 2 633 342.1 63 26 41 5.671 0.17722 0.00544 0.09490 0.01178 0.4967 0.0119 12.137 0.500 99 2 627 513.1 75 82 49 4.603 0.17455 0.00416 0.18192 0.00914 0.4826 0.0113 11.615 0.411 98 2 602 404.1 76 51 46 4.179 0.17758 0.00397 0.12364 0.00858 0.4724 0.0110 11.568 0.397 95 2 630 375.1 128 85 82 2.876 0.18269 0.00254 0.14031 0.00542 0.5106 0.0115 12.863 0.359 99 2 677 236.1 81 48 51 3.634 0.17985 0.00353 0.11231 0.00755 0.4925 0.0114 12.214 0.393 97 2 651 337.1 64 29 40 3.563 0.18265 0.00469 0.08715 0.01000 0.5070 0.0120 12.768 0.473 99 2 677 428.1 78 32 52 5.010 0.18273 0.00441 0.11372 0.00953 0.5099 0.0119 12.847 0.458 99 2 678 409.1 85 73 63 5.955 0.17844 0.00429 0.20745 0.00949 0.5158 0.0120 12.691 0.450 102 2 638 40

10.1 88 32 57 5.460 0.17291 0.00426 0.07258 0.00918 0.5023 0.0116 11.975 0.429 101 2 586 4111.1 131 25 77 1.877 0.18307 0.00219 0.04730 0.00443 0.5179 0.0117 13.073 0.350 100 2 681 2012.1 101 73 67 3.739 0.18491 0.00342 0.17858 0.00744 0.4982 0.0113 12.700 0.395 97 2 697 3113.1 107 56 57 1.723 0.18113 0.00239 0.08074 0.00487 0.4618 0.0104 11.534 0.318 92 2 663 2214.1 107 53 69 2.341 0.18377 0.00300 0.14016 0.00635 0.5233 0.0120 13.260 0.394 101 2 687 2715.1 140 85 91 2.403 0.18077 0.00253 0.16035 0.00541 0.5169 0.0116 12.884 0.360 101 2 660 2316.1 118 86 74 2.904 0.17930 0.00291 0.19754 0.00633 0.4829 0.0110 11.938 0.353 96 2 646 2717.1 122 48 80 3.849 0.18186 0.00360 0.06833 0.00767 0.5307 0.0121 13.308 0.426 103 2 670 3318.1 152 100 82 3.202 0.18300 0.00344 0.08692 0.00727 0.4416 0.0100 11.143 0.348 88 2 680 3119.1 219 78 117 1.383 0.18540 0.00171 0.09905 0.00344 0.4606 0.0102 11.774 0.294 90 2 702 1519.2 128 47 75 2.243 0.18367 0.00255 0.10523 0.00530 0.4900 0.0111 12.409 0.347 96 2 686 2316.2 89 34 58 2.213 0.18354 0.00281 0.10426 0.00585 0.5488 0.0126 13.887 0.405 105 2 685 2517.2 95 40 62 10.445 0.17779 0.00716 0.08280 0.01573 0.4205 0.0099 10.308 0.506 86 2 632 6712.2 130 95 90 3.203 0.18466 0.00272 0.17530 0.00589 0.5341 0.0120 13.598 0.386 102 2 695 24

169

112151: felsic volcanic rock, north-northeast of Pinjin


KURNALPI (SH 51-10) 122°43’38"E 30°02’20"S

Sampled on 29 July 1992


This sample is of a felsic volcanic rock within the Pinjin Domain, Eastern Goldfields.


A fine-grained, layered assemblage of quartz, feldspar, biotite, muscovite, and

carbonate, with accessory opaques, tourmaline, and rare zircon. The layering, outlined

by trains of biotite and muscovite, is probably relict flow-banding. A few small, partly

resorbed phenocrysts of plagioclase and microcline are present, suggesting a

carbonated rhyodacite. Metamorphism was medium grade, at greenschist/amphibolite

facies. Only a few small, fresh zircons, <30 µm long, were noted. GSWA Petrology

Report Number 1608.

Zircon morphology

The zircons recovered from this sample are light brown to dark brown, subhedral

(typically 100 × 300 µm), and generally metamict, with little or no obvious internal

structure.

Analytical details

This sample was analysed on 31 October and 7 November 1994. The counter

deadtime was 36 ns. During the analysis of this sample on the session of 31 October,

seven analyses of unknown samples (analyses 1.1–7.1) and two analyses of standards

were obtained. The Pb*/U calibration, based on eight analyses of standards, was

stationary during the entire analysis session and the calibration error was 3.23 (1σ%).

During the session of 7 November, five analyses of standards were obtained. The

Pb*/U calibration was stationary during this analysis session and the calibration error

was 2.11 (1σ%).

170

Results

Twenty-six analyses were made of 26 zircons. Results are given in Table 43 and


Interpretation

Twenty-four analyses have 207Pb/206Pb ratios within error of a single mean value (chi-

squared = 0.58) and defining an age of 2713 ± 4 Ma. This is interpreted as the time of

emplacement of the felsic volcanic rock. Two highly discordant analyses (10.1 and

18.1) have higher 207Pb/206Pb ratios defining an age of 2763 ± 4 Ma (chi-squared =

0.06). These are interpreted to be of xenocrystic zircons.

Figure 44. Concordia plot for sample 112151: felsic volcanic rock, north-northeast ofPinjin

171

Table 43. Ion microprobe analytical results for sample 112151: felsic volcanic rock, north-northeast of Pinjin


1.1 89 26 53 0.854 0.18689 0.00146 0.08085 0.00279 0.5341 0.0176 13.763 0.480 102 2 715 13

2.1 187 75 95 0.765 0.18705 0.00102 0.11411 0.00197 0.4444 0.0145 11.460 0.386 87 2 716 93.1 80 23 34 1.814 0.18497 0.00242 0.11414 0.00513 0.3568 0.0117 9.099 0.336 73 2 698 224.1 72 21 41 0.891 0.18440 0.00182 0.06919 0.00359 0.5119 0.0169 13.015 0.464 99 2 693 165.1 201 385 79 0.967 0.18760 0.00121 0.14749 0.00246 0.3327 0.0108 8.607 0.292 68 2 721 116.1 125 41 68 0.495 0.18599 0.00105 0.09880 0.00190 0.4835 0.0158 12.399 0.420 94 2 707 97.1 180 48 105 0.319 0.18657 0.00084 0.07028 0.00139 0.5310 0.0173 13.661 0.458 101 2 712 78.1 194 111 90 1.323 0.18739 0.00132 0.09922 0.00270 0.4013 0.0086 10.369 0.243 80 2 719 129.1 225 81 102 1.191 0.18670 0.00128 0.10976 0.00262 0.3899 0.0084 10.038 0.234 78 2 713 11

10.1 339 360 100 3.884 0.19192 0.00225 0.29693 0.00512 0.2054 0.0044 5.435 0.139 44 2 759 1911.1 134 52 71 1.170 0.18556 0.00145 0.10365 0.00293 0.4578 0.0099 11.712 0.280 90 2 703 1312.1 219 71 95 0.884 0.18716 0.00119 0.10639 0.00236 0.3801 0.0082 9.809 0.227 76 2 717 1013.1 227 163 103 2.225 0.18734 0.00166 0.16854 0.00360 0.3614 0.0078 9.335 0.226 73 2 719 1514.1 157 42 88 0.693 0.18727 0.00112 0.07384 0.00207 0.5064 0.0110 13.076 0.303 97 2 718 1015.1 43 22 27 2.383 0.18460 0.00351 0.12599 0.00757 0.5049 0.0118 12.850 0.409 98 2 695 3116.1 180 64 90 0.718 0.18640 0.00121 0.08180 0.00229 0.4505 0.0097 11.577 0.270 88 2 711 1117.1 152 58 86 0.592 0.18649 0.00122 0.10636 0.00230 0.4973 0.0109 12.786 0.301 96 2 711 1118.1 317 340 100 2.272 0.19284 0.00196 0.19074 0.00426 0.2472 0.0053 6.572 0.164 51 2 767 1719.1 143 39 82 0.997 0.18523 0.00164 0.07249 0.00324 0.5103 0.0113 13.033 0.323 98 2 700 1520.1 367 278 105 4.290 0.19200 0.00276 0.19676 0.00614 0.2110 0.0046 5.586 0.153 45 2 759 2421.1 180 64 111 4.725 0.18389 0.00333 0.08511 0.00730 0.4860 0.0109 12.323 0.377 95 2 688 3022.1 210 92 117 4.051 0.18635 0.00320 0.08235 0.00693 0.4477 0.0100 11.504 0.344 88 2 710 2823.1 214 87 117 1.385 0.18812 0.00146 0.13348 0.00301 0.4609 0.0100 11.955 0.285 90 2 726 1324.1 224 75 99 1.736 0.18823 0.00168 0.10149 0.00347 0.3767 0.0081 9.778 0.238 76 2 727 1525.1 222 112 98 1.842 0.18684 0.00179 0.11980 0.00375 0.3681 0.0079 9.484 0.234 74 2 715 1626.1 275 128 111 1.660 0.18482 0.00154 0.14441 0.00328 0.3332 0.0071 8.492 0.203 69 2 697 14

172

101348: biotite monzogranite, Brady Well


EDJUDINA (SH 51-6) 121°54’31"E 29°47’03"S



This sample is of a monzogranite interpreted from field evidence to post-date D3

deformation.


A massive, partly recrystallized, coarse grained, seriate biotite monzogranite with

sparse tabular K-feldspar phenocrysts. The rock consists of anhedral, subequant quartz

(25 vol.%), subhedral tabular oscillatory-zoned plagioclase (29 vol.%), anhedral

interstitial K-feldspar (40 vol.%), and biotite (3 vol.%). Accessory minerals include

opaques, magnetite, zircon, sphene, and apatite.

Zircon morphology

The zircons recovered from this sample are euhedral and equant to elongate (up to

200 × 500 µm). Most grains have internal igneous zoning and are strongly metamict.

Analytical details

This sample was analysed on 9 September 1994. The counter deadtime was 36 ns. Six

analyses of the CZ-3 standard were obtained during the analysis of this sample. The

Pb*/U calibration was mobile during the analysis session and unknown samples were

processed in four batches using bracketing standards. The calibration error for batch 1,

consisting of standards 1–3, was 0.677 (1σ%). For batch 2, consisting of standards 3

and 4, the calibration error was 1.13 (1σ%). For batch 3, consisting of standards 4 and

5, the calibration error was 0.401 (1σ%). For batch 4, consisting of standards 5 and 6,

173

the calibration error was 0.873 (1σ%). A minimum calibration error of 1.5 (1σ%) was

assumed for all analyses of unknown samples. Compared to the standard, high 204Pb

counts were measured on unknown samples. Common-Pb corrections were therefore

applied using the 204Pb correction method and using Cumming and Richards (1975)

2700 Ma common-Pb.

Results

Seventeen analyses were made of 14 zircons. Results are given in Table 44 and shown


Figure 45. Concordia plot for sample 101348: biotite monzogranite, Brady Well

174

Table 44. Ion microprobe analytical results for sample 101348: biotite monzogranite, Brady Well


1.1 879 422 205 1.531 0.12001 0.00083 0.13936 0.00183 0.2033 0.0031 3.363 0.058 61 1 956 122.1 897 175 283 0.587 0.14641 0.00048 0.06986 0.00091 0.2944 0.0044 5.944 0.094 72 2 304 63.1 178 110 94 0.509 0.17936 0.00096 0.12844 0.00183 0.4597 0.0072 11.369 0.195 92 2 647 94.1 949 596 445 0.821 0.15447 0.00048 0.18804 0.00102 0.3948 0.0060 8.408 0.133 90 2 396 55.1 77 34 46 1.034 0.18359 0.00192 0.11670 0.00384 0.5119 0.0085 12.957 0.268 99 2 686 176.1 52 35 29 1.464 0.18267 0.00264 0.19981 0.00562 0.4525 0.0079 11.397 0.273 90 2 677 247.1 46 13 26 1.534 0.18103 0.00266 0.07583 0.00534 0.4919 0.0087 12.279 0.299 97 2 662 248.1 1 027 934 674 0.188 0.18351 0.00031 0.18154 0.00057 0.5546 0.0084 14.033 0.217 106 2 685 38.2 668 449 567 0.268 0.18578 0.00037 0.15288 0.00066 0.7299 0.0111 18.698 0.292 131 2 705 37.2 55 19 32 1.216 0.18180 0.00245 0.09118 0.00493 0.5066 0.0088 12.698 0.295 99 2 669 229.1 778 466 624 0.696 0.19740 0.00043 0.17528 0.00085 0.6631 0.0101 18.047 0.282 117 2 805 4

10.1 86 46 52 0.779 0.18800 0.00172 0.15285 0.00343 0.5146 0.0086 13.338 0.266 98 2 725 1511.1 327 346 107 0.974 0.18882 0.00115 0.09929 0.00222 0.2862 0.0044 7.452 0.128 59 2 732 1012.1 698 229 291 0.565 0.16271 0.00056 0.09652 0.00107 0.3765 0.0057 8.448 0.135 83 2 484 613.1 479 1 464 137 1.507 0.18083 0.00120 0.16483 0.00252 0.2357 0.0036 5.876 0.102 51 2 660 1114.1 130 81 63 0.965 0.18565 0.00150 0.11354 0.00294 0.4176 0.0067 10.691 0.201 83 2 704 136.2 54 38 35 1.153 0.17962 0.00226 0.18620 0.00473 0.5222 0.0092 12.933 0.295 102 2 649 21

175

Interpretation

Many analyses indicated high U and Th concentrations (up to 1027 and 1464 ppm

respectively) and were reversely or normally highly discordant. Seven analyses of five

zircons (3.1, 5.1, 6.1, 7.1, 7.2, 13.1, and 6.2) have 207Pb/206Pb ratios belonging to a

single population (chi-squared = 0.74) corresponding to an age of 2658 ± 13 Ma.

These zircons are characterized by generally lower U and Th contents and this age is

interpreted as representing the time of emplacement of this granitoid rock. The other

analyses, characterized by higher U and Th contents, are interpreted as disturbed

members of the main population.

176

93901: granodiorite, Scotia – Split Rock


KALGOORLIE (SH 51-9) 121°22’02"E 30°15’00"S



This sample is of a granodiorite interpreted from field evidence to pre-date, or have

intruded synchronously with, D2 deformation.


A weakly foliated, coarse-grained hornblende-bearing granodiorite. The foliation is

due to weak alignment of biotite and the recrystallization of quartz in elongate

masses. The sample consists of anhedral aggregates of quartz (35 vol.%), subhedral

tabular plagioclase (50 vol.%), finer-grained recrystallized, polysynthetically twinned

K-feldspar (10 vol.%), pale brown – green-brown biotite (3 vol.%), and subhedral

prisms of hornblende (2 vol.%). Accessory minerals include sphene, epidote, opaques,

carbonate, zircon, and magnetite.

Zircon morphology

The zircons recovered from this sample are euhedral and equant to elongate (up to

100 × 250 µm). Some grains have internal igneous zoning but many lack internal

structure.

Analytical details


36 ns. Seven analyses of the CZ-3 standard were obtained during the analysis of this

sample. The Pb*/U calibration was mobile during the analysis session and the

unknown samples were processed in four batches using bracketing standards. The

calibration error for batch 1, consisting of standards 1–3, was 0.659 (1σ%). For

batch 2, consisting of standards 3 and 4, the calibration error was 2.44 (1σ%). For

177

batch 3, consisting of standards 4–7, the calibration error was 1.79 (1σ%). A

minimum calibration error of 1.5 (1σ%) was assumed for unknown samples.

Results

Eighteen analyses were made of 18 zircons. Results are given in Table 45 and shown


Interpretation

Sixteen analyses of 16 zircons have 207Pb/206Pb ratios belonging to a single

population (chi-squared = 0.46) corresponding to an age of 2657 ± 5 Ma. This age is

interpreted as the time of emplacement of this granitoid rock. Analysis 10.1, of a high

U and Th grain, also belongs to this population but is highly discordant. Two analyses

(11.1 and 16.1) have 207Pb/206Pb ratios corresponding to an age of 2698 ± 6 Ma (chi-

squared = 0.06) and are interpreted to be of xenocrystic zircons.

Figure 46. Concordia plot for sample 93901: granodiorite, Scotia – Split Rock

178

Table 45. Ion microprobe analytical results for sample 93901: granodiorite, Scotia – Split Rock


1.1 161 155 104 0.795 0.18033 0.00148 0.25752 0.00325 0.5088 0.0082 12.651 0.239 100 2 656 142.1 84 74 52 0.676 0.18248 0.00202 0.25380 0.00442 0.4937 0.0083 12.421 0.264 97 2 676 183.1 265 223 168 0.418 0.17997 0.00095 0.23122 0.00201 0.5132 0.0080 12.736 0.218 101 2 653 94.1 157 83 77 0.523 0.18025 0.00134 0.16342 0.00266 0.4194 0.0066 10.423 0.190 85 2 655 125.1 155 281 99 0.285 0.18174 0.00120 0.28182 0.00265 0.5045 0.0080 12.641 0.227 99 2 669 116.1 145 378 79 0.530 0.17946 0.00136 0.18575 0.00277 0.4551 0.0072 11.261 0.207 91 2 648 137.1 88 64 56 0.667 0.18003 0.00184 0.20080 0.00390 0.5176 0.0085 12.848 0.263 101 2 653 178.1 118 81 67 0.451 0.18211 0.00149 0.18840 0.00302 0.4693 0.0118 11.783 0.322 93 2 672 149.1 122 67 71 0.513 0.18021 0.00165 0.16021 0.00337 0.4949 0.0124 12.298 0.342 98 2 655 15

10.1 1 246 923 142 1.716 0.17932 0.00196 0.86593 0.00592 0.0624 0.0015 1.542 0.043 15 2 647 1811.1 136 103 72 0.402 0.18474 0.00145 0.21335 0.00296 0.4378 0.0110 11.151 0.304 87 2 696 1312.1 109 63 58 0.334 0.18130 0.00163 0.15716 0.00318 0.4591 0.0116 11.477 0.321 91 2 665 1513.1 118 85 71 0.467 0.17897 0.00159 0.18762 0.00322 0.5017 0.0096 12.380 0.272 99 2 643 1514.1 270 195 164 0.124 0.17985 0.00093 0.19811 0.00182 0.5105 0.0094 12.659 0.250 100 2 651 915.1 158 132 101 0.305 0.18112 0.00130 0.22628 0.00271 0.5222 0.0098 13.042 0.272 102 2 663 1216.1 166 123 86 0.607 0.18536 0.00148 0.21258 0.00306 0.4198 0.0079 10.729 0.228 84 2 701 1317.1 109 84 69 0.914 0.18108 0.00186 0.20771 0.00398 0.5132 0.0098 12.813 0.291 100 2 663 1718.1 100 78 59 0.705 0.17889 0.00186 0.20226 0.00390 0.4836 0.0093 11.928 0.274 96 2 643 17

179

101381: monzogranite, Cement Well – Barber Well


EDJUDINA (SH 51-6) 121°58’17"E 29°44’27"S



This sample is of a monzogranite interpreted from field evidence to pre-date, or have

intruded synchronously with, D2 deformation.


A massive to weakly foliated, moderately recrystallized, medium-grained,

equigranular, sparsely porphyritic biotite–hornblende monzogranite. The sample

consists of subequant, anhedral quartz (25 vol.%), subhedral, tabular, oscillatory-

zoned plagioclase (38 vol.%), anhedral interstitial K-feldspar (30 vol.%), subhedral

prismatic hornblende (5 vol.%), and large irregular books of very pale brown to

brown-green biotite (2 vol.%). Accessory minerals include sphene, apatite, opaques,

zircon and carbonate.

Zircon morphology

The zircons recovered from this sample are large (up to 300 × 600 µm), equant to

elongate and euhedral, and most are metamict. Most grains have internal igneous

zoning but a few lack any internal structure.

Analytical details


36 ns. Nine analyses of the CZ-3 standard were obtained during the analysis session.

The Pb*/U calibration was mobile during the analysis session and the unknowns were

processed in three batches using bracketing standards. The calibration error for

batch 1, consisting of standards 1–4, was 1.79 (1σ%). For batch 2, consisting of

standards 5 and 6, the calibration error was 1.08 (1σ%). For batch 3, consisting of

standards 6–8, the calibration error was 1.61 (1σ%). A minimum calibration error of

1.5 (1σ%) was assumed for analyses of unknown samples.

180

Results



Interpretation

Fifteen analyses of 15 zircons have 207Pb/206Pb ratios belonging to a single population

with little excess scatter (chi-squared = 1.20), corresponding to an age of

2675 ± 11 Ma. This age is interpreted as the time of emplacement of this

monzogranite. Two analyses (4.1 and 17.1) have higher 207Pb/206Pb ratios

corresponding to an age of 2736 ± 36 Ma (chi-squared = 3.20), and are interpreted to

be of xenocrysts. Analysis 2.1 indicates an age of 2526 ± 9 Ma and may be of a

disturbed member of the main population.

Figure 47. Concordia plot for sample 101381: monzogranite, Cement Well – Barber Well

181

Table 46. Ion microprobe analytical results for sample 101381: monzogranite, Cement Well – Barber Well


1.1 36 23 22 0.628 0.18599 0.00383 0.17613 0.00796 0.5061 0.0116 12.979 0.424 98 2 707 342.1 418 165 210 0.404 0.16686 0.00090 0.11524 0.00169 0.4503 0.0082 10.361 0.204 95 2 526 93.1 31 21 19 1.792 0.17993 0.00526 0.19023 0.01146 0.4867 0.0114 12.073 0.479 96 2 652 494.1 116 91 70 0.353 0.18829 0.00179 0.21682 0.00360 0.4973 0.0097 12.909 0.294 95 2 727 165.1 110 81 66 0.559 0.18320 0.00201 0.20307 0.00414 0.4980 0.0098 12.578 0.297 97 2 682 186.1 128 31 40 1.462 0.17796 0.00330 0.11353 0.00693 0.2703 0.0052 6.632 0.188 59 2 634 318.1 80 50 43 0.773 0.18421 0.00257 0.19541 0.00533 0.4394 0.0076 11.160 0.262 87 2 691 237.1 148 121 91 0.328 0.18492 0.00124 0.22795 0.00255 0.5000 0.0080 12.748 0.231 97 2 697 119.1 136 59 72 0.568 0.18006 0.00150 0.11765 0.00283 0.4673 0.0076 11.601 0.222 93 2 653 14

10.1 33 23 21 1.816 0.17608 0.00452 0.17191 0.00980 0.5307 0.0105 12.885 0.443 105 2 616 4311.1 53 41 33 0.974 0.18280 0.00284 0.20783 0.00607 0.5016 0.0095 12.642 0.328 98 2 678 2612.1 39 32 26 2.223 0.18146 0.00473 0.21070 0.01048 0.5228 0.0105 13.080 0.456 102 2 666 4313.1 53 37 32 0.892 0.18740 0.00281 0.19164 0.00587 0.5021 0.0095 12.972 0.332 96 2 719 2514.1 342 145 188 0.158 0.18169 0.00074 0.11802 0.00121 0.4895 0.0081 12.262 0.215 96 2 668 715.1 121 49 62 0.887 0.18119 0.00188 0.13735 0.00383 0.4395 0.0076 10.981 0.233 88 2 664 1716.1 42 33 27 1.108 0.18262 0.00375 0.21601 0.00819 0.5018 0.0101 12.634 0.385 98 2 677 3417.1 45 9 11 0.592 0.19946 0.00558 0.17813 0.01177 0.2074 0.0039 5.703 0.203 43 2 822 4618.1 87 17 37 0.845 0.18533 0.00254 0.06392 0.00484 0.3850 0.0069 9.838 0.234 78 2 701 23

182

98267: biotite monzogranite, Snot Rocks


KALGOORLIE (SH 51-9) 120°47’40"E 30°17’43"S


Five kilometres west-northwest of Pool-On-The-Road Dam.


This sample is of a monogranite interpreted from field evidence to post-date D2

deformation but pre-date D3 deformation.


A moderately foliated, coarse-grained, equigranular biotite monzogranite. The sample

consists of anhedral aggregates of quartz (35 vol.%), subhedral tabular plagioclase

(40 vol.%), larger anhedral K-feldspar (20 vol.%), and small aggregates of pale to

dark brown biotite (4 vol.%). Accessory minerals include magnetite, titanohematite,

apatite, sphene, and zircon.

Zircon morphology

The zircons recovered from this sample vary in size (up to 150 × 400 µm), and are

elongate and euhedral. Many are metamict. Most grains have internal igneous zoning.

Analytical details

This sample was analysed on 2 October 1994. The counter deadtime was 36 ns. Six

analyses of the CZ-3 standard were obtained during the analysis of this sample. The

Pb*/U calibration error was 2.55 (1σ%). Compared to the standard, high 204Pb counts

were measured on unknown samples. Common-Pb corrections were therefore applied

using the 204Pb correction method and assuming 2660 Ma common-Pb, determined

using the method of Cumming and Richards (1975).

183

Results



Interpretation

Seventeen analyses of 17 zircons have 207Pb/206Pb ratios belonging to a single

population with little excess scatter (chi-squared = 1.21) corresponding to an age of

2660 ± 3 Ma. This age is interpreted as the time of emplacement of this monzogranite.

Analysis 3.1 indicates an age of 2464 ± 5 Ma and may be of a disturbed member of

the main population.

Figure 48. Concordia plot for sample 98267: biotite monzogranite, Snot Rocks

184

Table 47. Ion microprobe analytical results for sample 98267: biotite monzogranite, Snot Rocks


1.1 1 337 853 769 0.099 0.18031 0.00037 0.17600 0.00065 0.4913 0.0126 12.214 0.316 97 2 656 32.1 255 120 136 2.400 0.18125 0.00203 0.18176 0.00438 0.4183 0.0108 10.453 0.308 85 2 664 193.1 2 066 1 551 639 0.459 0.16080 0.00052 0.17798 0.00107 0.2642 0.0067 5.857 0.153 61 2 464 54.1 150 111 93 0.966 0.17897 0.00177 0.21572 0.00375 0.5034 0.0132 12.422 0.362 99 2 643 165.1 169 96 102 2.528 0.18360 0.00244 0.19655 0.00529 0.4675 0.0122 11.834 0.364 92 2 686 226.1 182 116 108 0.916 0.18069 0.00155 0.14410 0.00311 0.5038 0.0131 12.552 0.356 99 2 659 147.1 146 73 86 0.286 0.17900 0.00129 0.13461 0.00229 0.5182 0.0136 12.790 0.359 102 2 644 128.1 1 158 363 638 0.078 0.18092 0.00040 0.08467 0.00053 0.5043 0.0129 12.579 0.326 99 2 661 49.1 1 008 418 583 0.190 0.18094 0.00046 0.12671 0.00077 0.5104 0.0131 12.734 0.331 100 2 662 4

10.1 128 478 112 2.575 0.17821 0.00259 0.42135 0.00612 0.5921 0.0156 14.548 0.461 114 2 636 2411.1 237 105 164 1.513 0.17875 0.00171 0.25523 0.00376 0.5322 0.0138 13.117 0.377 104 2 641 1612.1 81 62 51 0.550 0.17989 0.00220 0.20296 0.00457 0.5241 0.0140 13.000 0.401 102 2 652 2013.1 175 135 107 0.343 0.18189 0.00121 0.20481 0.00239 0.5081 0.0132 12.742 0.353 99 2 670 1114.1 77 50 45 0.993 0.17857 0.00249 0.17576 0.00512 0.4918 0.0132 12.109 0.385 98 2 640 2315.1 502 256 293 0.437 0.18234 0.00078 0.15705 0.00149 0.4985 0.0128 12.533 0.333 97 2 674 716.1 1 088 550 638 0.057 0.18135 0.00039 0.13729 0.00060 0.5158 0.0132 12.898 0.334 101 2 665 417.1 1 536 699 914 0.037 0.18040 0.00030 0.12487 0.00044 0.5288 0.0135 13.153 0.339 103 2 657 318.1 712 204 408 0.051 0.18157 0.00048 0.08091 0.00059 0.5263 0.0135 13.176 0.344 102 2 667 4

185

98256: biotite syenogranite, Siberia Battery


KALGOORLIE (SH 51-9) 121°55’14"E 30°13’41"SSampled on 26 October 1988 AMG Zone 51, 299900E 6654100N

Located about 2 km southwest of Siberia Battery.


This sample is of a granitoid interpreted from field evidence to post-date D3

deformation.


This sample is a massive, medium- to coarse-grained, equigranular biotitesyenogranite. The sample consists of quartz (40 vol.%), irregular anhedral K-feldspar(39 vol.%), subhedral tabular plagioclase (20 vol.%), and pale to dark brown biotite(1 vol.%). Accessory minerals include opaques (ilmenite and magnetite), zircon, andsecondary fluorite.

Zircon morphology

The zircons recovered from this sample are light brown to dark brown, euhedral toirregular in shape (typically 100 × 350 µm), and have no obvious internal structure.Many grains are mildly to strongly metamict.

Analytical details

This sample was analysed on 6 October 1994. The counter deadtime was 36 ns. Fiveanalyses of the CZ-3 standard were obtained during the analysis of this sample. ThePb*/U calibration was stationary during the analysis session and the calibration errorwas 3.70 (1σ%). Compared to the standard, slightly higher 204Pb counts weremeasured on unknown samples. Common-Pb corrections were therefore applied usingthe 204Pb correction method and assuming the isotopic composition of Broken Hillcommon-Pb. However, essentially identical results are produced if a common-Pbcomposition of 2700 Ma common-Pb, determined using the method of Cumming andRichards (1975), is assumed.

186

Results

Fifteen analyses were made of 8 zircons. Results are given in Table 48 and shown on a

concordia plot in Figure 49.

Interpretation

All analyses indicate extremely high U and Th concentrations. Some analyses are

strongly reverse discordant, probably due to the gain of radiogenic Pb in these sites.

Seven analyses of four zircons (1.1, 1.2, 2.2, 2.3, 5.1, 5.2, and 7.2) have 207Pb/206Pb

ratios scattering about a single value defining an age of 2673 ± 3 Ma (chi-squared =

6.14). This is interpreted as the best estimate of the time of emplacement of the

monzogranite. One analysis (4.1, not shown on Fig. 49) indicates a concordant age of

1427 ± 4 Ma. This may indicate the time of a resetting event.

Figure 49. Concordia plot for sample 98256: biotite syenogranite, Siberia Battery.Analysis 4.1 (concordant at 1427 ± 5 Ma) not shown

187

Table 48. Ion microprobe analytical results for sample 98256: biotite syenogranite, Siberia Battery


1.1 15 414 20 248 13 509 0.006 0.18222 0.00013 0.38314 0.00027 0.6496 0.0240 16.321 0.605 121 2 673 12.1 17 601 22 166 13 880 0.003 0.18237 0.00016 0.33859 0.00030 0.6017 0.0222 15.131 0.561 114 2 675 13.1 3 379 1 976 3 086 0.027 0.20847 0.00022 0.11723 0.00027 0.7998 0.0296 22.988 0.854 131 2 894 24.1 10 709 10 155 3 094 0.328 0.09006 0.00021 0.25013 0.00057 0.2477 0.0092 3.076 0.115 100 1 427 45.1 7 124 3 961 4 245 0.008 0.18206 0.00017 0.15025 0.00026 0.5196 0.0192 13.042 0.484 101 2 672 26.1 5 632 2 252 3 239 0.127 0.16880 0.00022 0.15592 0.00039 0.5023 0.0186 11.690 0.435 103 2 546 23.2 6 590 3 658 5 338 0.019 0.18961 0.00016 0.11763 0.00020 0.7196 0.0266 18.811 0.698 128 2 739 12.2 10 516 6 629 6 687 0.007 0.18288 0.00015 0.17030 0.00024 0.5458 0.0202 13.762 0.510 105 2 679 12.3 15 010 14 604 11 331 0.004 0.18215 0.00011 0.26352 0.00022 0.6062 0.0224 15.225 0.564 114 2 673 11.2 5 973 5 004 4 000 0.010 0.18282 0.00019 0.22788 0.00036 0.5511 0.0204 13.893 0.516 106 2 679 21.3 21 316 170 619 48 736 0.005 0.18179 0.00009 2.16862 0.00080 0.7890 0.0292 19.776 0.732 140 2 669 17.1 12 507 4 523 8 791 0.005 0.18349 0.00011 0.10896 0.00014 0.6319 0.0234 15.987 0.592 118 2 685 17.2 14 184 6 415 10 207 0.006 0.18196 0.00010 0.12490 0.00013 0.6397 0.0236 16.050 0.594 119 2 671 15.2 6 183 3 158 4 198 0.009 0.18251 0.00019 0.13820 0.00027 0.5971 0.0221 15.025 0.558 113 2 676 28.1 8 845 8 280 6 158 0.005 0.18401 0.00015 0.25480 0.00030 0.5618 0.0208 14.254 0.529 107 2 689 1

188

104932: garnet–biotite–muscovite syenogranitegneiss, Sundowner drillhole


RUDALL (SF 51-10) 122°03’44"E 22°27’39"S

Sampled on 10 May 1990 AMG Zone 51, 403500E 7515850N

CRA Exploration drillhole 88SDD1 (Sundowner), intervals 13.60–14.88 and 16.27–

17.17 m.


This sample is a drillcore of gneiss from the Watrara Inlier of the Rudall Complex.


This sample consists of a strongly foliated, coarse-grained assemblage of quartz,

feldspar, biotite, muscovite, and garnet, and has been metamorphosed to amphibolite

facies. The abundance of garnet and muscovite is unusual for an orthogneiss and

raises the possibility that a sedimentary component has been incorporated into this

gneiss. GSWA Petrology Report Number 1596.

Zircon morphology

The zircons isolated from this sample are anhedral, irregular-shaped grains, light

brown to dark brown, and extensively cracked and pitted. Euhedral igneous zoning

can be distinguished in many grains and thin, radially cracked rims are apparent in a

few.

Analytical details


was 22 ns. Analyses were carried out using six-scan data acquisition. Six analyses of

189

the SL-13 standard were obtained during the entire session. The P*/U calibration was

stationary during the analysis time with a calculated error of 1.87 (1σ%).

Results



Interpretation

No analyses of rim zircon were obtained. The analyses fall into two broad

populations: one with concordant U–Pb analyses and a range of 207Pb/206Pb ages

between 1904 and 2064 Ma, which may indicate non-zero age Pb-loss; and the second

Figure 50. Concordia plot for sample 104932: garnet–biotite–muscovite syenogranitegneiss, Sundowner drillhole

190

Table 49. Ion microprobe analytical results for sample 104932: garnet–biotite–muscovite syenogranite gneiss, Sundowner drillhole


1.1 1 080 813 434 0.371 0.12019 0.00046 0.20770 0.00107 0.3476 0.0065 5.76 0.11 98 1 959 72.1 415 184 167 0.752 0.12752 0.00089 0.11745 0.00191 0.3659 0.0070 6.43 0.14 97 2 064 122.2 451 106 173 0.781 0.12474 0.00091 0.05896 0.00187 0.3657 0.0069 6.29 0.13 99 2 025 133.1 663 64 234 0.211 0.12301 0.00055 0.02671 0.00094 0.3548 0.0067 6.02 0.12 98 2 000 84.1 182 97 102 0.217 0.17709 0.00100 0.13851 0.00183 0.4921 0.0096 12.02 0.25 98 2 626 95.1 1 751 261 939 0.000 0.17641 0.00025 0.03982 0.00018 0.5125 0.0096 12.47 0.24 102 2 619 23.2 458 208 178 0.264 0.12353 0.00064 0.12486 0.00128 0.3589 0.0068 6.11 0.12 98 2 008 96.1 86 87 52 -0.040 0.17768 0.00132 0.27169 0.00287 0.4869 0.0098 11.93 0.27 97 2 631 127.1 662 156 371 0.330 0.18687 0.00055 0.06228 0.00087 0.5153 0.0097 13.28 0.26 99 2 715 58.1 108 72 60 1.202 0.17826 0.00234 0.18283 0.00507 0.4544 0.0091 11.17 0.28 92 2 637 229.1 367 151 145 0.543 0.12411 0.00093 0.10888 0.00197 0.3660 0.0070 6.26 0.13 100 2 016 13

10.1 516 366 212 2.136 0.17636 0.00154 0.14504 0.00332 0.3373 0.0064 8.20 0.18 72 2 619 1411.1 892 674 360 0.652 0.11999 0.00061 0.21426 0.00144 0.3437 0.0065 5.69 0.11 97 1 956 912.1 333 174 122 0.337 0.11658 0.00086 0.14837 0.00187 0.3337 0.0064 5.36 0.11 97 1 904 1313.1 171 79 84 1.267 0.17757 0.00191 0.15045 0.00406 0.4119 0.0080 10.09 0.24 85 2 630 1814.1 196 127 108 0.039 0.17194 0.00106 0.17502 0.00206 0.4773 0.0093 11.32 0.24 98 2 577 1015.1 499 199 276 0.251 0.17981 0.00063 0.10718 0.00110 0.4964 0.0094 12.31 0.24 98 2 651 616.1 200 153 89 1.974 0.12031 0.00199 0.20141 0.00462 0.3670 0.0071 6.09 0.16 103 1 961 30

191

with higher 207Pb/206Pb ages of between 2577 to 2715 Ma and showing variable

degrees of modern Pb-loss. There are no obvious morphological differences between

the zircons of these two groups. Assuming that the lower 207Pb/206Pb ages of analyses

1.1, 11.1, and 12.1 of the former group are due to non-zero age Pb-loss, a minimum

age of crystallization of this population, calculated excluding these analyses, is

2015 ± 26 Ma (chi-squared = 4.13). An alternative (and less plausible) interpretation is

that crystallization of this population occurred over a substantial time interval or

during several short-duration events, in which case the best estimate of the mean age

of this population, calculated by pooling all analyses in this group, is 1993 ± 38 Ma

(chi-squared = 14.25). The 207Pb/206Pb ages of the older (2577 to 2715 Ma) group do

not form a single coherent population and their 207Pb/206Pb ages cannot be pooled.

Although several interpretations of these results are possible, the most reasonable is

that the zircons of the c. 2600 Ma population are xenocrysts or were derived from a

sedimentary component incorporated into the gneiss and that the igneous component

of the gneiss crystallized at 2015 ± 26 Ma. An alternative interpretation, that the

c. 2600 Ma date is the crystallization age of the orthogneiss and the younger dates

reflect metamorphic disturbance, is considered less plausible, because no 207Pb/206Pb

ages intermediate between those of the two groups were detected, and zircons

belonging to the younger (c. 2015 Ma) group lack chemical and morphological

features (such as low Th/U) consistent with a metamorphic origin.

192

104934: biotite syenogranite gneiss (Green Pygmy)


RUDALL (SF 51-10) 122°05’04"E 22°35’04"S

Sampled on 10 May 1990 AMG Zone 51, 405885E 7502185N

CRA Exploration drillhole 88GPD1 (Green Pygmy), intervals 245.96–246.59, 249.6–

251.0, and 265.23–266.13 m.


This sample is of an orthogneiss within the southern part of the Watrara Inlier, Rudall

Complex.


The rock is a strongly foliated biotite syenogranite (near monzogranite) gneiss,

consisting of biotite, microcline, plagioclase (calcic oligoclase), and quartz, with

abundant epidote, common titanite, and accessory apatite, allanite, and opaques.

Deformation of K-feldspar phenocrysts has resulted in the formation of layers of near

monomineralic microcline. Metamorphic grade is lower amphibolite facies. GSWA


Zircon morphology

The zircons extracted from this sample are transparent, light brown to dark brown,

and euhedral to subhedral. Many grains have abundant opaque and rod-shaped

inclusions, and some have euhedral igneous zoning. Rims and cores cannot be

distinguished.

Analytical details

This sample was analysed on 25 and 26 January 1991 on SHRIMP-1. The counter


Fifteen analyses of the SL-13 standard were obtained during the entire session. The

193

Pb*/U calibration was stationary during the analysis time with a calculated error of

2.70 (1σ%).

Results

Twenty-eight analyses were made of 26 zircons. Results are given in Table 50 and


Interpretation

All analyses form a single population on concordia, with the scatter in the 207Pb/206Pb

ratios only slightly in excess of that attributable to analytical error (chi-squared =

2.44). The mean 207Pb/206Pb value of the population corresponds to an age of

1787 ± 12 Ma. This is interpreted as the crystallization age of the granitic protolith to

the orthogneiss.

Figure 51. Concordia plot for sample 104934: biotite syenogranite gneiss (GreenPygmy)

194

Table 50. Ion microprobe analytical results for sample 104934: biotite syenogranite gneiss (Green Pygmy)


1.1 218 301 93 0.18 0.10778 0.00098 0.38604 0.00315 0.3283 0.0090 4.879 0.146 104 1 762 172.1 191 147 69 0.20 0.11071 0.00134 0.21249 0.00329 0.3163 0.0088 4.828 0.153 98 1 811 223.1 246 189 89 0.90 0.10687 0.00193 0.20803 0.00459 0.3096 0.0086 4.561 0.160 100 1 747 334.1 640 30 181 0.27 0.11006 0.00095 0.00922 0.00172 0.2909 0.0080 4.415 0.131 91 1 800 165.1 125 201 54 0.14 0.11125 0.00174 0.46275 0.00612 0.3156 0.0089 4.841 0.165 97 1 820 286.1 214 151 75 0.52 0.10790 0.00153 0.19695 0.00364 0.3091 0.0086 4.598 0.151 98 1 764 267.1 270 158 96 0.08 0.11249 0.00119 0.16834 0.00268 0.3217 0.0089 4.990 0.154 98 1 840 198.1 172 164 65 0.80 0.10260 0.00217 0.26384 0.00549 0.3129 0.0088 4.427 0.164 105 1 672 399.1 1 988 805 675 0.03 0.10972 0.00034 0.11534 0.00064 0.3216 0.0087 4.865 0.134 100 1 795 6

10.1 197 226 73 0.31 0.10902 0.00180 0.32070 0.00488 0.3003 0.0084 4.514 0.155 95 1 783 3011.1 154 131 57 0.56 0.10618 0.00204 0.23294 0.00505 0.3134 0.0088 4.588 0.165 101 1 735 3512.1 176 198 70 0.48 0.10850 0.00182 0.32490 0.00496 0.3167 0.0089 4.739 0.163 100 1 774 3113.1 193 191 73 0.53 0.10479 0.00171 0.27672 0.00451 0.3129 0.0087 4.521 0.154 103 1 711 3014.1 218 255 84 0.27 0.10918 0.00137 0.31855 0.00396 0.3122 0.0087 4.700 0.150 98 1 786 2315.1 350 406 134 0.24 0.10657 0.00109 0.32251 0.00317 0.3098 0.0085 4.552 0.139 100 1 741 1916.1 232 239 85 0.17 0.10970 0.00135 0.28545 0.00372 0.3030 0.0084 4.583 0.145 95 1 794 2217.1 143 127 54 0.49 0.10819 0.00211 0.24715 0.00533 0.3169 0.0090 4.728 0.172 100 1 769 3618.1 216 246 87 0.20 0.10977 0.00129 0.32241 0.00385 0.3242 0.0090 4.907 0.155 101 1 796 2119.1 342 410 135 0.45 0.10486 0.00150 0.32997 0.00413 0.3154 0.0087 4.560 0.149 103 1 712 2620.1 215 219 83 0.05 0.10912 0.00117 0.28622 0.00345 0.3201 0.0089 4.816 0.149 100 1 785 2021.1 114 117 45 0.17 0.11144 0.00197 0.29509 0.00555 0.3215 0.0091 4.940 0.174 99 1 823 3222.1 115 131 42 0.25 0.11688 0.00273 0.34898 0.00746 0.2886 0.0082 4.652 0.181 86 1 909 4223.1 175 197 70 0.25 0.10752 0.00165 0.31042 0.00475 0.3259 0.0091 4.832 0.162 103 1 758 2823.2 181 228 71 -0.10 0.11486 0.00279 0.35384 0.00726 0.3107 0.0087 4.920 0.194 93 1 878 448.2 233 248 87 0.10 0.10982 0.00160 0.29758 0.00434 0.3076 0.0086 4.657 0.154 96 1 796 27

24.1 244 181 89 0.12 0.11029 0.00124 0.20249 0.00299 0.3225 0.0089 4.905 0.153 100 1 804 2025.1 175 178 66 0.25 0.10721 0.00191 0.28026 0.00503 0.3121 0.0088 4.614 0.162 100 1 753 3326.1 204 225 77 0.21 0.10976 0.00156 0.32391 0.00448 0.3027 0.0084 4.581 0.150 95 1 795 26

195

112379: biotite monzogranite (augen) gneiss,Split Rock


RUDALL (SF 51-10) 122°10’47"E 22°32’20"S

Sampled during 1991


This sample is of a K-feldspar porphyritic orthogneiss within the southern part of the

Watrara Inlier, Rudall Complex.


This rock comprises irregular-shaped augen of microcline, 3–10 mm in diameter, in a

medium-grained, strongly oriented matrix of quartz, sericitized plagioclase,

microcline, and biotite. Abundant epidote and minor to accessory granular sphene,

zircon, and apatite are associated with biotite. The microcline augen commonly

contain anhedra of exsolved albite and mosaic quartz. This rock is a monzogranite,

which has undergone low- to medium-grade metamorphism. GSWA Petrology Report

Number 1616.

Zircon morphology

The zircons extracted from this sample are light brown to dark brown. They are

euhedral and have euhedral igneous zoning.

Analytical details

Heavy minerals were isolated from about 850 g of sample using conventional heavy-


196

This sample was analysed on 29 August 1994. The counter deadtime was 36 ns.

Analyses were carried out using seven-scan data acquisition. Six analyses of the CZ-3

standard were obtained during the session. The Pb*/U calibration was mobile during

the analysis time, so the standard data was processed in four batches. The calibration

error for batch 1, consisting of standards 1 and 2, was 2.55 (1σ%). For batch 2

(standards 2 and 3), the calibration error was 1.28 (1σ%). For batch 3 (standards 3 and

4), the calibration error was 0.50 (1σ%), and for batch 4 (standards 4, 5, and 6), the

calibration error was 0.40 (1σ%). A calibration error of 1.50 (1σ%) was assumed for

batches 2, 3, and 4.

Results

Twenty-one analyses were made of 21 zircons. Results are given in Table 51 and


Figure 52. Concordia plot for sample 112379: biotite monzogranite (augen) gneiss,Split Rock

197

Table 51. Ion microprobe analytical results for sample 112379: biotite monzogranite (augen) gneiss, Split Rock


1.1 161 126 59 0.480 0.11067 0.00154 0.21657 0.00370 0.3167 0.0083 4.832 0.151 98 1 810 252.1 75 81 29 0.938 0.11053 0.00380 0.30412 0.00931 0.3138 0.0086 4.782 0.223 97 1 808 633.1 269 242 97 0.238 0.10767 0.00111 0.25162 0.00284 0.3072 0.0080 4.561 0.133 98 1 760 194.1 307 288 114 0.205 0.10782 0.00106 0.26746 0.00277 0.3103 0.0049 4.613 0.091 99 1 763 185.1 121 148 49 0.532 0.10853 0.00225 0.34204 0.00596 0.3215 0.0055 4.811 0.137 101 1 775 386.1 309 255 114 0.434 0.10718 0.00134 0.22948 0.00327 0.3147 0.0050 4.651 0.100 101 1 752 237.1 219 415 101 0.414 0.10931 0.00141 0.53544 0.00476 0.3215 0.0053 4.846 0.107 101 1 788 248.1 269 365 111 0.569 0.10656 0.00150 0.37435 0.00419 0.3199 0.0052 4.700 0.107 103 1 741 269.1 174 112 59 1.169 0.10553 0.00250 0.19223 0.00587 0.2926 0.0049 4.257 0.131 96 1 724 44

10.1 198 244 76 2.148 0.10912 0.00330 0.31525 0.00805 0.2951 0.0050 4.440 0.162 93 1 785 5511.1 142 145 53 1.145 0.10364 0.00268 0.27359 0.00667 0.3066 0.0054 4.381 0.144 102 1 690 4812.1 113 149 48 1.287 0.10859 0.00401 0.36680 0.01016 0.3184 0.0060 4.767 0.207 100 1 776 6713.1 117 193 52 1.469 0.10492 0.00397 0.44479 0.01046 0.3177 0.0060 4.596 0.204 104 1 713 7014.1 267 357 111 0.717 0.11017 0.00179 0.38880 0.00493 0.3167 0.0052 4.810 0.118 98 1 802 3015.1 271 427 115 0.506 0.10968 0.00184 0.45477 0.00548 0.3106 0.0052 4.698 0.118 97 1 794 3116.1 73 112 33 1.050 0.11224 0.00402 0.43486 0.01101 0.3317 0.0068 5.134 0.223 101 1 836 6517.1 369 496 154 0.895 0.10655 0.00187 0.38011 0.00496 0.3176 0.0052 4.666 0.119 102 1 741 3218.1 161 151 62 0.775 0.10681 0.00250 0.25704 0.00620 0.3224 0.0057 4.747 0.148 103 1 746 4319.1 180 163 67 1.352 0.10316 0.00288 0.24297 0.00698 0.3095 0.0055 4.402 0.154 103 1 682 5220.1 102 151 42 0.792 0.11189 0.00441 0.41833 0.01143 0.3067 0.0060 4.732 0.218 94 1 830 7221.1 314 302 105 2.163 0.10646 0.00284 0.28719 0.00690 0.2608 0.0043 3.829 0.127 86 1 740 49

198

Interpretation

All analyses form a single population on concordia and the scatter in the 207Pb/206Pb

ratios is within that attributable to analytical error (chi-squared = 0.88). The mean207Pb/206Pb value of the population corresponds to an age of 1765 ± 15 Ma. This is

interpreted as the crystallization age of the granitic protolith to the orthogneiss.

199

112397: coarse-grained porphyritic biotitemonzogranite (augen) gneiss, Watrara Inlier


RUDALL (SF 51-10) 122°03’35"E 22°28’15"S

Sampled during 1991


This sample is of a K-feldspar porphyritic orthogneiss within the Watrara Inlier,

Rudall Complex.


A coarse-grained gneiss, with augen of microcline up to 15 mm across and oligoclase

up to 5 mm across, in a matrix of recrystallized quartz, oligoclase, microcline, and

strongly oriented layers of green biotite. Associated with biotite is abundant epidote,

minor muscovite, and large grains of sphene up to 1 mm across. Accessory minerals

include apatite, zircon, and opaques. The original biotite monzogranite was probably

porphyritic and many of the microcline augen have retained a granitic texture,

enclosing small plagioclase crystals and biotite flakes. Metamorphic grade is medium

to low. GSWA Petrology Report Number 1616.

Zircon morphology

The zircons extracted from this sample are large (>500 × 150 µm), light brown to dark

brown, euhedral to irregular in shape, and have euhedral igneous zoning.

Analytical details



This sample was analysed on 4 September 1994. The counter deadtime was

36 ns. Analyses were carried out using seven-scan data acquisition. Four analyses of

the CZ-3 standard were obtained during the session. The Pb*/U calibration was

200

stationary with a calibration error of 0.740 (1σ%). A calibration error of 1.50 (1σ%)

was assumed for analyses of unknown samples.

Results

Fifteen analyses were obtained from 15 zircons. Results are given in Table 52 and


Interpretation

All analyses form a single population on concordia with the scatter in the 207Pb/206Pb

ratios within that attributable to analytical error (chi-squared = 0.76). The mean207Pb/206Pb value of the population corresponds to an age of 1787 ± 5 Ma. This is

interpreted as the crystallization age of the granitic protolith to the orthogneiss.

Figure 53. Concordia plot for sample 112397: coarse-grained porphyritic biotitemonzogranite (augen) gneiss, Watrara Inlier

201

Table 52. Ion microprobe analytical results for sample 112397: coarse-grained porphyritic biotite monzogranite (augen) gneiss,Watrara Inlier


1.1 370 306 137 0.021 0.10915 0.00037 0.23935 0.00097 0.3172 0.0048 4.773 0.076 99 1 785 62.1 141 169 57 0.094 0.10908 0.00079 0.35006 0.00221 0.3186 0.0049 4.792 0.085 100 1 784 133.1 208 224 80 0.109 0.10813 0.00060 0.30989 0.00167 0.3140 0.0048 4.681 0.079 100 1 768 104.1 86 98 33 0.235 0.10832 0.00109 0.33086 0.00296 0.3115 0.0048 4.653 0.091 99 1 771 185.1 84 104 33 -0.083 0.10964 0.00152 0.35056 0.00389 0.3155 0.0049 4.769 0.105 99 1 793 256.1 172 207 68 0.070 0.10884 0.00060 0.35182 0.00182 0.3144 0.0048 4.718 0.079 99 1 780 107.1 275 311 105 0.048 0.10980 0.00047 0.32555 0.00137 0.3091 0.0047 4.679 0.076 97 1 796 88.1 93 98 37 -0.076 0.11109 0.00115 0.30984 0.00300 0.3228 0.0050 4.944 0.097 99 1 817 199.1 144 153 55 0.168 0.10888 0.00075 0.30671 0.00207 0.3121 0.0048 4.686 0.082 98 1 781 13

10.1 181 188 70 0.080 0.10870 0.00057 0.29880 0.00161 0.3163 0.0048 4.741 0.079 100 1 778 911.1 525 33 159 0.047 0.10957 0.00032 0.01751 0.00046 0.3119 0.0047 4.712 0.074 98 1 792 512.1 134 114 50 0.868 0.10939 0.00112 0.25165 0.00274 0.3070 0.0047 4.631 0.090 96 1 789 1913.1 249 241 94 0.063 0.10921 0.00054 0.28155 0.00146 0.3136 0.0048 4.722 0.078 98 1 786 914.1 201 254 79 -0.017 0.10983 0.00103 0.36384 0.00266 0.3107 0.0047 4.704 0.089 97 1 797 1715.1 143 112 51 0.084 0.10913 0.00073 0.22720 0.00182 0.3111 0.0048 4.680 0.082 98 1 785 12

202

104989: muscovite quartzite, Fingoon Quartzite


RUDALL (SF 51-10) 122°18’50"E 22°40’39"S



This sample is of a quartzite from the Fingoon Quartzite of the Rudall Complex.


The abundant small (0.04 mm) grains of zircon in this sample are probably detrital. A

few grains are anomalously large and may be irregular. One is as large as

0.18 × 0.11 mm and has higher relief inclusions. Irregular, equally abundant grains of

rutile, somewhat larger than the average zircon, seem at least in part to be

intergranular. These tend to conform to quartz grains and seem thus to be crystallized

in the rock rather than detrital. The texture is of metamorphic origin with granoblastic

quartz and very well-oriented muscovite. The quartz–muscovite assemblage does not

closely constrain the metamorphic grade. This rock is a muscovite quartzite with a

strong muscovite-defined fabric, almost a quartz–muscovite schist. GSWA Petrology

Report Number 1596.

Zircon morphology

The zircons extracted from this sample are ovoid, pitted, large (typically 400 ×

250 µm), colourless, and light pink-brown or dark brown. Some grains have internal

euhedral igneous zoning.

Analytical details



203


36 ns. Analyses were carried out using five-scan data acquisition. Seven analyses of

the CZ-3 standard were obtained during the session. The Pb*/U calibration was

stationary with a calibration error of 1.25 (1σ%). A calibration error of 1.50 (1σ%)

was assumed for analyses of unknown samples.

Results

Nineteen analyses were obtained from 19 zircons. Results are given in Table 53 and


Interpretation

Eighteen analyses form a single population on concordia with the scatter in the207Pb/206Pb ratios within that attributable to analytical error (chi-squared = 0.66). The

mean 207Pb/206Pb value of the population corresponds to an age of 1790 ± 10 Ma. As

the zircons are clearly detrital, this date provides a maximum age for the deposition of

the quartzite. One analysis (16.1) indicates an older 207Pb/206Pb age of 1955 ± 15 Ma.

Figure 54. Concordia plot for sample 104989: muscovite quartzite, Fingoon Quartzite

204

Table 53. Ion microprobe analytical results for sample 104989: muscovite quartzite, Fingoon Quartzite


1.1 132 138 52 0.465 0.10866 0.00203 0.29281 0.00514 0.3206 0.0054 4.802 0.128 101 1 777 342.1 395 115 126 0.218 0.10951 0.00089 0.08480 0.00180 0.3088 0.0048 4.662 0.086 97 1 791 153.1 154 241 64 0.263 0.10981 0.00140 0.43520 0.00436 0.3084 0.0051 4.669 0.103 96 1 796 234.1 105 155 44 0.595 0.11101 0.00257 0.41562 0.00686 0.3163 0.0055 4.841 0.148 98 1 816 425.1 205 149 75 0.377 0.11108 0.00141 0.21795 0.00339 0.3160 0.0051 4.840 0.105 97 1 817 236.1 198 101 70 0.326 0.11093 0.00121 0.14464 0.00268 0.3245 0.0052 4.963 0.102 100 1 815 207.1 452 52 140 0.227 0.10949 0.00071 0.03010 0.00124 0.3135 0.0049 4.733 0.083 98 1 791 128.1 97 137 43 0.411 0.11062 0.00202 0.40120 0.00580 0.3342 0.0057 5.097 0.136 103 1 810 339.1 192 349 84 0.304 0.11031 0.00125 0.52112 0.00409 0.3095 0.0050 4.708 0.098 96 1 804 21

10.1 101 74 37 0.482 0.10866 0.00180 0.20176 0.00428 0.3177 0.0054 4.760 0.120 100 1 777 3011.1 155 184 57 0.763 0.10950 0.00165 0.34027 0.00437 0.2876 0.0046 4.342 0.102 91 1 791 2712.1 225 274 90 0.372 0.10917 0.00111 0.34652 0.00308 0.3137 0.0050 4.722 0.094 98 1 786 1813.1 196 235 78 0.356 0.10865 0.00116 0.34583 0.00327 0.3142 0.0050 4.707 0.095 99 1 777 2014.1 322 142 103 0.282 0.10851 0.00083 0.12837 0.00179 0.2991 0.0046 4.475 0.081 95 1 775 1415.1 139 96 45 1.398 0.10537 0.00212 0.17470 0.00492 0.2800 0.0045 4.067 0.111 92 1 721 3716.1 222 282 98 0.430 0.11994 0.00099 0.35229 0.00273 0.3427 0.0054 5.667 0.106 97 1 955 1517.1 136 101 50 0.476 0.11036 0.00148 0.21344 0.00354 0.3164 0.0051 4.814 0.107 98 1 805 2418.1 225 85 76 0.239 0.11009 0.00101 0.11832 0.00216 0.3177 0.0050 4.822 0.092 99 1 801 1719.1 108 110 40 0.366 0.10773 0.00167 0.31005 0.00451 0.3004 0.0050 4.462 0.107 96 1 761 28

205

111854: biotite–muscovite granodiorite gneiss,Poonemerlarra Creek west


RUDALL (SF 51-10) 122°17’06"E 22°36’02"S

Sampled during 1991


This sample is of an orthogneiss from the Rudall Complex.


Elongate to very elongate augen of coarsely polygranular quartz in this sample are set

in a medium-grained matrix dominated by andesine and biotite but also containing

muscovite, opaques, and microcline. Secondary epidote is abundant and there is minor

carbonate. Accessory minerals include opaques and apatite. Metamict masses

surrounded by epidote suggest rather large grains of allanite. Quartz is subordinate in

the feldspar-dominant portions of the slide. The quartz masses probably represent

former very coarse quartz grains that have maintained their integrity better than have

the primary feldspar and micas. Other possible explanations for this include

metamorphic segregation or dismemberment of quartz veins, but relict coarse grains

seem most probable. It is also possible that the coarse quartz aggregates were

phenocrysts in a fine (now metamorphically coarsened) quartzofeldspathic matrix, but

this too seems less likely than a differentially comminuted, coarse- and even-grained

rock. There is at least a small amount of zircon present. The rock has been

dynothermally metamorphosed, probably at medium metamorphic grade. Plagioclase

has a composition of An35 and An40, yet epidote is common: thus the grade is well

into the greenschist–amphibolite transition or the lower part of the amphibolite facies.

The rock is a medium-grained biotite–muscovite granodiorite gneiss with coarse-

grained quartz augen. GSWA Petrology Report Number 1596.

206

Zircon morphology

The zircons extracted from this sample are large (typically 400 × 250 µm), euhedral,

colourless, and light brown or dark brown. Some grains have internal euhedral

igneous zoning, and many have mineral and fluid inclusions.

Analytical details



This sample was analysed on 5 September 1994. The counter deadtime was

36 ns. Analyses were carried out using five-scan (for analysis 1.1 only) and seven-

scan data acquisition. Seven analyses of the CZ-3 standard were obtained during the

session. The Pb*/U calibration was stationary with a calibration error of 1.25 (1σ%).

A calibration error of 1.50 (1σ%) was assumed for all unknown analyses.

Results



Interpretation

Eleven analyses form a single population with the scatter in the 207Pb/206Pb ratios

slightly in excess of that attributable to analytical error (chi-squared = 2.07). The

mean 207Pb/206Pb value of the population corresponds to an age of 1778 ± 17 Ma.

This is interpreted as the crystallization age of the granitic protolith to the orthogneiss.

One analysis (5.1) indicates an older 207Pb/206Pb age of 2327 ± 12 Ma.

207

Figure 55. Concordia plot for sample 111854: biotite–muscovite granodiorite gneiss,Poonemerlarra Creek west

208

Table 54. Ion microprobe analytical results for sample 111854: biotite–muscovite granodiorite gneiss, Poonemerlarra Creek west


1.1 240 307 97 0.211 0.10967 0.00087 0.36946 0.00260 0.3144 0.0049 4.754 0.087 98 1 794 142.1 129 229 55 0.335 0.10912 0.00116 0.48127 0.00369 0.3089 0.0049 4.647 0.093 97 1 785 193.1 127 119 47 0.165 0.11102 0.00114 0.26927 0.00293 0.3112 0.0049 4.763 0.095 96 1 816 194.1 97 136 40 0.350 0.10734 0.00131 0.40282 0.00391 0.3158 0.0050 4.674 0.100 101 1 755 225.1 259 141 117 1.021 0.14836 0.00100 0.19281 0.00222 0.3788 0.0058 7.748 0.136 89 2 327 126.1 182 260 77 0.203 0.10907 0.00087 0.41030 0.00266 0.3190 0.0049 4.797 0.088 100 1 784 157.1 87 82 35 0.357 0.10604 0.00136 0.28053 0.00355 0.3283 0.0053 4.801 0.104 106 1 732 248.1 117 125 46 0.337 0.10682 0.00111 0.30620 0.00302 0.3223 0.0051 4.747 0.095 103 1 746 199.1 177 211 74 0.197 0.10698 0.00107 0.34408 0.00295 0.3330 0.0052 4.911 0.096 106 1 749 18

10.1 112 137 44 3.608 0.10188 0.00334 0.48799 0.00846 0.2620 0.0042 3.680 0.141 90 1 659 6111.1 162 373 78 0.271 0.10871 0.00103 0.65492 0.00385 0.3152 0.0049 4.724 0.091 99 1 778 1712.1 212 213 85 0.067 0.10956 0.00064 0.28958 0.00184 0.3303 0.0051 4.989 0.086 103 1 792 11

209

104937: coarse-grained biotite monzogranite,Mount Crofton


PATERSON RANGE (SF 51-6) 122°00’E 21°37’S


Sampled about 175 m southeast of survey marker.


This sample is of a monzogranite that has intruded clastic sediments of the Wilke

Quartzite, Yeneena Group.


This sample is a coarse, little-deformed biotite monzogranite with microcline

megacrysts in a coarse- to very coarse-grained groundmass of biotite, quartz, and

largely euhedral plagioclase displaying euhedral igneous zoning. Titanite, apatite,

zircon, and opaques are common. There is some secondary chlorite after altered

biotite. GSWA Petrology Report Number 1596.

Zircon morphology

The zircons isolated from this sample are light pink to dark red-brown, euhedral,

ranging in size up to 200 × 550 µm, strongly zoned, and generally metamict. They

have no obvious rims or cores.

Analytical details

This sample was analysed on 21 August 1993 on SHRIMP-1. Analyses were carried

out using five-scan data acquisition. Nine analyses of the SL-13 standard were

obtained during the entire session. The Pb*/U calibration was stationary during the

analysis period with a calculated error on Pb*/U of 2.15 (1σ%).

210

Results

Seventeen analyses were obtained from 16 zircons. Results are given in Table 55 and


Interpretation

Although five analyses are discordant, all analyses have 207Pb/206Pb ratios that scatter

about a single mean value, suggesting that all belong to a single population having a

common age, but that some have lost radiogenic Pb recently. The scatter about the

mean value is only slightly in excess of that attributable to analytical sources (chi-

squared = 2.70). The 207Pb/206Pb age of all pooled analyses is 614 ± 18 Ma. If the four

discordant analyses (7.1, 11.1, 13.1, and 16.1) are excluded, the remaining analyses

define a single population having a weighted mean 206Pb/238U ratio corresponding to

an age of 621 ± 13 Ma (chi-squared = 1.46). This is interpreted as the best estimate of

the time of crystallization of the Mount Crofton granite.

Figure 56. Concordia plot for sample 104937: coarse-grained biotite monzogranite,Mount Crofton

211

Table 55. Ion microprobe analytical results for sample 104937: coarse-grained biotite monzogranite, Mount Crofton

Grain U Th Pb ƒ206% 207Pb/206Pb ±1σ 206Pb/238U ±1σ 207Pb/235U ±1σ % 206Pb/238U ±1σ 207Pb/206Pb ±1σ.spot (ppm) (ppm) (ppm) concordance Age Age

1.1 9 564 11 277 1 192 0.034 0.06069 0.00023 0.1025 0.0022 0.858 0.019 100 629 13 628 81.2 6 277 4 050 691 0.168 0.06117 0.00038 0.1019 0.0022 0.859 0.020 97 625 13 645 132.1 3 101 5 573 455 0.094 0.06078 0.00048 0.1056 0.0023 0.885 0.021 102 647 13 632 173.1 221 180 26 0.181 0.06234 0.00250 0.1048 0.0023 0.901 0.043 94 643 13 686 866.1 2 105 2 250 247 0.213 0.05962 0.00074 0.0980 0.0021 0.806 0.021 102 603 12 590 277.1 637 576 68 0.303 0.06068 0.00179 0.0907 0.0020 0.759 0.029 89 560 12 628 648.1 2 944 1 855 320 0.212 0.05955 0.00055 0.1004 0.0022 0.824 0.020 105 617 13 587 209.1 2 285 1 354 249 0.129 0.05897 0.00062 0.1015 0.0022 0.825 0.021 110 623 13 566 23

10.1 760 561 85 1.294 0.05627 0.00215 0.0975 0.0021 0.756 0.035 130 600 12 463 8511.1 2 236 461 204 0.137 0.05974 0.00058 0.0940 0.0020 0.775 0.019 98 579 12 594 2112.1 1 018 908 115 0.643 0.05526 0.00157 0.0965 0.0021 0.736 0.028 141 594 12 423 6313.1 1 332 1 133 136 0.539 0.05844 0.00141 0.0859 0.0019 0.692 0.024 97 532 11 546 5314.1 1 345 30 126 0.378 0.05890 0.00108 0.1016 0.0022 0.825 0.025 111 624 13 563 4015.1 4 040 4 229 484 0.109 0.06020 0.00038 0.1007 0.0022 0.836 0.019 101 618 13 611 1416.1 1 384 767 104 0.704 0.05950 0.00148 0.0665 0.0014 0.546 0.019 71 415 9 585 5417.1 566 551 73 1.084 0.06355 0.00256 0.1041 0.0023 0.912 0.044 88 638 13 727 8518.1 2 047 1 153 224 0.272 0.05931 0.00078 0.1012 0.0022 0.827 0.022 107 621 13 579 29

212

104938: pegmatite, Coondegoon


RUDALL (SF 51-10) 122°32’E 22°33'


This sample was taken from a dyke, located about 45 km east of the Green Pygmy site

(sample 104934).


This rock is a deformed very coarse-grained to pegmatitic albite-dominant

metasyenogranite. It is believed to have intruded orthogneiss.


This sample consists of coarse to very coarse anhedral grains of albite and very coarse

masses of medium-grained polygranular quartz set in a subordinate, deformed matrix

of muscovite, quartz, feldspar, and coarse-grained epidote. The rock is a muscovite–

quartz–epidote–albite (microcline) metasyenogranitic pegmatoid. GSWA Petrology

Report Number 1596.

Zircon morphology

Two types of zircon morphology can be distinguished. The most abundant type

(designated type 1) are light brown, structureless, and with a wide variety of shapes,

including large equant to irregular-shaped and elongate grains. Rims and cores cannot

be distinguished in this type. A second morphological type (type 2), represented by

grains 3, 9, 11, and 14, are dark brown, euhedral to subrounded, and have obvious

cores enclosed in rims of variable thickness.

213

Analytical details

This sample was analysed on 24 and 25 January 1991 on SHRIMP-1. The counter


Fifteen analyses of the SL-13 standard were obtained during the entire session. The

Pb*/U calibration was stationary during the analysis time with a calculated error of

2.70 (1σ%).

Results

Seventeen analyses were obtained from 15 zircons. The results are given in Table 56


Figure 57. Concordia plot for sample 104938: pegmatite, Coondegoon

214

Table 56. Ion microprobe analytical results for sample 104938: pegmatite, Coondegoon


1.1 3 085 838 733 0.042 0.08390 0.00030 0.07654 0.00055 0.2376 0.0064 2.748 0.076 106 1 290 72.1 4 342 1 411 833 0.059 0.07801 0.00029 0.09452 0.00061 0.1898 0.0051 2.042 0.057 98 1 147 73.1 404 128 115 1.301 0.10278 0.00206 0.09838 0.00459 0.2636 0.0072 3.735 0.134 90 1 675 374.1 1 573 250 345 0.010 0.08416 0.00045 0.04742 0.00072 0.2257 0.0061 2.619 0.074 101 1 296 105.1 2 213 325 495 0.080 0.08362 0.00039 0.04160 0.00064 0.2304 0.0062 2.656 0.074 104 1 284 96.1 2 829 224 606 0.124 0.08272 0.00036 0.02268 0.00058 0.2242 0.0061 2.557 0.071 103 1 263 87.1 2 705 692 630 0.012 0.08471 0.00028 0.07155 0.00049 0.2341 0.0063 2.734 0.076 104 1 309 78.1 2 194 421 494 0.022 0.08524 0.00033 0.05582 0.00050 0.2292 0.0062 2.694 0.075 101 1 321 79.1 233 221 77 5.972 0.10286 0.00591 0.42667 0.01450 0.2139 0.0060 3.033 0.203 75 1 676 1069.2 1 080 160 238 0.346 0.08333 0.00077 0.04255 0.00154 0.2250 0.0061 2.585 0.077 102 1 277 18

10.1 2 157 325 473 0.052 0.08421 0.00038 0.04434 0.00062 0.2258 0.0061 2.621 0.073 101 1 297 911.1 1 030 122 228 3.084 0.08183 0.00213 0.03530 0.00484 0.2060 0.0056 2.324 0.093 97 1 242 5112.1 4 075 1 018 949 0.060 0.08320 0.00027 0.07006 0.00050 0.2344 0.0063 2.689 0.074 107 1 274 613.1 3 230 696 748 0.018 0.08369 0.00028 0.06123 0.00045 0.2349 0.0064 2.711 0.075 106 1 285 614.1 293 286 115 0.930 0.10888 0.00205 0.28312 0.00513 0.3183 0.0088 4.779 0.169 100 1 781 3415.1 3 383 863 797 0.059 0.08433 0.00030 0.07246 0.00056 0.2364 0.0064 2.749 0.076 105 1 300 72.2 3 233 822 753 0.037 0.08391 0.00029 0.07290 0.00054 0.2338 0.0063 2.705 0.075 105 1 291 7

215

Interpretation

With the exception of analysis 2.1, which has high U and Th and a significantly lower207Pb/206Pb ratio, analyses of morphological type 1 and the rims of grains 9 and 11

(morphological type 2) form a single population with a mean 207Pb/206Pb value

corresponding to an age of 1291 ± 10 Ma. This is interpreted as the crystallization age

of the metasyenogranite. The error in 207Pb/206Pb ratios is slightly in excess of that

attributable to analytical error (chi-squared = 3.75), suggesting some open-system

behaviour of U and Pb in these zircons. Although analysis 2.1 has a significantly

lower 207Pb/206Pb ratio than the main population, analysis 2.2 on the same grain is

within error of the main population, suggesting that parts of this grain have lost

radiogenic Pb. Analyses 3.1, 9.1, and 14.1, on cores of zircons belonging to

morphological type 2, have significantly higher 207Pb/206Pb ages, which are within

error of 1726 ± 155 Ma (chi-squared = 1.60). Although imprecise, this date is identical

to that obtained for orthogneiss sample 104934, suggesting that these zircons are

xenocrysts that were incorporated into the syenogranite magma by contamination

from the adjacent orthogneiss, and that the rims on these zircons formed during

crystallization of the dyke.

216

112341: micromonzogranite (meta-aplite) dyke,Rudall airstrip


RUDALL (SF 51-10) 122°10’22"E 22°33’38"S

Sampled during 1991


This sample is of an aplite dyke that intrudes the main porphyritic orthogneiss phase

of the Rudall Complex.


This rock is a medium-grained (0.5 mm), slightly foliated, granoblastic assemblage of

microcline, quartz, and sericitized plagioclase with minor biotite, muscovite, epidote,

and opaques, and accessory zircon. A medium-grade meta-aplite. GSWA Petrology

Report Number 1616.

Zircon morphology

The zircons recovered from this sample are light brown to dark brown, subhedral,

rounded or irregular in shape (typically 100–200 µm) and commonly metamict, with

little or no obvious internal structure evident.

Analytical details



This sample was analysed on 2 and 3 November 1994. The counter deadtime was

36 ns. Eight analyses of the CZ-3 standard were obtained during the entire session.

The Pb*/U calibration was stationary during the analysis time with a calculated error

of 4.05 (1σ%). Compared to the standard, slightly higher 204Pb counts were measured

on unknown samples. Common-Pb corrections were therefore applied using the 204Pb

217

correction method and assuming the isotopic composition of 1780 Ma common-Pb,

determined using the method of Cumming and Richards (1975).

Results

Sixteen analyses were obtained from 16 zircons. The results are given in Table 57 and


Interpretation

With the exception of analysis 9.1, all analyses form a single population (chi-squared

= 0.60) with a mean 207Pb/206Pb value corresponding to an age of 1778 ± 16 Ma. This

is interpreted as the crystallization age of the meta-aplite. Analysis 9.1 has a

significantly lower 207Pb/206Pb ratio than the main population, and has been disturbed

by later metamorphic events.

Figure 58. Concordia plot for sample 112341: micromonzogranite (meta-aplite) dyke,Rudall airstrip

218

Table 57. Ion microprobe analytical results for sample 112341: micromonzogranite (meta-aplite) dyke, Rudall airstrip


1.1 201 384 89 1.797 0.10948 0.00177 0.53633 0.00483 0.2964 0.0121 4.475 0.205 93 1 791 292.1 510 308 174 0.761 0.10833 0.00080 0.16723 0.00182 0.3034 0.0123 4.531 0.191 96 1 772 133.1 126 168 53 2.320 0.11039 0.00266 0.37594 0.00660 0.3081 0.0127 4.689 0.235 96 1 806 444.1 208 421 99 1.090 0.10987 0.00152 0.57621 0.00453 0.3191 0.0130 4.834 0.216 99 1 797 255.1 172 258 74 1.950 0.10929 0.00223 0.41879 0.00572 0.3114 0.0128 4.692 0.225 98 1 788 376.1 131 144 55 2.704 0.10762 0.00294 0.30997 0.00710 0.3166 0.0130 4.698 0.245 101 1 760 507.1 145 297 68 5.779 0.10570 0.00409 0.47563 0.01009 0.2954 0.0122 4.305 0.258 97 1 727 718.1 74 107 34 3.510 0.11434 0.00468 0.40616 0.01144 0.3148 0.0131 4.962 0.308 94 1 870 749.1 184 262 73 2.152 0.09936 0.00237 0.42389 0.00606 0.2850 0.0117 3.905 0.195 100 1 612 44

10.1 153 284 73 1.804 0.10792 0.00238 0.52726 0.00642 0.3223 0.0132 4.796 0.235 102 1 765 4011.1 96 115 42 4.023 0.10436 0.00420 0.32525 0.01006 0.3188 0.0132 4.587 0.281 105 1 703 7412.1 127 192 58 2.268 0.10922 0.00278 0.42253 0.00710 0.3233 0.0133 4.868 0.249 101 1 786 4613.1 147 179 64 2.248 0.10731 0.00256 0.34231 0.00630 0.3275 0.0135 4.845 0.243 104 1 754 4414.1 153 211 69 2.223 0.10645 0.00254 0.38970 0.00641 0.3275 0.0135 4.807 0.240 105 1 739 4415.1 190 293 80 5.612 0.10518 0.00399 0.40419 0.00965 0.2755 0.0113 3.996 0.237 91 1 717 7016.1 156 289 77 1.784 0.11214 0.00240 0.53743 0.00654 0.3322 0.0137 5.136 0.250 101 1 834 39

219

104980: monzogranite gneiss, Graphite Valley


RUDALL (SF 51-10) 122°18’02"E 22°43’56"SSampled on 14 August 1992


This sample is of an orthogneiss within the Rudall Complex.


Very large masses of quartz in this sample are set in a heterogranularquartzofeldspathic, biotite–muscovite matrix with medium to coarse grains ofmicrocline. Both saussuritic plagioclase and microcline are abundant but microclinemay be dominant. The rock is probably a comminuted very coarse-grained igneousrock, the elongate quartz masses being the remains of coarse-grained quartz, and thefeldspathic masses the remains of the mica–feldspathic fraction. Relict coarse-grainedmicrocline is probably remnant from the coarse-grained phase of the feldspar.Accessory minerals include minor opaques and apatite. Secondary minerals includethe abundant saussuritic epidote, probably most, if not all, of the muscovite, andsparse carbonate. Zircon is abundant as an accessory. The rock has been profoundlyrecrystallized, although in this rock the microcline megacrysts as well as the largequartz masses may be relict from coarse grains of the precursor. The metamorphicgrade is not distinct but falls in the intermediate range. The rock is a porphyroclasticand quartz-augen–biotite–muscovite monzogranite gneiss. GSWA Petrology ReportNumber 1596.

Zircon morphology

The zircons recovered from this sample are dark brown, subhedral, rounded orirregular in shape, large (typically 250–500 µm), and generally metamict. Internaleuhedral igneous zoning is evident in most grains.

Analytical details

Heavy minerals were isolated from about 890 g of sample using conventional heavy-liquid and magnetic techniques.

220

This sample was analysed on 2 and 3 November 1994. The counter deadtime was

36 ns. Eight analyses of the CZ-3 standard were obtained during the entire session.

The Pb*/U calibration was stationary during the analysis time with a calculated error

of 4.05 (1σ%). Compared to the standard, slightly higher 204Pb counts were measured

on unknown samples. Common-Pb corrections were therefore applied using the 204Pb

correction method and assuming the isotopic composition of 1780 Ma common-Pb,

determined using the method of Cumming and Richards (1975).

Results

Fourteen analyses were obtained from 14 zircons. The results are given in Table 58


Interpretation

All analyses form a single population with a mean 207Pb/206Pb value corresponding to

an age of 1801 ± 4 Ma (chi-squared = 0.67). This is interpreted as the crystallization

age of the granitoid precursor to this gneiss.

Figure 59. Concordia plot for sample 104980: monzogranite gneiss, Graphite Valley

221

Table 58. Ion microprobe analytical results for sample 104980: monzogranite gneiss, Graphite Valley


1.1 268 186 107 3.546 0.10514 0.00258 0.23762 0.00605 0.3087 0.0126 4.476 0.225 101 1 717 452.1 595 159 207 0.650 0.11075 0.00081 0.07609 0.00170 0.3320 0.0135 5.070 0.214 102 1 812 133.1 378 403 156 1.139 0.11027 0.00127 0.30932 0.00318 0.3252 0.0133 4.944 0.216 101 1 804 214.1 424 371 169 2.422 0.10930 0.00170 0.27082 0.00404 0.3102 0.0126 4.674 0.212 97 1 788 285.1 501 151 162 0.305 0.11005 0.00055 0.08604 0.00109 0.3116 0.0127 4.728 0.196 97 1 800 96.1 201 445 95 0.749 0.11012 0.00117 0.62237 0.00381 0.3120 0.0127 4.738 0.206 97 1 801 197.1 635 162 203 0.503 0.10974 0.00057 0.07168 0.00116 0.3093 0.0126 4.680 0.195 97 1 795 98.1 383 818 177 0.984 0.11057 0.00102 0.60907 0.00310 0.3044 0.0124 4.640 0.199 95 1 809 179.1 580 566 215 0.266 0.10998 0.00055 0.27628 0.00146 0.3082 0.0125 4.674 0.194 96 1 799 9

10.1 605 1 081 264 0.251 0.11022 0.00051 0.48149 0.00176 0.3159 0.0128 4.800 0.199 98 1 803 811.1 4 987 11 434 2 600 0.025 0.11013 0.00013 0.64212 0.00064 0.3448 0.0140 5.235 0.213 106 1 802 212.1 725 665 276 0.566 0.10969 0.00061 0.26180 0.00154 0.3172 0.0129 4.797 0.200 99 1 794 1014.1 1 245 1 415 475 0.489 0.11030 0.00045 0.31102 0.00118 0.3070 0.0125 4.668 0.193 96 1 804 713.1 725 769 273 0.365 0.10922 0.00053 0.29906 0.00141 0.3073 0.0125 4.628 0.192 97 1 786 9

222

112106: foliated monzogranite, Minyari


PATERSON RANGE ( SF 51-6) 122°24’31"E 21°27’34"S

Sampled 21 August 1991


This sample is of a foliated monzogranite of the Mount Crofton granitoid suite, Telfer

region.


This rock is coarse-grained with a myrmekitic texture common between the feldspars.

Plagioclase is very weakly and anhedrally zoned within the mid-oligoclase

compositional range, except at the immediate rims of grains where compositional

zoning is marked to a more sodic composition. Strictly euhedral grain boundaries are

rare. The foliation described in the field description is weak in thin section, defined

mostly by biotite, and, to a lesser extent, by the felsic minerals. Accessory minerals

include apatite, minor opaques, rutile associated with chlorite after biotite, minuscule

carbonate, and locally abundant, large, zonally altered zircon (0.121 × 0.085 mm). The

texture could be interpreted as igneous if there were good euhedral oscillatory

plagioclase zoning. Clearly there are recrystallization effects, such as

myrmekitization. But overall, the rock seems basically to be igneous, most probably

with a flow foliation, although possibly with a post-crystallization foliation due to

mild deformation. Metamorphism is not prominent, though it has perhaps effected

some recrystallization after imposition of the foliation, if the foliation is not a primary

flow feature. The mineralogical assemblage is not one that would reflect metamorphic

grade above the upper part of the greenschist facies. Myrmekite suggests some re-

equilibration, but this could be late-magmatic/deuteric. A coarse-grained microcline–

biotite monzogranite near syenogranite. GSWA Petrology Report Number 1596.

223

Zircon morphology

The zircons recovered from this sample are light brown to dark brown, euhedral in

shape, large (up to 500 µm long), and generally metamict. Many contain fluid and

mineral inclusions. Internal euhedral igneous zoning is evident in most grains,

although a minority are structureless.

Analytical details



This sample was analysed on 9 November 1994. The counter deadtime was 36 ns.

Seven analyses of the CZ-3 standard were obtained during the analysis session. The

Pb*/U calibration was mobile during the session due to retuning of the instrument,

with all seven standard analyses defining a calibration error of 3.71(1σ%). The

analyses have therefore been processed in two batches. The first batch, consisting of

three standards and 11 unknown samples, gave a calibration error of 1.86 (1σ%). The

second batch, consisting of four standards and nine unknown samples, gave a

calibration error of 2.06 (1σ%). Compared to the standard, slightly higher 204Pb

counts were measured on a few unknown samples. Processing of these analyses using

Cumming and Richards (1975) 650 Ma common-Pb produces indistinguishable

results to those determined using Broken Hill common-Pb, so the latter has been used

for all analyses.

Results

Twenty-two analyses were obtained from 22 zircons. The results are given in Table 59


Interpretation

The analyses fall into three groups. Group 1 analyses (7.1, 13.1, and 14.1), of the rims

of strongly zoned euhedral grains, are concordant and form a single population with a

mean 206Pb/238U value corresponding to an age of 680 ± 30 Ma (chi-squared = 0.20).

224

These analyses are interpreted to be of xenocryst zircons. Group 2 analyses (1.1, 2.1,

3.1, 4.1, 5.1, 6.1, 8.1, 9.1, 10.1, 11.1, 12.1, 20.1, 21.1, and 22.1), of grains

morphologically identical to those in Group 1, form a single population with little

excess scatter (chi-squared = 1.36) indicating a slightly younger 206Pb/238U age of

633 ± 13 Ma. This is interpreted as the crystallization age of the granitoid. Group 3

analyses (15.1, 16.1, 17.1, 18.1, and 19.1) indicate younger 206Pb/238U ages of

between about 600–400 Ma. These analyses are interpreted as having lost radiogenic

Pb during a disturbance event.

Figure 60. Concordia plot for sample 112106: foliated monzogranite, Minyari

225

Table 59. Ion microprobe analytical results for sample 112106: foliated monzogranite, Minyari

Grain U Th Pb ƒ206% 207Pb/206Pb ±1σ 206Pb/238U ±1σ 207Pb/235U ±1σ % 206Pb/238U ±1σ 207Pb/206Pb ±1σ.spot (ppm) (ppm) (ppm) concordance Age Age

1.1 170 131 20 2.241 0.05253 0.00435 0.0992 0.0021 0.719 0.063 198 610 12 308 1902.1 317 223 36 1.189 0.05811 0.00252 0.0997 0.0021 0.799 0.040 115 612 12 534 953.1 3 425 2 557 411 0.061 0.06191 0.00027 0.1077 0.0022 0.920 0.020 98 660 13 671 94.1 1 225 848 144 0.232 0.06146 0.00061 0.1056 0.0022 0.895 0.021 99 647 13 655 215.1 266 87 29 1.241 0.06226 0.00243 0.1034 0.0022 0.888 0.041 93 634 13 683 836.1 1 200 705 133 0.255 0.06183 0.00062 0.1027 0.0021 0.876 0.021 94 630 12 668 217.1 2 747 2 081 341 0.156 0.06133 0.00036 0.1099 0.0023 0.929 0.021 103 672 13 651 128.1 474 433 61 0.739 0.06301 0.00153 0.1029 0.0021 0.894 0.030 89 631 12 709 519.1 949 1 319 129 1.838 0.06188 0.00161 0.0993 0.0021 0.847 0.030 91 610 12 670 56

10.1 389 128 42 0.998 0.06093 0.00211 0.1043 0.0022 0.876 0.037 100 640 13 637 7411.1 934 142 137 5.721 0.06361 0.00330 0.1022 0.0021 0.896 0.052 86 627 13 729 11012.1 494 109 55 2.436 0.05881 0.00282 0.1027 0.0019 0.833 0.045 113 630 11 560 10513.1 4 008 1 756 464 0.241 0.05988 0.00038 0.1119 0.0021 0.924 0.019 114 684 12 599 1414.1 545 330 70 2.595 0.05664 0.00347 0.1116 0.0021 0.872 0.058 143 682 12 477 13615.1 465 1 161 45 6.167 0.06169 0.00513 0.0640 0.0012 0.544 0.048 60 400 7 664 17916.1 291 119 31 3.100 0.05339 0.00453 0.0961 0.0019 0.708 0.063 171 592 11 345 19317.1 354 803 53 7.849 0.05260 0.00698 0.0929 0.0019 0.674 0.092 184 573 11 312 29418.1 287 226 35 6.395 0.05139 0.00645 0.0842 0.0017 0.596 0.077 202 521 10 258 26219.1 532 1 251 69 3.227 0.05873 0.00312 0.0970 0.0018 0.785 0.046 107 597 11 557 11620.1 330 174 38 1.679 0.06038 0.00293 0.1034 0.0020 0.861 0.047 103 634 11 617 10521.1 563 423 68 1.181 0.05912 0.00188 0.1043 0.0020 0.850 0.033 112 639 11 571 6922.1 838 569 100 0.941 0.06067 0.00143 0.1063 0.0020 0.889 0.028 104 651 12 628 51

226

111843: biotite–muscovite monzogranite gneiss,Poynton Creek


RUDALL (SF 51-10) 122°18’57"E 22°34’22"S

Sampled during 1991




This is a strongly layered biotite–muscovite granodiorite gneiss in which quartz layers

alternate sharply with feldspar layers. The feldspar is predominantly heavily

saussuritized plagioclase but there are scattered grains of microcline. Both saussuritic

and intergranular epidote is abundant. Cores of many clusters of epidote are metamict,

probably signifying former allanite. There is some secondary carbonate. The rock has

been thoroughly metamorphosed with apparently full recrystallization of all major

phases. A strong foliation has been imposed on the rock, presumably by the

elongation of, and subgrain development in, coarse feldspar and quartz grains.

Recrystallization has been sufficiently intense that subgrain development has

dominated over grain elongation (that is, monomineralic grain aggregates are strongly

elongated, but individual grains are not). Metamorphic grade is not high, and is

intermediate at most. There is too much epidote in the rock for a substantial amount of

Ca to be in plagioclase, and Ca in plagioclase (in the presence of excess epidote) is a

measure of grade. The Ca content of plagioclase was not directly determined. A

biotite–muscovite granodiorite gneiss. GSWA Petrology Report Number 1596.

227

Zircon morphology

The zircons recovered from this sample are typically dark brown, euhedral, up to

350 µm long, and commonly highly metamict. Many contain mineral inclusions.

Internal euhedral igneous zoning is evident in most grains.

Analytical details



This sample was analysed on 10 December 1994. The counter deadtime was

36 ns. Five analyses of the CZ-3 standard were obtained during the analysis session.

The Pb*/U calibration was stationary during the session, with all five standard

analyses defining a calibration error of 3.82 (1σ%). Compared to the standard,

significantly higher 204Pb counts were measured on a few unknown samples. These

analyses were processed using Cumming and Richards (1975) 1800 Ma common-Pb.

However, using Broken Hill common-Pb produces identical results.

Results

Sixteen analyses were obtained from 12 zircons. The results are given in Table 60 and


Interpretation

Fourteen analyses of eleven zircons form a single concordant population (chi-squared

= 0.88) with a mean 207Pb/206Pb value corresponding to an age of 1795 ± 17 Ma. This

is interpreted as the crystallization age of the granitoid precursor to this gneiss.

Analyses 3.1 and 11.1 have higher 207Pb/206Pb ages and are interpreted to be of

xenocrysts.

228

Figure 61. Concordia plot for sample 111843: biotite–muscovite monzogranite gneiss,Poynton Creek

229

Table 60. Ion microprobe analytical results for sample 111843: biotite–muscovite granodiorite gneiss, Poynton Creek


1.1 151 237 71 5.483 0.10874 0.00402 0.47232 0.00987 0.2964 0.0115 4.444 0.253 94 1 778 672.1 325 84 111 0.127 0.10943 0.00078 0.07281 0.00146 0.3333 0.0128 5.029 0.201 104 1 790 133.1 186 142 87 0.253 0.13030 0.00121 0.21504 0.00277 0.4019 0.0156 7.220 0.296 104 2 102 164.1 248 324 132 7.243 0.10505 0.00410 0.40759 0.00986 0.3330 0.0129 4.823 0.282 108 1 715 725.1 610 688 288 0.904 0.11106 0.00114 0.33595 0.00291 0.3681 0.0142 5.637 0.231 111 1 817 196.1 259 514 233 22.798 0.11486 0.00970 0.48241 0.02300 0.3640 0.0146 5.764 0.564 107 1 878 1537.1 136 193 60 2.866 0.10742 0.00278 0.41235 0.00689 0.3072 0.0119 4.550 0.223 98 1 756 478.1 238 233 95 5.039 0.10547 0.00271 0.18750 0.00625 0.3036 0.0117 4.416 0.216 99 1 723 479.1 394 217 151 4.026 0.10943 0.00194 0.12296 0.00442 0.3147 0.0121 4.748 0.210 99 1 790 321.2 174 249 90 6.939 0.11481 0.00369 0.43679 0.00892 0.3214 0.0124 5.088 0.271 96 1 877 587.2 124 183 54 0.223 0.11048 0.00150 0.42757 0.00441 0.3285 0.0127 5.003 0.213 101 1 807 25

10.1 324 294 130 1.783 0.11056 0.00152 0.26315 0.00362 0.3220 0.0124 4.908 0.208 99 1 809 2510.2 278 269 124 4.846 0.11062 0.00272 0.28751 0.00640 0.3194 0.0123 4.872 0.235 99 1 810 4511.1 461 91 196 5.109 0.11809 0.00197 0.06734 0.00443 0.3481 0.0134 5.668 0.248 100 1 928 302.2 402 84 162 5.789 0.10859 0.00237 0.07189 0.00537 0.3245 0.0125 4.859 0.226 102 1 776 40

12.1 129 194 95 20.438 0.09665 0.00801 0.44249 0.01902 0.3201 0.0126 4.265 0.410 115 1 560 156

230

112310: granodiorite gneiss, Dunn Creek west


RUDALL (SF 51-10) 122°16’49"E 22°33’45"S

Sampled during 1991




This sample contains a medium-grained, moderately oriented and layered,

granoblastic assemblage of altered plagioclase, quartz, lesser microcline and epidote,

minor biotite, and accessory muscovite, allanite, apatite, and zircon. Layering has

resulted from concentrations of epidote and biotite, and stringers of quartz. A low-

grade metamorphosed granodiorite. GSWA Petrology Report Number 1616.

Zircon morphology

The zircons recovered from this sample are typically dark brown, euhedral in shape,

up to 400 µm long, and commonly metamict. Internal euhedral igneous zoning is

evident in most grains.

Analytical details





The Pb*/U calibration was stationary during the analysis of standards 1–8, with these

standard analyses defining a calibration error of 1.88 (1σ%). During the analysis of

231

standards 8–9 (unknown analyses 15.1–18.1), the Pb*/U calibration was mobile and a

calibration error of 5.39 (1σ%) was determined. Compared to the standard,

significantly higher 204Pb counts were measured on a few unknown samples. The

analyses with high 204Pb counts were processed assuming Cumming and Richards

(1975) common-Pb. The remaining analyses were processed assuming Broken Hill

common-Pb.

Results

Eighteen analyses were obtained from 18 zircons. The results are given in Table 61


Figure 62. Concordia plot for sample 112310: granodiorite gneiss, Dunn Creek west

232

Table 61. Ion microprobe analytical results for sample 112310: granodiorite gneiss, Dunn Creek west


1.1 1 182 60 408 0.045 0.12140 0.00029 0.01430 0.00032 0.3533 0.0067 5.914 0.114 99 1 977 42.1 819 228 266 0.098 0.11069 0.00038 0.07774 0.00065 0.3160 0.0060 4.823 0.095 98 1 811 63.1 172 91 65 0.527 0.12049 0.00136 0.15297 0.00302 0.3407 0.0066 5.661 0.134 96 1 963 204.1 884 305 294 0.121 0.10985 0.00038 0.10009 0.00072 0.3181 0.0060 4.818 0.095 99 1 797 65.1 1 072 328 364 1.200 0.11099 0.00067 0.09185 0.00146 0.3143 0.0059 4.811 0.099 97 1 816 116.1 1 406 895 563 0.061 0.12104 0.00028 0.18089 0.00061 0.3569 0.0067 5.956 0.115 100 1 972 47.1 991 386 350 2.079 0.10884 0.00091 0.11467 0.00204 0.3125 0.0059 4.690 0.101 98 1 780 158.1 1 400 55 478 0.035 0.12117 0.00027 0.01073 0.00025 0.3505 0.0066 5.856 0.113 98 1 974 49.1 865 326 322 0.356 0.12129 0.00051 0.10673 0.00103 0.3482 0.0066 5.822 0.116 97 1 975 7

10.1 309 176 118 0.155 0.12127 0.00069 0.15958 0.00147 0.3455 0.0066 5.777 0.119 97 1 975 1011.1 315 160 122 0.306 0.12059 0.00080 0.14249 0.00172 0.3524 0.0068 5.859 0.123 99 1 965 1212.1 575 334 224 2.189 0.11953 0.00122 0.17499 0.00277 0.3254 0.0062 5.363 0.122 93 1 949 1813.1 1 777 192 501 1.713 0.10949 0.00066 0.02692 0.00142 0.2706 0.0051 4.086 0.084 86 1 791 1114.1 925 352 331 0.542 0.11835 0.00055 0.10725 0.00116 0.3328 0.0063 5.431 0.109 96 1 932 815.1 424 127 173 1.624 0.12070 0.00116 0.09208 0.00253 0.3699 0.0200 6.156 0.345 103 1 967 1716.1 439 212 180 0.163 0.12158 0.00059 0.13597 0.00121 0.3764 0.0203 6.309 0.346 104 1 980 917.1 1 228 109 453 0.603 0.12015 0.00047 0.02457 0.00091 0.3659 0.0197 6.061 0.331 103 1 958 718.1 679 139 283 4.590 0.11871 0.00159 0.08259 0.00355 0.3427 0.0185 5.610 0.321 98 1 937 24

233

Interpretation

The analyses fall into 3 groups. Group 1 analyses (1.1, 3.1, 6.1, 8.1, 9.1, 10.1, 11.1,

12.1, 15.1, 16.1, 17.1, and 18.1) form a single population with no excess scatter (chi-

squared = 0.93), with a mean 207Pb/206Pb value corresponding to an age of

1972 ± 4 Ma. These analyses are interpreted to be derived from an older granitoid

component within the orthogneiss. Group 2 analyses (2.1, 4.1, 5.1, 7.1, and 13.1) of

grains morphologically similar to those in Group 1, form a single population with

little excess scatter (chi-squared = 1.62), indicating a younger 207Pb/206Pb age of

1802 ± 14 Ma. These analyses are interpreted to be derived from a younger granitoid

component within the orthogneiss. Group 3, consisting of analysis 14.1, has a207Pb/206Pb age of 1932 ± 8 Ma, and is probably a disturbed member of Group 1.

234

113002: granodiorite gneiss, Cotton Creek


RUDALL (SF 51-10) 122°34’33"E 22°48’05"S

Sampled during 1992




Not available.

Zircon morphology

The zircons recovered from this sample are typically clear to light yellow-brown,

euhedral in shape, and up to 400 µm long. Many contain mineral and fluid inclusions.

Internal euhedral igneous zoning is evident in many grains.

Analytical details





The Pb*/U calibration was stationary during the analysis of standards 1–8, with

standard analyses defining a calibration error of 1.88 (1σ%).

235

Results

Fourteen analyses were obtained from 14 zircons. The results are given in Table 62


Interpretation

All fourteen analyses form a single population with a mean 207Pb/206Pb value

corresponding to an age of 1769 ± 7 Ma (chi-squared = 0.64). This is interpreted as

the crystallization age of the granitoid precursor to this gneiss.

Figure 63. Concordia plot for sample 113002: granodiorite gneiss, Cotton Creek

236

Table 62. Ion microprobe analytical results for sample 113002: granodiorite gneiss, Cotton Creek


1.1 421 303 152 0.239 0.10819 0.00063 0.20633 0.00152 0.3159 0.0060 4.712 0.097 100 1 769 112.1 381 428 151 0.160 0.10923 0.00063 0.31972 0.00183 0.3211 0.0061 4.836 0.100 100 1 787 113.1 315 229 113 0.280 0.10824 0.00083 0.20596 0.00199 0.3158 0.0060 4.712 0.101 100 1 770 144.1 197 123 42 0.907 0.10579 0.00190 0.33566 0.00494 0.1680 0.0032 2.450 0.068 58 1 728 335.1 272 167 96 0.368 0.10777 0.00086 0.17379 0.00200 0.3163 0.0061 4.701 0.102 101 1 762 156.1 169 111 61 0.351 0.10883 0.00115 0.18682 0.00270 0.3186 0.0062 4.781 0.111 100 1 780 197.1 226 205 85 0.371 0.10791 0.00105 0.25911 0.00267 0.3178 0.0061 4.728 0.107 101 1 764 188.1 224 174 80 0.472 0.10661 0.00111 0.21684 0.00270 0.3102 0.0060 4.560 0.105 100 1 742 199.1 278 203 100 0.285 0.10840 0.00087 0.21004 0.00210 0.3137 0.0060 4.688 0.102 99 1 773 15

10.1 603 408 213 0.196 0.10835 0.00050 0.19301 0.00119 0.3132 0.0059 4.679 0.094 99 1 772 811.1 213 246 83 0.830 0.10741 0.00130 0.32688 0.00340 0.3101 0.0060 4.592 0.110 99 1 756 2212.1 211 141 75 0.473 0.10864 0.00113 0.18525 0.00263 0.3145 0.0061 4.711 0.108 99 1 777 1913.1 158 97 55 0.692 0.10706 0.00150 0.17155 0.00348 0.3083 0.0060 4.552 0.115 99 1 750 2614.1 408 360 149 0.253 0.10766 0.00064 0.24719 0.00166 0.3111 0.0059 4.618 0.095 99 1 760 11

237

104981: biotite–muscovite monzogranite gneiss,southern part of Graphite Valley


RUDALL (SF 51-10) 122°15’33"E 22°46’28"SSampled on 14 August 1992




This rock is a moderately foliated, equigranular, granofelsic, leucocratic biotite(–muscovite) monzogranite gneiss. The plagioclase is sodic oligoclase. The mostabundant accessory is apatite. There are few, if any, opaques. Secondary epidote ismainly intergranular, suggesting prolonged annealing. The rock has been substantiallymetamorphosed at moderate grade, perhaps to the transition between greenschist andamphibolite facies. GSWA Petrology Report Number 1596.

Zircon morphology

The zircons recovered from this sample are typically light yellow-brown to darkbrown, euhedral (but with rounded terminations), and up to 350 µm long. Internaleuhedral igneous zoning is evident in some grains, but most are structureless.

Analytical details

Heavy minerals were isolated from about 830 g of sample using conventional heavy-liquid and magnetic techniques.

This sample was analysed on 15 December 1994. The counter deadtime was36 ns. Six analyses of the CZ-3 standard were obtained during the analysis session.The Pb*/U calibration was stationary during the session, with all six standard analysesdefining a calibration error of 1.92 (1σ%). Low 204Pb counts, comparable to thosemeasured on the standard, were measured on most unknown samples and Broken Hillcommon-Pb was assumed. However, analysis 4.1 had significantly higher measured204Pb counts and Cumming and Richards (1975) 1600 Ma common-Pb was used for

this analysis.

238

Results

Nineteen analyses were obtained from 19 zircons. The results are given in Table 63


Interpretation

Seventeen analyses of 17 zircons form a single concordant population (chi-squared =

1.02) with a mean 207Pb/206Pb value corresponding to an age of 1775 ± 10 Ma. This is

interpreted as the crystallization age of the granitoid precursor to this gneiss. Analysis

14.1 has higher 207Pb/206Pb and 206Pb/238U ages and is interpreted as that of a

xenocryst. Analysis 2.1 is discordant and has a younger 207Pb/206Pb age than the main

population. This analysis site is interpreted to have lost some radiogenic Pb.

Figure 64. Concordia plot for sample 104981: biotite–muscovite monzogranite gneiss,southern part of Graphite Valley

239

Table 63. Ion microprobe analytical results for sample 104981: biotite–muscovite monzogranite gneiss, southern part of Graphite Valley


1.1 238 365 80 2.183 0.10582 0.00245 0.39497 0.00620 0.2444 0.0048 3.566 0.115 82 1 729 422.1 604 537 172 1.477 0.10139 0.00134 0.32263 0.00336 0.2226 0.0043 3.112 0.077 79 1 650 253.1 241 284 99 0.633 0.10905 0.00127 0.33730 0.00339 0.3236 0.0064 4.865 0.117 101 1 784 214.1 428 399 140 6.305 0.09969 0.00529 0.36253 0.01278 0.2169 0.0044 2.981 0.176 78 1 618 995.1 463 637 197 0.522 0.10802 0.00087 0.40136 0.00253 0.3217 0.0062 4.791 0.105 102 1 766 156.1 338 692 155 1.310 0.10996 0.00163 0.63519 0.00481 0.2960 0.0058 4.488 0.117 93 1 799 277.1 349 376 133 1.011 0.10772 0.00138 0.31934 0.00351 0.3012 0.0059 4.474 0.110 96 1 761 238.1 406 528 167 0.642 0.10693 0.00109 0.37395 0.00297 0.3157 0.0062 4.655 0.108 101 1 748 199.1 447 524 180 0.371 0.10971 0.00080 0.34268 0.00224 0.3179 0.0062 4.808 0.104 99 1 795 13

10.1 1 262 1 029 391 0.859 0.10851 0.00071 0.27928 0.00178 0.2526 0.0049 3.779 0.080 82 1 774 1211.1 242 273 90 0.912 0.10786 0.00160 0.29552 0.00403 0.2981 0.0059 4.433 0.116 95 1 764 2712.1 313 458 132 0.651 0.10824 0.00121 0.41868 0.00338 0.3138 0.0061 4.683 0.111 99 1 770 2013.1 238 528 115 0.675 0.10913 0.00139 0.64729 0.00462 0.3134 0.0062 4.716 0.117 98 1 785 2314.1 77 151 37 1.011 0.11523 0.00301 0.58117 0.00876 0.3179 0.0067 5.051 0.179 94 1 883 4715.1 642 219 205 0.403 0.10801 0.00071 0.09627 0.00148 0.3044 0.0059 4.533 0.096 97 1 766 1216.1 359 479 134 0.566 0.11035 0.00109 0.38746 0.00304 0.2838 0.0055 4.318 0.099 89 1 805 1817.1 338 97 110 0.857 0.11034 0.00129 0.08532 0.00278 0.3058 0.0060 4.653 0.112 95 1 805 2118.1 440 343 155 0.837 0.10774 0.00114 0.22252 0.00273 0.2998 0.0058 4.454 0.104 96 1 761 1919.1 179 240 74 1.046 0.10677 0.00195 0.38240 0.00512 0.3135 0.0063 4.616 0.132 101 1 745 33

240

110056: biotite–hornblende granodiorite gneiss,Rooney Creek


RUDALL (SF 51-10) 122°21’24"E 22°34’10"S

Sampled during 1991




Not available.

Zircon morphology

The zircons recovered from this sample were typically light yellow-brown to dark

brown, rounded or euhedral, but with rounded terminations, up to 200 × 350 µm in

size. Internal euhedral igneous zoning is evident in most grains but a few are

structureless.

Analytical details




36 ns. Five analyses of the CZ-3 standard were obtained during the analysis session.

The Pb*/U calibration was stationary during the session, with all five standard

analyses defining a calibration error of 2.70 (1σ%). Compared to the standard, high204Pb counts were measured on most unknown samples. Broken Hill common-Pb was

241

used for analyses 7.1, 8.1, 16.1, 17.1, and 18.1. Common Pb calculated using the

method of Cummings and Richard (1975) was used for the remaining analyses.

Results

Nineteen analyses were obtained from 19 zircons. The results are given in Table 64


Interpretation

The analyses can be assigned to six groups. Group 1 analyses, consisting of 12

analyses of 12 zircons, form a single population (chi-squared = 1.48) with a mean

Figure 65. Concordia plot for sample 110056: biotite–hornblende granodiorite gneiss,RooneyCreek

242

Table 64. Ion microprobe analytical results for sample 110056: biotite–hornblende granodiorite gneiss, Rooney Creek


1.1 914 371 358 4.722 0.11724 0.00141 0.09254 0.00318 0.3196 0.0087 5.166 0.160 93 1 915 222.1 366 290 202 1.182 0.15683 0.00108 0.22941 0.00240 0.4443 0.0121 9.608 0.278 98 2 422 123.1 401 223 169 10.049 0.10267 0.00339 0.17283 0.00786 0.2791 0.0076 3.952 0.180 95 1 673 614.1 542 26 182 1.371 0.11040 0.00108 0.01279 0.00228 0.3298 0.0090 5.020 0.150 102 1 806 185.1 606 357 243 11.395 0.10478 0.00301 0.14284 0.00693 0.2585 0.0071 3.734 0.157 87 1 710 536.1 439 116 147 9.184 0.10583 0.00321 0.06356 0.00733 0.2430 0.0066 3.545 0.154 81 1 729 567.1 568 287 234 0.174 0.12260 0.00051 0.13847 0.00106 0.3767 0.0102 6.368 0.178 103 1 994 78.1 537 485 208 0.229 0.10963 0.00061 0.25215 0.00157 0.3284 0.0089 4.965 0.141 102 1 793 109.1 708 193 245 6.803 0.11125 0.00214 0.04824 0.00487 0.2737 0.0074 4.199 0.148 86 1 820 35

10.1 444 373 173 2.552 0.10805 0.00154 0.21807 0.00362 0.3154 0.0086 4.699 0.152 100 1 767 2611.1 272 549 135 4.841 0.10848 0.00277 0.63806 0.00725 0.2934 0.0080 4.388 0.174 93 1 774 4712.1 343 320 164 1.065 0.12856 0.00115 0.26003 0.00273 0.3880 0.0106 6.878 0.204 102 2 078 1613.1 326 424 136 0.221 0.11017 0.00076 0.37405 0.00229 0.3234 0.0088 4.912 0.142 100 1 802 1314.1 485 822 228 5.538 0.11349 0.00219 0.49607 0.00545 0.2936 0.0080 4.594 0.162 89 1 856 3515.1 1 516 67 636 0.812 0.13717 0.00046 0.01695 0.00090 0.4104 0.0111 7.761 0.215 101 2 192 616.1 191 377 92 0.612 0.10762 0.00134 0.55491 0.00421 0.3296 0.0090 4.891 0.154 104 1 759 2317.1 127 60 66 1.108 0.15786 0.00180 0.13204 0.00381 0.4499 0.0125 9.793 0.306 98 2 433 1918.1 188 156 75 0.649 0.10850 0.00140 0.23402 0.00339 0.3368 0.0092 5.038 0.160 105 1 774 2319.1 618 147 246 2.126 0.12335 0.00116 0.07031 0.00256 0.3595 0.0098 6.115 0.182 99 2 005 17

243

207Pb/206Pb value corresponding to an age of 1790 ± 17 Ma. This is interpreted as the

crystallization age of the granitoid precursor to this gneiss. Group 2, consisting of

analysis 1.1, has a 207Pb/206Pb value corresponding to an age of 1915 ± 22 Ma. Group

3, consisting of analyses 7.1 and 19.1, has a mean 207Pb/206Pb value corresponding to

an age of 1996 ± 5 Ma (chi-squared = 0.29). Group 4, consisting of analysis 12.1, has

a 207Pb/206Pb value corresponding to an age of 2078 ± 16 Ma. Group 5, consisting of

analysis 15.1, has a 207Pb/206Pb value corresponding to an age of 2192 ± 6 Ma. Group

6, consisting of analyses 2.1 and 17.1, has a mean 207Pb/206Pb value corresponding to

an age of 2425 ± 7 Ma (chi-squared = 0.18). Analyses belonging to groups 2–6 are

interpreted to be of xenocrysts, either derived from the source rocks of the granitoid

precursor to the gneiss, incorporated during magma emplacement or introduced by the

incorporation of a sedimentary component into the gneiss during later (post-

crystallization) deformation.

244

Reference

CUMMING, G. L., and RICHARDS, J. R., 1975, Ore lead ratios in a continuously

changing Earth: Earth and Planetary Science Letters, v. 28, p. 155–171.

€¦ · ii minister for mines the hon. george cash, jp, mlc director general k. r. perry director,...

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