Project 8831

Geochemistry and Gold Metallogenic Studies, Sulphide-Pap Lakes Area1

D. C. Armstrong2 and G.R. Parslow3

Armstrong, D.C. and Parslow, G.R. (1988): Geochemistry and gold metallogenic studies, Sulphide-Pap Lakes area; in Summary of Investigations 1988, Saskatchewan Geological Survey; Saskatchewan Energy and Mines, Miscellaneous Report 88-4.

Investigations into the geochemistry and gold metal­logenesis of the Sulphide - PAP Lakes area were con­tinued during 1988 in the field areas described in the 1987 Summary of Investigations (Armstrong and Parslow, 1987). This report provides an update on work conducted over the winter of 1987 - 88 and includes the preliminary results of the regional geochemical investiga­tion.

The study focuses on the central portion of the Stanley {west half) area (NTS 73P-7CN)) and supplements the 1 :20,000 geological map of Sulphide Lake area produced by Sibbald (1987).

1. Objectives and Sampling Methodology A regional geochemistry study was initiated in the Sul­phide - PAP Lakes area during 1987 and continued in 1988. Major aims are to characterize the volcanic and plutonic rocks, to determine their probable geotectonic setting at the time of emplacement and to establish their relationship to the Central Metavolcanic Belt of the La Range Domain. It has been suggested that the Nut Bay Belt (which includes the Sulphide - PAP Lakes area) may represent a southern, dismembered continuation of the Central Metavolcanic Belt (Coombe et al., 1986; Thomas, 1987). Watters (1981, 1984, 1985, 1986) and Harper et al. (1986) have conducted extensive regional geochemical studies of the Central Metavolcanic Belt, mainly in the Star-Waddy Lakes area, but to date very little data are available for the Nut Bay Belt.

During the two field seasons a total of 503 samples were collected as outlined below. A sample location map is included in the accompanying map package.

a) Sulphide Lake area (215 samples prefixed 87SL and 88SL)

Samples comprise mafic to falsie metavolcanics and vol­caniclastics, some associated intrusives and metasedi­ments, plus mineralized samples and quartz veins taken from trenches. The samples of volcanics were taken in order to define geochemically different map units and enable discrimination of the tectonic setting of the area. It is felt that good coverage of Sibbald's (1986, 1987)

unrts, as mapped, has been achieved. Mineralized samples and quartz veins taken from the Studer A, B and C zones and the Gem prospect are for ore petrography, fluid inclusion and stable isotope work.

b) Contact Lake Pluton (64 samples prefixed 87CL and BBCL)

This pluton, also referred to as the Little Deer Pluton, is a composite intrusion of gabbroic to granitic composi­tion with an areal extent of 60 km2

. The margins of the pluton consist mainly of the most mafic (gabbroic) phases, while the central portions consist of the more fal­sie phases; most boundaries are gradational. Using the classification of Harper et al. (1986) for the Star-Waddy Lakes area, the Contact Lake Pluton appears to be a type 1 intrusive. These are early, synvolcanic, composite plutons showing moderate to strong zonation. The close proximity of the pluton to the gold occurrences in the Sulphide-PAP Lakes area suggests that it may have played an important role in the mineralization process, erther as a direct source or as a heat engine for circulating fluids. The samples collected are to be used to characterize the pluton geochemically and es· tablish the relationship of rts different zones. A com­parison with the chemistry of the volcanic sequence will be possible. It is also hoped to ascertain the role of the pluton in the genesis of the gold deposrts.

c) PAP Lake zones (91 samples prefixed 87PA and BBPA)

Shear zone hosted gold mineralization occurs wrthin the PAP zone dioritic to gabbroic sills. Samples were taken from this locality in order to allow comparison of the chemistry and mineralogy of sheared versus unsheared rock. It is also intended to determine if the PAP zone sills and the Contact Lake Pluton are comagmatic. Quartz vein samples were taken for fluid inclusion and stable isotope studies.

d) Drill core samples, Studer A, Band C zones, Sulphide Lake area (97 samples)

Altered and mineralized samples were taken from drill core in order to compare them with the equivalent un-

(1) Pl'ojecl contracted to the University of Regina wtth funds provided under the Canada Component of rne Canada - Saskatcnewan Subsidiary Agreement on Mineral Development 1984-89

(2) School of Earth Sciences, Unlverslly of Birmingham, Birmingham, U. K. (3) Depa,tmenl ol Geologk:al Sciences, University of Regina

100 Summary of Investigations 1988

mineralized rocks collected during surface mapping. These will be used to test for the presence of enhance­ment and/or depletion haloes around the ore bodies and for ore petrography.

e) Other prospects (34 samples)

In addition to the main prospects of interest, samples were taken from the Main Camp (8), Turtle Lake (7), Jepson Lake {3), Ramsland (8), Preview (3), Clear­water A {3) and Discovery zone (2) showings.

f) U/Pb geochronology (2 samples)

U/Pb age determinations will be carried out by the University of Kansas on the two samples collected. Sample number HUDBB-021 is a feldspar- and quartz­phyric crystal tuft collected from a small island in Sul­phide Lake. HUDBB-022 is a sample of the granitic phase of the Contact Lake Pluton. It is hoped that the dates gained will help to establish the relationship of the Su I phide - PAP Lakes area with the rest of the La R onge metavolcanic belt.

g) Analysis of Samples

After conventional sample preparation, all of the 1987 whole rock samples were analyzed for major and trace elements and LOI. Major elements were determined using a Jarrell-Ash Model 975 Plasma Atomcomp Induc­tively Coupled Plasma Source Spectrometer (Si02, Ti02, Al203, Fe203, MgO, Cao, MnO and P205) and a Perkin-Elmer 603 Atomic Absorption Emission Spectro­photometer (Na20 and K:!0); both facilities were provided by the University of Regina. Trace element con­centrations (Zn, Cu, Ni, Rb, Sr, Y, Zr, Nb, Ba, U, Th, Pb, Ti, V and Cr) were determined using pressed powder pellets on a Phillips PW1400 X-Ray Fluorescence Spectrometer at Aston University, Birmingham, England.

2. Preliminary Interpretation of the Vol­canic Rocks, Sulphide Lake Area

Thirty-five samples of basalts from the Sulphide Lake area were used for the discrimination plots presented here. The rocks were selected on the basis of Si02 < 52 percent and screened to remove cumulates and metasediments.

The AFM diagram for major elements (Irvine and Baragar, 1971) and the (Y + Zr)- (Ti02 x 100)-(Cr) trace element plot (Davies et al., 1979) can be used to distin­guish between tholeiitic and calc-alkaline trends in vol­canic rocks. When the Sulphide Lake basalts are plotted on an AFM diagram (Figure 1) they show a distinct tholeiitic character. On the (Y + Zr) -(Ti02 x 100)- (Cr) discrimination plot (Figure 2) the basalts again clearly fol­low a tholeiitic trend.

The K20 - Ti02 - P205 plot (Figure 3) devised by Pearce et al. (1974) to discriminate between oceanic and con­tinental settings shows the Sulphide Lake basalts falling in the oceanic field with high concentrations of Ti02

Saskatchewan Geological Survey

F

;A I \

/ • I \ _I , • \

,~,/ . . ::·r , I •

,/ .. I

I

/! Cale-alkaline

I A !__ _____________ ---····-· .- ~ M

Figuf9 1 - AFM plot, Sulphide Lake af9a basalts. Field boun­daries after Irvine and Baragar (1971).

I f-CA.......

Ti0,x100

I I

I

·.

.. I Y+ZrL__ ____________ _ _____ •:..:,Cr

Figuf9 2 - (Y+Zr)-(Ti02 X 100)-(Cr) plot, Sulphide Lake area basalts. Field boundaries after Davies et al. (1979).

Ti 0 ,

o~c

non-oceanic

K ,0 L_ ________ _______ ___, P ,0 ,

Figure 3 - K-zO- Ti02 - P-z()5 discrimination plot, Sulphide Lake area basalts. Field boundaries after Pearce et al. (1974).

107

Ti/ 100

\ \ \

Yx3

Figure 4 - (Zr)-(Ti/100)- (Y X 3) discrimination plot, Sulphide Lake af8a basalts. Field boundaries after Pearce and Gann (1973). A & B, low-potassium tholeiites; B, ocean floor basalts; B & C, ca/c-alkafine basalts; D, 'within-plate' basalts.

relative to K20 and P205. The basalts in the study area are well discriminated on the Pearce and Cann (1973) (Zr)-(Ti/100}-(YX3) discrimination plot (Figure 4) with the majority of the samples clustering in the ocean floor basalt field. On the (Zr)-(Ti/100)-(Sr/2) diagram (Figure 5) of Pearce and Cann (1973) there is some scat­ter but the samples straddle the ocean floor basalt and low-potassium tholeiite field boundary. The scattering of the data points in this diagram is probably the result of strontium mobility during metamorphism.

The log Ti-log Zr diagram (Pearce, 1982) is used to dis­criminate arc lavas from 'within plate' lavas and also has a MOAB field superimposed on the other two. On this diagram (Figure 6) the basalts plot within the MOAB

Ti/ 100

I \ /

/ /

I I

I

Zr ~------

\

Sr/2

Figuf8 5 - (Zr)-(Ti/100)-(Sr/2) discrimination plot, Sulphide Lake arva basalts. Field boundaries after Pearce and Gann (1973). A, low-potassium tholeiites; B, ca/c-alkalintJ basalts; C, ocean floor basalts.

108

field and the majority of the intermediate and felsic samples fall within the arc lava field.

From this combined evidence it appears that the Sul­phide Lake area basalts exhibit a strong tholeiitic ocean floor character along with an island arc affinity. The sug­gestion that these rocks were erupted during the first stages of development of an arc sequence where ocean floor material is still a significant component of the rocks would be an explanation of the trends exhibited. The Sulphide Lake basalts could represent a structurally lower level of the Central Metavolcanic Belt sequence not exposed elsewhere.

When all the volcanic rocks in the Sulphide Lake area (66 samples) are taken together and plotted on the AFM diagram (Figure 7) the intermediate to falsie rocks (>52 percent Si02) display a calc-alkaline trend in strong contrast to the basalts. This calc-alkaline trend is

-E a. a. -

10·

1 o·

~" - ,... - - - - - -- --.'c~,4.-.... ~.J.J>

' ,, \ ,,

' ' ' \

' ' '

\ ,' 1 o' -~---~~ .... '1--___ .,,.,:_~~

1 o 1 o· 1 o' Zr (ppm)

• - mafic • -intermediate & felsic

\

\

Figure 6 - Log-log Ti plot, Sulphide Lake area volcanics. Field boundaries after Pearce (1982). MORB, mid-ocean ridge basalt; A, arc lavas; B, 'within-plate" lavas.

also clearly displayed on the (Y + Zr) - (Ti02 x 100) - (Cr) trace element plot (Figure 8) for all the volcanic rock samples. A clear compositional break between the basalts and the rest of the volcanics is also evident on this plot, indicating that the mafic and felsic volcanics in the area are not cogenetic and that it cannot be as­sumed that the falsie material was produced as a result of fractionation of the mafic material. There also ap­pears to be a distinct lack of intermediate composition volcanics in the area.

Sibbald (1986) produced a generalized stratigraphic suc­cession for the supracrustal rocks in the study area and on the basis of way-up criteria suggested that these­quence faces to the southeast. Since the rocks dip steeply northwest the sequence is overturned. The basalts in this study were collected mainly from unit 3 of Sibbald's stratigraphic succession. This unit is described

Summary of ln....,,stigations 1988

F

.' ... ill\ •-maf•c , • - intermedia te

& l c ls ic I Thol eiiti c \

I \ / . . \

/~/ ... }::v;'\ I • • •

./ .. ... .,.:.. . . . I ' • \ /,:/ _,: \iM

Cale-alka line

// A L--.

Figure 7 - AFM plot, Sulphide Lake area volcanics. Field boun­daries after /Nine and Ba.raga, (1971).

as a sequence of mafic pillowed flows with_ intercal~ted mafic sills (Sibbald, 1986). In contrast, the 1ntermed1ate to felsic material was taken from unit 4 of the succes­sion. This unit comprises felsic to intermediate metavol­caniclastics with minor pillowed flows and interlayered pelitic metasediments, in part carbonaceous and sul­phidic (Sibbald, 1986). Therefore the two rock types have a spatial separation and on this basis can not be assumed to have the same origin.

One explanation for the geochemical patterns displayed by the rocks could be that the basalts represent early arc material, which retains a strong oceanic character, whereas the more felsic material was erupted later when the island arc was more fully developed. This would also fit with Sibbald's (1986) suggestion of a southeast younging direction. Another possibility is that the basalts represent ocean floor material totally unrelated to the later calc-alkaline material, with the two units becoming juxtaposed at a later date,

-. . ,

F

Cal e-alkaline

A L,_ ___ ___ _ ___ _ --- - - ~ M

Figure 9 - AFM plot, Contact Lake Pluton samples. Field boun­daries after /Nine and Ba.ragar (1971).

Saskatchewan Geological Survey

Ti0,x 100

/\

~ i:;;::ediate & f el sic

, ' , \

I '

!\:: ~ '~, '\ ,1'-CA.- •• -.: • ~ • •. '- "'C.~

./ . . I •

Y•Zr/ - - • • • • ' Cr

Figure 8 - (Y + Zr)-(T/02 x 100)- (Cr) plot, Sulphide Lake area volcanics. Field boundaries after Davies et al. ( 1979).

3. Preliminary Interpretation of the Plutonic Rocks, Sulphide Lake Area

Numerous bodies of gabbroic to granitic composition in­trude the supracrustal sequence of metavolcanic and metasedimentary rocks in the study area, The largest in­trusion in the area is the composite Contact Lake P1uton which, as previously mentioned in this report, ranges in composition from granitic in the centre, through granodioritic to diorite/ gabbro at the margins.

An AFM plot (Figure 9) of samples collected from all zones of the p luton in 1987 clearly shows the calc­alkaline nature of the pluton. The granitic phases show a tightly constrained compositional trend with typical alkali enrichment, whereas the intermediate to mafic phases show much more scatter, indicating a greater d&­gree of compositional variation. This is consistent with the field observation that the outer zones of the pluton are highly composite and multiphase in character.

TiO,x 100

I I •

Li,.~ ·, .. :__. . . ....... . . . . . . ........... ..

: . .......:.. • \!,. I •• ;-.- -,.....

Figure 10 - (Y +Zr)-(TI0 2 X 100) - (Cr) plot, Contact Lake Pluton samples, Field boundaries after Davies et al. (1979).

109

WPG - 102 ... r.· E 0. 0. . ' -.c a: 10

VAG ORG

0 0 10

Y+Nb (ppm)

Figum 11 - Rb-Y+Nb discrimination plot, Contact Lake Pluton 'granftic' rocks. Field boundaries after Pearce et al. (1984). VAG, 'volcanic arc' granites; ORG, 'ocean ridge' granites; WPG, 'wfthin-plate' granites; syn-COLG, syn-collision granites.

The calc-alkaline character of the pluton is also evident on the (Y +Zr)-(Ti02 x 100)-(Cr) plot (Figure 10). Despite the scatter of data points, it can be seen that the pluton evolved from an early tholeiitic trend through to a later calc-alkaline trend.

Work by Pearce et al. (1984} has demonstrated that it is possible to discriminate between 'granitic' rocks (>56 percent Si02) from different tectonic settings on the basis of trace element relationships. Applying these discrimination criteria, the zoned Contact Lake Pluton clearly falls within the volcanic arc granite field (Figure 11 ). This is entirely consistent with the idea of the intrusive rocks being produced as a result of calc­alkaline plutonism during the later stages of arc develop­ment.

The setting and character of the Contact Lake Pluton ap­pears, from the work done by Watters (1986) on other plutons in the Central Metavolcanic Belt, similar to other intrusives in the La Range Domain.

4. Preliminary Interpretation of the Fluid Inclusion Studies Representative samples of vein quartz from different prospects and different vein generations within each prospect were collected to provide material for a fluid in­clusion study. It is hoped the study, when completed, will provide information on temperature of ore deposi­tion and composition of the mineralizing fluids. It will also form the basis of a comparison between the dif­ferent styles of mineralization in the project area.

110

Thirty specimens collected in 1987 have been prepared as 0.3 mm thick, doubly polished quartz wafers and a Linkham TH600 heating and freezing stage is in use for thermometric measurements.

To date only a petrographic examination of the in­clusions has been completed. The quartz in all the wafers studied so far consists of a mosaic of small grains, indicating a history of repeated movement along t_he yein, which resulted in crushing and some recrystal­hzat1on of the quartz. The quartz contains abundant in­clusions, most of which are very small (5 to 1 O µm across) which is typical of gold-bearing quartz veins (Roedder, 1984). Many are too small to be used for measurements but some that are amenable to heating and freezing studies have been identified. No inclusions seen can be interpreted as primary in origin; however, this is not thought to be a problem, as it has been sug­gested (Roedder, 1984) that gold is usually introduced by late fluids after the bulk of the quartz has crystallized.

The most common occurrence of the inclusions is as trails along healed fracture surfaces, sometimes cross­cutting several grains or contained within a single grain. Three-dimensional clusters are also present.

A complex assemblage of several types of inclusions has been observed. The most common inclusion types are:

1) monophase gaseous C02 inclusions; 2} two phase (liquid plus vapour) dilute aqueous in­

clusions; 3) immiscible liquid (liquid1 plus liquid2 plus vapour) in­

clusions, which contain an aqueous solution sur­rounding a C02-rich liquid, which in turn surrounds a C02-rich vapour bubble; and

4} occasional two-phase (liquid plus solid) aqueous in-clusions containing daughter crystals.

Such a diverse assemblage could be produced as a result of unmixing of an originally homogeneous fluid due to temperature and pressure reduction, possibly as a result of boiling. A full interpretation should be pos­sible when thermometric measurements have been com­pleted.

A trial bulk inclusion analysis was undertaken on six samples of quartz to gain information on the C02/H20 ratio of the fluids. The samples were coarsely crushed, hand picked and cleaned to ensure purity, degassed and then decrepitated under vacuum. The released gases were passed through a manometer to measure gas pressure.

The non-aqueous condensible phases of the first sample were sent to a gas chromatograph and output in­dicated that C02 constituted 99 percent of this fraction. On this basis it was assumed that all manometric read­ings for C02 + represented C02. The results are given in Table 1.

From these preliminary results it can be seen that the samples associated with the larger prospects (e.g., PAP SW zone, Studer C zone) do appear to have a higher

Summary of Investigations 1988

Table 1 - C02j'H,.O Ratios of Quartz Inclusion Fluids

Sample mole x 10-6/g

Prospect Name No. N.C. CD.!+ H,.O C0'2/H,.O

PAP SW Zone 87PA0043 0.24 0.76 3.87 0.20 87PA0006 0.19 3.12 3.28 0.95

Studer C Zone SU87/41 0.28 0.91 2.74 0.33 (@32.5 m)

87Sl0085 0.40 1.16 7.56 0.15

Clearwater A 87CWCXXJ1 0.18 0.33 6.80 0.05

Turtle Lake 87TL0002 0.08 0.10 2.46 0.04

N. C. non-<:ondenslt>le gases (H2, Ar2, O:!. N2, CH.i, etc.) CO:!+ CO:! (> 99 percent) plus traces of other condensible gases at

-196"C

C02/H20 ratio than the smaller prospects. The C02/H20 ratio could be an indicator of the grade of mineralization, as the presence of C02""rich fluids has been reported from many gold localities. Further analyses will be undertaken in an attempt to ascertain if the C02/H20 ratio and C02 yield have any relationship to the gold grades in the various prospects.

5. Acknowledgements Once again the senior author would like to thank Tom Sibbald (Saskatchewan Energy and Mines) and Rob Chapman (SMDC) for encouragement, assistance and many lively discussions throughout the summer's work. Both authors would also like to thank Andrea Mc­Dougall (field assistant) for her enthusiastic help during the field season and assistance with sample preparation at the University of Regina, Bill Gaskarth (University of Birmingham, U.K.), Sierd Eriks (SMOG), and Andrew Gracie (Resident Geologist, Saskatchewan Energy and Mines, La Ronge). Thanks also to Vern Studer and Gill Williams without whom the summer's work at Sulphide Lake would not have been the same!

Financial and logistical support were provided by the Natural Environment Research Council (U.K.), Sas­katchewan Energy and Mines, the Saskatchewan Mining Development Corporation on behalf of the Sulphide Lake and Preview Lake joint ventures, and the University of Regina.

6. References Armstrong, D.C. and Parslow, G.R. (1987): Gold metallogenic

studies, Sulphide and PAP Lakes area; in Summary of In­vestigations 1987, Sask. Geol. Surv., Misc. Rep. 87-4, p52-57.

Saskatchewan Geological Survey

Coombe, W., Lewry, J.F. and Macdonald, R. (1986): Regional geological setting of gold in the La Ronge Domain, Sask­atchewan; in Clark, L.A. (ed.), Gold in the Western Shield; Can. Inst. Min. Metall., Spec. Vol. 38, p26-56.

Davies, J.F., Grant, R.W.E. and Whitehead, R.E.S. (1979): Im­mobile trace elements and Archean volcanic stratigraphy in the Timmins mining area, Ontario; Can. J. Earth Sci., v16, p3Q5.311.

Harper, C., Thomas, D.J. and Watters, B.R. (1986): Geology and petrochemistry of the Star -Waddy Lakes area, Sask­atchewan; in Clark, L.A. (ed.), Gold in the Western Shield; Can. Inst. Min. Metall., Spec. Vol. 38, p57-85.

Irvine, T.N. and Baragar, W.R.A. (1971): A guide to the chemi­cal classification of the common volcanic rocks; Can. J. Earth Sci., v8, p523-548.

Pearce, J.A. (1982): Trace element characteristics of lavas from destructive plate boundaries; in Thorpe, R.S. (ed.), Andesites; J. Wiley and Sons, Chichester, p525-547.

Pearce, J.A. and Cann, J.R. (1973): Tectonic setting of basic volcanic rocks determined using trace element analysis; Earth Planet. Sci. Lett., v19, p290-300.

Pearce, T.H., Gorman, B.E. and Birkett, T.C. (1974): The Ti02-K20- P20s diagram: a method of discriminating between oceanic and non-oceanic basalts; Earth Planet. Sci. Lett., v24, p419-426.

Pearce, J.A., Harris, N.B.W. and Tindle, A.G. (1984): Trace ele­ment discrimination diagrams for tectonic interpretation of granitic rocks; J. Petrol., v25, p956-983.

Roedder, E. (1984): Fluid Inclusions; Mineral. Soc. Arn., Reviews in Mineralogy, v12, 644p.

Sibbald, T.1.1. (1986): Bedrock geological mapping, Sulphide Lake area (part of NTS 73P-7); in Summary of Investiga­tions 1986, Sask. Geol. Surv., Misc. Rep. 86-4, p63-64.

(1987): Bedrock geology, Sulphide Lake area (part --o~f~N-T~S 73P·7); 1:20,000 scale prelim. map with Summary

of Investigations 1987, Sask. Geol. Surv., Misc. Rep. 87-4.

Thomas, D.J. (1987): Gold deposits of the La Ronge Domain; Geol. Assoc. Can./Mineral. Assoc. Can., Joint Annu. Meet., Saskatoon, Field Trip Guidebook No. 4, 70p.

Watters, B.R. (1981): Geochemistry of metavolcanic rocks in the La Range Domain; in Summary of Investigations 1981, Sask. Geol. Surv., Misc. Rep. 81-4, p34-37.

____ (1984): Geochemical patterns for metavolcanic rocks in the La Ronge Domain; in Summary of Investiga­tions 1984, Sask. Geol. Surv., Misc. Rep. 84-4, p88-91.

____ (1985): Geochemistry of metavolcanic and plutonic rocks, Star Lake and Waddy Lake area; in Sum­mary of Investigations 1985, Sask. Geol. Surv., Misc. Rep. 85-4, p28-34.

--~- (1986): Geochemistry and geochronology of metavolcanic and plutonic rocks in the Central Metavol­canic Belt; in Summary of Investigations 1986, Sask. Geol. Surv., Misc. Rep. 86-4, p76-83.

111