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Trace Element Geochemistry in the Waddy - Windrum Lakes Area

by C.T. Harper

Harper, C.T . (1987) : Trace element geochemistry in the Waddy - Windr1111 Lakes area; in Sumnary of Investigations 1987 , Saskatchewan Geological Survey; Saskatchewan Energy and Mines, Miscellaneous Report ST-4.

Lithogeochemical studies carried out between 1984 and 1986 in conjunction with 1 :20,000 scale remapping of the north-central part of the La Ronge Domain (Harper, 1984, 1985, 1986) were designed to characterize the petrogenetic framework of this volcanosedimentary-plutonic terrane. Although major and specific immobile trace element geochemist.ry has been well documented (Watters, 1984, 1985, 1986; Watters and Pearce, 1986; Harper et al., 1986; Thomas et al., 1987; and Watters et al., 1987), very little information has been released on the more economic-related t.race elements, such as Au, Ag, As, Cu, Pb, Zn, Ni, Cr and Mo. This report presents a preliminary summary of the trace element results for the Waddy - Windrum Lakes area (Fig. l, Tables l and 2 and l :50,000 scale map, in pocket). The purpose is to define regional background values for these elements for the major volcanic and intrusive rock types in the area. Particular emphasis is given to gold because of its current high profile. A more exhaustive statistical treatment of the data will be presented in a future publication.

Geologic Setting

The Waddy - Windrum Lakes area lies in the Early to Middle Proterozoic La Range Domain, which in this area comprises parts of the Crew Lake, Central Metavolcanic and Maclean Lake Belts (Fig. 1). The Central Metavolcanic Belt consists of ultramafic to felsic metavolcanics, metavolcaniclastics and metasedimentary rocks, into which a variety of relatively simple to complex multiphase, ultramafic, and mafic to felsic plutons have been intruded. The Crew Lake and Maclean Lake Belts, to the northwest and southeast respectively, comprise psammitic to pelitic metagreywacke gneisses, calc-siHcate and varied amphibolitic gneisses with minor intercalated metavolcanics. Both belts have been int.ruded by generally uniform intermediate to felsic plutons. The transition between the three belts varies from gradational to abrupt, but most commonly is marked by major tectonic breaks, such as the Mclennan Lake Tectonic Zone. Field observation and the major and immobile trace element geochemistry indicates that the La Range Domain e volved in an island arc environment (Watters, 1984, 1985, 1986; Harper et al., 1986).

Project funded under the Saskatchewan c~nent of the Canada-Saskatchewan Subsidiary Agreement on Mineral Development 1984-89.

0 .) 10 ~ ... '.-.~_!. !t.;._

·. X' GOLD DEPOSIT

Figure 1 - Index map showing the dis tribution of the six maps canpiled for this report : l) Waddy North; 2) Waddy South; 3) Tower Lake; 4) Hook Lake ; 5) Windrum Lake; and 6) Jaysmith Lake. Crosses indicate intrus ive rocks, with the major plutons marked: KL , Kenwood lake; NLO, Nistoass ini Lake; CL, Contact Lake; BY, Boundary Lake ; BL, Brindson Lake; PC, Payn Creek; HL, Hook Lake; IL , Is land Lake; and SL, Star Lake Plutons. Major tectonic zones include; LLTZ, Looney lake; ALTZ, Alpat Lake; and MLTZ, Mclennan Lake Tectonic Zones . Gold deposits shown are: TW, Twin; W, Weedy; K, Komis and EP; TE, Tower East; J , Jojay; R, Rod- Jolu; S, Star Lake 21 Zone; and T, Tamar .

Presentation of Results

The range and mean values for the 18 trace elements which were routinely analyzed are summarized in Tables I and 2. Obviously mineralized samples were not included in this tabulation. It should also be noted that sample populations for several subdivisions are small (as low as eight), and thus the results may not be fully significant statistically.

The metabasalts (Table l) are subdivided into three groups because of distinctive macroscopic, petrologic and chemical characteristics. Intrusive rock types are subdivided into ultramafic, mafic to intermediate (i.e. , gabbro-diorite) and felsic (i.e. , granodiorite-granite) groups (Table 2). Although

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Table l - Summary of Trace Element Data for Volcanic Rocks of the Waddy - Windrum Lakes Area. All values in ppm except Au, which is in ppb. Numbers in parentheses indicate population size.

l ower Waddy Lake Lower Wdddy lake Al 1 other

Elen-ent Magnesium Basalt Fe lholei ite Basal ts Andesi tes Oacit es Rhyo l ites

Range Mean (8) Range Hean (8) Range Mean (30) Range Mean ( 17) Range Mean (8) Range Mean (22)

Ba 14- 133 51 41-329 107 13-764* 195(29) 249-819 458 40-651 389 88-1009 484 Sr 65-94 12 81-319 164 59-866 329 213-674 339 153-504 288 69-686 230 Zr 25-55 37 24- 110 68 22- 136 63 62-220 136 60- 181 127 34-3 11 134 y 1-8 3 1-24 15 6-26 14 7-30 18 3-27 11 1-38 13 La 0.2-4 1. 5 0.6- 10 5 3-21 9 11 -26 16 7-20 12 l-46 17 Th 0 .2- 15# 5 0.2-6# 3 l.7- 16 4 3- 11# 4 3-12# 4 3- 19 6 v 97-223 150 147-411 270 126-441 238 43-304 162 53-174 102 1-158 44 Cr 142-2300 855 37-285 157 9-1448 314 1-118 31 1-58 25 1-416* 8(21) Ni 70-435 186 28- 76 56 13-388 98 3-58 25 8-42 l 2- 139* 8(21) Co 27-64 50 27-66 50 22-103 46 6 -54 27 7-56 18 1-56 13 Cu 1-235* 49(7) 14-104 50 3-152 71 3-363* 54( 15) 8-160* 21(6) 2-1 97* 20(21) Pb -2# <2 2-3# <2 . 4 2-410* 3(28) 2- 112* 6.5( 15) 2-36#* 4.6(7) 2-35 10 Zn 15-57 32 40-106 74 57-2400* 90(29) 67-164 110 40-541* 72(7) 13-541* 62(21) Mo 5- 10# <6.6 5-6# 5 5-19# 6.3 5-16# 7 5-7# 5 5-11 5.6 Au 1-89* 10(7) 1.7-10 4.2 0.2-60* 7.7(29) 0.5-29* 7.4( 15) 0.5-23 8. 1 0.5-40* 6 .9(21) Ag o. 1-0.2# <0 .2 0. 1-0.2# <0. 2 0. 1-0.5# <0.2 0. 1-2.8# 0 .2( 14) 0.1-0.3# 0.2 0. 1-0. 7# 0.2 As 0.2-1.4 0. 7 0.2-2.0# <0.8 0.1-8. 0.6(25) 0.2-6.2 2.0( 14) 0.4-1 4* 2.0(7) 0. 1-410* 3. 8(21) Be 1-2# 1.1 1-4# <1.9 1-5# 2 1-4# <1. 8 - I# 1 1-2# 1 Cd 1-5# 1.6 1- 13# 4 1-12# 2.7 1- 14# 3.4 1-4# 1.7 1-7# 1. 7

# - numerous va lues at or below detection l imit fo r that element * - obviously ananalous sa111>l es (s) omitted fran calculation of mean

Table 2 - Summary of Trace Element Data for Intrusive Rocks of the Waddy - Windrum Lakes Area. All values are in ppm except Au, which is in ppb. Numbers in parentheses indicate population size.

El ement Ultramaf i c Maf i c - Intermediate Fel s i c {>63% Si02)

Range Mean {20 ) Rang e Hean (25) Range Mean (50 )

Ba 3-67 21 53-1950 569 330-11 73 695 Sr 2- 316"' 7 ( 18) 106- 1254 622 109-1124 641 Zr 9-112 39 20-196 92 18-1 81 76 y 1- 10 l . 6 2-31 15 1-31 7 La 1-7 2 4-59 22 3-35 15 Th 3-1 3 5.6 3-1 2 6 3-19 7 v 42- 225 94 16-264 155 2- 122 43 Cr 226- 5300 2966 11-3600"' 370(24) 1-171 31 Ni 87- 1417 670 14-325 96 2-53 14 Co 46-1 20 84 7-77 36 1-95 18 Cu 1-125"' 7(1 9) 1-150 32 1-114 10 Pb - 2# 2 2-15 4 2-55 10 Zn 18-87 55 31-116 79 21 -1 00 46 Mo 5-19 6 5-1 3 <6 s- 23# 5.6 Au 1 .0-108"' 2. 4(19) 0. 7-23 4.2 0. 7-29 3. 7 Ag 0 .2-0 .1# 0.2(17) 0 .1-0. 5# <0 .2 0 .1-0. 7# 0.2 As 0 .2- 11* 1 .6( 18) 0 . 2- 2.2 0. 7 0 . 2-12 0.9 Be - 1# <l na na na na Cd 1-5 2. l na na na na

# - nume rous va l ues at or bel ow detection limi t f or that e l ement "' - obv iousl y anoma l ous sample (s) omitted from cal culat ion of mean na - data not availabl e

60 VOLCANIC ROCKS

50 Rhyolite

Dacite

Andesi te

40 Basalt >-v Fe tholeii te z ~;,\;

• " I ~

"" ; I ~ I Mg basalt :::, 30 ,,,, ,,; , .. - ..

0 \'1\ I..,

..... ~

"" 20

ro

0 0 6 12 18 24 30 36 42 >60

GOLD (ppb)

Figure 2 - Corroined histogram for all volcanic rocks .

some of the intrusive phases have very distinctive chemical signatures, the use of a few subdisions is preferred in calculating regional background values. Further geochemical analysis of the major plutonic bodies is underway.

Average gold concentrations in the volcanics are generally about twice the average in the corresponding intrusive rock types. Copper and zinc concentrations are generally greater in the volcanics than their intrusive equivalents, whereas the reverse is the case for Ba and Sr (except for the ultramafic intrusives). The other elements do not show such well defined trends.

Histograms for gold, showing the combined effect for all the volcanic (Fig. 2) and intrusive (Fig. 3) rock types, reveal highly skewed background populations. In both cases, almost 60 percent of the samples contain less than 6 ppb and 2 ppb Au, respectively, for the volcanic and intrusive rocks. For volcanic rocks, 20 ppb Au is probably anomalous, whereas 15 ppb Au is considered anomalous for intrusive rocks. These values are used to distinguish anomalous samples on the accompanying map.

The 1:50,CXJO scale map shows the sample locations on a simplified geological base (derived from the original six 1 :20,000 scale geological maps), which outlines the various intrusive rocks and the boundaries of the Central Metavolcanic Belt. Major faults, gold deposits and prospects, mineral

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60

so

40 >-u z w

~ 30 ..... ~ I&.

20

10

0 0 2 4

INTRUSIVE ROCKS

I Felsic

Ma fie - intermediate

Ultramafic

8 12 16 20 24 2 B 32 GOLD (ppb)

Figure 3 - Cont>ined histogram for all intrusi ve rocks .

occurrences and areas of quartz veining and alteration are also depicted. Analytical results for nine elements, including Cu, Pb, Zn, Ni, Cr, Mo, Au, As and Ag, are listed on the maps for each sample location. For Mo and Ag, only those values exceeding the detec tion limits of 5 ppm and 0.2 ppm, respectively, are shown. Samples containing high background and anomalous concentrations of gold are shaded appropriately.

Discussion

Gold exploration in the La Range Domain is intensifying. Emperical observations suggest that the most common visual guides to gold mineralization, apart from visible gold, include a combination of the following:

l) the presence of sulphides, typically pyrite but locally pyrrhotite, chalcopyrite, galena and arsenopyrite, may be guides to elevated gold concentrations;

2) the presence of quartz veining, associated shearing and, in most cases, wall rock alteration of varying intensity; and

3) the close proximity to intrusive rocks; gold occurs either within or adjacent to them.

Target areas associated with pyrite are of several types, including 1) carbonaceous meta-argillites,

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2) sulphide-facies iron formation, 3) metamorphic aureoles surrounding the late silicic plutons such as the Round Lake, Windrum Lake and Bryenton Lake Stocks, 4) in and adjacent to many faults/shear zones, and 5) in many of the felsic metavolcanic rocks, particularly those west of Lower Waddy Lake.

Geochemically, gold is its own best pathfinder element. In some places, elevated copper and arsenic concentrations accompany higher and/or anomalous gold concentrations, but neither element could be used alone as a guide to gold mineralization in this region. None of the other trace elements appear to show any strong correlation to gold mineralization.

Even with the limited data base available, several zones of anomalous gold concentrations are indicated. These include:

I) the area northeast and southwest of the Weedy Lake gold deposits;

2) a broad but discontinuous zone south and paralleling the Byers Fault, extending from near the narrows on Waddy Lake west-southwest to Oven Lake; and

3) the area surrounding the Windrum Lake Stock.

Single-site gold anomalies may also be important targets for gold mineralization. Some of the better anomalies include:

I) the 108 ppb value (sample 84-33) west of the north end of Greenhill Lake, hosted by a sheared ultramafic dyke or sill;

2) sample 84-1042, located at the north end of a small island in Upper Waddy Lake, gave 1200 ppb Au in diorite of the Dog Creek Stock adjacent to the trace of an east-west structure (repeat analysis was not done);

3) a pyritic quartz vein (sample 85-518), near the sheared contact of a large basaltic xenolith in the Boundary Lake Pluton, 3 km west of Round Lake, contains 80 ppb Au;

4) a coincident copper (8000 ppm) and gold (200 ppb) anomaly (sample 85-73) on the west shore at the south end of Redhill Lake, hosted by a sheared siliceous pyrite-pyrrhotite-bearing horizon (sulphide-facies iron formation) within a succession of ultramafic volcanics and intrusives;

5) a 100 ppb Au anomaly (sample 85-569) on the east side of Partington Lake about 200 m south of the Byers Fault occurs in a pyritic quartz vein in sheared diorite along a north-northeast-trending fault;

6) a 117 ppb Au anomaly (sample 86-2161), I km east of the south end of Ahol Lake, occurs in a

magnetite-bearing garnet-hornblende rock (oxide-silicate-fades iron formation); and

7) a non-in situ Mo (5000 ppm), Cu (4500 ppm) and Au (l 90 ppb) anomaly (sample 86-608) was derived from chalcopyrite-molybdenite-pyrite­bearing quartz vein material found at an old prospecting camp near the west end of a small lake I km north of Island Lake; the source of this material is not known.

References

Harper, C.T. (l9B4): Geological mapping, Waddy Lake area (part of NTS 640-4 and -5): in Summary of Investigations, 1984, Sasl<. Geol. Surv., Misc. Rep. 84-4, p6-20.

____ (1985): Bedrock geological mapping, Waddy - Tower Lakes area (part of NTS 640-4 and -5 and 74A-l and -8); in Summary of Investigations, 1985, Sask. Geol. Surv ., Misc. Rep. 85-4, p6-17.

_ ___ (1986): Bedrock geological mapping, Windrum Lake area (part of NTS 640-4, 73P-16, and 74A-l); in Summary of Investigations, 1986, Sask. Geo!. Surv ., Misc. Rep. 86-4, p8- l 8.

Harper, C.T., Thomas, O.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; CIM Spec. Vol. 38, p57-85.

Thomas, 0 . J. and Watters, B.R. (1987): The Star Lake Pluton and its gold mineralization - an overview; in Gilboy, C.F. and Vigrass, L. W ., (eds.), Economic Minerals of Saskatchewan; Sask. Geol. Soc., Spec. Publ. 8, p54-57.

Thomas, D.J ., Watters, B.R. and Harper, C.T. ( 1987): The character of Early Proterozoic plutonism in the Central Metavolcanic Belt, northern Saskatchewan; Geo!. Assoc. Can./Mineral. Assoc. Can., Joint Annu. Meet., Saskatoon, 1987, Prag. Abstr., v 12, p95.

Watters, 8 .R. (1984): Geochemical patterns for metavolcanic rocks of the La Range Domain; in Summary of Investigations, 1984, Sask. Geol. Surv., Misc. Rep. 84-4, p88-91.

____ ( 1985): Geochemistry of meta volcanic and plutonic rocks, Star Lake and Waddy Lake areas; in Summary of Investigations, 1985, Sask. Geo!. 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. Geo!. Surv ., Misc. Rep. 86-4, p76-83.

Watters, 8.R. and Pearce, J .A. (1986): Metavolcanic rocks of the La Range belt in the Churchill Province, Saskatchewan: geochemical evidence for a volcanic arc origin; paper presented at symposium on Proterozoic Volcanism, Nottingham, April, 1986 (to be published in a Geol. Soc. Lon., Spec. Publ.).

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Watters, B.R., Thomas, D. J . and Harper, C.T. ( 1987): Tectonic setting of Early Proterozoic volcanism of the La Range Domain, northern Saskatchewan; Geo!. Assoc. Can./Miner. Assoc. Can., Joint Annu. Meet., Saskatoon, 1987, Prog. Abstr. vl 2, plOO.