Archean Volcanism and Sedimentation in the Bousquet Gold District, Abitibi Greenstone Belt, Quebec: Implications for Stratigraphy and Gold Concentration

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Archean volcanism and sedimentation in the Bousquet gold district, Abitibi greenstone belt, Quebec: Implications for stratigraphy and gold concentration

WILLIAM E. STONE* Department of Geology, University of Western Ontario, London, Ontario, Canada N6A 5B7

ABSTRACT INTRODUCTION able, and folded about a regional-scale syncline and that the depositional environment of the Research on the nature and distribution of The Bousquet gold district of Bousquet host rocks of the gold orebodies may have Archean rock types in the Bousquet gold dis- Township, Quebec (Fig. 1), is one of the most played a significant role in the concentration of trict, Abitibi, Quebec, provides new con- productive gold-mining districts in the Abitibi the gold. straints on deposition, stratigraphy, and gold greenstone belt (Valliant and Hutchinson, 1982; concentration. Facies changes and textures Savoie and others, 1986; Tourigny and others, REGIONAL SETTING indicate that within the Blake River Group of 1988; Stone, 1988). Restriction of the gold the district, basalt to the east is more prox- orebodies to specific rock types on a district The Bousquet gold district is located in the imal to an eruptive center which shoaled up- scale suggests a stratigraphic control on gold south part of the Abitibi greenstone belt, Quebec ward, andesite was deposited in relatively concentration (Stone, 1989). Consequently, an (Fig. 1). According to Thurston and Franconi shallow subaqeuous conditions as pyroclastic understanding of the primary nature, origin, and (1983) and Jensen (1985), the south part of the flow deposits and turbidites around volcanic stratigraphy of the rocks which host and sur- Abitibi consists of supergroups (unnamed) that complexes formed on the basalt eruptive cen- round the gold orebodies is crucial to the inter- are composed of komatiite to calc-alkalic rhyo- ter, and dacite accumulated as lava which pretation of their origin. General agreement on lite and, in some places, alkalic volcanic rock erupted into a very shallow subaqueous set- the nature of the stratigraphic section in the (Jensen, 1985) accumulated during cycles of ul- ting. Turbidites in the Kewagama and Cadil- Bousquet gold district, however, has been lack- tramafic to felsic volcanism. The structurally lac groups originated from the volcanic ing. Gunning (1941), Valliant and Hutchinson lower supergroups are unconformably overlain complexes and accumulated in the form of (1982), Eliopoulos (1983), and Bateman (1984) by the upper supergroup. subaqueous fans, whereas those in the Pon- have concluded that the stratigraphic section The upper supergroup contains komatiite, ba- tiac Group are from an unknown source and consists of rock units which are well preserved, saltic komatiite, and olivine normative basalt at accumulated on an abyssal plain. In this con- conformable, and folded about a regional-scale its base, and quartz normative tholeiitic and text, the Cadillac-Larder break formed in- syncline; but Tourigny and others (1988) have calc-alkalic basalt to calc-alkalic dacite and itially as a low-angle normal fault zone. concluded that it consists of rock units which are rhyolite of the Blake River Group at its top Field relations and petrography of the internally disrupted and bound by major tec- (Dimroth and others, 1982; Jensen, 1985). rocks in the district indicate that the strati- tonic discontinuities. These conflicting views of Rocks which underlie the Bousquet gold district graphic section consists of generally well pre- the stratigraphic section are based mainly on constitute a nearly complete section through the served and largely conformable rock units. geologic relationships observed during study of southeast part of the upper supergroup. Opposing stratigraphic tops in the volcanic individual mine properties within the Bouquet gold district rather than on those observed dur- rocks of the Blake River and Piché groups ROCK UNITS suggest that they could be correlatives dis- ing comprehensive district-scale study. An im- proved understanding of the geology on a posed on opposite limbs of a regional-scale The Bousquet gold district (Fig. 1) is under- district scale can only help to resolve the debate syncline, the axial plane of which passes lain by Archean, steeply dipping to subvertical, about the stratigraphic section and improve the through the Cadillac Group. Accordingly, the volcanic, plutonic, and sedimentary rocks which geologic base for later interpretation of the con- rocks of the Blake River, Piché, and Cadillac are crosscut by Proterozoic mafic dikes. The trols on origin of the gold orebodies. groups may be part of a vast, largely subsided stratigraphic relationships of rock units in the and reworked volcanic complex. The shallow This paper describes the nature and distribu- district have been much debated (Table 1). subaqueous depositional environment of the tion of primary rock types in the Bousquet gold Furthermore, a recent study (Tourigny and oth- andesite and dacite in the Blake River Group district and interprets their depositional envi- ers, 1988) has concluded that deformation has could have economic significance because ronments; it also speculates briefly about the obscured much of the stratigraphy. Conse- boiling of hydrothermal fluid may have con- implications of these findings to the nature of the quently, the stratigraphy of the district is pres- tributed to the concentration of gold in the stratigraphic section and origin of gold ore- ently unknown, and therefore the rock units are Bousquet gold district. bodies. It is shown that the distribution, listed in order of their occurrence from north to petrography, and composition of the rocks are south, as the rocks are described. •Present address: Department of Geology, McMas- generally consistent with the notion that the The Malartic Group (Gunning, 1941) in the ter University, Hamilton, Ontario, Canada L8S 4M1. rock units are well preserved, largely conform- Bousquet gold district consists of mainly basalt

Geological Society of America Bulletin, v. 102, p. 147-158, 9 figs., 4 tables, January 1990.

147

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MAP AREA LOCATION MAP I— 1J 85° '75° 50' KAPUSKASING, QUETICÖ: STRUCTURAL,/ SUB. ABITIBI ZONE Figure 1. Map showing the distribution of rock types in the I GREENSTONE Bousquet gold district, Bousquet and Cadillac Townships, ' I LU Timmins BELT Quebec. The map is a compilation of this research and of Z| 3 o a Savoie and others (1986) and Gorman (1986). Ml, Malartic O Group (volcanic rocks); Kw, Kewagama Group (sedimentary vV rocks); Br, Blake River Group (volcanic rocks); Mp, Mooshla pluton (synvolcanic plutonic rocks); Cd, Cadillac Group (sedimentary rocks); Ph, Piché Group (volcanic rocks); Pt, Pontiac Group (sedimentary rocks).

flows (Fig. 1) and lesser pyroclastic basalt and dence for partial age equivalence of the Kewa- quartz diorite, trondhjemite, and tonalité. The gabbro plugs and sills. The basalt horizon over- gama Group and the Blake River Group Blake River Group has been interpreted to be lies a regional extensive horizon of komatiite (Gunning, 1941; Dimroth and others, 1983a; older than the Cadillac Group (Gunning, 1941; flows, which is north of the district and extends Imreh, 1984). Alternatively, others (Tourigny Holubec, 1972; Latulippe, 1976; Imreh, 1984), eastwards to Val d'Or (Thurston and Franconi, and others, 1988) interpret the intercalation and to be the youngest rock in the district (Elio- 1983). The Malartic Group has been interpreted to be tectonic rather than primary in origin. poulos, 1983) (Table 1). Tourigny and others to be the oldest rock unit in the district, and to Generally, the Kewagama Group has been con- (1988), however, have concluded that the north be partly equivalent to the Kewagama Group sidered to be older than the Blake River Group part of the Blake River Group is relatively well (Table 1). (Table 1). preserved, whereas the south part is deformed to The Kewagama Group consists of sandstone The Blake River Group (Gunning, 1941) the extent that stratigraphy is obscured. The an- with lesser amounts of siltstone and mudstone consists of basalt, andesite, and dacite (Fig. 1). It desite, dacite, and tonalité host the gold ore- (Fig. 1). Intercalation of the Kewagama Group also consists of the Mooshla pluton, a synvol- bodies of the Bousquet gold district (Valliant and with the Blake River Group (Fig. 1) has been canic (Valliant and Hutchinson, 1982) compos- Hutchinson, 1982; Stone, 1989; Stone and oth- interpreted as primary in origin and cited as evi- ite intrusion (Guha and others, 1982) of gabbro, ers, 1988; Tourigny and others, 1989).

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EXPLANATION SYMBOLS

PROTEROZOIC Township boundary Highway Mafic dikes M Railway ARCHEAN a MINE - Operating or under development SEDIMENTARY ROCKS 1 - Dumagami Mudstone and iron formation 2 - Bousquet No. 2 3 - Bousquet No. I Volcanic clast conglomerate 4 - Doyon Sandstone Geologic contact - Group Mixed clast conglomerate Informal rock type contact Erosional contact VOLCANIC AND SYNVOLCANIC PLUTONIC ROCKS Glomeroporphyritic lava Tonalite Fault Bedding, dip unknown, top known [¿3 Trondhjemite Bedding, dip known, fop known Dacite Bedding, vertical, top known Quartz diorite Bedding, overturned, top known Pillowed flow, dip unknown, top known Andesite Pillowed flow, dip known, top known Gabbro Sampled locations IV V V vi jv y y vj Basalt Figure 1. (Continued).

The Cadillac Group (Gunning, 1941; Gor- rock (Fig. 1) in the southeast part of the Bous- 15 m thick. Westward, pillowed basalt seems to man, 1986) consists mainly of sandstone and quet gold district. It consists, from top to bot- pass into clinopyroxene crystal tuff and thick lesser, although locally significant, amounts of tom, of andesite flows and pyroclastic rock, deposits of pillow breccia. Pillow shapes and siltstone, mudstone, conglomerate, and iron- volcanic clast conglomerate, andesite flows, and flow sequences in lavas and graded bedding in formation (Fig. 1). It has been interpreted to be basalt flows. The Piché Group has been inter- the tuffs face south. the youngest rock unit in the district (Gunning, preted to be equivalent to the Blake River 1941; Holubec, 1972; Latulippe, 1976; Imreh, Group, and to be correlative with the Malartic Kewagama Group 1984), and to be equivalent to the Kewagama Group (Table 1). Group (Eliopoulos, 1983) (Table 1). Intercala- The Pontiac Group is a thick and extensive Sandstone in the Kewagama Group occurs as tion of the Cadillac Group with the Blake River unit of mainly sandstone, siltstone, and feldspathic wacke and lesser lithic wacke (Fig. Group has been interpreted as primary in origin mudstone (Fig. 1). It has been interpreted to 1). Samples of the feldspathic wacke contain and cited as evidence for partial age equivalence be partly equivalent to the Kewagama Group, larger grains of plagioclase than quartz and more of the Cadillac Group and the Blake River to the Malartic Group, and to the Cadillac plagioclase than quartz (Table 2; Fig. 2). Lithic Group (Gunning, 1941; Valliant and Hutchin- Group, and to be the oldest rock unit in the wacke is most prevalent near contact with the son, 1982). Alternatively, others (Tourigny and area (Table 1). Blake River Group. Lithic fragments in the others, 1988) have interpreted the intercalations wacke are of graywacke, dacite, mudstone, and to be tectonic rather than primary in origin. PETROGRAPHY AND COMPOSITION aggregative plagioclase. Analyses of samples The Cadillac-Larder break (Fig. 1) in the Bousquet gold district occurs within the Cadillac In this paper, rocks are referred to in terms of TABLE 1. SIMPLIFIED STRAT1GRAPHIC COLUMNS FOR Group (Gorman, 1986). It is the most promi- unmetamorphosed protoliths. Primary minerals ARCHEAN ROCKS IN THE SOUTHEAST PART OF THE ABITIBI GREENSTONE BELT, QUEBEC nent linear feature in the district, but its nature is and textures in the rocks are, however, variably as yet unclear. Farther west, in the Rouyn area, overprinted by tectonic fabrics and recrystallized Gunning Holubec Latulippe Imreh Eliopoulos it marks a lithologic break between volcanic in the greenschist to amphibolite facies, particu- (1941) (1972) (1976) (1984) (1983) rock to the north and sedimentary rock to the larly in the immediate vicinity of the gold Cadillac Cadillac Cadillac Cadillac south, and has been interpreted to be a fault orebodies. Pontiac

active during deposition of the rocks (Dimroth Blake River Blake River Blake River Blake River Blake River and others, 1982), and as a boundary between Malartic Group Piché two geologic blocks (Hubert and others, 1984; Kewagama Kewagama Kewagama Kewagama Cadillac Pontiac Malartic Kewagama Ludden and others, 1986). Basalt flows in the Malartic Group of the Malartic Pontiac Piché Malartic Malartic The Piche Group (Latulippe, 1976; Gorman, Bousquet gold district (Fig. 1) are of aphyric Malartic Piché Pontiac Pontiac 1986) is a band of volcanic and sedimentary olivine normative tholeiite and are less than

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TABLE 2. MEAN FRAMEWORK GRAIN PERCENTAGES SANDSTONE IN SANDSTONE Figure 2. QFL ternary dia- i KEWAGAMA GROUP gram (modified from Dott, 1964, QUARTZ- • CADILLAC GROUP WACKE Rock type Group N Q:P:L» by Williams and others, 1982) K PONTIAC GROUP showing the modal proportions Feldspathic wacke Kewagama 3 31:51:32 Cadillac 7 43:43:14 of framework constituents in Pontiac 4 58:27:15 sandstone samples. Lithic wacke Kewagama I 17:51:32 Pontiac 1 36:30:34

High plagioclase arkosic wacke Cadillac 1 0:100:0

•Averaged percentages of quartz (Q), plagioclase (P), and lithic fragments (L).

FELDSPATHIC WACKE LITHIC WACKE

SEDIMENTARY ROCKS

1.0 & • • MUDSTONE-KEWAGAMA, CADILLAC, PONTIAC GROUPS J • k SANDSTONE-KEWAGAMA, CADILLAC, PONTIAC GROUPS have Na20 > K20 (Fig. 3) and large A1203, Fe2C>3*, and MgO (Table 3). The sedimentary Figure 3. Composition of the rocks are, in places, interbedded with thin hori- o sedimentary rocks. 1, gray- zons of basalt tuff. CM wacke; 2, lithic wacke; and 3, Beds of the sandstone are mainly massive, and S arkose (diagram from Pettijohn they alternate rhythmically with thin beds of silt- o and others, 1973). The sandstone or mudstone (divisions A and E of the

Si02/AI203 is arkosic wacke, scours, flames, and imbricated mudchips. A en O Cadillac Group; the sandstone smaller proportion of beds have a base of sand- / 3 I sample with the largest Si02/ stone which grades upward into siltstone and AI2O3 is from the matrix of mudstone (divisions A, B, D, and E of the mixed-clast conglomerate, Cadil- Bouma sequence). Sedimentary structures in the lac Group. Kewagama Group indicate considerable varia- 1.0 bility in facing direction and paleocurrents, 0 1.0 2.0 which is consistent with the abundant fold closures observed and suggests that the rocks are Log (Si02/Al203) folded.

TABLE 3. COMPOSITION OF THE SEDIMENTARY ROCKS Blake River Group

Rock type sst sst* sslt sst sst mst mst mst cgl§ cgl" Basalt and Gabbro. Basalt and gabbro in the Group Kw Cd Cd Cd Pt Kw Cd Pt Cd Ph Analyses 4 I 1 5 2 1 3 3 1 2 Blake River Group occur at its base (Valliant and Hutchinson, 1982; Savoie and others, 1986; sio 64.71 76.14 54.43 67.86 67.28 60.11 59.40 58.08 74.52 61.88 2 Tourigny and others, 1988; Fig. 1) as quartz Ti02 0.57 0.42 0.86 0.53 0.55 0.69 0.73 0.79 0.24 0.90 AI2O3 16.54 11.76 19.47 15.29 15.63 20.17 20.86 21.18 13.46 14.10 normative, pillowed and massive tholeiite (Figs. Fe203 5.55 3.56 6.88 5.24 5.77 7.28 7.12 7.94 2.64 4.33 MnO 0.06 0.06 0.11 0.07 0.06 0.07 0.07 0.08 0.07 0.11 4, 5; Table 4). The proportion of the latter is MgO 3.22 1.54 5.33 2.14 2.85 3.89 4.06 4.23 1.46 3.55 CaO 2.49 1.56 4.84 2.99 2.20 1.38 0.96 1.18 2.37 9.85 greatest in the east part of the Bousquet gold Na20 4.64 3.19 4.58 4.06 4.01 2.48 2.66 2.87 4.39 3.74 district (east of the Dumagami Mine; Fig. 1). K20 2.07 1.66 3.22 1.70 1.51 3.80 3.99 3.53 0.76 1.35 P2O5 0.13 0.10 0.28 0.12 0.13 0.11 0.14 0.13 0.08 0.17 Flow contacts, pillow shapes, flow sequences,

Ba 544 475 1266 273 392 861 729 684 144 345 and graded flow tops indicate south to south- Cr 187 175 321 199 224 225 220 224 58 580 west facing. In the east part of the Bousquet gold Nb 4 4 5 7 5 9 8 11 8 Ni 47 33 64 53 46 99 81 106 18 117 district, vesicularity of basalt increases upward. Rb 61 45 89 50 42 96 101 82 18 23 Sr 477 378 1125 311 355 118 166 196 309 617 The gabbro occurs as sills and plugs and as V 136 93 128 113 128 168 173 188 52 183 Y 14 13 18 23 18 12 18 18 11 19 the northernmost part of the Mooshla pluton. Zr 117 80 158 158 119 108 119 91 97 109 The composition of gabbro samples generally overlaps that of the basalt samples (Fig. 5; Table Note: sst, sandstone (feldspathic wacke); mst, mudstone; egl, conglomerate, Kw, the Kewagama Group; Cd, Cadillac Group; Pt, Pontiac Group; Ph. Piché Group. Analyses made by XRF at the University of Western Ontario. 4), but a significant proportion are distinctly 'Siliceous lithic wacke. tpiagiolcase-rich arkosic wacke. more Fe-rich. ^Dacite dast in volcanic-clast conglomerate. Andesite and Quartz Diorite. Andesite in ••Average of two andesite clasts in volcanic-clast conglomerate. the Blake River Group is interlayered with da-

ed clasts which is overlain sequentially by a 1-m-thick interval of ungraded more closely packed clasts and a 3-m-thick interval of normally graded and matrix-supported clasts with a fine-grained, indistinctly banded, and locally scoured top. Andesite beds in the center and west part of the Bousquet gold district (the area of the Bousquet No. 1 Mine and of the Doyon Mine, respectively; Fig. 1) are of two types. One type (Fig. 6B) consists of a 2-m-thick, massive base, which near the top grades abruptly into a 50-cm-thick interval of coarsely crystalline material, which in turn is locally scoured by base of the next bed. The second bed type (Fig. 6C) contains clasts within a 1-m interval at the base and grades crudely upward through a 2-m interval into an indistinctly banded top 50-cm thick, which in turn is scoured by base of the next bed. The distribution of clasts and orientation of the scours in the three bed types indicate that the andesite faces to the south. Outcrops of the inverse-to-normally graded andesite beds contain clasts which have a siliceous rim as much as 2 cm thick (Fig. 6D). In these outcrops, siliceous pods are present; to-

VOLCANIC ROCKS ward the center, these pods become progressively less siliceous and more vesicular. These * Clast, volcanic clast pods are similar in shape to the andesite clasts. conglomerate, Cadillac Group Quartz diorite in the Blake River Group of x Clast, volcanic clast conglomerate, Piché Group the Bousquet gold district occurs as the largest phase in the Mooshla pluton (Fig. 1; Table 4). • Dacite Samples are generally calc-alkalic (Fig. 5). • A Andesite - Blake River Group, Dacite, Trondhjemite, and Tonalite. Dacite Piché Group in the Blake River Group occurs as semicontin- A T Basalt - Blake River Group, Piché Group uous horizons which are interlayered with andesite (Fig. 1). The dacite horizon most studied Î/ is that south and east of the Mooshla pluton, and it hosts orebodies of the Bousquet and Duma- * gami mines. The horizon consists mainly of a series of massive dacite, breccia, and micro- A A breccia, and microbreccia and tuff sequences. A section through a massive dacite, breccia and microbreccia, and microbreccia and tuff sequence in the dacite is exposed in the east part of the Bousquet gold district (Fig. 7), at the bound- OOI 0.10 1.0 ary between Bousquet and Cadillac townships Nb/Y (Fig. 1). The massive dacite here is a steep-sided Figure 4. Composition of volcanic rocks from the area of Bousquet Township. (A) 1, tho- mound about 200 m2 in outcrop and, locally, is leiitic basalt; 2, Fe-rich tholeiitic basalt; 3, Mg-rich tholeiitic basalt; 4, calc-alkalic basalt; flow banded and brecciated. It is flanked to the 5, calc-alkalic andesite; 6, calc-alkalic dacite; 7, calc-alkalic rhyolite; 8, tholeiitic andesite; east, west, and south, but never to the north, by 9, tholeiitic dacite; 10, tholeiitic rhyolite (diagram from Jensen, 1976). (B) 1, subalkalic basalt; breccia and microbreccia, an unsorted and un- 2, andesite/basalt; 3, andesite; 4, rhyodacite/dacite; 5, rhyolite (diagram from Floyd and Win- stratified deposit of subangular to subrounded chester, 1978). dacite fragments as large as 1 by 3 m (Fig. 8A) which are variably fragmented (Fig. 8B), contain smaller fragments and are supported by a cite (Fig. 1). Samples of the andesite are calc- plagioclase-phyric andesite clasts as much as matrix of lapilli-size dacite fragments and quartz alkalic (Fig. 4; Table 4). Generally, andesite not 1 m across. A typical bed in the east part of the and plagioclase grains (Fig. 8C). The breccia in the immediate vicinity of the gold orebodies Bousquet gold district is inverse-to-normally and microbreccia appears to pass progressively occurs as beds 2 to 10 m thick with lapilli- graded (Fig. 6A) and consists of a 1-m-thick outward into microbreccia and tuff, which con- to block-sized, scoriaceous, amygdaloidal, or base with inversely graded and matrix-support- sists of variable amounts of lapilli-size dacite

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Fs + Fe + Ti SYNVOLCANIC INTRUSIONS

x Tonalité • Trondhjemite • Quartz diorite a v Gabbro - Blake River Group, Piché Group

O.IO -

0.01

\ N

0.001 0.01 0.10 1.0 Nb/Y

Figure S. Composition of synvolcanic intrusive rocks from the area of Bousquet Township (diagrams from Jensen, 1976 [left], and Floyd and Winchester, 1978 [right]). The phase field labels are explained in the caption of Figure 3.

fragments and large quartz grains (Fig. 8D), and the massive dacite and that stratigraphic tops in intrusion in the east part of the trondhjemite is variably banded. The small areal extent of the this dacite horizon are to the south. phase may be tonalite (Fig. 1; Table 4). breccia and microbreccia; proximity to the mas- Trondhjemite in the Blake River Group of the sive dacite; and confinement south, east, and Bousquet gold district occurs as a small phase in Cadillac Group west of the massive dacite suggest that its deposi- the southeast part of the Mooshla pluton (Fig. 1; tion is related to brecciation during formation of Table 4) and as dikes in massive dacite. A small Sandstone, Siltstone, and Mudstone. Sand- stone in the Cadillac Group (Fig. 1) occurs as

TABLE 4. AVERAGE MAJOR (wt%), TRACE (ppm) AND CIPW NORM COMPOSITION OF feldspathic wacke (Fig. 9A) and lesser lithic VOLCANIC AND COEVAL PLUTONIC ROCK TYPES IN THE BOUSQUET GOLD DISTRICT wacke and arkosic wacke. Samples of the feldspathic wacke generally contain larger grains of Rock type bs bs gb gb ad dr ad dc tr tn Group Br Ph Br Ph Br Br Ph Br Br Br plagioclase than quartz and as much or more Analyses 13 3 17 4 14 8 4 6 14 3 plagioclase than quartz (Table 2; Fig. 2). Lithic wacke is most prevalent in outcrops near contact Si02 52.60 52.87 50.06 49.99 57.36 59.74 58.83 69.74 73.05 64.24 Ti02 1.17 1.22 1.30 1.41 1.00 1.14 1.23 0.62 0.48 0.83 with the Blake River Group and the Piche A1203 14.95 15.53 15.16 14.51 17.79 17.53 16.47 15.22 13.78 17.01 Fe203 12.07 11.60 13.67 13.99 7.53 7.64 7.31 3.96 3.06 5.95 Group, and in and near horizons of conglomer- MnO 0.17 0.26 0.24 0.21 0.12 0.09 0.12 0.07 0.04 0.05 ate; the lithic fragments are mostly of gray wacke MgO 6.13 5.85 7.07 6.73 2.97 2.71 5.17 1.40 1.28 2.20 CaO 9.52 7.16 10.19 11.13 8.80 5.68 4.87 3.03 2.21 4.42 or dacite, although fragments of iron formation, Na20 2.23 4.81 2.04 1.66 3.48 4.22 4.74 3.71 4.44 3.46 K2O 1.06 0.62 0.17 0.25 0.72 0.86 1.00 2.08 1.58 1.63 basalt, mudstone, and aggregative plagioclase P205 0.08 0.08 0.11 0.11 0.22 0.37 0.25 0.16 0.08 0.20 are present locally. Analyses of samples are in Ba 48 98 58 70 255 418 297 433 733 331 general similar to those of samples from the Cr 168 85 172 161 33 3 189 7 1 Nb 7 5 6 7 7 11 9 13 13 14 Kewagama Group (Fig. 3), but in detail they Ni 114 91 129 138 22 3 120 8 1 1 have relatively slightly more Si02 and slightly Rb 2 16 4 7 15 22 29 58 42 45 Sr 158 188 178 442 197 320 314 187 85 284 less A1203, K20, and Sr (Table 3). V 384 338 360 339 230 142 217 98 54 76 Y 33 30 25 24 25 41 26 36 34 34 Beds of the feldspathic wacke occur in two Zr 65 67 43 39 96 105 192 171 249 204 Ap 0.2 0.3 0.5 0.9 0.4 0.2 0.2 0.3 0.6 0.7 sequences: massive or graded beds which alter- II 2.3 2.5 1.9 2.2 1.2 0.9 2.4 3.0 2.4 1.9 nate rhythmically with thin beds of siltstone or Mt 2.3 2.3 2.2 2.3 2.2 2.2 2.3 2.3 2.2 Or 6.3 1.0 4.3 5.1 12.3 11.4 2.6 2.4 0.2 mudstone, and alternating beds with divisions A, Ab 19.1 17.5 29.6 35.9 31.5 38.1 31.4 20.4 40.3 33.6 An 28.0 32.1 31.0 26.5 18.7 13.5 24.4 28.4 20.9 26.1 B, D, and E of the Bouma sequence. The first Di 15.9 15.1 9.4 0.0 0.0 0.0 10.6 15.0 2.9 sequence is most common in the north and Hy 22.2 27.5 10.0 14.1 7.2 4.4 24.6 26.3 16.0 01 0.0 0.0 0.0 0.0 0.0 0.0 1.4 0.0 0.0 south margins of the group, and it exhibits 3.8 1.7 10.96 13.5 30.2 32.6 0.0 2.0 19.4 Q scours (Fig. 9B), load casts, flames, imbricated Note: bs, basalt; gb, gabbro; ad, andesite; dr. diorite; de, dacite; tr, trondhjemite; tn, tonalité; Br, Blake River Group; Ph, Piché Group. Analyses made by XRF at mudchips, slump folds, and slide zones. The se- the University of Western Ontario. quence with Bouma divisions A, B, D, and E is

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Figure 6. Andesite of the Blake River Group. (A) Outcrop of inverse-to-normally graded bed in east part of the Bousquet gold district, looking west. Variation in clast size and proportion of clasts to matrix defines graded bedding, which suggests stratigraphic top is south (left). (B) Outcrop of a normally graded bed in the center of the Bousquet gold district (area of the Bousquet No. 1 Mine), looking west. (C) Outcrop of a normally graded bed in the west part of the Bousquet gold district (area of the Doyon Mine), looking west. Note how the top of the bed is scoured by base of the next bed. (D) Clasts is an inverse-to-normally graded bed. Note the vesicularity and the irregular siliceous rims (resistant) on the clasts. Arrows in A, B, and C point to contact between beds; the hammer is for scale.

most common near the center of the group. The arkosic wacke are lower than those of the feld- Larder break (Fig. 1). The horizon of volcanic sedimentary structures indicate considerable var- spathic wacke (Fig. 3). Northward, the arkose clast conglomerate near the center of the Cadil- iability in facing direction and paleocurrents, appears to pass into more stratified arkosic lac Group contains as much as 25% rounded which is consistent with the abundant fold clo- wacke and finally into feldspathic wacke. pebbles and cobbles of dacite, supported by a sures observed and suggests that the rocks are Iron-Formation. Iron-formation in the Bous- matrix of graded and, locally, cross-bedded lithic folded. The feldspathic wacke is interbedded quet gold district occurs only in the Cadillac wacke. The dacite clasts are identical to the da- with thin horizons of basalt, andesite, and dacite. Group, as minor bands of magnetite-rich rock cite in the Blake River Group (Table 4). The The arkosic wacke is present in outcrops near which are generally less than 1 m thick. The horizon of volcanic-clast conglomerate, just contact between the Cadillac and Piché groups, bands occur in sequences that are relatively north of the Cadillac-Larder break, contains which is scoured (Gorman, 1986), in the south- mudstone and siltstone dominated near the poorly sorted and matrix-supported pebbles and east part of the Bousquet gold district (Fig. 1). It center of the group (Fig. 1). cobbles of andesite, tonalite, diorite, graywacke, is plagioclase-rich (Pacht, 1984), framework Volcanic-Clast Conglomerate. Horizons of and basalt in the form of indistinctly graded beds supported, and indistinctly laminated; it lacks volcanic-clast conglomerate in the Cadillac with scoured contacts. The andesite cobbles in lithic fragments and interbedded siltstone and Group crop out near its center, in the east part of this conglomerate horizon resemble the andesite mudstone. Analysis of a sample indicates that the Bousquet gold district, and near the south lava of the Piche Group. Presence of large clasts,

the Si02/Al203 and Na20/K20 ratios of the margin of the group, just north of the Cadillac- Bouma sequences, and scours in these volcanic-

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clast -conglomerate horizons indicate deposition as turbidites (Walker, 1975,1984). Mixed-Clast Conglomerate. The most prominent horizon of mixed-clast conglomerate crops out in the south margin of the Cadillac Group, west of Lake Norman (Gorman, 1986; Fig. 1). It contains matrix-supported and rounded pebbles and cobbles of plagioclase-phyric diorite, quartz- and plagioclase-phyric quartz diorite, tonalite, granodiorite, diorite, graywacke, dacite, and basalt; and minor clasts of jasper, chert, and veined quartz, mainly in the form of massive beds, although graded beds are present locally, and interbedded sedimentary rock is scoured. The presence of graded bedding and scours suggests that deposition of much of this mixed-clast-conglomerate horizon was by high-concentration turbidity currents (Walker, Figure 7. Map of an exposed cross section of a massive dacite, breccia, and microbreccia and 1975, 1978). tuff sequence of dacite. The rocks are depicted as flat-lying (the section is south-facing). Mixed-clast conglomerate also crops out in

Figure 8. Dacite. (A) Breccia. The hammer is for scale. (B) Brecciated fragment in the breccia. (C) Photomicrograph of the microbreccia matrix of the breccia. The matrix consists of a fine-grained, plagioclase-phyric fragment with an irregular but sharp contact with coarser- grained matrix (scale bar = 1 mm). (D) Photomicrograph of two large quartz grains in the microbreccia and tuff. The grains are somewhat hexagonal in shape and have deep, smooth-sided embayments filled by matrix (scale bar = 0.5 mm).

Figure 9. Sedimentary rocks of the Cadillac Group. (A) Photomicrograph of feldspathic wacke. Quartz grains are clear, plagioclase grains are cloudy, and biotite grains are dark (scale bar = 1 mm). (B) Outcrop of sandstone with graded bedding, high-angle cross-bedding, and scours. Stratigraphic top is to the south (top of photograph). (C) Pebbles and cobbles in the mixed-clast conglomerate. Note bedding in the pebbles of feldspathic wacke. (D) Pebble train in sandstone channel within mixed-clast conglomerate.

the Cadillac Group, just west of highway 395, in deep-sea channels that feed submarine fans Piché Group north of the Cadillac-Larder break (Fig. 1). In (compare with Hein and Walker, 1982). The the south part of this conglomerate, outcrops are occurrence of turbidites to the north and south Andesite in the Piché Group occurs as two massive and clast supported; they consist mainly of this conglomerate and its fining northward horizons of plagioclase-phyric pillowed or mas- of pebble- and boulder-sized clasts of feldspathic (stratigraphically upward), however, seem more sive plagioclase-phyric rock (Gunning, 1941; wacke (Fig. 9C). Northward, the proportion of easily explained in the context of deposition in a Gorman, 1986), separated by a horizon of conglomerate relative to sandstone decreases. submarine channel (Walker, 1978, 1985). volcanic-clast conglomerate (below) (Fig. 1).

The sandstone occurs mainly in the form of lens- Cadillac-Larder Break. The Cadillac-Larder The Si02 contents and Zr/Ti02 versus Nb/Y oid channels with pebble trains (Fig. 9D); lo- break (Fig. 1) in the east part of the Bousquet ratios of samples of the andesite (Table 4; Fig. 4) cally, it has large-scale, high-angle planar gold district is a very schistose zone of rock 15 to suggest that it is indeed andesite and calc-alkalic, cross-beds. Samples of the sandstone contain 60 m wide which strikes and dips approximately but most of the analyses plot in the basalt field of twice as much quartz as plagioclase and abun- parallel to bedding in the Cadillac Group (Gun- the Jensen Cation plot, and the Cr and Ni con- dant lithic fragments of wacke, dacite, and ning, 1941). In the center and west parts of the tents resemble those of the basalt in the Blake mudstone. Analysis indicates that the sandstone Bousquet gold district, the break is not exposed, River and Piché groups. Consequently, it is pos- is enriched in Si02 relative to AI2O3 (Fig. 3). but recovered diamond drill core (Gunning, sible that the andesite may actually be silicified The features of this mixed-clast conglomerate 1941; Gorman, 1986) indicates that here it is basalt. Shapes of the pillows indicate that strati- resemble those of fluvial conglomerate (com- one or more zones of talc and chlorite schist graphic tops are to the north. pare with Dimroth and others, 1982; Ojakan- separated by lenses of wacke, basalt tuff, and The horizon of volcanic clast conglomerate in gas, 1985) and those of conglomerate deposited granitoid rock. the Piché Group is as much as 100 m thick (Fig.

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1). The south part of the conglomerate appears breccia, and plagioclase phenocrysts in the an- ited the andesite, perhaps as a subaqueous apron to be massive and clast supported, and it con- desite of the Piché Group indicate subaqueous of volcaniclastic-andesite debris around the vol- tains clasts as large as 1.5 x 3.5 m. On the other eruption. By analogy with similar rocks else- canic complex. hand, the north part has a larger proportion of where (Dimroth and others, 1978; Gente and By analogy with similar more recent volcani- sandstone and is more stratified, with beds from others, 1986), the westward lateral change from clastic-andesite rocks elsewhere (Tasse and oth- 50 cm to 5 m thick which are clast or matrix massive basalt and gabbro to more pillowed ba- ers, 1978; Lajoie, 1984), the westward lateral supported, and massive, normally graded or salt in the Blake River Group represents in- transition in the andesite of the Blake River inverse-to-normally graded, and scoured (Gor- creased distance of flow from the eruptive Group from pyroclastic-flow andesite deposits man, 1986). The normally graded beds taken center, and the upward increase in vesicularity in the east to the proximal turbidites of together consist of divisions A, B, C, D, and E of in the east suggests upward shoaling. Accord- pyroclastic-andesite debris in the west suggests the Bouma sequence. Generally, the clasts in the ingly, basalt of the Blake River Group in the east increased distance of flow from the eruptive cen- conglomerate are identical to the andesite of sur- is more proximal to an eruptive center, which ter. Consequently, the pyroclastic-flow deposits rounding lava flows (Table 4). The similarity of shoaled upward. Presence of local upward- are more proximal to the eruptive center. Pres- the clasts to the andesite in surrounding lava shoaling eruptive centers suggests that this basalt ence of calc-alkalic andesite as pyroclastic-flow flows together with the coarse, unsorted, unstrat- sequence may be part of a tholeiitic shield vol- deposits and turbidites overlying the tholeiitic ified, and clast-supported nature of much of the cano rather than part of a lava plain (compare basalt suggests that calc-alkalic volcanism in- conglomerate suggest local provenance and that with Dimroth and others, 1982). volved the development of at least one central deposition may have been as talus, debris flows, The abundance of scoriaceous and amygda- volcanic complex with significant topographic and turbidites, perhaps in response to breakup of loidal clasts in the andesite of the Blake River relief on the tholeiitic shield volcano. Although andesite flows by fault-scarp collapse during Group indicates an origin by pyroclastic erup- the Mooshla pluton is synvolcanic, there is little syn volcanic tectonism (Gente and others, 1986). tion. The presence of siliceous rims on clasts and evidence to suggest that it represents the site of Basalt flows in the Piché Group occur at the siliceous pods similar in shape to the andesite the eruptive center of the andesite or the basalt top, in contact with the sedimentary rocks of the clasts is interpreted to represent variable silicifi- of the Blake River Group. Cadillac Group (Fig. 1). The flows are generally cation of the andesite clasts. Siliceous rims and Volatile streaming is more likely to occur in less than 15 m thick and are of aphyric olivine pods in analogous rocks elsewhere have been shallow water than in deep water (Wright and normative tholeiite (Fig. 4). Pillow shapes, attributed to siliciScation in response to volatile Coward, 1977; Fisher, 1984). Therefore, pres- shape of gas cavities, and flow sequences indi- streaming prior to, during, or following em- ence of the silicified clasts, which reflect volatile cate that the basalt faces north. placement of the rock as hot, gas-supported streaming (above), and the lack of interbedded material in the form of pyroclastic flows (Wright terrestrial sedimentary rock, as well as the vesic- Pontiac Group and Coward, 1977; Lajoie, 1984; Howells and ularity of the clasts, indicate eruption, and per- others, 1986; Cas and Wright, 1987). By anal- haps emplacement, of at least the pyroclastic- Sandstone in the Pontiac Group (Fig. 1) oc- ogy, the inverse-to-normally graded andesite flow deposits in a relatively shallow subaqueous curs as feldspathic wacke and lesser lithic wacke. beds in the east were emplaced at high tempera- marine setting. Samples of the former contain larger grains of ture as gas-supported andesite debris by pyro- In the dacite of the Blake River Group in the quartz than plagioclase and as much or more clastic flows. Gas-escape pipes, glass shards, Bousquet gold district, the spatial association of quartz than plagioclase (Table 2; Fig. 2). Lithic and axiolitic overgrowths, which are present the massive dacite, breccia and microbreccia, wacke occurs in outcrops near the north contact in many pyroclastic-flow deposits elsewhere and microbreccia and tuff rocks resemble facies of the group. The lithic fragments are mostly of (Wright and Coward, 1977; Cas and Wright, relationships in rhyolite flows (de Rosen-Spence graywacke or dacite, although fragments of 1987), were not recognized in the andesite, but and others, 1980; Manley and Fink, 1987) mudstone and aggregative plagioclase are pres- they could have been obliterated during subse- rather than those in felsic pyroclastic deposits. ent locally. Generally, samples from the Pontiac quent metamorphism and deformation. By analogy, the massive dacite and breccia and Group appear to be similar in composition to On the other hand, the andesite beds in the microbreccia are interpreted to be lava domes those from the Cadillac and Kewagama groups center and west parts of the Bousquet gold dis- and brecciated lava, respectively, which are dif- (Table 3; Fig. 3). trict appear to lack evidence for gas transport ferent facies of dacite flows, whereas the micro- Within the Pontiac Group, the feldspathic and hot emplacement, and therefore they are not breccia and tuff is interpreted to be a mixture of wacke, unlike that in the Cadillac and Kewa- pyroclastic flow deposits. Instead, the presence brecciated lava and, perhaps, ash tuff (for exam- gama groups, occurs mainly as alternating beds of graded bedding and scours together with the ple, hyalotufl). In this context, the dome facies is with divisions A, B, D, and E of the Bouma lack of siltstone or mudstone indicate that these central to the eruptive site, whereas the breccia sequence. Sedimentary structures indicate con- beds are proximal turbidites of pyroclastic an- and microbreccia and the microbreccia and tuff siderable variability in facing direction and pa- desite debris (compare with Walker, 1975; facies are more proximal. Passage upward and leocurrents, which is consistent with the abun- Rupke, 1978). Given that during down-slope laterally from the dome to the breccia and mi- dant fold closures observed and suggests that the movement, subaqueous pyroclastic flows gradu- crobreccia suggests that flow advance caused rocks are folded. ally mix with water and become turbidity cur- brecciation. rents (Cas and Wright, 1987), the andesite The dacite flows in the Bousquet gold district, VOLCANISM turbidites in the Bousquet gold district could be compared to felsic flows in the Rouyn area, con- the down-slope equivalents to the pyroclastic- tain smaller domes and appear devoid of lava Presence of pillows and pillow breccia in the flow deposits. Explosive eruption of the andesite tongues and lobes. These features suggest that basalt of the Malartic, Blake River, and Piché could have caused pyroclastic flows and, down- dacite lava extruded in the Bousquet gold district groups; and the presence of pillows, flow-top slope, turbidity currents, which together depos- more readily brecciated. Generally, in more re-

cent settings, subaerial and subaqueously erupt- Blake River and Piché groups. Spatial associa- by tectonic discontinuities which are major (that ed felsic lava is viscous and relatively immobile. tion of the conglomerate horizons with the is, of regional significance; Tourigny and others, The resultant felsic flows contain small domes Cadillac-Larder break suggests that their deposi- 1988). Certainly, the contacts between the strat- but lack lava lobes and tongues (Pichler, 1965), tion could have been in response to tectonism in igraphic units are at least locally more deformed whereas deep (greater than 1.5 km) subaque- this area during volcanism and sedimentation. than the surrounding rock, but this might be ously erupted and emplaced felsic lava is more The clasts of diorite and tonalite in the conglom- expected at contacts of massive volcanic rock fluid and contains large domes and lava lobes erates could be fragments of synvolcanic plu- and well-layered sedimentary rock (Dimroth (Cas, 1978; de Rosen-Spence and others, 1980). tons (Posehn, 1975). Accordingly, features of the and others, 1983a; Dimroth and Rocheleau, The relatively small size of the domes and the sandstone and conglomerate in the Cadillac and 1985). Furthermore, the opposing facing direc- lack of lava lobes and tongues suggest that dacite Kewagama groups are consistent with prove- tions of the rocks in the Blake River Group and lava extruded in the Bousquet gold district nance of largely andesite and dacite and synvol- in the Piché Group are consistent with the pres- erupted into a very shallow subaqueous setting. canic plutons, such as that represented by the ence of a regional-scale syncline (Cadillac syn- present exposure of the Blake River and Piché cline), the axial plane of which passes through SEDIMENTATION groups. Interbeds of basalt, andesite, and dacite the Cadillac Group (Gunning, 1941; Valliant tuff and lava in the Kewagama and Cadillac and Hutchinson, 1982). Accordingly, the rocks The prevalence of interbedded sandstone and groups suggest coeval sedimentation and volcan- in the center of the Cadillac Group are the mudstone, conglomerate, lithic fragments and ism. Therefore, deposition of the turbidites may youngest in the district, and the rocks of the synsedimentary deformation, and rapid facies have been in response to synvolcanic tectonism Blake River and Piché groups are, at least in changes indicates that the margins of the Cadil- and gravitational collapse on nearby volcanic part, correlatives disposed on opposite limbs lac Group, parts of the Piche Group, and the centers and along the Cadillac-Larder break, (Gunning, 1941; Valliant and Hutchinson, Kewagama Group are composed of turbidites slump-sliding downslope, and generation of tur- 1982). In this context, the rocks of the Blake which resemble those in the proximal parts of bidity currents (Jones, 1967; Mitchell, 1970; River and Piché groups could be remnants of a submarine fans (Walker, 1978, 1984). Conse- Barret, 1977; Walker, 1984). In this context, the large volcanic complex, rocks of the Cadillac quently, these rocks in the Bousquet gold district Cadillac-Larder break formed initially as a low- Group may be the reworked product of this vol- are interpreted to be proximal turbidites, al- angle normal fault zone (Zheng and others, canic pile, and the Cadillac-Larder break does though less proximal than the andesite turbidites 1988). not separate two distinct geologic blocks. in the Blake River Group. On the other hand, Alternatively, the monotonous, relatively thin The suggestion that the rocks of the Kewa- the greater prevalence of more thinly bedded, bedded and fine-grained nature of the turbidites gama Group and rocks at the margins of the finer grained, and classical turbidites, together in the Pontiac Group, together with the preva- Cadillac Group are proximal turbidites of sim- with the lower proportion of conglomerate, in- lence of graded sandstone-mudstone couplets ilar composition implies that the Kewagama and dicate that the central part of the Cadillac Group and paucity of synsedimentary deformation, Cadillac groups may be, at least in part, correla- contains a significant proportion of relatively suggest that they are relatively distal (Rupke, tives. The notion that the Kewagama Group more medial turbidites. Furthermore, the pres- 1978; Howell and Normark, 1982; Walker, represents debris shed from the Blake River ence of iron-formation in the central part of the 1984). The widespread, monotonous, and very Group (yet it appears to underlie the Blake Cadillac Group and its spatial association with thick nature of the Pontiac Group probably re- River Group) is not necessarily contradictory if mudstone could reflect the presence of reduced, flects deposition in a tectonically stable envi- the former wedges out both westward and stagnant, and perhaps relatively deep areas in ronment with little relief, such as an abyssal down-dip into the latter and therefore represents the basin. plain. The relationship of the Pontiac Group sediment which filled a subsident marginal

The abundance of plagioclase, large Fe203* rocks to the rocks farther north is uncertain; they trough (Brocher and ten Brink, 1987). Subsi- and MgO contents, and low A^Oj/NajO indi- may be distal equivalents of the proximal turbi- dence appears to have played a significant role cate that the feldspathic wacke and, in particu- dites in the Cadillac and Piché groups (Valliant in evolution of the Abitibi because the rocks lar, the arkosic wacke were derived from a and Hutchinson, 1982), distally deposited debris were subvertical prior to development of the relatively unweathered source (Pettijohn and shed from the Malartic Group (Stone, 1988), or main foliation, lineation, and folds (Dimroth others, 1973). It has been argued that regionally unrelated (Lajoie and Ludden, 1984; Ujike, and others, 1983a; Jensen, 1985; Tourigny and extensive sandstone with abundant quartz must 1984; Gariepy and others, 1984). others, 1988). have provenance with granite or gneiss (Petti- Most of the gold oreobodies in the Bousquet john and others, 1973). Ayres (1983), however, IMPLICATIONS gold district are hosted by the volcaniclastic an- has argued that abundant quartz in graywacke desite turbidites and the breccia and microbrec- of Archean greenstone belts could be derived The results of this study indicate that stratig- cia facies of the dacite flows in the Blake River from erosion of felsic ash flows, which, in more raphy is generally preserved throughout the Group (Stone, 1988; Stone and others, 1988). recent settings, erodes rapidly to make gray- Bousquet gold district, except in the immediate Origin of the gold orebodies within these rocks wacke with abundant quartz. A local source for vicinity of the gold orebodies. Although much has been interpreted to have involved a rela- the quartz in the Cadillac and Kewagama more study is needed before the stratigraphy can tively early, initial concentration of gold (Tou- groups of the Bousquet gold district seems rea- be completely understood, preservation of pri- rigny and others, 1989) in response to boiling of sonable because of the abundance of dacite and mary texture within meters of, and (locally) at hydrothermal fluid (Stone, 1988,1989). If con- andesite fragments and embayed detrital quartz contacts between, the rock units, together with centration of the gold resulted, at least in part, grains in the sandstone and conglomerate and the evidence consistent with local derivation of from boiling of hydrothermal fluid, then the the similarity of K20/Na20 ratios of the feld- much of the sediment, is inconsistent with the shallow subaqueous depositional setting of the spathic wacke to the dacite and andesite of the notion that the stratigraphic units are separated host rocks would have facilitated the boiling. On

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the other hand, the host rocks for the massive Dott, R. H., 1964, Wacke, graywacke and matrix—What approach to imma- Pacht, J. A., 1984, Petrologic evolution and paleogeography of the Late Cre- ture sandstone classification: Journal of Sedimentary Petrology, v. 34, taceous Nanaimo Basin, Washington and British Columbia: Implica- sulfide deposits of the Rouyn area (felsic and p. 625-632. tions for Cretaceous tectonics: Geological Society of America Bulletin, Eliopoulos, D. G., 1983, Geochemistry and origin of the Dumagami pyritic v. 95, p. 766-778. intermediate volcanic rocks; Hutchinson and gold deposit, Bousquet Township, Quebec [M.Sc. thesis]: London, Pettijohn, F. J., Potter, P. E., and Siever, R., 1973, Sand and sandstone: New " Burlington, 1984) accumulated in deeper water Ontario, University of Western Ontario, 263 p. York, Springer-Verlag, 618 p. Fisher, R. V., 1984, Submarine pyroclastic rocks, in KokelaoT, B. P., and Pichler, H., 1965, Acid hyaloclastites: Bulletin Volcanologique, v. 28, (about 1.5 km; de Rosen-Spence and others, Howells, M. F., eds.. Marginal basin geology: Volcanic and associated p. 293-310. sedimentary and tectonic processes in modem and ancient marginal Posehn, G., 1975, The metaconglomerate and metagrey wacke at Booster Lake, 1976, 1980), which likely retarded boiling, and basins: Geological Society of London Special Publication 16, p. 5-28. Manitoba: Centre for Precambrian Studies, University of Manitoba, a much smaller proportion of gold relative to Floyd, P. A-, and Winchester, J. A., 1978, Identification and discrimination of 1975 Annual Report, p. 85-91. altered and metamorphosed volcanic rocks using immoble trace ele- Rupke, N. A., 1978, Deep clastic seas, in Reading, H. G., ed., Sedimentary base metal concentrated. Consequently, the ments: Chemical Geology, v. 21, p. 291-306. environments and fades: New York, Elsevier, p. 372-415. Gariepy, C., Allègre, C. 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Evolution of Archean supracrustal sequences: Geolog- REVISED MANUSCRIPT RECEIVED JUNE 23, 1989 Earth Sciences, v. 20, p. 1355-1373. ical Association of Canada Special Paper 28, p. 23-48. MANUSCRIPT ACCEPTED JUNE 30,1989

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