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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 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 Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/102/1/147/3380751/i0016-7606-102-1-147.pdf by guest on 24 September 2021 148 W. E. STONE ' V W W V V vvvvvvvv '^LaPause =Township ' V. V V Y V-V-V -M- Lake ' Bousquet'v '5ÄI Lake Preissac ' V VV W V V v jChassignolle /v V V V \ 'VVVVVVVV (VVVVV\ ' V vV V V V V v / V V • vvvvvwN • VVVVVVVV)? 'VVVVVVVV v-fä v v v v v^ / V V rvvvvwv ' V V^/ V V V V Vjt V VVVVVVi / V V VV VV W VVVVVVVVi 'VVWVV V v V V V-U.V WW \V V wvMIvwvYw^vvvvwWNJW , 'VVVVVVW V V V^V WW v 'VVVVVVVV VtV VVVVVVMV VV VV W V# VVVVVVVVVV H * »Ovvvvvvvvvvvvvv ^V V . .^j-'VVwP/V - y W WV VV VV V V/AV v v \Av VvvVVVWVqv A^VVVVVVVVVVV • v v vvKfi^Av v v v vv v y y w vV VVVVVVVVV7I7/VVVVVVVVVVW ^Wf^vSsJ V V V 4: vvvvvvwln/vvwvvvvvvvv vvvvvvv\ 1 VVVVVVVV yvvvvfv\ - ' " 1 v\® - <VÌ'0V V V V \ V V^r V V V V V V V V V V V V V V V VV V V V V V VV AMp; J V V V V vvvvvwvvvvvvv VV V 4 v vvvvvvvvvvvvv V V V VW vvvnvvvvvvvv VV V WW VW v VVVVVVVV WW vv\ ° www g'W V V* I VV V V 3*"gv V V » «'Vi^VV V VV VW " V V VW /vvvvfytyvvvvvvvvv V O Y , VVVVVVVV VW WW /vvw wÔftiv #v www iv v v v v v v™ |TV v v v v v v v^v v v v y v / w vv v w®" v vvvvvvvv tvyvvvvyvvvvvvv wyUV- u V-VV Vp< w W v vV vVV v %# V KÎ.V Wf V VVVVVVVVVV v v v v K^-'r'^i D rs 2:2. •"¿i'U'-SÎ.*,*.».«. •W'*'«.'.'.'. - - - ^7?.-1^.. .Vi- TT. ¿ài T ICdi y w v w v www ' - " ™ 1 U 'V TIC-|Pfi f iCaT 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 (sed- imentary 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.
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