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Selbaie |
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Quebec, Canada |
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Cu Zn Ag
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Super Porphyry Cu and Au
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The Selbaie copper-zinc-silver-gold deposit is located on the northern margin of the Archaean Abitibi sub-province in the Superior Province of the Canadian Shield. It is some 170 km due north of Noranda in Quebec, Canada and falls within the thick succession of felsic tuffs that characterise the Harricana-Turgeon Belt which also host the Detour Lake deposit to the west in Ontario and the Matagami district ores to the east in Quebec.
The host sequence comprises calc-alkalic pyroclastics which grade upwards from sub-aqueous debris flows, through pumiceous tuff to densely welded ignimbrite to form a 1200 m thick intra-caldera sequence developed on a substrate of marine basalt and andesite. Mineralisation occurs within this sequence on the south-western flank of the Brouillan tonalite, a central intrusion within the caldera, and takes the form of local early stratabound massive sulphides and later epithermal veins.
Economically viable mineralisation occurs in three zones, each with its own characterisitic ore style. The largest is the A1 Zone which comprises a broad zone of fracture controlled and disseminated mineralisation with, in decreasing order - pyrite, sphalerite, chalcopyrite and rare galena. Sulphides occur in quartz-carbonate veins controlled by fractures striking at 75 to 80° and dipping 50 to 60°S and a second set with the same strike but dipping at 70 to 80°N. Veinlets horsetail from the larger veins, while tuffs contain interstitial disseminations.
The A2 Zone is the root to A1, approximately 300 m east of the latter. It lies within felsic porphyries and takes the form of well defined veins rather than veinlets. In general it has a higher Cu content, with pyrite, chalcopyrite and sphalerite.
The B Zone is some 1 km WNW of A1 and is controlled by a NE (30°) trending fault that dips at 30°SE. Cu and Zn sulphides occur in a zone of quartz-carbonate veining up to 30 m wide in the immediate hangingwall of the fault. Veins are up to 50 cm thick. The upper 100 m of this zone has been subjected to supergene enrichment with chalcocite, digenite, bornite, covellite and native copper, accompanied by limonite and kaolinite. In the primary ore pyrite predominates over chalcopyrite and sphalerite.
Stratabound massive sulphides are also present but economically less significant. Chert and massive pyrite are associated with chert breccia and related rocks, while cherty, carbonate rich pyritic bands are found at the unconformity between felsic tuffs and the overlying andesites. Two such bands occur within the A1 Zone, generally carrying <0.1% Cu, but locally 10 to 300 g/t Ag, 0.5 to 2% Zn and 0.2 to 1.0% Pb.
Past production plus reserves in 1993 were:
A1 Zone: - 23.2 Mt @ 0.68% Cu, 2.25% Zn, 39 g/t Ag, 0.45 g/t Au
A2 Zone: - 2.8 Mt @ 2.78% Cu, 0.92% Zn, 24 g/t Ag, 1.2 g/t Au
B Zone: - 3.9 Mt @ 3.23% Cu, 0.60% Zn, 34 g/t Ag, 1.3 g/t Au
Total - 29.9 Mt @ 1.21% Cu, 1.91% Zn, 37 g/t Ag, 0.63 g/t Au.
For detail see the reference(s) listed below.
The most recent source geological information used to prepare this decription was dated: 1993.
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd. Unauthorised copying, reproduction, storage or dissemination prohibited.
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Selected References:
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Larson J E, Hutchinson R W 1993 - The Selbaie Zn-Cu-Ag deposits, Quebec, Canada: an example of evolution from subaqueous to subaerial volcanism and mineralization in an Archean caldera environment: in Econ. Geol. v88 pp 1460-1482
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Piche M and Jebrak M, 2006 - Determination of alteration facies using the normative mineral alteration index: Selbaie Cu-Zn deposit, northern Abitibi greenstone belt, Canada: in Can. J. Earth Sci. v43 pp 1877-1885
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Porter GeoConsultancy Pty Ltd (PorterGeo) provides access to this database at no charge. It is largely based on scientific papers and reports in the public domain, and was current when the sources consulted were published. While PorterGeo endeavour to ensure the information was accurate at the time of compilation and subsequent updating, PorterGeo, its employees and servants: i). do not warrant, or make any representation regarding the use, or results of the use of the information contained herein as to its correctness, accuracy, currency, or otherwise; and ii). expressly disclaim all liability or responsibility to any person using the information or conclusions contained herein.
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