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St Eugene |
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British Columbia, Canada |
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Ag Pb Zn
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Super Porphyry Cu and Au
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The St Eugene silver, lead zinc deposit is located near Moyie, in the Purcell Mountains of southeastern British Columbia, Canada. It was discovered in 1893 and worked intermittently between 1895 and 1925 and was the first of the Cominco's mine.
The deposit is interpreted to be a hydrothermal vein developed within the (Belt)/Purcell Supergroup and metamorphosed in the 1.35 to 1.3 Ga East Kootenay orogeny. The vein is surrounded by a hydrothermal metasomatic alteration halo. Three other veins are considered to be extensions of the St. Eugene vein. These are the Society Girl deposit to the east and the Aurora and Guindon deposits to the west.
These vein systems cut the middle and upper members of the Aldridge Formation (cut by the 1468 Ma tholeiitic Moyie sill complex) and the overlying Creston Formation. These units are part of the Belt / Purcell Supergroup, described in the records of the Sullivan Zn-Pb deposit in British Columbia, Canada and the Coeur d Alene District deposits in Idaho, USA, which are hosted by the same sequence.
The St. Eugene vein system has a strike length of 3300 m and vertical extent of 1300 m. It occupies two parallel fault zones striking at 110° and dipping at 65° SW which are perpendicular to the axial plane of the Moyie anticline. These faults are linked by a series of cymoidal veins striking at 55° and dipping at 10 to 20° SE. The northern fault hosts the most productive zones with veins segments up to 10 m thick containing one or more bands or lenses of massive galena up to 1.3 m thick.
The St. Eugene vein system is surrounded by a symmetrical zoned halo of alteration zones subdivided into four facies separated by gradational contacts, comprising the: i). garnet-chlorite zone, composed of disseminated chlorite (<25%), garnet (5 to 25%), tschermakite (<2%) and sulphides (<5%); ii). internal zone, which is is <10 m thick and consists of disseminated muscovite (25%) and chlorite (<5%), cut by quartz-chlorite veins; iii). intermediate zone, which is <16 m thick and is characterised by disseminated chlorite (<5%) and biotite (10 to 20%) in wall rock cut by quartz-chlorite±biotite veins; and iv). external zone characterised by disseminated calcite (<2%).
The ore comprised galena and sphalerite with variable amounts of pyrite, pyrrhotite, chalcopyrite and silver sulfosalts, such as tetrahedrite, freibergite, and pyrargyrite, in a gangue of quartz. Calcite occurred locally with quartz.
The alteration and mineralisation is similar to that at Coeur d'Alene.
Between 1895 and 1929 production totalled (Joncas and Beaudoin, 2002):
1.48 Mt of ore at and average grade of 7.6% Pb, 1% Zn, 123 g/t Ag, 0.05 g/t Au, for
113 300 t Pb, 14 480 t Zn, 182.69 t Ag and 0.079 kg Au (Jonacs & Beaudoin, 2002).
Other sources quote a figure of 1 Mt @ 200 g/t Ag, 5% Zn, 15% Pb (Belluz & Knapp, 1994).
For more detail consult the reference(s) listed below.
The most recent source geological information used to prepare this decription was dated: 2002.
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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Jonacs I, Beaudoin G 2002 - The St. Eugene Deposit, British Columbia: a metamorphosed Ag-Pb-Zn vein in Proterozoic belt - Purcell Rocks: in Econ. Geol. v97 pp 11-22
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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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