The Estrades is a 2.68-million- ton mineral inve ntory of base metal- and precious metal- bearing volcanogenic massive sulphides. Located about 150 km north of Rouyn-Noranda, Que., and 26 km east of the Inco/Golden Knight Golden Pond deposits (NMM, December/86) in the northwest corner of Estrades Twp., the deposit grades 0.13 oz gold and 3.13 oz silver per ton, 7.39% zinc and 0.85% copper. It is east-west-striking with a length of 1,500 m and a thickness ranging from 0.5-8 m and has been drilled to a depth of 640 m. The dip varies from steep-northerly near surface to vertical to steep-southerly at depth. Discovery of the Golden Pond deposit by Inco Ltd. in 1981 triggered extensive staking in the Casa Berardi area. Claims in Estrades Twp. were staked by the Noramco group to cover airborne geophysical anomalies detected by the Quebec government- sponsored input survey. In 1984 Teck Corp. formed an agreement with Golden Group Explorations and Golden Hope Resources to provide technical and managerial expertise on their large blocks of claims, with Golden Group and Golden Hope to provide the exploration funds. Teck, by completing a feasibility study and incurring expenditures equal to that which has been spent on the property prior to the feasibility study, can earn a 50% interest. Golden Group and Golden Hope would retain a 30% and 20% interest respectively.
Detailed surface exploration of the properties began in 1984 with coverage by magnetic and max-min ii surveys. Geochemistry of basal till was examined through sampling more than 300 overburden drill holes, but no significant base metal or precious metal anomalies were detected. Diamond drill holes were spotted on the basis of geophysical anomalies. In November, 1985, diamond drill hole No 3 was commenced to test the max- min ii response over an airborne input anomaly. Core from this hole assayed 0.2 oz gold per ton, 9 oz silver per ton, 3% copper and 15% zinc over 10.7 m.
Most of the Casa Berardi greenstone belt is covered by a thick mantle of glacial till with lack of outcrop hindering geological interpretation. Regional geology is dominated by an east-west-striking sequence of clastic sedimentary rocks alternating with intermediate to mafic volcanic flows and pyroclastic rocks and graphitic, sulphidic and cherty exhalites.
The stratigraphic sequence at the Estrades deposit, from south to north, consists of felsic volcanic rock; a thin unit of sedimentary rock; a thick unit of intermediate to mafic volcanic rock; a second felsic volcanic unit which hosts the deposit; and mafic to intermediate volcanic rock. This sequence averages 500 m in width and is cut by a west-northwest-striking fault which dips 60 – 70 degrees west and offsets the eastern part southward about 150 m. All rocks are intruded by a mafic dike which is, in part, implaced within the fault. The stratigraphic sequence is interpreted to face south. All rocks are metamorphosed to the greenschist facies and are foliated parallel to the regional strike.
The deposit is a lenticular body of massive sulphide within strongly foliated quartz-sericite schist. The massive sulphide is confined to five distinct lenses which have a near-vertical plunge and are open to depth. A 10-20-m-thick stringer zone consisting predominantly of chalcopyrite exists on the north side of the massive sulphides. Sulphide minerals, in order of abundance, consist of pyrite, sphalerite and chalcopyrite, minor galena and pyrrhotite. Less common sulphide minerals include arsenopyrite, tetrahedrite and its silver-rich variety freibergite. A variety of secondary copper sulphides and copper-silver sulphosalts and seleno-sulphides and native bismuth have been identified. The sulphide minerals exhibit a fragmental texture.
Most of the gold is within the massive sulphide and, to a lesser extent, in quartz-sericite schist adjacent to massive sulphide. The quartz-sericite schist which hosts the ore horizon is depleted in sodium and enriched in magnesium relative to felsic volcanic rocks of the region.
Drilling of the main Casa Berardi horizon, which strikes east-west across the northeastern part of the property, has indicated pyrite, arsenopyrite and some anomalous gold values. Pamela Phillips is a Toronto-based consulting geologist. For the information, she would like to thank Teck Corp. — in particular P. J. Dillon and Dr Matthew Blecha.
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