The property, which consists of 19 patented and seven unpatented claims, lies in the northeastern limb of the east-west-striking, 65 degrees north-dipping, Archean-age, Mishibishu Lake greenstone belt of metamorphosed volcanic and sedimentary rocks. The rocks are intruded by felsic stocks and batholiths, as well as diabase dykes and sills. The greenstone belt, about 34 miles long, 10 miles wide, and convex to the north, is folded into an isoclinal synform with an east-west-trending axis. Both parallel and transverse faults, with varying degrees of movement, cut the rocks.
From north to south, the south- facing stratigraphic sequence consists of mafic volcanic rock with minor iron formation, quartz-sericite schist with auriferous quartz veins in the Main shear zone, quartz grit and conglomerate with minor mafic volcanic rock. The sequence is intruded by the Mishibishu Lake granitic stock and diabase dykes and metamorphosed to the greenschist facies. The rocks strike east-west and dip approximately 65 degrees to the north.
The mineralization occurs predominantly in two quartz veins, termed the Main and South vein structures, which lie within the quartz-sericite schist in the Main shear zone. The two quartz veins cross-cut the stratigraphy at 20 degrees and plunge 35 degrees to the east. The Main vein structure, which is more than 2,000 ft in strike length, varies from 6 to 8 ft in true width and dips 70 degrees to the north. The South vein structure, a splay off the Main vein structure, extends for 600 ft, and varies in width from 8 to 12 ft.
Where the two vein structures merge, the mineralized area exceeds 35 ft in true width. Late stage, northwest-trending faults are common and displace the vein structures a distance of 1 to 3 ft. The vein structures are open both along strike and down dip.
Gold is free milling and occurs mainly in the native state. It also is associated with pyrite and arsenopyrite on fracture planes. The Main vein structure is generally lower-grade than the South vein structure and has 5% sulphide minerals, of which galena and arsenopyrite constitute 80%, pyrite 15%, and chalcopyrite and sphalerite trace amounts. Visible gold is more prominent in the Main than in the South vein structure.
Gold in the South vein structure is very fine-grained. Galena, arsenopyrite, pyrite and minor chalcopyrite and sphalerite, in decreasing order of abundance, constitute 2% to 5% of the rock and occur primarily as disseminations and as mattes and clots within the quartz. Gold also occurs in the quartz-sericite schist wallrock.
Alteration surrounding the auriferous quartz veins consists of pervasive silicification and sericitization, albitization, carbonatization and chloritization. Minor tourmaline occurs within the quartz veins.
The Magnacon mine started production in June, 1989, and now is milling a blend of approximately 80% stockpiled development muck and 20% underground ore. Muscocho expects to be near full production at 600 tons per day of underground ore by mid-October, 1989. The orebody is accessible by a 10×16-ft ramp and ore is trucked to surface and treated in the cyanide-leach zinc-precipitation gold mill on-site. Pamela Phillips is a geologist and project co-ordinator for Greenstone Resourc es. She would like to thank Muscocho Explorations for its assistance — in particular, K. Sutherland, P. Mordaunt, and C. McAleenan. lion
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