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The geology of the Willroy property Manitouwadge Lake, Ontario Chown, Edward Holton Macphail


Manitouwadge, a copper-zinc-silver mining camp, lies 150 miles east of Port Arthur, Ontario, and 25 miles north of Lake Superior. A series of volcanics and sediments, now metamorphosed and migmatized to hornblende schists, quartz feldspar gneisses, and granite gneiss, underlies the Manitouwadge area. These have been folded into an overturned syncline which strikes east-west and plunges gently to the northeast. Three sets of faults are known with at least four periods of movement. The latest of these has offset the mineral deposits and some of the north striking diabase dykes. The two important deposits lie on the south limb of the syncline near the contact between granite and quartz feldspar gneiss. The Willroy property is adjacent to, and immediately west of, the Geco mine. The gneisses on the Willroy property exhibit a complete gradation from quartzite to iron rich hornblende gneiss, and are thought to be sediments that have been metamorphosed to a grade indicated by the amphibolite facies. Detailed mapping and drill hole correlation indicates the presence of several small folds in the east striking formations. All the sulphide deposits occur within individual formations where they are folded. The folds appear to be related to the major deformation, as are numerous pegmatite dykes which cut across the gneisses. The ore occurs in three tabular sulphide replacement bodies, with a strike parallel to that of the enclosing formations. These orebodies plunge to the east at 45 degrees, parallel to the plunge of the folds. The ore consists of pyrite, pyrrhotite, chalcopyrite, sphalerite, galena and tetrahedrite. Silver is present, and is apparently contained in the sulphide minerals. Although precise structural controls are not known, the sulphide deposits of the area all occur adjacent to small folds. Further work in the area might well be concentrated on outlining and prospecting similar structures.

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