Abstract

The Nigadoo deposit is a telescoped vein at and near the margin of an epizonal quartz-feldspar porphyry body. The vein minerals are coarse-grained and consist mainly of pyrrhotite, pyrite, sphalerite, galena, chalcopyrite, arsenopyrite, and stannite in a multi-generation calcite gangue. The Fe content of sphalerite suggests a temperature of formation of 670 degrees C., which contrasts with the obvious low-metamorphic rank of the wall-rocks. The B. M. and S. No. 6 deposit, consisting essentially of pyrite with galena and sphalerite, is a large, lenticular, massive, fine-grained replacement in greenschist wall-rocks. Along the footwall an adjoining zone contains pyrrhotite, chalcopyrite, and a little sphalerite and galena. In general the Fe content of the sphalerite is higher where it occurs with pyrrhotite than where it accompanies pyrite, but details of spatial and compositional variation suggest that the relationships are considerably more complex. Sphalerite compositions suggest a maximum temperature of formation near 480 degrees C. which would exceed the suggested upper limit of the greenschist facies by about 250 degrees C. The writer believes that the temperature data proves that both deposits are of epigenetic origin.

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