Comparative ore mineralogy and mineral chemistry of VMS deposits from the Snow Lake area (Manitoba, Canada)

The ore mineralogy of five VMS deposits (Photo Lake, Osborne Lake, Ghost Lake, Stall Lake, and the previously studied Chisel Lake) from the Paleoproterozoic Snow Lake arc assemblage (Manitoba, Canada) was compared in an attempt to define any systematic trends, and possibly understand the ore mineralogy controlling factors. Optical microscopy, scanning electron microscopy, and electron microprobe analyses were used to characterize the ore mineralogy of these deposits, both of the main minerals always present (pyrite, pyrrhotite, sphalerite, chalcopyrite, and galena), and the large variety of minerals present in trace amounts. A significant variation in the abundance of the main sulfide minerals was observed between the five deposits, despite them having very similar host rocks and being of the same age and deposit type, from sphalerite-dominated (Ghost Lake) and pyrite-sphalerite-dominated (Chisel Lake), to pyrrhotite-chalcopyrite-dominated (Stall Lake) and pyrite-dominated (Osborne Lake). Chalcopyrite Considering the five deposits studied, chalcopyrite varies between 7 and 25 vol%, sphalerite between 5 and 45 vol.%, and galena from absent to 4 vol.%. Chalcopyrite and galena have typical chemical compositions; the degree of Fe replacement of Zn in sphalerite (between 6.4 and 7.9 wt%) allowed the estimation of a crystallization temperature of approximately 320°C, consistent across the deposits except for Photo Lake (~340°C). A significant variation between the five deposits was also observed for minerals present in trace amounts (mostly sulfides, but also oxides, and tellurides, with a significant Bi paragenesis for some of the deposits).