Mackinawite-bearing Chalcopyrite Dot in Sphalerite: A Breakdown Product of ISS

Abstract

It is well known that mackinawite-bearing chalcopyrite dots occur commonly in sphalerites from some sulfide deposits. Microscopic examination of many polished sections from various ore deposits in Japan and Korea, reveals that the sphalerite with those dots is found only in pyrrhotite-predominant deposits. On the basis of phase relations in the central portion of the Cu-Fe-S system, it is concluded that the dots have originally been intermediate solid solution (iss), and later they broke down to chalcopyrite and mackinawite during the cooling of deposits without the supply of sulfur from outside of the sphalerite. The presence of the dots (called iss dots) in sphalerite could be regarded as a direct evidence for the presence of iss instead of chalcopyrite in the ore before cooling.