Phase relations in the central portion of the Cu-Fe-Zn-S system between 800.DEG. and 500.DEG.C.

Abstract

Phase equilibrium in the central portion of the Cu–Fe–Zn–S system was studied by the evacuated silica glass tube method, and phase relations involving chalcopyrite, intermediate solid solution(iss), bornite, pyrrhotite and sphalerite have been determined between 800° and 500°C. Besides, compositional fields of each solid solution have been clarified. Chalcopyrite appearing only in experiments at 500°C has very limited solid solution field close to the stoichiometric CuFeS2, and dissolves small amounts of zinc less than 0.9 atm.%. However, iss having an extensive solid solution field dissolves considerable amounts of zinc from 12.7 atm.% at 800°C to 3.3 atm.% at 500°C, and these maximum solubilities of zinc are observed in more iron-rich iss than the cubanite composition at each temperature. Meanwhile, sphalerite solid solution also dissolves considerable amount of copper, and the CuS content in sphalerite increases with that of FeS in sphalerite above 600°C. The maximum observed CuS contents are 10.7 mole % at 800°C, 8.6 mole % at 700°C and 4.6 mole % at 600°C in sphalerite containing higher FeS than 40 mole %. Therefore, entry of copper into sphalerite is dependent upon both temperature and sulfur fugacity.