Experimental Study on Cu-Fe-S Minerals (1st Report)

Application of EPMA to Synthetic Products

Abstract

The phase relations in the system Cu-Fe-S, especially the one among chalcopyrite, cubanite and pyrrhotite, were studie at temperatures of 600°, 700° and 800°C by synthesis using the rigid silica glass tube method.The total composition of samples was selected as it ranges on the line which connects CuFeS₂ and FeS.Electron probe microanalysis was applied for the determination of the composition of synthetic products, especially for that of the phase boundaries of chalcopyrite and pyrrhotite solid solutions. The following results were obtained.(1) The complete solid solution between chalcopyrite and pyrrhotite would not be formed even above 800° at the present experimental condition, because the region of pyrrhotite solid solution extends to the sulfer-rich direction while that of chalcopyrite solid solution retreats to the copper-rich side at temperatures above 600°.(2) The most iron-rich end of the chalcopyrite solid solution shifts from the slightly iron-rich composition to the iron-poor one than cubanite when the tethperature of synthesis rises from 600° to 800°, though the boundary of the region was unable to determine precisely by EPMA.(3) Pyrrhotite can contain Cu approximately 2.5 wt.% at 600°C, 4% at 700°C and 6% at 800°C.(4) Some causes of error at the analysis of composition by EPMA are discussed briefly.