Abstract

The S-rich portion of the Fe-Ni-S system has been investigated between 100 degrees and 1000 degrees C. under equilibrium vapor pressures with especial emphasis on the FeS 2 -NiS 2 join. Pyrite (FeS 2 ) and vaesite (NiS 2 ) coexist between 729 degrees + or - 3 degrees and 137 degrees + or - 6 degrees C. Above this temperature range, a (Fe, Ni) (sub 1-x) S solid solution coexists with S liquid, whereas below 137 degrees C. bravoite [(Fe, Ni)S 2 ] is stable on the join between pyrite and vaesite. The solubility of FeS 2 in vaesite is a maximum of 27.9 wt % at 729 degrees C.; other points on the solvus are 13.5% at 600 degrees C, 6.5% at 500 degrees C, 2.5% at 400 degrees , 0.7% at 300 degrees , and 0.1% at 200 degrees C. The heat of mixing, delta H, is constant at 9.8 kcal/mole. The maximum NiS 2 solubility in pyrite of 7.7 wt % also occurs at 729 degrees C. It decreases to about 6.8% at 700 degrees C. but could not be determined at lower temperatures. When pyrite and vaesite coexist, the vaesite solvus is a useful geothermometer. A determination on material from the Kasompi Mine, Katanga, indicates a formation temperature of 390 degrees C. Bravoite, generally a secondary mineral, can form only below 137 degrees C. C. Most nickeliferous pyrites were deposited at relatively low temperatures where the equilibrium Ni solubility is well below 1%. It is concluded, in the light of the experimental evidence, that most of the Ni occurs in metastable solid solution in these pyrites.

First Page Preview

First page PDF preview
You do not currently have access to this article.