The opaque minerals and economic geology of the nemeiben ultramafic complex, saskatchewan, canada

Abstract

The main rock types of the Nemeiben ultramafic complex form grossly concentric layers of clinopyroxenite, websterite, wehrlite and dunite. These rocks were partially amphibolitized late in the Hudsonian orogeny; consequently numerous relict primary textural and mineralogical features are preserved. Disseminated primary magmatic nickeliferous pyrrhotite, pentlandite, chalcopyrite, magnetite and chromite occur throughout this complex and local concentrations of sulfides occur. Textures, mineralogy and chemistry of these phases are indicative of a high temperature magmatic origin. Unmixing phenomena in pyrrhotite are attributable to post crystallization dissociation of a high temperature Fe-Ni-Cu-Co monosulfide solid solution. A secondary assemblage of fine-grained iron oxides, sulfides and native metals developed in altered ultramafic rocks. Magnetite and hematite, bravoite, violarite and millerite are among the minerals formed during serpentinization. Trace amounts of nickeliferous copper, native gold and silver occur in hematite veinlets and at the center of hematized former sulfide grains. Supergene alteration has affected most of the sulfides. Thus the most plausible explanation of the opaque minerals is that they represent a metamorphosed primary magmatic assemblage modified by supergene alteration.