Abstract

Serial sectioning was carried out on a single sample of oriented pyrrhotite–pentlandite ore from the Durkin Shoot at Kambalda. This permitted the sequential investigation of a number of pyrrhotite properties including grain morphologies, triple-junction angles, grain lattice orientation, microhardness, peak broadening in X-ray diffractograms, and approximate Fe/S ratios of the monoclinic pyrrhotite by microprobe analysis.The present study confirms the presence of previously identified flattened tabular (F) and equant polyhedral (E) pyrrhotite morphologies, and establishes that the E type has recrystallized from the F variety. The latter is composed of subgrain aggregates with C axes that tend to be oriented perpendicular to the pyrrhotite foliation. Formation of the E type pyrrhotite from the F variety involved subgrain rotations, subgrain coalescence, and grain growth. This was accompanied by definite reductions in σ values for triple-junction angles and in microhardness, as well as apparent reductions in X-ray line broadening and Fe/S ratios for the pyrrhotite. The recrystallization is regarded as a late, low-temperature feature of the regionally metamorphosed nickel sulfide ore.

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