Abstract

Interspinifex ores are developed where pools of sulfide liquid overlie thermally eroded komatiite flows, such that sulfide occupies the space between spinifex olivine plates. Microbeam X-ray fluorescence mapping and 3-D X-ray computed tomography have been used to investigate microstructures and chemical zonation within interspinifex ores from Coronet shoot, Kambalda. Sulfide compositions in the interspinifex space match the composition of the overlying sulfide pool. Aluminous silicate, interpreted as displaced silicate melt, forms a film at the silicate-sulfide interface, locally developing dome-like plumes. The film and plumes are characterized by fine skeletal chromite that diminishes in abundance over about a decimeter downward into the interspinifex zone. These relationships are strong evidence for a primary magmatic origin for this ore type, driven by the strong tendency of dense, inviscid sulfide liquid to infiltrate and melt underlying rocks. Such infiltration-melting interfaces may be a common feature at the base of massive sulfide ores, taking different forms depending on the lithological and fracturing characteristics of the footwall rocks.

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