Abstract

Molybdenite from the Voznesensk porphyry Cu ± (Mo,Au) deposit, southern Urals, Russia, displays high Re content and a well-documented oscillatory zoning for this mineral. The molybdenite forms part of a quartz-molybdenite-pyrite-chalcopyrite assemblage cemented at low-temperatures by pumpellyite and tobermorite. Oscillatory zoning occurs as micro-bands up to 200 μm wide and 200–600 μm long oriented parallel to the basal cleavage, as well as within basal planes of molybdenite sheets. The micro-bands are Re-enriched to different degrees (0.3–1.0 wt.%, typically they contain 0.6–0.8 wt.% Re). Outside these structures the Re content in molybdenite is up to 0.25 wt.%, usually <0.10–0.15 wt.%. It is suggested that the Re in the Voznesensk molybdenite retains its original growth pattern, marked by sharp concentration variations, and is not the result of leaching through post-crystallization diffusion. Variations in the number, width, and Re-content in individual micro-zones observed within the oscillatory zones may suggest involvement of extrinsic mechanisms of micro-zone formation. However, the Re content of the Voznesensk molybdenite (ICP-MS and EPMA data) is almost uniform along the studied vertical and lateral interval of the mineralization, suggesting no major variation in Re concentration in the fluid and favoring uniform, self-organization processes causing Re enrichment and oscillatory zoning in molybdenite. Despite the strong degree of epigenetic post-crystallization deformation of the molybdenite flakes and their cementation by low-temperature tobermorite, there is no essential change of the primary micro-zoning in the distribution of Re and any evidence of its epigenetic migration.

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