Rhenium distribution in molybdenite from the Vosnesensk porphyry Cu ± (Mo,Au) deposit (Southern Urals, Russia)

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, selforganization 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