Indicator minerals for magmatic sulfide mineralisation

Summary

Small conduit or chonolith style intrusions dominated by olivine- and pyroxene-rich cumulates are well known to be favourable hosts to magmatic Ni-Cu-(PGE) sulfide mineralization. In many cases, such mineralization is closely associated with partially assimilated country rock xenoliths, volatile-enriched vari-textured or taxitic rocks and other evidence for assimilation of country rocks. We used the technique of microbeam XRF element mapping along with LA-ICP-MS to reveal other distinctive features and chemistries of a number of diverse mineralized small intrusions: transient saturation in Cr-rich spinel; complex zoning patterns of Cr in cumulus and poikilitic pyroxenes, and occasional development of dendritic growth textures in olivine. We further suggest that these features are indicative of dynamic assimilation of conduit wall rocks accompanied by rapid, disequilibrium fluctuations in silica content and redox state, and that these features may be if not diagnostic then at least indicative of Ni-Cu sulfide mineral potential in magmatic conduit systems.

• chromite
• spinel
• pyroxene
• LA-ICP-MS
• Synchrotron