Supra-subduction zone ophiolites as favorable hosts for chromitite, platinum and massive sulfide deposits

Abstract

Supra-subduction zone ophiolites, as exemplified by the Zambales Ophiolite Complex, host extensive chromitite, volcanic-hosted massive sulfide deposits and, to a lesser degree, platinum-group minerals. In contrast, mid-ocean ridge basalt ophiolites are almost barren of economic mineral deposits. The high degree of partial melting, high water pressure, changes in oxygen fugacity, temperature, pressure and magma mixing could explain the chromitite deposits in zupra-subduction zone ophiolites. Platinum-group minerals are modeled to be derived from multi-stage melting events that also characterize supra-subduction zone ophiolites. The presence of capping rocks and the tectonics of emplacement are believed to be critical in the preservation of volcanic-hosted massive sulfides in ophiolites. Marginal basins (= SSZ ophiolites) are more easily emplaced than the large, open sea oceanic basin ophiolites which are usually subducted. Geochemical and tectonic controls point to supra-subduction zone ophiolites as more promising exploration targets.