Unconventional Deposite of Pt and Pd: A Review with Implications for Exploration

ABSTRACT In this paper we review potential “unconventional” (i.e., amagmatic) sources of Pt and Pd. We list several geological environments in which Pt and Pd have been concentrated to economic grades (if not tonnages). One is intracratonic rifts where hot oxidized brines are generated by surface evaporation and/or halite dissolution and circulate to depth through a preponderance of oxidized lithologies. Pt and Pd occur with U or Cu and with minor Au. Second is deformed passive margin sequences rich in carbonaceous metasedimentary rocks where Pt and Pd occur with Au or Ni and Mo. Hydrothermal fluids in this environment are most likely to be relatively reduced and obtain sulfur for transport of PGE as bisulfıde complexes from the pyritic and carbonaceous host rocks. Third are surface environments where oxidized low-salinity waters, buffered by atmospheric oxygen, interact with Pt- and Pd-enriched source rocks such as ophiolitic ultramafıc rocks. In the known deposits, Pt and Pd are potential byproducts to Au, Cu, Ni, Mo, or U. A low-risk exploration strategy is to recognize potential for Pt and Pd enrichment in similar deposits. A high-risk exploration strategy acknowledges the possibility that Pt and Pd may be offset, or even remote from the other metal concentrations and may be a primary exploration target. Reactive transport modeling is suggested as a predictive exploration tool.