Abundances of platinum group elements in native sulfur condensates from the Niuatahi-Motutahi submarine volcano, Tonga rear arc: Implications for PGE mineralization in porphyry deposits

Abstract

Some porphyry Cu-Au deposits, which are enriched in Pd, are potentially an importantsource of Pd. Magmatic volatile phases are thought to transport the platinum group elements(PGEs) from the porphyry source magma to the point of deposition. However, the compatibilitiesof the PGEs in magmatic volatile phases are poorly constrained. We report PGE and Reconcentrations in native sulfur and associated altered dacites from the Niuatahi-Motutahi volcano,Tonga rear arc, in order to determine the compatibility of PGEs and Re in magmaticvolatile phases, and their mobility during secondary hydrothermal alteration. The native sulfurwe analyzed is the condensate of a magmatic gas exsolved from the Niuatahi-Motutahimagma. The PGE concentrations are moderately enriched in the sulfur in comparison to theassociated fresh dacite, with enrichment factors (EF) of 4-105, whereas Au, Cu and Re arestrongly enriched with EFs of ~7500, ~2000 and ~300 respectively. The compatibility of thePGEs into magmatic volatile phases is therefore significantly lower than it is for Au, Cu andRe. The compatibility of PGEs decrease in the order: Ru > Pt > Ir > Pd. This trend is alsoobserved in condensates and sublimates from other localities.ion. However, the compatibilitiesof the PGEs in magmatic volatile phases are poorly constrained. We report PGE and Reconcentrations in native sulfur and associated altered dacites from the Niuatahi-Motutahi volcano,Tonga rear arc, in order to determine the compatibility of PGEs and Re in magmaticvolatile phases, and their mobility during secondary hydrothermal alteration. The native sulfurwe analyzed is the condensate of a magmatic gas exsolved from the Niuatahi-Motutahimagma. The PGE concentrations are moderately enriched in the sulfur in comparison to theassociated fresh dacite, with enrichment factors (EF) of 4-105, whereas Au, Cu and Re arestrongly enriched with EFs of ~7500, ~2000 and ~300 respectively. The compatibility of thePGEs into magmatic volatile phases is therefore significantly lower than it is for Au, Cu andRe. The compatibility of PGEs decrease in the order: Ru > Pt > Ir > Pd. This trend is alsoobserved in condensates and sublimates from other localities.