Experimental study of the partitioning of Cu, Ag, Au, Mo and W among pyrrhotite and immiscible Fe-S-O and silicate melts

Abstract

Partition coefficients have been determined for several transition metals amongst a rhyolitic silicate melt, pyrrhotite, and an immiscible Fe-S-O melt. Two sets of experiments were performed in sealed silica tubes at 1035°C-1045°C, FMQ-NNO O2, and logS2 ~1 bar, and analyzed by EMPA and LA-ICP-MS. Experiments yielded D^Fe-S-O/melt ±1σ(mean) for Au =300±100, Ag =120±20, Cu >200, Mo =90±10 and W =9±3, and D^po/melt for Au =120±50, Ag =58±8, Cu >200, Mo =35±3 and W =1.2±0.6x10-3. Some preliminary data are also presented on the partitioning of Si, Ti, V, Co, Zn, Re, Th and U. Modeling predicts the loss to a daughter melt of up to 50% of the initial Au, >37% Cu, 24% Ag, 19% Mo, and 2% W when Fe-S-O melts are removed with other cumulate phases during fractionation. This would reduce the metal available to potential intrusion-related hydrothermal ore deposits.