Sulfide Solubilities in Buffered Systems from 400 to 600°C and 0.5 to 2 Kb and Depositional Implications

Abstract

Experimental studies have been conducted on the solubility of iron and other base metal sulfides in chloride solutions equilibrated with a synthetic quartz monzonite plus assemblages in the Fe-Cu-S-O system. Extraction vessel and cold-seal techniques were used. Most experimentation was on the pyrrhotite-pyrite-magnetite buffer for fixing fS₂ and fO₂, but K feldspar-muscovite-quartz controlled hydrogen ion activity in all cases. At 1 m total chloride and 1 kb, iron concentrations in a system containing only Fe as the base metal were 1,000 ± 150, 7,000 ± 700, 12,400 ± 1,000 and 14,000 ± 1,200 ppm at 400, 500, 600, and 700°C respectively. At 500°C different Cl₋ concentrations, pressures, and additional buffers in the Fe-Cu-S-O system were investigated. Pb and Zn concentrations at 500°C and 1 kb on po-py-mt in a system containing galena, sphalerite, molybdenite, silver sulfide and chalcopyrite, were both about 2,450 ± 500 ppm, and Fe was decreased to about 4,100 ppm. Cu, Mo and Ag were present in very low to trace concentrations, on the order of 10 to 100 ppm. Major controls on mineral solubilities are total chloride and pressure, as well as temperature. Although the data show considerable variation, at 2 m Cl₋, 500°C and 1 kb, Fe concentration is increased to approximately 20,000 ppm in the pure Fe system. Similarly, at 1 m Cl and 2 kb it is decreased to about 1,700 ppm and at 0.5 kb it is increased to about 14,000 ppm. Similar relations were observed for Pb and Zn.