Sulfur and sulfides in the Cretaceous, magnetite-series granitoids of the Kitakami Mountains, Japan

Abstract

Sulfur content and sulfide minerals were examined on Cretaceous granitoids of the Kitakami Mountains. All but one (Akagane mine stock) belong to the magnetite series. The sulfur content increases with decreasing normative ab+or+qz, indicating that mafic magmas are much capable of dissolving sulfur than felsic magmas. The content goes up also to the following order: (i) calc-alkaline batholith and stock, (ii) alkaline stock and (iii) mineralized stock, especially of the ilmenite series. Sulfides of the magnetite-series rocks are largely pyrite and chalcopyrite, and rarely pyrrhotite. Other sulfides as arseno-pyrite, molybdenite and unidentified minerals, are present only locally. These sulfides may have been re-equilibrated during slow cooling of magmas but are considered ultimately magmatic in origin. Solubility of sulfur in the magnetite-series, calc-alkaline magmas may be as low as 40 ppm at a granodiorite composition, while that of the magnetite-series, alkaline magmas would be higher (_??_200 ppm). Ilmenite-series granodioritic melt of the Akagane mine stock seems to contain even more sulfur (_??_600 ppm). Sulfide mineral assemblage of the stock is the same as that of skarn deposits indicating that sulfur and copper of the ore deposits are largely magmatic in origin.