The Scadding gold mine, east of the Sudbury igneous complex, Ontario; an OICG-type deposit?

The Scadding mine is only one of several small gold deposits and prospects in the regionally albitized Huronian metasedimentary rocks of the Sudbury-Wanapitei Lake area of Ontario. The locally brecciated, albitized and chloritized metasedimentary rocks that host the Scadding gold deposit have elevated Co, Cu, Ni, Fe, As and REE concentrations, and locally contain a wide variety of REE-rich minerals. Gold occurs as inclusions in pyrite, chalcopyrite and in chlorite. Fluid-inclusion data obtained from mineralized quartz veins indicate that gold was deposited from highly saline hydrothermal fluids (36-38 wt% NaCl) having a temperature range of 340-390 degrees C. These fluid inclusions coexist with other, less abundant primary fluid inclusions of low salinity and comparable temperature. The lack of evidence for phase separation in the saline and dilute inclusions suggests the mixing of brines with dilute meteoric or metamorphic fluids as the possible mechanism for gold precipitation. We propose that Scadding is a modified iron oxide - copper - gold (IOCG) deposit in which Fe sulfides dominate over Fe oxides. Fluctuating Cl/S values in the hydrothermal fluids could explain the relative enrichment of the rocks in pyrite with respect to Ti-poor magnetite and hematite, both of which occur in the chlorite-rich (pyrite-poor) assemblages.