Geochemistry of hydrothermal fluids associated with intrusion hosted gold mineralization, Yukon Territory

The mid-Cretaceous Tombstone Plutonic Suite in the Yukon and Alaska contains several examples of intrusion-related gold deposits. These include Fort Knox (158.3Mt @ 0.83g/t Au) and Dublin Gulch (50.3Mt @ 0.93g/t Au), in addition to numerous, auriferous, sheeted vein prospects such as Emerald Lake, Scheelite Dome and Mike Lake. Tungsten skarns are also associated with several of the intrusions. The majority of gold mineralization in the belt is hosted by quartz-rich and sulfide-poor veins which invariably occur in nearly vertical, sheeted, east-west orientations. Fluid inclusion analyses of several sheeted vein systems across the belt indicates that low salinity (<10 wt. % NaCl), carbonic fluids are ubiquitous. High salinity fluids (30-40 wt. % NaCl equiv.) are locally common, particularly in shallower systems. Laser raman analysis of vapour bubbles indicates that methane and nitrogen are more abundant in deeper systems, and is the major gaseous phase in tin-tungsten skarns.