Fluid inclusion and oxygen isotope studies of high-grade quartz-scheelite veins, Cantung mine, Northwest Territories, Canada: Products of a late-stage magmatic-hydrothermal event

High-grade quartz-scheelite veins (up to 3.7 wt. % WO3) in the Open Pit orebody of the Cantung mine, Tungsten, NWT occur 300 m vertically above a Cambrian limestone-Cretaceous monzogranite contact along which the E-Zone orebody, a world-class tungsten skarn, is developed. The trend of the 80 m wide quartz-scheelite vein swarm is nearly parallel to the strike and dip of a near-vertical aplite dike along the edge of the Open Pit. Adjacent to these quartz-scheelite veins, dark green alteration selvedges overprint earlier light green skarn alteration, indicating that the high-grade quartz-scheelite veins are not part of the early skarn-forming event, but represent a distinct, later event.; Oxygen isotope data from quartz-scheelite pairs yield equilibrium temperatures of 430° to 595°C. These temperatures indicate that the quartz-scheelite veins are related to a deep magmatic-hydrothermal system and are likely a distal expression of a protracted skarn-forming event, perhaps related to aplite dike emplacement. Quartz-scheelite veins did not form in a shallower, cooler, hydrothermal system during uplift.; Primary ore fluids in quartz-scheelite veins from the Open Pit orebody, in skarn-related quartz veins from the E-Zone skarn orebody, and in aplite dikes are grossly similar H2O-CO2-NaCl+/-CH 4 fluids. However, two distinct end-member fluids have been documented: aplite-related fluids and skarn-related fluids. Fluids in high-grade quartz-scheelite veins contain components of both end-member fluids. Fluids in veins from the Open Pit orebody contain an aplite-related fluid end-member even when occurring up to 70 meters from the nearest exposed aplite dike. Thus, quartz-scheelite veins and aplite dikes in the Open Pit orebody may have a genetic relationship in addition to their structural relationship.; I envision a conceptual model for the Cantung hydrothermal system in which ore-grade tungsten deposits formed where fluids emerged from the granite and encountered rocks favorable for skarn development (e.g. cleaner 'Ore Limestone' versus cherty 'Swiss Cheese Limestone'). Due to the folded geometry of the sedimentary sequence in other areas along the granite contact, fluids emerging from the granite encountered strata less favorable to skarn development (i.e. argillite). Where these less favorable units were breached by fracture systems, potential skarn-forming fluids (and aplite dikes) gained access to host rocks more conducive to ore development vertically distal to the granite contact. The presence of magmatic ore fluids distal to intrusions is intriguing and has significant implications for mineral resource assessment in the region.