Fluid inclusion gas studies,carrock fell tungsten deposit,england: implications for regional exploration

A fluid inclusion investigation of the Carrock Fell tungsten deposit, Northern England, confirms that the quartz-wolframite-scheelite veins associated with the Caledonian Skiddaw Granite are almost exclusively related to an exocontact hydrothermal system developed at the margin of a local cupola. Fluid circulation, as defined by the spatial variation in temperature and H₂O/CO₂ ratios for inclusions in vein quartz, reveals a strong structural control. The zone of maximum flow, which extends 0–400 m out from the granite contact, is characterised by high H₂O/CO₂ ratios and corresponds closely with the known distribution of high-grade oreshoots. Based on the fluid inclusion gas signature for the Carrock Fell deposit, a distinction can be made between potentially tungstaniferous quartz veins and those related to Cu-Pb-Zn deposits in the absence of diagnostic ore minerals. Also, a regional survey of quartz veins in the Lake District suggests that at several localities the fluids have a close affinity with those at Carrock Fell. This is interpreted as the high-level, distal expression of tungsten mineralisation at depth. Evidence for similar mineralisation elsewhere in the British Caledonides favours those granites in the paratectonic zones of Ireland and southern Scotland.