Mineralisation at the Carrock Fell Tungsten Mine, N. England: Paragenetic, fluid inclusion and geochemical study

Geochronology (Re–Os and U–Pb) and fluid inclusion studies of molybdenite mineralisation associated with the Shap, Skiddaw and Weardale granites, UK

“…The non-aqueous compositions of mineralising fluids and Re concentrations in molybdenite are consistent with a non-magmatic source for sulphide mineralisation, in contrast to earlier W mineralisation. 3,59 Instead, mineralising fluids extensively interacted with the surrounding country rocks, becoming enriched in isotopically heavy sulphur, N 2 and CH 4 . The elevated non-aqueous component of these fluids (up to 12?5 wt-%) facilitated boiling between 275 and 400uC and at hydrostatic pressures of 375-475 bars.…”

“…Post-dating the latter is sulphide mineralisation (arsenopyrite, pyrite, chalcopyrite, molybdenite, sphalerite, bismuth) that occurs in quartz stringers in fractures of the veins and greisen zones. 3 Calcite¡siderite¡fluorite veining postdates sulphide mineralisation. Small E-W trending quartz-galena-sphalerite veins cross-cut the Carrock Fell mineralisation and are thought to be part of the Caldbeck Fell Pb-Zn systems to the north.…”

“…Acicular zircons, typically 150650650 mm with visible melt inclusions, were preferentially selected in order to avoid crystals with inherited cores. A bulk zircon fraction was annealed at 850uC in quartz glass beakers for 48 h. The zircon crystals were ultrasonically washed in 4 N HNO 3 , rinsed in ultra-pure water, then further washed in warm 4 N HNO 3 before rinsing with distilled water to remove surface contamination. The annealed, cleaned bulk zircon fraction was then chemically abraded in 200 mL 29 N HF and 20 mL 8 N HNO 3 at 180uC for 12 h following a modified chemical abrasion technique to remove portions of grains which have suffered Pb-loss.…”

“…The annealed, cleaned bulk zircon fraction was then chemically abraded in 200 mL 29 N HF and 20 mL 8 N HNO 3 at 180uC for 12 h following a modified chemical abrasion technique to remove portions of grains which have suffered Pb-loss. 42 Chemically abraded zircons were washed several times in ultra-pure water, in warm 3 N HCl for several hours on a hot-plate, rinsed again in ultra-pure water and 8 N HNO 3 and split into single grain fractions ready for dissolution. A mixed 205 Pb-235 U tracer was used to spike all fractions.…”

Silver mineralization at the Vale das Gatas tungsten mine, Portugal

“…Preliminary fluid inclusion data suggest that quartz associated with the formation of the wolframite crystallized at temperatures in excess of 225 ~ This is 25 to 125 ~ lower than pressure uncorrected homogenisation temperatures for tungsten mineralization at the Borralha mine 50 km northwest of Vale das Gatas (Noronha, 1974) and Panasqueira (Bussink, 1984). Bulk salinities fall within the range 2-10 wt.% NaC1 equivalents noted for many other quartzwolframite deposits (Bussink, 1984;Ball et al, 1985;Kelly and Rye, 1979;Bril, 1982). The second episode of laminar textured mineralization occupies reactivated veins and gives generally lower temperatures around 194 ~ Sulphides, including the Ag-bearing sulphides, appear to be associated with both episodes of metalliferous mineralization.…”