H. Falck– Northwest Territories Geological Survey, Yellowknife, NT, Canada
At the Salkeld Lake (Nonacho Basin, NWT) showing, stockwork- and shear-style Cu-Ag±Mo-Pb-Zn mineralization cross-cuts quartz-rich granitic gneiss, quartzite and alkali feldspar granite. Three mineralized variants occur: (i) disseminated/fracture-hosted chalcopyrite; (ii) massive quartz veins containing bornite (up to ~8 wt% Ag)-chalcocite-chalcopyrite (up to ~3 wt% Ag)-calcite vug infillings; (iii) sulfide-quartz breccias containing Cd-rich (up to ~1 wt%) sphalerite, galena, bornite, and chalcopyrite. Sulphide precipitation was accompanied by epidote-muscovite-(adularia-carbonate) alteration (i.e., propylitic-like). Hot-cathode CL imaging shows three generations of quartz: (i) early magmatic or high grade metamorphic (basement host rock-related); (ii) pre-mineralization, vein-related, replacing or brecciating type (i) quartz; (ii) syn-mineralization fracture- and breccia-associated, postdating type (ii). Fluid inclusion analysis reveals three types of inclusions: (i) aqueous, vapour-rich (Vaq; at room T) linked to type (iii) quartz and mineralization; (ii) early (?) aqueous, two-phase (Laq+V) and (iii) early (?) aqueous-carbonic (CO2±N2) two- or three-phase (Laq+Lcarb±Vcarb). Type (ii) fluid has variably low salinity (0.7-6.2 wt% NaCleq) with minimum Ttrapping between 160°C to 350°C. Type (iii) fluid is low salinity (6.6-7.5 wt% NaCleq) with minimum Ttrapping between 290°C and 300°C. Tentatively, the data are consistent with an intrusion-related system formed as a result of decompression and mixing with meteoric water, distinct from other mineralization styles in the basin.