Investigation of a Pb-Ag-Au-rich hangingwall in lens 4 of the Chisel North mine, Snow Lake, Manitoba (NTS 63K16): preliminary results

Preliminary petrographic and electron microprobe study of mineralized samples collected from the Pb-AgAu–enriched hangingwall of lens 4 in the Chisel North mine was undertaken in order to characterize the setting of the mineralization, study the effect of metamorphism and evaluate possible structural controls. The hostrock is a medium-grained garnet-bearing amphibolite with disseminated arsenopyrite and galena-rich veinlets. The petrographic examination indicates that there is likely no paragenetic relationship between arsenopyrite and gold. Galena veinlets are characterized by complex intergrowth and replacement textures between galena and various sulphosalts. The sulphosalts are the main Ag-bearing phase and native Au is commonly found as inclusions or in contact with Ag-rich sulphosalts. The observation of common minute inclusions of native gold along late, galena-rich veins is indicative of a late emplacement of the Au mineralization; however, rare inclusions of sulphide and Au in garnet or amphibole porphyroblasts suggest that the hangingwall was enriched in Pb-Ag-Au prior to attainment of peak metamorphic conditions. Although most of the Au mineralization occurs in association with late sulphide veinlets, the presence Au-sulphide inclusions in porphyroblasts suggests that the actual mineralization is the result of remobilization of an earlier Au generation.