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Abstract

The Blende Zn-Pb-Ag deposit is located approximately 75km northeast of Keno Hill, Yukon, within the southern Wernecke Mountains. Epigenetic mineralization is hosted by dolomitic siltstone of the Paleoproterozoic Gillespie Lake Group, the uppermost unit of the Wernecke Supergroup. Sulphides are found as cements in breccias developed in an axial planer cleavage within the hinge zone of a kilometre scale anticline. The sulphide paragenesis consists of three stages of growth. The earliest is pyrite veining with minor sphalerite which have δ 34 S values of +9.4 to +58.1‰. This is crosscut by main stage mineralization consisting of sphalerite and galena with δ 34 S data that ranges from +15.6 to +34.9‰ and a Pb-Pb age of 1.50 to 1.44 Ga, with some pyrite and minor tetrahedrite and chalcopyrite. Coarser euhedral sphalerite and galena make up the late stage of sulphide growth and have isotopic values of +16.3 to +32. 8‰ and a Pb-Pb similar to that of the main stage galenas. The gangue minerals consist of fine to coarse grained dolomite and quartz, and are present in five paragenetic stages. These include the host rock with δ 13 C of 0.0 to +1.0‰ and δ 18 O of +19.7 to +21.6‰. There are two vein sets that predate sulphide mineralization and these have δ 13 C values of 0.0 to +0.5‰ and δ 18 O values of +19.6 to +21.7‰. The main stage veining that accompanies the main stage sulphides has a range in δ 13 C and δ 18O from 0.0 to +0.3‰ and +18.0 to +20.8‰, respectively. Finally, euhedral dolomite that occurs with the late stage sulphide has carbon isotopic data that ranges from -0.5 to + 0.2‰ and δ 18 O from +18.1 to +19.0‰. Evidence suggests a Mesoproterozoic age of mineralization that postdates a Paleoproterozoic deformation event, involves circulation of seawater transporting metals and sulphur, and derived components for the gangue mineralogy from the host dolomitic siltstone.