Abstract

Carbonate-hosted Pb and Zn mineralization in the Quesnel Lake district (Flipper Creek, Dolomite Flats, Main, Gunn, and Que deposits) forms an ~8-km-long belt in metasedimentary and metavolcanic rocks of the Cariboo terrane, a displaced piece of the ancestral North American margin. The mineralization is strata-bound, dolostone hosted, and consists of Pb- and Zn-bearing sulfide and nonsulfide minerals. The supergene nonsulfides mimic the morphology of preexisting sulfides occurring as disseminations, veins, and fracture fillings, and irregular replacement zones in the Neoproterozoic to Upper Cambrian dolostones of the Cunningham Formation. The main sulfides are galena, sphalerite, and minor amounts of pyrite, which have been partially or completely transformed into nonsulfide minerals by supergene processes. The main nonsulfide minerals are smithsonite [ZnCO3] and hemimorphite [Zn4Si2O7(OH)2⋅(H2O)], with variable amounts of cerussite [PbCO3], anglesite [PbSO4], hydrozincite [Zn5(CO3)2(OH)6], and iron oxides.

The δ18OVSMOW, δ13CVPDB, and 87Sr/86Sr values of the nonmineralized and mineralized dolostones are indistinguishable and consistent with the composition of carbonates that underwent postdepositional recrystallization and isotopic reequilibration during deep burial fluid-rock interaction. The δ18OVSMOW and δ13CVPDB values range from 17.4 to 20‰ and −0.8 to +1.4‰, respectively, and 87Sr/86Sr values are above 0.71048. Carbon and oxygen ratios of smithsonite show a limited range of values, which are slightly lower than those of the host dolostones with δ18OVSMOW values of 16.9 to 17.8‰ and δ13CVPDB values of −1.6 to −0.9‰. The carbon isotope values suggest that the host dolostones are the carbon source for smithsonite. The δ18O smithsonite values are lower than typical values for nonsulfides formed under warm, humid, and arid-to-hyperarid climates elsewhere in the world. The precipitation temperatures derived from the isotope data for the Quesnel Lake smithsonite vary between 9° and 33°C. This temperature range is favorable for supergene smithsonite formation.

For most deposits of the Quesnel Lake district examined in this study, close spatial relationships (including textures and morphological similarities) between sulfide and nonsulfide zones, coexisting sulfide-nonsulfide assemblages, and stable oxygen and carbon isotope data suggest that the oxidation of sulfides occurred after the Laramide orogeny (<55 Ma), during intervals when the climate was relatively warm. Several periods of warm temperatures during the Eocene, early Oligocene, early to middle Miocene, and Holocene may have been favorable for the supergene oxidation of sulfides and the formation of nonsulfides. This process may be ongoing today. The occurrence of nonsulfides in northern latitudes has been poorly documented in the past. This paper raises awareness about the presence of carbonate-hosted nonsulfide Pb-Zn deposits in the northern Cordillera and their potential as a source of zinc.

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