OXYGEN AND CARBON ISOTOPIC COMPOSITION OF CARBONATES FROM PINE POINT LEAD-ZINC ORE DEPOSITS

The cycle of mineralization at Pine Point is characterized by the formation of dolomite followed by the deposition of the lead-zinc nfinerals and the precipitation of calcite. The temperature of formation of these minerals was never much over 100° C and decreased slowly towards the end of mineralization. Temperature determinations based on the isotopic difference of syngenetic carbonates have not been possible as co-precipitation of calcite and dolomite did not occur. The oxygen isotopic composition of the mineralizing fluids was estimated on the basis of the O 18 content of the hydrothermal dolomites and confirms the assumption that the hydrothermal fluids were of stratafugic origin and comparable to forlnation waters encountered in the subsurface (calculated ω 18 = - 1.0 ± 1 per mil). The mineralization ended with the influx of isotopically lighter surface water into the system. This event is recorded in the gradually decreasing 0 ls content of the late calcite. The carbon incorporated in most of the hydrothermal carbonates originated essentially from the dissolution of marine carbonates by the hydrothermal fluids and only a few of the calcites associated with sulfide minerals show the influence of biogenic carbon dioxide, which was probably produced by sulfate reducing bacteria. The dissolution and reprecipitation of hydrothermal calcites combined with a decrease in temperature led to an enrichment in heavy carbon in the latest calcites paralleling the observed decrease in heavy oxygen. © 1969 Society of Economic Geologists, Inc.