SULFUR ISOTOPES AND PINE POINT LEAD-ZINC MINERALIZATION

S 34/S 32 ratios were determined for 156 specimens of sulfides, sulfates, elemental sulfur and pyrobitumen, in and contiguous to the Pine Point lead-zinc ore field. Sulfur in the sulfides of the major orebodies is consistently enriched in S a4 as compared to the meteoritic standard, with a relatively narrow range of variation. The mean aS a4 value of 118 samples is 4-20.1 per mil, with the standard mean deviation of 4±2.6 per mil. This is remarkably similar to the data for the evaporitic anhydrites of the Middle Devonian Elk Point basin which the ore-bearing dolomitized Presqu'ile reefs rim (+19-+20 per rail). The sulfate in formation brines from nearby strata of the same geological age also shows a similar isotopic composition. Sulfur in minor syngenetic or diagenetic sulfides in the country rocks appears unrelated to the sulfur in the ore and returns widely scattered 8S a4 values ranging from 4-9 to -19 per mil which may be interpreted as normal biogenic sulfur. Bacterial reduction of sulfate is currently active in spring waters of the ore field, producing H 2S and S markedly depleted in S a4 with respect to SO4 =. Sulfur in pyrobitumens in and near the orebodies is depleted in S a4 as compared with the sulfur in the ore and evaporite sulfate, with ωS 34 values ranging from 4-3 to 4-7 per mil. A sulfur sample obtained from a gas processing plant at the nearby Middle Devonian Rainbow oil field also shows a similar isotopic value (4-9 per mil). From the composite data, the most plausible source of the Pine Point sulfur appears to be the Middle Devonian sea-water sulfate, probably supplied in the form of connate brines or solutions from the contiguous evaporite basin. Reduction mechanism of sulfate to sulfide with little isotopic fractionation remains a matter of debate. © 1969 Society of Economic Geologists, Inc.