DELTA-C-13-DELTA-O-18-SR-87 SR-86 COVARIATIONS IN ORE-STAGE CALCITES AT AND AROUND THE GAYS RIVER ZN-PB DEPOSIT (NOVA-SCOTIA, CANADA) - EVIDENCE FOR FLUID MIXING/

The delta(13)C-delta(18)O-Sr-87/Sr-86 variations around carbonate-host ed deposits can in theory help characterize ore-stage gangue minerals and discriminate between single fluid or two-fluid mixing models durin g mineralization. This paper reports on the combined use of delta(13)C -delta(18)O-Sr-87/Sr-86 data in dolostone within die Gays River deposi t and up to 30 km around it. The deposit, at the southern margin of th e Maritimes basin, is hosted in carbonate banks of the Gays River Form ation, a unit of the Visean Lower Windsor Group in Nova. Scotia. A pre vious delta(13)C-delta(18)O study restricted to the Gays River deposit (and independant from an Sr-87/Sr-86 investigation) had previously le d to the conclusion that a single brine was responsible for mineraliza tion. The present isotopic investigation was governed by the paragenet ic succession which includes presulfide dolomite, synsulfide calcites - both uniform and zoned under cathodoluminescence, and postsulfide ca lcite uniform under cathodoluminescence. Results for presulfide dolomi te (avg delta(13)C = +3 parts per thousand, delta(18)O(V.PDB) = 6 part s per thousand, and Sr-87/Sr-86 = 0.7080) plot near the normal marine isotopic ratios, whereas postsulfide calcite shows slightly more radio genic Sr-87/Sr-86 ratios (avg 0.7090). At the deposit, isotopic result s for calcite associated with the high-grade sulfide zone cluster arou nd a delta(18)O(V.PDB) of - 17.0 per mil and an Sr-87/Sr-86 of 0.7120, and clearly characterize the mineralizing system. Regional C, O, and Sr isotope data are similar to those at the deposit and indicate there fore a regional flushing of the Gays River Formation by fluids of the mineralizing system. The overall isotopic variation through time from pre- to syn- then postsulfide conditions in the delta(18)O - Sr-87/Sr- 86, delta(13)C-delta(18)O and delta(13)C-Sr-87/Sr-86 diagrams is inter preted to be similar for pre- and postsulfide conditions, marked by a warm, slightly radiogenic parent brine. This chemical system was distu rbed by a much more radiogenic and high-temperature fluid during miner alization. Although most of die mineralizing trend can be explained ei ther by a single-brine model or a mixing brine model, the mixing model allows for a much simpler evolution if the suite of conditions - on a regional basis - is considered through time. ''Show me your delta(18) O-Sr-87/Sr-86 profile, and I will tell you what you drink!'' (adapted old. spanish proverb).