SCAPOLITE IN 2 CANADIAN GOLD DEPOSITS - NICKEL PLATE, BRITISH-COLUMBIA AND HEMLO, ONTARIO

Scapolite from the Nickel Plate gold-skarn deposit, British Columbia, and the Archean Hemlo gold deposit, Ontario, has been studied in detai l. Chlorine-carbonate scapolite is commonly present at Nickel Plate in both the mineralized and barren exoskarn and endoskarn, although it i s generally more abundant within, and adjacent to, the sulfide-gold or ebodies. Less commonly, scapolite also occurs in rare, vuggy cavities developed in a limestone-boulder-bearing unit (the Copperfield breccia ) and in marble beyond the outer limits of the skarn envelope. Scapoli te equilibria involving coexisting garnet - plagioclase calcite - quar tz in the CASCH system yielded X(CO2) of 0.04 +/- 0.02 and temperature s of 500 +/- 20 degrees C at a pressure of 1 kbar. Fluid inclusions in scapolite from exoskarn, endoskarn and a vuggy cavity yielded similar temperatures of homogenization (250-470 degrees C, and mostly between 320 and 400 degrees C) and salinities (15.6 to 19 wt.% NaCl equivalen t). At Nickel Plate, there is no apparent correlation between the Cl c ontent of scapolite and the spatial proximity of the mineral to ore; i nstead, Cl content corresponds to EqAn content which, in turn, relates to the anorthite component of associated plagioclase. We suggest that the Cl content of scapolite is not directly proportional to the chlor inity of the coexisting fluid, but father is strongly controlled by cr ystal structure (i.e., by charge-balance constraints imposed by the sc apolite framework). The occurrences of Cl-bearing scapolite at the Nic kel Plate deposit also provide further support for chloride complexes in the transport and deposition of gold in skarn systems. Sulfate-carb onate scapolite (EqAn(65)), coexisting plagioclase (An(30-35)) and cal cite at the Hemlo deposit crystallized immediately after the peak regi onal metamorphism and predated gold mineralization. The sulfate conten t of the scapolite at Hemlo is directly controlled by coexisting miner al assemblages (i.e., anhydrite-bearing and anhydrite-absent) and is c onsistent with the experimental calibration of Kotel'nikov (1987).