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Great Bear Magmatic Zone; Canada; IOCG; Geochemistry
Abstract:
The NICO deposit is located within the Great Bear magmatic zone, Northwest Territories, Canada. Most part of the mineralization lies within the Bowl Zone, and is hosted by the metasedimentary Treasure Lake Group (TLG). The oxygen isotope (delta O-18(fluids)= 5.6-7.0%o) analyses from NICO suggest a parental magmatic-hydrothermal fluid. The sulphur isotopes data (3.3-6.7 parts per thousand) could either indicate a felsic magmatic origin or a well homogenized mixture between sulphur of crustal and magmatic reservoirs. Two calcite samples from pre- (S1; delta C-13=-4 parts per thousand, delta O-18=11 parts per thousand) and post- (S3; delta C-13=-5.5 parts per thousand, delta O-18=13.2 parts per thousand) ore quartz veins have carbon and oxygen isotopes values also consistent with a magmatic origin. A third sample of the S3 veins suggests the emplacement of reduced carbon (delta C-13=-15.5). Trace element analyses of the least altered rocks of the TLG suggest that S (similar to 1310 pm), as well as As (similar to 31 ppm) might have been leached from a Carbonate unit of the TLG. Conversely, the Au (<2 to 7 ppb), Co (3-19), Bi (<2 ppm) and Cu (3-19 ppm) are likely derived from magmatic-hydrothermal fluids, due to their low contents in the TLG. Micro thermometric analyses of liquid-vapor (LV-Bi) and liquid vapor-solid (LVS-Bi) bearing inclusions containing Bi solids, demonstrates that the Bi-rich fluids from NICO deposit were complex saline (LV-Bi, 2-16 wt. % NaCl equiv., 8-22 wt. % CaCl2 equiv.) to highly-saline (LVS-Bi, >37 wt. % NaCl equiv.) Na-Ca-Cl-H2O brines formed at temperatures of >271.4 degrees C. A pressure correction carried out using the composition and homogenization temperature (137-216 degrees C) of the LV-Bi inclusions and the native Bi melting point (271.4 degrees C) indicates a depth of formation for NICO of 5-8 km.
