Halogen and stable chlorine isotope analysis of quartz hosted fluid inclusions from porphyry copper deposits

Halogen ratios (Br/Cl) and delta37Cl values have been determined for fluid inclusion leachates extracted from quartz veins from porphyry copper deposits in Butte, Montana, U.S.A, and Bingham Canyon, Utah, U.S.A. Analyzed samples were dominated by low-salinity parental magmatic fluid inclusions that were trapped as a single-phase aqueous fluid in the one-phase field of the NaCl-H2O system. Br/Cl from early pre-Main Stage and later Main Stage veins at Butte range from 0.60-1.88 x 10 -3M, and Br/Cl for quartz veins from the potassically altered host monzonite at Bingham range from 0.18-3.68 x 10-3M. Butte delta 37Cl values range from -0.8 to -2.3‰, and delta37 Cl values for Bingham are lower ranging from -0.9 to -4.1‰. Resultant data indicate a juvenile source of salinity in parental hydrothermal fluids related to porphyry deposit formation, and suggest that a significant partitioning of 35Cl and 37Cl occurs between Cl-bearing silicates and NaCl-dominated aqueous brines.