Isotope Geochemistry and Fluid Inclusion Studies of the Hashitu Porphyry Molybdenum Deposit, NE China

The Hashitu porphyry molybdenum deposit is a newly-discovered Climax-type Mo deposit in NE China, in which the Mo-bearing quartz veins are hosted mainly in approximately coeval granites and porphyries. The deposit reserves more than 100 Mt Mo ores with grades varying from 0.08 to 0.36% with an average of 0.13%. Fluid inclusion studies indicate that the Hashitu ore forming fluids were characterized by relatively high temperature (372 degrees to 454 degrees C and locally >600 degrees C), high salinity (29.6 to 74 wt% NaCl eqv), high pressure (33.5 to 159.9 MPa), high-medium density (0.7 to 1.5 g/cm(3)), high fO(2) and CO2-bearing fluids. Molybdenite deposition is interpreted to have occurred at a temperature range of 300 to 400 degrees C, a pH of 3.5 to 5.6, and log fO(2) between - 32.20 and -25.76. Isotopic analyses (O, H, S, Mo and Pb) indicate a magmatic origin for both the ore-forming fluids and the metals; there may have been a minor metal contribution from the underlying volcanic rocks. Boiling is interpreted to have played an important role in molybdenite precipitation.