Helium and argon isotope geochemistry of the Tibetan Qulong porphyry Cu-Mo deposit, China

The Qulong porphyry Cu-Mo deposit, generated in the Miocene post-collisional extension environment of the Gangdese Copper (Molybdenum) Metallogenic Belt, is one of the largest porphyry Cu deposits in China. This study reports the noble gas isotopic compositions of volatiles released from fluid inclusion reserved in pyrite from the Qulong deposit. He-3/He-4 and Ar-40/Ar-36 ratios range from 0.54 to 1.015 Ra and 300-359, respectively. Concentrations of He-4 and Ar-40 range from 1.77 to 2.62 x 10(-8) cm(3) STP and 1.7-34 x 10(-8) cm(3) STP, respectively. The isotopic composition of noble gases indicates that the ore-forming fluids of the Qulong Cu-Mo deposit were a mixture of fluid containing mantle component, which is exsolved from the porphyry magma, and crustal fluid characterized by atmospheric Ar and crustal radiogenic He. The delta S-34 values of pyrite and molybdenite range from - 0.52 parts per thousand to 0.31 parts per thousand, with an average of - 0.12 parts per thousand, indicating a magmatic origin. More mantle components were involved in the Cu-Mo deposit than in the Mo-Cu deposit in the Qulong-Jiama ore-district.