Variation of molybdenum isotopes in molybdenite from porphyry and vein Mo deposits in the Gangdese metallogenic belt, Tibetan plateau and its implications

We present Mo isotopic ratios of molybdenite from five porphyry molybdenum deposits (Chagele, Sharang, Jiru, Qulong, and Zhuonuo) and one quartz-molybdenite vein-type deposit (Jigongcun) along the Gangdese metallogenic belt in the Tibetan Plateau. These deposits represent a sequence of consecutive events of the India-Asia collision at different periods. Additional molybdenite samples from the Henderson Mo deposit (USA), the oceanic subduction-related El Teniente (Chile), and Bingham (USA) porphyry Cu-(Mo) deposits were analyzed for better understanding the controls on the Mo isotope systematics of molybdenite. The results show that molybdenite from Sharang, Jiru, Qulong, and Zhuonuo deposits have similar delta Mo-97 (similar to 0 aEuro degrees), in agreement with the values of the Henderson Mo deposit (-0.10 aEuro degrees). In contrast, samples from the Changle and Jigongcun deposit have delta Mo-97 of 0.85 aEuro degrees to 0.88 aEuro degrees and -0.48 %, respectively. Molybdenite from the El Teniente and Bingham deposits yields intermediate delta Mo-97 of 0.27 and 0.46 aEuro degrees, respectively. The Mo isotopes, combined with Nd isotope data of the ore-bearing porphyries, indicate that source of the ore-related magmas has fundamental effects on the Mo isotopic compositions of molybdenite. Our study indicates that molybdenite related to crustal-, and mantle-derived magmas has positive or negative delta Mo-97 values, respectively, whereas molybdenite from porphyries formed by crust-mantle mixing has delta Mo-97 close to 0 aEuro degrees. It is concluded that the Mo isotope composition in the porphyry system is a huge source signature, without relation to the tectonic setting under which the porphyry deposits formed.