Jin-Xiang Li

Geochronologic and isotope geochemical constraints on magmatism and associated W-Mo mineralization of the Jitoushan W-Mo deposit, middle-lower Yangtze Valley

The Jitoushan W–Mo ore body is a typical skarn-type deposit with the potential for porphyry Mo mineralization at depth. As it is newly discovered, only a few studies have been conducted on the geochronology and ore genesis of this deposit. The ore district consists of Cambrian to Silurian sedimentary and low-grade metasedimentary strata, intruded by granodiorite, diorite porphyry, granite porphyry, and quartz porphyry. Skarn W–Mo ore bodies are hosted in the contact zone between the granodiorite and Cambrian limestone strata. Within the granodiorite near the contact zone, quartz vein type and disseminated sulphide mineralization are well developed. The Mo-bearing granite porphyry has been traced at depth by drilling. Our results reveal two discrete magmatic events at ca. 138 and ca. 127 Ma in the study area. The molybdenite Re–Os isochronal age of 136.6 ± 1.5 million years is consistent with the first magmatic event. The zircon Hf isotope (ϵHf(t) = −12.55−3.91), sulphide isotopes (δ34S = 3.32–5.59‰), and Re content of molybdenite (Recontent = 6.424–19.07 μg) indicate that the ore-forming materials were mainly derived from the deep crust. The regional tectonic system switched from a Late Jurassic transpressive regime to an earliest Cretaceous extensional regime at ca. 145 Ma, and at ca. 138 Ma, the Jitoushan W–Mo deposit formed in an extensional setting.

The Xiongcun Cu-Zn-Au deposit in the western segment of the Gangdese, Tibet: A Mesozoic VHMS-type deposit cut by late veins

The Xiongcun Cu-Zn-Au deposit lies in the western segment of the Gangdese porphyry copper belt and in the forearc basin of the Southern Gangdese volcanic arc. The deposit is hosted by Cretaceous marine intermediate and basic volcanic clastic rocks that filled a supra-subduction forearc basin. The mineralized alteration zone is 2 km in length and varies in width from 100 m to 400 m with an average of about 200 m. The mineralized horizon is divided into a lower stringer mineralization and upper massive, sub-massive and banded mineralization. Laminated and banded mineralization lies in the hanging wall. Weak sulfidation is documented in the footwall. In addition, some late veins and lenticular sulfide bodies cut the early formed sulfide horizons. The most prospective ore bodies are developed in the upper mineralization horizon. Alteration is zoned with distal propylitization and proximal silicification, sericitization ± chrolitization in the ore body. Fluid inclusion analysis, sulphur isotopes, and trace elements of sulfides reveal that the deposit has the similar features compared with ancient volcanic-hosted massive sulfide deposits (VHMS) and modern active chimney. Based on these characteristics, we propose the deposit is a deformed VHMS-type deposit that formed in the forearc of the Gangdese volcanomagmatic arc during Mesozoic subduction. Second stage veins, inferred to form during collision between the India subcontinent and Eurasia cut the VHMS deposit prior to or simultaneous with intrusion of a post-mineral Himalayan-age diorite porphyries.