Geology and Geochronology of the Xietongmen (Xiongcun) Cu-Au Porphyry District, Southern Tibet, China

Abstract

The Xietongmen district is located 260 km west-southwest of Lhasa in the Tibet Autonomous Region, China. The district occurs within the Gangdese belt, which forms the eastern part of the Trans-Himalayan magmatic belt and is the product of complex magmatic activity that began during the Late Triassic or Early Jurassic and ended in the Eocene. The Xietongmen Cu-Au and Newtongmen Cu-Au-Mo deposits contain a total measured and indicated resource of approximately 610 million metric tons, with additional mineralization in the Langtongmen and Olitongmen Cu-Au prospects. Porphyry mineralization in the Xietongmen district formed during Middle Jurassic volcanic arc activity in the Lhasa terrane, prior to its accretion to the southern margin of Eurasia, and establishes that an economically important, but only recently recognized, metallogenic event is present in the region.Rock types in the Xietongmen district range from Early Jurassic to Eocene in age. Early Jurassic (~188−177 Ma) volcanic, volcaniclastic, and coeval intrusive rock types are crosscut by Middle Jurassic (176−171 Ma) hornblende diorite and quartz diorite porphyry dikes and stocks, including intrusions related to porphyry Cu-Au ± Mo mineralization. The Jurassic igneous assemblage was intruded by mafic dikes between the Late Jurassic and the Cretaceous, then by an Eocene (50−47 Ma) biotite granodiorite batholith and related dikes, and finally by, volumetrically minor lamprophyre dikes. The most important structures in the Xietongmen district are four E-striking, moderately N-dipping, sinistral-oblique thrust faults. Crosscutting and suturing relationships between the TSF-2 thrust fault, located in the south part of the district, and intrusions dated to between 174 and 180 Ma constrain the main stage of thrust fault activity to the Middle Jurassic. The Contact and Adit-1 thrust faults truncate the Xietongmen deposit and form the footwall and hanging wall to mineralization, respectively. Numerous zones of cataclasis deform the Xietongmen deposit between these bounding thrust surfaces. The strongly deformed Langtongmen Cu-Au prospect is located ~1.3 km west of the Xietongmen deposit and occurs in the immediate hanging wall of the Adit-1 thrust fault. The Newtongmen deposit and the Olitongmen Cu-Au prospect occur to the north in the hanging wall to the SBF thrust fault and are not strongly deformed.Mineralization and hydrothermal features in the Xietongmen district are fully compatible with porphyry Cu-Au ± Mo deposits. Alteration, vein types, and mineralization are zoned around quartz diorite porphyry intrusions. Early K silicate alteration and related veins occur within and proximal to the intrusions and contain the highest grade mineralization. In the Xietongmen deposit, the grade of mineralization decreases outward from a core of early biotite-rich K silicate alteration, through a transitional zone in which early K silicate alteration is partially overprinted by quartz-sericite-pyrite alteration, to a peripheral zone of poorly mineralized quartz-sericite-pyrit...

Early Jurassic intra‐oceanic arc system of the Neotethys Ocean: Constraints from andesites in the Gangdese magmatic belt, south Tibet

“…G. Xu et al, 2008) along with Miocene-age adakite-like stocks, dykes, and ultrapotassic and potassic volcanic rocks (Chung et al, 2005;Hou, Gao, Qu, Rui, & Mo, 2004;Liu et al, 2014). Lang et al, 2014;Tafti, 2011;Tafti et al, 2014;Tang et al, 2015). Similarly, these porphyries are hosted by the Early Jurassic volcano-sedimentary sequences of the Xiongcun Formation, and are interpreted to have formed in an intra-oceanic arc related to northerly subduction of the Neotethyan oceanic lithosphere (Tang et al, 2015).…”

“…Detailed information is given in Appendix S5. SeeFigure 1for location Geological map of the Xiongcun deposit district and its neighboring area, showing the volcanic rocks of the Bima Formation of the Sangri Group and sampling locations of this study (modified fromLang et al, 2014;Oliver, 2006;Tafti et al, 2014). SeeFigure 2for location In our study area, the Bima Formation is composed of a lower mafic tuff and upper andesite interbedded with limestone with a total thickness of 944 m(Figures 4, 5).…”

“…I deposit body in the Xiongcun deposit district formed at ca 167–161 Ma, slightly later than that of No. II deposit ( ca 181–175 Ma; Lang et al, ; Tafti, ; Tafti et al, ; Tang et al, ). Similarly, these porphyries are hosted by the Early Jurassic volcano‐sedimentary sequences of the Xiongcun Formation, and are interpreted to have formed in an intra‐oceanic arc related to northerly subduction of the Neotethyan oceanic lithosphere (Tang et al, ).…”

“…It is known that nearly 97 % of porphyry Cu–Au deposits around the globe formed in subduction‐related settings (Cooke, Heithersay, Wolfe, & Caderon, ; Sillitoe, ; W. D. Sun et al, ). However, the Gangdese porphyry Cu–Au metallogenetic belt appears to be an exception to this general association because most of the porphyry Cu–Au deposits were generated in post‐collisional setting (Hou & Cook, ) with the exception of the Xiongcun porphyry Cu–Au deposit that formed in the more traditional setting (Lang et al, ; Tafti, Lang, Mortensen, Oliver, & Rebagliati, ; Tafti, Mortensen, Lang, Rebagliati, & Oliver, ). Recently, Tang et al () proposed that this deposit was formed during the subduction of Neotethyan oceanic crust within an intra‐oceanic arc setting.…”

Composition and age of Jurassic diabase dikes in the Xiongcun porphyry copper–gold district, southern margin of the Lhasa terrane, Tibet, China: Petrogenesis and tectonic setting

“…3) have been discovered in the Xiongcun district (Figure d). The mineralization was hosted in the Jurassic porphyries and the surrounding contemporary volcanic rocks (Lang et al, ; Tafti et al, ; Tafti, Lang, Mortensen, Oliver, & Rebagliati, ; J. X. Tang et al, ; J. X. Tang et al, ). The No.…”