Geological characteristics, metallogenesis, and tectonic setting of porphyry-skarn Cu deposits in East Kunlun Orogen

摘要

The East Kunlun Orogen (EKO), as the west segment of the Central China Orogen, is the most important Triassic polymetallic metallogenic belt in China. In this paper, we summarize the geological characteristics (stratigraphy, structure, ore-related plutons, wall rock alteration, and orebodies), ore-forming fluids and materials, geochronology, and petro-geochemistry of the representative porphyry-skarn Cu-polymetallic deposits, including the Saishitang, Hutouya, and Kaerqueka deposits in the EKO. The porphyry-skarn Cu deposits in the EKO are mainly distributed in tectonic units of the Qimantagh Belt and the Elashan Belt. Among them, the skarn Cu deposits provide the majority of Cu resources, which mainly occur in the contact zone between the Triassic granitoids and the volcanic-sedimentary rocks (e.g., the Ordovician-Silurian Tanjianshan Group and the Early to Middle Triassic Hongshuichuan Group), and the skarn and orebodies are mainly controlled by interlayer-gliding structures. Ore-forming fluids of the porphyry Cu deposits are magmatic mixed with meteoric water, whereas the fluids of skarn Cu deposits are mainly of magmatic origin. The higher O-18 (>10 parts per thousand) of garnet and pyroxene in prograde skarn and wide range of sulphur isotopic compositions (S-34 values from -8.9 parts per thousand to 11.0 parts per thousand) suggest that ore-forming materials of skarn Cu deposits were partially derived from the country rocks. Based on detailed field investigations, we identified four Cu mineralization types, including veinlet-disseminated Cu (Mo, Au) mineralization occurring within the intrusions, proximal skarn Cu (Fe, Pb, Zn, Au) mineralization, distal skarn Cu mineralization, and distal skarn Pb-Zn (Cu) mineralization. The porphyry-skarn Cu deposits are associated with magmatism that occurred mainly during 235-218Ma. The ore-related granitoids are mostly calc-alkaline I-type granites, derived from partial melting of the Precambrian basement rocks with various