Identification of the first high-sulfidation epithermal ore-bearing lithocap in the western section of the Gangdese metallogenic belt and its significance

Abstract

Several lithocaps have been recently identified in the western section of the Gangdese metallogenic belt (GMB) and can be used to guide exploration of porphyry-high sulfidation epithermal deposits. In this work, we report the first ore-bearing lithocap (Mangla) within the GMB and carry out field mapping, geochronology, and shortwave infrared reflectance spectroscopy analyses. The zircon U-Pb (16.93 Ma) and alunite ⁴⁰Ar-³⁹Ar (19.24 Ma) isotope ages reveal that the protoliths and alteration of the Mangla lithocap occurred during one Cenozoic magmatic event, which corresponds with the mineralization ages of porphyry-skarn copper-polymetallic deposits in the eastern GMB. The alteration mineral assemblages, including alunite, dickite, pyrophyllite, kaolinite, and diaspore, along with enargite, colusite, Cu-S binary system minerals covellite and digenite, chalcopyrite and bornite, validate the characterization of a typical high-sulfidation epithermal mineralization system. Laterally, several alteration centers have been identified at the surface, and the vertical alteration is composed of deep high-temperature mineral assemblages (pyrophyllite + diaspore + topaz) that shift upward to low-temperature minerals, which are influenced primarily by faults, elevation, lithological permeability, fluid cooling and pH reduction. Notably, the vuggy quartz ± alunite and alunite + pyrophyllite zones within the lithocap are favorable locations for copper–gold mineralization, and a comprehensive epithermal mineralization system is preserved in this area, indicating the potential for underlying deep porphyry systems. Considering the presence of extensive continental volcanic coverage and notable analogous alteration features in the region, we assert that the area of Miocene continental volcanic rocks in northwestern Xizang presents substantial potential for copper–gold exploration.