Fault-controlled exhumation and preservation of the Zhunuo porphyry copper Deposit, western Gangdese, Tibet

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The Zhunuo deposit is the westernmost large porphyry copper deposit in the Gangdese porphyry copper belt. Petrological, geochemical, and thermochronological studies have reported its genesis, magmatic-hydrothermal evolution, and the effects of post-mineralization faulting. However, as exploration deepens, previous understandings of ore preservation have not been fully confirmed. We present new apatite (U-Th)/He (AHe) analyses targeting the post-mineralization Nongsang fault to assess the impact of fault activity on the ore body and explore potential directions for future exploration. AHe ages obtained from Miocene samples in this study range from 18.7 ± 1.1 Ma to 7.7 ± 0.4 Ma, and the associated experimental data were used for thermal history reconstruction. Two-stage cooling processes of the Zhunuo deposit have been identified: an initial rapid cooling due to heat dissipation from the magma reaching thermal equilibrium with the surrounding rock, followed by a slower cooling period influenced by tectonic movements and exhumation. The Nongsang fault has been confirmed as a high-angle normal fault, with a dip direction of 74° and a dip angle of 85°. Constraints from the age-elevation relationship, combined with the elevation difference between the matched ore layers on both sides of the fault, revealed a fault displacement of at least 300 m. The primary mining area in the western footwall of the fault has experienced more intense erosion of no less than 1.8 km, exposing numerous ore-related intrusions at the surface. In contrast, the eastern hanging wall has undergone relatively less exhumation, retaining a voluminous Eocene quartz porphyry cap and possibly containing undiscovered, undisturbed ore bodies. Tectonic activity plays a crucial role in the exhumation and preservation of the Zhunuo deposit. It is suggested that in the broad volcanic-covered areas west of the Zhunuo deposit, large-scale porphyry deposits with significant potential may still be buried underground, based on comparisons of tectonic control and post-mineralization preservation of porphyry deposits at different locations in the Gangdese porphyry copper belt.