Eocene porphyry copper deposits in the eastern Tibetan Plateau, China: Uplift, denudation, and implications for mineral exploration

Abstract

The subduction–collision processes associated with the Indo‐Eurasian plates resulted in the formation of a major belt of porphyry copper deposits in the eastern Tibetan Plateau. Identifying the emplacement depths of the ore‐hosting porphyry intrusions and quantifying their denudation degree, which in turn is a function of the uplift and structural history, are fundamental to formulate guidelines for ore prospecting. In this study, we investigate three important porphyry deposits located adjacent to the Diancangshan–Ailaoshan Suture. From SW to NE, these are the Bijiashan, Xiaolongtan, and Fenshuiling deposits. Our study focuses on the relationship among uplift, denudation, and mineral preservation through the application of mineral thermobarometry, integrated with published zircon U–Pb dates. Application of amphibole–plagioclase thermobarometry yields emplacement temperature–pressure (T–P) conditions of 833.99°C and 284.18 MPa for Bijiashan, 804.72°C and 163.88 MPa for Xiaolongtan, and 748.67°C and 116.70 MPa for Fenshuiling. Our data show a progressive decrease in the emplacement depth from southwest to northeast, with average depths of 9.80 km in the Bijiashan deposit, 5.65 km in the Xiaolongtan deposit, and 4.02 km in the Fenshuiling deposit, providing important clues on the exhumation history since the Eocene in the eastern Tibetan Plateau. Higher degree of denudation and faster uplift are noticed close to the Diancangshan–Ailaoshan Suture, with all the deposits belonging to the shallow denudation category and large prospecting potential. We integrate these results with geochronological data, alteration characteristics, and exhumation parameters to trace the tectonic history and to provide guidelines for exploration.