Exhumation and preservation of the Bangbule Pb-Zn-Cu deposit in the western Gangdese metallogenic Belt, Tibet: Constraints from fission track thermochronology and fault gouge dating

Abstract

The Bangbule Pb-Zn-Cu deposit is a large-scale skarn deposit that was recently discovered in the western Gangdese Metallogenic Belt. Previous studies have focused mainly on ore genesis and ore-forming fluid, while exhumation and preservation after mineralization have not been the focus. We report fission track ages (ZFT: 43 ± 3 to 52 ± 3 Ma; AFT: 24 ± 2 to 32 ± 3 Ma, MTL: 12.2 ± 1.9 to 13.0 ± 1.6 μm) and the timing of fault activation (44.3 ± 0.9 Ma), revealing the processes of cooling/exhumation and we evaluate the preservation of the deposit. The Bangbule deposit experienced two rapid exhumation events since the Eocene (52–24 Ma and 12 Ma to present) and a slower stage during the late Oligocene to middle Miocene (24–12 Ma). The exhumation thickness (1.6–3.1 km) after mineralization was similar to the metallogenic depth (peak: 1.5–2.5 km). The volcanic rocks of the Dianzhong Formation partially protect the deposit, making mineral exploration of the Bangbule deposit feasible. Since the Oligocene, due to climate change and deep subducted slab tearing, the exhumation thickness in the western Gangdese (∼0.6–3.1 km) has generally been lower than that in the middle-eastern part (∼3–8 km). The lower degree of exhumation may be one of the reasons why less large-scale deposits have been discovered in the western Gangdese.