Zinc and cadmium isotopic constraints on ore formation and mineral exploration in epithermal system: A reconnaissance study at the Keyue and Zhaxikang Sb–Pb–Zn–Ag deposits in southern Tibet

Abstract

The Keyue Sb–Pb–Zn–Ag deposit is a medium-sized deposit near the super-large Zhaxikang Sb–Pb–Zn–Ag deposit within the North Himalayan Metallogenic Belt (NHMB). These two deposits, separated only by a regional NS-trending normal fault with strike-slip properties, have similar ore-forming elements and mineral associations, ore characteristics, ore paragenetic sequence, wall rocks, and H–O–S–Pb isotopic and fluid inclusion characteristics. Herein, we establish Zn–Cd isotopic connections between these two proximal ore deposits. As a means to draw comparisons, we conducted Zn–Cd isotopic research of the Keyue deposit to compare it with that of the Zhaxikang deposit. Both the δ66Zn and δ114/110Cd values of sphalerite from the Keyue deposit display a temporally decreasing trend from stage 2 (δ66Zn: 0.15‰–0.58‰, average value = 0.29‰; δ114/110Cd: –0.23‰ to 0.38‰, average value = 0.05‰) to stage 3 (δ66Zn: –0.28‰ to 0.12‰, average value = –0.06‰; δ114/110Cd: –0.38‰ to –0.32‰, average value = –0.35‰), which was also found in the Zhaxikang deposit. A simple three-phase separation distillation models this temporally decreasing trend, which resulted from the Zn–Cd isotopic fractionation that is most likely related to vapor–liquid-solid dynamics of ore-forming fluid. This distillation model was further augmented by the general geochemical characteristics and fluid inclusion data. A congruence among several geological and geochemical evidence points to the genetic relationships between these two ore deposits that have the same metal origins and experience similar ore formation processes. A three-phase separation model has been established to imitate this evolution, which reveals substantial exploration potential for Zn–Cd at depths below 4100 m within the Zhaxikang orefield. In summary, Zn–Cd isotopes have the potential to trace metal sources, monitor fluid evolution, constrain ore formation, and provide insights into mineral exploration.