Constraints on ore-forming fluid evolution and guidance for ore exploration in the Zhaxikang Sb–Pb–Zn–Ag deposit in southern Tibet: insights from silver isotope fractionation of galena

This study reports the high-precision silver (Ag) isotopic compositions of the dominant Ag-bearing mineral (galena) in the representative Zhaxikang polymetallic deposit, which experienced a complex ore-forming process that can be divided into two episodes composed of six stages (first episode: Pb–Zn mineralization, stages 1 and 2; second episode: Sb mineralization, stages 3 to 6). The objective of this case study is to investigate the Ag isotopic fractionation mechanisms in a hydrothermal ore-forming system and explore the potential application of Ag isotopes. The earlier-generated stage 2 galena (0.17–6.07‰) has higher δ109AgNIST 978 Ag values with a significantly broader range in comparison to the subsequent stage 3 galena (–3.65 to 2.27‰). The δ109AgNIST 978 Ag values of galena also decrease from deep to shallow along with the trend of orebody V. These temporally and spatially decreasing trends indicate that the second episode of ore-forming fluid overprinted the first episode of mineralization along with the trend of orebodies from deep to shallow within the Zhaxikang orefield. A simple triple-phase separation model captures the temporal and spatial patterning of the data resulting from Ag isotopic fractionation, which is most likely related to the solid–liquid-vapor dynamics of the ore-forming fluid. According to approximate theoretical calculations, there is still great prospecting potential for Ag at depth within the Zhaxikang orefield. In summary, the Ag isotopes have the potential to trace phase changes, monitor ore-forming fluid evolution, constrain ore formation processes, and provide insights into ore exploration.