Cd isotopic constraints on the sources of Zn-Sb deposits: A case study of the Jianzhupo Zn-Sb deposit, Guangxi Province, China

Abstract

Antimony (Sb) is identified as a critical metal in many countries. The source of hydrothermal Sb-bearing deposits is currently debated in two opposing models (magmatic fluids or country rocks). Some Sb-bearing hydrothermal systems host abundant cadmium (Cd). Due to the close association of Cd and Sb in hydrothermal systems and the distinct Cd isotopic signatures between magmatic and sedimentary rocks, Cd isotopes have the potential to trace the metal origin in Sb-bearing deposits. Here, we conducted Cd isotope analyses of sulfide (jamesonite and sphalerite) collected from the Jianzhupo Zn-Sb deposit, SW China. A narrow range of δ114/110Cd relative to NIST SRM 3108 Cd standard was observed in sphalerites (−0.15‰ to +0.18‰; mean = 0.03‰ ± 0.10‰, one standard deviation [1SD]), identical to that of intermediate igneous rocks (−0.20‰ to +0.15‰); in contrast, pure jamesonites show a large range of δ114/110Cd (−0.42‰ to +0.17‰; mean = −0.22‰ ± 0.20‰, 1SD), differing from those of sphalerite. Different Cd isotope signatures between jamesonite and sphalerite are unlikely to have been triggered by sulfide precipitation, vapor-liquid phase separation, diffusion, and different Cd-S bond strengths. Instead, based on a comparison of δ114/110Cd and Zn/Cd ratio of sulfide and potential source rocks, we propose that a mixing of two ore-forming endmembers, derived from igneous and sedimentary rocks, may better explain the sulfide Cd isotopic signatures. This is supported by the well-defined positive correlation between δ114/110Cd and Zn/Cd ratio in sulfides. This study shows a novel application of Cd isotopes for metallogenetic tracing and demonstrates that Sb-bearing hydrothermal systems can incorporate metals from multiple sources.