A newly discovered low Sb isotopic endmember in global Sb ore deposits, evidence from Tibet (SW China)

Tibet in SW China hosts numerous Sb mineralization, with a number of Sb-only and Sb-polymetallic ore deposits and occurrences distributed across both southern and northern parts. Here we present in-situ Sb isotope compositions of stibnite from multiple ore deposits in this region, spanning Sb-only, Sb–Au, and Sb–Pb–Zn ore systems across seven deposits and mineralizations. The principal Sb-bearing mineral in all deposits is stibnite. Mineralogical determination and Sb isotope composition of stibnite have been performed on well selected samples. Antimony isotope composition has the potential to record variability in Sb source reservoirs and the evolution of mineralizing fluids. Measurements were performed in-situ at Leibniz University Hannover using deep UV-fs laser ablation system coupled to MC-ICP-MS, following Kaufmann et al. (2021).

Obtained stibnite δ¹²³Sb values range from -0.69 to +0.81‰ (relative to NIST SRM 3102a). Evident isotope fractionation of 0.94 ‰ measured in stibnite is observed in Sb–Pb–Zn ore deposit, which may indicate several episodes of stibnite formation. In general, other ore deposits show limited antimony isotope fractionation (< 0.45 ‰) within deposit, which is consistent with the well-established Rayleigh crystallization model of fluid evolution. While the maximum deviation within an Sb-Au deposit is ~0.25 ‰, with an average value of -0.07±0.14 ‰ (2SD), the range among Sb-only deposits is much greater, exceeding 1.2 ‰, with the mean of ~0.05±0.67 ‰ (2SD). In one of the Sb-only deposits in northern Tibet, the most negative δ¹²³Sb value of -0.69±0.46 ‰ and a deviation of 0.7 ‰ were observed, while the other deposits in southern Tibet show an intra deposit range below 0.44 ‰ and the lowest values of -0.06 ‰. According to the well-known Sb isotope variations during ore formation, our new data reveal that the metal sources for Sb mineralization in northern and southern Tibet might have been distinct. This may further indicate that the Sb isotopes can be used to constrain metal sources and metallogenic domains at a large scale across the Tibetan Plateau.

 

Kaufmann, A.B., Lazarov, M., Kiefer S., Majzlan, J., Weyer S. (2021): In-situ determination of antimony isotope ratios in Sb minerals by femtosecond LA-MC-ICP-MS, JAAS 36(7).