Telescoped boiling and cooling mechanisms triggered hydrothermal stibnite precipitation: Insights from the world’s largest antimony deposit in Xikuangshan China

Abstract

Society annually consumes 250% more Sb relative to the year 1960 and a sustainable supply of antimony depends critically on understanding the precipitation mechanism of stibnite (Sb 2 S 3 ) that is the globally predominant source of this important technology metal.Previous solubility studies revealed that antimony is transported in mesothermal hydrothermal fluids mainly as thioantimonite (H 2 Sb 2 S 4 , HSb 2 S 4 -, Sb 2 S 4 2-) and hydroxothioantimonite (Sb 2 S 2 (OH) 2 ). Thioantimonite can transform to hydroxothioantimonite as the decline of H 2 S concentration. However, whether this transition occurs in hydrothermal systems and its role in stibnite precipitation are unknown.In this work, bulk Sb isotope measurements for stibnite from the world's largest Sb deposit in Xikuangshan China were conducted to address ore fluid evolution and stibnite precipitation mechanisms. The abundance of the stable antimony isotopes 121 Sb and 123 Sb were measured in stibnite from the Xikuangshan orebodies and reported as δ 123 Sb. The δ 123 Sb values show a trend of decreasing first and then increasing from proximal to distal parts of orebodies. This reveals that 123 Sb had been preferentially partitioned from the ore fluid into stibnite first, then 123 Sb remained preferentially dissolved in the ore fluid. These data indicate that the dominant Sb-complex transforms to Sb 2 S 2 (OH) 2 from H 2 Sb 2 S 4 with consuming of H 2 S. Speciation diagram considerations indicate that stibnite precipitation from the ore fluid was controlled by two telescoped processes: 1) boiling of the ore fluid induced a decrease in H 2 S that reduced the solubility of H 2 Sb 2 S 4 , and 2) subsequent cooling that induced a decrease in the solubility of Sb 2 S 2 (OH) 2 . This study highlights that understanding the controls of Sb isotope fractionation is critical to constrain fluid evolution and stibnite precipitation mechanisms in Sb-rich mineral systems. In particular, the stable Sb This is the peer-reviewed, final accepted version for American Mineralogist, published by the Mineralogical Society of America.The published version is subject to change. Cite as Authors (Year) Title. American Mineralogist, in press.

Determination Of Sb Isotope Ratios In Stibnite Using Fs-LA-MC-ICP-MS And Two Potential Reference Materials Study

“…2 The sustainable supply of Sb hinges upon a thorough comprehension of ore fluid evolution and the precipitation mechanisms of stibnite within hydrothermal antimony deposits. 3 Achieving these objectives requires a nuanced exploration of Sb isotopes.…”