Re–Os and Pb isotope features of pyrite in the Shihangli graphite deposit: implications of coal-generated graphite mineralization in central Hunan, South China

The coal metamorphism in Central Hunan provides valuable information about hydrothermal activity and water/rock reactions. Learning how to collect age data on hydrothermal fluid systems is necessary for understanding the history and genetic mechanisms of large-scale coal-generated graphite deposits. The Shihangli graphite deposit, formed by significant siliceous hydrothermal alteration, is the most distinctive in Central Hunan. Re–Os dating of pyrite from the Shihangli graphite deposit demonstrates that the coal-generated graphite mineralization age is ~ 127.6 ± 3.8 Ma. Based on in-situ mineral analysis, the hydrothermal pyrite in the Shihangli graphite deposit is mostly enriched in Sb, As, Au, W, Ag, Cu, Pb, and Zn. Based on the pyrite Re–Os isochron, the initial (¹⁸⁷Os/¹⁸⁸Os) values of pyrite were 1.03 ± 0.24 and the Os(t) values varied from 571.8 to 755.1. Pyrite from the Shihangli graphite deposit comprises a Pb isotope composition similar to that of the Madiyi Formation bulk rock and stibnite from the Xikuangshan Sb deposit. Based on the Re–Os, Sr, S, and Pb isotopic compositions of sulfides in the graphite and Sb deposits in Central Hunan, the Madiyi Formation was likely the primary source of ore-forming elements (Sb, Au, and As). The Re–Os and Pb isotope compositions of pyrite most likely reflect when large-scale fluid migration and coal-generated graphite mineralization occurred in Central Hunan.