Occurrence and distribution of Se and Te in the Jilongshan Au-Cu skarn deposit from the Middle-Lower Yangtze River metallogenic belt, China

The Jilongshan Au-Cu skarn deposit is located at the Jiurui ore district of the Middle-Lower Yangtze River metallogenic belt (MLYB), which is a significant metallogenic belt for dispersed elements. The Jilongshan deposit hosts abundant critical metal elements (e.g., Se, Te, and Bi) and shows potential for the comprehensive utilization of these critical mineral resources. This study examines the mineralogical textures and compositions of sulfides and sulfosalts from the Jilongshan deposit through EPMA, TIMA, and LA-ICP-MS analyses to clarify the nature of the occurrence and distribution of Se and Te. Based on the host rocks, the ores can be divided into porphyry-hosted, marble-hosted, and skarn-hosted types. Selenium content is significantly higher in porphyry- hosted and skarn-hosted ores compared to marble-hosted ore, while Te is most abundant in marble-hosted ore. Apart from rare minerals such as clausthalite (PbSe), hessite (Ag2Te), and hedleyite (Bi7Te3), Se and Te predominantly occur as isomorphism within pyrite (similar to 70 %) and tetrahedrite (similar to 20 %). On the basis of mineral assemblages and textures, tetrahedrite can be recognized as three generations, including Ttr1 (replacing Fe-Cu sulfides), Ttr2 (intergrown with Pb-Zn sulfides), and Ttr3 (replacement of last pyrite). Selenium is enriched in minerals precipitated in the Fe-Cu stage, including hydrothermal pyrite, chalcopyrite, and Ttr1, with the average of 345 ppm, 183 ppm, and 592 ppm, respectively, while Te mainly concentrates in minerals formed in the Pb-Zn stage, such as galena (143 ppm), Ttr2 (3112 ppm), and Ttr3 (489 ppm). These findings align with previous studies on the Se-Te relationship and may indicate that Se is more likely to be enriched at a higher temperature, while Te exhibits the opposite trend. The variation in sulfur fugacity within fluid systems may also play a role in the enrichment of these critical elements. Additionally, the regional distribution and enrichment of Se and Te in the porphyry-skarn deposits of the MLYB also shows certain regularity. Selenium is more likely to be enriched in high-temperature porphyry ores, while Te is most abundant in relatively low-temperature interlayer ores.