YUE Qiu-yu1, ZHAI De-gao1*, ZHAO Gang1, ZHAO Qing-qing1, He Gen-wen2, LIU Jia-jun1

(1. School of Earth Sciences and Resources, China University of Geosciences (Beijing), Beijing 100083, China;
2. Gannan Geological Survey Team, Bureau of Geology and Mineral Resources Exploration and Development of Jiangxi Province, Ganzhou 34100, China)

Abstract: The Niuxingba－Liumukeng deposit, located in the Yinkeng orefield of Jiangxi Province, is a typical Ag-Au polymetallic deposit in the Yudu-Ganxian metallogenic belt. Based on the field investigation and mineralogical studies, three stages of the hydrothermal mineralization of this deposit have been identified. They include the quartz-pyrite-arsenopyrite stage (I), the quartz-galena-sphalerite-sulfosalt stage (Ⅱ), and the quartz-carbonate stage (Ⅲ). The silver mineralization occurred mainly in the Stage Ⅱ. The results of electron probe microanalysis (EPMA) show that the silver occurred in forms of independent silver minerals and micron sized silver mineral inclusions in the ores. The independent silver minerals include tetrahedrite [(CuAg)12(SbAs)4S13], freibergite [(CuAg)12(SbAs)4S13], polybasite [(AgCu)16Sb2S11)] and argentite-acanthite [(Ag2S)]. The micron sized Ag-bearing mineral inclusion is dominated by tetrahedrite [(CuAg)12(SbAs)4S13] hosted in galena. In this study, we found a unique exsolution texture of tetrahedrite-chalcopyrite-galena, indicating that the ore-forming fluid could be rich in Pb-Cu-Sb-Ag. Combined with our new data and the previous studies of the deposit, we have proposed that the physicochemical condition variations, including the decrease of temperature and oxygen fugacity and the increase of pH, could be main factors causing the significant precipitation of silver from the ore-forming fluid. In addition, a large amount of bismuth-bearing minerals, e.g., pavonite (AgBi3S5), matildite (AgBiS2), emplectite (CuBiS2) have been identified in ores of the deposit. The close intergrowth between these bismuth-bearing and silver-bearing minerals indicates that they may have a close genetic relationship. It is believed that the presence of bismuth in the ore-forming fluid could promote the silver enrichment and mineralization of the deposit.

Keywords: Niuxingba－Liumukeng deposit; silver minerals; bismuth mineral; silver occurrence; enrichment mechanism

ACTA MINERALOGICA SINICA Vol. 43, No. 3, 2023, Page 311