Geology and geochemistry of the Furong Tin Deposit, Hunan Province, P.R. China

Abstract

Recently, a giant tin deposit, the Furong deposit, has been discovered in the Qitianling granitoid, Hunan, South China. The tin mineralization occurs as disseminated crystals or veins of cassiterite. The cassiderite is found in narrow envelopes of chlorite alteration within the granite. The Qitianling granite has distinctly different petrology and mineralogy from common S-type tin granites. The oxygen and hydrogen isotope data indicate a dominant influence of surface-derived meteoric water associated with chlorite alteration. Variations in δ¹⁸O of fresh and altered granites are due to continuous isotopic exchange reaction between hydrothermal fluids and granites at variable water/rock ratios. The sulfur isotope compositions of sulfides from the tin ores indicate that both the granite and the strata supported the sulfur for mineralization. The Pb isotopic compositions of sulfides are same as those of feldspars from the granite. Thus, Pb in the ores might come from the granite. Fractional crystallization of the magma and tin deposition directly from exsolved magmatic-hydrothermal fluids may not be the major mechanism for the tin mineralization in this deposit. Instead, we suggest that interactions between fluids of meteoric origin and the granite may contribute to the release and deposition of tin.