Indium Mineralization in the Xianghualing Sn-Polymetallic Orefield in Southern Hunan, Southern China

Although numerous W–Sn–Pb–Zn polymetallic deposits are located in southern Hunan, and In-bearing deposits are related to W–Sn–Pb–Zn polymetallic deposits, Indium mineralization in southern Hunan is poorly studied. In order to investigate the In mineralization of the Xianghualing orefield, which is a typical orefield in southern Hunan, ore bulk chemistry, microscopic observation, and electron-probe microanalysis of vein-type (type-I) and porphyry-type (type-II) Sn–Pb–Zn orebodies were studied. The In contents of the type-I orebodies varies from 0.79 to 1680 ppm (avg. 217 ppm, n = 29), and that of the type-II orebodies varies from 10 to 150 ppm (avg. 64 ppm, n = 10). Although chalcopyrite and stannite contain trace amounts of In, sphalerite is the most important In-rich mineral in the orefield. Sphalerite in type-I orebodies contains from <0.02 to 21.96 wt % In, and in type-II orebodies contains from <0.02 to 0.39 wt % In. Indium-rich chemical-zoned sphalerite contains 7 to 8 wt % In in its core and up to 21.96 wt % In in its rim. This sphalerite may be the highest In-bearing variety in Southern China. The Cd contents of the In-rich sphalerite ranges from 0.35 to 0.45 wt %, which places it in the the “Indium window” of the Cu–In–S phases. The geological and structural features of the Xianghualing orefield indicate that the In mineralization of the two types of In-bearing Sn–Pb–Zn orebodies is related to the volatile-rich, In-rich, A-type granites, and is controlled by the normal faults of magmatic-diapiric activity extensional features.