The Yejiwei deposit, which is located in the southern Hunan W-Sn-Pb-Zn Metallogenic Belt in south China, is a large-scale porphyry-skarn-veinlet-type deposit containing 806 t In. Mineralization occurs as porphyrytype Sn (stockworks), skarn-type Sn-Cu, marble-hosted-type Sn-Cu (veinlet), and vein-type Pb-Zn ores. Thirty-five ore samples were collected from the Yejiwei deposit for bulk and mineral chemical composition, microscopic observation and electron microprobe analyses. The porphyry-type Sn ores contain variable amounts of In (2.3-76 ppm; mean of 17.4 ppm) with local In enrichment (226 ppm) and 1000 × In/Zn values are 3.8-52.4. The skarn-type Cu-Sn ore is richest in In (12.3-214 ppm; mean of 114 ppm), and 1000 × In/Zn values are 2.4-117. In contrast, the In content of the marble-hosted-type Cu-Sn ores is relatively low (7.4-34.9 ppm; mean of 20.3 ppm), and 1000 × In/Zn is in the range of 0.61-5.5, and the vein-type Pb-Zn ores in the external zone contain the lowest In contents (7.2-17.0 ppm; mean of 12.1 ppm) with 1000 × In/ Zn values of 0.07-0.09. The ore minerals in the deposit include pyrite, pyrrhotite, cassiterite, and In-bearing minerals of sphalerite, chalcopyrite, and stannite. Although only trace amounts of sphalerite are hosted in the porphyry ores, the sphalerite contains the highest In content (0.27-10.1 wt.% In) in the deposit. We observed the highest In contents of all In-bearing sphalerite reported in China. The In contents of sphalerite in the skarn-type ore range from 0.15 to 0.56 wt.%, whereas the marble-hosted-, and vein-type ores have lower In contents (0.00-0.04, and 0.03-0.06 wt.%, respectively). The In resources of the Yejiwei deposit are mainly hosted in skarn ores of the No. 31 and No. 32 orebodies. The genesis of In in the Yejiwei deposit was closely related to the shallow intrusive environment of related igneous rocks. As W-Sn-Mo-Bi-Cu-Pb-Zn-Ag mineralization is widespread in south Hunan, this study would suggest a focus on skarn-type Sn-Zn deposits for the future prospecting of In resources.

Abstract:Although native bismuth is a relatively common mineral, native antimony is less abundant, and Sb-Bi alloys are relatively rare phases in Nature. Sb-Bi alloys and Ag-Cu-Pb-Sb-Bi sulphosalts have been discovered in the Jialong vein-type Cu-Sn deposit in North Guangxi, South China. The Jialong deposit is hosted by schist within the contact zone of a Neoproterozoic granite. Four stages of ore formation are recognised, with the Sb-Bi alloy-and sulphosalt-bearing assemblage formed during the third stage. Sulphosalts include Pb-Bi-Ag sulphosalts (pavonite), Sb-Bi sulphosalts (tintinaite, terrywallaceite), and Sb sulphosalt (ullmanite, freibergite, bournonite). Grains of Sb-Bi alloy measure 2-20 µm in diameter, show rounded margins and occur together with galena along the edges or internal fissures of sulphosalts. The Sb-Bi alloys do not coexist with bismuthinite, BiS (an unnamed mineral), or with native bismuth. Two phases of Sb-Bi alloys are identified based on back-scattered electron image observations and electron microprobe analysis. The textural and thermodynamic relationships indicate that Phase I was formed before Phase II. Phase I contains high Sb (69.15-80.12 wt %) and lower Bi (18.01-27.85 wt %), while Phase II contains low Sb (0.89-25.24 wt %) and high . Cooling in the range of 270-400 • C and decreasing sulphur fugacity promote precipitation of Sb-Bi alloys and sulphosalts during the late stage of incursion of Sb-and Bi-bearing magmatic hydrothermal fluids.