Trace elements of Indium-bearing sphalerite from tin-polymetallic deposits in Bolivia, China and Japan: A femto-second LA-ICPMS study

Indium-bearing tin-polymetallic base metal deposits in Japan (Toyoha, Ashio and Akenobe), China (Dulong and Dachang), and Bolivia (Potosi, Huari Huari, Bolivar and Porco), were studied using femto-second Laser Ablation ICPMS (fsLA-ICPMS) and EPMA analyses for major and minor elements in sphalerite, paying special attention to In concentrations.Sphalerite is a principal mineral in these tin-polymetallic deposits and a broad range of In concentration is measured in the ores. There are distinct differences in mode of occurrence of the sphalerite and the distribution of In. The highest In concentration (up to 18 wt.%) occur as a Zn–In mineral within black sphalerite zones in an oscillatory-zoned sphalerite from the Huari Huari deposits. Additionally, jamesonite from the Huari Huari deposit also contains anomalous In values, ranging from several hundreds to thousands μg/g. Sphalerite from the Toyoha and the other Bolivian deposits are characterized by oscillatory and chemical zoning, whereas those from Akenobe and the Chinese deposits are represented by homogeneous distribution of In. The 1000In/Zn values of sphalerite are in good agreement with those of the ore grade for each of the selected tin polymetallic deposits indicating that sphalerite is the principal host of In.The In-bearing sphalerite principally involves the combined coupled substitutions (2Zn2 +) ↔ (Cu+, In3 +), (3Zn2 +) ↔ (Cu+, Ag+, Sn4 +) and (3Zn2 +) ↔ (2Cu+, Sn4 +). The first of these is apparent in sphalerite from Huari Huari and Bolivar, whereas the second is prominent in sphalerite from Toyoha, Ashio, Potosi, Porco and Dachang. Akenobe and Dulong sphalerite features the dominant coupled substitution of (2Zn2 +) ↔ (Cu+ or Ag+, In3 +), owing to their poor Sn content. Occasionally, sub-micron inclusions of minerals such as stannite and Pb–Sb-bearing sulfides can occur in sphalerite, contributing to high Cu–Sn and high-Ag contents, respectively. The observed correlations of each element in the In–Cu–Ag–Sn-bearing sphalerite can be proposed as a fundamental reason for the indium enrichment related to sulfur-rich oxidized magmatism. In addition, the Ag content in sphalerite is considered a possible indicator of formation depth, which ranges from plutonic to subvolcanic environments.

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► 1000In/Zn values of sphalerite are good agreement with those of the ore grade.
► The In-bearing sphalerites indicate 4 principle substitutions.
► An oxidized magma is important for enrichment of indium and chalcophile elements.
► Ag content in sphalerite can be a possible indicator for depth.