INDIUM RESOURCES AND METALLOGENY IN JAPAN, CHINA AND BOLIVIA

Indium-bearing deposits, mainly tin-polymetallic base metal deposits in Japan, China, and Bolivia, were studied by ICP/MS and femto-second Laser Abration ICPMS (fsLA-ICPMS) for major and minor elements, paying special attention to In concentration.

The chemical analyses for ore composites give the following In-amounts and 1000In/Zn ratio, respectively; From Japan: 1,030 ppm and 2.1 (Toyoha), 295 ppm and 3.2 (Ashio), 328 ppm and 13.7 (Ikuno), 125 ppm and 0.35 (Akenobe); From China: 183 ppm and 5.6 (Dulong), 297 ppm and 2.3 (Dachang); From Bolivia: 292 ppm and 4.0 (Potosi), 3,080 ppm and 11.3 (Huari Huari), 584 ppm and 1.7 (Boliver), 499 ppm and 1.23 (Porco), and 213 ppm and 0.61 (Colquiri). Applying the In contents of the ore composites to the produced and remaining ores, the total amount of indium in the Bolivian tin-polymetallic deposits is speculated to be more than 12,000 tons In, which is larger than that of South China (11,000 tons) and the Japan (9,000 tons).

Indium occurs mostly in less transparent black sphalerite. Sphalerites of the deposits in Japan and Bolivia readily display oscillatory and chemical zoning partly comprising high concentration of In (up to .>1 wt %) bands coexisting with Cu-Sn rich zone (e.g., petrukite) in a single crystal. In contrast, sphalerites of Dulong and Dachang deposits in China have no optical zoning and homogeneous In content with an average 1,229 ± 546 ppm (1σ). Sphalerites in Toyoha, Potosi, and Dachang deposits are incorporated minor amounts of Sn and Ag, implying association of silver-tin polymetallic environment with the concentration of indium.

The observed correlation of the In-bearing sulfides with Sn mineralization can be proposed as fundamental reason for the indium enrichment related to oxidized or reduced magmatisms. Besides, averaged In contents of host sediments in the studied area are not particularly anomalous except for Dachang area. For Japanese Islands arc, there are essentially possible reducing sediments such as accretionary terrains intruded by various deep oxidized magmas containing sulfur. In contrast, Bolivian and Chinese In-mneralized areas are spatially associated with ilmenite-series granitoids ranging from subvolcanic to plutonic environments where a dominant transport of S-rich vapor separated from the magma to precipitate indium upon cooling.