Indium contents of some sedimentary and igneous rocks in the In-mineralized areas in China, Japan and Bolivia.

Abstract

Abstract: In-rich vein-type base metal deposits, such as those of Toyoha mine, Ashio mine, Dachang mine and Bolivian Snpolymetallic belt, occur generally in sedimentary terranes. Trace amounts of indium in the sediments in the Dachang area of China were reported to have an average of 1.0 ppm for the D₃-stage shale (n=3) and averages of 0.3-0.7 ppm for the D₁-stage black shale by Pasava et al. (2003). We also analyzed shales and some fine sandstone and limestone of the same area, and found an anomalous value of 1.04 ppm In on the D₃-stage black shale, and an average of the sediments of 0.22 ppm In for the Dachang mine area. Averaged In contents of host sediments in the famed In-mineralized areas in this world are as follows: 0.072 ppm in the Toyoha mine area, 0.068 ppm in the Boliver mine area, and 0.053 ppm in the Ashio mine area, which are more or less the same as 0.066 ppm of a normal pelitic rock (JSl-1) of the Toyoma slate, Kitakami Mountains. It is concluded that the host sediments of In-mineralized areas are not particularly anomalous in terms of In-contents as sedimentary rocks, except for the Dachang area. This normal amounts of In could possibly extracted by acid ore fluids from granitic magma, then precipitated In by neutralization and lowering temperature of the ore fluids.