Indium-Bearing Ore from the Goka Mine Naegi District, Southwestern Japan

Abstract

Indium-containing ore was found from the Goka mine. The ore is mainly composed of sulfides like chalcopyrite, sphalerite, stannite, arsenopyrite, galena, cassiterite and gangue minerals. Microprobe analyses indicate that the indium carriers in the Goka mine are sphalerite (<1.89 wt%In), stannite (<9.63 wt%In), chalcopyrite (<0.4 wt%In), and cassiterite (<1.21 wt%In). In addition to the minerals mentioned above, Zn-Cu-Fe-In-Sn-S minerals of varying chemical composition are observed. Their formula is expressed as mCu(In, Sn)S2•n(Zn, Fe)S, where most of the analysis data show m:n=1:2 or 1:4. The occurrence of the indium minerals at the Goka mine gives an additional evidence that the tin-polymetallic veins are important indium concentrating geologic bodies. Introduction Indium is an important rare metal which is used for dental alloy, low melting point alloy, bearings, electronics industry and so on. Japan is the No. 1 producer of indium in the world and produced 16 tons of indium concentrate in 1986 (ROSKILL INFORMATION SERVICES LTD., 1987). But the domestic supply for the indium ore comes exclusively from the Toyoha mine. It is, therefore, important to explore the new types of indium-bearing deposits in addition to the Toyoha mine. Recently MURAO and ANDOH (1989) pointed out that the xenothermal type*1 deposit is an important indium concentrating geologic body in nature: According to their research, tin-polymetallic veins embedded in rhyolite carry indium as indium minerals or impurity of sulfides. For example, a new indium mineral, sakuraiite was described by KATO (1965) from the Ikuno deposit which is situated at the north of the ilmenite-series Sanyo granite. Thus the present authors focus their attention to the Goka mine, now abondaned, which has similar geologic condition to the Ikuno: the polymetallic vein is embedded in volcanic rock beside the ilmenite series Naegi granite. The samples were collected from the waste of the Goka deposit and were served for the EPMA analyses. Goka Mine The Goka mine is located in the Naegi district, about 60 km northeast of Nagoya City (Fig. 1). The naegi district has been famous for the uraniferous pegmatite mineralization (e.g. SAKAMAKI et al., 1961) around the Uppermost Cretaceous Naegi granite which is well fractionated ilmenite-series granite with extremely high ratio of Rb/Sr and high concentration of fluorine (ISHIHARA and TERASHIMA, 1977). According to SAKAMAKI et al. (1961), the veins in this district exhibit the zonal arrangement from the granite outwards: raremetal bearing pegmatites, W-Sn-Bi, W-AsBi, and Cu-Pb-Zn-As zones. But the zonation rather seems to start from the granoReceived on September 11, 1989, accepted on December 8, 1989 * Geological Survey of Japan , Higashi 1-1-3, Tsukuba 305, Japan. ** School of Science and Engineering , Waseda University, Nishiwaseda 1-6-1, Shinjuku, Tokyo 169, Japan.