Occurrence and Chemistry of Indium-containing Minerals from the Toyoha Mine, Hokkaido, Japan

OHTA Eijun

doi:10.11456/shigenchishitsu1951.39.218_355

Toyoha lead-zinc-silver vein-type deposit in Hokkaido, Japan produces an important amount of indium as well as tin and copper. Bismuth, tungsten, antimony, arsenic, and cobalt are minor but common metals. Indium minerals recognized are; unnamed Zn-In mineral (hereafter abbreviated as ZI) whose composition is at the midst of sphalerite and roquesite, unnamed Ag-In mineral (AI) of AglnS₂ composition, roquesite (RQ) and sakuraiite. Observed maximum weight percentages of indium in chalcopyrite, kesterite (KS) and stannite are 1.0, 1.86 and 20.0, respectively. Indium concentration in sphalerite ranges from O.On to a few weight percent in most case, but exceeds ten weight percent at some points. Detailed EPMA analyses have revealed that such high concentration is attributed to a continuous solid solution between sphalerite (SP) and ZI. Continuous solid solutions between RQ₉₀ZI₁₀ and RQ₃₇ZI₆₃, and between KS₁₀₀ZI₀and KS₃₀ZI₇₀ are also detected. These solid solutions are attributed to coupled substitutions of 2(Zn, Fe) for CuIn, and of (Zn, Fe)In for CuSn. Other substitutions found between chalcopyrite and stannite and between stannite/kesterite and roquesite are of (Fe⁺², Zn)Sn for 2Fe⁺³ and of (Fe⁺², Zn)Sn for 2In respectively. Economically most important indium carriers in Toyoha are ZI and indium-bearing sphalerite. Next to sphalerite are kesterite, stannite and the anisotropic chalcopyrite. The occurrence of these minerals indicates that these minerals have been formed by pulsatile mineralization whose peak temperatures were 50 to 100°C higher than the hitherto estimated maximum formation temperature, about 300°, of the deposit.

Occurrence and Chemistry of Indium-containing Minerals from the Toyoha Mine, Hokkaido, Japan

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