Paragenesis of Epithermal Acid-Sulfate Type Gold Deposits in Kagoshima Prefecture
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Imai et al. (1996) prepared a paper on epithermal gold deposits in the Nansatsu district of Kagoshima Prefecture. The Akeshi mine in this district contains acid-sulfate type deposit. This deposit, which occurs in Miocene-Pliocene silicified volcanics, contains gold and copper ore. Imai et al. (1996) described the paragenetic relationship of native gold, barium-pharmacosiderite, tripuhyite, scorodite and "limonite". However, the methods for determining those minerals were not described. In the present paper, they have been added.The authors classify the ores in this deposit into three kinds:(i) Unoxidized pyrite-gold ore, in which the pyrite holds small amounts of Au, Ag, As, and Sb.(ii) Unoxidized gold-copper ore, containing native gold, pyrite, and luzonite and/or energite.(iii) Oxidized high-grade gold ore.The present authors identified native gold, "limonite", barium-pharmacosiderite (Ba [Fe43+(OH)5 (As O4)3]·5H2O), tripuhyite (Fe3+Sb5+O4), scorodite(Fe3+As5+O4·2H2O) and barite in the oxidized high-grade ore using a transparent and reflecting microscope, EPMA, and X-ray diffraction analysis. "Limonite" is mainly composed of goethite, accompanied by small amounts of lepidocrocite, hematite, and jarosite. Slender quartz veinlets, accompanied by "limonite", native gold, barium-pharmacosiderite, tripuhyite, and scorodite, penetrated the silicified rock.From the paragenetic relationship, the authors concluded that some of the oxidized high-grade gold ore was derived and enriched from unoxidized pyrite-gold ore and gold-copper ore in hypogene condition by the latest mineralizing solution.
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