The gold ore of the Harmony mine is hosted by conglomerate of the Basal Reef, Central Rand Group in the Witwatersrand Basin, the world's largest gold-producing province of South Africa. The conglomerate contains detrital rock fragments such as quartzite, shale, with minor greenstone. It accompanies mineral fragments of quartz, feldspar, zircon, chromite, pyrite, uraninite and minor gold. Quartz grains in the studied samples typically occur as rounded pebbles or granules. Under a cathodoluminescence (CL) microscope, quartz shows various colors, light blue, bluish purple, reddish purple, orange and brown. Preservation of several colors suggests that the metamorphic grade of conglomerate is very low. Grains of quartz were probably supplied from different source rocks because luminescence colors of quartz pebble are variable even in neighboring pairs. Quartz grain associated with uraninite shows zonal texture with inner part and thin rim under the CL microscope. A thin layer (∼ 50 μm) with reddish luminescence typically surrounds the inner part of a quartz grain which shows bluish to brownish luminescence. Such texture of quartz suggests that the inner parts of quartz grains represent original CL color, and that the outer parts were caused by radiation damage. Some quartz shows the thin layer of reddish CL color in its crack. This texture shows the relation of the hydrothermal solution containing uranium and precipitation of microsize uraninite. Chemical composition of gold grains are 82.0-85.4 atm.% Au, and Hg content in gold is very low. Low Hg concentration in gold is consistent with the weakness of post-depositional hydrothermal modification of gold ore.

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Study of the stability of radioactive minerals in a placer deposit in the Naegi District, southeastern Gifu Prefecture, Central Japan contributes to understanding the modes of nuclide migration under various hydrogeological environments in the tectonically active Japanese Island Arc system. The placer deposit is embedded in basal conglomerates of the lowermost alluvial sequences, exposed to a near-surface, oxidizing hydrogeological environment. The mineral samples, ranging in mesh size from 120 to 250, were identified after sieving and magnetic separation to be mainly cassiterite, thorite, monazite, and topaz, with subordinate amounts of zircon, fergusonite-(Y), xenotime and wolframite. Observations using optical and scanning microscopy indicated that many grains of zircon have well-preserved crystal faces. Most monazite and fergusonite-(Y) grains are partly abraded and corroded whereas thorite grains are highly abraded and corroded. This indicates that under an oxidizing hydrogeological environment, the mechanical durability and geological stability decrease from zircon to monazite/fergusonite-(Y) to thorite, which correlates well with the Mohs's hardness scale. Cut and polished thorite grains display a high degree of alteration. The altered portions have higher Th, Fe and Y contents, and lower U and Si contents in comparison with the unaltered portions, indicating leaching of U and Si. In the fergusonite-(Y) grains, the altered portions have higher Th, Nb and Ta contents, and lower U and Y contents in comparison with the unaltered portions, indicate leaching of U and Y. Thus it is determined that uranium is strongly leached in an oxidizing hydrogeological environment. The leaching behaviour is dependent on mineralogy and is consistent with thermodynamic estimates. The alteration rate of fergusonite-(Y) was calculated to range from 0.05 to 0.000025 μm/year based on the thickness of the external alteration film and the duration of exposure to the oxidizing conditions. The lifetimes of fergusonite, monazite and thorite are estimated to be of the order of 10⁵-10⁷, 10⁵-10⁷ and 10⁴ -10⁶ years, respectively. Although leaching or release of uranium from radioactive minerals to the surface geological environment is estimated to be long duration under an oxidizing hydrogeological environment, total amount of uranium released to surface geological environment is negligible because radioactive minerals are generally rare.

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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.

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In 2008, oil prices decreased gradually after the record of 147.27 US$/bbl (WTI in NYMEX) on July 11, and rapidly after the failure of Lehman Brothers on September 15. Metal prices also decreased, although the trend was not as similar as oil. In spite of the economic depression caused by the financial crisis, Japanese mining, petroleum and trading companies, and JOGMEC (Japan Oil, Gas and Metals National Corporation) have reported many fruitful results in exploration and development of mineral and energy resources, which have been carried out in these several years and decades. For example, JOGMEC confirmed extension of prominent copper-gold mineralization in the Frontera area of Andean Cordilleras straddling the border between Chile and Argentine, which was expected to be more than 100 million tons.

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