Colombia produces numerous mineral products such as oil, coal, gold, silver, platinum, nickel, emerald etc. and is thought to have still greater potential resource supplies. On the other hand, Japan depends on other countries for most of its supply of mineral resources and it is very important to insure the supply of these resources. As for copper, our country once was an exporting country of this material, but in 1990, 99.6% of Japanese demand for copper was met through import. At that time, in 1990, the El Roble mine was developed by a joint venture as the first mechanized underground copper mine in Colombia.
The El Roble mine is located at El Carmen de Atrato which is about 80km southwest of Medellín, Colombia. The ore deposit is of submarine volcanogenic massive sulfide type and a high grade copper-gold deposit. The reserves of minable ore is about one million metric tons with copper content of 3.8%, gold content of 2.7g/t and silver content of 8.4g/t.
A lot of laboratory works and detailed field surveys were conducted during the exploration program and provided effective guides for the exploitation. In particular the lithogeochemistry of minor elements and stable isotopes of the host rocks proved of great use for determination of targets in this area.
The geology and ore deposit of the mine are described, and an example of the explorations by a Japanese company in overseas countries is reported in this paper.

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The Sumikawa geothermal field is located on the north-east slope of the Yakeyama volcano, Akita prefecture. The Mitsubishi Materials Corporation has developed geothermal energy in this field after successful operation of the Ohnuma geothermal power plant. Subsurface geologic formations consist of dacitic pyroclastics, marine sediments, andesite lava and granodiorite intruded to these Tertiary formations. These formations are covered with the Quaternary andesite lava and lacustrine sediments. In this field, geothemal fluids are prominently found in subsurface fractures. Subsurface temperture recorded at the depth of 2, 000 m exceeds 300°C. The geothermal heat sources are probably lying beneath the YakeyamaHachimantai volcanic chain located to the south of the developing field. The geothermal resources are of the liquid dominated type accompanied by vapor dominated region at the top of the reservoir. According to the geothermal systems of the field, the production wells have carefully designed by. casing profile, drilling methods together with separating production zones have customized to prevent blowout of vapor and to produce large flow rate of vapor. Also well spacing has designed to recover efficiently heat energy during recycling of reinjection water. Numerical reservoir simulations suggest that the potential reservoir is large enough to produce vapor for 50M We an extended period of time. The Sumikawa geothermal power plant will be fully operated in early 1995. Authors have all actively engaged in the management of the Sumikawa geothermal energy developing field.

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南白老塊状重晶石鉱床の生成に関与した熱水溶液の地球化学的特徴を明らかにするために重晶石の⁸⁷Sr/⁸⁶Srr同位体比が分析された.重晶石の⁸⁷Sr/⁸⁶Srr比(0.70556-0.70647)は,鉱床下盤の安山岩の0.70450と中新世海水の0.7088の間にあることがわかった.得られた同位体比は北鹿の黒鉱鉱床の重晶石よりも低い範囲を示した.南白老鉱床の層状鉱体中の硫化物に富む鉱石および珪化帯中の網状鉱石の重晶石のSr同位体比は0.70561と0.70576の間の範囲にあった.一方,層状鉱体の主要構成物である重晶石鉱石は前者に比べやや高い比(0.70556-0.70647)であった.鉱石タイプの間のSr同位体組成の違いの原因を,海底の直下また海底上における重晶石の生成に対する海水の寄与の時間的および空間的な変化に帰することができる.南白老重晶石のストロンチウムおよび酸素同位体の特徴は,典型的な黒鉱鉱床と比べて,鉱化流体の同位体組成に隔たりがあったこと,また鉱石生成の温度が違っていたことに起因すると考えられる.

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lineament analysis and computer simulation analysis were carried out in order to understand the fracture systems around the Hishikari mine and the mechanism of the gold-quartz vein systems.
Pull-apart structure, fault gauge and drag fold, which are ovserbed in the quartz veins, indicate uplift of the basement(NAITO, 1993). Lineaments are divided into four directions, NW, NE, EW and NS directions, and four ring shaped lineaments are extracted by aerial photographic interpretation. The Hishikari mine is located in the central part of ring shaped lineaments. The distribution of ring shaped lineaments coincides with the basement structure estimated from gravity anomaly. It was understood that the ring shaped lineaments indicate the tectonic uplift of the Cretaceous basement, from the results of computer simulation analysis (Vertical Basement Displacement Method).
It is resulted that the fracture analysis provides the practical information about the buried vein systems in prospecting for epithermal gold deposits.

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The Yanomaki halloysite mine is a massive and irregularly shaped mineral deposit, that is developed in small leucocratic granitic bodies. Because the quality of the mineral deposit deteriorates with increasing depth, the Yanomaki halloysite mine is produced due to weathering of the upper parts of the leucocratic granitic bodies.
The leucocratic granitic bodies (we temporarily call them as "quartz-plagioclase rocks") lie within a Paleogene biotite granite pluton, and are composed mainly of plagioclase (oligoclase to andesine), quartz and minor amounts of titanite. Ca contents of the plagioclase are distinctly higher than those in the host granite. Mafic minerals are rare. The quartz-plagioclase rocks are associated with greisens and pegmatites on a small scale, and field relations between the quartz-plagioclase rocks and the host granite are gradational. This evidence suggests that the quartz-plagioclase rocks are "metasomatic anorthosite" formed by alteration by a Ca-rich hydrothermal fluid. A large amount of K₂O was leached out of the host granite by the hydrothermal fluid during feldspathization. The K₂O probably remobilized into the sericite mineralization found in adjacent areas.
The quartz-plagioclase rocks also can be mined for feldspathic resources. The total quantity of the rocks is estimated to be more than 6x10⁵ tons, and approximately 2x10⁵ tons of the rocks can be mined at the present open cut.

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リン鉱床は650-530mysのVendian-Cambrian期に生成した.そのピークは下部Cambrian期である.その時期は骨状組織が広く発達していることで特徴づけられる.リン鉱物を含む堆積物は,その時代の全ての大陸(南極を除く)にしられている.リン鉱床はふつう有機物の多い堆積中に見られる.堆積性リン鉱床は,微細状,微粒状,団塊状,有機体状に分けられる.最も多いのは,微細状,微粒状である.微細状と微粒状リン鉱床は,化学的沈殿物と考えられる.このリン鉱床中のリン鉱物は,ほとんどフッ素,炭酸塩を含むアパタイトである.

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