Alluvial mining

Japanese: 砂鉱床採掘 - さこうしょうさいくつ（英語表記）alluvial mining

There are deposits containing useful minerals, such as gold dust, tin dust, or iron sand, in unconsolidated soil and sand. When rocks are weathered and decomposed, the useful minerals contained within them are separated, carried by water or wind, and precipitated and deposited in another location. They are called placer deposits, and are separated and concentrated during transportation. Many of them contain minerals that are difficult to dissolve and have a high specific gravity, such as gold, cassiterite, or ilmenite, and unique methods are used to mine them. In riverbeds and beaches, dredging is done with a dredger (gold extracting ship), and in hilly areas, methods such as cutting the material with a high-pressure jet of water and using the water flow to separate the minerals are used.

Source: Heibonsha World Encyclopedia, 2nd Edition Information

Japanese:

砂金や砂スズ，あるいは砂鉄など，未固結の土砂の中に有用鉱物を含む鉱床がある。岩石が風化･分解し，その中に含まれていた有用鉱物が分離し，水または風によって運ばれ，別の場所に沈殿堆積したもので，運搬の途中で分別され濃縮されており，砂鉱床といわれる。金やスズ石，あるいはチタン鉄鉱(イルメナイト)など，溶けにくく，比重の大きい鉱物を含むものが多く，その採掘には独特な方法が行われる。河川敷や海浜などでは浚渫（しゆんせつ）船(採金船)によるドレッジングdredgingが，丘陵地などでは高圧ジェット水による切崩しと水流を利用した分別をする方法などが行われる。

出典　株式会社平凡社世界大百科事典第２版について　情報

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