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Uranium ore deposits are economically recoverable concentrations of uranium within the Earth's crust. Uranium is one of the more common elements in the Earth's crust, being 40 times more common than silver and 500 times more common than gold.〔(【引用サイトリンク】title=Cameco – Uranium 101 )〕 It can be found almost everywhere in rock, soil, rivers, and oceans.〔(【引用サイトリンク】url=http://www.cameco.com/uranium_101/uranium_science/uranium/#two )〕 The challenge is to find those areas where the concentrations are adequate to form an economically viable deposit. Globally, the distribution of uranium ore deposits is widespread on all continents, with the largest deposits found in Australia, Kazakhstan, and Canada. To date, high-grade deposits are only found in the Athabasca Basin region of Canada. Uranium deposits are generally classified based on host rocks, structural setting, and mineralogy of the deposit. The most widely used classification scheme was developed by the International Atomic Energy Agency (IAEA) and subdivides deposits into 15 categories. ==Uranium== (詳細はmetallic weakly radioactive chemical element. It has the chemical symbol U and atomic number 92. The most common isotopes in natural uranium are 238U (99.27%) and 235U (0.72%). All uranium isotopes present in natural uranium are radioactive and fissionable, and 235U is fissile (will support a neutron-mediated chain reaction). Uranium, thorium, and potassium are the main elements contributing to natural terrestrial radioactivity. Uranium has the highest atomic weight of the naturally occurring elements and is approximately 70% denser than lead, but not as dense as tungsten, gold, platinum, iridium, or osmium. It is always found combined with other elements.〔(【引用サイトリンク】 title=Uranium )〕 Along with all elements having atomic weights higher than that of iron, it is only naturally formed in supernova explosions.〔(【引用サイトリンク】title=WorldBook@NASA: Supernova )〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「uranium ore」の詳細全文を読む スポンサード リンク
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