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Russian Geology and Geophysics

2006 year, number 12


F.A. Letnikov
Institute of the Earth's Crust, Siberian Branch of the RAS, 128 ul. Lermontova, Irkutsk, 664033, Russia
Keywords: Fluid, asthenosphere, Earth, core, plume, ore, lithosphere
Pages: 1271-1281


After the Earth had melted in the conditions of mostly reduced fluids, its chemistry included two distinct groups of light and heavy elements with high and low oxygen affinity, respectively. Light elements, with their density lower than in Fe but oxygen affinity higher than in FeO, accumulated in the essentially oxygenic sphere composed of silicates and oxides. Heavy elements with low oxygen affinity and native Fe sank to the Earth's center and formed the iron core. Thus the Earth's protomaterial partitioned to make an oxygen-free core where liquid iron stores enormous amounts of H2, CO, CH4, S, H2S, and other reduced gases surrounded by an almost 3000 km thick mantle in which the constituent minerals contain 75-80% oxygen. This separation of elements at the beginning of the Earth's history predetermined the specific behavior of fluids in all deep processes, including metallogeny, for the billions of years which followed.
Self-organization of the Earth's upper layers by means of granite formation produced the crust. Having lost its granite-forming components, the mantle graded into solid depleted mantle underlain by non-depleted asthenosphere impregnated with fluids. The mineralizer capacity of asthenospheric fluid systems correlates with their T and P conditions and the related maturity of lithospheric blocks. Therefore, the deep-seated origin of mineral deposits stems from two feeding fluid super-systems, the core and the asthenosphere, each with its typical chemistry. The two sources produced the respective metallogenic provinces with the chemistry of deposits controlled by the causative mineralizer systems.