mineral deposits in the zone of chemical weathering of rock near the earth’s surface. Weathering deposits were formed in past geological eras—and are being formed in modern times—upon decomposition of abyssal rock that has been brought to the earth’s surface and is not resistant under the new thermodynamic conditions. Under the influence of water, oxygen, carbon dioxide, and inorganic and organic acids, as well as accumulations of protozoan organisms, the rock breaks down and is transformed from aggregates of complex silicates to simpler oxides and hydroxides. Some of the newly formed compounds are dissolved and carried away by groundwater and then redeposited at a certain depth from the surface, forming infiltration weathering deposits of uranium, copper, and native sulfur. The poorly soluble part accumulates near the surface, forming residual weathering deposits of nickel, iron, manganese, bauxite, magnesite, and kaolin.
REFERENCESmirnov, V. I. Geologiia poleznykh iskopaemykh, 2nd ed. Moscow, 1969.
V. I. SMIRNOV