Abstract:So far a substantial number of fairly important commercial hydrothermal uranium deposits have been found in the carbonate-siliceous-pelitic metamorphic rocks, especially in those of Precambrian period, But very few reports are available in foreign countries about the hydrothermal uranium deposits occurring in non-metamorphic Paleozoic carbonate- siliceous- pelitic rocks. In China, however, the hydrothermal uranium deposits of significant economic value are frequently observed appearing in non-metamorphic carbonate-siliceous-pelitic rocks of the Sinian-Permian systems. These deposits mainly occur in limestone, dolomite, silicalite, siliceous limestone, calc-silicalite and various other rocks composed of carbonaceous, peliticancl siliceous sediments, which are of the Upper Sinian, Cambrian, Lower and Middle Silurian, Devonian, Lower and Middle Carboniferous and Lower Permian systems. The formation of these deposits is controlled by strata-bound, time-bound as well as structural and lithologic factors and is concentrated in the period of 120-20 m. y. As a result, deposits of this type are, without exception, strictly controlled by the structure, especially by fracture structure, and orebodies of these deposits, present in the rocks rich in various uranium-concentrators, are predominantly governed by the interformational fractures. These deposits were not formed exclusively by the action of surficialwater or descending ground water, they also obviously bear the stamp of hydrothermal superimposition and transformation. The paragenetic associations of minerals, characteristic textures of ore and the data of fluid inclusions suggest that uranium mineralization .was confined to a certain stage during the hydrothermal metallogenic process, at the temperatures between 250℃ to 900℃. Sources of aquae and ore constituents are of distinct double mixing nature. Aquae were primarily the deep-cyclic meteoric waters heated by magmatism, tectonism, metamorphism and geothermal temperature increase, mixed with hydrothermal fluids derived from the depth. Uranium and other ore constituents were derived mainly from uranium source beds and bodies (of them, the most important and extensively distributed were Lower Paleozoic uranium-rich beds and bodies formed during the stage of sedimentation-diagenesis, initial uranium enriched boclies formed at the supergene stage as well as granites and intermediate-acidic volcanic rocks adjacent to the deposits) and uranium reservoirs in which uranium orebodies occur. Besides, a minor part of them came from the depth. Uranium concentration was chiefly the result of the transformation of these beds and bodies by the superimposed hydrothermal fluids. During the Cretaceous-Tertiary magmatism,faulting movement and formation of continental red beds, uranium deposits of this type were eventually formed by the hydrothermal transformation of uranium source beds and bodies, Uranium reservoirs and/or initial uranium enriched bodies in the process of the movement of the ascending hydrothermal solutions towards the areas of pressure depletion caused by intense faulting movement, Precipitation and concentration of uranium took place at intermediate-low temperatures and pressures. These deposits, therefore, are products of special stages and environments during the geological and tectonic evolution in China.
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张待时.1983.中国碳、硅、泥岩中热液迭造型铀矿床成因探讨[J].矿床地质,2(2):87~94.1983.An investigation on the genesis of the uranium deposits of the hydrothermal superimposition and transformation type in carbonate-siliceous-pelitic rocks in China[J].Mineral Deposits2(2):87~94
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