The main purpose of this paper is to present a fundamental concept of U-Pb isotopic spectrum-system and to apply this idea to the interpretation of the mechanism of uranium ore formation. It is evident from a number o...The main purpose of this paper is to present a fundamental concept of U-Pb isotopic spectrum-system and to apply this idea to the interpretation of the mechanism of uranium ore formation. It is evident from a number of examples of uranium deposits that the uranium deposits formed in various processes are characterized by different types of U-Pb isotopic spectrum-system.展开更多
Isotopic ages of Precambrian metamorphic rocks from western Anhui have beeu determined, giving, a whole-rock Rb-Sr isochron age of 2.7 b.y. and two groups of mineral Rb-Sr isochron ages ranging from 2.3 to 2.2 and 1.8...Isotopic ages of Precambrian metamorphic rocks from western Anhui have beeu determined, giving, a whole-rock Rb-Sr isochron age of 2.7 b.y. and two groups of mineral Rb-Sr isochron ages ranging from 2.3 to 2.2 and 1.8 to 1.4 b.y. respectively. These ages represent the time of cooling of the rocks affected by thermal events. U-Th-Pb ages indicate that the U-Pb isotopic system was disturbed during metamorphism. But Th-Pb, Pb-Pb and whole-rock Rb-Sr ages are relatively concordant while K-At and Rb-Sr ages are all the same. Initial ^87Sr/^86Sr ratios in the metamorphic rocks are within the range of 0.704---0.707.This shows that these rocks contain significant amounts of sialic materials.展开更多
The uranium deposit studied in this paper occurs in a Precambrian (Xuefengian)granite batholith. The emplacement age of the granite is 760 m.y. The average content of uranium in the granite is 7 ppm, but the yield of ...The uranium deposit studied in this paper occurs in a Precambrian (Xuefengian)granite batholith. The emplacement age of the granite is 760 m.y. The average content of uranium in the granite is 7 ppm, but the yield of leachsd U is higher With an average of about 33.8%. The granitic rocks, contain; Some uraninite. Uranium mineralization mainly takes the form of siliceous veins With an age of 47 m.y. K-feldspar. present in the granite and pyrite associated with pitchblende were massspectrometrically analyzed for Pb isotopic compositious, characterized by anomalous lead. A reasonably linear array can be seen on the ^207Pb/^206Pb--^205Pb/^204Pb plot, implying a genetic connection between the rock and the ore, and a derivation of rock-forming materials from. a uranium-rich source. According to the continuous-growth model for anomalous lead, evolution, two isochrons give the. ages-of about 764 m.y. and 708 m.y.for ore-forming materials, close to the emplacement age of .the granite batholith. This indicates that the ore-forming materials came from the granite batholith. Eight granite samples collected from the mining .area were analyzed, but no uranium-lead ages could be worked out because of the pregressive destruction of the closed U-Pb isotopic system since granite emplacement, which resulted in the loss of uranium(78%). It can be imagined that in the period of continental weathering the surface water would infiltrate downwards, leaching out large amounts of uranium from the granitic rocks to form infiltration solution. The solution was heated at great depth and then found its way upwards, on which it dissolved constantly U from the rocks to form the uranium deposit.展开更多
Based on the evolutionary theory of U-Pb isotopic system, we have studied the genetic model for a uranium deposit occurring in the carbonate-silicolite-pelite. The data show that the U-deposit is characterized by a mu...Based on the evolutionary theory of U-Pb isotopic system, we have studied the genetic model for a uranium deposit occurring in the carbonate-silicolite-pelite. The data show that the U-deposit is characterized by a multi.stage evolution with respect to its U-Pb isotopic system, and the mechanism of its genesis can be expained by later repeated superimposition of mineralization which took place at about 200±10 m.y.; 100±10 m.y., 60 ± 10 m.y.and 11 ± 1 m.y. ago. These mineralization stages are closely related to the regional geological tectonic activity.展开更多
Valence dipolarization is an important factor and one of the basic rules govering the formation of the earth's crust, the evolution of ultrabasic-basic→intermediateacidic→ultraacidic rock series, magmatie differ...Valence dipolarization is an important factor and one of the basic rules govering the formation of the earth's crust, the evolution of ultrabasic-basic→intermediateacidic→ultraacidic rock series, magmatie differentiation of igneous intrusions and the distribution and concentration of rare and radioactive elements in igneous rocks, and orthomagmatic metallogenesis. Ichor, transmagmatic fluids or ascending thermal fluids from the upper mantle, produced by dewatering, degassing, dealkalization, desilification and the loss of heat are all exclusive valence dipolarizing agents within the earth.Ca- and Mg-skarns are products of anti-valence dipolarization. Alkaline metasomatism is regarded as valence dipolarization in the hydrothermal stage.展开更多
文摘The main purpose of this paper is to present a fundamental concept of U-Pb isotopic spectrum-system and to apply this idea to the interpretation of the mechanism of uranium ore formation. It is evident from a number of examples of uranium deposits that the uranium deposits formed in various processes are characterized by different types of U-Pb isotopic spectrum-system.
文摘Isotopic ages of Precambrian metamorphic rocks from western Anhui have beeu determined, giving, a whole-rock Rb-Sr isochron age of 2.7 b.y. and two groups of mineral Rb-Sr isochron ages ranging from 2.3 to 2.2 and 1.8 to 1.4 b.y. respectively. These ages represent the time of cooling of the rocks affected by thermal events. U-Th-Pb ages indicate that the U-Pb isotopic system was disturbed during metamorphism. But Th-Pb, Pb-Pb and whole-rock Rb-Sr ages are relatively concordant while K-At and Rb-Sr ages are all the same. Initial ^87Sr/^86Sr ratios in the metamorphic rocks are within the range of 0.704---0.707.This shows that these rocks contain significant amounts of sialic materials.
文摘The uranium deposit studied in this paper occurs in a Precambrian (Xuefengian)granite batholith. The emplacement age of the granite is 760 m.y. The average content of uranium in the granite is 7 ppm, but the yield of leachsd U is higher With an average of about 33.8%. The granitic rocks, contain; Some uraninite. Uranium mineralization mainly takes the form of siliceous veins With an age of 47 m.y. K-feldspar. present in the granite and pyrite associated with pitchblende were massspectrometrically analyzed for Pb isotopic compositious, characterized by anomalous lead. A reasonably linear array can be seen on the ^207Pb/^206Pb--^205Pb/^204Pb plot, implying a genetic connection between the rock and the ore, and a derivation of rock-forming materials from. a uranium-rich source. According to the continuous-growth model for anomalous lead, evolution, two isochrons give the. ages-of about 764 m.y. and 708 m.y.for ore-forming materials, close to the emplacement age of .the granite batholith. This indicates that the ore-forming materials came from the granite batholith. Eight granite samples collected from the mining .area were analyzed, but no uranium-lead ages could be worked out because of the pregressive destruction of the closed U-Pb isotopic system since granite emplacement, which resulted in the loss of uranium(78%). It can be imagined that in the period of continental weathering the surface water would infiltrate downwards, leaching out large amounts of uranium from the granitic rocks to form infiltration solution. The solution was heated at great depth and then found its way upwards, on which it dissolved constantly U from the rocks to form the uranium deposit.
文摘Based on the evolutionary theory of U-Pb isotopic system, we have studied the genetic model for a uranium deposit occurring in the carbonate-silicolite-pelite. The data show that the U-deposit is characterized by a multi.stage evolution with respect to its U-Pb isotopic system, and the mechanism of its genesis can be expained by later repeated superimposition of mineralization which took place at about 200±10 m.y.; 100±10 m.y., 60 ± 10 m.y.and 11 ± 1 m.y. ago. These mineralization stages are closely related to the regional geological tectonic activity.
文摘Valence dipolarization is an important factor and one of the basic rules govering the formation of the earth's crust, the evolution of ultrabasic-basic→intermediateacidic→ultraacidic rock series, magmatie differentiation of igneous intrusions and the distribution and concentration of rare and radioactive elements in igneous rocks, and orthomagmatic metallogenesis. Ichor, transmagmatic fluids or ascending thermal fluids from the upper mantle, produced by dewatering, degassing, dealkalization, desilification and the loss of heat are all exclusive valence dipolarizing agents within the earth.Ca- and Mg-skarns are products of anti-valence dipolarization. Alkaline metasomatism is regarded as valence dipolarization in the hydrothermal stage.
