| 豫西太华群混合岩特征及其与金钼矿化的关系 |
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| 引用本文：.1986.Characteristics Of Migmatites In 'Taihua Group Of Western He:Nan In Relation "To Gold And Molybdenum Mineralizations[J].Mineral Deposits,5(4):71~81 |
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| Characteristics Of Migmatites In 'Taihua Group Of Western He:Nan In Relation "To Gold And Molybdenum Mineralizations |
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| Abstract:Along the southern margin of North China platform, i, e., in western Henan, migmatites are extensively developed. Investigation shows that there do exist close genetic relationships of Taihua Group and its migmatization to molybdenum deposits in this area and gold deposits in this group. Migmatites are dominated by metasomatic textures. Conditioning the behavior of all other rock-forming elements, SiO2, K2O and Na2O seem to play a leading role in the process of migmatization which is actually a multistage metasomatic process noted for replacement of primitive rocks by the solutions. The behavior of REE, most minor elements and rock-forming elements is basically in conformity with the simple mixing model of two systems, and the balance mode of elements is characterized by "addition-dilution” instead of by the commonly described "gain-loss". This process is accompanied by the substitution of low-density minerals for high-density minerals and the expansion of the protolith in volume. lt is therefore conceivable that the diverse elemental concentrations of different types of raigmatites are the result of the mixture of elements from the protolith and those from the "brought-in” vein material in varying proportions. The variation range and tendency of elemental abundances with the intensification of migmatization depend on the difference in elemental concentration of these two systems, i, e., the larger the difference, the wider the variation range, and this is called "law of concentration difference". Based upon this law, in combination with the variation tendency of elements during the migmatization, the following compositional features of the migmatizing solution might be deduced: (1) the main components are H2O, SiO2, K2O and Na2O; (2) it is rich in incompatible elements of upper mantle, and characterized by ∑LREE＞＞∑HREE and Th＞＞U; (3) like rubidium, strontium also possesses the features of incompatible elements; (4) the solution is exactly deficient in such elements as magnesium, chromium and nickel which are abundant in pyrolite and katametamorphic rocks of lower crust. All this indicates that the solutions are dominantly derived from lower crust or/and upper mantle. The elements whose behavior accords with the concentration law has less possibility of mineralization during migmatization. Studies show that as molybdenum and gold do not fally with the law and have most distinct tendency of enrichment in the process of migmatuation, they are likely to form ores. This presumption is supported by the extensive distribution of gold deposits in Taihua Group and the close relationship of molybdenum mineralization to the basement of the platform iB this area. Plenty of data suggest that the formation of Morich fluid or pal/ngenic magma through the migmatization of the group makes up an iridispensable link in porphyry molybdenum mineralization of the area, and the Xiaoqinling gold metallogenic belt is exactly formed by the inheritance and/or superimposition of the multistage gold enrichment derived by multicycle migmatization and granitization of the group. |
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