| 内蒙白云鄂博铌、稀土、铁矿床的成矿时代和矿床成因 |
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| 引用本文：.1991.Metallogenic epoch and genesis of the Bayan Obo niobium-REE-iron deposit, Inner Mongolia[J].Mineral Deposits,10(1):59~70,58 |
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| 中文摘要:藉助于Sm-Nd同位素研究，得出白云鄂博矿床主矿体Sm-Nd全岩（全矿）等时线年龄为1.58Ga, Sm-Nd模式年龄为1.61Ga，εNd(t)=+6.1。结合矿床地质地球化学特征，氧、锶硫等同位素研究，作者认为，白云鄂博铌稀土铁矿床主要成矿于元古代，成矿物质来自地幔，是通过火山喷气沉积而形成。在加里东时期，随着碳酸岩（carbonatite）及碱性辉长岩的侵入，有一些成矿物质从深部带来，并引起广泛的交代作用。在海西时期，随着矿区南部花岗岩的侵入，矿床受到改造，交代作用进一步发育。此时没有多少成矿物质从深部或外部带入矿体。白云鄂博矿床成因上应属于碱性一碳酸岩杂岩型铌稀土铁矿床。 |
| 中文关键词:白云鄂博矿床 成矿时代 矿床成因 Sm-Nd同位素 |
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| Metallogenic epoch and genesis of the Bayan Obo niobium-REE-iron deposit, Inner Mongolia |
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| Abstract:Geotectonically, the Bayan Obo deposit is located on the northern margin of the North China platform. When the Proterozoic Bayan Obo Group Was formed, the area was likely a rift tectonic environment. Dolomite, the main wall rock(or host rock)of the orebody of the Bayan Obo ore deposit, shows distinct stratified structure and is remarkably similar to REE- and Nb-rich carbonatite rocks in other parts of the world in mineral constituents, petrochemical composition and RE as well as REE composition. K-feldspatite, another host rock of the orebody, might have been formed as a rssult of volcanic exhalation, and is unlikely a common slate. The Sm-Nd whole rock(whole ore)isochron age of the principal orebody of the Bayan Obo deposit is 1.58 Ga, and the Sm-Nd model age is 1.61Ga, with εNd(t)being+6.1. The data suggest that the ore deposit was formed in middle Proterozoic, and the ore-forming material came from the mantle. Middle Proterozoic seems to be the time when Bayan Obo Group Was deposited, and the REE metallization occurred together with the deposition of the strata. The isochron age is close to the model age, implying that the ore-forming material was precipitated to form the ore deposit immediately after its separation from the mantle, without much contamination by the crustal substances. Besides the metallogenic age of middle Proterozoic, the ages of Galedonian period and Hercynian period have also been recorded: for the former period, the Rb-Sr jsochron age of Kuangou carbonatite vein determined by the authors is 433 Ma with 87Sr/86Sr(i)being 0.706; for the latter period, the Th-Pb age of eschynite from the ore deposit and the Rb-Sr isochron age of biotite granite from the southern part of the ore district were already determined by previous workers. These data indicate that the ore-forming process was of polyphases. In addition, δ18Omagnetite values of massive iron ore are -2.99一+3.55‰, and δ18Omagnetite values of kaersulite type iron ore are +0.76一+1.92‰. These values, together with the sulfur isotopic data obtained by previous workers, also suggest that the ore-forming materal for the ore deposit Was derived from deep sources. It might be considered that the ore-forming process of the Bayan Obo deposit was of polyphases, but the major metallization took place in middle Pro-terozoic. The ore-forming material was brought upward in the form of volcanic exhalation from the mantle and then through sedimentation formed ore deposit which was genetically of alkalic rock-carbonatite rock type. In Galedonian period, with the intrusion of carbonaite veins, small amounts of ore-for- ming material might have been brought upward from the depth and led to extensive metasomatism. In Hercynian period, with the intrusion of granite from the south, the ore deposit was transformed and the metasomatism was further developed)nevertheless, little ore-forming material was brought into the orebody from the depth or the outside at that time. |
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