Geochemical constraints on the genesis of the Bayan Obo Fe–Nb–REE deposit in Inner Mongolia, China
Geochemical constraints on the genesis of the Bayan Obo Fe–Nb–REE deposit in Inner Mongolia, China
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DOI：
10.1016/j.gca.2008.12.003
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发表时间：
2009-03
影响因子：
5
通讯作者：
Xiaoyong Yang;Wei-dong Sun;Yuxu Zhang;Yong‐Fei Zheng
中科院分区：
文献类型：
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作者：
Xiaoyong Yang;Wei-dong Sun;Yuxu Zhang;Yong‐Fei Zheng
通过对白云鄂博Fe-Nb-REE矿床的碳酸盐岩、围岩（H8白云岩）、白云鄂博杜拉哈拉碳酸盐岩脉和白云鄂博富稀土白云岩的微量元素和同位素组成的测定，探讨了巴彦鄂博Fe-Nb-REE存款的成因。富稀土碳酸盐岩脉样品的稀土元素和微量元素配分模式与矿化碳酸盐岩样品的稀土元素和微量元素配分模式一致，表明富稀土碳酸盐岩与成矿之间存在成因联系。成矿碳酸盐岩的碳、氧同位素变化较大，δ 13 C =-7.98 ‰ ~-1.12 ‰，δ 18 O =8.60-25.69‰，与幔源碳酸盐岩的碳、氧同位素有明显的差异。白云岩-方解石同位素分馏异常表明，白云岩-方解石在巴彦鄂博碳酸岩脉、矿体和H8大理岩中处于不平衡状态。在巴彦鄂博Fe-Nb-REE矿床存款东南约25 km处的黑脑包矿化沉积海相泥晶岩中也发现了这种同位素特征。这些事实表明，巴彦鄂博存款中的碳酸盐矿物是沉积碳酸盐岩被地幔流体交代的结果，可能来自富含稀土元素的碳酸盐岩浆。矿体和碳酸岩脉的Nd同位素初始值一致，表明矿体、碳酸岩脉和碳酸岩脉可能具有相似的稀土元素来源。
Trace element and isotopic compositions of carbonate from ore bodies, country rock which hosts the ore bodies (H8 dolomite), a carbonatite dyke exposed in Dulahala near Bayan Obo, and rare earth element (REE)-rich dolomite in Bayan Obo have been determined to understand the genesis of the Bayan Obo Fe–Nb–REE ore deposit, the world’s largest resource of REE. The REE and trace element distribution patterns of samples from the REE-rich carbonatite dykes are identical to those of mineralized carbonate rocks, indicating a genetic linkage between the REE-rich carbonatite and mineralization in this region. By contrast, carbon and oxygen isotopes in the mineralized carbonate varied significantly, δ13C=−7.98‰ to −1.12‰, δ18O=8.60–25.69‰, which are distinctively different from those in mantle-derived carbonatite. Abnormal isotopic fractionations between dolomite and calcite suggest that these two minerals are in disequilibrium in the carbonatite dyke, ore bodies, and H8 marble from Bayan Obo. This isotopic characteristic is also found in mineralized sedimentary marine micrite from Heinaobao, ∼25km southeast of the Bayan Obo Fe–Nb–REE ore deposit. These facts imply that the carbonate minerals in the Bayan Obo deposit have resulted from sedimentary carbonate rocks being metasomatised by mantle-derived fluids, likely derived from a REE-enriched carbonatitic magma. The initial Nd isotope values of ore bodies and carbonatite dykes are identical, indicating that ore bodies, carbonatite dykes and veins may have a similar REE source.