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首页> 外文期刊>Contributions to Mineralogy and Petrology >Deducing the source and composition of rare earth mineralising fluids in carbonatites: insights from isotopic (C, O, Sr-87/Sr-86) data from Kangankunde, Malawi
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Deducing the source and composition of rare earth mineralising fluids in carbonatites: insights from isotopic (C, O, Sr-87/Sr-86) data from Kangankunde, Malawi

机译：在碳酸石中推导出稀土矿物质液的源和组成：来自康卡通，马拉维的同位素（C，O，SR-87 / SR-86）数据的见解

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摘要

Carbonatites host some of the largest and highest grade rare earth element (REE) deposits but the composition and source of their REE-mineralising fluids remains enigmatic. Using C, O and Sr-87/Sr-86 isotope data together with major and trace element compositions for the REE-rich Kangankunde carbonatite (Malawi), we show that the commonly observed, dark brown, Fe-rich carbonatite that hosts REE minerals in many carbonatites is decoupled from the REE mineral assemblage. REE-rich ferroan dolomite carbonatites, containing 8-15 wt% -REE2O3, comprise assemblages of monazite-(Ce), strontianite and baryte forming hexagonal pseudomorphs after probable burbankite. The Sr-87/Sr-86 values (0.70302-0.70307) affirm a carbonatitic origin for these pseudomorph-forming fluids. Carbon and oxygen isotope ratios of strontianite, representing the REE mineral assemblage, indicate equilibrium between these assemblages and a carbonatite-derived, deuteric fluid between 250 and 400 degrees C (delta O-18 + 3 to + 5 parts per thousand(VSMOW) and delta C-13 -3.5 to -3.2 parts per thousand(VPDB)). In contrast, dolomite in the same samples has similar delta C-13 values but much higher delta O-18, corresponding to increasing degrees of exchange with low-temperature fluids (< 125 degrees C), causing exsolution of Fe oxides resulting in the dark colour of these rocks. REE-rich quartz rocks, which occur outside of the intrusion, have similar delta O-18 and Sr-87/Sr-86 to those of the main complex, indicating both are carbonatite-derived and, locally, REE mineralisation can extend up to 1.5 km away from the intrusion. Early, REE-poor apatite-bearing dolomite carbonatite (beforsite: delta O-18 + 7.7 to + 10.3 parts per thousand and delta C-13 -5.2 to -6.0 parts per thousand; Sr-87/Sr-86 0.70296-0.70298) is not directly linked with the REE mineralisation.
机译：Carbonatites宿主一些最大和最高级别的稀土元素（REE）沉积物，但它们的REE-矿物质流体的组成和来源仍然是神秘的。使用C，O和SR-87 / SR-86同位素数据与Ree-Rich Kangankunde CarbonaTite（马拉维）的主要和微量元素组成一起，我们表明常见的深褐色，Fe富含Fe的铁矿质矿物质在许多碳酸盐中与REE矿物组合分离。含有8-15wt％-REE2O3的REE富含菲尔根白云石碳酸盐碳酸盐含有Monazite-（Ce），锶和尺寸在可能的缅甸伯士店之后形成六角形假形象的组合。 SR-87 / SR-86值（0.70302-0.70307）确认这些伪形形成的液体的碳酸根源。锶型锶矿石的碳和氧同位素比代表雷恩矿物组合，表明这些组件和碳酸酯衍生的晶体之间的平衡在250至400摄氏度之间（Delta O-18 + 3至+ 5份（Vsmow）和Delta C-13 -3.5至-3.2份（VPDB））。相反，相同样品中的白云石具有类似的Delta C-13值，但ΔO-18的更高，对应于具有低温流体（<125℃）的增加程度，导致Fe氧化物的exolution导致黑暗这些岩石的颜色。富含REE的石英岩，其出现在侵入之外，具有类似的ΔO-18和SR-87 / SR-86至主要复合物的综合体，表明两者都是碳酸根衍生的，当地，REE矿化可以延伸到距离入侵1.5公里。早期，携带磷灰石白云石碳酸盐石（Beforsite：Delta O-18 + 7.7至+ 10.3份每千次，Delta C-13 -5.2至-6.0份）; SR-87 / SR-86 0.70296-0.70298）没有与REE矿化直接相关联。

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