Abstract The Bayan Obo deposit in North China is famous for its enormous rare-earth element (REE) resources in the world. The carbonatite dykes occurring around the orebodies are considered to be closely related to the REE mineralization. Here we present new geochemical and C O isotopic data of the ‘Wu’ carbonatite dyke, together with integrated studies of fluid inclusion preserved in the quartzite spatially associated with the dyke and Rb Sr dating to reveal the dyke genesis and metallogenic process. The dyke has a geochemical signature and C isotopic composition similar to those of typical magmatic carbonatite, suggesting an igneous origin. It is also characterized by significant enrichment in REEs with extreme differentiation between light and heavy REEs, and negative Sr, Zr, and Ti anomalies, indicating that the magma evolved through fractional crystallization. The quartzite surrounding the dyke underwent strong fenitization. The types, microthermometric data and chemical compositions of the fluid inclusions suggest that the fluids preserved in the quartzite have great similarity with carbonatitic fluids, and Rb Sr dating of these fluid inclusions from the quartzite yielded an isochron age of 368 ± 43 Ma, indicating that there was an early Paleozoic activity of carbonatitic fluids caused by intrusion of the carbonatite dyke. During the early Paleozoic, the Bayan Obo deposit was under a subduction setting. The REE- and CO2-rich fluids/melts were released from subducted sediments during the subduction, and metasomatized and overprinted the pre-existing mineralization hosted in the dolomite, resulting in large-scale REE enrichment and mineralization.

中文翻译：

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华北白云鄂博稀土矿区碳酸岩脉及相关稀土矿化：地球化学、CO同位素和Rb Sr定年证据

摘要 华北白云鄂博矿床以丰富的稀土元素（REE）资源着称于世。矿体周围的碳酸岩脉被认为与稀土矿化密切相关。在这里，我们展示了“吴”碳酸岩岩脉的新地球化学和 CO 同位素数据，以及对保存在与岩脉和 Rb Sr 年代学相关的石英岩中的流体包裹体的综合研究，以揭示岩脉的成因和成矿过程。该岩脉具有与典型岩浆碳酸岩相似的地球化学特征和 C 同位素组成，表明其为火成岩成因。它还具有稀土显着富集的特点，轻稀土和重稀土的极端分化，以及负的 Sr、Zr 和 Ti 异常，表明岩浆通过分步结晶演化。堤坝周围的石英岩经历了强烈的非硝化作用。流体包裹体的类型、显微测温数据和化学成分表明，保存在石英岩中的流体与碳酸岩流体具有很大的相似性，这些石英岩流体包裹体的 Rb Sr 测年得出等时线年龄为 368 ± 43 Ma，表明由于碳酸岩脉的侵入，导致了早古生代碳酸岩流体的活动。早古生代，白云鄂博矿床处于俯冲环境。在俯冲过程中，从俯冲沉积物中释放出富含 REE 和 CO2 的流体/熔体，并交代和叠印在白云岩中的预先存在的矿化，