Carbonate-bearing fluorapatite rocks occur at over 30 globally distributed carbonatite complexes and represent a substantial potential supply of phosphorus for the fertiliser industry. However, the process(es) involved in forming carbonate-bearing fluorapatite at some carbonatites remain equivocal, with both hydrothermal and weathering mechanisms inferred. In this contribution, we compare the paragenesis and trace element contents of carbonate-bearing fluorapatite rocks from the Kovdor, Sokli, Bukusu, Catalão I and Glenover carbonatites in order to further understand their origin, as well as to comment upon the concentration of elements that may be deleterious to fertiliser production. The paragenesis of apatite from each deposit is broadly equivalent, comprising residual magmatic grains overgrown by several different stages of carbonate-bearing fluorapatite. The first forms epitactic overgrowths on residual magmatic grains, followed by the formation of massive apatite which, in turn, is cross-cut by late euhedral and colloform apatite generations. Compositionally, the paragenetic sequence corresponds to a substantial decrease in the concentration of rare earth elements (REE), Sr, Na and Th, with an increase in U and Cd. The carbonate-bearing fluorapatite exhibits a negative Ce anomaly, attributed to oxic conditions in a surficial environment and, in combination with the textural and compositional commonality, supports a weathering origin for these rocks. Carbonate-bearing fluorapatite has Th contents which are several orders of magnitude lower than magmatic apatite grains, potentially making such apatite a more environmentally attractive feedstock for the fertiliser industry. Uranium and cadmium contents are higher in carbonate-bearing fluorapatite than magmatic carbonatite apatite, but are much lower than most marine phosphorites.

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碳酸盐岩衍生含碳酸盐氟磷灰石矿床的成因和组成

含碳酸盐的氟磷灰石岩石分布在全球 30 多个碳酸盐岩复合体中，代表了化肥行业磷的大量潜在供应。然而，在一些碳酸盐岩中形成含碳酸盐氟磷灰石的过程仍然模棱两可，推断出热液和风化机制。在这篇文章中，我们比较了来自 Kovdor、Sokli、Bukusu、Catalão I 和 Glenover 碳酸岩的含碳酸盐氟磷灰石岩石的共生和微量元素含量，以进一步了解它们的起源，并评论元素的浓度可能对肥料生产有害。每个矿床中磷灰石的共生作用大致相同，由几个不同阶段的含碳酸盐氟磷灰石覆盖的残余岩浆颗粒组成。第一个在残余岩浆颗粒上形成外延过度生长，然后形成块状磷灰石，依次由晚自形和胶体磷灰石世代横切。在组成上，共生序列对应于稀土元素 (REE)、Sr、Na 和 Th 浓度的大幅降低，而 U 和 Cd 则增加。含碳酸盐的氟磷灰石表现出负的 Ce 异常，归因于地表环境中的含氧条件，并且结合结构和成分的共性，支持这些岩石的风化成因。含碳酸盐氟磷灰石的 Th 含量比岩浆磷灰石颗粒低几个数量级，有可能使这种磷灰石成为化肥行业对环境更具吸引力的原料。含碳酸盐氟磷灰石中的铀和镉含量高于岩浆碳酸磷灰石，但远低于大多数海相磷灰石。