Pyrochlore-group minerals are common in the Neoproterozoic Sevattur carbonatite complex. This complex is composed of dolomite-, calcite-, banded- and blue carbonatite together with pyroxenite, albitite and diverse syenites. This work reports the paragenetic-textural types and compositional variation of pyrochlore hosted by dolomite carbonatite, banded carbonatite and albitite together with that of alteration assemblages containing belkovite and baotite. On the basis of composition, five different types of pyrochlore are recognised and termed Pcl-I through to Pcl-V. The Pb-rich Pcl-I are present exclusively as inclusions in U-rich Pcl-IIa in dolomite carbonatite. The alteration assemblages of Pb-poor Pcl-IIb + Ba-rich or Ba–Si- rich Pcl-IV + belkovite (dolomite carbonatite) and Si-rich Pcl-V + baotite (banded carbonatite) formed after Pcl-IIa differ in these carbonatites. The albitite hosts extremely U-Ti-rich Pcl-III, mantled by Ba-rich potassium feldspar. In common with the banded carbonatite, Pcl-V is formed by alteration of Pcl-III where this mantle is partially, or completely broken. The Ba-Si-enrichment of Pcl-IV and Pcl-V together with the ubiquitous presence of baryte in all Sevattur lithologies suggests late-stage interaction with a Ba-Si-rich acidic hydrothermal fluid. This fluid was responsible for leaching silica from the associated silicates and produced Pcl-V in the silicate-rich lithologies of the banded carbonatite and albitite. The absence of Pcl-V in dolomite carbonatite is a consequence of the low modal abundance of silicates. The complex compositional diversity and lithology specific pyrochlore alteration assemblages suggest that all pyrochlore (Pcl-I to Pcl-IV) were formed initially in an unknown source and transported subsequently in their respective hosts as altered antecrysts.

烧绿石族矿物常见于新元古代 Sevattur 碳酸盐岩复合体中。该复合体由白云石、方解石、条带状和蓝色碳酸岩以及辉石岩、钠长岩和各种正长岩组成。这项工作报告了由白云石碳酸岩、条带状碳酸岩和钠长石以及含有白云石和皂石的蚀变组合组成的烧绿石的共生结构类型和成分变化。根据成分，可以识别五种不同类型的烧绿石，并将其命名为 Pcl-I 到 Pcl-V。富含 Pb 的 Pcl-I 仅作为白云岩碳酸岩中富含 U 的 Pcl-IIa 中的包裹体存在。Pb-贫Pcl-IIb+富Ba或Ba-Si富Pcl-IV+belkovite（白云石碳酸岩）和富SiPcl-V+宝钛矿（带状碳酸岩）在Pcl-IIa之后形成的蚀变组合在这些方面有所不同碳酸岩。钠长石含有极其富含 U-Ti 的 Pcl-III，被富含 Ba 的钾长石覆盖。与带状碳酸岩一样，Pcl-V 是由 Pcl-III 的蚀变形成的，其中该地幔部分或完全破裂。Pcl-IV 和 Pcl-V 的 Ba-Si 富集以及所有 Sevattur 岩性中普遍存在的重晶石表明后期与富含 Ba-Si 的酸性热液相互作用。这种流体负责从相关硅酸盐中浸出二氧化硅，并在带状碳酸盐岩和钠长石的富含硅酸盐的岩性中产生 Pcl-V。白云石碳酸岩中不存在 Pcl-V 是硅酸盐模态丰度低的结果。复杂的成分多样性和岩性特定的烧绿石蚀变组合表明所有烧绿石（Pcl-I 到 Pcl-IV）最初都是在未知来源中形成的，然后在各自的宿主中作为改变的前晶运输。