The Neoproterozoic Sevattur complex is composed essentially of calcite and dolomite carbonatites together with pyroxenites and diverse syenites. This work reports the compositions and paragenesis of different pyrochlore generations hosted by albitite veins in this complex. The pyrochlore are distinctive, being exceptionally rich in uranium (26 to 36 wt.% UO2). Five types of pyrochlore (Pcl-I to Pcl-V) are recognised on the basis of composition and texture. With the exception of Pcl-V, the majority of the pyrochlore (Pcl-II to Pcl-IV) are surrounded by a thick orbicular mantle of Ba-rich potassium feldspar. This mantle around Pcl-V is partially-broken. Pcl-I is restricted to the cores of crystals, and associated with Pcl-II and -III and is relatively rich in Nb (0.53–0.62 apfu) together with more A-site vacancies (0.37–0.71 apfu) compared to Pcl-II to Pcl-IV. Other pyrochlore (Pcl-II to Pcl-IV) are characterised by elevated Ca and Ti compared to Pcl-I, which are related to the (3Nb5+ + Na+ → 3Ti4+ + U4+) and (2Nb5+ → 2Ti4+ + Ca2+) substitutions, respectively. These substitutions represent replacement of Pcl-II to Pcl-IV. Alteration and Ba-enrichment in all the pyrochlore are marked by interaction with an externally-derived Ba-rich hydrothermal fluid following the (2Nb5+ → 2Ti4+ + Ba2+) substitution. This substitution, coupled with extensive metamictisation leads to the formation of Ba-rich (15.9–16.3 wt.% BaO) patchy-zoned Pcl-V. The orbicular mantles around Pcl-I to Pcl-IV have prevented extensive metamictisation and extensive secondary alteration compared to Pcl-V, where mantling is partially disrupted. The compositional and textural variation suggests that Pcl-II to Pcl-IV form by nucleation on Pcl-I, and are transported subsequently as antecrysts in the host albitite.

新元古代 Sevattur 杂岩主要由方解石和白云石碳酸岩以及辉石岩和各种正长岩组成。这项工作报告了该复合体中钠长石脉所承载的不同烧绿石世代的组成和共生。烧绿石是独特的，特别富含铀（26 至 36 wt.% UO 2）。根据成分和质地，可以识别五种类型的烧绿石（Pcl-I 到 Pcl-V）。除 Pcl-V 外，大部分烧绿石（Pcl-II 到 Pcl-IV）都被富含钡的钾长石厚球状地幔包围。Pcl-V 周围的地幔部分破裂。Pcl-I 仅限于晶体的核心，并与 Pcl-II 和 -III 相关，并且含有相对丰富的 Nb（0.53–0.62 apfu）和更多的A位点空位 (0.37–0.71 apfu) 与 Pcl-II 到 Pcl-IV 相比。与 Pcl-I 相比，其他烧绿石（Pcl-II 到 Pcl-IV）的特点是 Ca 和 Ti 升高，这与 (3Nb 5+ + Na + → 3Ti 4+ + U 4+ ) 和 (2Nb 5+ → 2Ti 4+ + Ca 2+ ) 取代，分别。这些替换代表 Pcl-II 替换为 Pcl-IV。所有烧绿石中的改变和富 Ba 的标志是与外部衍生的富 Ba 热液相互作用，遵循 (2Nb 5+ → 2Ti 4+ + Ba 2+） 代换。这种取代加上广泛的metamictisation导致形成富含Ba（15.9-16.3 wt.% BaO）的片状区Pcl-V。与 Pcl-V 相比，Pcl-I 到 Pcl-IV 周围的圆形地幔阻止了广泛的转移和广泛的二次改变，其中地幔部分被破坏。成分和质地的变化表明 Pcl-II 到 Pcl-IV 是通过 Pcl-I 上的成核形成的，随后作为母体钠长石中的前晶被运输。