The Pakkanadu carbonatite-alkaline complex (PCAC) is one of the nine carbonatite-alkaline complexes, situated along the NE-SW trending Dhramapuri Rift Zone in Southern Granulite Terrain in South India. This oval-shaped intrusion comprises of syenite–carbonatite–dunite–pyroxenite association. The carbonatites of this deformed complex are dominated by calcite carbonatite over dolomite carbonatite and ankerite. The present study mainly focuses on identifying evidence of rare-earth element (REE) remobilization and enrichment based on petrography, mineral chemistry and whole-rock geochemistry of the PCAC carbonatites and associated rocks. Chief rare-earth and rare metal bearing minerals in these rocks include monazite-(Ce), allanite-(Ce), chevkinite-(Ce), pyrochlore, besides strontianite and barite. Geochemically, the studied carbonatites and fenites have enriched, but variable Ba (5300–236,900 ppm), Sr (4360–98,700 ppm), La (84–11,500 ppm), Ce (155–17,200 ppm) and Nd (55–3000 ppm), and Sr/Ba (0.06–3.23) molar ratio. The ΣREE range from 3508 to 32,300 ppm, dominantly contributed by light rare-earth elements (LREE). Presence of a component geochemically similar to benstonite carbonatite is reported during the present study. Geochemically the studied rocks are characterised by enrichment of LREE and elevated concentrations of incompatible, with positive spikes Ba, Sr and strong depletion of Nb, Ta, Ti, Zr and P in primitive mantle-normalized spider diagram. Besides these characters, the presence of phlogopite, amphibole, early magmatic monazite-group minerals and fluorapatite in the Pakkanadu carbonatites indicate that the initial carbonatite magma was enriched in REE, and generated by a low degree of partial melting of a metasomatised fertile mantle in intra-plate rift setting. In addition, low Nb/Y ratio (≤ 1.0), Zr/Sm (up to 6.4) and Hf/Sm (up to 0.12), very high Ba content is indicative of fluid-related metasomatism. The textural relations and mineral chemistry of REE-bearing mineral phases indicate that carbo-hydrothermal processes resulted in remobilization and enrichment of REE. All these factors point towards REE fertility in the PCAC carbonatites and associated fenites.

Pakkanadu 碳酸岩-碱性杂岩 (PCAC) 是九个碳酸岩-碱性杂岩之一，位于印度南部麻粒岩地块沿 NE-SW 走向的 Dhramapuri 裂谷带。这种椭圆形侵入体由正长岩-碳酸岩-纯铜岩-辉石岩组合组成。该变形杂岩的碳酸岩以方解石碳酸岩为主，其次是白云石碳酸岩和铁白云石。本研究主要侧重于基于 PCAC 碳酸岩和伴生岩的岩相学、矿物化学和全岩地球化学来确定稀土元素 (REE) 再活化和富集的证据。这些岩石中主要含稀土和稀有金属的矿物包括独居石（Ce）、钠长石（Ce）、方镁石（Ce）、烧绿石，此外还有菱锶矿和重晶石。从地球化学角度来说，研究的碳酸岩和芬铁矿富集，但Ba（5300–236,900 ppm）、Sr（4360–98,700 ppm）、La（84–11,500 ppm）、Ce（155–17,200 ppm）和Nd（55–3000 ppm）变化，和 Sr/Ba (0.06–3.23) 摩尔比。ΣREE 范围为 3508 至 32,300 ppm，主要由轻稀土元素 (LREE) 组成。在本研究中报告了地球化学上与膨润土碳酸岩相似的成分的存在。在地球化学上，所研究的岩石的特征是轻稀土富集和不相容浓度升高，在原始地幔归一化蜘蛛图中，Ba、Sr 呈正尖峰，而 Nb、Ta、Ti、Zr 和 P 严重贫化。除了这些特征之外，还存在金云母、角闪石、帕卡纳杜碳酸岩中的早期岩浆独居石族矿物和氟磷灰石表明，最初的碳酸岩岩浆富含稀土元素，是由板内裂谷环境中交代的肥沃地幔的低度部分熔融产生的。此外，低Nb/Y比（≤1.0）、Zr/Sm（高达6.4）和Hf/Sm（高达0.12）、非常高的Ba含量表明与流体相关的交代作用。含稀土矿物相的结构关系和矿物化学表明，碳热液过程导致稀土元素的再活化和富集。所有这些因素都表明 PCAC 碳酸岩和相关的芬特岩中存在 REE 肥力。4）和Hf/Sm（高达0.12），非常高的Ba含量表明与流体相关的交代作用。含稀土矿物相的结构关系和矿物化学表明，碳热液过程导致稀土元素的再活化和富集。所有这些因素都表明 PCAC 碳酸岩和相关的芬特岩中存在 REE 肥力。4）和Hf/Sm（高达0.12），非常高的Ba含量表明与流体相关的交代作用。含稀土矿物相的结构关系和矿物化学表明，碳热液过程导致稀土元素的再活化和富集。所有这些因素都表明 PCAC 碳酸岩和相关的芬特岩中存在 REE 肥力。