Insights to Pyrochlore and Apatite Evolutionary Trends: Constraints From Mineral and Bulk Chemistry of Saidiwasan Sövites, Gujarat, India

ABSTRACT The Saidiwasan (also known as Siriwasan) carbonatite‐sill is located approximately 10 km to the north of the well‐known Ambadungar carbonatite–alkaline complex within the Chhota Udaipur carbonatite‐alkaline province. This complex comprises prominent sövite plugs within carbonatitic breccias, each exhibiting diverse and variable mineralogical assemblages that include pyroxene, amphibole, apatite, pyrochlore, perovskite and titanite. The enrichment of rare earth elements (REEs) in the Saidiwasan sövites is closely associated with the presence of pyrochlore, perovskite, apatite and monazite. This study employs detailed mineral chemistry to elucidate the secondary processes affecting pyrochlore and apatite grains. Primary magmatic pyrochlore in Saidiwasan sövites are characterised by elevated concentrations of calcium, niobium, fluorine and sodium, which are subsequently replaced by secondary cation‐deficient grains due to supergene weathering. These alterations primarily occur at the A site and occasionally at the B site, involving the substitution of fluorine by hydroxide (OH–) groups. During alteration, calcium and sodium are leached from the pyrochlore structure, with charge balance maintained by the substitution of REE, Th, U, Ba or Sr. In the later supergene stages, marginal and fractured zones of pyrochlore grains experience metamictization, resulting in Pb‐rich and cation‐deficient hydrated varieties. Fluoro‐apatites within the sövites display significant REE concentrations and are relatively unaltered. LREE constitute the dominant proportion of the total REE content in Saidiwasan apatite. Based on mineral chemistry and bulk rock analyses, this study aims to provide a comprehensive understanding of the Saidiwasan sövites. Despite its promising characteristics, the Saidiwasan carbonatite complex remains underexplored and largely overlooked within the Chhota Udaipur Province, although it possesses significant potential for hosting economically viable mineral deposits, thus warranting further investigation and exploration.