Geochemistry and abundance of Rare Earth Elements (REE) in metamict allanite bearing syenites of dancherla and adjoining areas in Ananthapur, district, Andhra Pradesh, India

The results of EDXRF, EPMA, SEM and XRD data of the radioactive phases of metamict allanites from syenitic rocks in and around the Dancherla main body and Dancherla injection in Ananthapur, district, Andhra Pradesh are presented. This stands to be the first report of the presence of allanite in the study area. SEM studies show U and Th blebs/patches on the rim of allanite. The major element data confirm syenite chemistry as silica is undersaturated as SiO₂ content ranges from ∼40–50% and coupled with Al₂O₃ ∼10–15% and <10% FeO (t) respectively and with enriched Zr (260ppm) and appreciable amounts (20 ppm) of Nb, Ta, Y and Hf respectively. The total (ΣREE) is >2.01%, ΣLREE (2%) and ΣHREE (0. 1%). The EPMA data shows on an average (La₂O₃+Ce₂O₃+Nd₂O₃+EuO along with Y₂O₃) ∼ (67–84 wt%) while the rest account for other oxides and it appears to be a cerium, neodymium bearing allanite phase, which is also well corroborated by XRD data. The cerium and neodymium bearing Allanite (Ce, Nd) is typically black to dark brown and brownish violet in colour, occurring largely as euhedral, tabular or as thin crystals and sometime as flaky, acicular and in prismatic crystal forms of > 200 μm size and in polycrystalline aggregates upto 0.4 mm in dimension. The investigated samples of allanite indicate coupled solid solution, replacement and substitutions of Ca²⁺. (author)