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Compositional variation and genesis of pyrochlore, belkovite and baotite from the Sevattur carbonatite complex, India

Published online by Cambridge University Press:  14 April 2021

Monojit Dey
Affiliation:
Department of Earth and Climate Science, Indian Institute of Science Education and Research Tirupati, Rami Reddy Nagar, Karakambadi Road, Mangalam, Andhra Pradesh 517507, India
Sourav Bhattacharjee
Affiliation:
Department of Earth and Climate Science, Indian Institute of Science Education and Research Tirupati, Rami Reddy Nagar, Karakambadi Road, Mangalam, Andhra Pradesh 517507, India
Aniket Chakrabarty*
Affiliation:
Department of Earth and Climate Science, Indian Institute of Science Education and Research Tirupati, Rami Reddy Nagar, Karakambadi Road, Mangalam, Andhra Pradesh 517507, India
Roger H. Mitchell
Affiliation:
Department of Geology, Lakehead University, Thunder Bay, Ontario, Canada P7B 5E1
Supriyo Pal
Affiliation:
Department of Earth Sciences, Indian Institute of Technology Roorkee, Roorkee, Uttarakhand 247667, India
Supratim Pal
Affiliation:
Department of Geology, Durgapur Government College, Durgapur, West Bengal 713214, India
Amit Kumar Sen
Affiliation:
Department of Earth Sciences, Indian Institute of Technology Roorkee, Roorkee, Uttarakhand 247667, India
*
*Author for correspondence: Aniket Chakrabarty, Email: aniket_chakrabarty@rediffmail.com;aniketc@iisertirupati.ac.in

Abstract

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.

Information

Type
Article – Gregory Yu. Ivanyuk memorial issue
Copyright
Copyright © The Author(s), 2021. Published by Cambridge University Press on behalf of The Mineralogical Society of Great Britain and Ireland

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