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Metasomatically controlled sillimanite–corundum deposit: A case study from Sonapahar, Meghalaya, Northeast India

Abstract

The Sonapahar sillimanite-corundum deposit of Meghalaya, Northeast India occurs within high-grade metapelites and exhibits an unusual association of sillimanite-quartz, corundum-quartz, sapphirine-phlogopite-corundum-sillimanite rock. Pockets of sillimanite and corundum occur within the host quartz sillimanite schist with contrasting chemical signature, where the SiO2/Al2O3 ratio is 2.5–3 for the host quartz sillimanite schist and 0.12–0.7 in sillimanite rocks. Earlier it was explained that the sillimanite-corundum rock was produced from metamorphosed paleosol, but the present study suggests that metasomatism had a major role to modify the host quartz-sillimanite schist into sillimanite-corundum rocks during post-peak metamorphism. Field disposition and structural control of the area show that pockets of sillimanite-corundum rock are restricted near the shear zones. Shear zones were the pathways for movement of hydrothermal fluids, conversion of host bulk chemistry by selective leaching and, finally, enrichment of sillimanite-quartz or corundum-quartz pockets within the quartz sillimanite schist.

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Acknowledgements

Authors are grateful to the Director General of the Indian Geological Survey for enabling this paper to be published. We also thank Dr Somnath Dasgupta, Associate Editor and two anonymous reviewers for their critical review of the manuscript. The findings given here are based on the authors’ own understanding and do not, in essence, reflect the view of the Geological Survey of India. The authors also recognise the assistance of Shri Teddy Lyngdoh in the field.

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Authors

Contributions

SN conceived the idea and contributed to the manuscript. SN carried out mapping, analytical data, graphs, simulation and interpretation under the supervision of TP.

Corresponding author

Correspondence to Susobhan Neogi.

Additional information

Communicated by Somnath Dasgupta

Appendices

Appendix 1

Table A1 Phase chemical analysis of the existing minerals in Cordierite gneiss.

Appendix 2

Table A2 Thermo-barometric analysis of the equilibrium and disequilibrium mineral phases in cordierite gneiss.

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Neogi, S., Pal, T. Metasomatically controlled sillimanite–corundum deposit: A case study from Sonapahar, Meghalaya, Northeast India. J Earth Syst Sci 130, 120 (2021). https://doi.org/10.1007/s12040-021-01609-y

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Keywords

  • Meghalaya
  • sillimanite
  • corundum
  • shear zone
  • metasomatism