Journal of Geological Society of India (Online archive from Vol 1 to Vol 78)

Datta Mainkar ¹, Bernd Lehmann ²

Affiliations
1 C-52, Gayatri Nagar, Raipur - 492 007, Chhattisgarh, IN
2 Institute of Mineralogy and Mineral Resources, Technical University of Clausthal, 38678, Clausthal-Zellerfeld, DE

Abstract

Drill core from the diamondiferous Behradih pipe consists of pelletal-textured and olivine macrocrystic diatreme facies kimberlite variably affected by talc-serpentine-carbonate alteration. Crustal xenoliths of resorbed feldspar, syenite, granite, and basalt are common. The rocks have C.I. ≥ 1.6, 40-43 wt% SiO₂, <5 wt% Al₂O₃, and Mg numbers of 83-87. The trace element composition is typical of kimberlitic rocks and excludes a lamproitic affinity.

Keywords

Kimberlite, Petrography, Geochemistry, Behradih, Mainpur, Chhatisgarh.

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Bernd Lehmann ¹, Craig Storey ², Datta Mainkar ³, Teresa Jeffries ⁴

Affiliations
1 Institute of Mineralogy and Mineral Resources, Technical University of Clausthal, 38678, Clausthal-Zellerfeld, DE
2 Department of Earth Sciences, University of Bristol, Wills Memorial Building, Queen’s Road, Bristol BS8 1RJ, GB
3 C-52, Gayatri Nagar, Raipur 492-007, Chhattisgarh, IN
4 Department of Mineralogy, The Natural History Museum, Cromwell Road, South Kensington, London, SW7 5BD, GB

Abstract

We report in-situ U-Pb dating by laser-ablation quadrupole-based ICP-MS on autometasomatic titanite from the Bhejripadar tuff-facies kimberlite. The lower intercept of the discordia on the Tera-Wasserburg concordia diagram gives 620±30 (2σ) Ma, and the weighted average of ²⁰⁷Pb corrected ²⁰⁶Pb/²³⁸U data (n=19) gives 616±24 (2σ) Ma, i.e. within error of the Tera-Wasserburg lower intercept age. This Neoproterozoic age around 620 Ma is likely to represent the age of both the kimberlite volcanism of the Tokapal-Bhejripadar system, and the chemoclastic sedimentation in the lower Indravati Group.

Keywords

Kimberlite, Titanite, LA-ICP-MS, U-Pb dating, Tokapal, Bhejripadar, Chhattisgarh, India.

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Kamlesh Kumar ¹, Bernd Lehmann ²

Affiliations
1 Atomic Minerals Directorate for Exploration and Research, Central Region, AMD Complex, Civil Lines, Nagpur - 440 001, IN
2 Institute of Mineralogy and Mineral Resources, Technical University of Clausthal, Clausthal -Zellerfeld, DE

Abstract

No Abstract.

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Bernd Lehmann ¹, Datta Mainkar ², Boris Belyatsky ³

Affiliations
1 Institute of Mineralogy and Mineral Resources, Technical University of Clausthal, Adolph-Roemer-Strasse 2a, 38678 Clausthal-Zellerfeld, DE
2 Directorate of Geology and Mining of Chhattisgarh, Raipur - 492 006 (Chhattisgarh), IN
3 Institute of Precambrian Geology and Geochronology, Russian Academy of Sciences, Makaraeva 2, 199034 St Petersburg, RU

Abstract

The crater-Facies kimberlite system at Tokapal occurs within the Late Proterozoic chemoclastic cover sequence of the Indravati Basin on the Meso-Proterozoic/Archaean Bastar craton in central India. The pyroclastic lapilli tuffs consist of pseudomorphs of olivine macrocrysts and juvenile lapilli set in a fine-Grained talc-Serpentine-Carbonate matrix with locally abundant spinel and titanite. No garnets or diamonds have been found so far. The inequigranular and locally bedded texture is largely preserved, although the olivine component has been completely destroyed. The multiple kimberlite system has about circular shape (2 5 km in diameter) and is probably the oldest and largest crater-Facies kimberlite system known in the world. The satellite Bhejripadar system of similar petrographic and chemical characteristics is situated about 4 km to the northwest and has a few hundred meters of diameter.

Samples from both systems have mostly moderate degree of contamination( 35-50 wt% SiO₂, <4 wt% A1₂O₃,) and Mg numbers of 82-89. The trace element patterns are typical of kimberlitic rocks (REE, Cr, Ni, Nb, Zr), with mobile elements strongly leached due to intense postmagmatic alteration and weathering (Ba, Sr, Rb, alkalis). The Nd isotope composition of E_Nd around 2 (T=1100 Ma) is diagnostic of archetypal (Group I) kimberlites and similar to the diamondiferous Majhgawan pipe with E_Nd 0 and the kimberlites of southern India with E_Nd2 (T=1080 Ma). The Early Paleozoic diamondiferous Kodomali kimberlite pipe from the nearby Mainpur kimberlite field also has E_Nd1 to 2 (T=480 Ma), suggestive of a slightly depleted to undifferentiated asthenospheric mantle source for all Indian kimberlitic rocks.

Keywords

Kimberlite, Crater-Facies, Petrography, Geochemistry, Tokapal, Chhattisgarh.

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