Are Majhgawan-Hinota pipe rocks truly group-I Kimberlite? |
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| Authors: | Ravi Shanker S Nag A Ganguly A Absar B P Rawat G S Singh |
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| Institution: | (1) Geological Survey of India, Northern Region, 226 024 Lucknow;(2) Department of Geological Sciences, Jadavpur University, 700 032 Calcutta |
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| Abstract: | The diamond bearing pipe rocks in Majhgawan-Hinota (more than four pipes) occur as intrusives in sandstones of Kaimur Group.
These Proterozoic (974 ±30-1170 ±20 Ma) intrusive rocks, occupying the southeastern margin of Aravalli craton, were called
as ‘micaceous kimberlite’ in tune with the reported kimberlite occurrences from other parts of the world. Judging from the
definition of kimberlite, as approved by the IUGS Subcommission on Systematics of Igneous Rocks, it is not justified to call
these rocks as ‘micaceous kimberlite’. Rather the mineralogical assemblages such as absence of typomorphic mineral monticellite
(primary), abundance of phlogopite cognate, frequent presence of barite and primary carbonate mostly as calcite coupled with
ultrapotassic and volatile-rich (dominantly H2O) nature and high concentration of incompatible elements (such as Ba, Zr, Th, U), low Th/U ratios, low REE and no Eu-anomaly
clearly indicate a close similarity with that of South African orangeites. Thus orangeites of Proterozoic age occur outside
the Kaapvaal craton of South Africa which are much younger (200 Ma to 110 Ma) in age. |
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| Keywords: | Pipe rocks mineralogy chemistry Proterozoic age kimberlite orangeite Majhgawan-Hinota Madhya Pradesh |
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