A spectrum of potentially diamondiferous lamproites and minettes from the Jharia Coalfield, eastern India

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doi: 10.1016/0377-0273(92)90037-E
Authors:Rock, N. M. S.; Griffin, B. J.; Edgar, A. D.; Paul, D. K.; Hergt, J. M.
Author Affiliations:Primary:
University of Western Australia, Department of Geology, Nedlands, West. Aust., Australia
Other:
University of Leeds, United Kingdom
University of Western Ontario, Canada
Geological Survey of India, India
Open University, United Kingdom
Volume Title:Essays on magmas and other earth fluids; a volume in appreciation of Prof. Peter G. Harris
Volume Authors:Cox, K. G., editor; Baker, P. E.
Source:Essays on magmas and other earth fluids; a volume in appreciation of Prof. Peter G. Harris, edited by K. G. Cox and P. E. Baker. Journal of Volcanology and Geothermal Research, 50(1-2), p.55-83. Publisher: Elsevier, Amsterdam, Netherlands. ISSN: 0377-0273
Publication Date:1992
Note:In English. 54 refs.; illus., incl. 10 tables, sketch maps
Summary:Abundant Cretaceous lamprophyric sills in the Gondwana coalfields show a comagmatic continuum from olivine-lamproites to lamproites and minettes. Four sills in the Jharia coalfield have exotic mineralogy, dominated by olivine (Fo85-92) and phlogopite (5- 10% TiO2, 5-13% Al2O3), with subordinate K- (titanian) richterite and/or arfvedsonite, and spectacularly zoned Sr-rich apatite (up to 20% SrO). Accessory to minor phases include clinopyroxene (titanian diopside to aegirine-augite), K-feldspar (Or> 96), variable spinel (up to 47% Cr2O3), perovskite, niobian ilmenite, niobian rutile, sphene and Ba-poor priderite. Complex primary carbonate assemblages involve breunnerite, ferroan dolomite, witherite, alstonite and ?strontianite. The whole rocks show low Al2O3 (5-7%) combined with high K2O (4-5%), MgO (<= 30%) and Cr (up to 1500 ppm), plus extreme TiO2 (up to 8.5%), Sr, Zr (<= 6000 ppm each), Ba (<= 8000 ppm), and LREE (Ce <= 3000 ppm). In many rocks K/Al (molecular) > 0.7, (Na + K)/Al > 1, and K/(Na + K) > 0.6. Radiogenic isotopes (epsilon Sr +7 to +21 and epsilon Nd - 1.5 to -3.1) imply derivation from a metasomatized lithosphere mantle source with time-integrated Rb/Sr and Sm/Nd slightly higher than Bulk Earth. Intensive carbonation in some rocks may reflect fluids derived from the magmas themselves, from carbonatite-like fluids, and perhaps from coking of the invaded coal seams. Minor crystal fractionation within sills has yielded complementary olivine lamproites and feldspathic lamproites; the latter grade ultimately into minettes via increase of Al2O3 and decrease of MgO. Positive indicators of diamond potential in these rocks include their bulk compositional similarity to diamondiferous olivine lamproites elsewhere, their Cr-rich spinels, and perhaps their tectonic position; negative factors include their quiet emplacement, the noted differentiation, and the associated coking of the coal seams. [R.E.S.]
Subjects:Carbonates; Coal; Coal fields; Cretaceous; Diamond deposits; Differentiation; Emplacement; Geochemistry; Igneous rocks; Intrusions; Lamproite; Lamprophyres; Lithostratigraphy; Mesozoic; Mineral composition; Minette; Petrography; Plutonic rocks; Sedimentary rocks; Sills; Asia; Bihar India; Dhanbad India; India; Indian Peninsula; Jharia coal field; Jharia India; Jharkhand India; Eastern India; Organic residues
Abstract Numbers:93M/1049
Record ID:1996025113
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom
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