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

Abstract

Abundant Cretaceous (≈ 110 Ma) 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 potassium (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, ferro..