Potassic Rocks from the Gondwana Coalfields of India: Closing Pandora’s Box of Petrological Confusion?

The nomenclature of potassic lamprophyres occurring in the Gondwana coalfields is discussed from a mineralogical-genetic viewpoint. The concept of a lamprophyre facies and the mineralogical character of calc-alkaline minette and peralkaline phlogopite sanidine lamproite is described. It is concluded that none of the Gondwana coalfields rocks represent calc-alkaline minettes and that there is no "minette-lamproite" association. The Gondwana potassic rocks, together with similar potassic rocks from Majhgawan and the Mainpur region, are considered to be formed from differentiates of distinct magmas formed by the partial melting of metasomatic veins in the lithospheric mantle, and as such cannot be classified using nomenclatural schemes devised for other petrological provinces. The Gondwana potassic rocks, which are the expression of potassic metasomatized lithospheric magmatism in the northern Singhbhum craton, are considered not to be Kaapvaal craton-type orangeites or Kimberley craton-type lamproites, but might be described as lamproites (var.Damodar). It is recommended that use of the terms: "minette-lamproite association"; kimberlite-clan rocks"; and "lamprophyre clan rocks" be discontinued as they serve no useful petrogenetic purpose.