0016-7622/2013-81-6-733/$ 1.00 © GEOL. SOC. INDIA JOURNAL GEOLOGICAL SOCIETY OF INDIA Vol.81, June 2013, pp.733-736 K-rich Titanate from the Jharia Ultrapotassic Rock, Gondwana Coal Fields, Eastern India, and its Petrological Significance N. V. CHALAPATHI RAO 1 , ANUP K. SINHA 2 , SURESH KUMAR 1 and RAJESH K.SRIVASTAVA 1 1 Department of Geology, Centre of Advanced Study, Banaras Hindu University, Varanasi - 221 005 2 Dr. K.S. Krishnan Geomagnetic Res. Lab., Indian Institute of Geomagnetism, Jhunshi, Allahabad - 221 505 Email: nvcr100@gmail.com Abstract: We report a rare accessory groundmass mineral of K-rich titanate, having a composition close to that of potassium triskaidecatitanate (K 2 Ti 13 O 27 ), from an underground drill-core sample of ultrapotassic rock from south- western part of the Jharia coal field in the Damodar valley, at the northern margin of the Singhbhum craton, Eastern India. Potassium triskaidecatitanate is regarded as a typomorphic mineral of orangeites (Group II kimberlites) of Kaapvaal craton, southern Africa, and its occurrence in the Jharia ultrapotassic rock is significant since ultrapotassic suite of rocks elsewhere from the Damodar valley have been recently suggested to be peralkaline lamproites based on mineral-genetic classification. The important role played by a unique geodynamic setting (involving a thinned metasomatised lithospheric mantle and inheritance of an Archaean subduction component) at the northern margin of the Singhbhum craton in deciding the petrological diversity of the early Cretaceous ultrapotassic intrusives from the Damodar valley is highlighted in this study. Keywords: K-titanate, ultrapotassic, Jharia, Damodar Valley, Singhbhum craton. GEOLOGICAL SETUP AND PETROGRAPHY The Damodar valley, located within the Chhottanagpur Gneissic Complex, at the northern-most edge of the Singhbhum craton, eastern India, is studded with several Gondwana coal fields in disconnected sedimentary basins along the E-W trending fault system (Fig.1A). These coal fields are intruded by swarms of igneous intrusions of mafic and ultramafic composition which occur mostly as dykes and sills but also as rare cylindrical bodies (e.g., Kent et al. 1992; Mukherjee and Ghose, 1999; Paul, 2005). Available age data suggests that the mafic as well as ultramafic magmatism is of ca.114 Ma and is very likely to be related to the interaction between the Kerguelen mantle-plume activity and the Indian lithosphere during the early Cretaceous (Kent et al. 1998). The borehole sample JH8/BH2 of this study is from Talgoria area, Parbatpura coal block, southwestern part of Jharia coal field (Fig.1B). Geologically the Parbatpura coal block is predominantly occupied by the rocks of Barren Measure Formation and inliers of Barakar Formation. The area is bounded by latitude 23 o 39'30"N to 23 o 42'55"N and longitude 86 o 19'15"E to 86 o 22'30" E. The Barakar Formation consists of coal beds and is intruded by dolerite, and ultrapotassic dykes and sills. Petrography of the sample JH8/BH2 reveals that it is characterised by INTRODUCTION The Cretaceous ultrapotassic intrusives occurring in the Gondwana coal fields of Jharia, Raniganj, Bokaro, and Karanpura in the Damodar valley, Chhotanagpur Gneissic Terrain, at the northern most margin of the Singhbhum craton in eastern India (Fig.1), have been a subject of petrological interest for more than a century (see Mitchell, 2007). These rocks are widely regarded as “difficult to classify” rocks displaying petrological and geochemical characteristics of orangeites (Group II kimberlites), lamprophyres, and lamproites (Mukherjee, 1961; Middlemost et al. 1988; Rock et al. 1992; Basu et al. 1997; Kent et al. 1998; Jia et al. 2003; Srivastava et al. 2009). Recently, Mitchell and Fareeduddin (2009) carried out a comprehensive mineral- genetic study of two ultrapotassic dykes from the Ranigunj coal field and infer them to be lamproites (sensu lato) and place them in the spectrum of such peralkaline rocks (var. Damodar) having a common parental magma which was generated from partial melting of the ancient metasomatised lithospheric mantle. The purpose of this note is to report the occurrence of a rare K-titanate mineral from one such ultrapotassic dyke in the Jharia coal field and relate its significance in the context of petrological complexity and nomenclature of the Early Cretaceous peralkaline intrusives from the Damodar valley.