Origin and diamond prospectivity of Mesoproterozoic kimberlites from the Narayanpet field, Eastern Dharwar Craton, southern India: insights from groundmass mineralogy, bulk‐chemistry and perovskite oxybarometry

Abstract

The Mesoproterozoic Narayanpet Kimberlite Field (NKF) is located~200 km north of the well-known Wajrakarur Kimberlite Field (WKF) in the Eastern Dharwar Craton, southern India. Whereas a majority of the WKF occurrences are diamondiferous and contain mantle xenoliths and xenocrysts, their paucity is a characteristic feature of the NKF. This has been attributed alternately to the derivation of NKF magmas from a shallower depth, or to variability in thickness of the Sub-Continental Lithospheric Mantle (SCLM) beneath the Eastern Dharwar Craton. Recently, exploration by De Beers resulted in the discovery of a number of new kimberlite occurrences from the NKF, with some of their geochemical features and radiogenic isotope systematics subsequently becoming available. In this paper, we present detailed petrography, groundmass mineral composition and new bulk-rock geochemistry data for a number of NKF rocks and attempt to further constrain their origin. We also investigate the influence of redox conditions on diamond prospectivity by estimating oxygen fugacity ( f O 2 ) from Fe-Nb oxybarometry on NKF groundmass perovskites. We identify for the first time in the NKF the presence of volcaniclastic (fragmental textured) facies kimberlite belonging to the diatreme portion of the intrusion. Rarity of olivine macrocrysts and the presence of diopside are hallmarks of the NKF kimberlites, in contrast to archetypal kimberlites of southern Africa. Mineral components of the groundmass display features that are characteristic to both archetypal kimberlites and to orangeites, and it is not straight forward to apply conventional mineral-genetic schemes in the nomenclature of the NKF pipes. Low f O 2 of the NKF magma (ΔNNO (nickel-nickel oxide) = −1.9 to −3.2), indistinguishable from that of diamondiferous kimberlites world-wide, indicates that redox conditions were favourable for diamond prospectivity, and that magmatic emplacement could, instead, have played a major role in their low diamond potential.

Issues and Limitations of Broad Band Remote Sensing of Kimberlite—A Case Example from Kimberlites of Dharwar Craton, India

“…Narayanpet kimberlite field (NKF) is one of the major kimberlite field of Dharwar craton and occurring at the eastern part of Dharwar craton. The NKF Kimberlites, in general, are very small bodies and these kimberlites lack mantle xenoliths [25]. Narayanpet kimberlites are emplaced in granodiorites and gneisses and structurally controlled by E-W and NE-SW trending lineament [15].…”

“…However, the ASTER convolved spectral profile of olivine rich kimberlite is featureless (Figure 3). Further, laboratory spectral profiles of kimberlites are convolved to ASTER bandwidth of SWIR channels for spatial mapping of kimberlite using sub pixel algorithm as the exposures of Narayanpet kimberlites are very small in size in comparison to the pixel size of ASTER data [25]. As the ASTER convolved laboratory spectral profiles of serpentinised and carbonate rich kimberlites are characterised with an absorption feature at around 2.33 micrometer ( Figure 3); hence, mean of ASTER convolved spectral profile carbonate and serpentine-rich kimberlite is used as a single end member for targeting the kimberlite based on sub-pixel mapping algorithm (Figure 3).…”

The Indian Precambrian: correlations and connections

“…Chalapathi Rao et al . () investigate the kimberlites from the Narayanpet Kimberlite Field and suggest that the low diamond potential in this region could be related to magmatic emplacement history, rather than to the depth of magma generation or extant redox conditions. Jayananda et al .…”

Petrology, bulk-rock geochemistry, indicator mineral composition and zircon U-Pb geochronology of the end-Cretaceous diamondiferous Manipur orangeites, Bastar craton, central India

“…The findings of our study are also consistent with those reported earlier by (i) Jha et al, (2002) wherein pyrope population in the Mainpur pipes has been inferred to be dominated by calcic-lherzolite variety corresponding to G9 and some eclogitic (G3, G4 and G5) and iron-titanian-low calcium (G1 and G2) garnets with the sub-calcic harzburgitic category (G10) pyrope garnet population between 1 and 5% and (ii) Mukherjee et al, (2000) who reported garnets of eclogitic paragenesis from the Behradih pipe. , 2004;Chalapathi Rao and Srivastava, 2009;Chalapathi Rao and Dongre, 2009;Chalapathi Rao et al, 2011b). and Brazil (McDonald et al, 1995) and China (Zhang et al, 2010).…”

“…Oxygen fugacity (fO 2 ) (NNO) conditions of the Behradih and Kodomali orangeites compared with those recorded by cratonic mantle lithosphere, mantle-derived magmas and global kimberlites (adapted fromCanil and Bellis, 2007). Data for Dutoitspan kimberlites is fromOgilvie-Harris et al, (2009); NKF kimberlites(Chalapathi Rao et al, 2011b).…”