Journal of Geological Society of India (Online archive from Vol 1 to Vol 78)

V. Srinivas Choudary ¹, T. K. Rau ¹, K. S. Bhaskara Rao ¹, M. Sridhar ¹, K. K. Sinha ¹

Affiliations
1 Project: Diamond, OP: Andhra Pradesh, Geological Survey of India, Southern Region, Hyderabad – 500 068, IN

Abstract

A cluster of four kimberlite bodies was discovered on the left bank of the Penner River near Timmasamudram village. Falling in the area known for alluvial diamond occurrences within the Wajrakarur Kimberlite Field (WKF), this cluster is located between the Kalyandurg Kimberlite Cluster in the west and Chigicherla Kimberlite cluster in the east. With the addition of kimberlite bodies in the present cluster, christened as the Timmasamudram Kimberlite Cluster (TKC), the total number of kimberlite bodies in WKF reaches to 27. Texturally, mineralogically and chemically, the kimberlite bodies in TKC match with the archetypal Group-I kimberlites. Typically they fall in the non-micaceous kimberlite field. The mantle xenocrystic mineral chemistry shows conditions congenial for diamond formation in these pipes, which is further supported by actual microdiamond recovery from the soft kimberlitic yellow ground.

Keywords

Kimberlite, Timmasamudram Kimberlite Cluster, Group-I kimberlites, Microdiamonds, Andhra Pradesh.

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M. Sridhar ¹, V. S. Chowdhary ¹, S. S. Nayak ¹, Re Augustine ¹

Affiliations
1 Geological Survey of India, Hyderabad - 560 068, IN

Abstract

Three kimberlite pipes are reported from Siddanpalli village in Gadwal area, Mahbubnagar district, Andhra Pradesh, bringing to light a new kimberlite cluster. Significance of the find lies in the fact that these kimberlite pipes are located in the Krishna river basin well known for its alluvial diamond mining activity since historic times. These pipes are being studied for their diamond potential.

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T. Ajit Kumar Reddy ¹, M. Sridhar ², S. Ravi ², V. Chakravarthi ², S. Neelakantam ²

Affiliations
1 Geological Survey of India, 3-5-170/G, Narayanguda, Hyderabad - 500 029, IN
2 Geological Survey of India, Hyderabad - 500 068, IN

Abstract

Search for primary source rocks of diamond in close proximity of the well known alluvial gravel workings for diamonds along the palaeochannels of the River Krishna, has resulted in the discovery of a lamproite field comprising several lamproite clan rocks in parts of Krishna and Nalgonda districts of Andhra Pradesh (South India). These rare rock types are defined in this work as 'lamproites', on the basis of their occurrence in a unique tectonic setting and containing one or more of the typomorphic minerals and having the requisite rock geochemical characters of members of the suite as a whole. These bodies with an exotic and diagnostic mineralogy, composition and textures occur in a complex tectonic setting with unique intrusive history. The discovery of this lamproite field is considered very significant from the point of diamond exploration as it is located very close to the famous Golconda Mines along the banks of the River Krishna which yielded many of the celebrated diamonds in the past. This field is christened "Krishna Lamproite Field", in view of the proximity of the lamproite occurrences to the Krishna River having the alluvial placer diamonds. These rocks are emplaced along the eastern margin of the Precambrian Dharwar Craton, at the contact between the northeastern periphery of the Proterozoic Cuddapah Basin and the Archaean crystalline basement rocks, in the form of dykes (usually in clusters) and plugged conduits. The emplacement is controlled by major faultslfractures, trending in NNW-SSE and WNW-ESE directions and occur closely associated with mafic (dolerite) dykes and followed the same channels for their emplacement. The lamproites contain glass, numerous vesicles, and xenoliths of the basement granite-gneiss, dolerite and probably platformal sediments of the Cuddapah Basin, besides exhibiting fragmental and pyroclastic textures supgestive of near-surface emplacement. Radiometric age determinations suggests emplacement of these lamproites took place around 1224±14 Ma, probably during the reactivation of major crustal lineaments coinciding with the uplift of the mid-Proterozoic Nallamalai sediments of the Cuddapah Basin.

Diopside, phlogopite, tetra-ferri phlogopite, richterite, sanidine, apatite and pseudomorphs of leucite, enstatite and olivine are the major primary constituent minerals present. Diopside-leucite-lamproite, phlogopite-leucitelamproite, olivine-lamproite and richterite-phlogopite-lamproites are the variants. The bodies are ultrapotassic (molar K₂O/Na₂O >10), and contain high TiO₂, P₂O₅, K₂O, MgO, Ba, Sr, Zr, Cr, Ni, La and Ce, pointing to crystallisation from typical lamproite magma. The presence of mantle peridotite xenoliths and xenocrystic minerals such as chromediopside, spinel and garnet indicate deep seated mantle derivation of the Krishna lamproites.

Keywords

Lamproites, Petrology And Geochemistry, Emplacement, Major Faults/Fractures, Krishna Lamproite Field, Andhra Pradesh.

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A. R. Nambiar ¹, T. Ajit Kumar Reddy ², M. Sridhar ², S. Ravi ², V. Chakravarthi ², S. Neelakantam ²

Affiliations
1 Geological Survey of India, Op.: Karnataka and Goa, Vasudha Bhavan, Bangalore - 560 078, IN
2 3-5-17Q/G, Narayanguda, Hyderabad - 500 029, IN

Abstract

No Abstract.

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