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T. K. Rau ¹

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

Abstract

The Panna Diamond Belt (PDB) occupying the northern margin of the Vindhyan Basin in Panna district, Madhya Pradesh hosts the primary, secondary and tertiary sources of diamond. It comprises the basement Bundelkhand granitoids to the north overlain by Vindhyan Supergroup of rocks (Mid to Upper Proterozoic) to the south. The diamond mining activity is confined mainly to the Baghain plateau and to a lesser extent to the Gahadra plateau. The two kimberlite pipes known in PDB are Majhgawan and Hinota pipes (~1100 Ma), emplaced in Baghain Sandstone lying to the west of PDB. The basal conglomerate interbeds of Jhiri Shale (Upper Rewa) and Itwan Sandstone (Lower Rewa) have been extensively mined for diamond in the past. The alluvial and colluvial (Quaternary and Recent) placer diamond workings, both ancient and present, spread over the Baghain plateau mainly between Panna town in the west and Paharikhera in the east. Exploration indicated significantly higher incidence (~30 cpht) of diamond with high percentage of gem quality diamonds.

Keywords

Vindhyan Basin, Panna Diamond Belt, Kimberlite/Lamproite, Proterozoic Diamondiferous Conglomerates, Diamondiferous Gravels.

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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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S. Ravi ¹, T. K. Rau ¹, N. S. Reddy ¹, S. S. Nayak ¹

Affiliations
1 Geological Survey of India, Southern Region, Hyderabad – 500 068, IN

Abstract

The diamondiferous Upper Proterozoic conglomerates and the associated sandstone beds display sedimentary structures that are suggestive of provenance in the northwest, i.e. towards the Tungabhadra river drainage basin. Multidisciplinary surveys in this region have led to the discovery of a kimberlite body (350 m x 470 m), concealed under alluvial soil spread on the left bank of the Tungabhadra River near Mantralayam. The study area, represented by the granitoids of Peninsular Gneissic Complex with remnants of Gadwal schist belt, presents a domal upwarp that plunges into the river. The domal surface displays intense fracturing with prominent NW-SE/WNW-ESE and subordinate NE-SW trends, which show marked preponderance and dilation on the northern low angle plunge parts. Traverses coupled with extensive stream sediment sampling and the study of specific mineral chemistry is suggestive of presence of kimberlite, which is supported by actual recovery of micro-diamonds from the yellow ground. The kimberlite contains mantle nodules of phlogopite-bearing websterite and siliceous mica-garnet-chrome diopside bearing lherzolite; the selective non-silicification of interstitial chrome diopside in the latter being enigmatic. The silicification of these mantle nodules could be due to the emplacement of kimberlite into a surface water body and subsequent action of silicasaturated groundwater.

Keywords

Kimberlite, Microdiamonds, Mantle Nodules, Tungabhadra River, Kurnool District, Andhra Pradesh.

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T. K. Rau ¹

Affiliations
1 Director, Project Diamond, OP: A.P., Geological Survey of India, SR, Hyderabad - 560 068, IN

Abstract

Micro- and macro-diamonds were recovered and studied from the heavy mineral concentrates of beach samples from the southern tip of India. Ranging in size from 0.30 mm x 0 30 mm to 1.50 mm x 2.05 mm, the diamonds are the modified forms of octahedron, dodecahedron and cube and their combinations. Bigger sizes are represented by the broken/cleaved fragments. The diamonds exhibit varied tints of which white, pink and yellow are prominent. This is the second report of diamonds from the beach sands of India and the first of its kind from the Kanyakumari coast with charnockite and khondalite suites of rocks exposed in the hinterland, which shows an important structural grain in the form of the WNW-ESE trending Achankovil shear zone passing close to the present occurrence. The possible ultra-High pressure metamorphic and shock origins of these diamonds in SGT are discussed.

Keywords

Diamonds, Beach Sands, Kanyakumari Coast, Tamil Nadu.

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