Indian Jewelry » Diamond Gemstone India

As in Madhya Pradesh, diamonds occur in three different geological environments in Andhra Pradesh, viz;
(1) Kimberlite pipes of Wajrakarur-Lattavara area;
(2) Secondary Conglomerates of the Kurnool group;
(3) Quaternary Gravels of the Krishna and other river basins.

Nine kimberlite bodies, including two recently discovered by NGRI and GSI have so far been located in a 100 sq. km. area in Wajrakarur- Lattavaram belt of Anantpur district. Bodies are small in area and are circular to elliptical or dyke-like in shape, emplaced within the Archean Granite gneisses.

Conglomerates & Gravels:
The Banganapally formation comprising the conglomerates in its basal parts within the western part of Cuddapah Basin occurs in a discontinuous manner over a strike length of 250 kms. The conglomerates range in thickness from 1-50 cms. with increasing incidences in some other portions. Quaternary Gravels of Krishna, Tungbhadra, Pennar, Maneru and other rivers have been worked in the past. The gravel horizons are 0.3 to 2.5 m. thick, having thin overburden.

In Andhra Pradesh, till recently, only six kimberlite bodies were known in the Wajrakarur area of Anantpur district. In the last few years, in quick succession six more bodies have been discovered. Only eight out of the total 12 bodies were found to be diamondiferrous. The narrow, elongated dyke-shaped pipe NO.7 extending over a kilometre in length has a fair concentration of diamonds with incidence up to about 9 ct/100 t. The other diamondiferrous pipes namely, pipes 1,3, 4 & 6, show an encouraging zone of about 250m. x 180m. with an incidence of 5 ct/100 t.

The proterozoic conglomerate rocks in a belt extending over a distance of about 45 kms. In Kurnool district have been found to be diamondiferrous. The exploration in conglomerates of Banganapally- Nereducherla belt, however, indicated a poor incidence of diamonds of up to about 2 ct/100 t. The gravels along Krishna river and Pennar river terraces are also well known for their diamondiferrous nature. Most of the large size diamonds of historic renown were recovered from the Krishna river gravels. However, the recent exploration carried out by GSI in Chandralapadu, Patempadu, Veldikottaplem, Kodavatikallu and Pekkunuru blocks revealed average diamond incidence to be less than 1 ct./100t.

Orissa : Land of Gems:
Besides the above known occurrences in Andhra Pradesh, Madhya Pradesh and Chhatisgarh, some diamonds have also been found in the States of Orissa, Maharashtra and recently in Rajasthan and Karnataka.
Of these, the multi-gem producing State of Orissa is the most promising, in which De Beers and Ashton Mining of Australia have lately been taking interest. Australia is conducting a survey. The State Government too has undertaken prospecting. If these official searches and surveys prove fruitful, other companies might join the Orissa explorations.