Unexplored treasure trove in Eastern Ghats

Visakhapatnam: Andhra Pradesh's Eastern Ghats region is sitting on invaluable reserves of hundreds of tonnes of precious and semi precious gemstones like alexandrite, chrysoberyl, chrysoberyl cat's eye, aquamarine, ruby, moonstone, zircon, sillimanite, garnet, tourmaline. A carat of alexandrite in the open market fetches around close to a lakh rupees.

Though there were instances of illegal mining in some parts of Narsipatnam in Visakhapatnam district for the first time the reserves of these gem stones have been estimated.  

Gem stone explorers from Visakhapatnam belonging to Mineral Exploration Division of the Department of Geology at Andhra University led by Prof C. Kasipathi had found that 51.26 tonnes of alexandrite reserves alone are available in Visakhapatnam district.

Considering the geology, field relations, structural features and lithological controls, geoscientific exploration was carried out in some of the important gem bearing locations of AP to estimate these reserves.

Geological mapping, physiographic contouring, structural parameters, pitting, trenching, drilling and sampling were carried out, in addition to Electrical Resistivity surveys were conducted to find out the reserves.

The estimation of these gemstones was discussed in a paper published in Canadian Journal of Pure and Applied Sciences.

The collected samples were categorised in the laboratory and characterised with their physical and optical parameters. The samples were also graded and the ratio of gemstone resource and the gangue was also determined. Reserves were estimated using cross-section methods. The gemstone concentration levels with different lithological units were also determined.

"A new province of invaluable precious and semi-precious gemstone resources has been explored from parts of Eastern Ghats Mobile Belt (EGMB) in the states of Andhra Pradesh and Orissa, India for the first time. The pegmatites are the immediate hostages and intruded through the gneissose bands of khondalite and leptynite rocks thus made the EGMB, India as a special precious province of gemstones," said Prof Kasipathi in the paper.

 He added that the mineral 'alexandrite' must have formed at a very high temperature, when compared to the other precious minerals. The chemical composition of alexandrite is more or less the same as that of chrysoberyl, but constitutes a little amount of chromium impingement in its chemical structure, which results in green coloured mineral.