MORE THAN 99 per cent of the total primary gold in the country comes from a vast expanse of over 40,000 sq km area covering major parts of Karnataka, Andhra Pradesh, Tamil Nadu and Kerala. Therefore, it is imperative to fully assess the gold potential of the gold-fertile land of southern India.

It is very likely that for the first time Kerala is heading for gold mining. And once the mines are established, the greens of the Malappuram and Attapadi valley will turn into grey. The entire natural and ecological balance will be disturbed.

Sustaining economy

Yet, to sustain the economy of the country, extraction of natural wealth from the earth's crust is essential. As there is science to explore the wealth, there is also technology to exploit and mine with modern techniques and there is legislation also to control the degradation of the environment.

Moreover, with the opening of the mining industry, job opportunity will open up for many people including the local tribes, the area will be developed and the state's economy will also flourish. But gain in economy and loss in ecological balance are to be weighed with a positive attitude.

For this, a systematic study on environmental impact assessment needs to be carried out with the objective of assessing the likely environmental implications of a proposed developmental activity including mining at the planning and designing stage of the project under national environmental policy/legislation.

The importance of required control of the associated environmental impacts due to land use, socio-economy, ecology, air pollution, water quality, noise and vibrations, aesthetics and amenities caused by mining should be taken care of.

For this consultation amongst the project developer, the affected people, non-government organisations, public representatives and planning authorities are to be carried out. All aspects of environmental, socio-economic and particularly compensation for settlement and rehabilitation package and other issues as required by the decision makers should be dealt with a positive attitude. Environmental impacts can be anticipated from the experience of similar gold mining projects in Karnataka. Scientific data from the working gold mines will substantiate the anticipation.

Assessment of anticipated impacts, however, becomes significant to locality and mining material specifications, as also type and technique of mining.

Hydrothermal solutions

Gold is available in acid and basic volcanic rocks of Archaean age, the oldest known rocks in India ranging in age from more than 3000 million years to 2000 million years.

In general the volcanoes culminate with effluents of hydrothermal solutions that carry precious metals in the form of naked elements, oxides or sulphides.

These hydrothermal solutions intrude into the older rocks as quartz veins. In Dharwar region these quartz veins within volcanic rocks host the gold.

These rocks may be broken due to mechanical and chemical weathering into sand size particles and carried by streams and channels. Gold occurs also in these sands as placers.

Recent exploration result for gold occurrence in Kerala is highly encouraging. Attapadi, Nilambur and Mankada areas in Malappuram district have been recorded as highly potential.

Attapadi gold belt in sheared gneissic rocks is found in three subparallel auriferous load zones where some blocks having 250 to 500 metre length and 1.5 to 2 metre width could be identified as most promising ones.

Similarly six lensoid gold bearing load zones in high grade metamorphics at Nilambur and two gold load zones of over 2.50 metre width in sulphide rich high grade rocks at Mankada are also recorded.

Kottathara area of Nilambur region holds more than 80,000 tonnes of gold in its reserve with up to 13.8 grams per tonne of the ore in the laterite. Gold worth about Rs.600 crores at current prices is present in this area.

Cluster mining

The state government is planning to go for `cluster mining' in the area to fix the occurrences of gold. Four grams of gold per tonne of the ore in any ore load zone is economically viable if the exploitation continues for at least twenty years.

However, the exploration for gold should be taken up cautiously because of its low level of concentration and erratic distribution due to complex structure of the terrain.

Each area should have distinct exploration strategy as also the exploitation strategy following proper assessment of ore potential and establishing adequate resource of workable grade for sustainable commercial exploitation.

Though the geological environment for gold mineralisation is apparently similar for both older Kolar and newer Attapadi-Nilambur area one may wonder why Kerala was not so far explored for gold.

Available as host

However, basic and ultrabasic volcanics are also available as host for gold mineralisation elsewhere in Karnataka where more than 100 occurrences of gold mineralisation are reported.

Kolar has so far produced 800 tonnes of gold up to an average depth of 2750 metres over a strike length of 8 kilometres.

However, presence of intrusive granitic rocks into the volcanics in Karnataka has been given top priority for gold exploration while its western extension is devoid of such intruded granite, which might be the plausible reason for delay in the exploration strategy.

AMITAVA BANERJEE

Geological Survey of India

Chennai

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