Traditional Gem Mining
The most popular method is mining in pits (depth 2ft – 25ft) and tunnelling. Surface gemming and dredging in river beds are other methods which depend on the nature and the location of the gem deposits. In general, gems are concentrated in a layer of coarse pebble like material with some clay and fine sand. This gem gravel, known as illam is generally found below the alluvial deposits.
Where illam is close to the surface the pits are shallower and circular but the deep pits have a rectangular shape. The scaffolding are made using planks and staves. The space between the staves and earth is stuffed with leaves to prevent walls from collapsing. The water is pumped out by using motors. The tunnelling will be resorted to only if the illam vein runs horizontally. The illam in pits are excavated using crow bars whilst river dredging is done using mammoties. Traditional mining is mainly in a small scale with manpower alone.
Mechanised Gem Mining
In Sri Lanka where the gem deposits are scattered mainly in highly populated Sabaragamuwa province, Uva province and southern province, there are very few possibilities of using machinery as machinery could be made use of only for mining in a large scale. Some of the machinery that could be used are bulldozers, drilling machines, air compressors, excavators, loaders, dump trucks, heavy water pumps, etc. Such machinery will definitely help mining in a large area within a short period. The advantages of using machinery are the quick exploitation of our limited mineral resources and the drop in manpower employment.
Environmental Aspects and Restoring the Land after Mining
The mining activities could damage the environment easily. Therefore the restoration of land after mining is very important factor to look into.
Generally the top soil is the most important layer of soil for re-cultivation. Therefore the miner should see that he keeps the top soil separately and place it on the top of the pit once he closed the pit after mining. In the way the traditional miners are working, it is not that easy as removing the top layer in a large area by using machinery.
The second layer that we should take care of is the clay layer if there is any. The clay layer is very important to keep the water table in balance.
In some places in Elahera due to the high water table (6ft) prevalent in mining areas and also due to, the fact that the alluvial deposits – the gem gravel are found in a depth of 20 – 25ft, the mining could be carried out only by using mechanised excavators.
In traditional mining only the illam within the mine and tunnel will be taken out. The rest will remain undiscovered under the earth. But in mechanised mining a very large area could be covered to get the entire illam.