Mining has been a very important element in the economic history of modern Goa and a significant foreign exchange earner for the state. Recently, it has been designated as the industry at par with tourism. It has provided the trigger to boost economy of the mining talukas. Certain natural factors like the presence of coastline, a very good natural harbour at Marmugao and a number of navigable perennial rivers have promoted the economic exploitation of mineral deposits. Transport of ores by barges is the cheapest option as compared to road and rail transport.
Goa is a major iron ore exporting state and over 60% of Country's iron ore export is from Goa. In terms of foreign exchange earnings it amounts to nearly Rs.1000 crore per annum. Mining in Goa is done by open cast method which necessitates the removal of overburden overlying the iron ore formations. On an average about 2.5 to 3 tones of mining waste has to be excabvated so as to produce a tone of iron ore. The average annual production of iron ore is about 15 to 16 million tones, in the process removal of which about 40 to 50 million of mining waste is generated. Such a huge quantity of mining waste creates a problem for its storage thereby causing severe environmental pollution.
Mining Belt of Goa
The mining belt of Goa covers approximately 700 sq. km and is mostly concentrated in four talukas namely, Bicholim of North Goa district and Salcete, Sanguem and Quepem of South Goa district. Mining and associated activities have greatly affected the natural landscape in and around these areas, which is characterized by the presence of pits and waste rejects.
The mining belt of Goa is divided into three regions based on the concentration of the iron ore, namely, Northern, Central and Southern Zone. Usgao River is the dividing line for northern and central zone and Sanguem River between the central and southern zone. The maximum area under mining is in Sanguem Taluka followed by Bicholim, Sattari and Quepem.
Operation mechanism - In Goa, opencast type of mining techniques are used to extract iron/manganese ores. It is carried out by forming systematic benches on the hilltop and along hill slopes and the pits are laterally extended in stages in all directions with increasing depth. In general, bench height and width are maintained at 7m and 10m respectively. The pit configurations are planned in such a way that the overall pits slopes remains at 30 degree or less with the horizontal.
Sequence of mining operation involves -
- Systematic removal of lateritic overburden. Soft Laterite is removed by dozing and ripping. Drilling and blasting is practiced in hard and compact Laterite
- Extraction of lumpy ore zone followed by powdery ore zone.
- Wet or dry processing of the mined material so as to attain the desired cut-off grade of the iron ore. (i.e. 62% of iron) for export purpose.
Impact on Environment
Mining has also created a degraded environment and is also a matter of concern. Damage to the environment is mainly done by the reject dumps, pumping out of muddy waters from the working pits including those where the mining operations have gone below the water table, and slimes from the beneficiation plant. The damage is more evidenced during monsoon where the rain water carries the washed out material from the waste dumps to the adjoining low-lying agricultural fields and water streams. It is stated that the slimes and silts, which enter the agricultural field are of such character that they get hardened on drying. The washed out material from the dumps and the flow of slimes from the beneficial plants besides polluting the water causes Siltation of water- ways, especially during monsoon. Such silting of water ways over the years may trigger years even flooding of the adjacent fields and inhabitated areas, especially during monsoon.
Several major environmental problems caused due to mining operations are as under:
- Land degradation
- Groundwater pollution
- Surface water pollution
- Dust pollution
- Damage to beaches