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Issues with open cast mines

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February 03, 2022

What is the issue?

Open cast mines in Jharkhand continues to be a death trap.

What are open cast mines?

  • Open-pit mining, also known as opencast mining, is a surface mining technique that extracts minerals from an open pit in the ground.
  • It is the most common method used throughout the world for mineral mining and does not require extractive methods or tunnels.
  • Generally a traditional ‘cone-shaped’ excavation is done.
  • The technique is used when mineral or ore deposits are found relatively close to the surface of the earth.
  • Open-pits are sometimes called ‘quarries’ when they produce building materials and dimension stone.
  • Dhanbad has 105 mining leases altogether comprising underground, open cast and exhausted mining areas.
  • Some leases are not operational because of lack of statutory clearances.

How the mining is done?

  • Opencast mining operations involve the removal of huge quantities of overburden, dumping, and backfilling of the excavated area
  • Overburden removal refers to the removal of top-soil to expose the coal seams making them ready for mining.
  • Tailings are a by-product of mining. After ore is processed the resultant waste stream is termed “tailings”.
  • Backfill typically contains these tailings.

What are the advantages of Open cast mining?

  • Full visualization of exposed orebody and negligible ore loss
  • Greater concentration of operations, better grade control and blending,
  • No need of artificial light with natural ventilation round the clock.
  • Greater safety, minimum mining hazards like gasification, roof and wall support.
  • Easy pumping of sub surface water
  • No restriction of working with heavy and bulky machineries.
  • Lower capital and operating costs,
  • Minimum mine development work
  • Early production and quick return of capital invested.

What are the impacts of such mining?

  • Ecosystem Damage - The ecosystem that was present at the time prior to mining activity is basically destroyed.
  • Soil degradation – Various mining activities, particularly open pit, affect the topsoil and subsoil to a great extent by changing the natural soil characteristics. e.g. texture, grain size, moisture, pH, organic matter, nutrients etc.
  • Overburden differs substantially from previous local soils, and some maybe even toxic for plants.
  • Loss of agricultural and forestland - In case of open cast mining there will be complete loss of agricultural land and deforestation in and around the pit.
  • Water pollution - Water pumped into mines can affect local water table depths, resulting in the release of acidic mining water into surface waters.
  • The damage of natural drains and waste dumps may act as a barrier to the natural flow of rainwater
  • Water logging and Flash Flood - This will result in water logging and flash floods which will damage the agriculture and to local properties downstream.
  • The seasonal filling of nearby reservoirs and recharging of the groundwater around the area will be affected.
  • Landslides - Opencast mining on hill slopes, particularly in areas of heavy rainfall, is vulnerable to landslides causing loss of human life, property and deforestation.
  • This can be controlled by geo-technically designed slope of the mine and adequate support system.
  • Affects livelihood - The land owners, often tribal population, and contractual farmers living within the Mining Lease area are affected.

How to overcome these issues?

  • Loss of Agriculture - New agricultural land is developed and aforestation is done under overall land-use planning.
  • Soil degradation - Topsoil and subsoil must be removed separately and stockpiled at an easily accessible place.
  • These soils can selectively be re-laid to reclaim degraded land for agriculture
  • Water logging and Flash Flood - The changes in the drainage pattern can be anticipated from the expected post-mining surface contours.
  • Action plan for the surface drainage pattern can be designed accordingly.
  • Landslides - This can be controlled by geo-technically designed slope of the mine and adequate support system.
  • Rehabilitated people must be compensated by cash, separate housing, employment, health care, education, and other facilities.

 Reference

  1. https://indianexpress.com/article/explained/jharkhand-open-cast-mines-death-trap-7753272/
  2. https://www.sciencedirect.com/topics/earth-and-planetary-sciences/opencast-mining
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