Opencast mining has become increasingly unpopular with non-governmental organisations and government authorities owing to its high environmental footprint, but the method is still the most economical option for mining houses, says minerals industry consultant Venmyn director Neil McKenna.
“Compared with underground mining, the single biggest challenge faced by opencast mining is its environmental impact as a result of the large mining footprint associated with bulk commodity mining.”
For instance, the South Cotabato province of the Philippines banned opencast mining in 2010. The ban is hindering the progress of diversified miner Xstrata’s $5.9-billion Tampakan mine. The project is considered to be the biggest undeveloped copper/gold prospect in South-East Asia, with an estimated yearly average production of 375 000 t of copper and 360 000 oz of gold over an initial 17-year mine life.
Xstrata’s Philippines-based subsidiary, Sagittarius Mines, announced in January that it had been denied an environmental clearance certificate (ECC) for the project by the country’s Department of Environmental and Natural Resources (DENR). Sagittarius filed a petition for reconsideration of its application on January 27.
However, Tampakan, which was scheduled to start production in 2016, has no definitive timeline because the DENR has failed to set a deadline for reconsideration of the ECC rejection, the Chamber of Mines of the Philippines (COMP) said in March.
The COMP is asking the government, through the DENR, to intervene directly in the long-standing dispute over provincial ordinances that contradict national law. The country’s Zamboanga del Norte province also banned opencast mining last year.
“South Africa and the world have placed a considerable weight on environment-friendly and responsible mining,” says McKenna.
Miners would almost always choose opencast mining over underground mining if environ-mental and social concerns were taken out of the equation, he notes.
As underground mining operations take place below surface, they generally do not create as much air and noise pollution, contribute less to groundwater, surface water and soil pollution, and are not as visually intrusive, says McKenna.
Opencast mining can also result in the loss of flora and fauna through the destruction of habitats.
As a result, more resistance to opencast mining is experienced in areas that overlap inhabited or conservation areas.
McKenna says the biggest potential for growth in the opencast mining industry is in bulk commodities, such as coal and iron-ore, as increased prices and demand are making these more viable for opencast mining, even at lower grades.
He adds that, when it comes to minerals, the method of mining is dependent on a host of factors, such as mining costs and the depth and size of mineral deposits.
Employee costs, consumable and mining supply costs, environ-mental compliance costs and utility costs may, in some cases, tip the balance in favour of one or other mining method, says McKenna.
Opencast mines tend to be preferred for their low operating costs when the orebody is close to the surface and also where problematic roofing conditions influence the safety of underground-mining operations.
McKenna adds that there is a global trend towards deepening opencast mines, owing to commodity price increases providing mining companies with the opportunity to mine deeper at a more profitable rate.
“South African coal companies are now able to mine deeper than before, as a result of the growing market for metallurgical and export-quality coal.”