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:: Responsible Mining: Evidently not in Minas Gerais
Last week's tailings dam breach at the Córrego do Feijão iron ore mine in Brumadinho, near Belo Horizonte in Minas Gerais state in Brazil, is not only an appalling human tragedy but also a major setback to the international mining industry's bid to improve its image and to promote responsible and sustainable mining.
The Córrego do Feijão mine is one of four in Vale's Paraoeba complex, which includes two processing plants. The complex produced 26 million tonnes of iron ore in 2017, or about 7 percent of Vale's output, with Córrego do Feijão accounting for 7.8 million tonnes.
There have been many tailings dam breaches over the past decades, but Minas Gerais has the worst record, too many serious accidents involving burst tailings dams having occurred in this area. In 2014 three workers were killed when a barrier gave way at a dam belonging to Herculano Mineração, an iron ore mining company. In 2007 heavy rains caused the Mineração Rio Pomba Cataguases bauxite mine to burst leaving 5,000 homeless. In 2001 five workers at the Mineração Rio Verde Ltda iron ore mine were killed when the tailings dam failed.
But only three years ago the Bento Rodrigues dam disaster of November 5, 2015 was then the worst environmental disaster in Brazil's history, killing 19 people when the Fundão iron ore containment dam failed and released 60 million cubic meters of iron ore waste. The mine was operated by Samarco, a joint venture between Vale and BHP.
It is estimated that between one and four breaches occur each year at tailings dams world-wide, roughly 10 times the failure rate of water dams. The largest tailings dams, at copper mines high in the Peruvian Andes, are colossal, already as tall as the Hoover Dam and have permits to rise even further. Unlike water retention dams, a tailings dam is raised in succession throughout the life of the particular mine. Typically, a base or starter dam is constructed, and as it fills with a mixture of tailings and water, it is raised.
The disposal of tailings adds to the production costs so it is necessary to make disposal as cheap and as safe as possible. This requirement led initially to the development of the once commonly used upstream method of tailings dam construction, so named because the centerline of the dam moves upstream into the pond. In this method, a small starter dam is placed at the extreme downstream point and the dam wall is progressively raised on the upstream side. The tailings are discharged by spigoting off the top of the starter dike and, when the initial pond is nearly filled, the dyke is raised and the cycle repeated. Various methods are used to raise the dam; material may be taken from the dried surface of the previously deposited tailings and the cycle repeated, or more commonly, the wall may be built from the coarse fraction of the tailings, separated out by cyclones, or spigots, the fines being directed into the pond.
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