Seventeen people have been confirmed dead and dozens more are still missing following the collapse of two waste dams at an open pit iron mine in Minas Gerais State, Brazil. The incident happened at Samarco Mineracão's Alegria Mine, which is jointly owned by Brazilian mining company BHP Bilton and Australian multinational Vale, happened on Thursday 5 November 2015, releasing a wall of water 15-20 m high which engulfed the village of Bento Rodrigues, which has a population of about 600 people, and reached about 7 km from the mine, sparking fears of pollution reaching the Gualaxo do Norte river.
Devastation in the Brazilian village of Bento Rodrigues after it was hit by a flash flood following the collapse of two retention dams at a mine on 5 November 2015. TV Globo/ AFP./Getty Images.
Tailings ponds are used to store sediment-laden waters from mines; such
waters typically contain a high proportion of fine silt and clay
particles, which take time to settle out of the water. The resulting
water may be fairly clean, or may contain other pollutants (typically
acids, either generated by the local geology or used in the mining
process), and need further treatment. In some instances acid is added to such pools in order to dissolve the product, which is then released from the resultant chemical slurry by further treatment, however this is not a typical procedure at iron ore mines, and was not employed at the Alegria Mine. However while the pollution caused by the breach of the ponds is likely to be less severe than caused by the breach of an acidified pond, deposits producing metal ores still often produce a variety of toxic chemicals in themselves, and the cleanup costs of such a spill are likely to be considerable.
Damage caused by the 5 November 2015 mine dam collapse in Minias Gerais State, Brazil. Felipe Dana/AP.
The cause of the incident is not immediately clear. Both dams had passed inspections by local environmental officials in July this year. Seismologists at the University of Sao Paulo reported four minor Earth tremors in the region in the hour before the collapse, but a visual inspection of the dams carried out immediately had failed to reveal any problems, so it is unclear if the two events were collected. The mine will remain closed indefinitely while the incident is investigated, and the mine operators are likely to face calls for high levels of compensation and probably several law suits following the incident.
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