The destructive collapse of the large iron-ore slimes dam at the Samarco mine, in Brazil, is putting pressure on companies to have their tailings technologies reviewed by independent auditors – as well as forcing a relook at the efficacy of how mine waste is currently stored.
Dry stacking is once again beginning to pop up as an alternative to wet tailings storage, particularly in areas of water shortage.
Following the Merriespruit tailings dam disaster in Virginia, in the Free State, in 1994, a new focus was placed on slimes dam safety but that did not stop disasters from occurring in Papua New Guinea and Canada and now also Brazil.
Seventeen people were killed at Merriespruit and 80 houses destroyed and now 11 have died in Brazil, 600 people have been displaced and water halted to 260 000 in what has been described as an “environmental catastrophe”, with liability falling on Samarco’s joint owners, Vale and BHP Billiton.
Already tougher rules are being proposal in Brazil for a new mining code to include stricter regulations for tailings dams that could make dry processing obligatory.
Dry stacking, which is often put forward as a way of mitigating disasters, removes water from processed ore using pressure filters and allowing the mine waste to be stacked in a more controlled fashion.
Those in favour of it say that dry stacking can also reduce waste seepage into groundwater that risks extending environmental liability after mine closure but it has not really taken off.
A tailings dam breach at the Mount Polley copper mine, in British Columbia, Canada, last year led experts to recommend that mines raise their tailings game.
The Greens Creek gold mine, in Alaska, is reportedly a dry stacker and reports suggest that the La Coipa mine, in Chile’s Atacama Desert, and Hudbay Minerals’ proposed Rosemont copper mine, in the US state of Arizona, also plan to dry-stack.
The Porgera mine, in Papua New Guinea, is said to be working on mixing tailings with coarse waste rock and mud to create a product that can be stored on the surface in dumps and the Silvertip lead mine, in British Columbia, is expected to use a combination of dry and underground storage.
The probability of civil lawsuits at Samarco could be a catalyst for even more widespread change.
The BHP Billiton spin-off company, South32, said at its annual general meeting in Perth last week that it would be reviewing its tailings dam risk in the light of the Samarco tragedy, as can be read on page 14 of this edition of Mining Weekly.
South32 has 34 tailings dams of various sizes across its portfolio of assets in Africa, including residue dams associated with the company’s smelters.
Detailed risk assessments had been done at all of the dams, which were of relatively low materiality.
The Brazilian disaster has also prompted Principles for Responsible Investment MD Fiona Reynolds to call for appropriate environmental, social and governance issues within executive management goals and incentive schemes to create and protect long-term shareholder value.