Mining hydrologist Geoff Beale of Schlumberger Water Services is urging mining companies to “take careful consideration of closure when planning their initial and expanded site layoffs” to reduce the chance of being saddled with mine pollution liability issues in perpetuity.
In a presentation to the Northern Nevada Section of the Society for Mining, Metallurgy and Exploration Monday night, Beale noted that mine operators increasingly adopt a “mine to close” approach when planning their initial and expanded site layouts.
Beale reminded his audience that the controlled mine closure has only occurred within the past two decades, and that many of the mines entering the closure stage now were developed before closure regulations existed.
Nevertheless, he stressed, it is best for miners to manage mine closure issues, rather than handing it over to government agencies, which immediately reduces efficiency and raises cost, such as can be the case with foreign governments of developing nations.
In his talk, Beale observed that mine closure practices and science address four general categories: 1) open pit mines in arid environments, such as those found in Nevada; 2) open pit mines in temperate/humid environments; 3) underground mines in elevated terrains; and 4) underground mines in lowland terrain. Beale called underground mines in lowland terrain the easiest to manage for closure, while underground mines in elevated terrain are the most difficult.
Issues which may have to be managed during mine closure include pit backfilling, rapid flooding to form a pit lake, managing pit slope instability on closure programs, and how to minimize the potential for acid generation and achieve acceptable post-mining water quality. The management of Acid Mine Drainage is often a primary obstacle for mine closure.
Ironically, the same sinkhole problems which plague Florida now have become a post-closure mine issue in South Africa, Beale observed.
While studies are important for developing broad closure concepts and for identifying crucial closure issues at the early stage of the mining cycle, Beale noted, “There will be a much greater understanding of actual closure conditions during the final years of mine operations when a longer period of monitoring data is available. Experience has shown that it is better for the closure studies to identify bounding conditions and uncertainty, and the potential requirement for mitigation, rather than attempt to provide exact predictions.”
The actual closure process will then have the flexibility to deal with unanticipated problems as they occur, he added.
Closure planning must consider both the short-term when sufficient infrastructure is in place to allow hands-on management and long-term closure “where sustainability with minimal management is usually desirable for all stakeholders.”
The European Union and other countries have encouraged mining companies and regulators to “work together to develop risk-based closure approaches that achieve sustainability and social gain, rather than meeting rigid numerical standards,” which is the basis of the U.S. regulatory process, Beale observed.
Beale cites several case studies of what he considered to be good closure work conducted at the Sleeper gold mine in Nevada, the Haile gold mine in South Carolina, the Kori Kollo gold mine in Bolivia, and the Golden Cross gold/silver mine in New Zealand.
Ironically, three months after mine closure work had been completed at Haile, the price of gold soared and Beale has to remove much of what had been installed to manage mine closure.
Meanwhile, Beale observed that mining companies are sometimes unfairly blamed for post-closure issues over which those companies had no control. For instance, the post-closure land use of a mine can negate the mitigation and monitoring infrastructure built into a mine’s post-closure planning and implementation.
As an example, Beale noted that the operators of the Kori Kollo gold mine ensured they left behind what he said was “a pristine lake.” However, the possibility that farmers “could pump the hell out of it for agriculture” will not leave a pristine lake for posterity.
In some countries, government corruption could mean that money mining companies allocated for post-mine closure monitoring and mitigation, instead winds up in somebody’s back pocket, he observed.
To address some of the aforementioned concerns, Beale said an effort is being made to train other industries that take over reclaimed mine sites to also manage for closure.