Not Your Grandfather’s Mining Operation

Can sulfide ore bodies be mined safely?
Yes. Preventing and treating ARD can be done both safely and successfully. Preventing oxidation of sulfide minerals is a critical step toward mitigating the environmental impacts of mining sulfide ore bodies.

The science has even evolved to the point where minerals from a sulfide ore body can be analyzed from core samples to determine if the material even has the potential to generate ARD before it is excavated from the ground. This information is used to prevent the occurrence of ARD or to contain it.

Leaving a positive environmental legacy
The environmental consequences from some early mining operations have left an historical legacy of negative environmental impacts that still affect the public’s perception of mining. A better scientific understanding of these environmental impacts – including ARD, coupled with advances in mining practices and mine design – have enabled modern miners to better predict, plan for, and prevent or control adverse environmental impacts. Modern mining operations have also demonstrated that the long-term environmental impacts of sulfide mining – principally water quality and air quality – can be adequately addressed.

There is an orderly process in place for environmental review and permitting in the state of Minnesota, with the bulk of the cost paid by the project developer, not by taxpayers. This process was enacted into law and implemented by the state’s regulatory agencies – specifically the Minnesota DNR and the Minnesota PCA. Environmental groups were involved in that process. The agencies have personnel to deal with the technical matters involved in the evaluation of issues, and access to outside, specialized consultants (EIS contractors) to assist them – again, at the project developer’s expense.

Numerous environmentally progressive practices are proposed for the PolyMet and Franconia projects in northeastern Minnesota. These include:

No smelter
The world’s cleanest process is planned by PolyMet and Franconia. Concentrate is treated in autoclaves, much like large pressure cookers, with virtually no air and water emissions. This fully enclosed hydrometallurgical process is also dramatically more energy-efficient than traditional smelting, using only about half the amount of energy to produce copper. A residue by-product is gypsum, which may become salable for wall board, or “sheetrock.”

Waste rock
There is an extensive waste characterization process before and during operation. If waste rock is determined to be potentially reactive, it will be protected to prevent ARD. The deposits within the Duluth Complex are low in sulfur, thus reducing the problem. In open-pit mining, such as planned for PolyMet, most of the waste rock to be mined is very low in sulfur. In underground mining as at Franconia’s Birch Lake or Maturi properties, relatively much less waste rock will be mined than in the open pits.

For both economic and environmental reasons, the project operator will have strong incentives to recover the maximum amount of sulfur-bearing minerals and subject them to the autoclave hydrometallurgical part of the process.