“Uncontrolled discharge of acid mine drainage into waterways poses a risk to downstream users and to aquatic life, riparian vegetation and water resource use. In today’s society, poor practices cannot be tolerated if mining is to be sustainable.”

This is the core message from N. Currey’s keynote address to the eighty or so folk who attended the Sixth Australian Workshop on Acid and Metalliferous Drainage in Tasmania this April 2008. He continues to hit hard:

“The term ‘treatment in perpetuity’ has entered the mining vernacular as a result of intractable acid mine drainage issues that prevent relinquishing of mining leases, despite the closure of mining operations.”

He advocates more “planning” at all stages of mine development, operation, and closures as a way to deal with acid mine drainage. He makes the usual call for “risk management” of acid mine drainage. And he lists criteria for closure:

  • The post-mined landscape is safe and is stable from physical, geochemical and ecological perspectives.
  • The quality of the surrounding water resources is protected.
  • The agreed sustainable post-mining land use is established and clearly defined to the satisfaction of the community and government.
  • Success criteria are agreed with relevant stakeholders, monitored and reported to stakeholders.

There is nothing new or substantive about these ideas; and to date none of them has been fleshed out to successful application. They remain but a staple of the conference circuit.

G.W. Wilson from the University of British Columbia presumably has tenure and can tell the hard facts with no fear of retribution. In his paper Why are we still battling ARD? he starts to tell the truth, but all too quickly slips back into protecting his commercial funding base. Wilson notes that “the total global cost for the environmental liability associated with acid rock drainage is estimated to be in the order of $100 billion.” Then he asks the cogent question: “So why is it still a largely unsolved environmental problem, with no proven universal solution at hand?”

Wilson ascribes the failure to solve acid mine and acid rock drainage problems to the problems stemming from these factors:

  • Time scales for mine life cycles, testing, field observation and evaluation;
  • Physical scale-up from small scale testing to field scale application;
  • A high reliance on conceptual and numerical models; and finally
  • A general lack of full-scale, longer-term (i.e., several decades) performance data to test, verify, and correct system designs and procedures.

In short, it all takes a long time and we have not been around long enough? Blame it on computer junk in and computer junk out?

Wilson acknowledges that construction of covers over waste rock dumps to control acid rock drainage is a not a solution that works. Thus he asks: “whether our current methods of conventional slurry discharge and truck-dumped waste rock using high tip faces, are correct?”

He continues: “We have been using these methods for decades, and while they are economical based on net present value, they are providing mined earth structures that have high environmental liabilities and pose closure problems that we seem unable to solve.”

His proposal is that we add lots of chemicals to the acid generating rock and tailings to limit acid generation. Alternatively, we mix the tailings and rock together to make a dense mass with low permeability to air and water, thereby limiting the generation of acid and the egress of the acidic seepage from the mass.

As a consultant with a background firmly rooted in construction, M.J. Gowan and his co-authors from Golder Associates tackle the same issue, but with greater honesty and bluntness. Maybe fear of legal liability is a better mother of honesty than the rights that go with tenure?

Gowan et al. note that at small mines, the following approach may be able to ameliorate acid mine drainage:

  • Burial of the reactive material below the water table to mitigate the oxidation of pyrite;
  • Neutralization by mixing with an alkaline reagent (e.g., sea water, lime, dolomite, calcite or magnesite); and
  • Separation, special storage and management of the reactive materials using hydrocyclones or floatation systems.

Gowan et al. also note that these approaches may not work or be economical at large mines, and they conclude: “a proactive action to avoid environmental harm is not to mine at all.”

They recognize that this is an extreme option, but argue that not mining “may be the best alternative, particularly when the cost of managing acid mine drainage for the life of the mine and for an indeterminate period thereafter, could cost more than the value of the mineral resource.”

Recently I was at a mine where the operators sought a new tailings disposal facility. Without hesitation, they opted for below-grade disposal: in a mined-out open pit; in a newly-excavated pit; as backfill in the underground workings; or in a newly-constructed bedrock cavern.

Gowan et al. recognize the preferability of below-grade disposal of acid drainage generating tailings. They note that bulking of the tailings precludes placement of all tailings as backfill in underground mine working. That leaves you with the option of a new specially pit or cavern dug into non-acid generating rock. Expensive, but necessary if you seek to avoid intolerable, perpetual costs to protect water quality and the life that depends thereon.

Or seek an ore body in a desert. Personally I invest only in such operations, both as a matter of fiscal benefit and responsible investing.

Lest you think I have been too negative in my assessment of the current state of practice of acid rock and acid mine drainage or the ability of practitioners to deal with facts and challenges, let me call to your attention the paper by T.D. Chatwin of the International Network for Acid Prevention. He says, correctly I submit: “If we and our children are to continue the ‘quality of life’ that we have grown to expect, the mining industry must prosper [so that it may] supply the raw materials that feed the economies of the world. For the mining industry to prosper, the issues of acid rock drainage must be addressed. We have the education, experience, and the ever growing knowledge base.”

Chatwin notes that his organization has hired Golder Associates to compile a comprehensive guide to managing acid mine and acid rock drainage. Let us hope that Golders involves Gowan et al in this effort. Personally I doubt the guide will be worth much if it fails to tell us when to walk away from an ore body because the value of the ore is less than the cost of perpetual treatment of acid from the mine and its wastes.