Anna & I recently attended a lecture at UPenn in which Mark Logsdon the President and Principal Geochemist at Geochimica spoke about his research in hydrogeological and hydrogeochemical studies of acid mine drainage, planning mine closures, water-quality site investigations, and geochemical modeling. The lecture focused on water-quality issues and their management, specifically for metals mines, using examples from Marks recent experience in North and South America, Australia, Indonesia, Papua New Guinea, and Laos. We had the opportunity to ask Mark some questions about his experiences and his research of a new tailing remediation system. Below are our questions and Marks answers, offering us some insight into the nuances of the metal mining industry.
*How long is the average gold/silver mine operational?
Gold and silver mines, that is mines that are exclusively for precious metals, tend to be quite small, and therefore short-lived. Most silver and gold mines in Nevada that have been developed in the last 20 years will have life of span of 10-15 years. There are a few exceptions, such as the big open-pit mines at Elko (Barrick Goldstrike, for example), that will probably be 20-25 years. Very rare exceptions, such as the Homestake Mine in Leed, SD exist, but they tend to be a very different kind of gold deposit – deep vein systems in metamorphic rocks, that are extremely rare.
* What happens to the mine site after it is no longer functional?
The closure plan, pretty much everywhere in the world now, will have three major components. Firstly, a physical restructuring so that all slopes are safe and stable and surfaces can be revegetated. Secondly, a program for long-term management of water quality. This may have to include long-term, even “perpetual” water treatment, though what this actually means is still pretty murky. Thirdly, the company has to settle up with its employees and work out some sort of staged withdrawal that allows a socio-economic transition for the nearby towns that have grown to depend on it commercially. This also is a new feature (say the last 10 years).
*How do you ensure that sufficient funds are set aside for clean up & maintenance when maintenance is seemingly never-ending?
Mines operate under a set of permits, and one or more of those permits (usually a “permit to Mine” from the state) will specify (a) the general terms of closure (see last Q) and (b) require the submission and approval of a closure plan, usually 5-10 years before the operation closes. The closure plan has to have costs associated with it, and the terms of the Permit to Mine require the miner to obtain a bond (from a reliable source) that covers all of those costs. The money going into the bond payments earns interest, and so it is a perpetually funded source. (Of course, assuming that the banking system survives.)
*When you spoke at Penn, you mentioned that in most cases, enough money is available for clean up; the real issue is who will monitor the clean up. Couldn’t the funds ensure that there was an infrastructure to continually monitor the clean up? Does oversight (governmental or otherwise) become the issue?
The funds ensure that there is money available to pay someone. The problem is to determine who that someone would be. Generally the fund includes money for regulatory oversight of the site, but it does not assume that the regulators will do the work. In fact, neither regulators nor companies think this is a good idea. So, there has to be some agreement on how the work will actually be done. The best (imo) approach is to establish a local company, as part of the socio-economic closure plan, far enough in advance that they can be trained to do the work. This leaves at least some residual economic benefit (through direct payments and multipliers) for the home team.
Photograph by David Maisel Mining Project 6 (Ray Arizona)
*Does a third-party usually project the cost required, and the amount dedicated by the mining companies for clean-up efforts? How much money is generally invested in clean up?
This varies by jurisdiction. In Canada it is always an independent estimate, on which the company may comment. In US and Australia, it is almost always a canopy plan, on which they comment (and ultimately must approve). Mine closures today might run from a few tens of million dollars to well over a billion, depending on the size, longevity, and nature of the problems. A 10-year silver mining project in Nevada, if they run well, may be able to get out for $10-20 M. Costs estimates for the mining complexes at Butte MT or the Coeur d’Alene District in Idaho run into the billions of dollars.
*If the 1872 law is changed and U.S. mines begin paying royalties to the government, where do you think this money will/should be directed?
This is one of the key stumbling blocks. The Government generally would like the funds to be designated for General Use, either actually to the General Fund or at least to the general budgets of the parent Departments (which would be either Interior (for BLM and parks) or Agriculture (for Forest Service). The Companies would like to see the royalties targeted in ways that are closely tied to mining (e.g., USGS; funding for mining research, support for overseas mining on development basis…). Probably a portion will go to the equivalent of Superfund, to pay for orphan-mine cleanups. Given the dire condition of the budget, I’d say General Fund wins.
*In the US are there any systems in place that will pay back communities that have been negatively affected by mining (especially in sites where the mining has occurred on public or indigenous lands)?
There have been quite a number of mining Superfund sites – large portions of SW MO, SE KS, and NE OK (the: tri-State District); Leadville, CO; the Coeur d’Alene drainage; Butte, MT; old mines in and around several national parks; most of the old uranium mine son Navajo land. These remedial projects, some of which will continue for decades at least, provide local jobs in construction and other support services. Do they “pay back” the communities? Hard to say, and easy to argue about. In many cases the communities (Leadville, Butte and Leed are very good examples) are there only because there was mining to begin with, and pretty much all they have came form the mine. It’s not just negative.
*What sort of regulations exist in the US for mines to monitor the air pollution produced during the smelting process?
All smelters are and have been since it was passed in 1976 controlled by the Clean Air Act. The permitting and monitoring requirements are very extensive.
* Does the lining in the tailing ponds wear over-time? If so, how often is the lining in the tailing ponds changed?
Very few tailing ponds are lined; except for uranium tailings and cyanide leach systems. The longevity of the liners for these systems is not very well understood. Usually they will have multiple liners, at least one of which is compacted clay that presumably never “wears out.” The synthetic liners are designed to last 100 years, but there is no special reason to think they will fail at that point – just no engineering basis to predict longevity beyond that. In 100 years, tailings should all be fully drained. Therefore, with a cover that limits infiltration (and can be replaced) a 100-year lifetime for liners should protect water resources. No one changes liners – there is no practicable way to do it.
Photograph by David Maisel Mining Project 10 (Butte Montana)
*What happens to all the waste rock? Is that too deposited into tailing ponds or re-integrated into the mountain?
In general, it remains in big piles on the sides of the mine – often in old valleys, where it has to be contoured at closure to prevent catastrophic landslides. There it stays, sort of incorporated back into the mountain, but as loose rock, nor bedrock. Sometimes, especially if there are multiple pits, it may be possible to backfill part of the waste rock into pits, but in a single pit, such as Bingham Canyon that I talked about, that is not possible, because they are still mining in that pit.
*Could you explain again how the tailing remediation system that you designed in Bingham County actually works?
The contaminated water is low-pH (acidic) and contains dissolved metals. We pump that contaminate water out of the plume and inject it into the tailing line. The tailing flowing down the line contains calcite (CaCO3) and some other minerals that are soluble at low pH. So the acidity of the water reacts with the acid-neutralizing minerals of the tailing. By properly balancing the amount of contaminated water and tailing, we can neutralize all the low-pH water. As the pH of the neutralized solutions rises, metals become insoluble and precipitate out. When the metals precipitate, they become solids, just like the 150,000 tons per day of solids we already are sending as tailing, and all that mass stays in the tailing impoundment.