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The Physical Footprint of a Mine
I am flying over Sudbury on a clear autumn day. I can see the city and the surrounding towns, the roads and railways, power lines, rivers, lakes, and hills. But I also see three huge turquoise and rusty-orange tailings lakes (one thirty-five square kilometres in size), the Glencore and Vale smelters, and the old refineries. Everywhere there are blackened slag heaps and waste rock piles. A number of open-pit mines dot the surface, as do the head frames of underground mines. Smoke streams from the superstack. From this height, I am aware of how much the footprint of these mines has grown since my last flight just a few years ago. Despite reclamation and re-greening programs, the mines and their wastes are quickly devouring the landscape.
The mining industry likes to say that mines are just âa little hole in the groundâ1 and are a âtemporary use of the land.â2 This is not true. This chapter provides an overview of the extent of the footprint of an operating mine and offers some important definitions for understanding mining.
The minerals and gems we mine are the product of movements of the earthâs crust over billions of years. Although they are scattered in various concentrations everywhere in the earthâs rocks, to be concentrated into deposits that are economically viable, they have undergone dramatic heating, cooling, and gravity separation. Metals have different weights and different specific gravity. As the earthâs crust dances with the shifting of tectonic plates, the eruption of volcanoes, the impact of meteorites, and the cooling effects of water, mineral depositsâof gold, copper, uranium, zinc, diamondsâare formed.
We call these deposits ore bodies.
To get to the ore body, the mining company will have to displace any people from the land where the mine will be built, then remove the overburdenâthe trees, plants, and soilâcovering it, and then remove the rock surrounding or covering the ore body.
The amount of desired metals or gems in the ore body is called the grade. Depending on what metal or gem you are talking about, this may be shown as grams per ton or ounces per ton (for gold), a percentage of the metal in the ore body (copper), or carats per ton (diamonds). In Canada and elsewhere, the grade of ore has been decreasing as deposits that are profitable to mine are being used up. It used to be that copper grade had to be 4 to 5 percent and gold grade 5 grams per ton (gpt) before it was considered worth mining. But now the Gibraltar Mine in British Columbia has ore with a copper grade of 0.26 percent and a molybdenum grade of 0.008 percent; the Mount Milligan Mine (also in British Columbia) grades 0.19 percent for copper and 0.3 gpt for gold.
Mining is a waste management industry. The process creates an extremely high volume of waste: the overburden, the waste rock that is removed to get to the ore, and the ore body that has been crushed into powder at the mill and rejected, called tailings. Some mines dispose of almost 100 percent of the rock they smash up, along with various chemicals that are added in the course of extracting the minerals. The volume will definitely be larger than it was before mining because of the blasting and milling process.
Mining is a rapid, ferocious, and continuous assault on the earth. A mineâs footprint gets bigger every day it operates. Although it may take a long time to get permits, financing, plans, and equipment in place to start operating (something the industry complains loudly about), once the company has all this, a new road and a few holes in the ground can become a two-kilometre-wide, five-hundred-metre-deep open pit within a few years. In ten to fifteen years, the deposit will likely be mined out and the mine will be closed. Unless, of course, the company discovers a new ore body nearby, and then the process will continue.
Mining happens in two main ways: underground mines and open pits (or a combination of the two). The type of mine is determined by the nature of the ore body. If the ore body is concentrated, then underground mining may be possible. If, however, it is dispersed and low grade, an open pit is the only economic option for the company.
The tunnels and shafts of underground mines can extend for kilometres under old mining districts like Timmins and Sudbury, and will go down until the ore runs out or until heat from the centre of the earth makes it impossible to continue. The Kidd Mine in Timmins is the worldâs deepest base-metal mine below sea level, with a mine that is almost three kilometres deep.
Open-pit mines are among the largest human-made structures on earth. The Bingham Canyon Mine, located southwest of Salt Lake City, Utah, in production since 1906, is the deepest open-pit mine in the world and is more than 1.2 kilometres deep and approximately 4 kilometres wide. The Dome Mine open pit in Timmins removed over 286 million tons of gold-bearing rock over more than one hundred years to create a hole 340 metres deep and 800 to 900 metres across.
Diamonds are found in âkimberlite pipes,â carrot-shaped intrusions into the earthâs crust of magma from deep in the earth, where carbon from ancient forests has been trapped and compressed into diamonds. Two diamond mine complexes, Ekati and Diavik, are both located in the Lac de Gras area of the Northwest Territories, about three hundred kilometres north of Yellowknife. Ekati was the first diamond mine in Canada, and it started mining its first pipe in 1998. Just twenty years later, it has six open pits and three underground mines. The mine itself is only one part of the footprint, as the following section illustrates.
The Diavik Footprint
The Diavik Diamond Mine in the Northwest Territories is one of the largest open-pit mines in the world and provides an excellent example of the awesome size of open-pit mines.3
Situated on an island in Lac de Gras in the Northwest Territories, the mine has produced roughly eight million carats a year since it opened in 2003. It consists of three open pits (with another being developed).
Satellite image of the Northwest Territoriesâ Diavik Diamond Mine.
Image from Planet Labs, Inc., 2016. Creative Commons 4.0 License.
The slope of pit walls is a major concern for mine engineers as the walls have to be designed so that the rock benches donât collapse or slide. Most pit walls cannot withstand an angle greater than forty to forty-five degrees from horizontal. As a result, the radius of the pit gets bigger and bigger the deeper it goes.4 At a certain point, the mine can only be continued with underground tunnels. When Diavik faced this problem in 2012, the mineâs life was extended with further mining underground.
The waste from the pitsâwaste rock that is not used for road and dike constructionâis stored in processed kimberlite piles (tailings) and in waste rock dumps.
The complex also houses a processing plant, power and boiler plants, fuel tanks, and water and sewage processing facilities. An explosives plant and storage facility are also on site. It is serviced by a six-hundred-kilometre ice road built by the owners of the Ekati and Diavik mines.6 The Diavik airport, with a 1,600-metre gravel runway, is big enough for a Boeing 737 jet. Power is largely provided by diesel generators; a wind farm provides 11 percent of the energy requirements.7
Like Diavik, all mines extend their physical impact beyond the mine site through roads, power lines, railways, and ports. They may require hydro dams and the creation of large reservoirs to get their power. They are major producers of greenhouse gases, and major users of water.
Roads are often the most serious problem created by a mine. They can affect animal and plant distribution, kill many animals, and create impassable barriers for others. In addition to habitat loss, roads also enable exotic species to invade and out-compete native plants. They create an âedge effectâ that can cha...