20.1 Metal Deposits
Mining has always been a major part of Canada’s economy. Canada has some of the largest mining districts and deposits in the world, and for the past 150 years, we have been one of the most important suppliers of metals. Extraction of Earth’s resources goes back a long way in Canada. For example, the First Nations of British Columbia extracted obsidian from volcanic regions for tools and traded it up and down the coast. In the 1850s, gold was discovered in central British Columbia, and in the 1890s, even more gold was discovered in the Klondike area of Yukon. These two events were critical to the early development of British Columbia, Yukon, and Alaska.
Canada’s mining sector had revenues in the order of $37 billion in 2013. The majority of that was split roughly equally among gold, iron, copper, and potash, with important but lesser amounts from nickel and diamonds (Figure 20.3). Revenues from the petroleum sector are significantly higher, at over $100 billion per year.
A metal deposit is a body of rock in which one or more metals have been concentrated to the point of being economically viable for recovery. Some background levels of important metals in average rocks are shown on Table 20.1, along with the typical grades necessary to make a viable deposit, and the corresponding concentration factors. Looking at copper, for example, we can see that while average rock has around 40 ppm (parts per million) of copper, a grade of around 10,000 ppm or 1% is necessary to make a viable copper deposit. In other words, copper ore has about 250 times as much copper as typical rock. For the other elements in the list, the concentration factors are much higher. For gold, it’s 2,000 times and for silver it’s around 10,000 times.
| Metal | Typical Background Level | Typical Economic Grade* | Concentration Factor |
| Copper | 40 ppm | 10,000 ppm (1%) | 250 times |
| Gold | 0.003 ppm | 6 ppm (0.006%) | 2,000 times |
| Lead | 10 ppm | 50,000 ppm (5% | 5,000 times |
| Molybdenum | 1 ppm | 1,000 ppm (0.1%) | 1,000 times |
| Nickel | 25 ppm | 20,000 ppm (2%) | 800 times |
| Silver | 0.1 ppm | 1,000 ppm (0.1%) | 10,000 times |
| Uranium | 2 ppm | 10,000 ppm (1%) | 5,000 times |
| Zinc | 50 ppm | 50,000 ppm (5%) | 1,000 times |
| *It’s important to note that the economic viability of any deposit depends on a wide range of factors including its grade, size, shape, depth below the surface, and proximity to infrastructure, the current price of the metal, the labour and environmental regulations in the area, and many other factors. |
Table 20.1 Typical background and ore levels of some important metals [SE]
It is clear that some very significant concentration must take place to form a mineable deposit. This concentration may occur during the formation of the host rock, or after the rock forms, through a number of different types of processes. There is a very wide variety of ore-forming processes, and there are hundreds of types of mineral deposits. The