The world production of diamonds in 1990 was more than 100 million carats (metric carats, or CM; 1 carat = 0.2 grams), compared to 75 million in 1985, and 15 million in 1950. This represents a more than 14% per year growth rate. The value of 1990 production was about US$4.5 billion (1992 US$), and diamond is the fourth-ranked commodity in the world in terms of value, after Fe, Au, Cu, and Zn. Primary sources of diamonds are the mantle-derived igneous rocks eclogite and peridotite, brought to the surface by rare ultrabasic magmas, kimberlite and lamproite being the most common. Secondary diamond deposits, such as the marine deposits of southwest Africa, are derived from primary sources by weathering processes that acted for several million years to transport and concentrate diamonds at favourable localities.
Of approximately 5,000 known kimberlites world-wide, fewer than 50 are or have been mined successfully. There have been fewer than 15 major producers (more than 3 million carats/year), with only 6 major discoveries made in the last 50 years. The Point Lake pipe, the first discovered in the Lac De Gras kimberlite field in Canada's Northwest Territories, is potentially another major poducing pipe. The Point Lake discovery is a clear success story in diamond exploration, and as such, it is given a brief review here. As the surrounding kimberlite field is still undergoing exploration, the information available is incomplete, and estimates of the importance of diamond deposits are preliminary. However, initial results at the time of writing indicate strong potential for one or several diamond mines to be developed in the Northwest Territories.
Why explore for diamonds in North America?
- North America has the largest craton and stable platform area in the world.
- Relative to Siberia and South Africa, hundreds of kimberlites remain to be discovered.
- North America is underexplored for diamonds.
- Large gem diamonds have been found as alluvials in North America.
- Several areas are known to have favourable mineral chemistry.
- Operating costs of open-pit kimberlite mines are very low.
- Capital costs are similar to other mines; tailings are non-acid generating, and no strong chemicals are used during extraction.
- Transport costs for final products are negligible.
- Diamond prices generally increase at a level that keeps pace or exceeds inflation.
- The occasional large diamond found during production can be regarded as a bonus (a 100-carat flawless gem can be sold for about US$1.7 million).