In the previous post on Insight Into Diamonds, the formation of diamonds was discussed. Now it is time to get an insight into diamond mines and mining industry.
Currently, there are a very limited number of economically viable diamond mines in operation, and to put it into perspective, the largest 30 mines supplying 90% of global demand.
There are 10,000 known kimberlite pipes around the world, only 1,000 of them are diamondiferous, 100 of those are economically viable to mine. 30 Kimberlites are currently active and 20% of the total production ends up as a gem-quality polished diamond fit for use in the jewelry industry.
Diamonds rarely present themselves in inaccessible areas and usually located in the most inhospitable regions of the world. Therefore developing a viable diamond mine requires exploration geologists operating in a high-risk environment, leading to worthless discoveries in pursuit of high-value economic diamond deposits. The amount of work and investment that goes into discovery is huge but even bigger than that is developing a mining plan which is a prerequisite of financing the prospective project. A feasibility study needs to be conducted in order to determine the full costs of mining, including capital and building costs as well as ongoing operational costs. This extensive process can take between two to three years before the mining company can start mining construction.
There are various types of diamond mining; Open Pit, Underground, Alluvial and Marine!
In brief, Open Pit refers to a very cost-effective mining method for kimberlite deposits. In open-pit mining, a large carrot-shaped hole is dug in the ground, starting from the widest part at the surface and gradually getting narrower at depth. Open-pit mining exposes the entire diamond-bearing kimberlite so no ore is missed. One point in the feasibility of an open-pit mine is the strip ratio which is the ratio of waste material subject to mining to reach the diamond-bearing ore inside. The amount of host rock or the amount of material on top of the kimberlite that needs to be extracted first, also known as over-burden can be a crucial element to determine the feasibility of the mine.
Underground mining usually comes into the picture after an open-pit mine is no longer feasible to extend its pit walls outward to support digging to a lower depth. There are also some examples of exclusively underground mining from inception, the most common method of underground mining is block caving. This method relies on the kimberlite rock being weaker than the hosting rock, therefore a large tunnel is dug at a shallow angle to reach the ore and then a large void is extracted underneath the target kimberlite which allows the kimberlite to collapse into the void and safely hauled away through tunnels to surface. Underground mining can extend the life of a mine by 10-20 years. While the investment is significant to make the transition from open pit to underground mining but when completed it is a much more cost-effective option for mining at a lower depth.
Alluvial mining happens where natural erosion has eroded the surface of a diamond-bearing kimberlite rock and transported it to other locations. These diamonds are easier to access, as they are usually found in the surface of rivers which makes them easy to extract and process without a need for explosives and crushing operations. The only challenge for Alluvial mining is that the diamonds have been transported over millions of years through very expansive geography and usually large scale mining operations won’t find them feasible investment while the artisanal sector would consider it.
Marine mining is facilitated through ships that vacuum the seabed through long hoses at depth up to 500 feet and up to 460,000 cubic feet per hour. The mixture of water and gravel is transported to land-based recovery facilities to extract diamonds. Marine operations are known for recovering high-quality diamonds which is due to the intense natural processes that occurred over millions of years and would break stones with inclusions.