In previous post on an Insight Into Diamonds , 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 gem quality polished diamond fit for use in jewellery industry.
Diamonds rarely present themselves in the accessible areas and usually located in the most inhospitable regions of the world. Therefore developing a viable diamond mine requires exploration geologists operating in high-risk environment, leading to worthless discoveries in pursuit of high value economic diamond deposit. 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 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 mine 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 dig in the ground, starting from the widest part at the surface and gradually getting narrower at depth. Open pit mining expose the entire diamond bearing kimberlite so no ore is missed. One point in feasibility of an open pit mine is the strip ratio which is the ratio of waste material subject to mining to reach to the diamond bearing ore inside. The amount of host rock or the amount of material on top of the kimberlite that need to be extracted first, also known as over-burden can be a crucial element to determine the feasibility of the mine.
Underground mining are usually come into picture after an open pit mine is no longer feasible to extend its pit walls outward to support digging to 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 kimbertlite 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 transition from open pit to underground mining but when completed it is a much more cost effective option for mining at 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 surface of rivers which makes them easy to extract and process without a need of explosives and crushing operations. The only challenge for Alluvial mining is that the diamonds have been transported over millions of years through a very expansive geography and usually large scale mining operations won’t find them feasible investment while artisanal sector would consider it.
Marine mining is facilitated through ships that vacuum the seabed through long hoses at depth up tp 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 intense natural process that occurred over millions of years and would break stones with inclusions.