Mining (2.04)
Mining is an important part of the equation in diamond’s value. Specifically, mining is the process of first locating and then extracting the rough. Of course diamond mining could be as easy as stooping over and digging up a large, fine, ten carat octahedral crystal out of a muddy river bed.
Generally, alluvial mining is the least difficult and therefore is primarily worked
with picks, shovels and pans. Alluvial deposits are usually found in small pockets and therefore are quickly exhausted. Only in very productive areas would heavy machinery get involved such as front-loaders and bulldozers.
Kimberlite pipes exist all over the world but very few actually contain diamonds.
Even when they are diamond bearing, the pipe has to be rich enough to justify the major expense involved in setting up and running a mining operation. Just a few of the many aspects that must be considered include location, climate conditions, political climate, water access, power access, and communications.
Bench mining (or benching) is a process of blasting benches or slots in the sides of the open pit area where the kimberlite pipes lay. The gravel is directed down through funnels to the below-ground processing area. It is then crushed into pieces of six inches or less before it it hauled to the surface for further processing.
Mining is difficult, dirty, and dangerous work, requiring the movement of thousands of tons of rock everyday to make it all worthwhile. Some mines may only produce a single one-carat finished diamond out of 250 tons of rock. Eventually the yield of a pipe no longer supports the costs of mining and the operation must be closed down. The Kimberly Mine was 3,601 feet deep when it was closed.
measuring about 1¼ inches across. It is then forced across a series of screens called grizzlies, which separate the larger and smaller chunks. The small pieces of kimberlite are placed in a mechanical rocker box where rotating paddles circulate water to separate the lighter and heavier minerals. The lighter materials eventually float off and the heavier diamond-bearing gravel collects at the bottom of the box.
One of diamond’s characteristics is its high affinity for oil or grease. Since before the turn of the century, grease has been used for sorting out diamond in such inventions as the grease table. The separated gravel is washed over a table covered with a thick layer of grease, leaving diamond rough behind, adhering to the table. The grease belt, a more modern version of the earlier grease table, uses a greased conveyer belt for continuous processing. Again, the diamond-bearing gravel is washed across the belt and the remaining rough is collected at the far end of the conveyor.
A major advance in the recovery systems came in 1958, when Soviet scientists
invented the X-ray separation system. Relying on the fact that diamonds fluoresce under X-rays, the concentrated gravel passes through X-ray beams. When fluorescence occurs, an intense air stream is triggered that forces the diamond rough into a separate collection area.♦