Selling Diamonds

(via Diamond Promotion Service) Diamond Mining: 15. It is believed that diamonds were formed by heat and pressure, millions of years ago, deep within the earth. Later, the magma in which the diamonds were embedded was forced to the surface through fissures like the throats of ancients volcanoes. This material then cooled into formations that we call ‘pipes’. Diamond pipes are being mined today in Botswana, Siberia, South Africa and Tanzania.

16. However, all these formations did not remain intact. Exposed to rain and heat cold for millions of years, many diamond-bearing pipes weathered away. Because the diamonds were so hard, they didn’t break up like the other material. Rather, they were carried along by streams and rivers. When their size or specific gravity was too much for the force of the water, they dropped to the river beds. These are called alluvial deposits, and most of the world’s diamonds come from alluvial mining. The pipe mine in Botswana was discovered by geologists who backtracked from an alluvial deposit along the course of an ancient river.

17. In certain areas of southern Africa, it is believed that some rivers carried diamonds all the way to the Atlantic Ocean, where wave wash deposited them in marine terraces. Some of these terraces are now on dry land, where they are being mined. There is another theory that the diamonds were washed up on the beaches from volcanic pipes on the ocean floor.

18. A diamond pipe is usually composed of a rock-like material called kimberlite, or blue ground. When a diamond pipe is mined, the first step is to dig into it from the surface, like the excavation for a huge building. This is called open-cast mining. It can continue until the hole is too deep for the ore to be brought to the surface easily, but this depth can be 800 to 1000 feet. The Finsch Mine in South Africa, the Williamson Mine in Tanzania and the Orapa Mine in Botswana are open cast mines.

19. When the hole gets too deep, the mine goes underground. Vertical shafts are sunk into the ‘country rock’ away from the pipe. Although there are different methods for underground mining, the basic technique is to drive horizontal tunnels from the shafts into the pipe and then to dig out the diamond-bearing ore from below. This, of course, makes the hole deeper, and the tunnels are driven at successively lower levels until the entire pipe has been mined out, leaving only a hole where the pipe had been. The Big Hole at Kimberley, now the site of a diamond museum, is what remains after the Kimberley Mine was mined out in 1914; now filling with water, it is 1335 feet deep, one of the deepest man-made holes on earth.

20. After the diamond-bearing ore is brought to the surface from either open cast or underground mine, it is put through a long and complex recovery process. The ore is broken up in mills that exert enough force to break the kimberlite, but not the diamonds it contains. Then the broken ore goes through a series of washings, jiggings and screenings that remove much of the waste material. Then what’s left is put into huge tanks that look like mud puddles; the liquid is heavier than water, however, so that the diamonds and other heavier minerals can sink to the bottom in a concentrate while the lighter waste material floats off.

Selling Diamonds (continued)