Mining a Kimberlite Pipe
Mining of a diamond-bearing pipe starts with the dig of a pit into the pipe. In this process, called "open-pit" or "open-cast" mining, the primarily loose and eventually hard ore material is removed with large hydraulic shovels and ore trucks. Hard rock is drilled and blasted with explosive so the broken material can be removed. When deep, rich ore warrant it, the mining goes underground with vertical shafts descending to horizontal drifts, or passageways that enter the pipe.
In bedrock nearby to the pipe, shafts are sunk and drifts are tunneled into the pipe. Concrete-lined tunnels are drilled under a large vertical section, perhaps 140 to 180 meters (400 to 600 feet) of kimberlite. Along the tunnels are draw points, or openings in the concrete casing where kimberlite is drilled and annoying to cave in a section above the tunnel. Broken kimberlite falls during the draw points and is scraped out of the tunnel with a drag or scraper bucket attached to a cable and winch, working much like a clothes line on a pulley. The kimberlite above the tunnels falls under its own weight and leads to a slow, incessant caving of ground that is removed through the draw points. The scraped kimberlite rubble is loaded into cars on a lower level and moved to a crusher subversive. The crushed ore is then conveyed to skips that take the ore up the vertical shaft for processing.
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