The headframe at Frank Smith mine in South Africa stands above the
vertical access shaft to underground workings, and controls the cable and
cars moving in the shaft. click to zoom in table.
Mining of a diamond-bearing pipe starts with the excavation of a pit
into the pipe. In this process, called "open-pit" or
"open-cast" mining, the initially loose and eventually hard ore
material is removed with large hydraulic shovels and ore trucks. Hard rock
is drilled and blasted with explosives so the broken material can be
removed. When deep, rich ore warrants it, the mining goes underground with
vertical shafts descending to horizontal drifts, or passageways that
enter the pipe.
In bedrock adjacent to the pipe, shafts are sunk and drifts are
tunneled into the pipe. The highly mechanized and efficient method known as
block caving is shown in the adjacent model. Concrete-lined tunnels are
excavated 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.
The open pit at the Udachnaya (Lucky) pipe in Sakha Republic, Russia,
has produced many millions of carats of diamond. The bench steps are
about 20 m high.
drilled and blasted to cave in a section above the tunnel. Broken
kimberlite falls through 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, continuous 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
underground. The crushed ore is then conveyed to skips that carry the ore up the
vertical shaft for processing.
A cross section of the underground workings at the Dutoitspan mine,
Kimberley, South Africa. Adapted from De Beers
Frank Smith Mine photo: George E. Harlow, AMNH
dachnaya photo: Courtesy Almazy Rossi-Sakha Co., Ltd
