01. OPEN CAST MINING
Open cast or 'open pit' mining is a technique of extracting gemstones, such as Diamond and metal ores, like gold and silver, from the surface of the earth by digging downwards, eventually creating a pit. This method is used when the gems lie near the surface of the ground and the earth covering the gemstones is relatively thin. Open cast Diamond mines can be enormous, up to 1.2km wide. Coloured gemstone mines are much smaller.
To minimise damage and to prevent excessive rock fall, most of the walls are blasted at an angle less than vertical. The walls are gradually stepped in to help prevent rocks from falling all the way from the top to the bottom of the mine. There is usually a haul road at the side of the mine to transport the gemstones, ore and waste rock.
When open cast mines are exhausted, they often undergo land rehabilitation to fill and stabilise them. In arid areas, they are sometimes converted into recreational parks, residential communities or wetland areas.
02. UNDERGROUND MINING
Underground mining consists of digging shafts and tunnels underground to reach buried ore deposits which are then brought to the surface via the tunnels. There are three main types of underground mining for gemstones:
Tunelling is used when gemstones, such as Emerald, are located as a seam running near the surface. A tunnel is made from the surface down to the gem-bearing rock. This mining is usually done by blasting or using a pick-axe to remove the gem rough.
Chambering consists of a vertical shaft being sunk into the rock surrounding the vein. Tunnels are driven into the vein from the main shaft at various levels. The gemstones are retrieved by being blasted and then transported to the surface via the shaft.
Block caving, often used in Diamond mining, is a method that involves undermining a gemstone, then allowing it to steadily collapse under its own weight. An undercut is driven under the gem-bearing rock where 'drawbells' are excavated – this is an empty space which allows the gem-bearing rock to fall.
03. RIVER DIGGING
All kinds of gemstones can be found in rivers and lakes (depending on where you are in the world), including Opal, Ruby, Amethyst, Jasper, Garnet, Topaz and Beryl. When these gemstones have been deposited in river or lake beds they are usually mined using one of the two following methods:
Wet Digging, also known as panning, is a method where gemstones are collected while washing the sediment and small rocks from a river. Firstly, the miner identifies areas where the gravel on the riverbed may contain gems. Then a large pan is filled with water and shaken back and forth to settle the heavy material to the bottom of the pan. The lighter material is washed over the top of the pan and larger rocks are removed. These steps are repeated until there is about a tablespoon or two of gemstones and sediment left in the pan.
Dry Digging involves blocking off the flow of the river at both ends using dams, to create a dry area of the river which the miners can then use to collect gemstones.
04. SEA MINING
Gemstone deposits may be on the beach, like the Namaqualand Diamond deposits in West Africa, or they may be off-shore. Off-shore deposits usually involve deep sea mining.
Deep sea mining is a relatively new process that takes place on the ocean floor. The gemstones are usually extracted using a hydraulic suction stystem or a continuous-line bucket system. The latter is the preferred method and operates like a conveyor belt running from the sea floor to the surface where the ship or mining site extracts the desired gems and returns the trailings back to the ocean. The costs involved in this method mean that it is only used to extract Diamonds.
It's also worth mentioning organic gems such as Amber and Pearl. Amber, although often excavated using pit mining, can also be fished out of the sea using a net (Baltic Amber comes from the Baltic Sea). Pearls are gathered by divers who collect the Pearl-bearing molluscs from the sea bed.
Wherever your gemstone has come from and however it made its way to your collection, each piece is incredibly special, displaying all the wonders of Mother Nature.