Mining Sapphire in Australia
The most important sources for sapphire are Burma, Kashmir, Sri Lanka, Madagascar, Thailand and Australia. Though Australia is most famous for opal, they are major exporters of sapphire as well, with much of the material being heated and cut in Thailand. As many Australian miners will tell you, much of the sapphire sold as Thai is actually mined in Australia!
A major source of sapphire is Queensland in Australia's northeast. In fact sapphire has been mined commercially for more than 100 years on the Anakie field in Central Queensland, which also yields gem-quality zircon and, more rarely, diamonds. Sapphire is found in a wide range of colors, including blue, green, yellow, gold, orange, pink, mauve, purple and spectacular multi-colored gems in blue, green and yellow. The most famous of all Queensland sapphires is the 733 ct Black Star of Queensland. Found on Klondyke Ridge in 1935 by 14 year old Roy Spencer, it was allegedly used as a door stop for many years by his father Harry Spencer.
Sapphire is of volcanic origin and occurs in alluvial deposits, which are up to 20 meters below the surface. Throughout the ages, sapphires and other heavy minerals were transported and deposited in layers and thus tend to be concentrated in 'runs' along particular channels.
Sapphire fields in the Queensland area use various methods for the mining of sapphires, depending on the depth at which they are found and the weight and hardness of the surrounding materials or "wash". In some places simple hand mining methods may be suitable for working surface and shallow wash deposits. Deeper ground is mined by digging shafts, while some fields consist of large-scale open-cut mining lease operations involving the use of heavy earth excavation equipment.
Depending on the type of material surrounding the mined sapphires, processing the mined material in order to collect the sapphires can vary from rudimentary hand sieving and cleaning, to more sophisticated mechanized methods. A typical production method for a shaft mine involves first digging out the mine walls with a jackhammer to loosen the ground. The material is then transported by wheelbarrow to a large drum placed at the bottom of the shaft. Once full, the drum is pulled up via a motorized winch known as the "up and over," and taken to the sapphire processing machinery.
A conveyor belt then carries the sapphire bearing wash into a turning "trommel" which is made of layers of fine and coarse mesh. This sorts out the particles that are too fine as well as the larger sized rocks, called "overburden". The fine sand is discarded while the large rocks are set aside for a quick check to make sure there is not a large sapphire amongst them.
The medium sized wash drops into a pulsater that has eight trays with running water flowing through it. Sapphires are very heavy, so they will remain where they are dropped; the lighter rocks are moved along by the pulsater then dropped onto a tray for removal to the waste pile.
At the end of the day the "sapphire trap" is sorted in order to find the heavy sapphire and zircon, and finally, the best stones are selected to facet into cut gems.
- Prima Pubblicazione: May-09-2008
- Ultima modifica: August-23-2017
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