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Email:
rwp@rockwalkpark.com
Man As Mole
It has often been mentioned that an element of civilization is Man’s emergence from caves. However, has he really? Caves continue to fascinate and attract. For example, spelunking is the sport of cave exploration, with new and exciting discoveries being reported as such exploration penetrates into unknown underground passages. Other caves and caverns offer a world of marvelous rock formations, such as stalactites and stalagmites.
Coober Pedy
But these aren’t the only underground openings that beckon to Mankind. Many underground passages are man-made, in the form of mines to extract minerals for example. Other passages are for protection … perhaps from enemy forces, from wildlife, or from the elements. One such example is Coober Pedy, in South Australia .
Coober Pedy is a man-made wonder, recognized as the largest producer of opal in the world. The name of the town is an anglicised version of Aboriginal words “kupa piti”, assumed to mean “white man in a hole”. However, the mining pits aren’t the only underground openings. This town of 3,500 people is located in the Australian outback, where there is little rainfall, and temperatures can rise to around 500C during the Australian summer. After the first discovery of opal in this area in 1915, settlement began,
and soldiers returning from the first World War introduced the unusual and unique method of living underground in ‘dugouts’, as many had done in the trenches at the front.
These dugouts not only referred to houses, but eventually came to include other underground services such as hotels, restaurants, and churches. As a result, people could live and work underground
in relatively cool surroundings compared to the suffocating heat on surface. Approximately 50% of the current population live in underground ‘dugout’ homes.
Early miners at Coober Pedy were so longing for vegetation of some kind that they actually constructed ‘The First Tree’ from scrap metal taken from vehicle wrecks along nearby roads and tracks.
Coober Pedy has such a unique setting that it was chosen as the site for movies such as Mad Max Beyond Thunderdome, Fire in the Stone, Ground Zero, Until the End of the World, Stark, Pitch Black, and Siam Sunset.
Opals
The Coober Pedy opal fields cover an area of 4,954 square kilometres, including about 70 individual fields. However, the fields, themselves, lie on the edge of an ancient ‘inland sea’ which once covered much of central Australia. The sedimentary beds deposited at the edge of that ‘sea’ are sandstone and siltstone, with the sandstone beds in which the bulk of the precious opal is found being some 30 metres deep. After the seawater receded, periodic lowering of the water table, possibly caused by climactic change, carried silica-rich solutions downward to deposit opal in rock cavities and cracks.
Opal has been recognized by the Australian Federal government as the ‘National Gemstone of Australia’. Considered ‘more beautiful than diamonds’, most of the opal found around Coober Pedy is ‘white or milky opal’ or ‘crystal opal’. That means the base body colour is either white or almost transparent, with flashes of blue, green, red, and orange. Generally, depending upon the quality of the gem, red-fire flashes are more valuable than green, which, in turn, is more valuable than a stone showing flashes of just blue.
Purchasing an opal can be a rewarding experience, but it pays to learn some background before making the decision. For example, some opals are solid all the way through, whereas others consist of slices fastened on top of another base mineral. Also other types of opal exist. For example, black opal, considered the most valuable of all, is mined at Lightning Ridge in New South Wales, and boulder opal, quickly gaining popularity, is produced from the south-western parts of Queensland, such as Quilpie.
Up to 90% of all opal found is valueless potch, but the remaining 10% is the brilliantly coloured and highly prized gem. In common opal or potch, the silica spheres are irregular in shape and molecular structure. Accordingly, white light is unable to be diffracted, so that there is no colour.
Prospecting & Mining
Opals may be sometimes be collected from mullock piles by fossicking or noodling, once one has obtained a fossicking permit, and permission from claim owners. This process involves searching through heaps of discarded mullock for pieces of opal missed by the miners. Many locals make a living off this technique, and it is popular with tourists. Opal Miners, on the other hand, require a Precious Stones Prospecting Permit (PSPP) from the Dept. of Primary Industries office at Coober Pedy. This entitles them to peg a claim of either 50 X 50 m, or 50 X 100 m.
The earliest form of prospecting was by sinking or digging a shaft with a pick and shovel. Driving or tunneling along the level was then carried out with picks and shovels. When traces of opal were found, a handpick or screwdriver was used. Waste material or mullock was lifted to surface by hand windlass. These were later replaced by power winches or automatic bucket tippers.
Now, most prospecting shafts are made by using a Caldwell drill. Holes about one metre in diameter are excavated using an auger bucket. The drills can dig to a depth of 30 metres in about 3 hours. Mullock is now brought to the surface using truck-mounted blowers which run like a vacuum cleaner.
Another change has been the increased use of mining machines since the 1970’s. Boggers – tunneling machines with revolving cutting heads and small front end loaders – have been introduced. Where the level is shallow, bulldozers are used to remove the overburden, and spotters follow close behind watching for opal. If opal is discovered, the seam is then worked by handpick.
For some extra info on Coober Pedy, check out http://www.webopal.com
