The Formation & Mining of Coober Pedy Opal
By Carmen Hui
The Mining of Coober Pedy Opal
Mining History in Coober Pedy
In January 1915, Coober Pedy was discovered. After that, Coober Pedy become the opal capital of the world and proved to be the most consistent opal producing area in South Australia. The first opal pegged here was by Jim Hutchinson and his son Bill (Willie) when they were looking for water.
By 1921, the 20 Mile Field was discovered. This meant that the opal bearing are covered over 40
miles in length. Production grew steadily until 1929 due to the the Great Depression. The opal demand fell and there were only about thirty miners on the fields. In 1946, there was another great discovery at Geraghty Hill, also known as Eight Mile. As it was at the same time as the end of the World War 2, it created a huge increase in production.
During the 1960's,the mining industry expanded rapidly because of the many European migrantswho came to seek their fortunes. The 60's and 70's saw opal mining develop into a multi million dollar industry with Coober Pedy developing into a modern mining town. The peak period of production is at the 90’s. There were approximately 1000 miners in Coober Pedy.
Comparing with other opal fields, Coober Pedy has had a long history of fruitful production. There are news finds year after year. However, the production has already been declining, even
though the opal demand in the market is increasing. This is due to the fact that less young
people are entering the opal mining industry. The original miners are getting older and there are around 100 miners in Coober Pedy.
Recently, the government releases the land on Shell Patch Reserve about 35 kilometres north of Coober Pedy, which was excluded from mining in 1977.
The newly-released land may stimulate the mining industry and boost the local economy.
The opal level at Coober Pedy is not deep and its depths ranges from between 10 feet and 80 feet below the surface. Vertical shafts are sunk to the opal level and horizontal tunnels are made by following the track of the opal.
The opal level are approximately divided into three. They are about 10-25 feet, 35-50 feet and 60-80 feet below the surface. The finest opals are usually from the shallower level, while the opals found in the deeper levels usually cracks as the pressure is greater underground. It is not infrequent that a number of opal levels occur below another, but none of the levels are truly consistent throughout the field.
The Eight Mile field is claimed to produce the best opals ever found at Coober Pedy, while the nearby Olympic Field is claimed to produce the second-best opals.
Apart from the two fields, Southern cross, Shell patch, Hans peak, Greek gallery and 17 Miles are the famous fields in Coober Pedy.
Steps and Methods of Mining
Applicating prospecting permit
The miner has to apply for a current precious stones prospecting permit. One has to pay for a fee when applying for the permit, the registration of claims and other relevant documents.
Miner has to select a prospecting sit outside the downtown of Coober Pedy. Figure 3a indicates the major mining working area in Coober Pedy. A mining claim is at least 50mx50m in size or larger.
Prospecting and sinking a shaft
The next step is drilling a shaft down until the opal level is found. Prospecting drill is used and it can drill around 10 holes a day. The material brought up by the auger is checked by the miner to look for opal or signs of opal dirt. The above process is repeated until the opal level is found. Then the miner records the depth of the opal level by a gamma ray pole.
Calweld drill is used to make the shaft. The auger of it is about 1 meter diameter which is larger than that of prospecting drill (9 inches). It can make the shaft with about 2 meters diameter.
1. Prospecting drill drilling holes to desired levels
2. Holes not carring valuable opal that are ﬁlled in
3. Hole having opals that is logged the depth by gamma ray
4. Calweld drill sinking a shaft
5. Calweld holes -- approximately 2 metres diameter
6. First level
7. Second level
Following the opal level
2. Hopper holding dirt until released to form dump
4. Jacks stabilising rear of vehicle and preventing weight in
hopper tipping truck backwards
5. Windlass whose wire cable supports pipe and lowers them
6. Long ladder from the land surface to the underground
7. Miner using jackpick and bogger
8. Tunnelling machine
The traces of opal are followed by tunneling. The tunnelling machine is lowered down the shaft in two pieces and assembled down below. The teeth of the machine break up the sandstone, which falls onto the bottom of the tunnel. As the machine moves forward, the waste is screwed backward and removed by the blower, which acts like a big vacuum cleaner. The blower brings the dirt up to the surface.
There is a strong light in front of the tunnelling machine. When the operator sees opal or hears the sound of metal on glass, he will immediately stop the machine. The area is then worked by hand.
Bulldozer open cut
Instead of the shaft and tunnel process, some miners use another technique called ‘bulldozer opal cut’. A bulldozer and excavator are used to remove the sandstone. When the opal level is reached, one or more miners who are called checkers, follow closely behind the bulldozer looking for the traces of opal in the sandstone.
1. Bulldozer pushing overburden
2. Checker watching for opal in case the opal level is shallower than expected
3. Excavator digging trenches to get
to the opal level
There is one more method to find opal called ‘noodling’. This is a process of searching the waste dumps to see whether there is any opal the miners missed. Waste dump is placed into a hopper by an end loader. The rock is then sorted from the sand and dirt using vibrating screen. The sorted rock is transported to a dark room. Using ultraviolet light, the checkers pick out all material that look fluorescent white as they may be opal. Afterwards, the precious opal is sorted out from potch using normal light.
1. Hopper--material loaded here
2. Vibrating Screen
3. Fine particle removed
4. Conveyor belt with rock fragments
5. Darkened cabin with ultraviolet
light and checkers
6. Waste material dump
Miners in Coober Pedy
Opal mining is a risky business. Most miners form partnerships with two or three men to share the work due to the risks involved. An agreement is usually reached over a drink in the local bar and sealed with no more formality than a handshake. Unlike other mining industries, opal mining is performed by sole trader and smaller partnerships. This is because there is no way to analyse the potential value of a mine by any explorers, miners or geologists. As a result, large companies will not invest in opal mining, which makes opal mining and investment in the industry different than larger scale mining operations.
Risks involved as a miner
It is tough to be a miner. Mining is becoming more expensive while production is slowing down as the long-time miners aged. There are fewer than 100 miners left in Coober Pedy.
Perspectives on opal mining
The production cannot keep up with huge overseas demand. The demand of opal rough is increasing especially in Asian market and the opal prices have gone through the roof. However the locals in opal fields are frustrated as they cannot find enough rough to meet the demand. Although some of them fear the opal supply is almost exhausted as the production is declining in recent years, some miners are still more optimistic and believe there is still an adequate supply of opal rough to be found. The problems of opal shortages are due to a lack of government support for new exploration initiatives.
Safety Precaution of Mining
Never enter a mine without a safety helmet on.
Never work in a mine without plenty of light, which can be very dangerous as there may be ‘monkeys’ in the floor. (monkey= a shaft connecting two opal dirt levels)
Never walk around the top of the shaft or stand under the ladders when someone is climbing up or down since it can cause a serious accident even a small pebble falling from the surface and hitting anyone.
Always make sure you have plenty of fresh air.
Always check out an old mine thoroughly before starting. If there are cracks in the roof, stay out of the mine.
Don’t fill in shafts and tunnels. This is prohibited in Coober Pedy. It is because when the tunnel is filled, a new miner who pegs the same place does not know where is mined before, then if he digs a few feet below an old tunnel, the sandstone will collapse on him.
Warning to Visitors
For those who are not living in Coober Pedy, it is not recommended to venture out there whilst it is hot. It is better to wait until evening or the cool of the morning. Inside the opal field, you must never walk backwards as you may not aware of the mining hole or shaft and fall in it.