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Coober Pedy

Climate

Between April and October the weather is very pleasant. Typical of a semi desert climate, the days (16 to 20° C) are mild to warm but the desert nights are cold. From November to March the weather warms up and summer temperatures can range from 35° C to the 45° C in the shade, with occasional dust storms. The annual rainfall in the area is minimal at around 175 mm (5 inches) per annum and can fall during any time of the year.

History

For thousands of years Aboriginal people walked across this area. Because of the desert environment, these people were nomadic hunters and gatherers who travelled constantly in search of food and water supplies as well as to attend traditional ceremonies.

In January 1915, the New Colorado Prospecting Syndicate, consisting of Jim Hutchison and his 14 year old son William, PJ Winch and M McKenzie had unsuccessfully been searching for gold south of Coober Pedy. The men had set up camp and were searching for water when young Willie found pieces of opal on the surface of the ground. This was on the 1st February 1915 and 8 days later the first opal claim was pegged.

Coober Pedy was originally known as the Stuart Range Opal Field, named after John McDouall Stuart, who in 1858 was the first European explorer in the area. In 1920 it was re-named Coober Pedy, an anglicised version of Aboriginal words "kupa piti", commonly assumed to mean "white man in a hole".

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Coober Pedy Today
Aerial photograph "Coober Pedy - Today"
courtesy of Peter Caust.

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Coober Pedy 1956                                   

In 1917 the Trans Continental Railway was completed. A number of construction workers followed by soldiers returning from World War 1 came to the opal fields, introducing the unique method of living underground in "dugouts". Conditions were harsh and the environment did not lend itself to easy living. Water and provisions had to be carted great distances and under very trying conditions. Even with the introduction of very large underground water tanks things improved only marginally, the entitlement of water being only 24 gallons (60 litres) per week.

Today the town water supply comes from an underground source 24 kilometres north of the town, then pumped through an underground pipeline to the water works where it is treated by reverse osmosis and pumped through a reticulated town water supply system. The treatment process is expensive consequently water costs $5 for 1,000 litres. The water quality is excellent and people should hold no fears about drinking it.

During the Great Depression of the late 1930's and 1940's, opal prices plummeted and production almost came to a standstill.

Typical of Coober Pedy's history of boom and bust, an Aboriginal woman named Tottie Bryant made a sensational opal find at the Eight Mile field in 1946, starting a new rush to the fields.

During the 1960's, the mining industry expanded rapidly due to the many European migrants who 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.

Local Services

Shopping
Monday, Tuesday, Wednesday, Friday & Saturday - 8.30am to 7.00pm
Thursday - 7.00am to 7.00pm
Sunday - 9.00am to 6.00pm

Bank (Westpac)
Monday to Thursday - 9.30am to 4.30pm
Friday 9.30am - 5.00pm

Post Office
Monday to Friday 9.00am - 5.00pm

RAA Agent
Coober Pedy Auto - located on Flat Hill Road

Medical
Coober Pedy Hospital
Chemist
Dentist
Doctor's Surgery

Emergency
Police
Fire Brigade
Mine Rescue/SES

Churches
Kupa Piti Aboriginal Christian Centre, Assembly of God, Brethren Church, Catacomb Anglican, Uniting Church, Jehovah's Witness, Revival Church, Greek Orthodox, Roman Catholic, Serbian Orthodox.

Service Clubs
Lions, RSL, Italo-Australian Miners Club, United Yugoslav Australia Association, Croatian Club, Greek Community Club, Serbian Club, Coober Pedy Fire Service.

Opal

What is Opal?
Opal is a form of silica, chemically similar to quartz, but containing water within the mineral structure. Precious opal generally contains 6-10% water and consists of small silica spheres arranged in a regular pattern.

Opal occurs in many varieties, two of which are precious opal and potch.

Colour in precious opal is caused by the regular array of silica spheres and voids diffracting white light, and breaking it up into the colours of the spectrum. The diameter and spacing of the spheres controls the colour range of an opal.

Small spheres (approx. 150-200 nm; I nm = 1 0'9 m) produce opal of blue colour only, whereas larger spheres (350 nm) produce red colour. Opal with red colour can display the entire spectrum.

Opal colours also depend on the angle of light incidence and can change or disappear when the gem is rotated.

In potch opal, the silica spheres may be absent or too small or irregularly arranged to produce colour.

potch

Potch
scanning electron
micrographs (x 40 000)

precious

Precious Opal
scanning electron
micrographs (x 40 000)

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Geology of Opal
All precious opal in South Australia occurs in rocks affected by weathering during the Tertiary Period (1.8-70 million years ago).

The weathering process broke down minerals of the country rock to produce kaolin (a clay) and soluble silica. It also created cavities in the rock by dissolving soluble minerals and fossil shells. These cavities, together with faults and fractures in the rock, provided pathways for underground water containing the soluble silica.

Periodic lowering of the watertable, possibly caused by changes in climate, carried silica-rich solutions downwards to deposit opal in the rock cavities.

Value and Presentation
Attempts have been made to establish guidelines for determining opal prices but they have been largely unsuccessful because of the gem's infinite variation in colour pattern.

The main factors influencing the price paid for opal are:

  • Background colour - black opal (a gem with a dark background) is more valuable than clear opal (crystal opal) which in turn is generally more valuable than white or milky opal.
  • Dominant fire colour - red-fire opal is generally more valuable than a predominantly green opal, which in turn is more valuable than a stone showing only blue colour.
  • Colour pattern - harlequin opal, where the colour occurs in patches, is generally more valuable than pinfire opal where the colour is in small specks.

There is a marked difference between the value of uncut opal and that of a cut and polished stone.

Opals may be cut and polished in a number of ways, depending on the nature and thickness of the colour band. Under the Trade Standards Act, all opal sold in South Australia must be clearly labelled to show the type of opal and how it is presented.

Solid (cabochon)
Most cutters prefer to produce the opal as a solid cut en cabochon if the gem is sufficiently thick.

Doublet
A thin veneer of opal may show enhanced colour with a dark backing. This can be achieved by cementing either black or grey silica material or a thin slice of common opal to the back of the opal with epoxy resin.

97-0640mesa

Triplet
A slice of quartz may be used to cap the thin opal veneer to protect it from abrasion. This produces a three-tiered gemstone known as a triplet, which can often display brilliant colours. It is a cheaper method of presentation and can enhance the appearance of the opal.

Matrix Opal
Matrix comprises precious opaline silica as an infilling of pore spaces in silty claystone; it generally shows fine pinfire colour in the natural state. The colour may be enhanced by soaking the specimen in a sugar solution and then boiling in acid to deposit carbon in the available pore spaces, resulting in a dark background. Matrix opal is only found at Andamooka and is generally cut and sold en cabochon.

Synthetic Opal
Synthetic opal, such as Gilson, is opaline silica produced in the laboratory and having a similar structure to that of precious opal. The following observations can help to differentiate between natural and synthetic opal:

  • synthetic stones generally show brighter colours, and colour patches are often larger than in natural opal
  • colour grain boundaries are generally highly irregular in synthetic opal
  • within each colour grain in synthetic opal there are numerous sub-grains that produce a distinctive snakeskin pattern
  • synthetic material generally shows a more ordered array of colours since artificial material does not duplicate the intricate pattern of natural opal.

Imitation Opal
This is non-opaline material, such as coloured tinsel, set in clear plastic or epoxy resin.

Mining Opal
Miners, with a Mining Permit, can peg a claim either 50m x 5Om or 5Om x IOOm to mine for opal.

The earlier form of mining was by sinking or digging a shaft with a pick and shovel. Driving or tunnelling along the level was then carried out with picks and shovels. When traces of opal are found a handpick or screwdriver is used.

Nowadays most if not all prospecting shafts are made by using a Calweld-type drill which are used to excavate holes about one metre in diameter using an auger bucket The drills can dig to a maximum depth of about 28 to-30 metres and the opal fields are pitted with thousands of abandoned Calweld shafts.

Waste material or mullock, from the shafts and drives, was originally lifted to the surface by hand windlass, later being replaced by power winches (Yorke hoists) or automatic bucket tippers. Today truck-mounted blowers, which operate like vacuum cleaners, are more commonly used for bringing mullock to the surface.

Since the 1970's, there has been a rapid increase in the use of mining machines. Tunnelling machines with revolving cutting heads and small underground front-end loaders, called boggers, have been introduced.
There is a marked difference between the value of uncut opal and that of a cut and polished stone.

Bulldozers are employed to remove overburden and expose the level where it is shallow. Spotters follow behind watching for opal and the seam is then worked over by handpick.

Opal Mining

Opal Mining

 

Noodling
Most cutters prefer to produce the opal as a solid cut en cabochon if the gem is sufficiently thick.

This is the process of searching through heaps of discarded mullock for pieces of opal missed by the miners. Many locals make a living off this method and it is popular with tourists. Permission must be obtained from the claim owner to fossick on his/her claim. The most productive heaps are those excavated by bulldozers where opal may have been crushed or overlooked by careless operators. Noodling machines, in which mullock is passed through a darkroom on a conveyor belt beneath ultra violet lights are also used, and this is another form of mining. Great care must be taken on the opal fields due to the thousands of open shafts.
Information supplied courtesy of Primary Industries & Resources, SA.
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Contact Details
Lot 773 Hutchison St
PO Box 425
Coober Pedy SA 5723