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great artesian basin
 
 
OPAL IN AUSTRALIA

Geography: The Water Problem

Leechman, in his book entitled The Opal Book (R0384), lists some 200 localities for opal in Australia. These include the names of many mines, and also localities in which the opal that is called 'common opal' occurs - a type which does not have the internal physical structure to produce the play of colour of precious opal. Most of the Victorian localities, for example, would be of this type, and that at Angaston, (the earliest report of the occurrence of opal) is similar.

Some of the other localities are occurrences of volcanic opal, i.e. opal occurring in volcanic rocks. Occasionally the latter may show a true play of colour; material of this kind has come from localities such as Springsure and Maleny in Queensland, and Tintenbar and Rocky Bridge Creek in New South Wales. Little commercial opal has been produced from volcanic rocks in Australia; it is usually rather transparent, occurs in small pieces in vugs in the volcanics, and tends to crack or craze readily.

The major opal fields occur around the southern boundary of the Great Artesian Basin, that area resulting from a great incursion of the sea during Cretaceous times. These localities are well inland in very dry areas, which made the exploitation of the deposits in the early days a difficult and hazardous operation. It has generated a special breed of people, and the resulting settlements each have a special character of their own. However they do have certain things in common, apart from the life of their people revolving around and depending on, opal.

One of the major factors they have in common is that they all occur in very hot, dry areas of Australia, where shade temperatures will often reach 45°C and more in summer. The rainfall, especially in the South Australian fields is very low; the average annual rainfall at Coober Pedy, for example, is about 150 mm. In addition, the rainfall is very irregular, and there can be periods when no significant rain falls for two years or more.

The remoteness of these areas, accessible in the early days by little other than bush tracks, combined with the lack of water, created difficult conditions for the miners. The nearest towns, if some of them could be glorified by that name, were hundreds of kilometres away in some instances, so that food and other supplies were slow in arriving and expensive.

In the Lightning Ridge area the problems of water supply in the early days often caused disagreements between local landholders and the miners. In drought times almost the only source of water was the dams built for stock; miners depended on this water in difficult times, but the landholders were often not co-operative. It took some years of political lobbying before the New South Wales government agreed to build a dam to ensure a satisfactory long term water supply for the opal mining industry.

Water supply problems were overcome, at least partially, by various means. Although White Cliffs was in a rather isolated area some 1000 km west of Sydney, it was only about 85 km from Wilcannia, a small settlement on the Darling River. Not only was the Darling a reliable source of water, but it was also a major artery for the transport of wool and other agricultural products in the 19th century. The Darling flowed into the Murray River some 350 km to the south, itself Australia's greatest river. The Murray flows for some 2500 km from the highlands in the southeast of the continent, westwards to South Australia, and then southwards until it empties into the Southern Ocean.

Although the Darling from time to time dried up into discontinuous pools of water, preventing river transport for periods of time, there was always water available for domestic requirements. The water could be transported to White Cliffs by horse or bullock-drawn tankers. Similarly, other supplies could be obtained from Wilcannia, as this was an important stagepost on the Sydney to Broken Hill road. By the time the opal field had become an important producer, the great base metal mines of Broken Hill had been exploited for some 20 years, and this town had become by far the most important in the far west of the State of New South Wales.

The next major field to be developed was Coober Pedy. This was some 1000 km north of Adelaide, the capital of the State of South Australia. Water supply was a particularly difficult problem due to the low and intermittent nature of the rainfall. Water of varying quality was available from sub-artesian bores, but good quality water had to be brought some distance by tanker.

Later, the State Government constructed concrete tanks into which rainwater could be funnelled. This solved the basic problem, although in drought times, water still had to be brought in by tanker, by this time motorised. Later, as part of a research project, CSIRO (Commonwealth Scientific and Industrial Research Organization, Australia) built solar stills which produced a good supply of high quality water for domestic purposes.

The primary supply was from bores which yielded mainly brackish (salty) water. In recent years, this water has been purified by the process of reverse osmosis.

Andamooka was established along a creek, mostly dry, between low, rocky hillocks. A well was dug which gave a small supply of water, but in dry years it became necessary to bring in water by tanker. By this time it was the middle 1930's, so that motorised tankers were available, and there was some grading of outback roads by government authorities.