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Source: stellalapis. Today, Coober Pedy SA is the main producer of white opal, though in recent years this field has expanded and all types of opals are found. Other centres in SA include Andamooka and Mintabe. Boulder opals opals in concretionary ironstone are mined in Queensland from numerous localities in a zone extending from the Eulo and Cunnamulla district in the south and northwest for a distance of over km to Kynuna in the north. The towns of Quilpie, Yowah and Winton are the main opal mining and wholesale centres.
Opal deposits are found in very old weathered profiles developed in sedimentary rocks of late Oligocene and early Miocene age. These profiles are for the most part concealed below surficial sand and soil cover and it is comparatively rare that outcrops containing precious opals occur.
As a consequence, the remaining in situ opal resource is considered by geologists to be very large. However, future development will increasingly rely on sophisticated geological and geophysical exploration methods. A hand operated winch was used to haul buckets of excavated material to the surface. Today this industry is highly mechanized but is still in the hands of individuals who work within small mining leases or claims which are operated according to different state mining regulations.
For example, except under special circumstances, only underground mining is allowed in NSW, whereas in South Australia both underground and open cut mining are permissible. In Queensland open cut mining is the norm and bulldozers and 20 to 40 tonne excavators are widely used. Exploration is undertaken by surface prospecting and drilling. The use of 9-inch auger drills is the favourite choice for opal miners, as these drills are capable of recovering fairly large samples of the opalised zones.
Many of these rigs are equipped with wet puddlers or dry rumblers rotating screens to separate harder drill chips which may include opal from the enclosing softer sediments.
Visitors to the region will be amazed by the vastness of the plains and the undulating nature of the landscape. There is a wide variety of animal and bird life in the area, generally best seen around dusk and dawn on minor roads and tracks.
The Opalton Field, also called the Fermoy Field was one of the largest and most extensively worked opal deposits in Queensland. It is a good example of typical opal country in western Queensland and offers the visitor the opportunity to experience first hand the remoteness and harsh conditions endured by the opal miners.
The Yowah opal field is the southern-most opal mining centre of western Queensland. Many of the locals in Coober Pedy prefer to live underground in dugouts where it is cool in summer and warm in winter. Situated km north of Adelaide, Andamooka miners work over an area of about 52 square kilometres on the Arcoona plateau in shafts, large bore-holes, open-cut excavations and small tunnels.
Mintabie is situated km south of the Northern Territory border, and approx. The opal mined here excited the world and the town soon developed, by the 's it had a population of more than 3, White Cliffs produced fine quality seam material in such volumes the world had not previously seen. Sadly, the main run was worked out by and the field all but died out. The Queensland fields are spread across 1,km and produce almost all the world 's supply of boulder opal. This opal is produced from scattered locations in the vicinity of Yowah, Eromanga, Quilpie, Jundah, Opalton and Winton.
Almost all the opal is won by open cutting. Large and small ironstone boulders are split in the search for that illusive opal vein. This field was discovered in by kangaroo shooters.
The 'Ridge produces almost all of Australia's sensational black opals and today despite a recent decline in production it is still the largest producer of opal by value.
In the late 's the Corcoran field 30 km to the west of the township produced stunning black opal in great quantities. The population soared to over 8, people. At this time opal sold for record prices sometimes at more per carat than good quality diamond.
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