Australia’s Opal Fields are all located in the Great Artesian Basin, mainly in New South Wales, Queensland and South Australia. Each region produces a distinctive type of opal. Some of the bigger mining fields are Lightning Ridge and White Cliffs in New South Wales, Coober Pedy in South Australia and Yowah in Queensland. Mining for precious opal in Australia began in the 1890s.
NEW SOUTH WALES OPAL FIELDS - BLACK AND WHITE OPAL
The New South Wales opal fields are all situated in arid inland areas, on ridges surrounded by black soil plains. The sedimentary opal deposits occur in deeply weathered Cretaceous rocks formed 65 to 135 million years ago within the Great Artesian Basin. The opal is found at shallow depths in sedimentary rocks through which there has been considerable silica seepage into cavities and other structures. Gradual loss of water from the silica gel has resulted in hardening of the material and the formation of opal.
Lightning Ridge is famous for Black Opal and White Cliffs for Light Opal, which comprises White Opal and Crystal Opal.
LIGHTNING RIDGE NSW
The town of Lightning Ridge is located 770 kilometers north-west of Sydney and 72 kilometers north of Walgett. It has a population of about 1200 and its rich history and colourful reputation draw around 8, 000 visitors each year, many of them hoping for a lucky find fossicking the mullock heaps.
Lightning Ridge supposedly got its name after a shepherd and his flock sheltered from a wild storm among the trees on the ridge. Two hundred of the sheep were killed by a ferocious lightning strike and the rest scattered to the four winds in fright.
Opal was first discovered in this area in the late 1880s but the first shaft was not put down until the early 1900s. At this time, Black Opal's commercial potential had not been widely realized. Buyers were unfamiliar with it, and its dark tones - due to the dark colour of the base rock - were not popular. All Opal mined at Lightning Ridge is between depths of 1 to 30 metres. It is found as rounded nodules, called nobbies, and less commonly in seams.
The deposits of gem quality opals where formed during the Cretaceous period. During this period the area was filled with fresh water, creating sediment that formed around the Opal. There are over 200 different opal fields that can be found on the ridges of Cretaceous rocks at Lightning Ridge. They can be found in small groups dotted around the area but Lightning Ridge, Jag Hill and Mehi, Coocoran, Wyoming, Grawin/Carter’s and Glengarry/Sheepyard are the main opal field groups here.
WHITE CLIFFS NSW
The White Cliffs opal fields are located in the top left-hand corner of New South Wales, near the Queensland and South Australian borders. The town of White Cliffs is located 295 kilometres north-east of Broken Hill and was the first viable commercial opal field in Australia. Opal was first discovered there in 1884. A sample was sent to Tillie Wollaston, a geologist in Adelaide, who immediately recognized the quality of the find. He was able to promote the White Cliffs opal in Europe and America. Their only previous source, Hungarian Opal, had finished a hundred years earlier.
White Cliffs' Light Crystal Opal is formed in horizontal seams in the ground. Compared to other opal, Light Crystal Opal is quite easy to value and grade and does not break when cut and polished. As it occurs in seams it can be cut in standard sizes without losing valuable stone. Black Opal, on the other hand, usually occurs in ‘nobbies’ and is cut to maximize the size of the finished gem. This is the principle reason for the commercial success of White Opal.
White Cliffs became the world’s number one producer of seam opal and for thirty years it provided the bulk of all the commercially accepted opal in the world market. However, supply slowly dwindled as the richer area was mined out and eventually conditions proved too harsh. Scarcity of water, and diseases such as cholera and typhoid had a big impact and the final nail in the coffin - World War 1 - put a stop to trade with Germany, the biggest opal buyers and dealers of the day.
Today, the White Cliffs Opal Fields produce only a very small amount of White and Crystal Opal and there are still a few miners who continue to fossick among the old diggings, hoping to strike it lucky.