Aurora Australis — One million dollar baby! the world's most valuable cut & polished black opal harlequin pattern with dominant red-green-blue play of colour (Source from http://www.opalsdownunder.com.au)
Opal Fields at Lightning Ridge
Some of the traditional fields at Lightning Ridge are summarised below.
The Three Mile — This is the most extensively worked and by far the most productive area on the field, and at one time 1,000 people were engaged in opal mining there. In recent years relatively large-scale open cut mining has been carried out.
Thorleys Six Mile — The first shaft on the field is reported to have been sunk in this area in February, 1902. Sinking ranged from 6 m to 12 m. The Finch clay facies was very rich in opal in some of the claims and the material recovered included a lot of clear potch. A rush to this long-abandoned area in May 1970 resulted in the recovery of many good quality black opals, very close to where the first shaft on the field was sunk.
Nobbys (Old Nobby) — One of the first shafts on the Lightning Ridge field was sunk at Nobbys. Opal was initially found in gravel at the foot of the ridge. A considerable amount of opal has been recovered from a lens at a depth of 6 m; however, the rocks are extremely hard and difficult to work. Even the Finch clay facies itself is much harder than on the rest of the field. The shafts here range from less than 1 m to about 12 m in depth.
New Nobby (or New Rush) — New Nobby was first worked intensively in 1960 when a prospecting shaft about 12 m deep returned precious opal, resulting in a rush to the area and the sinking of about 100 shafts. There are two lenses of Finch clay facies, at depths of 5–6 m and 10.5–11 m.
Deep Four Mile — Sinking averaged about 18 m with no shallow ground. A reasonable quantity of good quality opal was extracted from five claims here in the 1930s. There are various opal dirt levels present and the deepest shaft is 28.5 m deep.
McDonalds Six Mile (or The Six Mile) — The depth to the Finch clay facies ranges from 9 m to 12 m on the crest of the hill to 1.8 m at the base of the hill. The best opal was found in the deeper ground.
Rouses Six Mile — The location of this area is uncertain but it is known to be close to McDonalds Six Mile. This was a rush on shallow ground. The depth of sinking ranged from 1.8 to about 4.5 m. Only two claims produced significant quantities of opal. Much of the opal was in the form of big black nobbies.
Nine Mile — Extensive workings are present in this area. The workings are down to 12 m deep on the crest of the hill, but become shallower towards the base of the hill, and amongst the gravels on the adjoining flat very shallow workings are present. The Finch clay facies in this locality is red due to ironstaining. The depth to the main Finch clay facies lens is between 6 m and 8.4 m below the crest of the hill. Potch was found interspersed with the opal.
Nebea Hill — This field was discovered in 1973. Opal was found in two levels: the first at 10 m depth and the second between 12 and 14 m. It was estimated that eight claims produced over $3,000,000 worth of opal in 2 years. Large-scale open-cut mining followed intensive underground mining.
Shallow Belars — Diggings range from 0.3 m to 3.6 m in depth. Some good quality opal was recovered, consisting of opalised bivalves along the contact between the Finch clay facies and the overlying Wallangulla Sandstone Member.
Hawks Nest — Sinking ranged between 1.2 m and 12 m. Lenses up to 2.7 m thick are present and some good quality precious opal has been produced. In some shafts three opal-bearing lenses at 3.6 m, 6.9 m and 12 m were intersected.
Bald Hill — The main lens of Finch clay facies is clearly defined and occurs at depths of about 13 m, but in places five lenses were encountered in the main workings. It is reported that one shaft 30 m deep intersected eleven lenses, each containing traces of opal. The opal nodules commonly occur deep in the lenses of Finch clay facies. which are frequently over 4 m thick and contain interbedded kaolinitic sandstone horizons. Most of the precious opal from this area was recovered from the main workings over an area of only 120 m by 30 m.
New Chum and Old Chum — Opal lenses as shallow as 1.5 m were encountered in some shafts, with another at about 9 m. Most shafts are between 3 and 10 m deep. In some shafts there were no intersections with the Finch clay facies even though shafts were sunk to 15 m. A stone of 100 carats was recovered from the New Chum area. Opal float was found in gravels on the side of the hill in the Old Chum area and the workings there were up to 3 m deep.
|Opal Fields - Lightning Ridge Region||6.5 MB|
Opal Fields surrounding Lightning Ridge
Most opals are now being found away from the township, in areas including the following.
Coocoran — The Coocoran Lake opal fields are approximately 20 km west of Lightning Ridge. First mined in the Depression years, this field was the site of a major rush in the early 1990s and currently produces an estimated 80% of the black opal output of Lightning Ridge.
On the Coocoran fields the opal occurs at depths of between 10 and 30 m, but most commonly around 15 to 20 m. As in most fields close to Lightning Ridge, the opal largely occurs as nobbies which are found near the top of claystone beds beneath strongly weathered and leached clay-rich sandstone beds.
Sheepyard — This field near Glengarry was found in 1985 and was the centre of a major opal rush. Opal is found at approximate depths of 4 to 12 m as seam opal, not nobbies. Black and light opal occur.
Grawin — The workings at Grawin, 42 km south-west of Lightning Ridge, are very extensive and a large amount of opal has been won, particularly at Hammonds Hill and Richards Hill. Throughout the Grawin field, workings range from 12 to 18 m deep on the crests of hills and from 1.2 to 1.8 metres on the flat. Opal occurs mainly in seams with very few nobbies. Most of the gems won are light coloured, often with green dominant and a greasy lustre.
Glengarry — This field is similar in many respects to Grawin, four km to the north-east. The opal is always found in seams and opal nodules have not been recorded from this location. It is estimated that $600 000 worth of opal was recovered between January and June 1972 . The opal-bearing claystone occurs at depths between 2.7 and 4.5 m.
Mulga Rush and Wee Warra North — Located between Grawin and Glengarry, these fields were found in late 1999. As with the Sheepyard, the area was the centre of a major rush with over 500 mineral claims being granted in the first 4 months of the discovery. Opal is found at approximate depths of 3 to 20 m. The opal found is seam opal, not nobbies. It does however produce black and light opal.
Carters Rush — This field, about 5 km north-east of Grawin, was first developed in 1974. The opal levels are patchy and vary in depth between 12 and 15 m. The opal is similar to that found at Grawin.
New Angledool (Mehi) — This field was discovered in 1924. Opal was found at a shallow level and prospecting carried out by diving adits into the side of a ridge. Shafts to a depth of 9 m have been sunk from the crest of the hill.