Opal... rainbow of the desert

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warrumbungle mountains

The Warrumbungles

OPAL IN AUSTRALIA

The New South Wales Fields

The earliest reports of precious opal in New South Wales refer to its occurrence in volcanic rocks. It was found in various localities, and, although attempts were made to exploit the discoveries, none were commercially viable. It was not until the discovery of high quality precious opal in sedimentary rocks in the area known as Wallungulla, now Lightning Ridge, and later White Cliffs, that the industry became established.

Volcanic opal
As early as 1882 opal was reported from volcanic rocks in New South Wales, and there was apparently a small production from such areas. In the Department of Mines publication, Description of Minerals of New South Wales, published in that year, it is stated that: "Precious or Noble Opal - The precious opal of New South Wales has the milky body colour usually possessed by this mineral, and the same brilliant play of colours; the dominant colours of the scintillations are metallic green, pink, and red. Some of the best specimens form, when polished, very fine gem-stones; but here as elsewhere the valuable specimens obtained bear but a small proportion of the whole. The best have been obtained from Rocky Bridge Creek, Abercrombie River, county Georgiana; the matrix is a fine-grained bluish-grey amygdaloidal trachyte, some 30 feet (about 10 m) thick, which is so much altered that it can be abraded by the thumbnail; the opal has filled by infiltration certain of the vesicular cavities and crevices in this rock; it is associated with much common opal free from any play of colour and hyalite." The opals found were quite small; stones of 1.80, 0.93 and 0.57 carats were recorded. There is no mention of opal occurring in any sedimentary environments.

In 1896 Curran (R1606) gave a brief description of the same deposit of volcanic opal, as well as some details of the White Cliffs area at that time. Regarding the volcanic opal he states: "At Rocky Bridge Creek the opal fills vesicular cavities in a decomposed acidic or andesitic lava. The lava rests on auriferous gravels and sands of the usual Tertiary type. Some of the stones found here are of the highest possible quality. The larger stones found are rather milky but show fine colours. The small gems lately got by Mr. S. Davis of Carcoar, are not to be surpassed, - equal to the best Hungarian. As is well known the Wilcannia and Queensland opals are found encrusting or filling cracks, and the finest stones often want depth. The Rocky Bridge opals occur in the matrix in rounded pea-shaped pieces. When a good stone of this kind is found, it can be cut to the best advantage. I do not think that the search for these opals has ever been remunerative. There is difficulty in getting out the gem, - at least the miner finds it difficult without a cutting wheel. At present some men are at work, and as first-class stones have been found and the vesicular lava is extensively developed, more gems are certain to come to light." Another early report of precious opal in volcanic rocks in New South Wales was that by Pittman in 1907 (R1596). The opal occurred at Tooraweanah in the Warrumbungle Mountains, a very picturesque area of ancient lavas. It lies about 42 km northeast of Gilgandra. Pittman states: "The gem was found to occur filling the cavities in a vesicular trachyte, and traces of it were seen in several adjoining parishes. It was evident, however, that the deposits are not likely to be of commercial value, for, although there is a fairly good play of colour in some of the stones, the amygdules are of a comparatively small size, while the matrix is hard and tough; it is therefore almost impossible to extract the opal without fracturing it. There were about twenty miners at work on the deposits, and some of them had done a considerable amount of prospecting in the way of irregular excavations in the trachyte. Upon the foregoing facts being represented to them, however, they decided that the prospects were not sufficiently encouraging, and in a short time the field was deserted."