The Queensland Opal Fields are found in a belt of deeply weathered cretaceous sedimentary rocks known as the "Winton Formation".
The Cretaceous Period existed between 145 million years ago and 66 million years ago. The climate during this period was quite warm and obviously wet. What is inland Australia now, consisted of a vast inland sea which which spread and shrank at least four times during this period. When the sea had receded there would have been vast rivers, swamps and pools and these would have deposited layers of silt, clay and sand that later turned into the siltstone , sandstone and mudstone that make up the Winton Formation.
This inland sea, known as the "Eromanga Sea" covered large parts of Queensland and Central Australia. In some parts of Queensland the Winton Formation is more than 400 metres thick.
The sea ceased to exist around 95 million years ago.
During this period many dinosaurs appeared, among them the honed Triceratops and Centrosaurus. Most of those found in Queensland would have existed in the late Cretaceous Period.
Opal was discovered in Queensland as far back as 1869 at a place called Listowel Downs. This is in the Barcoo district of western Queensland.
How opal was found in such a location is anybody's guess. Quite often opal was found quite accidentally. People drilling for water have unearthed opal. Kangaroo shooters have discovered surface floaters in out of the way places and miners looking for gold have stumbled upon strange stones with flashes of colour. Once word had got out that opal had been found, men headed out into this quite forboding country with pack-horses, equipment and very basic food to try and find this elusive gem. These men were very hardy and had to exist in a climate that was extremely hot, dry and dangerous. There was no-one around to assist them if they were sick or hurt and water and food would have been very scarce.
There are different types of opal found in Queensland. Then we see referred to most of the time is the boulder opal. This form of opal forms in cracks in iron-stone boulders with the opal forming thin veins of often brilliant coloured crystal opal. It takes a special skill to cut and polish this type of opal as the veins are often thin and curved.
Another form of this opal is the matrix boulder opal where the opal occurs as small flecks or patterns within the iron-stone boulder. This can result in intricate patterns which are extremely beautiful.
The mining of this sort of opal is usually carried out using large machinery such as bulldozers or front end loaders. The boulders are dug out of the open cut and then cracked open to reveal the veins of opal. It is a very destructive form of mining and much opal is damaged. Miners often sell these broken boulders at markets in the opal fields.
In some of the fields opal is found in a band at the juncion of the sandstone and clay sub-layer. This opal is in the form of nodules and cylindrical pipes. Both crystal and black opal have been found.
There are, of course, other types of opal found in Queensland. Extremely beautiful crystal opal was found at Duck Creek, which is located near Toompine which is south of Quilpie. I was lucky to have visited this field and Sheepyard Creek in 1966. The fields were largely deserted then but there was evidence of fairly extensive workings with may shafts still in existence. We were lucky enough to pick up small pieces of the crystal opal from around old camp fires where the miners used to sit and chip away the edges of the stones they had uncovered.
According to Len Cram, a leading writer and historian of Australian opal, Duck Creek produced some of the worlds best crystal opal in its heyday. Unfortunately lack of water was a major problem and led to outbreaks of typhoid and yellow fever. Opal mining certainly had its drawbacks in the 1890's as if digging in the hard ground in intense heat was not hard enough.
Duck Creek is now part of the Toompine opal field and this field covers the area from Quilpie to Yowah. It covers areas such as Lushingtons, Sheepstation Creek, Coparella, Emu Creek and Pride of the Hills. I visited Pride of the Hills in 1966 and spent a pleasant week there picking up small pieces of matrix some of which I still have today. On trip to Andamooka I met a miner called Otto who told me he had carted his dozer all the way from Andamooka to Pride of the Hills and levelled the hill looking for boulder opal. Unfortunately for him he found very little.
The first recorded find of opal in the area was at Bull Creek in 1885.
HayRicks, perhaps the greatest boulder opal mine in Queensland, is located in this area. It is approximately 100 km north of Quilpie. It was discovered in 1929 and virtually destroyed by bulldozers in 1980.
Len Cram visited the area in 1956 and saw the largest slab of opal he had ever see. It was 39 feet length and about 3 inches across. A truly magnificent sight.
Fifteen km east of Hayricks is "The Red Show". Here Joe Knehr Found the second largest piece of opal ever recorded. It was red crystal pipe opal and was over four feet in length and weighed twenty eight pounds. It is hard to imagine a piece of opal that big.
About 100 km west of Quilpie lies the town of Eromanga.Opal was found in the area in the 1870's and led to an influx of miners who somehow soon heard of the finds.
Sandstone opal was found near here at "The Little Wonder" Mine. This mine is situated 50 km west of Eromanga. The Kyabraa Hills where Joe Bridle found opal is further to the north west.
A good web site to read more about the Queensland Opal Fields is Mac Opals.