Lightning Ridge is a town located 743 km southwest of Brisbane. Its economy is mainly based on mining, the sale of opals and tourism. Indeed, many Australian tourists visit this region in winter. It was here that Jack Murray found the first black opals in 1900.
Lightning Ridge opals form about 6 to 18 meters deep, often very close to the contact zone between the sandstone rock (sandstone), which is on the surface, and the clay which is at the bottom. Each miner is entitled to two concessions of 50 meters by 50 meters renewable each year.
Once the miner has found a location, he has 28 days to study the soil before leasing the concession. He carried out this study with samples collected at a depth rangingup to 10 meters. As soon as he has his concession, he digs a hole about 20 to 30 meters deep by about 1.5 meters in diameter.
The miner lowers his equipment as the hole gets bigger. To solidify the mine, he places pine trunks vertically.
The crushed rocks are sucked up to the surface through a large tube, then unloaded directly into a truck. At the end of the day, the miner unloads the truck into what is called an agitator, an old mixer truck or a concrete mixer. Rocks spin slowly for 2-5 days in water which dissolves clay and sandstone. When the process is complete only the opals, common and precious, are left.
Yowah
Small town of 50 permanent inhabitants, located about 1000 km from Brisbane. This is where we find the Yowah Nuts.
These opals, also called nuts, are found in small, round iron-bearing rocks the size of a small avocado. It is when they are sawed in half that the opals are found, either in the center or as veins. Their formation was a mystery until geologists discovered that these rocks were once more porous and therefore let in water laden with silica.
We met Eddie Maguire who had the great generosity to show us much of his opal collection. This artist has been working with opals for many years. Most of the time they are simply sawn in half, to show off their exceptional beauty, and placed on a custom-carved wooden base.
Like Boulder Opals, Yowah Opals are rarely completely mined from the bedrock. It is also in these "nuts" that we find Matrix opals.
Quilpie
Probably one of the highlights of our trip was a visit to the Eric Stelzer mine which is about 2 hours from Quilpie and which is only accessible by an off-road ride.
We had the chance to stay directly at the mine for two days. This is the first open pit opal mine we have visited, most of which is underground. This is where the Boulders Opals are located. Miners know how deep the opals are; depth which roughly corresponds to the old river beds.
As at Lightning Ridge and Yowah, Quilpie soil is predominantly sandstone and clay; we can distinguish ferruginous rocks (Boulders) imprisoned there. Often the miner breaks a few on the spot to see their potential before bringing larger quantities back to camp. Most of the time he can already notice a few streaks of color.
On our second day at the mine, Eric took advantage of the presence of his son Colin, a geologist, to go and test another mine about 45 minutes away. It was with the help of a drone that they were able to take pictures of the topography of the place.
