Cypress props up opal industry
June 13, 2003, by Howard SpencerState Forests has been propping up the opal fields of Lightning Ridge for decades. 
But the curious thing is that the closest State Forest is about 250km away; too far to make it a practical source of the white cypress pine, or Callitris glauca, used to make mine pit props in the 100-year-old mining area.
Instead, the cypress has come from Crown timber under the control of State Forests from Western Lands Leases. These leases are over some of the 2.7 million hectares of leasehold land that State Forests manages for timber in western NSW.
White cypress pine can be found throughout these inland slopes and plains. Luckily for Lightning Ridge and its companion mining areas of Grawin, Glengarry, Sheepyards, Carters and Coocoran, the cypress grows close enough to the pits for cypress cutter Cliff Bennett to supply the continuing demand.
"The miners have got to have these props," says Cliff. "They will literally save your life if you are a miner."
Props are purposely cut lengths of timber used to support the roof of a mine shaft, set in place by the miner as he excavates his claim. They are topped, or capped, with hardwood or cypress. Props are cut from lengths of between seven and 15 feet, although the average is eight feet.
Underground, these sturdy, termite-resistant logs are used every few metres, depending on the pit and the pocket of the miner. Cliff delivers props that he and the miners describe in pre-decimal terms. An eight-foot long prop will be eight inches or more in diameter. According to Department of Mineral Resources specifications, there should be 25cm of diameter for every 300cm in length.
The Department says that when fitted with a cypress cap the load capacity was up to 67 tons. Hardwood will carry a bigger load, but cypress with a cypress cap gives visual (buckling or splitting) and audible (a loud cracking sound) warnings of a potential cave-in.
Long-time Lightning Ridge miner Max Caslick wouldn't be in a mine without the props. "We prop right to the boundary of the claim," says Max, pointing to the eerie underground forest of logs marching into the gloom of his generator-powered lighting system.
The generator also powers a 'blower', which is in reality a giant vacuum that sucks up the opal-bearing clay dug out by a hydraulic digger. Unlike most miners, who take the hot summer months off, Max and a partner mine all year round, and prop the roof of the mine as they go. Each mine claim is 50m by 50m, giving a potential of 2,500 square metres of roof being held up with cypress props.
Props give two main signs of a possible cave-in. If the roof subsides, it can force the cypress timber into the floor, leaving the fibrous bark to bow and buckle. The other sign is a break in the cap near the roof.
"If you see either of those, you get out," says Max. But the risks can be worth it. "This is the only game I know where you can be a millionaire overnight," says Max.
Like all high return ventures, there are the downsides. Max estimates that 70 per cent of miners make little or nothing, another 20 per cent make a living and 10 per cent are millionaires.
"These opal miners come from all walks of life," says Max, formerly of Port Macquarie, now with 18 years up at 'The Ridge' as the locals call their home.
"Some are doctors, some are lawyers, and there are people from all over the world. They just like opal mining."
Apart from the pit props, there are other moves to make the industry safer. All incoming miners staking a claim have to undertake a two-day course in mining, with a strong emphasis on safety.
Cliff Bennett has attended a State Forests contractor safety course, which sets out new obligations for safety in the forest. He will be required to complete a first aid course as well as study other issues that relate to a site safety plan.
He might also have to do the mining course: after seven years cutting props, and the previous 39 years spent cutting railway sleepers, Cliff has now caught the bug and bought a mining lease at 'The Ridge'.
Everything about Lightning Ridge has a feeling of age about it. And given that the opals form from silica gels that were laid down millions of years ago, it is no wonder.
Max Caslick and his fellow miners have been unearthing dinosaur and other fossils from a time up to 120 million years ago when the area was part of a giant inland sea.
In New South Wales the most important seams of opal are found in sedimentary rock, with the opal lying at shallow depths, usually less than 30 metres.
Silica weathered from overlying rock percolates down through the rock mass to a cavity or fault where it is deposited as a gel. Gradual loss of water from the gel results in hardening of the material and the formation of opal, the whole process taking hundreds of thousands of years.
Opals are made up of minute spheres of silica which have grown around a central nucleus. Precious opal consists of larger silica spheres arranged in a regular pattern. The orderly arrangement of the spheres creates a regular three-dimensional array of spaces and voids between the spheres.
Diffraction and interference of light waves travelling through the transparent spheres and voids produce the brilliant play of colours that can be seen in precious opal. And with these amazing colours it's no wonder many are seduced by the lure of the gem - and take to the shafts propped up by cypress.
Source: NSW Dept. of Primary Industries
Photos by Howard Spencer