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Archive for March 2nd, 2009

Australian Opal Gemstones

Monday, March 2nd, 2009

Australian Opal GemstonesOpal was first discovered at Lightning Ridge in the 1880s, and the first recorded mine shaft was sunk in 1901, probably by boundary rider Jack Murray.

For years, mines were dug by hand using picks and shovels. It was incredibly hard work, in an isolated place distinguished by extreme heat, lack of water, and scant facilities. The miners dug square-sided shafts, which they climbed with their backs and legs braced against the walls. Initially, tunnels were no higher than required for a miner to crawl through, and dirt was hauled to the surface in buckets made of hide, tied to ropes. A windlass could make the job a bit easier.

No major advances in technology occurred until the 1960s, when local miner Eric Catterall, crippled by childhood polio, invented an automatic hoist to carry his dirt to the surface. In that decade, artesian water became available to wash the opal dirt, making separation of opal from the dirt more efficient. Other significant developments have included the invention of the blower and agitator (see below) and introduction of the Calweld drill for sinking shafts and prospecting drills for locating potentially opal-bearing ground.

The town of Lightning Ridge sprang up around the opal fields in the first decade of the twentieth century, but it took a while for black opal to achieve the worldwide acclaim it enjoys today - because nobody understood the dark, brilliant form of opal mined at Lightning Ridge. Determined efforts won a lucrative market for black opal, which in 2008 was declared the State Gemstone Emblem of New South Wales.

Opal mining is a life of stamina and hard physical work, skill and luck, hope and disappointment…and - every now and again - the reward of discovering one of the earth’s most rare and enchanting treasures as light touches it for the first time in eternity.

The technology and technological history of opal mining is fascinating. Every Australian opal field has produced innovations in mining machinery and methods, adapted to its particular geological, technological and social setting.

It isn’t easy to find opal. A miner may work for weeks, months or years without finding enough gem opal even to cover expenses. So deciding where to mine is one of the most important decisions an opal miner can make.

Some miners use a prospecting drill to sink a series of exploratory holes into the ground. Each hole is about 230mm diameter. Samples are brought to the surface and examined to see whether the sediments appear likely to contain opal and if so, at what depth.

There are also surface indications of opal - opal tends to form near fault lines and trees often grow on fault lines because the faults hold water. Wild Orange trees, in particular, are often said to be indicators of opal. Aerial photographs can be useful for identifying lines of trees along fault lines, or lineaments.

Once miners are underground, they learn to ‘read’ the geological indicators in the mine face to identify the ground that is most likely to contain opal.

At Lightning Ridge each opal mining claim measures a maximum of 50 metres by 50 metres. Each person may hold a maximum of two mineral claims at any one time. As at January 2008, there were more than 4,500 mineral claims in the Lightning Ridge Mineral Claims District.

Before registering a claim or commencing mining, the miner must complete a Mine Safety Course conducted by NSW Department of Primary Industries. Mine Management and Environment courses are also required in some circumstances.

Extracts from: Opal Mining. The Australian Opal Center.

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