Individuals rather than large mining companies do mining in Australian opal fields. The reason for this is that opal is particularly elusive; it is not found in great amounts at a particular level or in a particular area, but is found at varying depths beneath surface and is usually found at levels up to 25 metres deep.
Although in reality all that is needed to get started mining opal is a pick, most miners now consider a jackhammer and an electric hoist – a machine used to get opal-bearing dirt to surface – minimum equipment needed. Most shafts are now drilled using a drilling rig. After a shaft has been sunk and opal level identified, horizontal drives are dug.
After bringing dirt to surface, it is initially processed by washing away all ordinary dirt and leaving behind potential opal stones. This is usually done in an “agitator,” a modified stationary cement mixer. Water is pumped through while dirt rotates inside. Sludge pours from mesh-covered openings in side of agitator as dirt is washed away. What remains are known as tailings.
This final process is either most exciting or disappointing part of hard work of opal mining. It is at this point that it becomes apparent how much, if any, opal there is among all dirt that has been mined.
Sinking a Shaft:
This is one of most effective ways of finding opal, but also most laborious. The length of shaft can be as short as three meters or as long as twenty.
A variety of tools are needed, including a hand windlass or motorised winch that is placed over hole, lifting dirt to surface. Some miners will use an expensive vacuum-cleaner apparatus called a “blower.”
Once bottom of shaft has been reached (where opal-bearing dirt begins), miner begins gouging away very slowly. A horizontal tunnel is dug in hope of finding a seam of precious opal or scattered “nobbies.”
Puddling and Rumbling:
This technique is used once opal dirt has been transported away from surface, usually by trucks. The dirt is first placed in a large mesh-lined drum. Water is pumped through it as it rotates, turning dirt into sludge.
The sludge escapes through mesh in sides, leaving only pieces of rocks, and hopefully opal.
Open-cut mining is created by running over a large area of ground with a bulldozer, slicing away dirt until opal level is reached. Although this method is very expensive, chances of finding opal are increased as a larger area can be mined at once.
Noodling: Noodling is when a person goes over what other miners have rejected as rubbish. All that is needed by a “noodler” is a sieve and a very keen eye.
Unprocessed opal straight from ground is known as “rough.” The miner may sell it at this stage, or he may choose to continue processing himself. Although potential value of opal can be estimated while material is unprocessed, its actual value cannot be established at this stage. The rough opal, although it may look as if it will cut well to produce valuable stones, may have faults within it. Conversely, an ordinary looking piece of rough may produce a magnificent gem. The choice of selling “in rough” or continuing processing belongs to miner.