In periods of rising groundwater levels, the sediments increased in volume as the clay minerals swelled, causing considerable micro-faulting or ‘slides’ as the miners call them. The relationship or intersection of slides and large scale faulting associated with major lineaments, coupled with strong sandstones interspersed with claystone lenses are essential clues to the puzzle of finding opal.

The rugged early miners suffered an unenviable, primitive existence. Although mining was economical; requiring only picks, shovels, cowhide buckets, windlass, a carbide lamp and explosives; water and supplies were often carted many kilometres by camel and later by automobile.

To this day the Opal mining industry consists of numerous small businesses, partnerships and private individuals, invariably large corporations have failed in their Opal ventures.
The mineral rights in Australia belong to the Crown, in order to commence digging for Opal a mining claim or lease 50mx50m or larger is pegged and registered. These days, application fees, annual rent, pastoral compensation, native title compensation and environmental bonds may add up to considerably more than $2000. Not so long ago you could have a go at mining for $50, however that still gets you a prospecting right for fossicking only, no digging allowed, enough to infect you with the opal-bug.

Most Opal mines are initiated by sinking shafts; this once took several days by hand, but now takes only an hour or so using Auger drilling rigs.
Having ‘bottomed’ on a promising level, a drive should be made to connect with a second shaft. This creates airflow and ventilation to avoid the very real threat of carbon monoxide poisoning.
All the while the miner is interpreting changes in the ground; dipping levels or opal profiles which could contain roof or toe levels or both; trying to drive across faults and looking to find  'traces' of Opal preferably leading up to ‘pockets’(patches of opal less than 1m wide) or ‘runs’(tens of meters wide) of Opal.

Windlass, Pick & Shovel	Auger  Drilling

Underground miners now use rotary tunnelling machines, diggers, bobcats and to a lessening degree jackhammers to remove the prospective ‘mullock’ or opal dirt. Mechanical hoists and ‘blowers’ (large vacuum extractors) now haul the mullock to the surface, having replaced the tedious hand windlass.
Most Opal is found by hand, gouging and checking the level, except at Lightning Ridge where the majority is found after the opal-dirt has been washed by an ‘agitator’. One in a row of large concrete mixers which sluice the sticky clumps of opal dirt at numerous tailings dam sites around the ‘Ridge’.
Professional Opal miners in South Australia employ heavy machinery and ‘Noodling plants’ to process discarded opal dirt and their own mullock; sieving and collecting the fines by conveyer into a dark room for UV inspection – as White opal fluoresces under Ultraviolet light. At all of the fields there are ‘noodlers’, tourists and locals, who fossick discarded mullock dumps.
In Queensland open-cut mining is preferred, employing bulldozers and excavators to cut wide trenches in the ground. Miners known as ‘checkers’ are required to walk behind and inspect the wake of the bulldozer or the excavator bucketfuls as the opal levels begin to surface.