Mintabie opal from South Australia is famous for producing milky white to almost black opal.The Mintabie opal field is situated along the west of the main north-south road between Alice Springs and Adelaide. Compared to other opal fields, this field is populated with malle and mulga trees rising along sandy soil.
Opal Mining methods at Mintabie
The most common form of mining is pit or shaft sinking with pick and shovel, and a hand-operated winch to remove mullock.
Bulldozers and excavators are now commonly used to expose the opal level when it is at relatively shallow depths, then the opal is carefully removed by pick. In deeper areas, shafts are generally sunk by large diameter bucket drills (Calweld drills), then reamed out to allow tunnelling machines, bobcats or boggers to be lowered.
A variety of methods are used to remove the mullock from underground workings:
Tip trucks and Self unloaders haul a bucket to the surface on two parallel rails which are curved above the ground such that the bucket empties a few metres away from the shaft. An automatic reversing switch is tripped to return the bucket underground.
Blowers are truck-mounted machines similar to large vacuum cleaners. A fan or blower driven by a stationary diesel engine draws mullock out of the shaft through connected metal pipes to collect in a bin at the surface, which empties automatically when full.