In1956 Arthur Molyneux made a new kind of dry puddler for separating the nobbies (opal nodules) from the softer claystone in which they occurred.
He cut down and perforated a 44-gallon drum, which he fitted to the back of his tractor and used the posthole auger inside it to break up the dirt. It was a simple arrangement with a bar attached to the auger that extended almost from side to side in the drum, clearing the bottom by about an inch.
This design was improved on by using heavy steel mesh for the drum, and a rotating circular plate with three beaters at the bottom of the drum to break up the dirt.
Puddlers provided an effective way of processing the mounds of dirt left around hundreds of abandoned shafts on the old opal fields.
Until the introduction of the dry puddler many of the old dumps were 20 feet high, but by the end of the 1960s, there were few left.
There was a great variety of dry puddlers, ranging from tractors, using the power take-off, to trucks, cars, and homebuilt contrivances using small motors, such as a Villiers or Briggs & Stratton.
In the 1960s, with more water available from bores and dams, many miners added pumps and sprays to their puddlers to improve their efficiency and reduce opal breakage. In these wet puddlers, the water mixed with the fine clay dirt to make a slurry which escaped more easily than dry dirt through the mesh walls of the drum.
During the 1960s Eric Catterall, and other miners wanting to process larger quantities of dirt, began using rumblers, large cylinders with steel mesh walls which rotated slowly around a horizontal axis. The movement broke the clay dirt down to a fine dust, or to a slurry if water was added, leaving the harder claystone and opal behind to be removed and sorted later. Many variations were made in the designs of rumblers to improve their effectiveness.
Tony [Fitzgerald] developed an automatic dumping system that gradually emptied the remains onto the back of the truck ready for puddling. His idea was soon copied, and within a few months every rumbler had one fitted.
In 1975 Gary Stone had built one of the largest wet rumblers but he found it needed too much repair when processing large volumes of dirt. He bought an old cement mixer and modified it for processing – this proved to be far more effective.
I bought a six yard cement mixer in Dubbo, took the manhole cover off and replaced it with quarter inch mesh to let the slurry out. I fed the tailings from the rumbler into the mixer. When the mixer was reversed, we didn’t find broken opals in the tailings, even the fragile opalised fossils were okay.
It worked so well that I took a gamble and bought a 10-yard cement mixer to replace the rumbler and fed raw opal dirt straight out of the mine into it. Surprisingly, it worked just as good – so much so, that it was the end of the rumblers and eventually changed the way opal was mined at Lightning Ridge, dramatically increasing production.
To reduce operating costs, some miners installed vibrating screens to separate the larger rocks from the smaller lumps of rock and claystone before feeding dirt from the mines into agitators.
We use a power screen with six-millimetre openings in the steel mesh to pre-screen the dirt and remove the one-third which is in particles over six millimetres.