New Opal Fields Are Found
By Using a Prospecting-Drill
A miner needs a prospecting-drill if there is any chance of him finding a big patch of black opal.
These drilling rigs drill a 9-inch in diameter hole to obtain a sample from the opal level underground. Most drilling rigs in the Lightning Ridge area use the auger drill principle.
When an auger drills up opal or potch, it is coated with fine damp sandstone. The potch and colour is almost impossible to see without washing this coating off the sample.
One 9-inch hole is about a 1/22,000th sample of a 50m by 50m claim. This is a very small sample. Most miners will drill at least 20 holes in a claim to get an indication as to the amount of opal, if any, is present in the claim.
An auger prospecting drill has a difficult time drilling through the first 15 feet, because of the silcrete level. This is exceptionally hard ground to drill. Sometimes an auger drill operator will leave a hole unfinished because the ground is too hard to drill.
Some miners have a percussion-drilling rig. It uses an air operated hammer drill that drills through the silcrete level regardless of how hard it is. Once through the silcrete, the hammer drill is removed and is replaced by a rotary bit.
The sample is pushed to the surface by compressed air and then goes through a cyclone to extract the air and dust before being deposited on a conveyor belt.
Exact level depths can be obtained using these drilling rigs. Unlike an auger drill, where the deeper it goes the more inaccurate the level depths become.
The white material coming out of the top of the mast is dust from the dust extracting feature of this drilling rig. Air drills create quite a bit of dust.
Yes it is old, but it works well.
prospecting-drill back to mining industry
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