The-Caldwell-Drilling-Rig

The-Caldwell-Drilling-Rig is used in the opal fields for miners to access the opal levels. The levels can vary from 4m in depth to 25m. Sometimes there are multiple levels.

A Caldwell can drill a hole from .9m to 1.5m in diameter. Most holes are drilled at 1.0m to 1.2m; this allows enough room to lower mining gear.

Most fields in the Lightning Ridge area have exceptionally hard ground from about 2m to 5m down. This hard ground is called silcrete and is too hard for a Caldwell to drill. The silcrete level needs to be drilled and blasted. Usually, depending on the hardness, the Driller drills till until it becomes too hard then lowers ladders down and uses an air drill to drill 6 to 8 blast holes in the silcrete. Sometimes this has to be done up to 4 times before the ground becomes soft enough to continue with the Caldwell.

The-Caldwell-Drilling-Rig bit is basically a large metal bucket with tungsten cutting teeth on the bottom. The operator drills till the bucket is full, raises it to the surface, winches it off to the side and his offsider pulls a release rope and the floor of the bucket opens to empty the dirt.

Every time the bucket is filled the hole is advanced about 300mm.

When the hole is almost to the opal level everyone involved gets anxious because there could be opal come up with the level. When the level is brought up the driller will stop drilling to give the owner of the hole a chance noodle through the dirt in search for opal.

This photo was taken looking down a hole being drilled.

The-Caldwell-Drilling-Rig back to mining industry