mev

It is a bit of a special situation having to do with opals.

Coober Pedy is in an area with naturally occurring opals. Many of these are found in seams some 50m-100m below the surface. At the time I visited, Australia had a bit of wild-west spirit where anyone can stake a claim of 100mx100m and then go mining for opals. You can't have more than one (or two?) claims at a time and there were not a lot of large institutional mines. Instead, there were what I called three generation of miners:

1. First generation has a machine to dig a vertical shaft down to the opal field. These are big enough to fit a person and what the signs were warning about. Once they get to the seam, the first generation miners dig horizontally looking for opals. When they think they've mostly exhausted things, they give up their claim.
2. Second generation stakes a claim on some land that already has the vertical holes dug. They go back down to the seams, and using explosives follow those seams a bit further until they think they've exhausted things and give up their claim. Sometimes they bring large amounts of rock to the surface to sift through looking for opals.
3. Third generation stakes a claim on land that has big piles dirt. They have machines that are efficient and go through those large dirt piles once more to find opals that might have been missed.

The net result is in a not very large area, that land has some ~~250,000 mine shafts. Many of them are 1 or 1.5 meters wide and go down 30-100 meters deep. So the signs really do point out a hazard where you want to be careful when wandering around away from the road.


An example of opal mining debris brought to the surface to look for opals


This was already in the museum in 2001 when I took this photo. However the sign was actually used earlier in the town drive in theatre to remind patrons to not drive their trucks directly from the fields to the movies without offloading explosives.