What you will learn from this earthcache
- Understanding the geological processes that lead to the formation of opals.
- Identifying different types of mines and their characteristics.
- Appreciating the human endeavor involved in mining opals at Coober Pedy.
Logging Requirements:
To log your visit to this EarthCache, please send me a message with the answers to the following questions:
- How has the process of opal formation contributed to the types of mines used at Coober Pedy.
- Identify and describe two types of mine holes that can been at the listed coordinates.
- Explain the challenges faced by miners.
- Describe safety measures taken around mine holes and their importance.
Opal formation:
Welcome to Coober Pedy, the opal capital of the world! This unique town is renowned for its underground homes and, more importantly, its rich opal mines. Opal is a precious gemstone that forms in sedimentary rock and is valued for its stunning play of colors.
Coober Pedy's opal deposits are a result of millions of years of geological processes. The region was once covered by a vast inland sea. As the sea retreated, silica-rich solutions filled the voids and cracks in the rocks. Over time, these silica solutions solidified to form opal. The unique combination of sedimentary processes and the presence of silica has made Coober Pedy one of the most prolific opal mining areas in the world.
Opal mining:
The opal level at Coober Pedy ranges from between 3m and 25m feet below the surface.
Shaft and Tunnel
Vertical shafts are sunk to the opal level and horizontal tunnels are made by following the track of the opal. Traces of opal are followed by horizontal tunneling. A tunnelling machine is lowered down the shaft in two pieces and assembled down below. As the machine moves forward, the waste is screwed backward and removed by the blower, which acts like a big vacuum cleaner. The blower brings the dirt up to the surface. When the operator sees opal or hears the sound of metal on glass, he will immediately stop the machine. The area is then worked by hand.
Open Cut
Instead of the shaft and tunnel process, some miners use another technique called ‘bulldozer opal cut’. A bulldozer and excavator are used to remove the sandstone. When the opal level is reached, one or more miners who are called checkers, follow closely behind the bulldozer looking for the traces of opal in the sandstone.
Opal mining is a dangerous venture, especially for those working alone. Tunnels often don't have enough oxygen, and cave-ins may occur. Sudden storms can also flood them. Workers face extreme heat above ground and claustrophobia below ground.
Additional Information:
- Please respect the environment and follow all safety guidelines during your visit.
- Photography is encouraged, but be mindful of any restrictions regarding mine operations and safety.