Opal Quest Mine
Access point 6, Coober Pedy, South Australia state, Australia
Occurrence
Opal, chalcedony, and gypsum formed in cracks during weathering and diagenesis processes in the Early Cretaceous Aptian (120 Ma) Bulldog Shale of the Marree Subgroup. The Bulldog Shale was formed under shallow marine environment and produces a lot of fossils. Fossils were replaced by opal during the diagenesis process. The Marree Subgroup overlies unconformably the Late Jurassic Algebuckina Sandstone and Paleozoic sediments.
Outcrop of a vein of common opal. The milky blue part is the opal vein. The pale brown host is weathered shale of the Cretaceous Bulldog Shale. Opal veins are parallel to the ground surface. Silica in the Bulldog Shale was dissolved during the weathering process and was precipitated at a underground level. So these veins are traced along the ground surface until they are cut by faults.
Reported Minerals
- Opal
- Opal (after bivalvia fossil)
- Gypsum
Mineral Assemblages
- Opal - Gypsum
- Limonite - Opal
Localities
- Shimo-jinya (Conglomerate, Lithiophorite)
- Mount Orihime (Chert, Lithiophorite)
- Masaka (Chert, Lithiophorite)
- Umoona Mine (Opal deposit)
- Old Timers Mine (Gypsum, Fibrous)
- Opal Quest Mine(Gypsum, Rosette)
- Moon plain (Gypsum, Tabular)
- Jweller's shop noodling area (Chalcedony)