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- Title
Queensland Precious Opal Deposits and Associated Critical Mineral Enrichment within Silicified Palaeochannels.
- Authors
Senior, Brian R.; Deveson, Byron J.
- Abstract
Queensland boulder opal host rocks were investigated and geochemical markers identified that are indicative of the presence of precious opal. Artesian groundwater migrating and accumulating in sandstone palaeochannels was subject to changes in pH, leading to opalisation within structural and stratigraphic permeability barriers. This process was accompanied by accumulation of several rare earth elements, elevated base metals, scandium, vanadium and possible occurrences of silver, palladium and gold. Alkaline groundwater moving surfacewards by capillary or fracture porosity and permeability from aquifers in the Eromanga Basin sequence, scavenged metals from 'basement' and from enclosing rocks that contain disseminated pyrite. During deep chemical weathering in the late Oligocene and early Miocene (Canaway profile), mixing of alkaline aquifer and meteoric acid groundwater led to complex pH changes. Colloidal silica and other substances were precipitated within former organic-rich, sedimentary rock layers within the palaeochannels.
- Subjects
OPALS; STRATIGRAPHIC geology; PERMEABILITY; POROSITY; AQUIFERS
- Publication
Australian Gemmologist, 2023, Vol 28, Issue 4, p190
- ISSN
0004-9174
- Publication type
Article