The geology of the Royal George area

Abstract

The Silurian (?) to Lower Devonian Mathinna Beds have been folded during the Tabberabberan Orogeny and later intruded by the Royal George Granite Complex of probable early Late Devonian age. The Complex is a high level stock, with sharp margins and a narrow contact metamorphic aureole. Its major rock types are coarse-grained granites, porphyries and microgranites, which are alkali-rich and have a low K/Rb ratio. The latter is suggestive of strong differentiation. Low grade tin mineralization is associated with the Complex. A Permian marine and non-marine succession is unconformable on the Mathinna Beds and granite. It is only 150 feet thick over a basement high near Royal George, but thickens to 406 feet at St. Pauls Dome to the west. The basement high may have been above sea level until the time of deposition of the Grange Mudstone Correlate. Silllike (?) Jurassic dolerite intrudes both the Permian strata and the overlying Triassic non-marine, arenaceous sediments. Fluvial and lacustrine (?) sediments may have been deposited behind Tertiary basalt which dammed (?) the South Esk River near Avoca.