Bobadah Explanatory Notes (1991)

Abstract

Mapping of the regional geology of the Bobadah 1:100 000 map sheet (8233) area included aerial photograph interpretation and ground traverses, complemented by geochemical and isotopic dating. Photographs and Figures, and an appendix on fossils, are included in the Notes. The map sheet area is in the northeastern corner of the Nymagee 1:250 000 map sheet area (cf. Notes on the Metallurgic Map and Mine Data Sheets for that area). The Bobadah region lies within the Cobar Peneplain, with gentle undulating to hilly topography and alluviated areas. Hilly areas are 'controlled' by silicic igneous rocks, more rounded hills are of granite and the subdued topography is underlain by metasediments. Broadly, the rocks form part of the Mineral Hill Synclinorial Zone (within the broader 'Girilambone'Wagga Anticlinorial Zone'), with the Ordovician Girilambone Group overlain unconformably by the Cobar Supergroup. As elsewhere, the Girilambone Group is complex and exhibits poor outcrops. In addition to Devonian granitic intrusions into the Cobar Supergroup the most extensive, but poorly outcropping, granite is the peraluminous mid-late Silurian Erimeran Granite complex (emplaced into the Girilambone Group with localised contact metamorphism). In the Bobadah area two definable formations (Alandoon Chert and Break O'Day Amphibolite) have been recognised in the Girilambone Group: quartz sandstones and pelites (turbiditic) with well-developed cleavage; schists; mafic volcanic rocks; and serpentinite (small body). Regional metamorphism has been low to moderate ' with some intense multiple deformation to higher grades. Rocks of the Cobar Supergroup (Kopyje Group and Tarran Volcanics), have been mapped as forming an elongate strip (NNW'SSE) across the centre of the area. The Kopyje Group includes two silicic volcanic accumulations (Babinda Volcanics and Majuba Volcanics) which interfinger with a (mostly) fine-grained clastic sequence (Balemund Formation). 

Reference

Pogson, D.J. 1991. Geology of the Bobadah 1:100 000 Sheet 8233. 130pp. New South Wales Geological Survey, Sydney.