The Wrightville 1:100000 sheet lies immediately south of Cobar in western New South Wales. Several copper gold mines in the northeast corner of the sheet constitute the southern part of the Cobar Mining Field. The Most of the sheet area is occupied by rocks of the Early Devonian Cobar Supergroup. These rocks are in fault contact with, or unconformably overlie, a basement sequence which consists of ?Cambro-Ordivician-?Silurian deformed turbidites and cherts (Ballast beds) which were intruded by Middle to Late Silurian granitoids. Rocks of the Cobar Supergroup accumulate in shelf areas in the northeast and southwest (Kopyje and Winduck Shelves respectively) but mainly in the deep-water Cobar Basin which occupied most of the sheet area. This basin was fault-bounded to the east and locally to the southwest. It was filled by several submarine turbidite distributary systems. The Nurri Group close to Cobar consists of lithic-rich material shed off basement to the east. The Amphitheatre Group further west consists of quartz-rich material reflecting granitic/vein sources to the northwest, west, and south. A threefold subdivision of the Amphitheatre Group into a lower part (C.S.A. Siltstone and lower Amphitheatre Group reflects progradation and then retreat of submarine fans.
Glen, R.A., 1986. Geology of the Wrightville 1:100000 Sheet 8034. New South Wales Geological Survey, Sydney.