Geological mapping in the Sussex area (Cobar region, New South Wales) highlights Ordovician to Early Devonian tectonics and mineral prospectivity

Abstract

Recent mapping by the Geological Survey of New South Wales in the Cobar district has led to an improved understanding of the Ordovician and Siluro-Devonian rocks. Mapping to date has been undertaken in the Sussex area, centred approximately 50km northeast of Cobar. The Ordovician Girilambone Group turbidite package has been subdivided, on the basis of lithological associations and conodont assemblages in cherts, into a separate Early Ordovician package and a Middle to Late Ordovician package. The depositional relationship between these two packages is not clear but an unconformity cannot be ruled out. The mapping has also confirmed the existence of slivers of Siluro-Devonian Cobar Supergroup rocks within the Sussex area. These occur both unconformably upon and in fault contact with the Girilambone Group. The lithological associations within the slivers are identical, suggesting that the sequence was once a more extensive sheet across the area. The existence of Cobar Supergroup rocks in the Sussex area increases its prospectivity for Cobar-style Au-Cu-Pb-Zn-Ag deposits. Reconnaissance inspections of areas north of the Sussex area suggest that rocks previously mapped as Ordovician may in fact be Cobar Supergroup equivalents, in turn increasing that area?s prospectivity.