GSV Report 120 - Corryong and parts of Rosewood and Kosciusko 1:100 000 map area geological report

Category: Geological Survey Reports	Product Code: MP-R-28607
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Abstract This report describes the geology of the Corryong 1:100 000 map area, including the Victorian parts of the Rosewood and Kosciusko 1:100 000 map areas (CORRYONG). It provides a summary of the previous work in the area, and describes the physiography, regional geology and geological history of the region. The geophysical interpretation, stratigraphy, intrusive rocks, structural geology, metamorphism and economic geology are described in detail and an assessment of the prospectivity is presented. At the end of the report is a comprehensive list of references, an excursion guide to some of the better exposures, a summary of the geophysical responses of all the rock units, whole rock geochemical data for some of the igneous rocks, a summary of all open file mineral exploration activity, geochemical analyses of rock chip samples and an index.

The geophysical data have greatly assisted the geological mapping. The geophysical characteristics of the rock units are discussed and the structural features evident in the geophysical data are incorporated into the structural synthesis for the map area.

The previous exploration and mining activity are described and an assessment of the prospectivity is presented. There is potential for gold deposits hosted by Ordovician sedimentary rocks, base metal mineralisation in the Silurian granites and Devonian dyke swarms, tin deposits associated with the Silurian S-type granites and fluorite deposits. There is also potential for economic feldspar deposits and dimension stone in the Devonian granites.

CORRYONG is within the Eastern Highlands, a mountainous tract of country covering a large portion of eastern Victoria. There are several wide, flat river valleys cutting into the highlands and draining into the Murray River system.

CORRYONG is in the eastern part of the Lachlan Fold Belt. It is within the Omeo Structural Zone, incorporating parts of the High Plains and Corryong subzones, and the Wagga–Omeo Metamorphic Belt.

The oldest rocks in the map area are Ordovician deep marine sedimentary rocks of the Adaminaby and Bendoc groups. These rocks were folded and faulted, and intruded by large volumes of Silurian–Devonian granite. There are two calderas within the map area, the Mount Burrowa Caldera and the northern part of the Dartella Caldera. The formation of the Mount Burrowa Caldera was preceded by the intrusion of the large Tintaldra Dyke Swarm. Devonian granites intruded the area after the eruption of the caldera.

The geological history of the area involved deposition of a large volume of turbidites in a deep water setting that were then deformed and intruded by granite during the Benambran and Bindian orogenies. A period of extension in the Early Devonian resulted in the formation of the Mount Burrowa and Dartella calderas of the Cravensville Igneous Province. The area was deformed again during the Tabberabberan Orogeny. Erosion has been the most important geological process since the Devonian, except for a period of extension and uplift at about 100 Ma, related to the breakup of the Gondwana supercontinent.
The structural history involves deformation, metamorphism and intrusion in the early Silurian Benambran Orogeny, followed by southward transport of the Omeo Zone during the Bindian Orogeny. Post-early Devonian deformation produced a series of mostly north- to northeast-trending faults associated with cataclasites and alteration zones, and probably reactivated existing NNW-trending faults. Much later movement, followed by erosion, led to large relief changes across some of the northeast trending faults, such as the Walwa Fault.

Bibliographic reference Simpson, C.J., Hendrickx, M.A., Bibby, L.M., Allen, R.J., Page, D.J. , Woodfull, C.J., Fergusson, C.L. & Carney, C.M. 2001. Corryong and parts of Rosewood and Kosciusko 1:100 000 map area geological report. Geological Survey Report 120.