New data, new insights: an example from Western Victoria

Abstract

The aeromagnetic surveys flown under the Victorian Initiative for Minerals and Petroleum and by others give a major regional dataset over western Victoria. This paper presents a new interpretation of the structural and tectonic history for the early Palaeozoic rocks of the region derived from integrating the aeromagnetic, regional mapping and other datasets. It provides a new geological model for exploration beneath the thin Murray Basin cover. Two distinct packages of rocks are present in the western Victorian basement; the eastern Stawell Zone and the western Glenelg Zone. The Stawell Zone contains turbidites and oceanic basalts typical of much of the Victorian Lachlan Fold Belt and which host major gold deposits. They are weakly magnetic with the basalts and pyrrhotitic slates providing most magnetic expression. Recent Ar-Ar dating gives a deformation age of about 435 Ma. Their western boundary is the northern extension of the Moyston Fault. A new tectonic framework is proposed for the Glenelg Zone. Island arc volcanic rocks and metasediments of the Zone have been variably metamorphosed and simply deformed in the 500 Ma Delamerian Orogeny. The rocks lie in a similar structural and tectonic position to those of the Mount Read Volcanics and have potential for VHMS deposits. Correlations can also be made with other Cambrian VHMS deposits and prospective regions in eastern Australia. Along the South Australian border part of the Glenelg Zone, the Ozenkadnook Subzone, contains amphibolite grade rocks that have been complexly folded in a deformation that seems to be earlier than the Delamerian. These rocks are of uncertain affinity, but may be a northern correlative of the upper Proterozoic rocks seen in north-western Tasmania.