Recent Geophysical and Mapping Progress and Implications for Exploration

The Victorian Government through the Department of Agriculture, Energy and Minerals is undertaking a 3-year, $16.5 million Victorian Initiative for Minerals and Petroleum (VIMP) to support the state’s mineral and petroleum exploration industry. Projects being undertaken as part of the initiative include the acquisition of airborne magnetic and radiometric, gravity and regional seismic data, stratigraphic drilling and geophysical interpretation and geological mapping products. Major airborne surveys are being carried out in the north west of the State, the Eastern Highlands and the Otway Basin.

Geological mapping of the highly prospective Lachlan Fold Belt in Eastern Victoria has been hampered by difficult mountainous terrain. High level regional magnetic surveys contribute little to the detailed geological understanding. As part of VIMP, the Victorian Government has undertaking systematic helicopter geophysical helicopter surveys with a line spacing of 200m over an area of 30 000 km in the Eastern Highlands of Victoria to assist the detailed geological mapping required for mineral exploration.

A case study from the Orbost area of the Eastern Highlands illustrates the advances available in geological mapping with the timely collection of detailed airborne geophysics and the implications this has for future exploration in Eastern Victoria. The Orbost magnetic and radiometric data are of a high quality and detailed interpretation enables the production of accurate lithological and structural maps in an area which has significant potential for gold and base metals.

The magnetic data differentiate between various types of volcanics in the Buchan Rift, indicate multiple intrusions, show bedding and faults in many areas within the Palaeozoic sediments, and reveal a previously unknown pervasive west-northwest to northwest fault direction. The radiometric data show compositional differences between the outcropping granites, correlate well with the magnetic data in identifying different types of volcanics in the Buchan Rift, and provide a number of lithological boundaries in areas with little magnetic contrast between the rock types.