Magnetotelluric survey for undercover structural mapping, Central Victoria

Abstract

Over 2% of total world gold production has come from the Victorian gold fields; however, most of the shallow deposits have now been discovered, and new methods are required for exploration beneath the thick sedimentary cover of the Murray Basin. Consequently, as part of the GeoScience Victoria Gold Undercover Initiative, new magnetotelluric (MT) data have now been obtained to provide a greater understanding of potential gold bearing structures extending to mid-crustal and greater depths. Coinciding with part of the 2006 Central Victorian Seismic Survey, a 170 km long MT transect lies within the Bendigo and Melbourne Zones, two of the fault bounded subdivisions of the western Lachlan Fold Belt. Additional transient electromagnetic (TEM) data have now been obtained at each of the MT sites allowing further processing, including compensation for static shifts that are significant in this area. The revised MT section provides an image consistent with the seismic section. The major fault zones align with several dipping conductive slabs supporting the orientation and depth extent revealed by the seismic profile. There is some evidence in the MT data that near-surface geological structures can be extrapolated to mantle depths.

Key words:

• magnetotellurics
• resistivity
• conductivity
• static shifts
• transient electromagnetic
• gold undercover
• Murray Basin
• Western Lachlan Orogen

Acknowledgements

MT data were collected as part of a collaborative project between Monash University, GeoScience Victoria (GSV), the Korean Institute of Geoscience and Mineral Resources (KIGAM) and the Geological Survey of Japan (GSJ), including research funding from KIGAM and GSJ. TEM data were collected in whole by the primary author with assistance from Megan Hough and Jonathon Louey-Gung of Monash University. Comments and suggestions for the manuscript were also gratefully received from Dr Toshihiro Uchida at GSJ, with thanks also to the reviewers of the paper, F. E. M. (Ted) Lilley and one other, whose constructive and helpful comments were much appreciated.