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Geophysics of Iron-Oxide Copper-Gold Systems
Robert J Smith, Greenfields Geophysics, Melbourne, Australia.

in - Porter, T.M. (Ed), 2002 - Hydrothermal Iron Oxide Copper-Gold and Related Deposits: A Global Perspective, PGC Publishing, Adelaide, v. 2, pp 357-367.


   Geophysics is an essential part of most modern mineral exploration programs for iron oxide copper-gold deposits. This paper reviews the important physical properties, which are the basis for the application of geophysical methods, and attempts to illustrate and summarise the ways they have been applied with data and images from major deposits. Some comments are provided on their historical effectiveness and the role of these methods in an overall program, which must use all available data from geology, mineralogy, geochemistry and geophysics.


   Regional magnetic, gravity and radiometric data sets are now readily available in many parts of the world. They are valuable tools to assist in locating prospective areas, associated with magmatic intrusions and major structural controls. Radiometric data may also indicate potassic alteration haloes in areas where the signature is not obscured by excessive cover.
   Specific deposits themselves may or may not have a magnetic signature although they will almost certainly occur in an area of significant magnetic relief. Almost all known deposits in this class do give a significant gravity response but it may be difficult to recognise in areas of complex tectonics or steep terrain.
   IP/resistivity has proven to be the most generally useful of the electrical methods, but it also responds to barren sulphides, if present, and to magnetite and specularite. Consequently it will produce many "spurious" targets. EM methods have been less useful in general, due to the often disseminated nature of the targets, but they should not be ignored. Airborne EM may find more application in the future as new systems develop with improved sensitivity. MT methods should also be applicable, particularly where deep penetration is required, but little data is available.
   These deposits are difficult to categorise and hence there is no generally applicable recipe for successful exploration. It is important to use a range of tools and integrate all available geological, mineralogical, geochemical and geophysical data to understand them.

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