look at this tech explorer, page-7

Hi Towie.One main reason that results are not raining from the sky is that it is so good that those with leases are reluctant to give up equity to have these surveys over their patch.However,as exploration becomes more expensive and deposits more elusive and finance more expensive......the hi-tech will have to be used.No doubt BHPB will laugh all the way to the bank,owning the basic tech.It is interesting that Mark Creasey and Apex Resources are using gravity surveying over their 6500 sq km exploration to identify targets.M.C. is not known for wasting money and has done the gravity survey at ground level which is time consuming and expensive but you are able to retain your equity in the project.3 hours air time would probably be the time to do most surveys compared to many months on land.I'm sure this technology will turn up another Olympic Dam deposit so it is essential to follow where it is being employed.

some web sites
http://www.bhpbilliton.com/bbContentRepository/Presentations/May2003BaseMetalsHoustonpart2.pdf
http://www.minesite.com/archives/features_archive/2003/June-2003/falcon270603.htm