MC Camma, have a look at the report below from BHP 1978.
Page 10 of the report says it all, pretty sure the VEC prospectus makes reference to this BHP report.
http://geodocs.doir.wa.gov.au/viewer/multipageViewerAction.do?documentId=37797&viewMarkId=0&ct=true&at=none&btv=true&atv=false&vmtv=false&ac=ff0000&cabinetId=1200&pg=9&scl=64&bds=0|0|2560|3584