Geological exploration in the western United States by use of airborne scanner imagery

Synopsis

Airborne multispectral scanners have been operational in the western United States since 1985. Imagery has been acquired over known gold producing belts and from potentially prospective areas in Nevada, Oregon and adjacent states. Three scanners have been flown, manufactured by Daedalus, Geoscan and Collins; images from the first two of these have been used for the case histories in this review.

The western U. S. is a mature exploration province with a long history of mineral exploration and exploitation; many ‘discoveries’ in the last decade have been in the vicinity of old workings or prospects. In view of this a successful airborne scanner survey must be able to direct geologists to subtle alteration zones overlooked or disregarded by early prospectors, to mineralised zones within known alteration zones, or to previously undetected and potentially prospective geological structure. Case histories discussed and illustrated here demonstrate that new prospects are being discovered from interpretation of airborne scanner imagery, and new exploration plays can often be generated around existing prospects. Recommendations for the exploitation of archived image data and the planning of future surveys are presented.

This paper reviews methodologies for structural, geomorphic and lithological interpretation of pre-dawn acquired thermal infrared imagery and alteration mapping from mid-day acquired multispectral imagery.

An important new technique which depends on selective input of channels for Principal Component Analysis (PCA), and subsequent input of previously-generated Principal Component images for further PCA, has been developed during this study. The methodology is named the “Crōsta technique”. The images generated by this method are reliable and definitive for alteration mapping from both airborne and satellite multispectral images over the Great Basin area.