Digitally enhanced Landsat Thematic Mapper (TM) imagery was evaluated as a mapping aid for exploration geology in the Wheaton River District of the southern Yukon. Landsat TM data acquired on September 1986 was digitally processed to enhance lineaments and alteration zones. Geological mapping was conducted at a reconnaissance scale of 1:250 000 for a 45 km by 45 km area centred on the Wheaton District and at a detailed scale of 1:50 000 for the Mt. Skukum Volcanic Complex. Reconnaissance investigations showed that the TM imagery was valuable for detecting and mapping small scale geological lineaments and for recognizing limonitic rocks. The imagery, however, was not useful for identifying or differentiating lithologic units. A further limitation of the imagery was the loss of information in the shadows created by the extreme topography of the region and the low sun angle present at the time of image acquisition. Detailed field investigations conducted on the Mt. Skukum Volcanic Complex showed that edge enhanced Landsat images were capable of detecting most of the previously mapped faults and fractures, and some dikes. Three unmapped and potentially significant lineaments were mapped using the TM imagery. These new lineaments (Vesuvius-Chieftain Hill, Sulphide Creek, and Rhyolite Creek) are probably deep-seated fractures. Alteration zones, primarily iron oxide rich rocks, were also mapped successfully. Attempts at identifying hydrothermally altered rocks failed. Overall, Landsat TM imagery was found to be a valuable tool for mapping geological lineaments and iron oxide alteration zones at scales between 1:250 000 and 1:50 000.
