Using ground and airborne geophysical methods to constrain geologic mapping, and identify new mineral prospective zones in southeast Alaska

Abstract

Triassic Hyd Group rocks in southeastern Alaska are the most likely target for a volcanogenic massive sulfide (VMS) deposit according to available information. However, because of difficult access and extensive cover, the geology in this region is not well known in detail, and available maps have necessarily been of a reconnaissance nature. Ground and airborne geophysical methods offer perhaps the most cost-effective means for improving the geological mapping, as long as the key geologic units (including the Hyd Group) can be differentiated. This appears to be possible, despite the complication of regional metamorphism which can change both magnetite content as well as resistivity of the key units. Careful selection of ground profiles in areas where the geology is well known has allowed us to develop a geophysical signatures matrix for a large section of southeastern Alaska from Admiralty Island in the north to Prince of Wales Island in the south. We used the ground geophyical signatures with the airborne geophysical data to develop a predictive geophysical model for the key geologic units, and these in turn have been used to substantially modify the earlier geologic maps. This has resulted in an increase of more than 30% in ground now known to be underlain by Triassic Hyd Group rocks, with a concomitant increase in prospective land.