NEW PROCESSING OF AIRBORNE ELECTROMAGNETIC AND MAGNETIC SURVEY DATA FROM SELECTED AREAS IN ALASKA

Public-domain airborne geophysical surveys (combined magnetics and electromagnetics), mostly collected for and released by the State of Alaska, Division of Geological and Geophysical Surveys (DGGS), are a unique and valuable resource for geologic interpretation and geophysical methods development. A new joint effort by the United States Geological Survey (USGS) and the DGGS aims to add value to these data through the application of newly developed advanced inversion methods and through innovative maps, interpretative profiles and displays. Our goal is to make these geophysical data even more valuable for interpretation of geologic frameworks and application to geotechnical studies.

The DGGS program for data collection and distribution has released data annually beginning in 1994, 39 individual surveys have been released to the public and with 4 more to be released. The locations of the DGGS surveys were mainly selected to increase mineral exploration interest in areas suggested by Alaska’s mineral industry and Native regional corporations. The primary focus of the DGGS program has been on timely geophysical data release with emphasis on mineral exploration targets and includes follow-up detailed geologic mapping. In addition to the DGGS surveys, some additional datasets collected by the Bureau of Land Management, the USGS, and other entities are also included in our work.

The USGS has recently developed new data processing (inversion) methods for both airborne EM data and aeromagnetic profile data. New data processing has been started in four of the DGGS survey areas (Fortymile40/Good Pasture, Styx, Alaska Highway, and Nome). In addition to apparent resistivity maps provided by the original contracts, new products from the EM data include resistivity depth sections along profiles used to produce maps of resistivity depth and elevation slices. Processing of magnetic data has resulted in susceptibility depth sections as well as enhancement of near surface and deep sources that better relates the spatial correlation of the two types of data. The resulting resistivity and magnetic susceptibility depth sections integrated with map products such as depth or elevation slices and trend analysis can be used in a wide variety of geologic and tectonic framework studies.