ALASKA AIRBORNE-GEOPHYSICAL/GEOLOGICAL MINERAL INVENTORY PROGRAM: INTEGRATING AIRBORNE GEOPHYSICAL SURVEYS, GEOLOGIC MAPPING, AND MINERAL-RESOURCE ASSESSMENTS

The Alaska Airborne-Geophysical/Geological Mineral Inventory (AGGMI) program was established in 1992 to acquire geophysical and—where feasible—geological data for about 63,000 square miles of State-interest land with perceived high mineral potential. The program is funded by the State of Alaska and run by the state Division of Geological & Geophysical Surveys (DGGS). Standard products include airborne magnetic and electromagnetic data flown with one-quarter-mile (400 m) line spacing, inch-to-mile geologic maps, and geochemical and geologic reports. To date, more than 16,650 square miles of high-mineral-potential State-interest land have been geophysically surveyed and 6,600 square miles have been geologically mapped through this program. The AGGMI program provides geophysical and geological data to guide mineral exploration work and resource management. At least one major ore deposit in Alaska was found using the geophysical data and new geologic mapping produced by DGGS. Products are available to the public at nominal prices, and digital data are available for free through the DGGS website (www.dggs.alaska.gov/).

Integrating geophysical data with detailed geologic mapping significantly improves geologic map interpretations. Many areas of Alaska contain <5% bedrock outcrop, and use of the geophysical data before, during, and after geologic field work enables extrapolation of geologic units, structures, and ideas within and beyond survey boundaries. Various imaging techniques, unsupervised/supervised statistical classifications, and other methods targeting specific characteristics of geophysical ± geological data expand our ability to identify probable faults and map units, make preliminary comparisons between areas, and identify potential mapping inconsistencies. In addition to geologic field mapping, the DGGS obtains geochemical, geochronological, petrographic, and other geologic data. All datasets are then used to determine an area’s geologic framework and to develop appropriate mineral deposit models. The DGGS Council project on the Seward Peninsula, Alaska, is used to demonstrate these process steps.