QUANTITATIVE GEOPHYSICAL INTERPRETATION OF AIRBORNE ELECTROMAGNETIC SURVEY DATA, STYX RIVER AREA, ALASKA

Mineralization in the Styx River area of south-central Alaska consists of porphyry deposits, plutonic complexes, dike swarms, and volcanic fields exposed intermittently along the Styx River headwaters in the western Alaska Range. Active exploration targets include porphyry copper ± molybdenum ± gold, reduced intrusion-related gold, and polymetallic vein deposit types.

Two helicopter airborne electromagnetic (AEM) surveys have been flown over the Styx River area by the Alaska Division of Geological & Geophysical Surveys (DGGS), one in 2008 and a second block in 2013, covering an area of 2300 square kilometers. These surveys are being processed and interpreted as part of a larger joint project between the US Geological Survey (USGS) and the DGGS to add value to these data for geologic interpretation by performing advanced interpretation methods on the wealth of public-domain DGGS AEM datasets.

These data consist of frequency-domain DIGHEM V surveys which can be numerically processed and interpreted to yield a three-dimensional model of electrical resistivity. We describe the numerical interpretation methodology (inversion) in detail, from quality assessment to interpretation. We show two methods of inversion used in these datasets, deterministic and stochastic, and describe how we use these results to define calibration parameters and assess the quality of the datasets. We also describe the difficulties and procedures for combining datasets acquired at different times.

Ultimately, we present a regional scale 3D voxel model of the Styx River area along with a targeted model of the Copper Joe prospect, in the southeastern section of the survey area. We provide geophysical interpretations of both to present the differences in interpretation of a regional scale dataset versus a targeted survey.