Magnetotelluric Data in the Delta River Mining District, near the Tangle Lakes area of southcentral Alaska

By Louise Pellerin and Jay Sampson

During the summer of 2002, magnetotelluric (MT) data were acquired at seventeen stations in the Bureau of Land Management (BLM) Delta River mining district in south-central Alaska as shown in Figure 1. Eight stations along profile Line M (M0 ­ M7) form a 37 km northeast trending transect. The nine stations of profile Line G (G2 ­ G10) form a nearly parallel 37 km transect offset 18 km to the west of Line M. The northernmost station of Line M is located in the rugged Delta Mountains east of Rainbow Ridge while the northernmost station of Line G is located just south of the Denali Fault on the west side of Isabela Pass. Both lines are centered along strike of the Amphitheater Mountains with Line M extending south of the Denali Highway.

The MT survey permits interpretation of structures and lithologic packages at depth. Various rock assemblages and structural features are crossed by these transects. MT data obtained in this study in conjunction with magnetic and gravity data were acquired to provide the following information:

1. An estimate of the thickness of the Nikolai basalts in the Amphitheater Syncline.

2. Whether or not the Fish Lake and Tangle ultramafic complexes join at depth or are at different stratigraphic horizons beneath the Amphitheater Mountains Syncline.

3. A determination if there is a deep rooted magmatic feeder or a sequence of sedimentary material beneath the Amphitheater Syncline.

4. The dip and orientation of the Rainy and Broxson Gulch thrust systems.

5. Identification of other structures along the profile.

The purpose of this report is to release the MT sounding data. No interpretation of the data is included.

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