Ground Geophysical Profiles in the Duncan Canal - Zarembo Island Area of the Stikine Geophysical Survey, Southeast Alaska

by: Jeff Wynn, Susan Karl, Bruce Smith, and Anne McCafferty

(Abstract - paper presented at: Alaska Miners Association Annual Meeting, Dec. 1999, Anchorage, AK)

As part of the Stikine Geophysical Survey follow-up study, a series of ground geophysical profiles were acquired during May of 1998. They were acquired on Kupreanof and Zarembo Islands. No profiles were acquired on Prince of Wales Island, Etolin Island, or Groundhog Basin, primarily because of time and resource constraints. Prioritization of the ground follow-up was done by the USGS science team as a whole. The principle objectives for acquiring these profiles were to (1) utilize and expand on an earlier geophysical signature analysis of Admiralty Island to the north (Karl, Wynn, and Taylor, in preparation), (2) develop geophysical characteristics (signatures) of specific geologic units in the Duncan-Zarembo area for subsequent classification, (3) use these results to help identify lithologic transitions under areas of extensive vegetation or mud flats, (4) test the geophysical characteristics (signatures) of known sulfide occurrences in the area, and (5) to verify airborne geophysical anomalies on the ground.

The Duncan-Zarembo science team decided to focus on Triassic rocks in the field area because of their potential to host volcanogenic massive sulfide (VMS) deposits, such as the Greens Creek mine on north Admiralty Island (Newberry and Brew, 1997). The locations for the geophysical profiles were chosen to cross key rock units, structures, and mineral occurrences, in order to identify positions and orientations of geologic contacts, to verify airborne geophysical survey contacts, and to define ground-based geophysical signatures of units to help interpret the airborne geophysical data.

The ground geophysical equipment used during the ground follow-up studies included (1) a total-field magnetometer, (2) a magnetic susceptibility meter, and (3) a VLF-EM resistivity mapping device. The geophysical profiles acquired are listed in Table 1.

Thumbnail map of Zarembo study area with link to larger, 55 Kb, version of the map.

A sketch map of Zarembo Island, located in the center of the study area, with a link to a larger (55 Kb) version of the map.

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Geological-geophysical profiles from Zarembo Island. The top profile illustrates resistivity and magnetic profiles. The bottom profile is a geologic cross section based on interpretation of the geophysical data.

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Index of the Duncan-Zarembo geophysical profiles discussed in this report.
Acquisition	IndexSheet	Profile Name
04 May 98	S.Kupreanof	Woewodski North Coast
05 May 98	N.Kupreanof	Hamilton2Bohemia, east part
06 May 98	S.Kupreanof	Lindenburg
07 May 98	S.Kupreanof	Hang Island - Lindenburg Extension
07 May 98	N.Kupreanof	Hamilton2Bohemia, central part
08 May 98	S.Kupreanof	North Castle Coastline
09 May 98	N.Kupreanof	Hamilton2Bohemia, southwest part
10 May 98	N.Kupreanof	Bruin
10 May 98	S.Kupreanof	Castle Island Short
11 May 98	S.Kupreanof	Little Duncan
12 May 98	S.Kupreanof	Harvey Lake - Olympia Mine
12 May 98	S.Kupreanof	Lost Show
14 May 98	Zarembo	Frenchie Creek CrossLine
14 May 98	Zarembo	Frenchie Creek UpStream
15 May 98	Zarembo	Rd 6592 NW Zarembo (Baht)
16 May 98	Zarembo	Kqd NW Zarembo
17 May 98	Zarembo	Road 6953 NE Zarembo
18 May 98	Zarembo	Road 6594-6590 SE Zarembo

For more information about this work, see U.S. Geological Survey Open-file Report 01-44.