DNR Report 290: 1991; Aeromagnetic Interpretation Pseudo-Geologic Maps, with Evaluation, in Lake of the Woods and Lake Counties, Minnesota

Project Funded by the Minerals Coordinating Committee Through the Mineral Diversification Program

Introduction extracted from Report 290, page 1:

INTRODUCTION (Shown are Paragraphs 3-6 of 7) ...The Department of Natural Resources (DNR), in a pilot program designed to test the practicality and accuracy of pseudo-geologic maps, selected two areas and contracted with private consultants to interpret the geophysical data and make maps of these areas. The DNR then evaluated these maps using a variety of methods to determine if they were accurate. The two areas were selected where previous work indicated good mineral potential and there is considerable state mineral ownership, but little or no current activity by private industry. One strip of four townships near Baudette, Minnesota, is in a faulted, Archean, granite-greenstone terrain where there are deep glacial deposits and good potential for gold or base metal deposits. The other four township block is in the McDougal Lakes area of Lake County, within the central Duluth Complex where geochemical surveys showed elevated base and platinum group mineral trends in glacial overburden. Glacial cover is not too deep over most of the area (the deepest glacial drift intersected in drill holes is sixty-one feet), and there are some outcrops.


The Baudette Area was mapped by Dr. Allan Spector from Toronto, Canada, who has a broad background in Archean granite-greenstone terranes having gold or base metal mineral potential. Dr. Robert Ferderer of Eagan, Minnesota, who has expertise in geophysical studies of the Duluth Complex, mapped the McDougal Lakes Area. These consultants both have the experience necessary to create pseudo-geologic maps and are familiar with the advanced computerized methodologies that are used.

The Baudette Area pseudo-geologic map was tested using drill hole data not provided to the consultant, ground geophysical traverses over selected features, and independent depth estimates. By withholding some drill hole data, we made the task more difficult and lowered the quality of the product to allow a comprehensive test of the method.

The pseudo-geologic map in the McDougal Lakes Area was tested using a variety of different methods. Six new drill holes were completed in six different map units. These holes were logged and described using thin sections and lithochemistry. Magnetic susceptibility and density measurements were also taken on the core, which has started a database of physical properties of Minnesota lithologies at the DNR. Ground geophysical traverses were done to test selected features. Reconnaissance outcrop mapping with assays was completed in a portion of the map area where a glacial drift pebble count study was also undertaken. The pebble count work was intended to determine if glacial drift pebble composition could be used to infer the lithology of the underlying bedrock in drift-covered areas. The pebble count, thin section, outcrop studies, and drill core logging were done by, or under the direction, of Dr. John C. Green, University of Minnesota - Duluth...


View or download report

Report 290: Report 290: 1991; Aeromagnetic Interpretation Pseudo-Geologic Maps, with Evaluation, in Lake of the Woods and Lake Counties, Minnesota; Baudette area: T157N-160N R33W, McDougal Lakes area: T59N-61N R9W-11W
(145 pages, 8.5 x 11 inches, 6.29 MB)
Authors: T.L. Lawler and E.A. Venzke

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View or download plates

Plate 1: Flight Path Plot Baudette Area
(37.74 x 13.65 inches, full size, 1.17 MB)
Author: Allan Spector and Associates Ltd Under Contract for MN DNR, Division of Minerals

Plate 2: Aeromagnetic Interpretation Baudette Area
(18.88 x 27.83 inches, full size, 1.02 MB)
Author: Interpretation by Allan Spector and Associates Ltd Under Contract for MN DNR, Division of Minerals

Plate 3: Aeromagnetic Data Interpretation for the McDougal Lakes Area, Duluth Complex
(24.45 x 17.45 inches, full size, 970 KB)
Author: Interpretation by Robert J. Ferderer Under Contract for MN DNR, Division of Minerals

Plate 4: Aeromagnetic Data Interpretation of a 12 Township Block Near Baudette
(27.21 x 28.07 inches, full size, 2.23 mb)
Author: Interpretation by Allan Spector and Associates Ltd Under Contract for MN DNR, Division of Minerals


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