DNR Reports 241: (1985-86); Economic Mineralization in the Duluth Complex

DNR Report 241-1: 1985; Saline Waters as Indicators of Economic Mineralization
DNR Report 241-2: 1986; Relationship of Structural Geology of the Duluth Complex to Economic Mineralization
DNR Report 241-4: 1986; Lithogeochemistry of Keweenawan Igneous Rocks

Introduction extracted from Report 241-1 It has long been known that ocean water, fresh water which has interacted with evaporites, evolved connate water in marine sedimentary rocks, and magmatic brines are all effective solvents of base metals, especially at temperatures above 300°C and at pH's below neutrality (White 1981). Because of this fact, it was thought that saline groundwater found in many wells located in the North Shore Volcanic Group and in the Duluth Gabbro Complex, NE Minnesota, might prove to be valuable in locating areas of economic mineralization. It was also hoped that saline groundwater in bedrock aquifers in contact with sulphide mineralization might have anomalously high values of base metals.

Therefore it was proposed to do the following: 1) locate saline wells within the North Shore Volcanic Group and Duluth Complex, 2) sample and analyze waters from these wells and if feasible to establish base-line values of trace metals, 3) sample and analyze saline wells associated with known areas of economic mineralization, 4) compile analyses of potable and not-potable wells from the literature, and 5) establish if there were any relationship between rock type and the incidence of saline wells.

Report 241-2: Relationship of Structural Geology of the Duluth Complex to Economic Mineralization: A final Report to the Minnesota Department of Natural Resources (Resides in Hibbing, MN)
(165 pages, 8.5 x 11 inches, 5 MB)
Authors: T.B. Holst, E.E. Mullenmeister, V.W. Chandler, J.C. Green, P.W. Weiblen

Report 241-4: Lithogeochemistry of Keweenawan Igneous Rocks: A final Report to the Minnesota Department of Natural Resources
(164 pages, 8.5 x 11 inches, 4.12 MB)
Authors: ¹J.C. Green

¹University of Minnesota Duluth, Department of Geology

Purpose and Content of this Study extracted from Report 241-4 (p.4) This investigation is intended to better characterize the chemical composition of Minnesota's Keweenawan igneous rocks as a whole, and also the compositions of significant minerals in some representative intrusive rocks, for the ultimate purpose of a clearer evaluation of their mineral potential. The principal data obtained are chemical analyses, including both major elements and an appropriate array of trace elements depending on the particular rock type and information sought, of carefully selected and prepared samples of the several rock groups discussed above. These analytical results are then discussed in terms of their implications for economic mineral concentrations.

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View or download plates

Report 241-2 Map Plates: Plates 1-3, 5-7: 6 of the 7 maps plates available for view and download in one single file.

(6 pages, various sizes, 25 MB, large file)
Author: MN DNR, Lands and Minerals Division

Georeferenced plates available

Send an email if you would like a zip file containing an ArcGIS File Geodatabase (9.3 and above) which includes the above mentioned map plates georeferenced for view in ArcGIS. The zip file is 150 mb and too large to store on DNR file servers.

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