Presently, there are no active gold or VMS mines in the Vermillion-Bigfork area, although favorable lithological and alteration mineral associations are present. As well, mineral occurrences of copper, zinc, and gold have been identified. The lack of economic discoveries in northern Minnesota may, in part, represent the difficulty in performing accurate and efficient mineral exploration due to a paucity of outcrops and the local presence of relatively thick glacial deposits.
The Mineral Resources Division of the Minnesota Department of Natural Resources (MDNR) completed a study (Lawler and Riihilouma, 1997) to evaluate the compositions of glacial clasts from gravel pits in the V ermillion-Bigfork area of northeastern Minnesota. This report indicated the presence of mineralized and altered clasts within the glacial drift. Lawler and Riihilouma (1997) have interpreted the mineralization and alteration present in these clasts to be indicative of lode gold and massive sulfide mineralization. At the present time, however, the sources of these clasts remain problematic.
Project 326, "Bedrock and Glacial Drift Mapping for VMS and Lode Gold Alteration in the Vermillion - Big Fork Greenstone Belt" initially set out to define possible source areas for the mineralized clasts areas (MCA's) defined by Lawler and Riihilouma (1997) by means of evaluating bedrock and glacial drift samples in northeastern Minnesota. A total of twenty two diamond drill holes (Table 2, Figure 2) were relogged to: a) better understand the geology (in particular, the physical volcanology) of these regions; b) identify and evaluate the metamorphosed hydrothermal alteration mineral assemblages that occur at each of these prospects; and c) evaluate the potential for volcanogenic massive sulfide (VMS) and/or lode gold mineralization in these areas...
The following report describes the methodology and findings of detailed investigations of selected diamond drill holes from the Five Mile Lake (Soudan Quadrangle, St. Louis County), Eagles Nest (Eagles Nest Quadrangle, St. Louis County), and Quartz Hill (Shagawa Lake Quadrangle, St. Louis County) prospects in the Vermilion district. These investigations have been performed to: a) better understand the geology (in particular, the physical volcanology) of these regions; b) identify and evaluate the metamorphosed hydrothermal alteration mineral assemblages that occur at each of these prospects; and c) evaluate the potential for volcanogenic massive sulfide (VMS) and/or lode gold mineralization in these areas. Diamond drill core logs, petrographic data, and lithogeochemical data performed on samples from the remaining diamond drill holes investigated during this study are contained in Appendices 2, 3, and 4, but are not described in detail during the remainder of the report.
This investigation consists of two parts; 1) a comprehensive study of lithology, alteration, and geochemistry at the Five Mile Lake, Eagles Nest, and Quartz Hill prospects, and 2) an investigation of the utility of glacial drift prospecting in the Vermilion District. This approach to glacial indicator tracing begins with a fundamentally different approach than previous studies. It begins at a known massive sulfide and lode gold prospect in the vicinity of Five Mile Lake. The unique lithologies are then traced in till from known sources. In this manner the lithologic relation between drift and bedrock can be assessed quantitatively. Length scales of dispersal of rock types of different resistance to erosion can be assessed and dilution and comminution coefficients can be calculated. From theses data sampling strategies can be developed that incorporate appropriate spacing for particular lithologic anomalies.
The results of this investigation indicate that the Vermilion District of northeastern Minnesota contains examples of deep water, flow dominated VMS systems (Noranda type), as well as shallow water, volcaniclastic-dominated (Mattabi type) VMS systems. In addition, glacial indicator tracing of lithologic anomalies in till provide an extremely valuable exploration tool.
Report 326 Part A: Discussion of Lithology, Alteration, and Geochemistry at the Five Mile Lake, Eagles Nest, and Quartz Hill Prospects
(139 pages, 8.5 x 11 inches, 6.26 MB)
Authors: 1G.J. Hudak and 2R.L. Morton
Report 326 Part B: The Utility of Glacial Drift Prospecting in the Vermilion District, Minnesota
(78 pages, 8.5 x 11 inches, 2.92 MB)
Authors: 2H.D. Mooers, 2P.C. Larson, and 2B. Shmagin
1University of Wisconsin Oshkosh, Department of Geology
2University of Minnesota Duluth, Department of Geology
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