Bedrock Geology Map of the Nickel Lake Macrodike and Adjacent Areas: Lake County, Northeastern Minnesota

Abstract

This map is the first of what is hoped (contingent on funding) to be a series of new detailed bedrock geology maps of the marginal zone of the South Kawishiwi Intrusion by the University of Minnesota Duluth's Natural Resources Research Institute (see Peterson, 2006). Such mapping will form the basis for continued exploration for Cu-Ni-PGE mineralization as well create the geologic base upon which environmental review associated with exploitation of such mineralization can be built. Recent detailed mapping at a scale of 1:5,000 by the authors was conducted west and south of the Boundary Waters Canoe Area Wilderness (BWCAW). Nearly 1,000 outcrops along approximately 100 kilometers of field traverses were examined to identify and confirm the internal lithologic variability, contact relationships, and structure of the Nickel Lake Macrodike between the BWCAW and Omaday Lake. The authors wish to acknowledge Dr. Paul Weiblen (emeritus professor of geology at the University of Minnesota) for his keen insight of the geology of the area and Dr. George Hudak and undergraduate student Jeremiah Gowey of the University of Wisconsin Oshkosh for assistance in mapping outcrops around and south of Omaday Lake. Additional reconnaissance mapping in early November by the senior author was conducted to field check compiled outcrop locations depicted on the 1957 INCO map of the Spruce Road Deposit and the 1968 Hanna Mining map of the South Filson Creek Deposit (both of which are publically available in the DNR archive at Hibbing, Minnesota). The reconnaissance mapping confirmed the location of gossaneous Cu-Ni bearing INCO outcrops and reconfirmed the outstanding field mapping of all types of Duluth Complex rocks by Hanna Mining Company geologists of the late 1960s (see figure of "Sources of Information"). This map has been built upon (in the areas surrounding depicted outcrops and historic drill holes) the 1966 map of the Gabbro Lake 15' quadrangle by Green et al. (Minnesota Geological Survey Miscellaneous Map M-2), which because of its quality has been the geologic foundation for this area for 40 years. The reader of this map should compare the author's interpretation of the bedrock geology to that depicted on M-2, which will undoubtedly highlight the need for continued detailed mapping of the marginal zone of the South Kawishiwi Intrusion (which was not the purpose of map M-2), especially in light of the greatly increased interest in the potential for exploiting the vast resources of Cu-Ni-PGE mineralization enclosed within these rocks. The Nickel Lake Macrodike is lithologically and structurally related to the South Kawishiwi Intrusion and the known Cu-Ni-PGE deposits of Birch Lake, Maturi, Maturi Extension, Spruce Road, and South Filson Creek. The citation for this map includes the caveat "Version 1", which points out the fact that the authors believe that more detailed geologic mapping and analytical studies (no petrography or geochemical analyses of recently collected samples has been completed) are needed to truly understand what the bedrock geology enclosed within the boundaries of this map sheet (and the area to the west-southwest) really is (ie. we've only begun to scratch the surface). This map and all associated GIS data (in ArcView 3.2 format) can be obtained online at http://www.nrri.umn.edu/egg/publicationlist.html.