Bedrock Geology of Lake Vermilion/Soudan Underground Mine State Park

Abstract

Lake Vermilion/Soudan Underground Mine State Park possesses a rich cultural and natural history that is directly related to the bedrock geology in this part of Minnesota’s Vermilion District. The bedrock geology comprises a complex record of Neoarchean-age (>2.5 billion years old) volcanic, sedimentary, hydrothermal, structural, and tectonic events associated with the Wawa-Abitibi Terrane within the southwestern part of the Superior Craton (Stott et al., 2007; Stott and Mueller, 2009; Lodge et al., 2013, 2015). Considerable geological research has been conducted since the late 1990s to study the stratigraphy, hydrothermal alteration, structural geology, and economic geology in the Vermilion District (Lawler and Riihilouma, 1997; Hudak and Morton, 1999; Peterson and Jirsa, 1999; Hovis, 2001; Jirsa et al., 2001; Newkirk et al., 2001; Odette et al., 2001; Peterson, 2001, 2005; Peterson et al., 2001; Hudak et al., 2002a, 2002b, 2006, 2007, 2012; Hocker et al., 2003; Peterson and Patelke, 2003; Hoffman, 2007; Jansen et al., 2009; Lodge et al. 2013, 2015). As well, numerous geological field trips have been conducted in this region since the mid-2000s (Hudak et al., 2004, 2014; Jirsa et al., 2004, 2016; Larson and Mooers, 2009; Peterson and Patelke, 2004; Peterson et al., 2009a, 2009b). Although several regional scale geologic maps exist for regions encompassing, and in close proximity to, Lake Vermilion/Soudan Underground Mine State Park (Ojakangas et al., 1978; Sims and Southwick, 1980, 1985; Sims, 1985; Southwick, 1993; Peterson and Jirsa, 1999; Jirsa et al., 2001; Peterson and Patelke, 2003; Hudak et al., 2002b; Hoffman, 2007), no coherent, detailed (1:10,000 scale) geologic map exists for the region comprising Minnesota’s newest state park. Minnesota Department of Natural Resources Parks and Trails staff have partnered with the Precambrian Research Center (PRC) at the Natural Resources Research Institute (NRRI) at the University of Minnesota Duluth to conduct geologic mapping in Lake Vermilion/Soudan Underground Mine State Park since 2010. This partnership had two primary goals: 1) to offer a collaborative opportunity to train upper-level undergraduate and graduate university geology students effective and efficient methods to conduct geologic mapping in Precambrian terranes; and 2) through geologic mapping, gain a deeper understanding of the geological processes and events associated with the development of the Vermilion District within the context of the larger Wawa-Abitibi Terrane. This partnership has led to the development of a new geologic map for Lake Vermilion/Soudan Underground Mine State Park (Peterson et al., 2016) which this report describes.