Browsing by Subject "Geologic mapping"
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Item An Addendum to: Geology and Sulfide Content of Archean Rocks Along Two Proposed Highway 169 Relocations to the North of Sixmile Lake, St. Louis County, Northeastern Minnesota and Geologic Investigations in the Armstrong Lake Area(University of Minnesota Duluth, 2012) Severson, Mark J; Heine, John JThis report summarizes the geochemical results pertaining to the sulfur contents of rock samples collected in the Sixmile Lake area, and thusly, serves as an addendum to a previous report by Severson and Heine (2010). Geologic mapping in the Sixmile Lake area was initiated at the request of the Minnesota Department of Transportation (Mn/DOT) and concentrated on areas where Highway 169 could potentially be re-routed. The second purpose of this addendum is to provide the appropriate GIS-related shape files that were omitted from the initial report by Severson and Heine (2010). These shape files have been finalized and are provided in this report. In addition, reconnaissance geologic mapping took place along other Highway 169 relocations in the Armstrong Lake/McComber Mine area. The results of that endeavor are provided in this report. The results of sulfur analyses for samples collected from the Sixmile Lake area show that most of the samples with ≥ 0.15% analyzed sulfur contents were correctly mapped as “anomalous sulfide zones” by Severson and Heine (2010). However, there were several instances where the visually-estimated pyrite contents did not compare well with the actual sulfur contents due to a “nugget effect” variation in the third dimension. This “nugget effect” variability is troublesome and suggests that some form of drilling should take place in the areas of future road cuts in order to obtain more representative S% values. Examination of rock exposures and recent drilling of the iron-formation in the vicinity of Shaft #2 in the McComber Mine area indicates that pyrite is present in much higher amounts when compared to Sixmile Lake. Thus, additional drilling will be needed in the McComber Mine/Shaft #2 subarea, and possibly in the Clear Lake subarea, in order to obtain a better understanding of the amount of pyrite present.Item Bedrock Geology of Lake Vermilion/Soudan Underground Mine State Park(University of Minnesota Duluth, 2016-06) Radakovich, Amy; Pignotta, Geoff; Schwierske, Kelly; Students from the 2010-2013 Precambrian Research Center Geology Field Camp; Hudak, George J; Peterson, Dean MLake 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.Item Data Compilation of United States Steel Corporation (USSC) Exploration Records in Minnesota(University of Minnesota Duluth, 2007) Severson, Mark J; Heine, John JAs a major landholder in Minnesota, United States Steel Corporation (USSC) conducted numerous exploration campaigns throughout the state. Until now, much of their explorationrelated information has been filed away in corporate files that were generally unavailable to the exploration community. With the recent sale of most of United States Steel’s mineral rights, this data is now the property of RGGS Land and Minerals, Ltd., L.P. The main objective of this proposal was to obtain permission from RGGS to acquire most of this exploration data, and then organize, compile, and summarize the data in a useable form that could then be transferred to, and open-filed, at the Minnesota Department of Natural Resources (MDNR) office in Hibbing, MN. Over 3,450 items were obtained from the exploration files that include: detailed geologic maps, maps with contoured geophysical results, geophysical profiles, maps showing soil sampling results, drill hole profiles with assay results, geologic cross-sections, and field books. A more complete inventory of these items is included with this report. Most of the data pertaining to 15 airborne surveys, flown for USSC, was acquired as part of this project. An additional four airborne surveys, flown for Marathon Oil Corp. and Kerr McGee Corp., were also acquired. Drill core, along with descriptive lithologic logs, for 24 drill holes was transferred from US Steel’s Minntac facilities to the MDNR. All of these items have been carefully inventoried and were transferred to the MDNR during May and June of 2007. Overall, United States Steel spent a great deal of effort exploring in Minnesota for iron, base metals, and precious metal deposits in the: Mesabi Iron Range; Vermilion Greenstone Belt; Duluth “Gabbro” Complex; Deer Lake Intrusive Complex of Itasca County; Emily Iron District; and portions of the Animikie Basin and Fold-and-Thrust Belt. This report is a dialog that describes not only the materials that were acquired and transferred to the MDNR, but also discusses, to a limited degree, the reasoning behind USSC’s exploration efforts and their end results. The exploration efforts of Marathon Oil in southwestern Minnesota, for uranium, are also discussed. When perusing all of these data, one may ask, “How successful was USSC in their exploration efforts?” Using hindsight, the authors suggest that USSC was moderately successful. They did find several bodies of mineable manganiferous iron ore in the Emily District, and they did find a large resource of oxidized taconite in the western portion of the Mesabi Range. However, both of these discoveries were overshadowed by development of the taconite facilities of Minntac, and they were relegated as less important at the time and subsequently shelved. USSC also found a low grade Cu-Ni deposit in the Duluth Complex that they called the Dunka Road deposit. This deposit was also put on hold during a regional Copper Nickel Study in the 1970s and was also shelved. This deposit, now referred to a the NorthMet deposit, is currently being actively developed by PolyMet Mining Corp., and is now in the environmental review stage prior to seeking mine-related permits. USSC also found several potential Fe-Ti deposits in the Duluth Complex, some of which are currently being looked at again as viable resources. The only areas where USSC failed to turn up anything economically significant are the: Vermilion greenstone belt; Deer Lake Complex of Itasca County; central portion of the Animikie basin (Meadowlands area); Fold-and-Thrust Belt (Aitkin-Carlton County); and west central Minnesota (Morris and Melrose blocks). However, even in these areas, interesting anomalies were located and the mapping and drilling that ensued eventually led to a better geological understanding of these poorly-exposed areas.Item Gafvert Lake Reconnaissance Mapping Project(University of Minnesota Duluth, 2005) Heine, John JItem Geology and Sulfide Content of Archean Rocks Along Two Proposed Highway 169 Relocations to the North Of Sixmile Lake, St. Louis County, Northeastern Minnesota(University of Minnesota Duluth, 2010) Severson, Mark J; Heine, John JItem The History of Gold Exploration In Minnesota(University of Minnesota Duluth, 2011) Severson, Mark JThis report is more or less an atlas with regard to gold exploration in the Archean rocks of northern Minnesota. The main objective of this study is to compile all available information (maps, assays, reports, etc.) from the historical records to produce a “Guidebook” that describes “who did what, where, and how, and what did they find” regarding the gold exploration history of northeastern Minnesota. In essence, detailed “due diligence” checks have been performed in this report, and the results are described for 62 orogenic gold prospects as follows: western Vermilion District with 29 gold prospects; Cook area with nine gold prospects; northeastern Itasca County area with nine gold prospects; Rainy Lake area with four gold prospects; Virginia Horn area with ten prospects; and the Koochiching-Beltrami-Roseau-Lake of the Woods counties area (no significant prospects). Out of 23 gold prospects that were extensively drilled and/or trenched in the western Vermilion District, the best prospects that returned the highest gold values, and collectively the most mineralized zones, are located in the area bordered by the Vermilion Fault and Mud Creek Shear zone. Most of these prospects are associated with subsidiary shear zones and/or rheological contacts on the edges of iron-formation lenses. Shear zone-hosted gold was also explored for in some detail elsewhere in the western Vermilion District at Spaulding Bay, Murray, and Eagles Nest Shear zones. Exploration for gold took place the most extensively, and for the longest period, at the Shagawa Lake stock. There are very few conclusions that can be drawn from the data that are available for the Cook area. The data suggest that the best gold potential is present at the Linden Grove area, where several faults converge and structural preparation would be increased. A review of the gold prospects in Itasca County suggests that significant gold shows are associated with an iron-formation trend in the Wilson Lake sequence. In almost all cases, the high gold values are associated with iron-formation, especially structurally-prepared and sulfide-replaced zones. Glacial overburden sampling campaigns have reiterated this gold-to-iron-formation connection. A review of the exploration activities conducted at the gold prospects in the Rainy Lake area suggests that significant gold anomalies are present within both the “iron-formation” unit of Day (1990) and the Rainy Lake-Seine River Fault Zone. However, the gold values obtained during drilling generally occur as isolated values in a select number of drill holes. Exploration to the west of Rainy Lake in the Koochiching-Beltrami-Roseau-Lake of the Woods area is confined to scattered drill holes that targeted geophysical anomalies. Exploration in the Virginia Horn has to date identified a “small but low-grade” gold deposit associated with a hypabyssal quartzofeldspathic intrusion informally known as the Viking porphyry. Visible gold, often with associated arsenopyrite, is present in quartz veins in the porphyry. However, gold shows are also present in the surrounding rocks, and more drilling is needed to fully assess the potential of the Virginia Horn.Item Igneous Stratigraphy and Mineralization in the Basal Portion of the Partridge River Intrusion, Duluth Complex, Allen Quadrangle, Minnesota(University of Minnesota Duluth, 1997-12) Severson, Mark J; Hauck, Steven AGeologic mapping of the igneous rocks of the Partridge River intrusion (PRI) within the Allen Quadrangle was conducted during the 1996-1997 period by Severson and Miller (1997). In addition to the surface geology, drill holes were logged in order to gain a better understanding of the third-dimensional geology and Cu-Ni mineralization of the quadrangle. Drill hole correlations of igneous units, along with cross-sections and a discussion of Cu-Ni±PGE enriched zones, are presented in this report. Detailed logging of drill core from over 400 drill holes indicates that there are at least seven major igneous units (Units I through VII) within the basal 3,000 feet of the PRI. These units, starting with Unit I at the base, are described in Severson and Hauck (1990) and are reiterated herein for drill holes within the Allen Quadrangle. Also present within the quadrangle and described in this report are late plug-like bodies of Oxide-bearing Ultramafic Intrusions (OUI), a Keweenawan sill within the Biwabik Iron-Formation (K-Sill), and a small Keweenawan(?) intrusive within the Archean rocks near a major fault zone. Establishment of an igneous stratigraphy for the PRI provides a framework that can be used to determine the nature and location of fault offsets between drill holes. The tenor of Cu-Ni mineralization is often locally increased along some of these faults. Fault zones, with or without increased mineralization, that are discussed in this report include faults in the Wetlegs Cu-Ni deposit, faults in the Wyman Creek Cu-Ni deposit, the Siphon Fault, and the Donora Fault. Many of these fault zones are depicted on the cross-sections that accompany this report. Enrichments in Platinum Group Elements (PGE) occur at several stratabound horizons within the Allen Quadrangle (using an arbitrary cutoff of >90 ppb Pd). All of these PGE-enriched horizons are present in sulfide-bearing troctolitic rocks that are positioned immediately below, and in some cases within, laterally continuous ultramafic layers. However, the overall Pd content in some of the horizons shows a definite decrease in an east-to-west direction. This trend suggests that as the magma of the PRI was intruded, in an east-to-west direction(?), it became progressively impoverished with respect to PGEs.