Browsing by Author "Severson, Mark J"

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    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 J
    This 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.
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    The Babbitt Copper-Nickel Deposit: Part B: Structural Datums
    (University of Minnesota Duluth, 1994-09) Severson, Mark J; Patelke, Richard L; Hauck, Steven A; Zanko, Lawrence M
    This portion of the investigation concentrated on determining specific structural and stratigraphic datums within the Babbitt Cu-Ni deposit of the Partridge River Intrusion, Duluth Complex, northeastern Minnesota. Structural datums and footwall lithologies were obtained by relogging the footwall portions of all surface drill holes (391) within the confines of the deposit. Specific lithologies recorded during relogging included depth to: 1) basal contact of the Duluth Complex with the footwall rocks; 2) distinctive units within the footwall Virginia Formation; and 3) top of the underlying Biwabik Iron-formation and the specific iron-formation submembers intersected in drill hole. In addition, 100 surface drill holes were relogged in detail and compared with 166 previously relogged drill holes. The top of Unit I, the main sulfide-bearing igneous unit of the Babbitt deposit, was determined for all 266 drill holes that were relogged. The top of the first significant sulfide-bearing zone (not always the top of Unit I) was also determined for the relogged drill holes. All these datum points are used to generate several contoured surface maps to gain a better understanding of the main structural features present within the Babbitt deposit. The contoured surface for the top of the Biwabik Iron-formation is an excellent means of displaying the major structural features, i.e., the Local Boy Anticline, Bathtub Syncline, and Grano Fault. These same features are evident in the contoured surface of the basal contact and indicate that pre-existing structures in the footwall were important to how the basal portion of the Duluth Complex was emplaced. Datum points within the upper portion of the Duluth Complex also suggest that these structures were reactivated throughout the emplacement history of the Duluth Complex (see discussion in Part C). Some of the structures were also important controls of Cu-Ni mineralization. A contoured surface of the bedrock ledge is also presented for the Babbitt deposit. Several structural features are outlined by the bedrock ledge. A crude subsurface geologic map is also portrayed for the bedrock ledge. In addition, an isopach map of glacial overburden thickness is included in this report.
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    The Babbitt Copper-Nickel Deposit: Part C: Igneous Geology, Footwall Lithologies, and Cross-Sections
    (University of Minnesota Duluth, 1996-03) Severson, Mark J; Patelke, Richard L; Hauck, Steven A; Zanko, Lawrence M
    Twenty-five cross-sections are presented that display the detailed igneous geology for several areas of the Babbitt Cu-Ni deposit. Shown in the cross-sections are the stratigraphic relationships of at least seven major igneous units - Units I through VII of the Partridge River Troctolite Series (PRTS). However, not all seven units are equally present throughout the deposit due to "pinch-out" relationships and lateral gradational rock type changes. In addition to these seven units, three new units are briefly discussed and include the: 1) Bathtub Layered Series (BTLS) of Hauck (1993); 2) Basal Ultramafic Unit (BU Unit) of Severson (1994); and 3) Upper Layered Series (ULS). Small plug-like bodies of Oxide-bearing Ultramafic Intrusions (OUIs) are also locally present within the Babbitt deposit. They intrude the rocks of the PRTS and are often positioned adjacent to, or within, fault zones. Rock types found within the footwall rocks beneath the Complex at the Babbitt deposit are also described. Metamorphic textural variations are described for select units within the Virginia Formation (RXTAL, DISRUPTED, and BDD PO units). These textural variations indicate that the effects of structural deformation, recrystallization, and partial melting are more pronounced than previously thought. The exact origin of the textures is unknown, but is believed to be associated with early stages of Duluth Complex emplacement. Also present within the basal portion of the Virginia Formation are early intrusive rocks that predate emplacement of the Partridge River intrusion (PRI). These early intrusive rocks are referred to as the Virg Sill and "Massive Gray" Unit ("MG" Unit); both are interrelated and are submembers of a single composite sill. At least three major structural features are present in the footwall rocks and include the: Local Boy Anticline, Bathtub Syncline, and Grano Fault (for a more detailed discussion see Part B - Severson et al., 1994). During intrusion of the Partridge River intrusion, specifically during emplacement of the lowest unit (Unit I), the Local Boy Anticline and Bathtub Syncline were important factors controlling how the base of the Complex was formed (see Part B). In addition, these same structures also appear to have been repeatedly reactivated during continued emplacement of the Complex and affected the distribution of specific units within overlying Unit III and the BTLS. Also, the distribution of the "MG" and Virg Sill units are affected by these same two structures. These relationships suggest that reactivation of the structures created "void spaces" into which specific PRTS units were emplaced. The exact details and of this complicated emplacement history have yet to be unraveled.
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    Bedrock Geology Map and Cu-Ni Mineralization Data for the Basal Contact of the Duluth Complex West of Birch Lake, St. Louis and Lake Countiues, Northeastern Minnesota
    (University of Minnesota Duluth, 2004) Peterson, Dean M; Patelke, Richard L; Severson, Mark J
    This map is the outcome of eight days of field mapping by Dean M. Peterson in 2001 (Peterson, 2002e), and 6 days of mapping by the authors in 2002. The discovery of large (hundreds of meters long) gossanous expanses of Cu-Ni mineralized rock in the basal zone of the South Kawishiwi intrusion (SKI) in 2001 (in a historically under-mapped area) lead to the acquisition of funds to complete the subsequent detailed geological mapping that resulted in the publication of this map sheet. The mapping was completed at a scale of 1:3,000 and was concentrated within the Cu-Ni-PGE mineralized horizon immediately east of the basal contact of the Duluth Complex. Three mapping traverses were completed to the west into the footwall Neoarchean Giants Range batholith, and to the east into the unmineralized rocks of the SKI stratigraphically overlying the mineralized zone. The information generated from the detailed geological mapping was integrated with previous work by Phinney (1967), Miller et al. (2001), and Miller et al. (2002c), outside of the corridors of detailed mapping during the final compilation of this geologic map (see Fig. 1). In addition, geologic units intersected in the scattered drill holes in the area (see Severson, 1994) have been projected updip to the surface. The faults depicted on the map are interpreted from analysis of aeromagnetic data, steepening of the dip of the basal contact of the Duluth Complex (Figs. 2 and 3), and topographic lineaments. Digital data will be available online at http://www.nrri.umn.edu/egg/ in the fall of 2004.
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    Compile and Make Digital the Lithologies for all NRRI Drill Logs, with Emphasis on the Duluth Complex Drill Holes (An Addendum to an Earlier NRRI Database)
    (University of Minnesota Duluth, 2009) Severson, Mark J; Oreskovich, Julie A; Patelke, Marsha Meinders
    This report and associated databases are updates on many of the holes that have been recently logged by the Natural Resources Research Institute (NRRI) in the Keweenawan Duluth Complex, the Paleoproterozoic Biwabik Iron Formation of the Mesabi Iron Range, and the Archean Deer Lake Complex of northeastern Itasca County, Minnesota. The main emphasis of this project was to update some of the databases that were presented in an earlier NRRI report (Patelke, 2003) with regard to lithologies in Duluth Complex drill holes that were logged by the NRRI since 2003 (and discussed in Severson and Hauck, 2008). To date, all of the publically available drill holes (except for around 30 drill holes) have now been logged in the Duluth Complex by the NRRI. These 30 holes are all that are missing from either the databases in this report or the databases in Patelke (2003). It is strongly suggested that the databases herein be combined, at the user’s discretion, with corresponding databases in Patelke (2003) in order to make an all- encompassing database for lithologies for all NRRI logged drill holes in the Duluth Complex. A secondary goal of this project was to present a header file database for all the holes that were recently drilled in the Duluth Complex (post-2003). Most of these holes are not yet publically available, but data regarding drill hole locations can be gleaned from abandonment files. Combining Duluth Complex header files in this report with the similar header file in Patelke (2003) could provide an all-encompassing database of locations for all of the holes drilled to date in the Duluth Complex (pre-2010 data). This combining of the data is left to the user’s discretion. Lastly, additional goals of this project (time permitting) were to present lithologic databases for all holes logged by the NRRI in the Mesabi Iron Range and, to a much lesser extent, holes logged by the NRRI in the Deer Lake Complex. The database for the Mesabi Iron Range contains information for almost 300 drill holes (over 5,947 lines of lithologic data) in regard to the lithologic picks pertaining to informal members and submembers of the iron-formation. The data in this file is about 80% complete in that not all of the iron-formation submembers are presented for holes drilled at the Keetac Taconite mine or in the Coleraine, MN, area (the latter holes are discussed in Zanko et al., 2003).
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    Data Compilation of United States Steel Corporation (USSC) Exploration Records in Minnesota
    (University of Minnesota Duluth, 2007) Severson, Mark J; Heine, John J
    As 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.
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    Detailed Bedrock Mapping of Lake Two, Pagami Creek Burn Area Boundary Waters Canoe Area, MN
    (2012-08) Shirley, Jake; Nowariak, Eric; Quigley, Brenna; Haynes, Jon; Severson, Alli; Severson, Mark J
    This map was made by four students from the Precambrian Research Center Field Camp under the supervision of Mark Severson and Jim Miller, and with assistance in the field from Alli Severson. The purpose of this map was to determine contact relationships between the troctolitic, anorthositic, and mixed rock units and re ne the work started by Jim Miller in 1981. This map was produced by detailed field mapping from August 7th through August 10th, 2012. Canoeing allowed access to the best burn areas with good outcrop exposure as shoreline mapping was completed by Jim Miler in 1981. The map was produced at a 1:10,000 scale.
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    Field Guide to the Geology of Precambrian Iron Formations in the Western Lake Superior Region, Minnesota and Michigan
    (University of Minnesota Duluth, 2010) Miller, James D; Cannon, William F; Fralick, Philip W; Severson, Mark J; Ojakangas, Richard W; Larson, Phil; Jongewaard, Peter K; Bird, Jeff; Campbell, Thomas J; Peterson, Dean M; Pointer, James; Marshak, Marvin; Jirsa, Mark Alan
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    Finish Logging of Duluth Complex Drill Core
    (University of Minnesota Duluth, 2007-10) Severson, Mark J; Hauck, Steven A
    From 1988 through 2005, NRRI personnel had logged 955 drill holes from the basal zone of the Duluth Complex. The major result of all this effort was the establishment of igneous stratigraphic packages, which in turn, were used to improve our understanding of the mineralization controls on the Cu-Ni deposits and the distribution of Platinum Group Elements (PGE). However, at the beginning of the biennium there were still over 220 drill holes (226,000 feet of core) that remained to be re-logged from portions of the Partridge River and South Kawishiwi intrusions. The main objective of this proposal was to complete a logging campaign of these remaining holes and establish a complete stratigraphic section for these two intrusions of the Duluth Complex. To date, 224 holes have been relogged for this project totaling 198,979 feet of drill core. This total includes several holes that were recently drilled in the Maturi Extension/Nokomis deposit by Duluth Metals, and several recently found drill cores from the Dunka Pit deposit. All of the newly logged holes, see appendix, are located in eight deposits within the Partridge River and South Kawishiwi intrusions; including a few scattered holes in the Cloquet Lake and Tuscarora intrusions. The vast majority of relogged holes were from the Babbitt/Mesaba deposit due to the incredibly large number of drill holes drilled there in the first place. While this project made a significant dent in the total amount of holes logged at the Babbitt deposit, there are still about 20 holes that yet remain to be logged. In an addendum to this report, these drill holes at the Babbitt deposit will be logged, and an unknown number of additional drill holes at the Maturi Extension will be logged.
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    Finish Logging of Duluth Complex Drill Core (and a Reinterpretation of the Geology at the Mesaba (Babbitt) Deposit)
    (University of Minnesota Duluth, 2008) Severson, Mark J; Hauck, Steven A
    This project was undertaken with the objective to finish logging all drill holes from the basal contact zone of the Duluth Complex. Logging of Duluth Complex holes by Natural Resources Research Institute (NRRI) personnel began in 1989, when Severson and Hauck (1990) defined the igneous stratigraphy for most of the Partridge River intrusion (PRI). During the ensuing years the NRRI logged a total of 955 holes and defined igneous stratigraphic sections for several more intrusions of the Duluth Complex. As of 2005, a remainder of over 220 holes had yet to be logged. At the end of this project, 295 holes, which include some recently-drilled holes, were logged with about 20 holes still to be logged from the far eastern end of the Mesaba deposit. Lithologic logs for most of the holes that have been logged since 1989 are now available on the NRRI Geology Group’s website at www.nrri.umn.edu/egg/. The vast majority of holes that were logged for this project were from the Mesaba (Babbitt) Cu-Ni±PGE deposit, and thus, this report deals mostly with that deposit. A result of logging a large number of holes at the Mesaba deposit indicates that most of the deposit does not exhibit a stratigraphic package that has been recognized within the nearby Partridge River intrusion. This suggests that most of the deposit is situated within another sub-intrusion, informally called the Bathtub intrusion (BTI). The BTI appears to have been fed by a vent in the Grano Fault area on the east side of the Mesaba deposit. Forty-two cross-sections from the Mesaba deposit, showing the geology in over 450 surface holes, are presented in this report. Another 26 cross-sections, showing the geology in 219 underground holes, are also presented for the Local Boy ore zone of the Mesaba deposit. All of these cross-sections are utilized to define the igneous stratigraphy of the BTI and adjacent PRI at the deposit. All publically-available drill holes have now been logged from the Dunka Pit Cu-Ni deposit located in the South Kawishiwi intrusion (SKI). Nineteen cross-sections through the deposit are presented in this report. These cross-sections show the geology, potential Cu-Ni ore zones in the holes, and the down dip extent of potential mineable zones of the Biwabik Iron Formation at depth. Additional areas in the SKI where holes were logged for this project include the Maturi, Spruce Road, and Nokomis deposits. Cross-sections and hung stratigraphic sections are presented, and they show the geology intersected in these newly-logged holes relative to previously-logged holes. Drill holes from two Oxide-bearing Ultramafic Intrusions (OUI) were also logged for this investigation. These logs include ten holes from the Longnose deposit and ten holes from the Water Hen deposit. Six cross-sections through the Longnose deposit are presented in this report. In summary, the holes logged in this investigation have added greatly to our understanding of the geology of basal portions of the Duluth Complex. In some cases, the previously defined igneous stratigraphic sections for the various intrusions have held up remarkably well as additional holes are drilled and logged. Of course, there are always some exceptions to the rule. In other cases, e.g., the Mesaba deposit, as more holes were logged and/or drilled, the igneous stratigraphy had to be modified in order to explain differences in a group of holes that were situated in the BTI versus the nearby PRI. This change serves as an example that definition of igneous units, and modes of mineralization, in the Duluth Complex is an iterative process and has to be continuously refined as more data, in the form of new drill holes, are generated.
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    Generalized Mineral Potential of the Mesabi Purchase Area, Northern Minnesota
    (University of Minnesota Duluth, 2012-10) Severson, Mark J; Hauck, Steven A; Heine, John J; Fosnacht, Donald R
    Most of the Mesabi Purchase is underlain by granitic rocks of the Giants Range Batholith that exhibit an extremely low mineral potential to host a metallic deposit. This low potential is demonstrated by the lack of mineral exploration and other core holes drilled in the area by mineral exploration companies. In fact, the vast majority of drill holes shown in the area are associated with scientific holes drilled by the Minnesota Geological Survey for mapping purposes as a follow-up of regional geophysical interpretations. The copper-nickel-PGE mineralization located to the east in the Duluth Complex does not occur in the Mesabi Purchase area. The various types of geologic terrains, and their mineral potential, albeit low in almost all cases, are listed below: • Giants Range Batholith granitic rocks (pink, purple, and orange units on map): 1. Rare Earth Elements (REEs - unknown, but most likely low to moderate potential in spatially-limited deposits; currently being investigated by NRRI throughout Minnesota); 2. Gold along fault zones or contact zones with Greenstone Belt (unknown potential, but unlikely in spatially-limited deposits); 3. Road Aggregate (crushed rock); and 4. Dimension Stone • Greenstone Belt (North Half of Block – green, pale green, and yellow units on map): 1. Copper-Zinc associated with Volcanic Hosted Massive Sulfide deposits (very low potential overall, with moderate potential in T.61N., R.17W.); 2. Gold associated with shear zones and faulted rock (very low potential overall, with weak potential in T.61N., R.17W.); • Small granitic to syenitic plutons associated with a Greenstone terrain (circular pink units on map) with a low to moderate potential of hosting Rare Earth Elements; 2 • Virginia Horn Greenstone Belt (extreme southeastern corner): 1. Gold associated with a syn-volcanic Quartz Feldspar Porphyry (very low potential that has been tested by three drill holes); and • Mesabi Iron Range (red unit on extreme southern fringe of block): 1. Magnetic Taconite ores (the potential of these ores are negligible as most of the rock has already been mined out at the Minntac West Pit, Minntac East Pit, and Minorca Pit); and 2. Road Aggregate (crushed rock – also negligible as in the above category). 3. Mine tailings for various aggregates, bridge deck surfaces, etc. Detailed Township and Range Descriptions T.61N., R.21W. Metasedimentary rocks of a Greenstone terrain are dominant and exhibit no known, or expected, mineral potential. Small syenitic plutons are present and may have a REE potential, but these are largely unexposed and mostly known from limited outcrops and a single drill hole (scientific/mapping drill hole). No known exploration for any type of mineral deposit has occurred in this township. T.61N., R.20W. Metasedimentary rocks of a Greenstone terrain with no known, or expected, mineral potential. Small syenitic plutons are present and may have a REE potential, but these are largely unexposed. No known exploration for any type of mineral deposit has occurred in this township. T.61N., R.19W. Mostly metasedimentary rocks of a Greenstone terrain (no known potential) with a small amount of mafic volcanic rocks that may have a weak potential of hosting a Cu-Zn or gold deposit. Small syenitic plutons are present and may have a REE potential, but these are largely unexposed. No known exploration for any type of mineral deposit has occurred in this township. T61N., R.18W. Both metasedimentary and mafic volcanic rocks of a Greenstone terrain are the dominant rock types. No known exploration for any type of mineral deposit has taken place in either of these rock types, and the expected mineral potential is extremely low. Granitic rocks of the Giants Range Batholith are present and exhibit a very low potential of hosting a REE deposit. Also present in the western half of the township is the Lost Lake Pluton that has been unsuccessfully explored for gold in the adjacent eastern township. The REE potential of the Lost Lake Pluton is unknown, and this pluton has been recently sampled by the NRRI. T.61N., R.17W. Both metasedimentary and mafic volcanic rocks of a Greenstone terrain are the dominant rock type. Limited exploration for gold deposits has taken place with unsuccessful results (two exploration drill holes with no follow-up). Granitic rocks of the Giants Range Batholith are present and exhibit a very low potential of hosting a REE deposit. Also present in the township is the eastern half of the Lost Lake Pluton that has been unsuccessfully explored for gold (two drill holes), but may exhibit REE potential. 3 T.60N., R.21W. Granitic rocks of the Giants Range Batholith are the most prevalent and may show a very low potential of hosting a REE deposit. A glacial drift covered Greenstone Belt is present along the western edge of the township – it exhibits a low mineral potential as this belt has never been explored by minerals companies (except further to the west). T.60N., R.20W. Granitic rocks of the Giants Range Batholith are the most prevalent. These rocks may exhibit a moderate potential of hosting a REE deposit (geochemistry results are pending in samples collected from three scientific/mapping drill holes). No known exploration for any type of mineral deposit has occurred in this township. T.60N., R.19W. This township is entirely underlain by granitic rocks of the Giants Range Batholith. These rocks may exhibit a moderate potential of hosting a REE deposit (geochemistry results are pending in samples collected from two scientific/mapping drill holes). No known exploration for any type of mineral deposit has occurred in this township. T.60N., R.18W. Granitic rocks of the Giants Range Batholith are the most prevalent. These rocks may exhibit a moderate potential of hosting a REE deposit (geochemistry results are pending in samples collected from two scientific/mapping drill holes). No known exploration for any type of mineral deposit has occurred in this township. T.60N., R.17W. About 70% of this township is underlain by granitic and schistose rocks of the Giants Range Batholith with a moderate potential of hosting a REE deposit (one scientific/mapping drill hole is present). The remaining 30% of the township is underlain by metasedimentary rocks of a Greenstone terrain with a no known, or expected, mineral potential. No known exploration for any type of mineral deposit has occurred in this township. T.59N., R21W. Granitic rocks of the Giants Range Batholith are the most prevalent, but have shown a low potential of hosting a REE deposit to date. A glacial drift covered Greenstone Belt is present in the extreme southern portion of the township – it exhibits a low mineral potential as this belt has never been explored by minerals companies (except further to the west). T.59N., R.20W. This township is entirely underlain by granitic rocks of the Giants Range Batholith. These rocks may exhibit a moderate potential of hosting a REE deposit (outcrop samples have been collected from some exposures to help ascertain this assessment). No known exploration for any type of mineral deposit has occurred in this township. 4 T.59N., R.19W. This township is entirely underlain by granitic rocks of the Giants Range Batholith. These rocks may exhibit a moderate potential of hosting a REE deposit (outcrop samples have been collected from some exposures to help ascertain this assessment). No known exploration for any type of mineral deposit has occurred in this township. T.59N., R.18W. This township is largely underlain by granitic rocks of the Giants Range Batholith. These rocks may exhibit a moderate potential of hosting a REE deposit. A wedge of highly metamorphosed Greenstone is present to the north of the Mesabi Range (on USS owned lands) and may exhibit an extremely low potential of hosting a gold deposit. No known exploration for any type of mineral deposit has occurred in this township. Mined out taconite (USS Minntac Mine) is present along the southern fringe of this township. T.59N., R.17W. This township is largely underlain by granitic rocks of the Giants Range Batholith. These rocks may exhibit a moderate potential of hosting a REE deposit. A wedge of highly metamorphosed Greenstone is present to the immediate north of the Mesabi Range and may exhibit an extremely low potential of hosting a gold deposit. No known exploration for any type of mineral deposit has occurred in this township. Mined out taconite is present along the southernmost fringe of this township (Minntac West Pit, Minntac East Pit, and Minorca Mine). T.59N., R.16W. About 85% of this township is underlain by granitic rocks of the Giants Range Batholith with a moderate potential of hosting a REE deposit. The remaining 15% of the township is underlain by mixed metasedimentary and volcanic rocks of a Greenstone terrain referred to as the “Virginia Horn.” Gold mineralization has been documented in the Virginia Horn in the township to the immediate southwest (T.58N., R.17W.). There has been limited exploration for gold in T.59N., R.16W with unsuccessful results (three drill holes). T.58N, R.19W. About 90% of the township is underlain by the Mesabi Iron Formation and the overlying Virginia Formation. The remaining 10% is underlain by igneous rocks of the Giants Range Batholith with low mineral potential.
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    Geologic and Stratigraphic Controls of the Biwabik Iron Formation and the Aggregate Potential of the Mesabi Iron Range, Minnesota
    (University of Minnesota Duluth, 2009) Severson, Mark J; Heine, John J; Patelke, Marsha Meinders
    The taconite mines on the Mesabi Iron Range of northeastern Minnesota generate millions of tons of mined waste rock annually that could potentially be used as aggregate material in road building projects. Paramount to defining potential aggregate horizons within the mined ironformation is an understanding of the stratigraphy as it relates to mined ore units and waste units at each of the respective taconite mines. However, each mine uses a different submember terminology to designate the various ore and waste horizons. The major emphasis of this investigation was to produce a stratigraphic “Rosetta Stone” of the Biwabik Iron Formation that ties the stratigraphy and differing submember terminology of one mine to all of the other mines on the Mesabi Iron Range. Toward that end, the Natural Resources Research Institute (NRRI) looked at core from over 380 drill holes, and some mine exposures, in the central and western Mesabi Iron Range (Biwabik to Coleraine, MN area) to develop a stratigraphic system that links all of the mined ore and waste submembers. The methodology used in this investigation was to log multitudinous deep drill holes from a single mine, hang all of the drill holes on a common datum (bottom of the Lower Slaty member), and then correlate all of the submembers, as used by that particular mine, making note of bedding features and other unique features that define a particular submember. This same system of “logging, hanging, and correlating” was done at each of the taconite mines (seven different mines/areas along the Mesabi Iron Range) to better understand each mine’s submember terminology. The hung stratigraphic-sections from each mine were then used to collectively make generalized stratigraphic columns for each of the mines. These stratigraphic columns were then added to the “Rosetta Stone” (Plate II of this report) that is used to illustrate how the submembers at one mine correlate with similar submembers at all of the other mines. In the end, this investigation identified 25 major “Rosetta” units that define the stratigraphy of the Biwabik Iron Formation that can be used to link together all of the differing submember nomenclatures from the various taconite mines. This division of the iron-formation into 25 major units, based primarily on their overall bedding characteristics, is applicable to only the central and western Mesabi Iron Range and does not include the more highly metamorphosed iron-formation of the eastern Mesabi Iron Range, e.g., to the east of Aurora, MN.
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    Geologic Mapping And Structural Analysis Of The Peter Mitchell Mine
    (University of Minnesota Duluth, 1996-02) Severson, Mark J
    At least 17 faults are located within the Peter Mitchell Mine. Most of the faults trend north to north-northeast; four faults trend northwest. The faults are near-vertical, with offsets ranging from <5 feet to >50 feet. Thirteen of the faults display a "scissors-type" offset in that the relative displacement along the length of the fault is more pronounced toward one end of the fault. In 10 faults, the amount of offset increases from north to south toward the Duluth Complex. Three faults exhibit increased amounts of offset away from the Duluth Complex. Collectively, the relative motion along the majority of the faults indicate that they were formed (and reactivated?) during emplacement of the Duluth Complex. Five basaltic dikes occur within the mine area. Only one of the dikes occupies a fault zone; the remainder are intruded along various joint sets. The age of the dikes is inferred to be late-Duluth Complex. Several large-scale folds also occur within the mine area. They trend northwest and diminish in intensity away from the Complex, indicating that folding was initiated during emplacement of the Complex.
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    Geological and Geochemical Reconnaissance for Rare Earth Element Mineralization in Minnesota
    (University of Minnesota Duluth, 2014) Hauck, Steven A; Heine, John J; Severson, Mark J; Post, Sara P; Chlebecek, Sara; Monson Geerts, Stephen D; Oreskovich, Julie A; Gordee, Sarah M
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    Geology and Cr-PGE Mineralization of the Birch Lake Area, South Kawishiwi Intrusion, Duluth Complex
    (University of Minnesota Duluth, 1997) Hauck, Steven A; Severson, Mark J; Ripley, Edward M; Goldberg, Steven A; Alapieti, Tuomo
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    Geology and Mineralization of the Serpentine Copper-Nickel Deposit
    (University of Minnesota Duluth, 1994-12) Zanko, Lawrence M; Severson, Mark J; Ripley, Edward M
    A geological model explaining the formation of mineralization at the Serpentine Cu-Ni deposit, located at the western edge of the Keweenawan (1.1 Ga) Duluth Complex near Babbitt, Minnesota, has been developed following detailed re-logging of drill core and compilation of geochemical (Cu-Ni-S) data. The model suggests that sulfide mineralization was influenced by a combination of factors, the most important being localized structural preparation of the Lower Proterozoic (1.8 Ga) Virginia Formation footwall. The drill core provides evidence that faulting and the emplacement of sills (both pre-and/or early-Duluth Complex) were responsible for this structural preparation. Both processes led to weakening and/or fracturing of the footwall, thereby allowing greater magma/footwall interaction to take place in a relatively confined area. This intimate interaction enhanced the genesis and distribution of Cu-Ni sulfide mineralization at the Serpentine deposit. A laterally extensive bedded pyrrhotite unit of the Virginia Formation is believed to have further contributed to the formation of semi-massive to massive sulfides present within the deposit by acting as a local source of additional sulfur (and minor additional Cu and Ni). Additional sulfur isotope work is necessary before an in situ sulfur source can be ruled out, however. A very general igneous stratigraphy has been determined for the Serpentine deposit, based on the idea that at least three distinct magmatic events and/or intrusive styles were responsible. The first (and earliest) contributed to the deposit's sulfide mineralization, due to its extensive interaction with the footwall; its rocks are a heterogeneous, gradational mixture of fine- to medium-grained troctolite, augite troctolite, and norite, loosely confined to the lowest one-half to two-thirds of the deposit. The second event produced rocks of greater homogeneity that are more plagioclase-rich, coarser grained, and relatively sulfide-poor; spatially, they tend to overlie those of the first. A third, but much less volumetrically significant, magmatic event and/or intrusive style probably occurred shortly after the second and was likely related to a faulting episode; it formed rocks that are predominantly ultramafic. Spatially, these ultramafic rocks are largely associated with the more homogeneous plagioclase-rich rocks, frequently occurring as linear sub-vertical bodies. Analytical work shows the platinum group element (PGE) potential of the Serpentine deposit is somewhat limited. The highest value (274 ppb rhenium) occurred in a massive sulfide sample. Only three samples contained more than 100 ppb palladium. Based on these results, the mechanisms and/or conditions for PGE enrichment that were present at the Local Boy deposit were lacking at the Serpentine deposit. A possible explanation is that the Serpentine deposit received additional sulfur from a local source, while the Local Boy deposit formed from a sulfide melt that: 1) formed elsewhere; 2) scavenged more PGEs from a more primitive(?) magma; and 3) moved an undetermined distance before being injected into structure zones, without the addition of local sulfur. Future investigations may shed more light on the apparent differences between these two deposits.
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    Geology and SEDEX Potential of Early Proterozoic Rocks, East-Central Minnesota
    (University of Minnesota Duluth, 2003) Severson, Mark J; Zanko, Lawrence M; Hauck, Steven A; Oreskovich, Julie A
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    Geology and Structure of a Portion of the Partridge River Intrusion: A Progress Report
    (University of Minnesota Duluth, 1988-09) Severson, Mark J
    Studies of the basal contact of the Partridge River intrusion, as deduced by compilation of all drill hole data and relogging of 37 drill holes, has indicated more structμre than previously recognized. Structure contour maps of the footwall rocks have been prepared showing the nature of the basal contact, the top of the Biwabik Iron-Formation, and the thickness of the Virginia Formation beneath the Partridge River intrusion. These data indicate that preexisting folds in the basement rocks at both Minnamax and Dunka Road exerted a strong control over the form of the base of the intrusion. Several northeasttrending normal faults and northwest-trending strike-slip(?) faults were al so delineated in this study which supports the half-graben model proposed by Weiblen and Morey (1980). A northeast~trending pre-Keweenawan fault has also been located in the Wetlegs area. Along this fault an inferred window of Biwabik Iron Formation is in direct contact with the Partridge River intrusion. Three oxidebearing ultramafic bodies {Longnose, Longear, and Section 17) are exposed at the surface along this zone. The spatial location of oxide-bearing ultramafics to areas where the iron formation is in direct contact with the Duluth Complex suggests that they may be genetically related. At least five major units within the basal portion of the Partridge River intrusion have been delineated for the Wetlegs area. They are present in 23 drill holes at Wetlegs and extend northeast into the Dunka Road Cu-Ni deposit and southwest into the Wyman Creek Cu-Ni deposit. From the base up, these units are characterized by: sulfide-bearing augite troctolite {175-1570 ft. thick); troctolite with abundant layers of picrite (melatroctolite), peridotite and dunite (450 ft. thick); a 250 ft. thick, fine-grained, mottled-textured troctolitic anorthosite ("marker bed" for the area); augite troctolite (400 ft. thick); and augite-bearing anorthositic troctol ite (250 ft. thick). To the northeast and southwest of Wetlegs, most of these units are present but the omission of particular units in either direction indicates an irregular stacked pattern. Establishment of an internal stratigraphy has provided an excellent opportunity to: 1) study the nature of any structural discontinuities present within the intrusion, 2) determine the extent and variability of intrusive lithologic units, 3) more fully understand any background geochemical variations that may be present within and between the l i tho logic units, and 4) better understand the origin of the Partridge River intrusion, the various Cu-Ni, CuNi- Ti and Fe-Ti deposits and their relationship to the origin of the Duluth Complex.
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