Severson, Mark JHauck, Steven AHeine, John JFosnacht, Donald R2016-07-292017-04-142016-07-292017-04-142012-10https://hdl.handle.net/11299/187095NRRI/TSR‐2012/01, Technical Summary Report, October 2012, (Revised January 14, 2013). Natural Resources Research Institute, University of Minnesota Duluth, 5013 Miller Trunk Highway, Duluth, MN 55811-1442Most 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.en-USGeneral mineral potentialGiants Range BatholithMesabi purchase areaNorthern MinnesotaNatural Resources Research InstituteUniversity of Minnesota DuluthTechnical Report