Data Compilation of United States Steel Corporation (USSC) Exploration Records in Minnesota

Abstract

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.