Geophysical Studies on the Architecture of Large Igneous Systems Hosting Magmatic Ore Deposits Completed
Platinum group elements, also known as PGEs, are a group of elements that have specific properties which make them useful for various applications in industry. One geologic setting that contains large concentrations of platinum group elements is layered mafic intrusions. This project will use new and preexisting geophysical datasets to characterize the internal structure of layered intrusions. Datasets include magnetic, gravity, magnetotellurics, and seismic tomography.
Science Issue and Relevance
Platinum group elements, also known as PGEs, are a group of elements that have specific properties which make them useful for various applications in industry. Even though industry within the U.S. is heavily reliant on platinum group elements, most of the supply comes from areas outside of the U.S. Platinum group elements are generally rare in the earth’s crust, but in specific geologic settings under specific conditions they may be concentrated in amounts high enough to be economically mined. One geologic setting that contains large concentrations of platinum group elements is layered mafic intrusions. Studying the internal structure of these intrusions along with the structure and chemistry of the rocks they intrude provides a better understanding of the mineral resource potential of the intrusion.
Layered mafic intrusions form as magma rises, cools, and crystallizes in the earth’s crust. They have specific chemistry and pattern of mineral crystallization and are often associated with continental rifting events. The Midcontinent Rift system found in the United States has a number of these intrusions; however, the intrusions in this area are not as well studied or understood as other systems around the world.
Methodology to Address Issue
This project will use new and preexisting geophysical datasets to characterize the internal structure of layered intrusions. Datasets include magnetic, gravity, magnetotellurics, and seismic tomography. Analyses completed for better exposed and more thoroughly studied intrusions around the world (Great Dyke, Zimbabawe, Muskox, Canada, and Skaergaard, Greenland) will be used as a starting point to identify key geophysical signatures that correspond with high concentration areas of critical minerals. The same analyses will be completed and applied to the less studied Duluth and Beaver Bay Complex, Minnesota, Mellen Complex, Wisconsin, and Glen Mountains Complex, Oklahoma.
This project will focus on three objectives:
- Characterization of the internal architecture of intrusions with specific attention on the feeder zones.
- Investigation of how proximity to feeder zones may affect both distribution and properties of magmatic deposits.
- Exploration of how crustal structure and geochemistry of the surrounding basement rocks influences the emplacement and geochemistry of the intrusions.
Potential result of our research
The potential for certain magmatic ore deposits is directly related to the internal structure of intrusions; the results of the study will be used to constrain mineral resource potential. Work will focus on intrusions of the Duluth, Beaver Bay, Mellen along with the the Glen Mountains, Oklahoma. The proposed work will also consider how sedimentary basins localize the emplacement of intrusions in the crust and provide sulfur sources leading to deposits within an intrusion.
Project Activities
Characterize known and suspected feeder zones for large layered intrusions: The character, mineralogy, and chemistry of the large layered intrusions vary based on location within the intrusion. Platinum group element concentrations increase near feeder zones, therefore it is beneficial to understand this zone as much as possible. Three dimensional (3D) inversion and advanced geophysical analysis will be used to constrain the physical state, tectonic history, and geodynamic processes of the regions underlying large igneous provinces. 3D views of electrical conductivity variations in the crust and upper mantle will be developed from magnetotellurics studies using existing regional and new detailed data.
Characterize layering of layered mafic intrusions: The potential for certain magmatic ore deposits is directly related to the internal structure of the intrusions. One way to better map the internal structure is to look at the magmatic layering and its relation to feeder zones. For this task, interpretation techniques of magnetic and electromagnetic data previously applied to the Stillwater and Bushveld intrusions will be applied to the Duluth Complex, Minnesota, the Mellen Complex, Wisconsin, and the Glen Mountains Complex, Oklahoma.
Mapping sedimentary basement rocks beneath layered mafic intrusions: Sulfur isotope studies of other magmatic ore deposits indicate that external sources of sulfur are necessary for their formation. However, little attention has been given to mapping the rocks that may be the source of the sulfur or to considering mass balance relations. This task will consider how the sedimentary basin rocks beneath the intrusions localize the emplacement of intrusions in the crust and provide sulfur sources leading to deposits within an intrusion. The Animikie Basin and the Duluth Complex provide an opportunity to model this interaction using preexisting and new electromagnetic and magnetotelluric data.
Advanced Geophysical Characterization of Layered Mafic and Ultramafic Intrusions (2013-2015): Initial studies were conducted to characterize and model the geology and mineral resource potential of layered intrusions in the U.S. based on advanced analysis of geophysical data typically used in exploration (gravity, magnetic, and shallow electromagnetic methods) as well as unconventional data sets (seismic, magnetotelluric) and comparison with the world's largest layered mafic intrusion and source of platinum group elements, the Bushveld Complex in South Africa. Mafic and ultramafic layered intrusions in the U.S. have potential for mineralization that may contain platinum group elements, notably the Stillwater Complex in Montana and the Duluth Complex in Minnesota.
Return to Mineral Resources Program | Geology, Geophysics, and Geochemistry Science Center | Geology, Minerals, Energy, and Geophysics Science Center
Below are other science projects associated with this project.
Critical commodity studies, Stillwater Complex, Montana and Duluth Complex, Minnesota
Below are data or web applications associated with this project.
Magnetotelluric data from Minnesota, Wisconsin, and Upper Michigan, 2015-2019
Principal facts of gravity data from the Stillwater Complex, Montana, 2013-2014 and 2020
Airborne electromagnetic and magnetic survey data, Stillwater Complex, Montana, May 2000 (ver. 2.0, June 2020)
Airborne electromagnetic and magnetic survey data, Stillwater Complex, Montana, May 2000
Below are publications associated with this project.
The 180-km-long Meers-Willow Fault System in the Southern Oklahoma Aulacogen: A potential U.S. mid-continent seismic hazard
3-D Modeling of the Duluth Complex from geophysical data
Geometry of the Bushveld Complex from 3D potential field modelling
Mapping the 3-D extent of the Stillwater Complex, Montana—Implications for potential platinum group element exploration and development
Crustal inheritance and a top-down control on arc magmatism at Mount St Helens
Making it and breaking it in the Midwest: Continental assembly and rifting from modeling of EarthScope magnetotelluric data
The F'derik-Zouerate iron district: Mesoarchean and Paleoproterozoic iron formation of the Tiris Complex, Islamic Republic of Mauritania
Mapping the 3-D extent of the Northern Lobe of the Bushveld layered mafic intrusion from geophysical data
Algoma-, Superior-, and oolitic-type iron deposits of the Islamic Republic of Mauritania (phase V, deliverable 83)
A geologic and mineral exploration spatial database for the Stillwater Complex, Montana
Overview of the magnetic signatures of the Palaeoproterozoic Rustenburg Layered Suite, Bushveld Complex, South Africa
Below are news stories associated with this project.
Below are partners associated with this project.
- Overview
Platinum group elements, also known as PGEs, are a group of elements that have specific properties which make them useful for various applications in industry. One geologic setting that contains large concentrations of platinum group elements is layered mafic intrusions. This project will use new and preexisting geophysical datasets to characterize the internal structure of layered intrusions. Datasets include magnetic, gravity, magnetotellurics, and seismic tomography.
Science Issue and Relevance
Platinum group elements, also known as PGEs, are a group of elements that have specific properties which make them useful for various applications in industry. Even though industry within the U.S. is heavily reliant on platinum group elements, most of the supply comes from areas outside of the U.S. Platinum group elements are generally rare in the earth’s crust, but in specific geologic settings under specific conditions they may be concentrated in amounts high enough to be economically mined. One geologic setting that contains large concentrations of platinum group elements is layered mafic intrusions. Studying the internal structure of these intrusions along with the structure and chemistry of the rocks they intrude provides a better understanding of the mineral resource potential of the intrusion.
Layered mafic intrusions form as magma rises, cools, and crystallizes in the earth’s crust. They have specific chemistry and pattern of mineral crystallization and are often associated with continental rifting events. The Midcontinent Rift system found in the United States has a number of these intrusions; however, the intrusions in this area are not as well studied or understood as other systems around the world.
Methodology to Address Issue
This project will use new and preexisting geophysical datasets to characterize the internal structure of layered intrusions. Datasets include magnetic, gravity, magnetotellurics, and seismic tomography. Analyses completed for better exposed and more thoroughly studied intrusions around the world (Great Dyke, Zimbabawe, Muskox, Canada, and Skaergaard, Greenland) will be used as a starting point to identify key geophysical signatures that correspond with high concentration areas of critical minerals. The same analyses will be completed and applied to the less studied Duluth and Beaver Bay Complex, Minnesota, Mellen Complex, Wisconsin, and Glen Mountains Complex, Oklahoma.
This project will focus on three objectives:
- Characterization of the internal architecture of intrusions with specific attention on the feeder zones.
- Investigation of how proximity to feeder zones may affect both distribution and properties of magmatic deposits.
- Exploration of how crustal structure and geochemistry of the surrounding basement rocks influences the emplacement and geochemistry of the intrusions.
Potential result of our research
The potential for certain magmatic ore deposits is directly related to the internal structure of intrusions; the results of the study will be used to constrain mineral resource potential. Work will focus on intrusions of the Duluth, Beaver Bay, Mellen along with the the Glen Mountains, Oklahoma. The proposed work will also consider how sedimentary basins localize the emplacement of intrusions in the crust and provide sulfur sources leading to deposits within an intrusion.
Project Activities
Characterize known and suspected feeder zones for large layered intrusions: The character, mineralogy, and chemistry of the large layered intrusions vary based on location within the intrusion. Platinum group element concentrations increase near feeder zones, therefore it is beneficial to understand this zone as much as possible. Three dimensional (3D) inversion and advanced geophysical analysis will be used to constrain the physical state, tectonic history, and geodynamic processes of the regions underlying large igneous provinces. 3D views of electrical conductivity variations in the crust and upper mantle will be developed from magnetotellurics studies using existing regional and new detailed data.
Characterize layering of layered mafic intrusions: The potential for certain magmatic ore deposits is directly related to the internal structure of the intrusions. One way to better map the internal structure is to look at the magmatic layering and its relation to feeder zones. For this task, interpretation techniques of magnetic and electromagnetic data previously applied to the Stillwater and Bushveld intrusions will be applied to the Duluth Complex, Minnesota, the Mellen Complex, Wisconsin, and the Glen Mountains Complex, Oklahoma.
Mapping sedimentary basement rocks beneath layered mafic intrusions: Sulfur isotope studies of other magmatic ore deposits indicate that external sources of sulfur are necessary for their formation. However, little attention has been given to mapping the rocks that may be the source of the sulfur or to considering mass balance relations. This task will consider how the sedimentary basin rocks beneath the intrusions localize the emplacement of intrusions in the crust and provide sulfur sources leading to deposits within an intrusion. The Animikie Basin and the Duluth Complex provide an opportunity to model this interaction using preexisting and new electromagnetic and magnetotelluric data.
Advanced Geophysical Characterization of Layered Mafic and Ultramafic Intrusions (2013-2015): Initial studies were conducted to characterize and model the geology and mineral resource potential of layered intrusions in the U.S. based on advanced analysis of geophysical data typically used in exploration (gravity, magnetic, and shallow electromagnetic methods) as well as unconventional data sets (seismic, magnetotelluric) and comparison with the world's largest layered mafic intrusion and source of platinum group elements, the Bushveld Complex in South Africa. Mafic and ultramafic layered intrusions in the U.S. have potential for mineralization that may contain platinum group elements, notably the Stillwater Complex in Montana and the Duluth Complex in Minnesota.
Return to Mineral Resources Program | Geology, Geophysics, and Geochemistry Science Center | Geology, Minerals, Energy, and Geophysics Science Center
- Science
Below are other science projects associated with this project.
Critical commodity studies, Stillwater Complex, Montana and Duluth Complex, Minnesota
Scientific research can make our resource assessments of critical minerals more effective. This project focuses on the Stillwater Complex, Montana, which has rocks enriched in platinum-group elements (PGE), chromium, cobalt, and nickel. Project objectives are to update databases, evaluate new mapping techniques, document new styles of mineralization, and document and support research on the... - Data
Below are data or web applications associated with this project.
Magnetotelluric data from Minnesota, Wisconsin, and Upper Michigan, 2015-2019
This dataset consists of 176 wideband magnetotelluric (MT) stations collected from 2015-2019 across parts of Minnesota, Wisconsin and the Upper Peninsula of Michigan. The U.S. Geological Survey (USGS) acquired these data as part of regional investigations into the geologic and tectonic framework of the area and to support mineral resource investigations. These data have been used to generate a 3DPrincipal facts of gravity data from the Stillwater Complex, Montana, 2013-2014 and 2020
Gravity data were collected during three separate campaigns during July of 2013, August and September of 2014, and September and October of 2020 at 168 sites on and around the Stillwater layered mafic complex in southern Montana. Measurements were taken with Lacoste & Romberg G-64, G-550, and G-161 gravimeters and reduced to obtain the complete Bouguer anomaly, with reference ties to absolute baseAirborne electromagnetic and magnetic survey data, Stillwater Complex, Montana, May 2000 (ver. 2.0, June 2020)
A helicopter-borne electromagnetic/magnetic survey was flown over the Stillwater area, southwest Montana from May 5 to May 16, 2000. The survey was conducted over the Stillwater Igneous Complex, a Precambrian layered mafic-ultramafic intrusion which is characterized by igneous layering. Electromagnetic data were acquired using DIGHEM helicopter-borne electromagnetic system. Magnetic data were collAirborne electromagnetic and magnetic survey data, Stillwater Complex, Montana, May 2000
A helicopter-borne electromagnetic/magnetic survey was flown over the Stillwater area, southwest Montana from May 5 to May 16, 2000. The survey was conducted over the Stillwater Igneous Complex, a Precambrian layered mafic-ultramafic intrusion which is characterized by igneous layering. Electromagnetic data were acquired using DIGHEM helicopter-borne electromagnetic system. Magnetic data were coll - Publications
Below are publications associated with this project.
The 180-km-long Meers-Willow Fault System in the Southern Oklahoma Aulacogen: A potential U.S. mid-continent seismic hazard
We integrate new high-resolution aeromagnetic data with seismic reflection data, well logs, satellite remote sensing, and field observations to provide a regional view of buried and exposed structures in the Southern Oklahoma Aulacogen and to assess their potential for future seismicity. Trends ranging from NW−SE to ∼E−W, peaking at 330° ± 4.5° and 280° ± 3°, dominate the magnetic lineaments of thAuthorsBrandon F. Chase, Folarin Kolawole, Estella A. Atekwana, Brett M. Carpenter, Molly Turko, Mohamed Abdelsalam, Carol A. Finn3-D Modeling of the Duluth Complex from geophysical data
The Mesoproterozoic Duluth Complex in northeastern Minnesota is one of the major plutonic components of the Midcontinent Rift System and hosts a variety of copper-nickel sulfide and platinum-group element deposits. The Duluth Complex is composed of a series of individual mafic and felsic intrusions emplaced 1110-1098 Ma within Paleoproterozoic sedimentary rocks of the Animikie basin and volcanic fAuthorsDana E. Peterson, Paul A. Bedrosian, Carol A. FinnGeometry of the Bushveld Complex from 3D potential field modelling
A full three-dimensional (3D) potential field model of the central and southern Bushveld Complex reveals information about the Complex in areas obscured by younger geological cover. Previously, two-dimensional gravity models and a few magnetic models limited to certain sections of the Bushveld Complex have been used to propose geometries for the Rustenburg Layered Suite, especially in the westernAuthorsJanine Cole, Carol A. Finn, Susan J. WebbMapping the 3-D extent of the Stillwater Complex, Montana—Implications for potential platinum group element exploration and development
Geophysical models characterize the exposed and interpreted buried extent of the Stillwater Complex, critical for understanding the origin of the layered mafic intrusion and its associated high-grade platinum group element resources. The 3D models, constrained by gravity, magnetic, xenolith, seismic, borehole, and rock property data indicate that the likely maximum extent of the Stillwater ComplexAuthorsCarol A. Finn, Michael L. Zientek, Heather L. Parks, Dana E. PetersonCrustal inheritance and a top-down control on arc magmatism at Mount St Helens
In a subduction zone, the volcanic arc marks the location where magma, generated via flux melting in the mantle wedge, migrates through the crust and erupts. While the location of deep magma broadly defines the arc position, here we argue that crustal structures, identified in geophysical data from the Washington Cascades magmatic arc, are equally important in controlling magma ascent and definingAuthorsPaul A. Bedrosian, Jared R. Peacock, Esteban Bowles-Martinez, Adam Schultz, Graham HillMaking it and breaking it in the Midwest: Continental assembly and rifting from modeling of EarthScope magnetotelluric data
A three-dimensional lithospheric-scale resistivity model of the North American mid-continent has been estimated based upon EarthScope magnetotelluric data. Details of the resistivity model are discussed in relation to lithospheric sutures, defined primarily from aeromagnetic and geochronologic data, which record the southward growth of the Laurentian margin in the Proterozoic. The resistivity signAuthorsPaul A. BedrosianThe F'derik-Zouerate iron district: Mesoarchean and Paleoproterozoic iron formation of the Tiris Complex, Islamic Republic of Mauritania
High-grade hematitic iron ores (of HIF, containing 60-65 wt%Fe) have been mined in Mauritania since 1952 from Superior-type iron deposits of the F'derik-Zouerate district. Depletion of the high-grade ores in recent years has resulted in new exploration projects focused on lower-grade magnetite ores occurring in Algoma-type banded iron formation (of BIF, containing ca. 35 wt% Fe). Mauritania is tAuthorsCliff D. Taylor, Carol A. Finn, Eric D. Anderson, Dwight C. Bradley, Mohamed Joud, Ahmed Taleb Mohamed, John D. Horton, Craig A. JohnsonMapping the 3-D extent of the Northern Lobe of the Bushveld layered mafic intrusion from geophysical data
Geophysical models image the 3D geometry of the mafic portion of the Bushveld Complex north of the Thabazimbi-Murchison Lineament (TML), critical for understanding the origin of the world's largest layered mafic intrusion and platinum group element deposits. The combination of the gravity and magnetic data with recent seismic, MT, borehole and rock property measurements powerfully constrains the mAuthorsCarol A. Finn, Paul A. Bedrosian, Janine Cole, Tshepo David Khoza, Susan J. WebbAlgoma-, Superior-, and oolitic-type iron deposits of the Islamic Republic of Mauritania (phase V, deliverable 83)
High-grade hematitic iron ores (or HIF, containing 60–65 percent Fe) have been mined in Mauritania from Superior-type iron deposits since 1952. Depletion of the high grade ores in recent years has resulted in a number of new projects focused on lower grade magnetite ores in Algoma-type banded iron formation (or BIF, containing approximately 35 percent Fe). Large deposits of oolitic-type iron oresAuthorsCliff D. Taylor, Carol A. Finn, Eric D. Anderson, M. Y. Joud, M. A. Taleb, John D. HortonA geologic and mineral exploration spatial database for the Stillwater Complex, Montana
The Stillwater Complex is a Neoarchean, ultramafic to mafic layered intrusion exposed in the Beartooth Mountains in south-central Montana. This igneous intrusion contains magmatic mineralization that is variably enriched in strategic and critical commodities such as chromium, nickel, and the platinum-group elements. One deposit, the J-M Reef, is the sole source of primary production and reserves fAuthorsMichael L. Zientek, Heather L. ParksOverview of the magnetic signatures of the Palaeoproterozoic Rustenburg Layered Suite, Bushveld Complex, South Africa
Aeromagnetic data clearly delineate the mafic rocks of the economically significant Bushveld Igneous Complex. This is mainly due to the abundance of magnetite in the Upper Zone of the Rustenburg Layered Suite of the Bushveld, but strongly remanently magnetised rocks in the Main Zone also contribute significantly in places. In addition to delineating the extent of the magnetic rocks in the complex,AuthorsJanine Cole, Carol A. Finn, Susan J. Webb - News
Below are news stories associated with this project.
- Partners
Below are partners associated with this project.