Description of the Research Opportunity
Layered mafic-ultramafic intrusions host the world’s largest resources of several critical minerals including platinum-group elements (PGE), Cr, Ni, Ti, and V (Cawthorn and others, 2005). As new technologies are developed, interest has emerged in using ultramafic rocks as reaction chambers for generating geologic hydrogen and for carbon storage (e.g., Blay-Roger and others, 2024; Kelemen and others, 2020). Many layered mafic-ultramafic intrusions include a lower ultramafic section containing Fe-rich silicate minerals (pyroxenes and olivine) that may produce hydrogen or sequester CO2 as a solid mineral during fluid-rock reaction.
The Stillwater Complex of Montana is a 2.7 Ga layered mafic-ultramafic intrusion with an exposed strike length of about 40 km and stratigraphic thickness of 6.5 km. The complex hosts a world-class PGE deposit, called the J-M Reef, and there is a long history of mining for PGE, Cr, and Ni-Cu resources. A large volume of well-exposed, olivine-bearing ultramafic rocks, called the Peridotite zone, are present in the lower part of the Stillwater stratigraphy. These rocks have been identified as a possible future site for geologic hydrogen production or carbon capture and storage (CCS; Smith and others, 2005). The Peridotite zone consists of dunite, harzburgite, and bronzitite cumulates of varying stratigraphic thicknesses (840 m in Chrome Mountain to 2065 m in Mountain View; Raedeke and McCallum, 1984). Along strike, the degree of serpentinization in the Peridotite zone is highly variable, but the least altered rocks are located near the Stillwater River Valley (i.e. Mountain View; Jenkins and Mungall, 2018). These fresh, olivine-rich rocks are in a river valley that excises the complex and where current mining activity provides extensive infrastructure. The thickness of the ultramafic rocks, their low degree of alteration, and the existing infrastructure all make the Stillwater Valley an attractive site for CCS and for producing geologic hydrogen. The total extent of the Stillwater Complex and its Peridotite zone remains poorly constrained at depth and therefore the total volume of ultramafic rock remains unknown. Serpentinization reactions that facilitate both carbon capture and geologic hydrogen are accelerated by increasing temperatures so possible hot and deeply buried parts of the intrusion may provide ideal conditions for driving serpentinization reactions (McCollom and Bach, 2009). Recent gravity modeling proposes that the intrusion may continue under Phanerozoic cover for several 10s of km to the north of the presently exposed outcrop (Finn and others, 2020).
The U.S. Geological Survey’s Mineral Resource and Energy Resource Programs are seeking a Mendenhall research fellow to conduct a deposit scale subsurface characterization of the geology of the Stillwater Complex with an emphasis on the concealed rocks in the vicinity of the Stillwater River Valley. This work will help to constrain the critical mineral (PGE, Ni, Cr), CCS, and geologic hydrogen generation potential of the intrusion. The project will integrate geophysics, geology, and/or thermal modeling to define rock volume, geometry, depths, and temperatures to further our understanding of the concealed rocks as a source of critical minerals, geologic hydrogen, and/or carbon sequestration. Opportunities for geophysical data acquisition and analysis include: 1) interpreting existing seismic lines that transect the eastern part of the Stillwater Complex and areas where it may extend beneath the surface, 2) filling in gaps in gravity data coverage, in proximity to the complex and its possibly buried northeast extension, followed by updated 2-D and 3-D gravity modeling, 3) passive seismic data collection and receiver function calculation to better constrain the thickness and properties of the crust and lower crust, which also impact gravity models, and 4) constrained inversion and forward modeling of existing magnetotelluric data to reduce ambiguity in both spatial and depth extent of the Stillwater Complex and overlying basin sediments. Existing underground workings and drill holes constrain the subsurface geology of the complex in the Stillwater River Valley, but existing and possible new geophysical data can further elucidate the geometry and volume of available complex rocks at depth.
Interested applicants are strongly encouraged to contact the Research Advisor(s) early in the application process to discuss project ideas.
References
Blay-Roger, R., Bach, W., Bobadilla, L.F., Reina, T.R., Odriozola, J.A., Amils, R., and Blay, V., 2024, Natural hydrogen in the energy transition: Fundamentals, promise, and enigmas: Renewable and Sustainable Energy Reviews, v. 189, p. 113888.
Cawthorn, R.G., Barnes, S.J., Ballhaus, C., and Malitch, K.N., 2005, Platinum Group Element, Chromium, and Vanadium Deposits in Mafic and Ultramafic Rocks, in One Hundredth Anniversary Volume: Society of Economic Geologists.
Finn, C.A., Zientek, M.L., Parks, H.L., and Peterson, D.E., 2020, Mapping the 3D extent of the Stillwater Complex, Montana—Implications for potential platinum group element exploration and development: Precambrian Research, v. 348, no. February, p. 105860.
Jenkins, M.C., and Mungall, J.E., 2018, Genesis of the Peridotite Zone, Stillwater Complex, Montana, USA: Journal of Petrology, v. 59, no. 11, p. 1–33.
Kelemen, P.B., McQueen, N., Wilcox, J., Renforth, P., Dipple, G., and Vankeuren, A.P., 2020, Engineered carbon mineralization in ultramafic rocks for CO2 removal from air: Review and new insights: Chemical Geology, v. 550, p. 119628.
McCollom, T.M., and Bach, W., 2009, Thermodynamic constraints on hydrogen generation during serpentinization of ultramafic rocks: Geochimica et Cosmochimica Acta, v. 73, no. 3, p. 856–875.
Raedeke, L.D., and McCallum, I.S., 1984, Investigations in the Stillwater Complex: Part II. Petrology and petrogenesis of the Ultramafic series: Journal of Petrology, v. 25, no. 2, p. 395–420.
Smith, N.J.P., Shepherd, T.J., Styles, M.T., and Williams, G.M., 2005, Hydrogen exploration: a review of global hydrogen accumulations and implications for prospective areas in NW Europe: Geological Society, London, Petroleum Geology Conference Series, v. 6, no. 1, p. 349–358.
Proposed Duty Station(s)
Spokane, Washington
Lakewood, Colorado
Areas of PhD
Geophysics, seismology, geology, or related fields (candidates holding a Ph.D. in other disciplines, but with extensive knowledge and skills relevant to the Research Opportunity may be considered).
Qualifications
Applicants must meet one of the following qualifications: Research Geophysicist or Research Geologist.
(This type of research is performed by those who have backgrounds for the occupations stated above. However, other titles may be applicable depending on the applicant's background, education, and research proposal. The final classification of the position will be made by the Human Resources specialist.)
