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The United States needs to improve access to commodities that are critical to the functioning of our society and economy. The platinum-group elements are identified as critical commodities (Fortier and others, 2018) and have a role to play in battery and clean-energy technology (U.S. Department of Energy, 2021). PGE have been listed as critical commodities for the United States for over 100 years; PGE deposits have been characterized and the scientific consensus on their origin has not changed substantially in decades. What research, after 100 years of work, can be done that will give us a new insights and perspective?
PGEs are produced from magmatic ore deposits which formed from sulfur-rich liquids that segregated from a silicate magma and crystallized. Most of the world’s production comes reef-type PGE deposits, in which PGE-enriched sulfide minerals are concentrated in thin rock layers (meters thick) in mafic-to-ultramafic layered intrusions that are thousands of meters thick. The J-M Reef, in the Neoarchean Stillwater Complex, Montana, is the highest-grade reef-type deposit in the world and will be the primary focus of the study.
Numerical modeling studies using MELTS, parameterized by mineralogical and geochemical data from reef-related rocks, propose that the PGE mineralized rocks of the J-M Reef formed by variable amounts of infiltration and reaction of a hot, contaminated komatiitic liquid with mushy footwall cumulates that were themselves crystallized from a lower crustally contaminated komatiite liquid. The model proposes infiltration of fresh, undepleted magma that upgrades, resident, moderately PGE-rich sulfide liquid in the footwall gabbronorite cumulates while dissolving pyroxene and feldspar and crystallizing olivine to form the olivine-bearing rocks of the Reef Package that host the J-M Reef. This model accounts for the unconformable relationship between the olivine-bearing rocks of the Reef Package and the underlying footwall stratigraphy and produces the extremely high PGE concentrations of J-M Reef sulfides.
The postdoctoral fellow (PDF) will conduct field-based studies to collect information to test the thermodynamic models in the field and extend the modeling to different mineralized layers. The PDF will design a research effort to search for textural, mineralogical, and compositional evidence of melt infiltration and reaction in Stillwater cumulate rocks. Emphasis will be placed on rocks associated with the J-M Reef but other rock units in the Stillwater Complex that may formed by a similar process can be studied. The PDF will be asked to extend thermodynamic numerically modeling of the PGE-enriched layers in the Stillwater Complex. Whole rock geochemistry and mineral chemistry will be needed to parameterize the model.
New ideas could result in paradigm shifts in our understanding of the genesis of PGE deposits and demonstrate what features must be mapped to assess mineral potential. If the new model for reef-type PGE is validated, it can be used to define mappable criterial (rock sequences and textures) in a mineral system that occurs in specific places and geologic time. The PDF will also have the opportunity to demonstrate the utility of thermodynamic modeling to assess the potential for PGE-mineralization in other geodynamic settings where mafic and ultramafic rocks are found. Some research now on developing process-based mappable criterial may lead to better assessment products and a workflow for conducting better mineral resource assessments.
Interested applicants are strongly encouraged to contact the Research Advisor(s) early in the application process to discuss project ideas.
Proposed Duty Station: Spokane, Washington
Areas of PhD: Geology, specifically economic geology of magmatic mineral deposits; igneous petrology of layered intrusions, 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 the qualifications for: 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.)
Human Resources Office Contact: Victor Mendoza, 650-439-2454, vjmendoza@usgs.gov
