20-31. Integration of gravity, magnetic, and radiometric geophysical methods to image 3D subsurface geology associated with mineral systems

CLOSED

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The USGS Earth Mapping Resource Initiative (Earth MRI) is a high-profile, national mapping and data collection effort addressing the Nation’s need for critical mineral independence and security.  Acquisition of airborne geophysical surveys is one of the three phases of new data collection under Earth MRI, which also includes geological mapping and topographic LIDAR surveys.  As of 2021, Earth MRI supported the collection of 19 new high-resolution airborne magnetic and radiometric geophysical surveys across the U.S. (https://ngmdb.usgs.gov/emri/#3/40/-96).  New survey areas are planned at the rate of 4-6 per year over areas of interest determined jointly by the USGS and State geological surveys (Hammarstrom et al., 2020). 

These areas of interest, which serve as catalysts for new geophysical survey acquisition, are defined, organized, and prioritized using a mineral systems concept (Hofstra and Kreiner, 2020).  The mineral systems concept encompasses all processes required to form an ore deposit in a given geotectonic setting and is based on current understandings of how ore deposits form within the framework of the tectonic history of the Earth.  For example, mafic magmatic mineral systems, which are commonly associated with large igneous provinces, involve processes that can lead to a variety of ores that host critical minerals, such as chromite, nickel-copper-platinum-group-element (PGE) sulfide, PGE (low sulfide), and iron-titanium oxide deposits.  Knowledge of mineral systems from the geotectonic setting and past mining history in an area helps predict the critical minerals that may be present, even if critical minerals were not the focus of past mining activity.  A mineral systems approach is also useful in areas with extensive cover, if a geotectonic setting that is favorable for the system can be recognized.

Recognizing geotectonic settings and their associated mineral systems under widespread cover is challenging and requires considerable use of geophysics.  Where rocks of interest are hidden by large expanses of surficial deposits, younger rocks, water, or vegetative cover, geotectonic settings traditionally have been inferred from regional geophysical data and sparse outcrop.  However, new detailed geophysical data from the Earth MRI program are showing that previous understandings were too broad.  Can we learn from these examples and other Earth MRI surveys about the geophysical expressions of specific mineral systems?  What is the best approach to integrating the new geophysical data with other geoscientific data to identify mineral systems under cover?  We seek novel and innovative approaches to this data integration that will aid in designing future Earth MRI surveys and advance our understanding of the geology of buried mineral systems in three dimensions.

The successful applicant will work with the research advisors to choose one or two specific mineral systems for study in an area covered by new Earth MRI geophysical data. Working within a collaborative and multi-disciplinary environment at the USGS, the post doc will examine aspects of the geotectonic setting and ore-forming components of the mineral system(s) to determine attributes that commonly have geophysical expression. Building on these attributes and from examination of the Fellow’s study area and appropriate examples from new Earth MRI surveys, the post doc will develop an approach to interpretation that helps identify or explore new insights about the geology of the mineral system(s) in three dimensions. 

The approach should focus on imaging buried and/or surficial geologic systems in 3D that may include structures, intrusions, volcanic materials, zones of hydrothermal alteration, and/or sedimentary processes, and to consider their role in the context of the chosen mineral system(s).  Airborne magnetic and radiometric data will be available from the Earth MRI program; existing gravity data are commonly available at regional scale across the U.S.  Heavy reliance on advanced interpretation methods is expected, such as derivative maps, targeted filtering, and forward or inverse modeling.  The approach should be developed using a good understanding of geology and petrophysical properties, especially magnetization, density, and natural radioactivity.  There also may be opportunities to incorporate additional geophysical datasets, such as electromagnetic (EM) ground or airborne surveys, passive seismic data, or collection of new gravity data. 

Interested applicants are strongly encouraged to contact the Research Advisor(s) early in the application process to discuss project ideas.

References:

Hammarstrom, J.M., Dicken, C.L., Day, W.C., Hofstra, A.H., Drenth, B.J., Shah, A.K., McCafferty, A.E., Woodruff, L.G., Foley, N.K., Ponce, D.A., Frost, T.P., and Stillings, L.L., 2020, Focus areas for data acquisition for potential domestic resources of 11 critical minerals in the conterminous United States, Hawaii, and Puerto Rico—Aluminum, cobalt, graphite, lithium, niobium, platinum-group elements, rare earth elements, tantalum, tin, titanium, and tungsten: U.S. Geological Survey Open-File Report 2019-1023B, https://doi.org/10.3133/ofr20191023B.

Hofstra, A.H., and Kreiner, D.C., 2020, Systems-Deposits-Commodities-Critical Minerals Table for the Earth Mapping Resources Initiative (ver. 1.1, May 2021): U.S. Geological Survey Open-File Report 2020–1042, 26 p., https://doi.org/10.3133/ofr20201042.

Proposed Duty Station: Lakewood, Colorado

Areas of PhD: Geophysics, geology, Earth sciences, 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 Geophysicist

(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: Sinar Santillano Oliveros, 303-236-9585, ssantillanooliveros@usgs.gov