Description of the Research Opportunity
Critical mineral enrichments occur in association with a wide variety of mineral systems and tectonic environments. Recent work has shown that precursor (i.e., Paleozoic) tectonic and magmatic events and crustal structure influenced the enrichment of critical minerals as by-products in Mesozoic mineral systems in Alaska (e.g., Kreiner et al., 2019). Many different styles of mineral systems are known or suspected to occur throughout the state, resulting from the diversity of geologic terranes and tectonic environments in which they originally formed, tectonic processes during accretion, and syn- and post-accretionary tectonic processes.
Much of southwestern Alaska is composed of magmatic arcs, accretionary complexes, and continental fragments. The boundaries between these features are often obscured by overlap successions of Cretaceous basin stratigraphy. The heritage and deep crustal architecture of most terranes are difficult to ascertain due to incomplete exposure and a lack of systematic investigation using modern analytical techniques. Mineral systems formed throughout the geologic evolution of the region, with various critical metal enrichments. Mineral systems can be divided into pre-, syn-, and post-Cretaceous origins. The pre-Cretaceous mineral systems formed as a result of tectonic processes that occurred during the formation of the continental fragments. Syn-Cretaceous mineral systems span accretionary-derived tectonic settings and multiple pulses of magmatic arc activity. Post-Cretaceous systems formed following the accretion of the continental fragments and are the result of magmatic arcs and young Cenozoic faulting. The tectonic setting, and origin of many mineral occurrences in the region remains enigmatic – including the giant Donlin gold deposit which contains large resources of Sb and As in addition to Au.
The information generated by the Mendenhall Fellow will have broad appeal to geologists interested in the relationship between crustal evolution and architecture and the formation and distribution of mineral deposits, the geologic evolution of accretionary orogens, and the isotopic composition and evolution of the crust and mantle in different tectonic environments. The findings will also be of great interest to the public who in recent years have become more aware of critical mineral resources and their presence in the United States and to various stakeholders in Alaska such as land managers and the minerals industry who rely on the USGS for informed, data-driven mineral resources research and assessments.
The goal of the research will be to use some combination of radiogenic (e.g., Pb, Rb-Sr, Nd, Hf, etc.) and(or) stable (e.g., O, H, S, C, N) isotope systems in bedrock, sediment, and mineralization lode samples to map the isotopic signatures and interpret the tectonic affinity and geologic evolution of the region. The proposed work may address one or more fundamental questions that include, but are not limited to, the following:
- What is the age and isotopic character of the basement to the accreted terranes in southwestern Alaska?
- How are igneous systems distributed, and what is the history and tectonic setting of magmatic activity in the region?
- What are potential linkages between crustal architecture, magmatic composition, and critical mineral endowment of mineral systems in southwest Alaska?
- How do accretionary processes modify original mineral systems and resource endowments?
- What is the age, geometry, and evolution of accretionary boundaries and potential control on mineral systems in the region?
These questions require a better and more integrated understanding of both the exposed bedrock geologic framework and regions that are concealed beneath overlap successions and younger cover. Once exposed regions are characterized, the same isotopic mapping approach can be applied to regions with poor bedrock exposure concealed beneath Cretaceous overlap basins or Quaternary colluvial, alluvial and vegetated cover. In poorly exposed regions, samples of modern and recent detrital sediment can be used as proxies to assess the isotopic and geochemical signature of defined catchments and to infer the origin and nature of the underlying bedrock. A full integration of geochronologic data with isotopic characteristics will provide a powerful and efficient means of studying crustal evolution, identifying crustal domains, mapping mineral systems, and evaluating the inherent controls on metallogenic potential and enrichments of critical elements in diverse geologic terranes.
The USGS Earth Mapping Resource Initiative (Earth MRI) is a high-profile, national mapping, data collection, synthesis and interpretation program focused on the Nation’s need for critical mineral independence and security. This initiative has multiple new geophysical surveys in Alaska in three priority areas–the Yukon-Tanana upland, the Kuskokwim Mountains region, and the Seward Peninsula and new geologic mapping and geochemical sampling in the Yukon-Tanana upland. Additional geochemical, and geologic mapping in these regions is ongoing. The successful Mendenhall Fellow will coordinate and integrate with this work and develop necessary datasets for better understanding the distribution of geologic basement domains, crustal architecture, and terrane evolution. The Fellow will benefit from collaborations with research staff inovled in Earth MRI in Alaska and other ASC geologists to better understand the bedrock geology of the region, as well as collaboration and mentorship from state and academic partners working to better understand the mineral systems hosting critical mineral resources. Suitable samples can be collected from a combination of active field work and research in southwest Alaska and augmented with archived materials curated by USGS. Limited new fieldwork, conducted in conjunction with active research in the region, may target specific areas for focused work.
Interested applicants are strongly encouraged to contact the Research Advisor(s) early in the application process to discuss project ideas.
Proposed Duty Station(s)
Anchorage, Alaska
Areas of PhD
Geology, geochemistry, economic 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 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.)
