Unconventional Stratabound Critical Mineral Deposits of the Midcontinent: Linkages Between Mineralization in Marine Epicontinental Sedimentary Basin Systems

Science Issue and Relevance

The Paleozoic stratigraphy of the midcontinent hosts a treasure-trove of critical minerals including, but not limited to, cobalt (Co), rare earth elements (REE), and lithium (Li). These stratabound mineral occurrences (confined to a single stratigraphic unit)  can be traced for 100's (even 1000's) of km in specific age horizons throughout the midcontinent. Historically, while some of these mineral occurrences were mined for primary elements like iron (Fe), manganese (Mn) and phosphate (PO₄), mining proceeded without consideration of potentially contained critical minerals largely because these metals were not of commercial interest at the time of mining, abundances were difficult to quantify, their presence was undetected, or in some cases, these metals had yet to be discovered. Recent Mineral Resources Program research has recognized that some of these vast primary metal accumulations also contain elevated concentrations of several critical minerals, which in today's market economy may be of interest in supplying the Nation's critical mineral needs.

For example, we have identified midcontinent phosphorite deposits (the primary source of fertilizer sustaining the world's food supply) that contain heavy REE (HREE) abundances that rival those of any REE deposit in the world. Initial studies demonstrate that these high-grade REEs abundances are 100% extractable, low in thorium, and consequently may constitute a viable and environmentally friendly source of REE that could eliminate REE shortages and simultaneously yield phosphate and other critical minerals as byproducts.

Methodology to Address Issue

This project will evaluate and inventory critical minerals in stratabound "Bathtub Rim" mineral occurrences in the midcontinent region. Ocean anoxic events (OAEs) resulted in the formation of “bathtub rim” deposits at redox boundaries along continental margins that concentrated various redox sensitive critical minerals, forming Fe–Mn oxides and REE enriched phosphorites deposits at the oxic-anoxic interface. The midcontinent represents an ideal laboratory in which to study genetic linkages between critical mineral accumulations and marine epicontinental sedimentary basin systems. The project has the following tasks:

Evaluation of Critical Elements in "Bathtub Rim Deposits" of the Midcontinent: We have identified previously unrecognized (or forgotten) ore-grade concentrations of REE and Mn, Co and equally critical elements, including U, Ni, PO₄, Sc, Sr, and F, in specific stratigraphic intervals that host "bathtub rim" deposits in the midcontinent. We will assess the occurrence and economic potential of a wide-range of sediment-hosted, critical mineral-containing, ore deposits. We will combine stratigraphic analysis with a full complement of chemostratigraphic analyses to constrain the boundaries of mineralized terranes and document the composition and critical mineral zonation in the appropriate stratigraphic intervals. Definition of mineralized terrane boundaries and stratigraphic intervals establishes system tracts that are directly transportable to the Earth Mapping Resources Initiative (Earth MRI) mineral assessments. Two deposit types we will focus on are: 1) sedimentary phosphate - REE, and -U, and 2) sediment hosted Mn-Co (Ni-REE) oxide.

Metallurgical Extraction of REE and Other Critical Minerals from Phosphate Deposits: The viability of REE resources is heavily dependent on the beneficiation costs and chemical REE extraction. The ease of beneficiation and chemical dissolution of sedimentary francolite allows the world's fertilizer industry to product 150 Mt/yr of inexpensive phosphate fertilizer. Importantly, preliminary experiments suggest that francolite dissolution from phosphate ores using dilute H₂SO₄ and HCl extracted 100% of the contained REE's (unlike the difficulties encountered in extracting REEs from traditional deposits). We will create a new USGS phosphate ore reference material from the Lafferty Creek, AR phosphate ore. We will conduct metallurgical extraction experiments to evaluate the possibility of extracting REE and other elements like F, U, Sc, Sr, Ga, Ge, Cd, and Sc, which are enriched in some phosphate deposits with the ultimate goal of encourage external partners to conduct large-scale pilot metallurgical studies.

Evaporite-Brine Systems of the Midcontinent: Previous investigations concerning the geology of the Upper Silurian Salina salt basin, which extends from Michigan, Ohio westward into Kansas, as well as the associated chronostratigraphic and paleogeographic relations indicate that this system presents an ideal opportunity to study processes that result in elevated critical mineral abundances and the formation of potash and Li-rich brines. We are inventorying previously collected brine data to pinpoint locations for further study using traditional brine chemistry/isotopic analysis, δ88Sr, and Li isotopes to better understand geologic controls on Li contents.