Systems-deposits-commodities-critical minerals table for the earth mapping resources initiative

Abstract

To define and prioritize focus areas across the United States with resource potential for 35 critical minerals in a few years' time, the U.S Geological Survey Earth Mapping Resources Initiative (Earth MRI) required an efficient approach to streamline workflow. A mineral systems approach based on current understanding of how ore deposits that contain critical minerals form and relate to broader geologic frameworks and the tectonic history of the Earth was used to satisfy this Earth MRI need. This report describes the rationale for, and structure of, a table developed for Earth MRI that relates critical minerals and principal commodities to the deposit types and mineral systems in which they are concentrated. The hierarchical relationship between systems, deposits, commodities, and critical minerals makes it possible to define and prioritize each system-based focus area once for all of the critical minerals that it may contain. This approach is advantageous because mineral systems are much larger than individual ore deposits and they generally have geologic features that can be "imaged" by the topographic, geologic, geochemical, and geophysical mapping techniques deployed by Earth MRI.

Focus areas for data acquisition for potential domestic resources of 11 critical minerals in Alaska—Aluminum, cobalt, graphite, lithium, niobium, platinum group elements, rare earth elements, tantalum, tin, titanium, and tungsten, chap. C of U.S. Geological Survey, Focus areas for data acquisition for potential domestic sources of critical minerals

“…Following the selection of the phase 2 critical minerals (table 1), mineral systems were identified (table 2) that contain these commodities as either primary or byproduct phases (e.g., Hofstra and Kreiner, 2020). Alaska contains mineral systems that have the potential to contain all of the phase 2 commodities except for aluminum.…”

“…Ore deposits, where potentially economic concentrations of critical commodities may occur, represent the culmination of the geologic processes that constitute the mineral system. Mineral systems require the following: (1) an energy driver (e.g., topography, geothermal gradient in the crust, or magma); (2) a source of components (e.g., metals) and fluid (e.g., melts, aqueous fluids, petroleum, and ligands to complex components); (3) transport pathways (e.g., faults, fractures, or permeable lithologic units); and (4) a physical and (or) chemical trap (e.g., mixing of fluids, reduced host rocks, boiling) (Hofstra and Kreiner, 2020). A productive mineral system must incorporate each of these critical criteria to generate a mineral deposit.…”

“…Critical minerals are rarely the primary mineral commodity being explored and (or) produced, in a mineral system, although exceptions to this general rule include some REEs, PGEs, and graphite deposits. Thus, understanding where, how, and why critical minerals are enriched in mineral systems is essential for more effectively predicting where undiscovered critical mineral resources are more likely to occur (Hofstra and Kreiner, 2020). Table 2 lists relevant mineral systems that are known or suspected to occur in Alaska together with the major commodities that the systems contain, phase 2 critical mineral commodities that may be present, and the deposit types for which prospectivity has been mapped across the State.…”

“…Basin brine path mineral systems generally form from the circulation of marine or terrestrial brines through permeable strata to upwelling and discharge sites where an ore deposit may form if appropriate conditions exist. The fluids are principally derived from dissolution of seawater evaporites (halite, gypsum, and others) in the sedimentary sections, resulting in high-salinity basinal brines (Emsbo, 2009;Hofstra and Kreiner, 2020). Fluids are circulated by topographic drivers, ambient geothermal heat in the crust, or magma emplacement.…”

“…The Alaska focus areas defined in this report were selected based on a mineral systems framework (Hofstra and Kreiner, 2020) and through careful consideration of published and ongoing statewide geospatial prospectivity mapping (Karl and others, 2016;Karl and others, U.S. Geological Survey, written commun., 2020) and other relevant datasets and publications (e.g., Wilson and others, 2015;Granitto and others, 2019;Kreiner and others, in press). Alaska focus areas are necessarily broad because of significant gaps in modern data coverage and quality across such a large, remote, and geologically complex State ( fig.…”