Science Essential Resources for Achieving a Carbon-Neutral Future Bella Brown October 27, 2023 Picture yourself driving an electric vehicle through a valley filled with a solar farm and surrounded by a line of wind turbines on a sunny day. Alternatively, envision adjusting your home’s thermostat to cool or heat it without contributing to the increase of greenhouse gases in the atmosphere. These images represent a peaceful and environmentally friendly future. But how can we turn these ideas into widespread reality? Achieving carbon neutrality in economies and daily habits will necessitate significant sources of mineral resources. This includes not just copper, which is crucial for the electrical grid and electric cars, but also a range of other metals that have not traditionally been the main focus of the mining industry. These metals are essential for meeting the demand for low-carbon transportation, energy, and battery storage technologies, among other uses. In the US, several mineral resources such as cobalt, nickel, lithium, manganese, germanium, gallium, indium, and graphite are imported for use in EV batteries, solar panels, wind turbines, and energy storage. These supplier countries may have a record of inadequate environmental, social, or governance practices, which are exacerbated by our growing dependence and consumption. In order to locate potential areas where important and other valuable minerals may be found, it is necessary to gain a deeper understanding of the geological and metallogenic conditions beneath us. The United States possesses some of the less common metals needed for these technologies. Some of the minerals required are found as secondary products in domestically mined ores for copper, lead, zinc, or gold. However, they have not been extracted due to low demand in the past. In some cases, critical minerals have been found in areas with restrictive regulations, hindering development. Additionally, the levels of these minerals in individual ore bodies have not been thoroughly studied, making it difficult to accurately identify and focus on critical mineral resources. In order to locate potential regions that may contain important minerals, it is important for us to gain a deeper understanding of the geological and metallogenic conditions beneath us. This requires obtaining new, reliable data, particularly in areas where little data has been collected previously. In 2019, the US Geological Survey (USGS) collaborated with the Association of American State Geologists and other government, state, and private organizations to launch the Earth Mapping Resources Initiative (Earth MRI). This initiative aims to gather top-quality data for assessing essential minerals. Earth MRI uses a mineral systems approach to identify regions for data collection, connecting large-scale geological processes to the creation and maintenance of mineral deposits. Within its initial years, this effort has provided valuable insights into the critical minerals landscape of the US. Possible Vulnerabilities in Vital Supply Networks In the United States, critical minerals refer to nonfuel mineral resources that are crucial for economic and national security, such as reducing our reliance on carbon-based fuels. These minerals may face potential risks in their supply chain. Unlike some other resources, mineral reserves are not evenly distributed worldwide and have traditionally been sourced from global suppliers. However, political concerns and interruptions in international trade can jeopardize our access to these critical minerals. In response, lawmakers have passed federal laws and issued executive orders tasking the USGS with identifying a list of critical minerals. The first version of the list was published in 2018 and contained 35 essential minerals. In 2022, the list was expanded to include 50 minerals and was revised to specifically mention rare earth elements (REEs) and platinum group elements as separate critical minerals. (They were previously grouped together on the 2018 list.) The US relies entirely on foreign imports for 21 of these critical minerals, and at least half of its supply for another 28. Researchers are examining rocks in the expansive and isolated Yukon-Tanana highlands in the central eastern region of Alaska to assess the potential for important mineral deposits including bismuth, arsenic, antimony, tungsten, tin, and rare earth elements, as well as valuable resources such as gold, copper, molybdenum, lead, and zinc. Credit: Douglas Kreiner, U.S. Geological Survey The main goal of the U.S. Geological Survey is to create fresh, reliable data sets that can aid in forecasting potential locations, methods, and reasons for the presence of vital minerals within the nation’s boundaries. In order to decrease the United States’ reliance on foreign supplies, it is necessary to identify, discover, permit, produce, and process domestic sources of critical minerals. Many of these minerals were previously produced during times of war with government assistance. While some, such as lithium and cobalt (essential for electric vehicle batteries), are still mined in the U.S., they only come from a few locations. Others, such as arsenic, tin, gallium, and scandium (necessary for semiconductors and high-performance alloys), have not been mined domestically in over 20 years. The lack of past exploration and production of critical minerals has led to a shortage of modern geological, geochemical, geophysical, and topographic data sets needed to create national mineral potential maps, which hinders the exploration of domestic mineral potential. Under the Earth MRI project, the USGS is receiving additional funding through the Bipartisan Infrastructure Law of 2021 to create new, reliable data sets that can be utilized for predictive analyses on the location, characteristics, and origins of essential minerals within the United States. The public has access to precompetitive data generated by state surveys and the USGS, while the private sector is responsible for exploring, discovering, verifying, and extracting resources, as well as establishing processing facilities and supply chains. As these efforts move forward together, the exploration and production of domestic resources become less financially risky. A Mineral Systems Approach Mineral systems refer to the necessary components, such as geological and tectonic conditions, source materials, and transportation mediums (such as fluids), that are needed to create ore deposits. These systems form over extended periods of time and across large areas, and their specific characteristics greatly impact the types and quantities of metals deposited. However, Earth’s systems are complex and diverse, and the necessary ingredients are not always combined in ideal ways to produce profitable ore deposits. In fact, the majority of mineral systems do not result in economic deposits. The task at hand is to identify the systems that do produce economic deposits and determine the crucial ingredients involved. Instead of looking at specific ore deposits, it is more beneficial to examine the overall mineral system to gain a comprehensive understanding of where critical minerals come from and where they are concentrated. By mapping these systems on a national scale, we can identify potential areas for critical mineral deposits based on the presence of necessary components. However, it is important to note that these maps should not be used as a replacement for prospectivity or resource maps, which define the most probable locations for mineralization within the footprints. A mineral systems framework was created for Earth MRI, which identified 23 different types of mineral systems in the United States that may contain important minerals. The USGS worked with state geological surveys to define the boundaries of these mineral systems, known as focus areas, where new data could help assess the potential for critical minerals. There are over 800 focus areas that can be used as a preliminary tool for prioritizing data collection (see Figure 1). Data on each focus area can be accessed through GIS mapping and analytical software [Dicken et al., 2022]. This includes information on the selection criteria for each area (such as identified ingredients), as well as details on known ore deposits, past and current production, estimated resources, and geological maps. The data also includes over 4,000 references. Over 800 specific regions, representing 23 various types of mineral systems, have been pinpointed in the United States and Puerto Rico as having the potential to produce valuable mineral deposits. The numbers in brackets in the key indicate the quantity of focus areas for each mineral system. To view a larger version, click on the image. Credit: Map adapted from Hammarstrom et al. ; data sourced from Dicken et al.  The information was utilized to create a map of key locations in the United States that may contain important mineral resources [Hammarstrom et al., 2023]. The range of sizes for the mineral system footprints depicted in Figure 1 indicates the various geological factors that impact the formation of mineral deposits. Certain mineral systems encompass large ancient drainage basins spanning thousands of square kilometers, while others are centered around small rock intrusions covering less than 5 square kilometers. The variations in the size and level of detail of focus areas also reflect the amount of data and knowledge available in different regions. For instance, focus areas in remote parts of Alaska are based on limited data compared to those in established or active mining areas in the western United States (see Figure 1). Certain focus areas may contain ongoing exploration projects or past mines that have produced critical minerals. As new geophysical or geochemical data and updated mapping become accessible, these regions with lower data coverage can be reevaluated for their potential to host critical mineral deposits. The process of collecting data has begun. Over 100 projects funded by the Earth Mapping Resources Initiative are currently in progress throughout the country, with state geological surveys covering various focus areas. Numerous areas in the country that are rich in minerals do not have detailed maps of their geology, geochemistry, and geophysics, which are essential for understanding mineral systems. To address this issue, over 100 projects funded by Earth MRI are currently being carried out by state geological surveys in various regions, in order to gather crucial new data on geology and geochemistry. As many mineral systems span across state boundaries, this has also led to collaborative efforts between states. The US Geological Survey (USGS) is collaborating with various states and collaborators to obtain precise aerial data on magnetism, radiation, and electromagnetism for mineral resource investigations. These geophysical surveys are typically conducted prior to or at the beginning of field work, allowing researchers to pinpoint important areas for further exploration through mapping and geochemical sampling. Additionally, the USGS 3D Elevation Program is working to fill in missing data in the country’s lidar coverage to support mapping and other related studies. The Earth MRI is mandated by the Bipartisan Infrastructure Law to supply a combination of topographic, geologic, geochemical, and geophysical data and finish a comprehensive national surface and subsurface mapping project within 10 years. This will also involve interpreting resources both above and below ground. Additionally, the USGS has launched a joint effort with Earth MRI to survey aboveground resources in abandoned mine areas and identify nearby aboveground resources that may contain critical minerals that were previously overlooked during past mining operations. Initial MRI findings The initial Earth MRI initiatives have yielded promising findings. A study conducted in northern Maine during the program’s first year identified a previously unknown occurrence of REE-niobium-zirconium in igneous trachyte rocks at Pennington Mountain [Wang et al., 2023]. This discovery was made possible by a regional aerial survey conducted by Earth MRI, which detected high levels of thorium and uranium. These elements are often associated with igneous rocks that contain REEs and other rare metals, such as niobium and zirconium. Further fieldwork was carried out to investigate these anomalies, combining ground radiometric surveys with portable X-ray fluorescence and whole-rock analyses of rock samples. The results confirmed the presence of REE and critical mineral enrichment in an area of approximately 1.2 square kilometers, with more concentrated mineralization in certain areas [Wang et al., 2023]. Airborne surveys conducted over a large area of the U.S. Atlantic Coastal Plain have revealed the possibility of finding titanium, zircon, and rare earth element (REE) deposits in heavy mineral sands along the coast [Shah et al., 2021]. This study has also shed light on complicated shoreline processes, such as the movement of heavy minerals from Virginia’s Piedmont region through major rivers and their subsequent transport along the coast by longshore currents, leading to their redeposition and accumulation onshore. This map displays magnetic anomaly information gathered in the southeastern region of Missouri as part of the Earth Mapping Resources Initiative (Earth MRI). To view a larger version, click on the image. Source: U.S. Geological Survey. Researchers in Illinois and Kentucky have collaborated on Earth MRI projects that involve using airborne magnetic and radiometric surveys along with detailed geological maps of the mineral-rich areas of the Illinois-Kentucky Fluorspar District and Hicks Dome. This interdisciplinary work has yielded valuable new information about the peralkaline REE system, which has a history of producing important minerals like barium and fluorine. It has also enhanced our understanding of the seismic hazards in this earthquake-prone region by providing more precise data on the location and nature of faulting through detailed mapping [Denny and Kershaw, 2021; Denny et al., 2020; Lukoczki et al., 2022; McCafferty and Brown, 2020; McCafferty and Connell, 2022]. Recent research in the Yukon-Tanana terrane in interior Alaska has focused on understanding how older tectonic terranes impact the chemistry and formation of newer magmatic hydrothermal mineral systems and their resulting deposits. In a study by Kreiner et al. , it was found that differences in the composition of rocks in two adjacent terranes played a significant role in the distribution of metals within their respective ores. This led to the enrichment of molybdenum, tungsten, and rhenium in porphyry copper systems of the Yukon-Tanana terrane, while the nearby ancestral North American basement terrane contained porphyry copper systems with higher concentrations of bismuth, arsenic, and gold. The Earth MRI project has significantly increased the quantity of top-notch magnetic data accessible for the contiguous United States and multiplied it by four for Alaska. Earth MRI has significantly increased the amount of accurate magnetic data available for the contiguous United States and Alaska. This data is utilized for mapping important mineral resources, as well as studying geothermal energy and water resources, and identifying areas at risk for natural disasters such as landslides, earthquakes, and floods. The Future of Earth MRI The journey towards establishing secure supply chains for domestic critical minerals will be lengthy and complex. How much progress we can achieve on this journey is highly dependent on the significant obstacles associated with resource development and processing. These obstacles involve access to land where the resources are located, the environmental consequences and public acceptance of extracting resources, and the timelines for developing and obtaining permits for mines. The decisions made regarding these challenges will greatly impact the country’s ability to successfully transition to carbon-neutral sources of energy. Prior to making these choices, we must first determine which essential minerals can be obtained within our own country to fulfill our needs. This is where the current and future initiatives of Earth MRI come into play, offering extensive and diverse data to both government and private industries for precompetitive purposes. Efforts are being made to provide access to the recently obtained data in formats that are suitable for analysis through an internet platform. These data are crucial for creating maps of potential minerals in extensive mineral systems and for conducting resource evaluations in partnership with the USGS Mineral Resources Program. Figure 2 displays the various Earth MRI datasets that can be combined for a specific region, such as the Yukon-Tanana upland in eastern Alaska. In Figure 2, we can see the various data layers and mineral potential mapping products for the Yukon-Tanana upland area in the Earth MRI project. These data layers include the Alaska state geologic map database, Alaska resource data file, Alaska geochemical database, Alaska radiometric age database, and airborne radiometrics and magnetics data. The mineral potential maps were created prior to the start of Earth MRI, but they demonstrate the types of products that will be made available through this project. These data sets are continually updated as new analyses, mapping, and geophysics funded by Earth MRI are completed. Once data collection is finished, the mineral potential maps for this region will be updated using these new data. Some key elements included in these maps are platinum group elements (PGE) and rare earth elements (REE). You can click on the image for a larger version. Our ultimate objective for Earth MRI is to establish the ability to effortlessly integrate new information and continuously update maps of mineral potential, highlighting areas where valuable resources are present or likely present in mineral deposits (see Figure 2) and mining waste. Additionally, we are investigating methods to integrate machine learning and artificial intelligence in order to streamline the integration and analysis of extensive datasets. Furthermore, we are working with international partners to establish the key criteria that define mineral systems that can be mapped. Once these criteria are established, they can be implemented into models to generate more accurate maps of mineral resources, both nationally and internationally. The maps that will be produced are a result of many years of gathering data, creating databases, developing mineral systems frameworks, and working together at local, national, and global levels. These maps will guide us towards achieving the objectives of transitioning to low-carbon energy sources. Acknowledgments Using names of businesses, companies, or products is solely for the purpose of providing descriptions and does not indicate endorsement by the United States government. References The bedrock geology of Hicks Dome in Hardin and Pope Counties, Illinois is described in a report by Denny and Kershaw (2021). The report, titled “Illinois County Geologic Map – EMRI Hicks Dome-BG,” consists of 2 sheets and is on a scale of 1:12,000. It was funded by a USGS-EMRI contract and published by the Illinois State Geological Survey in Champaign. The report is 145 pages in length. Denny, F. B., et al. (2020), Mines in the Illinois portion of the Illinois-Kentucky Fluorspar District, Circ. Ill. State Geol. Surv., 604, 73 pp., experts.illinois.edu/en/publications/mines-in-the-illinois-portion-of-the-illinois-kentucky-fluorspar–2. Dicken, C. L., et al. (2022), GIS, supplemental data table, and references for focus areas of potential domestic resources of critical minerals and related commodities in the United States and Puerto Rico, data release, U.S. Geol. Surv., Reston, Va., https://doi.org/10.5066/P9DIZ9N8. The United States Geological Survey has published a fact sheet (2023-3007) by Hammarstrom et al. (2023) detailing the national map of areas with significant potential for critical mineral resources. The publication is 4 pages long and can be accessed through the DOI link: https://doi.org/10.3133/fs20233007. Kreiner, D. C., et al. (2019), Links between tectonics, magmatism, and mineralization in the formation of Late Cretaceous porphyry systems in the Yukon-Tanana upland, eastern Alaska, USA, paper presented at 15th Biennial Meeting, Soc. for Geol. Applied to Miner. Deposits, Edinburgh, U.K. In 2022, Lukoczki and colleagues published a report on Phase I actions of the Earth Mapping Resources Initiative (Earth MRI) in the western Kentucky Fluorspar District. The report was published by the Kentucky Geological Survey as Report of Investigation 66. McCafferty, A. E., and P. J. Brown (2020), Airborne magnetic and radiometric survey, southeastern Illinois, western Kentucky, and southern Indiana, 2019, data release, U.S. Geol. Surv., Reston, Va., https://doi.org/10.5066/P9R05B0M. In 2022, McCafferty and Connell conducted a survey called “The Gap” over certain areas in southeast Missouri, southern Illinois, and western Kentucky. This survey involved capturing airborne measurements of horizontal magnetic gradients and radiometric data. The results of this survey have been released by the U.S. Geological Survey and can be accessed at https://doi.org/10.5066/P9TK8KMM. Shah, A. K., et al. (2021), Mapping critical minerals from the sky, GSA Today, 31(11), 4–10, https://doi.org/10.1130/GSATG512A.1 Wang, W., et al. (2023), A recently discovered trachyte-hosted rare earth element-niobium-zirconium occurrence in northern Maine, USA, Econ. Geol., 118, 1–13, https://doi.org/10.5382/econgeo.4993. Author Information Douglas C. Kreiner ([email protected]), U.S. Geological Survey, Anchorage, Alaska; Jane Hammarstrom, U.S. Geological Survey, Reston, Va.; and Warren Day, U.S. Geological Survey, Golden, Colo. Reference: Kreiner, D.C., Hammarstrom, J., & Day, W. (2023). The role of critical minerals in achieving a carbon-neutral future. Eos, 104. https://doi.org/10.1029/2023EO230403. 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