Graphite-forming mineral systems through time and space

George N.D. Case; U.S. Geological Survey Alaska Science Center, Anchorage, AK 99508, USA

Graphite is a critical mineral because of its significance for the growing battery market and high exposure to supply chain interruption. To improve mineral exploration and resource assessment outcomes, new models of graphite ore genesis in a mineral systems framework are warranted. Orogenic graphite is the most economically important graphite source and includes the metamorphic and orogenic mineral systems that generate flake and hydrothermal vein (lump and chip) deposits, respectively. High temperature metamorphism is a shared trait of these systems. Orogenic graphite deposits form in high-temperature metasedimentary rocks in continent-continent or continent-island arc collisional orogens. Orogenic flake graphite deposits form mainly via graphitization of organic carbon during regional metamorphism, but strain localization and anatexis of pelitic protoliths likely enhance graphite quality and grade. In contrast, orogenic vein graphite deposits crystallize from hydrothermal fluids rich in CO2 and CH4, probably sourced from devolatization of calcareous and carbonaceous metasedimentary rocks. Collation of geologic data from known graphite deposits worldwide indicates that episodes of organic carbon deposition in the Paleoproterozoic, Mesoproterozoic, and Neoproterozoic provided most carbon sources. Later supercontinent orogenesis at ca. 2,100 to 1,700 Ma (Columbia), ca. 1,300 to 1,000 Ma (Rodinia), and ca. 650 to 500 Ma (Gondwana) generated orogenic flake and vein graphite deposits, where favorable geologic factors coincided with organic ± carbonate carbon-rich strata. Fewer graphite deposits are known in the Phanerozoic, possibly owing to differences in extent of exhumation or protolith burial. High-temperature metasedimentary terranes that contain organic carbon-rich protoliths are preferable for hosting orogenic flake graphite deposits, whereas sequences that also contain carbonate protoliths are prospective for orogenic graphite veins; both can be present in the same orogen. Recognition of flake and vein graphite deposits as products of similar mineral systems related to orogenesis can boost the exploration success required to secure supply of this critical mineral.

Uncovering the Rates and Dates of Graphite Formation Using the Re-Os Decay System

Jonathan Toma, Yale University

Graphite Re-Os dating is an emerging geochronological tool for assessing the temporal histories of natural graphite. This method is unique in that it is the only known way to directly determine the timing of graphite forming events, which span across pre-solar (>4.56 Ga), solar (4.565-4.550 Ga), and terrestrial (<4.50 Ga) timescales. Graphite Re-Os dating can, therefore, be viewed as a major methodological advancement in fundamental graphite research. Here I will begin by showing that natural graphite (n = 17) is a common mineralogical host for Re, with Re contents comparable to other Re-enriched materials (sulfides, organic-rich sedimentary rocks, and hydrocarbons) in the Earth’s crust. Following this investigation, I will present several case studies that validate the graphite Re-Os method. These include graphite formed in mid-crustal shear zones and orogenic belts. I will then move away from this proof-of-concept approach and showcase how graphite Re-Os dating can be used to constrain carbon cycling events during orogenesis, supercontinent assembly, and subduction zone metamorphism. The future of graphite Re-Os dating will, however, prove to extend beyond these use cases, with important insights to be made in understanding the genesis of major graphite deposits around the world.  

Carbon mobility during metamorphism, an example from the Alabama Graphite Belt

Stowell, H.H., The University of Alabama; Bollen, E.M., Geological Survey of Alabama

Most resource-grade flake graphite results from concentration and recrystallization of carbon during metamorphism of organic-rich sediments. Important examples with sediment sources include: Balama (Mozambique), Mahenge and Nachu (Tanzania), Molo (Madagascar), Graphite Creek (USA), and Zavalyevsiry (Ukraine). The  £25% carbon in these and other graphite occurrences requires significant carbon mobility during metamorphism or graphite concentration from partial melting and melt loss. Large-scale metamorphic carbon mobility requires CO2 or CH4 bearing fluids. Above ~450°C, these species mix with H2O to form a single fluid, and at lower temperatures, they are immiscible. Evidence for mixed CO2-H2O and CH4-H2O fluids is found in fluid inclusions from a wide range of metamorphic minerals and rocks. Fluid inclusions from amphibole, garnet, ankerite, and omphacite indicate that mixed CH4-H2O fluids occur in >~20 kbar rocks. Although most graphite is metasedimentary, carbon mobilization in some veins likely results from CO2-CH4 redox associated with magmas from deep-seated/mantle rocks. The Alabama Graphite Belt (AGB) contains flake and vein graphite in sillimanite zone schists, gneisses, and quartzites extending across ~150 km in the eastern Blue Ridge terrane. The AGB reached  £700°C at 6 to 9 kbar and locally shows evidence of partial melting. Peak metamorphism and most graphite crystallization occurred at 353±3 Ma (garnet Sm-Nd). Flake graphite occurs in discontinuous layers up to 1.5 km thick, which contain <0.1 m-scale lenses and local ~0.01 m cross-cutting veins of lump graphite. Published δ13C values for AGB metasediments indicate crustal and likely biogenic carbon. Graphite veins are late and may have been emplaced by CO2 or CH4 bearing fluids following peak metamorphism; however, there is no evidence for large-scale mobility, and transport was likely centimeter scale. Preliminary data and likely correlation of Wedowee Group and AGB stratigraphy are compatible with biogenic graphite, low carbon mobility, and limited oxidation from metamorphic fluids.

Geologic Framework of Graphite Deposits in the Ruby Range, Southwest Montana: New Insights from Mapping and Petrochronology Investigations

Jesse G. Mosolf, Montana Bureau of Mines and Geology

Comprehensive geologic mapping establishes a geoframework critical to the exploration, responsible development, and scientific investigation of graphite deposits. In the Ruby Range of southwest Montana, graphite occurrences have been recognized for more than a century, with historical production exceeding 2,000 tons; however, the geologic controls on graphite formation remain incompletely understood. Since 2022, the Montana Bureau of Mines and Geology (MBMG) has expanded geologic mapping of graphite-bearing Precambrian basement rocks in the Ruby Range, producing detailed 1:24,000- and 1:100,000-scale maps as part of a long-term initiative supported by the USGS STATEMAP program. This work integrates remote sensing (LiDAR and GIS-based mapping) with petrography, bulk-rock geochemistry, and U-Pb geochronology to carefully document the local geologic framework and resource potential. Mapping reveals that the Ruby Range is underlain by a complexly deformed basement of polygenetic gneiss interlayered with metasupracrustal assemblages comprising marble, pelitic schist and gneiss, quartzite, banded iron formation, and amphibolite. Geochronological data indicate basement protolith formation at ~3.3 Ga, followed by magmatic–tectonothermal events at ~2.7 Ga, 2.55–2.45 Ga (Beaverhead/Tendoy Orogeny), and 1.8–1.7 Ga (Big Sky Orogeny). The basement rocks are intruded by diverse Archean–Proterozoic magmatic bodies, including ultramafic rocks, pegmatite, and diabase dikes. Marble-bearing assemblages in the southern Ruby Range host multiple generations of graphite mineralization. Recent petrochronology investigations document peak amphibolite–granulite metamorphism and graphite formation at ~1.8 Ga, coeval with the Big Sky Orogeny (e.g., Harms and Baldwin, 2022; Case et al., 2025; Taylor, 2025). Additional generations of graphite mineralization may be associated with earlier or later tectonic events, such as the Beaverhead Orogeny or Proterozoic crustal extension and magmatism. Continued research will further elucidate graphite mineralization in the Ruby Range, and the comprehensive geologic maps produced by MBMG will serve as a valuable resource for ongoing and future investigations.

Investigations in the Alabama graphite-V belt by the Geological Survey of Alabama

Elizabeth Bollen, Dane VanDervoort, John Whitmore
Geological Survey of Alabama, Tuscaloosa, Alabama

Graphite and vanadium (V) occur together within the Alabama graphite-V belt, which covers approximately 1,130 square km of the eastern Blue Ridge terrane in the northern Piedmont province of east-central Alabama. Due to historic flake graphite production in this belt and renewed interest by the exploration industry, the Geological Survey of Alabama (GSA), in partnership with the U.S. Geological Survey Earth Mapping Resources Initiative (Earth MRI), is conducting mapping and geochemical sampling projects to better characterize the critical mineral resources of the region. Flake graphite reserves in the Alabama graphite-V belt were previously estimated to be 23.5 million metric tons with V2O3 concentrations up to ≥1.0%; however, modern estimates indicate reserves greater than 71.2 million metric tons with V2O5 concentrations up to 0.2%. These resources are hosted in pelitic schist, gneiss, and quartzite of the Poe Bridge Mountain and Higgins Ferry Groups, which experienced regional upper amphibolite-facies conditions at approximately 350 Ma during southern Appalachian orogenesis. Graphite in these units occurs as ≤3.0 mm disseminated flakes in modal abundance between 1.0 and 15.0% and in rare 1.0- to 2.0-cm-thick veins. The V is present in variable concentrations within green disseminated roscoelitic muscovite. Additional tectonostratigraphic units with potential for hosting previously undeveloped graphite and V resources, such as the Wedowee Group, were recently identified and are the focus of the GSA’s ongoing mapping and geochemical sampling efforts. Earth MRI projects at the GSA have included mapping nine 1:24,000-scale quadrangles and analyzing geochemistry of 300 rock samples collected from graphitic and V-bearing lithologies. These data are being used in conjunction with recent high-quality airborne magnetic, radiometric, and resistivity geophysical surveys that were conducted by the Earth MRI program to better understand the structure and extent of graphitic lithologies in Alabama.

Toward targeted graphite exploration: Comparing the physicochemical properties of natural graphite from deposits around the world

M. Rebecca Stokes1; George N.D. Case1; Gabriela A. Farfan2; Aaron M. Jubb1
1) U.S. Geological Survey
2) Smithsonian Institute

The demand for natural crystalline graphite, a critical material in the lithium-ion battery (LIB) industry, is projected to increase by 500% through 2050, far outpacing current production. In LIBs, graphite is the primary anode material that is both host for Li ions and transfer platform for liberated electrons. Hence, the structure and trace element constituents of graphite can impact battery performance. Here we evaluate the heterogeneities of natural crystalline graphite in the context of targeted exploration. We examine eighteen graphite samples sourced from a variety of deposits globally, including flake- and vein-types, using δ13C isotopes, laser ablation inductively coupled mass spectrometry (LA-ICP-MS), Raman spectroscopy, scanning electron microscopy (SEM), and X-ray diffraction analysis. The δ13C results between -33‰ and +6‰ reflect biogenic, carbonate, and mixed/mantle sources. Results from LA-ICP-MS reveal major element concentrations (e.g., Fe and Mg) up to 1000s of ppm each with the sum of select redox sensitive elements (RSE; V, Ni, U, Mo) up to 50 ppm. Select elemental correlations suggest the presence of submicron-scale mineral inclusions like biotite (Mg and K) and zircon (Zr and Hf) and is confirmed by SEM imaging, whereas others, like the RSE, are likely present as trace elements in graphite. RSEs and Fe are elevated in the biogenic graphite samples with lower δ13C = -15‰ to -33‰, and negligible in the samples with higher δ13C. The second-order graphite region of Raman spectra shows variable turbostratic stacking (3-dimentional disorder) of graphene layers that correlates with samples that have lower δ13C along with RSE enrichment. Finally, X-ray diffraction analysis of ‘as-is’ graphite flakes using a Gandolfi stage reveals varying graphite polytype concentrations and crystallite size. These results, paired with geologic context, like carbon source, provide a template for predicting graphite characteristics that could be used to target deposits for application-specific exploration.

Comparing Natural, Synthetic, and Recycled Graphite for Lithium-Ion Batteries: Environmental and Economic Trade-Offs

Ehsan Vahidi, University of Nevada, Reno

Graphite is the primary anode material for lithium-ion batteries (LiBs); however, the various methods of producing the graphite produce different environmental impacts and economics. A comparative life cycle assessment (LCA) and technoeconomic analysis (TEA) of natural, synthetic, and recycled graphite have been conducted using TRACI methods and have shown that using recycled graphite can reduce global warming potential by around 70% of conventional graphite sources, primarily due to energy consumption and related consumables. The TEA analysis indicated that all methods of producing graphite would have positive cash flows; however, the recycled method had the highest profit potential ($127.6 million), shortest payback period (0.5 years), and highest return on investment (223.8%), which was partially due to revenues generated by mixed-metal leachate. Based on the low environmental impact and high return on investment, recycled graphite is the best choice for all three forms of graphite production over the life cycle of a 15-year graphite production facility and supports the use of global strategies that enhance supply chain resiliency for critical materials while also reducing carbon emissions.