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Abstract Volcano-sedimentary lithium (Li) deposits are a potential source of battery-grade Li, although the important factors controlling Li enrichment in these systems remain unclear. At Thacker Pass in Nevada, high-grade mineralization overprinted intracaldera lacustrine claystone made of authigenic Li-rich smectite with bulk grades of ~3,000 ppm Li, converting it to illitic claystone with grades of ~6,000 ppm Li. Some attribute this enrichment to burial diagenesis, whereas others propose lacustrine Li enrichment through leaching and climate-driven evapoconcentration enhanced by postdepositional hydrothermal alteration. To better understand Li enrichment in volcano-sedimentary systems, claystones from throughout Thacker Pass were analyzed using powder X-ray diffraction (PXRD), electron microprobe (EPMA), laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS), and stable isotope (clay δ18O, δ17O, and δ2H and carbonate δ13C and δ18O) methods. Compositional data suggest that illitization is required to achieve clay Li grades above ~0.9 wt % in Mg silicate clays because of a charge-coupled substitution that requires filling interlayer vacancies with K. Clay chemical trends and computational modeling exercises also suggest that F may be important in the formation of Li-rich clays by lowering kinetic barriers to clay precursor growth and illitization. The results are incompatible with diagenetic smectite/illite formation but are consistent with a model wherein authigenic smectite was subjected to hydrothermal alteration in the presence of a K-, Li-, and F-rich fluid that permeated the stratigraphy through a network of normal faults associated with caldera resurgence. These results also enhance our understanding of Li clay formation in other volcano-sedimentary systems. 

Abstract The importance of lithium for emerging industrial, aerospace, defense, and most significantly, lithium-ion battery technologies, is leading to a rapid increase in the demand for this critical resource. Although current global production of lithium is confined to historically exploited lithium-bearing pegmatites and closed-basin saline brines, new occurrences of these and several nascent types of lithium deposits are under varying stages of active exploration, development, and construction. This includes lithium resources associated with volcano-sedimentary deposits, continental and geothermal brines, and rare element granites. This paper presents an overview of lithium uses, production trends, the different types of lithium deposits, and their sizes, grades, and global distribution, as well as introducing the 24 papers in these two Special Issues of Economic Geology that review these lithium mineral systems and deposits in detail. These contributions include reviews and overviews of major deposit types, regional assessments of lithium provinces, deposit-specific research, and exploration techniques for finding additional resources. It is our hope that the scientific compilation and new insights presented in these two Special Issues of Economic Geology spur innovative thought and research in lithium deposit genesis and exploration to support the sustainable extraction of this critical element. 

Abstract Minerals are the fundamental constituents of Earth, and mineral names appear in scientific literature for disciplines including geology, chemistry, materials science, biology, and medicine, among others. Choosing a name is the full responsibility of the authors of new mineral proposals submitted to the International Mineralogical Association (IMA). Scientific nomenclature and its traditions have evolved over time, and consequently, mineral names track changes in the landscape of mineralogy with respect to language, technology, and culture. To evaluate these changes, the namesake information for all 5896 minerals approved by the IMA or “grandfathered” into use as of December 2022 was recorded and categorized within a workable database. The compiled information yields diverse insights into the intersection of science and culture and could also be used to project future trends. In this study, we used the name database to investigate gender diversity among mineral eponyms. More than half (ca. 54%) of all mineral species are named after people, the identities of whom are largely a reflection of the people that have historically been involved, in one way or another, in the geosciences and the mining industry. Of the 2738 people with minerals named for them, ∼6.1% are (interpreted to be) women. Nearly all minerals named for women were named during the last 60 years, although the growth rate in the year-on-year percentage of women among new mineral namesakes has slowed since about 1985. If current and historical trends hold, our model predicts that women will not comprise more than about 10.35% of newly established mineral namesakes in future years. The representation of women among mineral namesakes also differs starkly among countries. For example, Russians comprise 43.11% of women with minerals named for them but account for only 15.12% of all eponyms. However, there are additional disparities beyond the proportions of namesakes. For scientists who were alive when a mineral was named for them, women averaged 3.74 years older than men when evaluated over the same timespan (1954–2022). These results demonstrate that gender-based disparities are imprinted into current mineral nomenclature and indicate that gender parity among new mineral namesakes is impossible without unprecedented changes in the upstream demographics that are most likely to affect naming trends. 

Abstract The Duluth Complex is a large mafic intrusive system located in northeastern Minnesota emplaced as part of the 1.1-Ga Midcontinent Rift. Several Fe–Ti oxide-bearing ultramafic intrusions are hosted along the Western Margin of the Duluth Complex, and are discordant bodies present in a variety of geometries, hosted in multiple rock types, and dominated by peridotite, pyroxenite, and semi-massive to massive Fe–Ti oxide rock types. Their origin has been debated, and here we present geochemical evidence and modeling that supports a purely magmatic origin for the Titac and Longnose Fe–Ti oxide-bearing ultramafic intrusions. Ilmenite and titanomagnetite textures indicate a protracted cooling process, and δ34S values of sulfides reveal little assimilation of the footwall Virginia Formation, a fine-grained pelitic unit that contains sulfide-rich bands. We model the crystallization of a hypothetical parental magma composition to the host intrusion of Longnose using Rhyolite-MELTS and demonstrate that the accumulation of Fe–Ti oxides in the discordant intrusions cannot be explained by density-driven segregation of crystallized Fe–Ti oxides. Instead, we show that the development of silicate liquid immiscibility, occurring by the unmixing of the silicate melt into conjugate Si- and Fe-rich melts, can result in the effective segregation and transportation of the Fe-rich melt. The Fe-rich melt is ~2 orders of magnitude less viscous than the Si-rich melt, allowing the Fe-rich melt to be more effectively segregated and transported in the mush regime (crystallinities >50%). This suggests that viscosity, in addition to density, plays a significant role in forming the discordant Fe–Ti oxide-bearing ultramafic intrusions. We propose a genetic model that could also be responsible for the Fe–Ti oxide-rich layers or bands that are hosted within the igneous stratigraphy of mafic intrusions of the Duluth Complex. 

Critical minerals are essential for sustaining the supply chain necessary for the transition to a carbon-free energy source for society. Copper, nickel, cobalt, lithium, and rare earth elements are particularly in demand for batteries and high-performance magnets used in low-carbon technologies. Copper, predominantly sourced from porphyry deposits, is critical for electricity generation, storage, and distribution. Nickel, which comes from laterite and magmatic sulfide deposits, and cobalt, often a by-product of nickel or copper mining, are core components of batteries that power electric vehicles. Lithium, sourced from pegmatite deposits and continental brines, is another key battery component. Rare earth elements, primarily obtained from carbonatite- and regolith-hosted ion-adsorption deposits, have unique magnetic properties that are key for motor efficiency. Future demand for these elements is expected to increase significantly over the next decades, potentially outpacing expected mine production. Therefore, to ensure a successful energy transition, efforts must prioritize addressing substantial challenges in the supply of critical minerals, particularly the delays in exploring and mining new resources to meet growing demands.▪The energy transition relies on green technologies needing a secure, sustainable supply of critical minerals sourced from ore deposits worldwide.▪Copper, nickel, cobalt, lithium, and rare earth elements are geologically restricted in occurrence, posing challenges for extraction and availability.▪Future demand is expected to surge in the next decades, requiring unprecedented production rates to make the green energy transition viable. 

Sodic volcano-plutonic terranes in the Archean can be well preserved, but why oxidized S-rich sodic magmas and porphyry-type Cu-Au deposits are so rare remains poorly understood. Here we addressed this issue by measuring the S concentration and S6+/ΣS ratio of primary apatite grains in >2.7 Ga felsic volcanic rocks from the well-characterized Neoarchean Abitibi Greenstone Belt of the Superior Province, Canada. Whereas apatite grains in most samples contain low-S concentrations (<0.01 wt%, n = 24), a few apatite samples are S-rich (0.14 ± 0.03 wt%, 1σ) and have low-S6+/ΣS ratios (0.56 ± 0.17; 1σ, n = 4). Samples with S-poor apatite have variable whole-rock La/Yb ratios (generally <30) and zircon 10 000*(Eu/Eu*)/Yb ratios of 11 ± 8 (1σ), which may be products of plume-driven or over-thickened crustal melting. In contrast, the samples with S-rich apatite have elevated La/Yb ratios of 49 ± 15 (1σ), zircon 10 000*(Eu/EuN*)/Yb ratios of 26 ± 7 (1σ), and zircon δ18O values of 5.8 ± 0.1 ‰ (1σ), consistent with a deep, hydrous and homogeneous mantle-like source for the melts dominated by amphibole ± garnet fractionation that is reminiscent of subduction-like process. These are the first reported results documenting the predominant accommodation of relatively reduced S in S-rich apatite grains crystallized from terrestrial silicate melts, possibly reflecting slight oxidation associated with the hydration of Neoarchean mantle and crystal fractionation over the magma evolution. The more common S-poor apatite data suggest that suppressed oxidation of the parental sodic magmas led to weak S emission from Earth’s interior to its evolving surface, explaining the rarity of porphyry-type Cu deposits in >2.7 Ga Archean sodic volcano-plutonic terranes. 

Titanium (Ti) typically exhibits low mobility in geologic fluids due to the low aqueous solubility of common (Fe-)Ti oxide minerals. Consequently, Ti isotope variations (δ49/47Ti, given as δ49Ti) in geologic systems are primarily attributed to magmatic differentiation. Thus, the potential for fluid-mineral fractionation has received less attention. However, ligand-rich fluids are capable of mobilizing Ti as observed in natural systems and laboratory studies. As hydrothermal ore mineralization is commonly associated with ligand-rich brines capable of transporting significant quantities of metals, Ti isotopes may aid in understanding mineralization and alteration in complex hydrothermal systems. Here we present data from computational modeling of various Ti coordination complexes theorized to exist in geologic systems and/or under relevant experimental conditions as well as computed fractionation factors for various Ti-bearing crystalline phases to investigate the basic mechanics of equilibrium fluid-mineral Ti isotope fractionation. These results indicate that equilibrium fluid-mineral Ti isotope exchange between our modeled Ti complexes and phases with 6-coordinated Ti is predicted to generally lead to enrichment of heavy Ti isotopes in the fluid. Because minerals with 6-coordinated Ti (such as magnetite and ilmenite) are the most important reservoirs of Ti in the solid Earth, Ti isotope equilibration between terrestrial rocks and fluids can be generalized to enrich the fluid in heavy Ti isotopes. We also performed magnetite-ülvospinel leaching experiments to investigate fluid-mineral Ti isotope fractionation in this phase. Mineral leaching experiments varying acid strength, leaching temperature, and reaction time with HCl and HF qualitatively support the prediction that the fluid phase will become enriched in heavy Ti isotopes during fluid-mineral interactions that approach equilibrium with Ti-rich magnetite. Additionally, the leaching data also suggest that the fluid becomes slightly enriched in lighter Ti isotopes when Ti exchange is limited—potentially due to kinetic effects. Therefore, magnetite from natural systems may be depleted in heavy Ti isotopes during regenerative mineral replacement involving equilibration with fluids or may possibly become depleted in light Ti isotopes under a kinetic fractionation regime—leading to mineral δ49Ti values that are insufficiently explained by magmatic differentiation or inter-mineral fractionation. These results are a first look at fluid-mineral interactions that may affect Ti isotope fractionation in hydrothermal mineral systems, and Ti isotopes should be further studied as a potential method of understanding aqueous metal transport and tracing alteration in mineral deposits. 

Titanium (Ti) typically exhibits low mobility in geologic fluids due to the low aqueous solubility of common (Fe-)Ti oxide minerals. Consequently, Ti isotope variations (δ49/47Ti, given as δ49Ti) in geologic systems are primarily attributed to magmatic differentiation. Thus, the potential for fluid-mineral fractionation has received less attention. However, ligand-rich fluids are capable of mobilizing Ti as observed in natural systems and laboratory studies. As hydrothermal ore mineralization is commonly associated with ligand-rich brines capable of transporting significant quantities of metals, Ti isotopes may aid in understanding mineralization and alteration in complex hydrothermal systems. Here we present data from computational modeling of various Ti coordination complexes theorized to exist in geologic systems and/or under relevant experimental conditions as well as computed fractionation factors for various Ti-bearing crystalline phases to investigate the basic mechanics of equilibrium fluid-mineral Ti isotope fractionation. These results indicate that equilibrium fluid-mineral Ti isotope exchange between our modeled Ti complexes and phases with 6-coordinated Ti is predicted to generally lead to enrichment of heavy Ti isotopes in the fluid. Because minerals with 6-coordinated Ti (such as magnetite and ilmenite) are the most important reservoirs of Ti in the solid Earth, Ti isotope equilibration between terrestrial rocks and fluids can be generalized to enrich the fluid in heavy Ti isotopes. We also performed magnetite-ülvospinel leaching experiments to investigate fluid-mineral Ti isotope fractionation in this phase. Mineral leaching experiments varying acid strength, leaching temperature, and reaction time with HCl and HF qualitatively support the prediction that the fluid phase will become enriched in heavy Ti isotopes during fluid-mineral interactions that approach equilibrium with Ti-rich magnetite. Additionally, the leaching data also suggest that the fluid becomes slightly enriched in lighter Ti isotopes when Ti exchange is limited—potentially due to kinetic effects. Therefore, magnetite from natural systems may be depleted in heavy Ti isotopes during regenerative mineral replacement involving equilibration with fluids or may possibly become depleted in light Ti isotopes under a kinetic fractionation regime—leading to mineral δ49Ti values that are insufficiently explained by magmatic differentiation or inter-mineral fractionation. These results are a first look at fluid-mineral interactions that may affect Ti isotope fractionation in hydrothermal mineral systems, and Ti isotopes should be further studied as a potential method of understanding aqueous metal transport and tracing alteration in mineral deposits. 

This chapter discusses how radiogenic and stable isotopes can be used in the study of metallic mineral deposits. Although the chapter is mostly focused on the radiogenic (Pb, Os) and heavy stable (Fe, Cu, Zn) isotopes of metallic elements, we complement the discussion highlighting also the power of stable isotopes of light elements, which are major to significant components of hydrothermal fluids and rocks (e.g., H, B, C, N, O, S), as well as of radiogenic isotopes of elements (Sr, Nd, Hf ) that are useful in tracing fluid/magma sources and their interaction with the host rocks. In the first part of this chapter we discuss general aspects of isotopes clarifying the differences between stable non-radiogenic and stable radiogenic isotopes and, consequently, their different applicability to metallogenic studies. Due to their properties, stable non-radiogenic isotopes record mass-dependent fractionation that occur in many reactions associated with the formation of mineral deposits. Mass-dependent fractionation of stable non-radiogenic isotopes occurs both under equilibrium and non-equilibrium (kinetic) conditions of the reactions leading to ore mineral deposition and is controlled by various physico-chemical parameters, like, among the principal ones, temperature, oxygen fugacity, and biological activity. Therefore, stable non-radiogenic isotopes can inform us about the physico-chemical and, eventually, biological processes that control ore mineral deposition and also on the sources of some metals (e.g., transition metal isotopes of elements like Fe, Cu, Zn) or of the fluids (e.g., H, C, O, N, S isotopes) and even of metal ligands (e.g., S, Cl). We conclude the first part of the chapter providing some hints on the strategy of sampling and on the instrumentation related to isotopic studies. In the second part we discuss radioactive-radiogenic isotope systems and their applications in metallogenic studies of metallic mineral deposits. Stable radiogenic isotopes are characterized by relative variations that are controlled, in each geological system, by the addition of a radiogenic component of an isotope, derived from the decay of a radioactive parent, to the same radiogenic isotope already present in the Earth since its formation  4.55 Gyr ago. This relative variation is usually expressed as the ratio of a radiogenic isotope of an element to a non-radiogenic isotope of the same element. The ratio of these two isotopes has increased since the Earth formation and the magnitude of its variations depends on the radioactive/ radiogenic isotope ratios in different geological systems and on the time elapsed since the system has formed. The Earth is  4.55 Gyr old and has evolved from an initially homogeneous isotopic composition to reservoirs (e.g., mantle, crust) and crustal rocks with very variable radioactive/radiogenic isotope ratios due to magmatic, metamorphic, weathering, atmospheric and biologic processes, among others. This has resulted in extremely large variations of radiogenic isotopes in rocks and reservoirs of the Earth which can track various geological processes. In ore geology, stable radiogenic isotopes are best suited for tracing metal (e.g., Pb, Os) sources from different rocks and reservoirs (e.g., mantle, upper crust, lower crust), fluid-rock interactions (i.e., the hydrothermal plumbing system), or magma-host rock interactions (e.g., host rock assimilation by magmas associated with magmatic-hydrothermal deposits). Radioactive-radiogenic isotope systems allow us to determine also absolute ages of suitable minerals that are found in mineral deposits. This is an essential information in metallogeny that allows us to link the formation of a mineral deposit to a specific geological process and/or to specific periods of the Earth’s history. We discuss various dating methods that are extensively applied to date mineral deposits. These methods can be subdivided into those that allow a direct dating of ore minerals (e.g., RedOs dating of molybdenite, UdPb dating of cassiterite) and those that allow dating of minerals that are demonstrably related with the mineralization (e.g., UdPb dating of zircon from magmatic rocks associated with magmatic-hydrothermal deposits; Ar/Ar dating of K-bearing minerals resulting from alteration associated with various types of mineral deposits). We discuss pros and cons of using these various methods and also mention methods that are less used (because potentially less accurate and precise), but sometimes represent the only possibility to provide an age to deposit types that are notoriously difficult to date (e.g., MVT and Carlin-type deposits). We highlight the power of both stable radiogenic and non-radiogenic isotopes in unravelling the genesis of metallic mineral deposits through a series of conceptual and real examples applied to a broad range of mineral deposit types such as porphyry systems (i.e., porphyry deposits, high- and intermediate-sulfidation epithermal deposits, skarn, carbonate replacement deposits, sediment-hosted Au deposits), low-sulfidation epithermal deposits, IOCG deposits, ortho-magmatic deposits, volcanic-hosted massive sulfide deposits (VHMS), sediment-hosted deposits (stratiform copper, MVT), and supergene deposits. In the third part of the chapter, we discuss the use of transition metal stable non-radiogenic isotopes to mineral deposits. Although in its infancy, the application of transition metal isotopes to mineral deposit investigation is quickly growing because these isotopes allow us to address different aspects of the formation of mineral deposits compared to radiogenic isotopes. In particular, isotopes of transition metals (like stable isotopes of light elements) undergo mass-dependent fractionation processes that may be associated with different types of equilibrium and non-equilibrium chemical, physical and biological reactions occurring during the formation of mineral deposits. We focus on the applications of the isotopes of Cu, Fe and Zn to various deposit types, because isotopes of these transition metals are those that have been most extensively used in mineral deposit studies. Mass-independent fractionation may also occur for isotopes of some elements and could be a developing field that has not yet been extensively explored in the study of mineral deposits. 

Oxidation of the sub-arc mantle driven by slab-derived fluids has been hypothesized to contribute to the formation of gold deposits in magmatic arc environments that host the majority of metal resources on Earth. However, the mechanism by which the infiltration of slab-derived fluids into the mantle wedge changes its oxidation state and affects Au enrichment remains poorly understood. Here, we present the results of a numerical model that demonstrates that slab-derived fluids introduce large amounts of sulfate (S⁶⁺) into the overlying mantle wedge that increase its oxygen fugacity by up to 3 to 4 log units relative to the pristine mantle. Our model predicts that as much as 1 wt.% of the total dissolved sulfur in slab-derived fluids reacting with mantle rocks is present as the trisulfur radical ion, S₃^–. This sulfur ligand stabilizes the aqueous Au(HS)S₃^–complex, which can transport Au concentrations of several grams per cubic meter of fluid. Such concentrations are more than three orders of magnitude higher than the average abundance of Au in the mantle. Our data thus demonstrate that an aqueous fluid phase can extract 10 to 100 times more Au than in a fluid-absent rock-melt system during mantle partial melting at redox conditions close to the sulfide-sulfate boundary. We conclude that oxidation by slab-derived fluids is the primary cause of Au mobility and enrichment in the mantle wedge and that aqueous fluid-assisted mantle melting is a prerequisite for formation of Au-rich magmatic hydrothermal and orogenic gold systems in subduction zone settings.