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1. Uranium Redox and Deposition Transitions Embedded in Deep‐Time Geochemical Models and Mineral Chemistry Networks

   https://doi.org/10.1029/2023GC011267  

   Moore, E_K; Li, J.; Zhang, A.; Hao, J.; Morrison, S_M; Hummer, D_R; Yee, N. (February 2024, Geochemistry, Geophysics, Geosystems)

   Abstract Uranium (U) is an important global energy resource and a redox sensitive trace element that reflects changing environmental conditions and geochemical cycling. The redox evolution of U mineral chemistry can be interrogated to understand the formation and distribution of U deposits and the redox processes involved in U geochemistry throughout Earth history. In this study, geochemical modeling using thermodynamic data, and mineral chemistry network analysis are used to investigate U geochemistry and deposition through time. The number of U⁶⁺mineral localities surpasses the number of U⁴⁺mineral localities in the Paleoproterozoic. Moreover, the number of sedimentary U⁶⁺mineral localities increases earlier in the Phanerozoic than the number of U⁴⁺sedimentary mineral localities, likely due to the necessity of sufficient sedimentary organic matter to reduce U⁶⁺–U⁴⁺. Indeed, modeling calculations indicate that increased oxidative weathering due to surface oxygenation limited U⁴⁺uraninite (UO₂) formation from weathered granite and basalt. Louvain network community detection shows that U⁶⁺forms minerals with many more shared elements and redox states than U⁴⁺. The range of weighted Mineral Element Electronegativity Coefficient of Variation (wMEE_CV) values of U⁶⁺minerals increases through time, particularly during the Phanerozoic. Conversely, the range of wMEE_CVvalues of U⁴⁺minerals is consistent through time due to the relative abundance of uraninite, coffinite, and brannerite. The late oxidation and formation of U⁶⁺minerals compared to S⁶⁺minerals illustrates the importance of the development of land plants, organic matter deposition, and redox‐controlled U deposition from ground water in continental sediments during this time‐period. 

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2. Missing nitrogen source during ecosystem succession within retrogressive thaw slumps in Alaska

   https://doi.org/10.1088/1748-9326/acd0c2  

   Buckeridge, Kate M.; McLaren, Jennie R.; Mack, Michelle C.; Schuur, Edward A. G.; Schimel, Joshua (May 2023, Environmental Research Letters)

   Abstract Retrogressive thaw slumps (RTS)—thermal erosion of soil and vegetation after ground ice thaw—are increasing. Recovery of plant biomass after RTS is important for maintaining Arctic carbon (C) stocks and is regulated by nutrient availability for new plant growth. Many RTS are characterized by verdant shrub growth mid-succession, atypical of the surrounding nutrient-limited tundra. Here, we investigated the potential for internal and external sources of nitrogen (N) and phosphorus (P) to support mid-successional shrub growth at three Alaskan RTS chronosequences. We assessed patterns of soil and microbial CNP, soil NP cycling rates and stocks, N inputs via biological N₂-fixation, and thaw leachate over time after disturbance. We found a clear transfer of P stocks from mineral to organic soils with increasing site age, yet insufficient N from any one source to support observed shrub growth. Instead, multiple mechanisms may have contributed to mid-successional shrub growth, including sustained N-cycling with reduced plant biomass, N leaching from undisturbed tundra, uninvestigated sources of N₂-fixation, and most promising given the large resource, deep mineral soil N stocks. These potential mechanisms of N supply are critical for the regulation of the Arctic C cycle in response to an increasingly common climate-driven disturbance. 

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3. Applications of radiogenic and transition metal isotopes to the study of metallic mineral deposits

   https://doi.org/10.1016/b978-0-323-99762-1.00010-3  

   Chiaradia, Massimo; Mathur, Ryan; Vennemann, Torsten; Simon, Adam (January 2025, Elsevier)

   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. 

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4. Rock Magnetic Signature of Red Beds From the Intermontane Tarom Basin (NW Iran): Insights Into Middle to Late Miocene Environmental Conditions and Possible Forcing Mechanisms

   https://doi.org/10.1029/2023PA004811  

   Paknia, Mohammad; Ballato, Paolo; Bilardello, Dario; Zeeden, Christian; Jackson, Mike (January 2025, Paleoceanography and Paleoclimatology)

   Abstract The study of sedimentary magnetism in the intermontane Tarom Basin (northern Iran) offers insights into local paleoenvironmental conditions during global middle‐late Miocene climate changes and the topographic growth triggered by the Arabia‐Eurasia continental collision. Rock magnetic results reveal that the ∼16.2 to ∼10–9 Ma coarse‐grained deposits at the basin's southern margin present a homogenous magnetic mineral assemblage, reflecting sediment provenance. Conversely, the ∼13.2 to ∼7.6 Ma, fine‐grained deposits in the basin's depocenter include alternating playa‐lake and lacustrine deposits, recording dry, evaporative conditions, leading to hematite formation in a low‐temperature oxidizing environment, and wetter conditions that preserve the original detrital signal, respectively. Time series analyses show cyclicity in different period bands for magnetic susceptibility, but precession and obliquity cycles can hardly be resolved in the record. Comparison with deep‐sea oxygen isotope data suggests that from ∼13.2 to ∼10.8 Ma environmental conditions likely mirrored global climatic forcing, with lacustrine and playa‐lake deposits associated with increased and decreased global temperature, respectively. At ∼10.8 Ma, the basin likely recorded the Tortonian Thermal Maximum with the establishment of a lacustrine system. From ∼10.4 Ma, the magnetic susceptibility signal departed from the global climate record, possibly due to basin margin (western Alborz and Tarom mountains) and regional (Anatolian‐Iranian plateau) topographic growth, accompanied by increased precipitation seasonality, focused rainfall and augmented erosion rates. Finally, we suggest that before ∼10.8 Ma, the Hadley cells expanded northward, leading to a trade‐dominated system with moist air masses sourced from the Caspian, while from ∼10.8 Ma, westerlies dominance progressively prevailed. 

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5. Hunter-Gatherers Harvested and Heated Microbial Biogenic Iron Oxides to Produce Rock Art Pigment

   https://doi.org/10.1038/s41598-019-53564-w  

   MacDonald, Brandi Lee; Stalla, David; He, Xiaoqing; Rahemtulla, Farid; Emerson, David; Dube, Paul A.; Maschmann, Matthew R.; Klesner, Catherine E.; White, Tommi A. (November 2019, Scientific Reports)

   Abstract Red mineral pigment use is recognized as a fundamental component of a series of traits associated with human evolutionary development, social interaction, and behavioral complexity. Iron-enriched mineral deposits have been collected and prepared as pigment for use in rock art, personal adornment, and mortuary practices for millennia, yet little is known about early developments in mineral processing techniques in North America. Microanalysis of rock art pigments from the North American Pacific Northwest reveals a sophisticated use of iron oxide produced by the biomineralizing bacteriumLeptothrix ochracea;a keystone species of chemolithotroph recognized in recent advances in the development of thermostable, colorfast biomaterial pigments. Here we show evidence for human engagement with this bacterium, including nanostructural and magnetic properties evident of thermal enhancement, indicating that controlled use of pyrotechnology was a key feature of how biogenic iron oxides were prepared into paint. Our results demonstrate that hunter-gatherers in this area of study prepared pigments by harvesting aquatic microbial iron mats dominated by iron-oxidizing bacteria, which were subsequently heated in large open hearths at a controlled range of 750 °C to 850 °C. This technical gesture was performed to enhance color properties, and increase colorfastness and resistance to degradation. This skilled production of highly thermostable and long-lasting rock art paint represents a specialized technological innovation. Our results contribute to a growing body of knowledge on historical-ecological resource use practices in the Pacific Northwest during the Late Holocene. Figshare link to figures:https://figshare.com/s/9392a0081632c20e9484. 

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