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<jats:title>Abstract</jats:title> <jats:p>Ancient manganese (Mn) deposits are primarily characterized by the presence of Mn(II) carbonates that likely formed by the diagenetic reduction of precursor Mn(IV) oxides. As such, Precambrian sedimentary Mn deposits have been used as a line of evidence for the evolution of oxygen in Earth’s surface environments. However, recent studies have shown that these Mn(II)-carbonates have the ability to directly accumulate within anoxic water columns, where free oxygen does not play a role in their formation. This alternative pathway casts uncertainty on the robustness of using ancient Mn deposits to constrain the redox fabric of the past marine water columns. Here, we investigate the Wafangzi Mn and Fe ore deposit from the 1.45 billion-year-old Tieling Formation, North China. The deposit contains Mn(II, III) mineral phases (hausmannite, braunite) as inclusions, or unreacted residues, trapped within Mn(II) carbonate (Ca-rhodochrosite). Some nodules and oolites of Mn(II) and Fe(II)-carbonate phases are also present and display a banded structure with concentric rings. Mn(III) oxide (manganite) is present in a paragenetic assemblage along with hematite and replacement textures with braunite. The negative carbon isotope composition (δ13C, –7‰ to –4‰) from Mn(II) carbonate samples in the Wafangzi Mn deposit which are distinct from that of contemporaneous seawater (~0‰), along with petrographic and speciation analyses, collectively suggest that the Mn(II, III)- and Fe(II)-bearing mineral phases formed through the diagenetic reduction of primary Mn(IV)/Fe(III) minerals coupled to the oxidation of organic matter. Therefore, the Wafangzi Mn deposit suggests the presence of sufficiently oxygenated marine waters, overlying anoxic ferruginous deeper waters with a transitional manganous water layer that could have driven the redox cycling of Mn, Fe, and C. Given the contemporaneous economic Mn deposits in the 1.45 Ga Ullawarra Formation in Western Australia, our findings imply the existence of a transient, and perhaps widespread, pulsed oxygenation event in the mid-Proterozoic oceans.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The anisotropic textures, including unidirectional solidification textures and graphic intergrowths, characteristic for pegmatites, are interpreted to result from disequilibrium crystallization at high degrees of undercooling. Experimental studies have revealed the existence of thin boundary layers surrounding the rapidly growing crystals. Here, tourmaline-bearing samples from the outer zones of the Emmons pegmatite (Maine, U.S.A.) are used to examine if a boundary layer can also occur in natural samples. Crystal morphology is linked with geochemistry to understand the evolution of pegmatite melts and to constrain disequilibrium conditions at large degrees of undercooling. Petrographic studies and semiquantitative micro-X-ray fluorescence element mapping were conducted to identify crystal morphology and zonation, complemented with electron microprobe analyses to determine major and minor element compositions and LA-ICP-MS analyses of selected trace elements. Three textural groups were identified: comb-like tourmaline, quartz-tourmaline intergrowths, and radiating tourmaline. The intergrowths are optically coherent and are split into three different morphologies: central, second tier, and skeletal tourmaline. Most tourmaline is schorl, but chemical variation occurs on three different scales: between textural groups, between different morphologies, and intracrystalline. The largest scale geochemical variation is caused by the progressive evolution of the melt as it crystallized from the borders inwards, while the intracrystalline variations are attributed to sector zoning. A model is suggested where the systematic variation of Mg, Mn, and Fe within individual intergrowths is proposed to be the result of crystallization from a boundary layer, rich in water and other fluxing elements (e.g., Li, P, B), formed around the rapidly growing central tourmaline. Here, we show the first examples of boundary layers in natural pegmatites. Furthermore, the results bring into question whether boundary layer tourmaline can be used as a bulk melt indicator in pegmatitic melts.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>This issue of New Mineral Names provides a summary of the newly described minerals from 2023 and selected information for recent descriptions from October to December of 2023. New mineral name trends and observations are presented using an objective, data-driven, and curated examination of new mineral species and their broader implications.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The electrical conductivity of apatite single crystals along three main crystalline directions was measured in situ using a YJ-3000t multi-anvil apparatus and a combined system consisting of the impedance/gain-phase analyzer (Solartron 1260) and dielectric interface (Solartron 1296) at 973–1373 K and 1.0–3.0 GPa. The obtained results indicate that the relationship between the electrical conductivity and temperature conforms to the Arrhenius relation. At 2.0 GPa, the electrical conductivity of apatite with relatively high activation enthalpies of 1.92–2.24 eV shows a significant anisotropy with an extremely high anisotropic degree (τ = ~8–16) value. For a given [001] crystallographic orientation, the electrical conductivity of apatite slightly decreases with increasing pressure, and its corresponding activation energy and activation volume of charge carriers are 2.05 ± 0.06 eV and 9.31 ± 0.98 cm3/mol, respectively. All of these observed anomalously high activation enthalpy and positive activation volume values suggest that the main conduction mechanism is related to the monovalent fluorine anion at high temperature and high pressure. Furthermore, three representative petrological average schemes, including the parallel, Hashin-Shtrikman upper bound, and average models were selected to establish the functional relation for the electrical conductivity of the phlogopite-apatite-peridotite rock system along with the volume percentages of apatite ranging from 1 to 10% at 973–1373 K and 2.0 GPa. For a typical Hashin-Shtrikman upper bound model, the electrical conductivity-depth profile for peridotite containing the 10% volume percentage of apatite was successfully constructed in conjunction with our acquired anisotropic electrical conductivity results and available temperature gradient data (11.6 and 27.6 K/km) at depths of 20–90 km. Although the presence of apatite in peridotite cannot explain the high-conductivity anomalies in western Junggar of Xinjiang autonomous region, it may provide a reasonable constraint on those of representative apatite-rich areas.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Inorganic X-ray amorphous materials (iXAMs) such as vitreous phases, minerals having an insufficient number of repeating structural units to diffract X-rays, and inorganic solids with exclusively structural short-range order are ubiquitous in soils and relevant for numerous environmental processes, but are notoriously difficult to identify and quantify. To test for the quantification and chemical composition of iXAMs in soil, we prepared four mineral mixtures containing quartz, calcite, feldspars, and clay minerals in different proportions typical of soils and amended them with 10–70 wt% iXAMs in the form of a 1:1 weight mixture of ferrihydrite and opal-A. We quantified these iXAMs in mineral mixtures by analyzing powder X-ray diffraction (PXRD) data using the Rietveld method and compared the results for different sample preparation techniques (conventional and spray drying) based on the internal standard method in Rietveld analysis. The mineral mixtures were also analyzed for their chemical composition by X-ray fluorescence (XRF) spectrometry, and mass balance calculations combining Rietveld and XRF data were carried out to estimate the chemical composition of iXAMs in mineral mixtures. Both sample preparation methods showed no significant difference in determined iXAM contents and yielded accurate results for iXAM contents within ±3 wt% at the 95 % confidence level (2σ). The relative accuracy deteriorated with decreasing iXAM content, but remained below 10 % for iXAM contents &amp;gt; 10 wt% (mean = 3 %). The precision of iXAM content quantification in mineral mixtures prepared by spray drying was slightly better though statistically equivalent to the conventionally prepared mixtures (2σ = 1.49 and 1.61 wt%). The average precision of both sample preparation methods was ±2 wt% at the 95 % confidence level. Levels of detection and quantification of iXAMs in spray-dried mineral mixtures containing 1–10 wt% iXAMs were estimated at 0.8 and 4.0 wt%, respectively. The chemical composition of iXAMs in terms of major oxides was accurately assessed by mass balance calculations with average relative errors for nominal SiO2 and Fe2O3 contents of 9.4 and 4.3 %, respectively (range = 0.02–54.7 %). Even though adsorbed H2O and structural H2O/OH- as quantified by the loss 50 on ignition comprised an important portion of the iXAMs (15.3 wt%), their LOI in mineral mixtures as derived from mass balance calculations could only be quantified with an average relative error of 67.2 % (range = 1.30–371 %). We conclude that iXAMs in soil and related geomaterials present at levels &amp;gt; 4 wt% can be quantified by Rietveld analysis of PXRD data with an accuracy of ±3 wt% at best. Combined results of Rietveld and XRF analyses can yield accurate results for the chemical composition of iXAMs within a relative error of 10 % for major oxides, provided iXAM contents exceed 10 wt% and the content and chemical composition of all crystalline mineral phases is accurately assessed. The results presented in this study lay the foundation to explore iXAM contents and chemical compositions in soils and to examine their impact on soil physicochemical properties and biogeochemical element cycles.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Critical rare metal deposits are strategic resources as these metals are significant for high-tech industries. Among the critical rare metals, stannum (Sn) in nature is mostly found in Sn-oxide mineral, cassiterite (SnO2), and closely associated with granite or pegmatite. Carbonatite and alkaline rocks are more likely to contain huge amounts of critical rare metals, especially REEs and niobium (Nb). We reported abundant cassiterite (SnO2) and evaluated potential Sn mineralization in the Bayan Obo Fe-Nb-REE deposit in northern China, the largest REE deposit worldwide. In this paper, evidence for the Sn enrichment in a carbonatite-hosted REE deposit is given for the first time.</jats:p> <jats:p>REE-Fe ores are dominantly mined in the Bayan Obo deposit. Disseminated, banded and massive ores contain tens to hundreds ppm Sn and vein-type ores are notably rich in Sn (up to 1500 ppm). Through in situ micro-zonation mineralogical analyses, two occurrences of cassiterite and several Sn-rich minerals are identified in these REE-Fe ores. Abundant early-stage nanoscale cassiterite inclusions are present within magnetite grains in banded and massive REE-Fe ores, and ubiquitous late-stage granular cassiterite, Sn-rich rutile, titanite, and bafertisite are present in vein-type REE-Fe ores. Multiple U-Th-Pb dating of monazite and columbite-Mn in association with cassiterite yields peak ages of 425 Ma and 419±18 Ma, respectively, revealing coeval Sn and Nb mineralization. We concluded that Sn was derived from carbonatitic magmas, and the dense distribution of cassiterite inclusions in magnetite marked the pre-enrichment of Sn in the Bayan Obo deposit. Subsequent Early Paleozoic hydrothermal events led to the reactivation and further Sn mineralization. Similar to Nb, Sn was mineralized in the Bayan Obo deposit probably to form economically important resources. Our study highlights the potential of Sn mineralization associated with carbonatite-hosted REE deposits.</jats:p>