High Li Content Research Articles

Glassy Metal–Organic‐Framework‐Based Quasi‐Solid‐State Electrolyte for High‐Performance Lithium‐Metal Batteries

AbstractEnhancing ionic conductivity of quasi‐solid‐state electrolytes (QSSEs) is one of the top priorities, while conventional metal–organic frameworks (MOFs) severely impede ion migration due to their abundant grain boundaries. Herein, ZIF‐4 glass, a subset of MOFs, is reported as QSSEs (LGZ) for lithium‐metal batteries. With lean Li content (0.12 wt%) and solvent amount (19.4 wt%), LGZ can achieve a remarkable ion conductivity of 1.61 × 10−4 S cm−1 at 30 °C, higher than those of crystalline ZIF‐4‐based QSSEs (LCZ, 8.21 × 10−5 S cm−1) and the reported QSSEs containing high Li contents (0.32–5.4 wt%) and huge plasticizer (30–70 wt%). Even at −56.6 °C, LGZ can still deliver a conductivity of 5.96 × 10−6 S cm−1 (vs 4.51 × 10−7 S cm−1 for LCZ). Owing to the grain boundary‐free and isotropic properties of glassy ZIF‐4, the facilitated ion conduction enables a homogeneous ion flux, suppressing Li dendrites. When paired with LiFePO4 cathode, LGZ cell demonstrates a prominent cycling capacity of 101 mAh g−1 for 500 cycles at 1 C with the near‐utility retention, outperforming LCZ (30.7 mAh g−1) and the explored MOF‐/covalent–organic frameworks (COF)‐based QSSEs. Hence, MOF glasses will be a potential platform for practical quasi‐solid‐state batteries in the future.

The role of Li site occupancy on the Li-ion conductivity of Ta-doped Li6.75La3Zr1.75Ta0.25O12 solid electrolyte materials with high Li concentrations

Garnet-type Li7La3Zr2O12 has attracted much attention because of its promising properties of high ionic conductivity, good chemical stability against Li metal, and good mechanical strength. To better understand the Li conduction mechanism, the Li site occupancy and Li-ion conductivity are studied with a high Li concentration in the range of 6.70–7.15 mol per formula unit. Aluminum and silicon, which presumably were transferred to the sample from the Al2O3 crucible during processing, were included in the cubic garnet structure for the Rietveld refinements. The Li-ion conductivity increases with the occupancy of the octahedral Li site (Occupancy: 0.78–0.87, Li-ion conductivity: 3–5 × 10−4 S/cm). As the lithium content increases, the portion of lithium occupying the 96 h octahedral site increases and that occupying the 24d tetrahedral site decreases.

Assessment of Lithium, Macro- and Microelements in Water, Soil and Plant Samples from Karst Areas in Romania.

Lithium is a critical element for the modern society due to its uses in various industrial sectors. Despite its unequal distribution in the environment, Li occurrence in Romania was scarcely studied. In this study a versatile measurement method using ICP-MS technique was optimized for the determination of Li from various matrixes. Water, soil, and plant samples were collected from two important karst areas in the Dobrogea and Banat regions, Romania. The Li content was analyzed together with other macro- and microelement contents to find the relationship between the concentration of elements and their effect on the plants’ Li uptake. In Dobrogea region, half of the studied waters had high Li concentration, ranging between 3.00 and 12.2 μg/L in the case of water and between 0.88 and 11.1 mg/kg DW in the case of plants, while the Li content in the soil samples were slightly comparable (from 9.85 to 11.3 mg/kg DW). In the Banat region, the concentration of Li was lower than in Dobrogea (1.40–1.46 μg/L in water, 6.50–9.12 mg/kg DW in soil, and 0.19–0.45 mg/kg DW in plants). Despite the high Li contents in soil, the Li was mostly unavailable for plants uptake and bioaccumulation.

Role of extrusion temperature on the microstructure evolution and tensile properties of an ultralight Mg-Li-Zn-Er alloy

Role of extrusion temperature on the microstructure evolution and tensile properties of an ultralight Mg-10Li-5Zn-0.5Er alloy was studied. The results indicate that the second phases and grains are all refined after extrusion. It is firstly reported that there are two kinds of grains zone including micro-grained region and coarse-grained region in the as-extruded Mg-Li alloys with high Li content (≥ 9 wt%). As the extrusion temperature increases from 150 °C to 300 °C, the volume of micro-grained region decreases and finally almost disappears. The grain size of coarse-grained region increases as well. The amount of Mg-Li-Zn precipitates along the boundaries decreases and their quantity in the grains increases with grain coarsening. The strength rises slightly and the elongation decreases notably with the enhancement of extrusion temperature. As the extrusion temperature increases, the crack initiation appears from mainly around the bulky Mg-Zn-Er phases to mainly along the grain boundaries. Due to the grain refinement, the second phases strengthening, and the abundant slip systems of β-Li phase, the comprehensive properties of the as-extruded alloys have leading position in the field of wrought Mg-Li alloys and the optimum comprehensive tensile properties are gained in the alloy extruded at 275 °C.

Thermal processing conditions for the synthesis of near theoretical density Li5La3Ta2O12 ceramics for ceramic dual-mode detectors

A family of Li-containing garnet compounds, extensively investigated for Li-ion solid electrolyte applications, show great potential to be developed into transparent ceramic dual-mode scintillators. In particular, Li5La3Ta2O12 (LLTaO) shows promise as an efficient dual-mode scintillator due to its high Li content, high density, non-hygroscopicity, and high effective-Z. Often the synthesis of LLTaO ceramics involves solid state processing techniques starting with oxide and carbonate powders, calcining, sintering for the removal of residual porosity, and post-processing. This study focuses on two objectives: (1) establishing thermal processing boundary conditions for a flexible alkoxide-based sol-gel method for synthesizing fine-grained powders; and (2), consolidating powders via hot-pressing to form high-density ceramics. In this study, near single-phase ceramics were achieved by hot-pressing sol-gel powders with varying amounts of excess Li. Rietveld refinements were used to analyze X-ray diffraction data and provide a quantitative evaluation of the phases present in the hot pressed ceramics. Some of the diffraction data showed large low angle peak asymmetry, suggesting the presence of two cubic Li5La3Ta2O12 garnet phases with different lattice parameters. Depending on the synthesis and processing conditions, the refinement revealed ~ 90 wt% concentration of a phase with a ≈ 12.8 Å and ~ 10 wt% concentration of a phase with a ≈ 12.9 Å, indicating a remaining excess of Li in the hot pressed ceramics in the large lattice parameter phase. These synthesis experiments allowed for the determination of a baseline for Li loss during hot-pressing. X-ray excited radioluminescence and photoluminescence excitation and emission spectra were obtained from the hot pressed ceramics. The measured emission spectra featured broad tantalate emission and line emissions likely from a rare-earth impurity.

Layer spacing gradient (NaLi)1−xCoO2 for electrochemical Li extraction

Layer spacing gradient (NaLi)1−xCoO2 for electrochemical Li extraction

Microstructural control and mechanical properties of a high Li-containing Al-Mg-Li alloy

AlLi alloys, as promising ultra-light airframe structural materials, have attracted extensive attention with respect to improving their mechanical properties. However, due to the detrimental effect of Li, the strength and ductility of Al-Mg-Li alloys have been found to be relatively low. In this work, high strength and simultaneously improved ductility were achieved in an Al-Mg-Li alloy with a high Li content by accurately controlling the microstructure through equal channel angular pressing (ECAP) and post-heat treatment. During the ECAP procedure, ultrafine grains with precipitating S1 phases were obtained in the alloy. Then, relatively coarse S1 phases due to the high Li content were effectively refined, large amounts of fine metastable δ’ phase particles uniformly precipitated without precipitate-free zones (PFZs), and ultrafine grains remained during subsequent heat treatment, thus achieving a combination of high strength (>450 MPa) and good ductility (>13.5%). The heat treatment including short-term solution and ageing after severe plastic deformation (SPD) was verified to be applicable to other AlLi alloys to adjust the ultrafine microstructure and achieve an optimal combination of strength and ductility, which can increase the applications of AlLi alloys for lightweight key components in the aerospace field

Petrogenesis of Neoproterozoic rare metal granite-pegmatite suite in Jiangnan Orogen and its implications for rare metal mineralization of peraluminous rock in South China

Recent studies have demonstrated the Mesozoic explosive metallogeny of rare metals in China; however, Precambrian rare metal mineralization event is rarely reported or studied. The Jiangnan Orogen (JO) is a well-preserved Neoproterozoic orogenic belt in South China, and although it abounds with a huge amount of Neoproterozoic granitoids, lacks the equivalent amount granitic pegmatite. In this study, the geology, mineralogy, whole-rock composition, zircon U-Pb age and Hf isotope compositions of the Fanjingshan granite and surrounding rare metal pegmatites, and bulk composition of sedimentary wall rocks of the Taojinhe Formation in Guizhou province, western Jiangnan Orogen (JO), were studied to reveal the petrogenesis of the granite and pegmatite and the source relationship of the pegmatite with the Paleozoic and Mesozoic rare metal ore deposits in South China. The Fanjingshan granite and pegmatite both show Sn-Ta-Nb mineralization and have consistent zircon U-Pb ages of ca. 830 Ma, indicating the existence of the Neoproterozoic rare metal granite-pegmatite suite in the JO. The geology, mineralogy, whole-rock composition and zircon U-Pb age and Hf isotope study results demonstrate that the Fanjingshan rare metal pegmatite belongs to the Li-P-B-Sn-Ta-Nb granitic pegmatite in the Chemical composition-Mineral assemblage-Structural geology (CMS) classification (Dill, 2016), and has close spatial–temporal and source-differentiation connections with the Fanjingshan granite. The petrography and whole-rock composition studies revealed that the Taojinhe formation was formed by the deposition of mature and immature source materials from acidic igneous rocks in a continental arc setting. Comparison of the Hf isotope compositions of the Fangjingshan granite-pegmatite suite with those of the Fangjinshan Group and the high Li, Sn, Rb, W, Ta and Nb background concentrations in the Taojinhe Formation support the conclusion that the Taojinhe Formation was a contributing source to the granite-pegmatite suite. A comparative study of the Fanjingshan granite with synchronous S-type granitoids revealed that the granitoids in the eastern and western JO have distinct sources and degrees of differentiation, indicating the limited ore-forming potential of the Neoproterozoic granitoids in the eastern JO. The Fanjingshan rare-metal granite-pegmatite suite has consistent Hf isotope model ages of 1.6–2.3 Ga with the Paleozoic and Mesozoic Nb-Ta ± Sn-W ± Be-Li ore deposits in South China, indicating a common origin from the Paleoproterozoic crust and the source inheritance of the western JO from the Cathaysia Block.

Li-isotope exchange during low-temperature alteration of the upper oceanic crust at DSDP Sites 417 and 418

The record of the Li-isotopic composition of ancient-seawater has the potential to provide important insight into the Earth system. However, we still have an incomplete understanding of the controls on the magnitude and isotopic compositions of the fluxes of Li into and out of the ocean. An important sink for Li from seawater is through low-temperature hydrothermal alteration of the upper oceanic crust. Here we present a detailed study of three adjacent drill cores in 120 Myr old Atlantic crust (Holes 417A, 417D and 418A) that had very different sedimentation histories. Samples from Hole 417A, drilled on a topographic high and exposed to seawater for >20 Myr before sediment started to accumulate, have much higher Li contents (up to ∼70 ppm) than samples from the other sites where sediment began accumulating immediately after crustal accretion (up to ∼20 ppm). Despite this difference in Li content, the δ7Li of the altered basalts in all cores increases with depth over the upper ∼40 m from around −1‰ at the lava-sediment interface to 6 ± 2‰ at ∼40 m depth, remaining roughly constant with depth after this. If the uppermost lavas equilibrated with seawater, with a bulk fractionation factor of ∼0.980 ± 0.003, then the isotopic composition of seawater 120 Myr ago was ∼19 ± 3‰, within the range of other estimates for Cretaceous seawater. Fluid-rock reaction models, with the hydrological regime varying as a function of depth and sediment accumulation history, can explain the observed rock compositions. However, modelling shows that complexities related to the time-varying hydrological regime, along with the possibility of time-varying δ7Li of seawater, mean that the Li-isotopic composition of altered oceanic lavas cannot be uniquely interpreted. The bulk Li content and isotopic composition of the well-sampled 120 Myr crust in Holes 417A, 417D and 418A suggest that Cretaceous upper oceanic crust was a sink for ∼4×109 mol yr−1 of Li. Surprisingly, the bulk Li-isotopic composition of the lavas sampled at these sites (∼6‰) is not much higher than that of fresh MORB, and within uncertainty of that of high-temperature hydrothermal vent fluids; i.e., high- and low-temperature alteration processes approximately balanced one another for Li-isotopes in the late Cretaceous. This could be fortuitous; alternatively, if the ocean was at steady state the main source of Li to the ocean at this time may have had a δ7Li similar to that of high-temperature hydrothermal fluids.

Microstructural aspects of additive manufacturing of Al[sbnd]Li alloys with high Li content

Laser assisted powder bed fusion using a binary AlLi alloy with high Li content (Al–14 at.%Li) has been performed for the first time. The aim was to generate microstructures with extended concentration range of AlLi alloys in which the formation of the brittle δ–AlLi phase is avoided. From conventional casting processes it is known that the δ–AlLi phase is detrimental to mechanical properties and corrosion resistance. All processing steps from the production of ingots free of contamination, oxidation and macrosegregation to the synthesis of fine spherical powders appropriate for additive manufacturing to the powder bed fusion routine using ultra short pulses have been investigated. In comparison with as–cast microstructures, the fast cooling rate after laser assisted powder bed fusion leads to a uniform Li distribution in the primary α phase rather than to the formation of δ–AlLi, contributing to comparably high hardness of the samples.

From LiNiO2 to Li2NiO3: Synthesis, Structures and Electrochemical Mechanisms in Li-Rich Nickel Oxides

The Li–Ni–O phase diagram contains a variety of compounds, most of which are electrochemically active in Li-ion batteries. Other than the well-known LiNiO2, here we report a facile solid-state method to prepare Li2NiO3 and other Li-rich Ni oxides of composition Li1+xNi1–xO2 (0 ≤ x ≤ 0.33). We characterize their crystal and electronic structure, exhibiting a highly oxidized Ni state and defects of various nature (Li–Ni disorder, stacking faults, oxygen vacancies). We then investigate the use of Li2NiO3 as a cathode active material and show its remarkably high specific capacity, which however fades quickly. While we demonstrate that the initial capacity is due to irreversible O2 release, such process stops quickly in favor of more classical reversible redox mechanisms that allow cycling the material for >100 cycles. After the severe oxygen loss (∼15–20%) and prolonged cycling, the Bragg reflections of Li2NiO3 disappear. Analysis of the diffracted intensities suggests the resulting phase is a disordered rock salt-type material with high Li content, close to Li0.5Ni0.5O, never reported to date and capable of Li diffusion. Our findings demonstrate that the Li–Ni–O phase diagram has not been fully investigated yet, especially concerning the preparation of new promising materials by out-of-equilibrium methods.

Retarded layered-to-spinel phase transition in structure reinforced birnessite with high Li content

Li-birnessite is accompanied with Mn vacancies and structural disorder via traditional chemical synthesis method. A structure reinforced Li-birnessite has been developed by electrochemical conversion method. Reinforced birnessite with both high Li content and structural ordering retards layered-to-spinel phase transition.

The Geochemical Features of Ores and Host Rocks of the Malo-Taryn Orogenic Gold Deposit (Verkhoyansk–Kolyma Folded Area, Northeast Russia)

This paper presents the results of a study of the distribution of major, trace, and rare-earth elements in the terrigenous rocks, wall-rock metasomatites, and ore zones of the orogenic Malo-Taryn gold deposit (Verkhoyansk-Kolyma folded area , Northeast Russia). An important role in the formation of metasomatites and ore zones was played by hydromicatization, carbonatization, sulfidization, and silicification, which caused the different mobility of major elements and the predominant development of acidic low-temperature carbonic–calcium metasomatism. An increase in the quartz content in the wall-rock metasomatites and ore zones was accompanied by the removal of most rock-forming elements (K, Na, Al, Fe, Mg, and Тi) and input of Ca and CO2. The ores and metasomatites of the deposit are characterized by the As–Au–Sb–W geochemical specialization at low Bi, Co, Ni, Cr, Cu, and Zn and high Li, Ag, Cd, and Sc concentrations. Their REE distribution patterns in modified rocks are similar to those of the Upper Triassic host rocks, with some tendency to a decreasing REE total content. It was established that REE are removed during the formation of metasomatites and ores. The values of the Eu/Eu* (0.61–0.88) and Ce/Ce* (0.6–1.3) anomalies indicate slightly reducing conditions of ore formation with a limited involvement of oxidized meteoric water.

Ionic conductivity in LixTaOy thin films grown by atomic layer deposition

The material system Li-Ta-O is a promising candidate for thin-film solid-state electrolytes in Li-ion batteries. In the present study, we have varied the Li content x in LixTaOy thin films grown by atomic layer deposition (ALD) with the aim of improving the Li-ion conductivity. The amorphous films were grown at 225 °C on insulating sapphire and on conductive Ti substrates using tantalum ethoxide (Ta(OEt)5), lithium tert-butoxide (LiOtBu) and water as reactants. The film composition was determined by time-of-flight elastic recoil detection analysis (TOF-ERDA), displaying an almost linear relationship between the pulsed and deposited Li content. The ionic conductivities were determined by in-plane and cross-plane AC measurements, exhibiting an Arrhenius-type behaviour and comparatively weak thickness-dependence. Increasing Li content x from 0.32 to 0.98 increases the film conductivity by two orders of magnitude while higher Li content x = 1.73 results in decreased conductivity. A room-temperature conductivity σRT of ~10−8 S cm−1 is obtained for a 169 nm thick Li0.98TaOy film. The evolution of conductivity and activation energy suggests a competing effect between the concentration and the mobility of mobile Li ions when more Li are incorporated. The compositional dependence of Li transport mechanism is discussed.

Lithium dilution in Li-Sn alloys

Liquid lithium-tin (Li-Sn) alloys are being considered in alternative concepts of plasma facing components for nuclear fusion applications. Nevertheless, the high Li content and high melting temperature of Li-rich intermetallics may hinder their use due to a possible excessive evaporation of Li to the vessel with evident issues in fuel retention. Their formation was inhibited in this study in homogeneous alloys with Li contents as higher as 5 at.% via a mechanical alloying route of pure Li and Sn sources. A 50 at.% Li-Sn master powder was initially prepared and diluted afterwards with pure Sn to achieve the final compositions. The structure, elemental composition and homogeneity of the alloys were assessed by scanning electron microscopy, ion beam analysis and X-ray diffraction. 5 at.% Li and 1 at.% Li alloys composed by phases with low melting temperatures, LiSn, Li2Sn5 and β-Sn, mainly, were produced with reduced oxygen and metallic impurity contents.

Li and B isotopic fractionation at the magmatic-hydrothermal transition of highly evolved granites

The isotopic compositions of Li and B have great potential for the tracing of fluid sources and for the characterization of ore-forming processes. The fractionation of Li and B isotopes during the magmatic-hydrothermal transition in evolved granites, however, is not well understood as these rocks commonly show multiple late hydrothermal overprints. Tourmaline is sensitive to changes in melt and fluid compositions during its growth and resistant to alteration by later fluids, which makes it a good recorder of Li and B isotopic signatures and fractionation at late evolutionary stages of magmatic systems. To characterize the evolution of a Sn-ore forming granitic intrusion, we analyzed magmatic, hydrothermal, and detrital-sedimentary tourmaline from the Yuanbaoshan granite, associated cassiterite-tourmaline-quartz veins, and disseminated tourmaline-bearing cassiterite-sulfide ore in the sedimentary wall rocks.The Li and B isotopic compositions of tourmaline from these rocks do not covary, largely due to mineral-controlled decoupling during magmatic and hydrothermal processes. Because of the dominant role of tourmaline on the B budget of the rock, magmatic and hydrothermal tourmalines show little variation in δ11B (−12.5 to −8.2‰), a signature reflecting the metasedimentary protoliths of the melt. In contrast, several rock-forming minerals contribute to the budget of Li, which shows significant variation in δ7Li (−0.3 to +6.9‰). The isotopic fractionation of Li in tourmaline from rocks of the Yuanbaoshan area is controlled by three major processes: (i) fractional crystallization results in magmatic tourmaline having progressively higher δ7Li values and higher Li contents, (ii) the magmatic-hydrothermal transition leads to higher δ7Li values at lower Li contents in hydrothermal tourmaline, and (iii) extensive fluid-rock interaction adds isotopically light Li to hydrothermal tourmaline in the wall rocks. Extensive fluid-rock interaction also leached HREE, Mg, isotopically light B, and probably Sn from the granites and/or wall rocks. Tourmaline seems to robustly record progressive changes in Li isotopes in evolving magmatic-hydrothermal systems and hydrothermal mineral deposits.

Large-scale survey of lithium concentrations in marine organisms

Trace metals such as Cu, Hg, and Zn have been widely investigated in marine ecotoxicological studies considering their bioaccumulation, transfer along trophic webs, and the risks they pose to ecosystems and human health. Comparatively, Li has received little attention, although this element is increasingly used in the high-tech, ceramics/glass, and medication industries. Here, we report Li concentrations in more than 400 samples, including whole organisms and different organs of bivalves, cephalopods, crustaceans, and fish. We investigated species from three contrasting biogeographic areas, i.e. temperate (Bay of Biscay, northeast Atlantic Ocean), tropical (New Caledonia, Pacific Ocean), and subpolar climates (Kerguelen Islands, southern Indian Ocean), among diverse trophic groups (filter-feeders to meso-predators) and habitats (benthic, demersal, and pelagic). Although Li is homogeneously distributed in the ocean (at 0.18 μg/mL), Li concentrations in soft tissues vary greatly, from 0.01 to 1.20 μg/g dry weight. Multiple correspondence analyses reveal two clusters of high and low Li concentrations. Li distributions in marine organisms appear to be mostly geographically independent, though our results highlight a temperature dependency in fish muscles. Li is consistently bio-reduced through the trophic webs, with filter-feeders showing the highest concentrations and predatory fish the lowest. Strong variations are observed among organs, consistent with the biochemical similarity between Na and Li during transport in the brain and in osmoregulatory organs. Fish gills and kidneys show relatively high Li concentrations (0.26 and 0.15 μg/g, respectively) and fish brains show a large range of Li contents (up to 0.34 μg/g), whereas fish liver and muscles are Li depleted (0.07 ± 0.03 and 0.06 ± 0.08 μg/g, respectively). Altogether, these results provide the first exhaustive baseline for future Li ecotoxicology studies in marine coastal environments.

Chemical and isotopic features of Li-rich brines from the Salar de Olaroz, Central Andes of NW Argentina

The lithium-rich brines of the Salar de Olaroz in the Central Andes of NW Argentina are considered to be of great economic and strategic interest. This study focused on the fluid source(s) and geochemical processes governing the chemical and isotopic characteristics of the surficial waters of Olaroz (residual brines, ephemeral lakes, rivers and tributary streams), aiming to define the mechanisms leading to such a huge Li reservoir. The chemistry of the Rosario River, which is one of the main sources of recharge of the Salar de Olaroz, is mostly controlled by fluid inputs from hydrothermal systems located north of the salar (in the volcanic areas of Rosario de Coyaguayma, Pairique, and Cono Panizo). The hydrothermal fluids are characterized by relatively high Li concentrations, as they interact with Li-rich rocks pertaining to Miocene – Pliocene volcanic formations, Ordovician sedimentary deposits, and, possibly, pre-Ordovician crystalline basement. In the salar, the hyperarid climate regulates the relative proportion between supplied waters and evaporation, inducing deposition/dissolution of salts, which controls the concentrations of main ions in brines and ephemeral lakes. Hence, the peculiar combination of a Li-rich primary source, the hydrothermal scavenging by geothermal fluids that feed the Rosario River, and secondary concentration processes affecting the surficial water within the salar leads to the formation of the huge Li reservoir characterizing this area.

Temperature-dependent dielectric and structural properties of Li-doped (Na, K) NbO3 near the morphotropic phase region

In this study, pellet samples of (Na0.5K0.5)1-yLiyNbO3, (NKLN) y ≤ 0.06, were prepared using a conventional solid-state reaction method with double sintering. The temperature-dependent dielectric constant and high-temperature X-ray diffraction characteristics of the prepared compositions were observed. Four consistent distinct phases were determined according to the observations as follows. For the compositions where y ≤ 0.02, the phases exhibited monoclinic symmetry between room temperature and about 200 °C, tetragonal between about 200 °C and 400 °C, tetragonal with different symmetry between about 400 °C and 460 °C (the so-called X phase), and cubic symmetry above about 460 °C. For the compositions with higher Li concentrations (y) between 0.03 ≤ y ≤ 0.06, the X phase was not observed and two distinct phase transitions were observed from monoclinic to tetragonal at around 200 °C, and from tetragonal to cubic at around 460 °C.

The imprint of hydrothermal fluids on trace-element contents in white mica and tourmaline from the Panasqueira W\u2013Sn\u2013Cu deposit, Portugal

White mica and tourmaline are the dominant hydrothermal alteration minerals at the world-class Panasqueira W–Sn–Cu deposit in Portugal. Thus, understanding the controls on their chemical composition helps to constrain ore formation processes at this deposit and determine their usefulness as pathfinder minerals for mineralization in general. We combine whole-rock geochemistry of altered and unaltered metasedimentary host rocks with in situ LA-ICP-MS measurements of tourmaline and white mica from the alteration halo. Principal component analysis (PCA) is used to better identify geochemical patterns and trends of hydrothermal alteration in the datasets. The hydrothermally altered metasediments are enriched in As, Sn, Cs, Li, W, F, Cu, Rb, Zn, Tl, and Pb relative to unaltered samples. In situ mineral analyses show that most of these elements preferentially partition into white mica over tourmaline (Li, Rb, Cs, Tl, W, and Sn), whereas Zn is enriched in tourmaline. White mica has distinct compositions in different settings within the deposit (greisen, vein selvages, wall rock alteration zone, late fault zone), indicating a compositional evolution with time. In contrast, tourmaline from different settings overlaps in composition, which is ascribed to a stronger dependence on host rock composition and also to the effects of chemical zoning and microinclusions affecting the LA-ICP-MS analyses. Hence, in this deposit, white mica is the better recorder of the fluid composition. The calculated trace-element contents of the Panasqueira mineralizing fluid based on the mica data and estimates of mica-fluid partition coefficients are in good agreement with previous fluid-inclusion analyses. A compilation of mica and tourmaline trace-element compositions from Panasqueira and other W–Sn deposits shows that white mica has good potential as a pathfinder mineral, with characteristically high Li, Cs, Rb, Sn, and W contents. The trace-element contents of hydrothermal tourmaline are more variable. Nevertheless, the compiled data suggest that high Sn and Li contents are distinctive for tourmaline from W–Sn deposits.