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Magnetite is common in various magmatic and hydrothermal ore deposit types, and its trace element geochemistry has become increasingly used in ore genesis studies and mineral exploration. While fractional crystallization has been shown to influence the chemistry of igneous magnetite, the extent to which this process regulates the trace element composition of hydrothermal magnetite remains poorly understood. In this study, we analyzed trace elements in hydrothermal magnetite from the Baijian Fe-(Co) skarn deposit in eastern China and used Rayleigh and equilibrium fractionation modeling to demonstrate the importance of magnetite precipitation in controlling fluid and magnetite chemistry during Fe skarn mineralization. The Baijian Fe-(Co) skarn deposit has three stages of magnetite. From early Mag-1 to later Mag-2 and Mag-3, the concentrations of compatible elements (Ni and V) decrease, whereas those of incompatible elements (Zn, Mn, and Co) increase. There are obvious trends of increasing incompatible/compatible element ratios (e.g., Co/Ni, Zn/V, and Zn/Ni) and decreasing compatible/incompatible element ratios (e.g., V/Mn, Ni/Mn, and V/Co) from Mag-1 to Mag-3, with strong correlations between each of these ratios. Such systematic trace element variations in successive stages of magnetite can be best explained by increasing degrees of fractional crystallization with time. The wide range of incompatible/compatible element ratios (spanning 2-4 orders of magnitude) in Mag-2 and Mag-3 suggests that magnetite crystallization follows a process akin to Rayleigh fractionation. Results from this study highlight the significant role that magnetite crystallization during skarn formation has on the trace element chemistry of this mineral. Moreover, as the crystallization of magnetite progresses, the Co/Fe ratio of residual hydrothermal fluids is elevated, which favors the precipitation of Co in late-stage sulfides. This process helps to explain why some Fe skarn deposits, as well as magnetite-rich iron oxide-apatite and iron oxide-copper-gold deposits, are potentially important economic sources for Co, currently necessary as one component in Li-ion batteries. [ABSTRACT FROM AUTHOR]

The first widespread occurrence of rare Na-, Ca-, and Mg,Mn,Fe-bearing phosphate chladniite was observed in meteorite Graves Nunataks (GRA) 12510, which is a primitive achondrite that sits within the winonaite class. Numerous 1–500 μm chladniite grains were found, often on the margins between silicate clasts and the kamacite portions of the large metal veins that permeated through the sample. The largest chladniite grains are associated with merrillite, kamacite, taenite, troilite, albite, forsterite, diopside, and enstatite, with a few tiny chladniite grains and an apatite grain enclosed within merrillite. GRA 12510s average chladniite composition is Na2.7Ca1.25(Mg10.02Mn0.69Fe0.20)Σ10.91(PO4)9. Electron backscattered diffraction (EBSD) patterns indicate varying degrees of nucleation and growth of chladniite grains. Additionally, the first pure Raman spectrum of chladniite is described here, revealing primary ν1 bands at 954, 974, and especially 984 cm–1. The co-occurrence and close association of merrillite, apatite, chladniite, and P-bearing metallic phases within GRA 12510 suggests that the fO2 of IW-2 to IW-4 is an intrinsic property of the precursor chondritic material, and the phosphatephosphide reaction may have buffered the final winonaite and IAB iron meteorite phase assemblages. Altogether, chladniite appears to form alongside other phosphates, with their chemistries reflecting the diverse environment of their formation. Meteoritic chladniite likely formed through subsolidus oxidation of schreibersite, scavenging Na from albite, Ca from diopside, Mg from enstatite/forsterite, Fe from kamacite/taenite, and Mn from alabandite/chromite when available. A P0-P5+ redox-buffered environment also has implications for thermometry and fast cooling rates, although more experiments are needed to extrapolate powder reaction rates to those of larger crystals. Furthermore, phosphidephosphate buffered experiments may aid in investigating equilibrium chemistry at fO2 values between IW-2 and IW-4, which have been challenging to explore experimentally due to the limited availability of solid metal-metal oxide buffers between IW (Fe-FeO) and IW-5 (Cr-Cr2O3) at temperatures and pressures relevant to planetary interiors. Future investigations of phosphide-phosphate redox-buffered genesis at fO2 values between IW-2 and IW-4 have important implications for primitive meteorite constituents (e.g., CAI values), partially differentiated planetesimals and planets, including Mercury and core formation on Earth. [ABSTRACT FROM AUTHOR]

Apatite is an accessory phase in all the units of the internally zoned Berry-Havey complex pegmatite. This body presents a highly fractionated core zone, enriched in Li, F, B, Be, and P, which hosts three different types of pockets, some of them often containing tens to hundreds of gemmy euhedral Li-rich tourmaline crystals, together with other mineral phases such as lepidolite. Processes involved in the complex internal evolution of pegmatitic melts that give rise to zoned bodies containing pockets are not completely understood. To shed light on these processes, apatite from all the different units of the Berry-Havey pegmatite (wall zone, intermediate zone, core margin, and core zone pods) and from the three pocket types (Li-poor, Li-rich, and apatite seams) has been characterized petrographically and later analyzed for major (electronic microprobe) and trace elements (LA-ICP-MS). Results indicate that apatite chemistry changed significantly during the crystallization of the Berry-Havey pegmatite, reflecting the conditions at each stage and mainly depending on the fractionation degree, fO2, and paragenetic association. Fluorapatite is found in all the units except the core margin, the Li-poor pockets, and the seams, where Mn-bearing fluorapatite is present. A gradual increase of the Mn content in apatite from the pegmatite border (wall zone) inward, up to the formation of subrounded masses of Mn-Fe phosphate in the core zone pods, parallels the increasing fractionation of the melt. Phosphate crystallization would deplete the residual melt in Mn, probably causing the significant Mn-decrease observed in apatite from the core zone pods and Li-rich pockets. The late depletion of Mn could also be related to an increase of fO2 in the melt during the later stages of its evolution. Main trace element variations in apatite at both pegmatite and crystal scales correspond to REE, Y, and Sr. Yttrium and REE behave in a very similar way, decreasing inward, i.e., with fractionation of the pegmatitic melt (ΣREE from 1796 ppm in the apatite from the wall zone to 0 ppm in the core zone; and Y from 1503 ppm in the apatite from the wall zone to 0 ppm in the core zone); which could be due to early crystallization of REE-bearing phosphates such as monazite and xenotime. Strontium shows a more complex trend, with an initial depletion in apatite from the wall zone (52 ppm) to the intermediate zone (3 ppm) and a pronounced increase from the core margin (23–87 ppm) up to the core zone and pockets (up to 2.87 wt%). This increase of Sr at the latest fractionation stages of the pegmatite is interpreted to be associated with a late, incompatible character of this element in highly fractionated melts, related to the composition of feldspars from the core margin (mainly pure albite). The lack of Ca in feldspars would decrease affinity for Sr incorporation into their structure and, consequently, Sr would go preferentially to apatite in the core zone pods and, more markedly, in the pockets. Apatite also records changes in the redox conditions during crystallization, with the highest fO2 at the end of the crystallization, mainly reflected in the Eu and Ce anomalies. The chemistry of apatite also reflects the evolution of the pegmatitic melt during crystallization regarding the fluids saturation and pockets generation. Accordingly, at least two exsolution events took place during the Berry-Havey crystallization history: (1) at the beginning of the core zone crystallization, giving rise to the Li-poor pockets, and (2) after the crystallization of the Li-rich pods of the core zone, resulting in the Li-rich pockets. The apatite-rich seams may have crystallized between these two exsolution events or later, at a subsolidus stage, after a Na-autometasomatism episode. This study shows how a detailed petrographic and chemical characterization of apatite associated with different units of a highly fractionated, internally zoned pegmatite may help understand the crystallization history of pegmatitic melts. It is also evidenced that during the internal evolution of pegmatites, apatite chemistry records variations in the fO2, elemental fractionation, interaction with competing mineral phases, fluids activity and exsolution events. In addition, it is shown how apatite chemistry may be useful as an exploration tool for pegmatites. [ABSTRACT FROM AUTHOR]

Kidney stone disease is a global concern, and its prevalence is increasing. The objective of this review is to provide a thorough analysis of the many analytical techniques used in the study of kidney stones and to investigate the significance of major and trace components in the development of kidney stone formation. The samples included organic (uric acid) and inorganic (calcium oxalate and carbonate apatite). To study kidney stone analysis methods like XRD, FTIR, SEM, and ICP-MS, a systematic literature review was conducted. The quantities and effects of main (calcium, oxalate, phosphate) and trace (magnesium, zinc, copper) elements in kidney stone development were also examined. The review shows that XRD and FTIR are best for evaluating kidney stone crystalline structure and content, whereas SEM gives rich morphological insights. Its trace element detection sensitivity makes ICP-MS unique. Calcium oxalate and calcium phosphate, the most common components, affect kidney stone development. Trace elements like magnesium prevent stone formation, whereas zinc and copper may encourage crystallisation. Results revealed significantly higher calcium levels in inorganic components compared to organic ones. Uric acid stones exhibited lower element content except for copper and selenium, likely originating from the liver. Carbonate apatite stones showed higher element concentrations, particularly magnesium, compared to calcium oxalate stones. Principal component analysis (PCA) identified three principal components, explaining 91.91 % of the variance. These components reflected specific co-precipitation processes of elements, with distinct distributions among different stone types. This variability in element content among stone types could serve as valuable guidance for patient dietary considerations. [ABSTRACT FROM AUTHOR]

Apatite major and trace element chemistry is a widely used tracer of mineralization as it sensitively records the characteristics of the magmatic-hydrothermal system at the time of its crystallization. Previous studies have proposed useful indicators and binary discrimination diagrams to distinguish between apatites from mineralized and unmineralized rocks; however, their efficiency has been found to be somewhat limited in other systems and larger-scale data sets. This work applied a machine learning (ML) method to classify the chemical compositions of apatites from both fertile and barren rocks, aiming to help determine the mineralization potential of an unknown system. Approximately 13 328 apatite compositional analyses were compiled and labeled from 241 locations in 27 countries worldwide, and three apatite geochemical data sets were established for XGBoost ML model training. The classification results suggest that the developed models (accuracy: 0.851–0.992; F1 score: 0.839–0.993) are much more accurate and efficient than conventional methods (accuracy: 0.242–0.553). Feature importance analysis of the models demonstrates that Cl, F, S, V, Sr/Y, V/Y, Eu*, (La/Yb)N, and La/Sm are important variables in apatite that discriminate fertile and barren host rocks and indicates that V/Y and Cl/F ratios and the S content, in particular, are crucial parameters to discriminating metal enrichment and mineralization potential. This study suggests that ML is a robust tool for processing high-dimensional geochemical data and presents a novel approach that can be applied to mineral exploration. [ABSTRACT FROM AUTHOR]

A-type granites generally have much lower water, higher temperature, and incompatible element concentrations than I-type granitoids. Yet it remains unclear why I-A-type granitic complexes occur in convergent plate margins. Here we conduct geochemical analyses on apatite and mafic minerals from the late Cretaceous I-A-type granitic complex in Fuzhou area, SE China, aiming to decipher differentiation, fluid metasomatism, and degassing that primarily control the compositional diversity of felsic magmas. Apatites in both rock types are F-rich and show large H2O and δD variations, i.e., 341–3892 ppm H2O and –325 to +336‰ δD in I-type granitoids; 67–1366 ppm H2O and –251 to +1439‰ δD in A-type granites. H2O in apatite is negatively correlated with La/Sm and Sr/Y in the I-type granitoids, whereas it is positively correlated with Ce and total rare earth element (REE) concentrations in the A-type granites. Once H2O increases up to hundreds of ppm, both rock types show a rapid decrease of H2O/Ce, an increase of F/Cl, and extensive H isotope fractionation. Arfvedsonite occurs as a late crystallizing mineral in the A-type granite and has much higher contents of Na2O, K2O, F, and high field strength elements (HFSE) than hornblende in the I-type granitoids, indicating the addition of F-HFSE-rich alkaline fluids during its magmatic evolution. The consumption of arfvedsonite and formation of aegirine further indicate the role of fluid metasomatism and H2 degassing via a reaction of 3Na3Fe5Si8O22(OH)2 + 2H2O = 9NaFeSi2O6 + 2Fe3O4 + 6SiO2+5H2. The combined geochemical data demonstrate that the systematic differences in mineral assemblage, whole-rock composition, magma temperature, H2O content, and δD of apatite between the I- and A-type granites are likely attributed to varying degrees of differentiation, fluid metasomatism and magmatic degassing. The I-type granitoids experienced hornblende, biotite, plagioclase, K-feldspar, and apatite fractionation and close-system degassing. The A-type granite was likely formed from the I-type monzogranitic magma that was metasomatized by the mantle-derived F-HFSE-rich alkaline fluids to produce the peralkaline magma, which further experienced K-feldspar + plagioclase + biotite + apatite fractionation and open-system degassing. Further numerical estimation indicates that the primary magma of Fuzhou granitic complex contained ~3.0 wt% H2O, and the lower water content of A-type granite was likely attributed to strong degassing during its emplacement. Our results indicate that some peralkaline A-type granites can be generated from relatively water-poor I-type granitic magmas by fluid metasomatism and degassing. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The diverse suite of trace elements incorporated into apatite in ore-forming systems has important applications in petrogenesis studies of mineral deposits. Trace element variations in apatite can be used to distinguish between fertile and barren environments, and thus have potential as mineral exploration tools. Such classification approaches commonly employ two-variable scatterplots of apatite trace element compositional data. While such diagrams offer accessible visualization of compositional trends, they often struggle to efectively distinguish ore deposit types because they do not employ all the high-dimensional (i.e., multi-element) information accessible from high-quality apatite trace element analysis. To address this issue, we use a supervised machine-learning-based approach (eXtreme Gradient Boosting, XGBoost) to correlate apatite compositions with ore deposit type, utilizing such high-dimensional information. We evaluated 8629 apatite trace element data from five ore deposit types (porphyry, skarn, orogenic Au, iron oxide copper gold, and iron oxide-apatite) along with unmineralized magmatic and metamorphic apatite to identify discriminating parameters for the individual deposit types, as well as for mineralized systems. According to feature selection, eight elements (Th, U, Sr, Eu, Dy, Y, Nd, and La) improve the model performance. We show that the XGBoost classifier eficiently and accurately classifies high-dimensional apatite trace element data according to the ore deposit type (overall accuracy: 94% and F1 score: 89%). Interpretation of the model using the SHAPley Additive exPlanations (SHAP) tool shows that Th, U, Eu, and Nd are the most indicative elements for classifying deposit types using apatite trace element chemistry. Our approach has broad implications for the better understanding of the sources, chemistry, and evolution of melts and hydrothermal fluids resulting in ore deposit formation. [ABSTRACT FROM AUTHOR]

Modified magnetite and hydrothermal apatite in banded iron formations (BIFs) are ideal minerals for studying hydrothermal and metamorphic processes and are applied to linking with high-grade Fe mineralization and metamorphism in iron deposits hosted by BIFs. In this study, we have investigated the geochemical composition of modified magnetite and hydrothermal apatite and in situ U-Pb geochronology on apatite from the Huogezhuang BIF-hosted Fe deposit in northeastern China. The magnetite in metamorphosed BIF is modified, locally fragmented, and forms millimeter- to micrometer-scale bands. The apatite is present surrounding or intergrowing with magnetite, has corroded surfaces, and contains irregular impurities and fluid inclusions, indicating that it has been partly hydrothermally altered. Original element compositions (e.g., Fe, Al, Ti, K, Mg, and Mn) of magnetite in BIFs have been modified during high-grade Fe mineralization and retrogressive metamorphism with temperature reduction and addition of acids. The hydrothermally altered apatite has been relatively reduced in the contents of Ca, P, F, La, Ce, Nd, δCe, δEu, and total REEs compared to non-altered apatite. The magnetite and apatite in low-grade BIFs are poorer in FeOT than those from the high-grade Fe ores, indicating that Fe is remobilized during the transition from BIFs to high-grade Fe ores. The magnetite and apatite in high-grade Fe ores are overgrown by greenschist-facies minerals formed during retrograde metamorphism, suggesting that the high-grade Fe mineralization may be related to retrogressive metamorphism. In situ U-Pb geochronology of apatite intergrown with magnetite and zircon LA-ICP-MS U-Pb dating at Huogezhuang deposit reveals that the BIF-hosted magnetite was altered and remobilized at ca. 1950–1900 Ma, and deposition of the BIF began during the Late Neoarchean. The changes of elements in the modified magnetite and diferent geochemical compositions of the altered and unaltered apatite confirm that the modified magnetite and hydrothermal apatite can be efective in tracing high-grade Fe mineralization and retrogressive metamorphism in BIFs. [ABSTRACT FROM AUTHOR]

Nelsonite (Fe-Ti oxide-apatite rock) devoid of silicates offers a rare opportunity to investigate the magma processes for the formation of magmatic Fe-Ti oxide deposits. Both fractional crystallization and silicate liquid immiscibility have been put forward, but the lack of robust evidence has hindered unambiguously distinguishing the role of these two processes in Fe-Ti mineralization. The nelsonite and associated Fe-Ti-P-rich rocks hosted in the Proterozoic Damiao anorthosite complex represent a typical example for studying Fe-Ti ore-forming processes. We recognized a new type of nelsonite (type-I) in the Damiao complex, which is distinct from the two known types of nelsonite (type-II and type-III) from the same complex. The type-I nelsonite is characterized by its coexistence with oxide-apatite gabbronorite and granite in the same dike, and all these rocks have identical emplacement ages (1740 ± 7 Ma), subparallel REE patterns, and major-element compositions lacking intermediate compositions, suggesting derivation from conjugate Fe- and Si-rich melts generated by silicate liquid immiscibility. The large type-II nelsonite bodies form irregular dikes along fractures in anorthosite and constitute the major ore type. The type-III nelsonite occurs as conformable layers or pods within oxide-apatite gabbronorite and pyroxenite, and occupies the end part of the type-II dike. The latter two types of nelsonites formed by extensive fractional crystallization of residual magma with crystal accumulation and subsequent hydrothermal replacement. During residual magma evolution, silicate liquid immiscibility was crucial for Fe-Ti-P enrichment, fractional crystallization was responsible for enhancing oxide-apatite concentrations, and hydrothermal replacement was effective for mobilizing oxide-apatite concentrations. Our newly recognized nelsonite provides an unambiguous, outcrop-scale, field evidence for the operation of silicate liquid immiscibility process. We show that giant magmatic Fe-Ti oxide orebodies can form by a combination of processes involving silicate liquid immiscibility, fractional crystallization and hydrothermal mobilization. [ABSTRACT FROM AUTHOR]

Microbial Fe(II) oxidation has been proposed as a major source of Fe minerals during deposition of banded iron formations (BIFs) in the Archean and Proterozoic Eons. The conspicuous absence of organic matter or graphitic carbon from BIFs, however, has given rise to divergent views on the importance of such a biologically mediated iron cycle. Here, we present mineral associations, major element concentrations, total carbon contents and carbon isotope compositions for a set of lower amphibolite-facies BIF samples from the Neoarchean Zhalanzhangzi BIF in the Qinglonghe supra-crustal sequence, Eastern Hebei, China. Graphite grains with crystallization temperatures (~470 °C) that are comparable to that predicted for the regional metamorphic grade are widely distributed, despite highly variable iron (12.9 to 54.0 wt%) and total organic carbon (0.19 to 1.10 wt%) contents. The crystalline graphite is interpreted to represent the metamorphosed product of syngenetic biomass, based on its co-occurrence with apatite rosettes and negative bulk rock δ13Corganic values (–23.8 to –15.4‰). Moreover, the crystalline graphite is unevenly distributed between iron- and silica-rich bands. In the iron-rich bands, abundant graphite relicts are closely associated with magnetite and/or are preserved within carbonate minerals (i.e., siderite, ankerite, and calcite) with highly negative bulk rock δ13Ccarb values (–16.73 to –6.33‰), indicating incomplete reduction of primary ferric (oxyhydr) oxides by organic matter. By comparison, only minor graphite grains are observed in the silica-rich bands. Normally, these grains are preserved within quartz or silicate minerals and thus did not undergo oxidation by Fe(III). In addition, the close association of graphite with iron-bearing phases indicates that ferric (oxyhydr)oxides may have exerted a first order control on the abundance of organic matter. Combined, the biological oxidation of Fe(II) in the oceanic photic zone and subsequent burial of ferric (oxyhydr)oxides and biomass in sediments to form BIFs, suggests that a BIF-dependent carbon cycle was important in the Archean Eon. Although significant re-adsorption of phosphorus to ferric (oxyhydr)oxides and the formation of authigenic phosphate minerals at the sediment-water interface would be expected, oxidation of biomass in BIFs may have recycled at least a portion of the P (and other nutrients) released from reactions between organic matter and ferric (oxyhydr)oxides to the overlying water column, potentially promoting further primary productivity. [ABSTRACT FROM AUTHOR]

Rare earth elements (REE) in calcium apatite have been widely described in the literature. Based on the investigations of minerals and their synthetic analogs, the mechanism of substitution of REE3+ for Ca2+ and their structural positions are well established. Although the presence of REE in natural pyromorphite has been reported, the structural response of substitution of REE3+ for Pb2+ is not established. A better understanding of REE-rich Pb-apatite may facilitate the potential use of this mineral in industrial processes. Two La-doped pyromorphite analogs [Pb5(PO4)3Cl] and two control pyromorphite analogs (with the absence of La) were synthesized from aqueous solutions at 25 °C. Na+ and K+ were used as charge-compensating ions to facilitate the incorporation of trivalent REE cations (La3+ + Na+ ↔ 2Pb2+ and La3+ + K+ ↔ 2Pb2+). Microprobe analysis, scanning electron microscopy, and Raman spectroscopy were used to confirm the purity of obtained phases. High-precision crystal structure refinements (R1 = 0.0140–0.0225) of all four compounds were performed from single-crystal X-ray diffraction data. The La content varied from 0.12(1) to 0.19(1) atoms per formula unit with the counter ions of K+ and Na+, respectively. Both substituting ions were accommodated at the Pb1 site only. By comparing the La-doped pyromorphite analogs with their control samples, it was possible to detect small changes in bond distances and polyhedral volumes caused by the La substitution. Variations in individual and mean interatomic distances reflected the cumulative effect of both the amount of substitution and ionic radii of substituting ions (La3+, Na+, and K+). [ABSTRACT FROM AUTHOR]

The microstructures of selected F-, Cl-, and OH-bearing martian apatite grains, two in Northwest Africa (NWA) 998 (cumulus apatites, embedded in pyroxene) and a set of four in Nakhla (intercumulus apatites), were studied by focused ion beam–transmission electron microscopy (FIB-TEM) techniques. Our results show that the nanostructure of martian apatite is characterized by a domain structure at the 5–10 nm scale defined by undulous lattice fringes and slight differences in contrast, indicative of localized elastic strain within the lattices and misorientations in the crystal. The domain structure records a primary post-magmatic signature formed during initial subsolidus cooling (T <800 °C), in which halogens clustered by phase separation (exsolution), but overall preserved continuity in the crystalline structure. Northwest Africa 998 apatites, with average Cl/F ratios of 1.26 and 2.11, show higher undulosity of the lattice fringes and more differences in contrast than Nakhla apatites (average Cl/F = 4.23), suggesting that when Cl/F is close to 1, there is more strain in the structure. Vacancies likely played a key role stabilizing these ternary apatites that otherwise would be immiscible. Apatites in Nakhla show larger variations in halogen and rare-earth element (REE) contents within and between grains that are only a few micrometers apart, consistent with growth under disequilibrium conditions and crystallization in open systems. Nakhla apatite preserves chemical zonation, where F, REEs, Si, and Fe are higher in the core and Cl increases toward the outer layers of the crystal. There is no evidence of subsolidus ionic diffusion or post-magmatic fluid interactions that affected bulk apatite compositions in NWA 998 or Nakhla. The observed zonation is consistent with crystallization from a late-stage melt that became Cl-enriched, and assimilation of volatile-rich crustal sediments is the most plausible mechanism for the observed zonation. This work has broader implications for interpreting the chemistry of apatite in other planetary systems. [ABSTRACT FROM AUTHOR]

Apatite is an important petrogenetic indicator in extraterrestrial materials. Here, we report the mineralogical features of apatite and associated phases in three brachinites Northwest Africa (NWA) 4969, NWA 10637, and NWA 11756. Two types of apatite are observed: intergranular apatite and apatite inclusion within chromite and silicate minerals. The intergranular chlorapatite is enclosed by or penetrated by irregular porous merrillite, indicating chlorapatite replacement by merrillite. The intergranular chlorapatite is closely associated with a fine-grained pyroxene-troilite intergrowth along olivine grain boundaries, which is a sulfidization product of olivine. High-Ca pyroxene is observed as a constituent phase in the intergrowth for the first time. The apatite inclusions are either monomineralic or closely associated with subhedral-euhedral pore-free merrillite. In NWA 4969, the apatite inclusions show a large compositional variation from chlorapatite to fluorapatite and are systematically more F-rich than intergranular apatite; while the apatite inclusions in NWA 10637 and NWA 11756 are chlorapatite. Most of the two apatite types in brachinites contain oriented tiny or acicular chromite grains, suggesting the exsolution of chromite from apatite. We propose that apatite replacement by merrillite, formation of pyroxene-troilite intergrowth, and exsolution of chromite in apatite were caused by a shock-induced, transient heating event (~930–1000 °C) on the brachinite parent body. This heating event resulted in halogen devolatilization during replacement of the intergranular apatite by merrillite, which probably disturbed the Mn-Cr isotopic system in brachinites as well. We also propose that the apatite inclusions could be a residual precursor material of the brachinites. [ABSTRACT FROM AUTHOR]

Apatite is a ubiquitous phase in granite plutons and in most adjacent country rocks, thus contamination of a granite magma with wall-rock material results in two genetic types of apatite in the magma: cognate and foreign. These two textural and chemical varieties of apatite undergo textural and compositional changes to reach physical and chemical equilibrium (perfect assimilation) in the melt. Our experiments replicate the conditions in such contaminated granites. The starting materials consist of a peraluminous synthetic SiO2-Al2O3-Na2O-K2O (SANK 1.3) granite gel with A/NK of 1.3, synthetic F-apatite, synthetic Cl-apatite, and natural Durango apatite. Initial experiments in cold-seal hydrothermal pressure vessels at magmatically realistic temperatures of 750 °C and pressures of 200 MPa produced negligible reactions, even after run times of 2000 h. Instead, we used an argon-pressurized internally heated pressure vessel with a rapid-quench setup at temperatures of 1200 °C, pressure of 200 MPa, and run durations of 192 h. An advantage of this high temperature is that it exceeds the liquidus for quartz and feldspar; therefore, apatite is the only solid phase in the run products. The starting composition of each run was 90 wt% SANK 1.3 granite gel and 10 wt% crushed apatite (consisting of one, two, or three varieties), with and without 4 wt% added H2O. Run products were examined by SEM for texture and by EMPA and LA-ICP-MS for composition. The starting synthetic granite composition contains no Ca, F, Cl, or REEs thus, in every run, apatite was initially undersaturated in the melt. In all experiments, most large apatite grains consisted of anhedral shards with rounded corners, most small apatite grains were round, and a small proportion of apatite grains developed one or more crystal faces. In experiments with two or three apatite compositions, the run-product apatite grains had compositions intermediate between those of the starting-material grains, and they were homogeneous with respect to Cl, and probably F, but not with respect to REEs. The processes to reach textural equilibrium consist of dissolution until the melt is saturated in apatite, followed by Ostwald ripening to eliminate small grains and to develop crystal faces on larger ones. The processes to reach chemical equilibrium consist of dissolution of apatite, diffusion of cations (Ca, P, REE) and anions (F, Cl, OH) through the silicate melt, and solid-state diffusion in the undissolved apatite grains. The halogens approached chemical equilibrium in all experiments, but in the experiments containing Durango apatite, the REEs have not. Models involving radial diffusion into spherical apatite grains at the temperatures of the experiments show complete re-equilibration of the halogens, but changes in the REE concentrations affecting only the outer few micrometers. We conclude that the rate of chemical equilibrium for the halogens is greater than the rate of physical equilibrium for texture, which in turn is greater the rate of chemical equilibrium for REEs. We illustrate these processes with a natural example of contaminated granite from the South Mountain Batholith in Nova Scotia. Given that all granites are contaminated rocks, we propose that future petrogenetic studies focus on developing techniques for a minerals-based quantitative estimation of contamination (QEC). [ABSTRACT FROM AUTHOR]

Apatite is a common accessory phase in igneous and metamorphic rocks. Its stability in magmatic-hydrothermal and hydrothermal systems is known to be a key control on the mobility of rare earth elements (REE). To better constrain how apatite is altered during fluid-rock interaction at comparably low temperatures, batch-type apatite dissolution experiments were conducted at 150 and 250 °C at saturated water vapor pressure in acidic to mildly acidic (pH of 2–4) aqueous fluids having variable salinities (0, 0.5, and 5 wt% NaCl). The study reveals the dominance of apatite dissolution textures with the formation of micrometer-scale etch pits and dissolution channels developing prominently along the c-axis of the apatite crystals. Backscattered electron imaging shows an increase in apatite dissolution with increasing temperature and upon reacting the crystals with more acidic and higher salinity starting fluids. This study also demonstrates an increase in dissolved REE in the experimental fluids corroborating with the observed apatite dissolution behavior. Backscattered electron imaging of secondary minerals formed during apatite dissolution and scanning electron microscopy-based energy dispersive spectrometry peaks for Ca, P, and REE support the formation of monazite-(Ce) and minor secondary apatite as deduced from fluid chemistry (i.e., dissolved P and REE concentrations). The studied apatite reaction textures and chemistry of the reacted fluids both indicate that the mobility of REE is controlled by the dissolution of apatite coupled with precipitation of monazite-(Ce), which are enhanced by the addition of NaCl in the starting fluids. This coupled process can be traced by comparing the REE to P ratios in the reacted fluids with the stoichiometry of the unreacted apatite crystals. Apatite metasomatized at temperatures <300 °C is therefore controlled by dissolution rather than dissolution-reprecipitation reactions commonly observed in previous experiments conducted above 300 °C. Furthermore, this study demonstrates that the presence of NaCl plays a crucial role in increasing the solubility of apatite, which controls the availability of REE to form secondary phosphates even in mildly acidic aqueous fluids. This implies that both the effects of acidity/alkalinity of the fluids and the role of dissolved alkalis (NaCl and KCl), need to be considered for understanding the controls on REE in magmatic-hydrothermal systems. Lastly, the experiments of this study expand the known conditions at which apatite is susceptible to be overprinted by hydrothermal alteration from 900 °C down to 150 °C and highlights the necessity of appropriately screening apatite grains using backscattered electron and cathodoluminescence imaging for signs of hydrothermal alteration textures in igneous apatite. [ABSTRACT FROM AUTHOR]

We conducted a petrologic study of apatite within one LL chondrite, six R chondrites, and six CK chondrites. These data were combined with previously published apatite data from a broader range of chondrite meteorites to determine that chondrites host either chlorapatite or hydroxylapatite with ≤33 mol% F in the apatite X-site (unless affected by partial melting by impacts, which can cause F-enrichment of residual apatite). These data indicate that either fluorapatite was not a primary condensate from the solar nebula or that it did not survive lower temperature nebular processes and/or parent body processes. Bulk-rock Cl and F data from chondrites were used to determine that the solar system has a Cl/F ratio of 10.5 ± 1.0 (3σ). The Cl/F ratios of apatite from chondrites are broadly reflective of the solar system Cl/F value, indicating that apatite in chondrites is fluorine poor because the solar system has about an order of magnitude more Cl than F. The Cl/F ratio of the solar system was combined with known apatite-melt partitioning relationships for F and Cl to predict the range of apatite compositions that would form from a melt with a chondritic Cl/F ratio. This range of apatite compositions allowed for the development of a crude model to use apatite X-site compositions from achondrites (and chondrite melt rocks) to determine whether they derive from a volatile-depleted and/or differentiated source, albeit with important caveats that are detailed in the manuscript. This study further highlights the utility of apatite as a mineralogical tool to understand the origin of volatiles (including H2O) and the diversity of their associated geological processes throughout the history of our solar system, including at its nascent stage. [ABSTRACT FROM AUTHOR]

Apatite containing 14 wt% TREO (total rare earth oxide) and coexisting with calciobritholite with 37.2 wt% TREO has been synthesized at 800 °C and 10 kbar from a felsic melt with the addition of NaCl. The analysis of the experimental products with regression analysis of time-resolved (RATR) laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) data allowed to estimate the composition of the coexisting phases. The results suggest that equilibrium has been established during the run and both apatite and calciobritholite contained REE in [Si4+REE3+] to [Ca2+P5+] solid solution, whereas the coupled substitution [Na1+REE3+] to [2Ca2+] was insignificant despite crystallization from an alkaline, Na-rich melt. The coexistence of the apatite and calciobritholite and available experimental data allowed the miscibility gap to be constrained between apatite and calciobritholite, and suggest complete miscibility between apatite and britholite above 950 °C. The melt that produced coexisting apatite and calciobritholite was characterized by a significant Cl content of (0.51 wt%) and elevated REE (526 ± 19 ppm Ce) and low-P content (112 ± 49 ppm). The change of the accessory mineral association from monazite to apatite and calciobritholite with the addition of NaCl illustrates the importance of halogens for mineral associations. The partition coefficients of britholite are similar to those of apatite and are distinguished mainly by a higher preference for REE and Th. Henry's law was not acting for the total REE content in the melt because of the buffered system; however the partition coeficients could still be used for the prediction of the relative REE patterns for melts that generated high-REE apatite and/or calciobritholite. These results have implications for the interpretation of the phosphate associations in alkaline volcanic and plutonic rocks. [ABSTRACT FROM AUTHOR]

The environment model is used to describe the location of carbonate in nine carbonated apatites containing varied percentages of carbonate and Na+, K+, or NH4+ ions. Unlike the traditional model for carbonate substitution, which identifies different locations and orientations of the carbonate ion in the apatite structure, the environment model utilizes the different structural surroundings to describe the different types of carbonate. The A-type carbonate environment is assigned to channels lined only with calcium ions (A-channel configuration = Ca6) or to channels containing one Na+ or a vacancy (A′-channel configuration = Ca5Na or Ca5▢), and the B-type carbonate environment is the surroundings of the replaced phosphate ion. The assignments are made by peak-fitting the carbonate asymmetric stretch region (ν3) of the IR spectrum, following previously published criteria. These assignments lead to the conclusion that the percentage of channel carbonate (A- and A′-environments) is greater than that of B-type for each of these carbonated apatites. In general, the use of triammonium phosphate as the phosphate source in the synthesis produces apatites with larger amounts of channel carbonate (A- and A′-environments), while the use of sodium-containing phosphate reagents produces smaller amounts of channel carbonate. The environment model provides explanations for the differences within IR and NMR spectra obtained for apatites containing a range of total carbonate content. The B-type appearance of the carbonate ν3 region of the IR spectrum is found primarily in apatites containing sodium, which allows increased amounts of carbonation via co-substitution of Na+ with carbonate and creation of A′-environments with populations equal to that of B-type carbonate. The presence of ammonium or alkali metal salts with cations larger than Na+ results in the utilization of a charge-balance mechanism that produces vacancies rather than cation substitution in the channel. The carbonated apatites formed with primary utilization of the vacancy mechanism generally contain greater percentages of carbonate in the A-environment and carbonate IR spectra that contain an obvious high-frequency peak at about 1550 cm–1. The multiple peaks in the solid state 13C NMR spectra previously observed for carbonated apatite are attributed to substitution in the A-, A′-, and B-environments rather than different stereo-chemical orientations of the carbonate ion. [ABSTRACT FROM AUTHOR]

Partition coefficients for rare earth elements (REEs) between apatite and basaltic melt were determined as a function of oxygen fugacity (fO2; iron-wüstite to hematite-magnetite buffers) at 1 bar and between 1110 and 1175 °C. Apatite-melt partitioning data for REE3+ (La, Sm, Gd, Lu) show near constant values at all experimental conditions, while bulk Eu becomes more incompatible (with an increasing negative anomaly) with decreasing fO2. Experiments define three apatite calibrations that can theoretically be used as redox sensors. The first, a XANES calibration that directly measures Eu valence in apatite, requires saturation at similar temperature-composition conditions to experiments and is defined by: ( Eu 3 + ∑ Eu ) Apatite = 1 1 + 10 − 0.10 ± 0.01 × log (f o 2 ) − 1.63 ± 0.16 . The second technique involves analysis of Sm, Eu, and Gd in both apatite and coexisting basaltic melt (glass), and is defined by: ( Eu Eu ∗ ) D Sm×Gd = 1 1 + 10 − 0.15 ± 0.03 × log (f o 2 ) − 2.46 ± 0.41 . The third technique is based on the lattice strain model and also requires analysis of REE in both apatite and basalt. This calibration is defined by ( Eu Eu ∗ ) D lattice strain = 1 1 + 10 − 0.20 ± 0.03 × log (f o 2 ) − 3.03 ± 0.42 . The Eu valence-state partitioning techniques based on (Sm × Gd) and lattice strain are virtually indistinguishable, such that either methodology is valid. Application of any of these calibrations is best carried out in systems where both apatite and coexisting glass are present and in direct contact with one another. In holocrystalline rocks, whole rock analyses can be used as a guide to melt composition, but considerations and corrections must be made to either the lattice strain or Sm × Gd techniques to ensure that the effect of plagioclase crystallization either prior to or during apatite growth can be removed. Similarly, if the melt source has an inherited either a positive or negative Eu anomaly, appropriate corrections must also be made to lattice strain or (Sm × Gd) techniques that are based on whole rock analyses. This being the case, if apatite is primary and saturates from the parent melt early during the crystallization sequence, these corrections may be minimal. The partition coefficients for the REE between apatite and melt range from a maximum DEu3+ = 1.67 ± 0.25 (as determined by lattice strain) to DLu3+ = 0.69 ± 0.10. The REE partition coefficient pattern, as observed in the Onuma diagram, is in a fortuitous situation where the most compatible REE (Eu3+) is also the polyvalent element used to monitor fO2. These experiments provide a quantitative means of assessing Eu anomalies in apatite and how they be used to constrain the oxygen fugacity of silicate melts. [ABSTRACT FROM AUTHOR]

Apatite is a mineral of widespread importance in Earth and planetary science. Here we examine the behavior of a natural fluorapatite (FAp) crystal from Durango (Mexico) under compression to 61 GPa. Single-crystal X-ray diffraction experiments were carried out in a diamond-anvil cell using a synchrotron source. The apatite structure persists up to 32.4 GPa. Birch-Murnaghan equation of state parameters were fit to the pressure-volume data for fluorapatite for two cases: fixing V0 at its measured ambient value resulted in a bulk modulus, K0T, of 97.0(8) GPa and a pressure derivative of the bulk modulus, K′0T, of 3.3(1), while fixing V0 and K0T at its ambient value 90.5 GPa (derived from ultrasonically measured elastic constants) resulted in a K′0T value of 4.1(1). At 35.6 GPa, fluorapatite transforms to a triclinic phase (P1, Z = 4), designated here as fluorapatite II (FAp-II). This phase persists up to at least 61 GPa. The major structural differences between FAp and FAp-II involve the buckling of the Ca polyhedra along the c-axis and changes in the number and coordination of the Ca sites. Our study extends the pressure range over which fluorapatite has been examined by more than a factor of three, providing new insights into its structural response to high-pressure conditions. [ABSTRACT FROM AUTHOR]

Thermodynamic parameters have been measured for synthetic analogs of the mimetite- group minerals Pb5(AsO4)3X (X = OH, Cl, Br, I) belonging to the apatite supergroup. Phases precipitated from aqueous solutions under ambient conditions with well characterized structures and compositions were studied. For each phase, dissolution enthalpy was experimentally determined by oxide melt drop solution calorimetry in a molten solvent of sodium molybdate (3Na2O·4MoO3) at 976 K. The enthalpy of formation from the elements Δ H f , e l ∘ was calculated using thermochemical cycles and was −3030.6 ± 11.5, −3026.6 ± 15.8, −2967.6 ± 25.0, and −2993.1 ± 12.2 kJ/mol for Pb5.00(AsO4)3.00OH0.86(CO3)0.07, Pb5.00(AsO4)3.00Cl0.80(CO3)0.10, Pb5.00(AsO4)3.00Br0.80(CO3)0.10, and Pb5.00(AsO4)3.00I0.45OH0.35(CO3)0.10, respectively. These Δ H f , e l ∘ values exhibit typical trends for apatites: they increased (were less negative) with the increasing molar mass and ionic radius of X and decreased with the electronegativity and ionization energy of X. The compilation and comparison of data for Ca-, Pb-, P-, and As-apatites revealed correlations indicating that thermodynamic enthalpic stability is largely influenced by chemical factors (e.g., differences in electronegativities of the elements, ionization energy, or ionic characteristics of the bonds) and to a lesser extent by physical and geometric parameters in the crystal structure related to the mass and size of the X anion. Using the correlations, it was possible to estimate the value of hitherto unknown Δ H f , e l ∘ for Pb5(AsO4)3F, −3144.3 ± 66.5 kJ/mol. The observed relationships apply to the entire apatite supergroup and can be used to predict the values of Δ H f , e l ∘ for phases that have not been studied experimentally. The new data on environmentally significant phases will contribute to the modeling of mineral-water interactions, particularly for potential use in the remediation of soils and wastes contaminated with Pb and As and in the immobilization of radioactive waste containing I-129. [ABSTRACT FROM AUTHOR]

The Furong tin deposit (South China) is genetically associated with the multiphase Qitianling batholith that consists of main-phase and minor, but more fractionated, late-phase granites. Several tourmaline and apatite generations are distinguished. Tourmaline (Tur) variants comprise pre-ore Tur-1 as disseminations and nodules in the late-phase granite, pre- to syn-ore Tur-2 as replacements in nodules and as veins crosscutting the late-phase granite and nodules, syn-ore Tur-3 in tin greisens, pre- to syn-ore Tur-4 as veins in the altered main-phase granite, and syn-ore Tur-5 from tin skarns in a distinct Ca-rich environment. Apatite (Ap) generations include accessory Ap-G in the main-phase granite, and Ap-I to Ap-III from three stages related to skarn-type mineralization (garnet-diopside stage-I, pargasite-phlogopite-cassiterite stage-II, and sulfide-rich stage-III). Textural and compositional features suggest that all tourmaline variants are hydrothermal in origin with alkali and schorl to foitite composition and minor extensions to calcic and X-site vacant tourmaline groups, whereas all apatite generations belong to fluorapatite with Ap-G crystallizing from the magma and Ap-I to Ap-III being hydrothermal in origin. The narrow range of tourmaline δ11B values (–14.8 to –10.4‰) suggests a single magmatic boron source in the ore-forming fluids. The similar rare earth element patterns and εNd(t) values (–8.2 to –5.9 for Ap-G and –8.0 to –7.3 for Ap-I) between magmatic and hydrothermal apatite indicate that the skarn-forming fluids are dominantly derived from granites. The 87Sr/86Sr ratios of Ap-I to Ap-III (0.70733–0.70795) are similar to the carbonate wall rocks, but distinctly diferent from the more radiogenic granites, indicating Sr exchange with carbonate rocks. Integrating previous H-O isotopic data, the tourmaline and apatite elemental and B-Sr-Nd isotope results suggest that the greisen-type ore formed by interaction of B-, Na-, Li-, Zn-, and Sn-rich magmatic fluids with the late-phase granite in a closed and reduced feldspar-destructive environment, whereas the tin skarns resulted from mixing of magmatic fluids with meteoric water and interaction with the carbonate wall rocks in an open system where oxygen fugacity changed from reduced to oxidized conditions. During fluid-rock interactions and fluid mixing, considerable Ca, Mg, V, Ni, and Sr from the host rocks were introduced into the ore system. Coupled hydrothermal minerals such as tourmaline and apatite have great potential to fingerprint the nature, source, and evolution of fluids in granite-related ore systems. [ABSTRACT FROM AUTHOR]

The mineral apatite, Ca10(PO4)6(F,OH,Cl)2, incorporates sulfur (S) during crystallization from S-bearing hydrothermal fluids and silicate melts. Our previous studies of natural and experimental apatite demonstrate that the oxidation state of S in apatite varies systematically as a function of oxygen fugacity (fO2). The S oxidation states –1 and –2 were quantitatively identified in apatite crystallized from reduced, S-bearing hydrothermal fluids and silicate melts by using sulfur K-edge X‑ray absorption near-edge structure spectroscopy (S-XANES) where S6+/ΣS in apatite increases from ~0 at FMQ-1 to ~1 at FMQ+2, where FMQ refers to the fayalite-magnetite-quartz fO2 buffer. In this study, we employ quantum-mechanical calculations to investigate the atomistic structure and energetics of S(-I) and S(-II) incorporated into apatite and elucidate incorporation mechanisms. One S(-I) species (disulfide, S 2 2 − ) and two S(-II) species (bisulfide, HS−, and sulfide, S2−) are investigated as possible forms of reduced S species in apatite. In configuration models for the simulation, these reduced S species are positioned along the c-axis channel, originally occupied by the column anions F, Cl, and OH in the end-member apatites. In the lowest-energy configurations of S-incorporated apatite, disulfide prefers to be positioned halfway between the mirror planes at z = 1/4 and 3/4. In contrast, the energy-optimized bisulfide is located slightly away from the mirror planes by ~0.04 fractional units in the c direction. The energetic stability of these reduced S species as a function of position along the c-axis can be explained by the geometric and electrostatic constraints of the Ca and O planes that constitute the c-axis channel. The thermodynamics of incorporation of disulfide and bisulfide into apatite is evaluated by using solid-state reaction equations where the apatite host and a solid S-bearing source phase (pyrite and Na2S2(s) for disulfide; troilite and Na2S(s) for sulfide) are the reactants, and the S-incorporated apatite and an anion sink phase are the products. The Gibbs free energy (ΔG) is lower for incorporation with Na-bearing phases than with Fe-bearing phases, which is attributed to the higher energetic stability of the iron sulfide minerals as a source phase for S than the sodium sulfide phases. The thermodynamics of incorporation of reduced S is also evaluated by using reaction equations involving dissolved disulfide and sulfide species [ H n S 2 (aq) (2 − n) and H n S (aq) (2 − n) ; n = 0 , 1 , and 2] as a source phase. The ΔG of S-incorporation increases for fluorapatite and chlorapatite, and decreases for hydroxyl-apatite, as these species are protonated (i.e., as n changes from 0 to 2). These thermodynamic results demonstrate that the presence of reduced S in apatite is primarily controlled by the chemistry of magmatic and hydrothermal systems where apatite forms (e.g., an abundance of Fe; solution pH). Ultimately, our methodology developed for evaluating the thermodynamics of S incorporation in apatite as a function of temperature, pH, and composition is highly applicable to predicting the trace and volatile element incorporation in minerals in a variety of geological systems. In addition to solid-solid and solid-liquid equilibria treated here at different temperatures and pH, the methodology can be easily extended to different pressure conditions by just performing the quantum-mechanical calculations at elevated pressures. [ABSTRACT FROM AUTHOR]

The new apatite-group mineral pliniusite, ideally Ca5(VO4)3F, was found in fumarole deposits at the Tolbachik volcano, Kamchatka, Russia, and in a pyrometamorphic rock of the Hatrurim Complex, Israel. Pliniusite, together with fluorapatite and svabite, forms a novel and almost continuous ternary solid-solution system characterized by wide variations of T5+ = P, As, and V. In paleo-fumarolic deposits at Mountain 1004 (Tolbachik), members of this system, including the holotype pliniusite, are associated with hematite, tenorite, diopside, andradite, kainotropite, baryte and supergene volborthite, brochantite, gypsum and opal. In sublimates of the active Arsenatnaya fumarole (Tolbachik), pliniusite–svabite–fluorapatite minerals coexist with anhydrite, diopside, hematite, berzeliite, schäferite, calciojohillerite, forsterite, enstatite, magnesioferrite, ludwigite, rhabdoborite-group fluoroborates, powellite, baryte, udinaite, arsenudinaite, paraberzeliite, and spinel. At Nahal Morag, Negev Desert, Israel, the pliniusite cotype and V-bearing fluorapatite occur in schorlomite-gehlenite paralava with rankinite, walstromite, zadovite-aradite series minerals, magnesioferrite, hematite, khesinite, barioferrite, perovskite, gurimite, baryte, tenorite, delafossite, wollastonite, and cuspidine. Pliniusite forms hexagonal prismatic crystals up to 0.3 × 0.1 mm and open-work aggregates up to 2 mm across (Mountain 1004) or grains up to 0.02 mm (Nahal Morag and Arsenatnaya fumarole). Pliniusite is transparent to semitransparent, colorless or whitish, with a vitreous luster. The calculated density is 3.402 g/cm−3. Pliniusite is optically uniaxial (–), ω = 1.763(5), ε = 1.738(5). The empirical formulas of pliniusite type specimens calculated based on 13 anions (O+F+Cl) per formula unit are (Ca4.87Na0.06Sr0.03Fe0.02)Σ4.98(V1.69As0.66P0.45S0.12Si0.09)Σ3.01 O11.97F1.03 (Mountain 1004) and (Ca4.81Sr0.12Ba0.08Na0.05)Σ5.06(V2.64P0.27S0.07Si0.03)Σ3.01O12.15F0.51Cl0.34 (Nahal Morag). Pliniusite has a hexagonal structure with space group P63/m, a = b = 9.5777(7), c = 6.9659(5) Å, V = 553.39(7) Å3, and Z = 2. The structure was solved using single-crystal (holotype) X‑ray difraction, R = 0.0254. The mineral was named in honor of the famous Roman naturalist Pliny the Elder, born Gaius Plinius Secundus (AD 23–79). It is suggested that the combination of high temperature, low pressure, and high oxygen fugacity favors the incorporation of V5+ into calcium apatite-type compounds, leading to the formation of fluorovanadates. [ABSTRACT FROM AUTHOR]

Keywords: Apatite; time-resolved spectroscopy; Raman; luminescence; REE EN Apatite time-resolved spectroscopy Raman luminescence REE 1341 1352 12 07/05/22 20220701 NES 220701 Introduction Apatite [Ca SB 5 sb (PO SB 4 sb ) SB 3 sb (F,Cl,OH)] is one of the most common accessory minerals in both terrestrial rocks and meteorites. Fitting luminescence spectra A simple visual inspection of the spectra shows that: (1) luminescence spectroscopy is extremely sensitive down to the parts per million level and (2) the overall intensity of the luminescence signal dramatically increases with the activator concentration. Discussion Time-resolved luminescence for detecting REE and other emission centers If time-resolved spectroscopy allows for luminescence features in Raman spectra to be eliminated, it can also eliminate the Raman contribution from luminescence spectra. A major achievement would be to reach some quantification, or at least semi-quantification of luminescence activators in mineral phases from the luminescence signal, either directly from the spectra or through the study of luminescence lifetime. [Extracted from the article]

Its intended application to single-grain dating implies that the tracks should be counted in slow-etching faces with high-etching efficiencies, e.g., the prism faces of apatite ([25]). As a result of etching, etch pits develop at defects in slow-etching faces and hillocks on fast-etching faces. Because of this flattened shape and because they are often encompassed in the broad etch channels, etch pits in a prism surface are less conspicuous than in a basal face, and the apatite prism face is not considered as a pitted face despite its low-etch rate. Keywords: Apatite; fission track; etching; effective etch time; surface track; confined track EN Apatite fission track etching effective etch time surface track confined track 1190 1200 11 06/01/22 20220601 NES 220601 Introduction Fission tracks in apatite are ~20 m long ([11]; [44]) and ~10 nm wide ([71]; [70]; [57], [58], [59]), too thin to observe with a microscope. The fast-etching sides of the funnel at the intersection of the confined track with the host track expand at the expense of the slow-etching faces flanking the channel (Fig. [Extracted from the article]

Keywords: Tuite; ahrensite; Zagami; martian meteorite; high-pressure minerals EN Tuite ahrensite Zagami martian meteorite high-pressure minerals 1018 1029 12 06/01/22 20220601 NES 220601 Introduction Many meteorites from Mars ([2]; [26]; [49]; [59]), the Moon ([28]; [47]; [51]; [80]), Howardite-eucrite-diogenite (HED) meteorites ([48]; [52], [53]), and ordinary chondrites (e.g., [5]; [8]; [56]; [63]; [68]) are highly shocked, as evidenced by the observation of deformation in constituent minerals and formation of various high-pressure phases. Some tuite grains in Suizhou ([77]) and NWA 7755 ([73]) meteorites were found coexisting with Cl-rich apatite, with a Cl content of up to ~3.9 wt%, consistent with the possibility that they formed through decomposition of adjacent chlorapatite. 60 Shaw, C.S.J., and Walton, E. (2013) Thermal modeling of shock melts in Martian meteorites: Implications for preserving Martian atmospheric signatures and crystallization of high-pressure minerals from shock melts. [Extracted from the article]

Nanoparticles (25–50 nm) of chemically modified calcium phosphates Ca10−x−y Mii xNay(PO4)6−z (CO3)z(OH)2 (Mii – Cu2+, Zn2+) were synthesized via a wet precipitation method at room temperature. The Fourier-transform infrared spectroscopy data confirmed the partial substitution of PO43−{\text{PO}}_{4}^{3-} → CO32−{\text{CO}}_{3}^{2-} (B-type) in apatite-type structure. The influence of prepared phosphates on biofilm formation by pathogenic microorganisms was investigated. It was found that the samples Na+, CO32−{\text{CO}}_{3}^{2-}-hydroxyapatite (HAP) and Na+, Zn2+, CO32−{\text{CO}}_{3}^{2-}-HAP (5–20 mM) had the highest inhibitory effect on biofilm formation by Staphylococcus aureus strains. The sample Na+, CO32−{\text{CO}}_{3}^{2-}-HAP had the slight influence on the formation of the biofilm by Pseudomonas aeruginosa, while for the samples Na+, Cu2+, CO32−{\text{CO}}_{3}^{2-}-HAP and Na+, Zn2+, CO32−{\text{CO}}_{3}^{2-}-HAP such an effect was not detected. According to transmission electron microscopy data, a correlation between the activity of synthesized apatite-related modified calcium phosphates in the processes of biofilm formation and their ability to adhere to the surface of bacterial cells was established. The prepared samples can be used for the design of effective materials with antibacterial activity for medicine.

Alumino-oxy-rossmanite, ideally □Al3Al6(Si5AlO18)(BO3)3(OH)3O, is here described as a new member of the tourmaline supergroup. It is an early magmatic Al-rich oxy-tourmaline from a small pegmatitic body embedded in amphibolite and biotite-rich paragneiss. This new pink tourmaline was found in a Moldanubian pegmatite (of the Drosendorf Unit) that occurs in a large quarry near the village of Eibenstein an der Thaya, Waidhofen an der Thaya district, Lower Austria, Austria. The empirical formula of the holotype was determined on the basis of electron microprobe analysis (EMPA), secondary ion mass spectrometry (SIMS), spectroscopical methods (optical absorption and infrared spectroscopy), and crystal-structure refinement (SREF) as X(□0.53Na0.46Ca0.01) Y(Al2.37Mn30.21+ Li0.16□0.14 Mn20.07+ Fe30.03+ Fe20.01+ Ti40.01+) ZAl6(Si5.37Al0.41B0.22O18)(BO3)3V[(OH)2.77O0.23] W[O0.80(OH)0.15F0.05]. Chemical composition (wt%) is: SiO2 33.96, TiO2 0.10, Al2O3 47.08, B2O3 11.77, FeO 0.08, Fe2O3 0.23, MnO 0.52, Mn2O3 1.70, CaO 0.04, Li2O 0.25, ZnO 0.03, Na2O 1.51, H2O 2.79, F 0.09, total 100.11. The presence of relatively high amounts of trivalent Mn in alumino-oxy-rossmanite is in agreement with the observation that the OH groups are present at a lower concentration than commonly found in other Al-rich and Li-bearing tourmalines. The crystal structure of alumino-oxy-rossmanite [space group R3m; a = 15.803(1), c = 7.088(1) Å; V = 1532.9(3) Å3] was refined to an R1(F) value of 1.68%. The eight strongest X‑ray diffraction lines in the (calculated) powder pattern [d in Å (I) hkl] are: 2.5534 (100) 051, 3.9508 (85) 220, 2.9236 (78) 122, 4.1783 (61) 211, 2.4307 (55) 012, 2.0198 (39) 152, 1.8995 (30) 342, 6.294 (28) 101. The most common associated minerals are quartz, albite, microcline, and apatite. Beryl and, in places, schorl are also found as primary pegmatitic phases. Because of the low mode of associated mica (muscovite), we assume that the silica melt, which formed this pegmatite, crystallized under relatively dry conditions, in agreement with the observation that alumino-oxy-rossmanite contains a lower amount of OH than most other tourmalines. This new member of the tourmaline supergroup exhibits the most Al-rich end-member composition of the tourmaline supergroup (theoretical content: ~54 wt% Al2O3). The significant content of tetrahedrally coordinated Al could reflect the relatively high-temperature conditions (~700 °C) inferred for crystallization of the pegmatite. Alumino-oxy-rossmanite was named for its chemical relationship to rossmanite, □(LiAl2)Al6(Si6O18) (BO3)3(OH)3(OH), which in turn was named after George R. Rossman, Professor of Mineralogy at the California Institute of Technology (Pasadena, California, U.S.A.). [ABSTRACT FROM AUTHOR]

The Shatanjiao pluton, located in the eastern Tongling region (Eastern China), is of great research significance for the study of magma evolutionary processes because this pluton is related to the regional Cu-Au mineralization. Zircon U-Pb dating on two granodiorite samples from this pluton yields ages of 141.9 ± 3.1 Ma (MSWD = 0.07) and 141.9 ± 3.3 Ma (MSWD = 0.03), respectively, which overlap the range of intense Late Jurassic to Early Cretaceous magmatism in the Tongling region. Based on the Sr content of apatite from the Shatanjiao granodiorites, they are subdivided into high-Sr apatite (apatite-I: 754–1242 ppm, mean = 1107 ppm) and low-Sr apatite (apatite-II: 415–613 ppm, mean = 507 ppm). Both apatite-I and apatite-II are characterized by high-Sr and -Sr/Y ratios and inconspicuous negative-Eu anomalies, indicating that these granodiorites have a likely adakite affinity. Considering their low-Rb contents (<0.05 ppm), in situ Sr isotopes of these apatite grains show 87Sr/86Sr ratios of 0.70848–0.71494 and 0.70767–0.71585 for apatite-I and apatite-II, respectively, indicating that the 87Sr/86Sr ratios of both apatite groups can represent the Sr isotopic compositions of their host rocks. Moreover, the La/Sm and Sr/Th ratios of both apatite groups suggest that the studied granodiorites might be sourced from the partial melting of subducted ocean slabs and overlying sediments. Based on their zircon trace element compositions, the calculated temperature and oxygen fugacity for the magma are characterized by high temperatures (mean T = 646 °C) and high oxygen fugacity (mean Ce4+/Ce3+ ratios = 341). On the basis of MgO, FeO, SiO2, and ΣREE contents of apatite, we further suggest that apatite-I and apatite-II might have crystallized at the early and late stages of magma evolution, respectively. Because apatite-I has much higher Eu/Eu* ratios (0.56–0.76) but lower (La/Yb)N ratios (7.85–28.6) than apatite-II of 0.39–0.58 and 95.9–132, respectively, it is indicated that plagioclase, garnet, hornblende, and zircon might control the trace element composition of melt during the magma evolutionary history, which were recorded by the apatite. Therefore, apatite can be an ideal tracer to reflect the sequence of multistage magma evolution. [ABSTRACT FROM AUTHOR]

Identifying magma fertility is an important task in ore genesis research. In this paper, we use apatite chemistry and Sr-Nd isotopes for such a study. The apatite crystals are from four Cretaceous coeval granodiorite intrusions with different styles of hydrothermal mineralization in the Tongling ore district, South China. The selected intrusions are Hucun, Dongguashan, and Xinwuli, which host both porphyry and skarn Cu deposits, and the Chaoshan, which hosts a skarn Au deposit. The abundances of apatite major and trace elements, such as Mn, V, Ce, S, F, Cl, and Cu, together with the whole-rock compositions, are used to decipher the oxidation states, volatile compositions, and Cu fertility of the parental magmas. The apatite Sr-Nd isotope compositions are used as tracers for the magma sources. The results show that: (1) the parental magma of the Au-mineralized intrusion is less oxidized and has higher S-Cl contents than those of the Cu-mineralized intrusions, and (2) the proportion of mantle-derived melt is much higher in the former than in the latter. The results also reveal that the Cu-mineralized intrusions have highly variable apatite Cu-Cl-S compositions. Specifically, the Xinwuli intrusion has much higher Cu but lower Cl-S contents in apatite than the other two intrusions, indicating that a Cu-rich magma is not universally required for the formation of hydrothermal Cu deposits. This study demonstrates that apatite is a robust petrogenetic and metallogenic indicator for porphyry and skarn-type Cu-Au ore deposits. [ABSTRACT FROM AUTHOR]

Secondary hydrothermal reworking of REEs has been widely documented in carbonatites/alkaline rocks, but its potential role in the REE mineralization associated with these rocks is currently poorly understood. This study conducted a combined textural and in situ chemical investigation on the REE mineralization in the ~430 Ma Miaoya carbonatite-syenite complex, central China. Our study shows that the REE mineralization, dated at ~220 Ma, is characterized by a close association of REE minerals (monazite and/or bastnäsite) with pervasive carbonatization overprinting the carbonatites and syenites. In these carbonatites and syenites, both the apatite and calcite, which are the dominant magmatic REE-bearing minerals, exhibit complicated internal textures that are generally composed of BSE-bright and BSE-dark domains. Under BSE imaging, the former domains are homogeneous and free of pores or mineral inclusions, whereas the latter have a high porosity and inclusions of monazite and/or bastnäsite. In situ chemical analyses show that the BSE-dark domains of the apatite and calcite have light REE concentrations and (La/Yb)N values much lower than the BSE-bright areas. These features are similar to those observed in metasomatized apatite from mineral-fluid reaction experiments, thus indicating that the BSE-dark domains formed from primary precursors (i.e., represented by the BSE-bright domains) through a fluid-aided, dissolution-reprecipitation process during which the primary light REEs are hydrothermally remobilized. New, in situ Sr-Nd isotopic results of apatite and various REE minerals, in combination with mass balance calculations, strongly suggest that the remobilized REEs are responsible for the subsequent hydrothermal REE mineralization in the Miaoya complex. Investigations of fluid inclusions show that the fluids responsible for the REE mobilization and mineralization are CO2-rich, with medium temperatures (227-340 °C) and low salinities (1.42-8.82 wt‰). Such a feature, in combination with C-O isotopic data, indicates that the causative fluids are likely co-genetic with fluids from coeval orogenic Au-Ag deposits (220-200 Ma) in the same tectonic unit. Our new findings provide strong evidence that the late hydrothermal upgrading of early cumulated REEs under certain conditions could also be an important tool for REE mineralization in carbonatites, particularly for those present in convergent belts where faults (facilitating fluid migration) and hydrothermal fluids are extensively developed. [ABSTRACT FROM AUTHOR]

Mixing of cogenetic magmas represents an important process in granite petrogenesis but is difficult to identify and is consequently often overlooked due to the absence of obvious isotopic distinctions between the mixed melts. We have conducted in situ elemental and O isotope analyses on apatite from Cretaceous Zhangzhou calc-alkaline granite in southeast China. We integrated these data with microanalyses on other minerals (plagioclase, zircon, and titanite) as well as whole-rock geochemistry to decipher the mixing history of this granitic complex. The apatite occurs as an early crystallizing phase forming inclusions in biotite, plagioclase, and titanite, and is characterized by core-rim zonation textures with a dark core and bright rims in backscattered images. The core domains have remarkably higher SO3 and Li concentrations but much lower SiO2, REE, and Y concentrations than the rim domains. However, both the cores and rims show geochemical compositions similar to that from typical I-type granite and also have mantle-like O isotope compositions (the core has δ18O = 5.3-6.8‰ and the rim has δ18O = 5.2-6.4‰, respectively), indicating crystallization from granitic melts derived from newly accreted crust. The combined major and trace element and O isotope compositions of apatite and whole-rock geochemistry suggest that compositional evolution of the Zhangzhou granite involved mixing between two cogenetic magma batches, with variable degrees of subsequent differentiation. Batch I magma was a low-SiO2 and high-SO3 melt, whereas Batch II magma was a high-SiO2 and low-SO3 melt that experienced devolatilization. The high-S content in apatite cores further suggests the parental magma of the Zhangzhou granite likely originated from a sulfur-rich source comprising mainly newly accreted arc crust in response to subduction of the paleo-Pacific Ocean. The geochemical records of these magmatic processes are rarely observed in coeval zircon, titanite, and plagioclase. Our study, therefore, demonstrates that apatite geochemistry is potentially a more suitable monitor of complex magmatic evolution, including devolatilization and mixing of isotopically indistinguishable magmas. [ABSTRACT FROM AUTHOR]

Carbonatites and related alkaline rocks host most REE resources. Phosphate minerals, e.g., apatite and monazite, commonly occur as the main REE-host in carbonatites and have been used for tracing magmatic and mineralization processes. Many carbonatite intrusions undergo metamorphic and/or metasomatic modification after emplacement; however, the effects of such secondary events are controversial. In this study, the Miaoya and Shaxiongdong carbonatite-alkaline complexes, in the South Qinling Belt of Central China, are selected to unravel their magmatic and hydrothermal remobilization histories. Both the complexes are accompanied by Nb-REE mineralization and contain apatite and monazite-(Ce) as the major REE carriers. Apatite grains from the two complexes commonly show typical replacement textures related to fluid metasomatism, due to coupled dissolution-reprecipitation. The altered apatite domains, which contain abundant monazite-(Ce) inclusions or are locally surrounded by fine-grained monazite-(Ce), have average REE concentrations lower than primary apatite. These monazite-(Ce) inclusions and fine-grained monazite-(Ce) grains are proposed to have formed by the leaching REE from primary apatite grains during fluid metasomatism. A second type of monazite-(Ce), not spatially associated with apatite, shows porous textures and zoning under BSE imaging. Spot analyses of these monazite-(Ce) grains have variable U-Th-Pb ages of 210-410 Ma and show a peak age of 230 Ma, which is significantly younger than the emplacement age (440-430 Ma) but is roughly synchronous with a regionally metamorphic event related to the collision between the North China Craton and Yangtze Block along the Mianlue suture. However, in situ LA-MC-ICP-MS analyses of those grains show that they have initial Nd values same as those of magmatic apatite and whole rock. We suggest these monazite-(Ce) grains crystallized from the early Silurian carbonatites and have been partially or fully modified during a Triassic metamorphic event, partially resetting U-Pb ages over a wide range. Mass-balance calculations, based on mass proportions and the REE contents of monazite-(Ce) and apatite, demonstrate that the quantity of metasomatized early Silurian monazite-(Ce) is far higher than the proportion of monazite-(Ce) resulting from the metasomatic alteration of the apatite. Therefore, Triassic metamorphic events largely reset the U-Th-Pb isotopic system of the primary monazite-(Ce) and apatite but only had limited or local effects on REE remobilization in the carbonatite-alkaline complexes in the South Qinling Belt. Such scenarios may be widely applicable for other carbonatite and hydrothermal systems. [ABSTRACT FROM AUTHOR]

The genesis of the Dabaoshan stratabound base metal deposit has remained in dispute since its discovery. Scheelite is commonly present in both the Cu-S orebody and adjacent porphyry-style Mo-W mineralization and can provide insights into the hydrothermal history. In the stratabound Cu-S orebodies, there are three stages of mineralization: early-stage, Cu-(W), and late-stage. Two types of scheelite (here referred to as SchA and SchB) are identified in the Cu-(W) mineralization stage. SchA is anhedral and disseminated in massive sulfide ores. It coexists with chalcopyrite and replaces the preexisting arsenic-bearing pyrite. SchA exhibits chaotic cathodoluminescent (CL) textures and contains abundant mineral inclusions, including pyrite, chalcopyrite, arsenopyrite, uraninite, and minor REEbearing minerals. Chemically, SchA displays middle REE (MREE)-enriched patterns with negative Eu anomalies. SchB occurs in veins crosscutting the stratabound orebodies and shows patchy textures in CL images. Based on CL texture, SchB is subdivided into SchB1 and SchB2. SchB1 is CL-dark and occasionally shows oscillatory zoning, whereas SchB2 is CL-bright and relatively homogeneous. Chemically, SchB1 has a high-U content (mean = 552 ppm) and REE patterns varying from MREEenriched to MREE-depleted. In contrast, SchB2 is depleted in U (mean = 2.5 ppm) and has MREEenriched patterns. Compared with SchB, SchA is significantly enriched in Ba. Scheelite in the stratabound orebodies has similar Y/Ho ratios and trace-element characteristics as Sch3 in the Dabaoshan porphyry system. In situ U-Pb dating of hydrothermal apatite, collected from the Sch3-bearing veins in the footwall of stratabound orebodies, yielded a mineralization age of 160.8 ± 1.1 Ma. Zircon from the Dabaoshan granite porphyry yielded a U-Pb age of 161.8 ± 1.0 Ma. These two ages are consistent within uncertainty, suggesting that the ore-forming fluid responsible for tungsten mineralization in the stratabound orebodies was derived from the porphyry system. When fluid emanating from the deep porphyry system encountered the overlying Lower Qiziqiao Formation and stratabound orebodies, replacement reactions resulted in dramatic variations in physiochemical conditions (e.g., decrease in fO2, increase in Ca/Fe, As, Ba). During this process, U6+ was reduced to U4+, and As and Ba were leached out of the preexisting pyrite and host rock. Fluid-rock interactions triggered a rapid discharge of fluids, forming SchA with chaotic CL textures and abundant inclusions, but uniform REE patterns. SchB (characterized by patches with different chemical characteristics) may have been formed from repeated injection of ascending fluids into fractures crosscutting the preexisting massive sulfide ores. We propose that Jurassic porphyry Mo-W mineralization contributed to tungsten mineralization in the stratabound orebodies. Considering that Cu and W mineralization are genetically related, not only in the footwall but also in the stratabound orebodies, we infer that Cu in the stratabound orebodies was locally sourced from the Jurassic porphyry mineralization. [ABSTRACT FROM AUTHOR]

Hydroxylpyromorphite, Pb5(PO4)3(OH), has been documented in the literature as a synthetic and naturally occurring phase for some time but has not previously been formally described as a mineral. It is fully described here for the first time using crystals collected underground in the Copps mine, Gogebic County, Michigan. Hydroxylpyromorphite occurs as aggregates of randomly oriented hexagonal prisms, primarily between about 20-35 µm in length and 6-10 µm in diameter. The mineral is colorless and translucent with vitreous luster and white streak. The Mohs hardness is ~3 1/2-4; the tenacity is brittle, the fracture is irregular, and indistinct cleavage was observed on {001}. Electron microprobe analyses provided the empirical formula Pb4.97(PO4)3(OH0.69 F0.33Cl0.06)Σ1.08. The calculated density using the measured composition is 7.32 g/cm³. Powder X-ray diffraction data for the type material is compared to data previously reported for hydroxylpyromorphite from the talc mine at Rabenwald, Austria, and from Whytes Cleuch, Wanlockhead, Scotland. Hydroxylpyromorphite is hexagonal, P63/m, at 100 K, a = 9.7872(14), c = 7.3070(10) Å, V = 606.16(19) ų, and Z = 2. The structure [R1 = 0.0181 for 494 F>4σ(F) reflections] reveals that hydroxylpyromorphite adopts a column anion arrangement distinct from other members of the apatite supergroup due to the presence of fluorine and steric constraints imposed by stereoactive lone-pair electrons of Pb2+ cations. The F- anion sites are displaced slightly from hydroxyl oxygen anions, which allows for stronger hydrogen-bonding interactions that may in turn stabilize the observed column-anion arrangement and overall structure. Our modern characterization of hydroxylpyromorphite provides deeper understanding to a mineral useful for remediation of lead-contaminated water. [ABSTRACT FROM AUTHOR]

An intensive study of the geochemical characteristics (including the volatile elements Cl and S) of apatite associated with porphyry deposits was undertaken to address the debate about the crust- or mantle-derivation of their copper and gold and to better understand the controls on the transport of metals in magmatic fluids in post-subduction settings. New geochemical data on apatite reveal parameters to discriminate mineralized porphyry systems across Iran and western China (Tibet and Yunnan), from coeval barren localities across this post-subduction metallogenic belt. Apatites in fertile porphyries have higher Cl and S concentrations (reflecting water-rich crystallization conditions) than those from coeval barren ones. Our new isotopic data also indicate these volatiles are likely derived from pre-enriched sub-continental lithospheric mantle, metasomatized by previous oceanic subduction. This study demonstrates that refertilization of suprasubduction lithospheric mantle during previous collision events is a prerequisite for forming post-subduction fertile porphyries, providing an evidence-based alternative to current ore-enrichment models. [ABSTRACT FROM AUTHOR]

We measured the apatite etch rate vR in 5.5 M HNO3 at 21 °C as a function of orientation. Results for Durango apatite evidence that vR varies by a factor >5 with angle to the c-axis. Our measurements also provided track etch rates vT and surface etch rates vS. However, these cannot be combined for calculating track etching or counting efficiencies. By inserting the measured etch rates in a recent model, we calculate the geometries and dimensions of surface tracks in different apatite faces. The proposed model must be recalibrated for different etching protocols and adapted for other minerals. We submit that the new model justifies reviewing track counting efficiencies based on the existing (vB-vT) etch model. We anticipate that this will have an effect on practical aspects of fission track dating. Single-track step-etch data show that the confined track lengths increase with etch time at a decreasing average rate vL that differs from the track etch rate vT and the apatite etch rate vR. Both vT and vL exhibit large track-to-track differences that produce irreducible length variation related to the latent-track structure resulting from formation and annealing. Step etching and track width measurements are effective for reducing or eliminating procedure-related artifacts from track length data, and so for accessing more fundamental track properties. [ABSTRACT FROM AUTHOR]

The O–H stretching vibration mode in crystals of (Mn,Cl)-rich and F-poor minerals of the apatite-supergroup has been studied by micro-Raman spectroscopy. The main purpose was to check if such an analysis can provide a quick and simple method to assess the distribution of Ca and Mn together with traces of Fe + Mg (= Mn*) on nonequivalent cationic sites in the apatite structure, especially in small and strongly heterogeneous crystals directly in thin sections. The O–H stretching vibration mode can then be treated as a useful structural probe giving information on the M2 occupants bonded to XOH. Pieczkaite, with the empirical formula (Mn4.49Fe0.47Ca0.05Mg0.01)Σ5.01P2.99O12[Cl0.83(OH)0.17], displays the O–H stretching mode centered at ~3380 cm–1, which shows that the complete replacement of Ca by Mn* at the M2 site is connected with a shift of the O–H stretching band ~192 cm–1 toward lower wavenumbers in relation to the O–H Raman band position reported for hydroxylapatite. The value is high enough to be an indicator of the M2Mn*···OH content in any sample of Mn-enriched apatite. Studies of the fine structure of the band disclosed its dependence on (1) the local combinations of Ca and Mn* forming triplets of M2 cations bonded to the X anion, (2) the presence of OH+Cl at the two half-occupied X sites that form chemical bonds with the M2 cations varying in strength and length, and (3) the spatial geometry of the X–M2 bonds and polarizability of the monovalent X anion by varying cations in the M2M2M2 triplets. The deconvolution of the band into maximum eight component bands with constant Raman shifts opens the possibility of evaluating the averaged M2M2M2 triplet bonded to oxygen of the XOH group. If the OH/ (OH+Cl) fraction is known, the amounts of Ca and Mn* bonded to XOH can also be estimated. Application of the method to the holotype parafiniukite showed a slightly diferent distribution of Ca in M2M2M2 triplets than had been assumed from single-crystal X‑ray diffraction. However, it corroborates suggestions that in the apatite structure there may be a preference for M2Ca to be bonded to XOH and M2Mn* to XCl. Our results show that the proposed method can be used as an independent tool in structural studies of Mn-rich minerals of the apatite-supergroup, providing results complementary to single-crystal X‑ray diffraction. This method can easily be adjusted to modern apatite-type nanomaterials synthesized for biomedical and various industrial applications. [ABSTRACT FROM AUTHOR]

Parallel fission-track-surface intersections identify the grains in an etched apatite mount that have been polished parallel to their prism faces and mark the orientations of their c-axes. Their lengths (Dpar) are a practical kinetic parameter that is indicative of the track annealing rate of apatite. Little is known, however, about their geometrical properties in non-prism faces. We present a model calculation of the frequency distributions of the orientations, lengths, and widths of track-surface intersections in non-prism faces. The current model does not include the efects of surface etching or measurement imprecision. However, as far as it goes, it is consistent with measurements in apatite surfaces up to 30° to the c-axis. Regardless of the model, we submit that the statistical properties of the fission-track-surface intersections have practical uses. The distribution of their orientations is characteristic of the orientation of the etched surface relative to the c-axis. The distribution of their lengths presents a possible tool for investigating track etching, in particular for evaluating the tracks added and lost through surface etching. The distribution of their widths is a potential kinetic parameter independent of surface orientation and less susceptible to the factors, such as the sampling method and surface etch rate, that produce conflicting Dpar values. [ABSTRACT FROM AUTHOR]

We conducted in situ Cl isotopic measurements of apatite within intercumulus regions and within a holocrystalline olivine-hosted melt inclusion in magnesian-suite troctolite 76535 from Apollo 17. These data were collected to place constraints on the Cl-isotopic composition of the last liquid to crystallize from the lunar magma ocean (i.e., urKREEP, named after its enrichments in incompatible lithophile trace elements like potassium, rare earth elements, and phosphorus). The apatite in the olivine-hosted melt inclusion and within the intercumulus regions of the sample yielded Cl-isotopic compositions of 28.3 ± 0.9‰ (2σ) and 30.3 ± 1.1‰ (2σ), respectively. The concordance of these values from both textural regimes we analyzed indicates that the Cl-isotopic composition of apatites in 76535 likely represents the Cl-isotopic composition of the KREEP-rich magnesian-suite magmas. Based on the age of 76535, these results imply that the KREEP reservoir attained a Cl-isotopic composition of 28–30‰ by at least 4.31 Ga, consistent with the onset of Cl-isotopic fractionation at the time of lunar magma ocean crystallization or shortly thereafter. Moreover, lunar samples that yield Cl-isotopic compositions higher than the value for KREEP are likely affected by secondary processes such as impacts and/or magmatic degassing. The presence of KREEP-rich olivine-hosted melt inclusions within one of the most pristine and ancient KREEP-rich rocks from the Moon provides a new opportunity to characterize the geochemistry of KREEP. In particular, a broader analysis of stable isotopic compositions of highly and moderately volatile elements could provide an unprecedented advancement in our characterization of the geochemical composition of the KREEP reservoir and of volatile-depletion processes during magma ocean crystallization, more broadly. [ABSTRACT FROM AUTHOR]

The alteration of magmatic monazite and its consequences for monazite geochronology are explored in granitoids from the western part of the Ryoke belt (Iwakuni-Yanai area, SW Japan). Biotite-granite samples were collected in two plutons emplaced slightly before the main tectono-metamorphic event: the first one, a massive granite (Shimokuhara) adjoins schistose rocks affected by greenschist facies metamorphism; and the second, a gneissose granite (Namera) adjoins migmatitic gneiss that experienced upper-amphibolite facies conditions. Despite contrasting textures, the granite samples have similar mineral modes and compositions. Monazite in the massive granite is dominated by primary domains with limited secondary recrystallization along cracks and veinlets. It is variably replaced by allanite+apatite±xenotime±Th-U-rich phases. The outermost rims of primary domains yield a weighted average 206Pb/238U date of 102 ± 2 Ma while the Th-U phases show Th-U-Pb dates of 58 ± 5 and 15 to 14 ± 2-3 Ma. Monazite in the gneissose granite preserves sector- or oscillatory-zoned primary domains cross-cut by secondary domains enriched in Ca, Y, U, P, and containing numerous inclusions. The secondary domains preserve concordant 206Pb/238U dates spreading from 102 ± 3 to 91 ± 2 Ma while primary domain analyses are commonly discordant and range from 116 to 101 Ma. Monazite alteration textures in the two granites chiefly reflect differences in their post-magmatic histories. In the massive granite, monazite replacement occurred via a nearly stoichiometrically balanced reaction reflecting interaction with an aqueous fluid enriched in Ca+Al+Si±F during hydrothermal alteration of the granitic assemblage, likely below 500 °C. In the gneissose granite, a small amount of anatectic melt, probably derived from the neighboring metasedimentary rocks, was responsible for pseudomorphic recrystallization of monazite by dissolution-reprecipitation above 600 °C. Regardless of whether monazite underwent replacement or recrystallization, primary monazite domains preserve the age of magmatic crystallization for both plutons (102 ± 2 and 106 ± 5 Ma). Conversely, the age of monazite alteration is not easily resolved. Monazite replacement in the massive granite might be constrained using the Th-U-rich alteration products; with due caution and despite probable radiogenic Pb loss, the oldest date of 58 ± 5 Ma could be ascribed to chloritization during final exhumation of the granite. The spread in apparently concordant 206Pb/238U dates for secondary domains in the gneissose granite is attributed to incomplete isotopic resetting during dissolution-reprecipitation, and the youngest date of 91 ± 2 Ma is considered as the age of monazite recrystallization during a suprasolidus metamorphic event. These results reveal a diachronous, ca. 10 Ma-long high-temperature (HT) history and an overall duration of about 15 Ma for the metamorphic evolution of the western part of the Ryoke belt. [ABSTRACT FROM AUTHOR]

Northeastern China is an important Mo resource region in China, with more than 80 Mo deposits and occurrences. The Huojihe deposit located in the Lesser Xing'an Range represents one of the many Mesozoic porphyry Mo deposits in NE China and has been selected for investigation attempting to clarify the possible mechanisms controlling Mo mineralization. In this study, accessory minerals, including zircon and apatite from the causative intrusions (biotite monzogranite and granodiorite), have been analyzed to reveal their chemical and isotopic compositions, which provide insights into the nature of the source magmas and a better understanding of the factors affecting their mineralization potential. Zircon U-Pb dating shows that the biotite monzogranite from the Huojihe deposit formed at 181.6 ± 0.6 Ma, which is identical to the previously reported molybdenite Re-Os age (~181 Ma), indicating that the Mo mineralization is probably genetically related to the intrusion. The intrusion samples share homogeneous geochemical and Sr-Nd isotopic compositions, with initial 87Sr/86Sr ratios of 0.7072-0.7075 and slightly negative εNd (t) values from -2.3 to -1.4, reflecting a uniform magma source. The least-altered apatites show similar (or slightly enriched) initial 87Sr/86Sr ratios (0.7080-0.7108) and εNd (t) values (-4.0 to -1.8), whereas the hydrothermally altered apatites are characterized by significantly higher initial 87Sr/86Sr ratios (0.7091-0.7119) and more negative εNd(t) values (-4.9 to -4.4), probably due to the interaction between the hydrothermal fluids and wall rocks. The zircon εHf(t) values vary from -0.9 to 1.7, corresponding to a restricted range of TDM2 ages from 1279 to 1120 Ma. The Sr-Nd-Hf isotope results suggest that the primary magmas associated with the Mo mineralization could be generated from a dominantly Mesoproterozoic lower crust source, with rare contributions from the depleted mantle. The low Ga and Ce and high Eu contents in the magmatic apatite demonstrate that the original magmas have a relatively high oxygen fugacity, which is also supported by the high zircon CeN/CeN* (22-568) and EuN/EuN* (0.38-0.71) values. Estimates of absolute sulfur concentrations in the mineralization-related melt using available partitioning models for apatite return relatively low magmatic sulfur concentrations in Huojihe (20-100 ppm), indistinguishable from those of larger or smaller deposits or even barren magmatic bodies. Using the sulfur concentration data, a minimum volume of 10-50 km³ magma has been suggested to be necessary to produce the Huojihe Mo deposit based on mass balance modeling. Besides, the Mo concentration in the original magma has also been roughly estimated based on the magma size (10-50 km³) and the contained Mo in Huojihe (0.275 Mt). The magmatic Mo concentrations (2-10 ppm) are similar to many other porphyry Mo systems (e.g., the Climax-type porphyry Mo deposits), and are also comparable to subeconomic to barren magma systems. This study suggests that pre-degassing enrichments of Mo and S in the original magma is not necessarily important in the formation of the Huojihe Mo deposit; rather, factors other than melt composition may be more critical in forming a porphyry Mo deposit. This understanding might also apply to other porphyry Mo mineralized systems worldwide. [ABSTRACT FROM AUTHOR]

We report the occurrence of a previously unidentified mineral in lunar samples: a Cl-,F-,REE-rich silico-phosphate identified as Cl-bearing fluorcalciobritholite. This mineral is found in late-stage crystallization assemblages of slowly cooled high-Ti basalts 10044, 10047, 75035, and 75055. It occurs as rims on fluorapatite or as a solid-solution between fluorapatite and Cl-fluorcalciobritholite. The Cl-fluorcalciobritholite appears to be nominally anhydrous. The Cl and Fe2+ of the lunar Cl-fluorcalciobritholite distinguishes it from its terrestrial analog. The textures and chemistry of the Cl-fluorcalciobritholite argue for growth during the last stages of igneous crystallization, rather than by later alteration/replacement by Cl-, REE-bearing metasomatic agents in the lunar crust. The igneous growth of this Cl- and F-bearing and OH-poor mineral after apatite in the samples we have studied suggests that the Lunar Apatite Paradox model (Boyce et al. 2014) may be inapplicable for high-Ti lunar magmas. This new volatile-bearing mineral has important potential as a geochemical tool for understanding Cl isotopes and REE chemistry of lunar samples. [ABSTRACT FROM AUTHOR]

The solubility of apatite in anatectic melt plays an important role in controlling the trace-element compositions and isotopic signatures of granites. The compositions of glassy melt inclusions and nanogranitoids in migmatites and granulites are compared with the results of experimental studies of apatite solubility to evaluate the factors that influence apatite behavior during prograde suprasolidus metamorphism and investigate the mechanisms of anatexis in the continental crust. The concentration of phosphorus in glassy melt inclusions and rehomogenized nanogranitoids suggests a strong control of melt aluminosity on apatite solubility in peraluminous granites, which is consistent with existing experimental studies. However, measured concentrations of phosphorus in melt inclusions and nanogranitoids are generally inconsistent with the concentrations expected from apatite solubility expressions based on experimental studies. Using currently available nanogranitoids and glassy melt inclusion compositions, we identify two main groups of inclusions: those trapped at lower temperature and showing the highest measured phosphorus concentrations, and melt inclusions trapped at the highest temperatures having the lowest phosphorus concentrations. The strong inconsistency between measured and experimentally predicted P concentrations in higher temperature samples may relate to apatite exhaustion during the production of large amounts of peraluminous melt at high temperatures. The inconsistency between measured and predicted phosphorus concentrations for the lower-temperature inclusions, however, cannot be explained by problems with the electron microprobe analyses of rehomogenized nanogranitoids and glassy melt inclusions, sequestration of phosphorus in major minerals and/or monazite, shielding or exhaustion of apatite during high-temperature metamorphism, and apatite–melt disequilibrium. The unsuitability of the currently available solubility equations is probably the main cause for the discrepancy between the measured concentrations of phosphorus in nanogranites and those predicted from current apatite solubility expressions. Syn-entrapment processes such as the generation of diffusive boundary layers at the mineral-melt interface may also be responsible for concentrations of P in nanogranitoids and glassy melt inclusions that are higher than those predicted in apatite-saturated melt. [ABSTRACT FROM AUTHOR]

Britholite group minerals (REE,Ca)5[(Si,P)O4]3(OH,F) are widespread rare-earth minerals in alkaline rocks and their associated metasomatic zones, where they usually are minor accessory phases. An exception is the REE deposit Rodeo de los Molles, Central Argentina, where fluorbritholite-(Ce) (FBri) is the main carrier of REE and is closely intergrown with fluorapatite (FAp). These minerals reach an abundance of locally up to 75 modal% (FBri) and 20 modal% (FAp) in the vein mineralizations. The Rodeo de los Molles deposit is hosted by a fenitized monzogranite of the Middle Devonian Las Chacras-Potrerillos batholith. The REE mineralization consists of fluorbritholite-(Ce), britholite-(Ce), fluorapatite, allanite-(Ce), and REE fluorcarbonates, and is associated with hydrothermal fluorite, quartz, albite, zircon, and titanite. The REE assemblage takes two forms: irregular patchy shaped REE-rich composites and discrete cross-cutting veins. The irregular composites are more common, but here fluorbritholite-(Ce) is mostly replaced by REE carbonates. The vein mineralization has more abundant and better-preserved britholite phases. The majority of britholite grains at Rodeo de los Molles are hydrothermally altered, and alteration is strongly enhanced by metamictization, which is indicated by darkening of the mineral, loss of birefringence, porosity, and volume changes leading to polygonal cracks in and around altered grains. A detailed electron microprobe study of apatite-britholite minerals from Rodeo de los Molles revealed compositional variations in fluorapatite and fluorbritholite-(Ce) consistent with the coupled substitution of REE3+ + Si4+ = Ca2+ + P5+ and a compositional gap of ~4 apfu between the two phases, which we interpret as a miscibility gap. Micrometer-scale intergrowths of fluorapatite in fluorbritholite-(Ce) minerals and vice versa are chemically characterized here for the first time and interpreted as exsolution textures that formed during cooling below the proposed solvus. [ABSTRACT FROM AUTHOR]

Previous inter-laboratory experiments on confined fission-track length measurements in apatite have consistently reported variation substantially in excess of statistical expectation. There are two primary causes for this variation: (1) differences in laboratory procedures and instrumentation, and (2) personal differences in perception and assessment between analysts. In this study, we narrow these elements down to two categories, etching procedure and analyst bias. We assembled a set of eight samples with induced tracks from four apatite varieties, initially irradiated between 2 and 43 years prior to etching. Two mounts were made containing aliquots of each sample to ensure identical etching conditions for all apatites on a mount. We employed two widely used etching protocols, 5.0 M HNO3 at 20 °C for 20 s and 5.5 M HNO3 at 21 °C for 20 s. Sets of track images were then captured by an automated system and exchanged between two analysts, so that measurements could be carried out on the same tracks and etch figures, in the same image data, allowing us to isolate and examine the effects of analyst bias. An additional 5 s of etching was then used to evaluate etching behavior at track tips. In total, 8391 confined fission-track length measurements were performed; along with 1480 etch figure length measurements. When the analysts evaluated each other's track selections within the same images for suitability for measurement, the average rejection rate was ∼14%. For tracks judged as suitable by both analysts, measurements of 2D and 3D length, dip, and c-axis angle were in excellent agreement, with slightly less dispersion when using the 5.5 M etch. Lengths were shorter in the 5.0 M etched mount than the 5.5 M etched one, which we interpret to be caused by more prevalent under-etching in the former, at least for some apatite compositions. After an additional 5 s of etching, 5.0 M tracks saw greater lengthening and more reduction in dispersion than 5.5 M tracks, additional evidence that they were more likely to be under-etched after the initial etching step. Systematic differences between analysts were minimal, with the main exception being likelihood of observing tracks near perpendicular to the crystallographic c axis, which may reflect different use of transmitted vs. reflected light when scanning for tracks. Etch figure measurements were more consistent between analysts for the 5.5 M etch, though one apatite variety showed high dispersion for both. Within a given etching protocol, each sample reflected a decrease of mean track length with time since irradiation, giving evidence of 0.2–0.3 μm of annealing over year to decade timescales. [ABSTRACT FROM AUTHOR]

We conducted a series of monazite and xenotime dissolution experiments in a boron-bearing silicic melt at 1000-1400 °C and 800 MPa in a piston-cylinder apparatus. We present new measurements of monazite and xenotime solubility in hydrous (~3 wt% water), boron-bearing rhyolitic melts, as well as the diffusivities of the essential structural constituents of those minerals (LREE, P, and Y). We compare our results to the previous studies and discuss the implications of this study on the understanding of natural, silicic (granitic/rhyolitic) systems. We propose one equation describing the relationship between the solubility of xenotime and temperature in hydrous rhyolitic melts: ln Y = 18.3 ± 0.3 - 125499 ± 3356/RT and another for monazite: lnΣLREE = 18.6 ± 1.5 - 129307 ± 18163/RT. In the presence of sufficient phosphorous, the concentration of LREE needed for monazite saturation is within the uncertainty of the Y concentration needed from xenotime saturation and indicates that in the case of equilibrium crystallization the mineral that forms will only depend on the availability of LREE and Y and HREE. Given the similarity of the solubility of xenotime to that of monazite, we propose that previously published models of monazite solubility in silicic melts can potentially be applied to xenotime, and could, like monazite, serve as a geothermometer. In the case of disequilibrium crystallization in front of rapidly growing crystals, Y will diffuse faster than LREE and xenotime will only crystallize when LREE are depleted. We also found that the diffusion of Y is greater than the diffusion of P from dissolving xenotime, unlike the similar diffusivities of LREE and P during monazite dissolution. The significant difference between Y and P diffusivities suggests that the components forming xenotime diffuse as separate entities rather than molecular complexes. The dissolution of phosphates (monazite, xenotime, apatite) in hydrous, silicic melts with the addition of boron leads to liquid-liquid immiscibility at high temperatures where the saturation values of P and either light rare earth elements or Y are in the weight percent range. Immiscibility is not observable at low, magmatic temperatures, most probably due to the lower concentrations of P2O5 necessary for phosphate saturation at these conditions; however addition of other components, notably F, may result in liquid-liquid immiscibility at magmatic temperatures. [ABSTRACT FROM AUTHOR]

Garnet is a common metamorphic and igneous mineral with extensive solid solution that can be stable to mantle depths ≥400 km. High-T and/or high-P garnet may contain oriented lamellae of other minerals, most commonly simple oxides (e.g., rutile, ilmenite), apatite, and, in ultrahigh-P cases, silicates including pyroxene and amphibole. Lamellae have classically been considered to be precipitation features preserving a record of former garnet chemistry richer in the lamellae nutrients (e.g., Ti4+). Such microtextural origins in precipitation systems (e.g., alloys) have long been studied via the crystallographic orientation relationships (COR) that form between a host and a separating phase, and by the shape-preferred orientation (SPO) of the lamellae. Recently, however, alternative hypotheses to precipitation have been suggested that require emplacement of lamellae in garnet by fluids, or co-growth, overgrowth, or inheritance mechanisms. These hypotheses posit that lamellae cannot be used to study former garnet chemistry. Moreover, they predict that lamellae phases, SPO, and COR should differ widely between localities, as lamellae formation will be controlled by various local rock-specific factors such as fluid presence, fluid chemistry, or mineral growth sequence. On the other hand, if lamellae characteristics are largely consistent between localities, it likely reflects control by precipitation energetics, rather than external factors. There have been few comparative COR studies in geologic systems, but the integrative assessment of COR, SPO, and lamellae assemblages should fingerprint lamellae growth process. To test the precipitation and alternative hypotheses, we collected large electron backscatter diffraction (EBSD) data sets for rutile, ilmenite, and apatite lamellae in garnet from the Brimfield Schist, Connecticut (≥1000 °C metamorphism; Central Maine Terrane, U.S.A.). We analyzed these data alongside published EBSD data for rutile, ilmenite, and corundum from metapegmatites metamorphosed in the eclogite facies from the Austrian Alps (Griffiths et al. 2016). The apatite data set is the first of its kind, and reveals that apatite preferentially aligns its close-packed direction parallel to that of garnet (c-axisapatite//<111>garnet). We also recognize a rutile-garnet COR related to those in meteorites with Widmanstätten patterns that are unequivocal products of exsolution. This is the first identification of direct similarities between silicate-oxide and metal-metal COR of which we are aware. Significantly, this rutile-garnet COR is found in diverse geologic settings including Connecticut and Idaho (U.S.A.), Austria, Germany, Greece, and China over a broad range of bulk-rock compositions. Results for all lamellae minerals show that COR are largely consistent between localities and, furthermore, are shared between apatite, ilmenite, and corundum. Moreover, between 70% and 95% of lamellae have COR and there is a dominant COR for each lamellae phase. Calculations show that d-spacing ratios of host-lamellae pairs can successfully predict the most commonly observed specific COR (those COR with two or more axial alignments with the host). These results, especially similarity of COR from markedly different geologic settings and a low diversity of lamellae minerals, are fully consistent with lamellae formation by precipitation (likely via exsolution). In contrast, the alternative hypotheses remain unsupported by COR results as well as by mineralogical and petrological evidence. Lamellae with similar traits as those in this work should thus be considered precipitates formed during unmixing of garnet compositions originally stable at elevated or extreme pressures and temperatures. [ABSTRACT FROM AUTHOR]