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pre-Goldschmidt SIMS workshop, 10 July

EB
Elizabeth Bell
Tue, May 31, 2022 2:55 PM

Elizabeth Bell ebell21@ucla.edu
Fri, Apr 15, 12:11 PM
to msa-talk
Dear colleagues,

If you are attending Goldschmidt, I wanted to bring your attention to the
pre-Goldschmidt workshop, held Sunday 10 July, on secondary ion mass
spectrometry in geochemistry, biogeochemistry, cosmochemistry, and nuclear
forensics (
https://2022.goldschmidt.info/goldschmidt/2022/meetingapp.cgi/Session/3134),
organized by Ming-Chang Liu, Heather Cunningham, and me.

The workshop registration deadline is May 31st, and both in-person and
hybrid attendance will be possible.  We look forward to seeing you there!

Sincerely,
Beth Ann Bell

--
Elizabeth Bell, Ph.D.
Assistant Project Scientist
Dept. of Earth, Planetary, and Space Sciences, UCLA
https://sites.google.com/site/eabellgeo/

Elizabeth Bell <ebell21@ucla.edu> Fri, Apr 15, 12:11 PM to msa-talk Dear colleagues, If you are attending Goldschmidt, I wanted to bring your attention to the pre-Goldschmidt workshop, held Sunday 10 July, on secondary ion mass spectrometry in geochemistry, biogeochemistry, cosmochemistry, and nuclear forensics ( https://2022.goldschmidt.info/goldschmidt/2022/meetingapp.cgi/Session/3134), organized by Ming-Chang Liu, Heather Cunningham, and me. The workshop registration deadline is May 31st, and both in-person and hybrid attendance will be possible. We look forward to seeing you there! Sincerely, Beth Ann Bell -- Elizabeth Bell, Ph.D. Assistant Project Scientist Dept. of Earth, Planetary, and Space Sciences, UCLA https://sites.google.com/site/eabellgeo/
RR
Rachel Russell
Thu, Jun 2, 2022 1:30 PM

Dear American Mineralogist Readers,

Below are the Paper Highlights for this month’s issue of the American Mineralogist: International Journal of Earth and Planetary Materials. You may also view the American Mineralogist Paper Highlights list at here (http://www.minsocam.org/MSA/Ammin/AM_NotableArticles.html).

The DOI links below will take you to the abstract on GeoScienceWorld.

If you have “IP” access via your institution’s library, it should reveal the whole paper. Consult your institution’s IT department or friendly librarian.

If you have MSA membership, then authenticate in from the American Mineralogist menu (herehttp://www.msapubs.org/ directly). Once at the portal page, click the right-side American Mineralogist link, enter your user name (e-mail address), and your password (membership number). Then search via your browser’s search tools for the paper you want to read. (On Rachel’s computer, it is control-f but we think that is little different for everyone.)

Note that on GSW you can sign up for a table of contents to be sent you when the issue is live -- this is a feature open to anyone who registers on the site.

Thank you for reading American Mineralogist.

Sincerely,
Hongwu Xu

Don Baker

Periodic and non-periodic stacking in molybdenite (MoS2) revealed by STEM
https://doi.org/10.2138/am-2022-8019
Yang et al. used HAADF-STEM imaging to identify the stacking faults and domains of long-period molybdenite polytypes. Several layers of disordered domains intergrown with ordered 2H1 domain were recognized based on the contrast in HAADF image with one-dimensional lattice fringes. In addition, 30-layer long-period polytype and 2H3 polytype with three repetition domains were discovered for the first time. These results demonstrate that the presence of trace elements is strongly correlated with the existence of disordered domains in molybdenite crystals. It is suggested that non-equilibrium conditions related to compositional fluctuation of fluid during crystallization resulted in the oscillation of 2H1 and 3R polytypes and intergrowth of various disordered domains. The HAADF-STEM imaging method may be applied for studying other disordered layered crystals and twin minerals.

The effect of halogens (F, Cl) on the near-liquidus crystallinity of a hydrous trachyte melt
https://doi.org/10.2138/am-2022-8120
Feisel et al. employed the diffusion couple technique to investigate the effect of F and Cl on the crystallinity of a hydrous trachyte. In essence, their experiments demonstrate a significant drop of the liquidus temperature — as manifested by a Cpx-dissolution front — in response to rising Cl and F concentration. The liquidus depression was quantified and shown to linearly correlate with the concentration of F and Cl in the melt. They propose that F and Cl are causing the observed dissolution as they complex with the main components of Cpx. With this study, the authors illustrate the strong influence that halogens can exert on the phase equilibria of a melt and that even small fluctuations of their concentrations, e.g., caused by volcanic degassing, can control the stability of Fe-Mg-Ca mineral phases.

Occurrence of tuite and ahrensite in Zagami and their significance for shock-histories recorded in martian meteorites
https://doi.org/10.2138/am-2022-8020
The Zagami martian meteorite, one of the most famous martian falls, was highly shocked, as supported by the identification of many high-pressure polymorphs, e.g., stishovite, seifertite, liebermannite, and zagamiite. These phases are crucial for constraining how they were formed by asteroid impact on Mars. Gu et al. report on the discovery of two high-pressure minerals, tuite and ahrensite, identified in shock-induced melt pockets in Zagami meteorite, which could shed light on the phase decomposition under high P-T conditions. Tuite identified in this study has two formation pathways: decomposition of apatite and transformation of merrillite under high P-T conditions. Nanocrystalline ahrensite in the pyroxene clast from Zagami is likely the product of decomposition of pigeonite under high P-T conditions through a solid-state transformation mechanism. This dissociation of pigeonite to ahrensite/ringwoodite plus other phases may be widespread in other heavily shocked meteorites but potentially been overlooked in previous studies.

Zolenskyite, FeCr2S4, a new sulfide mineral from the Indarch meteorite
https://doi.org/10.2138/am-2022-8094
Ma and Rubin report a new sulfide mineral, zolenskyite (FeCr2S4), discovered in the Indarch meteorite, an EH4 enstatite chondrite, and discuss its origin and significance. Zolenskyite is a monoclinic polymorph of daubréelite that may have crystallized within chondrules at high temperatures from the early solar system.

A refined estimation of Li in mica by a machine learning method
https://doi.org/10.2138/am-2022-8029
Wang et al. use a compilation of >2000 mica compositions from various rock types, including Li2O and the following 10 major components: SiO2, Al2O3, TiO2, FeOT, MgO, MnO, CaO, Na2O, K2O, and F. These data are regressed using a multivariate polynomial regression (MPR) based machine learning (ML) method to refine the equation for estimating Li in micas over a wide range of chemical compositions. They then discuss the uncertainties and limitations of the refined equation and compare the performance of the MPR model with previously published empirical equations. Finally, they apply the refined equation to estimate the Li2O contents of micas from various types of rocks in central Inner Mongolia, NE China. Their results indicate that the MPR model is more precise and accurate and can be generalized to almost all types of micas. Above all, they provide a robust and convenient approach to conduct microanalysis of Li in mica, applying a combination of EMPA and machine learning methods, which can be widely used in mineralogy, petrology, and economic geology.

Olivine in picrites from Continental Flood Basalt provinces classified using machine learning
https://doi.org/10.2138/am-2022-8083
Cheng et al. provide a novel method using machine learning based on a large database of olivine composition in picrites from global Continental Flood Basalts to classify olivine with two distinct sources. This method is capable of classifying the overlapping data into correct groups, which cannot be done by traditional methods in several minutes with high accuracy.

Non-Arrhenian viscosity-temperature relationships for carbonate melts
https://doi.org/10.2138/am-2021-7752
Dingwell et al. report the first quantitative determination of a glass transition for a carbonate liquid. Specifically, they demonstrate the nature of the glass transition and viscosity of a mixed K2CO3-MgCO3 carbonate melt by performing scanning calorimetry and viscometry on samples of a supercooled carbonate phase. Using this low-temperature viscosity data combined with published higher temperature (high pressure) data as well as both classical and ab initio molecular dynamics simulation estimates, they determine a non-linear Vogel- Fulcher-Tammann (VFT) law fit and quantify the extent of fragility. The non-linear rate change in viscosity is an important parameter in understanding the nature of carbonatite lava flows on Earth and possibly Venus. The most widespread occurrence of carbonate melts is most likely in the deep mantles of terrestrial planets. At very small degrees of melting, alkali-rich carbonate melt may exist at lower temperatures (>1200 °C). These low temperatures are realistic for the shallow lithosphere beneath the old continental crust and are in the temperature range where a linear fit based on the high-temperature data will become inaccurate. This would have implications for modeling the transport properties of these melts to their surface expression or as metasomatizing agents.

Etching of fission tracks in monazite: Further evidence from optical and focused ion beam scanning electron microscopy
https://doi.org/10.2138/am-2022-8002
Jones et al. conducted a series of experiments on monazites from Victoria, Australia, to further understand their fission-track (FT) etching properties. Monazite is a mineral currently being developed in the FT system, and a crucial first step in its development is understanding its etching properties. This enables fission tracks to be observable under the optical microscope so that they can be analyzed and used to constrain the thermal history of rocks in the Earth’s uppermost crust (1–2 km).

The low-temperature shift of antigorite dehydration in the presence of sodium chloride: in situ diffraction study up to 3 GPa and 700 °C
https://doi.org/10.2138/am-2022-7962
The dehydration of serpentine mineral antigorite is regarded as the key step in metamorphic transformation of serpentinized rocks in subduction zones, which affects seismicity and feeds volcanic activity. Likhacheva et al. found that, in the presence of salt-bearing fluid, the reaction shifts to lower temperature by more than 150 °C in the pressure range of 2-4 GPa, which implies a broadened P-T region of serpentinite dehydration in subducting slab.

Chemistry-dependent Raman spectral features of glauconite and nontronite: Implications for mineral identification and provenance analysis
https://doi.org/10.2138/am-2022-8044
Baumgartner et al. provide a comprehensive Raman spectral characterization of nontronite and glauconite-nontronite mixed-layer phases from seafloor hydrothermal fields. It is shown that these phyllosilicates exhibit a series of Raman peaks that are strongly dependent on the exchange between trivalent and divalent cations in the trioctahedral sheets. The importance of these findings for a variety of applications is discussed.

Experimental determination of solubility constants of saponite at elevated temperatures in high ionic strength solutions
https://doi.org/10.2138/am-2021-7827
Xiong performed solubility experiments of Mg-saponite at 80 ºC to quantify the thermodynamic stability of this tri-octahedral smectite in the presence of nitrate cancrinite. In combination with the equilibrium constant at 80 ºC for the dissolution reaction of nitrate cancrinite from the literature, the author determined the solubility constant of saponite at 80 ºC to be –69.24 ± 2.08. Furthermore, the author extrapolated the equilibrium constant at 80 ºC to other temperatures (50-100 ºC) using the one-term isocoulombic method. The obtained equilibrium constants are expected to find applications in several fields, especially geological disposal of nuclear waste.

Hydrothermal troctolite alteration at 300 and 400 ºC: Insights from flexible Au-reaction cell batch experimental investigations
https://doi.org/10.2138/am-2021-7832
Hansen et al. present a comprehensive experimental study on the serpentinization of olivine-rich troctolites. Dickson-type reactors were used to simulate hydrothermal troctolite alteration by reacting fresh forsteritic olivine and anorthite-rich plagioclase with seawater-like fluids at two distinct temperature levels (300, 400 °C) and an elevated pressure level (40 MPa). Time series analyses of reaction concomitant fluid samples and detailed mineralogical and geochemical characterization of the final solid-phase assemblage were combined with comparative thermodynamic modeling to enable a comprehensive characterization of the alteration process. Presented results confirm earlier hypothesis that silica activity levels set by temperature-dependent coupled olivine serpentinization and plagioclase desilication reactions constitute a key control. They further demonstrate the crucial effect of variable reaction rates in different portions of a solid reactant that are closer to or further away from the solid-fluid interface.

Timescales and rates of intrusive and metamorphic processes determined from zircon and garnet in migmatitic granulite, Fiordland, New Zealand
https://doi.org/10.2138/am-2022-7967
Stowell et al. investigated the timing of pluton emplacement and metamorphism in the lower crust of the Fiordland magmatic arc using zircon and garnet geochronology. The isotope data provide precise dates which clearly indicate that high-temperature granulite facies metamorphism occurred less than 3 million years after intrusion of voluminous mantle-derived magmas. No heat source has been documented for the metamorphism; however, they speculate that underplating of magma caused heating. Subsequent cooling for this granulite orthogneiss at 15-25 °C/million years was considerably slower than previously estimated. The new isotope data provide precise ages and rates of cooling for a single outcrop and underline the importance of multiple chronometers and careful textural characterization for assigning meaningful ages to lower-crustal rocks.

In situ chemical and isotopic analyses and element mapping of multiple-generation pyrite: evidence of episodic gold mobilization and deposition for the Qiucun epithermal gold deposit in Southeast China
https://doi.org/10.2138/am-2022-8030
Ma et al. investigated the origin of high-grade ore shoots and visible gold in gold deposits by analyzing the multiple generations of pyrite in a representative epithermal gold system in SE China using a number of in situ analytical techniques (including LA-ICP-MS trace element analysis and mapping and LA-MC-ICP-MS sulfur isotope analysis). The results demonstrated that multiple remobilization and reprecipitation of gold were taken place in this epithermal gold deposit. The pressure-driven hydrothermal processes play an important role not only in initial invisible (refractory) gold enrichment but also in the re-enrichment of visible gold and some other trace metals during episodic deposition, replacement, and hydrothermal alteration of auriferous pyrite in gold deposits. This study demonstrates that detailed textural examination and in situ chemical and sulfur isotope analysis under robust geological and petrographic frameworks can effectively constrain the complex gold mobilization and deposition processes in hydrothermal ore deposits.

Hydrothermal mineralization of celadonite: Hybridized fluid-basalt interaction in Janggi, Korea
https://doi.org/10.2138/am-2022-8045
Park et al. discovered an exceptional celadonite mineralization in the Miocene lacustrine Janggi basin in the southeastern Korean Peninsula. This celadonite occurs as greenish earthy/vitreous materials filling the E-W trending fault zones in basaltic flows. Detailed fieldwork and whole-rock major, trace, and oxygen isotope analyses indicate that celadonites were formed in an open system of ~120 °C via the interaction of the hybridized fluid and basalts along with the physicochemical fault brecciation of the host rock. The cations required for the celadonite formation were supplied by the smectitization/zeolitization of rhyolitic mesostasis (for Al and part of K) and pyroxene microlites (for Fe and Mg) in the basaltic breccias during the associated oxidation of micro-nanoparticles by circulating fluids (for most of K). This mechanism is plausible, where both the magmatic fluid influx and the particle size reduction could be involved. This model suggests that any crustal rocks rich in ferromagnesian components could produce celadonite through the hydrothermal potassic alteration.

Gungerite, TlAs5Sb4S13, a new thallium sulfosalt with a complex structure containing covalent As-As bonds
https://doi.org/10.2138/am-2022-8003
Kasatkin et al. describe a new thallium sulfosalt mineral, gungerite, discovered in Russia. It possesses an interesting structural architecture, quite unique among the known sulfosalt structures: the structure consists of doughnut-shaped (As,Sb)–S clusters, which have van der Waals contacts to most of the surroundings and are connected to them only by sparse cation–sulfur bonds.

Nitscheite, a new mineral with an unusual uranyl-sulfate sheet
https://doi.org/10.2138/am-2022-7994
Inactive uranium mines have proven to be fruitful underground “natural laboratories”, providing insight into the factors driving the crystallization of uranium minerals. The great diversity observed for uranyl sulfate minerals stems primarily from the large number of stable linkages of uranyl pentagonal bipyramids and sulfate tetrahedra. The new uranyl sulfate nitscheite, described herein by Kampf et al., possesses a type of uranyl sulfate sheet not previously observed in nature.

Protocaseyite, a new decavanadate mineral containing a [Al4(OH)6(H2O)12]6+ linear tetramer, a novel isopolycation
https://doi.org/10.2138/am-2022-8059
Kampf et al. describe the new mineral protocaseyite found in a low-temperature, post-mining, secondary mineral assemblage in the Burro mine in the Uravan Mineral Belt of western Colorado, U.S.A. The crystal structure of this mineral contains a decavanadate polyoxometalate anion together with a novel 4-member aluminate polyoxometalate cation referred to as an Al-flatimer. Polyoxometalate ions have been the subject of numerous synthesis studies in recent years, largely because of their potential technological uses. Polyoxometalate ions have also been proposed to exist in solution as precursors of more extended structural components (chains, sheets, and frameworks) in mineral structures, but only rarely are polyoxometalate ions found as isolated units in minerals.

Fission-track etching in apatite: A model and some practical implications
https://doi.org/10.2138/am-2022-8055
Jonckheere et al. investigated the geometries of etched fission tracks in apatite based on a classic dissolution model. The results clarify long-standing misconceptions about estimates of apatite and track etch-rates inferred from the lengths and the cross-sections of etched tracks. It calculates surface track profiles and interprets the contours of confined tracks. The insight gained suggests some steps toward unifying etching protocols that might lead to greater agreement between track-based thermal histories.

Hydrothermal monazite trumps rutile: Applying U-Pb geochronology to evaluate complex mineralization ages of the Katbasu Au-Cu deposit, Western Tianshan, Northwest China
https://doi.org/10.2138/am-2022-8080
The Tianshan orogenic belt hosts several world-class gold deposits and is one of the largest gold provinces on Earth. Zheng et al. report detailed mineralogical studies, combined with zircon U-Pb, in situ hydrothermal monazite as well as rutile U-Pb ages, to constrain the timing of Cu mineralization and its possible link to the Au mineralization. Mineralogical studies show that chalcopyrite is the main Cu-bearing mineral in the Cu-Au ores, and it is closely associated with some native gold, monazite, and rutile. SIMS U-Pb dating of zircon from the ore-hosting granite and mafic enclave yielded concordant ages of 354.1 and 355.8 Ma, respectively. The diorite that intruded granite has a zircon U-Pb age of 352.0 Ma. The trace element compositions of the monazite suggest they were formed by hydrothermal fluids rather than inherited from the ore-hosting granite. Hydrothermal monazite coexisting with chalcopyrite and native gold has a concordant age of 348.7 Ma, and the W-rich hydrothermal rutile associated with the chalcopyrite has a U-Pb age of 345 Ma, indicating an early Cu-Au mineralization event prior to the major Au mineralization. The formation time of early Cu-Au mineralization is consistent with the emplacement age of diorite and may be of magmatic-hydrothermal origin, whereas the main Au has no genetic associations with magmatic rocks in the ore district and may belong to the orogenic type.

Dear American Mineralogist Readers, Below are the Paper Highlights for this month’s issue of the American Mineralogist: International Journal of Earth and Planetary Materials. You may also view the American Mineralogist Paper Highlights list at here (http://www.minsocam.org/MSA/Ammin/AM_NotableArticles.html). The DOI links below will take you to the abstract on GeoScienceWorld. If you have “IP” access via your institution’s library, it should reveal the whole paper. Consult your institution’s IT department or friendly librarian. If you have MSA membership, then authenticate in from the American Mineralogist menu (here<http://www.msapubs.org/> directly). Once at the portal page, click the right-side American Mineralogist link, enter your user name (e-mail address), and your password (membership number). Then search via your browser’s search tools for the paper you want to read. (On Rachel’s computer, it is control-f but we think that is little different for everyone.) Note that on GSW you can sign up for a table of contents to be sent you when the issue is live -- this is a feature open to anyone who registers on the site. Thank you for reading American Mineralogist. Sincerely, Hongwu Xu Don Baker Periodic and non-periodic stacking in molybdenite (MoS2) revealed by STEM https://doi.org/10.2138/am-2022-8019 Yang et al. used HAADF-STEM imaging to identify the stacking faults and domains of long-period molybdenite polytypes. Several layers of disordered domains intergrown with ordered 2H1 domain were recognized based on the contrast in HAADF image with one-dimensional lattice fringes. In addition, 30-layer long-period polytype and 2H3 polytype with three repetition domains were discovered for the first time. These results demonstrate that the presence of trace elements is strongly correlated with the existence of disordered domains in molybdenite crystals. It is suggested that non-equilibrium conditions related to compositional fluctuation of fluid during crystallization resulted in the oscillation of 2H1 and 3R polytypes and intergrowth of various disordered domains. The HAADF-STEM imaging method may be applied for studying other disordered layered crystals and twin minerals. The effect of halogens (F, Cl) on the near-liquidus crystallinity of a hydrous trachyte melt https://doi.org/10.2138/am-2022-8120 Feisel et al. employed the diffusion couple technique to investigate the effect of F and Cl on the crystallinity of a hydrous trachyte. In essence, their experiments demonstrate a significant drop of the liquidus temperature — as manifested by a Cpx-dissolution front — in response to rising Cl and F concentration. The liquidus depression was quantified and shown to linearly correlate with the concentration of F and Cl in the melt. They propose that F and Cl are causing the observed dissolution as they complex with the main components of Cpx. With this study, the authors illustrate the strong influence that halogens can exert on the phase equilibria of a melt and that even small fluctuations of their concentrations, e.g., caused by volcanic degassing, can control the stability of Fe-Mg-Ca mineral phases. Occurrence of tuite and ahrensite in Zagami and their significance for shock-histories recorded in martian meteorites https://doi.org/10.2138/am-2022-8020 The Zagami martian meteorite, one of the most famous martian falls, was highly shocked, as supported by the identification of many high-pressure polymorphs, e.g., stishovite, seifertite, liebermannite, and zagamiite. These phases are crucial for constraining how they were formed by asteroid impact on Mars. Gu et al. report on the discovery of two high-pressure minerals, tuite and ahrensite, identified in shock-induced melt pockets in Zagami meteorite, which could shed light on the phase decomposition under high P-T conditions. Tuite identified in this study has two formation pathways: decomposition of apatite and transformation of merrillite under high P-T conditions. Nanocrystalline ahrensite in the pyroxene clast from Zagami is likely the product of decomposition of pigeonite under high P-T conditions through a solid-state transformation mechanism. This dissociation of pigeonite to ahrensite/ringwoodite plus other phases may be widespread in other heavily shocked meteorites but potentially been overlooked in previous studies. Zolenskyite, FeCr2S4, a new sulfide mineral from the Indarch meteorite https://doi.org/10.2138/am-2022-8094 Ma and Rubin report a new sulfide mineral, zolenskyite (FeCr2S4), discovered in the Indarch meteorite, an EH4 enstatite chondrite, and discuss its origin and significance. Zolenskyite is a monoclinic polymorph of daubréelite that may have crystallized within chondrules at high temperatures from the early solar system. A refined estimation of Li in mica by a machine learning method https://doi.org/10.2138/am-2022-8029 Wang et al. use a compilation of >2000 mica compositions from various rock types, including Li2O and the following 10 major components: SiO2, Al2O3, TiO2, FeOT, MgO, MnO, CaO, Na2O, K2O, and F. These data are regressed using a multivariate polynomial regression (MPR) based machine learning (ML) method to refine the equation for estimating Li in micas over a wide range of chemical compositions. They then discuss the uncertainties and limitations of the refined equation and compare the performance of the MPR model with previously published empirical equations. Finally, they apply the refined equation to estimate the Li2O contents of micas from various types of rocks in central Inner Mongolia, NE China. Their results indicate that the MPR model is more precise and accurate and can be generalized to almost all types of micas. Above all, they provide a robust and convenient approach to conduct microanalysis of Li in mica, applying a combination of EMPA and machine learning methods, which can be widely used in mineralogy, petrology, and economic geology. Olivine in picrites from Continental Flood Basalt provinces classified using machine learning https://doi.org/10.2138/am-2022-8083 Cheng et al. provide a novel method using machine learning based on a large database of olivine composition in picrites from global Continental Flood Basalts to classify olivine with two distinct sources. This method is capable of classifying the overlapping data into correct groups, which cannot be done by traditional methods in several minutes with high accuracy. Non-Arrhenian viscosity-temperature relationships for carbonate melts https://doi.org/10.2138/am-2021-7752 Dingwell et al. report the first quantitative determination of a glass transition for a carbonate liquid. Specifically, they demonstrate the nature of the glass transition and viscosity of a mixed K2CO3-MgCO3 carbonate melt by performing scanning calorimetry and viscometry on samples of a supercooled carbonate phase. Using this low-temperature viscosity data combined with published higher temperature (high pressure) data as well as both classical and ab initio molecular dynamics simulation estimates, they determine a non-linear Vogel- Fulcher-Tammann (VFT) law fit and quantify the extent of fragility. The non-linear rate change in viscosity is an important parameter in understanding the nature of carbonatite lava flows on Earth and possibly Venus. The most widespread occurrence of carbonate melts is most likely in the deep mantles of terrestrial planets. At very small degrees of melting, alkali-rich carbonate melt may exist at lower temperatures (>1200 °C). These low temperatures are realistic for the shallow lithosphere beneath the old continental crust and are in the temperature range where a linear fit based on the high-temperature data will become inaccurate. This would have implications for modeling the transport properties of these melts to their surface expression or as metasomatizing agents. Etching of fission tracks in monazite: Further evidence from optical and focused ion beam scanning electron microscopy https://doi.org/10.2138/am-2022-8002 Jones et al. conducted a series of experiments on monazites from Victoria, Australia, to further understand their fission-track (FT) etching properties. Monazite is a mineral currently being developed in the FT system, and a crucial first step in its development is understanding its etching properties. This enables fission tracks to be observable under the optical microscope so that they can be analyzed and used to constrain the thermal history of rocks in the Earth’s uppermost crust (1–2 km). The low-temperature shift of antigorite dehydration in the presence of sodium chloride: in situ diffraction study up to 3 GPa and 700 °C https://doi.org/10.2138/am-2022-7962 The dehydration of serpentine mineral antigorite is regarded as the key step in metamorphic transformation of serpentinized rocks in subduction zones, which affects seismicity and feeds volcanic activity. Likhacheva et al. found that, in the presence of salt-bearing fluid, the reaction shifts to lower temperature by more than 150 °C in the pressure range of 2-4 GPa, which implies a broadened P-T region of serpentinite dehydration in subducting slab. Chemistry-dependent Raman spectral features of glauconite and nontronite: Implications for mineral identification and provenance analysis https://doi.org/10.2138/am-2022-8044 Baumgartner et al. provide a comprehensive Raman spectral characterization of nontronite and glauconite-nontronite mixed-layer phases from seafloor hydrothermal fields. It is shown that these phyllosilicates exhibit a series of Raman peaks that are strongly dependent on the exchange between trivalent and divalent cations in the trioctahedral sheets. The importance of these findings for a variety of applications is discussed. Experimental determination of solubility constants of saponite at elevated temperatures in high ionic strength solutions https://doi.org/10.2138/am-2021-7827 Xiong performed solubility experiments of Mg-saponite at 80 ºC to quantify the thermodynamic stability of this tri-octahedral smectite in the presence of nitrate cancrinite. In combination with the equilibrium constant at 80 ºC for the dissolution reaction of nitrate cancrinite from the literature, the author determined the solubility constant of saponite at 80 ºC to be –69.24 ± 2.08. Furthermore, the author extrapolated the equilibrium constant at 80 ºC to other temperatures (50-100 ºC) using the one-term isocoulombic method. The obtained equilibrium constants are expected to find applications in several fields, especially geological disposal of nuclear waste. Hydrothermal troctolite alteration at 300 and 400 ºC: Insights from flexible Au-reaction cell batch experimental investigations https://doi.org/10.2138/am-2021-7832 Hansen et al. present a comprehensive experimental study on the serpentinization of olivine-rich troctolites. Dickson-type reactors were used to simulate hydrothermal troctolite alteration by reacting fresh forsteritic olivine and anorthite-rich plagioclase with seawater-like fluids at two distinct temperature levels (300, 400 °C) and an elevated pressure level (40 MPa). Time series analyses of reaction concomitant fluid samples and detailed mineralogical and geochemical characterization of the final solid-phase assemblage were combined with comparative thermodynamic modeling to enable a comprehensive characterization of the alteration process. Presented results confirm earlier hypothesis that silica activity levels set by temperature-dependent coupled olivine serpentinization and plagioclase desilication reactions constitute a key control. They further demonstrate the crucial effect of variable reaction rates in different portions of a solid reactant that are closer to or further away from the solid-fluid interface. Timescales and rates of intrusive and metamorphic processes determined from zircon and garnet in migmatitic granulite, Fiordland, New Zealand https://doi.org/10.2138/am-2022-7967 Stowell et al. investigated the timing of pluton emplacement and metamorphism in the lower crust of the Fiordland magmatic arc using zircon and garnet geochronology. The isotope data provide precise dates which clearly indicate that high-temperature granulite facies metamorphism occurred less than 3 million years after intrusion of voluminous mantle-derived magmas. No heat source has been documented for the metamorphism; however, they speculate that underplating of magma caused heating. Subsequent cooling for this granulite orthogneiss at 15-25 °C/million years was considerably slower than previously estimated. The new isotope data provide precise ages and rates of cooling for a single outcrop and underline the importance of multiple chronometers and careful textural characterization for assigning meaningful ages to lower-crustal rocks. In situ chemical and isotopic analyses and element mapping of multiple-generation pyrite: evidence of episodic gold mobilization and deposition for the Qiucun epithermal gold deposit in Southeast China https://doi.org/10.2138/am-2022-8030 Ma et al. investigated the origin of high-grade ore shoots and visible gold in gold deposits by analyzing the multiple generations of pyrite in a representative epithermal gold system in SE China using a number of in situ analytical techniques (including LA-ICP-MS trace element analysis and mapping and LA-MC-ICP-MS sulfur isotope analysis). The results demonstrated that multiple remobilization and reprecipitation of gold were taken place in this epithermal gold deposit. The pressure-driven hydrothermal processes play an important role not only in initial invisible (refractory) gold enrichment but also in the re-enrichment of visible gold and some other trace metals during episodic deposition, replacement, and hydrothermal alteration of auriferous pyrite in gold deposits. This study demonstrates that detailed textural examination and in situ chemical and sulfur isotope analysis under robust geological and petrographic frameworks can effectively constrain the complex gold mobilization and deposition processes in hydrothermal ore deposits. Hydrothermal mineralization of celadonite: Hybridized fluid-basalt interaction in Janggi, Korea https://doi.org/10.2138/am-2022-8045 Park et al. discovered an exceptional celadonite mineralization in the Miocene lacustrine Janggi basin in the southeastern Korean Peninsula. This celadonite occurs as greenish earthy/vitreous materials filling the E-W trending fault zones in basaltic flows. Detailed fieldwork and whole-rock major, trace, and oxygen isotope analyses indicate that celadonites were formed in an open system of ~120 °C via the interaction of the hybridized fluid and basalts along with the physicochemical fault brecciation of the host rock. The cations required for the celadonite formation were supplied by the smectitization/zeolitization of rhyolitic mesostasis (for Al and part of K) and pyroxene microlites (for Fe and Mg) in the basaltic breccias during the associated oxidation of micro-nanoparticles by circulating fluids (for most of K). This mechanism is plausible, where both the magmatic fluid influx and the particle size reduction could be involved. This model suggests that any crustal rocks rich in ferromagnesian components could produce celadonite through the hydrothermal potassic alteration. Gungerite, TlAs5Sb4S13, a new thallium sulfosalt with a complex structure containing covalent As-As bonds https://doi.org/10.2138/am-2022-8003 Kasatkin et al. describe a new thallium sulfosalt mineral, gungerite, discovered in Russia. It possesses an interesting structural architecture, quite unique among the known sulfosalt structures: the structure consists of doughnut-shaped (As,Sb)–S clusters, which have van der Waals contacts to most of the surroundings and are connected to them only by sparse cation–sulfur bonds. Nitscheite, a new mineral with an unusual uranyl-sulfate sheet https://doi.org/10.2138/am-2022-7994 Inactive uranium mines have proven to be fruitful underground “natural laboratories”, providing insight into the factors driving the crystallization of uranium minerals. The great diversity observed for uranyl sulfate minerals stems primarily from the large number of stable linkages of uranyl pentagonal bipyramids and sulfate tetrahedra. The new uranyl sulfate nitscheite, described herein by Kampf et al., possesses a type of uranyl sulfate sheet not previously observed in nature. Protocaseyite, a new decavanadate mineral containing a [Al4(OH)6(H2O)12]6+ linear tetramer, a novel isopolycation https://doi.org/10.2138/am-2022-8059 Kampf et al. describe the new mineral protocaseyite found in a low-temperature, post-mining, secondary mineral assemblage in the Burro mine in the Uravan Mineral Belt of western Colorado, U.S.A. The crystal structure of this mineral contains a decavanadate polyoxometalate anion together with a novel 4-member aluminate polyoxometalate cation referred to as an Al-flatimer. Polyoxometalate ions have been the subject of numerous synthesis studies in recent years, largely because of their potential technological uses. Polyoxometalate ions have also been proposed to exist in solution as precursors of more extended structural components (chains, sheets, and frameworks) in mineral structures, but only rarely are polyoxometalate ions found as isolated units in minerals. Fission-track etching in apatite: A model and some practical implications https://doi.org/10.2138/am-2022-8055 Jonckheere et al. investigated the geometries of etched fission tracks in apatite based on a classic dissolution model. The results clarify long-standing misconceptions about estimates of apatite and track etch-rates inferred from the lengths and the cross-sections of etched tracks. It calculates surface track profiles and interprets the contours of confined tracks. The insight gained suggests some steps toward unifying etching protocols that might lead to greater agreement between track-based thermal histories. Hydrothermal monazite trumps rutile: Applying U-Pb geochronology to evaluate complex mineralization ages of the Katbasu Au-Cu deposit, Western Tianshan, Northwest China https://doi.org/10.2138/am-2022-8080 The Tianshan orogenic belt hosts several world-class gold deposits and is one of the largest gold provinces on Earth. Zheng et al. report detailed mineralogical studies, combined with zircon U-Pb, in situ hydrothermal monazite as well as rutile U-Pb ages, to constrain the timing of Cu mineralization and its possible link to the Au mineralization. Mineralogical studies show that chalcopyrite is the main Cu-bearing mineral in the Cu-Au ores, and it is closely associated with some native gold, monazite, and rutile. SIMS U-Pb dating of zircon from the ore-hosting granite and mafic enclave yielded concordant ages of 354.1 and 355.8 Ma, respectively. The diorite that intruded granite has a zircon U-Pb age of 352.0 Ma. The trace element compositions of the monazite suggest they were formed by hydrothermal fluids rather than inherited from the ore-hosting granite. Hydrothermal monazite coexisting with chalcopyrite and native gold has a concordant age of 348.7 Ma, and the W-rich hydrothermal rutile associated with the chalcopyrite has a U-Pb age of 345 Ma, indicating an early Cu-Au mineralization event prior to the major Au mineralization. The formation time of early Cu-Au mineralization is consistent with the emplacement age of diorite and may be of magmatic-hydrothermal origin, whereas the main Au has no genetic associations with magmatic rocks in the ore district and may belong to the orogenic type.