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Penelitian ini bertujuan untuk mengetahui evolusi hidrotermal dari fluida pembawa mineralisasi yang terdapat di Pit Ramba Joring, meliputi temperatur, tekanan, densitas dan kedalaman pembentukan mineralisasi. Penelitian ini menggunakan analisis inklusi fluida. Sampel yang dianalisis merupakan sampel yang terindikasi terbentuk bersamaan dengan mineralisasi bijih (syngenetik), pada dua tekstur utama bijih yaitu batuan dengan tekstur silica vuggy yang terbentuk pada kisaran Th 331ºC hingga 394ºC, Tm -15,19ºC hingga -12,94ºC dengan salinitas 14,42 wt% hingga 14,89 wt%. NaCl equivalent dan batuan dengan tekstur brecciated terbentuk pada kisaran Th 287,8°C hingga 398,2°C, Tm -14,89°C hingga -11,76ºC serta salinitas 13,91 wt% hingga 4,87 wt%. NaCl equivalent. Korelasi positif antara temperatur homogenisasi pembentukan mineralisasi dengan salinitas larutan menandakan bahwa proses leaching yang membentuk rongga pada batuan terjadi pada stage awal proses alterasi hidrotermal yang diawali dengan proses leaching membentuk rongga (vuggy silica) yang diikuti proses silisifikasi dengan tekstur brecciated, pada fase ini berlangsung pengendapan mineralisasi. Asal larutan yang menjadi larutan pembentuk endapan hidrotermal merupakan jenis larutan basinal water-seawater dalam bentuk connate water yang masih dipengaruhi oleh air permukaan/meteoric water yang menunjukkan adanya indikasi hubungan dengan magmatic water. Densitas fluida pembentuk bijih logam berkisar pada 0,8 gr/cm3 sampai dengan 0,9 gr/cm3 sedangkan proses pembentukan bijih pada Pit Ramba Joring termasuk dalam isothermal mixing dengan sedikit pengaruh pemanasan/boiling.

Numerous low-temperature geothermal waters are distributed extensively in Mangbang-Longling of western Yunnan in China, whose formation mechanism has not been completely investigated yet. This study focused on the hydrogeochemical evolution, reservoir temperature, and recharge origin of geothermal waters using hydrogeochemical and deuterium-oxygen (D-O) isotopic studies. The low-temperature geothermal waters were characterized by HCO3-Na type, while shallow cold spring was of the hydrochemical type of HCO3-Ca. The hydrogeochemical characteristics of low-temperature geothermal waters were mainly determined by the dissolution of silicate minerals based on the geological condition and correlations of major and minor ions. The reservoir temperatures of low-temperature geothermal waters ranged from 111°C to 126°C estimated by silica geothermometry and the silicon-enthalpy graphic method. Low-temperature geothermal waters circulated at the largest depth of 1794–2077 m where deep high-temperature geothermal waters were involved. The data points of δD and δ18O of the hot spring water samples in the study area show a linear right-up trend, indicating the δ18O reaction between the water and rock and a possible mixture of magmatic water from below. The low-temperature thermal waters were recharged by meteoric water at the elevation of 2362–3653 m calculated by δD values. Upwelling by heating energy, low-temperature geothermal waters were exposed as geothermal springs in the fault and fracture intersection and mixed by up to 72% shallow cold waters at surface. Based on acquired data, a conceptual model of the low-temperature geothermal waters in the Mangbang-Longling area was proposed for future exploitation.

While the external infiltration of water has been identified from modern geothermal and/or fossil hydrothermal systems through stable isotopes, the physicochemical boundary conditions like the initial oxygen isotopes of water $( {{\rm \delta }^{ 18}{\rm O}_{\rm W}^{\rm i} } ) $ and rock as well as alteration temperature were implicitly presumed or empirically estimated by the conventional forward modelling. In terms of a novel procedure proposed to deal with partial re-equilibration of oxygen isotopes between constituent minerals and water, the externally infiltrated meteoric and magmatic water are theoretically inverted from the early Cretaceous post-collisional granitoid and intruded Triassic gneissic country rock across the Dabie orogen in central-eastern China. The meteoric water with a $ {{\rm \delta }^{ 18}{\rm O}_{\rm W}^{\rm i} } $ value of −11.01 ‰ was externally infiltrated with a granitoid and thermodynamically re-equilibrated with rock-forming minerals at 140°C with a minimum water/rock (W/R)o ratio around 1.10 for an open system. The lifetime of this meteoric hydrothermal system is kinetically constrained less than 0.7 million years (Myr) via modelling of surface reaction oxygen exchange. A gneissic country rock, however, was externally infiltrated by a magmatic water with $ {{\rm \delta }^{ 18}{\rm O}_{\rm W}^{\rm i} } $ value of 4.21 ‰ at 340°C with a (W/R)o ratio of 1.23, and this magmatic hydrothermal system could last no more than 12 thousand years (Kyr) to rapidly re-equilibrate with rock-forming minerals. Nevertheless, the external infiltration of water can be theoretically inverted with oxygen isotopes of re-equilibrated rock-forming minerals, and the ancient hydrothermal systems driven by magmatism or metamorphism within continental orogens worldwide can be reliably quantified.

The cataclysmic basaltic eruption of Mt. Tarawera in 1886 represents a significant cultural and scientific event for New Zealand. This review utilises published and new observations, to reinterpret eruptive parameters encompassing the entirety of the eruption. The ∼17 km eruptive fissure, active for 4+ hours, extends across Mt. Tarawera to the hydrothermally active Waimangu region. Correlating published observations of bed thickness, componentry and microtextures from Mt. Tarawera to new bed descriptions and granulometry for the Rotomahana-Waimangu rift segment allows for a re-assessment of eruption variations along the length of the fissure. Variably thick pyroclastic fall sequences at Mt. Tarawera contrast with the pyroclastic surges and an eruption plume that together deposited the 'Rotomahana Mud' erupted along the Rotomahana-Waimangu segment. Providing insight into pre-eruptive conditions, new mineral chemistry from Mt. Tarawera provides the first constraints on crystallisation pressures (

Water diffusion is an important mechanism affecting magmatic water content, vapor bubble growth, and the dynamics of volcanic eruptions. Water diffusivity in silicate melts is dependent on temperature, pressure, H2O content and speciation, and melt composition. While a general model has recently been developed for water diffusivity in calc-alkaline (subalkaline) melts as a function of silica content, the effect of alkalis on water diffusion is less clear due to the lack of experimental data for alkali-rich melts and a systematic evaluation. Here, water diffusion in shoshonitic melt with up to 1.6 wt% H2O was investigated at 1654–1926 K and 1 GPa in a piston cylinder apparatus using both hydration and diffusion couple methods. Diffusion profiles measured by FTIR microspectroscopy are in accordance with a modified speciation-based diffusion model which takes into account different mobility of hydroxyl (OH) and molecular H2O (H2Om). The diffusivity ratio DOH/DH2Om in shoshonitic melt increases with increasing temperature and falls into the range of 0.24–0.55, greater than the values for all of the melts previously investigated. The remarkable contribution of OH to water diffusion in shoshonitic melt is attributed to a substantial presence of free OH species (OH bonding with network-modifying cations but here especially with K or Na). The total H2O diffusivity in shoshonitic melt can be expressed as: D H 2 O t = e - 12 . 11 - 16 765 T 1 + C e - 11 . 1 4 + 17 381 - 262.6 C T , where D is in m2/s, T is temperature in K, and C is H2Ot content in wt% (DH2Ot reduced to DOH at C = 0). The above equation replicates the experimental data within 0.1 natural log unit. The total H2O diffusivities at 1 wt% H2Ot in three alkali-rich melts, including shoshonite, trachyte and phonolite, appear to fall onto a single Arrhenian trend line over a broad temperature range of 1100–1900 K. Compared to the general water diffusivity model for calc-alkaline melts, water diffusivities in alkali-rich silicate melts are generally higher and roughly twofold at the same P-T-H2Ot-XSi conditions, with XSi being the mole fraction of Si among all cations. Excess alkalis decrease degree of melt polymerization and promote formation of mobile K-OH and Na-OH species, thereby having a positive influence on water diffusion and vapor bubble growth in magma.

The eastern Junggar Basin, controlled by continental extension (rift), was deposited by lacustrine dominated sediments during middle Permian Lucaogou period. An unusual porphyritic-like texture was observed in Lucaogou/Pingdiquan dark fine-grained organic-rich sediments in two sub-tectonic units in the basin. The “phenocrysts” are composed of two types of mineral assemblages. The first is a coarse euhedral calcite assemblage in the Jimusar Sag, and the second consists of dolomite, analcime, and pyrite in the Shishugou Sag. The lithological and mineralogical features indicate a hydrothermal origin for these phenocryst-like minerals. The chondrite-normalized rare earth element patterns show flat or positive Ce anomalies and negative Eu anomalies, which reflect a suboxic to anoxic, off-axis site from the center of the fault system, where the temperature of the hydrothermal fluid might be less than 250 °C. The high ratios of BaN/LaNat 1.6–65.5, strongly positive Sr anomalies at Sr/Sr* = 5.54–39.9, and relatively low87Sr/86Sr isotopes at 0.705002–0.705776 in the coarse calcite suggest an origin of mixed sources of lake water, underlying biogenetic sediments, and deep magmatic water. However, the low87Sr/86Sr ratios of 0.705321–0.705968 in the dolomite and δ34SV-CDTof 10.8‰–12.3‰ in the pyrite indicate that water–underlying-rock interaction and the abiotic thermochemical sulfate reduction of lake water or organic matter might have participated together resulting in the precipitation of the dolomite–analcime–pyrite assemblages in the Shishugou Sag.

Degassing dynamics play a crucial role in controlling the explosivity of magma at erupting volcanoes. Degassing of magmatic water typically involves bubble nucleation and growth, which drive magma ascent. Crystals suspended in magma may influence both nucleation and growth of bubbles. Micron- to centimeter-sized crystals can cause heterogeneous bubble nucleation and facilitate bubble coalescence. Nanometer-scale crystalline phases, so-called “nanolites”, are an underreported phenomenon in erupting magma and could exert a primary control on the eruptive style of silicic volcanoes. Yet the influence of nanolites on degassing processes remains wholly uninvestigated. In order to test the influence of nanolites on bubble nucleation and growth dynamics, we use an experimental approach to document how nanolites can increase the bubble number density and affect growth kinetics in a degassing nanolite-bearing silicic magma. We then examine a compilation of these values from natural volcanic rocks from explosive eruptions leading to the inference that some very high naturally occurring bubble number densities could be associated with the presence of magmatic nanolites. Finally, using a numerical magma ascent model, we show that for reasonable starting conditions for silicic eruptions, an increase in the resulting bubble number density associated with nanolites could push an eruption that would otherwise be effusive into the conditions required for explosive behavior.

The limited literature data on gold-bearing albite–pyroxene rodingites are summarized for the Agardag ultramafic massif in southern Tuva. These data are supplemented by new mineralogical, geochemical, thermobarogeochemical, and isotopic–geochemical results in order to reveal the physicochemical mineral formation conditions and sources of ore matter and fluids on gold deposition in rodingites. Rodingites and associated schistose nephritoids are near-fault metasomatites and are confined to a latitudinal tectonic zone in antigorite serpentinites. They formed in two stages. Stage I minerals (pyroxene, albite, etc.) are rodingites and stage II minerals (Na-bearing actinolite, albite, etc.) are nephritoids and veinlets that intersect rodingites. Disseminated sulfides of the Cu–S series (chalcocite, digenite, etc.) and Au minerals (tetra-auricupride and electrum) were deposited during both stages. The temperature regime (500–250°C) and low amount of CO2 in fluid ( $${{{\text{X}}}_{{{\text{C}}{{{\text{O}}}_{{\text{2}}}}}}}$$ = 0.017–0.025) correspond to the formation conditions of typical bimetasomatic rodingites. The degree of oxidation of gas components in fluids CO2/(CO2 + Σreduced gases) increases from rodingites (0.189) to nephritoids (0.299) and antigorite serpentinites (0.738). The O isotopic composition of silicates and calculated O isotopic composition of the fluid during antigorite serpentinization (5.8 to 7.6‰ δ18Оfl and –66 to –69‰ δDfl) correspond to juvenile and magmatic water in contrast to metamorphic water during nephritization and rodingitization (6 to 9.9‰ δ18Оfl and –39 to –46‰ δDfl) with involvement of heavy oxygen that was subjected to the sedimentary cycle. It is suggested that the magmatic ore-bearing fluid (7.3–7.6 wt % NaCl-equiv) separated from gabbroic melts. The oxidized fluid was modified to a reduced fluid during interaction with ultramafic rocks. The mafic and ultramafic rocks were the source of Na, REE, Au, Ag, Cu, and Ni. Deformations with the formation of veins and filling of veinlets are favorable for a high local gold concentration.

The metallogenic environment of the Irtysh gold belt in Xinjiang is studied in detail. The metallogenic geological background, metallogenic conditions and ore-controlling factors of the gold deposits in eastern, central and western regions of the metallogenic belt are compared. The metallogenic structure of the Irtysh tectonic belt has the characteristics of diverging to the west and converging to the east. Composite ore controlling by ductile shearing and magmatic activity in Irtysh gold belt result in zoned and segmented distribution of gold mineralization. Through the fluid inclusion research and H-O-S isotope analysis, the evolution regularity of gold ore-forming fluids in the region was analyzed. Synchrotron radiation X-ray fluorescence was used to analysis the concentration of metal elements in a single fluid inclusion, explaining the occurrence and migration process of Au in hydrothermal fluid. The source of ore forming minerals in western gold deposit is more closely related to magmatic activity, and the structural metamorphism of eastern gold deposit has greater influence on mineralization. Metallogenic fluids of gold deposits are characterized by metamorphic water (and magmatic water) in the early stage and mixed with meteoric water in the late stage. And the metallogenic elements are enriched in CO2 rich fluid. The Au is mainly activated, migrated and enriched with the mixed fluid of magmatic hydrothermal, metamorphic hydrothermal and atmospheric precipitation in the medium-low temperature, shallow to medium-deep environment.

We studied the fluid inclusions of the Jiguanshan Mo deposit in China, which is a large porphyry deposit located in the southern Xilamulun Metallogenic Belt. The irregular Mo ore body with various types of hydrothermal veinlets is hosted by Late Jurassic granite porphyry. Intense hydrothermal alterations in the deposit from the core to margin are silicification–potassium feldspar alteration, pyrite–quartz–sericite–fluorite alteration, and propylitic alteration. Based on the mineral assemblages and crosscutting relationships of ore veins, the ore-forming process were divided into three stages and two substages: quartz–pyrite veins (stage I) associated with potassic alteration; quartz–molybdenite–chalcopyrite–pyrite veins (substage II-1) and quartz–molybdenite–fluorite veins (substage II-2) associated with phyllic alteration; and fluorite–quartz–carbonate veins (stage III) with carbonation. Five major fluid inclusions (FIs) types were distinguished in the quartz associated with oxide and sulfide minerals, i.e. polyphase brine (Pb-type), opaque-bearing brine (Ob-type), solid halite (S-type), two-phase aqueous (A-type), and vapor (V-type) inclusions. The FIs of stage I were composed of liquid-rich S-, A-, and V-type FIs with homogenization temperatures and salinities of 490 to 511 °C and 8.9 to 56.0 wt% NaCl equiv., respectively. The FIs of substage II-1 are composed of Pb-, Ob-, S-, A-, and V-type FIs with homogenization temperatures and salinities of 352 to 460 °C and 3.7 to 46.1 wt% NaCl equiv, respectively. The FIs of substage II-2 are Ob-, S-, A-, and V-type FIs with homogenization temperatures and salinities of 234 to 309 °C and 3.7 to 39.2 wt% NaCl equiv, respectively. The FIs of stage III are A-type FIs with homogenization temperatures and salinities of 136 to 172 °C and 1.1 to 8.9 wt% NaCl equiv, respectively. Fluid boiling, which resulted in the precipitation of sulfides, occurred in stages I and II. The initial ore-forming fluids of the Jiguanshan deposit had high temperature, high salinity, and belonged to an F-rich NaCl ± KCl–H2O system. The fluids gradually evolved to low temperature, low salinity, and belonged to a NaCl–H2O system. Studies of the hydrogen and oxygen isotope compositions of quartz (δ18OH2O = − 7.3 to 6.3‰, δDH2O = − 104.3 to − 83.3‰) show that the ore-forming fluids gradually evolved from magmatic water to meteoric water.

Silicic magmas span a wide range of eruptive styles between explosive and effusive, and transitions between these styles are commonplace. Yet the triggers of switches in eruptive style remain poorly understood. Eruptions are mostly driven by degassing of magmatic water and their eruption style - effusive or explosive - is likely governed by the efficiency of outgassing as well as magma ascent rate. Microlites and phenocrysts are often purported to promote heterogeneous bubble nucleation and outgassing, both key variables in the degassing dynamics that become crucial in controlling the eruptive style. Here, in order to shed light on the role of nature, size and abundance of crystals on degassing of silicic magma, we experimentally investigate (heating-induced) vesiculation in a multiphase (microlite- and phenocryst-bearing), low-water content, and bubble-free, natural rhyolite. The experiments were conducted at magmatic temperature (∼900-1100 °C) and atmospheric pressure in an optical dilatometer. Our results indicate that microlites exert a large influence on bubble nucleation while the effect of phenocrysts is subordinate. Amongst the microlite phases, bubbles nucleate more easily on Fe-Ti oxides than other mineral phases. Bubble coalescence and connectivity are, in contrast, enhanced by the phenocrysts, more than microlites, in low-crystallinity magma. Comparing the bubble textures of the post-experimental samples with those produced in a phenocryst-free and microlite-poor silicic magma, we observe that the phenocryst- and microlite-bearing magma exhibits significantly more bubble coalescence and connectivity, as well as higher bubble number densities. These findings help to constrain the roles that pre- and syn-eruptive crystalline phases may play in degassing processes during ascent of silicic magma.

The Zhuxi deposit is a recently discovered W–Cu deposit located in the Jiangnan porphyry–skarn W belt in South China. The deposit has a resource of 3.44 million tonnes of WO3, making it the largest on Earth, however its origin and the evolution of its magmatic–hydrothermal system remain unclear, largely because alteration–mineralization types in this giant deposit have been less well-studied, apart from a study of the calcic skarn orebodies. The different types of mineralization can be classified into magnesian skarn, calcic skarn, and scheelite–quartz–muscovite (SQM) vein types. Field investigations and mineralogical analyses show that the magnesian skarn hosted by dolomitic limestone is characterized by garnet of the grossular–pyralspite (pyrope, almandine, and spessartine) series, diopside, serpentine, and Mg-rich chlorite. The calcic skarn hosted by limestone is characterized by garnet of the grossular–andradite series, hedenbergite, wollastonite, epidote, and Fe-rich chlorite. The SQM veins host high-grade W–Cu mineralization and have overprinted the magnesian and calcic skarn orebodies. Scheelite is intergrown with hydrous silicates in the retrograde skarn, or occurs with quartz, chalcopyrite, sulfide minerals, fluorite, and muscovite in the SQM veins. Fluid inclusion investigations of the gangue and ore minerals revealed the evolution of the ore-forming fluids, which involved: (1) melt and coexisting high–moderate-salinity, high-temperature, high-pressure (>450 °C and >1.68 kbar), methane-bearing aqueous fluids that were trapped in prograde skarn minerals; (2) moderate–low-salinity, moderate-temperature, moderate-pressure (~210–300 °C and ~0.64 kbar), methane-rich aqueous fluids that formed the retrograde skarn-type W orebodies; (3) low-salinity, moderate–low-temperature, moderate-pressure (~150–240 °C and ~0.56 kbar), methane-rich aqueous fluids that formed the quartz–sulfide Cu(–W) orebodies in skarn; (4) moderate–low-salinity, moderate-temperature, low-pressure (~150–250 °C and ~0.34 kbar) alkanes-dominated aqueous fluids in the SQM vein stage, which led to the formation of high-grade W–Cu orebodies. The S–Pb isotopic compositions of the sulfides suggest that the ore-forming materials were mainly derived from magma generated by crustal anatexis, with minor addition of a mantle component. The H–O isotopic compositions of quartz and scheelite indicate that the ore-forming fluids originated mainly from magmatic water with later addition of meteoric water. The C–O isotopic compositions of calcite indicate that the ore-forming fluid was originally derived from granitic magma, and then mixed with reduced fluid exsolved from local carbonate strata. Depressurization and resultant fluid boiling were key to precipitation of W in the retrograde skarn stage. Mixing of residual fluid with meteoric water led to a decrease in fluid salinity and Cu(–W) mineralization in the quartz–sulfide stage in skarn. The high-grade W–Cu mineralization in the SQM veins formed by multiple mechanisms, including fracturing, and fluid immiscibility, boiling, and mixing.

Oxygen isotope ratios in magnetite can be used to study the origin of iron-oxide ore deposits. In previous studies, only 18O/16O ratios of magnetite were determined. Here, we report triple O isotope data (17O/16O and 18O/16O ratios) of magnetite from the iron-oxide–apatite (IOA) deposits of the Yazd and Sirjan areas in central Iran. In contrast to previous interpretations of magnetite from similar deposits, the triple O isotope data show that only a few of the magnetite samples potentially record isotopic equilibrium with magma or with pristine magmatic water (H2O). Instead, the data can be explained if magnetite had exchanged O isotopes with fluids that had a mass-independently fractionated O isotope composition (i.e., MIF-O), and with fluids that had exchanged O isotopes with marine sedimentary carbonate rocks. The MIF-O signature of the fluids was likely obtained by isotope exchange with evaporite rocks of early Cambrian age that are associated with the IOA deposits in central Iran. In order to explain the triple O isotope composition of the magnetite samples in conjunction with available iron isotope data for magnetite from the deposits, we propose that magnetite formed from magmatic fluids that had interacted with evaporite and carbonate rocks at high temperatures and at variable water/rock ratios; e.g., magmatic fluids that had been released into the country rocks of a magma reservoir. Additionally, the magnetite could have formed from magmatic fluids that had exchanged O isotopes with SO2 and CO2 that, in turn, had been derived by the magmatic assimilation and/or metamorphic breakdown of evaporite and carbonate rocks.

The giant Yulong porphyry Cu Mo deposit was formed in postsubduction setting in eastern Tibet. Origin of the ore-related Yulong intrusion remains a matter of debate. This study presents new whole-rock major and trace element geochemistry, in-situ apatite Sr Nd and zircon Hf O isotopes, and mineralogical chemistry of the Yulong intrusion. Least-altered samples from the Yulong intrusion have high SiO2 (66.3–69.5 wt%) and Al2O3 (14.9–15.5 wt%) contents, high La/Yb (36.4–68.0) and Sr/Y (46.0–76.3) ratios, and low MgO (0.63–1.24 wt%) and Cr ( Nd isotopes show limited variations ((87Sr/86Sr)i = 0.7060–0.7068, eNd(t) = −4.8–0.2), which plot between Paleo-Tethys ocean-related arc magmas and the ancient crust in eastern Tibet. Zircon grains from this study and published studies have mostly positive yet variable eHf(t) values (−20.6 to +12.2) and young Hf model ages that overlap those of the Paleo-Tethys ocean-related arc magmas. The above Sr-Nd-Hf isotopes, together with the elevated zircon δ18O values (6.4 to 9.3‰) and arc-like trace element patterns, collectively suggest that the Yulong intrusion may have originated from partial melting of juvenile lower arc crust related to the subduction of the Paleo-Tethys ocean, with incorporation of a small amount of ancient crustal materials. Two generations of amphibole were recognized at Yulong. Their compositions are used to calculate crystallization depths, magmatic oxidation states, and water contents. The caculated results show that the early-stage euhedral high-Al (5.87–8.51 wt%) amphibole phenocrysts may have crystallized in the underlying magma chamber (7.1–12.5 km in depth), whereas the late-stage xenomorphic low-Al (3.47–4.87 wt%) amphibole grains may have crystallized in the porphyritic stock (4.0–5.6 km). Magmatic water contents decrease from early- (3.5–4.6 wt%) to late-stage (2.8–3.5 wt%) amphibole, which is interpreted to indicate fluid exsolution from the magma chamber during emplacement of the Yulong intrusion. Caculated oxidation states increase from early- (ΔNNO = 0.6–1.5) to late-stage (ΔNNO = 1.9–2.3) amphibole. Plagioclase phenocrysts show periodic or reverse core-to-rim zonation of An contents (range up to 25 mol%), which are coupled by FeO contents, probably suggesting magma recharge events. Collectively, we propose that the magma chamber beneath Yulong was recharged by a less evolved magma, and was saturated in fluids to produce intensive alteration and mineralization. The relatively high oxidation states allow the metals to be enriched in the evolving magma, and to be deposited in the hydrothermal alteration stage.

The processes that controlled accretion of water and volatiles to the inner solar system remain enigmatic, because it is difficult to determine the absolute concentrations of volatile elements in planetary bodies. In this contribution we study rare unequilibrated eucrites derived from the asteroid 4 Vesta, to determine the water and fluorine content of this asteroid by measuring the volatile content of pyroxene. Common thermal metamorphism in most equilibrated eucrites would have diffusively reset magmatic volatile contents. The unequilibrated eucrites are, therefore, the most suitable samples to determine primary magmatic volatile contents of 4 Vesta. We find H2O and F contents in pyroxenes of 4–11 µg/g and 0.12–0.23 µg/g. We also determine a H2O partition coefficient for clinopyroxene and melt equilibrated at 0.1 MPa of DH2O = 0.1, which is higher than values previously reported for higher pressures. The higher compatibility of H2O in this experiment could partially be due to high OH/H2O ratio at the low total water contents in this experimental charge, but only further more detailed experiments will fully delineate the reasons for the more compatible behavior for water at lower pressures. However, given the lack of H2O partitioning data at low pressures we conclude that our 0.1 MPa experiment is the most appropriate to calculate magmatic water contents for melt in equilibrium with eucrite pyroxene. After using appropriate partition coefficients we calculate melt concentrations of 50–70 µg/g H2O and 1.5–2.4 µg/g F. In turn, these are converted into bulk 4 Vesta water and F contents of 10–70 µg/g H2O and 0.3–2 µg/g F by assuming eucrite formation via either mantle partial melting or extraction from a magma ocean. We also measure the D/H of the clinopyroxenes and show that these are identical to the results of previous studies that reported D/H in eucrite apatite. These values match those found in carbonaceous chondrites suggesting that water in 4 Vesta accreted from carbonaceous chondrites and not from cometary material.

This paper explores the evolutional process of back-arc basin (BAB) magma system at final spreading stage of extinct BAB, Shikoku Basin (Philippine Sea) and assesses its tectonic evolution using a newly discovered oceanic core complex, the Mado Megamullion. Bulk and in-situ chemical compositions together with in-situ Pb isotope composition of dolerite, oxide gabbro, gabbro, olivine gabbro, dunite, and peridotite are presented. Compositional ranges and trends of the igneous and peridotitic rocks from the Mado Megamullion are similar to those from the slow- to ultraslow-spreading mid-ocean ridges (MOR). Since the timing of the Mado Megamullion exhumation corresponds to the very end of the Shikoku Basin opening, the magma supply was subdued and highly episodic, leading to extreme magma differentiation to form ferrobasaltic, hydrous magmas. In-situ Pb isotope composition of magmatic brown amphibole in the oxide gabbro is identical to that of depleted source mantle for mid-ocean ridge basalt (MORB). In the context of hydrous BAB magma genesis, the magmatic water was derived solely from the MORB source mantle. The distance from the back-arc spreading center to the arc front increased away through maturing of the Shikoku Basin to cause MORB-like magmatism. After the exhumation of Mado Megamullion along detachment faults, dolerite dikes intruded as a post-spreading magmatism. The final magmatism along with post-spreading Kinan Seamount Chain volcanism were introduced around the extinct back-arc spreading center after the opening of Shikoku Basin by residual mantle upwelling.

The formation of the Ailaoshan metallogenic belt was the result of: the Neoproterozoic super mantle plume, the Indosinian and South China blocks in the Late Triassic after the Paleo-Tethys Ocean closure, and Oligocene-Eocene continental-scale shearing related to the India-Eurasia collision. It is one of the most important Cenozoic gold ore province in the world. In this paper, the geological characteristics, isotopic geochemistry, and geochemical data of ore-forming fluids of four large-scale gold deposits in the Ailaoshan metallogenic belt (Mojiang Jinchang, Zhenyuan Laowangzhai, Yuanyang Daping, and Jinping Chang’an) are comprehensively compared. The features of host-rock alteration, metallogenetic periods and stages, geochronology, fluid inclusion, and C-H-O-S-Pb isotopes of gold deposits are summarized and analyzed. The gold mineralization in the Ailaoshan metallogenic belt occurred mostly in 50–30 Ma, belonging to the Himalayan period. The gold mineralization is closely related to silicification, argillation, carbonation, and pyritization due to the strong mineralization of hydrothermal fluid, the development of alteration products, and the inconspicuous spatial zonation of alteration types. The ore-forming fluid is mainly composed of mantle fluid (magmatic water) and metamorphic fluid (metamorphic water). The ore-forming materials of the Jinchang, Chang’an, and Laowangzhai gold deposits mainly originate the host-rock strata of the mining area, and the carbon is more likely to from marine carbonate. The carbon in the Daping gold deposit from the original magma formed by the partial melting of the mantle. Pb isotopes have characteristics of crustal origin, accompanied by mixing of mantle-derived materials and multisource sulfur mixing, and are strongly homogenized.

The Mt Cagua hydrothermal system is centered on a young volcano which last erupted in 1860. Even prior to drilling, surface features indicated active magmatic input at depth, such as acid SO4-Cl hot springs at high elevation, enriched in both 18O and D with respect to local groundwater, and fumaroles discharging gases suggesting a highly oxidizing, immature source. The proportion of “andesitic” or arc-type magmatic water in the steam discharge is ≈65%. The drilling of a directional well, deviated towards the crater, showed that the magmatic-hydrothermal interface, where temperatures are >400°C, is confined to a small volume. Fluid inclusion and alteration minerals indicate that it is occupied largely by vapor and is connected to surface fumaroles via a vapor conduit. Magmatic volatiles released into the system rapidly partition into a brine and a gas-rich vapor. When released into water-logged microfractures, short-lived acid sulfate waters form and precipitate a corresponding alteration assemblage. The inferred magmatic fluid at Cagua, based on fluid inclusions, has a Cl content of 15 000 to 30 000 mg/kg, a CO2 content of 4 molal and high H2S. Through dilution and boiling this fluid forms the waters of the groundwater-dominated hydrothermal envelope adjacent to the magmatic-hydrothermal interface.

Carbonate rocks are important targets of hydrocarbon exploration in the Gucheng area, Tarim Basin. In this study, the thin sections, carbon and oxygen isotopes, trace elements and rare earth elements of 25 carbonate samples from the Upper Cambrian and the Ordovician are conducted to research the original sedimentary environment of these carbonate rocks. The carbonate rocks have undergone high-temperature hydrothermal activity due to the movement of magmatic water in the Permian based on carbon and oxygen isotope and Euanom data. The Upper Cambrian and Ordovician are divided into five third-order sequences based on carbon isotopes and natural gamma-ray spectral logging combined with previous researches. The SQ1~SQ3 in the Upper Cambrian and Middle-Lower Ordovician predominant in sea-level decline cycle, whereas the SQ4 and SQ5 in the Middle-Upper Ordovician are dominated by sea-level rise cycle. Ceanom and Z values are suitable to analyze the redox environment and paleosalinity quantitatively, which suggests an oxidizing and marine origin in this area. The dolomites are formed in a paleoenvironment with a higher salinity, a stronger oxidation and a lower falling sea level than that of the limestones.

The amount of water dissolved in magmas at depth beneath volcanoes is fundamental to a wide range of magmatic and eruptive processes due to water’s dominant control on magma generation, viscosity, and buoyancy. Since magmas degas most of their initial water content upon ascent and eruption, the primary record of magmatic water evolution exists within melt inclusions trapped inside crystals, especially olivine. However, the discovery of rapid H+ diffusion through olivine has called into question the fidelity of the melt inclusion water record. How compromised is the vast existing and growing dataset of melt inclusion water contents? What are the circumstances favorable for recording primary or pre-eruptive water concentration? Even if inclusions are compromised, diffusive water loss can be exploited to constrain magma decompression rates, a critical parameter that affects conduit processes. Here, we outline the current understanding of factors controlling water loss: the olivine/melt partition coefficient, the diffusive transport of water through olivine, the distance between inclusion and crystal rim, the melt inclusion size, and the exterior magma’s water evolution. We combine these parameters into a regime diagram that can be used to guide when melt inclusions may be used as hygrometers and when they are better suited to act as magma speedometers. We develop diagnostic tools to recognize where and when water loss has occurred in a magma’s ascent history, and we outline quantitative tools that may be used to restore the primary and/or pre-eruptive water content. The intent of this paper is to guide researchers in the interpretation of existing melt inclusion data, and to aid in the design of new studies that maximize the valuable information that melt inclusions may convey on the evolution of water in magmas prior to eruption.

Geochemical studies have been conducted in the geothermal system of Jaboi manifestation, Sabang, Aceh. There are three sub-area of geothermal water sites in this area, that are production-injection wells of PT Sabang Geothermal Energy, Jaboi crater, and hot spring pond. The fumaroles were also found in the Jaboi crater. The mineral contents were analyzed by ion chromatography, alkalimetry, and spectrophotometry, the isotope was determined by Laser Absorption Spectrophotometer, while the gas contents were analyzed by Gas Chromatography-TCD. The obtained data were used to estimate the reservoir temperature by using geothermometers, FT-HSH diagram, and CH4/CO2-H2/Ar diagram. The graphical analysis were also done to obtain chemical and physical characteristics. The water analysis showed that the reservoir temperatures were in range of 253.2-416.5 °C. The water types of production-injection wells, Jaboi crater and hot spring pond were chloride, sulphate and bicarbonate-sulphate mixtures, respectively. The fluid equilibria showed that only production well was mature water while the other sites were immature ones. The water composition source of production-injection wells and hot spring pond were marine sedimentary rocks, Jaboi crater JK1 and JK4 were magmatic gas, and Jaboi crater JK2 was hot rock. The water origin of production-injection wells were both magmatic and meteoric, Jaboi craters were magmatic water, and hot spring pond was meteoric water. The gas analysis in Jaboi crater fumaroles showed that the reservoir temperature were in range of 196.9-362.8 oC, and the gas origin were earth’s crust. The reservoir temperatures showed a high-temperature geothermal system which is suitable for power plant.

The Tonggou Cu polymetallic deposit in the Bogda Orogenic Belt, Eastern Tianshan shows evidence for three stages of hydrothermal mineralization: early pyrite veins (Stage 1), polymetallic sulfide ± epidote–quartz (Stage 2), and late-stage pyrite–calcite veins (Stage 3). Fluid inclusion petrography and microthermometry analyses indicate that the liquid-rich aqueous inclusions (L), vapour-rich aqueous inclusions (V), and NaCl daughter mineral–bearing three phase inclusions (S) formed during the main stage of mineralization, and that the ore fluids represent high-temperature and high-salinity H2O-NaCl hydrothermal fluids that underwent boiling. Stable isotope (H, O) data indicate that the ore fluids of the Tonggou deposit were originally derived from magmatic water in Stage 2 and subsequently mixed with local meteoric water during Stage 3. Sulphur isotope compositions (6.7‰ to 10.9‰) are consistent with the δ34S values of pyrite from the Qijiaojing Formation sandstone, indicating the primary source of the sulphur ore. Furthermore, chalcopyrite grains separated from the chalcopyrite-rich ore samples yield an isochron age of 303 ± 12 Ma (MSWD = 1.2). These results indicate that the Tonggou deposit is a transition between high–sulfidation and porphyry deposits which formed in the Late Carboniferous. It also suggests an increased likelihood for the occurrence of Cu (Au, Mo) in the Bogda Orogenic Belt, especially at locations where the Cu-Zn deposits are thicker; further deep drilling and exploration are encouraged in these areas. Keywords: Fluid inclusion, Stable isotope, Chalcopyrite Re-Os geochronology, Tonggou deposit, The Eastern Tianshan

Recent work has suggested a possible temporal coincidence between greenhouse intervals and enhanced arc volcanism, motivating the hypothesis that magmatic and metamorphic CO2 emissions from volcanic arcs, particularly those intersecting crustal carbonates, may play a strong role in modulating the long-term carbon budget of the exogenic system. When hot fluid exsolving from arc magmas interacts with carbonate sequences on active margins, contact metamorphism releases CO2 to metasomatic fluids that transport carbon to shallow reservoirs. To estimate the magnitude of CO2 release, here we model how the infiltration of silica-saturated magmatic water into a porous medium facilitates the decarbonation reaction in contact aureoles. Analytical scalings and numerical simulations show that the propagation rate of the reaction front scales with the ratio of the infiltration flux to the mass of the rate-limiting reactant, and accordingly the CO2 flux increases linearly with the infiltration flux. This simple relationship allows for scaling to predict regional and global scale CO2 release at continental arcs if magma emplacement rate is known. Using the global rate of continental arc magma emplacement, we estimate that the present-day contact-metamorphic CO2 release range from ∼0.06 to 0.9 Tmol/yr, half-to-one orders of magnitude smaller than the field-based estimates of carbon output in modern arcs (1.5–3.5 Tmol/yr). Yet, the extrapolated CO2 release from Cretaceous continental arcs via simple infiltration-induced decarbonation is comparable to the release from mid-ocean ridges. CO2 released from continental arcs amplifies the background flux of CO2 from direct degassing of the magma, and therefore may have been key in causing the climatic greenhouse interval in the Cretaceous when there was heightened arc activity. Thus, our result supports the hypothesis that global arc flare-ups at continental margins effectively increase CO2 outgassing coinciding with green-house intervals in the geological past. The contribution by arcs to the tectonic CO2 input could be significant, which needs field-based studies to revise long-term climate models.

Rhyolite-hosted hydrothermal systems in the continental crust contain valuable energy and mineral resources that make them of special interest across several scientific disciplines. Despite extensive research on these systems, the temperature-dependence of chemical reactions between host rocks and aqueous-rich fluids and the mineralogical transformations resulting from these reactions are not well quantified. To expand our understanding of the controlling processes operating in these systems, we carried out seven laboratory experiments in which rhyolite was reacted with deionized water at 150 °C to 350 °C and 25 MPa. An additional experiment at 200 °C was carried out to examine the effect of dissolved CO2 on the reactions. The overarching goal of this experimental study was to provide new insights on the temperature-dependence of water-rock interaction in continental hydrothermal systems. We applied a wide range of chemical, isotopic and mineralogical methods to analyze the reacted rhyolite and waters, and the major observations are: (1) the rhyolite progressively hydrates with increasing temperature between 150 °C to a maximum of 8.2 wt% H2O at 275 °C; hydration then decreases until 350 °C in conjunction with the destruction of the rhyolite glass and crystallization of secondary mineral phases; (2) the ratio of molecular water (H2Om) to hydroxyl (OH−) of the water that is dissolved in the reacted rhyolite decreases from ∼7 at 150 °C to ∼4 at 250 °C; (3) the main secondary minerals formed are the zeolite ferrierite (T ≥ 275 °C); biotite, albite and cristobalite mainly form at higher experimental temperatures (T ≥ 300 °C); (4) the reacted waters are nearly saturated with respect to amorphous silica; (5) at temperatures ≥ 275 °C nearly all the chlorine is leached into solution; (6) fluorine leaching from the rhyolite gradually increases between 150 °C and 250 °C, but then gradually decreases at higher temperatures and is incorporated into a secondary mineral phase; (7) dissolved CO2 in the water enhances alkali metal cation leaching from the rhyolite; and (8) calculated Na-K and silica geothermometer temperatures differ from the experimental temperatures by varying amounts. In addition, apart from some small lithium isotope fractionation at temperatures ≤ 250 °C, the stable isotopes of boron, lithium and chlorine do not fractionate during rhyolite-water reactions, and the stable isotope compositions of these species in the reacted water are similar to those in the reactant rhyolite. These results provide new insights for a broad range of applications, including quantifying processes involving rhyolite glass hydration (obsidian hydration dating, perlite formation and discriminating secondary from magmatic water in rhyolitic matrix-glass of volcanic pyroclasts), for geothermal energy and mineral deposit exploration and for monitoring volcanoes.

The Hazinemagara (Gumushane) Pb-Zn deposit is located in the southern part of the Eastern Pontides Orogenic Belt in northeastern Turkey. It occurs as irregularly shaped ore bodies with breccia fill structure within the intraformational breccia or brecciated horizons of limestone in the Upper Jurassic-Lower Cretaceous Berdiga Formation. The dominant ore minerals are pyrite, sphalerite, galena, and tetrahedrite, and the major gangue minerals are calcite, quartz, and barite. Microthermometric investigations of the fluid inclusions show that the ore-forming fluids contain CaCl2 and MgCl2 in addition to NaCl. The salinity of the fluid ranges from 1.7% to 9.2% with an average of 5.7% (wt.% NaCl equivalent) (n - 93). The homogenization temperature of the fluid ranges from 160.0 to 386.0 degrees C with an average of 263.5 degrees C (n = 98). The plots of the delta D values of water trapped in fluid inclusions hosted by barite and quartz (in the range of 92 parts per thousand to 81 parts per thousand) and the delta O-18 values calculated for water in equilibrium with these minerals (4.1 parts per thousand to 18.5 parts per thousand) are closer to the magmatic range than any other water sources and suggest the presence of magmatic water in hydrothermal fluid with some modifications by interaction with fluid from surrounding sedimentary rocks. The sulfur isotope composition of sulfide minerals (in the range of -7.8 parts per thousand(VCDT) to +5.4 parts per thousand(VCDT) avg.: -2.0 parts per thousand; n = 13) indicates a magmatic source for sulfur. It is concluded that the magmatic water derived from deep-seated Eocene plutonic rocks (Kackar Granitoids-I and -II) possibly carried metals and the sulfur derived from the source magma or leached from magmatic rocks on the pathway along the fault zones and precipitated mainly within voids between limestone fragments in intraformational breccia horizons of the Berdiga Formation. The Berdiga Formation is observed in large areas within the Eastern Pontide region and the intraformational breccia horizons could provide large stratabound ore potential.

There has been a long-term debate about the timing of the incursion of meteoric water into porphyry systems and whether it plays an important role in ore precipitation. To evaluate the role of meteoric water in the mineralization in porphyry Mo deposits, typical hydrothermal veins of different stages from the Chalukou giant porphyry Mo deposit are selected for combined scanning electron microscope cathodoluminescence (SEM-CL), fluid inclusion microthermometry and high-resolution secondary ion mass spectroscopy (SIMS) oxygen isotope analyses. Multiple generations of quartz are identified in almost all of the veins. The barren quartz veins and quartz-magnetite veins of the early Mo mineralization stage are dominated by granular CL-bright quartz (EMQ1), which usually shows dissolution and re-deposition textures and are overprinted by CL-dark quartz (EMQ2)-filled healed fractures. The molybdenite precipitation in the quartz-molybdenite veins of the main Mo mineralization stage is synchronous with small volumes ( 85%) of CL-bright quartz (MMQ1). Similar to the quartz-molybdenite veins, the precipitation of pyrite in the quartz-pyrite veins during the transitional stage and sphalerite in the quartz-sphalerite-pyrite veins during the Zn-Pb mineralization stage are also directly associated with CL-dark quartz (TSQ2, ZPQ2). The SIMS oxygen isotopic values of EMQ1 and MMQ1 fall into the range of 5.42–9.79‰ with calculated equilibrium fluid compositions of 2.07–6.45‰, indicating a magma-dominated fluid composition, whereas MMQ2, TSQ2 and ZPQ2 have very low oxygen isotopic values from −4.68 to 4.29‰ with corresponding fluid compositions of −13.64 to −5.94‰, implying that the fluid formed by the mixing of magmatic water and a large proportion of meteoric water. The contrasting SEM-CL features and oxygen isotopic compositions of the two generations of quartz in the quartz-molybdenite veins demonstrate that the incursion of meteoric water into the hydrothermal system occurred earlier than the molybdenite precipitation. Based on these results and the crosscutting relationships and spatial distribution of the veins, we reconstructed the quartz evolutionary sequence during the vein development process. After the early precipitation of barren quartz, the reduction in fluid pressure from lithostatic to hydrostatic conditions allowed the incursion of convecting cool meteoric water into the relatively hot hydrothermal system, and the temperature of the evolved Mo-rich fluid decreased rapidly from >500 °C to

In the Zajkan Pb–Zn–Cu (Au–Ag) deposit of the Tarom–Hashtjin metallogenic belt (THMB), northwest Iran, mineralization occurs as quartz-base metal sulfide veins hosted by Eocene volcanic and volcaniclastic rocks of the Karaj Formation. Four stages of ore formation are identified at Zajkan: (1) quartz-chalcopyrite-pyrite veins, (2) quartz-galena-sphalerite ± chalcopyrite ± pyrite veins and breccias, (3) quartz-hematite veins and breccias, and (4) barren quartz-carbonate veinlets. The primary metallic minerals are pyrite, chalcopyrite, sphalerite, galena, and trace amounts of hematite; gangue minerals are mainly quartz, sericite, chlorite, and calcite. The main wall-rock alteration is silicification, and intermediate argillic, and propylitic alteration. The coexistence of different types of fluid inclusions (LV, VL, and V) in individual fluid inclusion assemblages in quartz and sphalerite suggests boiling and heterogeneous trapping. Excluding the heterogeneously entrapped fluid inclusions, the microthermometric measurements of primary LV fluid inclusion assemblages in quartz and sphalerite indicate that the veins were formed at temperatures between 217 and 273 °C from fluids with salinities between 1.7 and 6.4 wt% NaCl equiv. The oxygen isotopic compositions (δ18Owater-VSMOW of +3.7 to +1.1‰) indicate that the ore-forming fluids were mainly derived from magmatic water with the input of meteoric water in the later ore-stages. Sulfur isotopic values of sulfide minerals vary over a narrow range from −5.0 to −0.9‰VCDT (averaging −2.2‰VCDT), suggesting that sulfur was derived from a homogeneous magmatic source. The fluid inclusion and stable isotope data indicate that fluid boiling and mixing facilitated hydrothermal alteration and mineralization at Zajkan. Our data suggest that the Zajkan deposit is an intermediate-sulfidation style epithermal mineralization. The estimated ore formation depth of Zajkan indicates minor denudation in the region and may imply a great prospecting potential for other epithermal mineralization in the THMB.

The Baiyun gold deposit is located in the Qingchengzi orefield, NE China. The gold mineralization occurs mainly as auriferous quartz veins and auriferous altered rock. Wall-rock alteration includes silicification and potassic alteration along with minor sericitization, carbonatization, and chloritization. Three stages of mineralization are recognized: an early quartz and coarse-grained pyrite stage (Stage I), a middle quartz–gold and fine-grained pyrite–polymetallic sulfide stage (Stage II), and a late quartz–carbonate stage (Stage III). Four types of inclusions are recognized in the quartz veins: two-phase liquid-rich fluid inclusions (Type I), CO2 three-phase aqueous fluid inclusions (Type II), two-phase vapor-rich fluid inclusions (Type III), and pure liquid fluid inclusions (Type IV). The early stage quartz contains Type I–III fluid inclusions that yield low–medium homogenization temperatures (162 °C–350 °C), low salinities (1.57–10.33 wt% NaClequiv.), and belong to a NaCl–H2O–CH4–CO2 ± H2S hydrothermal fluid system. The middle-stage quartz also contains Type I–III fluid inclusions that yield low–moderate homogenization temperatures (148 °C–290 °C), variable salinities (1.02–16.43 wt% NaClequiv.), and belong to a NaCl–H2O–CO2–H2S ± N2 system. The late-stage quartz contains Type I, II, and IV fluid inclusions that yield homogenization temperatures and salinities of 150 °C–183 °C and 6.30–13.29 wt% NaClequiv, respectively, and belong to a NaCl–H2O–CO2 ± N2 system. Therefore, the ore-forming fluids of the Baiyun gold deposit are generally characterized by low–moderate homogenization temperatures and low–medium salinities, and belong to a NaCl–H2O–CO2–H2S ± N2 system. The coexisting Type I and II inclusions of the early and middle stages have similar Th ranges but weakly contrasting salinities, indicating that fluid boiling occurred. The H-O isotopic values (δ18OH2O = −0.7‰ to 5.6‰; δD = −108.3‰ to −74.0‰) and composition of the fluids suggest that the ore-forming fluids consisted mainly of magmatic water with a small amount of meteoric water and metamorphic fluids. Fluid inclusions in hydrothermal pyrite yield 3He/4He ratios of 0.43–0.52 Ra and 40Ar/36Ar ratios of 4648.7–7685.9, indicating the mixing of fluids with mantle and crustal components, which were mainly crust-derived. The δ34SV-CDT values of pyrite are between −12.5‰ and 1.9‰ (average −5.0‰), while δ34SV-CDT values of wall-rocks are between 7.0‰ and 18.7‰ (average 12.6‰). The 206Pb/204Pb, 207Pb/204Pb, and 207Pb/204Pb values of the pyrites are 17.416–18.908, 15.511–15.714, and 35.541–40.032, respectively, indicating that the ore-forming metals may came from Triassic magma and Gaixian Formation. Based on geological, fluid inclusion, and isotopic data, as well as data from previous studies, we propose that the Baiyun gold deposit is a magmatic–hydrothermal ore deposit.

Carbonatite-related rare-earth element (REE) deposits (CARDs) are the major global source of REEs. The ore-forming fluids of CARDs usually comprise multiple components and record complicated evolutions. The Maoniuping REE deposit, located in the eastern Tibetan Plateau, is the second-largest CARD in China and contains total reserves of 3.17 Mt of light rare-earth oxides (REOs). Geochronological and geological data show that the deposit was formed at ∼25 Ma and was only moderately affected by tectonic and hydrothermal activities, thereby allowing us to study the evolution of ore fluids as well as the mechanisms of REE mineralization. The Maoniuping REE deposit is spatially associated with a carbonatite–syenite complex and includes two sections: Guangtoushan and Dagudao. The Dagudao section is the main focus of exploration and hosts well-developed vein systems. In the uppermost vein system, minerals are zoned from the syenite wall-rock contact to the vein centers in the order of biotite, aegirine-augite, arfvedsonite, calcite, quartz, barite, fluorite, and bastnasite-(Ce). Based on geological observations and the petrography of fluid inclusions, the mineralization processes are classified into magmatic, pegmatitic, hydrothermal I, hydrothermal II, and REE stages. The inclusions in these stages include melt (M), melt–fluid (M–L), pure CO2 (C), aqueous–CO2 (L–C), aqueous–CO2 with crystals (L − C + S), liquid–vapor aqueous with crystals (L − V + S), and liquid–vapor (L–V) type inclusions. The magmatic stage is marked by a carbonatite–syenite complex with minor bastnasite-(Ce), whereas the pegmatitic stage consists of coarse-grained calcite, barite, fluorite, and quartz that contain M, M–L, and L–C type inclusions with a fluid system of NaCl–Na2SO4–H2O–CO2 at high temperature (>600 °C) and high salinity (>45 wt% NaCl equiv.). The hydrothermal I stage is characterized by fenitization and is marked by aegirine-augite and arfvedsonite containing abundant L–V and few L–C type inclusions. This stage is characterized by high temperatures (∼480 °C) and moderate salinity (10.2–17.9 wt% NaCl equiv.), with a fluid system of NaCl–Na2SO4–H2O and minor CO2 and CH4 + C2H6. The hydrothermal II stage is dominated by L–C, L − C + S, L − V + S, and L–V type inclusions that are hosted in barite, calcite, fluorite, and quartz, and formed at moderate to high temperatures (260–350 °C), with a wide range of salinity (9.4–47.8 wt% NaCl equiv.), a fluid system of NaCl–Na2SO4–CO2–H2O, and abundant CH4 + C2H6. During the REE stage, pervasive bastnasite-(Ce) containing abundant L–V type and few L–C type inclusions crystallized under low temperatures (160–240 °C) and low salinities (8.8–13.1 wt% NaCl equiv.) with a fluid system of NaCl–H2O and minor CO2 and CH4 + C2H6. The results of ion-chromatographic analysis show that the ore fluids are rich in Na+, K+, Cl−, F−, and (SO4)2−, and have low Cl−/(SO4)2− ratios (0.78–2.00), showing a marked contrast with the fluids of granite-related REE deposits (Cl−/(SO4)2− > 50) and a similarity to subcontinental lithospheric mantle (SCLM). The δD and δ18Ofluid values and the high N2/Ar ratios indicate that the ore fluids originated from carbonatitic magma and were dominated by magmatic water during the hydrothermal I stage, whereas magmatic and meteoric water co-existed during the hydrothermal II and REE stages. Moreover, the higher ratios of CO2/N2 (9–64) and CO2/CH4 (17–472) and the higher concentrations of CO2, CH4, C2H6, and N2 in the hydrothermal II stage compared with the hydrothermal I stage are attributed to intense immiscibility that resulted from decompression and is constrained to temperatures of 310–350 °C and pressures of 2.0–2.4 kbar. In contrast, microthermometric data and low CH4, C2H6, and N2 contents for the REE stage show that fluid cooling and mixing with meteoric water played an important role during the intensive mineralization of this stage, which occurred under shallow open-system conditions at temperatures of ∼200 °C and pressures of

The Hongyuntan magnetite deposit, which is located in the Aqishan–Yamansu belt of Eastern Tianshan, Xinjiang, is hosted within Carboniferous submarine volcanic-sedimentary sequences. The deposit is characterized by five metallogenic stages: Stage I (garnet–diopside), Stage II (magnetite–tremolite–chlorite–pyrite), Stage III (magnetite–quartz–albite–actinolite), Stage IV (pyrite–quartz–epidote) and Stage V (hematite–limonite). Pyrite associated with magnetite formed during the Stage II has a Re-Os isochron age of 324 ± 31 Ma. Four types of fluid inclusions were observed in the mineral assemblages, namely, two-phase liquid and vapor inclusions, multi-phase daughter mineral-bearing inclusions, multi-phase CO2-bearing inclusions, and monophase vapor inclusions. Microthermometry data reveal that the ore-forming fluids evolved from high-temperature (average 532.5 °C) and high-salinity (average 26.9 wt% NaCleqv) fluids to moderate–low-temperature (average 203.6 °C) and low-salinity (5.07 wt% NaCleqv) fluids. Magnetite precipitation may have been greatly assisted by mixing and boiling in Stage II and Stage III, respectively. The hydrogen and oxygen isotopic values of Stage I garnet (δDV-SMOW = −107.9‰ to −76.7‰, δ18Ofluid = 6.4–10.7‰) and Stage III quartz (δDV-SMOW = −85.5‰ to −83.2‰, δ18Ofluid = 3.8–4.7‰) indicate that the ore-forming fluids were dominated by magmatic water, whereas fluid mixing occurred during Stage II (δDV-SMOW = −117.3‰ to −112.6‰, δ18Ofluid = 3.3–5.7‰) and Stage IV (δDV-SMOW = −115.2‰ to −58.5‰, δ18Ofluid = −1.3‰ to 4.5‰). The variable δ34S values of pyrite (−3.8‰ to 4.7‰) and δ18Omgt values of magnetite (−0.6‰ to 4.1‰) suggest that they were not sourced from a single reservoir. The Hongyuntan magnetite deposit is spatially and temporally associated with volcanism and may be genetically related to it. The fluid inclusions and isotopic compositions of this deposit indicate that its ore-forming fluid was derived from the exsolution of deep-seated magmas and that fluid mixing could have effectively triggered the deposition of ore-forming materials. Multiple periods of volcanic activity could have incorporated additional heat and ore metals into the ore-forming system. Based on our data, we conclude that the origin of the Hongyuntan magnetite deposit is related to the volcanism in the Carboniferous period.

The past decade has seen a great number of studies dealing with magmatic water contents and how these could be retrieved by the nominally anhydrous minerals’ (NAMs) trace structural hydroxyl (water) contents. Constraints have been made to magmatic hygrometry with clinopyroxene and plagioclase. Although results suggest that the method is more flexible and reliable than melt inclusion studies, they also indicate that the trace hydroxyl contents could still be overprinted by syn- and post-eruptive processes. Clinopyroxenes can hold more structural hydroxyl than plagioclases. A comprehensive review is presented with the inclusion of all published results so far to compile the available pieces of information. As a case study, micro-FTIR measurements are made of a representative set of plagioclase phenocrysts from the Börzsöny Mts. (Carpathian–Pannonian Region). The samples were selected to represent the progress of the volcanic activity in time and space, considering the petrologic and geochemical evolution of volcanic products in well-defined volcanostratigraphic positions. The syn- and post-eruptive cooling rate seems to have the greatest effect on water retention. This means that the systematic investigation of water in volcanic phenocrysts can contribute to distinguish the slowly and rapidly cooling parts of the volcanostratigraphic units.