Alkaline Brines Research Articles

Ampere-Level Hydrogen Generation via 1000 H Stable Seawater Electrolysis Catalyzed by Pt-Cluster-Loaded NiFeCo Phosphide.

Seawater electrolysis can generate carbon-neutral hydrogen but its efficiency is hindered by the low mass activity and poor stability of commercial catalysts at industrial current densities. Herein, Pt nanoclusters are loaded on nickel-iron-cobalt phosphide nanosheets, with the obtained Pt@NiFeCo-P electrocatalyst exhibiting excellent hydrogen evolution reaction (HER) activity and stability in alkaline seawater at ampere-level current densities. The catalyst delivers an ultralow HER overpotential of 19.7mV at -10mA cm-2 in seawater-simulating alkaline solutions, along with a Pt-mass activity 20.8 times higher than Pt/C under the same conditions, while dropping to 8.3mV upon a five-fold NaCl concentrated natural seawater. Remarkably, Pt@NiFeCo-P offers stable operation for over 1000 h at 1 A cm-2 in an alkaline brine electrolyte, demonstrating its potential for efficient and long-term seawater electrolysis. X-ray photoelectron spectroscopy (XPS), in situ electrochemical impedance spectroscopy (EIS), and in situ Raman studies revealed fast electron and charge transfer from the NiFeCo-P substrate to Pt nanoclusters enabled by a strong metal-support interaction, which increased the coverage of H* and accelerated water dissociation on high valent Co sites. This study represents a significant advancement in the development of efficient and stable electrocatalysts with high mass activity for sustainable hydrogen generation from seawater.

Vanadium-Doped Heterogeneous Bimetallic Phosphides Derived from Layered Double Hydroxides for Saline Water Splitting.

The development of energy- and time-saving synthetic methods to prepare bifunctional and high stability catalysts are vital for overall water splitting. Here, V-doped nickel-iron hydroxide precursor by etching NiFe foam (NFF) at room temperature with dual chloride solution ("NaCl-VCl3"), is obtained then phosphating to obtain V-Ni2P-FeP/NFF as efficient bifunctional (oxygen/hydrogen exchange reaction, OER/HER) electrocatalysts, denoted as NFF(V, Na)-P. The NFF(V, Na)-P requires only 185 and 117 mV overpotentials to reach 10 mA cm-2 for OER and HER. When used as a catalyst for water splitting in a full cell, it can be stably sustained for more than 1000 h in alkaline brine electrolysis at both current densities of 100 and 500 mA cm-2. In situ Raman analyses and density functional theory (DFT) show that the V-doping-induced surface remodeling generates hydroxyl oxides as the true catalytic active centers, which not only enhances the reaction kinetics, but also reduces the free energy change in the rate-determining step. This work provides a cost-effective substrate self-derivation method to convert commercial NFF into a powerful catalyst for electrolytic brine, offering a unique route to the development of efficient electrocatalysts for saline water splitting.

Synthesis of jadarite in the Li2O–Na2O–B2O3–SiO2–NaCl–H2O system: FTIR, Raman, and Li and B K-edge XANES characterizations and theoretical calculations

Abstract. The occurrence of jadarite (LiNaSiB3O7OH) as a major ore mineral in the world-class lithium–boron deposit of the Miocene Jadar lacustrine basin (western Serbia) raises interesting questions about its formation conditions and potential associations for lithium mineralization in other sedimentary basins. This contribution reports on the first successful synthesis of jadarite in the Li2O–Na2O–B2O3–SiO2–NaCl–H2O system at temperatures from 180 to 230 ∘C and pH values from 6 to 12. Synthetic jadarite has been characterized by powder X-ray diffraction (PXRD), Fourier transform infrared (FTIR) spectroscopy, laser Raman spectroscopy, and synchrotron Li and B K-edge X-ray absorption near-edge structure (XANES). First-principles theoretical calculations reproduce the measured FTIR and Raman spectra and allow definitive assignments of vibration modes. Similarly, the measured Li and B K-edge XANES spectra are reasonably reproduced by first-principles theoretical calculations. Our synthesis results, together with its association with searlesite in the Jadar basin, suggest jadarite forms in deep sediments derived from Li-rich alkaline brines under high-temperature diagenetic conditions.

A novel Co-doped H2TiO3 spinning composite for efficient lithium recovery from alkaline lithium precipitation mother liquor

The efficient recovery of lithium from the alkaline mother liquor with high Na/Li ratios after Li2CO3 precipitation by adsorption has received extensive attention. However, synthesizing composite adsorbents with excellent adsorption capacity and rate still faces huge challenges. In this work, we synthesized a novel Co-doped Li2TiO3 lithium ion sieve (LTO-1/32Co) using the calcination method. After converting to Co-doped H2TiO3 (HTO-1/32Co) by pickling, the adsorption capacity of the material was 1.4 times higher than that of conventional H2TiO3. To realize the industrial application of the powdered HTO-1/32Co, it was coated with polysulfone (PSF) by the wet spinning method. The saturated adsorption capacity of the material could reach 60.79 mg·g−1, which was at the forefront of reported composite adsorbents. When the adsorbent was applied for lithium recovery from lithium precipitation mother liquor, the adsorption capacity could reach 40.12 mg·g−1, and the equilibrium time was only 50 min. The elution rate of Li+ could be maintained at 90.56 % with the dissolution loss of Ti no more than 0.43 % after six cycles. The developed fibrous composite adsorbent exhibits excellent adsorption/desorption performance and cyclic stability, making it a competitive candidate for efficient lithium recovery from lithium precipitation mother liquor and other lithium-rich alkaline brine resources.

Diagenetic evolution of tight sandstone and the formation of an effective reservoir in the lower member 3 of the Shahejie Formation, Bohai Bay Basin, East China

Heterogeneity in the physical properties of tight sandstones is mainly caused by complex diagenetic interactions in various combinations during the burial process. The tight sandstone oil in the Linnan Sag of Bohai Bay Basin has great development potential but it is unclear how effective reservoirs were formed, and this is a significant reason why exploration in the deep reservoir is so difficult. Here we studied the diagenetic evolution of the tight sandstone of Lower Member 3 of the Shahejie Formation, Linnan Sag, Bohai Bay Basin, by using cores, thin sections, XRD, SEM, grain-size analysis, high-pressure mercury intrusion porosimetry, fluid inclusions, and carbon and oxygen stable isotopes. Compaction, replacement, cementation and dissolution diagenesis are identified; all four processes mainly occur in the A phase of mesodiagenesis. The interaction of formation burial, thermal evolution of organic matter and dehydration of gypsum leads to the alternating presence of three stages of alkaline fluids and two stages of acidic fluids. The average dissolution porosity of the dissolution sandstone facies is greater than the lower limit of the porosity for the effective reservoir in the study area, which is key to the formation of effective reservoirs. By determining differential diagenetic evolution sequences of tight sandstone reservoirs under the constraints of different lithologies where sandstone is interbedded with mudstone, we are able to elucidate the formation of the effective reservoir as follows: (1) In the eodiagenetic stage, a large amount of early carbonate cement developed in the sandstone adjacent to the mudstone, filling the primary pores and forming a cementation sandstone facies. Smaller amounts of early carbonate cement developed in the interior of the sandstone, which “fixed” the primary pores, and has a positive effect on the formation of a large number of secondary pores in the dissolution stage. (2) In the early stage of mesodiagenesis (A1), due to the filling of primary pores, it is difficult for acidic fluids to enter the cementation sandstone facies adjacent to mudstone, and the dissolution is weak. But dissolution within the sand body was strong, producing a large number of dissolution pores and forming a dissolution sandstone facies that clearly enhanced the physical properties. (3) In a second early stage of mesodiagenesis (A2), dissolution still played a dominant role in the dissolution sandstone facies, due to the development of dissolution pores in the previous stage (it is easy for acidic fluids to enter the dissolution sandstone facies). The physical properties of the dissolution sandstone facies were once again enhanced and an effective reservoir gradually began to form. (4) At the end of mesodiagenesis stages A1 and A2 (26.2–24.6 Ma; 7.5–2.8 Ma), the reservoir experienced two phases of petroleum charging. The charging of the cementation sandstone facies developed at the margins of the sandstones was difficult due to the filling of primary pores. The dissolution sandstone facies are oil-bearing, with higher porosity, which indicates an effective reservoir. By coupling the thermal evolution of organic matter and the dehydration of gypsum with differential diagenetic evolution and the porosity evolution of reservoir, we are able to establish a reservoir genetic model that involves alternating seepage of organic acids and alkaline brines.

High-resolution X-ray fluorescence-based provenance mapping of Eocene fluvial distributary fans that fed ancient Gosiute Lake, Wyoming, USA

The Green River Formation of Wyoming, USA, is host to the world’s largest known lacustrine sodium carbonate deposits, which accumulated in a closed basin during the early Eocene greenhouse. Alkaline brines are hypothesized to have been delivered to ancient Gosiute Lake by the Aspen paleoriver that flowed from the Colorado Mineral Belt. To precisely trace fluvial provenance in the resulting deposits, we conducted X-ray fluorescence analyses and petrographic studies across a suite of well-dated sandstone marker beds of the Wilkins Peak Member of the Green River Formation. Principal component analysis reveals strong correlation among elemental abundances, grain composition, and sedimentary lithofacies. To isolate a detrital signal, elements least affected by authigenic minerals, weathering, and other processes were included in a principal component analysis, the results of which are consistent with petrographic sandstone modes and detrital zircon chronofacies of the basin. Sandstone marker beds formed during eccentricity-paced lacustrine lowstands and record the migration of fluvial distributary channel networks from multiple catchments around a migrating depocenter, including two major paleorivers. The depositional topography of these convergent fluvial fans would have inversely defined bathymetric lows during subsequent phases of lacustrine inundation, locations where trona could accumulate below a thermocline. Provenance mapping verifies fluvial connectivity to the Aspen paleoriver and to sources of alkalinity in the Colorado Mineral Belt across Wilkins Peak Member deposition, and shows that the greatest volumes of sediment were delivered from the Aspen paleoriver during deposition of marker beds A, B, D, and I, each of which were deposited coincident with prominent “hyperthermal” isotopic excursions documented in oceanic cores.

The Fate of the Chlorophyll Derivatives in Olives Preserved and/or Packaged in Presence of Exogenous Copper.

Chlorophyll pigments are thought to be responsible for the highly appreciated green color of unfermented Castelvetrano-style table olives, but no studies have considered the effects of a controlled addition of copper during storage or packaging at the industrial level. For this purpose, chlorophyll derivatives were analyzed in Nocellara cultivar table olives debittered industrially using the Castelvetrano method, via means of HPLC and MS analyses, following the addition of copper in alkaline brines stored at 4 °C for 3 months in 220 L barrels, and during the subsequent storage in acid brines in commercial 400 g packages at 4 °C for up to 18 months. The presence of copper in storage or in packaging brines both contributed significantly to maintaining the green color of the olives, which was associated with a specific pattern of chlorophyll derivatives, as evidenced by principal component analysis. Notably, re-greening was rapidly achievable also for olives that had yellowed for 18 months at a copper concentration below the limit of EU legislation. Finally, by means of PCA, we also demonstrated that a short-term thermic treatment can work as an accelerated predictive tool in determining the fate of chlorophyll derivatives.

Transmembrane fluxes during electrolysis in high salinity brines: Effects on lithium and other raw materials recovery

During the production of high purity lithium salts, magnesium and calcium will readily crystalize as either carbonates or hydroxides if their concentrations have not been depleted to below 2 ppm. Magnesium and calcium can be fully abated electrochemically by production of hydroxide anions via water electrolysis. While brine alkalization within an electrochemical reactor has shown great performance at proof-of-concept level, this is not feasible at industrial scale. Solids cannot be produced, nor accumulated within a water electrolyzer, and membrane fouling must be avoided at all costs. An alternative is to work on a brine that has been fully depleted from multivalent cations and produce an increase in pH beyond the needs for successful crystallization of the hydroxides. In this way, the super alkaline brine can be used as an external precipitating agent that does not dilute the other key components of the brine, namely lithium cations. We have studied the competing ion migration between chloride and hydroxide anions across an anion exchange membrane in a water electrolyzer as a function of current density. The most important differences were observed in the magnitude of the changes in the solution volumes. While water electrolysis and electro-osmotic effects were identified as processes contributing to these changes, only classical osmosis is responsible for the differential effects. In the range of study, applied current density values from 80-225 A m−2 produced higher hydroxide concentrations, although no current density values were identified to produce remarkable changes in the energy efficiency. Beyond pH 14, the passage of hydroxide across the membrane becomes faster than that of chloride.

A density functional theory insight into the extraction mechanism of lithium recovery from alkaline brine by β‐diketones

AbstractIn this study, the mechanism of lithium extraction with β‐diketones was investigated by resolving the reaction mechanism, thermodynamic property, and molecular interaction through density functional theory approach. Before the selective extraction of lithium, the β‐diketones had tautomerism with the product of enol. The enol structure was unsteady in alkaline environment so that Li+can be selectively extracted by taking the place of hydroxyl hydrogen. Meanwhile, the synergistic effect of TOPO intensified the extraction ability by the generation of strong electrostatic. Based on the calculated Gibbs energy changes, the parameters of extraction efficiency and separation factor were analyzed and they had qualitative consistence with the experimental results. Meanwhile, it was determined that the electron‐withdrawing effect of the subsistent group in the β‐diketones had a critical influence on the extraction separation performance. Besides, the theoretical model predicted successfully the transition of extraction complex from hydrophilicity to lipophilicity after the combination with synergistic reagent.

Pitting corrosion resistance of additive manufactured alloy 718 in alkaline brines at elevated temperatures

AbstractThe feasibility of additive manufacturing (AM) to produce industrial components, also for the oil and gas industry, has been demonstrated in the past. Therefore, current research efforts focus on demonstrating the reliability of AM materials subjected to demanding service conditions. In this regard, special attention has been paid to its corrosion resistance in harsh environments as one of the most critical properties in these applications. The beneficial combination of high strength, excellent thermal stability, and outstanding corrosion resistance makes alloy 718 (UNS N07718) the most used wrought and AM nickel alloy in the oil and gas industry. Wrought 718 has an extensive record of field performance in demanding oil and gas applications including directional drilling tools that undergo extreme mechanical loads in corrosive drilling fluids. On the other hand, limited data regarding the corrosion behavior of AM718 in typical drilling environments has been collected so far. In this research work, the pitting susceptibility of selective laser melted alloy 718 in simulated drilling environments has been studied. Open circuit potential measurements as well as cyclic potentiodynamic and potentiostatic polarization tests were used to characterize the pitting corrosion resistance of AM718 in alkaline brines at elevated temperatures. In addition, microstructural particularities in alloy 718 were investigated to explain the observed differences in the electrochemical behaviors.

Multiphase Alloy Nuclear Waste Forms Developed for Pyrochemical U-10Mo Scrap Recovery Waste Streams

The US High Performance Research Reactor (USHPRR) Conversion program is developing an Al-clad Zr-bonded U-10Mo nuclear fuel foil to enable the conversion of research reactors to high-assay low-enriched uranium (HALEU) alloy fuel. Fabrication scrap from the fuel manufacturing will be electrorefined to recover the HALEU, which will generate waste streams consisting of Zr, Mo, and residual U retained in the stainless steel anode basket used in the electrorefiner. Four alloys were formulated with different relative amounts of Zr, Mo, and 316L-SS to represent the expected range of waste compositions. Laboratory-scale ingots were made and metallurgically characterized to assess differences in the microstructures and distributions of the surrogate waste metals. Different amounts of the same dominant phases with similar compositions were formed in most materials: a γ-austenite based matrix, two ZrFe2 intermetallic phases that could host residual uranium, an FeCrMo sigma (σ) intermetallic phase, a chi (χ) phase, and a secondary austenite (γ2) phase. Electrochemical tests were conducted to compare the corrosion behaviors in acidic and alkaline brine solutions for a range of simulated environmental redox conditions. Corrosion of the Mo-rich γ and γ2 solid solutions and the σ and χ intermetallic phases occurred. The multiphase alloy waste form formulated with the lowest molybdenum and highest zirconium contents showed the highest corrosion resistance and has sufficient amounts of ZrFe2 to immobilize trace amounts of residual uranium in the waste stream. The alloy formulation strategy and testing approach will be presented with key results.Work conducted at Argonne National Laboratory is operated for the U.S. Department of Energy, Office of Science under contact DE-AC02-06CH11357.

Cultivation of a vampire: 'Candidatus Absconditicoccus praedator'.

Halorhodospira halophila, one of the most-xerophilic halophiles, inhabits biophysically stressful and energetically expensive, salt-saturated alkaline brines. Here, we report an additional stress factor that is biotic: a diminutive Candidate-Phyla-Radiation bacterium, that we named 'Ca. Absconditicoccus praedator' M39-6, which predates H. halophila M39-5, an obligately photosynthetic, anaerobic purple-sulfur bacterium. We cultivated this association (isolated from the hypersaline alkaline Lake Hotontyn Nur, Mongolia) and characterized their biology. 'Ca. Absconditicoccus praedator' is the first stably cultivated species from the candidate class-level lineage Gracilibacteria (order-level lineage Absconditabacterales). Its closed-and-curated genome lacks genes for the glycolytic, pentose phosphate- and Entner-Doudoroff pathways which would generate energy/reducing equivalents and produce central carbon currencies. Therefore, 'Ca. Absconditicoccus praedator' is dependent on host-derived building blocks for nucleic acid-, protein-, and peptidoglycan synthesis. It shares traits with (the uncultured) 'Ca. Vampirococcus lugosii', which is also of the Gracilibacteria lineage. These are obligate parasitic lifestyle, feeding on photosynthetic anoxygenic Gammaproteobacteria, and absorption of host cytoplasm. Commonalities in their genomic composition and structure suggest that the entire Absconditabacterales lineage consists of predatory species which act to cull the populations of their respective host bacteria. Cultivation of vampire : host associations can shed light on unresolved aspects of their metabolism and ecosystem dynamics at life-limiting extremes.

Magnesium isotope fractionation during alkaline brine evaporation and implications for Precambrian seawater chemistry

The chemical evolution of the ocean is one major component of the puzzle of how climate and life have co-evolved over the Earth's history. A “soda ocean” with high alkalinity, high pH, and low calcium concentration in Precambrian has been proposed to explain the emergence and evolution of early life. However, this hypothesis has not been widely accepted due to the lack of reliable tracers for the chemical composition of Precambrian seawater. Evaporite is formed during seawater/brine evaporation and thus has been widely used to reconstruct the ancient seawater/brine chemical composition. Here, evaporation experiments were conducted using Qinghai Lake (QHL) water, a modern soda lake, to provide an analogy of the Precambrian “soda ocean” evaporation and investigate the mineralogical and Mg isotopic signatures of alkaline brine-derived evaporites. Our results show that the evaporation path of QHL water overall covers the stages of hydrous Mg carbonates (hydromagnesite), halite, and bloedite [Na2Mg(SO4)2·4H2O] precipitation. The precipitation of hydrous Mg carbonates and bloedite is distinct from the modern seawater evaporation and is accompanied by the removal of up to 85% Mg from brine. The brine gradually becomes enriched in heavy Mg isotopes during evaporation due to the preferential incorporation of light Mg isotopes into precipitates. The fractionation of Mg isotopes is dominantly controlled by the bond structure during hydrous Mg carbonates and bloedite precipitation, and the latter is also slightly influenced by the kinetics in the highly concentrated brine. The Mg isotope fractionation during bloedite dissolution is limited due to the rapid congruent dissolution. The significant Mg isotopic fractionation observed within the hydrous Mg carbonates precipitation during the earliest QHL water evaporation indicates the potential Rayleigh distillation of Mg by alkalinity in the “soda ocean”, which is absent in the Phanerozoic oceans. Therefore, the large Mg isotope fractionation during alkaline brine evaporation can be applied to test the existence of Precambrian “soda oceans”.

Calathus: A sample-return mission to Ceres

Ceres, as revealed by NASA's Dawn spacecraft, is an ancient, crater-saturated body dominated by low-albedo clays. Yet, localised sites display a bright, carbonate mineralogy that may be as young as 2 Myr. The largest of these bright regions (faculae) are found in the 92 km Occator Crater, and would have formed by the eruption of alkaline brines from a subsurface reservoir of fluids. The internal structure and surface chemistry suggest that Ceres is an extant host for a number of the known prerequisites for terrestrial biota, and as such, represents an accessible insight into a potentially habitable “ocean world”. In this paper, the case and the means for a return mission to Ceres are outlined, presenting the Calathus mission to return to Earth a sample of the Occator Crater faculae for high-precision laboratory analyses. Calathus consists of an orbiter and a lander with an ascent module: the orbiter is equipped with a high-resolution camera, a thermal imager, and a radar; the lander contains a sampling arm, a camera, and an on-board gas chromatograph mass spectrometer; and the ascent module contains vessels for four cerean samples, collectively amounting to a maximum 40 g. Upon return to Earth, the samples would be characterised via high-precision analyses to understand the salt and organic composition of the Occator faculae, and from there to assess both the habitability and the evolution of a relict ocean world from the dawn of the Solar System.

The effect of hydrothermal fluids on Ordovician carbonate rocks, southern Ordos Basin, China

Hydrothermal processes have an important influence on the spatial distribution and formation of carbonate reservoirs, and play a critical role in certain deep reservoirs where hydrothermal fluid-rock interaction may result in permeability creation due to carbonate dissolution or permeability destruction due to the deposition of cementing minerals. This study analyzed certain hydrothermal indicator minerals (quartz, celestite, multi-stage calcareous fillings) in carbonate rocks from the Ordovician Majiagou Formation, southern Ordos Basin, China. The petrological and geochemical characteristics of these indicator minerals imply that the Majiagou Formation was affected by two metasomatic events related to the Hercynian–Indosinian and Yanshanian orogenies and linked to magmatic-hydrothermal fluids derived from basaltic melts. Most of the δCe and δEu values obtained from matrix dolomite samples were lower than one, but U/Th and V/C ratios showed positive anomalies. The δ13C and δ18O values of the matrix dolomite were concentrated between −12.8‰ and −6.0‰, whereas δ13C showed a bipolar distribution at the same depth. Elemental geochemistry results showed that the Ordovician carbonate rocks were subjected to freshwater leaching followed by evaporation and widespread hydrothermal dissolution successively. As a result of the multi-episodic hydrothermal activity that affected the southern Ordos Basin and the path of migration channel, a parental magmatic-hydrothermal fluid (fluid 1) that had been generated during the underplating of the southern North China Craton by Mesozoic alkaline basalt melts, separated into two types of fluids with different chemical properties: an acidic, hydrocarbon-bearing fluid (fluid 2a) mixed with Cambrian oil and gas and a weakly to moderately alkaline brine (fluid 2b), not in contact with hydrocarbons. Both fluids 2a and 2b then interacted with the Ordovician carbonate rocks with fluid 2a having undergone hydrothermal sulfate reduction with SO42- in the layers in which gypsum was developed, and convection of fluid 2a having resulted in brine formation. The reaction products of H2S and CO2 together with organic acid co-dissolved carbonate minerals in the Ordovician strata played a major role in the formation of a high porosity reservoir. Conversely, owing to the progressive reduction of temperature and solubility during fluid ascent, fluid 2b precipitated quartz-calcite fillings in the residual pore spaces, resulting in the localized destruction of the original reservoir permeability. In summary, this study analyzed the petrological and geochemical characteristics of 60 carbonate rock drill core samples, established the likely formation mechanism of fluids 2a and 2b, and determined the effects of these hydrothermal fluids on the Ordovician Majiagou Formation carbonate reservoir.

Mineral Vesicles and Chemical Gardens from Carbonate-Rich Alkaline Brines of Lake Magadi, Kenya

Mineral vesicles and chemical gardens are self-organized biomimetic structures that form via abiotic mineral precipitation. These membranous structures are known to catalyze prebiotic reactions but the extreme conditions required for their synthesis has cast doubts on their formation in nature. Apart from model solutions, these structures have been shown to form in serpentinization-driven natural silica-rich water and by fluid-rock interaction of model alkaline solutions with granites. Here, for the first time, we demonstrate that self-assembled hollow mineral vesicles and gardens can be synthesized in natural carbonate-rich soda lake water. We have synthesized these structures by a) pouring saturated metal salt solutions, and b) by immersing metal salt pellets in brines collected from Lake Magadi (Kenya). The resulting structures are analyzed by using SEM coupled with EDX analysis, Raman spectroscopy, and powder X-ray diffraction. Our results suggest that mineral self-assembly could have been a common phenomenon in soda oceans of early Earth and Earth-like planets and moons. The composition of the obtained vesicles and gardens confirms the recent observation that carbonate minerals in soda lakes sequestrate Ca, thus leaving phosphate behind in solution available for biochemical reactions. Our results strengthens the proposal that alkaline brines could be ideal sites for “one-pot” synthesis of prebiotic organic compounds and the origin of life.

Geochemical and hydroclimatic constraints on the formation of borate deposits in Da Qaidam Salt Lake of Qaidam Basin, northern Tibetan Plateau

The pinnoite deposit occurred in the lakebed of Da Qaidam Salt Lake in Qaidam Basin is rare in the world. This study focused on the pinnoite, ulexite and hydroboracite from Da Qaidam Salt Lake, through multi-index methods including mineralogy and geochemistry, aiming to interpret the mechanism of pinnoite and other borate minerals. The results showed that pinnoite as well as ulexite and hydroboracite in lakeside are formed in the lake environment with specific hydrogeochemical conditions (e.g., alkaline brine, hydrochemical types, boron concentration, boron ions, Mg/Ca ratio, dilution and mixing mechanism). The borate formation was controlled by a coupling mechanism, i.e., the inherent geochemical characteristics and the external conditions.

Fluids in High-Pressure Granulites

Properties of fluids in high-pressure granulites were studied in HP granulites (~8.7–11 kbar, ~800–900°С) and syngranulite fluid infiltration-driven HP metasomatites (~11–9 kbar, ~920–850°С) from the Lapland granulite belt of the Fennoscandian Shield. The study involved large-scale mapping of the rocks, microthermometry of mineral-hosted fluid inclusions, multiequilibrium mineral thermobarometry, and calculations of H2O activity based on mineral equilibria. The mafic pyroxene granulites and syngranulite metasomatites (quartz blastomylonites with orthopyroxene, sillimanite, and garnet; veins and vein-like bodies of orthopyroxene–garnet and diopside–scapolite rocks) contain similar assemblages of syngenetic fluid inclusions (which are hosted mostly in quartz and also in garnet, orthopyroxene, and scapolite) of contrasting chemical composition: nearly pure СО2 (distinctly predominant), brines (the dominant salts are CaCl2 and NaCl), and N2 ± H2O. These three types of inclusions coexist in the same generations of early inclusions: rarer primary (p) and predominant primary–secondary (ps). The CO2 inclusions have either high or low densities, and the N2 inclusions are of low density. The brine inclusions show a wide range of total salt contents (up to 30–35 wt%) and variable concentration proportions of the dominant salts: p-inclusions with a salinity of 20 wt% CaCl2 + 10 wt% NaCl; ps-inclusions with a salinity of 5 wt% CaCl2 + 20 wt% NaCl; p- and ps-inclusions with a salinity of 5–23 wt% NaCl eq; and p-inclusions with halite (up to 35 wt% NaCl). In general, CaCl2 is the predominant salt component in the early p- and ps-inclusions of the rocks. Considered together, currently available data (including Sr, Nd, and O isotope systems) on these rocks indicate that the external fluid flow during the origin of granulites was evidently of mantle origin. At the peak P–T parameters, the inclusions were entrapped from a heterogeneous fluid in which immiscible water–salt and CO2-rich fluids, which initially contained N2, coexisted. Data on the chemical composition and salt concentrations of the fluids, $${{a}_{{{{{\text{H}}}_{2}}{\text{O}}}}}$$ = 0.40–0.51, are compared with the theoretically predicted phase state of the fluids and the properties of the coexisting immiscible fluid phases at the estimated P–T parameters of granulite petrogenesis on the basis of numerical models in the H2O–CO2–NaCl and H2O–CO2–CaCl2 ternary systems. The location of the tie-lines and solvus were calculated to subsequently use for the thermodynamic prediction. The paper discusses similarity and the reasons for the difference between the theoretical compositions of the generated fluid phases and the composition of fluid inclusions, geochemical consequences of the heterogenization of granulite fluids (the formation of concentrated alkaline brines and a potentially acidic CO2-rich fluid phase, the values of the mass and volume fractions of these phases depending on variations in the composition of the initial homogeneous fluid, etc.). It follows that an extensive region of the compositions of aqueous fluids with different concentrations of CO2 and Na and Ca chlorides exists at the P–T parameters of HP granulites in which originally homogeneous fluid splits into compositionally contrasting fluid phases with different properties. This region of coexisting immiscible fluids significantly expands with increasing CaCl2 concentration. Hence, the lower crust at the level of the HP granulite facies may be the region where high-temperature immiscible fluids are generated. One of these fluids is a denser phase of alkaline brines, and the other is a less dense potentially acidic phase of H2O–CO2 fluids rich in CO2. Ascending along regional permeable zones, these fluid phases of deep origin can play an important role in magmatic, metamorphic, metasomatic, and ore-forming processes in the middle and upper crust.

Genesis of the Banxi Sb deposit, South China: Constraints from wall-rock geochemistry, fluid inclusion microthermometry, Rb–Sr geochronology, and H–O–S isotopes

The Banxi Sb deposit is located in the world-class central-western Hunan Sb belt in South China, with quartz-vein type Sb-only mineralization hosted by Neoproterozoic epimetamorphic clastic sedimentary rocks. In this contribution, microthermometric, Rb–Sr geochronological and H–O isotopic analyses on fluid inclusions trapped in quartz, S isotopic studies on stibnite, and major-trace elemental measurements on fluid-altered and unaltered wall-rocks are presented to constrain the genesis of the deposit. The fluid inclusions are characterized by low homogenization temperature (170–260 °C) and low salinity 3–7 wt% NaCl equiv., with a low fluid density of 0.72–0.93 g/cm3 and a pH of 5.59. The low δDw (fluid δ2H, –140‰ to –107‰) whereas positive δ18OV-SMOW (15.9–17.2‰) and δ18Ow (fluid δ18O, 5.9–8.4‰) values in quartz indicate that the mineralizing fluid was generated from the low-grade metamorphic basement rocks and received a certain input of meteoric water. The Rb–Sr isotopic compositions of quartz samples yielded an isochron age of 196 ± 4 Ma (1σ, MSWD = 0.70) for quartz-stibnite ores. A highly radiogenic 87Sr/86Sr value (0.72663–0.74002, initial 87Sr/86Sr = 0.72640) indicates that ore-forming materials are derived mainly from basement rocks, and a direct material contribution from local granitic rocks can be ruled out. The δ34SV-CDT values of stibnite range narrowly from 4.81‰ to 6.72‰ and are in the δ34SV-CDT range of the metamorphic rocks, indicating that the sulfur was sourced from the basement rocks by sulfate reduction. Compositional differences between fluid-altered (decolorized) and unaltered wall-rocks are obvious: the migrated SiO2, SO3, LREE, Hf, Nb, Zr, Ta, Th, U, Mo, Sn, W into altered wall-rocks suggests a deep basement metamorphic rocks-derived Si-rich alkaline brine for the fluid-rock interaction; while the leached Fe2O3, MgO, MnO, TiO2, Ba, Cs, Rb, As, Co, V, Ni, Sb, Sc, Cu, Pb and Zn from the altered rocks imply a material contribution of Banxi Group wall-rocks during the Sb mineralization process. Consequently, we conclude that the quartz-stibnite stage of the Banxi Sb deposit was formed during the Late Triassic orogeny in the Xuefeng Mountain region. Heated by granitic magmatism, Sb and S were leached from the basement rocks, forming an initial Si-rich and alkaline ore-bearing fluid. Precipitation of stibnite from the fluid resulted from interacting with wall-rocks and mixing of meteoric water, coupled by releasing of stress, decreasing of temperature and lowering of the pH at higher crustal levels.

Terrestrial heat flow and crustal thermal structure in the northern slope of Tazhong uplift in Tarim Basin

Considerable breakthroughs have been obtained recently in deep and ultra-deep carbonate strata of the northern slope of Tazhong uplift, which is characterized by a burial depth of more than 6300 m and is characterized by high burial temperature. However, the lack of systematic temperature research and effective temperature prediction for the ultra-deep strata in northern slope of the Tazhong has seriously restricted the petroleum exploration in the future. The continuous steady-state temperature logs and well test temperature were obtained, and the thermal conductivity were measured to analyze the current thermal state and deep thermal structure characteristics of the northern slope of Tazhong uplift. The geothermal gradient is generally between 19.4 and 28.5 ℃/km, and the geothermal heat flow is 34.3–59.2 mW/m2 with an average of 45.4 mW/m2, which is typical of low heat flow background of the Precambrian craton basin. In addition, the spatial distributions of the estimated formation temperature at the depth of 6˜8 km are also similar and are mainly controlled by the basement structural pattern. The temperature at the depth of 6000 m is 118˜172 ℃, the temperature at 7000 m is 136˜198 ℃, and the temperature at 8000 m is 190˜224 ℃. The temperature gradually increases from Shunbei to Shunnan area, but the temperature near SN4 fault zone is about 10˜20 °C higher than the surrounding rock. This thermal disturbances is possibly caused by hydrothermal fluids passing through the fracture system from the deep strata to the Ordovician strata, with hot alkaline brine from the Lower Cambrian providing heat source, and fault activities providing power and acting as channels for fluids upwelling. Furthermore, the 1-D theoretical crustal thermal structures of the Shunbei and Shunnan area were constructed by solving steady-state heat conduction equation. The results show that the thickness of the “thermal” lithosphere and the Moho temperature in Shunbei area are 177 km and 580 °C, respectively. However, the thickness of the “thermal” lithosphere in Shunnan area is relatively thin, with an average of 149 km. The heat flow distribution on the northern slope of Tazhong indicates the crustal heat flow contributes more to the surface heat flow and has the typical thermal structure characteristics of “hot crust and cold mantle” model.