Low-temperature Hydrothermal Conditions Research Articles

Vanished evaporites, halokinetic structure, and Zn-Pb mineralization in the world-class Angouran deposit, northwestern Iran

The Angouran deposit (19.3 Mt at 23.4% Zn and 4% Pb) is the second-largest Zn-Pb deposit in Iran. The deposit is hosted in a Neoproterozoic−Cambrian marble-schist sequence within a breccia pipe in a domal structure, with sulfide mineralization under low-temperature hydrothermal conditions (<200 ºC). The features of the ore-hosting breccias are similar to known halokinetic diapir breccias in the world but evaporite minerals are subtle. The common types of breccia clasts in the Angouran breccia pipe include a matrix-supported angular clast (float breccia) with highly variable sizes and orientations and exotic volcanic clasts. The volcanic clasts were derived from the underlying Miocene volcanic rocks, evidenced by the consistent petrography and zircon U-Pb ages dated at 20−19 Ma. Abundant smithsonite pseudomorphs after anhydrite and anhydrite inclusions within sphalerite and pre-ore marcasite in the breccia matrix indicate that the breccia pipe contains abundant anhydrite prior to the Zn-Pb mineralization. The enrichment of evaporite is also supported by the occurrence of considerable double-terminated quartz crystals that contain spherical and tabular carbonate inclusions and anomalously high Li, Na, and K concentrations, relatively high B concentration, and high δ18O values (up to 28.3‰). These observations suggest the Angouran deposit formed in a former halokinetic diapir breccia pipe. The halokinetic diapirism was possibly triggered by thrust loading of the marble-schist sequence over the Miocene evaporite beds during the Arabia-Eurasia continental collision. Halokinetic structures elsewhere in the Angouran region warrant this consideration. Most of the evaporite minerals in the breccia pipe were dissolved and replaced before and/or during subsequent Zn-Pb sulfide and smithsonite mineralization events. This study provides a good example for the identification of vanished evaporites, halokinetic structure, and associated Mississippi Valley-type mineralization.

Genesis of ferromanganese nodules associated with mud volcanoes in the southeastern Dongsha waters of the northern South China Sea: Implications for regional deep Mesozoic hydrocarbon prospects

The Dongsha waters of the South China Sea are the location of thick Mesozoic deposits and many mud volcanoes that suggest hydrocarbon accumulation. Knowledge of the mechanism, fluid source and evolution of these mud volcanoes, however, remains inadequate. Ferromanganese nodules have been sampled from several deep-water mud volcanoes in waters around Southeast Dongsha island and provide a unique opportunity to study the fluid origin and evolution of the mud volcanoes in the area. In this contribution, the petrology, geochemistry and C–O isotopes of fluid inclusions in the nodules have been analyzed. The ferromanganese nodules are composed of distinct black Fe–Mn crust layers and light-yellow nucleus that contain quartz that hosts fluid inclusions. The outermost layers mainly consist of iron manganese minerals with high Mn/Fe ratios (0.9∼1.57), whereas the nucleus are dominated by siliceous debris. Positive Ce anomalies (δCe: 1.45∼2.13) and negative Y anomalies in growth layers indicate an anoxic environment, which is conducive to hydromanganite precipitation. In contrast, negative Ce anomalies (δCe: 0.27∼0.96) and positive Y anomalies in the nucleus suggest oxidized conditions. The absence of obvious Eu anomalies may be related to low-temperature hydrothermal conditions. The nucleus is enriched in δ13C (−2.59∼1.09‰) and weakly depleted in δ18O (−4.94∼0.89‰), whereas the growth layers are strongly depleted both in δ13C (−16.94∼–12.57‰) and δ18O (−23.05∼–17.48‰). These values indicate that carbon in the nucleus is mainly inorganic carbon from volcanism, whereas the carbon in the growth layers is related to the leakage of deep old hydrocarbon. The fluid inclusions in the quartz from the nucleus show records of at least two periods of CO2-rich hydrothermal activity and an origin from deep Mesozoic strata before release by mud volcanism. Given the widespread mud volcanism, the quartz from the nucleus may come from debris carried by mud volcano eruptions; the quartz also experienced diagenesis related with micro-organisms. The growth layers are considered to be hydrogenic and affected by the leakage of mature thermogenic hydrocarbons from deep old strata. These findings provide insights into deep mature hydrocarbon sources and thermogenic activity and improve understanding of mud volcanism and deep oil and gas resources in the southeastern Dongsha waters.

CuSeO4 and Cu(SeO3OH)2·6H2O, two novel copper–selenium(VI) oxysalts

The two new copper(II) salts Cu(SeO4) and Cu(SeO3OH)2·6H2O were synthesized at low-temperature hydrothermal conditions (220 °C), and room temperature, respectively. Their atomic arrangements were studied based on single-crystal X-ray investigations [P21/n, a = 4.823(1), b = 8.957(2), c = 6.953(1) Å, β = 94.82(1)°, Z = 4; $$P{\overline 1}$$ , a = 6.133(1), b = 6.303(1), c = 8.648(2) Å, α = 70.45(1), β = 84.60(1), γ = 73.44(1)°, Z = 1]. Cu(SeO4) adopts the MnAsO4 structure type. It exhibits structural as well as topological relations with two formerly known isochemical compounds. They crystallize in the structure type ZnSO4 (mineral name zincosite, Pnma) respectively NiSO4 (Cmcm). The two minerals dravertite, CuMg(SO4)2, and hermannjahnite, CuZn(SO4)2, are isotypic with CuSeO4-P21/n; interestingly, also α-NaCu(PO4) belongs to this structure type: some rotation of the XO4 group allows a supplementary position for the Na atom. — Cu(SeO3OH)2·6H2O represents a new structure type. The protonated selenate group shows an extended Se—Oh bond distance (1.695 Å) as compared to the other Se—O bonds (1.614 to 1.626 Å). One OH dipole of the three independent H2O molecules represents a rather free hydrogen bond. For the other H atoms, the O—H···O lengths vary from 2.585 to 2.799 Å. Interestingly, the distance Ow7···Ow7 of only 2.791 Å does not represent an edge in a coordination polyhedron and it is not preliminary involved in the hydrogen bond scheme. All Cu2+ ions in the two title compounds are in a pronounced [4 + 2] coordination. The Cu2+[4+2] atoms in Cu(SeO4) are linked to chains along [100]; in Cu(SeO3OH)2·6H2O they are not connected among each other.

Lamellar Hierarchical Porous Carbon Prepared from Coal Tar Pitch through a Lamellar Hard Template Combined with the Precarbonization and Activation Method for Supercapacitors

The lamellar porous carbon favors the diffusion and penetration of electrolyte ions and presents a fantastic advantage as an energy storage electrode material. In this work, the lamellar Mg5(OH)4(CO3)2·4H2O template is synthesized via a simple precipitation method in the low-temperature hydrothermal condition. Lamellar hierarchical porous carbon (LHPC) is successfully synthesized through the Mg5(OH)4(CO3)2·4H2O hard template and the KOH activation method using coal tar pitch (CTP) as the carbon source. The effects of activation temperature and activator dosage on the morphology, microstructure, and supercapacitor performance are researched at length. LHPCs-1–700 displays a good lamellar structure and an abundant mesoporous structure, so as to exhibit superior capacitive performance compared with other carbon electrodes. The specific capacitance for LHPCs-1–700 reaches 298 F g–1 at 1 A g–1 and still maintains 234 F g–1 at 50 A g–1 with a high capacitance retention of 78.5% in the three-electrode system. The kinetic behavior of the LHPCs-1–700 electrode was also analyzed according to the CV data obtained at different scan rates, and it was found that the fast kinetic capacitance contribution was up to 87% at 200 mV s–1. The assembled LHPCs-1–700 symmetric supercapacitor delivered an energy density of 16.73 W h kg–1 with a power density of 859.4 W kg–1 in 1 M Na2SO4 solution. Besides, the specific capacitance retention rate could still reach 95.8% after 8000 cycles.

Targeted Crystallization of Rare Earth Carbonate Polymorphs at Hydrothermal Conditions via Mineral Replacement Reactions.

The interaction between rare earth element (REE)-rich (La, Pr, Nd, Dy) aqueous solutions, dolomite (CaMg(CO3)2), and aragonite (CaCO3) at low temperature hydrothermal conditions (25-220°C) is studied. The experiments result in the solvent-mediated surface precipitation and subsequent pseudomorphic mineral replacement of the dolomite and aragonite seeds by newly formed REE-carbonates. The host grains are replaced from periphery inward. The newly formed REE-bearing carbonates in La-, Pr-, and Nd-doped systems follow the crystallization sequence: lanthanite [REE2(CO3)3·8H2O] → kozoite [orthorhombic REECO3(OH)] → hydroxylbastnasite [hexagonal REECO3(OH)]. The interaction of Dy-bearing solutions with dolomite results only in the crystallization of kozoite [orthorhombic DyCO3(OH)]. However, experiments with aragonite reveal a two-step crystallization pathway: tengerite [Dy2(CO3)3·2-3(H2O)] → kozoite [orthorhombic DyCO3(OH)]. The temperature, the dissolution rate of the host mineral, and the ionic radii of the REE3+ in question are found to control the kinetics of the replacement reaction, the polymorph selection, and the crystallization pathways toward bastnasite. The findings allow to gain a more in-depth understanding of the formation REE-bearing carbonates, particularly the mineral bastnasite, which is the main source of REEs for industry. This knowledge can be used to improve REE separation, exploration, exploitation methods, as well to produce carbonate minerals with tailored structures.

A Low-Temperature Hydrothermal Synthesis of Prussian Blue Nanocrystal and Its Application in H2O2 Detection

Uniform Prussian blue Fe3[Fe(CN)6]2 nanocrystals were synthesized by a direct dissociation and reduction of the single-Fe(III)-source precursor K3Fe(CN)6 under low-temperature hydrothermal conditions. UV-visible absorption spectrum, Fourier transform infrared spectrum, X-ray diffraction, field emission scanning electron microscope, X-ray photoelectron spectra, high-resolution transmission electron microscopy, and electrochemical testing were used to characterize and verify the synthesized Prussian blue nanocrystal product. The size of the synthesized product had a strong dependence on the acidity condition and the concentration of K3Fe(CN)6 solution. This result may facilitate not only the exploration of preparing Fe3[Fe(CN)6]2 nanocrystals for particular applications but also an in-depth explanation of the nature of the hydrothermal reaction. The Prussian blue nanocrystals were deposited onto an electrode support through lyotropic liquid crystalline templates to detect hydrogen peroxide (H2O2) by reduction reaction. Cyclic voltammograms showed that the Prussian blue modified electrode was of excellent electrocatalytic activity for H2O2. This electrode demonstrated a detection limit (1 × 10−7 M) and a linear range starting from the detection limit and extending over 6 orders of magnitude of H2O2 concentrations (1 × 10−7 to 1 × 10−1 M), which was of excellent performance in detecting H2O2.

Coarse calcite grains in hydrocarbon-rich tuffaceous mudstone in a Permian volcanic lake—An indicator for subaqueous volcanic deposition and related hydrocarbon generation

Sediments originated from volcanic-hydrothermal activities show clear relationship with hydrocarbon generation and accumulation in fine-grained sedimentary rocks at a regional scale. However, the fundamental processes and mechanisms of this relationship are still poorly understood at a microscopic scale to hamper efficient hydrocarbon exploration. In addition, coarse grains common in volcanic lacustrine fine-grained sediments have been traditionally interpreted as diagenetic products during early and late burial. Our study, however, suggests that coarse calcite grains are not diagenetic, but formed by subaqueous explosion. The calcite grains occur in lacustrine fine-grained sedimentary rocks in the middle Permian Lucaogou Formation in the Santanghu intracontinental rift basin, NW China. They are sand sized, angular, mono- and polycrystalline, and discretely scatter in silt to clay-sized non-calcite pyroclastic matrix. The calcite grains and the mud matrix are interpreted as a pyroclastic debris flow deposit. In-situ 87Sr/86Sr ratios (0.704932–0.705840, and 0.705137 on average) of the calcite grains are similar to those of mantle rocks, indicating an origin closely related to mantle-derived fluids. The in-situ δ13C values (4.24‰ to 5.06‰, and 4.57‰ on average) and extremly negative δ18O values (−21.70‰ to −21.18‰, and − 21.49‰ on average) indicate that extensive hydrothermal alteration and microbial activities influenced the formation of the calcite. Element composition and homogenizaiton temperature of fluid incusions of calcite and biomarkers of the mudstone all suggest a relatively low-temperature hydrothermal condition in a saline and reducing environment. Furthermore, hydrocarbon-rich inclusions are rich in the calcite grains and have two modes of occurrence and maturity. They indicate that the organic matter was generated from algae bloom, which was caused by volcanic-hydrothermal activities. Alternatively, the hydrocarbon may have an inorganic origin originated from a mantle source. Our findings provide an alternative interpretation on the origin of coarse calcite grains in fine-grained sedimentary rocks and demonstrate a microscopic relationship between volcanic-hydrothermal activities and hydrocarbon generation and accumulation in a tectonic active rift basin.

Polytypism in mcalpineite: a study of natural and synthetic Cu3TeO6.

Synthetic and naturally occurring forms of tricopper orthotellurate, CuII3TeVIO6 (the mineral mcalpineite) have been investigated by 3D electron diffraction (3D ED), X-ray powder diffraction (XRPD), Raman and infrared (IR) spectroscopic measurements. As a result of the diffraction analyses, CuII3TeVIO6 is shown to occur in two polytypes. The higher-symmetric CuII3TeVIO6-1C polytype is cubic, space group Ia3, with a = 9.537 (1) Å and V = 867.4 (3) Å3 as reported in previous studies. The 1C polytype is a well characterized structure consisting of alternating layers of CuIIO6 octahedra and both CuIIO6 and TeVIO6 octahedra in a patchwork arrangement. The structure of the lower-symmetric orthorhombic CuII3TeVIO6-2O polytype was determined for the first time in this study by 3D ED and verified by Rietveld refinement. The 2O polytype crystallizes in space group Pcca, with a = 9.745 (3) Å, b = 9.749 (2) Å, c = 9.771 (2) Å and V = 928.3 (4) Å3. High-precision XRPD data were also collected on CuII3TeVIO6-2O to verify the lower-symmetric structure by performing a Rietveld refinement. The resultant structure is identical to that determined by 3D ED, with unit-cell parameters a = 9.56157 (19) Å, b = 9.55853 (11) Å, c = 9.62891 (15) Å and V = 880.03 (2) Å3. The lower symmetry of the 2O polytype is a consequence of a different cation ordering arrangement, which involves the movement of every second CuIIO6 and TeVIO6 octahedral layer by (1/4, 1/4, 0), leading to an offset of TeVIO6 and CuIIO6 octahedra in every second layer giving an ABAB* stacking arrangement. Syntheses of CuII3TeVIO6 showed that low-temperature (473 K) hydrothermal conditions generally produce the 2O polytype. XRPD measurements in combination with Raman spectroscopic analysis showed that most natural mcalpineite is the orthorhombic 2O polytype. Both XRPD and Raman spectroscopy measurements may be used to differentiate between the two polytypes of CuII3TeVIO6. In Raman spectroscopy, CuII3TeVIO6-1C has a single strong band around 730 cm-1, whereas CuII3TeVIO6-2O shows a broad double maximum with bands centred around 692 and 742 cm-1.

Experimental chondrite–water reactions under reducing and low-temperature hydrothermal conditions: Implications for incipient aqueous alteration in planetesimals

The presence of hydrous minerals in carbonaceous chondrites has been considered important evidence for the former presence of liquid water in parent asteroids. However, the evolution of water–rock reactions in hydrous asteroids remains not well constrained. Here, we conduct water–rock type experiments and chemical equilibria calculations under low-temperature hydrothermal and reducing conditions to investigate the alteration process and secondary mineral assemblages of chondritic rock in the earliest alteration stage. Using synthetic chondrite (mixtures of olivine (forsterite95), orthopyroxene (enstatite95), silicate glass, troilite and Femetal) as a starting material, our experiments were conducted at temperatures of 25 °C–80 °C for time periods between 1 and 460 days at a water-to-rock mass ratio of 10. A combination of X-ray diffraction (XRD) and transmission electron microscope (TEM) analyses revealed that the primary secondary phases consisted of pyrrhotite, an amorphous SiO2-rich phase and saponite at 80 °C, while the secondary phase consisted of an amorphous SiO2-rich phase and saponite at 25 °C. At both temperatures, the SiO2-rich phases and saponite densely covered the surface of the primary phases. The Fe/Mg ratios of saponite and amorphous SiO2-rich phases showed clear difference between 80 °C and 25 °C. Saponite that was formed at 80 °C was richer in Fe than the initial silicate phases, and the highest Fe/Mg ratios were obtained in the saponite encrusting the troilite and Femetal. These results suggest that the Fe distributed from the troilite and Femetal induced the formation of Fe-rich saponite. Some of the secondary minerals observed from our alteration experiments were consistent with those expected by chemical equilibria calculations. However, the formation of serpentine, the dominant secondary mineral expected from chemical equilibria calculations, was not observed in our experiments up to 460 days, probably because the preferential dissolution of SiO2-rich silicate glass in the earliest stage of alteration induced the formation of saponite rather than serpentine. The secondary mineral assemblage and its morphological characteristics, as observed by our alteration experiments, showed similarities with carbonaceous chondrites such as CM2 and CO3 chondrites. This alteration might be explained by water–rock reactions at low temperatures and by the short time alteration. These findings better constrain the temperatures and timescales of aqueous alterations in hydrous asteroids, as well as the role of water in the early solar system bodies.

Hydrothermal cerium oxide in manganese-oxide-cemented breccia, Quadrilátero Ferrífero of Minas Gerais, Brazil

Cerium (Ce) oxide has been found in Mn-oxide-cemented breccia in the Quadrilátero Ferrífero of Minas Gerais, and identified as cerianite-(Ce) on the basis of backscattered-electron imaging and energy-dispersive spectrometry. The Ce oxide compound occurs as nano- to microscale crystals that are dispersed within, or locally concentrated along, colloform bands of cryptomelane, and in open spaces. The breccia shows a prominent positive anomaly of Ce and has enrichment of Mn, Cd and Hg. The occurrence of abundant cryptomelane, a mineral typically formed under near-surface conditions, and its colloform bands that cement angular fragments of vein quartz suggest that Ce oxide directly precipitated as colloidal particles by supersaturation under low-temperature hydrothermal conditions that followed seismic rupturing. This scenario is remarkable because little is known about natural Ce oxide of hydrothermal origin.

Rare earth element uptake during olivine/water hydrothermal interaction

Ultramafic-hosted hydrothermal vent systems link the hydrosphere with the peridotitic mantle via serpentinization. Here, the fractionation and mobility of selected trace (Nd, Sm, Gd, Dy, Yb, Sr and Ba) and major cations (Si, Ca, Mg, Fe, Ni) during seawater-peridotite interaction was investigated through a series of experiments where natural olivine grains were reacted with an artificial seawater solution at a range of temperatures (15–90 °C) and grain size distributions. No evidence for any significant olivine dissolution or precipitation of carbonate and, Fe-oxy-hydroxide phases was observed in these experiments. Experimental data show a strong decoupling of REE (Nd, Sm, Gd, Dy, and Yb) from Sr and Ba under all experimental conditions, with Sr and Ba remaining quantitatively in solution. The REE were removed from the solution and were adsorbed onto olivine surface with kinetic rate constants (i.e. uptake over time) that increase with increasing temperature and increasing surface area (i.e. decreasing particle size). Dysprosium and Yb (heavy REE; HREE) were removed from solution with a faster rate than Nd and Sm (light REE; LREE). Gadolinium is decoupled from this trend, with a slower kinetic rate constant than Sm. The activation energies (Ea) of REE adsorption on olivine were higher for Nd and Sm than Dy and Yb. This suggests that the adsorbance of LREE is generally more dependent on temperature than the HREE. The Ea correlates well with the summed 1st, 2nd and 3rd ionization energies of REE suggesting a link between kinetic rates of element adsorption and electron configuration of the 4f-orbitals. Gadolinium has higher Ea than the other analyzed REE, consistent with the electron configuration of Gd3+ where all 4f-orbitals are filled with one electron each. These experimental data suggest that REE are adsorbed on the surface of olivine via inner sphere complexes under low-temperature hydrothermal conditions, when alteration processes are limited or extremely slow. Scavenging and fractionation of REE may occur within the recharge zone of peridotite-hosted hydrothermal systems at relatively low temperatures (<100 °C), leading to fluids with progressively higher LREE/HREE which could impose seawater-derived LREE enrichments in serpentinized peridotites during high temperature, high pressure water/rock interaction deeper in the oceanic lithosphere.

Pressure-Leaching Behavior of Nickel from Ni–Mo Ore in Aqueous Oxygenated Media

AbstractNi–Mo ore is a multi-metal complex and unique mineral resource that exists as a black shale. This ore contains more than 4 wt% Mo and at least 2 wt% Ni. Economic value is associated with deriving products from Ni–Mo ore that contains amorphous colloidal sulfides and that is highly active. Under low-temperature hydrothermal conditions (water at 120 °C or more) and in excess oxygen, amorphous sulfides are oxidized easily to metal-sulfate forms, which leads to nickel and molybdenum dissolution. In this study, the effects of agitation speed, temperature, oxygen partial pressure and particle size on the rate of nickel leaching were investigated. The leaching rate was nearly independent of agitation speed above 400 rpm and increased with a decrease in particle size. A temperature increase to 150 °C contributed significantly to the nickel leaching rate. Oxygen pressure influences nickel leaching, with an oxygen pressure of between 0.5 MPa and 0.7 MPa providing the greatest effect. The pressure-leaching behavior of nickel was fitted to a shrinking-core kinetic model. The mathematical analyses indicates that the dissolution process is chemical-reaction controlled during early dissolution, with an activation energy of 42.68 kJ/mol, and the reaction order with respect to the oxygen partial pressure was 0.79. Up to nearly 70 % nickel was dissolved into solution, and product layers of molybdenum and iron oxide were formed on the surface of the Ni–Mo ore particles, which prevented further nickel dissolution. Thereafter, nickel leaching was controlled by liquid-film diffusion, with an activation energy of 11.01 kJ/mol.

Iron Vacancies Accommodate Uranyl Incorporation into Hematite.

Radiotoxic uranium contamination in natural systems and nuclear waste containment can be sequestered by incorporation into naturally abundant iron (oxyhydr)oxides such as hematite (α-Fe2O3) during mineral growth. The stability and properties of the resulting uranium-doped material are impacted by the local coordination environment of incorporated uranium. While measurements of uranium coordination in hematite have been attempted using extended X-ray absorption fine structure (EXAFS) analysis, traditional shell-by-shell EXAFS fitting yields ambiguous results. We used hybrid functional ab initio molecular dynamics (AIMD) simulations for various defect configurations to generate synthetic EXAFS spectra which were combined with adsorbed uranyl spectra to fit experimental U L3-edge EXAFS for U6+-doped hematite. We discovered that the hematite crystal structure accommodates a trans-dioxo uranyl-like configuration for U6+ that substitutes for structural Fe3+, which requires two partially protonated Fe vacancies situated at opposing corner-sharing sites. Surprisingly, the best match to experiment included significant proportions of vacancy configurations other than the minimum-energy configuration, pointing to the importance of incorporation mechanisms and kinetics in determining the state of an impurity incorporated into a host phase under low temperature hydrothermal conditions.

Variation of the chemical composition of sediments under middle- and low-temperature hydrothermal conditions in the southern trough of Guaymas Basin, Gulf of California: Communication 2. Results of the study of grain size fractions of sediments

The chemical composition of grain size fractions of the Upper Pleistocene sediments in the southern trough of Guaymas Basin (Gulf of California) is studied based on materials from DSDP Hole 477 (191 m). The sediments are located in the upper part of the main long-lived hydrothermal system. Therefore, they were subjected to long-term reworking by the middle- and low-temperature solutions (100‒300°C) and short-term hydrothermal impact during the intrusion of basalt sills. The upper part of the main hydrothermal system is divided into three middle- to low-temperature hydrothermal alteration zones: lower (III), middle (II), and upper (I). In zone III (250‒300°C), hydrothermal alterations of sediments are most significant. The coarsegrained fractions are enriched in Fe, S, Ni, Cu, Zn, Mo, Co, Se, Cd, Bi, Pb, and Ag due to the formation of sulfides and precipitation of native metals. The silt fractions are enriched in Be, Sc, Nb, Ta, W, Th, U, Y, and REE. In contrast, the pelite fractions are depleted in most of these elements. The fine-dispersed (<0.001 mm) pelite fractions are appreciably enriched in Mg (due to the formation of the authigenic Mg-chlorite), as well as MnO, Cr, V, Ga, Pb, and Zr. Virtually all grain size fractions are depleted in K2O, Li, Rb, Cs, and Tl due to the dissolution of the K-bearing terrigenous minerals. In zones II (146‒170 m) and I (110‒146 m), where the temperature of hydrothermal solutions dropped successively from 250 to 180‒195 and 100°C, the sedimentary environment was unfavorable for the concentration of Fe, S, and a large group of ore elements that are typical for sediments in zone III. Intrusion of basalt sills and a short-term hydrothermal impact changed concentrations of several components in the sediments overlying the sill complex: CaO, K2O, Li, Rb, Cs, and Tl acquired a trend typical of the high-temperature lower zone III, whereas Fe, MgO, P2O5, TiO2, V, Sc, and Y distribution pattern became typical of the low-temperature upper zone I. Significant compositional variations in the grain size fractions of sediments are lacking beneath the sill base.

Variation of the chemical composition of sediments under middle- and low-temperature hydrothermal conditions in the southern trough of Guaymas Basin, Gulf of California: Communication 1. results of the study of bulk sediment samples

The paper presents the results of the study of variations in the content of macro- and microelements (rare earth elements included) in the Upper Pleistocene sediments from DSDP Hole 477. The variations took place at the depth interval 110–191 m in the course of temperature drop to about 100°C in the upper part of the hydrothermal system. Variations in the content of most chemical elements in sediments from DSDP Hole 477 are manifested more weakly than in the underlying sediments of the interval 191–267 m of DSDP Hole 477A that were altered at a temperature of about 300°C. For many chemical elements, influence of the sedimentary cover on the compositional transformation of solutions during their interaction with sediments attenuates with the cooling of its upper part to the point of its complete termination.

Astrobiological implications of dim light phototrophy in deep-sea red clays

Red clays of Central Indian Basin (CIB) under influence of trace of Rodriguez Triple Junction exhibited chemoautotrophy, low temperature hydrothermal alterations and photoautotrophic potential. Seamount flank TVBC-08, hosting such signatures revealed dominance of aerobic anoxygenic phototroph Erythrobacter, with 93% of total 454 pyrosequencing tags. Subsequently, enrichments for both aerobic (Erythrobacter) and anaerobic anoxygenic phototrophs (green and purple sulphur bacteria) under red and white LED light illumination, with average irradiance 30.66Wm−2, were attempted for three red-clay sediment cores. Successful enrichments were obtained after incubation for c.a. 120 days at 4°± 2 °C and 25°± 2 °C, representing ambient psychrophilic and low temperature hydrothermal alteration conditions respectively. During hydrothermal cooling, a microbial succession from anaerobic chemolithotrophy to oxygenic photoautotrophy through anaerobic/aerobic anoxygenic phototrophic microbes is indicated. Spectral absorbance patterns of the methanol extracted cell pellets showed peaks corresponding to metal sulphide precipitations, the Soret band of chlorosome absorbance by photosystem II and absence of peaks at Qy transition band. Dendritic nano-structures of metal sulphides are common in these sediments and are comparable with other sulphidic paleo-marine Martian analogues. Significant blue and redshifts have been observed for the experimental samples relative to the un-inoculated medium. These observations indicate the propensity of metal-sulphide deposits contributing to chemiluminiscence supporting the growth of phototrophs at least partially, in the otherwise dark abyss. The effects of other geothermal heat and light sources are also under further consideration. The potential of phototrophic microbial cells to exhibit Doppler shift in absorbance patterns is significant towards understanding planetary microbial habitability. Planetary desiccation could considerably influence Doppler effects and consequently spectral detection techniques exo-planetary microbial life.

A single-crystal X-ray and Raman spectroscopic study of hydrothermally synthesized arsenates and vanadates with the descloizite and adelite structure types

Studying the reason for the formation of two structural sub-types, seven arsenate and vanadate compounds of descloizite and adelite groups [specifically ( 1 ) CdCo(OH)(AsO 4 ), ( 2 ) CdCu(OH)(AsO 4 ), ( 3 ) SrCo(OH)(AsO 4 ), ( 4 ) SrZn(OH)(AsO 4 ), ( 5 ) SrCu(OH)(VO 4 ), ( 6 ) CdCo(OH)(VO 4 ), and ( 7 ) CdCu(OH)(VO 4 ) (bold numbers throughout paper refer to these compounds)] were synthesized under low-temperature hydrothermal conditions. 1 – 2 and 6 – 7 are isostructural with descloizite, and 3 – 5 are with adelite-group minerals and several synthetic compounds. Together with a sample of conichalcite, (8) CaCu(OH)(AsO 4 ), they were investigated using single-crystal X-ray diffraction [ R ( F ) = 0.0153–0.0283 for 1 – 5 and 8 ; for 6 and 7 , R ( F ) = 0.0603 and 0.0444, respectively] and Raman spectroscopy. Although crystallizing in different orthorhombic space groups, the atomic arrangements of descloizite-( Pnam ) and adelite-( P 2 1 2 1 2 1 ) type compounds adopt the same topology: the atomic arrangement is characterized by M 2O 6 octahedrons ( M 2 = Mg 2+ , Al 3+ , Mn 2+,3+ , Fe 2+ , Co 2+ , Ni 2+ , Cu 2+ , Zn 2+ ) edge-linked into chains. These chains are interconnected by X O 4 tetrahedrons ( X = Si 4+ , P 5+ , V 5+ , As 5+ , Mo 6+ ) into a three-dimensional framework. Cavities host M 1 atoms ( M 1 = Na + , Ca 2+ , Cd 2+ , Hg 2+ , Pb 2+ ); their coordination varies from 7 for descloizite-type representatives to 8 for adelite-type structures. The OH stretching frequencies in the Raman spectra are in good agreement with the observed O–H···O donor-acceptor distances. A detailed discussion of the crystal chemistry of these compounds and their influence on the space-group symmetry indicate a distinct dependence of the structural changes on the average ionic radii ( r M 1 + r X )/2.

Paired stable isotopes (O, C) and clumped isotope thermometry of magnesite and silica veins in the New Caledonia Peridotite Nappe

The stable isotope compositions of veins provide information on the conditions of fluid–rock interaction and on the origin of fluids and temperatures. In New Caledonia, magnesite and silica veins occur throughout the Peridotite Nappe. In this work, we present stable isotope and clumped isotope data in order to constrain the conditions of fluid circulation and the relationship between fluid circulation and nickel ore-forming laterization focusing on the Koniambo Massif. For magnesite veins occurring at the base of the nappe, the high δ18O values between 27.8‰ and 29.5‰ attest to a low temperature formation. Clumped isotope analyses on magnesite give temperatures between 26°C and 42°C that are consistent with amorphous silica–magnesite oxygen isotope equilibrium. The meteoric origin of the fluid is indicated by calculated δ18Owater values between −3.4‰ to +1.5‰. Amorphous silica associated with magnesite or occurring in the coarse saprolite level displays a narrow range of δ18O values between 29.7‰ and 35.3‰. For quartz veins occurring at the top of the bedrock and at the saprolite level, commonly in association with Ni-talc-like minerals, the δ18O values are lower, between 21.8‰ and 29.0‰ and suggest low-temperature hydrothermal conditions (∼40–95°C). Thermal equilibration of the fluid along the geothermic gradient before upward flow through the nappe and/or influence of exothermic reactions of serpentinization could be the source(s) of heat needed to form quartz veins under such conditions.

Monazite Alteration in H2O ± HCl ± NaCl ± CaCl2 Fluids at 150 ºC and psat: Implications for Uranium Deposits

Spectacular alteration of monazite by diagenetic/hydrothermal brines is well documented in some Proterozoic sedimentary basins in close relationship with high-grade uranium (U) deposits. Hence, monazite has been proposed as a viable source for some U deposits. However, monazite alteration remains enigmatic with regard to its high stability in relatively low temperature hydrothermal conditions. Here, the results of batch experiments in which 10 mg of natural monazite grains were reacted with 15 mL of Na-Ca-Cl (6 molal Cl) solutions as well as in pure water at 150 oC and saturated vapor pressure (psat) for one and six months are reported. The influence of pH (pH = 1, 3, 7) and relative molar proportions of Na and Ca (Na/(Na + Ca) = 0, 0.5, 1), were tested. Discrete alteration features (etch pits and roughened surfaces) appear in a minority of the one month experiments and are more developed in the six months experiments, especially at pH = 1 and 3. Although spectacular alteration of monazite, as seen around U deposits, could not be reproduced here, this study shows that monazite is unstable in the presence of fluids analogous to acidic deep basinal brines.

Three new alluaudite-like protonated arsenates: NaMg3(AsO4)(AsO3OH)2, NaZn3(AsO4)(AsO3OH)2 and Na(Na0.6Zn0.4)Zn2(H0.6AsO4)(AsO3OH)2

Three new arsenates, NaMg 3 (AsO 4 )(AsO 3 OH) 2 ( 1 ), NaZn 3 (AsO 4 )(AsO 3 OH) 2 ( 2 ) and Na(Na 0.6 Zn 0.4 )Zn 2 (H 0.6 AsO 4 ) (AsO 3 OH) 2 ( 3 ), were synthesised under low-temperature hydrothermal conditions. 1 is the first example of a synthetic hydrous Na-Mg arsenate, and 2 and 3 are the first synthetic hydrous Na-Zn arsenates with octahedrally coordinated Zn atoms. They are all isostructural with the protonated members of the alluaudite-supergroup compounds; 2 is synthetic end-member of o’danielite. Their crystal structures were determined from the single-crystal X-ray diffraction data collected at 293 K [space group C 2/ c , a = 11.972(2)/12.023(2)/12.458(3), b = 12.367(3)/12.385(3)/12.484(3), c = 6.743(2)/6.750(2)/6.839(2) A, β 112.67(3)/112.79(3)/113.83(3)°, V = 921.3(4)/926.7(4)/973.0(4) A 3 , Z = 4, for 1 , 2 , and 3 respectively]. The crystal structures consist of chains of edge-sharing M 1O 4 (OH) 2 and M 2O 6 octahedra ( M 1, M 2 = Mg for 1 , M 1, M 2 = Zn for 2 , and M 1 = Na, Zn, M 2 = Zn for 3) stacked parallel to (101) and connected by the AsO 4 tetrahedra. These chains form two types of channels parallel to the c -axis. While hydrogen atoms of the OH groups are situated in the channels of the first type, Na atoms are located in the second-type channels. Infrared and single-crystal Raman spectra were measured and evaluated in order to obtain further information on the anion groups and especially on the short hydrogen bonds. The OH stretching frequency is in good agreement with the observed O⋯O distances. Furthermore, the crystal chemistry of synthetic alluaudite-like arsenates is discussed in terms of structure distortion and measure of similarity among them.