Low-temperature Hydrothermal Fluids Research Articles

Petrology, mineralogy and geochemistry of the Lower Cretaceous oil-prone coal and host rocks from the Laoheishan Basin, northeast China

The coal and host rocks (mainly oil shale partings) in the Laoheishan basin (NE China) are oil-prone. This study uses petrological, mineralogical and geochemical analyses to determine the reasons of high oil yield in the coal, and the origin and modes of occurrence of the minerals and elements in the coal and oil shale partings. The obtained data show that this sub-bituminous B coal has higher oil yield (av. 10%) than oil shale partings (av. 5.7%), consistent with a higher hydrogen content in the coal. This oil-prone coal has potential for comprehensive utilization due to the relatively high gross calorific value (av. 17.23 MJ/kg) in the semi-coke. The maceral composition suggests that the relatively high hydrogen content in the coal is mainly caused by higher resinite content. Palynological analysis of coal and oil shale partings mainly proved the presence of gymnosperms and ferns, revealing that the paleovegetation is dominated by lygodiacean-/osmundacean ground ferns and cupressaceaen/taxodiaceaen canopy trees, these canopy trees would have provided abundant hydrogen rich components (e.g. resin) to the paleomire. All the identified sporopollen suggests a warm-humid subtropical paleoclimate.Minerals in the coal include kaolinite, quartz, illite (and/or illite/smectite), chlorite, feldspar, calcite, and traces of pyrite, rutile and zircon, similar to the oil shale partings. Most of the minerals (quartz, feldspar, clay minerals, rutile and zircon) occur in layers within detrovitrinite and probably are of detrital origin. Pyrite and calcite are of epigenetic origin and probably derived from hydrothermal fluids. Compared with average Chinese coal, the Laoheishan coal is enriched in Zr, Nb, In and Sb. Zirconium and Nb mainly occur in zircon. Indium is both organically and inorganically associated, whereas antimony largely occurs in pyrite. REY (rare earth elements and yttrium) distribution patterns of coals and oil shale partings are dominated by Heavy-REY enrichment, whereas roof and floor samples are Medium-REY enriched. The M-HREY enrichment is probably caused by low-temperature hydrothermal fluids. The sedimentary input is the major controlling factor of geochemical patterns in coal and host rocks. The source rocks are probably felsic-intermediate igneous rocks from the surrounding basement, as indicated by relatively high Al2O3/TiO2 ratios (7–38), cross-plot between Zr/Ti and Nb/Y, negative Eu anomalies (0.28–0.96), the presence of K-feldspar and plagioclase, and lithic fragment types (such as granite and andesite) in the samples. In addition, source rocks of sediments have caused high Zr and Nb concentrations in the coal.

Petrography and trace element signatures of iron-oxides in deposits from the Middleback Ranges, South Australia: From banded iron formation to ore

The Middleback Ranges is a major iron ore belt in the southeastern region of the Gawler Craton, South Australia, interpreted to be of BIF origin. Iron ore deposits are hosted within ∼2550 Ma metasedimentary rocks of the Middleback Group and occur as a series of N-S trending hills, forming a ∼60 km-long magnetic anomaly. A petrographic-geochemical study of iron-oxides from BIFs and iron ores was undertaken on samples from thirteen locations spanning the strike of the belt. Iron-oxides are texturally diverse due to multiple processes accompanying and postdating ore formation. Primary magnetite features preserved in the southern segment of the belt display distinct overprinting features (e.g., increased porosity, reworked grain boundaries) and multiple generations of growth associated with deposition of trace minerals, including native gold. Northwards along strike, this overprint is expressed by the pseudomorphic replacement of magnetite by hematite (martite) and is locally associated with brecciation, the presence of rare earth element (REE)-minerals, and replacement by iron-hydroxides. Whereas evidence of microplaty hematite accompanying martitization and predating iron-hydroxides is observed throughout the belt, distinct iron-oxide generations postdating the iron-hydroxides are inferred based on compositional zoning with respect to Si and intimate relationships between iron-oxides and -hydroxides. Chondrite-normalized fractionation trends obtained from the various iron-oxides and from different BIF types generally display LREE-enrichment and distinct positive Eu- and Y-anomalies. An increasing ΣREY- and LREE-trend accompanies martitization. The presence of specific element groups, e.g., granitophile elements (U, W, Sn, Mo), or transition metals (Cr, Mn, Co, Ni, Ti, V, Nb) within the lattice of iron-oxides suggests their formation in evolving environments associated with the emplacement of felsic and mafic lithologies, respectively. The impact of local setting on iron-oxide formation is highlighted by complex trace element signatures of iron-oxides; the northern segment of the belt is relatively enriched in As and Sb, while the southern segment is enriched in granitophile elements and REY. Further complexity is shown in the local variation of Mn and Zn in iron-oxides in the southern segment of the belt, where the Iron Magnet deposit shows the strongest correlation between the two elements. Various depositional settings for BIFs are inferred based upon Post-Archean Australian Shale-normalized REY fractionation trends of iron-oxides and various water types. These settings include environments where iron-minerals precipitate from mixtures of 1) anoxic seawater and high-temperature hydrothermal fluids, 2) anoxic seawater and low-temperature hydrothermal fluids, and 3) oxygen-richer seawater and low-temperature hydrothermal fluids. A genetic model for ore formation is proposed based upon textural and compositional variations observed in iron-oxides throughout the belt and includes formation resulting from supergene fluids rich in elements leached from local granites penetrating BIF, interaction with granite-derived hydrothermal fluids, and heat generated during emplacement of younger dikes. Recognition of petrographic features linked to changes in composition demonstrates the utility of iron-oxides to trace iron ore formation in a temporal and spatial context, with implications for ore genesis and models of mineral exploration.

Mercury stable isotope compositions in magmatic-affected coal deposits: New insights to mercury sources, migration and enrichment

Mercury (Hg) is commonly present at trace levels in coal deposits. Geological processes, particularly magmatic intrusion and hydrothermal cycling in coal-bearing strata can significantly increase Hg levels in coals. However, the effects of thermal stress, magmatic components, magmatic-hydrothermal fluids, low-temperature hydrothermal fluids on Hg enrichment are confounded in a magmatic-affected coal basin. Here, we demonstrate the use of stable Hg isotopes to understand the controlling factors on Hg enrichment in two well-known Chinese coal deposits affected by magmatic activities: Wulantuga low-temperature hydrothermal-altered coal deposit and Wolonghu magmatic-intruded coal deposit.The Wulantuga No. 6 coal seam is extremely enriched in Hg, varying from 0.37μg/g in middle coal benches to 40–90μg/g in the upper most and lowest coal benches. Approximately 2.5‰ variation in mass dependent fractionation (MDF, −3.07‰ to −0.58‰ in δ202Hg) is observed. δ202Hg vs. 1/[Hg] diagram suggests a mixture of three Hg end-members: original hydrothermal fluids, fractionated hydrothermal fluids and native coal-forming materials. In addition, Wulantuga coals all show positive mass independent fractionation (MIF) of odd isotopes, up to 0.87‰ in Δ199Hg and 0.66‰ in Δ201Hg. The Δ199Hg/Δ201Hg ratios range from 1.3 to 3.3, suggesting that a large fraction of photodegraded methylmercury was likely incorporated into the coal deposit. The magmatic-intruded Wolonghu No. 8 coal seam is only slightly to intermediately enriched in Hg, varying from 0.10μg/g to 0.40μg/g. The coals near the contact sill (≤5cm, −1.81‰ to −1.52‰) have similar δ202Hg as the magmatic sill rocks (−2.05‰ to −1.80‰), both with insignificant MIF values. Coals far from the contact sill (≥15cm) have δ202Hg values varying from −3.40‰ to −1.61‰ and Δ199Hg varying from 0.26‰ to 0.58‰, which are significantly enriched in light and odd Hg isotopes compared to coals near the contact sill. Δ199Hg and Δ201Hg in Wolonghu coals far from the contact sill resemble those of meteoritic waters and seawater in both magnitude and Δ199Hg/Δ201Hg ratio. Our two case studies show significant MDF and MIF of Hg isotopes, which inform on Hg migration and sequestration in the magmatic rocks and coal deposits, and on the roles of meteoric water and hydrothermal fluid circulation.

Exceptional discovery of a shallow-water hydrothermal site in the SW area of Basiluzzo islet (Aeolian archipelago, South Tyrrhenian Sea): An environment to preserve.

The geological, biological and geochemical features of a particular field of hydrothermal vents, discovered in the Panarea Volcanic Complex during a research survey carried out in 2015, are described for the first time. The site, located at 70–80 m depth off the South-western coast of the islet of Basiluzzo, was named Smoking Land for the presence of a large number of wide and high active chimneys and was characterized in terms of dissolved benthic fluxes, associated macrofauna and megafauna communities and preliminary mineralogy and geochemistry of chimney structures. On the whole field, a total of 39 chimneys, different in size and shape, were closely observed and described; 14 of them showed emission of low temperature hydrothermal fluids of marine origin characterized by acidified chemical conditions. The CTD and benthic chamber measurements highlighted that the Smoking Land is able to form a sea water bottom layer characterized by variable acidity and high DIC and trace elements concentrations; these characteristics weaken moving away from the chimney mouths. The SEM-EDS analysis of the collected solid samples revealed a chimney structure principally composed by amorphous and low crystalline Fe-oxyhydroxides of hydrothermal origins. The ROV explorations revealed a wide coverage of red algae (Peyssonnelia spp.) colonized by the green algae Flabiella petiolata and by suspension feeders, mainly sponges, but also bryozoans, and tubicolous polychaetes. Although novent-exclusive species were identified, the benthic communities found in association to the chimneys included more taxa than those observed in the surrounding no-vent rocky areas. These first findings evidence a submarine dynamic habitat where geological, chemical and biological processes are intimately connected, making the Smoking Land an important site in terms of marine heritage that should be safeguarded and protected.

Complexation of copper in acetate-rich low-temperature hydrothermal fluids: Evidence from ab initio molecular dynamics simulations

Acetate ions are widely distributed in various geo-fluids and can be enriched in metamorphic brines under saturated vapor pressure in the temperature range of 80 to 200°C. To examine the potential role of acetate in transporting metals, we conducted a series of ab initio molecular dynamics (MD) simulations to investigate the complexation of Cu+ with Cl−, HS− and acetate ions. All the ab initio MD simulations were conducted at the temperature of 150°C and pressures of 10bar or 1000bar. The ionic compositions of aqueous solutions for the simulations include four groups: (1) Cu+ and CH3COO−; (2) Cu+, CH3COO− and Cl−; (3) Cu+, CH3COO−, Cl− and HS−; and (4) Cu+, CH3COO− and HS−. The simulation results demonstrated some important regularities for complexation of copper with acetate. The static computation results suggest that Cu+ forms linear complexes with one or two acetate ions, rather than with one acetate ion in a nearly symmetric bidentate structure. The stoichiometry of the complexes, which can be represented by [Cu(CH3COO)(H2O)], [(CH3COO)2Cu]− and [Cu(CH3COO)Cl]−, depends on the fluid composition, environmental pressure and solvated structures of the acetate ligands in these complexes. Compared with Cl−, the acetate ion is a ligand of higher affinity for Cu+, and the solvated structure of acetate ligands can prevent Cl− from approaching Cu+. The presence of HS− also inhibits the formation of a Cu-Cl bond, thereby enhancing the stability of the Cu-OH2 bond in [Cu(CH3COO)(H2O)]. We also investigated the free energy surfaces of the ligand exchange reactions, CuCH3COO2-+2Cl-=CuCl2-+2CH3COO-andCuCH3COO2-+2HS-=CuHS2-+2CH3COO-. Combined with the results from ab initio MD simulations, we conclude that the order of affinity of Cu+ to form complexes in these conditions is HS−>CH3COO−>Cl−>H2O. These conclusions provide important evidence for evaluating the role of acetate ligands in transporting Cu during low temperature mineralization.

Extensive oxidative weathering in the aftermath of a late Neoproterozoic glaciation – Evidence from trace element and chromium isotope records in the Urucum district (Jacadigo Group) and Puga iron formations (Mato Grosso do Sul, Brazil)

The massive Fe and Mn deposits of the Urucum district (Banda Alta Formation) and the iron formations from Fazenda São Manoel (Puga Formation) in Mato Grosso do Sul, Brazil, are associated with glacigenic deposits and represent the youngest and largest sedimentary Fe and associated Mn formation (IF;MnF) deposits of Cryogenian age in the world. The Urucum district IFs studied are predominantly composed of pure classical plane-parallel and stratified hematite–chert–iron - and intercalated manganese (cryptomelane) micro- and mesobands, whereas the IFs at Fazenda São Manoel are closely associated with diamictites and shales. Although the precise depositional age is unknown, maximum age constraints for the Puga IFs are defined by the youngest detrital zircon with an U-Pb age of 706±9Ma (Babinski et al., 2013), a result which we here confirm by a U-Pb age of the youngest zircon of 695±17Ma from within shaly beds in the Urucum district IF succession. Redox-sensitive trace element signatures and tendency to hump-shaped Rare Earth Element+Yttrium (REY) patterns with negative Ce- but without Eu anomalies support the presence of an oxic surface water layer, fertilized by low temperature hydrothermal fluids injected from submarine thermal springs and/or, alternatively, by significant fresh water input directly derived from glacial meltdown. Strongly positively fractionated, authigenic chromium isotope signatures (average δ53Cr=1.10±0.4‰; n=16; 2σ) prevailing throughout the entire stratigraphic section indicate that riverine supply of continentally-derived Cr, remained more or less constant throughout the glacier meltdown and IF depositional period. Cycling across a redoxcline and predominant deposition of the IF in anoxic deeper seawater of the Jacadigo basin is supported by the peculiar presence of subchondritic Y/Ho ratios, by decreased negative Ce anomalies and by shifts of LREE patterns towards higher values in the Urucum district IFs that are independent of detrital contamination.The strongly positively fractionated Cr isotope signatures measured in these iron formations are compatible with those from other iron formations and black shales deposited during the late Neoproterozoic and Precambrian-Cambrian transition worldwide and are in support of prevailing high atmospheric O2 levels following the late Neoproterozoic glaciations that accompanied the evolution of macroscopic multicellular organisms.

Enrichment of germanium and associated arsenic and tungsten in coal and roll-front uranium deposits

Most of the World's germanium (Ge) is mined from Ge-rich lignite, where it is commonly associated with elevated arsenic (As), tungsten (W) and beryllium (Be) contents. Over the past decade, new evidence showing that World-class Ge deposits result from the interaction of hydrothermal fluids with organic matter in coal seams has emerged. Yet, the chemical state of Ge and associated metals in lignite remains poorly understood. We used Mega-pixel Synchrotron X-ray Fluorescence (MSXRF), X-ray Absorption Near Edge Structure (XANES) and Extended X-ray Absorption Fine Structure (EXAFS) to characterize the oxidation states and chemical bonding environment of Ge, As, and W in two world-class Mesozoic Ge-in-lignite deposits (Lincang, Yunnan, southwestern China; Wulantuga, Inner Mongolia, northeastern China); in lignite-bearing uranium (U) ores from the Beverley deposit (South Australia) hosted in Eocene sandstones; and in lignite and preserved wood in late Oligocene-Miocene fluviatile sediments (Gore, Southland, New Zealand). The aim was to improve our understanding of the enrichment mechanism of Ge in lignite and better evaluate the environmental mobility of Ge and some of the associated metals (specifically As and W) in lignite ores.In all samples, chemical maps show that Ge is distributed homogeneously (down to 2μm) within the organic matter. XANES and EXAFS data show that Ge exists in the tetravalent oxidation state and in a distorted octahedral coordination with O, consistent with complexing of Ge by organic ligands. In some pyrite-bearing samples, a minor fraction of Ge is also present as Ge(IV) in association with pyrite. In contrast, As displays a more complex speciation pattern, sometimes even in a single sample, including As(III), As(V), and As(−I/+II) in solid solution in sulfides. Arsenic in sulfides occurs in anionic and cationic forms, i.e., it shows both the common substitution for S22− and the substitution for Fe recently discovered in some hydrothermal pyrites. Tungsten was present as W(VI) in distorted octahedral (3+3) coordination. The EXAFS data confirm the absence or minor contribution of individual W-rich minerals such as scheelite or ferberite to W mass balance in the studied samples.These data show that Ge, W, and probably some As are scavenged via formation of insoluble, oxygen-bridged metal organic complexes in lignite. Destruction of the organic ligands responsible for fixing Ge and W (As) in these lignites is required for liberating the metals, e.g. from waste materials. Geochemical modelling suggests that Ge, W, Be and As all can be extracted from granitic rocks by dilute, low temperature hydrothermal fluids. Germanium is transported mainly as the tetrahedral Ge(OH)4(aq) complex, but fixed as an octahedral oxy-bridged organic complex. The same situation is valid for W, which is transported at the tetrahedral tungstate ion, but most likely scavenged via formation of a 6-coordinated metal-organic species. The Ge-Be-W±As association in Ge-rich coals reflects the source of the metals as well as related scavenging mechanisms.

Mineral characterization, clay quantification and Ar–Ar dating of faulted schists in the Carboneras and Palomares Faults (Betic Cordillera, SE Spain)

Two major clay-rich fault zones (Betic Cordillera, SE Spain) exhumed under arid conditions were studied to establish the origin and nature of phyllosilicates in deformed mica schists and the role of fault zones in the genesis of rocks rich in clay minerals. Both areas contain wide zones (≈200 m across) of alternating fault gouge and protolith creating a complex arrangement of sheared lenses along fault strand cores. Minerals in schists were characterized by X-ray diffractometry and scanning and transmission electron microscopy, and two samples were selected for 40 Ar/ 39 Ar dating of four clay grain-size fractions each. Quartz, chlorite and K-micas are the principal phases in all samples (crystalline protolith and faulted schists). Paragonite and Fe and Ti-oxides are present in some samples and, additionally, most of the damaged samples have kaolinite, illite and gypsum. Backscattered electron images show irregularly oriented stacks of phyllosilicates with curved shapes in the fault rocks and quartz grains deformed by brittle fracturing. Clay fabrics in the damaged rocks are poorly developed. Lattice fringe images of faulted damaged samples revealed defect-free dioctahedral mica and Fe-rich chlorite packets which were generally with no more than several tens of nm thickness, although chlorite grains were usually thicker than micas. Chlorite showed more obvious deformation features. The calculated ages of the authigenic clay component in the two samples are 6.3 ± 0.8 Ma and 6.2 ± 0.4 Ma, while the ages calculated for the protolith clays are 22.8 ± 1.9 Ma and 11.7 ± 1.3 Ma. The age of the authigenic clay overlaps the range of ages from the nearby Cabo de Gata volcanic series (SE Spain). Textural and chemical results point toward that although the fault gouge is mostly a product of mechanical crushing of the protolith, the presence of quartz provided a strong and fragile behaviour to the faulted rocks increasing their permeability, and creating permeable paths through which low-temperature hydrothermal fluids circulated producing an intense leaching of the parent material and promoting crystallization of new authigenic minerals (illite, kaolinite, smectite and gypsum).

A global Ge isotope budget

We present measurements of Ge isotope composition and ancillary data for samples of river water, low- and high-temperature hydrothermal fluids, and seawater. The dissolved δ74Ge composition of analyzed rivers ranges from 2.0 to 5.6‰, which is significantly heavier than previously determined values for silicate rocks (δ74Ge=0.4–0.7‰, Escoube et al., Geostand. Geoanal. Res., 36(2), 2012) from which dissolved Ge is primarily derived. An observed negative correlation between riverine Ge/Si and δ74Ge signatures suggests that the primary δ74Ge fractionation mechanism during rock weathering is the preferential incorporation of light isotopes into secondary weathering products. High temperature (>150°C) hydrothermal fluids analyzed in this study have δ74Ge of 0.7–1.6‰, most likely fractionated during fluid equilibration with quartz in the reaction zone. Low temperature (25–63°C) hydrothermal fluids are heavier (δ74Ge between 2.9‰ and 4.1‰) and most likely fractionated during Ge precipitation with hydrothermal clays. Seawater from the open ocean has a δ74Gesw value of 3.2±0.4‰, and is indistinguishable among the different ocean basins at the current level of precision. This value should be regulated over time by the isotopic balance of Ge sources and sinks, and a new compilation of these fluxes is presented, along with their estimated isotopic compositions. Assuming steady-state, non-opal Ge sequestration during sediment authigenesis likely involves isotopic fractionation Δ74Gesolid-solution that is −0.6±1.8‰.

Fe-Si Oxides Tracing the Ongoing Low-T° Hydrothermal Alteration of Exhumed Serpentinites at the Ultraslow-spreading Southwest Indian Ridge

On the smooth seafloor of exhumed mantle-rocks of the slow-spreading Southwest Indian Ridge, the secondary oxide and carbonate mineralizations record specific chemical signatures of the alteration of serpentinites by low-temperature hydrothermal seawater-dominated fluids. The uncommon characteristics of Fe-oxides forming nodule cortex or thick encrustments are their high Si, low Mn contents, trace elements (e.g. Cr) and REE behavior. Oxides composition evolves through time. Associated to oxides, carbonates (aragonite, calcite, dolomite) characterize the matrix of young indurated serpentinite breccias found at ridge axis. Such mineralogical and geochemical sequences trace, as proxies, the ongoing mantle-exhumation and serpentinization process linked to the detachment faults, and the late alteration reactions that impact on crust–ocean transfers and oceanic budget.

Environmental controls on biomineralization and Fe-mound formation in a low-temperature hydrothermal system at the Jan Mayen Vent Fields

Diffuse low-temperature hydrothermal vents on the seafloor host neutrophilic microaerophilic Fe-oxidizing bacteria that utilize the Fe(II) supplied by hydrothermal fluids and produce intricate twisted and branching extracellular stalks. The growth behavior of Fe-oxidizing bacteria in strongly opposing gradients of Fe(II) and O2 have been thoroughly investigated in laboratory settings to assess whether extracellular stalks and aligned biomineralized fabrics may serve as biosignatures of Fe-oxidizing bacteria and indications of palaeo-redox conditions in the rock record. However, the processes controlling the growth of biogenic Fe-oxyhydroxide deposits in natural, modern hydrothermal systems are still not well constrained. In this study, we aimed to establish how variations in the texture of stratified hydrothermal Fe-oxyhydroxide deposits are linked to the physicochemical conditions of the hydrothermal environment. We conducted 16S rRNA gene analyses, microscopy and geochemical analyses of laminated siliceous Fe-mounds from the Jan Mayen Vent Fields at the Arctic Mid-Ocean Ridge. Chemical analyses of low- and high-temperature hydrothermal fluids were performed to characterize the hydrothermal system in which the Fe-deposits form. Our results reveal synchronous inter-laminar variations in texture and major and trace element geochemistry. The Fe-deposits are composed of alternating porous laminae of mineralized twisted stalks and branching tubes, Mn-rich horizons with abundant detrital sediment, domal internal cavities and thin P- and REE-enriched lamina characterized by networks of ≪1μm wide fibers. Zetaproteobacteria constitute one third of the microbial community in the surface layer of actively forming mounds, indicating that microbial Fe-oxidation is contributing to mound accretion. We suggest that Mn-oxide precipitation and detrital sediment accumulation take place during periodically low hydrothermal fluid discharge conditions. The elevated concentrations of P and REE in distinct laminae suggest Fe-cycling and accumulation of diagenetic species at depth in the deposits during hydrothermal quiescence and co-precipitation of these species with Fe-oxyhydroxides at the mound surface with reinitiated hydrothermal discharge. The origin of the low-temperature hydrothermal source fluid and the Fe-deposits are evident by low LREE/HREE ratios and negative Eu-anomalies, which clearly differ from the LREE and Eu enrichment of nearby high-temperature white smoker venting fluids. Our study demonstrates that hydrothermal fluctuations exert the primary control on the formation of laminae and the activity of Fe-oxidizing bacteria in marine hydrothermal Fe-deposits and indicates that REE-patterns may be used to distinguish high-temperature plume fallout and biomineralized low-temperature Fe-deposits in the rock record.

Mineral composition and geochemical characteristics of the Li-Ga-rich coals in the Buertaohai-Tianjiashipan mining district, Jungar Coalfield, Inner Mongolia

The coals from the Jungar Coalfield, Inner Mongolia, China, have been found to be enriched in Ga and Li. These are valuable metals that are potentially recoverable from coals and/or coal combustion residues. Based on fifteen roof/floor/parting samples collected from one borehole and one hundred and forty one bulk coal samples collected from three boreholes in the Buertaohai-Tianjiashipan coal mining district, Jungar Coalfield, this paper reports new data on the mineral compositions and geochemical characteristics of the Jungar Li-Ga-rich coals, and provides new evidence for the origin and mode of occurrence of Al, Ga and Li in these coals.The main mineral phases occurring in the coals are kaolinite, boehmite, calcite, with small proportions of quartz, pyrite, ankerite, siderite, and trace amounts of microcline and rectorite. An unusual mineral phase, svanbergite (SrAl3(PO4)(SO4)(OH)6) also occurs as a main mineral constituent in the studied coals. The mineral phases in the roof/floor/parting samples are dominantly kaolinite, with a small proportion of quartz. Kaolinite is of both terrigenous and authigenic origin, which were possibly derived from terrigenous Yinshan Oldland sediment-source region and/or from recrystallization during the coal formation process. Boehmite and svanbergite are primarily of authigenic origin, and were dominantly derived from the weathered bauxite sediment-source region. Calcite may have formed by dissolution of limestone layers close to the margin of coal basin and subsequent deposition of the Ca or Mg-rich carbonates in the cells/fractures of the coal seams. Sulfide minerals in fractures may have been precipitated from epithermal fluids. Rectorite was probably formed by the reaction of kaolinite with epigenetic low-temperature hydrothermal fluids during diagenesis.Compared to common Chinese and worldwide coals, the studied Jungar coals are much more enriched in Al (4.4–6.1%), Li (70–79mg/kg), and Ga (14–19mg/kg). Titanium, P, Sr, Zr, Nb, Th, Ta, Hf, and rare earth elements (REEs) are also enriched in the studied coals to some extent. Aluminum in the coals mainly occurs in the form of kaolinite and boehmite, whereas, lithium may be associated with aluminosilicate minerals (kaolinite and illite if present) as well as svanbergite. Gallium principally occurs in kaolinite, and to a lesser extent, svanbergite. Strontium, P, and LREEs (La, Ce, and Rr, Nd and Sm) mainly present in svanbergite. The source of Li and Ga in Jungar coals is most likely from the Yinshan Oldland region, but there is also a possibility of migration from bauxite of the Benxi formation.

Genesis of the Tianbaoshan Pb–Zn–Cu–Mo polymetallic deposit in eastern Jilin, NE China: Constraints from fluid inclusions and C–H–O–S–Pb isotope systematics

The Tianbaoshan Pb–Zn–Cu–Mo deposit is located in the eastern part of Jilin–Heilongjiang region, NE China which is considered to be the eastern segment of the Central Asian Orogenic Belt. Field and geochronological evidences indicate that this deposit experienced three types of mineralization including Hercynian skarn, cryptoexplosion breccia pipe, and Yanshanian quartz vein. The early stages of the Pb–Zn–Cu mineral systems in skarn and cryptoexplosion breccia pipe are characterized by a high-temperature, high-salinity H2O–CO2–NaCl system of hydrothermal fluids that were possibly exsolved from the Hercynian wall-rock granodiorite. These fluids show H–O isotopic compositions similar to those of typical magmatic fluids. By contrast, the low-temperature hydrothermal fluids of the later stages are represented by low-salinity NaCl–H2O systems with low H–O isotopic values. The skarn and cryptoexplosive breccia pipe types of Pb–Zn–Cu mineralization tend to have weakly negative δ34S values of −4.0‰ to −0.8‰ (mean values of −2.31‰ and −2.16‰, respectively), indicating that the sulfur was sourced from the Hercynian magma. Therefore, the early stage ore-forming fluids of the skarn and cryptoexplosive breccia pipe were most likely sourced from high-temperature and high-salinity fluids closely related to the cooling and fractional crystallization of the Hercynian granodiorite, while the later stages changed to NaCl–H2O meteoric water influx. Whereas the ore-forming fluids of the quartz vein type of Mo mineralization were high-temperature, high-salinity NaCl–H2O systems that differed from those of the skarn and cryptoexplosion breccia pipe, but their H–O isotopic compositions also indicate a magmatic fluid. The weakly enriched δ34S values of molybdenite from the quartz vein type Mo mineralization (δ34S=0.2–2.8‰, average of 1.65‰) are comparable with those of other Mesozoic Yanshanian Mo deposits (δ34S=0.4‰–4.1‰, with an average of 1.39‰–3.15‰), but differ significantly from those of the Hercynian Pb–Zn–Cu skarn and cryptoexplosion breccia pipe. This indicates that the sulfur of quartz vein type of Mo originated from Mesozoic Yanshanian magmatism and that the ore-forming fluids were derived from Yanshanian magmatic rocks rather than being a product of the Hercynian activity. The δ13C values of the fluid inclusions in quartz from the skarn, cryptoexplosion breccia pipe and quartz vein types are in a narrow range of −19.5‰ to −9.3‰, similar to those of the Shanxiuling Group, which indicates that the carbon of the three types of mineralization had the same primary origin in the Shanxiuling Group. The lead isotope compositions of ores from the skarn and cryptoexplosion breccia pipe types of mineralization (206Pb/204Pb=18.0725–18.3627, 207Pb/204Pb=15.3721–15.5694 and 208Pb/204Pb=37.5542–38.8208) overlap with those of the Hercynian granodiorite and Shanxiuling Group marble, suggesting that the lead was probably derived from a mix of two different sources, the Shanxiuling Group and the Hercynian granodiorite. Whereas the lead isotope compositions of ores from the quartz vein type of Mo mineralization (206Pb/204Pb=18.3837–18.6949, 207Pb/204Pb=15.6824–15.7293 and 208Pb/204Pb=39.1009–39.1889) are significantly higher than those of the Shanxiuling Group marble and the Hercynian granodiorite. This indicates that the lead may be a product of Yanshanian magmatic activity instead of the nearby Hercynian granodiorite.

Multistage amphiboles from the Galinge iron skarn deposit in Qiman Tagh, western China: evidence of igneous rocks replacement

Amphiboles from the Galinge skarn deposit, the largest iron (Fe) polymetallic skarn deposit in the Qiman Tagh metallogenic belt (western China), were formed by multistage fluid-rock interactions. Mineral analysis of the various amphiboles suggest that they were formed by the replacement of mafic to intermediate igneous rocks. The two alteration phases have formed three generations of compositionally distinct amphiboles: Amp-I: Ferro-edenitic hornblende (FE); Amp-II: Deep bluish-green magnesian-hastingsite (MH); Amp-III: Light greenish-beige ferro-actinolite (FA). The Amp-I preserves the primary igneous amphibole composition, and was subsequently replaced by Amp-II. The amphibole Cl content markedly increases from the FE (0.176 − 0.582 wt.%) to the MH (0.894 − 3.161 wt.%), and abruptly drops in the FA (0.017 − 0.039 wt.%). The Cl-rich MH contains the lowest concentration of Si [5.64 − 6.28 atoms per formula unit (apfu)], and the highest (K + Na) values (0.72 − 1.06 apfu) in the amphibole A-site with a high K/(K + Na) of 0.491 to 0.429. Both Mg and Fe contents of the MH and FA vary widely, possibly due to the interactions of magma-derived hydrothermal fluids with the basaltic / andesitic host rocks. Formation of the Cl-rich MH may have been associated with the early high-temperature and high-saline hydrothermal fluids, meanwhile the Cl-poor FA may have formed from later low-temperature and low-saline hydrothermal fluids. The MH plays an important role for consuming Cl carried by hydrothermal fluids. The Cl-rich fluids may have mobilized some elements, such as Fe, Al, Mg, Ca and Ti from the host rocks. Considerable amounts of Ti, Al, Mg and Fe were incorporated into the sphene and Fe-Ti oxides that coexist with the MH.

Relict chromian spinels in Tulu Dimtu serpentinites and listvenite, Western Ethiopia: implications for the timing of listvenite formation

ABSTRACTSerpentinites (massive and schistose) and listvenite occur as tectonic sheets and lenses within a calcareous metasedimentary mélange of the Tulu Dimtu, western Ethiopia. The massive serpentinite contains high-magnesian metamorphic olivine (forsterite [fo] ~96 mol%) and rare relict primary mantle olivine (Fo90–93). Both massive and schistose serpentinites contain zoned chromian spinel; the cores with the ferritchromite rims preserve a pristine Cr/(Cr+Al) atomic ratio (Cr# = 0.79–0.87), suggesting a highly depleted residual mantle peridotite, likely formed in a suprasubduction zone setting. Listvenite associated with serpentinites of smaller ultramafic lenses also contain relict chromian spinel having identical Cr# to those observed in serpentinites. However, the relict chromian spinel in listvenite has significantly higher Mg/(Mg+Fe2+) atomic ratios. This suggests that a nearly complete metasomatic replacement of ultramafic rocks by magnesite, talc, and quartz to prevent Mg–Fe2+ redistribution between relict chromian spinel and the host, that is, listvenite formation, took place prior to re-equilibration between chromian spinel and the surrounding mafic minerals in serpentinites. Considering together with the regional geological context, low-temperature CO2-rich hydrothermal fluids would have infiltrated into ultramafic rocks from host calcareous sedimentary rocks at a shallow level of accretionary prism before a continental collision to form the East African Orogen (EAO).

Cryptic sediment-hosted critical element mineralization from eastern Yunnan Province, southwestern China: Mineralogy, geochemistry, relationship to Emeishan alkaline magmatism and possible origin

A previous study briefly described the occurrence of a new type of Nb(Ta)-Zr(Hf)-REY-Ga (REY: rare earth elements and yttrium) polymetallic mineralization in eastern Yunnan, southwest China. In this paper, the mineralogical and geochemical features have been further advanced through a study of two regionally extensive and relatively flat-lying mineralized layers from No. XW drill core. The layers are clay-altered volcanic ash and tuffaceous clay, and are dominated by clay minerals (mixed layer illite/smectite, kaolinite, berthierine, and chamosite); with lesser amounts of quartz and variable amounts of anatase, siderite and calcite; along with trace pyrite, barite, zircon, ilmenite, galena, chalcopyrite, and REE-bearing minerals. The mineralized samples have higher Al2O3/TiO2 values (13.7–41.4) and abundant rare metal elements (Nb, Ta, Zr, Hf, REE, Ga, Th, and U) whereas less mineralized samples are rich in V, Cr, Co, and Ni and have lower Al2O3/TiO2 values (2.32–7.67). The mineralized samples also have strong negative δEu in chondrite-normalized REE patterns. Two processes are most likely responsible for the geochemical and mineralogical anomalies of the mineralized samples: airborne volcanic ash and multi-stage injection of low-temperature hydrothermal fluids. Based on paragenetic analysis, this polymetallic mineralization is derived from the interaction between alkaline volcanic ashes and subsequent percolation of low-temperature fluids. The intense and extensive alkaline volcanism of the early Late Permian inferred from this study possibly originated from the coeval Emeishan large igneous province (ELIP). This unique Nb(Ta)-Zr(Hf)-REE-Ga mineralization style has significant economic and geological potential for the study of mineralization of the lowest Xuanwei Formation.

Hanging-Wall Vectoring for Buried Volcanogenic Massive Sulfide Deposits, Paleoproterozoic Flin Flon Mining Camp, Manitoba, Canada

The Paleoproterozoic Flin Flon mining district is one of the world’s most prolific volcanogenic massive sulfide (VMS) camps and includes a single stratigraphic interval that hosts the 85.5 million tonne (Mt) Flin Flon, 777, and Callinan Zn-Cu-(Au) deposits. Rapid seafloor burial of the VMS hydrothermal system by a thick succession of pillowed basalt resulted in the hanging-wall strata being affected to varying degrees by the still upward migrating fluids. This hanging-wall alteration hydrothermal fingerprint allows delineation of the regionally metamorphosed paleohydrothermal system, and its characterization has the potential to lead to discovery of buried, stacked, or structurally displaced mineralization. Evidence for the presence of continued seafloor hydrothermal activity above the Flin Flon-Callinan VMS horizon is observed in the pillowed flows, interlayered hyaloclastite-rich flow tops, and also within finely bedded interflow volcaniclastic sediment. A 30% to 60% metalliferous exhalative component was detected through geochemical and mineral analysis in interpillow volcaniclastic rocks, chert, and epidosite in the hanging-wall sequence. The regional distribution of Fe- and Mg-rich chlorite, epidote-clinozoisite, biotite-annite, actinolite-hornblende-ferrotschermakite, and stilpnomelane and albite-oligoclase modifies metamorphic isograds and defines discrete vertical fluid pathways controlled by synvolcanic growth faults and associated sill-dike swarms. Silica-enriched hanging-wall alteration zones are proximal to Fe-Ti basalt sills and occur as discrete hanging-wall zones parallel to the plunge of the 62 Mt Flin Flon deposit. Anomalous concentrations of Hg, Sb, Ag, Pb, Te, As, Au, and Bi form within these hanging-wall halo alteration zones, indicating migration of the more volatile metals present in the underlying VMS deposits. Synvolcanic depressions, dike swarms, and hydrothermal-metamorphic fluid corridors are detectable through trace element anomalies, trace mineral chemistry, and 18O isotope geochemistry. Oxygen isotope analysis of the Flin Flon-777-Callinan VMS hanging-wall strata defines a number of high δ O18 anomalies extending 1,200 m above that indicate that <300°C subseafloor hydrothermal activity continued after burial of the massive sulfide deposits. Coupled with the geochemical and mineral chemical anomalies, this is indicative of the presence of continued, relatively low temperature hydrothermal fluid “leakage” from a robust seafloor hydrothermal event that generated the VMS deposits. A combination of techniques, including mineral chemistry, isotope, and trace element data, is demonstrated to be successful in identifying and delineating zones of hanging-wall hydrothermal alteration in greenschist- to amphibolite-grade metamorphic rocks of the Flin Flon mining camp. Use of these, coupled with mapping to define periods of quiescence as marked by horizons of sedimentary rocks in the hanging-wall basalts of the Hidden Formation, has the potential to lead to discovery of deeply buried deposits on the Flin Flon horizon or deposits at higher stratigraphic levels. Our findings indicate that the basaltic hanging wall on the Flin Flon-777-Callinan hydrothermal system was an efficient cap on the system, with vestiges of continued hydrothermal fluid flow detected in the interpillow and interflow components. These volumetrically minor components are critical sampling media and are pertinent to global exploration for detection of VMS mineralization buried beneath thick mafic volcanic sequences.

Coupled RNA-SIP and metatranscriptomics of active chemolithoautotrophic communities at a deep-sea hydrothermal vent.

The chemolithoautotrophic microbial community of the rocky subseafloor potentially provides a large amount of organic carbon to the deep ocean, yet our understanding of the activity and metabolic complexity of subseafloor organisms remains poorly described. A combination of metagenomic, metatranscriptomic, and RNA stable isotope probing (RNA-SIP) analyses were used to identify the metabolic potential, expression patterns, and active autotrophic bacteria and archaea and their pathways present in low-temperature hydrothermal fluids from Axial Seamount, an active submarine volcano. Metagenomic and metatranscriptomic results showed the presence of genes and transcripts for sulfur, hydrogen, and ammonium oxidation, oxygen respiration, denitrification, and methanogenesis, as well as multiple carbon fixation pathways. In RNA-SIP experiments across a range of temperatures under reducing conditions, the enriched 13C fractions showed differences in taxonomic and functional diversity. At 30 °C and 55 °C, Epsilonproteobacteria were dominant, oxidizing hydrogen and primarily reducing nitrate. Methanogenic archaea were also present at 55 °C, and were the only autotrophs present at 80 °C. Correspondingly, the predominant CO2 fixation pathways changed from the reductive tricarboxylic acid (rTCA) cycle to the reductive acetyl-CoA pathway with increasing temperature. By coupling RNA-SIP with meta-omics, this study demonstrates the presence and activity of distinct chemolithoautotrophic communities across a thermal gradient of a deep-sea hydrothermal vent.

Multiple metal sources in the glaciomarine facies of the Neoproterozoic Jacadigo iron formation in the “Santa Cruz deposit”, Corumbá, Brazil

The Rapitan-type banded iron formation (BIF) in the Banda Alta Formation (Fm) of the Neoproterozoic Jacadigo Group in Brazil was deposited in a redox-stratified, marine sub-basin, which was strongly influenced by glacial advance/retraction cycles with temporary influx of continental freshwater and upwelling metal-enriched seawater from deeper anoxic parts. These new finding are based on new stratigraphic, whole-rock geochemical, and stable Fe and C isotope data from the “Santa Cruz” hematite deposit near Corumbá, Mato Grosso do Sul, where a stratigraphy of lower and upper dolomite-rich and intermediate chert-rich BIF facies with up to three intercalated diamictites is revealed. The Ca-Mg-Fe-Mn-carbonate-chert-hematite and chert-hematite BIF (∼30–45wt% Fe) of the lower dolomite-rich facies shows chemical signatures consistent with well-oxidized seawater, i.e. low (Pr/Yb)PAAS, strong negative CePAAS-, and positive GdPAAS- and YPAAS-anomalies, as well as negative-δ13C carbonate typical for Neoproterozoic glaciogenic carbonates. Sedimentation in a rather shallow water depth during relatively warm interglacial periods was likely influenced by abundant freshwater from fluviatile runoff and melting icebergs. In such conditions abundant microbial activity accommodated CO2 sequestration in carbonates as spheroids and mats and fractionated δ57Fe (−2.6 and −1.2‰) in primary Fe-hydroxides. In contrast, the intermediate chert-rich facies, characterized by chert-hematite BIF (∼35–55wt% Fe) and isolated hematite chert and hematite mud, recorded trace element signatures of non-oxidized (absence of Ce anomalies and variable YPAAS-anomalies), more metal-enriched (Fe, Mn, Si, Ni, Zn, Pb, U) seawater, thus deposition was within and below the shallow-level redoxcline during ice cover. Colder water and isolation from sunlight reduced microbial activity, and thus an almost non-fractionated δ57Fe (−0.7 to 0.0‰) fluid signature reveals that low-temperature (based on almost absence of Eu anomaly in BIF) hydrothermal (MOR) vents or (sub-) seafloor alteration of mafic or felsic rocks, or shales fertilized seawater with metals. All results lead to the model that the Jacadigo Group formed during one major marine transgression-regression cycle, and BIF facies in the Banda Alta Fm were a response to first- and second-order periodic variations of the depth of the redoxcline, induced by the juxtaposition of glacial advance/retraction cycles, active graben tectonics, and glacial isostatic adjustment or eustatic water level changes. The chert-rich BIF facies marked the maximum of transgression. Age and tectonic setting of the Jacadigo basin remains contentious: it may represent a continental back arc basin of the Brasiliano collision zone (∼590Ma), in which submarine alteration was possibly related to low-temperature hydrothermal fluids moving through the active graben system (as an alternative to basin-wide benthic pore water flux). This would place the Jacadigo group to the suite of Ediacarian “Gaskier” glaciations, although a relationship to the Marinoan glaciation (660–635Ma), mainly based on the published sedimentation age-bracket of 706–587Ma, is also possible.

Stable isotope composition of hypogenic speleothem calcite in Kalana (Estonia) as a record of microbial methanotrophy and fluid evolution

AbstractAeronian (Silurian Period) carbonate rocks in Kalana quarry in central Estonia contain cave and fracture structures filled with calcitic speleothem precipitates of atypical composition. Calcite crystals in dolomitized limestone cave walls have diverse shapes (equant-blocky, bladed and fibrous), but most of the cave walls and speleothems are covered with an up to 10 cm thick crust of microcrystalline botryoidal calcite. The morphology of precipitates suggests their formation in low hydrodynamic conditions in water supersaturated with calcite. Calcite in speleothems is associated with the mineralization of sulphur-bearing minerals, such as pyrite and abundant barite. Unlike that of speleothem calcite, the stable isotope composition of authigenic calcite shows extreme depletion in13C and large variations in δ13CPDBfrom –11 to –56‰, whereas the δ18OPDBvalues range from –5 to –12‰, suggesting calcite precipitation from a13C-depleted carbon source supplied by microbially mediated anaerobic oxidation of methane and/or other hydrocarbons at elevated temperatures (up to 70°C). Systematic variation in the δ13CPDBand δ18OPDBvalues of layered precipitates indicates a change from an initially biogenic methane source to an either thermogenic methane or hydrocarbon source in the low-temperature hydrothermal fluid. Calcite speleothems in Kalana possibly developed at the mixing front of sulphate-rich seawater or groundwater and low-temperature methane-bearing hydrothermal fluids in the phreatic zone of a hypogenic-hydrothermal (karst) system.