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The Solstad copper deposit, located in SE Sweden, is hosted by a quartz-rich rock sliver surrounded by a granite belonging to the 1.8 Ga Transscandinavian Igneous Belt. Ore petrographic studies have revealed a number of previously unrecognized opaque phases, including several Co phases, selenides and tellurides. Based on an in situ U-Pb investigation of zircons from a mineralized sample, it is suggested that zircons have a detrital origin and that the quartz-rich host rock is a xenolith belonging to the c. 1.88–1.86 Ga Västervik quartzite formation. A low-radiogenic galena sample implies that the source for the metals in the ore has a primitive origin, probably the basaltic lavas (now amphibolites) that are intercalated in the Västervik quartzite. Fluid inclusion studies in quartz distinguish four distinct ore fluids: (1) a hypersaline halite-bearing aqueous fluid related to an early (1.85–1.86 Ga) chalcopyrite depositional stage, (2) a subsequent CO2-rich fluid, that deposited native gold, tellurides, selenides and bismuthinite, developed (at ≥1.8 Ga) as a result of a phase separation, (3), a moderate- to high-salinity aqueous fluid did also develop at this event and led to the deposition of bornite and (4) a concluding, low-salinity aqueous fluid stage (at ≤1.8 Ga) caused oxidation to covelline and digenite of previously formed phases. It is proposed that the Solstad deposit and other Cu ± Co-rich sulphide (± magnetite) occurrences in the Västervik region along the southernmost margin of the 1.9–1.8 Ga Svecofennian Domain, represent a distinct ore type associated with quartzites and amphibolites.

Modern marine hydrothermal vents occur in a wide variety of tectonic settings and are characterized by seafloor emission of fluids rich in dissolved chemicals and rapid mineral precipitation. Some hydrothermal systems vent only low‐temperature Fe‐rich fluids, which precipitate deposits dominated by iron oxyhydroxides, in places together with Mn‐oxyhydroxides and amorphous silica. While a proportion of this mineralization is abiogenic, most is the result of the metabolic activities of benthic, Fe‐oxidizing bacteria (FeOB), principally belonging to the Zetaproteobacteria. These micro‐organisms secrete micrometer‐scale stalks, sheaths, and tubes with a variety of morphologies, composed largely of ferrihydrite that act as sacrificial structures, preventing encrustation of the cells that produce them. Cultivated marine FeOB generally require neutral pH and microaerobic conditions to grow. Here, we describe the morphology and mineralogy of filamentous microstructures from a late Paleoproterozoic (1.74 Ga) jasper (Fe‐oxide‐silica) deposit from the Jerome area of the Verde mining district in central Arizona, USA, that resemble the branching tubes formed by some modern marine FeOB. On the basis of this comparison, we interpret the Jerome area filaments as having formed by FeOB on the deep seafloor, at the interface of weakly oxygenated seawater and low‐temperature Fe‐rich hydrothermal fluids. We compare the Jerome area filaments with other purported examples of Precambrian FeOB and discuss the implications of their presence for existing redox models of Paleoproterozoic oceans during the “Boring Billion.”

Graphite formation temperatures in the 'Los Pobres' mine within the Ronda peridotite, Spain, previously reported to be between 770 and 820 degrees C, have been reinterpreted based on new temperature measurements using Raman spectroscopy. Additional in situ and bulk stable carbon isotopic measurements and fluid inclusion studies contributed to improved understanding of parts of the graphite formation process. Raman spectroscopy revealed that the formation of the 'Los Pobres' graphite extends to temperatures as low as 500 degrees C, indicating a broader temperature range than previously reported. Stable carbon isotopes and temperature estimates suggest two different crystallization events, followed by a late hydrothermal alteration of the host rock. The first event occurred at temperatures higher than similar to 600 degrees C, in which crystalline graphite was formed with a mixed C-13 composition as a result of the mixing of two different carbon-bearing sources. The second graphite formation event took place below similar to 600 degrees C, within the same system, but with lower purity and crystallinity of the graphite. In the third event, the temperature decreased to less than 550 degrees C, and hydrothermal fluids altered the host rock, precipitating silica and iron oxides in veins penetrating both the host rock and the deposited graphite.

Numerous sandstone-hosted Pb-Zn deposits occur along the present-day erosional front of the eastern Scandinavian Caledonides. The largest deposit is Laisvall (64.3 Mt at 4.0% Pb, 0.6% Zn and 9.0 g/t Ag) and since mineralisations generally share similar characteristics (reminding of both SEDEX and MVT-style) the term Laisvall-type has often been used. Typically, mineralised zones occur along sedimentary bedding and consist of disseminated galena and sphalerite and lesser amounts of calcite, fluorite, baryte, pyrite and sericite forming a cement that fill interstitial pores in Neoproterozoic/Eocambrian (e.g. Laisvall) to Cambrian (e.g. Vassbo) sandstones. Deposits occur both in autochtonous and allochtonous sedimentary rocks, and a broad consensus exists about their epigenetic nature, their spatial relationships to syn-sedimentary faults and that ore fluids have scavenged metals from the crystalline basement. However, the detailed ore depositional history and the timing of ore deposition have remained more controversial. New analyses aimed to complement earlier Rb-Sr data (crush-leach technique using sphalerite) fail to support a published three-point isochron age of 467 +/- 5 Ma. This is probably due to syn-ore mixing between fluids carrying isotopically variable strontium and inherited problems to analyse sphalerite grains that strictly were deposited from a single ore pulse. Tentatively, strontium in the ores originate from a mix of components derived from the basement, seawater and the local sedimentary host sequences. The lead component has highly radiogenic compositions, and data define sub-parallel linear arrays interpreted to essentially represent mixing of isotopically different types of lead released from regional basement rocks. There are obvious similarities when comparing features of deposits representing two Pb-Zn ore styles, the sandstone-hosted dissemination and the fracture-controlled mineralisation in the granite-dominated basement occurring further

The production of H-2 in hydrothermal systems and subsurface settings is almost exclusively assumed a result of abiotic processes, particularly serpentinization of ultramafic rocks. The origin of H-2 in environments not hosted in ultramafic rocks is, as a rule, unjustifiably linked to abiotic processes. Additionally, multiple microbiological processes among both prokaryotes and eukaryotes are known to involve H-2-production, of which anaerobic fungi have been put forward as a potential source of H-2 in subsurface environments, which is still unconfirmed. Here, we report fungal remains exceptionally preserved as fluid inclusions in hydrothermal quartz from feeder quartz-barite veins from the Cape Vani Fe-Ba-Mn ore on the Greek island of Milos. The inclusions possess filamentous or near-spheroidal morphologies interpreted as remains of fungal hyphae and spores, respectively. They were characterized by microthermometry, Raman spectroscopy, and staining of exposed inclusions with WGA-FITC under fluorescence microscopy. The spheroidal aqueous inclusions interpreted as fungal spores are unique by their coating of Mn-oxide birnessite, and gas phase H-2. A biological origin of the H-2 resulting from anaerobic fungal respiration is suggested. We propose that biologically produced H-2 by micro-eukaryotes is an unrecognized source of H-2 in hydrothermal systems that may support communities of H-2-dependent prokaryotes.

This study focuses on concentrations and fractionation of rare earth elements (REE) in a variety of minerals and bulk materials of hydrothermal greisen and vein mineralization in Paleoproterozoic monzodiorite to granodiorite related to the intrusion of Mesoproterozoic alkali- and fluorine-rich granite. The greisen consists of coarse-grained quartz, muscovite, and fluorite, whereas the veins mainly contain quartz, calcite, epidote, chlorite, and fluorite in order of abundance. A temporal and thus genetic link between the granite and the greisen/veins is established via high spatial resolution in situ Rb-Sr dating, supported by several other isotopic signatures (delta S-34, Sr-87/Sr-86, delta O-18, and delta C-13). Fluid-inclusion microthermometry reveals that multiple pulses of moderately to highly saline aqueous to carbonic solutions caused greisenization and vein formation at temperatures above 200-250 degrees C and up to 430 degrees C at the early hydrothermal stage in the veins. Low calculated Sigma REE concentration for bulk vein (15ppm) compared to greisen (75ppm), country rocks (173-224ppm), and the intruding granite (320ppm) points to overall low REE levels in the hydrothermal fluids emanating from the granite. This is explained by efficient REE retention in the granite via incorporation in accessory phosphates, zircon, and fluorite and unfavorable conditions for REE partitioning in fluids at the magmatic and early hydrothermal stages. A noteworthy feature is substantial heavy REE (HREE) enrichment of calcite in the vein system, in contrast to the relatively flat patterns of greisen calcite. The REE fractionation of the vein calcite is explained mainly by fractional crystallization, where the initially precipitated epidote in the veins preferentially incorporates most of the light REE (LREE) pool, leaving a residual fluid enriched in the HREE from which calcite precipitated. Fluorite occurs throughout the system and displays decreasing REE concentrations from

The production of H2 in hydrothermal systems and subsurface settings is almost exclusively assumed a result of abiotic processes, particularly serpentinization of ultramafic rocks. The origin of H2 in environments not hosted in ultramafic rocks is, as a rule, unjustifiably linked to abiotic processes. Additionally, multiple microbiological processes among both prokaryotes and eukaryotes are known to involve H2-production, of which anaerobic fungi have been put forward as a potential source of H2 in subsurface environments, which is still unconfirmed. Here, we report fungal remains exceptionally preserved as fluid inclusions in hydrothermal quartz from feeder quartz-barite veins from the Cape Vani Fe-Ba-Mn ore on the Greek island of Milos. The inclusions possess filamentous or near-spheroidal morphologies interpreted as remains of fungal hyphae and spores, respectively. They were characterized by microthermometry, Raman spectroscopy, and staining of exposed inclusions with WGA-FITC under fluorescence microscopy. The spheroidal aqueous inclusions interpreted as fungal spores are unique by their coating of Mn-oxide birnessite, and gas phase H2. A biological origin of the H2 resulting from anaerobic fungal respiration is suggested. We propose that biologically produced H2 by micro-eukaryotes is an unrecognized source of H2 in hydrothermal systems that may support communities of H2-dependent prokaryotes

The Seve Nappe Complex (SNC) of the Scandinavian Caledonides records a well‐documented history of high pressure (HP) and ultra‐high pressure (UHP) metamorphism. Eclogites of the SNC occur in two areas in Sweden, namely Jämtland and Norrbotten. The Jämtland eclogites and associated rocks are well‐studied and provide evidence for late Ordovician UHP metamorphism, whereas the Norrbotten eclogites, formed during the late Cambrian (Furongian)/Early Ordovician, have not been studied in such detail, especially in terms of the P–T conditions of their formation. Within the studied eclogite, clinopyroxene contains a high‐Na core and two rims: inner, medium‐Na and outer, low‐Na. Garnet consists of a high‐Ca euhedral core, low‐Ca inner rim and medium‐Ca outer rim. A similar pattern occurs within phengite, where high‐Si cores are enveloped by medium and low‐Si rims. The compositions of the mineral cores, inner rims and outer rims reflect three stages in the metamorphic evolution of the eclogite. Applied Quartz‐in‐Garnet geobarometry, coupled with Zr‐in‐rutile geothermometry reveal that garnet nucleation (E0 stage) took place at 1.5–1.6 GPa and 620–660°C. The eclogite peak‐pressure assemblage developed during the E1 stage, it consists of garnet+omphacite+phengite+rutile+coesite? and yields P–T conditions of 2.8–3.1 GPa and 660–780°C as constrained by conventional geothermobarometry and thermodynamic modelling in the NCKFMMnASHT system. Later, lower‐pressure stages E2 and E3 record conditions of 2.2–2.8 GPa, 680–780°C and 2.1 GPa, 735°C, respectively. The prograde metamorphic evolution of the eclogite is inferred from inclusions of epidote, amphibole and clinopyroxene within garnet. The presence of amphibole–quartz–plagioclase symplectites, secondary epidote/zoisite and titanite replacing rutile record the later retrograde changes taking place at <1.5 GPa (referred as E4 stage). The obtained P–T conditions indicate that the Norrbotten eclogites underwent a metamorphic evolution

Fossil microbiotas are rare in the early rock record, limiting the type of ecological information extractable from ancient microbialites. In the absence of body fossils, emphasis may instead be given to microbially derived features, such as microbialite growth patterns, microbial mat morphologies, and the presence of fossilized gas bubbles in lithified mats. The metabolic affinity of micro-organisms associated with phosphatization may reveal important clues to the nature and accretion of apatite-rich microbialites. Stromatolites from the 1.6 Ga Chitrakoot Formation (Semri Group, Vindhyan Supergroup) in central India contain abundant fossilized bubbles interspersed within fine-grained in situ-precipitated apatite mats with average δ13Corg indicative of carbon fixation by the Calvin cycle. In addition, the mats hold a synsedimentary fossil biota characteristic of cyanobacterial and rhodophyte morphotypes. Phosphatic oncoid cone-like stromatolites from the Paleoproterozoic Aravalli Supergroup (Jhamarkotra Formation) comprise abundant mineralized bubbles enmeshed within tufted filamentous mat fabrics. Construction of these tufts is considered to be the result of filamentous bacteria gliding within microbial mats, and as fossilized bubbles within pristine mat laminae can be used as a proxy for oxygenic phototrophy, this provides a strong indication for cyanobacterial activity in the Aravalli mounds. We suggest that the activity of oxygenic phototrophs may have been significant for the formation of apatite in both Vindhyan and Aravalli stromatolites, mainly by concentrating phosphate and creating steep diurnal redox gradients within mat pore spaces, promoting apatite precipitation. The presence in the Indian stromatolites of alternating apatite-carbonate lamina may result from local variations in pH and oxygen levels caused by photosynthesis–respiration in the mats. Altogether, this study presents new insights into the ecology of ancient phosphatic stromatolites and warra

Ultramafic rocks are hypothesized to support a subseafloor hydrogen-driven biosphere because of extensive production of bioavailable energy sources like H-2 or CH4 from fluid-rock interactions. Hence, the apparent lack of microbial remains in subseafloor ultramafic rocks, in contrast to their frequent observation in subseafloor basalts, is somewhat of a paradox. Here we report fossilized microbial remains in aragonite veins in ultramafic rocks from the 15 degrees 20N Fracture Zone area on the Mid-Atlantic Ridge (MAR), collected during Ocean Drilling Program (ODP) Leg 209. The microbial remains consist of filamentous structures associated with biofilms. The young age (<1 Myr) and absence of diagenesis result in fossilized microbial communities with a pristine composition characterized by carbonaceous matter (CM) and the enrichment in trace elements such as Ni, Co, Mo and Mn. Our study confirms the presence of the hypothesized deep subseafloor biosphere hosted in ultramafic rocks. We further show that host rock composition may influence the microbial elemental composition, which is recorded during the fossilization.

The toxicity of arsenic (As) towards life on Earth is apparent in the dense distribution of genes associated with As detoxification across the tree of life. The ability to defend against As is particularly vital for survival in As-rich shallow submarine hydrothermal ecosystems along the Hellenic Volcanic Arc (HVA), where life is exposed to hydrothermal fluids containing up to 3000 times more As than present in seawater. We propose that the removal of dissolved As and phosphorus (P) by sulfide and Fe(III)(oxyhydr)oxide minerals during sediment-seawater interaction, produces nutrient-deficient porewaters containing<2.0ppb P. The porewater arsenite-As(III) to arsenate-As(V) ratios, combined with sulfide concentration in the sediment and/or porewater, suggest a hydrothermally-induced seafloor redox gradient. This gradient overlaps with changing high affinity phosphate uptake gene abundance. High affinity phosphate uptake and As cycling genes are depleted in the sulfide-rich settings, relative to the more oxidizing habitats where mainly Fe(III)(oxyhydr)oxides are precipitated. In addition, a habitat-wide low As-respiring and As-oxidizing gene content relative to As resistance gene richness, suggests that As detoxification is prioritized over metabolic As cycling in the sediments. Collectively, the data point to redox control on Fe and S mineralization as a decisive factor in the regulation of high affinity phosphate uptake and As cycling gene content in shallow submarine hydrothermal ecosystems along the HVA.

An early Quaternary shallow submarine hydrothermal iron formation (IF) in the Cape Vani sedimentary basin (CVSB) on Milos Island, Greece, displays banded rhythmicity similar to Precambrian banded iron formation (BIF). Field-wide stratigraphic and biogeochemical reconstructions show two temporal and spatially isolated iron deposits in the CVSB with distinct sedimentological character. Petrographic screening suggests the presence of a photoferrotrophic-like microfossil-rich IF (MFIF), accumulated on a basement consisting of andesites in a similar to 150 m wide basin in the SW margin of the basin. A banded nonfossiliferous IF (NFIF) sits on top of the Mn-rich sandstones at the transition to the renowned Mn-rich formation, capping the NFIF unit. Geochemical data relate the origin of the NFIF to periodic submarine volcanism and water column oxidation of released Fe(II) in conditions predominated by anoxia, similar to the MFIF. Raman spectroscopy pairs hematite-rich grains in the NFIF with relics of a carbonaceous material carrying an average delta C-13 org signature of similar to-25%0. A similar delta C-13 org signature in the MFIF could not be directly coupled to hematite by mineralogy. The NFIF, which postdates large-scale Mn deposition in the CVSB, is composed primarily of amorphous Si (opal-SiO2 center dot nH(2)O) while crystalline quartz (SiO2) predominates the MFIF. An intricate interaction between tectonic processes, changing redox, biological activity, and abiotic Si precipitation are proposed to have collectively formed the unmetamorphosed BIF-type deposits in a shallow submarine volcanic center. Despite the differences in Precambrian ocean-atmosphere chemistry and the present geologic time, these formation mechanisms coincide with those believed to have formed Algoma-type BIFs proximal to active seafloor volcanic centers.

In the deep biosphere, microbial sulfate reduction (MSR) is exploited for energy. Here, we show that, in fractured continental crystalline bedrock in three areas in Sweden, this process produced sulfide that reacted with iron to form pyrite extremely enriched in S-34 relative to S-32. As documented by secondary ion mass spectrometry (SIMS) microanalyses, the S-34(pyrite) values are up to +132 parts per thousand V-CDT and with a total range of 186 parts per thousand. The lightest S-34(pyrite) values (-54 parts per thousand) suggest very large fractionation during MSR from an initial sulfate with S-34 values (S-34(sulfate,0)) of +14 to +28 parts per thousand. Fractionation of this magnitude requires a slow MSR rate, a feature we attribute to nutrient and electron donor shortage as well as initial sulfate abundance. The superheavy S-34(pyrite) values were produced by Rayleigh fractionation effects in a diminishing sulfate pool. Large volumes of pyrite with superheavy values (+120 +/- 15 parts per thousand) within single fracture intercepts in the boreholes, associated heavy average values up to +75 parts per thousand and heavy minimum S-34(pyrite) values, suggest isolation of significant amounts of isotopically light sulfide in other parts of the fracture system. Large fracture-specific S-34(pyrite) variability and overall average S-34(pyrite) values (+11 to +16 parts per thousand) lower than the anticipated S-34(sulfate,0) support this hypothesis. The superheavy pyrite found locally in the borehole intercepts thus represents a late stage in a much larger fracture system undergoing Rayleigh fractionation. Microscale Rb-Sr dating and U/Th-He dating of cogenetic minerals reveal that most pyrite formed in the early Paleozoic era, but crystal overgrowths may be significantly younger. The C-13 values in cogenetic calcite suggest that the superheavy S-34(pyrite) values are related to organotrophic MSR, in contrast to findings from marine sediments where superheavy pyrite has

A diamond drill core from the upper part of the Jeerinah Formation (similar to 2.63 Ga), underlying the Hamersley Group, deposited at a time when the oxygen concentrations in the marine environment were extremely low, was examined for microbial fossils. The paper presents organo-mineral structures in the form of twisted stalks produced by bacteria being present in the laminated black carbonaceous shale sediments. These twisted stalks are organo-mineral structures produced by microaerophilic Fe(II)-oxidizing-type bacteria such as Gallionella and/or Mariprofundus that are active at very low-oxygen concentrations, thus providing evidence for oxygen being present in the marine environment at 2.63 Ga.

Understanding metal scavenging by calcite in deep aquifers in granite is of importance for deciphering and modeling hydrochemical fluctuations and water rock interaction in the upper crust and for retention mechanisms associated With underground, repositories for toxic wastes. Metal scavenging into calcite has generally been established in the laboratory or in natural environments that cannot be unreservedly applied to conditions in deep crystalline rocks, an environment of broad interest, for nuclear waste repositories. Here, we report a microanalytical study: of calcite precipitated over a period of 17 years from anoxic, low-temperature (14 degrees C), neutral (pH: 7.4-7.7), and brackish (Cl: 1700-7100 mg/L) groundwater flowing in fractures at >400 m depth in granite rock. This enabled assessment of the trace metal uptake by calcite under these deep-seated conditions. Aquatic speciation modeling was carried out to assess influence of metal complexation on the partitioning into calcite. The resulting environment-specific partition coefficients were for several divalent ions in line with values obtained in controlled laboratory experiments, whereas for several other ions they differed substantially. High absolute uptake of rare earth elements and U(IV) suggests that coprecipitation into calcite can be an important sink for these metals and analogousactinides in the vicinity of geological repositories.

Polymetallic quartz veins, with up to 1500ppm indium, have been discovered recently in the Sarvlaxviken area within the 1.64Ga anorogenic multiphase Wiborg rapakivi batholith and adjacent 1.90Ga Svecofennian crust in SE Finland. Evidence from primary fluid inclusions in the Sarvlaxviken area provides new information on the hydrothermal transport and depositional processes of metals in anorogenic granites. Fluid inclusions with variable aqueous liquid and vapour proportions (5-90vol.% vapour) occur in quartz, cassiterite and fluorite belonging to three generations of polymetallic quartz veins. Microthermometry indicates that the veins were deposited at temperatures that range from similar to 500 degrees C down to <100 degrees C and salinities from 0 to 16 eq. mass% NaCl. Fluid inclusion data show that the depositional conditions were similar regardless of vein generation. The interpreted depositional processes involve phase separation with a combination of condensation, cooling and boiling of an initially low-salinity (<3 eq. mass% NaCl) aqueous magmatic vapour phase enriched in CO2-F-Cl-S and metals. Fluid inclusions with low salinities dominate, but higher salinities are recorded in metal-rich parts of the veins. The turbulent fluid flow, with complex geometry and temperature-salinity patterns, may explain why sulfide and/or oxide opaque minerals occur irregularly, and are locally the dominating vein minerals, but disappear completely into barren parts of the quartz veins. All fluids are considered to have been generated by the F-rich Marviken granite (and related granite dykes), which show all geochemical criteria for an ore-fertile granite. The quartz veins investigated in the adjacent Svecofennian country rocks are considered to represent the very last stage of a fluid with similar characteristics to the fluid responsible for the ore formation in the Sarvlaxviken area, but that had cooled to <100 degrees C.