Pyrite Formation Research Articles

Textures, trace element geochemistry and in-situ sulfur isotopes of pyrite from the Xiaojiashan gold deposit, Jiangnan Orogen: Implications for ore genesis

The northeastern Hunan region in the Jiangnan Orogen (South China) is endowed with many important gold deposits, whose genesis remains controversial. The Xiaojiashan is a representative gold deposit (7.77 t Au @ 2.88 g/t) in NE Hunan, and is characterized by multi-stage pyrite formation. Its mineralization can be divided into 3 stages: (I) quartz-ankerite-pyrite-gold; (II) quartz-ankerite-polymetallic sulfide-gold; (III) quartz-ankerite stage. Three pyrite generations were identified: fine-grained porous Py1 and coarse-grained Py2 in stage I, and core-rim-textured Py3 in stage II. Py1 and Py2 are enriched in Co, Ni, Se and Te, but depleted in As and Au. Comparatively, Py3a and Py3b have higher As, Au, and Zn, but lower Co, Ni, Se and Te contents, indicating the compositional variations of ore-forming fluids from stage I to stage II. The Au- and As-poor Py1 and Py2 have similarly low δ34S values (Py1: −33.30 to − 16.23 ‰; and Py2: −25.41 to − 15.45 ‰), indicating that the sulfur of Py1 and Py2 may have been derived from metamorphism of sedimentary strata, such as Neoproterozoic Lengjiaxi Group. Meanwhile, both the core (Py3a) and rim (Py3b) of the Au-As-rich Py3 have high δ34S values (Py3a: −3.44 to − 1.72 ‰; and Py3b: −1.00 to − 0.99 ‰), resembling typical magmatic sulfur. The trace element compositions and sulfur isotopes of pyrite in stages I and II suggest a distinct shift of ore-forming fluids source from metamorphic (stage I) to magmatic (stage II). Therefore, we propose that the Xiaojiashan gold mineralization was likely associated with early metamorphism and late magmatic-hydrothermal overprinting, and its multistage and complex ore-forming process had recorded the complexity of gold mineralization in NE Hunan.

Two hydrothermal events associated with Au mineralization in the Youjiang Basin, southwestern China

The Youjiang Basin in southwestern China hosts remarkably large amounts of Carlin-type Au deposits. In such deposits, Au is mainly ionically bound to arsenian pyrite characterized by core and rim textures. Understanding the formation mechanism of zoned pyrite may improve our understanding of the genesis of massive Carlin-type Au deposits. This study examined the elemental content, mineral composition, and pyrite texture and chemistry of wall rock and ore from the Lannigou Au deposit, one of the largest Carlin-type Au deposits in the Youjiang Basin, to identify the genetic mechanisms of zoned pyrite.Five distinct types of pyrites, i.e., pyrite 1 (Py1), 2 (Py2), 3 (Py3), 4 (Py4), and ore pyrite (OPy), were identified in the Lannigou Au deposit. Py1, Py2, and Py3 were mainly observed in the wall rock, whereas Py4 and OPy, constituting the core and rim of zoned pyrite, respectively, were only discovered in the ore. Mineral mapping of the wall rock and ore indicated that pyrite is scarce in the wall rock (0.021 vol%). However, the amount of zoned pyrite significantly increased in the ore (1.275 vol%). Py1, Py2, and Py3, showing framboidal, nodular, and fine euhedral microcrystal textures, had high Pb, Co, Ni, Mn, Zn, and Mo contents (medians ranging from 10 to 1,000 ppm) and variable δ34S compositions ranging from −5.1 to 35.4‰, implying a sedimentary (syngenetic or diagenetic) origin. Py4 was homogeneous and contained numerous illite and quartz inclusions and fractures. In contrast, OPy showed multiple As-rich sub-bands and a lack of illite or quartz inclusions and fractures. Py4 had significantly lower Au, As, Tl, and Cu contents than OPy; however, Py4 had Pb, Co, Ni, Mn, Zn, and Mo contents similar to OPy. The range of δ34S values for Py4 and OPy were both narrow, but Py4 (7.6 to 13.3‰, with an average of 9.1‰) had lower δ34S values than OPy (9.4–14.1‰, with an average of 12.4‰). These texture and chemical features indicate that Py4 likely sedimented from a pre-ore hydrothermal fluid, but not at the early stage of the ore-forming fluid.Hydrothermal pyrite cores were also widespread and exhibited textural and chemical differences compared to Au-rich pyrite rims from other Au deposits in the Youjiang Basin. Based on the two geochronological clusters of Au deposits in the Youjiang Basin, we inferred the occurrence of at least two episodes of large-scale hydrothermal events. The two hydrothermal fluid episodes, which contributed to the zoned pyrite formation, likely originated from the mixing of initial magmatic fluid with δ34S values of ∼0 ± 5‰ and basin brine with elevated δ34S values (δ34S > 18‰). Pre-ore hydrothermal pyrite likely resulted in the rapid non-equilibrium crystallization of ore pyrite; thus, more Carlin-suite elements were captured by ore pyrite. Additionally, low-grade Au orebodies may have locally formed during the pre-ore hydrothermal event. These multiple hydrothermal events may have been crucial for the formation of massive Carlin-type Au deposits in the Youjiang Basin.

Hydrochemistry and stable isotopes in a coastal lagoon affected by evaporation, Cabo de Gata (Almería)

The Salinas de Cabo de Gata are a natural coastal lagoon that has been anthropically transformed to favor the entry of seawater and its evaporation until saturation in sodium chloride. For this, it is compartmentalized in a series of ponds in which the seawater is guided by a circuit along which the salinity increases. Sediment samples have been taken at the bottom of these ponds and water samples to recognize which hydrogeochemical processes occur along the route. In the first ponds (evaporators) the suspended solids are decanted and carbonate precipitation occurs, along with the formation of pyrite linked to the high concentration of organic matter. On the other hand, in the last ponds (crystallizers) gypsum precipitation occurs when 70% evaporation is reached and, finally, halite when it reaches 90%. This precipitation notably changes the chemical composition of the waters, reducing the concentration of the ions present in the minerals that precipitate. From the isotopic point of view, gypsum precipitation also has its mark, reducing the proportions of 18O/16O and 2H/1H in the pond water. The study of these processes, in a mesoscale system, has great advantages for making palaeoenvironmental inferences at the basin scale, such as knowing what percentage of seawater must be evaporated so that gypsum or halite can precipitate in a basin.

Sulfide leaching of high-grade arsenic copper concentrates

Such factors as lower-grade copper ores, more demanding mining and technical conditions, and higher implementation costs for new development projects are typical for the Ural region in general and for the Uchalinsky Mining and Processing Plant (Uchalinsky GOK), developing tennantite-containing copper-sulfide ore reserves, in particular. Depending on the process flow design and the mineral composition of the ore, 10–70 % of arsenic is transferred into copper concentrates. The mass fraction of arsenic in the resulting copper concentrates may reach 2 %, significantly reducing the concentrate grade. Sulfide-alkaline leaching has been studied as a promising conditioning method for flotation copper concentrate. It ensures more effective arsenic removal and compliance of the final product with the requirements for further pyrometallurgical processing. The studies were carried out using a low-grade high-arsenic concentrate sample from the Uchalinsky GOK containing 16.04 wt. % Cu, 5.30 wt. % Zn, 1.36 wt. % As, and 0.19 wt. % S. It has been established that iron is predominantly occurring in the form of pyrite, with chalcopyrite and sphalerite unevenly distributed in its mass. The concentrate had high concentrations of fahlore minerals (tennantite, etc.). Studies were conducted to assess the effects of changes in the sulfide leaching process parameters (temperature, raw material size, NaOH and Na2S concentrations, solid-liquid ratio, duration) on the transfer of arsenic into the alkaline solution. The specific conditions have been established (t = 95 °C; Cm(NaOH) = 3.5 M, Cm(Na2S) = 1.5 M; solidliquid ratio = 5; duration of three hours or more) that ensure almost complete removal of arsenic from the flotation concentrate to obtain a conditioned copper product meeting the requirements of GOST R 52998-2008.

Petrographic and geochemical features of the B3 bauxite horizon (Cenomanian-Turonian) in the Parnassos-Ghiona area: A contribution towards the genesis of the Greek karst bauxites

The karst bauxites of the Parnassos-Ghiona Unit (Greece) are hosted within Upper Jurassic to Late Cretaceous carbonate rocks. Three bauxite horizons are intercalated within shallow water limestones. They are named B1, B2 and B3 from bottom to top. In this study we present the characteristics of the B3 horizon (Cenomanian-Turonian) sampled in Agia Anna, Variani and Shila 1 underground mines. The bauxite ore has a prevailing oolitic texture. Diaspore, boehmite, hematite and goethite are the major mineral components of the analyzed samples. Kaolinite, rutile and anatase are common minor phases. Pyrite occurs in a small number of samples. Ilmenite, rutile, chromite, zircon, baddeleyite and serpentine are common detrital minerals. Authigenic minor minerals are mostly represented by REE-phosphates, barite, and gypsum. The presence of pyrite and diaspore suggests that after a first stage of additional in situ weathering and bauxitization, the deposits were affected by early diagenetic reducing conditions (allowing the formation of pyrite) and significant diagenesis, resulting in diaspore formation. This three-stages genesis is reflected in complex correlations between major, minor and trace elements. The occurrence of detrital chromite and serpentine in the bauxite reflects mafic parental rocks. The mafic component likely originated from the ophiolite suites exposed in the vicinity of the Parnassos-Ghiona bauxites.

Impacts of sulfate-driven anaerobic oxidation of methane on the morphology, sulfur isotope, and trace element content of authigenic pyrite in marine sediments of the northern South China Sea

The presence of sulfate-driven anaerobic oxidation of methane (SD-AOM) generally influences the precipitation of authigenic pyrite in seepage areas. However, the relatively weak comprehensive studies on the morphological and geochemical characteristics of pyrite limit the understanding of its formation and application to diagenetic processes. Here, we analyzed the pyrite texture, abundance, sulfur isotopic composition, degree of pyritization, and the trace element (TE) content of pyrite from two sites (A27 and SH1) in a seepage area of the South China Sea, so as to better constrain the impacts of SD-AOM on pyrite formation. Pore-water results revealed that present-day methane seepages occurred at both sites. Under normal sedimentary environments, pyrite resulting from organiclastic sulfate reduction (OSR) showed low abundances with negative δ34S. In contrast, high contents of 34S-enriched pyrite aggregates, long pyrite tubes and large framboid sizes typified by radial overgrowths were documented at the lower part of both core sediments, suggesting the significant impacts of SD-AOM. At the proposed sulfate-methane transition zone (SMTZ), pyrite is a mixing product of OSR and SD-AOM, but the latter enhances the morphologic and isotopic anomalies of pyrite. Besides, SD-AOM increased the degree of pyritization and accelerated the pyrite-iron accumulation in sediments. With pyritization proceeding, Mo, Ni, Mn, and Cr were gradually incorporated into the pyrite phase, presenting a relatively high affinity of these TEs for pyrite in the studied locations. However, the contents of TE in pyrite were positively correlated with its concentrations in the current ocean, from which we can get that TE in diagenetic pyrite was basically influenced by seawater chemistry. The comprehensive results reflect that the authigenic pyrite can act as an excellent geological archive of modern and ancient oceans. In particular, pyrite formed in seepage-impacted sediments allows identifying the methane seepage and characterizing the biogeochemical cycling of carbon, sulfur, and TEs.

The Formation of Highly Positive δ34S Values in Late Devonian Mudstones: Microscale Analysis of Pyrite (δ34S) and Barite (δ34S, δ18O) in the Canol Formation (Selwyn Basin, Canada)

The sulfur isotope composition of pyrite in marine sedimentary rocks is often difficult to interpret due to a lack of precise isotopic constraints for coeval sulfate. This study examines pyrite and barite in the Late Devonian Canol Formation (Selwyn Basin, Canada), which provides an archive of δ34S and δ18O values during diagenesis. Scanning electron microscopy (SEM) has been combined with microscale secondary ion mass spectrometry (SIMS) analysis (n = 1,032) of pyrite (δ34S) and barite (δ34S and δ18O) on samples collected from nine stratigraphic sections of the Canol Formation. Two paragenetic stages of pyrite and barite formation have been distinguished, both replaced by barium carbonate and feldspar. The δ34Sbarite and δ18Obarite values from all sections overlap, between +37.1‰ and +67.9‰ (median = +45.7‰) and +8.8‰ and +23.9‰ (median = +20.0‰), respectively. Barite morphologies and isotopic values are consistent with precipitation from diagenetically modified porewater sulfate (sulfate resupply << sulfate depletion) during early diagenesis. The two pyrite generations (Py-1 and Py-2) preserve distinct textures and end-member isotopic records. There is a large offset from coeval Late Devonian seawater sulfate in the δ34Spyrite values of framboidal pyrite (-29.4‰ to -9.3‰), consistent with dissimilatory microbial sulfate reduction (MSR) during early diagenesis. The Py-2 is in textural equilibrium with barite generation 2 (Brt-2) and records a broad range of more positive δ34SPy-2 values (+9.4‰ to + 44.5‰). The distinctive highly positive δ34Spyrite values developed from sulfate limited conditions around the sulfate methane transition zone (SMTZ). We propose that a combination of factors, including low sulfate concentrations, MSR, and sulfate reduction coupled to anaerobic oxidation of methane (SR-AOM), led to the formation of highly positive δ34Spyrite and δ34Sbarite values in the Canol Formation. The presence of highly positive δ34Spyrite values in other Late Devonian sedimentary units indicate that diagenetic pyrite formation at the SMTZ may be a more general feature of other Lower Paleozoic basins.

Precipitation of greigite and pyrite induced by Thermococcales: an advantage to live in Fe- and S-rich environments?

SummaryThermococcales, a major order of archaea inhabiting the iron‐ and sulfur‐rich anaerobic parts of hydrothermal deep‐sea vents, have been shown to rapidly produce abundant quantities of pyrite FeS2 in iron–sulfur‐rich fluids at 85°C, suggesting that they may contribute to the formation of ‘low temperature’ FeS2 in their ecosystem. We show that this process operates in Thermococcus kodakarensis only when zero‐valent sulfur is directly available as intracellular sulfur vesicles. Whether in the presence or absence of zero‐valent sulfur, significant amounts of Fe3S4 greigite nanocrystals are formed extracellularly. We also show that mineralization of iron sulfides induces massive cell mortality but that concomitantly with the formation of greigite and/or pyrite, a new generation of cells can grow. This phenomenon is observed for Fe concentrations of 5 mM but not higher suggesting that above a threshold in the iron pulse all cells are lysed. We hypothesize that iron sulfides precipitation on former cell materials might induce the release of nutrients in the mineralization medium further used by a fraction of surviving non‐mineralized cells allowing production of new alive cells. This suggests that biologically induced mineralization of iron‐sulfides could be part of a survival strategy employed by Thermococcales to cope with mineralizing high‐temperature hydrothermal environments.

Investigation of destructive ground heave attributed to pyritic fill affecting new-build properties in the Dublin area of Ireland

As structural damage caused by expansion of pyrite bearing bedrock and fills had been documented in the UK and other countries since at least the 1960s, it was surprising that some thousands of cases involving extensive damage to residential and other properties near Dublin, Ireland came to light during the first decade of 2000. Although the stability of properties was not immediately endangered, their appearance and functionality were impaired with serious impact on their value, all of which was obviously very distressing to the owners. Various possible causes relating to the ground conditions, construction methods, structural design and materials used in construction were investigated. However, from the characteristics of the damage and the type of fill used beneath concrete floor slabs it was suspected that the presence of pyrite in the fill was resulting in it being subject to damaging expansion.The paper documents investigations carried out in 2008 into the damage caused to houses in one development in north Dublin. Detailed mineralogical and chemical characterisation of the materials concerned confirmed that both cubic and framboidal forms of pyrite were present in the fill material and there was evidence for in-situ expansive mineral formation. Early signs of isolated chemical attack to sub-surface footings and foundation structures was also evident and although no physical degradation of mortar and concrete was apparent, there was potential for deterioration of these buried structures in the longer-term. Various solutions to the problem were suggested, but it was concluded that replacement of the fill with effectively pyrite-free material was the best strategy for remediation.A lack of awareness in the construction industry, particularly the domestic housing sector, of the potential for problems due to pyrite was apparent. This resulted in protracted legal proceedings and new standards and specifications for fill materials were issued. This paper aims to contribute to the understanding of the behaviour of pyrite and its potential for causing problems in construction situations as even with compliance with standards, problems cannot be otherwise ruled out.

Pyrite oxidation by nitrate and nitrite in sodium bicarbonate solution under anoxic and abiotic conditions

Pyrite reactivity with nitrate and nitrite was assessed in long-term batch tests to assess its possible oxidation in anoxic conditions at pH 8.5, at room temperature and atmospheric pressure. This was done in the frame of compatibility studies of nitrate-containing radioactive waste with a pyrite-containing clay host rock for geological disposal. Abiotic pyrite suspensions were prepared under inert atmosphere in 15 mM bicarbonate medium, as this simulates the inorganic carbon and pH conditions in the pore water of Boom Clay, which is a potential host rock for geological disposal in Belgium. Two forms of pyrite powder were used, formed via different genetic pathways and exhibiting a different morphology, namely pyrite obtained by crushing a large crystal cluster and pyrite extracted from Boom Clay by flotation. The reactivity of these two pyrite forms with nitrate and nitrite is reported and compared. Overall, after 2–2.5 years under abiotic conditions and inert atmosphere, no significant reaction between crushed pyrite and nitrate was detected, while a very limited reaction was observed between Boom Clay pyrite and nitrate. Between pyrite and nitrite, which is known to be more reactive than nitrate, a slow reaction took place for both forms of pyrite, with no significantly higher reactivity with the Boom Blay pyrite. The variability between the replicates of Boom Clay pyrite were also larger than for crushed pyrite. Overall, nitrate and nitrite induced a very limited, if any, oxidation reaction of the pyrite powders. These observations are important in assessing the safety of geological disposal of nitrate-containing radioactive waste.

Occurrence of uranium minerals in the Xiaomeigou Formation in northern Qaidam Basin, Northwest China

The Lenghu sandstone type uranium deposit as industrial value in the northern Qaidam Basin, Northwest China. This study analyzed the LA-ICP-MS U-Pb dating of detrital zircons, mineralogical features, electron probe, backscatter electron imaging and track etch of the altered minerals from uranium-bearing strata in the Xiaomeigou Formation of Lower Jurassic on the basis of field investigation in order to trace the source, parent rock lithology, geochronological age, uranium minerals, compositional characteristics, occurrences of uranium mineralization.The U-Pb ages of detrital zircons from the ore-bearing member are ranging from 117 to 270 Ma and 370–480 Ma, respectively, indicating that the provenance and uranium source were mainly derived from the Permian-Triassic intermediate-acid igneous rocks in the eastern Altyn Tagh and western Saishiteng Mountains, a small amount of them are from the Ordovician-Silurian intermediate-acid igneous rocks in the Xiaosaishiteng Mountains. Two types of ores in Xiaomigou Formation in Lenghu region are mainly composed of graywacke and carbonaceous sandstone with main uranium minerals are coffinite, pitchblende and trace amounts of lead selenite. They are closely associated with clay minerals, organics and pyrite, which lie in the intergranular space of quartz, feldspar and other altered lithic mineral grains or in cleavage joints of altered clay minerals that occur in fine columnar, gel-like or irregular sawtooth shape. It is inferred that the Fe2+ in feldspar and biotite reacts with H2S or S2- bearing minerals participated in the formation of pyrite, where the U6+ was captured by late multiple fluid processes occurred reduction-precipitation-adsorption uranium mineralization in the reduction environment provided by Fe2+. Based on the analysis of the existence of high Y and low Y types of uranium minerals, it is inferred that uranium in uranium minerals is the residual of original uranium minerals derived from the pre-enrichment of uranium-bearing detrital particles in sedimentary and diagenetic stages, and at the later stage, the high radioactivity abnormal geological bodies migrated to the inner basin through the multi-stage reformation of uranium-containing and oxygen-containing fluids without Y or at very low contents.

Genesis and Distribution of Pyrite in the Lacustrine Shale: Evidence from the Es3x Shale of the Eocene Shahejie Formation, Zhanhua Sag, East China.

Pyrite is a common mineral in sedimentary rocks and is widely distributed in a variety of different morphologies and sizes. Pyrite is also widely distributed in the Es3x shale of the Eocene Shahejie Formation in the Zhanhua Sag, Bohai Bay Basin. A combination of geochemical and petrographic studies has been applied to address the formation and distribution of pyrite in the Es3x shale. The methods include thin section analysis to identify the representative samples of the shale-containing pyrite, total organic carbon (TOC) content analysis, X-ray fluorescence, X-ray diffraction, electron probe micro-analysis, and field emission scanning electron microscopy (FE-SEM) coupled with the energy dispersive spectrometer, to observe the characteristics, morphology, and distribution of pyrite in the lacustrine shale. The content of pyrite in the Es3x shale ranges from 1.4 to 11.2% with an average content of 3.42%. The average contents of TOC and total organic sulfur (TS) are 3.48 and 2.53 wt %, respectively. Various types of pyrites are observed during the detailed FE-SEM investigations including pyrite framboids, euhedral pyrite, welded pyrite, pyrite microcrystals, and framework pyrite. Pyrite framboids are densely packed sphere-shaped masses of submicron-scale pyrite crystals with subordinate large-sized euhedral crystals of pyrite. Welded pyrite forms due to the overgrowth and alteration of pyrite crystals within the larger pyrite framboids. Pyrite microcrystals are the euhedral-shaped microcrystals of pyrite. The framework pyrite is also observed and is formed due to the pyritization of plant/algal tissues. Based on the growth mechanism, the pyrites can be divided into syngenetic pyrites, early diagenetic pyrites, and late diagenetic pyrites. The presence of pyrite, especially the abundance of pyrite framboids, suggests that the environment during the Es3x shale deposition in the lacustrine basin was anoxic. Their dominant smaller size suggests the presence of an euxinic water column, which is consistent with the lack of in-place biota and high TOC contents. This research work not only helps to understand the pyrite mineralization, role of organic matter, and reactive iron in pyrite formation in the shale but also helps to interpret the paleoredox conditions during the deposition of shale. This research work can also be helpful to other researchers who can apply these methods and conclusions to studying shale in other similar basins worldwide.

Relations between pyrite morphologies and uranium mineralization in the Shuanglong region, northern China

Pyrite is widely distributed in ore-hosting sandstones of the Zhiluo Formation in the Shuanglong uranium deposit in the southern Ordos Basin, northern China. Sandstones from the uranium-bearing stratum was collected to analyze morphologies of pyrite and its relations with uranium mineralization by means of scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS). The results show that colloidal and framboidal pyrite, and pentagonal dodecahedron microcrystalline widely occur in sandstones, and uranium minerals are unevenly distributed around pyrite. According to the occurrences of pyrite, morphologies of pyrite are orderly evolved from microcrystalline, and the formation of pyrite is grouped into four periods. Moreover, the pyrite might preferentially or simultaneously precipitate over uranium minerals. The smaller the diameter of pyrite, the more favorable for uranium enrichment. Additionally, variation trends of U contents are opposed to those of the Fe and S contents as well as the Fe/S atomic ratios. Moreover, the decrease rate of S contents is greater than that of Fe contents. It indicates that S and Fe from pyrite both play roles in uranium mineralization, and the S contribution dominates over the Fe contribution. Additionally, the aforementioned conclusion is also supported by the existences of Fe (III), S, SO32-, and SO42. Compared with carbonaceous debris (CD), pyrite might play a dominant role in uranium enrichment. During the process of enrichment and reduction of uranium by pyrite, CD might provide beneficial reducing environment for precipitation and preservation of pyrite and uranium minerals. The study could provide guide for understanding metallogenic mechanism to some extent.

Desulfovibrio desulfuricans AY5 Isolated from a Patient with Autism Spectrum Disorder Binds Iron in Low-Soluble Greigite and Pyrite

The sulphate-reducing bacteria (SRB) of genus Desulfovibrio are a group of prokaryotes associated with autism spectrum disorders (ASD). The connection between the elevated numbers of Desulfovibrio in the gut of children with ASD compared with healthy children remains unresolved. A conceivable consequence of SRB overgrowth in the gut is the conversion of bioavailable iron into low-soluble crystalline iron sulphides, causing iron deficiency in the organism. In this study, we report the draft genome sequence and physiological features of the first cultivable isolate from a patient with ASD, Desulfovibrio desulfuricans strain AY5.The capability of the strain to produce crystalline iron sulphides was studied under different pH conditions. The most notable greigite(Fe3S4) and pyrite (FeS2) formation was revealed at pH 6.0, which suggests that the iron loss due to insoluble sulphide formation may occur in the proximal part of the gastrointestinal tract. Strain AY5 was adapted to grow under nitrogen-limiting conditions by N2 fixation. The urease found in the strain’s genome may play a role in resistance to acidic pH.

The arsenic spreading over thallus of Saccharina latissima of different habitats of the Barents Sea

The algae Saccharina latissima (Phaeophyceae) and bottom sediment were studied in two places of its habitat in the Zelenetskaya Bay of the Barents Sea: 1) in the zone of shipping traffic and ship parking (ZST&SP) and 2) algae plantations (AP) - the background part of the bay. According to the results of scanning electron microscopy and micro-X-ray spectral analysis, an active new formation of framboidal pyrite, iron oxides-hydroxides, and salt crystals were founded in the bottom sediment in the ZCST&SP of the bay. In the structure of the rhizoids of the thallom algae, inclusions of bottom sediment particles were revealed. The ICP MS method showed that the arsenic content in the S. latissima thallom significantly exceeds its level of presence in the bottom sediment. The maximum content of arsenic in algae from both habitats is determined in the rhizoids, and the lowest in the young part of the plate (meristem). The bottom sediment and thallom of S. latissima from the ZCST&SP contain two to three times more arsenic than the algae on the plantation.

An effective method to remove organic sulfur in coal: Effects on the physicochemical properties and combustion kinetics

The present work investigated an effective method to remove organic sulfur in coal utilizing different microorganisms (Nocardia mangyaensis and Pseudomonas putida). The most obvious finding to emerge from the sulfur forms analysis is that the organic sulfur removal of these two bacterial strains on Yunnan bumuga high-sulfur coal were 61.58% and 54.19%, respectively. This result may be confirmed by the Fourier transform infrared spectroscopy (FTIR) analyses that there were obvious decreases of intensity after biotreatment in the CS bond. Besides, the results of X-ray diffraction and X-ray photoelectron spectroscopy showed that major mineralogical phases in the forms of kaolinite and pyrite exist in raw coal. And more than 80% of thiophene and sulfoxide in the raw coal were removed by N. mangyaensis and P. putida. In addition, the results of the thermogravimetric analysis indicated that the combustion performance of biotreated coal samples was better than that of raw coal, and the most probable models to describe the combustion kinetics for biotreated coal and raw coal at different stages were obtained by the Arrhenius method and Coats–Redfern method.

Genesis of visible gold in pyrite in the Zhaoxian gold deposit, Jiaodong gold province, China: Constraints from EBSD micro-structural and LA-ICP-MS elemental analyses

Pyrite (FeS2) is one of the most common hosts for gold (Au) in different types of gold deposits, including visible and invisible gold. For visible gold in pyrite, it remains unclear whether it resulted from remobilization of invisible gold in the gold-hosting pyrite or from external input. This paper reports a case study from the Zhaoxian gold deposit, which is the deep extension of the well-known Jiaojia gold deposit, in the Jiaodong gold province. The texture and composition of Au-bearing pyrite from the Zhaoxian deposit were studied with petrographic, Electron Back-Scattered Diffraction (EBSD) mapping, and Laser Ablation – Inductively Coupled Plasma – Mass Spectrometry (LA-ICP-MS) methods. Four types of pyrite (Py-1 to Py-4), corresponding to four generations of veins, i.e., the pre-ore V1, syn-ore V2 and V3, and post-ore V4, were distinguished. Py-2 is volumetrically the most abundant among the four, and is the main host of visible gold. LA-ICP-MS analyses of pyrite indicate that gold contents in most analysis points are below the detection limit, with measured Au contents ranging from 0.02 to 0.17 ppm (median 0.09 ppm) in Py-1, and 0.03 to 2.45 ppm (median 0.07 ppm) in Py-2. EBSD analyses indicate that pyrite (Py-2) display brittle deformation features including microstructures, lattice dislocation, and grain boundary displacement. Visible gold in Py-2 occurs in micro-fractures, cavities, and grain boundaries. The generally low contents of Au in pyrite, including Py-2, and the brittle deformation features, suggest that the visible gold grains did not result from remobilization of invisible gold from pyrite. Rather, the majority of gold was introduced by fluids after the formation of the gold-hosting pyrite. These fluids were derived from the same sources as those precipitating the gold-hosting pyrite, but were more evolved and enriched in Au. Circulation of these auriferous ore-forming fluids in microfractures of pyrite and interstitial space resulted in precipitation of visible gold.

Extreme biogeochemical effects following simulation of recurrent drought in acid sulfate soils

Droughts are increasing in frequency and severity in many regions of the world and there are uncertainties how recurrent drought will impact acid sulfate soils, which can undergo extreme and persistent acidification (pH < 4) following oxidation. Using column experiments, we induced a 9 week drought/drying and 9 week rewetting phase in two acid sulfate soil profiles with sulfuric (pH < 4) and hypersulfidic materials from the Lower River Murray region of Australia's largest river system. These soils had not yet recovered from the extreme period of the ‘Millennium Drought’ between 2007 and 2010. pH, redox potential, dissolved metals and greenhouse gases (CO2, CH4 and N2O) were measured at multiple depths in each column every 3 weeks during the drying and rewetting phases. The solid phase of the Sulfuric and Hypersulfidic clay soil profiles in both column experiments were analysed for complete acid-base accounting (actual and retained acidity, potential acidity in the form of pyrite, and acid neutralising capacity) and reactive metals at the beginning and end of the experiment. Residual pyrite, present in high concentrations in the Sulfuric clay soil column, oxidised during the drying period, further lowering the pH (<4) and mobilising dissolved metals (Al, Cd, Cu, Ni, Zn). More reactive Fe and Al phases were formed during the drying-rewetting cycle while reactive Mn decreased. The soil pH did not recover (i.e. increase) during the rewetting phase in both the Sulfuric and Hypersulfidic clay soils, likely due to barriers to microbial reduction reactions, although Fe-oxidising bacteria were likely still active as CO2 was released. Acid sulfate soils may not recover in inter-drought periods and more severe impacts can be expected following recurrent droughts.

Significance of 56Fe depletions in late-Archean shales and pyrite

Sedimentary rocks and minerals formed during the final two-hundred million years of the Archean Eon (2.7 to 2.5 billion years ago, or Ga) are more depleted in 56Fe than at any other time in Earth’s past. Three hypotheses are proposed to explain these 56Fe depletions: (1) a very negative late-Archean seawater δ56Fe value, (2) “shuttling” of isotopically light Fe across the chemocline in redox-stratified settings, and (3) pyrite formation in an Fe(II)-rich ocean. Each of these scenarios has different implications for the initial oxidation of Earth’s surface, the climax of which – the Great Oxidation Event – immediately post-dates the appearance of these 56Fe depletions in the rock record. To help inform this debate, we measured the Fe isotope ratios of 120 shale and pyrite samples from Western Australia (Mt. McRae Shale and Jeerinah Formation) and South Africa (Klein Naute Formation) deposited between ∼2.65 Ga and ∼2.50 Ga. As in previous studies, we also find very strong sedimentary 56Fe depletions, to as low as δ56Fe = −2.06 ± 0.08‰ in bulk shales and δ56Fe = −2.31 ± 0.08‰ in pyrite. Some, but not all, of the severest 56Fe depletions appear alongside evidence of an Fe shuttle and local pyrite formation. These processes need not be mutually exclusive, and some combination of them likely played a partial, probably faciliatory role in driving some strong 56Fe depletions in our dataset. Most interestingly, and with little exception, the severest 56Fe depletions appear in samples deposited farther from shore under H2S-rich and anoxic (“euxinic”) conditions. We find it difficult to explain this connection without invoking the persistent presence of a very negative global seawater δ56Fe value during the latest Archean, one that was most consistently captured in sediments formed in distal euxinic settings. In order to impart this isotopic effect on seawater, the global seawater Fe(II) reservoir needed to have been partially oxidized during at least the final few hundreds of millions of years leading up to the Great Oxidation Event. Our new data add support to the idea that Earth’s initial oxidation was a long and protracted process rather than a rapid event.

Multiple sulfur isotopes discriminate organoclastic and methane-based sulfate reduction by sub-seafloor pyrite formation

The marine sulfate inventory represents the largest standing pool of electron acceptors, which, via microbial sulfate reduction, is responsible for roughly half of the organic matter mineralization globally in marine sediments. In addition to the oxidation of buried organic matter, sulfate reduction can be coupled to the oxidation of methane migrating upward. Multiple sulfur isotope ratios were measured for porewater sulfate, sulfide, elemental sulfur and pyrite from core samples collected from continental shelf (19–96 m water depth) in the Baltic Sea and slope (1098 m water depth) in the Andaman Sea, in order to test if their isotope systematics can be used to trace the two different sulfate reduction processes. For shallow shelf sediments (<43 cm below seafloor), both δ34S and Δ33S values of porewater sulfate increased with increasing depth as a result of organoclastic sulfate reduction (OSR). However, the Δ33S values of both porewater sulfate and sulfide decreased as the δ34S values increased downcore at 43–73 cm depth where sulfate reduction was coupled to anaerobic oxidation of methane (AOM). Pyrite in shelf sediments yielded positive Δ33S values, reflecting Δ33S of porewater sulfide produced by OSR. In contrast, pyrite in slope sediments yielded negative Δ33S values as low as −0.15‰, as a result of mixing of sulfides derived from OSR and AOM. This is consistent with the slowly migrating sulfate–methane transition (SMT) in slope sediments inferred from sulfur and iron speciation, carbon isotope ratios of carbonates, and magnetic susceptibility data. A stable SMT, focusing AOM at roughly the same depth over the past few millennia, further provides favorable conditions for prolonged pyrite formation with the development of cubic crystals, while the sulfur isotope difference between bulk pyrite and macroscopic pyrite reflects the significance of OSR throughout the sediment column. We conclude that minor sulfur isotopes provide a unique proxy that can be applied to differentiate OSR and AOM and the origin of pyrite in diverse sediments and sedimentary rocks. This contribution highlights strong local diagenetic controls on pyrite formation and its multiple sulfur isotopic composition in various marine settings.