Carbon In Fluids Research Articles

The source and evolution of ore fluids in the Heiniuwa gold deposit, Baoshan block, Sanjiang region: Constraints from sulfide trace element, fluid inclusion and stable isotope studies

The Heiniuwa gold deposit is located in the northwestern segment of the Longyang Au–Fe–Pb–Zn polymetallic ore cluster in the northern Baoshan block, Sanjiang region, SW China. This ore cluster is characterized by skarn Fe–Pb–Zn mineralization (∼120 Ma) in the central part and Au mineralization in the distal part. The genesis of the Heiniuwa deposit and its relationship with the skarn deposits remain unclear. All orebodies in Heiniuwa are hosted in the Upper Cambrian calcareous slate and siltstone of the Hetaoping Formation, and are controlled by the NS-striking faults. Three main paragenetic stages of mineralization have been recognized based on petrographic observation including, from early to late, a pyrite – arsenopyrite – quartz stage (stage I), a pyrite – pyrrhotite – sphalerite – galena – chalcopyrite – quartz – calcite stage (stage II), and a quartz – calcite – chlorite stage (stage III). Three types of fluid inclusions were identified in the quartz and calcite from the stage I to III in Heiniuwa, including liquid-rich (L-type), vapor-rich (V-type) and solid-bearing (S-type) inclusions. The S-type inclusions only occur in stage I quartz. The fluid inclusions from stage I homogenized at 185–326 °C (concentrating at 220–250 °C), with eutectic temperatures of −48.5 °C to −36.7 °C, final ice-melting temperatures of −11.34 °C to −0.8 °C and salinities ranging from 1.4 to 17.2 wt% NaCl equiv. The inclusions from stage II homogenized at 155–281 °C (concentrating at 190–230 °C), with eutectic temperatures of −51.6 °C to −37.5 °C, final ice-melting temperatures of −10.6 °C to −0.5 °C and corresponding salinities ranging from 0.9 to 14.6 wt% NaCl equiv. The inclusions from stage III homogenized at 116–202 °C (concentrating at 150–170 °C), with eutectic temperature of −45.5 °C to −37.5 °C, final ice-melting temperatures of −4.3 °C to −0.6 °C and salinities ranging from 1.3 to 7.2 wt% NaCl equiv. The microthermometry reveals that the ore-forming fluid of Heiniuwa gold deposit is a typical H2O–NaCl–CaCl2 fluid system. The carbon and oxygen isotopes of calcite show that δ13CPDB and δ18OSMOW values respectively range from −13.4‰ to −6.8‰ and 9.1‰ to 9.6‰ in stage II, and from −8.1‰ to −1.5‰ and 6.4‰ to 8.2‰ in stage III. The bulk marble and calcareous slate samples have δ13CPDB and δ18OSMOW values from −3.0‰ to −0.7‰ and 7.8‰ to 11.9‰, respectively. This suggests that the carbon in the ore-forming fluid was probably from a magmatic source. The δ18Ofluid values of ore-forming fluid vary from 1.6‰ to 2.5‰ in stage I, from −6.2‰ to 0.6‰ in stage II and from −10.8‰ to −2.5‰ in stage III. This indicates that the fluid in stage I is dominantly magmatic, whereas the fluid in stage III is close to meteoric water. The decrease of Na/Ca ratios of ore-forming fluid from stage I to stage III suggests that the interaction with carbonate wallrock is significant during fluid evolution. The sulfide δ34S values range from −5.7‰ to +4.6‰ (mean = +0.3‰, n = 19), agreeing with the explanation based on C–O isotopes and fluid inclusions that the ore-forming fluids are mainly magmatic in origin. In addition, LA-ICP-MS analysis of sulfides also supports this opinion. The stage I pyrite has Cu/Ni ratios greater than 1, and a high concentration of gold; in contrast, the stage II pyrrhotite samples display a very low concentration of gold. This suggests that gold mineralization mainly occurred in stage I. The mixing between magmatic hydrothermal fluid and meteoric water is considered to be a key factor controlling the gold deposition.

Adsorption Of Metamizole Sodium By Activated Carbon In Simulated Gastric And Intestinal Fluids

In vitro adsorption of metamizole sodium by activated carbon was studied at pH 1.2 and 7.5 in order to simulate gastric and intestinal fluids. In the first 5 minutes, more than eighty percent of the total adsorption occurred but the adsorption process achieved to the equilibrium in 1 hour. Time to reach equilibrium was not changed with the changing pH, concentration of the adsorbate or the adsorbent amount. The equilibrium data followed the Langmuir model and therefore fitted to L-type in accordance with the Giles classification for adsorption isotherms. The maximum removal capacities of the activated carbon for metamizole sodium were calculated using Langmuir equation and found as 185.19 mg/g and 161.29 mg/g at pH 1.2 and 7.5, respectively.

Isotope geochemistry of the Sarekuobu metavolcanic-hosted gold deposit in the Chinese Altay (NW China): Implications for the fluid and metal sources

The Late Triassic Sarekuobu lode gold (Au) deposit (reserves: 8.00 t Au at 3.68 g/t) is situated in the Kelan volcanic basin of the Chinese Altay Orogen, NW China. Gold mineralization is hosted in the deformed metavolcanic sequences of the Devonian Kangbutiebao Formation. Multi-isotope analyses were conducted to constrain the ore-forming fluid and metal sources of the Sarekuobu deposit. The measured δDV-SMOW values of the fluid inclusions from the mineralized quartz (stages II and III) are of −132.9‰ to −78.5‰. The measured δ18OV-SMOW values of the quartz range from 11‰ to 13.6‰ (the corresponding calculated δ18OH2O values for the ore fluids: 4.2–6.9‰), which are consistent with those of typical orogenic Au deposits worldwide and fall between the metamorphic water and meteoric water fields in the δ18OH2O vs. δDV-SMOW diagram. This implies that the ore-forming fluids were mainly derived from metamorphic devolatilization with some meteoric water input. Calcite in the late mineralization (Stage III) veinlets contains δ13CV-PDB of −5.2‰ to −1.2‰ and δ18OOV-PDB of −20.4‰ to −19.9‰, similar to the carbonates (limestone and marble) of the Kangbutiebao Formation, and plots near the marine/continental carbonate field(s) in the δ13CV-PDB vs. δ18OOV-PDB diagram. This suggests that the carbon in the late-stage hydrothermal fluids was originated from marine/terrestrial carbonates with organic sediment decarboxylation input. The δ34S values for the Au-hosting sulfides (1.8–8.2 ‰) overlap with the volcanic wall rocks of the Kangbutiebao Formation (−4.7–18.7‰), which suggests that the sulfur was most likely wall rock-derived. The Sarekuobu sulfides contain 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb values of 18.071–18.874, 15.520–15.669, and 37.860–38.961, respectively. The sulfide Sr and Nd isotopes are featured by their narrow compositional ranges and crustal affinities (i.e., (87Sr/86Sr)i = 0.70959–0.72216 and calculated εNd(t) = −3.20000 to −1.86000). All the Pb, Sr and Nd isotope compositions of the Sarekuobu ore sulfides are similar to those of the Kangbutiebao Formation wall rocks, indicating that the metals were mainly wall rock-derived. The structurally-controlled nature, the wall-rock metamorphism and alteration styles (e.g., silicic, chlorite, epidote and carbonate), and the abundance of CO2-rich and low-salinity fluid inclusions of the Sarekuobu deposit are similar to typical orogenic Au deposits. We therefore propose that the Sarekuobu Au deposit is a typical metavolcanic-hosted orogenic Au deposit, and was likely formed in a Triassic collisional-related setting.

Carbonate “clumped” isotope signatures in aragonitic scleractinian and calcitic gorgonian deep-sea corals

Abstract. Deep-sea corals are a potentially valuable archive of the temperature and ocean chemistry of intermediate and deep waters. Living in near-constant temperature, salinity, and pH and having amongst the slowest calcification rates observed in carbonate-precipitating biological organisms, deep-sea corals can provide valuable constraints on processes driving mineral equilibrium and disequilibrium isotope signatures. Here we report new data to further develop “clumped” isotopes as a paleothermometer in deep-sea corals as well as to investigate mineral-specific, taxon-specific, and growth-rate-related effects. Carbonate clumped isotope thermometry is based on measurements of the abundance of the doubly substituted isotopologue 13C18O16O2 in carbonate minerals, analyzed in CO2 gas liberated on phosphoric acid digestion of carbonates and reported as Δ47 values. We analyzed Δ47 in live-collected aragonitic scleractinian (Enallopsammia sp.) and high-Mg calcitic gorgonian (Isididae and Coralliidae) deep-sea corals and compared results to published data for other aragonitic scleractinian taxa. Measured Δ47 values were compared to in situ temperatures, and the relationship between Δ47 and temperature was determined for each group to investigate taxon-specific effects. We find that aragonitic scleractinian deep-sea corals exhibit higher values than high-Mg calcitic gorgonian corals and the two groups of coral produce statistically different relationships between Δ47–temperature calibrations. These data are significant in the interpretation of all carbonate clumped isotope calibration data as they show that distinct Δ47–temperature calibrations can be observed in different materials recovered from the same environment and analyzed using the same instrumentation, phosphoric acid composition, digestion temperature and technique, CO2 gas purification apparatus, and data handling. There are three possible explanations for the origin of these different calibrations. The offset between the corals of different mineralogy is in the same direction as published theoretical predictions for the offset between calcite and aragonite although the magnitude of the offset is different. One possibility is that the deep-sea coral results reflect high-Mg and aragonite crystals attaining nominal mineral equilibrium clumped isotope signatures due to conditions of extremely slow growth. In that case, a possible explanation for the attainment of disequilibrium bulk isotope signatures and equilibrium clumped isotope signatures by deep-sea corals is that extraordinarily slow growth rates can promote the occurrence of isotopic reordering in the interfacial region of growing crystals. We also cannot rule out a component of a biological “vital effect” influencing clumped isotope signatures in one or both orders of coral. Based on published experimental data and theoretical calculations, these biological vital effects could arise from kinetic isotope effects due to the source of carbon used for calcification, temperature- and pH-dependent rates of CO2 hydration and/or hydroxylation, calcifying fluid pH, the activity of carbonic anhydrase, the residence time of dissolved inorganic carbon in the calcifying fluid, and calcification rate. A third possible explanation is the occurrence of variable acid digestion fractionation factors. Although a recent study has suggested that dolomite, calcite, and aragonite may have similar clumped isotope acid digestion fractionation factors, the influence of acid digestion kinetics on Δ47 is a subject that warrants further investigation.

Isotopic characteristics of gold deposits in the Yangshan Gold Belt, West Qinling, central China: Implications for fluid and metal sources and ore genesis

The six main Triassic gold deposits of the Yangshan gold belt are hosted by Devonian metasedimentary rocks and Triassic granitic dikes. It has been suggested by previous workers that they are best classified as either Carlin-like or orogenic gold deposit types. Sulfide minerals spatially associated with disseminated and quartz vein-hosted gold mineralization at Yangshan were deposited in five stages that include syn-metamorphic, early ore, main ore, late ore, and post-ore stages. Based on the relationships defined by ore-mineral assemblages and paragenesis, H, O, C, S, Pb, and Sr isotopic data were obtained from sulfides, quartz, and ore host rocks. The δ18O values of quartz from gold-bearing veins range from 15.9‰ to 21.5‰, and the calculated δ18OH2O values of ore-forming fluids vary from 6.4‰ to 11.8‰, which are consistent with those from typical orogenic gold deposits. The δDH2O values of fluid-inclusions extracted from the quartz vary from −82‰ to −56‰, which are in accord with the δDH2O values of most orogenic gold deposits. Interpretation of the δ13CCO2 values (−4‰ to −2.5‰) in fluid inclusion, shows that marine carbonate is the dominant source for the carbon in the ore-forming fluids, with a minor contribution from magmatic sources. The δ34S values of hydrothermal pyrite, arsenopyrite, and stibnite range from −6.6‰ to 3‰, which suggests sulfur is derived from a deep source. The Pb isotope values for hydrothermal sulfides from both the granitic dike-hosted ores and phyllite-hosted ores overlap the fields for their respective wall rocks, which suggests the source of lead is either the local host rocks, or ore-related fluids that may have pervasively penetrated the host rocks. The age-corrected (87Sr/86Sr)i values of pyrite are 0.70627 to 0.71304, and values for arsenopyrite are 0.71258 to 0.71294, showing that the strontium in the ore fluid could have been derived from the granitic dikes and the regionally extensive Mesoproterozoic to Neoproterozoic Bikou Group. The concordance of δ34S, Pb and (87Sr/86Sr)i values between those for hydrothermal sulfides and country rocks suggests that these crustal rocks contributed the gold that was subsequently concentrated in the ore deposits. The syn-metamorphic stage and early ore stage fluids were likely derived from the country rocks during prograde metamorphism at depth. The oxygen isotope compositions indicate relatively widespread interaction of such fluids with δ18O-rich country rocks during the main ore stage. Compared with most orogenic gold deposits and Carlin-type gold deposits, the gold deposits in the Yangshan gold belt exhibit isotopic characteristics that are most like those of orogenic gold deposits.

Carbon speciation in saline solutions in equilibrium with aragonite at high pressure

The solubility of carbonate minerals and aqueous carbonate speciation in deep fluids is of critical importance to the long-term carbon cycle. However, no experimental data exist in the calcium carbonate–water–salt system at pressures greater than 10kbar. Here we present an integrated experimental and theoretical study of carbon speciation and solubility during equilibration of aragonite with NaCl solutions at 300°C from 20 to 70kbar. Using in situ Raman spectroscopy in a diamond anvil cell with NaCl concentrations up to 1.0m (5.5wt.%), bicarbonate and carbonate ions were the only C-bearing aqueous species spectroscopically detected in the fluids. The proportion of total dissolved bicarbonate to carbonate increased with NaCl concentration and was interpreted using a thermodynamic model to retrieve the dissociation constant of the NaHCO30 complex. The results were extended to higher temperatures using the Deep Earth Water (DEW) model to predict calcite solubility and speciation at 700°C and 10kbar in chloride solutions. With a one parameter extension of the Debye–Hückel model, the calculated solubilities agree with data from Newton and Manning (2002) up to 10m NaCl where the solubility is about 250millimolal. Such solubilities might contribute substantial transport of carbon in fluids at depth in subduction zones.

Effect of Carbon in the Dielectric Fluid and Workpieces on the Characteristics of Recast Layers Machined by Electrical Discharge Machining

Electrical discharge machining (EDM) is a popular non-traditional machining technique that is usually performed in kerosene. Carbon from the kerosene is mixed into the recast layer during EDM, increasing its hardness. EDM can be performed in deionized water, which causes decarburization. We studied the effects of carbon in the dielectric fluid and workpiece on the characteristics of recast layers. Experiments were conducted using gray cast iron and mild steel workpieces in deionized water or kerosene under identical operating conditions. Scanning electron microscopy revealed that the recast layer formed on gray iron was rougher than that produced on mild steel. Moreover, the dispersion of graphite flakes in the gray iron seemed to cause subsurface cracks, even when EDM was performed in deionized water. Dendritic structures and iron carbides were found in the recast layer of gray iron treated in deionized water. Kerosene caused more microcracks to form and increased surface roughness compared with deionized water. The microcrack length per unit area of mild steel treated in deionized water was greater than that treated in kerosene, but the cracks formed in kerosene were wider. The effect of the diffusion of carbon during cooling on the characteristics of the recast layer was discussed.

Geological and isotopic constraints on the origin of the Anle carbonate-hosted Zn–Pb deposit in northwestern Yunnan Province, SW China

The Anle Zn–Pb deposit, hosted by Upper Cambrian dolostone, is located in the southern Songpan–Ganzi Block in southwest China. In this deposit, ore bodies occur as stratiform lenses and consist of galena, sphalerite and pyrite as ore minerals, and quartz, dolomite and calcite as gangue minerals. The mineralization shows mainly vein, banded and brecciated structures. Four ore bodies have been found in the Anle deposit, with a combined 2.0milliontonnes (Mt) of sulfide ores at average grades of 1.64wt.% Pb, 6.64wt.% Zn and 45g/t Ag. Brown, brownish-yellow and yellow sphalerite samples have δ66Zn values ranging from +0.08 to +0.10‰ (average+0.09‰, n=3), +0.12 to +0.38‰ (average+0.24‰, n=8) and +0.40 to +0.50‰ (average+0.46‰, n=3), respectively. We interpret the progressively heavier Zn isotopes from brown to yellow sphalerite as being led by kinetic Raleigh fractional crystallization. Calcite samples have δ13CPDB and δ18OSMOW values ranging from −4.8 to −0.2‰ (average −1.7‰, n=7) and +17.9 to +21.4‰ (average +19.6‰, n=7), respectively. Whole-rock δ13CPDB and δ18OSMOW values of the Cambrian ore-hosting dolostone range from +0.1 to +1.1‰ (average +0.6‰, n=3) and +23.2 to +24.1‰ (average +23.6‰, n=3), respectively. This suggests that carbon in the ore-forming fluids was provided by the host dolostone through carbonate dissolution. δ34SCDT values of sulfide samples range between −1.3‰ and +17.8‰ with an average value of +6.3‰ (n=25), lower than evaporites (such as barite +19.8‰) in the overlaying Lower Ordovician sedimentary strata. The data suggest that sulfur in the hydrothermal fluids were derived from evaporites by thermo-chemical sulfate reduction (TSR). 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb ratios for sulfide minerals range from 17.63 to 17.86, 15.58 to 15.69 and 37.62 to 37.95, respectively. The data are similar to those of the age-corrected Cambrian ore-hosting dolostone (206Pb/204Pb=17.70–17.98, 207Pb/204Pb=15.58–15.65 and 208Pb/204Pb=37.67–38.06), but lower than those of age-corrected Ordovician sandstone and slate (206Pb/204Pb=18.54–19.58, 207Pb/204Pb=15.73–15.81 and 208Pb/204Pb=38.44–39.60). This indicates that ore Pb was most likely to be derived from the Cambrian ore-hosting dolostone. Therefore, our new geological and isotopic evidence suggests that the Anle Zn–Pb deposit is best classified to be an epigenetic carbonate-hosted Mississippi Valley-type (MVT) deposit.

Apoplastic and intracellular plant sugars regulate developmental transitions in witches' broom disease of cacao.

Witches' broom disease (WBD) of cacao differs from other typical hemibiotrophic plant diseases by its unusually long biotrophic phase. Plant carbon sources have been proposed to regulate WBD developmental transitions; however, nothing is known about their availability at the plant-fungus interface, the apoplastic fluid of cacao. Data are provided supporting a role for the dynamics of soluble carbon in the apoplastic fluid in prompting the end of the biotrophic phase of infection. Carbon depletion and the consequent fungal sensing of starvation were identified as key signalling factors at the apoplast. MpNEP2, a fungal effector of host necrosis, was found to be up-regulated in an autophagic-like response to carbon starvation in vitro. In addition, the in vivo artificial manipulation of carbon availability in the apoplastic fluid considerably modulated both its expression and plant necrosis rate. Strikingly, infected cacao tissues accumulated intracellular hexoses, and showed stunted photosynthesis and the up-regulation of senescence markers immediately prior to the transition to the necrotrophic phase. These opposite findings of carbon depletion and accumulation in different host cell compartments are discussed within the frame of WBD development. A model is suggested to explain phase transition as a synergic outcome of fungal-related factors released upon sensing of extracellular carbon starvation, and an early senescence of infected tissues probably triggered by intracellular sugar accumulation.

Important role for organic carbon in subduction-zone fluids in the deep carbon cycle

Earth’s deep carbon cycle is poorly constrained. Theoretical calculations suggest that large amounts of carbon are returned to Earth’s surface as organic and inorganic carbon ions dissolved in subduction-zone fluids.

Geology, isotope geochemistry and ore genesis of the Shanshulin carbonate-hosted Pb–Zn deposit, southwest China

The Shanshulin Pb–Zn deposit occurs in Upper Carboniferous Huanglong Formation dolomitic limestone and dolostone, and is located in the western Yangtze Block, about 270km west of Guiyang city in southwest China. Ore bodies occur along high angle thrust faults affiliated to the Weishui regional fault zone and within the northwestern part of the Guanyinshan anticline. Sulfide ores are composed of sphalerite, pyrite, and galena that are accompanied by calcite and subordinate dolomite. Twenty-two ore bodies have been found in the Shanshulin deposit area, with a combined 2.7milliontonnes of sulfide ores grading 0.54 to 8.94wt.% Pb and 1.09 to 26.64wt.% Zn. Calcite samples have δ13CPDB and δ18OSMOW values ranging from −3.1 to +2.5‰ and +18.8 to +26.5‰, respectively. These values are higher than mantle and sedimentary organic matter, but are similar to marine carbonate rocks in a δ13CPDB vs. δ18OSMOW diagram, suggesting that carbon in the hydrothermal fluid was most likely derived from the carbonate country rocks. The δ34SCDT values of sphalerite and galena samples range from +18.9 to +20.3‰ and +15.6 to +17.1‰, respectively. These values suggest that evaporites are the most probable source of sulfur. The δ34SCDT values of symbiotic sphalerite–galena mineral pairs indicate that deposition of sulfides took place under chemical equilibrium conditions. Calculated temperatures of S isotope thermodynamic equilibrium fractionation based on sphalerite–galena mineral pairs range from 135 to 292°C, consistent with previous fluid inclusion studies. Temperatures above 100°C preclude derivation of sulfur through bacterial sulfate reduction (BSR) and suggest that reduced sulfur in the hydrothermal fluid was most likely supplied through thermo-chemical sulfate reduction (TSR). Twelve sphalerite samples have δ66Zn values ranging from 0.00 to +0.55‰ (mean +0.25‰) relative to the JMC 3-0749L zinc isotope standard. Stages I to III sphalerite samples have δ66Zn values ranging from 0.00 to +0.07‰, +0.12 to +0.23‰, and +0.29 to +0.55‰, respectively, showing the relatively heavier Zn isotopic compositions in later versus earlier sphalerite. The variations of Zn isotope values are likely due to kinetic Raleigh fractional crystallization. The 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb ratios of the sulfide samples fall in the range of 18.362 to 18.573, 15.505 to 15.769 and 38.302 to 39.223, respectively. The Pb isotopic ratios of the studied deposit plot in the field that covers the upper crust, orogenic belt and mantle Pb evolution curves and overlaps with the age-corrected Proterozoic folded basement rocks, Devonian to Lower Permian sedimentary rocks and Middle Permian Emeishan flood basalts in a 207Pb/204Pb vs. 206Pb/204Pb diagram. This observation points to the derivation of Pb metal from mixed sources. Sphalerite samples have 87Sr/86Sr200Ma ratios ranging from 0.7107 to 0.7115 similar to the age-corrected Devonian to Lower Permian sedimentary rocks (0.7073 to 0.7111), higher than the age-corrected Middle Permian basalts (0.7039 to 0.7078), and lower than the age-corrected Proterozoic folded basement (0.7243 to 0.7288). Therefore, the Sr isotope data support a mixed source. Studies on the geology and isotope geochemistry suggest that the Shanshulin deposit is a carbonate-hosted, thrust fault-controlled, strata-bound, epigenetic, high grade deposit formed by fluids and metals of mixed origin.

Positive and negative responses of coral calcification to elevated pCO2: case studies of two coral species and the implications of their responses

Fragments of 2 coral species (Acropora nasuta and Pocillopora damicornis), collected from the South China Sea, were incubated for 94 d under controlled conditions of pCO(2) = 389, 700, and 1214 mu atm. Our incubation experiments showed that the net calcification rate of A. nasuta responded negatively to elevated pCO(2) in both short and mid-term incubations. In contrast, the net calcification rate of P. damicornis increased under elevated pCO(2) during the first 17 d, but then returned to background rates. Based on previous models, our modified models showed that the different responses of these 2 coral species depended on the dissolved inorganic carbon (DIC) and pH levels in coral calcifying fluid. In the studied models, the positive responses of coral calcification to higher pCO(2) could be explained by either low DIC due to a higher photosynthesis rate or a stronger H+ pump. If DIC in calcifying fluid is greatly reduced by photosynthesis, the de creased DIC in calcifying fluid may be benefited by enhanced external seawater CO2, which will partially offset the dissolution due to ocean acidification. Therefore, in addition to our experimental results, our model provides a theoretical basis showing how coral may respond negatively and positively to ocean acidification.

Metasomatism and graphite formation at a lithological interface in Malaspina (Alpine Corsica, France)

Multiple pieces of geologic evidence suggest that interfaces between contrasted lithologies exert a strong control on the fate of volatiles in subduction zones. Here we present results from a contact between serpentinites and sediments, located in Corsica and metamorphosed in the blueschist facies during the alpine orogeny. It was shown previously that carbonates in the sediments have been reduced to graphitic carbonaceous material within a 5–10-cm-thick reaction zone at the contact with serpentinites. In an effort to investigate the mechanisms governing this unusual process, bulk rock geochemical analyses incorporating a statistical analysis of compositional data are presented. Observations show that the fate of C was decoupled from that of other elements such as O, H, and large-ion lithophile elements—e.g. K, Sr, Ba...,As—that were extensively leached from the reaction zone. Notably, Na is strongly enriched in the reaction zone and structurally linked to pectolite. Reducing conditions, manifested by the depletion of O in the reaction zone compared to the bulk metasediment, were likely maintained by the presence of Fe(II) in the serpentinite. Moreover, thermodynamic calculations show that the low solubility of carbon in COH fluids at high-pressure and low-temperature conditions was the main driver for graphite precipitation synchronously with carbonate destabilization. This may have been kinetically favored by the presence of already existing graphitized carbonaceous material and phengite in the metasediment. Limited lateral flow might have contributed as well to the geochemical and petrological patterns observed in these rocks.

Study on Abrasion and Corrosion Resistance of Ti-6Al-4V Alloy Implanted by Carbon in Hank's Simulated Body Fluid

The corrosion characteristic of Ti-6Al-4V alloy implanted by carbon was investigated in Hanks simulated body fluid. The results indicated that a disordered film, which was composed of TiC and Ti by XRD analysis, was formed on the surface of Ti-6Al-4V when Carbon was implanted. Electrochemical tests manifested, after implanted, the alloys corrosion potentials and increased, polarization resistance were increased, and anodic polarization current density decreased in Hanks simulated body fluid. The electrochemical properties were improved. The reason was that the disordered carbide film formed on alloys surface prevented alloying elements form dissolution and enhanced its corrosion resistance. For C implanted sample, the anodic polarization current density was increase when the alloy was abraded. It manifested that friction and abrasion conditions made corrosive environment more serious and accelerated the corrosion process. The alloys friction coefficient and abrasion rate were obviously decreased, and its hardness was increased when it was implanted C.

The Chemistry of Carbon in Aqueous Fluids at Crustal and Upper-Mantle Conditions: Experimental and Theoretical Constraints

Carbon can be a major constituent of crustal and mantle fluids, occurring both as dissolved ionic species (e.g., carbonate ions or organic acids) and molecular species (e.g., CO2, CO, CH4, and more complex organic compounds). The chemistry of dissolved carbon changes dramatically with pressure ( P ) and temperature ( T ). In aqueous fluids at low P and T , molecular carbon gas species such as CO2 and CH4 saturate at low concentration to form a separate phase. With modest increases in P and T , these molecular species become fully miscible with H2O, enabling deep crustal and mantle fluids to become highly concentrated in carbon. At such high concentrations, carbon species play an integral role as solvent components and, with H2O, control the mobility of rock-forming elements in a wide range of geologic settings. The migration of carbon-bearing crustal and mantle fluids contributes to Earth’s carbon cycle; however, the mechanisms, magnitudes, and time variations of carbon transfer from depth to the surface remain least understood parts of the global carbon budget (Berner 1991, 1994; Berner and Kothavala 2001). Here we provide an overview of carbon in crustal and mantle fluids. We first review the evidence for the presence and abundance of carbon in these fluids. We then discuss oxidized and reduced carbon, both as solutes in H2O-rich fluids and as major components of miscible CO2-CH4-H2O fluids. Our goal is to provide some of the background needed to understand the role of fluids in the deep carbon cycle. ### Carbon in aqueous fluids of crust and mantle Numerous lines of evidence indicate that carbon may be an important component of crustal and mantle fluids. Fluid inclusions provide direct samples of carbon-bearing fluids from a range of environments. Carbon species in fluid …

Mineral Solubility and Aqueous Speciation Under Hydrothermal Conditions to 300 C - The Carbonate System as an Example

Carbon is a major element in the Earth’s system and plays an important role in many geochemical processes including metamorphism, volcanism, oceanic systems and atmospheric evolution. Knowledge and understanding of chemical speciation, mineral solubility and reactivity involving carbon are very important in order to qualitatively and quantitatively understand these processes. Indeed, dissolved inorganic carbon is among the major components of natural geothermal fluids. It originates from various sources including magmatic degassing, rock dissolution and organic matter degradation (e.g., Giggenbach 1992; Giggenbach et al. 1993; Simmons and Cristenson 1994; Sanoa and Marty 1995). Dissolved CO2 is the most common form of dissolved inorganic carbon in these systems, though other forms exist like CH4 and CO but usually in much lower concentrations than CO2 (e.g., Chiodini and Marini 1998; Stefansson and Arnorsson 2002). The concentrations of dissolved inorganic carbon (DIC) in geothermal fluids from active geothermal systems throughout the world are shown in Figure 1a together with the pH of the fluids. In general, the DIC concentration increases in geothermal fluids with increasing temperature from a few mmol per kg up to half a mole per kg of fluid. This increase is accompanied by a decrease in the fluid pH (Fig. 1b). Higher concentrations (not shown) are observed in fumarole fluids discharging volcanic gases (e.g., Chiodini et al. 1996). At Earth’s surface, CO2 also degasses through the soils in active geothermal systems (e.g., Chiodini et al. 1998). The chemistry and transport of DIC in natural geothermal systems is influenced by many processes including magma degassing, water-rock interaction and partitioning of CO2 between liquid and vapor phases upon boiling and phase separation. It has been concluded that the concentration of DIC and all other major elements besides incompatible elements such as Cl are …

Linking geochemical processes in mud volcanoes with arsenic mobilization driven by organic matter

The present study deals with geochemical characterization of mud fluids and sediments collected from Kunshuiping (KSP), Liyushan (LYS), Wushanting (WST), Sinyangnyuhu (SYNH), Hsiaokunshui (HKS) and Yenshuikeng (YSK) mud volcanoes in southwestern Taiwan. Chemical constituents (cations, anions, trace elements, organic carbon, humic acid, and stable isotopes) in both fluids and mud were analyzed to investigate the geochemical processes and spatial variability among the mud volcanoes under consideration. Analytical results suggested that the anoxic mud volcanic fluids are highly saline, implying connate water as the probable source. The isotopic signature indicated that δ18O-rich fluids may be associated with silicate and carbonate mineral released through water–rock interaction, along with dehydration of clay minerals. Considerable amounts of arsenic in mud irrespective of fluid composition suggested possible release through biogeochemical processes in the subsurface environment. Sequential extraction of As from the mud indicated that As was mostly present in organic and sulphidic phases, and adsorbed on amorphous Mn oxyhydroxides. Volcanic mud and fluids are rich in organic matter (in terms of organic carbon), and the presence of humic acid in mud has implications for the binding of arsenic. Functional groups of humic acid also showed variable sources of organic matter among the mud volcanoes being examined. Because arsenate concentration in the mud fluids was found to be independent from geochemical factors, it was considered that organic matter may induce arsenic mobilization through an adsorption/desorption mechanism with humic substances under reducing conditions. Organic matter therefore plays a significant role in the mobility of arsenic in mud volcanoes.

Inorganic chemistry, gas compositions and dissolved organic carbon in fluids from sedimented young basaltic crust on the Juan de Fuca Ridge flanks

The permeable upper oceanic basement serves as a plausible habitat for a variety of microbial communities. There is growing evidence suggesting a substantial subseafloor biosphere. Here new time series data are presented on key inorganic species, methane, hydrogen and dissolved organic carbon (DOC) in ridge flank fluids obtained from subseafloor observatory CORKs (Circulation Obviation Retrofit Kits) at Integrated Ocean Drilling Program (IODP) boreholes 1301A and 1026B. These data show that the new sampling methods (Cowen et al., 2012) employed at 1301A result in lower contamination than earlier studies. Furthermore, sample collection methods permitted most chemical analyses to be performed from aliquots of single large volume samples, thereby allowing more direct comparison of the data. The low phosphate concentrations (0.06–0.2μM) suggest that relative to carbon and nitrogen, phosphorus could be a limiting nutrient in the basement biosphere. Coexisting sulfate (17–18mM), hydrogen sulfide (∼0.1μM), hydrogen (0.3–0.7μM) and methane (1.5–2μM) indicates that the basement aquifer at 1301A either draws fluids from multiple flow paths with different redox histories or is a complex environment that is not thermodynamically controlled and may allow co-occurring metabolic pathways including sulfate reduction and methanogenesis. The low DOC concentrations (11–18μM) confirm that ridge flank basement is a net DOC sink and ultimately a net carbon sink. Based on the net amounts of DOC, oxygen, nitrate and sulfate removed (∼30μM, ∼80μM, ∼40μM and ∼10mM, respectively) from entrained bottom seawater, organic carbon may be aerobically or anaerobically oxidized in biotic and/or abiotic processes.

Tracing iron-fueled microbial carbon production within the hydrothermal plume at the Loihi seamount

The Loihi hydrothermal plume provides an opportunity to investigate iron (Fe) oxidation and microbial processes in a system that is truly Fe dominated and distinct from mid-ocean ridge spreading centers. The lack of hydrogen sulfide within the Loihi hydrothermal fluids and the presence of an oxygen minimum zone at this submarine volcano’s summit, results in a prolonged presence of reduced Fe within the dispersing non-buoyant plume. In this study, we have investigated the potential for microbial carbon fixation within the Loihi plume. We sampled for both particulate and dissolved organic carbon in hydrothermal fluids, microbial mats growing around vents, and the dispersing plume, and carried out stable carbon isotope analysis on the particulate fraction. The δ 13C values of the microbial mats ranged from −23‰ to −28‰, and are distinct from those of deep-ocean particulate organic carbon (POC). The mats and hydrothermal fluids were also elevated in dissolved organic carbon (DOC) compared to background seawater. Within the hydrothermal plume, DOC and POC concentrations were elevated and the isotopic composition of POC within the plume suggests mixing between background seawater POC and a 13C-depleted hydrothermal component. The combination of both DOC and POC increasing in the dispersing plume that cannot solely be the result of entrainment and DOC adsorption, provides strong evidence for in-situ microbial productivity by chemolithoautotrophs, including a likelihood for iron-oxidizing microorganisms.

Ecological implications of organic carbon dynamics in the traps of aquatic carnivorous Utricularia plants.

Rootless aquatic carnivorous Utricularia exude up to 25% of their photosynthates into the trap lumen, which also harbours a complex microbial community thought to play a role in enhancing Utricularia nutrient acquisition. We investigated the composition of organic carbon in the trap fluid, its availability for microbial uptake, the influence of plant nutrient status and trap age on its biodegradability, and the composition of prokaryotic assemblages within the traps of three aquatic Utricularia species. Using ion chromatography and basal respiration rate measurements we confirmed that up to 30% of total dissolved organic carbon in Utricularia trap fluid in oligotrophic conditions was easily biodegradable compounds commonly found in plant root exudates (mainly glucose, fructose and lactate). The proportion of these compounds and their microbial utilisation decreased with increasing mineral nutrient supply and trap age. Fluorescence in situ hybridisation analyses showed that microbial trap assemblages are dominated by alpha and beta Proteobacteria, and that the assemblage composition is affected by changes in the ambient mineral nutrient supply. We suggest that organic carbon dynamics within the traps, involving both the plant and associated microbial assemblages, underlies the acquisition of key nutrients by Utricularia and may help explain the evolutionary success of the genus.