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USGS1981

Seawater sulfate reduction and sulfur isotope fractionation in basaltic systems: interaction of seawater with fayalite and magnetite at 200–350°C

Sulfate reduction during seawater reaction with fayalite and with magnetite was rapid at 350°C, producing equilibrium assemblages of talc-pyrite-hematite-magnetite at low water/rock ratios and talc-pyrite-hematite-anhydrite at higher water/rock ratios. At 250°C, seawater reacting with fayalite produced detectable amounts of dissolved H 2 S, but extent of reaction of solid phases was minor after 150 days. At 200°C, dissolved H 2 S was not detected, even after 219 days, but mass balance calculations suggest a small amount of pyrite may have formed. Reaction stoichiometry indicates that sulfate reduction requires large amounts of H + , which, in subseafloor hydrothermal systems is provided by Mg metasomatism. Seawater contains sufficient Mg to supply all the H + necessary for quantitative reduction of seawater sulfate. Systematics of sulfur isotopes in the 250 and 350°C experiments indicate that isotopic equilibrium is reached, and can be modeled as a Rayleigh distillation process. Isotopic composition of hydrothermally produced H 2 S in natural systems is strongly dependent upon the seawater/basalt ratio in the geothermal system, which controls the relative sulfide contributions from the two important sulfur sources, seawater sulfate and sulfide phases in basalt. Anhydrite precipitation during geothermal heating severely limits sulfate ingress into high temperature interaction zones. Quantitative sulfate reduction can thus be accomplished without producing strongly oxidized rocks and resultant sulfide sulfur isotope values represent a mixture of seawater and basaltic sulfur.

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USGS1981

The aluminosilicate fraction of North Pacific manganese nodules

Nine nodules collected from throughout the deep North Pacific were analyzed for their mineralogy and major-element composition before and after leaching with Chester-Hughes solution. Data indicate that the mineral phillipsite accounts for the major part (> 75%) of the aluminosilicate fraction of all nodules. It is suggested that formation of phillipsite takes place on growing nodule surfaces coupled with the oxidation of absorbed manganous ion. All the nodules could be described as ternary mixtures of amorphous iron fraction (Fe-Ti-P), manganese oxide fraction (Mn-Mg Cu-Ni), and phillipsite fraction (Al-Si-K-Na), these fractions accounting for 96% of the variability of the chemical composition.

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USGS1981

The origin of epigenetic graphite: Evidence from isotopes

Stable carbon isotope ratios measured in syngenetic graphite, epigenetic graphite, and graphitic marble suggests that syngenetic graphite forms only by the metamorphism of carbonaceous detritus. Metamorphism of calcareous rocks with carbonaceous detritus is accompanied by an exchange of carbon between the two, which may result in large changes in isotopic composition of the non-carbonate phase but does not affect the relative proportions of the two reactants in the rock. Epigenetic graphite forms only from carbonaceous material or preexisting graphite. The reactions involved are the water gas reaction (C + H 2 O → CO + H 2 ) at 800–900°C, and the Boudouard reaction (2CO → C + CO 2 ), which probably takes place at temperatures about 50–100°C lower.

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USGS1981

Pyrolysis gas chromatography-mass spectrometry to characterize organic matter and its relationship to uranium content of Appalachian Devonian black shales

Gas Chromatographic analysis of volatile products formed by stepwise pyrolysis of black shales can be used to characterize the kerogen by relating it to separated, identified precursors such as land-derived vitrinite and marine-source Tasmanites . Analysis of a Tasmanites sample shows exclusively n- alkane "> n-alkane and -alkene pyrolysis products, whereas a vitrinite sample shows a predominance of one- and two-ring substituted aromatics. For core samples from northern Tennessee and for a suite of outcrop samples from eastern Kentucky, the organic matter type and the U content (<10−120ppm) show variations that are related to precursor organic materials. The samples that show a high vitrinite component in their pyrolysis products are also those samples with high contents of U.

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USGS1981

Fractionation of carbon and hydrogen isotopes by methane-oxidizing bacteria

Carbon isotopic analysis of methane has become a popular technique in the exploration for oil and gas because it can be used to differentiate between thermogenic and microbial gas and can sometimes be used for gas-source rock correlations. Methane-oxidizing bacteria, however, can significantly change the carbon isotopic composition of methane; the origin of gas that has been partially oxidized by these bacteria could therefore be misinterpreted. We cultured methane-oxidizing bacteria at two different temperatures and monitored the carbon and hydrogen isotopic compositions of the residual methane. The residual methane was enriched in both 13 C and D. For both isotopic species, the enrichment at equivalent levels of conversion was greater at 26°C than at 11.5°C. The change in δD relative to the change in δ 13 C was independent of temperature within the range studied. One culture exhibited a change in the fractionation pattern for carbon (but not for hydrogen) midway through the experiment, suggesting that bacterial oxidation of methane may occur via more than one pathway. The change in the δD value for the residual methane was from 8 to 14 times greater than the change in the δ 13 C value, indicating that combined carbon and hydrogen isotopic analysis may be an effective way of identifying methane which has been subjected to partial oxidation by bacteria.

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USGS1981

Sm-Nd systematics of a tonalitic augen gneiss and its constituent minerals from northern Michigan

The Sm-Nd isotopic system of a tonalitic augen gneiss and its constituent minerals from northern Michigan was disturbed during metamorphism. Sm-Nd zircon ages are lower than the wholerock Sm-Nd model age. However, closely associated pairs of minerals (for example, sphene and biotite or apatite and plagioclase) retain their apparent metamorphic ages. The Sm-Nd model age for the tonalitic augen gneiss of 3919 ± 30 myr , appears to reflect open system behavior during metamorphism. A mineralogically different gneiss from the same location has a Sm-Nd model age of 3520 ± 70 myr . The two whole rocks differ in their Sm-Nd and Rb-Sr systematics and in their chondrite-normalized rare earth element (REE) patterns. The whole-rock-normalized mineral REE patterns show the contribution of the major and trace minerals to the REE content of the whole rock. The trace minerals contain a significant amount of the total REE.

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USGS1981

Experimental seawater-basalt interaction at 300°C, 500 bars, chemical exchange, secondary mineral formation and implications for the transport of heavy metals

Seawater and NaCl solutions were reacted with basalt (basalt glass and diabase) for several months at 300°C, 500 bars and a water/rock ratio of 10. During reaction, seawater was significantly modified, increasing in Ca, H 2 S, CO 2 . SiO 2 , K. Fe, Mn. Ba, Al and H + , and decreasing in Mg and SO 4 . Basalt glass was completely replaced by smectite, wairakite, anhydrite and hematite, and diabase was partially replaced by mixed layered smectite-chlorite, anhydrite and magnetite (?). Diabase was altered more slowly than basalt glass and the corresponding changes in seawater chemistry were less pronounced. Basalt glass reacted with a 0.45 m NaCl solution resulted in the formation of smectite, albite. truscottite and wairakite. Solutions from this experiment were characterized by a relatively high pH and dominated by Ca for Na exchange reactions. At no point in this experiment were heavy metals solubilized, in contrast to the seawater experiments. This behavior illustrates the fundamental importance of seawater chemistry to heavy-metal solubility; that is, the removal of Mg from seawater generates acidity which maintains heavy metals in solution. Apparently seawater chlorinity is not capable of enhancing heavy-metal solubility by chloride complexing. Seafloor heavy-metal deposits can result from the following: Seawater-basalt interaction at moderate temperature (&sim;-300°C and high effective water/rock ratios; or at relatively high temperatures (&sim;-400°C) and low (e.g.< 10) water/rock ratios.

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USGS1981

Age estimations based on amino acid racemization: Reply to comments of J.F. Wehmiller

Determining geologic ages of fossils by amino acid racemization techniques is often difficult because of the uncertainties in assumptions about diagenetic temperatures. Two kinetic model methods have been employed. Method 1, used by us, assumes that racemization of amino acids in the bivalve mollusk Saxidomus giganteus from Willapa Bay, Washington, follows linear kinetics. Ages are calculated by means of first-order kinetic equations. Method 2, used by Wehmiller, involves an empirical non-linear kinetic model Method 1 is simpler in concept and more easily applied. Wehmiller claims that ambiguities in paleotemperature arise when method 1 is used and that these ambiguities can be reconciled by the use of method 2. We show that application of method 1 can also provide reasonable temperature histories and leads to age estimates that are consistent with the geologic history of the sedimentary deposits at Willapa Bay.

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USGS1981

Crystal growth of calcite from calcium bicarbonate solutions at constant P CO 2 and 25°C: a test of a calcite dissolution model

A highly reproducible seeded growth technique was used to study calcite crystallization from calcium bicarbonate solutions at 25°C and fixed carbon dioxide partial pressures between 0.03 and 0.3 atm. The results are not consistent with empirical crystallization models that have successfully described calcite growth at low P CO 2 (< 10 −3 atm). Good agreement was found between observed crystallization rates and those calculated from the calcite dissolution rate law and mechanism proposed by Plummer et al . (1978).

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USGS1981

Rates of manganese oxidation in aqueous systems

The rate of crystal growth of Mn 3 O 4 (hausmannite) and βMnOOH (feitknechtite) in aerated aqueous manganous perchlorate systems, near 0.01 M in total manganese, was determined at pH levels ranging from 7.00 to 9.00 and at temperatures from 0.5 to 37.4°C. The process is autocatalytic, but becomes psuedo first-order in dissolved Mn 2+ activity when the amount of precipitate surface is large compared to the amount of unreacted manganese. Reaction rates determined by titrations using an automated pH-stat were fitted to an equation for precipitate growth. The rates are proportional to surface area of oxide and degree of supersaturation with respect to Mn 2+ . The oxide obtained at the higher temperature was Mn 3 O 4 , but at 0.5° C only βMnOOH was formed. At intermediate temperatures, mixtures of these solids were formed. The rate of precipitation of hausmannite is strongly influenced by temperature, and that of feitknechtite much less so. The difference in activation energy may be related to differences in crystal structure of the oxides and the geometry of polymeric hydroxy ion precursors.

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USGS1981

13C 12C exchange between calcite and graphite: A possible thermometer in Grenville marbles

The fractionation of 13 C between calcite and graphite, Δ(Cc-Gr). is consistently small (2.6–4.8 permil) in 34 assemblages from upper amphibolite- and granulite-facies marbles of the Grenville Province. In 25 samples from the Adirondack Mountains, New York, it decreases regularly with increasing metamorphic temperature. The fractionations are independent of absolute δ 13 C values of calcite (−2.9 to +5.0). For T = 600–800° C , the Adirondack data are described by Δ ( Cc - Gr ) = −0.00748 T (° C ) + 8.68. This good correlation between Δ and T suggests that carbon isotope equilibrium was attained in these high-grade marbles and that the theoretical calculations of this fractionation by Bottinga are approximately 2 permil too large in this temperature range. Because of the relatively high temperature sensitivity suggested by these results and by Bottinga's calculations, and the pressure independence of isotope fractionation, Δ(Cc-Gr) may provide a very good thermometer for high-grade marbles. Comparison of this field calibration for Δ(Cc-Gr) vs temperature with results from other terranes supports the utility of Δ(Cc-Gr) for geothermometry and suggests that graphite is much more sluggish to exchange than calcite, that exchange between calcite and graphite occurs at temperatures as low as 300°C, and that equilibrium may normally be attained only when peak metamorphic temperatures are greater than 500–600°C. Because 13 C exchange is an unavoidable metamorphic process at temperatures above 300°C, high values of δ 13 C(Gr) in moderate- to high-grade carbonate-bearing rocks do not provide a sufficient criterion to infer an abiogenic origin for the graphite.

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USGS1982

Chemistry and isotope ratios of sulfur in basalts and volcanic gases at Kilauea volcano, Hawaii

Eighteen basalts and some volcanic gases from the submarine and subaerial parts of Kilauea volcano were analyzed for the concentration and isotope ratios of sulfur. By means of a newly developed technique, sulfide and sulfate sulfur in the basalts were separately but simultaneously determined. The submarine basalt has 700 ± 100 ppm total sulfur with δ 34 S Σs of 0.7 ± 0.1 ‰ ">‰ 0.7 ± 0.1 ‰ . The sulfate/sulfide molar ratio ranges from 0.15 to 0.56 and the fractionation factor between sulfate and sulfide is +7.5 ± 1.5‰ ">‰ +7.5 ± 1.5‰ . On the other hand, the concentration and δ 34 S Σs values of the total sulfur in the subaerial basalt are reduced to 150 ± 50 ppm and −0.8 ± 0.2‰ ">‰ −0.8 ± 0.2‰ , respectively. The sulfate to sulfide ratio and the fractionation factor between them are also smaller, 0.01 to 0.25 and +3.0‰, respectively. Chemical and isotopic evidence strongly suggests that sulfate and sulfide in the submarine basalt are in chemical and isotopic equilibria with each other at magmatic conditions. Their relative abundance and the isotope fractionation factors may be used to estimate the ƒo 2 "> ƒo 2 and temperature of these basalts at the time of their extrusion onto the sea floor. The observed change in sulfur chemistry and isotopic ratios from the submarine to subaerial basalts can be interpreted as degassing of the SO 2 from basalt thereby depleting sulfate and 34 S in basalt. The volcanic sulfur gases, predominantly SO 2 , from the 1971 and 1974 fissures in Kilauea Crater have δ 34 S values of 0.8 to 0.9%., slightly heavier than the total sulfur in the submarine basalts and definitely heavier than the subaerial basalts, in accord with the above model. However, the δ 34 S value of sulfur gases (largely SO 2 ) from Sulfur Bank is 8.0%., implying a secondary origin of the sulfur. The δ 34 S values of native sulfur deposits at various sites of Kilauea and Mauna Loa volcanos, sulfate ions of four deep wells and hydrogen sulfide from a geothermal well along the east rift zone are also reported. The high δ 34 S values (+5 to +6%. o ) found for the hydrogen sulfide might be an indication of hot basalt seawater reaction beneath the east rift zone.

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USGS1982

The solubilities of calcite, aragonite and vaterite in CO2-H2O solutions between 0 and 90°C, and an evaluation of the aqueous model for the system CaCO3-CO2-H2O

Calculations based on approximately 350 new measurements (Ca T -PCO 2 ) of the solubilities of calcite, aragonite and vaterite in CO 2 -H 2 O solutions between 0 and 90°C indicate the following values for the log of the equilibrium constants K C , K A , and K V respectively, for the reaction CaCO 3 (s) = Ca 2+ + CO 2− 3 : where T is in o K. At 25°C the logarithms of the equilibrium constants are −8.480 ± 0.020, −8.336 ± 0.020 and −7.913 ± 0.020 for calcite, aragonite and vaterite, respectively. The equilibrium constants are internally consistent with an aqueous model that includes the CaHCO + 3 and CaCO 0 3 ion pairs, revised analytical expressions for CO 2 -H 2 O equilibria, and extended Debye-Hückel individual ion activity coefficients. Using this aqueous model, the equilibrium constant of aragonite shows no PCO 2 -dependence if the CaHCO + 3 association constant is between 0 and 90°C, corresponding to the value log K Cahco + 3 = 1.11 ± 0.07 at 25°C. The CaCO 0 3 association constant was measured potentiometrically to be between 5 and 80°C, yielding log K CaCO 0 3 = 3.22 ± 0.14 at 25°C. The CO 2 -H 2 O equilibria have been critically evaluated and new empirical expressions for the temperature dependence of K H , K 1 and K 2 are , and log K 2 = −107.8871 − 0.03252849 T + 5151.79/ T + 38.92561 log T − 563713.9/ T 2 which may be used to at least 250°C. These expressions hold for 1 atm. total pressure between 0 and 100°C and follow the vapor pressure curve of water at higher temperatures. Extensive measurements of the pH of Ca-HCO 3 solutions at 25°C and 0.956 atm PCO 2 using different compositions of the reference electrode filling solution show that measured differences in pH are closely approximated by differences in liquid-junction potential as calculated by the Henderson equation. Liquid-junction corrected pH measurements agree with the calculated pH within 0.003-0.011 pH. Earlier arguments suggesting that the CaHCO + 3 ion pair should not be included in the CaCO 3 -CO 2 -H 2 O aqueous model were based on less accurate calcite solubility data. The CaHCO + 3 ion pair must be included in the aqueous model to account for the observed PCO 2 -dependence of aragonite solubility between 317 ppm CO 2 and 100% CO 2 . Previous literature on the solubility of CaCO 3 polymorphs have been critically evaluated using the aqueous model and the results are compared.

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USGS1982

Phase relations in the system NaCl-KCl-H2O. Part I: Differential thermal analysis of the NaCl-KCl liquidas at 1 atmosphere and 500, 1000, 1500, and 2000 bars

A simple differential thermal analysis (DTA) technique has been developed to study phase relations of various chemical systems at elevated pressures and temperatures. The DTA system has been calibrated against known melting temperatures in the system NaCl-KCl. Isobaric sections of the liquidus in the system NaCl-KCl have been determined at pressures of 1 atmosphere and 500, 1000, 1500, and 2000 bars. Using the least-squares method, the following equation was used to fit the experimental data: T(°C)= ∑ i=0 6 a i X i KCl "> T(°C)=∑i=06a i X i KCl where T is the liquidus temperature, X KCl is mole fraction of KCl, and a i (listed below) are the derived empirical constants. P (bars) a o "> ao a 1 "> a1 a 2 "> a2 a 3 "> a3 a 4 "> a4 a 5 "> a5 a 6 "> a6 1 atm. 800.1 −334.2 781.6 −6490.3 17553.1 −17638.4 6098.3 500 813.5 −354.9 743.3 −6011.7 16406.4 −16516.3 5702.8 1000 824.5 −406.7 1446.8 −8818.4 21253.5 −20343.7 6839.4 1500 838.6 −418.7 1434.7 −8819.0 21557.9 −20908.4 7123.1 2000 848.5 −381.5 1246.9 −8605.0 21785.8 −21449.1 7375.8 The liquidus temperatures estimated from these equations are within ±3°C of experimental values. The measured liquidus temperatures at 1 atmosphere agree with the best available data to within 5°C. The melting temperatures for pure end members at higher pressures agree with the values calculated from the Simon equation (Clark, 1959) to within 3°C. No previous melting data are available for the intermediate compositions at elevated pressures. Using the data in both heating and cooling scans, the minimum melting temperature at 1 atmosphere in the system was located at 658° ± 3° C where the sample has an equimolar composition.

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USGS1982

The solubility of quartz in aqueous sodium chloride solution at 350°C and 180 to 500 bars

The solubility of quartz in 2, 3, and 4 molal NaCl was measured at 350°C and pressures ranging from 180 to 500 bars. The molal solubility in each of the salt solutions is greater than that in pure water throughout the measured pressure range, with the ratio of solubility in NaCl solution to solubility in pure water decreasing as pressure is increased. The measured solubilities are significantly higher than solubilities calculated using a simple model in which the water activity in NaCl solutions decreases either in proportion to decreasing vapor pressure of the solution as salinity is increased or in proportion to decreasing mole fraction of water in the solvent.

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USGS1982

The effect of sulfate on aluminum concentrations in natural waters: some stability relations in the system Al2O3-SO3-H2O at 298 K

While gibbsite and kaolinite solubilities usually regulate aluminum concentrations in natural waters, the presence of sulfate can dramatically alter these solubilities under acidic conditions, where other, less soluble minerals can control the aqueous geochemistry of aluminum. The likely candidates include alunogen, Al 2 (SO 4 ) 3 · 17H 2 O, alunite, KAl 3 (SO 4 ) 2 (OH) 6 , jurbanite, Al(SO 4 )(OH) · 5H 2 O, and basaluminite, Al 4 (SO 4 )(OH) 10 · 5H 2 O. An examination of literature values shows that the log K sp = −85.4 "> Ksp= −85.4 for alunite and log K sp = −117.7 "> Ksp= −117.7 for basaluminite. In this report the log K sp = −7.0 "> Ksp= −7.0 is estimated for alunogen and log K sp = −17.8 "> Ksp= −17.8 is estimated for jurbanite. The solubility and stability relations among these four minerals and gibbsite are plotted as a function of pH and sulfate activity at 298 K. Alunogen is stable only at pH values too low for any natural waters (<0) and probably only forms as efflorescences from capillary films. Jurbanite is stable from pH < 0 "> pH < 0 up to the range of 3–5 depending on sulfate activity. Alunite is stable at higher pH values than jurbanite, up to 4–7 depending on sulfate activity. Above these pH limits gibbsite is the most stable phase. Basaluminite, although kinetically favored to precipitate, is metastable for all values of pH and sulfate activity. These equilibrium calculations predict that both sulfate and aluminum can be immobilized in acid waters by the precipitation of aluminum hydroxysulfate minerals. Considerable evidence supports the conclusion that the formation of insoluble aluminum hydroxy-sulfate minerals may be the cause of sulfate retention in soils and sediments, as suggested by Adams and Rawajfih (1977), instead of adsorption.

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USGS1982

Adsorption of natural dissolved organic matter at the oxide/water interface

Natural organic matter is readily adsorbed by alumina and kaolinite in the pH range of natural waters. Adsorption occurs by complex formation between surface hydroxyls and the acidic functional groups of the organic matter. Oxides with relatively acidic surface hydroxyls, e.g. silica, do not react strongly with the organic matter. Under conditions typical for natural waters, almost complete surface coverage by adsorbed organic matter may be expected for alumina, hydrous iron oxides and the edge sites of aluminosilicates. Potentiometric titration and electrophoresis indicate that most of the acidic functional groups of the adsorbed organic matter are neutralized by protons from solution. The organic coating is expected to have a great influence on subsequent adsorption of inorganic cations and anions.

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USGS1983

Large partition coefficients for trace elements in high-silica rhyolites

The partitioning of 25 trace elements between high-silica rhyolitic glass and unzoned phenocrysts of potassic and sodic sanidine, biotite, augite, ferrohedenbergite, hypersthene, fayalite, titanomagnetite, ilmenite, zircon, and allanite has been determined by INAA on suites of samples from the mildly peralkaline lavas and tuff of the Sierra La Primavera, Mexico, and the metaluminous, compo. sitionally zoned, Bishop Tuff, California. The partition coefficients are much larger than published values for less silicic compositions; the range of values among Primavera samples that differ only slightly in temperature or bulk composition approaches that previously reported from basalts to rhyodacites. Intrinsic temperature dependence of the crystal/liquid partitioning is apparently small. The high values of partition coefficients reflect principally the strongly polymerized nature of the alkali-aluminosilicate liquid, whereas the marked variability of values for partition coefficients is attributed to differences in the concentrations of complexing ligands and/or different degrees of melt polymerization. Great variation in the values of partition coefficients that are potentially applicable to early stages in the partial melting of crustal rocks complicates assessment of 1. (1) source regions for granitic melts and 2. (2) contributions by crustal-melt increments to andesites.

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