two pulses of mineralization and genesis of the zhaxikang sb pb zn ag deposit in southern tibet constraints from fe zn isotopes abstract zhaxikang is one large sb pb zn ag deposit located in the north himalaya of southern tibet to date the genesis of this deposit still remains controversial here we present new pyrite fe and sphalerite zn isotopic data for the first three stages of mineralization fe zn isotopic data for mn fe carbonate that formed during the first two stages of mineralization and zn isotopic data for the slate wall rocks of the jurassic ridang formation to discuss the genesis of the zhaxikang deposit the overall 56 fe and 66 zn values range from 0 80 to 0 43 and from 0 03 to 0 38 respectively the 56 fe values of mn fe carbonates are lighter than those of associated pyrite in six mineral pairs indicating that the iron carbonates are preferentially enriched in light fe isotopes relative to pyrite the sphalerite has lighter 66 zn values than associated mn fe carbonates in three mineral pairs the 56 fe values of pyrite that formed during the first three stages of mineralization gradually increase from stage 1 0 33 to 0 09 through stage 2 0 30 to 0 19 to stage 3 0 16 0 43 in comparison the sphalerite that formed during these stages has 66 zn values that gradually decrease from stage 1 0 16 0 35 through stage 2 0 09 0 23 to stage 3 0 03 to 0 22 these data in conjunction with the observations of hand specimens and thin sections suggest that the deposit was overprinted by a second pulse of mineralization this overprint would account for these fe zn isotopic variations as well as the kinetic rayleigh fractionation that occurred during mineralization the temporally increasing 56 fe and decreasing 66 zn values recorded in the deposit are also coincident with an increase in alteration again supporting the existence of two pulses of mineralization the 56 fe values of the first pulse of ore forming fluid were calculated using theoretical equations yielding values of 0 54 to 0 34 that overlap with those of submarine hydrothermal solutions 1 to 0 however the 56 fe values of the stage 3 pyrite are heavier than those of typical submarine hydrothermal solutions which suggests that the second pulse of mineralization was probably derived from a magmatic hydrothermal fluid in addition the second pulse of ore forming fluid has brought some fe and taken away parts of zn which results the lighter 66 zn values of sphalerite and heavier 56 fe values of pyrite from the second pulse of mineralization overall the zhaxikang deposit records two pulses of mineralization and the overprint by the second pulse of mineralization causes the lighter 66 zn values and heavier 56 fe values of modified samples

an empirical determination of the minimum number of measurements needed to estimate the mean random vitrinite reflectance of disseminated organic matter abstract in coal samples published recommendations based on statistical methods suggest 100 measurements are needed to estimate the mean random vitrinite reflectance r v r to within 2 our survey of published thermal maturation studies indicates that those using dispersed organic matter dom mostly have an objective of acquiring 50 reflectance measurements this smaller objective size in dom versus that for coal samples poses a statistical contradiction because the standard deviations of dom reflectance distributions are typically larger indicating a greater sample size is needed to accurately estimate r v r in dom however in studies of thermal maturation using dom even 50 measurements can be an unrealistic requirement given the small amount of vitrinite often found in such samples furthermore there is generally a reduced need for assuring precision like that needed for coal applications therefore a key question in thermal maturation studies using dom is how many measurements of r v r are needed to adequately estimate the mean our empirical approach to this problem is to compute the reflectance distribution statistics mean standard deviation skewness and kurtosis in increments of 10 measurements this study compares these intermediate computations of r v r statistics with a final one computed using all measurements for that sample vitrinite reflectance was measured on mudstone and sandstone samples taken from borehole m 25 in the cerro prieto mexico geothermal system which was selected because the rocks have a wide range of thermal maturation and a comparable humic dom with depth the results of this study suggest that after only 20 30 measurements the mean r v r is generally known to within 5 and always to within 12 of the mean r v r calculated using all of the measured particles thus even in the worst case the precision after measuring only 20 30 particles is in good agreement with the general precision of one decimal place recommended for mean r v r measurements on dom the coefficient of variation v standard deviation mean is proposed as a statistic to indicate the reliability of the mean r v r estimates made at n 20 this preliminary study suggests a v v 0 2 suggests an unreliable mean in such small samples

early stages of core segregation recorded by fe isotopes in an asteroidal mantle ureilites displays 56 fe values higher than average chondrite 29 segregation of fe sulfide melts explains the high 56 fe values in ureilites 30 formation of a core can begin at very low degrees of melting through the circulation of a fe s melt 31 through a silicate mantle 32 33 earth and planetary science letters in press 11 3 15 34 2 35 abstract 36 37 ureilite meteorites are achondrites that are debris of the mantle of a now disrupted 38 differentiated asteroid rich in carbon they provide a unique opportunity to study the differentiation 39 processes of such a body we analyzed the iron isotopic compositions of 30 samples from the ureilite 40 parent body upb including 29 unbrecciated ureilites and one ureilitic trachyandesite alm a 41 which is at present the sole large crustal sample of the upb the 56 fe of the whole rocks fall within a 42 restricted range from 0 01 to 0 11 with an average of 0 056 0 008 which is significantly 43 higher than that of chondrites we show that this difference can be ascribed to the segregation of s 44 rich metallic melts at low degrees of melting at a temperature close to the fe fes eutectic and 45 certainly before the onset of the melting of the silicates 1100 c in agreement with the marked s 46 depletions and the siderophile element abundances of the ureilites these results point to an efficient 47 segregation of s rich metallic melts during the differentiation of small terrestrial bodies 48 49

effect of concentration of dispersed organic matter on optical maturity parameters interlaboratory results of the organic matter concentration working group of the iccp abstract the main objective of this work was to study the effect of the kerogen isolation procedures on maturity parameters of organic matter using optical microscopes this work represents the results of the organic matter concentration working group omcwg of the international committee for coal and organic petrology iccp during the years 2008 and 2009 four samples have been analysed covering a range of maturity low and moderate and terrestrial and marine geological settings the analyses comprise random vitrinite reflectance measured on both kerogen concentrate and whole rock mounts and fluorescence spectra taken on alginite eighteen participants from twelve laboratories from all over the world performed the analyses samples of continental settings contained enough vitrinite for participants to record around 50 measurements whereas fewer readings were taken on samples from marine setting the scatter of results was also larger in the samples of marine origin similar vitrinite reflectance values were in general recorded in the whole rock and in the kerogen concentrate the small deviations of the trend cannot be attributed to the acid treatment involved in kerogen isolation but to reasons related to components identification or to the difficulty to achieve a good polish of samples with high mineral matter content in samples difficult to polish vitrinite reflectance was measured on whole rock tended to be lower the presence or absence of rock fabric affected the selection of the vitrinite population for measurement and this also had an influence in the average value reported and in the scatter of the results slightly lower standard deviations were reported for the analyses run on kerogen concentrates considering the spectral fluorescence results it was observed that the max presents a shift to higher wavelengths in the kerogen concentrate sample in comparison to the whole rock sample thus revealing an influence of preparation methods acid treatment on fluorescence properties

iron isotope variations in holocene sediments of the gotland deep baltic sea holocene sediments from the gotland deep basin in the baltic sea were investigated for their fe isotopic composition in order to assess the impact of changes in redox conditions and a transition from freshwater to brackish water on the isotope signature of iron the sediments display variations in 56fe differences in the 56fe 54fe ratio relative to the irmm 14 standard from 0 27 0 09 to 0 21 0 08 samples deposited in a mainly limnic environment with oxygenated bottom water have a mean 56fe of 0 08 0 13 which is identical to the mean fe isotopic composition of igneous rocks and oxic marine sediments in contrast sediments that formed in brackish water under periodically euxinic conditions display significantly lighter fe isotope signatures with a mean 56fe of 0 14 0 19 negative correlations of the 56fe values with the fe al ratio and s content of the samples suggest that the isotopically light fe in the periodically euxinic samples is associated with reactive fe enrichments and sulfides this is supported by analyses of pyrite separates from this unit that have a mean fe isotopic composition of 1 06 0 20 for 56fe the supply of additional fe with a light fe isotopic signature can be explained with the shelf to basin fe shuttle model according to the fe shuttle model oxides and benthic ferrous fe that is derived from dissimilatory iron reduction from shelves is transported and accumulated in euxinic basins the data furthermore suggest that the euxinic water has a negative dissolved 56fe value of about 1 4 to 0 9 if negative fe isotopic signatures are characteristic for euxinic sediment formation widespread euxinia in the past might have shifted the fe isotopic composition of dissolved fe in the ocean towards more positive 56fe values

equilibrium oxygen hydrogen and carbon isotope fractionation factors applicable to geologic systems as demonstrated by the chapters in this short course stable isotope techniques are an important tool in almost every branch of the earth sciences central to many of these applications is a quantitative understanding of equilibrium isotope partitioning between substances indeed it was harold urey s 1947 thermodynamically based estimate of the temperature dependence of 18o 16o fractionation between calcium carbonate and water and a recognition of how this information might be used to determine the temperatures of ancient oceans that launched the science of stable isotope geochemistry the approach pioneered by urey has since been used to estimate temperatures for a wide range of geological processes e g emiliani 1955 anderson et al 1971 clayton 1986 valley this volume in addition to their geothermometric applications equilibrium fractionation data are also important in the study of fluid rock interactions including those associated with diagenetic hydrothermal and metamorphic processes baumgartner and valley this volume shanks this volume finally a knowledge of equilibrium fractionation is a necessary first step in evaluating isotopic disequilibrium a widespread phenomenon that is increasingly being used to study temporal relationships in geological systems cole and chakraborty this volume in the fifty four years since the publication of urey s paper equilibrium fractionation data have been reported for many minerals and fluids of geological interest these data were derived from 1 theoretical calculations following the methods developed by urey 1947 and bigeleisen and mayer 1947 2 direct laboratory experiments 3 semi empirical bond strength models and 4 measurement of fractionations in natural samples each of these methods has its advantages and disadvantages however the availability of a variety of methods for calibrating fractionation factors has led to a plethora of calibrations not all of which are in agreement in this chapter we evaluate the major methods for determining fractionation factors

detection of natural weathering of upper mcalester coal and woodford shale oklahoma u s a abstract natural weathering refers to the natural oxidation of organic and inorganic matter in rocks at the surface and in the shallow subsurface the objective of this study is to apply routine geochemical analyses including organic petrography to coal and shale samples extending from the weathered to unaltered zones to illustrate the effects of weathering on organic matter in coal and shale some significant observations from the upper mcalester coal and the woodford shale are 1 a sulfate index si using sulfur form analysis data that reveals the transformation of pyrite to sulfate minerals is a very sensitive weathering indicator it increased in weathered samples 2 rock eval pyrolysis data such as hydrogen index hi and oxygen index oi are very sensitive to weathering oi hi increased in weathered samples 3 vitrinite reflectance decreased in weathered samples and 4 petrographic signs of weathering include microfractures pitted surface dark reaction rims and high relief sulfate index and petrographic signs of weathering should be used on surface and shallow subsurface rock samples as an indication of the extent of weathering the validity of other analyses can then be evaluated accordingly

a comparison of vitrinite reflectance measurements made on whole rock and dispersed organic matter concentrate mounts abstract a comparison of mean random vitrinite reflectance r v r values calculated from measurements on polished whole rock and on concentrates of dispersed organic matter dom mounts of the same samples generally show little difference compared to measurements on dom mounts r v r measurements by the same microscopist on corresponding whole rock samples are up to a few tenths of a percent lower over the range of 0 6 3 2 r v r and have a slightly higher standard deviation whole rock mounts have an advantage over dom mounts in the identification of first cycle vitrinite and differentiation of solid bitumen from vitrinite

characteristics of type iii kerogen in coal bearing strata from the pennsylvanian upper carboniferous in the ruhr basin western germany comparison of coals dispersed organic matter kerogen concentrates and coal mineral mixtures abstract quality quantity and maturity of coal and dispersed terrigenous organic matter were studied on six coal bearing intervals in duckmantian strata pennsylvanian upper carboniferous of the ruhr basin western germany between 10 and 40 samples were collected from fresh drill cores of each interval typically consisting of a coal seam as well as clastic roof and floor strata sandstone siltstone claystone coal seams constitute about 8 vol of the succession studied the samples were analysed by organic petrological methods and rock eval pyrolysis maturity expressed in terms of vitrinite reflectance is between 0 75 and 1 0 for the six successions studied the total amount of dispersed organic matter in clastic rocks is about half of that stored in coal seams both containing predominantly vitrinite significant differences between rock eval parameters determined on whole rock samples and kerogen concentrates were observed especially with respect to hydrogen index hi values thus the hi of the coal is about twice as high as that of the dispersed organic matter although the maceral composition is similar the effects of minerals were further examined by rock eval pyrolysis of artificial mixtures of coal lignite powder and different minerals reduced hi values are partly explained by the retention of generated hydrocarbons on mineral surfaces and partly by reactions of generated fluids with pyrite in kerogen concentrates

standardization of reflectance measurements in dispersed organic matter results of an exercise to improve interlaboratory agreement vitrinite reflectance generally is considered the most robust thermal maturity parameter available for application to hydrocarbon exploration and petroleum system evaluation however until 2011 there was no standardized methodology available to provide guidelines for vitrinite reflectance measurements in shale efforts to correct this deficiency resulted in publication of astm d7708 standard test method for microscopical determination of the reflectance of vitrinite dispersed in sedimentary rocks i n 2012e2013 an interlaboratory exercise was conducted to establish precision limits for the d7708 measurement

iron isotopes in hot springs along the juan de fuca ridge we present fe isotope data for high temperature hydrothermal fluids sulfides and basalts from the juan de fuca ridge usgs basalt standard bcr 2 and the canyon diablo iron meteorite the fe isotopic compositions of all samples fall within a range of 1 however there is a small but statistically significant isotopic variation between fe dissolved in hydrothermal fluids and fe in canyon diablo specifically the hydrothermal fluids are lighter compared to canyon diablo yielding 56fe 56fe 54fe sample 56fe 54fe canyon diablo 1 1000 values from 0 30 to 0 77 in contrast the bcr 2 basalt and canyon diablo are isotopically indistinguishable measurements of 56fe in juan de fuca ridge basalts and sulfides suggest that fe isotopes are fractionated in hydrothermal systems however the data do not exclude the possibility of small 56fe differences between the rocks from which fluid fe is derived and other igneous fe in which case fractionation in igneous systems is indicated regardless these results are evidence of non biological mass fractionation of fe isotopes in nature further venting of hydrothermal fluids into the overlying water column could provide a source of isotopically light fe to the deep oceans contributing to fe isotopic variations observed in deep sea sediments

iron isotope fractionation during oceanic crust alteration abstract the purpose of this work is to study the mobility and budget of fe isotopes in the oceanic crust and in particular during low temperature interaction of seawater with oceanic basalt we carried out this investigation using samples from ocean drilling program odp site 801c drilled during leg 129 and leg 185 in jurassic pacific oceanic crust seaward of the mariana trench the site comprises approximately 450 m of sediment overlying a section of 500 m of basalt which includes intercalated pelagic and chemical sediments in the upper basaltic units and two low temperature 10 30 c ocherous si fe hydrothermal deposits fe was chemically separated from 70 selected samples and 57fe 54fe ratios were measured by mc icp ms isoprobe the isotopic ratios were measured relative to an internal standard solution and are reported relative to the international fe standard irmm 14 based on duplicate measurements of natural samples an external precision of 0 2 2 has been obtained the results indicate that the deep sea sediment section has a restricted range of 57fe which is close to the igneous rock value in contrast large variations are observed in the basaltic section with positive 57fe values up to 2 05 for highly altered basalts and negative values down to 2 49 for the associated alteration products and hydrothermal deposits secondary fe minerals such as fe oxyhydroxides or fe bearing clays celadonite and saponite have highly variable 57fe values that have been interpreted as resulting from the partial oxidation of fe2 leached during basalt alteration and precipitated as fe3 rich minerals in contrast altered basalts at site 801c which are depleted in fe up to 80 display an increase in 57fe values relative to fresh values which suggest a preferential leaching of light iron during alteration the apparent fractionation factor between dissolved fe2 and fe remaining in the mineral is from 0 5 to 1 3 and may be consistent with a kinetic isotope fractionation where light fe is stripped from the minerals alternatively the formation of secondary clays minerals such as celadonite during basalt alteration may incorporate preferentially the heavy fe isotopes resulting in the loss of light fe isotopes in the fluids because microbial processes within the oceanic crust are of potential importance in controlling rates of chemical reactions fe redox state and fe isotope fractionation we evaluated the possible effect of this deep biosphere on fe isotope signatures the fe isotope systematics presented in this study suggest that even though iron behavior during seafloor weathering may be mediated by microbes such as iron oxidizers 57fe variations of more than 4 may also be explained by abiotic processes further laboratory experiments are now required to distinguish between various processes of fe isotope fractionation during seafloor weathering

microscale heterogeneity of fe isotopes in 3 71 ga banded iron formation from the isua greenstone belt southwest greenland we present fe isotope compositions for magnetite crystals from 3 7 ga banded iron formation bif from the isua greenstone belt and younger spatially related pyrite obtained in situ by secondary ion mass spectrometry sims across a distance of several millimeters individual magnetite crystals of bif show 56 fe values up to 2 and within single magnetite rich layers there is a 2 range in 56 fe the highest positive 56 fe values are consistent with those predicted by the equilibrium fractionation factor for oxidation of ferrous to ferric fe in aqueous solution at a likely early archean ocean temperature of 70 c and further suggest that subsequent precipitation of ferric oxides was sufficiently slow that kinetic fractionation effects were minimal these high values also imply that the supply of oxidant was limited heterogeneity in 56 fe values is attributed to diagenetic reactions occurring in limited volume pore waters isolated from the bulk ocean 56 fe 0 with development of isotope reservoir effects secondary pyrite in bif and a conglomerate also show a distinct enrichment in heavy fe isotopes interpreted as redistribution and or fractionation during postformational events

identification of indigenous vitrinites for improved thermal maturity evaluation abstract the four methods that we use to improve the analysis of vitrinite reflectance of well cuttings samples are discussed the criteria for properly identifying the indigenous vitrinites a five fold classification of dispersed vitrinites in sediments first cycle second cycle low gray high gray and gray vitrinites a recording of the reflectance value vitrinite type data for each vitrinite particle analyzed a computer assisted microscope system that generates reflectance histograms of the identified vitrinite type data for easy interpretation using this approach we have minimized inaccuracies caused by the presence of mud additives cavings reworked vitrinites and solid bitumen

copper deposition during quartz dissolution by cooling magmatic hydrothermal fluids the bingham porphyry abstract scanning electron microscope cathodoluminescence imaging is used to map successive generations of fluid inclusions in texturally complex quartz veinlets representing the main stage of ore metal introduction into the porphyry cu au mo deposit at bingham utah following conventional fluid inclusion microthermometry laser ablation inductively coupled plasma mass spectrometry la icpms is applied to quantify copper and other major and trace element concentrations in the evolving fluid with the aim of identifying the ore forming processes textures visible in cathodoluminescence consistently show that the bulk of vein quartz q1 characterized by bright luminescence crystallized early in the vein history cu fe sulfides are precipitated later in these veins in a microfracture network finally filled with a second generation of dull luminescing q2 quartz mapping of brine and vapor inclusion assemblages in these successive quartz generations in combination with la icpms microanalysis shows that the fluids trapped before and after cu fe sulfide precipitation are very similar with respect to their major and minor element composition except for copper copper concentrations in inclusions associated with ore formation drop by two orders of magnitude in a tight pressure temperature interval between 21 and 14 mpa and 425 350 c several hundred degrees below the temperature of fluid exsolution from the magma copper deposition occurs within a limited p t region in which sulfide solubility shows strong normal temperature dependence while quartz solubility is retrograde this permits copper sulfide deposition while secondary vein permeability is generated by quartz dissolution the brittle to ductile transition of the quartz feldspar rich host rocks occurs in the same temperature range which further enhances vein reactivation and promotes cooling and expansion of fluids ascending across the transition from lithostatic to hydrostatic conditions

the effect of early diagenesis on the fe isotope compositions of porewaters and authigenic minerals in continental margin sediments abstract iron isotope compositions in marine pore fluids and sedimentary solid phases were measured at two sites along the california continental margin where isotope compositions range from 56fe 3 0 to 0 4 at one site near monterey canyon off central california organic matter oxidation likely proceeds through a number of diagenetic pathways that include significant dissimilatory iron reduction dir and bacterial sulfate reduction whereas at our other site in the santa barbara basin dir appears to be comparatively small and production of sulfides fes and pyrite was extensive the largest range in fe isotope compositions is observed for fe ii aq in porewaters which generally have the lowest 56fe values minimum 3 0 near the sediment surface and increase with burial depth 56fe values for fes inferred from hcl extractions vary between 0 4 and 0 4 but pyrite is similar at both stations where an average 56fe value of 0 8 0 2 was measured we interpret variations in dissolved fe isotope compositions to be best explained by open system behavior that involves extensive recycling of feflux this study is the first to examine fe isotope variations in modern marine sediments and the results show that fe isotopes in the various reactive fe pools undergo isotopic fractionation during early diagenesis importantly processes dominated by sulfide formation produce high 56fe values for porewaters whereas the opposite occurs when fe iii oxides are present and dir is a major pathway of organic carbon respiration because shelf pore fluids may carry a negative 56fe signature it is possible that the fe isotope composition of ocean water reflects a significant contribution of shelf derived iron to the open ocean such a signature would be an important means for tracing iron sources to the ocean and water mass circulation

equilibrium high temperature fe isotope fractionation between fayalite and magnetite an experimental calibration abstract the iron isotopic fractionation factor between magnetite and fayalite was measured at high temperature in a piston cylinder apparatus for the first time the three isotope method matsuhisa j goldsmith j r and clayton r n 1978 mechanisms of hydrothermal crystallisation of quartz at 250 c and 15 kbar geochim cosmochim acta 42 173 182 has been used to determine equilibrium fractionation between two minerals directly the experimentally determined temperature dependent iron isotope fractionation between fayalite and magnetite is described by 10 3 ln 57 mag fa 57 fe mag fa 0 30 0 024 10 6 t 2 the equation predicts measurable fractionation at magmatic temperatures our work bears on the magnitude of fe isotope fractionation attending differentiation in magmatic systems and provides a new isotope thermometer for co existing fayalite and magnetite

experimental quantification of the fractionation of fe isotopes during metal segregation from a silicate melt abstract fractionation of fe isotopes between a silicate melt and metallic alloys has been quantified experimentally at 1500 c the effects of oxygen fugacity and run duration have been investigated to distinguish between kinetic and equilibrium fractionations a new experimental setup is presented in which metallic fe is produced by reduction of oxidized iron from a silicate melt due to a change of redox conditions this metallic fe is physically removed from the silicate and sequestered as a pt fe alloy bulk analyses of the silicate and metallic fractions using multi collector icp ms methods are coupled with in situ analyses using an ion microprobe experimental results indicate that significant isotopic fractionation of fe occurs during metal segregation during the early stages of the experiments we find evidence for kinetic fractionation caused by faster diffusion of 54 fe along concentration gradients in the alloy this process leads to the formation of a metallic phase which is isotopically light compared to the residual silicate metal silicate fractionation up to 2 35 a m u the data are used to quantify the difference in diffusion coefficient of each isotope of iron providing a means to predict fe isotope fractionation during fe diffusion in metallic alloys on the other hand this state of affairs is transient in nature and at superliquidus temperature the systems rapidly reach a state of isotopic equilibrium in which the metal is isotopically heavier than the silicate melt by about 0 2 0 15 a m u these results are consistent with the range of variation observed in natural samples these kinetic and equilibrium data provide an experimental framework to understand the observed variability among igneous and meteoritic materials formed at high temperature particularly for iron and pallasite meteorites

integrated fe and s isotope study of seafloor hydrothermal vents at east pacific rise 9 10 n abstract in this study we report on coupled fe and s isotope systematics of hydrothermal fluids and sulfide deposits from the east pacific rise at 9 10 n to better constrain processes affecting fe isotope fractionation in hydrothermal environments we aim to address three fundamental questions 1 is there significant fe isotope fractionation during sulfide precipitation 2 is there significant variability of fe isotope composition of the hydrothermal fluids reflecting sulfide precipitation in subsurface environments 3 are there any systematics between fe and s isotopes in sulfide minerals the results show that chalcopyrite precipitating in the interior wall of a hydrothermal chimney displays a limited range of 56fe values and 34s values between 0 11 to 0 33 and 2 2 to 2 6 respectively the 56fe values are on average slightly higher by 0 14 relative to coeval vent fluid composition while 34s values suggest significant s isotope fractionation 0 6 0 2 during chalcopyrite precipitation in contrast systematically lower 56fe and 34s values relative to hydrothermal fluids by up to 0 91 and 2 0 respectively are observed in pyrite and marcasite precipitating in the interior of active chimneys these results suggest isotope disequilibrium in both fe and s isotopes due to s isotopic exchange between hydrothermal h2s and seawater so42 followed by rapid formation of pyrite from fes precursors thus preserving the effects of a strong kinetic fe isotope fractionation during fes precipitation in contrast 56fe and 34s values of pyrite from inactive massive sulfides which show evidence of extensive late stage reworking are essentially similar to the hydrothermal fluids multiple stages of remineralization of ancient chimney deposits at the seafloor appear to produce minimal fe isotope fractionation similar affects are indicated during subsurface sulfide precipitation as demonstrated by the lack of systematic differences between 56fe values in both high temperature fe rich black smokers and lower temperature fe depleted vents

iron isotopes in the early marine diagenetic iron cycle measurements of fe oxyhydroxides reactive fe iii in two shallow sediment profiles from reducing and oxic environments on the arabian sea margin demonstrate fe isotope fractionation during early marine diagenesis reactive fe iii has 56 fe values between 0 77 and 0 19 values are lowest at the top of the sediment profile and considerably lower than bulk sediment fe 56 fe 0 preferential reduction and dissolution of light fe isotopes during diagenesis leaves behind an increasingly smaller and heavier reactive fe iii residual initially the isotopic composition of reactive fe iii evolves down core according to the fractionation factor typical of microbial dissimilatory fe reduction deeper in the profile 56 fe values remain unchanged despite further fe reduction here another process with a different fractionation factor becomes dominant probably reduction by dissolved sulfide the 56 fe of the residual reactive fe iii suggests that 25 of the initially present reactive fe iii was reduced by microbial fe reduction when fe is diagenetically recycled between reducing sediments at depth and an oxic top layer the process depending on recycling efficiency may result in the accumulation of light fe in the top layer while the complementary heavier residual is buried fe diffusing from the seafloor back into the ocean should reflect the low 56 fe diagenetic source of dissolved fe

petrographic maturity parameters of a devonian shale maturation series appalachian basin usa iccp thermal indices working group interlaboratory exercise abstract this paper presents results of an interlaboratory exercise on organic matter optical maturity parameters using a natural maturation series comprised by three devonian shale samples huron member ohio shale from the appalachian basin usa this work was conducted by the thermal indices working group of the international committee for coal and organic petrology iccp commission ii geological applications of organic petrology this study aimed to compare 1 maturation predicted by different types of petrographic parameters vitrinite reflectance and spectral fluorescence of telalginite 2 reproducibility of the results for these maturation parameters obtained by different laboratories and 3 improvements in the spectral fluorescence measurement obtained using modern detection systems in comparison with the results from historical round robin exercises mean random vitrinite reflectance measurements presented the highest level of reproducibility group standard deviation 0 05 for low maturity and reproducibility diminished with increasing maturation group standard deviation 0 12 corrected fluorescence spectra provided by 14 participants showed a fair to good correspondence standard deviation of the mean values for spectral parameters was lowest for the low maturity sample but was also fairly low for higher maturity samples a significant improvement in the reproducibility of corrected spectral fluorescence curves was obtained in the current exercise compared to a previous investigation of toarcian organic matter spectra in a maturation series from the paris basin this improvement is demonstrated by lower values of standard deviation and is interpreted to reflect better performance of newer photo optical measuring systems fluorescence parameters measured here are in good agreement with vitrinite reflectance values for the least mature shale but indicate higher maturity than shown by vitrinite reflectance for the two more mature shales this red shift in max beyond 0 65 vitrinite reflectance was also observed in studies of devonian shale in other basins suggesting that the accepted correlation for these two petrographic thermal maturity parameters needs to be re evaluated a good linear correlation between max and tmax for this maturation series was observed and max 600 nm corresponds to tmax of 440 c nevertheless if a larger set of devonian samples is included the correlation is polynomial with a jump in max ranging from 540 to 570 nm up to 440 c of tmax the max mostly reaches up to 500 nm beyond a tmax of 440 c max is in the range of 580 600 nm this relationship places the red shift when the onset of the oil window is reached at tmax of 440 c moreover the correlation between hi and max r2 0 70 shows a striking inflection and decrease in hi above a max of 600 nm coincident with the approximate onset of hydrocarbon generation in these rocks

coupled fe and s isotope variations in pyrite nodules from archean shale ron and sulfur isotope compositions recorded in ancient rocks and minerals such as pyrite fes2 have been widely used as a proxy for early microbial metabolisms and redox evolution of the oceans however most previous studies focused on only one of these isotopic systems herein we illustrate the importance of in situ and coupled study of fe and s isotopes on two pyrite nodules in a c 2 7 ga shale from the bubi greenstone belt zimbabwe fe and s isotope compositions were measured both by bulk sample mass spectrometry techniques and by ion microprobe in situ methods secondary ion mass spectrometry sims spatially resolved analysis across the nodules shows a large range of variations at micrometer scale for both fe and s isotope compositions with 56 fe and 34 s values from 2 1 to 0 7 and from 0 5 to 8 2 respectively and 33 s values from 1 6 to 2 9 the fe and s isotope variations in these nodules cannot be explained by tandem operation of dissimilatory iron reduction dir and bacterial sulfate reduction bsr as was previously proposed but rather they reflect the contributions of different fe and s sources during a complex diagenetic history pyrite formed from two different mineral precursors 1 mackinawite precipitated in the water column and 2 greigite formed in the sediment during early diagenesis the in situ analytical approach reveals a complex history of the pyrite nodule growth and allows us to better constrain environmental conditions during the archean

pyrite rb sr sm nd and fe isotopic constraints on the age and genesis of the qingchengzi pb zn deposits northeastern china abstract sr nd fe isotopes are reported for pyrites and whole rocks of ores and associated rocks for the qingchengzi pb zn deposits in the northeasern china to investigate the age sources and processes of the pb zn mineralization rb sr leaching isotopic dating of pyrites that crystallized coeval with galena and sphalerite from five subsamples of ores yields isochron ages of 143 12 ma to 159 12 ma with a weighted mean age of 151 8 5 2 ma this age can be interpreted to be the timing of pb zn mineralization coeval with the emplacement of late jurassic granites in the region the pyrites have negative end 152 ma values of 17 6 to 22 0 among the neoarchean ttg rocks paleoproterozoic meta sedimetary rocks i e wall rocks and granites and mesozoic mafic dykes and granites however the initial 87sr 86sr ratio of 0 7188 0 0004 is similar to those of late jurassic granites and paleoproterozoic rocks 0 7082 0 7183 distinct from those of mafic dykes 0 7069 0 7110 indicating the ore forming materials i e pb and zn were mainly derived from wall rocks and late jurassic granites combined with the previously published h o isotopes the new age and sr nd isotopic data indicate that the mineralizaing fluids were mainly derived from dehydration of granitic magmas interacted with meteoric water that extracted pb and zn from the wall rocks the 56fe values of pyrites in the pb zn ores and paleoproterozoic meta sedimentary rocks range from 0 23 to 1 09 and 0 49 to 0 17 respectively distinct from those of paleoproterozoic basement rocks and mesozoic rocks 0 03 to 0 28 combined with nd isotopes the large range of 56fe values for pyrites would be the result of rapid precipitation of pyrites in the wall rocks and contemperal deposition of pyrites in the residual fluids during interaction between wall rocks and ore forming fluids collectively our new sr nd fe isotopes of pyrites not only constrain the age and sources of pb and zn mineralization but also reveal the detailed mineralization processes providing a new method to constrain the genesis of hydrothermal pb zn deposits

contrasting behavior of oxygen and iron isotopes in banded iron formations revealed by in situ isotopic analysis abstract in situ o and fe isotope measurements of magnetite and hematite in banded iron formations bifs from the 2 5 ga dales gorge member of the brockman iron formation hamersley group western australia document distinct fine scale isotopic zonation for hematite o 18 values vsmow range from 7 1 to 0 6 and fe 56 values range from 0 50 to 1 53 magnetite has a o 18 range of 5 6 to 7 0 and a fe 56 range of 0 76 to 1 33 notably magnetite shows significant o isotope variability at a o 18 values exists between low si core and si rich overgrowth iron isotope compositions are homogeneous to 0 2 in fe 56 values within individual grains or layers hematite is always isotopically heavier than co existing magnetite by 0 1 0 4 in fe 56 within individual samples and there is a large variation 2 in fe 56 values between bif samples at the m scale e g between meso or macro bands of the dales gorge member in situ isotopic results highlight the distinct behavior of o and fe isotopes during interaction with post deposition diagenetic or metamorphic fluids the large variations in o 18 values of iron oxides likely reflect exchange with fluids during post depositional events at temperatures up to ca 280 c and the lower o 18 values of fe oxides are interpreted to reflect less isotopic modification and lower temperatures o 18 variations support a model where initial fe oh 3 precipitates that formed in the photic zone were converted to hematite during very early diagenesis followed by production of magnetite over a range of temperatures during later diagenesis metamorphism in contrast magnetite and hematite seem to have preserved the initial fe 56 values of early fe oh 3 precipitates despite significant changes in o isotope compositions in magnetite the consistency in apparent fe isotope fractionation between co existing hematite and magnetite suggests that they share a common precursor where magnetite was formed in soft sediment through in situ reduction by microbial processes and possibly including reaction with aqueous fe ii combined in situ fe o isotope analyses allow distinctions to be made between near primary and post depositional signatures in bifs which bears on the use of bifs as paleo environmental proxies and recorders of microbial processes

iron isotope systematics from the batu hijau cu au deposit sumbawa indonesia abstract this study examines the fractionation of iron isotopes as a reflection of processes that govern the co magmatic formation of a hydrothermal ore system of a classic porphyry copper deposit we present iron isotope analyses measured using multi collector icpms of magmatic intrusive rocks and coeval hypogene ore minerals from the batu hijau porphyry copper gold deposit in sumbawa indonesia isotopic analysis were made of the intrusive magmatic host rocks to the deposit ranging from sub volcanic andesite and quartz diorite to tonalite and of hypogene chalcopyrite bornite and magnetite ore mineral separates iron isotope values of andesite and quartz diorite range from 57fe 0 17 0 05 to 0 26 0 05 the more felsic differentiated dacite and tonalite have heavier iron isotope values 57fe 0 27 0 08 to 0 32 0 08 than the intermediate and mafic rocks heavy iron isotopes are positively correlated with sio2 and negatively correlated with mgo cao tio2 and v suggesting that crystallisation of clinopyroxene amphibole and magnetite is the primary control on isotopic evolution of the melt these isotopic trends are supported by thermodynamic rhyolite melts modelling of crystal fractionation using published mineral melt fractionation factors and demonstrate that the isotopic evolution of the batu hijau melts was controlled by crystal fractionation magnetite from the batu hijau ore deposit is isotopically heavier 57fe range from 0 24 0 14 to 0 74 0 14 than coexisting chalcopyrite from 0 62 0 04 to 0 16 0 05 and bornite from 0 72 0 23 to 0 08 0 03 consistent with theoretical fractionation factors derived from spectroscopy comparison of our mineral data with data from other deposits defines a range of 57fe values for hypogene chalcopyrite from porphyry copper deposits from 1 26 to 0 29 models of rayleigh type fractionation assuming an initial hydrothermal fluid composition which is isotopically light 57fe between 0 5 and 0 1 produces mineral compositions that match our analytical data the modelled isotope values are in agreement with experiments demonstrating that hypogene chalcopyrite has isotopic compositions reflecting the isotopic value of the hydrothermal fluid however hypogene chalcopyrite from this study is significantly lighter than values of chalcopyrite separates from the renison tin deposit which span a range of 0 28 0 06 to 1 32 0 06 we propose that the presence or absence of pyrrhotite influences the relative differences in 57fe values of chalcopyrite between porphyry copper and tin deposits because of its preference for isotopically light iron which in turn is controlled by both oxygen and sulfur redox conditions in the fluid

the origin of oil in the cretaceous succession from the south pars oil layer of the persian gulf the origin of the oil in barremian hauterivian and albian age source rock samples from two oil wells spo 2 and spo 3 in the south pars oil field has been investigated by analyzing the quantity of total organic carbon toc and thermal maturity of organic matter om the source rocks were found in the interval 1 000 1 044 m for the kazhdumi formation albian and 1 157 1 230 m for the gadvan formation barremian hauterivian elemental analysis was carried out on 36 samples from the source rock candidates gadvan and kazhdumi formations of the cretaceous succession of the south pars oil layer spol this analysis indicated that the om of the barremian hauterivian and albian samples in the spol was composed of kerogen types ii and ii iii respectively the average toc of analyzed samples is less than 1 wt suggesting that the cretaceous source rocks are poor hydrocarbon hc producers thermal maturity and ro values revealed that more than 90 of oil samples are immature the source of the analyzed samples taken from gadvan and kazhdumi formations most likely contained a content high in mixed plant and marine algal om deposited under oxic to suboxic bottom water conditions the pristane nc17 versus phytane nc18 diagram showed type ii iii kerogen of mixture environments for source rock samples from the spol burial history modeling indicates that at the end of the cretaceous time pre permian sediments remained immature in the qatar arch therefore lateral migration of hc from the nearby cretaceous source rock kitchens toward the north and south of the qatar arch is the most probable origin for the significant oils in the spol

experimental determination of fe isotope fractionation between aqueous fe ii siderite and green rust in abiotic systems abstract iron isotope fractionation between aqueous iron and siderite has been measured using abiotic synthesis experiments at 20 c applying a rayleigh distillation model to three experiments in which siderite feco3 was continuously precipitated from solutions over the course of tens of hours the derived fractionation factor is 103ln fe ii siderite 0 48 0 22 2 this experimentally determined fractionation factor is significantly smaller by 1 5 than that calculated from vibrational frequencies and mossbauer shifts geochim cosmochim acta 64 2000 849 865 geochim cosmochim acta 65 2001 2487 2497 and lies on the high end of that inferred from natural mineral assemblages where the fe ii aq siderite fractionation factor was inferred to lie between 1 7 and 0 3 contrib mineral petrol 144 2003 523 547 the measured fe ii aq siderite fractionation from this study suggests that siderite from archean and proterozoic rocks which have moderately negative 56fe values 1 5 to 0 5 may reflect precipitation from fe ii aq whose origin was hydrothermal in contrast natural siderites that have higher 56fe values apparently require non hydrothermal sources of fe and or different pathways of formation or may reflect the effects of cation substitution on the fe ii aq carbonate fractionation factor

subsurface processes at the lucky strike hydrothermal field mid atlantic ridge evidence from sulfur selenium and iron isotopes at lucky strike near the azores triple junction the seafloor setting of the hydrothermal field in a caldera system with abundant low permeability layers of cemented breccia provides a unique opportunity to study the influence of subsurface geological conditions on the hydrothermal fluid evolution coupled analyses of s isotopes performed in conjunction with se and fe isotopes have been applied for the first time to the study of seafloor hydrothermal systems these data provide a tool for resolving the different abiotic and potential biotic near surface hydrothermal reactions the 34s between 1 5 and 4 6 and se values between 213 and 1640 ppm of chalcopyrite suggest a high temperature end member hydrothermal fluid with a dual source of sulfur sulfur that was leached from basaltic rocks and sulfur derived from the reduction of seawater sulfate in contrast pyrite and marcasite generally have lower 34s within the range of magmatic values 0 1 and are characterized by low concentrations of se 50 ppm for 82se 76se ratios the 82se values range from basaltic values of near 1 5 to 7 the large range and highly negative values of hydrothermal deposits observed cannot be explained by simple mixing between se leached from igneous rock and se derived from seawater we interpret the se isotope signature to be a result of leaching and mixing of a fractionated se source located beneath hydrothermal chimneys in the hydrothermal fluid at lucky strike we consider two sources for s and se 1 the end member hydrothermal fluid with basaltic se isotopic values 1 5 and typical s isotope hydrothermal values of 1 5 2 a fractionated source hosted in subsurface environment with negative 34s values probably from bacterial reduction of seawater sulfate and negative 82se values possibly derived from inorganic reduction of se oxyanions fluid trapped in the subsurface environment is conductively cooled and has restricted mixing and provide favorable conditions for subsurface microbial activity which is potentially recorded by s isotopes fe isotope systematic reveals that se rich high temperature samples have 57fe values close to basaltic values 0 whereas se depleted samples precipitated at medium to low temperature are systematically lighter 57fe values between 1 to 3 an important implication of our finding is that light fe isotope composition down to 3 2 may be explained entirely by abiotic fractionation in which a reservoir effect during sulfide precipitation was able to produce highly fractionated compositions

multiple sulphur and iron isotope composition of detrital pyrite in archaean sedimentary rocks a new tool for provenance analysis abstract multiple s 34 s and 33 s and fe 56 fe isotope analyses of rounded pyrite grains from 3 1 to 2 6 ga conglomerates of southern africa indicate their detrital origin which supports anoxic surface conditions in the archaean rounded pyrites from meso to neoarchaean gold and uranium bearing strata of south africa are derived from both crustal and sedimentary sources the latter being characterised by non mass dependent fractionation of s isotopes 33 s as negative as 1 35 and large range of fe isotope values 56 fe between 1 1 and 1 2 most sediment sourced pyrite grains are likely derived from sulphide nodules in marine organic matter rich shales sedimentary exhalites and volcanogenic massive sulphide deposits some sedimentary pyrite grains may have been derived from in situ sulphidised fe oxides prior to their incorporation into the conglomerates as indicated by unusually high positive 56 fe values sedimentary sulphides without significant non mass dependent fractionation of s isotopes were also present in the source of some conglomerates the abundance in these rocks of detrital pyrite unstable in the oxygenated atmosphere may suggest factors other than high p o 2 as the cause for the absence of significant non mass dependent fractionation processes in the 3 2 2 7 ga atmosphere rounded pyrites from the c 2 6 ga conglomerates of the belingwe greenstone belt in zimbabwe have strongly fractionated 34 s 33 s and 56 fe values the source of which can be traced back to black shale hosted massive sulphides in the underlying strata the study demonstrates the utility of combined multiple s and fe isotope analyses for provenance reconstruction of archaean sedimentary successions

fe isotope fractionation in magmatic hydrothermal mineral deposits a case study from the renison sn w deposit tasmania abstract we present 50 new iron isotopic analyses of source granite and mineral separates from the renison tin deposit in western tasmania the aim of the study is to characterise the composition of minerals within a tin deposit associated with a reduced s type magma we have analysed bulk samples of granite and separates of pyrrhotite pyrite arsenopyrite magnetite chalcopyrite and siderite by multi collector inductively coupled mass spectrometry the isotopic compositions of mineral separates are consistent with theoretical predictions of equilibrium fractionation based on mossbauer spectroscopy and other parametric calculations mineral mineral pairs yield temperatures of formation that are in agreement with prior detailed fluid inclusion studies but are spatially inconsistent with declining fluid temperatures with distance from the causative intrusion limiting the use of fe isotopes as a potential geothermometer at least in this case comparison of our data with published data from other deposits clearly demonstrates that pyrite magnetite and chalcopyrite from the hottest ore fluids 300 400 c at renison are isotopically heavier than minerals sampled from a deposit formed at similar temperatures but associated with a more oxidised and less differentiated intrusion

the effect of diagenesis and fluid migration on rare earth element distribution in pore fluids of the northern cascadia accretionary margin analytical challenges in obtaining high quality measurements of rare earth elements rees from small pore fluid volumes have limited the application of rees as deep fluid geochemical tracers using a recently developed analytical technique we analyzed rees from pore fluids collected from sites u1325 and u1329 drilled on the northern cascadia margin during the integrated ocean drilling program iodp expedition 311 to investigate the ree behavior during diagenesis and their utility as tracers of deep fluid migration these sites were selected because they represent contrasting settings on an accretionary margin a ponded basin at the toe of the margin and the landward tofino basin near the shelf s edge ree concentrations of pore fluid in the methanogenic zone at sites u1325 and u1329 correlate positively with concentrations of dissolved organic carbon doc and alkalinity fractionations across the ree series are driven by preferential complexation of the heavy rees simultaneous enrichment of diagenetic indicators doc and alkalinity and of rees in particular the heavy elements ho to lu suggests that the heavy rees are released during particulate organic carbon poc degradation and are subsequently chelated by doc ree concentrations are greater at site u1325 a site where shorter residence times of poc in sulfate bearing redox zones may enhance ree burial efficiency within sulfidic and methanogenic sediment zones where ree release ensues cross plots of la concentrations versus cl li and sr delineate a distinct field for the deep fluids z 75 mbsf at site u1329 and indicate the presence of a fluid not observed at the other sites drilled on the cascadia margin changes in ree patterns the presence of a positive eu anomaly and other available geochemical data for this site suggest a complex hydrology and possible interaction with the igneous crescent terrane located east of the drilled transect

application of iron and zinc isotopes to track the sources and mechanisms of metal loading in a mountain watershed abstract here the hydrogeochemical constraints of a tracer dilution study are combined with fe and zn isotopic measurements to pinpoint metal loading sources and attenuation mechanisms in an alpine watershed impacted by acid mine drainage in the tested mountain catchment 56fe and 66zn isotopic signatures of filtered stream water samples varied by 3 5 and 0 4 respectively the inherent differences in the aqueous geochemistry of fe and zn provided complimentary isotopic information for example variations in 56fe were linked to redox and precipitation reactions occurring in the stream while changes in 66zn were indicative of conservative mixing of different zn sources fen environments contributed distinctively light dissolved fe 0 4 acidic drainage from mine wastes contributed heavier dissolved fe 0 5 and lighter zn 0 2 isotopes relative to the fen upwelling of fe rich groundwater near the mouth of the catchment was the major source of fe 56fe 0 leaving the watershed in surface flow while runoff from mining wastes was the major source of zn the results suggest that given a strong framework for interpretation fe and zn isotopes are useful tools for identifying and tracking metal sources and attenuation mechanisms in mountain watersheds

secular variation of iron isotopes in north atlantic deep water a high precision iron isotope time series for a ferromanganese crust demonstrates that the iron isotope composition in north atlantic deep water has changed substantially over the past 6 million years and that iron isotope variations in the crust are closely correlated to those of lead isotopes the close correlation between the two isotope series indicates that the observed iron isotope variations predominantly reflect those of iron input from terrigenous sources and provides no evidence for biologically induced mass fractionation within north atlantic deep water

vitrinite reflectance as a possible indicator of metamorphic grade and stratigraphic position of formations a study of oligocene metapelites in ne taiwan abstract a total of 47 samples of oligocene metapelites collected from the northeastern ne hsuehshan range taiwan were studied by measuring vitrinite reflectance the vitrinite reflectance of the three studied stratigraphic units from top to bottom are as follows the tatungshan formation r max mean maximum vitrinite reflectance 1 35 2 76 and r m mean random vitrinite reflectance 1 18 2 56 the tsuku formation r max 2 89 3 51 and r m 2 37 3 26 and the kankou formation r max 4 06 5 97 and r m 3 04 5 07 either r max or r m changes continuously along the studied geologic sections and the variation serves well as a metamorphic grade indicator in the studied area each stratigraphic formation has its own characteristic vitrinite reflectance value range it is postulated that in the future vitrinite reflectance can also serve as an indicator of stratigraphic position of formations to aid stratigraphic identification and correlation in geologic mappings

fe isotope fractionation during phase separation in the nacl h2o system an experimental study with implications for seafloor hydrothermal vents abstract phase separation has been proposed as a possible mechanism contributing to the fe isotope composition of hydrothermal fluids at mid ocean ridges the uncertainty results largely from the emphasis on field data that can involve competing processes that obscure cause and effect of any one process to better understand the potential significance of phase separation in the nacl fe h 2 o system on fe isotope fractionation temperature and pressure of a fe bearing nacl fluid in a titanium flow reactor were carefully adjusted to produce vapor liquid halite while the fe isotope composition between coexisting phases was monitored two different p t regions were emphasized 1 424 420 c 35 2 31 5 mpa and 2 464 466 c 29 8 24 7 mpa both regions were chosen to simulate the range of physical conditions that are experienced by hydrothermal fluids at mid ocean ridges mors decompression induced phase separation in both p t regions results in the vapor phase becoming enriched in the heavier isotopes of fe as the fe cl ratio decreases the coexisting nacl rich liquid phase remains essentially constant with respect to fe cl ratio and fe isotope composition coinciding with the lowest vapor chlorinity in the vapor liquid stability field the fe cl ratio of the vapor abruptly increases while the fe isotope fractionation between the vapor and liquid 10 3 ln v l 56 54 reached a maximum value of 0 145 0 048 subsequently fe isotope fractionation decreased upon transition into the vapor halite stability field p t region 2 we infer that the observed fe isotope fractionation between vapor liquid halite is caused by differences in fe speciation among coexisting chloride bearing phases the experimental study confirms for the first time that measurable fe isotope variability can result from phase separation in high temperature hydrothermal systems the species dependent fe isotope fractionation reported here is small relative to predicted mineral mineral and mineral fluid fractionations especially if redox effects are involved as might occur during vent fluid seawater mixing reactions and or magmatic activity associated with seafloor eruptive episodes

application of integrated vitrinite reflectance and famm analyses for thermal maturity assessment of the northeastern malay basin offshore vietnam implications for petroleum prospectivity evaluation abstract several exploration wells have intersected a cenozoic coal bearing fluvial deltaic mudstone and sandstone succession in the northeastern vietnamese part of the malay basin and have successfully tested seismically identified direct hydrocarbon indicators dhis the oil and gas condensate discovery well 46 cn 1x encountered a 55 m thick section of lacustrine mudstones having considerable potential as an oil source vitrinite reflectance vr measurements from these alginite bearing rocks introduce several problems in thermal maturity evaluation including associated vr suppression and delineation of cavings and bitumens reliable thermal maturity gradients however may be established using a combination of conventional vr measurements and equivalent vr eqvr values derived from the fluorescence alteration of multiple macerals famm technique these measurements performed on dispersed organic matter dom in cuttings from 46 cn 1x allow separation of low reflecting bitumens and vitrinite in cavings from indigenous vitrinite and the famm results indicate vr suppression of 0 14 in an alginite bearing mudstone with a high hydrogen index value on the basis of available raw vr data a highly irregular maturity trend is determined with the deepest sample 2675 2680 m having a vr of 0 4 ro the eqvr value however for the deepest sample is 0 70 the maturity trend determined from the famm data and vr data omitting samples having suppressed vr indicates that the top of the oil window vr of 0 75 ro is located at about 2800 m depth modelling the geothermal gradient using the easy ro algorithm yields 40 c km for both of the two maturity profiles this is in the low end of the range for the malay basin modelled temperature histories indicate onset of hydrocarbon generation for the uppermost oligocene source rocks between 2 ma and present day which post dates trap formation seismic facies patterns suggest that lacustrine oil prone units are in the oil window in the same graben complex a few km nw of the investigated well and these rocks are likely to be the source of the hydrocarbons found in the well a more widespread occurrence of hydrocarbons sourced from this kitchen is indicated by other discoveries and mapping of dhis in the area

the nadun cu au mineralization central tibet root of a high sulfidation epithermal deposit abstract a new high sulfidation epithermal cu au occurrence nadun has been discovered adjacent to the cretaceous duolong porphyry cu au deposit within the bangong nujiang metallogenic belt central tibet the nadun cu au mineralization is hosted in a tectonic hydrothermal breccia with advanced argillic alteration which occurs above sandstone associated with quartz pyrite veins the granodiorite porphyry with strong argillic alteration yields a zircon u pb age of 119 1 1 3 ma whereas the weakly argillic granodiorite porphyry intruded into the breccia has a younger age of 116 1 1 3 ma this indicates that cu au epithermal mineralization likely occurred between 116 ma and 119 ma consistent with the duration of magmatic hydrothermal activity at duolong 115 118 ma and providing evidence that nadun and duolong were formed during the same event moreover the nadun and duolong porphyries have similar hf isotopic compositions ehf t values ranging from 8 8 to 8 1 mean 5 0 1 1 n 32 likely indicating that the deposits are comagmatic in addition boiling assemblages in vapor rich inclusions coexisting with brines occur in early stage quartz pyrite veins and likely record phase separation at a temperature of 550 300 c and pressure of 700 110 bars most liquid rich fluid inclusions formed at the breccia stage show similar salinity 1 7 19 3 wt nacl equiv to vapor rich inclusions from the underlying quartz pyrite veins likely indicating vapor contraction during cooling at elevated presssure this suggests that quartz pyrite veins may act as conduits for ore forming fluid traveling from the porphyry to the epithermal hydrothermal system o and h isotopic compositions 18ofluid 0 42 9 71 and d 102 to 66 suggest that ore forming fluids are dominantly from a magmatic source with a minor addition of meteoric water at a later stage the s and fe isotope compositions of sulfides 34s 5 9 to 0 5 and 57fe 2 15 to 0 17 decrease from the quartz pyrite vein to breccia ore indicating that ore forming fluids gradually become so42 enriched and relatively oxidized this body of evidence suggests that the nadun cu au mineralization may represent the root of a high sulfidation epithermal deposit

fe isotope fractionation between chalcopyrite and dissolved fe during hydrothermal recrystallization an experimental study at 350 c and 500 bars abstract equilibrium fe isotope fractionation between chalcopyrite and dissolved fe was determined in acidic chloride bearing fluid at 350 c and 500 bars the study utilized deformable gold cell technology which allowed time series sampling of solution during chalcopyrite recrystallization and isotope exchange a key element of the experimental design involved the addition of anomalous dissolved 57 fe to an on going experiment as a means of determining the degree and rate of isotope exchange taking explicit account of imposed chemical and isotopic mass balance constraints of fe in fluid and mineral chalcopyrite reservoirs these data indicate that no more than 1000 h is required for the isotopically anomalous dissolved fe reservoir to exchange completely with the coexisting chalcopyrite the experimental calibration of the rate of fe isotope exchange for the 57 fe spiked experiment provides critical insight for the time necessary to achieve fe isotope exchange in two non spiked but otherwise identical experiments the fe isotope data indicate that the equilibrium fractionation between chalcopyrite and dissolved fe 56 fe cpy fe aq at 350 c is small 0 09 0 17 2 and is in good agreement with recent theoretical equilibrium predictions owing to the apparent rate of fe isotope exchange at 350 c it is likely that chalcopyrite formed at high temperature deep sea vents black smoker systems achieves isotopic equilibrium and effectively records the fe isotopic composition of the coexisting end member hydrothermal fluid comparison of the experimental mineral fluid equilibrium fractionation factors with conjugate chalcopyrite and dissolved fe pairs sampled from high temperature hydrothermal vent systems at axial caldera and main endeavour field juan de fuca ridge are in agreement with this inference the experimental data were further used to determine the mineral mineral equilibrium fe isotope fractionation between pyrite chalcopyrite 56 fe pyr cpy at 350 c by combining previously determined pyrite fe 2 aq equilibrium fractionation data with chalcopyrite fe 2 aq from this study the empirically determined 56 fe pyr cpy value 0 90 0 34 2 is consistent with theoretical predictions and when coupled with mineral fluid fe isotope fractionation systematics and experimentally determined exchange rates helps to delineate processes of sulfide mineralization in hydrothermal systems

a century of climate variability in central dronning maud land east antarctica and its relation to southern annular mode and el nino southern oscillation stable isotope records of oxygen and hydrogen were studied from a 65 m long ice core retrieved from the central dronning maud land east antarctica in order to reconstruct the coastal antarctic climate variability during the last century and its relation to the southern annular mode sam and el nino southern oscillation enso the 18 o records showed a significant relation to the sam with a dominant 4 years variability except during specific periods 1918 1927 19381947 1989 2005 when enso teleconnection was established through the in phase relation between sam and southern oscillation index soi the combined influence of enso and sam was seen on surface air temperatures in this region mainly during the austral summer season from 1989 to 2005 further a significant relationship between 18 o and sam was observed on a decadal scale which overrides the intermittent influence of enso major shifts in the deuterium excess record were observed during periods of enso teleconnections which support a shift in moisture source regions during the periods of stronger enso teleconnections surface air temperatures estimated using the 18 o t spatial slope for this region depicted a significant warming of 1 c for the past century the study reveals that throughout the last century sam was the dominant mode of climatic variability in the coastal region of central dronning maud land on a decadal scale

in situ fe isotope ratio determination in fe ti oxides and sulfides from drilled gabbros and basalt from the iodp hole 1256d in the eastern equatorial pacific abstract in situ fe isotope measurements have been carried out to estimate the impact of the hydrothermal metamorphic overprint on the fe isotopic composition of fe ti oxides and fe sulfides of the different lithologies of the drilled rocks from iodp hole 1256d eastern equatorial pacific 15 ma crust formed at the east pacific rise most igneous rocks normally have a very restricted range in their 56fe 54fe ratio in contrast fe isotope compositions of hot fluids 300 c from mid ocean ridge spreading centers define a narrow range that is shifted to lower 56fe values by 0 2 0 5 as compared to igneous rocks therefore it is expected that mineral phases that contain large amounts of fe are especially affected by the interaction with a fluid that fractionates fe isotopes during exsolution precipitation of those minerals we have used a femtosecond uv laser ablation system to determine mineral 56fe 54fe ratios of selected samples with a precision of one key observation is that the temperature dependent inter mineral fractionations of fe isotopes between magnetite and ilmenite are systematically shifted towards higher values when compared to theoretically expected values while synthesized well equilibrated magnetite ilmenite pairs are compatible with the theoretical predictions theoretical considerations including factors of different aqueous fe chlorides and rayleigh type fractionations in the presence of a hydrous chlorine bearing fluid can explain this observation the disagreement between observed and theoretical equilibrium fractionation the fact that magnetite in contrast to ilmenite shows a slight downhole trend in the 56fe values and the observation of small scale heterogeneities within single mineral grains imply that a general re equilibration of the magnetite ilmenite pairs is overprinted by kinetic fractionation effects caused by the interaction of magnetite ilmenite with hydrothermal fluids penetrating the upper oceanic crust during cooling or incomplete re equilibration at low temperatures furthermore the observation of significant small scale variations in the 56fe 54fe ratios of single minerals in this study highlights the importance of high spatial resolution analyses of stable isotope ratios for further investigations

fe isotope variations in the modern and ancient earth and other planetary bodies iron the fourth most abundant element in the earth s crust has four naturally occurring stable isotopes 54fe 5 84 56fe 91 76 57fe 2 12 and 58fe 0 28 and the natural mass dependent isotope variations of fe in the rock record span a range of 4 per mil in 56fe 54fe ratios fig 1 the field of fe isotope geochemistry is relatively new but has received considerable attention because it may allow us to gain a better understanding of how fe is cycled in different environments iron typically occurs as either reduced ferrous fe in oxygen poor environments or as oxidized ferric iron in oxygen rich environments notably only the reduced species is soluble in oxygenated aqueous solutions unless the ph is low in the archean and early proterozoic the earth may have been relatively oxygen poor e g kasting et al 1979 grandstaff 1980 holland 1994 suggesting that there may have been significant quantities of fe 0 9 millimolar dissolved in the oceans as fe ii aq e g ewers 1983 sumner 1997 the extensive iron formations of archean to early proterozoic age may have been deposited from such fe ii rich oceans e g beukes and klein 1992 in the modern oxic oceans however fe contents are exceedingly low 1 nanomolar in the open oceans e g martin and gordon 1988 bruland et al 1991 martin 1992 johnson et al 1997 and it is now recognized that marine productivity is fe limited in parts of the open oceans e g martin and fitzwater 1988 martin et al 1989 1994 the differences in the behavior of fe with redox state and the significant isotope fractionations 1 or more in 56fe 54fe that are associated with redox conditions suggests that fe isotope studies will be extremely useful for tracing

multiple sulfur isotope fractionation and mass transfer processes during pyrite precipitation and recrystallization an experimental study at 300 and 350 c abstract equilibrium multiple sulfur isotope fractionation factors 33s 32s and 34s 32s between aqueous so4 h2s and coexisting pyrite under hydrothermal conditions were determined experimentally at 300 350 c and 500 bars two different experimental techniques were used to determine the fractionation factors and the rate of s isotope exchange between pyrite and constituent aqueous species h2s and so4 1 closed system gold capsule pyrite h2s exchange experiments and 2 complimentary time series experiments at 300 and 350 c 500 bars using flexible gold cell hydrothermal equipment which allowed monitoring the multiple s isotope composition of dissolved s species during pyrite precipitation and subsequent recrystallization the three isotope technique was applied to the multiple s isotope data to demonstrate equilibrium s isotope fractionation between pyrite and h2s results at 350 c indicate ln 34 pyrite h 2 s 1 9 and ln 33 pyrite h 2 s 1 0 the ln 34 pyrite h 2 s is not only different in magnitude but also in sign from the commonly used value of 1 from ohmoto and rye 1979 this experimental study also demonstrated initial s isotope disequilibrium amongst the aqueous s species and pyrite during rapid precipitation despite aqueous speciation indicating pyrite saturation at all stages textural crystallographic and s isotope interpretations suggest that pyrite formed by means of the fes pathway the initial s isotope disequilibrium between formed pyrite and dissolved s species was effectively erased and approached isotopic equilibrium upon recrystallization during the course of 4297 h interpretation of seafloor hydrothermal vent sulfides using the revised equilibrium 34s 32s fractionation between pyrite and h2s suggests that pyrite is close to s isotope equilibrium with vent h2s contrary to previous conclusions the experimental data reported here broaden the range of pyrite formation mechanisms at seafloor hydrothermal vents in that mineral formation pathway and equilibration rates need to be considered to account for the well recognized s isotope variability that often characterizes these systems

fractionation of cu fe and zn isotopes during the oxidative weathering of sulfide rich rocks abstract we measured the fe cu and zn isotopic compositions of the fluids generated during leaching experiments with pyrite chalcopyrite and sphalerite rich rocks and with a sphalerite mineral separate our study demonstrates that the oxidative weathering of sulfide rich rocks can produce substantial variations in fe 1 75 to 1 0 56 fe solution pyrite rock and cu 0 0 to 2 0 65 cu solution chalcopyrite rock isotopes and small variations in zn isotopes 0 0 to 0 2 66 zn solution sphalerite in the fluid phase relative to the rock for the fe and cu systems we suggest that isotopic fractionation is caused by electron exchange driven e g fe ii fe iii and cu i cu ii redox reactions at the surfaces of the sulfide minerals that occur during air and aqueous chemical reactions under acidic conditions these reactions tend to enrich the fluid phase in the heavier fe and cu isotopes however under circumneutral ph conditions the fe isotopic composition in solution was controlled by the precipitation of fe iii oxide phases which enriched the solution in the lighter fe isotopes this investigation provides a preliminary framework for interpreting the impact of sulfide oxidation reactions on the distributions of stable fe cu and zn isotopes in natural waters

application of organic petrography in north american shale petroleum systems a review abstract organic petrography via incident light microscopy has broad application to shale petroleum systems including delineation of thermal maturity windows and determination of organo facies incident light microscopy allows practitioners the ability to identify various types of organic components and demonstrates that solid bitumen is the dominant organic matter occurring in shale plays of peak oil and gas window thermal maturity whereas oil prone type i ii kerogens have converted to hydrocarbons and are not present high magnification sem observation of an interconnected organic porosity occurring in the solid bitumen of thermally mature shale reservoirs has enabled major advances in our understanding of hydrocarbon migration and storage in shale but suffers from inability to confirm the type of organic matter present herein we review organic petrography applications in the north american shale plays through discussion of incident light photographic examples in the first part of the manuscript we provide basic practical information on the measurement of organic reflectance and outline fluorescence microscopy and other petrographic approaches to the determination of thermal maturity in the second half of the paper we discuss applications of organic petrography and sem in all of the major shale petroleum systems in north america including tight oil plays such as the bakken eagle ford and niobrara and shale gas and condensate plays including the barnett duvernay haynesville bossier marcellus utica and woodford among others our review suggests systematic research employing correlative high resolution imaging techniques and in situ geochemical probing is needed to better document hydrocarbon storage migration and wettability properties of solid bitumen at the pressure and temperature conditions of shale reservoirs

using reflectance crossplots and rotational polarization for determining first cycle vitrinite for maturation studies abstract vitrinite reflectance on dispersed sedimentary organic matter is traditionally determined from histograms of vitrinite and inertinite reflectance measured on either whole rock samples or kerogen concentrates or from particles usually in whole rock preparations chosen by morphology and relative reflectance to be first cycle vitrinite this paper discusses an alternative method discrimination of first cycle vitrinite using apparent maximum and minimum reflectance data plotted on reflectance crossplots the use of crossplots increases the confidence that the macerals identified as first cycle vitrinite are optically similar the maximum minimum data in this study were collected on a quantitative reflectance microscope outfitted with rotational polarization a technique that eliminates the usual difficulty in collecting such data on very small macerals by stage rotation

the experimental calibration of the iron isotope fractionation factor between pyrrhotite and peralkaline rhyolitic melt abstract a first experimental study was conducted to determine the equilibrium iron isotope fractionation between pyrrhotite and silicate melt at magmatic conditions experiments were performed in an internally heated gas pressure vessel at 500 mpa and temperatures between 840 and 1000 c for 120 168 h three different types of experiments were conducted and after phase separation the iron isotope composition of the run products was measured by mc icp ms i kinetic experiments using 57 fe enriched glass and natural pyrrhotite revealed that a close approach to equilibrium is attained already after 48 h ii isotope exchange experiments using mixtures of hydrous peralkaline rhyolitic glass powder 4 wt h 2 o and natural pyrrhotites fe 1 x s as starting materials and iii crystallisation experiments in which pyrrhotite was formed by reaction between elemental sulphur and rhyolitic melt consistently showed that pyrrhotite preferentially incorporates light iron no temperature dependence of the fractionation factor was found between 840 and 1000 c within experimental and analytical precision an average fractionation factor of 56 fe 54 fe pyrrhotite melt 0 35 0 04 2se n 13 was determined for this temperature range predictions of fe isotope fractionation between fes and ferric iron dominated silicate minerals are consistent with our experimental results indicating that the marked contrast in both ligand and redox state of iron control the isotope fractionation between pyrrhotite and silicate melt consequently the fractionation factor determined in this study is representative for the specific fe 2 fe ratio of our peralkaline rhyolitic melt of 0 38 0 02 at higher fe 2 fe ratios a smaller fractionation factor is expected further investigation on fe isotope fractionation between other mineral phases and silicate melts is needed but the presented experimental results already suggest that even at high temperatures resolvable variations in the fe isotope composition can be generated by equilibrium isotope fractionation in natural magmatic systems

the iron isotope composition of enstatite meteorites implications for their origin and the metal sulfide fe isotopic fractionation factor abstract despite their unusual chemical composition it is often proposed that the enstatite chondrites represent a significant component of earth s building materials based on their terrestrial similarity for numerous isotope systems in order to investigate a possible genetic relationship between the fe isotope composition of enstatite chondrites and the earth we have analyzed 22 samples from different subgroups of the enstatite meteorites including eh and el chondrites aubrites main group and shallowater and the happy canyon impact melt we have also analyzed the fe isotopic compositions of separated magnetic and non magnetic phases from both enstatite chondrites and achondrites on average eh3 5 chondrites 56fe 0 003 0 042 2 standard deviation n 9 including previous literature data as well as el3 chondrites 56fe 0 030 0 038 2 sd n 2 have identical and homogeneous fe isotopic compositions indistinguishable from those of the carbonaceous chondrites and average terrestrial peridotite in contrast el6 chondrites display a larger range of isotopic compositions 0 180 enstatite achondrites aubrites also exhibit a relatively large range of fe isotope compositions all main group aubrites are enriched in the light fe isotopes 56fe 0 170 0 189 2 sd n 6 while shallowater is isotopically relatively heavy 56fe 0 045 0 101 2 sd n 4 number of chips we take this variation to suggest that the main group aubrite parent body formed a discreet heavy fe isotope enriched core whilst the shallowater meteorite is most likely from a different parent body where core and silicate material remixed this could be due to intensive impact induced shearing stress or the ultimate destruction of the shallowater parent body analysis of separated enstatite meteorite mineral phases show that the magnetic phase fe metal is systematically enriched in the heavier fe isotopes when compared to non magnetic phases fe hosted in troilite which agrees with previous experimental observations and theoretical calculations the difference between magnetic and non magnetic phases from enstatite achondrites provides an equilibrium metal sulfide fe isotopic fractionation factor of 56femetal troilite 56femetal 56fetroilite of 0 129 0 060 2 se at 1060 80 k which confirms the predictions of previous theoretical calculations

ancient geochemical cycling in the earth as inferred from fe isotope studies of banded iron formations from the transvaal craton variations in the isotopic composition of fe in late archean to early proterozoic banded iron formations bifs from the transvaal supergroup south africa span nearly the entire range yet measured on earth from 2 5 to 1 0 in 56fe 54fe ratios relative to the bulk earth with a current state of the art precision of 0 05 for the 56fe 54fe ratio this range is 70 times analytical error demonstrating that significant fe isotope variations can be preserved in ancient rocks significant variation in fe isotope compositions of rocks and minerals appears to be restricted to chemically precipitated sediments and the range measured for bifs stands in marked contrast to the isotopic homogeneity of igneous rocks which have 56fe 0 00 0 05 as well as the majority of modern loess aerosols riverine loads marine sediments and proterozoic shales the fe isotope compositions of hematite magnetite fe carbonate and pyrite measured in bifs appears to reflect a combination of 1 mineral specific equilibrium isotope fractionation 2 variations in the isotope compositions of the fluids from which they were precipitated and 3 the effects of metabolic processing of fe by bacteria for minerals that may have been in isotopic equilibrium during initial precipitation or early diagenesis the relative order of 56fe values appears to decrease in the order magnetite siderite ankerite similar to that estimated from spectroscopic data although the measured isotopic differences are much smaller than those predicted at low temperature in combination with on going experimental determinations of equilibrium fe isotope fractionation factors the data for bif minerals place additional constraints on the equilibrium fe isotope fractionation factors for the system fe iii fe ii hematite magnetite fe carbonate 56fe values for pyrite are the lowest yet measured for natural minerals and stand in marked contrast to the high 56fe values that are predicted from spectroscopic data some samples contain hematite and magnetite and have positive 56fe values these seem best explained through production of high 56fe 54fe reservoirs by photosynthetic fe oxidation it is not yet clear if the low 56fe values measured for some oxides as well as fe carbonates reflect biologic processes or inorganic precipitation from low 56fe ferrous fe rich fluids however the present results demonstrate the great potential for fe isotopes in tracing the geochemical cycling of fe and highlight the need for an extensive experimental program for determining equilibrium fe isotope fractionation factors for minerals and fluids that are pertinent to sedimentary environments

the detection of weathering in coal by petrographic rheologic and chemical methods abstract this study examines petrographic rheologic proximate and ultimate analyses techniques to investigate the effects of natural weathering on coal the applicability of such tests to both the detection of weathering and to the prediction of the properties of a fresh coal based upon analyses of a weathered sample is discussed rheologic parameters and a petrographic staining technique showed the most sensitive response to weathering the latter test is considered the most suitable of these for the detection of weathering as it is independent of prior knowledge of the properties of the fresh coal and of the petrographic composition a petrographic approach is also considered most suitable for estimation of fresh coal characteristics from weathered samples rank may be closely approximated and petrographic type determined microscopically even on highly weathered samples and these two parameters may be used to estimate properties such as volatile matter calorific value and dilatation minor modification should be made to vitrinite reflectance measurements according to the degree of weathering as revealed by selective staining

iron isotope fractionation between aqueous ferrous iron and goethite abstract the equilibrium fe isotope fractionation factor between aqueous fe ii and goethite has been experimentally measured to be 1 05 0 08 in 56 fe 54 fe 2 at 22 c using the three isotope method experiments were done using two sizes of goethite 81 11 nm and 590 42 nm and the experimental products were subjected to serial extraction using acid partial dissolution techniques to determine if surface fe iii atoms have different isotopic properties than the bulk goethite these experiments indicate that the interaction of fe ii aq and goethite is dynamic and results in complete or near complete fe isotope exchange over 30 days involving at least four components fe ii aq goethite sorbed fe ii and fe iii surface the equilibrium fractionation factor between fe ii aq and fe ii sorb is the same for both sizes of goethite at 56 fe fe ii aq fe ii sorb 1 24 0 14 this fractionation factor is significantly different than the results of previous studies on fe ii sorption to goethite the proportion of the fe iii surface component is greatest in the experiments that used the smallest goethite and the fe iii surface fe ii aq fractionation is estimated to be at least 2 1 the high fe iii surface fe ii aq fractionation may exert a significant influence on the fe isotope compositions of aqueous fe ii in natural systems that contain nanoparticulate goethite including those involving bacterial iron reduction these results demonstrate that the isotopic properties of nano scale minerals may be distinct from micron scale or larger minerals as is the case for other thermodynamic properties of nanoparticles

determination of the fe ii aq magnetite equilibrium iron isotope fractionation factor using the three isotope method and a multi direction approach to equilibrium abstract magnetite is ubiquitous in the earth s crust and its presence in modern marine sediments has been taken as an indicator of biogeochemical fe cycling magnetite is also the most abundant fe oxide in banded iron formations bifs that have not been subjected to ore forming alteration magnetite is therefore an important target of stable fe isotope studies and yet interpretations are currently difficult because of large uncertainties in the equilibrium stable fe isotope fractionation factors for magnetite relative to fluids and other minerals in this study we utilized the three isotope method 57fe 56fe 54fe to explore isotopic exchange via an enriched 57fe tracer and natural mass dependent fractionation using 56fe 54fe variations during reaction of aqueous fe ii fe ii aq with magnetite importantly we employed a multi direction approach to equilibrium by reacting four 57fe enriched fe ii solutions that had distinct 56fe 54fe ratios which identifies changes in the instantaneous fe isotope fractionation factor and hence identifies kinetic isotope effects we find that isotopic exchange can be described by two 56fe 54fe fractionations where an initial rapid exchange 66 isotopic mixing within 1 day involved a relatively small fe ii aq magnetite 56fe 54fe fractionation followed by slower exchange 25 isotopic mixing over 50 days that was associated with a larger fe ii aq magnetite 56fe 54fe fractionation this later fractionation is interpreted to approach isotopic equilibrium between fe ii aq and the total magnetite all four fe ii solutions extrapolate to the same final equilibrium 56fe 54fe fractionation for fe ii aq magnetite of 1 56 0 20 2 at 22 c additional experiments that synthesized magnetite via conversion of ferrihydrite by reaction with aqueous fe ii yield final 56fe 54fe fractionations that are identical to those of the exchange experiments our experimental results agree well with calculated fractionation factors using the reduced partition function ratios for fe h 2 o 6 2 from rustad et al 2010 and stoichiometric magnetite from mineev et al 2007 and these relations may be combined with the experimental constraints to determine the temperature dependence of the fe ii aq magnetite fractionation factor 10 3 ln f e i i aq magnetite 0 145 0 002 10 6 t 2 0 10 0 02 where t is in k part of the reason for large discrepancies in calculated fe isotope fractionation factors for magnetite likely lies in the stoichiometry of the mineral in specific studies given the significant effect of octahedral versus tetrahedral fe isotope fractionation that has been calculated when our results are applied to bif genesis our experimentally determined fe ii aq magnetite fractionation factor indicates that magnetite siderite mineral pairs in 2 5 ga bifs did not form in fe isotope equilibrium with each other or with ancient seawater iron oxides in such bifs are therefore more likely to have formed through processes that were isolated from equilibrium with the oceans indicating that such bif minerals may not be suitable proxies for ancient paleoenvironments

fe isotope fractionation on fes formation in ambient aqueous solution iron sulfide phases are the ultimate repository of iron and reduced sulfur in sediments the sulfur isotope geochemistry of pyrite has had much to tell us about modern and ancient earth environments and it is likely that fe isotopes will too once fractionations for key processes are known we report the results of an experimental study of fe isotope fractionation on precipitation of fes synthetic mackinawite from excess aqueous fe ii solutions by addition of sodium sulfide solution at 2 40 c the results show a significant kinetic isotope effect in the absence of a redox process no detectable effect of temperature on the fractionation factor was observed the fe isotope fractionation for zero age fes is fe ii fes 0 85 0 30 across the temperature range studied giving a kinetic isotope fractionation factor of fe ii fes 1 0009 0 0003 on ageing the fes in contact with aqueous fe ii becomes progressively isotopically heavier indicating that the initial fractionations are kinetic rather than equilibrium from published reaction mechanisms the opportunity for fe isotope fractionation appears to occur during inner sphere ligand exchange between hexaqua fe ii and aqueous sulfide complexes fe isotope fractionation on mackinawite formation is expected to be most significant under early diagenetic situations where a readily available reactive fe source is available since fes aq is a key reactive component in natural pyrite formation kinetic fe isotope fractionations will contribute to the fe isotope signatures sequestered by pyrite subject to the relative rate of fes2 formation versus fes fe ii aq isotopic equilibration

coupled fe and s isotope evidence for archean microbial fe iii and sulfate reduction direct fossil evidence for early microbial life on earth is rare microbiological data indicate that sulfate and iron reduction are both among the earliest forms of microbial respiration and direct evidence for the early origin of sulfate reduction comes from sulfur isotopic anomalies in ancient sediments fe isotope geochemistry potentially provides a new way of identifying microbial iron reduction early in earth9s history we present fe isotopic data for sedimentary pyrite from the 2 7 ga belingwe sedimentary basin in zimbabwe isotopically light fe and a remarkable covariation between fe and s isotopes provide strong evidence for coexisting fe and s reduction our results are consistent with an early origin for sulfate reduction and provide direct geochemical evidence for the antiquity of bacterial fe reduction the covariation of fe and s isotopes may provide a useful new tracer of microbial evolution early in earth history

a rapid method for determining organic matter maturity using raman spectroscopy application to carboniferous organic rich mudstones and coals abstract a simple and rapid automated raman maturity method is calibrated using a suite of carboniferous organic rich mudstones and coals from the inch of ferryton 1 borehole in the midland valley of scotland sediments in the borehole have been thermally matured by intrusion of a quartz dolerite sill generating vitrinite reflectance vr values ranging from 0 5 to 6 0 vro calibration curves are tested on eight other uk wells penetrating carboniferous shales and coals in the midland valley and southern pennine basin the g band full width at half maximum g fwhm is the best raman parameter to estimate the thermal maturity of organic matter om in the oil and gas window 0 5 to 3 vro and has a very strong correlation with vro

iron isotope fractionation in the earth s lower mantle the two main iron bearing silicate phases in the mantle ferroperovskite and ferropericlase are expected to partition iron isotopes differently theoretical calculations suggest that the spin state of iron strongly influences the iron isotopic composition of ferropericlase whereas the iron isotopic composition of ferroperovskite is almost independent of spin state

vitrinite recycling diagnostic criteria and reflectance changes during weathering and reburial abstract the aim of this study was first to review or even identify reliable diagnostic criteria to distinguish recycled and autochthonous vitrinite particles and second to examine and try to explain the impact of weathering and reburial on optical changes reflectance of recycled material the work was based on indigenous and recycled particles of two sample sets from two wells drilled in the senegalese margin basin and the ardeche paleomargin se france respectively in addition to reflectance measurements the studied samples have also been analysed by rock eval pyrolysis for both sample sets hydrogen index hi and oxygen index oi values suggest a type iii organic matter of dominant terrestrial origin two main diagnostic criteria appear particularly useful to identify indigenous and recycled vitrinite particles the first is the clear genetic relationship between telinite and collotelinite the second is the presence of pyrite framboid inclusions in indigenous vitrinite the pyrite vitrinite association illustrates the relationship between sulphate reduction pyritisation and in situ organic matter transformation through gelification process however application of both diagnostic criteria requires some additional information about depositional conditions i e anoxicity and thermal maturity of the studied samples weathering has no or only very limited effect on vitrinite reflectance during their new burial history recycled vitrinites follow a reflectance evolution path close to that of inertinites and thus appear as transitional materials between vitrinite and inertinite macerals consistently this behaviour implies that recycled vitrinite reflectance changes during burial diagenesis do not solely depend on their chemical composition but most probably too on combined chemical and structural changes inherited from their past burial history and from the impact of weathering during their recycling stage

new data on equilibrium iron isotope fractionation among sulfides constraints on mechanisms of sulfide formation in hydrothermal and igneous systems abstract fe s and cu reduced partition function ratios factors allow calculation of equilibrium isotope fractionation factors factors for chalcopyrite are calculated from experimental and theoretical partial phonon densities of state states kobayashi et al 2007 the fe factors for mackinawite are calculated from mossbauer spectroscopy data bertaut et al 1965 excellent agreement exists between fe factors for chalcopyrite calculated from the experimental and theoretical 57fe phonon densities of states supporting the reliability of the fe factors for chalcopyrite the 34s factor for chalcopyrite is consistent with experimental data on equilibrium sulfur isotope fractionation factors among sulfides and theoretical 34s factors except those recently calculated by a dft approach up to date experimental isotope exchange data on equilibrium fe isotope fractionation factors between minerals and aqueous fe were critically reevaluated in conjunction with fe factors for minerals and the following expressions for factors for aqueous fe2 and fe3 were obtained 10 3 ln fe aq 3 1 0063 10 6 t 2 t 273 k 10 3 ln fe aq 2 0 6537 10 6 t 2 t 273 k application of these new factors to fe and s isotope fractionation at seafloor hydrothermal conditions shows that chalcopyrite may precipitate in equilibrium with fe in hydrothermal fluids in contrast fe and s isotope compositions of pyrite are may not be controlled by isotope equilibration with fe in the hydrothermal fluid previously reported data on fe isotope fractionation between pyrite and chalcopyrite in intrusions in the grasberg igneous complex seem to be reasonable and are in general agreement with previous non isotopic estimates fe isotope fractionation between pyrite and chalcopyrite appear to reflect equilibrium in the intrusions of the grasberg igneous complex and fe isotopes may therefore be considered as a potential geothermometer the pyrite chalcopyrite fe isotope geothermometer however cannot be applied to the skarn facies of the grasberg complex where the initial fe isotope compositions may have been disturbed by subsequent processes related to skarn formation

selective blackening of bioclasts via mixing zone aragonite neomorphism in late triassic limestone zlatibor mountains serbia a peculiar facies of the norian rhaetian dachstein type platform carbonates which contains large amounts of blackened bioclasts and dissolutional cavities filled by cements and internal sediments occurs in the zlatibor mountains serbia microfacies investigations revealed that the blackened bioclasts are predominantly solenoporaceae with a finely crystalline originally aragonite skeleton of fine cellular structure blackening of other bioclasts also occurs subordinately solenoporacean dominated reefs developed behind the platform margin patch reef tract were the main source of sand sized detritus the blackened and other non blackened bioclasts are incorporated in automicrite cement radiaxial fibrous calcite cements in the dissolutional cavities are also black dark grey or white reworked black pebbles were reported from many occurrences of peritidal deposits in those cases the blackening took place under pedogenic meteoric diagenetic conditions in contrast in the inner platform deposits of the ilidz ya limestone the blackening of bioclasts occurred in a marine meteoric mixing zone as indicated by petrographic features and geochemical data of the skeleton replacing calcite crystals attributes of mixingzone pore waters were controlled by mixing corrosion different solubility of carbonate minerals and microbial decomposition of organic matter in the moderate energy inner platform environment large amounts of microbial organic tissue were accumulated and subsequently decomposed triggering selective blackening in the course of early shallow burial diagenesis the d 18 o and d 13 c values of the mixing zone precipitates and replacive calcite do not produce a linear mixing trend variation mainly resulted from microbial decomposition of organic matter that occurred under mixing zone conditions the paragenetic sequence implies cyclic diagenetic conditions that were determined by marine meteoric and mixing zone pore fluids the diagenetic cycles were controlled by sea level fluctuations of moderate amplitude under a semi arid to semi humid climate

redox changes in a seafloor hydrothermal system recorded in hematite chalcopyrite chimneys abstract hydrothermal chimneys composed of hematite and chalcopyrite grow at the irina ii vent site logatchev hydrothermal field mid atlantic ridge hematite and chalcopyrite form layers that repeatedly alternate within the chimney wall the repeating alternation of hematite and chalcopyrite implies for repeating changes in the physico chemical parameters of the vent fluid the modeled stability diagrams of hematite and chalcopyrite at the physico chemical conditions of the irina ii hydrothermal site showed that the precipitation of these two fe minerals is primarily governed by the activity of h2s and ph fe isotope studies suggest that the successive deposition of chalcopyrite 56 54fe 0 20 and hematite 56 54fe 0 60 layers in the irina ii chimneys is a result of redox changes in the hydrothermal fluid the replacement of hematite by either magnetite or chalcopyrite at some places also suggests for a redox inversion in the hydrothermal system from oxic to reduced chondrite normalized rare earth element distribution patterns of the hematite layers show a strong negative eu anomaly which is interpreted to be a result of crystal chemical control on the rare earth element fractionation during hematite precipitation sr isotope systematics indicate significant and variable incorporation of seawater from 40 to 80 in the hydrothermal system nd pb isotope studies show that nd and pb in chalcopyrite and hematite layers are derived mainly from the underlying mafic and ultramafic rocks the chimneys are young 5 13 1 28 kyrs b p and their wall thickened inward the duration of redox cycles oxic and reducing within the scale of a single chimney is about several hundred years the hematite layers are enriched in w in sn and u indicating that primary hematite hydrothermal deposits at the seafloor may be a potential source for these strategic trace elements high concentrations of these elements in the studied hematite layers can be explained by their easy ion substitution for fe3 in the hematite crystal lattice whereas the most plausible source of the elevated w in and sn contents are the hydrothermal fluids the seawater is the possible major source of u

sulfur controlled iron isotope fractionation experiments of core formation in planetary bodies abstract a series of high pressure and temperature experiments were conducted to better constrain the fe isotope fractionation during core mantle differentiation in planetesimal and planetary bodies synthetic mixtures of oxides and metal having varying amounts of sulfur approximating terrestrial and martian compositions were melted at 1 2 gpa and 1650 c iron isotopic equilibrium between the resulting metal and glass run products was verified for all experiments using the three isotope technique purified fe from metal and glass was analyzed by multiple collector icp ms in high resolution mode iron alloy and silicate glass show a well resolved 57femetal silicate of 0 12 0 04 in a sulfur free system isotope fractionation increases with sulfur content to 0 43 0 03 at 18 wt sulfur in the metal these results cannot be easily interpreted within the context of known fe isotope ratios in most natural samples of planetary and asteroidal mantles and therefore suggest more complex processes affected the fe isotope fractionation therein however to reconcile martian meteorite iron isotopic signatures with geophysical models using this new experimental data requires a smaller amount of sulfur in the martian core than previous estimates with an upper limit of 8 wt

iron and sulphur isotopes from the carajas mining province para brazil implications for the oxidation of the ocean and the atmosphere across the archaean proterozoic transition abstract mineralogical analyses and major and trace element geochemistry combined with iron and sulfur isotopes were applied to banded iron formations bifs and pyrite bearing sandstones from the carajas mineral province brazil the bifs belong to the 2 7 ga old grao para group and show a rather simple mineralogy hematite and quartz or cryptocrystalline silica their ree y patterns suggest deposition under marine sub oxic conditions fe isotopes show highly positive values 57 fe irmm 14 2 06 0 34 in average which can be explained by the partial oxidation of fe 2 aq in the surface ocean subsequent to the upwelling of deep anoxic seawater the resulting iron oxy hydroxides likely formed in the shallow photic zone as a seasonal process and acquired highly positive iron isotope signature values consistent with a rayleigh distillation model the pyrite bearing sandstones belong to the aguas claras formation of palaeoproterozoic younger age and were cored at the base of the giant azul manganese deposit diagenetic pyrite is characterized by positive 57 fe irmm 14 1 02 0 2 and 34 s vctd 11 97 0 12 average values that are different from values of modern marine biogenic pyrite results likely indicate that dissolved sulfate was the limiting factor controlling biogenic pyrite formation at that time near zero 33 s values 0 013 0 003 indicate minimal mass independent sulfur isotope fractionation mif s consistent with the 2 1 ga age previously obtained from the aguas claras pyrites this result suggests deposition at a time when the oxygen partial pressure in the atmosphere was already high enough 10 5 to 10 2 pal or present atmospheric level to hinder mif s by photochemical reactions incidentally this also confirms that the giant mn deposit of carajas is in the same age range 2 1 0 2 ga as other mn ores in gabon and south africa pointing to the importance of mn precipitation in paleoproterozoic times

stable isotope thermometry at high temperatures determination of accurate temperatures for geological events has been the grail of stable isotope geochemistry since the seminal 1947 paper by urey in theory this should be simple calibrated mineral pairs are common analysis is rapid and there is no significant pressure correction however in spite of widespread application the promise of reliable thermometry has been elusive stable isotope temperatures in metamorphic and igneous rocks are often controversial is the fractionation between two phases a thermometer speedometer rate dependant hygrometer p h2o dependant or chimera a number of factors have contributed to this uncertainty including incomplete and sometimes conflicting calibration of isotope fractionation factors limited understanding of the kinetics of mineral exchange and the lack of microanalytical techniques this situation has improved dramatically over the past decade permitting reliable and detailed thermal histories to be inferred in a landmark paper bottinga and javoy 1975 empirically calibrated the oxygen isotope fractionation factors among ten rock forming minerals at t 500 c their compilation shows that 84 of analyzed samples contain at least three minerals meeting a concordance test for equilibrium they concluded the great majority of igneous and metamorphic rocks has conserved a state of oxygen isotope exchange equilibrium if correct this bodes well for thermometry however this conclusion was contested by deines 1977 who critically examined the existing data and concluded that less than half of the rocks analyzed to date would yield concordant 18o derived temperatures while seeming irreconcilable both conclusions are based on fact all rocks contain some degree of disequilibrium but many also preserve a thermometric record it is the purpose of this review to discuss the new strategies for reliable isotope thermometry and to explore disequilibrium processes so they may be recognized and properly interpreted the organization of this paper will be to discuss the assumptions

quantitative evaluation of gas generation from the upper paleozoic coal mudstone and limestone source rocks in the ordos basin china abstract significant quantities of tight gas resources have been discovered in the upper paleozoic interval in the ordos basin central china the gas is believed to have been derived primarily from the upper paleozoic coal mudstone and limestone source rocks an integrated organic geochemistry and basin modeling approach was applied to quantitatively evaluate gas generation from the three types of source rocks source specific gas generation kinetics were first established on the basis of sealed gold tube pyrolysis experiments gas generation was then modeled in 1d and 3d using the source specific kinetics obtained the results show that 1 near the depositional and thermal center e g well zt 1 gas generation occurred much earlier and was greater than that of the sh 360 well which is away from the depositional and thermal center 2 c2 c5 gases in the zt 1 well underwent thermal cracking while gases in the sh 360 well did not experience any secondary thermal alteration 3 hydrocarbon gases were mainly generated during the early cretaceous 135 96 ma and the late jurassic 161 135 ma 4 the cumulative amounts of gas generation from the coal mudstone and limestone source rocks are 147 23 1012 57 85 1012 and 12 73 1012 m3 respectively with coal seams being a major contributor about 67 6 to the upper paleozoic gas system followed by the mudstone about 26 6 and limestone about 5 8 by comparing with previous work and a default kinetics basin model our source specific kinetics basin model is more suitable for simulating gas generation in the upper paleozoic source rocks within the ordos basin

significance of iron isotope mineral fractionation in pallasites and iron meteorites for the core mantle differentiation of terrestrial planets abstract seven bulk chondrites with 57 fe 54 fe values between 0 1 and 0 relative to irmm 14 tend to be slightly lighter than 11 bulk iron meteorites which have 57 fe 54 fe values ranging from 0 04 to 0 2 at the mineral scale taenite from two iron meteorites cranbourne and toluca shows 57 fe 54 fe values heavier by up to 0 3 than their kamacite counterpart thus calling into question the significance of bulk iron meteorite data on three pallasites esquel marjalahti and springwater we measured a heavier iron isotope composition for the metal fractions compared to the coexisting olivines as previously observed on two other pallasites eagle station and imilac but the range of 57 fe 54 fe differences from 0 32 to 0 07 is larger than that originally found troilite from two pallasites appears to be even heavier than the metal fraction whereas schreibersite is lighter than its olivine counterpart there is thus a general tendency for minerals within a given rock to show a heavier fe isotope composition as the coordination number of fe increases although troilite is an exception to this rule iron meteorites are classically considered as remnants of asteroid cores and pallasites as core mantle interfaces the simultaneous finding that the metal fractions of pallasites have a higher 57 fe 54 fe signature than the coexisting olivines and that the iron meteorites are slightly heavier than chondrites could be taken as an indication that planetary core mantle differentiation is accompanied by sizeable iron isotope fractionation in this hypothesis mass balance constraints imply that resultant planetary mantles should be isotopically lighter than the chondritic starting material that is not observed however since all planetary mantles analyzed so far have 57 fe 54 fe values equivalent to or heavier than those of chondrites it thus appears that the moderate temperature and pressure metal silicate fractionation that occurred in pallasite and iron parent bodies is not readily transposable to planets as far as fe isotopes are concerned instead these mantle signatures could reflect equilibrium fractionation at a higher temperature or the lack of a global core mantle equilibration at the planetary scale overall these new results show that the mass dependent isotopic scatter observed among inner solar system bodies from the bulk rock to the planetary scale 0 3 57 fe 54 fe is more restricted than previously thought this likely confirms a homogenization process that occurred in the protoplanetary accretion disk between refractory inclusion condensation and chondrule formation