neutralization of sulfuric acid solutions by calcite dissolution and the application to anoxic limestone drain design abstract batch reactor br experiments were conducted to measure the effect of hydrodynamics and gypsum coatings on calcite neutralization rates a factorial array of br experiments measured the h concentration change by calcite dissolution over a ph range of 1 5 3 5 and na2so4 concentrations of 0 1 m the rate of h concentration change with time was determined by numerical differentiation of h concentration versus time regression modeling showed that for uncoated calcite rates are only significantly affected by ph r 10 2 32 a h 0 76 whereas for calcite coated with gypsum only time had a significant effect on calcite dissolution rates r 10 1 96t 0 53 because transport limited dissolution rates for uncoated calcite are a function of the ph and reynolds number a model was developed to express the effects of these two variables on the rate of h consumption for a solution with a darcy velocity q through a porous medium with a particle radius rp such that r 1 08 10 3 q 0 31 r p 0 69 m h 0 87 this equation was integrated via a numerical model to simulate the performance of an idealized anoxic limestone drain ald this model predicts the ph and alkalinity change along the length of an ald the model shows that the efficiency of an ald is greater when the darcy velocity is low and the particle radius is small in addition the growth of gypsum coatings causes the rate of h neutralization to decline as the square root of time as they form and block the h transport to the calcite surface supersaturation with respect to gypsum leading to coating formation can be avoided by diluting the ald feed solution or by replacing limestone with dolomite

the δ18o of primary and secondary waters in hydrous volcanic glass abstract we present analyses of phyllosilicates volcanic glass and a series of experiments and observations on the 18o of water extracted by rapid thermal pyrolysis at 1450 c using the tcea thermal conversion elemental analyzer the study includes the same hydrous glasses that were previously analyzed for their d values of extracted water seligman et al 2016 we utilize natural phyllosilicates where water is present as oh only natural magmatic and experimentally quenched glasses in which water occurs as h2om and oh and glasses that underwent low temperature secondary hydration by meteoric water almost completely as h2om our study documents that 1 thermal extraction and simultaneous pyrolysis of h2ot into co and h2 produces little or no exchange

stable isotope and rare earth element evidence for recent ironstone pods within the archean barberton greenstone belt south africa there is considerable debate about the mode and age of formation of large up to 200 m long hematite and goethite ironstone bodies within the 3 2 to 3 5 ga barberton greenstone belt we examined oxygen and hydrogen isotopes and rare earth element ree concentrations of goethite and hematite components of the ironstones to determine whether these deposits reflect formation from sea floor vents in the archean ocean or from recent surface and shallow subsurface spring systems goethite d 18 o values range from 0 7 to 1 0 and dd from 125 to 146 which is consistent with formation from modern meteoric waters at 20 to 25 c hematite d 18 o values range from 0 7 to 2 0 which is consistent with formation at low to moderate temperatures 40 55 c from modern meteoric water ree in the goethite and hematite are derived from the weathering of local sideritic ironstones silicified ultramafic rocks sideritic black cherts and local felsic volcanic rocks falling along a mixing line between the eu eu and shale normalized hreeavg lreeavg values for the associated silicified ultramafic rocks and felsic volcanic rocks contrasting positive ce ce of 1 3 to 3 5 in hematite and negative ce ce of 0 2 to 0 9 in goethite provides evidence of oxidative scavenging of ce on hematite surfaces during mineral precipitation these isotopic and ree data taken together suggest that hematite and goethite ironstone pods formed from relatively recent meteoric waters in shallow springs and or subsurface warm springs

oxygen isotopes in iron iii oxides abstract quartz sio 2 and hematite fe 2 o 3 possess considerably different gram formula weights and different stoichiometric coefficients for their oxygen these differences mean that the numerical values of sio 2 and fe 2 o 3 compositions when reported as weight percent are not the same as the numerical values of x o i e oxygen in the mineral as a mole percent of the total oxygen in a binary quartz hematite system consequently end member quartz and hematite 18 o values which are determined from linear extrapolations of 18 o vs weight percent fe 2 o 3 data from binary mixtures can be in error by as much as several per mil extrapolation to end member 18 o values in binary quartz hematite systems should always be performed using mole fraction of oxygen as the compositional variable the hematite water fractionation curve of yapp and the quartz water curve of knauth and epstein were used together with the kinetic isotope exchange model of criss et al to constrain the depositional environment of the late proterozoic quartz hematite banded iron formation deposits of urucum brazil the depositional temperatures permitted by the model assumptions employed here range from 0 to 35 c or 54 c the permitted range of depositional water 18 o values is from 6 6 or 8 9 to 0 0 while the range of permitted depositional conditions is rather large it does encompass the possible cool temperatures and brackish or fresh waters which are indicated by sedimentologic evidence in these deposits

fe si oxyhydroxide deposits at a slow spreading centre with thickened oceanic crust the lilliput hydrothermal field 9 33 s mid atlantic ridge diffuse and focused low temperature fluids emanate at 9 33 s mid atlantic ridge and precipitate fe sioxyhydroxides that form chimneys mounds and flat lying deposits this extensive vent field named lilliput lies at the axial zone of a spreading segment with a significantly thickened crust 11 km theoretically much more heat needs to be removed from a thick crust spreading center compared to a spreading center with typical thickness of 6 km therefore settings with thickened crust should be favourable for supporting very powerful hydrothermal systems capable of producing large mineral deposits this is the first report on the composition of seafloor hydrothermal deposits at abnormally thickened oceanic crust due to hotspot ridge interaction our studies revealed that generally the lilliput hydrothermal deposits are very similar in morphology structure composition and lateral extent to other low temperature hydrothermal deposits of mid ocean ridges and intraplate volcanoes deposits at the lilliput vent field are composed of si containing goethite and ferrihydrite have very low contents of a number of transition and rare earth elements and show ree distribution patterns with negative ce and eu anomalies the speciation and precipitation of the main deposit forming elements fe and si at the hydrothermal field appear to be partially controlled by live microbes and exuded organic compounds the 18o values of the precipitated silica containing feoxyhydroxides point to low temperature formation and sr nd pb isotope variations suggest that the hydrothermal precipitates scavenged metals predominantly from the ambient seawater these findings are in agreement with the biogeochemical scenario for their precipitation

oxygen isotopic composition of ferric oxides from recent soil hydrologic and marine environments low temperature synthesis experiments on ferric oxide water systems have resulted in disparate oxygen isotope fractionation temperature t curves in this study recent ferric oxides mostly goethites of holocene age were collected and analyzed from a variety of modern soil stream and marine environments where formation temperature and the oxygen isotopic composition 18o of the water from which ferric oxides precipitated can be independently measured or estimated this allows comparison of experimental t relationships with data from natural systems selective dissolution methods were refined for the pretreatment of fine grained minerals in order to obtain reliable 18o values for pure and crystalline ferric oxides the difference 18o between the 18o value of goethite and that of local mean meteoric water ranges from 1 5 to 6 3 for soil goethites from new jersey indiana michigan iowa south dakota and taiwan we argue that these variations are largely the result of differences between the 18o of formation water and that of local mean meteoric water induced probably by 18o enrichment of soil waters by evaporation or other processes in soil horizons where ferric oxides are forming a marine goethite sample from scotland and a subaqueous bog iron sample from new jersey which can not be biased by evaporative processes provide crucial natural evidence that the difference in 18o between goethite and formation water is 1 5 at 10 c this result is consistent with our prior laboratory synthesis results bao and koch 1999 but in conflict with other experimental calibrations given the highly variable 18o value of soil or other surface water as well as the potential of initially formed ferric oxides for reequilibration with subsurface burial fluids during maturation to crystalline phases an understanding of formational and diagenetic conditions is absolutely essential when attempting to use the oxygen isotope composition of ferric oxides as a paleoclimatic proxy

carbon isotopes in continental weathering environments and variations in ancient atmospheric co2 pressure abstract abundance and carbon isotope data from an fe co3 oh component in apparent solid solution in oolitic goethites have been used to infer ancient atmospheric co2 pressures a test of the validity of these estimates might be comparisons of the carbon isotope compositions of fe co3 oh in oolitic goethites with time equivalent pedogenic calcites temporal trends of the oolitic goethite and pedogenic calcite 13c values are generally similar but time equivalent samples from each of these two groups are not common in the existing data to facilitate discussion of the concept comparisons were made of available goethite and calcite samples even though ages of the compared samples in each pair were not identical in four out of the five comparisons fe co3 oh abundance and 13c data were combined with pedogenic calcite 13c data to calculate physically reasonable soil co2 concentrations for the ancient calcitic soids this suggests that the compared oolitic goethite and pedogenic calcite systems were responding to the same global scale phenomenon i e atmospheric co2 atmospheric pco2 as determined from the goethites in these four well behaved cases ranged from values indistinguishable from modern within analytical uncertainty to values up to approximately 16 time modern modern atmospheric pco2 was taken to be 10 3 5 atm one interpretation of the fifth anomalous comparison is that atmospheric co2 levels increased from about 3 times modern to about 18 times modern from the triassic into the early jurassic this inferred value for the pco2 of the early jurassic atmosphere is not uniquely constrained by the existing data and needs to be substantiated however even considerably lower early jurassic atmospheric pco2 values of 6 to 9 times modern i e 1 3 to 1 2 of the estimated value of 18 times modern would still indicate significant differences between the global carbon cycles then and now these results highlight the need for more research on the behavior of the atmosphere during and after the triassic jurassic transition

reconstructing thermal properties of firn at summit greenland from a temperature profile time series we have constrained the value for thermal diffusivity of near surface snow and firn at summit station greenland using a fourier type analysis applied to hourly temperature measurements collected from eight thermistors in a closed off air filled borehole between may 2004 and july 2008 an implicit finite difference method suggests that a bulk diffusivity of 25 3m2 a 1 is the most reasonable for representing macroscale heat transport in the top 30 m of firn and snow this value represents an average diffusivity and in a conduction only model generates temperature series whose phase shifts with depth most closely match those of the summit borehole data rms difference between measurements and model output is 6 days this bulk value derived numerically and corroborated analytically is useful over large tracts of the greenland ice sheet where density and microstructure are unknown

laboratory and field evaluation of a flushable oxic limestone drain for treatment of net acidic drainage from a flooded anthracite mine pennsylvania usa abstract this paper demonstrates the use of dissolution rate data obtained in the laboratory to indicate the potential quality of effluent from a field scale oxic limestone drain old treatment system for neutralization of dilute acidic mine drainage amd effluent from the reevesdale mine south dip tunnel a large source of amd and base flow to the wabash creek and little schuylkill river in the southern anthracite coalfield of east central pennsylvania is representative of amd with low concentrations but high loadings of dissolved fe al and other metals because of a high flow rate in january 2003 rapid neutralization of the amd from the reevesdale mine was achieved in laboratory tests of its reaction rate with crushed limestone in closed collapsible containers cubitainers the tests showed that net alkaline effluent could be achieved with retention times greater than 3 h and that effluent alkalinities and associated dissolution rates were equivalent for fe oh 3 coated and uncoated limestone on the basis of the laboratory results a flushable old containing 1450 metric tons of high purity calcitic limestone followed by two 0 7 m deep wetlands were constructed at the reevesdale mine during the first year of operation monthly data at the inflow outflow and intermediate points within the treatment system were collected april 2006 2007 the inflow to the treatment system ranged from 6 8 to 27 4 l s with median ph of 4 7 net acidity of 9 1 mg l caco 3 and concentrations of dissolved al fe and mn of 1 0 1 9 and 0 89 mg l respectively the corresponding effluent from the old had computed void volume retention times of 4 5 18 h with median ph of 6 6 net acidity of 93 2 mg l caco 3 and concentrations of dissolved al fe and mn of

environmental memory and a possible seasonal bias in the stable isotope composition of u th he dated goethite from the canadian arctic abstract goethite ax 2 from axel heiberg island 80 n on the margin of the arctic ocean is the dominant mineral in a sample of petrified eocene wood but u th and he measurements suggest that the goethite feooh crystallized in the latest miocene pliocene ca 5 5 to 2 8 ma measured d and 18 o values of ax 2 are 221 6 and 9 6 0 5 respectively the inferred d and 18 o values of the ancient water were about 139 and 18 6 respectively with a calculated temperature of crystallization of 3 5 c which compares with the modern summer j j a temperature of 3 c and contrasts with a modern mat of 19 c published results from various biological proxies on nearby ellesmere island indicate a pliocene 4 ma mat of either 6 or 0 4 c and corresponding seasonal amplitudes of about 18 or 13 c a conductive heat flow model suggests that a temperature of 3 c could represent goethite crystallization at depths of 100 200 cm for mat 6 c or 250 450 cm for mat 0 4 c over seasonally restricted intervals of time the 18 o value of the ax 2 water 18 6 is more positive than the modern j j a precipitation 22 in combination the paleotemperatures and 18 o values of ancient waters from ax 2 and published results from three eocene or pliocene proxy sites on axel heiberg and ellesmere islands are consistent with a warm season bias in those isotopic proxies the results are also consistent with higher proportions of j j a precipitation in the annual total if so this emphasizes the importance of seasonality at high latitudes even in times of warmer global climates and suggests that the arctic hydrologic cycle as expressed in the seasonal distribution and isotopic composition of precipitation perhaps modified by a warmer arctic ocean differed from modern the 13 c value of the fe co 3 oh component in the ax 2 goethite is 6 6 which is much more positive than expected if crystallizing goethite incorporated co 2 derived primarily from oxidation of relict eocene wood with 13 c values of about 24 this apparent paradox may be resolved if the goethite is a product of oxidation of 13 c rich siderite which had previously replaced wood in an eocene methanogenic burial environment thus the goethite retains a carbon isotope memory of a diagenetic eocene event but a d and 18 o record of the latest miocene pliocene arctic climate

temperature measurements and heat transfer in near surface snow at the south pole to study near surface heat flow on the antarctic ice sheet snow temperatures were measured at south pole station to a depth of 3 m at 15 min intervals during most of 1992 solar heating and water vapor transport were negligible during the 6 month winter as was inter grain net thermal radiation leaving conduction as the dominant heat transport mechanism the rate of temperature change at depth over 15 min intervals was smaller than that at the surface by one order of magnitude at 20 cm depth and two orders of magnitude at 1 m depth a finite difference model with conduction as the only heat transfer mechanism and measured temperatures as the upper and lower boundary conditions was applied to foursets of three thermistors each the thermal conductivity was estimated as that which minimized the difference between modeled and measured 15 min changes in temperatures at the center thermistor the thermal conductivity obtained at shallow depths above 40 cm was lower than that given by existing parameterizations based on density probably because the snow grains were freshly deposited cold and poorly bonded a model using only vertical conduction explains on average 87 ofthe observed 15 min temperature changes at less than 60 cm depth and 92 below 60 cm the difference between modeled andmeasured temperature changes decreased with depth the discrepancies between model and observation correlated more strongly with the air snow temperature difference than with the product of that difference with the square of the wind speed suggesting that the residual errors are due more to non vertical conduction and to sub grid scale variabilis of the conductivity than to windpumping the residual heating rate not explained by the model of vertical conduction exceeds 0 2 w m 3 only in the top 60 cm of the near surface snow

oxygen and hydrogen isotope variations among goethites α feooh and the determination of paleotemperatures abstract a plot of d vs 18o values from a diverse group of natural goethites defines a data array which is approximately parallel to the meteoric water line the 18o values range from 9 5 to 4 4 per mil while the corresponding d values vary from 202 to 94 per mil there is considerable scatter in the d vs 18o array which can be attributed primarily to different temperatures of mineral formation as determined previously yapp and pedley 1985 and confirmed in this study the goethite water d h fractionation factor is essentially independent of temperature over the range from 25 c to 145 c however the goethitewater 18 o 16 o fractionation factor does vary with temperature as indicated by initial goethite synthesis experiments conducted at 25 c 44 c and 62 c the synthetic goethite 18 g w values suggest that the natural goethites in this study formed at temperatures that may range from about 8 c to 66 c support for the validity of these approximate calculated temperatures is provided by a natural goethite sample from the atlantis ii deep in the red sea these results suggest that goethite can be used as a single mineral low temperature geothermometer perhaps more importantly goethite can be used in low temperature oxygen isotope mineral pair geothermometers such as chert goethite calcite goethite phosphate goethite etc

a stable isotope study of lateritic bauxites abstract stable isotope analyses of gibbsitic samples from a number of lateritic bauxites suggest that the accepted oxygen and hydrogen isotope fractionation factors for the mineral at surficial temperatures are incorrect a new ox of 1 0143 0 002 and hy of 0 998 0 015 is proposed for gibbsite and in addition an ox of 1 0175 0 001 and hy of 0 975 0 008 is proposed for boehmite at surficial temperatures application of these fractionation factors suggests that gibbsite from many of the equatorial bauxites analyzed formed in equilibrium with meteoric waters similar to those which commonly accompany monsoon type rainfall these waters are generally depleted in 18o and d compared to precipitation derived from tradewinds the isotopic composition of gibbsite from the mid tertiary weipa bauxite in north queensland indicates equilibrium with waters similar in isotopic composition to modern groundwaters in the region this suggests that a monsoon type climate similar to that of the present has prevailed in the region since at least the mid tertiary the oxygen and hydrogen isotope composition of gibbsite from the paragominas deposit in brazil is markedly out of isotopic equilibrium with modern tradewind derived regional rainfall but in equilibrium with waters comparable to those derived from monsoonal rains this suggests that since the formation of the deposit the climate has changed and the monsoons no longer operate in the region thus the link between the isotopic composition of bauxite minerals and the nature of the climate prevailing during their formation can be used to define tropical regions which have previously experienced a monsoonal climate providing valuable information on the nature of atmospheric circulation in the past

paleoenvironmental reconstruction from chemical and isotopic compositions of permo pennsylvanian pedogenic minerals mineralogical and chemical analysis of late pennsylvanian and early permian paleosols from the eastern shelf of the midland basin north central texas usa are used to test hypothesized climate change in late paleozoic western equatorial pangea previously defined independently on the bases of sedimentologic and paleontologic proxies and climate models the 0 2 m size phyllosilicate fraction in the studied paleosols exhibits down profile trends in mineralogy and chemical composition that are consistent with modern weathering profiles suggesting a dominantly pedogenic origin a stratigraphic trend from kaolinite dominated profiles in upper pennsylvanian paleosols to profiles dominated by smectite and hydroxy interlayered 2 1 phyllosilicates in lower permian paleosols indicates a relatively rapid decrease in soil weathering and leaching in the latest pennsylvanian followed by a more gradual decrease in leaching throughout the early permian the chemical composition cation ratios and exchange capacity of these phyllosilicates further corroborates this shift toward less intensive leaching presumably in response to climate change from humid to progressively more arid conditions the phyllosilicates in the 0 2 m size fraction and contemporaneous pedogenic calcites from the permo pennsylvanian paleosols exhibit a long term stratigraphic increase in their 18o values of as much as 3 2 and 5 2 respectively this long term trend is consistent with a transition throughout the latest pennsylvanian through early permian toward progressively more evaporatively enriched soil waters superimposed on the long term trend is an apparent rapid enrichment 1 5 to 2 in phyllosilicate 18o values immediately above the pennsylvanian permian boundary observed oxygen isotope fractionation between the phyllosilicates and calcites within individual paleosols indicate isotopic disequilibrium between mineral pairs this is attributed to a minor detrital component in the pedogenic clay dominated phyllosilicate fraction coupled with the effects of seasonality of mineral formation inferred 18o compositions of late paleozoic meteoric water 2 to 4 are compatible with less intensive soil leaching under conditions of increasing aridity possibly coupled with a shift in local precipitation from a continental source to a marine source

polymetamorphic relations in iron ores from the iron quadrangle brazil the correlation of oxygen isotope variations with deformation history this study deals with the oxygen isotope composition of hematite rich ore bodies in the iron quadrangle brazil the area studied can be divided into two different regions a western w zone of greenschist facies assemblages and an eastern e zone of amphibolite facies with transitions into granulite facies assemblages

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

composition and origin of hydrothermal ironstones from central pacific seamounts abstract ironstones recovered from five late cretaceous seamounts in the central pacific region probably formed during late stage edifice building volcanism ironstones are dense and compact with the appearance of brown chert the ironstones are characterized by a goethite mineralogy with feooh contents up to 88 extreme fractionation of fe and mn low trace element and rare earth element abundances low co zn ratios and isotopic equilibration temperatures of about 20 45 c these characteristics indicate that the ironstones formed from hydrothermal fluids ironstones probably formed below the seawater seafloor interface as indicated by their occurrence as a proximal hydrothermal deposit presence of primary goethite cement pervasive replacement of rocks by goethite and absence of interbedded pyro clastic beds

an investigation of the thermal conductivity of snow thermal conductivity of snow has been investigated experimentally using the thermal probe method which is a transient method of measurement the measurements have been made over a wide range of snow density for fresh and dense snow for varying temperatures and for different conditions of water content snow grain type etc both in the field and in the laboratory the results are presented along with detailed sample descriptions thermal conductivity of snow increases with density and water content it also increases with temperature and the effect is more pronounced for temperatures between 15 and 0 c

permo pennsylvanian palaeotemperatures from fe oxide and phyllosilicate δ18o values abstract the oxygen isotope composition of fossil roots that have been permineralized by hematite are presented from eight different stratigraphic levels spanning the upper pennsylvanian and lower permian strata of north central texas hematite 18o values range from 0 4 to 3 7 the most negative 18o values occur in the upper pennsylvanian strata and there is a progressive trend toward more positive 18o values upward through the lower permian strata this stratigraphic pattern is similar in magnitude and style to 18o values reported for penecontemporaneous authigenic palaeosol phyllosilicates and calcites suggesting that all three minerals record similar paragenetic histories that are probably attributed to temporal palaeoenvironmental changes across the late pennsylvanian and early permian landscapes palaeotemperature estimates based on paired 18o values between penecontemporaneous hematite and phyllosilicate samples suggest these minerals co precipitated at relatively low temperatures that are consistent with a supergene origin in a low latitude soil forming environment hematite phyllosilicate 18o pairs indicate 1 relatively low soil temperatures 24 3 c during deposition of the upper pennsylvanian strata followed by 2 a considerable rise in soil temperatures 35 37 3 c during deposition of the lowermost permian strata significantly d and 18o values of contemporaneous phyllosilicates provide single mineral palaeotemperature estimates that are analytically indistinguishable from temperature estimates based on hematite phyllosilicate oxygen isotope pairs the results between the two temperature proxy methods suggest that the inferred large temperature change across the upper pennsylvanian lower permian boundary might be taken seriously if real such a significant climate change would have undoubtedly had far reaching ecological effects within this region of pangaea notably there are important lithological and palaeobotanical changes such as disappearance of coal and coal swamp floras across the upper pennsylvanian early permian boundary of north central texas that may be consistent with major climatic change toward warmer conditions

oxygen and hydrogen isotope compositions in clay minerals a potential single mineral geothermometer the opposite slopes of the isotopic fractionation of hydrogen and oxygen in the clay water system and the well known relationship between d and 18o in meteoric waters allow the isotopic composition of clay minerals to be used as a single mineral geothermometer equations can be derived which are valid for continental systems where meteoric waters are common the following equation was derived for smectite 3 54 106t 2 18osm 0 125 dsm 8 95 0 150 this equation was used to determine the isotopic composition and temperature of the waters involved in the transformation of volcanic rock to bentonite at the cortijo de archidona southeastern spain site the values obtained 6 t 21 c i e environmental temperatures confirm the reliability of this equation

climatic implications of surface domains in arrays of δd and δ18o from hydroxyl minerals goethite as an example abstract paired d h and 18o 16o analyses of natural goethites range from 224 to 93 for d and from 15 5 to 2 8 for 18o the isotopic systematics of these goethites seem to be most closely mimicked by the goethite water d h and 18o 16o fractionation curves of yapp 1987 yapp 1990 most of these goethites are of unknown age but the large range of their isotopic compositions illustrates the possible paleoenvironmental significance of surface domains calculated for hydroxyl minerals a modern surface domain msd for goethite in coordinates of d and 18o was calculated from the following information a scatter in the modern relationship between surface temperatures and 18o of meteoric water rozanski et al 1993 b average annual surface air temperatures from 0 c to 30 c for the meteoric water sample sites c the meteoric water line mwl of craig 1961 and d the goethite water isotopic fractionation factors of yapp 1987 yapp 1990 goethites that had formed in continental environments in approximate thermal equilibrium with the earth s modern atmosphere would be expected to lie within the msd and 16 of 31 goethites do so the remaining 15 are outliers of the 16 msd samples 12 including the three samples from active soil or bog environments are concordant the calculated isotopic temperatures of the concordant goethites range from 6 c to 27 c and are the same within analytical uncertainty as the modern average surface air temperatures at the respective sites calculated temperatures of the four discordant msd samples range from 7 c to 25 c and are higher than corresponding modern surface temperatures a warm earth surface domain wesd was calculated with an assumed temperature of 35 c for the tropics eight of the 15 outlier samples plot within the portion of the wesd that does not overlap the msd thus these eight goethites may have formed at times when the earth s global climate was warmer than at present temperatures calculated from the eight wesd samples range from 20 c to 33 c and suggest lower latitudinal temperature gradients as predicted by climate models of a warmer earth calculated temperatures of the seven samples that lie outside both the msd and the wesd non sd samples range from 19 c to 69 c the non sd status of these seven samples suggests that they formed in environments dominated by subsurface heat sources surface domains can be calculated for any hydroxyl mineral for which both the hydrogen and oxygen isotope mineral water fractionation factors are known the concept of surface domains provides a criterion for assessing the likelihood that a particular sample records information on ancient climatic temperature

intracrystalline site preference of oxygen isotopes in goethite a single mineral paleothermometer abstract the crystal structure of goethite feo oh has two distinct oxygen sites one with exclusively fe o bonds the other with bonds to both iron and hydrogen we developed a method to assess the oxygen isotope contrast between these sites by measuring both the bulk goethite and the oxygen released in the conversion of goethite to hematite the method involves collecting the water released by dehydroxylation fluorinating that population of extracted atoms and measuring the resulting oxygen isotope composition extracted o 18 then on a separate aliquot all structural oxygen is fluorinated and measured bulk o 18 using synthetic goethite precipitates grown under controlled environmental conditions we found significant temperature dependent fractionation e bulk extracted 5 51 0 26 10 6 t 2 44 5 2 8 t in kelvin this intracrystalline fractionation forms the basis of a single phase paleothermometer with an estimated uncertainty of 2 3 c the temperature dependence appears to be independent of the isotopic composition of the parent fluid from which the goethite formed and the ph of that fluid this intracrystalline thermometer can be used to simultaneously determine the formation temperature of a goethite and the isotopic composition of the water from which it formed natural goethites analyzed with this technique yield geologically reasonable formation temperatures of between 15 and 41 c

very high18o enrichment in archean cherts from south india implications for archean ocean temperature stable carbon and oxygen isotopic compositions of essentially unmetamorphosed archean 2 6 gyr old cherts and carbonates of the dharwar sequence of southern india from the northernmost part of the dharwar shimoga supracrustal belt kalche and nagargali have been determined the cherts from the nagargali area which preserve oolitic texture and cryptocrystalline silica show highly enriched 18 o values ranging from 28 to 31 4 o relative to smow such values are the highest yet reported from archean nondetrital sediments but are similar to those of modern marine cherts on the assumption of a seawater 18 o of 0 0 calculation of temperature based on the maximum 18 o value of 31 4 0 yields a value of 40 c this is significantly less than 70 80 c reported for the archean oceans based on cherts and chert phosphate pairs diagenetically recrystallized microcrystalline chert dolomite pairs of kalche area exhibit a range of oxygen isotopic ratios similar to those reported for archean cherts and carbonates from other parts of the world the temperature of diagenesis is estimated to be about 68 c

weathering geochronology by u th he dating of goethite nine samples of supergene goethite feooh from brazil and australia were selected to test the suitability of this mineral for u th he dating measured he ages ranged from 61 to 8 ma and were reproducible to better than a few percent despite very large variations in u and th in all samples with internal stratigraphy or independent age constraints the he ages corroborated the expected relationships these data demonstrate that internally consistent he ages can be obtained on goethite but do not prove quantitative 4he retention to assess possible diffusive he loss stepped heating experiments were performed on two goethite samples that were subjected to proton irradiation to produce a homogeneous distribution of spallogenic 3he the 3he release pattern indicates the presence of at least two diffusion domains one with high helium retentivity and the other with very low retentivity at earth surface conditions the low retentivity domain which accounts for 5 of 3he contains no natural 4he and may represent poorly crystalline or intergranular material which has lost all radiogenic 4he by diffusion in nature diffusive loss of 3he from the high retentivity domain is independent of the macroscopic dimensions of the analyzed polycrystalline aggregate so probably represents diffusion from individual micrometer size goethite crystals the 4he 3he evolution during the incremental heating experiments shows that the high retentivity domain has retained 90 95 of its radiogenic helium this degree of retentivity is in excellent agreement with that independently predicted from the helium diffusion coefficients extrapolated to earth surface temperature and held for the appropriate duration considering both the high and low retentivity domains these data indicate that one of the samples retained 90 of its radiogenic 4he over 47 5 ma and the other retained 86 over 12 3 ma thus while diffusive loss corrections to supergene goethite he ages are required these initial results indicate that the corrections are not extremely large and can be rigorously quantified using the proton irradiation 4he 3he method

oxygen and hydrogen isotope compositions of permian pedogenic phyllosilicates development of modern surface domain arrays and implications for paleotemperature reconstructions abstract mineralogic chemical and oxygen and hydrogen isotope compositions of 15 different phyllosilicate samples from permo pennsylvanian age paleosols of the eastern shelf of the midland basin of texas and the southern anadarko basin are presented mixtures of 2 1 phyllosilicates and kaolinite dominate most samples although some samples consist of relatively pure 2 1 phyllosilicates chemical and mineralogic data are used in conjunction with published thermodynamic data to calculate hydrogen and oxygen isotope fractionation factors for each sample in turn application of measured oxygen and hydrogen isotope compositions of the phyllosilicates to temperature dependent fractionation equations are used to calculate paleotemperatures of crystallization the d values of the phyllosilicates range from 69 to 55 the 18 o values range from 19 5 to 22 7 if these samples preserve a record of equilibrium with paleo meteoric waters the isotopic compositions of the phyllosilicates correspond to paleotemperatures of phyllosilicate crystallization ranging from 22 3 c to 35 3 c in particular the stratigraphic trend of calculated temperatures from midland basin samples suggests that early permian surface temperatures may have been up to 10 c warmer than those of the latest pennsylvanian

stratigraphy and mineralogy of the manganese ores of urucum mato grosso brazil preliminar results of geological mapping and microscopic studies are presented the mineral deposits of urucum are clearly different from the rest of the banded iron formations in brazil urucum is essentially younger and probably late proterozoic the sequence is unmetamorphic two main types of manganese ore exist in urucum namely

carbonate mineral water interactions in sulfide rich mine tailings the chemical composition and mineralogy of coatings on carbonate minerals from mine tailings have been studied using aqueous geochemical methods time of flight laser ionization mass spectrometry tof lims and transmission electron microscopy tem the goal is to study major and trace element partitioning between the aqueous and solid phase and to infer mechanisms that control the concentrations of elements in the pore water of sulfide rich mine tailings pore water samples and carbonate mineral grains were collected from four geochemically distinct zones within the tailings oxidation of sulfide minerals near the surface results in a large range in pore water ph 3 85 to 6 98 and aqueous concentrations of metals and sulfate with increasing depth in the tailings mineral water interactions lead to increasing ph and decreasing concentrations of metals and sulfate calculated mineral saturation indices trends in the abundance of ca fe mg and mn in tof lims profiles through the secondary coatings and electron diffraction patterns obtained from the coatings suggest that precipitation dissolution of jarosite group minerals gypsum goethite akaganeite amorphous fe oxyhydroxides and siderite control the aqueous ca fe na k and so4 concentrations the occurrence of secondary coatings on primary minerals is widespread and reactions with the secondary minerals rather than the primary mineral substrate probably represent the principal controls on trace element distributions in the pore water the data indicate that adsorption surface complexation and co precipitation reactions are important controls on the concentrations of trace elements in the pore water the occurrence of siderite coatings on the surface of ankerite grains suggests that fe bearing dolomite structure carbonate minerals dissolve incongruently this corroborates inferences made by previous workers that solubility differences between calcite and siderite lead to calcite dissolution and siderite precipitation during acid neutralization the accumulation of secondary coatings will diminish the rate of mineral dissolution reactions involving the primary minerals consequently the use of kinetic rate constants obtained from the literature for simulating the dissolution of primary mineral phases such as the carbonates and alumino silicates will likely overestimate the actual rates

isotopic reconstruction of past continental environments abstract vertebrate fossils and continental sediments provide a rich record of variations in the isotopic composition of surface environments to interpret these records a greater understanding of isotopic sources as well as fractionations associated with animal physiology soil geochemistry and diagenesis has been essential tooth enamel and fish otoliths yield subannual records of surface environments whereas soil minerals may integrate signals over many thousands of years carbon isotope variations in fossil vertebrates and soils record changes in the structure of vegetation and the isotope composition and concentration of atmospheric co2 oxygen isotope variations may be indirectly related to climate through reconstruction of the oxygen isotope composition of meteoric water or directly related to temperature through application of oxygen isotope paleothermometry to soil minerals or otoliths in africa nitrogen isotope variations show promise as a proxy for rainfall abundance though the gen

quantitative paleoenvironmental and paleoclimatic reconstruction using paleosols abstract paleosols fossil soils are preserved throughout the geologic record in depositional settings ranging from alluvial systems to between basalt flows until recently paleosols were studied using primarily qualitative methods in recent years paleopedology has shifted from a largely qualitative field based on comparisons with modern analogues to an increasingly quantitative endeavor some of this change has been a result of applying existing techniques to new materials but many of the innovations have been the result of applying new techniques to new materials including thermodynamic modeling of soil formation isotope geochemistry and applications of empirical relationships derived from modern soils a variety of semi quantitative and quantitative tools has been developed to examine past weathering and pedogenesis and to reconstruct both paleoenvironmental and paleoclimatic conditions at the time that the paleosols formed though it is often not possible to achieve the same temporal resolution as with marine records for paleoclimatic reconstructions proxies based on paleosols are potentially a much more direct means of making paleoclimatic reconstructions because soils form at the earth s surface in direct contact with the atmospheric and climatic conditions at the time of their formation paleoclimatic and environmental properties that may be reconstructed using the new proxies include provenance weathering intensity mean annual precipitation and temperature during pedogenesis nutrient fluxes into and out of the paleosols the atmospheric composition of important gases including co2 and o2 the moisture balance during pedogenesis the soil gas composition reconstructed vegetative covering and paleo altitude

using oxygen isotope chemistry to track hydrothermal processes and fluid sources in itabirite hosted iron ore deposits in the quadrilatero ferrifero minas gerais brazil the quadrilatero ferrifero brazil is presently the largest accumulation of single itabirite hosted iron ore bodies worldwide detailed petrography of selected hypogene high grade iron ore bodies at e g the aguas claras conceicao pau branco and pico deposits revealed different iron oxide generations from oldest to youngest magnetite martite hematite pseudomorph after magnetite granoblastic recrystallised microplaty fine grained 100 m hematite laser fluorination oxygen isotope analyses of selected iron ore species showed that the 18o composition of ore hosted martite ranges between 4 4 and 0 9 and is up to 11 depleted in 18o relative to hematite of the host itabirite during the modification of iron ore and the formation of new iron oxide generations e g microplaty and specular hematite an increase of up to 8 in 18o values is recorded calculated 18o values of hydrothermal fluids in equilibrium with the iron oxide species indicate 1 the involvement of isotopically light fluids e g meteoric water or brines during the upgrade from itabirite hosted hematite to high grade iron ore hosted martite and 2 a minor positive shift in 18ofluid values from martite to specular hematite as result of modified meteoric water or brines with slightly elevated 18o values and or the infiltration of small volumes of isotopically heavy metamorphic and or magmatic fluids into the iron ore system the circulation of large fluid volumes that cause the systematic decrease of 18o 16o ratios from itabirite to high grade iron ore requires the presence of e g extensive faults and or large scale folds

oxygen isotope exchange kinetics of mineral pairs in closed and open systems applications to problems of hydrothermal alteration of igneous rocks and precambrian iron formations the systematics of stable isotope exchange between minerals and fluids are examined in the context of modal mineralogical variations and mass balance considerations both in closed and in open systems on mineral pair 18 o plots samples from terranes that have exchanged with large amounts of fluid typically map out steep positively sloped non equilibrium arrays analytical models are derived to explain these effects these models allow for different exchange rates between the various minerals and the external fluids as well as different fluid fluxes the steep arrays are adequately modelled by calculated isochron lines that involve the whole family of possible exchange trajectories these isochrons have initially steep near vertical positive slopes that rotate toward a 45 equilibrium slope as the exchange process proceeds to completion the actual data point array is thus analogous to the hand of an isotopic clock that measures the duration of the hydrothermal episode the dimensionless ratio of the volumetric fluid flux to the kinetic rate parameter u k determines the shape of each individual exchange trajectory in a fluid buffered system u k 1 the solutions to the equations 1 are independent of the mole fractions of the solid phases 2 correspond to taylor s open system water rock equation and 3 yield straight line isochrons that have slopes that approach 1 f where f is the fraction reacted of the more sluggishly exchanging mineral the isochrons for this simple exchange model are closely congruent with the isochrons calculated for all of the more complex models thereby simplifying the application of theory to actual hydrothermal systems in nature in all of the models an order of magnitude of time in units of kt separates steep non equilibrium arrays e g slope 10 from arrays approaching an equilibrium slope of unity on a diagram because we know the approximate lifetimes of many hydrothermal systems from geologic and heat balance constraints we can utilize the 18 o 16 o data on natural mineral assemblages to calculate the kinetic rate constants k s and the effective diffusion constants d s for mineral h 2o exchange these calculated values k qtz 10 14 k feld 10 13 10 12 agree with experimental determinations of such constants in nature once the driving force or energy source for the external infiltrating fluid phase is removed the disequilibrium mineral pair arrays will either 1 remain frozen in their existing state if the temperatures are low enough or 2 re equilibrate along specific closed system exchange vectors determined solely by the temperature path and the mineral modal proportions thus modal mineralogical information is a particularly important parameter in both the open and closed system scenarios and should in general always be reported in stable isotopic studies of mineral assemblages these concepts are applied to an analysis of 18 o 16 o systematics of gabbros plagioclase clinopyroxene and plagioclase amphibole pairs granitic plutons quartz feldspar pairs and precambrian siliceous iron formations quartz magnetite pairs in all these examples striking regularities are observed on and plots but we point out that plots have many advantages over their equivalent diagrams as the latter are more susceptible to misinterpretation using the equations developed in this study these regularities can be interpreted to give semiquantitative information on the exchange histories of these rocks subsequent to their formation in particular we present a new interpretation indicating that precambrian cherty iron formations have in general undergone a complex fluid exchange history in which the iron oxide magnetite precursor has exchanged much faster with low temperature 400 c fluids than has the relatively inert quartz

mineralogical and geochemical characterization of supergene cu pb zn v ores in the oriental high atlas morocco in the moroccan high atlas two sulfide deposits hosted by jurassic dolostones underwent significant weathering in the cu deposit of jbel klakh several stages of supergene mineralization are distinguished 1 the replacement of hypogene sulfides in the protolith chalcopyrite by secondary sulfides in the cementation zone bornite digenite chalcocite covellite 2 the formation of oxidized minerals in the saprolite malachite azurite brochantite where the environment becomes more oxidizing and neutral and 3 the precipitation of late carbonates calcite and iron hydr oxides in the laterite the precipitation of carbonates is related to the dissolution of dolomitic host rocks which buffers the fluid acidity due to the oxidation of sulfides in the jbel haouanit pb zn deposit the mineral assemblage is dominated by typical calamine minerals cu minerals chalcocite covellite malachite and a cu pb zn vanadate mottramite galena is successively weathered in anglesite and cerussite sphalerite is weathered in smithsonite which is rapidly replaced by hydrozincite late iron hydr oxides are mainly found at the top of both deposits laterite both deposits are thus characterized by specific mineral zoning from laterite to protolith related to variations in the mineralogy and ore grades and probably caused by varying eh ph conditions

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

non sulfide zinc deposits of the moroccan high atlas multi scale characterization and origin six non sulfide zn pb ore deposits were investigated in the moroccan high atlas to understand processes and timing of their formation sulfide and non sulfide ores are hosted in lower jurassic reefal to para reefal limestone zn pb carbonates zn silicates and associated hydrated phases directly replace the stratabound primary ore bodies or fill cavities along fractures related to the atlasic compression field observation has been complemented by a multidisciplinary approach e g xrd raman sem epma for the mineralogical characterization all six ore deposits present similar parageneses revealing three successive stages for ore deposition 1 formation of the protore sulfides 2 early supergene weathering with formation of zn pb bearing carbonates and iron oxi hydroxides and 3 late supergene weathering with deposition of zn carbonates zn silicates and hydrated phases direct replacement of primary sulfides is accompanied by precipitation of zinc non sulfide minerals in cavities or internal sediments filling the proposed three step scenario can be placed within the tectonic evolution of the moroccan high atlas belt deposition of primary sulfides is contemporaneous with opening of the tethyan and atlantic oceans during the tertiary intracontinental deformation has given rise to the high atlas fold and thrust belt and to regional uplift as a result zn pb sulfides hosted in carbonates experienced oxidation under an arid climate to form karst related zn pb non sulfide ore bodies

the implication of the oxygen isotope records in coexisting cherts and phosphates 18 o values have been determined for 53 coexisting chert phosphate pairs from the phanerozoic and precambrian in addition 18 o values were also determined for 18 biogenic phosphates from the phanerozoic the oxygen isotope data for the chert phosphate pairs permit the calculation of the temperatures of formation of the chert phosphate pairs as well as the 18 o of the waters in which they equilibrated in turn the calculated 18 o of the waters permit the calculation of temperatures from the isotopic data of the biogenic phosphates the temperatures for the tertiary and mesozoic samples are compatible with the literature values determined from oxygen isotope data for well preserved calcareous marine skeletal remains the temperatures calculated from the chert phosphate pairs of the paleozoic are usually higher and vary in cycles of about a 150 million year period the early precambrian temperatures are as high as 80 c and decrease with time the use of chert phosphate pairs for temperature determinations are sufficiently promising to warrant further investigations of this type on well preserved chert phosphate or carbonate phosphate pairs

time dependence of snow microstructure and associated effective thermal conductivity this paper presents a sequential evaluation of snow microstructure and its associated thermal conductivity under the influence of a temperature gradient temperature gradients from 28 to 45 k m 1 were applied to snow samples having a density range 180 320 kg m 3 the experiments were conducted inside a cold room in a specially designed heat flux apparatus for a period of 4 weeks a constant heat flux was applied at the base of the heat flux apparatus to produce a temperature gradient in the snow sample a steady state approach was used to estimate the effective thermal conductivity of snow horizontal and vertical thick sections were prepared on a weekly basis to obtain snow micrographs these micrographs were used to obtain snow microstructure using stereological tools the thermal conductivity was found to increase with increase in grain size bond size and grain and pore intercept lengths suggesting a possible correlation of thermal conductivity with snow microstructure thermal conductivity increased even though surface area and area fraction of ice were found to decrease the outcome suggests that changes in snow microstructure have significant control on thermal conductivity even at a constant density

isotopic evidence for holocene climate change in the northern rockies from a goethite rich ferricrete chronosequence abstract climate proxy records often show regional heterogeneity due to the complex interplay of large scale atmospheric circulation patterns and local topographic features this is especially prevalent in the mountainous regions of the western united states where the interaction of two seasonally distinct weather systems can result in locally abrupt climate boundaries here we establish oxygen isotope ratios of goethite from ferricrete chronosequences formed by natural acid rock drainage as a new source of spatially small scale holocene climate information systematic study of these deposits may prove useful in understanding regional variations in response to global holocene climate change oxygen isotope ratios of goethites from the mountainous northeastern yellowstone region show an increase of 3 over the past 9000 years we attribute this isotopic change to a local increase of isotopically heavier summer precipitation since the early holocene possibly augmented by seasonal temperature differences brought on by orbitally forced insolation changes over the past 9000 years our interpretation is compatible with palynology studies as well as holocene climate simulations which indicate a decrease in monsoon intensity from 9000 years b p to the present unlike the southwestern united states this change may have resulted in wetter summers in our study area

stable isotope records of hydrologic change and paleotemperature from smectite in cenozoic western north america abstract the oxygen and hydrogen isotopic composition of soil water 18ow and dw hereafter reflect the history of water through processes such as source evaporation precipitation and vapor recycling temperature humidity evaporation and post condensation processes can affect 18ow and dw as such isotope proxy records are often limited in their ability to constrain paleoclimate paleoecology or paleoelevation without independently corroborating data smectite preserves both the hydrogen and oxygen isotope signature of parent water and therefore provides critical insight into meteoric water line relationships and paleotemperature here we use in situ pedogenic smectite 18o and d records to characterize the evolution of the hydrologic cycle in cenozoic western north america we incorporate 192 samples 119 of which are previously unpublished from 11 cenozoic basins representing a range of environments in the basin and range rocky mountains and great plains our results indicate that the processes controlling smectite isotopic compositions vary both regionally and temporally in some localities such as oligocene to pleistocene western nebraska change in temperature is the primary control on smectite isotopic composition in other basins such as in miocene trapper creek id isotope values lie along the meteoric water line suggesting change in meteoric water composition is responsible for the variation in most basins especially those in the neogene basin and range smectite line slope suggests either evaporation of previously meteoric water or a combination of change in paleotemperature and meteoric water composition smectite geothermometry suggests mineral formation temperatures of 30 40 c in the middle miocene in the rocky mountains great plains and basin and range and a decrease of 10 15 c since the middle miocene climatic optimum consistent with clumped isotope and paleofloral temperature estimates

trace rare earth element and oxygen isotopic systematics for the genesis of banded iron formations evidence from kushtagi schist belt archaean dharwar craton india abstract the ree distribution pattern shapes free 5 92 and 27 87 ppm in chert and hematite respectively positive eu anomalies eu eu 3 25 and 2 1 and la n yb n ratios 0 75 and 0 87 of the chert and hematite layers of the oxide facies bifs of kushtagi schist belt indicate that these constituents were derived from hydrothermal solutions generated and emplaced at an archaean ocean ridge however their oxygen isotopic composition have been modified by mixing with the ambient ocean water and diagenetic reactions 18o values 13 9 17 4 c and 8 6 to 3 3 in chert and hematite respectively yield 150 250 c temperature in the diagenetic and lowest greenschist facies field the mixing model of hydrothermal solutions with ocean water of 1 1000 ratio will not significantly change the oxygen isotope ratio of the ambient ocean water therefore while the trace element data have retained hydrothermal signatures oxygen isotopic signatures are imprinted by diagenetic processes

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

dissolution of calcitic marble and dolomitic rock in high iron concentrated acid mine drainage application to anoxic limestone drains oxidation of sulphide mining waste can generate acid mine drainage amd that has the potential to seriously affect the ecosystems acid mine drainage is characterised by a high acidity high concentrations of sulphates and metals to reduce the environmental impacts due to amd neutralisation using limestone drains is an option proposed in the literature and used around the world the present study focuses on the influence of the carbonate rock mineralogy and their particle size on the neutralising capacity the tests were performed in two different anoxic conditions in batch reactors and in columns having a hydraulic retention time of 15 h the results showed that the neutralisation capacity of calcite was more important than for dolomitic rock and smaller particle size gave higher alkalinity production fine calcite dissolved faster in contact with amd a characterization of metal precipitate in sludge and in limestone coating was performed and demonstrated that gypsum lepidocrocite and goethite were the predominant secondary minerals to be formed finally this study underlines that anoxic limestone drain cannot be used alone to treat high iron concentrated amd

new evidence on magnetite oxygen isotope geothermometers at 175 and 112 c in wairakei steam pipelines new zealand abstract millimeter deep surface layers of magnetite occur in the steam pipelines of the wairakei geothermal power station as part of serious corrosion discovered after 15 years of service these quasi experimental growths provide the following oxygen isotope calibration points of magnetite and h 2 o below the previously available experimental range 175 c 7 9 0 5 and 112 c 3 7 0 5 the data support the earliest proposed magnetite h 2 o fractionation curve by j r o neil and r n clayton with an isotopic cross over near 50 c and could indicate a relatively low temperature origin for some precambrian iron formations

characterization of limestone reacted with acid mine drainage in a pulsed limestone bed treatment system at the friendship hill national historical site pennsylvania usa abstract armoring of limestone is a common cause of failure in limestone based acid mine drainage amd treatment systems limestone is the least expensive material available for acid neutralization but is not typically recommended for highly acidic fe rich waters due to armoring with fe iii oxyhydroxide coatings a new amd treatment technology that uses co2 in a pulsed limestone bed reactor minimizes armor formation and enhances limestone reaction with amd limestone was characterized before and after treatment with constant flow and with the new pulsed limestone bed process using amd from an inactive coal mine in pennsylvania ph 2 9 fe 150 mg l acidity 1000 mg l caco3 in constant flow experiments limestone is completely armored with reddish colored ochre within 48 h of contact in a fluidized bed reactor effluent ph initially increased from the inflow ph of 2 9 to over 7 but then decreased to 6 during operation limestone removed from a pulsed bed pilot plant is a mixture of unarmored rounded and etched limestone grains and partially armored limestone and refractory mineral grains dolomite pyrite the 30 of the residual grains in the pulsed flow reactor that are armored have thicker 50 to 100 m more aluminous coatings and lack the gypsum rind that develops in the constant flow experiment aluminium rich zones developed in the interior parts of armor rims in both the constant flow and pulsed limestone bed experiments in response to ph changes at the solid solution interface