mass occurrence of benthic coccoid cyanobacteria and their role in the production of neoarchean carbonates of south africa abstract the sparse archean fossil record is based almost entirely on carbonaceous remnants of microorganisms cellularly preserved due to their early post mortem silicification hitherto as an exception sedimentary carbonate rocks from the neoarchean nauga formation of south africa contain calcified microbial mats composed of microbiota closely resembling modern benthic colonial cyanobacteria chroococcales and pleurocapsales their remains visible under the scanning electron microscope sem after etching of polished rock samples comprise capsular envelopes mucilage sheaths and groups of cells mineralized by calcium carbonate with an admixture of al k mg fe silicates the capsular organization of the mucilaginous sheaths surrounding individual cells and cell clusters forming colonies and the mode of mineralization are the characteristic common features of the neoarchean microbiota described and their modern analogues the new findings indicate massive production of calcium carbonates by benthic coccoid cyanobacteria in the neoarchean and offer a solution to the problem of the origin of archean carbonate platforms stromatolites and microbial reefs

mitigation of liquefaction induced lateral deformation in a sloping stratum three dimensional numerical simulation finite element fe simulations are increasingly providing a versatile environment for conducting lateral ground deformation studies in this environment mitigation strategies may be assessed in order to achieve economical and effective solutions on the basis of a systematic parametric study three dimensional fe simulations are conducted to evaluate mitigation by the stone column sc and the pile pinning approaches mildly sloping saturated cohesionless strata are investigated under the action of an applied earthquake excitation for that purpose the open source computational platform opensees is employed through a robust user interface that simplifies the effort intensive pre and postprocessing phases the extent of deployed remediation and effect of the installed sc permeability are investigated the influence of mesh resolution is also addressed generally sc remediation was found to be effective in reducing the sand stratum lateral deformation for a similar stratum with permeability in the silt range sc remediation was highly ineffective in contrast pile pinning appeared to be equally effective for the sand and silt strata permeability scenarios overall the conducted study highlights the potential of computations for providing insights toward the process of defining a reliable remediation solution

carbon dioxide fixation within mine wastes of ultramafic hosted ore deposits examples from the clinton creek and cassiar chrysotile deposits canada carbon dioxide co2 is sequestered through the weathering and subsequent mineralization of the chrysotile mine tailings at clinton creek yukon territory and cassiar british columbia canada accelerated weathering is attributed to a dramatic increase in surface area which occurs during the milling of ore we provide a detailed account of the natural process of carbon trapping and storage as it occurs at clinton creek and cassiar including mineralogy modes of occurrence methods of formation for carbonate alteration light stable isotope geochemistry and radiocarbon analysis powder x ray diffraction data were used to identify weathering products as the hydrated magnesium carbonate minerals nesquehonite mgco3 3h2o dypingite mg5 co3 4 oh 2 5h2o hydromagnesite mg5 co3 4 oh 2 4h2o and less commonly lansfordite mgco3 5h2o textural relationships suggest that carbonate precipitates formed in situ after milling and deposition of tailings samples of efflorescent nesquehonite are characterized by 13c values between 6 52 and 14 36 per mil 18o values between 20 93 and 26 62 per mil and f14c values fraction of modern carbon between 1 072 and 1 114 values which are consistent with temperature dependent fractionation of modern atmospheric co2 during mineralization samples of dypingite hydromagnesite collected from within 0 2 m of the tailings surface give 13c values between 1 51 and 10 02 per mil 18o values between 17 53 and 28 40 per mil and f14c values between 1 026 and 1 146 which suggests precipitation from modern atmospheric co2 in a soil like environment field observations and isotopic data suggest that hydrated magnesium carbonate minerals formed in two environments nesquehonite formed in an evaporative environment on the surface of tailings piles and dypingite and hydromagnesite formed in the subsurface environment with characteristics similar to soil carbonate in both cases these minerals

cyanobacterial precipitation of gypsum calcite and magnesite from natural alkaline lake water results from transmission electron microscopy provide direct evidence for cyanobacterial biomineralization of gypsum and calcite in aquatic environments laboratory simulations using filter sterilized natural lake water inoculated with synechococcus sp isolated from fayette ville green lake new york revealed epicellular biomineralization of gypsum calcite and magnesite experimental electron microscopical and sedimentological evidence indicates that synechococcus is responsible for a major proportion of the marl sediment and carbonate bioherms in green lake the elucidated role of synechococcus in biomineralization and its ubiquitous distribution in nature have widespread implications for cyanobacterial mineralization in marine and freshwater environments since late archean time

hydromagnesite precipitation in the alkaline lake dujiali central qinghai tibetan plateau constraints on hydromagnesite precipitation from hydrochemistry and stable isotopes abstract the mineral hydromagnesite mg5 co3 4 oh 2 4h2o is a common form of hydrated mg carbonate in alkaline lakes yet the processes involved in its formation are not well understood this study focuses on dujiali lake in the central qinghai tibetan plateau qtp which is one of the few environments on the earth s surface with extensive holocene precipitation of hydromagnesite the hydrogeochemistry of surface waters and the mineralogical stable isotope 13c and 18o and radiogenic isotope content of hydromagnesite deposits were analyzed to investigate formation mechanisms the chemical composition of surface water around dujiali lake evolved from the rock weathering type waters of t1 ca mg hco3 water type to more concentrated sodic waters of t2 na so4 cl water type due to evaporation xrd results show that the mineralogical composition of samples is pure hydromagnesite analysis of oxygen isotopes in the hydromagnesite indicates that supergene formation with authigenic carbonate crystallization from evaporation water is the dominant precipitation process combined carbon oxygen isotope analysis suggests atmospheric co2 provided a carbon source for the precipitation of hydromagnesite these findings suggest that hydromagnesite precipitation at lake dujiali is mainly inorganic in nature and the greenhouse gas co2 is trapped and stored in the hydromagnesite directly from the atmosphere ams radiocarbon dating of samples indicates co2 was sequestered between 5845 30 to 6090 25 cal a bp in the dujiali lake hydromagnesite deposit the study contributes to improved understanding of hydromagnesite formation in modern and ancient playas

a stable isotope study of magnesites from the rum jungle uranium field australia implications for the origin of strata bound massive magnesites the contrast between the scanty magnesite deposition in modern sedimentary environments and the large strata bound magnesites of the past constitutes a magnesite problem which unlike the dolomite problem has so far attracted little attention from the geologists magnesite beds up to 700 m thick from the lower proterozoic rocks of the rum jungle uranium field northern territory of australia offer attractive circumstances for studying the isotope systematics of coarse crystalline magnesite and coexisting dolomite magnesites yield 18o and 13c compositions of 11 2 to 14 6 smow and 1 0 to 5 8 pdb respectively dolomites yield 18o and 13c values of 11 7 to 21 9 and 4 0 to 2 9 respectively and show an 18o enrichment gradient away from the magnesite fluid inclusion homogenization temperatures used in conjunction with the isotope determinations and an approximate magnesite water equation indicate that magnesites were formed in the temperature range of 100 200 c from fluids that became progressively enriched in 18o the results support an epigenetic metasomatic replacement model of dolomite by magnesite under the influence of invasive hot mg rich basinal fluids strata bound massive magnesites which abound particularly in archean proterozoic rock sequences generally preserve the sedimentary structures but do not retain primary isotopic compositions and are therefore unsatisfactory indicators of oceanic isotope evolution and ocean paleotemperatures

terrestrial oxygen isotope variations and their implications for planetary lithospheres oxygen isotopes provide key data on the formation and evolution of the solar system particularly for earth and other rocky bodies that are principally constituted of oxygen rich phases the dynamic interactions between earth s lithosphere hydrosphere biosphere and atmosphere are elucidated by a wealth of oxygen isotope data that in turn provide a template for predicting the types of variations that occur on other planets these isotopic variations are basically controlled by two master effects first isotopic fractionations among coexisting phases tend to be greatest at low temperatures and are also large when they involve interactions between solids or liquids and gaseous phases second material balance effects require the 18 o contents of the most abundant phases to be close to the planetary average and restrict extreme isotopic enrichments or depletions to minor phases these dual controls of fractionation and material balance work in concert with practically any other dynamic process to foster the upward enrichment and increased heterogeneity of 18 o contents on earth and by implication in planetary lithospheres in general upward 18 o enrichment in planetary lithospheres is promoted by the tendency for the least dense silicate and oxide minerals to concentrate 18 o relative to more dense minerals and also by convective transfer fractional crystallization hydrothermal alteration and other processes earth s continents and the uppermost parts of its ocean floor consequently have higher 18 o contents than average upper mantle material and normal sediments carbon dioxide and oxygen gas are all very rich in 18 o heterogeneity is evident in the large ranges of 18 o values observed in sediments at least 8 to 38 and terrestrial igneous rocks at least 10 5 to 16 and in the even larger ranges in natural waters and atmospheric gases all representing materials that constitute or interacted with oxygen reservoirs near earth s surface key identified processes include weathering precipitation from water phase changes exchange with infiltrating hydrothermal fluids and assimilation of wallrocks having disparate compositions all such processes that promote the upward enrichment and heterogeneity of 18 o complicate the deduction of the bulk planetary contents of this isotope

three dimensional oxygen isotope imaging of convective fluid flow around the big bonanza comstock lode mining district nevada oxygen isotope analyses of propylitized andesites from the con virginia and california mines allow construction of a detailed three dimensional image of the isotopic surfaces produced by the convective fluid flows that deposited the famous big bonanza orebody on a set of intersecting maps and sections the 18o isopleths clearly show the intricate and conformable relationship of the orebody to a deep 500 m gyre of meteoric hydrothermal fluid that circulated along and above the comstock fault near the contact of the davidson granodiorite the core of this gyre 18o 0 to 3 8 encompasses the bonanza and is almost totally surrounded by rocks having much lower 18o values 1 0 to 4 4 this deep gyre may represent a convective longitudinal roll superimposed on a large unicellular meteoric hydrothermal system producing a complex flow field with both radial and longitudinal components that is consistent with experimentally observed patterns of fluid convection in permeable media

a depositional model for hydromagnesite magnesite playas near atlin british columbia canada this study formulates a comprehensive depositional model for hydromagnesite magnesite playas mineralogical isotopic and hydrogeochemical data are coupled with electron microscopy and field observations of the hydromagnesite magnesite playas near atlin british columbia canada four surface environments are recognized wetlands grasslands localized mounds metre scale and amalgamated mounds composed primarily of hydromagnesite mg co oh 4ho which are interpreted to represent stages in playa genesis water chemistry precipitation kinetics and depositional environment are primary controls on sediment mineralogy at depth average 2 m ca mg carbonate sediments overlay early holocene glaciolacustrine sediments indicating deposition within a lake post deglaciation this mineralogical change corresponds to a shift from siliciclastic to chemical carbonate deposition as the supply of fresh surface water for example glacier meltwater ceased and was replaced by alkaline groundwater weathering of ultramafic bedrock in the region produces mg hco groundwater that concentrates by evaporation upon discharging into closed basins occupied by the playas an uppermost unit of mg carbonate sediments hydromagnesite mounds overlies the ca mg carbonate sediments this second mineralogical shift corresponds to a change in the depositional environment from subaqueous to subaerial occurring once sediments emerged from the water surface capillary action and evaporation draw mg hco water up towards the ground surface precipitating mg carbonate minerals evaporation at the water table causes precipitation of lansfordite mgco 5ho which partially cements pre existing sediments forming a hardpan as carbonate deposition continues the weight of the overlying sediments causes compaction and minor lateral movement of the mounds leading to amalgamation of localized mounds radiocarbon dating of buried vegetation at the ca mg carbonate boundary indicates that there has been ca 8000 years of continuous mg carbonate deposition at a rate of 0 4 mm yr the depositional model accounts for the many sedimentological mineralogical and geochemical processes that occur in the four surface environments elucidating past and present carbonate deposition

solubility of the hydrated mg carbonates nesquehonite and dypingite from 5 to 35 c implications for co2 storage and the relative stability of mg carbonates abstract hydrated mg carbonate minerals form during the weathering of ultramafic rocks and can be used to store atmospheric co2 to help combat greenhouse gas fueled climate change optimization of engineered co2 storage and prediction of the composition and stability of mg carbonate phase assemblages in natural and engineered ultramafic environments requires knowledge of the solubility of hydrated mg carbonate phases and the transformation pathways between these metastable phases in this study we evaluate the solubility of nesquehonite mgco3 3h2o and dypingite mg5 co3 4 oh 2 5 or 8 h2o and the transformation from nesquehonite to dypingite between 5 c and 35 c using constant temperature batch reactor experiments the logarithm of the solubility product of nesquehonite was determined to be 5 03 0 13 5 27 0 15 and 5 34 0 04 at 5 c 25 c and 35 c respectively the logarithm of the solubility product of dypingite was determined to be 34 95 0 58 and 36 04 0 31 at 25 c and 35 c respectively with eight waters of hydration this is the first reported dypingite solubility product the transformation from nesquehonite to dypingite was temperature dependent and was complete within 57 days at 25 c and 20 days at 35 c but did not occur during experiments of 59 days at 5 c this phase transformation appeared to occur via a dissolution reprecipitation mechanism external nesquehonite crystal morphology was partially maintained during the phase transformation at 25 c but was eradicated at 35 c together our results facilitate the improved evaluation of mg carbonate mineral precipitation in natural and engineered ultramafic mineral weathering systems that sequester co2 and for the first time allow assessment of the saturation state of dypingite in aqueous solutions

sequestration of atmospheric co2 in chrysotile mine tailings of the woodsreef asbestos mine australia quantitative mineralogy isotopic fingerprinting and carbonation rates since closure of the woodsreef asbestos mine located in the great serpentinite belt gsb new south wales australia extensive carbonate rich crusts have formed by recessive weathering of fine grained material on the surface of the tailings pile a relationship exists between the mode of carbonate occurrence the mineralogy and the isotopic fingerprint of carbonates from the tailings pile vertical carbonate crusts covering most of the tailings predominantly consist of the hydrated mg carbonate hydromagnesite mg5 co3 4 oh 2 4h2o which has precipitated from evaporating meteoric waters incorporating atmospheric co2 as reflected in high 18o 13c and f14c signatures respectively low and variable concentrations of magnesite dolomite and calcite represent bedrock carbonate which has formed during alteration of the serpentinite bedrock before mining and is characterised by moderately high 18o low 13c and f14c a signature typical for weathering derived magnesite deposits in the gsb the carbonate fraction of deep cement samples collected from 70 to 120 cm below the surface representing the bulk tailings material at depth predominantly consists of pyroaurite mg6fe2 co3 oh 16 4h2o and despite stable isotope signatures similar to bedrock contains significant radiocarbon this indicates that pyroaurite forming under different conditions as hydromagnesite may represent an additional trap for atmospheric co2 in the woodsreef mine tailings the distribution of carbonates and quartz together with the absence of isotopic mixing trends between bedrock carbonate and atmospheric derived carbonate strongly indicates that dissolution and re precipitation of bedrock carbonate is not a dominant process in the woodsreef tailings the cations for carbonate formation are instead derived from the dissolution of serpentine minerals lizardite and chrysotile and brucite the internal standard method and the reference intensity method have been used with x ray diffraction data to estimate the abundance of the two major carbonate minerals hydromagnesite and pyroaurite respectively considering the formation of hydromagnesite on the outer surface of the tailings pile alone or together with formation of pyroaurite within the tailings pile we conclude that between 1400 and 70 000 t of atmospheric co2 have been sequestered in the mine tailings since closure of the mine 29 a ago carbonation rates of 27 g c m 2 y 1 and 1330 g c m 2 y 1 are significantly higher than background rates of co2 uptake by chemical weathering and demonstrate the potential of passive carbonation of mine tailings as a cost and energy effective alternative for storage of co2 in carbonate minerals

hydromagnesite replacement of biomineralized aragonite in a new location of holocene stromatolites lake walyungup western australia holocene stromatolites are described from lake walyungup a coastal hyposaline lake in south western australia at summer low water this groundwater fed depression comprises two permanent shallow water bodies and an ephemeral southern pool set within an areally extensive littoral zone of variably cemented carbonate crust up to 5 m of organic rich carbonate mud has been deposited within each of these basins in less than 7000 years stromatolites rim the water bodies with individual columns up to 2 m tall stromatolite capped tepee structures in subparallel alignment are widespread in the littoral crust suggesting a linkage between stromatolite growth and zones of groundwater discharge lake walyungup stromatolites regardless of external morphology and setting are coarsely laminated and have aragonitic mesoclot microfabrics these microfabrics are similar to those from lithified portions of active thrombolitic microbialites from nearby lake clifton hydromagnesite is a minor to subdominant phase up to 47 wt of the carbonate mineral assemblage in lake walyungup it occurs mainly in the littoral zone as a diagenetic replacement of precursor aragonite particularly within the mesoclot fabric of stromatolites but also in sediments strandline and dune sand crusts derived mainly from erosion of stromatolites in contrast with nonreplaced and impermeable inorganic aragonitic cements stromatolite mesoclots are microper meable micropermeability is inferred to facilitate hydromagnesite diagenesis dolomite is also present in minor amounts as a pore fill in stromatolites and as a subdominant to dominant up to 100 wt phase in thin mudcracked micrite layers within the crust package the layered dolomite may be precipitated directly from the lake water major element abundance of the lake water is na mg2 k ca2 for cations and cl so42 hco3 co32 for anions compared to other nearby coastal lakes lake walyungup has a high ph 9 0 and an extremely high molar mg ca ratio of 90 groundwater in the area has a mg ca ratio generally less than 1 the unusual mg ca ratio in lake walyungup is partially a result of in lake processes with additional minor contribution of mg2 sourced from basal marine sand because no mg rich bedrock source has been found in the region

enhanced co2 mineral sequestration by cyclic hydraulic fracturing and si rich fluid infiltration into serpentinites at malentrata tuscany italy abstract the magnesite deposits of malentrata tuscany italy were derived from serpentinite silicification carbonation of the ligurian ophiolite and represent a natural analogue of in situ co 2 mineral sequestration carbonation of magnesium silicate minerals e g serpentine olivine at temperatures below 200 c is an exothermal process involving incorporation of carbon dioxide into stable carbonates e g magnesite dolomite serpentinites at malentrata were transformed to a brownish friable rock characterized by the occurrence of opal chromian montmorillonite fe rich magnesite and minor iron sulfides and oxides widespread lenses of cohesive rocks occur within the altered serpentines resulting from the complete silicification of the protolith the pervasive alteration of serpentinite was accompanied by the formation of a network of magnesite and dolomite veinlets and large magnesite dolomite veins along major structures field observations petrography and mineral chemistry define the following crystallization sequence in the major veins i early microgranular fe poor magnesite ii comb textured fe rich magnesite and dolomite cementing the early brecciated magnesite vein infill and iii late quartz chalcedony and rare opal in the cavities the mineral assemblage observed both in veins and in host rock is indicative of low temperature hydrothermal alteration driven by si and co 2 rich fluids under relatively low ph conditions pervasive and cyclic hydraulic fracturing maintained a high structural permeability during the whole hydrothermal event creating conduits for the input and output fluids the concomitant presence of co 2 and silica in the fluid enhanced the congruent dissolution of serpentine and hampered immediate carbonate deposition the mg bearing solutions were focused out of the reactor zone and promoted massive carbonate veining along the main structural discontinuities this two steps reaction dissolution of serpentinite followed by carbonate precipitation outside the reacting volume seems to be very efficient and provide new insights on in situ and ex situ induced mineral carbonation and its industrial applications

a stable isotope study of the magnesite deposits associated with the alpine type ultramafic rocks of yugoslavia veins and stockworks of fine grained microcrystalline to cryptocrystalline massive magnesite are common in the ultramafic masses of the ophiolite zone of the inner dinarides strata bound deposits of the same kind of magnesite and or dolomite in miocene fresh water basins lie above and beside the ultramafic masses a carbon and oxygen isotope study of 12 magnesite deposits in yugoslavia addresses their genesis and bearing on a possible relationship between epigenetic and syngenetic magnesites all but one of the vein deposits have delta 13 c pdb values between 10 and 15 per mil the exception oshve has values averaging 3 1ppm and each deposit has a characteristic value all sediment hosted deposits have delta 13 c values between 9 and 5 per mil again with relatively restricted characteristic fields for each the two stockworks analyzed have delta 13 c values ranging from 10 6 to 4 3 per mil but only one of these has values that coincide with the associated sediment hosted magnesite deposits with the exception of the oshve vein deposit delta 18 o smow values range from approximately 24 to 36 per mil and correlate positively with the delta super 13 c values r 0 90 n 42 some of the sediment hosted magnesite bela stena and dolomite braneshci cherenje deposits were deposited in lakes assumed temperature of 20 degrees c with a calculated water delta 18 o value of 2 per mil suggestive of meteoric water lower lake temperatures would yield more negative values assuming that meteoric water with this delta 18 o value was the mineralizing solution then a temperature of deposition of approximately 70 degrees c is indicated in those veins not intimately related to dikes the delta 13 c values of or 75 degrees c the suggested low temperatures are consistent with the monomineralic purity of the vein magnesites at these low temperatures gravity driven circulating carbonated meteoric waters would react with harzburgite or serpentinite dissolving magnesium which precipitates as magnesite on pressure drop as co 2 escapes the higher delta 13 c values in certain sediment hosted and stockwork magnesites indicate the involvement of atmospheric co 2 and possibly carbonate released to the hydrothermal system during contact metamorphism this latter process is particularly attractive for the oshve vein deposit with the unusual delta 18 o and delta 13 c values of 19 and 3 1 per mil respectively as this is the one vein which is intimately related to a dacite dike

sedimentology of the saline lakes of the cariboo plateau interior british columbia canada abstract there are several hundred saline lakes in interior british columbia including muddy siliciclastic playas saline playas perennial lakes including meromictic sulphate lakes and ephemeral lakes some with permanent salts the lake waters have highly variable compositions with na co3 cl na co3 so4 cl mg na so4 and na mg so4 the dominant types of brine on the cariboo plateau where they are most abundant the saline lakes are small shallow and occupy depressions within glacial and glacio fluvial deposits most are groundwater fed the region is characterized by extremely cold winters and short hot summers dense coniferous forest mantles much of the plateau and surrounds most of the lakes most basins comprise three main subenvironments hillslope mudflat saline and dry and lake ephemeral or perennial fluvial sediments are of little significance mudflats are primarily a zone of extensive interstitial carbonate precipitation from shallow groundwaters including abundant magnesite and hydromagnesite the amount of carbonate formed varies with groundwater composition some mudflats are carbonate dominated others are predominantly siliciclastic with only highly soluble interstitial salts forming sedimentary structures are disrupted by carbonate precipitation and displacive salt crystallization springs and ephemeral seepages are locally present microbial mats form extensively along many littoral zones and around springs laminates are preserved in some cores efflorescent salt crusts cover saline mudflats around most lakes and playas subaqueous salts including natron epsomite bloedite mirabilite are precipitated during late summer autumn and winter in several hypersaline lakes some by evaporative concentration others by brine cooling and freeze out several hypersaline ephemeral lakes have an unusual spotted morphology with hundreds of individual brine pools within carbonate siliciclastic muds most recent sedimentation in the cariboo lakes has been autochthonous with a predominance of carbonates evaporites and organic rich muds this reflects the dense vegetation in the catchment which has stabilized soils and limited clastic influx the predominance of groundwater recharge the lack of basin marginal relief and the common occurrence of inflow waters with ca mg hco 3 co 3 near unity which provide abundant carbonate sediment

numerical study of shear stress distribution for discrete columns in liquefiable soils abstractdiscrete columns such as stone and soil cement columns are often used to improve the liquefaction resistance of loose sandy ground potentially subjected to strong shaking the shear stress reduction in the loose ground resulting from the reinforcing effect of these stiffer discrete columns is often considered as a contributing mechanism for liquefaction mitigation current design practice often assumes that discrete columns and soil deform equally in pure shear i e shear strain compatible deformation in addition because the discrete column is stiffer than the soil it is assumed to attract higher shear stress thereby reducing the shear stress in the surrounding soil in this paper shear stress reduction in liquefiable soils and shear strain distribution between liquefiable soil and discrete columns along with the potential of development of tensile cracks is investigated using three dimensional linear elastic finite element analysis parametric analyses are performed for a range of geom

chemical and isotopic signatures of waters associated with the carbonation of ultramafic mine tailings woodsreef asbestos mine australia extensive carbonate crusts have formed on the tailings of the woodsreef asbestos mine sequestering significant amounts of co2 directly from the atmosphere the physico chemical ph t conductivity chemical cations dissolved inorganic carbon dic and isotopic 2h 18o 13cdic f14c signatures of waters interacting with the tailings and associated carbonate precipitates provide insight into the processes controlling carbonation we observe two distinct evolutionary pathways for a set of stream and meteoric derived water samples respectively with both groups generally being characterised as moderately alkaline bicarbonate dominated and mg rich waters stream water samples are supersaturated with co2 and therefore prone to degassing which in combination with evaporation drives carbonate supersaturation and precipitation isotopic signatures indicate soil co2 as the main carbon source in the stream waters entering the tailings pile whereas water emerging downstream of the tailings pile may also contain carbon from the dissolution of isotopically light bedrock magnesite in an open system with respect to soil co2 the evolution of meteoric derived waters on the other hand partly occurs under co2 limited conditions which results from reduced co2 ingress at depth and or a temporal lag between fluid alkalisation and kinetically hindered uptake of co2 into alkaline solution a high ph mg rich meteoric water absorbs atmospheric co2 after discharging into a tunnel within the tailings pile resulting in high dic concentrations with atmospheric carbon isotope signature evaporation of the water at the discharge point in the tunnel drives precipitation of hydromagnesite mg5 co3 4 oh 2 4h2o displaying a clear atmospheric isotope signature broadly consistent with previous estimates of carbon and oxygen isotope fractionation during precipitation of hydrated mg carbonate

quantifying carbon fixation in trace minerals from processed kimberlite a comparative study of quantitative methods using x ray powder diffraction data with applications to the diavik diamond mine northwest territories canada abstract the capacity of mine waste to trap co2 is in some cases much larger than the greenhouse gas production of a mining operation in mine tailings the presence of secondary carbonate minerals that trap co2 can therefore represent substantial fixation of this greenhouse gas the abilities of three methods of quantitative phase analysis to measure trace nesquehonite mgco3 3h2o in samples of processed kimberlite have been assessed the method of reference intensity ratios rir the internal standard method and the rietveld method with x ray powder diffraction data tests on synthetic mixtures made to resemble processed kimberlite indicate that both the rir and rietveld methods can be used accurately to quantify nesquehonite to a lower limit of approximately 0 5 wt for conditions used in the laboratory below this value estimates can be made to a limit of approximately 0 1 wt using a calibration curve according to the internal standard method the rir method becomes increasingly unreliable with decreasing abundance of nesquehonite primarily as a result of an unpredictable decline in preferred orientation of crystallites for rietveld refinements structureless pattern fitting was used to account for planar disorder in lizardite by considering it as an amorphous phase rietveld refinement of data collected from specimens that were serrated to minimize preferred orientation of crystallites gives rise to systematic overestimates of refined abundances for lizardite and underestimates for other phases the resulting pattern of misestimates may be mistaken for the effect of amorphous and or nanocrystalline material in samples this effect is mitigated by collecting data from non serrated specimens which typically give relative errors on refined abundances for major and minor phases in the range of 5 20 however relative error can increase rapidly for abundances less than 5 wt nonetheless absolute errors are sufficiently small that estimates can be made for the amount of co2 stored in secondary nesquehonite using the rir method or the rietveld method for abundances 0 5 wt and a calibration curve for abundances

high modulus columns for liquefaction mitigation this paper presents the performance of a shopping complex in turkey where the soils were improved with jet grout columns and preload fills and subjected to the 1999 kocaeli earthquake m57 4 under construction at the time of the earthquake the carrefour shopping center covers an area of 55 000 m 2 and is founded on shallow footings mats and slabs on grade that rest on soft saturated alluvial sediments consisting of clays silts and sands high modulus columns constructed by jet grouting were installed at close to moderate spacings to reduce anticipated static settlements in the clays and mitigate liquefaction in the sands the site was subjected to a peak acceleration of approximately 0 2g during the earthquake grouting had been completed for about two thirds of the site when the earthquake struck following the event a field reconnaissance found stark contrast between the performance of the improved and unimproved sections the jet grout treated areas suffered no apparent damage whereas the unimproved sections of the complex along with nearby untreated building sites commonly suffered liquefaction related settlements of up to 10 cm this is the only case history known to the authors that documents the field performance of high modulus columns used in this manner for liquefaction mitigation and direct instrumented measurement of liquefaction induced settlements

carbonate precipitation in the alkaline lake specchio di venere pantelleria island italy and the possible role of microbial mats abstract alkaline lakes like the hydrothermally affected lake specchio di venere pantelleria island central mediterranean are typical geological settings harbouring calcified microbial mats the present work is focused on the discrimination between biotic and abiotic processes driving carbonate precipitation in this lake using hydrochemical mineralogical and isotopic data hydrochemical analyses demonstrate that the lake is nearly 10 fold supersaturated with regard to aragonite and seasonally reaches hydromagnesite supersaturation microscopic observations depict organosedimentary laminated structures consisting of microbial communities and aragonitic precipitates which are rather disseminated in pores than directly linked to microorganisms oxygen isotopic data indicate that authigenic carbonate crystallisation from evaporating water is the dominant precipitation process further suggested by the absence of textural evidence of diagenetic processes conversely the observed 13c values reflect an influence of extracellular polymeric substances eps on carbon fractionation during the precipitation process due to the selective sequestration of 12c in the biomass the above considerations suggest that at lake specchio di venere the carbonate precipitation is mainly of inorganic nature but a minor role played by biologically influenced processes in microbial mats is not excluded

living hydromagnesite stromatolites from turkey abstract salda golu lake in southern turkey is a highly alkaline ph 9 freshwater lake in which composite stromatolites several metres high are formed by microbially induced precipitation of hydromagnesite the magnesium and carbonate in the lake waters were dissolved during passage through ultramafic rocks precipitation is brought about by the flora of diatoms and cyanobacteria forming the surface of the stromatolites but does not occur in direct contact with cells stromatolites have previously been reported from environments ranging from fully marine through brackish water to a variety of freshwater lacustrine and fluvial situations the principal importance of these structures lies in their novel mineralogy hydromagnesite mg4 oh 2 co3 3 3h2o is commonly regarded as a low temperature hydrothermal mineral

the hydromagnesite playas of atlin british columbia canada a biogeochemical model for co2 sequestration abstract anthropogenic greenhouse gas emissions may be offset by sequestering carbon dioxide co2 through the carbonation of magnesium silicate minerals to form magnesium carbonate minerals the hydromagnesite mg5 co3 4 oh 2 4h2o playas of atlin british columbia canada provide a natural model to examine mineral carbonation on a watershed scale at near surface conditions co2 is biogeochemically sequestered by microorganisms that are involved in weathering of bedrock and precipitation of carbonate minerals the purpose of this study was to characterize the weathering regime in a groundwater recharge zone and the depositional environments in the playas in the context of a biogeochemical model for co2 sequestration with emphasis on microbial processes that accelerate mineral carbonation regions with ultramafic bedrock such as atlin represent the best potential sources of feedstocks for mineral carbonation elemental compositions of a soil profile show significant depletion of mgo and enrichment of sio2 in comparison to underlying ultramafic parent material polished serpentinite cubes were placed in the organic horizon of a coniferous forest soil in a groundwater recharge zone for three years upon retrieval the cube surfaces as seen using scanning electron microscopy had been colonized by bacteria that were associated with surface pitting degradation of organic matter in the soil produced chelating agents and acids that contributed to the chemical weathering of the serpentinite and would be expected to have a similar effect on the magnesium rich bedrock at atlin stable carbon isotopes of groundwater from a well situated near a wetland in the southeastern playa indicate that 12 of the dissolved inorganic carbon has a modern origin from soil co2 the mineralogy and isotope geochemistry of the hydromagnesite playas suggest that there are three distinct depositional environments 1 the wetland characterized by biologically aided precipitation of carbonate minerals from waters concentrated by evaporation 2 isolated wetland sections that lead to the formation of consolidated aragonite sediments and 3 the emerged grassland environment where evaporation produces mounds of hydromagnesite examination of sediments within the southeastern playa wetland suggests that cyanobacteria sulphate reducing bacteria and diatoms aid in producing favourable geochemical conditions for precipitation of carbonate minerals the atlin site as a biogeochemical model has implications for creating carbon sinks that utilize passive microbial geochemical and physical processes that aid in mineral carbonation of magnesium silicates these processes could be exploited for the purposes of co2 sequestration by creating conditions similar to those of the atlin site in environments artificial or natural where the precipitation of magnesium carbonates would be suitable given the vast quantities of mg rich bedrock that exist throughout the world this study has significant implications for reducing atmospheric co2 concentrations and combating global climate change

hydromagnesite stromatolites and sediments in an alkaline lake salda golu turkey abstract salda lake in sw turkey is a highly alkaline ph 9 water body with waters enriched in magnesium microbial stromatolites along shorelines contain a microflora of diatoms and cyanobacteria with extensive associated biofilms together these are responsible for precipitation of hydromagnesite although distribution is not congruent with either cells or films deposition has continued over several thousand years and is independent of both lake volume and the general concentration of lake waters the lake is rimmed on three sides by serpentinites and on the fourth by dolomite the bulk of the water entering the lake is meteoric fed via extensive gravelly alluvial fan deltas with predominantly serpentinite pebbles whose total areas and catchments exceed that of the lake these waters are significantly cooler than surface waters of the lake and there is no evidence for derivation from hot springs the magnesium is thought to have been leached from the gravels extensive areas of recent sediments accumulating on shorelines have apparently formed by mechanical breakdown of microbialites similar deposits form conspicuous terraces in two areas and point to the long term effectiveness of these processes terrace deposits are modified by a variety of subaerial processes including growth of hydromagnesite cements no microbial structures are preserved in these and it is presumed that they are destroyed during reworking fine grained hydromagnesite sediment derived from shorelines and from terraces is suspended in the water column during storms and is probably redeposited as turbidites in the deeper parts of the lake sediments of this kind may be a useful analogue for some ancient and economically important stratiform magnesite deposits