sequestration of atmospheric co2 in a weathering derived serpentinite hosted magnesite deposit 14c tracing of carbon sources and age constraints for a refined genetic model abstract the attunga magnesite deposit is texturally and geochemically distinct from other spatially associated serpentinite hosted magnesite deposits in the great serpentinite belt new south wales australia such as the hydrothermal piedmont magnesite deposit or widespread silica carbonate alteration zones cryptocrystalline magnesite at attunga predominantly occurs in nodular masses and irregular desiccated veins that occupy pre existing cracks and pore spaces resulting from fracturing and weathering of the host rock incipient weathering of the serpentinite host rock is accompanied by a decrease in volume and the mobilisation of mgo and cao from the serpentinite pore spaces and permeability created during weathering and fracturing of the host rock provide access for co2 mgo and cao bearing meteoric waters which led to an increase of volume during carbonation sio2 is only mobilised during more advanced stages of weathering and late stage infiltration of sio2 bearing waters and precipitation of opal a lead to local silicification of the serpentinite stable carbon and oxygen isotope signatures show that nodular magnesite at attunga has formed under near surface conditions incorporating carbon from c3 photosynthetic plants and oxygen from meteoric waters radiocarbon concentrations in the magnesite preclude subducted carbonaceous sediments as the source of carbon and together with distinct stable carbon and oxygen isotope signatures indicate that magnesite at attunga precipitated from low temperature supergene fluids even though there is no direct geochemical and isotopic evidence some textural observations and field relationships for weathering derived magnesite deposits suggest the prior existence of a possibly early triassic hydrothermal magnesite deposit at attunga the presence of a pre existing magnesite deposit may entail the localised formation of the weathering derived magnesite at attunga but the predominance of weathering related textures and geochemical signatures indicate that weathering is the integral magnesite mineralisation process at attunga conventional radiocarbon ages of about 50 ka represent a maximum age constraint for the formation of the magnesite deposit during quaternary weathering a significant amount of atmospheric co2 has been sequestered via the biosphere and carbonation of serpentinite at attunga

the stable isotopic composition of modern soil carbonate and its relationship to climate the oxygen isotopic composition of modern soil carbonate is well correlated with the isotopic composition of local meteoric water the carbon isotopic cycle for co 2 in soils can be described in terms of the proportion of biomass using the c 4 photosynthetic pathway and the co 2 respiration rate of the soil at low soil respiration rates significant atmospheric co 2 mixing can occur in general the carbon isotopic composition of soil carbonate is related to the proportion of c 4 biomass present in soil but soils that freeze to the depth of carbonate formation often have a significant atmospheric component this suggests that freezing of the soil solution should be considered as another important mechanism for soil carbonate formation because of these relationships the isotopic composition of soil carbonate may be a paleoclimatic and paleoecologic indicator in cases in which diagenetic alteration has not occurred

methane derived authigenic carbonates formed by subduction induced pore water expulsion along the oregon washington margin authigenic magnesian calcite dolomite and aragonite are precipitated in the uppermost terrigenous sediments of the washington oregon accretionary prism by subduction induced dewatering these distinctive carbonates are methane derived and occur at sites of concentrated pore water expulsion unique biologic communities that subsist at least indirectly on methane suess et al 1985 are also found at some of these sites the methane which is dominantly biogenic is carried to the uppermost sediments of the prism by fluids and is oxidized by sulfate reducers before being incorporated into a carbonate cement carbonate precipitation occurs below the oxic layer probably no deeper than several centimetres to a few metres below the seabed cementation may be induced by three factors 1 increased carbonate alkalinity resulting from microbial sulfate reduction 2 decreased co 2 solubility resulting from a pressure decrease when the pore water escapes the prism and or 3 the addition of ca 2 and mg 2 ions from sea water near the sediment water interface the convergent margin setting engenders precipitation of authigenic carbonates in several ways compressive stresses induce anomalously rapid compaction and dewatering rates and they may cause overpressuring in migrating pore water thereby delaying precipitation of carbonates until pressure is released near the sediment water interface structural deformation of the accretionary prism creates pathways such as fault zones secondary fracture porosity and dipping permeable layers often exposed by mass movement for efficient advection and expulsion of methane enriched pore water these characteristic conditions which lead to the precipitation of methane derived carbonates may be found at other convergent margins

the new england batholith constraints on its derivation from nd and sr isotopic studies of granitoids and country rocks abstract nd and sr isotopic compositions are reported for the granitic suites which comprise the late palaeozoic to earliest mesozoic new england batholith of eastern australia some of the granitic suites are typically i type in their mineralogy chemistry and isotopic compositions implying a derivation from igneous infracrustal source rocks whereas other suites have characteristics consistent with a derivation from a protolith which was predominantly sedimentary and relatively felsic s types the i type granitoids of the nundle suite have nd values 3 3 to 6 1 that are amongst the most primitive yet documented for a relatively felsic sio 2 65 plutonic suite and these values imply a derivation from either a depleted upper mantle source or more probably a complex source region involving both volcanic arc rocks and detrital material their compositions are distinctly more primitive than those of the new england super suite which constitutes the permian core of the batholith this extensive super suite comprising granitoids traditionally designated as i type has an overall range in initial nd and sr isotopic compositions of 1 7 to 4 6 and 0 70458 to 0 70624 respectively although the majority of plutons have initial nd isotopic compositions which fall into a very narrow range 1 0 1 5 units this limited range is remarkable considering the extreme lithological diversity and range in chemical composition of the analysed samples sio 2 47 74 and implies a source region of considerable volume having reasonably uniform isotopic compositions but variation in chemistry a similarly uniform source isotopically is also indicated for the s type granitoids of the carboniferous hillgrove suite and carboniferous permian bundarra suite with initial nd values of 0 8 to 2 3 and initial 87 sr 86 sr compositions of 0 70474 to 0 70577 showing only limited ranges five pelites three felsic and four mafic greywackes representing typical country rocks from different stratigraphic levels have initial nd values 1 7 to 6 6 and initial 87 sr 86 sr compositions 0 70378 to 0 70585 which essentially mirror the compositional variation in the granitoids a chemical mineralogical and isotopic bimodality in these sediments indicates two very distinctive sources one felsic rhyodacitic the other relatively mafic andesitic which were separated spatially and temporally in many but not all areas of early to mid palaeozoic new england a model is presented in which the s type granitoids are derived from a predominantly felsic source i e pelites and felsic greywackes whereas some of the granitoids belonging to the new england super suite may have been derived from source rocks consisting of both felsic and mafic sedimentary components the distinction between many s type and i type granitoids in new england is unclear for two principal reasons a because the granitoids and their respective source rocks are relatively young geologically so that their isotopic systems have not evolved to any considerable extent and b because of the intrinsic igneous chemical compositions of any sedimentary component that may be involved in their genesis

origin of ultramafic hosted magnesite on margarita island venezuela ultramafic hosted deposits of magnesite mgco3 have been studied on margarita island venezuela to elucidate the source of carbon and conditions of formation for this type of ore petrographic mineralogic and 18o data indicate that magnesite precipitated on margarita in near surface environments at low p and t 13c ranges from 9 to 16 pdb within the magnesite and 8 to 10 pdb within some calcite and dolomite elsewhere on the island the isotopically light dolomite fills karst and the calcite occurs as stock work veins which resemble the magnesite deposits these carbon isotopic ratios are consistent with a deep seated source rather than an overlying source from a zone of surficial weathering however there is not much enrichment of precious metals and no enrichment of heavy rare earth elements as would be expected if the carbon had migrated upward as aqueous carbonate ions the carbon probably has risen as a gaseous mixture of co2 and ch4 which partially dissolved in near surface water before leaching cations and precipitating as magnesite and other carbonates the process probably is ongoing given regional exhalation of carbonaceous gases

metamorphic fluids and transtension in the cantabrian mountains of northern spain an application of the conodont colour alteration index conodont colour alteration index cai values from upper paleozoic rocks in the cantabrian zone of northern spain show that temperatures during hercynian metamorphism locally exceeded 300 c various temperature domains have been defined which are generally separated by fundamental structures these domains do not correspond with the tripartite subdivision based on stratigraphic analysis the observed cai values of conodonts are in general agreement with the mineral paragenesis areas with high cai values display extensive alteration and mineralization and where cai values exceed 4 4 5 200 c slaty cleavage has developed the cantabrian zone is an area of very low grade metamorphism where peak conditions were reached in upper carboniferous to lower permian times the characteristics of the metamorphism and its spatial relationship with major faults suggest that fluids were the main source for regional heating and that fluid transport was focussed along crustal scale structural features the overall deformation regime in this part of the variscan orogen of western europe is interpreted to be large scale transtension this is in agreement with earlier proposed models for the formation of upper palaeozoic basins in this area

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

in situ carbonation of peridotite for co2 storage the rate of natural carbonation of tectonically exposed mantle peridotite during weathering and low temperature alteration can be enhanced to develop a significant sink for atmospheric co2 natural carbonation of peridotite in the samail ophiolite an uplifted slice of oceanic crust and upper mantle in the sultanate of oman is surprisingly rapid carbonate veins in mantle peridotite in oman have an average 14c age of 26 000 years and are not 30 95 million years old as previously believed these data and reconnaissance mapping show that 104 to 105 tons per year of atmospheric co2 are converted to solid carbonate minerals via peridotite weathering in oman peridotite carbonation can be accelerated via drilling hydraulic fracture input of purified co2 at elevated pressure and in particular increased temperature at depth after an initial heating step co2 pumped at 25 or 30 c can be heated by exothermic carbonation reactions that sustain high temperature and rapid reaction rates at depth with little expenditure of energy in situ carbonation of peridotite could consume 1 billion tons of co2 per year in oman alone affording a low cost safe and permanent method to capture and store atmospheric co2

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

a tem microstructural study of dolomite with curved faces saddle dolomite electron diffraction analytical electron microscopy and high voltage high resolution electron microscopy have been used to investigate crystal defects in calcium rich saddle dolomites having pronounced curvature of the faces results show that branching ribbon like defects in these so called saddle dolomites are thin coherent laths of calcitic material the ribbons are profuse and explain the characteristic calcium excess found in most saddle dolomites because the lattice spacings of calcite are between 3 8 and 6 7 larger than the corresponding lattice spacings of dolomite a calcitic ribbon causes local distortion of the host dolomite the branching ribbons have a predominant 10 14 orientation and are generally present in high density they may represent the source of crystal distortion that ultimately manifests itself on the macroscopic scale the calcitic ribbons form during growth from aqueous solution although they have features in common with similar defects found in carbonatite carbonates this fine scale intergrowth microstructure may be a variant of even finer scale modulated structures found in other sedimentary calcian dolomites

hydrothermal dolomitization in a complex geodynamic setting lower palaeozoic northern spain burial hydrothermal dolomitization is a common diagenetic modification in sedimentary basins with implications for oil and gas reservoir performance outcrop analogues represent an easily accessible source of data to refine the genetic models and assess risk in hydrocarbon exploration and production the palaeozoic succession of northern spain contains numerous excellent exposures of epigenetically dolomitized limestones particularly in the carboniferous and cambrian the epigenetic dolomites in the cambrian carbonates of the lancara formation are volumetrically small but have a large aerial distribution across different tectonic units of the variscan fold and thrust belt coarse crystals abundant saddle dolomite cement negative 18o and fluid inclusion homogenization temperatures between 80 c and 120 c characterize these dolomites which are petrographically and geochemically similar to the tens of kilometre sized hydrothermal dolomites replacing the upper carboniferous succession in the same area in both cases the dolomitizing fluids are derived from highly evaporated sea water modified to a limited degree through fluid rock interaction the dolomitization events affecting both cambrian and carboniferous strata are probably related to the same post orogenic hydrothermal fluid flow the formation of the post collisional latest carboniferous cantabrian arc fostered dolomitization the extension related to bending of the arc generated deep reaching faults and strike slip movements which favoured the circulation of hot dolomitizing fluids in the outer parts of this orocline a similar dolomitization process affected other areas of europe after the main stages of the variscan orogeny dolomitization was a continuous uninterrupted isochemical process limestone replacement resulted in a major porosity redistribution and focused the fluid flow into the newly created porous zones replacement was followed immediately by partial to complete cementation of the pores including zebra fabrics and vugs with saddle dolomite the amount of porosity left depends on the volume of cement and therefore on the volume of fluids available

the new england batholith eastern australia geochemical variations in time and space the new england batholith australia is part of the upper paleozoic new england fold belt with most plutons intruded into the deformed trench complex metasedimetary rocks in the southeast part of the fold belt the batholith was emplaced in two major periods of plutonism the first during the upper carboniferous and the second during the upper permian and triassic with a major phase of metamorphism and deformation including westward overthrusting of the trench complex sedimentary rocks between the two periods on the basis of petrography geochemistry and isotopic characteristics the granitoids of the batholith are subdivided into five named intrusive suites and a group of leucoadamellites the differences between the six groups are considered to reflect differences in their source rock types the carboniferous granitoids are peraluminous s type and are divided into the bundarra plutonic suite a belt of very coarse grained adamellites with cordierite garnet and the hillgrove plutonic suite a belt of biotite rich garnet deformed adamellites and granodiorites both suites have 18o greater than 10 negative 34s 87sr 86sr initial ratios about 0 706 are ilmenite bearing and have low feo3 ratios the bundarra plutonic suite however is consistently sio2 rich greater than 70 contains cordierite and has higher 18o than the hillgrove plutonic suite the two s type suites are inferred to have formed by partial melting of the deepest parts of a wedge of trench complex sedimentary rocks oceanwards of an andean volcanic chain to the west analagous to the lower tertiary s type plutons of the sanak baranof plutonic belt of southern alaska of the remaining four groups of plutons emplaced during the upper permian and triassic two are metaluminous i type granitoids one the clarence river plutonic suite new name a group of k poor granodiorites and tonalites with low 87sr 86sr initial ratios average 0 7035 and the other the moonbi plutonic suite a group of k rich adamellites with low 87sr 86sr initial ratios average 0 7045 18o less than 10 and 34s positive the clarence river plutonic suite is inferred to have formed from the partial melting of a large ion lithophile element poor gabbro source region and the moonbi plutonic suite from a large ion lithophile element rich shoshonite source region a third group the uralla plutonic suite is less metaluminous has higher 87sr 86sr initial ratios average 0 706 18o only just less than 10 and negative 34s and is considered to have formed in a region containing a physical mixture of metaluminous and peraluminous source rocks gabbro and metasedimentary rocks plutons of the fourth group are leucoadamellites largely emplaced after the other suites with low 18o indicating an i type source it is argued that this group has resulted from low degrees of dry partial metling of an i type source region that had undergone an earlier melting event these four groups of plutons are largely confined to a narrow belt parallel to but 100 km west of the present rifted margin of australia their origin may be related to crustal thickening attendant on the overthrusting that occurred early in the permian and or a temperature increase in the lower crust due to the recovery of normal continental geotherms following the cessation of subduction

paired stable isotopes o c and clumped isotope thermometry of magnesite and silica veins in the new caledonia peridotite nappe abstract the stable isotope compositions of veins provide information on the conditions of fluid rock interaction and on the origin of fluids and temperatures in new caledonia magnesite and silica veins occur throughout the peridotite nappe in this work we present stable isotope and clumped isotope data in order to constrain the conditions of fluid circulation and the relationship between fluid circulation and nickel ore forming laterization focusing on the koniambo massif for magnesite veins occurring at the base of the nappe the high 18 o values between 27 8 and 29 5 attest to a low temperature formation clumped isotope analyses on magnesite give temperatures between 26 c and 42 c that are consistent with amorphous silica magnesite oxygen isotope equilibrium the meteoric origin of the fluid is indicated by calculated 18 o water values between 3 4 to 1 5 amorphous silica associated with magnesite or occurring in the coarse saprolite level displays a narrow range of 18 o values between 29 7 and 35 3 for quartz veins occurring at the top of the bedrock and at the saprolite level commonly in association with ni talc like minerals the 18 o values are lower between 21 8 and 29 0 and suggest low temperature hydrothermal conditions 40 95 c thermal equilibration of the fluid along the geothermic gradient before upward flow through the nappe and or influence of exothermic reactions of serpentinization could be the source s of heat needed to form quartz veins under such conditions

impact of diagenesis and low grade metamorphosis on isotope δ26mg δ13c δ18o and 87sr 86sr and elemental ca mg mn fe and sr signatures of triassic sabkha dolomites abstract dolomite is a common rock forming mineral in the geological record but its value as archive of ancient seawater 26 mg signatures and their variations in time is at present underexplored unknown factors include the sensitivity of 26 mg ratio to processes in the diagenetic and low grade metamorphic domain this paper documents and discusses the first detailed 26 mg data set from early diagenetic and burial dolomites samples come from the upper triassic hauptdolomit dolomia principale the dolomites italy and include coeval dolomicrites that underwent differential burial diagenesis and low grade metamorphosis in a temperature range between about 100 and more than 350 c magnesium isotope data are complemented by dolomite 13 c 18 o and 87 sr 86 sr isotope ratios as well as ca mg mn fe and sr elemental abundances and data on the dolomite crystal structure as indicated by dolomicrite 87 sr 86 sr ratios and petrographic evidence sabkha calcian d1 dolomites precipitated from evaporated seawater and stabilized at an early marine pore water diagenetic stage to d2 dolomites analysed here with increasing burial temperature dolomite 26 mg ratio scatter in the data set decreases with increasing mg ca ratio and degree of order specifically 26 mg ratio variability is reduced from 0 36 2 at burial temperatures beneath 100 c to about 0 14 2 at temperatures in excess of 350 c respectively with mean 26 mg values ranging constantly near 1 9 this suggests that at least for the rock buffered system investigated here dolomicrite 26 mg proxy data are conservative and preserve near pristine values even at elevated burial temperatures at present the main element of uncertainty is the mg isotope fractionation factor between evaporated seawater and dolomite a possible solution to this problem includes the compilation of data from modern sabkha environments including pore water and calcian dolomite 26 mg isotope signatures

carbonate sedimentation and diagenesis associated with mg ca chloride brines the permian san andres formation in the texas panhandle abstract the san andres evaporitic sequence in the palo duro basin includes several thick carbonate units in its lower part and many thin units in its upper part evaporites are concentrated in the northern part of the northern shelf of the midland basin and carbonates predominate to the south within the palo duro basin the carbonates in the lower part of the sequence differ from those in the upper part in containing skeletal lithofacies and in having lower mn fe and terrestrial organic content the br content in halite in the lower part of the sequence is consistently high whereas halite in the upper part is commonly br depleted the sr content in dolomite calcite and anhydrite and 18o values are about the same in the en ire san andres sequence in the palo duro basin depleted 13c values in dolomite and low pristane phytane ratios occur toward the south na cl and k cl ratios attributed to liquid inclusions in almost all carbonates are characteristic of marine brines evaporated beyond halite saturation na in the dolomite lattice is generally low and increases from north to south at the same stratigraphic levels the lower part of the formation was deposited in a broad shelf basin or lagoon sufficiently deep to maintain long periods of steady state circulation during which little halite dissolution and no potash magnesia mineral precipitation occurred the upper part of the formation was deposited in smaller water bodies sensitive to fluctuations in inflow of marine water as well as meteoric water diagenesis of the carbonates occurred in contact with saline mg ca chloride brines evolved through anhydrite and halite precipitation skeletal mold formation anhydrite cementation dolomitization and high sr calcite cementation associated with celestite are all cogenetic products of such a brine rock interaction 18o of dolomite calcite and chert indicates apparent equilibrium relationships with the same solution temperatures have never exceeded 40 to 45 c and imply the 18o of such a solution to be about 3 the somewhat depleted 18 up o composition of the proposed halite saturated brine resulted from the reversal in the dependence of 18o on increased evaporation in highly saline brines the proposed diagenetic model implies that following early diagenetic processes the rock sequence remained as a closed but compacting system unchanged by later fluid introduction low sr values in dolomite are indicative of recrystallization and not fresh water diagenesis

new discoveries of coal in mozambique development of the coal resource estimation methodology for international resource reporting standards abstract the coal in mozambique s tete province has been known about for a long time as the artist explorer thomas baines first captured onto canvass a coal outcrop on the banks of the zambezi in the late 1850s the first geological works in the tete province referred to the studies of coal occurrence and were undertaken by richard thornton 1859 a geologist on the zambezi expedition under dr david livingstone and guyot however most of the recent exploration has been conducted to ascertain the economic potential of the coal resources within the region the majority of these resources are located within remnants of the ecca group of rocks of the karoo supergroup in the zambezi graben of the tete province of mozambique the coalfield consists of various sub basins and is considered the largest undeveloped coal province in the world amongst others it forms host to the well publicised moatize metallurgical and thermal coal deposit reported to contain 2 4 gt of coal and located within the moatize sub basin in late 2004 a consortium of companies headed by brazilian iron ore miner vale won the right to develop the moatize coal deposit other companies which tendered for this right were bhp billiton rio tinto and anglo american vale is partnered in this project with american metals and coal international amci a north american coal producer which owns 5 of the consortium the consortium bid 122 8 m for the rights to explore and develop the coal deposit the allocation of the tender award to vale opened the way for smaller investors such as the zambezi energy corporation zec who decided in late 2004 to develop a number of projects within licence blocks in the zambezi graben investment within the region has accelerated rapidly over the last couple of years and the region has seen a number of developments during this time the authors have helped to develop the potential of new coal resources and have modified the traditional coal resource estimation techniques such that they can be used for reporting coal resources according to the terminology and guidelines given in the jorc the joint ore reserves committee code jorc 2004 the paper describes the complexities of the underlying regional and local resource geology and describes the challenges of producing resource estimates to international standards such as jorc

factors and processes governing the 14c content of carbonate in desert soils epsl elsevier earth and planetary science letters 125 1994 385 405 factors and processes governing the 14c content of carbonate in desert soils ronald amundson a yang wang a oliver chadwick b susan trumbore c leslie mcfadden d eric mcdonald d steven wells e michael deniro f a division of ecosystem sciences 108 hilgard university of california berkeley ca 94720 usa b earth sciences division jet propulsion laboratory pasadena ca 91109 usa c department of geosciences university of california irvine ca 92717 usa d department of earth and planetary sciences university of new mexico albuquerque nm 87131 usa e department of earth sciences university of california riverside ca 92521 usa f department of geological sciences university of california santa barbara ca 93106 usa received 1 september 1993 revision accepted 14 april 1994 abstract a model is presented describing the factors and processes which determine the measured 14c ages of soil calcium carbonate pedogenic carbonate forms in isotopic equilium with soil co 2 carbon dioxide in soils is a mixture of co 2 derived from two biological sources respiration by living plant roots and respiration of microorganisms decomposing soil humus the relative proportion of these two co z sources can greatly affect the initial 14c content of pedogenic carbonate the greater the contribution of humus derived co 2 the greater the initial 14c age of the carbonate mineral for any gwen mixture of co 2 sources the steady state co 2 distribution vs soil depth can be described by a production diffusion model as a soil ages the 14c age of soil humus increases as does the steady state 14c age of soil co 2 and the initial 14c age of any pedogenic carbonate which forms the mean 14c age of a complete pedogenic carbonate coating or nodule will underestimate the true age of the soil carbonate this discrepancy increases the older a soil becomes partial removal of outer and younger carbonate coatings greatly improves the relationship between measured 14c age and true age although the production diffusion model qualitatively explains the 14c age of pedogenic carbonate vs soil depth in many soils other factors such as climate change may contribute to the observed trends particularily in soils older than the holocene 1 introduction r a d i o c a r b o n d a t i n g o f s e d i m e n t a r y d e p o s i t s in d e s e r t s is h i n d e r e d by a lack o f o r g a n i c carbon paradoxically most o f the d e p o s i t s in t h e s e re mk gions a r e b l a n k e t e d with i n o r g a n i c c a r b o n in the f o r m o f p e d o g e n i c c a r b o n a t e since t h e early 1960s 14c ages have b e e n c a l c u l a t e d for t h e s e c a r b o n a t e s 1 fig 1 illustrates t h a t an a p p r o x i m a t e 1 1 r e l a t i o n s h i p exists b e t w e e n 14c ages of soil c a r b o n a t e a n d coexisting o r g a n i c m a t e r i a l s a n d ages d e t e r m i n e d by o t h e r m e a n s see also 2 3 t h e s e r e l a t i o n s h i p s a r e n o t perfect s o m e c a r b o n a t e is y o u n g e r t h a n i n d e p e n d e n t ages sug 0012 821x 94 07 00 1994 elsevier science b v all rights reserved ssdi 0012 821x 94 00097 i

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

fault development and stress evolution of the post hercynian asturian basin asturias and cantabria northwestern spain abstract the asturian basin an emerged part of the north iberian continental margin has been investigated in terms of fault development and stress evolution the mesozoic history of this domain is mainly linked to the extensional faulting processes which preceded the opening of the bay of biscay preserved jurassic faulted blocks and associated half graben structures bounded by wnw ese to nw se faults are related to a late jurassic kimmeridgian rifting stage this fault system seems to have played a major role during the mesozoic structuring of the basin suggesting an extension oriented approximately ne sw the cenozoic evolution is related to the iberia eurasia convergence and collision leading to compressional and subsequent extensional structures the direction of compression documented in various sites was nnw sse during an initial early middle eocene stage reoriented probably in the oligocene to ne sw this succession of stress regimes was applied to the same three major fault systems ne sw nw se and e w which were inherited from the variscan orogeny some of them having already been involved in the latest stephanian early permian rifting episode during the tertiary compressional phase the nw se trend which is believed to have controlled the late jurassic tectonic development was rejuvenated into dextral strike slip faults whereas the ne sw system moved in a sinistral sense the e w system was reactivated as reverse faults giving rise to a partial inversion of the basin

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

formation of 18o depleted dolomite within a marine evaporitic sequence triassic reichenhall formation austria dark grey bituminous dolostones interbedded with marine derived anhydrite horizons occur in the triassic reichenhall formation of western austria fossils are rare and indicate a hostile hypersaline depositional environment the dolomites are finely crystalline fairly stoichiometric well ordered and non ferroan closely spaced samples 94 in total of individual dolomite units have been analysed for their carbon and oxygen isotopic composition the data indicate surprisingly low 18o values 5 7 to 2 1 0 pdb whereas the 13c values are comparable to the contemporary triassic seawater 0 2 to 2 6 0 pdb sedimentological evidence including i lack of any evidence for extensive dissolution ii distinct oxygen and carbon isotope ratios of individual dolomite units iii covariance of carbon and oxygen isotopes within some dolomite layers and iv inclusions of celestite in dolomite indicates a nearly closed system after early diagenesis combining this information with water rock interaction calculations suggests that the lightest oxygen isotope compositions are the result of freshwater influx into the basin during very early dolomite formation a secondary factor may be dolomite recrystallization at elevated temperatures during burial

chemical and 13c 12c and 18o 16o isotope evolution of alkaline drainage waters and the precipitation of calcite carbon and o isotope ratios demonstrate that calcite precipitating from alkaline tunnel drainage waters has formed by two distinct chemical mechanisms calcium carbonate sulfate ground water dissolves portlandite preferentially this leads to an increase of ca2 ph and the co32 hco3 ratio so that calcite is precipitated the c content of this calcite is a mixture of c from soil co2 and the dissolved limestone resulting in 13c 13 pdb the o isotope composition 18o 24 smow corresponds to thequilibrium fractionation between calcite and water the precipitation continues as atmospheric co2 is absorbed by the alkaline solutions in this type of calcite the c isotope composition 13c 25 pdb is controlled by the individual reaction rate constants for the hydroxylation of 13co2 and 12co2 the o isotope composition 18o 11 smow is a mixture of the compositions of atmospheric co2 and oh the isotope compositions may be used in order to evaluate the proportions of the two different mechanisms of calcite precipitation other mechanisms which cause chemical changes of the ground water are the formation of ettringite from initially unhydrated c3a phases and the formation of brucite precipitation and dissolution rates for the various solids range from 10 3 to 10 4 kg d m2

clumped isotope thermometry of magnesium carbonates in ultramafic rocks abstract magnesium carbonate minerals produced by reaction of h 2 o co 2 with ultramafic rocks occur in a wide range of paragenetic and tectonic settings and can thus provide insights into a variety of geologic processes including 1 deposition of ore grade massive vein cryptocrystalline magnesite 2 formation of hydrous magnesium carbonates in weathering environments and 3 metamorphic carbonate alteration of ultramafic rocks however the application of traditional geochemical and isotopic methods to infer temperatures of mineralization the nature of mineralizing fluids and the mechanisms controlling the transformation of dissolved co 2 into magnesium carbonates in these settings is difficult because the fluids are usually not preserved clumped isotope compositions of magnesium carbonates provide a means to determine primary mineralization or re equilibration temperature which permits the reconstruction of geologic processes that govern magnesium carbonate formation we first provide an evaluation of the acid fractionation correction for magnesium carbonates using synthetic magnesite and hydromagnesite along with natural metamorphic magnesite and low temperature hydromagnesite precipitated within a mine adit we show that the acid fractionation correction for magnesium carbonates is virtually indistinguishable from other carbonate acid fractionation corrections given current mass spectrometer resolution and error in addition we employ carbonate clumped isotope thermometry on natural magnesium carbonates from various geologic environments and tectonic settings cryptocrystalline magnesite vein deposits from california red mountain magnesite mine austria kraubath locality turkey tutluca mine eskisehir district and iran derakht senjed deposit exhibit broadly uniform 47 compositions that yield apparent clumped isotope temperatures that average 23 7 5 0 c based on oxygen isotope thermometry these clumped isotope temperatures suggest mineralization at shallow crustal depths in the presence of meteoric water hydrous magnesium carbonates from a 400 km latitudinal transect along the serpentinized peridotite bodies of the california coast ranges record clumped isotope temperatures between 14 2 and 22 7 2 8 c in agreement with historical maximum temperatures during the rainy season for california talc carbonate alteration of ultramafic rocks in greenland isua supracrustal belt and vermont ludlow yields clumped isotope alteration temperatures of magnesite and dolomite between 326 and 490 c broadly consistent with paragenesis and thermodynamic analysis for co 2 metasomatism of ultramafic rocks these metamorphic carbonates extend the applicability of clumped isotope thermometry to high temperature magnesium carbonate systems and indicate equilibrium blocking temperatures for magnesite of 490 c our study demonstrates the applicability of the clumped isotope approach to provide information on the formation of magnesium carbonates as ore resources surface records of climate and metamorphic assemblages

petrogenesis of gold bearing listvenites from the carbonatized mantle section of the neoproterozoic ess ophiolite western arabian shield saudi arabia abstract the variably serpentinized mantle peridotites of the late neoproterozoic ess ophiolite western saudi arabia are highly altered along shear zones and thrust planes to form erosion resistant listvenites the listvenites are distinguished petrographically and geochemically into three types carbonate silica carbonate and silica birbirite listvenites geochemical analyses are consistent with expectations from petrography carbonate listvenite is low in sio2 content but high in mgo fe2o3 and cao relative to silica carbonate and birbirite which is remarkably high in sio2 at the expense of all other components the total ree contents are low in silica carbonate and carbonate listvenites but highly enriched in birbirite with a large positive eu anomaly the host serpentinites have all the characteristics typically associated with highly depleted mantle harzburgite protoliths in supra subduction fore arc settings bulk compositions are low in al2o3 and cao with high mg molar mg mg fe relict cr spinel has high cr molar cr cr al and low tio2 and relict olivine has high mg and nio content the cr spinel relics are also found in the listvenites those in serpentinite and carbonate listvenites have significantly higher mg than those in silica carbonate and birbirite suggesting re equilibration of cr spinel in the later phases of listvenitization the varieties of listvenite capture successive stages of fluid mediated replacement reactions the carbonate listvenite appears to have developed syn contemporaneously with serpentinization whereas silica carbonate listvenite and birbirite formed later the listvenite formation resulted in leaching and removal of some components accompanied by deposition of others in the solid products notably co3 sio2 ree especially eu au zn as sb and k our data show that listvenitization concentrated gold at sub economic to economic grades measured gold concentrations in the host serpentinite are 0 5 1 7 ng g versus 4 2569 ng g in carbonate listvenite 43 3117 ng g in silica carbonate listvenite and 5 281 ng g in birbirite the listvenite deposits in the jabal ess area merit further exploration for gold

direct effects of co2 and temperature on silicate weathering possible implications for climate control a critical uncertainty in models of the global carbon cycle and climate is the combined effect of organic activity temperature and atmospheric co2 on silicate weathering here we present new dissolution rates of anorthite and augite which indicate that silicate weathering in organic rich solutions is not directly affected by soil co2 but is very sensitive to temperature apparently co2 accelerates silicate weathering indirectly by fertilizing organic activity and the production of corrosive organic acids the weathering dependencies highlight the ability of silicate weathering to act as a global thermostat and damp out climate change when used as input in steady state carbon cycle and climate models

seam modeling and resource estimation in the coalfields of western anatolia abstract western anatolia turkey includes a number of lignite bearing neogene fields with difficult modeling and estimation problems resulting from severe tectonic movements and highly variable coal quality the paper considers the eynez soma and omerler tuncbilek coal fields and introduces a simple but effective way of defining the geological discontinuities that are vital for selective mining method after doing statistical analysis for both fields data taken from core samples of diamond drill holes are used to model fault blocks in order to establish a 3d coal seam model then block small mining unit modeling is performed for both coal fields and some coal quality parameters are estimated and assigned to the predefined blocks for estimation process a new method of wrinkling and unwrinkling is introduced and composited data is detrended each block is kriged by using the detrended data in unwrinkled space the volume of the blocks is converted into in situ tonnages based on their estimated densities in eynez the densities are derived from the mean lower calorific value of the blocks using the relationship between lower calorific value and density in omerler the block densities are estimated from the composited values of densities of the lithologic units in coal horizon by using ordinary kriging

syn tectonic meteoric water derived carbonation of the new caledonia peridotite nappe exceptional outcrops recently exposed in the koniambo massif allow the study of the serpentine sole of the peridotite nappe of new caledonia southwest pacific ocean many magnesite veins are observed with characteristics indicating that they were emplaced during pervasive top to the southwest shear deformation the oxygen isotope composition of magnesite is homogeneous 27 4 18o 29 7 while its carbon isotope composition varies widely 16 7 13c 8 5 these new data document an origin of magnesite from meteoric fluids laterization on top of the peridotite nappe and carbonation along the sole appear to represent complementary records of meteoric water infiltration based on the syn kinematic character of magnesite veins we propose that syn laterization tectonic activity has enhanced water infiltration favoring the exportation of leached elements like mg which has led to widespread carbonation along the serpentine sole this calls for renewed examination of other magnesite bearing ophiolites worldwide in order to establish whether active tectonics is commonly a major agent for carbonation

origin of ultramafic hosted vein magnesite deposits abstract large deposits of magnesite mgco3 occur either as carbonated ultramafic rocks or as sedimentary beds the origins of both sedimentary and ultramafic hosted deposits remain controversial as does the relationship between them ultramafic hosted deposits are reviewed herein with an emphasis on veins rather than massive bodies magnesium apparently has been supplied to magnesite veins by their ultramafic host uncertainties concerning ultramafic hosted deposits include the source state and mode of transportation of carbon the cause of its precipitation and the mineralogy of the initial precipitate genetic questions about ultramafic hosted vein deposits are summarized with the aid of flow charts the preferred route through these charts attributes most vein magnesite to an influx of metamorphic degassing co2 and ch4 into groundwater which flows through serpentinite or peridotite the source of co2 ch4 is considered to be deeper than 10 km because metamorphism 300 c is required to release carbonaceous volatiles of the type which apparently induced observed magnesite mineralization however vein magnesite precipitation generally has occurred within just a few hundred meters of the earth s surface vein deposits are considered to be genetically related to massive bodies but the massive bodies typically contain less 12c the 12c rich co2 which has produced vein deposits is attributed to a fluid phase variably mixed ch4 co co2 which rose until it reached upper crustal groundwater the hypothetical water poor fluid presumably became slightly oxidized hence richer in soluble co2 as it encountered near surface sulfate bearing water co2 enriched water is envisioned to have been expelled regionally due to tectonic processes leaving little mineralogical evidence of its expulsion through non ultramafic rock co2 rich water which happened to encounter either serpentinite or peridotite presumably has produced magnesite vein deposits and a common silicate byproduct nontronite according to the following reaction 12 mg3si2o5 oh 4 serpentine 36 hco3 4 fe3o4 o2 12 fesi2o5 oh nontronite 36 mgco3 magnesite 36 oh 18h2o

self subduction of the pangaean global plate one of the most striking and rare occurrences in the earth s history is the amalgamation of most of the continental lithosphere into one supercontinent the most recent supercontinent pangaea lasted from 320 to 200 million years ago here we show that after the continental collisions that led to the formation of pangaea plate convergence continued in a large wedge shaped oceanic tract we suggest that plate strain at the periphery of the supercontinent eventually resulted in self subduction of the pangaean global plate when the ocean margin of the continent subducted beneath the continental edge at the other end of the same plate our scenario results in a stress regime within pangaea that explains the development of a large fold structure near the apex of the palaeotethys ocean extensive lower crustal heating and continental magmatism at the core of the continent as well as the development of radially arranged continental rifts in more peripheral regions of the plate

spatial patterns of diagenesis during geothermal circulation in carbonate platforms geothermal convection of seawater deep in carbonate platforms could provide the necessary supply of magnesium for dolomitization at temperatures high enough to overcome kinetic limitations we used reactive transport simulations to predict the rates and spatial patterns of dolomitization during geothermal convection in a platform that was 40 km across and 2 km thick in the simulations porosity and permeability decrease with depth to account for sediment compaction dolomitization of a platform consisting of medium grained 0 0 5 mm sediments occurred in a broad band ranging from 2 5 km depth near the margin to 1 5 km depth near the platform center the area of dolomitization is deep enough that temperatures exceed 50 c but not so deep that low permeabilities restrict mass transport complete dolomitization in the center of this zone is estimated to require at least 60 my incorporation of permeability contrasts permeable beds and reactive beds focused dolomitization strongly and reduced the estimated time required for dolomitization by as much as 50 percent dolomitization created magnesium depleted calcium rich fluids in less than 10 ky and results support a link between dolomitization and anhydrite precipitation where adequate sulfate is available

late miocene nonmarine sedimentation and formation of magnesites in the acigol basin southwestern anatolia turkey abstract the late miocene lacustrine acigol basin sw turkey formed as an orogen top extensional half graben with the subaqueous accommodation controlled by the lake level and the bulk accommodation provided by active subsidence along a wsw trending normal fault at the basin s southern margin the basin fill sedimentary succession consists of terminal alluvial fan facies overlain by ephemeral lake margin facies and perennial lake facies with widespread fluvial facies at the top the distal alluvial fan facies include massive to stratified sandstones and massive mudstones with intervening nodular dolostones and incipient pedogenic horizons the lake margin facies are micritic magnesites passing laterally into peloidal irregularly laminated magnesites towards the palaeolake margin and overlain by marlstones and dolostones all with abundant evidence of episodic subaerial exposure desiccation cracks pedogenic features and tepee structures the perennial lake facies are micritic magnesites passing upwards into clayey dolostones and dolomitic or clayey marlstones the fluvial facies capping the succession include planar cross stratified conglomerates channel fill deposits planar parallel stratified planar cross stratified and rippled cross laminated sandstones crevasse fill and crevasse splay deposits and assemblages of mudstones intercalated with thin sandstone beds overbank floodplain deposits the sedimentological mineralogical and geochemical data reveal large variations in the basin s hydrological regime including short term oscillations and bulk rise of the lake level periodical changes in the mg ca ratio and terrigenous mud supply and a negative covariance of 18 o and 13 c fluctuations the composition of terrigenous sediment and the chemistry of water supplied to the lake were controlled by the weathering chemical leaching and erosion of the ultramafic dolomitic bedrock in the catchment area the bedrock yielded mg rich carbonate solutions that caused the deposition of mg carbonates in the lake despite short term lake level fluctuations the lake s net water budget remained positive it is suggested that the region s present day climate and mg rich alkaline lakes can serve as an analogue for the climatic and hydrological conditions in the late miocene acigol basin

geological controls on prediction of coalbed methane of no 3 coal seam in southern qinshui basin north china article i nfo in order to better understand the geological controls on coalbed methane cbm in southern qinshui basin sqb north china geological surveys and laboratory experiments including coal petrology analysis proximate analysis and methane adsorption desorption were conducted results show that the coals from the sqb contain 0 59 3 54 moisture 3 5 15 54 ash yield 73 62 88 92 fixed carbon and 2 14 4 04 hydrogen with c h ratios in the range of 19 96 36 25 the vitrinite reflectance ro m ranges from 1 95 to 3 49 the coals are composed of 18 5 97 4 vitrinite and 2 4 81 4 inertinite the geologic structures coal bearing strata and coal depositional environment were studied by both field geological research and laboratory tests a positive relationship is found between cbm content and basin hydrodynamics in which cbm easily concentrates in the groundwater stagnant zone because of the water pressure furthermore integrated geographical information system gis and analytical hierarchy fuzzy prediction method ahp were used to evaluate the cbm resources in the sqb the results show that the amount of cbm associated with the no 3 coal seam in the sqb is 3 62 10 11 m 3 t he cbm resource concentration gas in place per square kilometer in the sqb is in the range of 0 72 2 88 10 8 m 3 km 2 with an average of 1 21 10 8

paleozoic ophiolitic assemblages within the southern new england orogen of eastern australia implications for growth of the gondwana margin several ophiolitic assemblages occur in the southern new england orogen the development of these rocks and their relations to the rest of the orogen have major implications for the tectonic evolution of eastern gondwana a major narrow but elongate belt of early cambrian supra subduction zone ophiolite crops out along and near the peel manning fault system and is juxtaposed against younger arc and subduction complex terranes no pre permian links with the rest of the new england orogen have been established for this terrane it may represent portions of lachlan fold belt basement which underlies younger westward overthrust new england terranes and has been diapirically emplaced at higher crustal levels as serpentinite matrix melange middle to late devonian ophiolitic rocks in the yarras complex comprise basement to the birpai subterrane and represent a crustal cross section through a rifted island arc correlatives of this terrane also occur within the more extensive gamilaroi terrane to the west of which deeper crustal levels are not exposed the various components of serpentinite matrix melange in the ngamba terrane at port macquarie superficially appear to represent a dismembered ophiolite association however the various components of the melange exhibit a wide range of ages metamorphism and tectonic affinities rendering a genetically related origin unlikely this terrane includes fragments of ocean floor accreted into a late devonian subduction complex which was later affected by early carboniferous forearc serpentinite diapirism and high mg series magmatism zircon inheritance in triassic dikes which intrude the melange attest to the development or later emplacement of this forearc region over an older lachlan fold belt basement ultramafic rocks of the bundjalung terrane in the east of the new england region probably formed at deep levels in an intraoceanic island arc and are intruded by boninitic dikes the tectonic development of the neo was significantly more complicated than has been suggested in earlier published models periodic accretion of island arc systems some of which are now represented by supra subduction zone ophiolites to the eastern margin of gondwana suggests multiple phases of subduction with the possibility of polarity reversals throughout the history of accretion lateral accretion was not the only means by which gondwana continental crust grew and there was considerable postaccretion continentward overthrusting of younger terranes copyright 1994 by the american geophysical union

a strontium isotopic study of formation waters from the illinois basin u s a abstract the isotopic composition of sr has been measured in 73 formation water samples from paleozoic strata in the illinois basin 87sr 86sr ratios range from 0 7079 to 0 7108 with the exception of four samples the waters are more radiogenic than corresponding paleozoic sea water values the relatively narrow range of slightly elevated 87sr 86sr rations is uniformly distributed in waters throughout the stratigraphic column and in silurian waters across the basin isotopic analyses of core samples from reservoir rocks show an absence of water rock sr isotopic equilibration basin lithology and analyses of detrital rock units indicate that clay minerals in shales and in quartz sandstone matrices represent the only significant source of radiogenic sr for the waters silurian and devonian water show a two component mixing relation which suggests that they comprise a single hydrogeological system that evolved when radiogenic water from new albany shales entered silurian devonian carbonate rocks and mixed with marine interstitial water regional migration of the waters and associated petroleum within the silurian devonian strata proposed in other studies is consistent with the sr isotopic data under favorable circumstances subsurface waters are capable of retaining a sr isotopic recor of their evolution

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

emerald mineralisation in colombia fluid chemistry and the role of brine mixing emerald mineralisation in colombia is located in two distinct zones along the borders of the eastern cordillera some 80 km apart mineralisation in the western zone has been dated at ca 35 ma whereas in the eastern zone it is 30 ma older crush leach analysis of the electrolyte chemistry of fluid inclusions contained in emerald quartz calcite dolomite and fluorite from both zones demonstrates that in each region brines associated with emerald mineralisation range between two extremes with many samples yielding intermediate compositions fluid 1 found mainly in emerald hosted fluid inclusions is dominated by nacl with high cl br ratios indicating that the salinity was derived by dissolution of halite most probably from the local salt beds fluid 2 found notably in quartz hosted fluid inclusions is of similar salinity but contains less na and significant concentrations of ca k fe cl and other cations it has lower cl br ratios more comparable with formation waters but is inferred to have obtained part of its salinity by halite dissolution bivariate plots of almost all cations have linear or sublinear trends regardless of the mineral hosting the inclusions or the locality from which the samples originated demonstrating that mixing of the two saline fluids has occurred because the same two fluids occur in both eastern and western zones despite the difference in space and time it is inferred that fluid compositions were rock controlled by similar interactions with evaporites and black shales in both instances it is proposed that beryllium was transported as be f complexes in the nacl fluid and was precipitated as emerald after mixing with the calcic brine caused precipitation of fluorite and parisite

formation of weathering derived magnesite deposits in the new england orogen new south wales australia implications from mineralogy geochemistry and genesis of the attunga magnesite deposit nodular cryptocrystalline weathering derived magnesite deposits in the new england orogen australia provide a significant source of high purity magnesite common textural features and related isotopic fingerprints indicate a close genetic relationship between weathering derived magnesite deposits hosted by ultramafic rocks at attunga and by sediments at kunwarara while silica carbonate rock alteration and rare hydrothermal magnesite vein deposits reflect contrasting conditions of formation localised weathering of carbonates in a soil environment shifts stable isotopic composition towards low 13c and high 18o typical for weathering derived magnesites while intrusion related fluids do not significantly change the isotopic composition of affected carbonates at attunga magnesite consists of irregular nodular veins and masses filling faults and cracks in the weathered serpentinite host rock as well as soft powdery magnesite in pervasive serpentinite alteration zones the high grade magnesite at attunga can be contaminated by amorphous silica and serpentine relicts but does not contain dolomite or ferroan magnesite as observed for its hydrothermal equivalent the piedmont magnesite deposit or other widespread deposits of silica carbonate rock in the great serpentinite belt heavy 18o values are compatible with a supergene formation from meteoric waters while low 13c suggests c3 photosynthetic plants as the predominant source of carbon for the attunga magnesites we infer that weathering derived nodular magnesite deposits hosted in ultramafic rocks like the attunga magnesite deposit have formed in a two step process involving the hypogene formation of a pre cursor magnesite deposit and complete supergene overprinting by meteoric waters that acquired carbon from percolation through soil

geology of barcode type coking coal seams mecondezi sub basin moatize coalfield mozambique abstract the geology of barcode type coking coal seams including basin setting stratigraphy sedimentary facies coal forming environments seam morphology and implications for exploitation in the mecondezi sub basin moatize coalfield mozambique is presented the moatize coalfield is located along the zambezi valley gondwana rift that developed over heterogeneous precambrian basement in between the zambia and zimbabwe cratons basement heterogeneities controlled basin development coal seams occur in a kilometer thick lower karoo succession classified into vuzi and moatize formations of late carboniferous to permian age coal seam stratigraphy in ascending order shows six seams namely the sousa pinto chipanga bananeiras intermedia grande falesia and andre the grande falesia seam has attained a maximum thickness of up to 250 m making it one of the thickest coal seams known so far in the world based on sedimentary attributes the lower karoo coal succession is classified into three facies assemblages named vuzi transitional and moatize the karoo sedimentation commenced with the deposition of tillite diamictite and rhythmite of vuzi assemblage over precambrian basement in periglacial environments during the late carboniferous the succeeding transitional assemblage is characterized by the presence of coal beds in association with diamictite thereby signaling the onset of coal forming environments during the interludes of glacial retreat the moatize assemblage includes coal seams mudstone rhythmite and sandstone deposited in delta plain mire environments coal seam morphology is barcode in type and characterized by cyclic stacking pattern of thin beds of coal carbonaceous mudstone and mudstone high ash contents of the coal are attributed to flooding of low level mires and ground water fluctuations in a tectonically unstable basin setting the coal is bituminous vitrinite rich medium to high volatile and medium in rank as a coking coal it compares well with some of the coking coals of limpopo area in south africa constraints on exploitation of barcode type coal seams are linked to barcode morphology which can be overcome by selective mining of coal

isotope geochemistry of caliche developed on basalt enormous variations in oxygen and carbon isotopes occur in caliche developed on 3 ma basalts in 3 volcanic fields in arizona significantly extending the range of 18o and 13c observed in terrestrial caliche within each volcanic field 18o is broadly co variant with 13c and increases as 13c increases the most 18o and 13c enriched samples are for subaerial calcite developed on pinnacles knobs and flow lobes that protrude above tephra and soil the most 18o and 13c depleted samples are for pedogenic carbonate developed in soil atmospheres the pedogenic caliche has 18o fixed by normal precipitation in local meteoric waters at ambient temperatures and has low 13c characteristic of microbial soil co2 subaerial caliche has formed from 18o rich evapoconcentrated meteoric waters that dried out on surfaces after local rains the associated 13c enrichment is due either to removal of 12c by photosynthesizers in the evaporating drops or to kinetic isotope effects associated with evaporation caliche on basalt lava flows thus initially forms with the isotopic signature of evaporation and is subsequently over layered during burial by calcite carrying the isotopic signature of the soil environment the large change in carbon isotope composition in subsequent soil calcite defines an isotopic biosignature that should have developed in martian examples if mars had a warm wet early period and photosynthesizing microbes were present in the early soils the approach can be similarly applied to terrestrial precambrian paleocaliche in the search for the earliest record of life on land large variations reported for 18o of carbonate in martian meteorite alh84001 do not necessarily require high temperatures playa lakes or flood runoff if the carbonate is an example of altered martian caliche

dissolution precipitation processes governing the carbonation and silicification of the serpentinite sole of the new caledonia ophiolite the weathering of mantle peridotite tectoni cally exposed to the atmosphere leads commonly to natural carbonation processes extensive cryptocrystalline mag nesite veins and stock work are widespread in the ser pentinite sole of the new caledonia ophiolite silica is systematically associated with magnesite it is commonly admitted that mg and si are released during the laterization of overlying peridotites thus the occurrence of these veins is generally attributed to a per descensum mechanism that involves the infiltration of meteoric waters enriched in dissolved atmospheric co 2 in this study we investigate serpentinite carbonation processes and related silicifica tion based on a detailed petrographic and crystal chemical study of serpentinites the relationships between serpen tine and alteration products are described using an original method for the analysis of micro x ray fluorescence images performed at the centimeter scale our investigations highlight a carbonation mechanism together with precipitation of amorphous silica and sepiolite based on a dis solution precipitation process in contrast with the per descensum mg si enrichment model that is mainly concentrated in rock fractures dissolution precipitation process is much more pervasive thus although the texture of rocks remains relatively preserved this process extends more widely into the rock and may represent a major part of total carbonation of the ophiolite

massive hydrothermal dolomites in the southwestern cantabrian zone spain and their relation to the late variscan evolution abstract large scale massive burial dolomitization affected upper carboniferous carbonates of the southwestern variscan cantabrian zone spain replacive and void filling dolomites formed and were post dated by calcite cementation the process of dolomitization was due to the circulation of hypersaline and hydrothermal marine derived brines controlled by rock anisotropies the dolomites probably formed in early permian time during post thrusting orocline formation in an extensional setting lithospheric delamination induced increased heat flow and allowed thermal convection of the fluids the dolomites from the cantabrian zone are excellently exposed and represent an interesting outcrop analogue for hydrocarbon reservoirs elsewhere in comparable geotectonic settings of the european variscan orogen large masses of similar dolomites could have formed if mg rich brines were available

tectono thermal evolution in a region with thin skinned tectonics the western nappes in the cantabrian zone variscan belt of nw spain the palaeotemperature distribution in the transition from diagenesis to metamorphism in the western nappes of the cantabrian zone somiedo la sobia and aramo units are analysed by conodont colour alteration index cai and illite crystallinity ic structural and stratigraphic control in distribution of cai and ic values is observed both cai and ic value distributions show that anchizonal conditions are reached in the lower part of the somiedo unit a disruption of the thermal trend by basal thrusts is evidenced by cai and ic values there is an apparent discrepancy between the ic and cai values in carboniferous rocks of the aramo unit the ic has mainly anchizonal values whereas the cai has diagenetic values discrepant ic values are explained as a feature inherited from the source area in the carboniferous rocks of the la sobia unit both ic and cai indicate diagenetic conditions the anchimetamorphism predated completion of emplacement of the major nappes it probably developed previously and or during the early stages of motion of the units temperature probably decreased when the metamorphosed zones of the sheets rose along ramps and were intensely eroded in the context of the iberian variscan belt influence of tectonic factors on the metamorphism is greater in the internal parts where the strain and cleavage are always present than in the external parts cantabrian zone where brittle deformation and rock translation are dominant with an increasing role of the burial on the metamorphism

petrographic ree fluid inclusion and stable isotope study of magnesite from the upper triassic burano evaporites secchia valley northern apennines contributions from sedimentary hydrothermal and metasomatic sources sparry and microcrystalline magnesite are minor constituents of the upper triassic burano evaporite formation of the northern apennines in italy petrography and geochemistry of magnesite suggest three modes of formation 1 evaporitic precipitation of stratified microcrystalline magnesite layers associated with sulfate and carbonate rocks most ree are below icp ms detection limits 18o is 20 2 smow and 13c is 2 6 pdb 2 hydrothermal infill of fe rich 9 78 wt feo lenticular sparry magnesite this type of magnesite is characterized by very low lree concentrations whereas hrees are relatively high the fluid inclusion composition is nacl mgcl2 h2o salinity is 30 wt nacl equiv and total homogenization temperatures range from 204 309 c 18o is 17 5 and 13c is 1 3 the partial or total replacement of dolostones by lenticular sparry magnesite lrees are lower in magnesite compared with the partly replaced dolostones magnesite yields 18o and 13c compositions of 17 3 to 23 6 and 0 5 to 1 4 respectively whereas the partly replaced dolostones yield 18o and 13c values of 25 0 to 26 2 and 1 3 to 1 9 respectively complete replacement of dolostones produced massive lenticular sparry magnesite rock containing ooids and axe head anhydrite relicts lrees are depleted compared to unaffected dolostones 18o and 13c compositions range from 16 4 to 18 4 and 0 4 to 0 9 respectively these data and the association between fracture filling and replacive magnesite suggests a metasomatic system induced by hydrothermal circulation of hot and saline mg rich fluids these processes probably occurred in the oligocene miocene when the burano formation acted as main detachment horizon for the tuscan nappe during the greenschist facies metamorphism of the apuane complex thrusting over the apuane zone produced large scale fluid flow focused at the tuscan nappe front sources of mg rich fluids were metamorphic reactions in the apuane complex and dissolution of mg salts at the thrust front considering a maximum tectonic burial depth of 10 km as inferred from the geometry of the chain the pressure corrected temperature of magnesite precipitation 380 to 400 c and the calculated fluid composition 18o 13 3 1 2 are in the range of the published apuane metamorphic temperatures 300 450 c and fluid compositions 18o 7 16 the results of this study support the hydrothermal metasomatic model for the formation of sparry magnesite deposits at the expense of dolostone units involved in thrusting and low grade metamorphism as proposed for the northern graywacke zone alps and the eugui deposit western pyrenees

stable isotope evidence for near surface low temperature formation of mg hydro carbonates in highly altered greek mesozoic serpentinites authigenic magnesite hydromagnesite and huntite associated with intensely altered and serpentinized ophiolitic rocks in attica mainland greece occur predominantly as veinlets and nodules within a totally weathered former serpentinite groundmass carbonate 18 o values are consistent with post geothermal fluid temperatures between 25 and 70 c but mostly between 25 and 30 c from a dominantly meteoric sourced groundwater indicating near surface low temperature conditions despite the proximity of a volcanic centre with strong co 2 flux 75 of the carbon isotope data imply little or no incorporation of this co 2 into the authigenic mg hydro carbonates indeed many 13 c values are more negative than soil zone calcrete values and in this setting mg hydro carbonate 13 c values below 6 vpdb probably indicate disequilibrium effects in alkaline groundwaters geothermal fluids and groundwaters were mainly routed through structural conduits some of the low temperature hydromagnesite subsequently dehydrated to magnesite under near surface conditions and huntite is probably a diagenetic transformation of hydromagnesite forming close to the volcanic centre where fluid mg ca ratios were low the isotopic signatures are distinct from previously published balkan east mediterranean magnesite data arrays but are consistent with many other ultramafic associated magnesium carbonates worldwide their association with likely fluid compositions provides important context for mg hydro carbonate formation as geothermal conditions cool to near surface temperatures

new distribution coefficient for the incorporation of strontium into dolomite and its implications for the formation of ancient dolomites late tertiary dolomites form the bahamas exhibit a strong inverse correlation between sr and mol mgco sub 3 it is proposed that this relation is a result of a distribution coefficient dependent on the concentration of ca in dolomite because these dolomites precipitated from water with a sr sup 2 ca sup 2 ratio similar to that of seawater a distribution coefficient d sub sr sup dolomite of 0 0118 is calculated for sr in stoichiometric dolomite this coefficient increases by about 0 0039 for every additional mol caco sub 3 in nonstoichiometric dolomite these data have three important implication first the new d sub sr sup dolomite is substantially lower than previously suggested second a relation has been established among the sr sup 2 ca sup 2 ratio of dolomite forming waters the major element composition of dolomites and the sr content of dolomites allowing the determination of the sr sup 2 ca sup 2 ratio of fluids involved in the formation of ancient dolomites third some published data sets on dolomites show a similar relation between sr content and major element composition suggesting that these dolomites may also have formed from seawater other data sets deviate from the correlation defined by little bahama bank dolomites indicating either dolomitization in fluids other than seawater or changes ofmore the sr sup 2 ca sup 2 ratio of seawater through time less

mineralogy stable isotope geochemistry and paragenesis of magnesite deposits from the ophiolite belt of eastern iran a large number of magnesite deposits with reserves totaling several million tons occur in eastern iran these deposits are found as veins within ultramafic rocks afzalabad vein type and as lenses overlying the surrounding flysch sedimentary strata torshak strata bound the occurrence of both vein type and strata bound deposits is not common among magnesite deposits worldwide the afzalabad magnesite is texturally heterogeneous and characterized by higher mg and lower ca sr as ba and b contents than the torshak magnesite these compositional differences are also reflected by the unit cell parameters of the magnesite however magnesites from both localities have similar carbon and oxygen isotope compositions that are characteristically heavy 13c values of 7 2 to 8 2 18o values of 27 5 to 33 6 such high values are unlike those for magnesite found near and within other ultramafic complexes worldwide but are similar to the isotopic compositions of magnesite found in lagoon or hypersaline basin environments however the settings of eastern iran magnesite deposits differ from those formed in lagoons or hypersaline environments instead we infer that evaporating surface water containing dissolved atmospheric co2 percolated through fractures in ultramafic rocks acquiring mg by hydrolysis of mg rich minerals as the fluids subsequently ascended magnesite precipitated in the fractures within the ultramafic complex and in the open channelways in the surrounding flysch strata