origin of iron rich mississippi valley type deposits the abundance of iron in mississippi valley type lead zinc deposits and districts varies greatly some deposits contain large amounts and others are almost free of iron iron in mississippi valley type deposits is largely paragenetically early pyrite or marcasite that was replaced by sphalerite and galena often in the central part of the deposit or district sedimentary exhalative and irish type base metal deposits which also form from basinal brines have similar variations in iron content calculated metal contents of brines in equilibrium with galena sphalerite and pyrite show that iron is significantly more abundant than lead and zinc in high temperature 200 c relatively acid brines with low sulfur contents whereas zinc dominates under most other conditions including brines with high temperatures and high sulfur contents these results suggest that iron rich mississippi valley type deposits form from brines expelled from the deepest hottest parts of sedimentary basins

stable isotopic variations of clay minerals a key to the understanding of kupferschiefer type mineralization germany isotopic compositions of silicate minerals and carbonates of selected kupferschiefer samples from the hessian depression and from the lower rhine basin have been studied in detail in the area of the richelsdorf ore district stable isotope analyses of the cu mineralized sections in the kupferschiefer show that the metal enrichment processes are associated with significant changes in the oxygen and hydrogen isotope composition of the clay minerals the isotopic compositions of the 2 size fractions reflect a decrease of approximately 4 in 18o 18 4 to 13 7 and an increase of nearly 50 in d 74 to 25 with decreasing distance from the rote faule zone this isotopic zonation in the kupferschiefer shale is explained by fluid rock interaction with ascending oxidizing hypersaline solutions which transported high amounts of base metals from the lower permian red beds into the kupferschiefer horizon acting as a geochemical trap the estimated isotopic composition of the involved water 18o between 3 0 and 6 5 d between 10 and 3 supports the characterization of the ore bearing solutions as basinal brines internal oxygen isotope fractionation of illite from samples next to rote faule corresponds to a temperature of approximately 130 c which is suggested as the temperature of metal precipitation in the lower rhine basin the metal content does not exceed values commonly observed in black shales enhanced base metal pb zn mineralization is observed only in the bottom section of the kupferschiefer the results of the oxygen and hydrogen isotope analyses of the selected core samples provide no evidence for correlation between isotopic composition of the silicate minerals and the extent of lead and zinc sulphide precipitation futhermore they do not point towards isotopic exchange reactions between clay minerals within the kupferschiefer shale and fluids out of isotopic equilibrium with the investigated mineral phases however it is shown that the lack of detectable interaction between the rock and external fluids as reflected by these data in general coincides with the proposed concept that the base metals pb and zn as well as ba have been coprecipitated from carboniferous formation waters

geochemistry of laterites stability of al goethite al hematite and fe super 3 kaolinite in bauxites and ferricretes an approach to the mechanism of concretion formation

origin of the copper cobalt deposits of the zambian copperbelt an epigenetic view from nchanga the zambian copperbelt is arguably the most significantly mineralized neoproterozoic basin on earth preserving a truly spectacular scale of mineralization in excess of 1 109 t of ore at 2 7 copper has been extracted to date and there are also major cobalt accumulations the origin of these deposits has been hotly debated for more than six decades yet the driving forces that generated this system are poorly understood in particular the relationships between tectonics paleo fluid circulation and ore deposition we present new field and isotopic data for the nchanga deposits in which the bulk of the mineralization is hosted by shale capped feldspathic arenites and arkoses that have undergone recrystallization and hydrothermal alteration within a host rock package controlled by low angle thrust faults by using in situ laser combustion we show for the first time that the range of 34s for copper cobalt ore sulfides 1 to 18 cannot have the same source as diagenetic pyrite 1 to 17 we suggest a new epigenetic model for the formation of these spectacular nchanga orebodies that involves the introduction of metal and sulfate bearing hydrothermal fluids into quartzofeldspathic units during basin inversion with sulfide derived from thermochemical reduction of the sulfate near the site of deposition

lower cambrian paleosols from the cantabrian mountains northern spain a comparison with neogene quaternary estuarine analogues abstract the lower cambrian barrios beds cantabrian mountains consist of a siliciclastic succession deposited in deltaic environments punctuated by intertidal and fluvial systems in the barrios de luna area this succession displays a progradational depositional systems tract that contains linkages between upper offshore tidal sand bars fluvial channels and floodplain environments the uppermost fluvial channels are encased within floodplain or interfluvial deposits some of which develop muddy paleosols the detailed micromorphological scanning electron microscopy sem geochemical and mineralogical studies of their pedogenic profiles indicate the presence of three well differentiated horizons fragmentation and shrinking of the upper horizons originated a network of channel like to vuggy porosity occluded by microlaminated clays cyclically emplaced by tidal floods and seasonal oxidation the middle horizons have concretionary to vermicular textures associated with microbioturbation and bacterial colonization and the lower ones are mottled containing numerous preserved lithorelics the barrios sulfidic ustifluvent paleosols represent short time pedogenic events under semiarid subtropical conditions and support previous studies of cambrian microbial life on subaerially exposed microenvironments

kinetic constraints on illitization reactions and the effects of organic diagenesis in sandstone shale sequences abstract based on water rock interaction modelling and kinetic considerations the present study is aimed at testing the impact of organic matter maturation on two kinds of diagenetic reactions leading to the alteration of the petrophysical properties of sandstones 1 clay mineral conversion to illite with k feldspar being a local potential source of k and 2 dissolution precipitation processes produced in sandstones by the action of water soluble organic species derived from adjacent shales assuming firstly that the chemical reactions take place in closed systems the nature and timing of diagenetic reactions in marine sandstone shale formations were modelled for a 50 120 c temperature range in order to improve understanding of the factors that control the illitization reaction with k feldspar coexisting with aluminous clay illite is modelled here as a muscovite type mineral we tested the effects of an energy barrier on illite growth by allowing or preventing the muscovite illite precipitation reaction to occur while using several illitization reaction rates we also compared the stable mineral parageneses predicted for organic material free systems with those predicted in the case of organic diagenesis release of co 2 ch 4 acetic and oxalic acids similarities and discrepancies between numerical results and natural mineral assemblages suggest that the illitization reaction depends on the nature of the reacting clays kaolinite conversion to end member illite involves high energy conditions 2 kcal mol 1 which are not met when the pore water equilibrates with the mineral matrix from undersaturated conditions in a closed system to overcome this barrier the fluid should be oversaturated with respect to k feldspar an external source of k or a ph increase in an open system is necessary for this reaction no particular effect of organic diagenesis on this reaction was found in the present study on the other hand smectite to illite conversion involves a lower energy barrier and can operate in closed systems where k feldspars are the source of k the maturation of organic matter may speed up the smectite to illite conversion rate by increasing the gibbs free energy of illite growth interactions between sandstone and shale were examined by modelling the transfer of aqueous species of organic origin from shale to sandstone fluid expulsion from shale had little or no effect on diagenesis in adjacent sandstones during each flushing cycle mainly because organic protons and ligands were neutralized in the source rock however the diffusion of shale derived cations through sandstone as organometallic complexes mg ca fe al appears to be an efficient process during carbonate cementation in sandstones where oxidizing conditions enhance the decomposition of such complexes

a model for fibrous illite nucleation and growth in sandstones we have developed a model for the formation of fibrous illite in sandstones where kaolinite is a primary reactant and potassium is derived from in situ k feldspar grain dissolution or imported into the model reference frame illite fiber nucleation and growth are modeled using arrhenius expressions that consider saturation state in addition to temperature and time nucleation occurs on pore walls and muscovite and detrital illite may be defined as energetically favorable substrates the model is integrated with other touchstone models to account for the influence of other diagenetic processes on surface area and reactant volumes and to provide input for permeability simulations we evaluated the illite model performance on two data sets 1 jurassic quartzose samples from offshore mid norway with maximum temperatures ranging from 108 to 173c 226 to 343f and 2 miocene lithic samples from offshore southeast asia that have maximum temperatures ranging from 157 to 182c 315 to 360f the model matches measured abundances of illite kaolinite and k feldspar in both data sets using identical kinetic parameters predicted k ar ages are consistent with available data given uncertainties associated with detrital contaminants although no illite particle size data are available from the analyzed samples modeled crystallite thicknesses from the norway data set are comparable to published measurements of 0 004 to 0 012 m from north sea samples with similar temperature histories

dolomitization of shallow water mixed silicilastic carbonate sequences the lower triassic ramp succession of the transdanubian range hungary abstract the lower triassic succession of the transdanubian range in hungary comprises limestones dolomite marl sandstones and siltstones deposited in tidal flat lagoon and ooid shoal environments on the marginal ramp of the western neotethys seven cores were chosen for petrographic and stable isotope investigations aiming to reconstruct the paragenetic sequence with special regard to the dolomitization and hydrothermal events five lithotypes were differentiated i dolomite ii sandy silty clayey dolomite and dolomarl iii dolomitic siltstone and sandstone iv dolomitic limestone and v limestone in these lithotypes three types of dolomites are present non ferroan replacive ferroan replacive and ferroan cement fabric retentive and fabric destructive non ferroan replacive dolomitization are interpreted to have occurred by seepage reflux supporting evidence includes the presence gypsum and anhydrite in the lower triassic beds stable isotope values of the ferroan dolomite 18o of 10 7 to 4 2 and 13c of 4 8 to 4 7 suggest dolomitization by fluids of relatively high temperature the similar stable isotope values 18o of 9 3 to 5 8 and 13c of 1 9 to 2 5 of the non ferroan dolomite phase suggest that the reflux dolomite was overprinted by this second dolomitization event traces of exotic minerals such as barite chalcopyrite galena and sulphosalts were found as fillings of vugs and fractures in the dolomite cemented sandstone the metals could have been sourced from the underlying permian red sandstone beds the heterogeneous sediment composition had profound impact on the diagenesis of these sedimentary successions

comparative studies of organic matter petrography of the late palaeozoic black shales from southwestern poland abstract there are at least two sapropelic units associated with late palaeozoic black shales in central europe the older unit of late carboniferous age is the lower part of the anthracosia shales in the intrasudetic basin and the younger one is the well known zechstein kupferschiefer in both the foresudetic monocline and the northsudetic basin the first unit is of lacustrine origin while the second one represents deposition in a shallow marine depositional environment both units contain high amounts of organic matter thus being typical black shales the organic matter dispersed in these shales was studied petrographically in general the vitrinite reflectance of the shales studied indicates variable but moderate organic matter maturity 0 68 1 25 equivalent to the oil window detailed microscopic studies of the organic material dispersed in the lower unit of the anthracosia shales showed that liptinite especially alginite is the most abundant component secondary altered organic matter i e solid hydrocarbons rarely occurs organic components together with mineral matter constitute a lacustrine sapropelic association a humic terrestrial association and an intermediary association the character and predominance of alginite and lacustrine sapropelic association are indicative of an open lacustrine depositional environment in general this organic composition is typical of type i kerogen microscopic analysis of the kupferschiefer revealed a mixture of liptinite vitrinite and inertinite macerals and other organic components such as amorphous sapropelic mass asm and solid bitumens the most common organic components are liptinite macerals bituminite and alginite predominate and are diagnostic macerals of this unit the amount of bituminite locally exceeds 85 vol other liptinite macerals such as sporinite and liptodetrinite are present in significantly lower amounts one exception being asm which may be present in higher amounts humic constituents vitrinite and inertinite are rare present in small amounts in the kupferschiefer beds the organic matter composition points to type ii kerogen for this unit

the origin of the kupferschiefer type mineralization in the richelsdorf hills germany as deduced from stable isotope and organic geochemical studies abstract the kupferschiefer horizon in the richelsdorf section federal republic of germany acted as a geochemical trap by accumulating metals from ascending brines chemical composition of the extracted bitumens reflects a drastic change in the degree of oxidation of the organic matter towards rote faule this alteration pattern corresponds with regular changes in the isotopic composition of organic carbon and carbonate as well as with the base metal zonation around rote faule the enrichment of the organic material in 13c suggests the preferential release of isotopically light hydrogen equivalents through progressive degradation and oxidation of organic matter the opposite tendency towards lower 13c and 18o values of carbonate minerals provides evidence for isotopic reequilibration between carbonate and isotopically light oxidizing solutions the occurrence of isotopically heavy organic carbon together with low 13c and 18o values of carbonate suggests that 12c rich co2 generated due to oxidation of organic material may have been a source of carbonate the results reveal a post sedimentary formation of high grade mineralization and associated rote faule by ascending oxidizing brines they are in agreement with the results of mineralogical and geochemical studies which provided evidence for metal precipitation from basinal brines enriched in na and sulphate s the organic geochemical and isotopic data suggest that metal precipitation was caused by thermochemical sulphate reduction with organic matter acting as a reducing agent and proton donor

groundwater dolocretes from the upper triassic of the paris basin france a case study of an arid continental diagenetic facies thick dolomite cemented horizons dolocretes occur within a fluvial sandstone mudstone sequence of late triassic age in the western part of the paris basin france two types of dolomites can be distinguished a nodular dolomitic beds less than a few metres thick which formed within mottled overbank siltstones and mudstones and b massive dolomite up to 16 m thick which occurs in coarse grained channel sandstones and conglomerates the majority of the dolomite consists of a finely crystalline groundmass of dolomicrospar and less commonly dolomicrite glaebules irregular spar filled cracks spheroidal dolomite silicification and vuggy porosity are locally abundant in the massive dolomite in contrast biologically induced micromorphological features such as rhizocretions and alveolar septal fabrics were observed in the thin nodular dolomite beds the dolomite is near stoichiometric well ordered and non ferroan 18o values range from 7 7 to 0 4 o pdb and 18o values range from 5 1 to 1 8 0 pdb and no obvious difference in the stable isotopic composition between both types of dolomites was observed sr isotope ratios range from 0 7101 to 0 7126 and are invariably higher than the contemporary triassic sea water a vadose pedogenic origin for the thin dolocrete layers is indicated by the occurrence of rhizocretions and other biological structures several features however argue against a pedogenic origin for the massive carbonates most notably the absence of biologically induced structures the occurrence in coarse grained channel and not overbank deposits and the great thickness these units are thus interpreted as groundwater in origin phreatic calcretes of quaternary age widespread in inland australia are regarded as a modern analogue for the triassic paris basin dolocretes petrographic observations argue in favour of primary proto dolomite precipitation although early diagenetic replacement of calcite by proto dolomite cannot be ruled out strontium and carbon isotope data of early diagenetic dolocrete cements and oxygen isotope data of early diagenetic silica indicate an entirely non marine continental origin for the groundwaters the poorly ordered and non stoichiometric protodolomite probably underwent stabilization upon further burial resulting in a near stoichiometric well ordered dolomite that clearly lacks evidence for pervasive recrystallization

a comparative analysis of some late carboniferous basins of variscan europe vegetation diversity and pattern changes and their relation to tectono sedimentary histories are compared between selected euramerican late palaeozoic coalfields to understand better the controls on the dynamics of the pennsylvanian terrestrial ecosystems and to demonstrate the problems with comparing data from various basins the analysis is based on data from the following basins of different geotectonic and palaeogeographical positions the cratonic pennines basin the foreland south wales and upper silesia basins and the fault related intra sudetic and central and western bohemia basins the analysis indicates that complex factors are responsible for changes in plant diversity and vegetation patterns these are related to climate tectonics preservation potential sampling biases and the current state of revision of the flora in each basin plant diversity patterns in the basins differ because of local controls and or the character and detail of the available data maximum diversity varies among the basins within the langsettian and duckmantian substages two apparent step like drops in diversity were detected within coal bearing strata of most basins at the duckmantian bolsovian boundary and at the bolsovian asturian boundary further and more prominent falls are related to transitions from coal bearing to non coal bearing mostly red bed strata or vice versa during stephanian times interpretation of climatic signals recorded in the sedimentary successions indicates that westphalian and middle stephanian times were wet intervals whereas early and late stephanian times were drier

fluid rock reaction weakening of fault zones the presence of weak phyllosilicates may explain the low shear strengths of fault zones if they define well developed fabrics the growth of phyllosilicates is favored in meteoric water dominated granitic fault systems where mineral aqueous fluid equilibria predict that modal phyllosilicate will increase via feldspar replacement reactions in deeper more alkaline rock dominated regimes the reactions reverse and feldspars tend to replace phyllosilicates in mg rich mafic rocks however phyllosilicates chlorite biotite can replace stronger framework and chain silicates in both shallower approximately 10 km meteoric h sub 2 o dominated and in deeper alkaline rock dominated regimes where these phyllosilicates precipitate in active fault zones they contribute directly to reaction softening because low temperature deformation of phyllosilicates is not governed by frictional processes alone but can occur by pressure independent dislocation glide the strength of phyllosilicate rich fault rocks can be low at all depths low strain rate creep during interseismic periods can align phyllosilicate grains in foliated gouge and phyllonites where preferred orientations are strong and contiguity of phyllosilicates is large strengths of rocks within fault zones may approach minimum strengths defined by single phyllosilicate crystals fault zones containing localized high concentrations of phyllosilicates with strong preferred orientations in well defined folia can exhibit aseismic slip especially where mafic mg rich rocksmore occur along the fault like parts of the san andreas fault 104 refs 6 figs 1 tab less

the role of detrital anhydrite in diagenesis of aeolian sandstones upper rotliegend the netherlands implications for reservoir quality prediction the rotliegend upper permian reservoir interval in the southern permian basin spb contains low permeability streaks corresponding to anhydrite cemented intervals an integrated study was conducted using core cuttings thin sections and well log data from a gas exploration well and two geothermal wells that target the zone of interest this study aims at understanding the origin and nature of these low permeability streaks as well as their impact on reservoir properties and to establish a predictive model of their spatial distribution high resolution xrf core scanning analysis allowed to extrapolate spot observations in thin sections to the entire core diagenetic history includes grain rearrangement and anhydrite haematitic clay coatings dolomite rims quartz overgrowths kaolinite and second generation carbonates as cementing phases coupling of all data reveals the detrital origin of the anhydrite gypsum grains which were deposited together with the coarse grained sand fraction in an aeolian sandflat environment such partially or completely dissolved grains acted as local sources of anhydrite cement and as nuclei for precipitation explaining its preferential occurrence in coarsegrained laminae thick gypscretes in the vicinity likely supplied the anhydrite gypsum grains a conceptual model is proposed including the location of nearby gypscretes and the prevailing west southwest aeolian transport direction on the southern rim of the spb

the role of migrating oil field brines in the formation of sediment hosted cu rich deposits oil field brines commonly contain ppm quantities of zn pb and h 2 s but negligible quantities of cu theoretical analysis of the water rock interactions expected during migration through evaporitic and red bed sequences suggests that these reducing oil field brines can become transformed into far more oxidized fluids capable of transporting cu pb zn and sulfate and of forming sediment hosted cu rich deposits calculation of the chemical mass transfer accompanying reaction of a typical reducing brine with anhydrite hematite and quartz followed by the assemblage quartz k feldspar muscovite hematite chlorite and cuprite reveals that the aqueous phase becomes greatly undersaturated with respect to sphalerite galena chalcopyrite bornite pyrite and pyrrhotite as it achieves log f sub o 2 values well above the magnetite hematite buffer consistent with saturation with respect to anhydrite hematite and chalcocite and ore forming concentrations of copper and sulfate consequently evaporites are not only possible sources of salinity and oxidized sulfur for evolving basinal brines but may be crucial to the development of the f sub o 2 conditions required to transport cu in ore forming concentrations reaction of the oxidized brine with organic matter approximated by graphite and diagenetic pyrite results in precipitation of the zonation sequence chalcocite bornite chalcopyrite and pyrite with variable amounts of hematite covellite sphalerite and galena depending on the relative rates of reaction of the graphite and pyrite

stratigraphic and petrographic comparison of the creta and kupferschiefer copper shale deposits stratigraphic and petrographic characteristics of the creta copper shale deposit in the flowerpot shale of southwestern oklahoma are compared with the betterknown rudna deposit in the kupferschiefer of south western poland at creta early diagenetic mineralization is indicated by 1 copper sulfide replacement of large spores and of pyrite 2 lack of compaction of replaced spores relative to unreplaced spores 3 enclosure of uncompacted mud and copper sulfides by early matrix gypsum and 4 location of the ore bed within a thick sequence of fine grained low permeability sediments this contrasts sharply with evidence of late diagenetic copper mineralization in the kupferschiefer at rudna mineralization of copper shales appears to occur over a wide time scale relative to diagenesis of the host sediments

incised valley fill stratigraphy of the upper cretaceous succession proximal orange basin atlantic margin of southern africa seismic stratigraphic analysis of a grid of 7860 km of shallow seismic sleevegun data plus lithological and biostratigraphic foraminifera data interpreted from core and sea bed samples have been integrated into a detailed geological model for the upper cretaceous succession of the proximal orange basin emphasis has been placed on the palaeoenvironmental interpretation of incised valley fill sequences of this succession seismic reflection geometries for the middle albian to lower cenomanian interval show that the entire coast was dominated by aggradational fluvial braid plain facies the lower turonian to upper coniacian succession marks the appearance of repeated major incision into the exposed coastal plain by large fluvial drainage networks this succession is characterized by fourth order fluvial to marine sequences with valley incision up to 25 km wide and 70 m deep detailed palaeoenvironmental analysis indicates periodically waterlogged highly reducing fluvial floodplain environments with valley systems that were flooded to create wave dominated estuaries major fluvial activity during the turonian was in an area that lies offshore of the present day swartlintjies to groen river mouths in the southern part of the orange basin during the coniacian the site of fluvial activity changed to the central orange basin offshore of the present day buffels river these observations contradict previously published views that a dominant orange river drainage system existed since the albian at a position coincident with the present day mouth

radiation and extinction patterns in permian floras from north china as indicators for environmental and climate change abstract permian continental sequences from north china contain previously unrecognized episodes of plant radiation and elevated extinction the earliest extinction in the lower shihhotse formation roadian guadalupian records a 45 floral species loss and is tentatively correlated with global extinctions amongst dinocephalian reptiles two younger extinctions are dated by correlating the illawara reversal and palaeomagnetic polarity sequences from shanxi province against global palaeomagnetic history missing data from the shanxi sequence are evaluated using a novel approach estimating likely maximum and minimum sequence changes that provide age estimates for post illawara events in north china the second extinction in the middle upper shihhotse formation is more significant and is dated to the mid capitanian with a loss of 56 of plant species coinciding with two phases of volcanism of the emeishan large igneous province in south china previously linked to the mid capitanian marine mass extinction the youngest extinction in the upper upper shihhotse formation late capitanian to mid wuchapingian is catastrophic and represents the end of range in the sequence changes in sedimentary facies suggest it to be related to global climatic warming and drying other viable causal mechanisms for the extinction episodes include plate motion and collision global climate change volcanism and biological competition

searching for travertines calcretes and speleothems in deep time processes appearances predictions and the impact of plants common models for modern calcite precipitation in and around caves soils springs and streams involve co 2 supplied by thick high p co 2 biogenic soils which were probably thin or non existent before vascular plants indeed plant influenced chemical weathering might have caused accelerated terrestrial carbonate production from the devonian onwards however terrestrial carbonates have also been documented from the archaean proterozoic cambrian ordovician and silurian mechanisms which could have caused non marine carbonates to precipitate without organic rich soils are described and some geological events likely to have influenced non marine carbonate precipitation up to the origin of vascular plants are highlighted as organisms have evolved so have the petrographic characteristics of non marine carbonates some examples of this are also given here

fluid rock interactions in the rhine graben a thermodynamic model of the hydrothermal alteration observed in deep drilling abstract deep drilling at soultz sous forets france on the western flanks of the rhine graben has penetrated hercynian granite underlying mesozoic sediments veins are present throughout the drilled granite and there are flows of warm water localized in fractures within the granite detailed mineralogical study of core material from the research drillhole eps 1 has been carried out in order to assess the alteration history of the soultz granite part of the crystalline basement of the rhine graben the results of the study have been used in conjunction with analyses of present day fluids from deep drilling in the rhine graben reported in the literature to model thermodynamically the alteration process and in particular to evaluate if it is likely to be continuing today reaction path calculations show that if deep basinal brines such as are known from sediments of the central rhine graben react with hercynian granite they will form different alteration assemblages depending on both the path that the fluid follows e g descending through sediments or through granite and the extent of preexisting alteration of the granite the calculations suggest that fluid now sampled from granite in eps 1 achieved its peak temperature c 200 c while within permo triassic sandstone the modeling also indicates that present day fluids from the rhine graben system are capable of producing the vein quartz and possibly also the baryte veins seen in the eps 1 core much of the alteration present in the granite in the vicinity of veins and fractures may have been produced by a flow regime similar to that prevailing today

a stable isotope and organic geochemical study of the relationship between the anthracosia shale and kupferschiefer mineralization se poland abstract there are at least two mineralized horizons that occur in association with the rotliegendes red bed sediments of central europe the first is the well known kupferschiefer at the top of the rotliegendes the second is the upper anthracosia shale of the north sudetic depression in the middle part of the red bed section in the present study upper anthracosia shale has been investigated by use of various geochemical methods and results have been compared with those obtained from previous studies of the kupferschiefer both mineralized horozins show the same organic geochemical phenomena and isotope variations interpreted as a result of post depositional migration of mineralizing fluids originating from red bed sediments both organic rich horizons acted as reducing traps for migrating metals therefore the processes that led to the base metal emplacement in the ore grade areas of the kupferschiefer are shown to have an universal character also with regards to the upper anthracosia shale the patchy occurrence of cu mineralization in the anthracosia shale horizons is related to the fault controlled movement of mineralized fluids the cu dominated composition of mineralization is explained by the simplicity of the base metal source preferentially rotliegendes formation waters of mostly meteoric origin new data on the isotopic compositions of c in organic materials and of c and o in carbonates combined with an organic geochemical study of a non mineralized section through the lower anthracosia shale provide information on the sedimentary environment and conditions during diagenesis the changes during sedimentation of the lower anthracosia shale are related to subsidence the thickness of water column sedimentation rate redox potential and paleoclimatic conditions in the center of the profile from the lower anthracosia shale the amounts of calcite and organic carbon concomitantly increase which can be explained by the development of anoxic bottom waters due to enhanced subsidence of the basin the water column might have temporarily increased resulting in increased biomass production and better preservation of organic material in the lower and the upper parts of the profile the biomass production was significantly lower due to increased rate of sedimentation and probably decreasing water column

geochemical modeling of the zoned footwall alteration pipe hellyer volcanic hosted massive sulfide deposit western tasmania australia the mineralogy of hydrothermal alteration assemblages siliceous core chlorite zone sericite zone in the footwall pipe of the hellyer volcanic hosted massive sulfide vhms deposit is controlled mainly by the temperature ph and redox state of the hydrothermal fluids based on the results of our numerical modeling the zoned alteration system could have formed by a combination of water rock interaction and cooling with a siliceous core predicted to form at the center of the conduit passing outward to a chlorite dominated zone a sericite rich zone and finally grading out to unaltered andesite these mineralogical changes relate to a gradual evolution of fluid chemistry water rock ratio ph and temperature from the core to the margin of the system initial temperatures were probably close to 350 degrees c and the hydrothermal fluids were reduced h2s dominated at low temperatures 200 degrees c a peripheral alteration zone consisting mostly of k feldspar chlorite sericite and hematite is predicted to form this low temperature zone has not been recognized at hellyer but elevated k2o contents and local k feldspar development have been noted at other vhms deposits suggesting that this zone might form at low temperatures and low water rock ratios in the footwall of vhms deposits if the existence of barren outer k feldspar alteration zones is confirmed the findings could have important implications for exploration specifically with regards to distinguishing ore related alteration zones from barren alteration systems

isotopic constraints on fluid evolution and precipitation mechanisms for the boleo cu co zn district mexico stable and radiogenic isotope composition of stratiform cu co zn mineralization and associated sedimentary rocks within the boleo district of the miocene santa rosalia basin baja california sur constrains the evolution of seawater and hydrothermal fluids and the mechanisms responsible for sulfide and oxide deposition stable isotope geochemistry of limestone and evaporite units indicates a strong paleogeographic influence on the chemistry of the water column near shore limestone at the base of the boleo formation is characterized by modified marine carbon 13cpdb 6 0 to 4 4 and oxygen 18osmow 19 5 to 26 2 isotope composition due to the influx of 13c and 18o depleted fluvial water sulfate sulfur isotope composition 34scdt 17 21 to 22 3 and 18osmow 10 7 to 13 1 for basal evaporite and claystone facies are similar to miocene seawater strontium isotopes are less radiogenic than expected for miocene seawater due to interaction with volcanic rocks low s c ratios high mn contents and sedimentological evidence indicate the basin water column was oxidizing the oxygenated basin restricted sulfide precipitation to within the sedimentary pile by replacement of early diagenetic framboidal pyrite and pore space filling by cu co zn sulfides to produce disseminated sulfides quartz mn oxide oxygen isotope geothermometry constrains mineralization temperature between 18 and 118 c sulfur isotopes indicate the following sources of sulfide 1 bacterial sulfate reduction within the sedimentary pile produced negative 34s values 20 in framboidal pyrite and 2 bacterial sulfate reduction at high temperature 80 118 c within the sedimentary pile during the infiltration of the metal bearing brines produced cu co zn sulfides with negative but close to 0 34s values isotope modeling of fluid rock reaction and fluid mixing indicates 1 sedimentary and marine carbonates 13c 11 6 to 3 2 and 18o 19 0 to 21 8 precipitated from basin seawater pore water that variably mixed with isotopically depleted meteoric waters and 2 hydrothermal calcite 13c 7 9 to 4 3 and 18o 22 1 to 25 8 formed by dissolution and replacement of authigenic marine calcite by downward infiltrating metalliferous brine and brine sediment exchange that prior to reaction with calcite had mixed with isotopically depleted pore water the downward infiltration of metalliferous brine is inferred from lateral and stratigraphic metal distributions and from the concentration of cu sulfides along the upper contact of pyrite bearing laminae the co existence and textural relationships among framboidal pyrite base metal sulfides carbonate and mn fe oxides including magnetite within mineralized units are consistent with carbonate replacement and high temperature bacterial reduction within the sedimentary pile occurring simultaneously below a seawater column under predominantly oxygenated conditions

revisiting the paleogene climate pattern of east asia a synthetic review abstract east asian paleogene climates have long been regarded as controlled by the planetary wind system which might result in a climate pattern with three latitudinally distributed zones two humid zones located separately in the north and south were lithologically designated by coals and oil shales while an arid zone in the middle was represented by red beds and evaporites because the middle arid zone was located along 30 n paleolatitude its presence had been further linked with a then subtropical high however this long standing model has recently been challenged by growing evidence from petrology sedimentology paleontology paleobiogeography paleoclimatology and climate modeling here we review the primary data from these disciplines and reinterpret their climate significances to revisit the east asian climate pattern during the paleogene petrologically while the occurrence of coals and or oil shales is accepted as an indicator for overall humid climates that of red beds and or evaporites is highly equivocal to exclusively indicate perennial arid climates unless their origins are carefully investigated in reality generic red beds merely represent an oxidizing environment not essentially associated with a single specific climate type meanwhile evaporites although typically precipitated in arid environments may be deposited in either perennial dry or seasonal monsoonal climates there is no solid evidence so far to convincingly support that the landscape of the so called middle arid zone was dominated by desert and or steppe under a then subtropical high during most of the paleogene the plant function type study additionally suggests that the middle arid zone appears to be lack of xerophytic vegetation even though some xerophytic or sclerophyllous plant taxa did sporadically occur interestingly paleozoological data show that the paleogene mammalian faunas were somewhat equably distributed over east asia strongly suggesting the evident absence of a critical biogeographical or climatic barrier stretched across the middle arid zone as the planetary wind model implied in contrast to the planetary wind model monsoonal or monsoon like paleogene climates have been broadly reported from the northern middle and southern east asia as well as adjacent regions of russia and kazakhstan if only the indicators for humid climates are considered simply due to the uncertainty of those for perennial arid climates east asia must have had a relatively dry region in the continental interior during the late eocene to oligocene transition likely caused by the continentality and or the rain shadow effect along with the global cooling the monsoonal interpretation is highly in agreement with the evidence from floras faunas basin analyses and modeling experiments and well explicates the paleogene climate distribution and seasonal dynamics of east asia however further studies will be largely needed to verify whether uniformly according to the modern criteria the paleogene climates of the east asia interior can be accurately attributed to the arid category

comparison of outcrop and subsurface sandstone permeability distribution lower cretaceous fall river formation south dakota and wyoming quantification of permeability structure in outcrop reservoir analogs documents the distribution of flow units and barriers important for reservoir management and simulation differences in burial history and diagenesis of the outcrop analog and the subsurface reservoir must be quantified however before outcrop permeability data can be used to model subsurface strata appropriately a case study of the lower cretaceous fall river formation shows that permeability differences between facies are accentuated by diagenesis and permeability variation increases with the extent of burial diagenesis the fall river formation which is exposed in outcrop around the black hills uplift in wyoming and south dakota usa produces oil from fluvial and estuarine valley fill sandstones in the adjacent powder river basin outcrop sandstones were buried to 2 km before being uplifted at the end of the cretaceous whereas reservoir sandstones remained at depths of 2 4 km throughout the tertiary the permeability of outcropping fall river sandstones has a log normal distribution the main controls on permeability in outcrop sandstones are 1 ductile grain content 2 grain size both properties being controlled by the energy of the depositional environment and 3 hematite cement an uplift related diagenetic feature not present in the subsurface hematite was preferentially precipitated along zones of permeability contrast including sequence boundaries complicating the determination of changes in primary depositional permeability at important flow unit boundaries in contrast the permeability of fall river reservoir sandstones at a depth of 4 km has a bimodal distribution and is controlled by ductile grain content grain size and quartz cement volume quartz cementation and compaction due to ductile grain deformation were more extensive in the estuarine facies resulting in a greater permeability reduction during burial diagenesis than was observed in fluvial sandstones abundant stylolites developed in sandstones with clay partings or mud clasts features that are common in estuarine sandstones the stylolites acted as an internal source of silica sandstones near the stylolites typically have low permeability that probably resulted from above average volumes of quartz cement diagenesis increased the coefficient of variation of permeability in all facies in the subsurface this diagenetic overprint should be considered if outcrop permeability data are used to model a subsurface reservoir having a very different burial history

experimental study of dissolution rates of actinolite in cacl2 hcl h2o up to 400 c abstract actinolite dissolution rates in aqueous hcl and aqueous cacl2 hcl have been measured at temperatures ranging from 25 to 400 c at 23 mpa under conditions far from equilibrium using a flow through reactor the relative release rates for the various elements in actinolite due to breaking of metal oxygen bonds are all different all of the release rates vary with temperature and ph the release rate of si increases as temperature rises from 20 to 300 c but then decreases at higher temperatures other metallic ions such as ca mg fe and al are all released more rapidly than si at temperatures between 25 and 300 c but more slowly at temperatures 300 c the ratios of mca msi and mmg msi in the effluent at 200 c are close to the stoichiometric proportions of these elements in actinolite but differ from stoichiometric values at temperatures both above and below 200 c actinolite dissolution in aqueous hcl at 100 c yields element ratios close to stoichiometric values in the mineral but again the ratios vary at higher and lower temperatures our experiments demonstrate that under conditions far from equilibrium dissolution rates depend on both ph and the activity of aqueous mi zi where zi is the valence of the metal mi in the mineral and mi zi refers to ca2 mg2 or al3 the ion exchange model suggests that metal hydrogen ion exchange reaction on the surface is a key step for mineral dissolution and that a si rich mi deficient precursor complex is formed on the mineral surface at temperatures r a exp e a rt a h zi a mi zi where is the order with respect to the ratio of activity of hydrogen ions and dissolved metal ions mi the mg h exchange coefficient is 0 55 at 100 c the apparent activation energy ea 14 4 kj mol and a 0 23 10 3 m cm 2 s 1 our results show that water properties vary strongly within the critical region which affects the dissolution mechanism thus the release rates for various elements at temperatures above 300 c are different from those at temperatures below 300 c high resolution transmission electron microscopy hrtem and scanning electron microscopy sem studies indicate that a fe al rich si deficient layer is formed on the surface at temperatures above 300 c x ray photoelectron spectroscopy xps analyses show that the surface layer that formed by reaction with aqueous hcl at 400 c is a hydrated silicate composed of si oh and mi oh as well as si o and mi o bonds

groundwater ferricretes from the silurian of ireland and permian of the spanish pyrenees abstract haematite nodule horizons occur in alluvial lacustrine deposits from the mill cove formation silurian of dingle ireland and the unidad roja superior permian of the spanish pyrenees these horizons generally less than 1 m thick are not associated with palaeosol profiles but are hosted by laminated or structureless bioturbated mudstones to sandstones the sequences contain weakly developed calcrete profiles the haematite nodules are interpreted as having formed around fluctuating water tables and are analogous to present day groundwater ferricretes laterites or plinthites fe2 mobilised during periods of reducing groundwaters was segregated into ferric oxide nodules during falls in the water table or during influxes of oxygenated meteoric waters the prevailing climate during deposition of both sequences was probably semi arid and the presence of ferricrete like horizons is not evidence of humid climates the horizons represent early diagenetic effects not related to prevailing soil moisture regime

petrology and mineralogy of laterites in southern and eastern australia and southern africa abstract field observations of laterites in southern and eastern australia and in southern africa reveal a variety of ferruginous horizons and crusts referred to herein as ferricretes their geomorphic and stratigraphic relationships with bedrock sediments and soils indicate formation throughout long intervals of geological time in landscapes which are also characterised by zones of bleached and iron mottled materials there does not appear to be a genetic relationship between the ferricretes and the weathered zones in the sense of the so called laterite profile many of the ferricretes form part of existing soil profiles petrographic studies of a variety of ferricretes have identified three broad categories a ferruginised bedrock b fe impregnated and indurated sediments including sands clays and organic sediments and c ferricretes of complex sedimentary and pedogenic origin type a and b ferricretes characteristically have simple fabrics often with single generation secondary fe oxides type c ferricretes have complex fabrics with many generations of hematite goethite and in some variants gibbsite in the matrix and in ferruginous clasts and pisoliths maghemite is a common constituent of the pisoliths the characteristics of ironstone gravelly duplex soils which are common in the contemporary landscapes provide the framework for a model involving multiple stages in the development of these ferricretes the origins of the various secondary oxide minerals in ferricretes are assessed on the basis of knowledge about the formation of these minerals in pedogenic environments examples are given of the intricate patterns of distribution of the minerals in thin section from which definitive data may be obtained on environmental conditions for integration with field based geomorphic studies

groundwater fluctuations and footslope ferricrete soils in the humid tropical zone of southern cameroon reference ecos article 2007 065view record in web of science record created on 2007 11 28 modified on 2016 08 08

origin of the nchanga copper cobalt deposits of the zambian copperbelt the zambian copperbelt forms the southeastern part of the 900 km long neoproterozoic lufilian arc and contains one of the world s largest accumulations of sediment hosted stratiform copper mineralization the nchanga deposit is one of the most significant ore systems in the zambian copperbelt and contains two major economic concentrations of copper and cobalt hosted within the lower roan group of the katangan supergroup a lower orebody copper only and upper orebody copper and cobalt occur towards the top of arkosic units and within the base of overlying shales the sulfide mineralogy includes pyrite bornite chalcopyrite and chalcocite although in the lower orebody sulfide phases are partially or completely replaced by malachite and copper oxides carrollite is the major cobalt bearing phase and is restricted to fault propagation fold zones within a feldspathic arenite hydrothermal alteration minerals include dolomite phlogophite sericite rutile quartz tourmaline and chlorite quartz veins from the mine sequence show halite saturated fluid inclusions ranging from 31 to 38 wt equivalent nacl with homogenisation temperatures thtot ranging between 140 and 180 c diagenetic pyrites in the lower orebody show distinct relatively low 34s ranging from 1 to 17 whereas arenite and shale hosted copper and cobalt sulfides reveal distinctly different 34s from 1 to 12 for the lower orebody and 5 to 18 for the upper orebody there is also a clear distinction between the 34s mean of 12 1 3 3 n 65 for the upper orebody compared with 5 2 3 6 n 23 for the lower orebody the 13c of dolomites from units above the upper orebody give 13c values of 1 4 to 2 5 consistent with marine carbon however dolomite from the shear zones and the alteration assemblages within the upper orebody show more negative 13c values 2 9 to 4 0 and 5 6 to 8 3 respectively similarly shear zone and upper orebody dolomites give a 18o of 11 7 to 16 9 compared to lower roan dolomites which show 18o of 22 4 to 23 0 two distinct structural regimes are recognized in the nchanga area a weakly deformed zone consisting of basement and overlying footwall siliciclastics and a moderate to tightly folded zone of meta sediments of the katangan succession the fold geometry of the lower roan package is controlled by internal thrust fault propagation folds which detach at the top of the lowermost arkose or within the base of the overlying stratigraphy and show vergence towards the ne faulting and folding are considered to be synchronous as folding predominantly occurred at the tips of propagating thrust faults with local thrust breakthrough the data from nchanga suggests a strong link between ore formation and the development of structures during basin inversion as part of the lufilian orogeny sulfides tend to be concentrated within arenites or coarser grained layers within shale units suggesting that host rock porosity and possibly permeability played a role in ore formation however sulfides are also commonly orientated along but not deformed by a tectonic fabric or hosted within small fractures that suggest a significant role for deformation in the development of the mineralization the ore mineralogy hydrothermal alteration and stable isotope data lend support to models consistent with the thermochemical reduction of a sulfate and metal enriched hydrothermal fluid at the site of mineralization there is no evidence at nchanga for a contribution of bacteriogenic sulfide produced during sedimentation or early diagenesis to the ores

hydrocarbon bearing fluid inclusions in fluorite associated with the windy knoll bitumen deposit uk abstract hydrocarbon bearing fluid inclusions in fluorite associated with an outcropping bitumen deposit at windy knoll derbyshire have been analysed in situ using a combination of microthermometry fourier transform infrared ftir microspectrometry and ultraviolet uv microscopy the inclusions in these samples can be considered as a series with two endmembers aqueous inclusions containing a low density vapour phase and inclusions containing liquid oil with no detectable aqueous phase the majority of the inclusions are mixed types containing both aqueous and liquid hydrocarbon phases although microthermometry distinguishes at least two different aqueous fluids with varying homogenization temperatures and salinities the oil fraction is cogenetic and trapped together with just one fluid a low salinity low calcium brine with an average homogenization temperature of 134 c the majority of the liquid hydrocarbon bearing inclusions fluoresce bright blue under uv illumination with peaks around 475 nm characteristic of paraffinic oils the ftir spectra of these inclusions are dominated by peaks assigned to aliphatic c h bonding however inclusions have also been found which display a fluorescence typical of the red shift associated with less mature oils the ftir spectra display peaks assigned to c o c o and o ch2 bonding this study presents new data on the in situ analysis of hydrocarbon bearing fluid inclusions from this important area of natural petroleum seepage and ore mineralization the results suggest a direct link between the fluid inclusion populations the outcropping bitumens and fluorite deposition

pennsylvanian continental cyclothem development no evidence of direct climatic control in the upper freeport formation allegheny group of pennsylvania northern appalachian basin abstract the occurrence of lacustrine carbonates in the allegheny group upper middle pennsylvanian continental cyclothems of the northern appalachian basin has been attributed to climatic alternation of wet coal deposition and dry carbonate deposition periods however we present evidence from facies associations coal and carbonate petrography and carbonate stable isotope geochemistry for a uniformly wet climate throughout deposition of one of the earliest continental cyclothems the upper freeport formation uff we propose a depositional model comprising a large wetland complex drained by an anastomosed fluvial system containing a mosaic of channels freshwater siliciclastic and carbonate lakes and peat bogs swamps on a siliciclastic floodplain carbonate phases represent bio induced precipitates modified by lake dynamics and not evaporative deposits absence of covariant isotopic trends between 18o and 13c and a relatively small range of 18o values 1 9 to 6 4 pdb that are close to or lighter than predicted paleoprecipitation for the pennsylvanian equatorial regions indicate hydrologically open short residence time lake systems in support of our sedimentary model combined sedimentologic and isotopic data do not indicate reduced effective moisture precipitation evaporation during intervals of limestone deposition the uff lakes developed in a relatively wet climate zone without significant episodic closure due to climatically induced water deficit lithologic patterns within the uff cyclothem are primarily attributed to the evolution of anastomosed fluvial systems controlled by subsidence in an active foreland basin rather than to short term climatic change or eustacy

palaeosols in westphalian coal bearing and red bed sequences central and northern england westphalian a c coal bearing strata and red beds in the pennine basin of central and northern england contain a wide variety of palaeosols in coal bearing facies associations alluvial gley semi gley organic and rare well drained palaeosols reflect the predominance of poor drainage conditions during deposition in red beds more evolved ferruginous and ferallitic palaeosols testify to free drainage conditions during deposition catenary relationships can be inferred between most of the palaeosols in both facies associations providing further information on the palaeogeomorphology of the depositional systems and assisting in the understanding of the environments and conditions of coal seam formation

diagenesis of shallowly buried cratonic sandstones southwest sinai egypt abstract in spite of their age quartzose and feldspathic lower carboniferous sandstones deposited on the arabian shield in western sinai remain friable and porous average of 19 maximum of 25 except for strongly cemented ferricretes and silcretes these fluvial and shallow marine sandstones were not buried more than 1 5 km until late cretaceous and younger time when the deepest rocks reached 2 5 km owing to shallow burial depths and episodic exposure meteoric water dominated the pore system for most of geologic time iron oxides had multiple diagenetic stages and yield carboniferous and late cretaceous paleomagnetic signatures and oxygen isotopic data for authigenic quartz sparry calcite and kaolinite yield meteoric signatures the most significant diagenetic changes were 1 cementation by iron oxide that locally reaches 40 in groundwater ferricretes 2 reduction in porosity to 19 from an assumed original porosity 45 19 porosity was lost by compaction and 7 by cementation 3 generation of diagenetic quartzarenites by the loss of 7 detrital feldspar by kaolinization and dissolution and 4 development of three thin mature silcretes apparently by thermal groundwaters some outcrop samples have halite and gypsum cements of young but uncertain origin recycled from topographically higher younger rocks or from aerosols mature silcretes are strongly cemented by microcrystalline quartz multiply zoned syntaxial quartz and originally minor opal quartz overgrowths in most sandstones average only 2 2 but display a variety of textures and in places overprint isopachous opal now dissolved grain coats these features have more in common with incipient silcrete cement than normal burial quartz cement most silica was imported in groundwater

alteration halos in the tordillos sediment hosted copper deposit of the neuquen basin argentina abstract the tordillos sediment hosted cu deposit is located in the north central sector of the huincul high structure in the neuquen basin argentina it is hosted in sedimentary rocks of the huincul formation an upper cretaceous redbed sequence deposited in a fluvial environment field mapping petrography and chemical analysis of the authigenic clay sulfate carbonate and sulfide minerals at tordillos have identified systematic variation in alteration and paragenesis with time and with respect to the main feeder zones the alteration associated with cu mineralization provides evidence of a multistage infiltration of fluids spatially associated with paleo hydrocarbon migration driven by tertiary tectonism early diagenesis formed hematite kaolinite and calcite1 that have been preserved in the reddish brown mudstones later influx of hydrocarbons and warm reduced formation waters from deeper reservoir rocks is associated with dissolution of early cements and clasts and precipitation of new minerals in the thickest paleo channels of the huincul formation dissolution of early cements hematite kaolinite calcite1 and barite1 and clasts locally increased the porosity of sandstones up to 24 and destroyed hematite that changed sandstones and conglomerates from red to yellowish grey bitumen impregnations are abundant along with calcite2 3 and 4 pyrite minor montmorillonite quartz overgrowth and coarse barite2 crystals with primary organic fluid inclusions at the contact with hydrocarbon tubes the mno enrichment of calcite in stages 3 and 4 reflects their precipitation under reduced conditions grey and greenish grey sandstones with montmorillonite v hematite smectite chlorite group minerals and pyrite respectively are exposed between the reddish brown mudstones and the yellowish grey sandstones and conglomerates the grey and greenish grey horizons are representative of abrupt changes in eh ph conditions between regional early oxidizing solutions responsible for the formation of early diagenetic redbeds and later infiltration of reducing fluids responsible for alteration of sedimentary rocks copper mineralization is located inside the altered sandstones and conglomerates zones forming halos surrounding vertical tubes containing bitumen these tubes are interpreted as the conduits through which migrated hydrocarbons formation waters and subsequent chloride and metal rich fluids in these places pyrite calcite and barite cements of the altered rocks have been dissolved and replaced by copper rich sulfides and then by late supergene cu minerals interconnection among stacked permeable paleo channels in the mid section of the huincul formation facilitated the migration of several generations of fluids during early diagenesis hydrocarbon up flow and exhumation of the neuquen group resulting in the development of alteration halos and cu mineralization that can be used both in outcrop and drill core during exploration for sediment hosted cu mineralization

origins of stratiform and stratabound fe cu zn horizons in the lower proterozoic moran lake group labrador central mineral belt zn cu and fe are concentrated as stratiform and stratabound sulphide rich beds in the lower proterozoic warren creek formation moran lake group central labrador upper member sedimentary rocks have a hydrothermal like fe enrichment but a dominantly hydrogenous signature as indicated by high al2o3 relative to sio2 and high al and fe relative to mn the upper member shales and sulphide rich beds were deposited as fe rich pelagic sediments the paucity of mn and abundance of fe in typical shale samples and lack of cu pb and zn fractionation in stratiform massive sulphide beds that contain up to 4702 ppm zn 533 ppm cu and 15 ppm pb suggest that deposition occurred in restricted brine pools i e cu and zn were precipitated rapidly and were not fractionated stratabound sphalerite mineralization containing 3 7 zn and 121 ppm cu but no pb was deposited in a porous lithology at the top of the warren creek formation and represents a unique style of metal concentration the stratiform deposits proba

review and update of the applications of organic petrology part 1 geological applications abstract organic petrology developed as coal petrology at the beginning of the 20th century dedicated mainly to the study of coals because of their utilization in industry coal petrology was then considered a branch of coal science later with the development of specialized nomenclature classification of coal components and the standardization and improvement of analytical microscopical methods this discipline expanded in interests and name becoming organic petrology organic petrology carries a broader context being as well a tool applied in the study of dispersed organic matter in sedimentary rocks due to its importance in exploration for fossil fuel resources at present organic petrology is a discipline widely recognized for its role in fundamental and applied research with respect to both coal utilization and in geosciences throughout the 20th century several important monographs have been published on the discipline of organic petrology including stach s textbook of coal petrology 1st edition 1935 2nd 1975 3rd 1982 updated as the more general organic petrology by taylor et al 1998 more recently the text applied coal petrology the role of petrology in coal utilization was published by suarez ruiz and crelling 2008 this review is the first in a two part review series that describes and updates the role of organic petrology in geosciences a second part complementing this one and focused on the applications of organic petrology to other scientific fields will follow

processes that control mineral and element abundances in shales abstract a shale s composition can be used to infer physical chemical and biological processes that have acted on it over its life history and this knowledge is used to surmise conditions at the time when each process was active this review lists the most important processes that control shale mineral and element abundances during each of the five stages of its life history 1 during weathering transport and deposition the most important processes are chemical weathering hydraulic sorting and mixing adsorption reverse weathering and incorporation of organic matter and biominerals 2 during early diagenesis the most important processes are exchange across the water sediment interface compaction microbial respiration mineral transformations and concretion formation 3 during burial diagenesis the most important processes are compaction catagenesis and metagenesis and mineral transformations 4 during exhumation the most important processes are decompaction brine invasion groundwater penetration and microbial respiration 5 during weathering the most important processes are organic matter oxidation mineral oxidation and hydrolysis groundwater transport and disaggregation this classification of processes provides a way to envision how concurrent and consecutive processes that occurred over a shale s life history have affected its mineralogy and chemical composition

nodular silcretes of the cypress hills formation upper eocene to middle miocene of southern saskatchewan canada siliceous nodules in the upper eocene to middle miocene cypress hills formation in southern saskatchewan formed on the distal portions of an extensive braidplain the nodules are similar to silcretes described elsewhere in the literature but their morphology and occurrence suggests that they are of a rare variety the silcretes are discrete equant to disc shaped nodules 1 3 cm thick and up to 15 cm long the silicretes form horizontal discontinous layers parallel to bedding within an unweathered profile void spaces and fractures within the nodules are lined or filled with drusy quartz the silcretes contain less than 0 07 tio2 the tio2 sio2 al2o3 and tio2 sio2 fe2o3 ratios are similar to values obtained from nodules formed in an arid to semi arid environment based on comparison with modern silcretes this interpretation is confirmed by independent sedimentological and palaeontological climatic evidence for an arid to semi arid climate throughout oligocene time in the western canadian plains

diagenesis and evolution of the lower eocene red bed sandstone reservoirs in the dongying depression china abstract the diagenetic evolution of the lower eocene red bed high quality reservoirs in the dongying depression was systematically investigated through an integrated petrographic petrophysical fluid evolution and thermal history analysis the reservoirs experienced several phases of diagenesis including compaction carbonate cementation gypsum and ankerite cementation feldspar and carbonate dissolution quartz overgrowth cementation and clay mineral cementation and transformation an early alkaline diagenetic environment caused significant cementation of calcite and gypsum in the reservoir sandstone units near the sandstone mudstone contacts acidic formation fluids caused widespread dissolution of the feldspar and carbonate cements leading to synchronous occurrences of primary intergranular pores and acidic dissolution pores from the middle parts of the reservoir sandstone units to the sandstone mudstone contacts dissolution wanes gradually with ferro carbonate progressively diminishing migration of exogenetic thermal fluid along faults may have contributed to the gradual decrease in dissolution and the gradual increase in cementation from the lower part to the upper part of fault blocks the alternating alkaline and acidic diagenetic environments and the distribution of diagenetic products caused the development of the high quality red bed reservoirs in the middle part of the thick layered sandstone units in the lower part of fault blocks because of the spatial and temporal relationships between the diagenetic stages and their products lithological traps of a diagenetic origin were developed in the red bed reservoirs

geochemistry of the kupferschiefer poland cu pb and zn are the main metals occurring in sulfides in the kupferschiefer they are arranged in the three distinct zones around rote faule in the order cu pb and zn copper zones are enriched in transition metals i e ag ni co v and mo ranging from 600 to 1500 ppm they are concentrated especially in the bottom part of black shale re is associated with mo the re mo ratio in cu pb and k castaingites is about 1 70 in copper zones near the contact with lead zones au platinum group metals pgm and u are concentrated ranging from traces to several hundred ppm the main mechanism of concentration of transition metals was catalytic autooxidation and dehydrogenation of organic matter the noble metals form either independent minerals or are present in organic matter and thucholite in the lead zones at the contact with cu zones an increased content of ag 100 1500 and hg 5 800 ppm is present the average hg content for the black shale of the zone is 61 ppm a natural gas exploited from the rotliegendes beneath the kupferschiefer carries in aerosols significant amount of pb cu mn fe ag and hg this suggests the rotliegendes as a pathway or as a source of metals for the kupferschiefer the presence of k castaingite intergrown with silvinite kcl may suggest k dominated brines as the mineralizing fluids

climato environmental controls on clay mineralogy of the hettangian bajocian successions of the mecsek mountains hungary an evidence for extreme continental weathering during the early toarcian oceanic anoxic event abstract clay mineralogy has been successfully used in palaeoclimatic interpretation of jurassic rocks in the mecsek zone hungary the clay mineral assemblages of the hettangian sinemurian fluvial and shallow marine coal bearing siliciclastic rocks gresten facies mecsek coal and vasas marl formations comprise predominantly illite smectite i s mixed layer minerals illite ill and kaolinite kao with the presence of berthierine and or chlorite these clay mineral suites suggest a humid subtropical climate with short term climate changes of high and low rainfall and a high supply of terrigenous clastics to the basin in the pliensbachian part of the sequence studied which is composed of predominantly hemipelagic mudstones allgau facies with intercalations of redeposited sandstone and limestone bodies the hosszuheteny calcareous marl mecseknadasd sandstone and kecskehat limestone formations are predominantly made up of illite and very little kaolinite and i s mixed layer minerals kao ill 1 suggesting a humid climate and intense continental weathering possibly related to the oceanic anoxic event in contrast rocks of the bajocian komlo calcareous marl formation contain high proportions of i s mixed layer mineral and illite with sparse occurrence of kaolinite kao ill 0 or kao ill

alluvial fan and wetland interactions evidence of seasonal slope wetlands from the silurian of south central wales uk distal environs of the ludlow age trichrug formation from south central wales uk detail deposition on the outer fringe of an ephemeral debris flow dominated alluvial fan debrites and subordinate sheetflood deposits are interbedded with sporadic thin sandstone dominated heterolithic units deposited in shallow ephemeral ponds in the axial valley the latter slope wetland system fringed the permeable alluvial fan deposits being maintained by streamflow precipitation and ground water recharge a prolonged high water table is indicated by low chroma intervals interpreted as the result of gleying a variety of redoximorphic indicators including colour mottling and ferricrete concretions are evidence of iron mobilization and concentration associated with a seasonally fluctuating water table the slope wetlands were colonized periodically by skolithos generating organisms most likely to have been arthropods the widespread occurrence of redoximorphic indicators and ferricrete contrasts markedly with calcrete vertisols in penecontemporaneous continental deposits lower old red sandstone of the region it is likely that the alluvial fan toe area was the site of a wetland depression which maintained a high though fluctuating water table in contrast the alluvial channel reaches of the surrounding drainage network were significantly better drained with floodplains prone to wetting and drying and vertisol palaeopedogenesis

preserved organic matter and miospores in buried middle devonian givetian paleosols indicators of weathering oxidation and maturity abstract preserved organic matter and miospores from buried middle devonian givetian cumulate hydromorphic floodplain paleosols in a fluvio deltaic setting reflect the intensity of pedogenic processes as indicated by pedologic evidence amorphous organic material fungal clusters cuticle and miospores were examined in the paleosols and compared with organic matter in unweathered parent material the paleosols include protosols gleysols and a calcisol and range from mature to immature strongly oxidized to strongly gleyed and are with and without calcareous nodules the indicators of increasing soil maturity are 1 increased abundance of amorphous organic residue and fungal clusters relative to miospores and cuticle and 2 increased ripping edge degradation and fungal bacterial and mineral alteration of miospores

mineralogy and trace element geochemistry of gas shales in the united states environmental implications abstract this paper presents a compilation of published mineralogic and trace element data from nine gas shales in the united states formations analyzed include the antrim bakken barnett eagle ford haynesville marcellus new albany utica and woodford these mineralogic and trace element data can be used to assess the potential for environmental impacts during hydraulic fracturing impacts addressed in this study include 1 the potential for acid rock drainage generation during gas shale weathering 2 the distribution of trace elements in gas shales and comparison with regulatory guidelines and 3 the implications for environmental management of well cuttings the use of the mineralogic data to assess the fracability of the gas shales is also considered compilations of the mineralogy and geochemistry of gas shales can be a valuable resource for managing real and perceived environmental problems associated with their exploitation comprehensive environmental assessment to fully address these issues in addition to other potential environmental impacts will require collection and collation of additional data on the mineralogy and trace element geochemistry of gas and other hydrocarbon producing shales

coastal laterite profiles at po chue tam lantau island hong kong the origin and implication abstract seven lithostratigraphic units were identified from a 180 m long up to 6 m high coastal cliff exposure at po chue tam lantau island hong kong they include older slope wash debris flow deposits raised beach deposits slope debris stream flood gravels hyperconcentrated flood gravels and younger slope wash laterite profiles had developed in the older slope wash and the debris flow deposits the profile in the former includes from bottom to top slightly weathered but ferruginized bedrock a mottled pebble cobble zone and a vesicular laterite horizon in contrast the profile in the latter consists of only debris flow deposits that contain detrital laterite fragments and underlying slightly weathered bedrock the deposits have been cemented and indurated there are no genetic links between the main zones in the laterite profiles this is evidenced by the sharp bed contact the absence of a leaching zone in the bedrock and the general constraint of the main zones by stratigraphic sequences the present study highlights that both relative accumulation of iron from pedogenic weathering and absolute accumulation of iron from a lateral source through groundwater and or surface water occur concomitantly and superimpose upon each other this leads to the development of a polygenetic laterite profile rather than a single monogenetic profile caution should be exercised to ascertain the origin of laterite before attempting to explore the paleoclimatic imprints or reconstruct landscape evolution laterites of both pedogenic and groundwater origins can represent paleosurfaces that required prolonged subaerial exposure quiescent tectonism and climatic stability

experimental study of the hydrothermal formation of kaolinite kaolinite was hydrothermally precipitated starting from amorphous aluminosilicates with si al ratio from 1 8 to 0 76 at temperatures of 150 175 200 225 and 250 c at time periods varying from 6 h to 60 days the solutions were analysed for ph si al and k and their saturation state was calculated by using the computer program solmineq 88 the solids were studied by surface area xrd and dta tg analyses kaolinite was the only crystalline phase found in the products of the runs and its formation and crystallinity depended on time temperature and si al ratio of the starting material the kaolinite yield increased as starting material was aged for longer times products synthesized at higher temperature contain more kaolinite which was more crystalline than in the experiments carried out at lower temperature the gel with si al 0 99 produced the most disordered kaolinite and better crystallinity was obtained from products richest in al or si the process of kaolinite formation was the result of two stages during the first one aggregates of domains having a kaolinite like structure were formed the second stage corresponded to the formation of hexagonally outlined platy crystals the formation rates indicated that the first stage was approximately one order of magnitude faster than the second stage with average activation energies of 82 5 kj mol 1 and 71 5 kj mol 1 respectively si al ratio of the starting material exerted only a slight influence on the activation energies the precipitation rates obtained for the second stage were consistent with literature data and may be considered precipitation rates of kaolinite in hydrothermal environments

lateritization and ground water alteration phenomena in the triassic budra formation south western sinai field and laboratory investigations of the triassic budra formation of wadi budra south west sinai have demonstrated the existence of surface pedogenic laterites developed within overbank facies of fluviatile sediments during times of hiatus the laterite profiles up to 7 m thick comprise a zone of high iron concentrations 21 47 73 17 which includes a concretionary unit and either overlies a zone of slightly mottled host rock or rests directly upon unaltered sandstone a pallid zone is noticeably absent the primary depositional horizontal fabric of the finely laminated sediments of the overbank facies has strongly influenced the final fabric of the laterite the pronounced alternations of iron rich pisolitic and iron deficient laminae highlight the influence of inherent fabric primary bedding on pedogenesis the micromorphology of the laterites is characterized by bimasepic plasmic fabrics abundant elongate voids partially infilled with cryptocrystalline kaolinite and an abundance of randomly oriented skew planes illuviation of clay minerals to considerable depths is evident sesquioxidic and kaolinitic glaebules concentrated within the concretionary units of the laterite have a flattened ellipsoidal shape and occur as both massive and concentrically structural varieties at gebel mussaba salama to the north zoned iron mineralization occurs at various levels within the fluviatile sandstones which underlie the overbank facies this is interpreted as being a non pedogenic ground water alteration phenomenon induced by a rising water table within the buried alluvial channels iron mineralization probably records minor fluctuations of the water table during standstill periods lateritization in the triassic budra formation provides important evidence that the widely recorded late triassic lateritization and bauxitization event of the neighbouring east mediterranean countries extended south to the continental areas bordering the tethyan ocean

seismic facies analysis of westphalian sequences of the southern north sea abstract differing seismic facies are observed from within the westphalian sequences of the southern north sea a review of published synthetic seismograms and seismic data from known coal bearing basins establishes seismic facies types and their relationships similar reflection character is recognized from westphalian sequences in the southern north sea and lithologies confirmed by borehole information probable sand silt or clastic prone upper coal measures westphalian c d stages and coal prone lower and middle coal measures westphalian a b and part c stages can be defined and mapped providing information on the regional distribution of source and reservoir rocks and stratigraphic plays it is suggested that sand prone channel complexes or clastic dominated areas within the mainly a b stages can be recognized and mapped providing information on migration pathways and stratigraphic plays

diagenetic history of fluvial and lacustrine sandstones of the hartford basin triassic jurassic newark supergroup usa abstract the early introduction of clays into continental sandstones has been attributed to mechanical infiltration by percolation of clay rich surface waters into grain framework or cutans formed from pedogenic processes the discovery of pedogenic mud aggregates as traction load mud in ancient fluvial deposits suggests that permeability and porosity of terrigenous sandstones can be influenced at deposition and control early diagenetic patterns this study compares diagenesis in fluvial subaerially exposed sandstones with lacustrine subaqueous sandstones in a triassic jurassic continental rift basin hartford basin newark supergroup diversity of diagenetic minerals and sequence of diagenetic alteration can be directly related to depositional environment the fluvial sandstones in the new haven arkose east berlin formation and shuttle meadow formation of the hartford basin are dominated by concretionary calcite and early calcite cement infiltrated clays illite smectite pedogenic mud aggregates smectite and illite smectite grain coating clays illite hematite illite chlorite hematite quartz overgrowths late stage carbonate cements calcite ferroan calcite pore filling clays illite kaolinite with minor amounts of smectite smectite chlorite illite smectite and hematite however pedogenic processes in these fluvial sandstones retarded the development of quartz and feldspar overgrowths and carbonate authigenesis as well as the quality of diagenetically enhanced porosity dark gray black lacustrine subaqueous sandstones and mudrocks in the east berlin and shuttle meadow formations are dominated by pyrite concretionary dolomite and early dolomite cement radial grain coating clays smectite chlorite illite smectite late stage carbonate cements dolomite ferroan dolomite ankerite albite and pore filling clays smectite chlorite illite smectite illite chlorite clay minerals exist as detrital mechanically infiltrated and neoformed clay the fluvial sandstones in the new haven arkose are dominated by illite the east berlin and shuttle meadow formations are dominated by illite in the fluvial sequences and smectite chlorite and illite smectite in the lacustrine sandstones dolomite ferroan dolomite and ankerite are restricted to lacustrine sandstones whereas calcite and ferroan calcite to fluvial sandstones albite predominantly precipitated in lacustrine rather than fluvial environments through intergranular dissolution of plagioclase by acidic meteoric water dissolution of unstable mafic minerals and sodium rich brines and evaporites developed from groundwater albitization and carbonate cementation are the most pronounced late stage diagenetic processes affecting both types of hartford sandstones

weathering indices as climate proxies a step forward based on congo and sw african river muds abstract despite the influence of other geological and geomorphological factors chemical weathering at the earth s surface is strongly controlled by climate thus a measure of weathering intensity determined from soils or sediments should provide information about the climatic conditions associated with their formation available geochemical and mineralogical data on modern fluvial and marine muds from different regions of southern africa and its atlantic continental margin are used to review the links between sediment composition and climatic properties together with the possible causes of variance although river muds may not be generated exclusively in a single sedimentary cycle and erosion and weathering processes do not necessarily take place in a spatially homogeneous way significant relationships between mineralogical and geochemical signatures of river mud and rainfall in the corresponding catchment area were recognised our study shows that the composition of clay is strongly influenced by climatically driven weathering whilst coarser mud fractions tend to be more affected by provenance grain size hydraulic sorting and recycling in the marine environment the climatic signal may be lost even in clay because of hydraulic fractionation authigenic mineral growth and mixing with foreign particles given the ubiquitous character of fluvial muds and the easy and non expensive methods available for separating and analysing clay fractions their geochemical fingerprints represent a most precious source of information concerning climate any geochemical parameter used as a regional proxy of climate however still requires that the diversity of geological geomorphological and biological factors that affect its value are cautiously considered

the hydrothermal transformation rate of kaolinite to muscovite illite batch reactor experiments were performed to measure the rate of the reaction 1 5 kaolinite k muscovite h 1 5 water at temperatures ranging from 250 to 307 c in these experiments the rate of kaolinite conversion to muscovite illite was monitored as the rate of production of h runs were performed in small volume 50 ml titanium hydrothermal reactors charged with well crystallized georgia kaolinite indian ruby muscovite and 25 ml of kcl solution 0 5 2 0 m both solids and solutions were monitored at specific intervals throughout each experiment the determined rate law is dmh dt dmk dt amm k mk k mh where mk and mh are the concentrations of potassium ion and hydrogen ion k and k are the forward and reverse rate constants in kg m 2 sec 1 am is the total surface area of the muscovite in m2 and m is the mass of the solution in kg the initial rate method was used to find k and k was found by fitting data to an integrated rate equation temperature functions for the rate constants are in k 12 90 1 87 104 t r2 0 98 and in k 6 03 1 21 104 t r2 0 95 the activation energies ea for the forward and reverse reaction are 155 15 kj mol 1 and 101 10 kj mol 1 respectively

ferricrete formation and relief inversion an example from central sudan abstract the development of a ferricrete in relationship to the structural and morphological evolution is demonstrated by the example of jebel howag kordofan sudan products of deep lateritic weathering have been reworked by mass wasting processes in this material a ferricrete developed in a low landscape position by lateral migration and absolute enrichment of iron subsequently relief inversion brought the hard ferricrete into its present high position during the miocene this ferricrete plateau was disrupted by faulting which has been used to indicate the minimum age of the ferricrete the composition and structure of the jebel howag ferricrete are identical with those of ferricretes formed on deep lateritic weathering profiles compositional differences such as al goethite and high v contents distinguish such ferricretes from ferruginized sediments

diffusion and reaction controlled cu pb zn ore mineral precipitation in a reducing system a model applied to the pattern of ore mineral precipitation in the kupferschiefer and other black shales the major ore minerals in black shale hosted copper deposits typically have a zoned distribution in this paper a numerical model that couples the processes of chemical reaction and interdiffusion of metals and sulfur is applied to reproduce the pattern of mineral precipitation in a reducing black shale environment the results indicate that under reducing conditions discrete regions of sulfide precipitation develop and with time these regions evolve toward the source of the metals the model shows that the observed spatial distribution of the different sulfides may be a consequence of reaction and diffusive supply of metals and sulfur rather than changes in eh although this result does not prove that variations in eh and ph were not responsible for the zoned mineral distribution in black shales it does illustrate the need to consider reactive transport modeling when one attempts to model ore deposition in black shales comparison of these results with published data on the kupferschiefer black shale hosted copper deposits reveals a number of similarities including a similar pattern of sulfide distribution and the same sense of asymmetry in plots of sulfide concentration vs distance

reactive flow models of the anarraaq zn pb ag deposit red dog district alaska the red dog ore deposit district in the brooks range of northern alaska is host to several high grade shale hosted zn pb deposits due to the complex history and deformation of these ore deposits the geological and hydrological conditions at the time of formation are poorly understood using geological observations and fluid inclusion data as constraints numerical heat and fluid flow simulations of the anarraaq ore deposit environment and coupled reactive flow simulations of a section of the ore body were conducted to gain more insight into the conditions of ore body formation results suggest that the ore body and associated base metal zonation may have formed by the mixing of oxidized saline metal bearing hydrothermal fluids 200 c with reducing hs rich pore fluids within radiolarite rich host rocks sphalerite and galena concentrations and base metal sulfide distribution are primarily controlled by the nature of the pore fluids i e the extent and duration of the hs source forward modeling results also predict the distribution of pyrite and quartz in agreement with field observations and indicate a reaction front moving from the initial mixing interface into the radiolarite rocks heuristic mass calculations suggest that ore grades and base metal accumulation comparable to those found in the field 18 zn 5 pb are predicted to be reached after about 0 3 my for initial conditions 30 ppm zn 3 ppm pb 20 deposition efficiency

mineralogical changes in organic rich posidonia shale during natural and experimental maturation abstract the diagenesis of clay minerals and organic matter in posidonia shale has been typically studied independently of each other here the results of an experimental investigation focused on the mineralogical changes of organic rich shales are presented to understand the dissolution and precipitation processes of minerals as a function of thermal maturity three core samples of posidonia shale hils syncline germany with increasing natural thermal maturity wickensen wic 0 53 r0 dohnsen doh 0 73 r0 haddessen had 1 45 r0 were reacted in experimental aliquots of 0 3 m kcl solution rock fluid ratio 1 5 sealed in gold capsules at 300 c and 120 bars for 27 days following treatment the calculated maturities easy r0 values of the two samples with the lowest vitrinite reflectance values indicates thermal enhancement wic 1 14 r0 doh 1 15 r0 whereas the most mature sample remained unchanged had 1 45 r0 the educts and products were analysed by transmission electron microscopy tem combined with energy dispersive x ray spectroscopy edx and x ray diffraction xrd in all experiments kaolinite and carbonates were extensively dissolved whereas quartz underwent partial dissolution reaction products consisted of lath shaped mg2 rich 1md illite together with k feldspar in the form of sanidine trioctahedral saponite precipitated only in the oil producing sample wic along with less sanidine and 1md illite the unexpected formation of metastable 1md illite at 300 c instead of stable 2m1 illite is attributed to low k reactivity due to either depletion of this element by the early formation of sanidine and or the chemical effects of organic acids that shift the stable phase into the k poor stability field the precipitation of saponite and the limited sanidine and 1md illite formation in sample doh is attributed to high dolomite content and hence mg2 availability along with the more extensive release of hydrocarbon compounds and further reduction of k reactivity in this sample it is concluded that the neoformation of metastable phases 1md illite and trioctahedral smectite observed in short term higher temperature experiments may differ significantly from prolonged mineral transformations occurring under natural conditions

predictive modeling of co2 sequestration in deep saline sandstone reservoirs impacts of geochemical kinetics abstract one idea for mitigating the increase in fossil fuel generated co 2 in the atmosphere is to inject co 2 into subsurface saline sandstone reservoirs to decide whether to try such sequestration at a globally significant scale will require the ability to predict the fate of injected co 2 thus models are needed to predict the rates and extents of subsurface rock water gas interactions several reactive transport models for co 2 sequestration created in the last decade predicted sequestration in sandstone reservoirs of 17 to 90 kg co 2 m 3 to build confidence in such models a baseline problem including rock water chemistry is proposed as the basis for future modeling so that both the models and the parameterizations can be compared systematically in addition a reactive diffusion model is used to investigate the fate of injected supercritical co 2 fluid in the proposed baseline reservoir brine system in the baseline problem injected co 2 is redistributed from the supercritical sc free phase by dissolution into pore brine and by formation of carbonates in the sandstone the numerical transport model incorporates a full kinetic description of mineral water reactions under the assumption that transport is by diffusion only sensitivity tests were also run to understand which mineral kinetics reactions are important for co 2 trapping the diffusion transport model shows that for the first 20 years 20 a after co 2 diffusion initiates co 2 is mostly consumed by dissolution into the brine to form co 2 aq solubility trapping from 20 to 200 a both solubility and mineral trapping are important as calcite precipitation is driven by dissolution of oligoclase from 200 to 1000 a mineral trapping is the most important sequestration mechanism as smectite dissolves and calcite precipitates beyond 2000 a most trapping is due to formation of aqueous hco 3 ninety seven percent of the maximum co 2 sequestration 34 5 kg co 2 per m 3 of sandstone is attained by 4000 a even though the system does not achieve chemical equilibrium until 25 000 a this maximum represents about 20 co 2 dissolved as co 2 aq 50 dissolved as hco 3 aq and 30 precipitated as calcite the extent of sequestration as hco 3 at equilibrium can be calculated from equilibrium thermodynamics and is roughly equivalent to the amount of na in the initial sandstone in a soluble mineral here oligoclase similarly the extent of trapping in calcite is determined by the amount of ca 2 in the initial oligoclase and smectite sensitivity analyses show that the rate of co 2 sequestration is sensitive to the mineral water reaction kinetic constants between approximately 10 and 4000 a the sensitivity of co 2 sequestration to the rate constants decreases in magnitude respectively from oligoclase to albite to smectite

a multistage origin for kupferschiefer mineralization new re os age determinations on mineralized material from the polish kupferschiefer elucidate the timing of mineralization and thus the likely mechanisms of ore deposition three mineralization parageneses were analysed a chalcocite as pore space filling in sandstone b disseminated cu mo mineralization in shale and c massive bedded copper sulphides the resulting ages fall into two ranges 245 2 1 6 264 7 1 8 ma and 162 3 0 8 184 3 2 2 ma these results substantiate previous age determinations although no upper triassic ages were found in this study some of the younger ages for the mineralization could represent alteration and recrystallization of existing sulphides the results confirm that mineralization took place in several stages from soon after kupferschiefer sediment deposition in the upper permian and for at least 100 m y after until at least the cretaceous the genesis of the mineralization can be explained by the episodic release of hydrothermal fluids from the subsiding adjacent southern permian sedimentary basin although the relative importance of each successive mineralizing event for introducing additional metals is as yet unknown

rare earth elements and carbon oxygen isotopes of calcite from the tongjiachong cu deposit south china implications for fluid source and mineral precipitation abstract calcite is a major gangue mineral in many types of hydrothermal deposits and its chemical and carbon oxygen isotopic signatures can shed light on the metallogenic evolution the tongjiachong cu deposit located in the northern margin of the yangtze block in south china is hosted by dolostone of the ediacaran doushantuo formation empirical geothermometric calculation indicates that the pre ore chlorite was formed at 265 305 c copper mineralization occurs mainly as veinlets in a calcite chalcopyrite bornite ankerite assemblage exsolution lamellae of chalcopyrite from bornite indicate that both minerals were formed coevally at 200 250 c mineral chemical analysis on the syn ore hydrothermal calcite from tongjiachong suggests that all the calcite samples are enriched in rare earth elements and yttrium reys rey 53 7 119 9 ppm they have similar y ho 38 3 42 3 and varying la ho 21 8 86 7 and display consistent convex paas normalized rey patterns the distinct positive eu anomalies 2 38 3 45 and lack of yb anomalies 0 92 1 05 suggest initial fluid temperatures of 250 to 420 c and calcites deposition temperatures of dolomite samples from the dolostone ore host show a marine carbonate c o isotopic affinity 13cpdb 4 0 to 2 7 18osmow 19 8 to 20 2 comparatively the hydrothermal calcite contains lower 13cpdb 7 4 to 6 1 and 18osmow 14 1 to 14 8 and display a positive 13cpdb vs 18osmow correlation simulated calculations of water rock w r interactions and ore geological constraints suggest that the initial fluids were likely originated from organic rich formation water we proposed that w r reactions may have been the main drive for calcite precipitation at tongjiachong whilst decreasing temperature and w r reactions may have led to the chalcopyrite precipitation

the rožna uranium deposit bohemian massif czech republic shear zone hosted late variscan and post variscan hydrothermal mineralization three major mineralization events are recorded at the ro na uranium deposit total mine production of 23 000 t u average grade of 0 24 u 1 pre uranium quartz sulfide and carbonate sulfide mineralization 2 uranium and 3 post uranium quartz carbonate sulfide mineralization 1 k ar ages for white mica from wall rock alteration of the pre uranium mineralization style range from 304 5 5 8 to 307 6 6 0 ma coinciding with the post orogenic exhumation of the moldanubian orogenic root and retrograde metamorphic equilibration of the high grade metamorphic host rocks the fluid inclusion record consists of low salinity aqueous inclusions together with h2o co2 ch4 co2 ch4 and pure ch4 inclusions the fluid inclusion paragenetic and isotope data suggest that the pre uranium mineralization formed from a reduced low salinity aqueous fluid at temperatures close to 300 c 2 the uraniferous hydrothermal event is subdivided into the pre ore ore and post ore substages k ar ages of pre ore authigenic k feldspar range from 296 3 7 5 to 281 0 5 4 ma and coincide with the transcurrent reorganization of crustal blocks of the bohemian massif and with late stephanian to early permian rifting massive hematitization albitization and desilicification of the pre ore altered rocks indicate an influx of oxidized basinal fluids to the crystalline rocks of the moldanubian domain the wide range of salinities of fluid inclusions is interpreted as a result of the large scale mixing of basinal brines with meteoric water the cationic composition of these fluids indicates extensive interaction with crystalline rocks chlorite thermometry yielded temperatures of 260 c to 310 c during this substage uranium was probably leached from the moldanubian crystalline rocks the hydrothermal alteration of the ore substage followed or partly overlapped in time the pre ore substage alteration k ar ages of illite from ore substage alteration range from 277 2 5 5 to 264 0 4 3 ma and roughly correspond with the results of chemical u pb dating of authigenic monazite 268 50 ma the uranium ore deposition was accompanied by large scale decomposition of biotite and pre ore chlorite to fe rich illite and iron hydrooxides therefore it is proposed that the deposition of uranium ore was mostly in response to the reduction of the ore bearing fluid by interaction with ferrous iron bearing silicates biotite and pre ore chlorite the th data on primary mostly aqueous inclusions trapped in carbonates of the ore substage range between 152 c and 174 c and total salinity ranges over a relatively wide interval of 3 1 to 23 1 wt nacl eq gradual reduction of the fluid system during the post ore substage is manifested by the appearance of a new generation of authigenic chlorite and pyrite chlorite thermometry yielded temperatures of 150 c to 170 c solid bitumens that post date uranium mineralization indicate radiolytic polymerization of gaseous and liquid hydrocarbons and their derivatives the origin of the organic compounds can be related to the diagenetic and catagenetic transformation of organic matter in upper stephanian and permian sediments 3 k ar ages on illite from post uranium quartz carbonate sulfide mineralization range from 233 7 4 7 to 227 5 4 6 ma and are consistent with the early tethys central atlantic rifting and tectonic reactivation of the variscan structures of the bohemian massif a minor part of the late variscan uranium mineralization was remobilized during this hydrothermal event

chemical mass transfer modelling of ore forming hydrothermal systems current practise and problems abstract chemical mass transfer modelling is a numerical approach to predicting the progress of multicomponent fluid rock reactions in natural hydrothermal systems based on thermodynamic data for minerals and fluid species quantitative simulations of hydrothermal wall rock alteration and ore mineral deposition can be used to develop and test geological models for ore formation which are a basis for mineral exploration and resource assessment in practice the application of thermodynamic mass transfer modelling to specific ore forming systems faces two main problems even for the limiting assumption of local equilibration between fluids and minerals the first problem relates to the geometry of fluid rock interaction where the scheme of the model must be adjusted to the geological question of interest one dimensional reactor models defining reaction progress as a function of integrated fluid flux along a path through a chemically reactive rock do not necessarily provide a more realistic description of chemical mass transfer than simple titration models without temporal and spatial dimension because in most ore depositing systems the fluids are partially channelized by structures like veins or faults the efficiency of metal extraction at the ore deposition site is commonly determined by a sensitive balance between fluid focusing on one hand and wall rock reaction promoting ore mineral precipitation on the other an example of gold and scheelite mineralization associated with mesothermal quartz veins illustrates how ore deposition and alteration zoning parallel to the main fluid flow direction in partially channelized systems can be described by a two dimensional multibox model the second problem relates to the extent and quality of thermodynamic data explicit consideration of fe bearing silicate solid solutions is essential for predicting realistic mass balance in complex fluid silicate sulphide reactions associated with hydrothermal ore formation although a high level of internal consistency of multicomponent data sets has been achieved by simultaneous fitting of multiple thermodynamic and equilibrium measurements significant inconsistencies persist among the most comprehensive data compilations published for the three main groups of species relevant to hydrothermal ore deposits aqueous species in high temperature aqueous brines silicate oxide carbonate minerals including fe mg silicates and sulphur bearing minerals including sulphides and sulphates discrepancies between thermodynamic predictions and observed brine composition and mineral assemblages in the salton sea geothermal system suggest that the redox scale for rock forming silicates may be inconsistent with that of sulphides and aqueous s c o h species this analysis is preliminary but illustrates the importance of field testing of thermodynamic data particularly for hydrothermal conditions between 150 and 450 c which lie between the high temperatures of reliable equilibrium experiments among rock forming minerals 500 c and the low temperatures of many experiments defining the thermodynamics of aqueous species mostly

a polygenetic palaeosol from the silurian wenlock of southwest ireland a problematic palaeosol unit caps a thick basalt at the top of the clogher head formation dunquin group late wenlock silurian in the dingle peninsula southwest ireland the main part of the unit consists of an altered calc alkaline basalt with a fine clay assemblage of chlorite corrensite and smectite probably resulting from weathering during wenlock times the uppermost part of the unit consists of detrital silicates which were admixed by bioturbation and well defined burrow fills are present the underlying weathered basalt was possibly truncated before the detrital horizon was deposited and finally the whole unit underwent a phase of surface water gleying a catenary relationship existed locally with the pseudo gley developed lower in the landscape while contemporaneous basalts in topographically higher better drained areas largely escaped the effects of gleying these now exhibit reddened tops the complex history and the possiblity of the incompleteness of the profile makes accurate assessment of the soil climate function difficult however the occurrence of calcrete bearing palaeosols in the overlying mill cove formation supports the view that the basalt was weathered under a sub humid or semi arid climate considering the alteration of the dunquin group to actinolite prehnite grade the preservation of the smectite is highly unusual there is no evidence for its origin due to more recent weathering or interstratal neoformation it is thus interpreted as a relict product of the original weathering phase

hydrochemistry of the saline groundwaters of the lower mersey basin permo triassic sandstone aquifer uk saline groundwater occurs at depth in the triassic sandstones of the northern end of the cheshire basin in northwest england major and minor ion data suggest that the origin of the salinity is dissolution of evaporite deposits the salinity probably developed in an interval following the tertiary inversion of the basin which would have allowed faulted contact between the sandstones and the overlying evaporite sequence of the mercia mudstone group isotope evidence suggests the saline waters to have been considerably diluted by presumably dispersive mixing with a meteoric water recharged under cool and therefore quaternary climatic conditions comparison with other uk permo triassic basin brines suggests the merseyside waters are not unusual except in terms of the importance of exchange reactions and dilution by quaternary recharge waters these factors are due to the shallow maximum burial depth of the aquifer and the preservation of smectites and also to the geometry of the aquifer and its low permeability faults in the light of the water chemistry data it is suggested in a slight modification of the proposal of naylor et al q geol soc lond 146 685 699 1988 that the cheshire basin mineralization resulted from mixing of the relatively oxidized so4 rich evaporite brines with the reduced so4 poor metal rich barich coal measures brines which were expelled through faults from the coal measures during basin inversion some degree of oxyhydroxide stripping of the sandstones by the coal measures brines would have enhanced metal concentrations the water resulting from the mixing of brines would have been far from equilibrium and the barite and sulphide precipitation followed along the faults

mesozoic and cenozoic sandstone hosted copper deposits in south china mesozoic and cenozoic sandstone hosted copper deposits in south china are confined to the variegated rock formation of the faulted basins the intermontane basins and piedmont basins around a copper bearing old land the variegated rock formation is generally of fluviolacustrine delta facies shore facies and shore cauce facies the ore bodies are stratiform occurring in the light coloured beds of the variegated rock formation the mineralization comprises chalcocite bornite chalcopyrite native copper covellite pyrite and hematite showing obvious zonation the associated profitable elements in the ore are mainly silver lead zinc molybdenum selenium and uranium the copper deposits are believed to have been formed through three processes of enrichment i e weathering copper bearing weathered crust was formed as a result deposition source bed formed and diagenesis ore body formed the variegated rocks with cu ag pb zn u mo cl and organic carbon anormalies and a great deal of pyrite distributed in the faulted basins around the cu bearing old land are recognized as the most favourable area for copper ore exploration

warwickshire group pennsylvanian red beds of the canonbie coalfield england scotland border and their regional palaeogeographical implications late carboniferous red beds 700 m thick at outcrop and in the subsurface of the canonbie coalfield can be assigned to the warwickshire group they are preserved within the axial part of the solway syncline and are divisible into the eskbank wood canonbie bridge sandstone and becklees sandstone formations sedimentation largely took place on a well drained alluvial plain characterized mainly by early primary oxidation of the strata large northerly flowing braided river systems were common with overbank and floodplain fines deposited lateral to the channels soils formed during intervals of low sediment aggradation the canonbie succession includes some of the youngest carboniferous rocks preserved in the uk correlation of the eskbank wood formation is equivocal but using petrographical heavy mineral zircon age dating and palaeocurrent data the canonbie bridge sandstone formation can be unambiguously correlated with the halesowen formation of warwickshire the pennant sandstone formation of south wales and the offshore boulton formation this suggests that southerly derived detritus travelled considerable distances from the variscan highlands of brittany and or central germany across the southern north sea and uk areas to a position some hundreds of kilometres north of that previously recognized the becklees sandstone formation has much in common with the salop formation of the english midlands it appears to have no preserved equivalent elsewhere in the uk or in the uk sector of the southern north sea but resembles stratigraphically higher parts of the southern north sea succession seen in the dutch sector

distinguishing early groundwater alteration effects from pedogenesis in ancient alluvial basins examples from the palaeogene of southern portugal colour mottling and horizons of secondary carbonates are common in ancient alluvial sequences and are normally interpreted as pedogenic features they have been used to assess palaeoclimates soil drainage conditions and deposition rates palaeogene alluvial deposits in the sado and lisbon basins of portugal exhibit prominent colour variations and mottle patterns as well as carbonate accumulations both at the bases of fining upwards cyclothems and as thick units up to 20 m capping alluvial megasequences however these colour and carbonate features are interpreted as the products of shallow saline reducing groundwaters unrelated to pedogenesis such non pedogenic products are easily mistaken for soil formed ones and criteria for differentiating the two are reviewed to assist interpretations in other alluvial deposits key criteria are thickness gradational tops and bases absence of soil horizon features occurrence in coarser alluvium and prevalence of hydromorphic colour and mottling patterns

transport of rare earth elements by hydrocarbon bearing brines implications for ore deposition and the use of rees as fluid source tracers abstract low temperature 100 160 c hydrocarbon bearing brines mobilize ree at concentrations up to several thousand ppm total rare earth elements ree at el hammam morocco the major element chemistry na ca mg and temperature of the fluids in this system are consistent with those of oil field brines in contrast ree concentrations in the fluid suggest a significant element input from a magmatic source spatially related lamprophyres predating the formation of el hammam share a similar trace element signature therefore hydrocarbon bearing basinal brines seem to have leached some of these elements through fluid rock interaction from the lamprophyres supporting the ability of oil field brines to mobilize not only base metals as in mississippi valley type mvt deposits but also rare earth elements the stability constants of ree aqueous complex at temperatures of 100 160 c the chemistry of oil field brines worldwide and the partitioning behavior of ree between fluorite and water at el hammam indicate that acetate carbonate and fluoride are likely to be major contributors to ree mobilization in these settings the direct implications of the low temperature transport of ree by oil bearing brines is that in systems where these kind of fluids occur the ree signature observed may not reflect the source of the fluid as much as a combination of fluid source and fluid rock interaction in addition oil field brines can efficiently scavenge transport and deposit ree leading to anomalously high accumulations such as the el hammam fluorite deposit and may also contribute to ree mobilization and concentration in other systems

hydrochemistry on the yilgarn block western australia ferrolysis and mineralisation in acidic brines abstract in the southeastern part of western australia internal drainage and a semi arid climate have resulted in extensive development of playas the brines beneath the playas wedge outwards and force local infiltration to crop out at playa margins as discharge zones the discharging water contains dissolved fe2 oxidation and hydrolysis ferrolysis of which generates very acidic water ph 2 8 at least some of the alkalinity generated by the original reduction of fe3 has been sequestered as subsurface calcrete within local soils the acidity causes the dissolution of kaolinite which is abundant in playa sediments and as a thick capping on weathered bedrock giving water with a low ph and high concentrations of dissolved al and si evaporation and mixing with playa brines containing high concentrations of k and so4 causes alunite to precipitate as ph rises from a minimum of 2 8 at chlorinities of 1 to 2 m to 6 at chlorinities of 4 8 m the alunite deposits formed by this process are many orders of magnitude larger than occurrences elsewhere in the world the large scale mobilisation of si during this process may be one mechanism for the formation of silica cemented rocks silcrete that are widespread in the australian regolith

extremely negative and inhomogeneous sulfur isotope signatures in cretaceous chilean manto type cu ag deposits coastal range of central chile abstract chilean manto type cmt cu ag hydrothermal deposits share a characteristic association of volcano sedimentary jurassic to lower cretaceous host rocks style of mineralization ore and associated mineralogy and geochemistry with ore grades typically 1 cu that make this family of deposits significant and interesting both academically and economically although often stratabound geological evidence supports an epigenetic origin for these deposits we present a detailed stable isotope study of la serena and melipilla naltahua lower cretaceous deposits central chile which reveals extremely negative 34 s values to 50 which are among the lowest values found in any ore deposit in addition the range of 34 s values from sulfides in the two areas is very wide 38 3 to 6 9 in la serena and 50 4 to 0 6 in melipilla naltahua these new data significantly extended the reported range of 34 s data for cmt deposits co existing sulfates range from 7 9 to 14 3 and are exclusive to la serena deposit the wide sulfide isotopic range occurs at deposit and hand specimen scale and suggests a polygenic sulfur source for these deposits where bacteriogenic sulfide dominates while sulfur isotope data for the bulk of jurassic cmt deposits northern chile suggests a predominant magmatic source in their origin mean 2 7 1 9 1 contributions of a magmatic component is only likely to be involved at melipilla naltahua deposit the 13 c values obtained for calcites associated with the mineralization range from 20 1 to 0 2 also suggesting polygenic carbon sources with the likely strong involvement of degradation of organic matter and leaching of limestone two different genetic models with involvement of hydrocarbon are proposed for both areas for melipilla naltahua a two step model can be developed as follows 1 framboidal pyrite growth with very low 34 s formed by bacterial sulfate reduction in an open system and with diagenetic degradation of oil related brines leaving pyrobitumen 2 cu bearing stage replacing of framboidal pyrite inheriting depleted sulfur as low as 50 4 together with sulfides directly precipitated from a hydrothermal fluid with 34 s close to 0 for la serena a single step model fits best without framboidal pyrite generation cu bearing sulfides were precipitated mainly in veins where cu plus base metal bearing hydrothermal fluids mixed with h 2 s generated by bacterial sulfate reduction in the host rocks isotopic evidence clearly illustrates that bacterial activity perhaps enhanced by hydrothermal activity was fed by hydrocarbon brines and sulfate remobilized from continental evaporites it is possible that variable ecological conditions led to different extents of isotopic fractionation adding to the typical sulfur isotopic heterogeneity of such bacterial systems for both areas the cu bearing stage occurred during the peak to waning stages of the very low grade metamorphism that affected the lower cretaceous sequence

metalliferous manganese oxide mineralization associated with the boleo cu co zn district mexico apart from its large reserves of cu co zn mineralization contained within stratiform ore beds or mantos the boleo district of central baja mexico also contains significant concentrations of mn oxides typically 2 3 wt mn interspersed with hydrothermal sulfides and both hydrothermal and weathering related metal oxide minerals within the mantos mn oxides occur as concentric nodules disk shaped concretions laminae granules or aggregates veins dendrites and various replacements the oxides are composed of varying amounts of hollandite cryptomelane todorkite romanechite pyrolusite and x ray amorphous mn oxide chemically the manto oxides are unique owing to their extraordinarily high abundances of co cu pb and zn typically 2 5 wt but up to 23 wt existing mineralogical and geochemical classifications are ambiguous regarding the genetic classification of mn oxides within the mantos a new mno 2 fe 2 o 3 t mgo diagram is proposed in order to discriminate among highly metalliferous mn oxides based on the new classification scheme manto mn oxides record a complex interaction between hydrothermal and diagenetic processes to better understand the mechanism of oxide deposition radiogenic isotopes sr and pb and ree geochemistry were used to delineate fluid and metal sources isotopic and ree constraints indicate that the boleo mn oxides are largely hydrothermal in origin however they show varying degrees of modification resulting from diagenetic processes hydrothermal mn oxides are syngenetic synsedimentary to syndiagenetic in origin and were precipitated in association with sulfides reflecting localized variations in redox conditions within the manto sequence due to the downward infiltration of metal bearing brines apart from morphological and stratigraphic evidence e g occurrence of nodular crusts along the upper contact of the manto a syngenetic origin is supported by a single k ar date of 7 0 0 2 ma which is within the estimated age range for deposition of boleo formation clastic sediments interaction between brine and seawater or brine and pore fluid as it infiltrates the sedimentary pile produced hydrothermal precipitates with certain hydrogenetic attributes i e positive ce anomaly lree enrichment on the other hand oxides with hydrogenetic and with mixed hydrothermal hydrogenetic affinities represent diagenetic alteration and remobilization of earlier formed hydrothermal oxides by meteoric fluids by far the greatest degree of remobilization occurred in response to compactional dewatering of the manto where the dewatering pore waters enriched the uppermost manto strata in mn fe zn co and to lesser degrees cu later diagenetic modifications coincided with the development of a supergene overprint which typifies boleo formation strata at elevations above the present day water table

classification and genesis of calcrete and gypsite lithofacies in paleodrainage systems of inland australia and their relationship to carnotite mineralization calcrete and gypsite lithofacies are chemical sedimentary rocks irre spective of age and or stratigraphic position the depositional environments of these deposits indicate that since early tertiary silting up of inland drainage developed internal salt lake systems with gypsite as the dominant evaporitic lithotype elongate bodies of phreatic calcrete formed in paleochannels almost all primary calcretes and gypsites have been modified by phreatic and vadose diagenetic processes because the diagenetic processes are complex stratigraphic analysis is difficult carnotite mineralization is probably not contemporaneous with calcretization assuming that waters from fertile uraniferous sources are flowing through the sediments several controls will govern carnotite mineralization ponding by physical or chemical barriers solution chemistry p co2 co 3 hco 3 v u and k concentrations eh ph and postdepositional physical or chemical changes for significant carnotite bodies to remain primary deposition must have been followed by a freezing mechanism to preserve the deposit diagenetic conditions which may cause remobilization vary between deposits therefore it may be unwise to use a single deposit as the basis for a widely applicable exploration model modified journal abstract

multiphase reddening and weathering events in upper carboniferous red beds from the english west midlands sediments of the halesowen and salop formations westphalian d stephanian in the west midlands were deposited on the southern margin of the pennine basin during a period of relative tectonic quiescence during the variscan orogeny the clastic framework of the predominantly red sandstones and mudstones in the salop formation includes large detrital hematite grains these yield a primary component of magnetization indicating that sediments were deposited close to the carboniferous palaeo equator variscan uplift erosion and subsequent deep oxidation in an arid climate during the permian resulted in the precipitation of finer hematite in rocks of both formations which are now found at depths of over 150 m below the present day ground level these grains carry secondary magnetizations which indicate formation at palaeolatitudes of between 5 and 15 n the position that britain occupied during the permian the pattern of permian remagnetization particularly in borehole samples suggests that the secondary fine grained hematite was precipitated as a result of lateral flow of meteoric water through connected permeable sandstone units rather than downward percolation through the entire succession present day surface weathering has resulted in the dissolution of the finer grains of hematite and in some cases where permeabilities are relatively high it has also affected the coarser fraction consequently the record of late carboniferous and permian magnetization events is commonly incomplete in strata close to the present day ground level