impact of poroelastic response of sandstones on geothermal power production during geothermal power production using a borehole doublet consisting of a production and injection well the reservoir conditions such as permeability k porosity and skempton coefficient b at the geothermal research site gross schoenebeck germany will change besides a temperature decrease at the injection well and a change of the chemical equilibrium also the pore pressure pp will vary in a range of approximately 44 mpa 10 mpa in our reservoir at 3850 to 4258 m depth this leads to a poroelastic response of the reservoir rocks depending on effective pressure p eff difference between mean stress and pore pressure resulting in a change in permeability k porosity and the poroelastic parameter skempton coefficient b hence we investigated the effective pressure dependency of flechtinger sandstone an outcropping equivalent of the reservoir rock via laboratory experiments the permeability decreased by 21 at an effective pressure range from 3 to 30 mpa the porosity decreased by 11 p eff 6 to 65 mpa and the skempton coefficient decreased by 24 p eff 4 to 25 mpa we will show which mechanisms lead to the change of the mentioned hydraulic and poroelastic parameters and the influence of these changes on the productivity of the reservoir the most significant changes occur at low effective pressures until 15 to 20 mpa for our in situ reservoir conditions p eff 43 mpa a change of 10 mpa effective pressure will result in a change in matrix permeability of less than 4 and in matrix porosity of less than 2 besides natural fracture systems fault zones and induced hydraulic fractures the rock matrix its only one part of geothermal systems all components can be influenced by pressure temperature and chemical reactions therefore the determined small poroelastic response of rock matrix does not significantly influence the sustainability of the geothermal reservoir

experimental study of the stress dependence of the absolute and relative permeabilities of some tight gas sandstones connected porosity and dry gas permeability at 5 mpa hydrostatic stress have been measured for thirteen tight gas sandstone samples originating from a rotliegend sandstone reservoir in germany the samples have then been preserved into hermetic chambers at fixed relative humidity rh values until mass and water saturation level stabilisation this allows a first characterisation of pore size distribution showing that most of the pore network is constituted with pores with entrance radii greater than 50 nm the relative gas permeability was then measured for different water saturation and hydrostatic stress up to 60 mpa the analysis of the results has allowed us to identify the limiting conditions water saturation and hydrostatic stress for the apparition of a hydraulic cut off also called the permeability jail dry gas permeability at low confining pressure 5 mpa has appeared to be a good indicator of the sensitivity of a sample to both hydraulic stress and liquid saturation this gives an efficient tool to predict the global behaviour of the gas reservoir despite its heterogeneity with a single gas permeability measure

in situ sulfur isotope analysis of sulfide minerals by sims precision and accuracy with application to thermometry of 3 5 ga pilbara cherts abstract secondary ion mass spectrometry sims measurement of sulfur isotope ratios is a potentially powerful technique for in situ studies in many areas of earth and planetary science tests were performed to evaluate the accuracy and precision of sulfur isotope analysis by sims in a set of seven well characterized isotopically homogeneous natural sulfide standards the spot to spot and grain to grain precision for 34 s is 0 3 for chalcopyrite and pyrrhotite and 0 2 for pyrite 2sd using a 1 6 na primary beam that was focused to 10 m diameter with a gaussian beam density distribution likewise multiple 34 s measurements within single grains of sphalerite are within 0 3 however between individual sphalerite grains 34 s varies by up to 3 4 and the grain to grain precision is poor 1 7 n 20 measured values of 34 s correspond with analysis pit microstructures ranging from smooth surfaces for grains with high 34 s values to pronounced ripples and terraces in analysis pits from grains featuring low 34 s values electron backscatter diffraction ebsd shows that individual sphalerite grains are single crystals whereas crystal orientation varies from grain to grain the 3 4 variation in measured 34 s between individual grains of sphalerite is attributed to changes in instrumental bias caused by different crystal orientations with respect to the incident primary cs beam high 34 s values in sphalerite correlate to when the cs beam is parallel to the set of directions uuw from 111 to 110 which are preferred directions for channeling and focusing in diamond centered cubic crystals crystal orientation effects on instrumental bias were further detected in galena however as a result of the perfect cleavage along 100 crushed chips of galena are typically cube shaped and likely to be preferentially oriented thus crystal orientation effects on instrumental bias may be obscured test were made to improve the analytical precision of 34 s in sphalerite and the best results were achieved by either reducing the depth of the analysis pits using a kohler illuminated primary beam or by lowering the total impact energy from 20 kev to 13 kev the resulting grain to grain precision in 34 s improves from 1 7 to better than 0 6 2sd in both procedures with careful use of appropriate analytical conditions the accuracy of sims analysis for 34 s approaches 0 3 2sd for chalcopyrite pyrite and pyrrhotite and 0 6 for sphalerite measurements of 34 s in sub 20 m grains of pyrite and sphalerite in 3 5 ga cherts from the pilbara craton western australia show that this analytical technique is suitable for in situ sulfur isotope thermometry with 50 c accuracy in appropriate samples however sulfides are not isotopically equilibrated in analyzed samples

pyrite formation in an anoxic estuarine basin in a shallow fjord like estuary the upper and lower basins of the pettaquamscutt river rhode island each contain water columns stratified into oxic and anoxic plus sulfidic layers both water columns contain iron monosulfides and pyrite from just below the oxic anoxic interface down to the sediment water interface concentrations of iron monosulfides increase with increasing depth in the water columns but concentrations of pyrite are relatively constant with depth suspended pyrite is present only as framboids whereas the underlying sediments contain dominantly framboids but also euhedral grains and infilled framboids based on pyrite textures s isotopic compositions of water column and sediment sulfides and settling rate calculations about 70 of the pyrite burial flux to the pettaquamscutt sediments is accounted for by framboids forming at the oxic anoxic interface and settling to the sediment water interface the remaining pyrite burial flux is secondary pyrite nucleation and growth within the sediments represented by euhedral grains and infilled framboids the s isotopic composition of pyrite in the pettaquamscutt sediments and presumably of pyrite in the sediments of other modern anoxic basins and analogous ancient sediments therefore contains a component originating near the oxic anoxic interface and a component added below the sediment water interface pyrite framboids form in the water column where there is high supersaturation with respect to pyrite and slight undersaturation with respect to the iron monosulfides we propose that framboid nucleation and growth occurs in the water column adjacent to and below the oxic anoxic interface where supplies of ferrous species sulfide species and suitable electron acceptors are available infilled and overgrown framboids from in the sediments as a result of surface nucleation and continued pyrite growth on framboids that originate above the sediment water interface

multi fractal distribution analysis for pore structure characterization of tight sandstone a case study of the upper paleozoic tight formations in the longdong district ordos basin abstract with proven gas potential the gas charging and accumulation mechanisms for the upper paleozoic tight gas reservoir in the longdong district of the ordos basin remain controversial pore structure is the most direct and critical factor that affects gas charging and accumulation in the reservoir however the pore structure characterization of tight sandstone is far more difficult than that for conventional reservoir rocks due to significant heterogeneity the present work aims to introduce a new quantitative method for pore structure characterization that integrates multi fractal distribution analysis an effective and profitable method for quantitative heterogeneity analysis and high pressure mercury intrusion porosimetry hpmip twenty one samples from targeted tight formations with different gas bearing status were obtained for analysis the results show that the best formations for gas charging and accumulation in the upper paleozoic tight sandstone formations in the longdong district are the formations with more large pores more homogeneous small pores and well developed micro fractures the existence of micro fractures is the key factor that affects gas charging and accumulation tight sandstone samples were categorized into three types in accordance with the hpmip curve configuration due to the high heterogeneity of pore structures analyses based solely on hpmip curve configuration has its shortcomings which can be compensated by multi fractal distribution analysis the multi fractal distribution of target tight formations could be interpreted as two linear segments representing large pores and small pores the separating points of the two segments vary from 0 1 m to 0 5 m in different samples due to different pore structures large pores are not ideal fractals in gas bearing formations due to the existence of micro fractures whereas they are fractals in dry formations where micro fractures are not developed small pores are all ideal fractals with the highest heterogeneity in type samples and the lowest heterogeneity in type samples a conclusion was made in this work if the slope of segment one in the multi fractal distribution of mercury saturation shg versus capillary pressure pc is larger than 1 this measure could be accepted as an empirical indicator for the existence of micro fractures

ion microprobe determination of sulfur isotope variations in iron sulfides from the post betze sediment hosted disseminated gold deposit nevada usa abstract secondary ion mass spectrometric analyses of ore samples from the post betze sedimenthosted disseminated gold deposit were utilized to constrain elemental distribution of au and as in iron sulfide phases most of the au was deposited very early in the paragenetic sequence although au and as are covariant in arsenian pyrite au apparently was depleted much more rapidly from the hydrothermal solutions than was as sensitive high resolution ion microprobe shrimp sulfur isotope analyses of iron sulfides from the post betze deposit vary widely from 34 s 29 to 23 and provide important information on the origin of sulfur and constraints on depositional mechanisms ore solutions had high 34s values and were most likely derived at least in part from thermochemical reduction of lower paleozoic seawater derived sulfate possibly bedded barite late stage ore fluids 34 s sulfide 12 to 29 are extremely depleted in 34s relative to main stage ore fluids 34 s sulfide 16 23 although such low 34s values can be generated hypothetically from the original ore fluids by oxidation possibly boiling the stability of pyrite is compromised introduction of and mixing with fe rich fluids is necessary to deposit pyrite having low isotopic values

determining the porosity exponent m and lithology factor a for sandstones and their control by overburden pressure a case study from the gulf of suez egypt the porosity exponent m represents an important parameter in archie s equation it is routinely used in well logging interpretation and formation evaluation it reflects some petrophysical rock properties such as the petrofabrics pore fabrics and overburden pressure obp data measured at ambient conditions for a total of 55 sandstone core samples were obtained from 8 wells varying in depositional facies geologic age degree of consolidation and cementation material and then measured again at obp similar to the actual reservoir conditions to check the effect of obp on archie s parameters and to introduce a model of high reliability other published data sets were also used to confirm the study results based on the best fit regression analysis several empirical relationships were introduced to relate the porosity exponent to pore volume lithology factor and permeability the effect of obp on the porosity exponent was also investigated in relation to the petrophysical parameters given the above a new statistical model is proposed to relate the porosity exponent to the permeability of the studied sandstone samples in the gulf of suez egypt the effect of confining pressure on the studied porosity exponent m and the lithology factor a is significant when porosity is less than or equal to 10 from the present study categorization of the studied samples into flow units and rock types using the hydraulic flow unit and the discrete rock types increased the reliability of the obtained relationships and increased the applicability of the obtained equations in addition the value of the lithology factor a fluctuates around 1 0 92 1 04 regardless of the applied processing method whereas the value of the porosity exponent m fluctuates around 1 83 the obtained relationships between the formation resistivity factor and porosity have a very high reliability 0 949 correlation coefficient 0 969

age constraints on jerritt canyon and other carlin type gold deposits in the western united states relationship to mid tertiary extension and magmatism carlin type gold deposits are difficult to date and a wide range of ages has been reported for individual deposits therefore several methods were employed to constrain the age of the gold deposits in the jerritt canyon district dated igneous rocks with well documented crosscutting relationships to ore provided the most reliable constraints k ar and 40 ar 39 ar dates on igneous rocks are as follows andesite dikes 324 ma sericitic alteration in andesite dikes 118 ma basalt dikes 40 8 ma quartz monzonite dikes 39 2 ma and calc alkaline ignimbrites 43 1 to 40 1 ma of these only the andesite and basalt dikes are clearly altered and mineralized the gold deposits are therefore younger than the 40 8 ma basalt dikes the sericitic alteration in the andesite dikes is unrelated to the gold deposits a number of dating techniques did not work k ar and 40 ar 39 ar dates on mica from mineralized ordovician to devonian sedimentary rocks gave misleading results the youngest date of 149 ma from the smallest 187 os 188 os initial 0 9 3 6 but did not yield a meaningful isochron due to very low re and os concentrations and large analytical uncertainties paleomagnetic dating techniques failed because the hydrothermal fluids sulfidized nearly all of the iron in the host rocks leaving no remnant magnetism when published isotopic dates from other carlin type deposits in nevada and utah are subject to the rigorous evaluation developed for the jerritt canyon study most deposits can be shown to have formed between 42 and 30 ma k ar and 40 ar 39 ar dates on the youngest preore igneous rocks range from 41 to 32 ma whereas the oldest postore igneous rocks range from 35 to 33 ma hydrothermal adularia from the twin creeks deposit yields similar 40 ar 39 ar dates of 42 ma k ar dates on supergene alunite range from 4 to 30 ma k ar and 40 ar 39 ar dates on micas separated from sedimentary 395 43 ma and igneous 145 38 ma rocks are usually much older than the gold deposits and most are suspect because they are from incompletely reset preore micas or from mixtures of preore and ore stage mica fission track dates on zircons are also generally older than the deposits 169 35 ma and are not completely reset by mineralization apatites are likley to be reset by the hydrothermal systems and by younger thermal events and yield dates 83 22 ma that are younger than those from zircon independent support of a mid tertiary age is provided by the low delta d sub h 2 o values of hydrothermal fluids from 10 widely separated carlin type deposits 134 or 23ppm the low delta d sub h 2 o values are consistent with a mid tertiary age when the climate was cool but are inconsistent with the cretaceous and jurassic ages favored by some workers when the climate was warm the age and distribution of carlin type deposits coincides with areas that underwent extension and calc alkaline magmatism over the same time period despite this relationship the deposits lack clear spatial or genetic relationships to mid tertiary epizonal plutons rather many deposits are localized along preexisting crustal fault zones in the getchell trend structures tapped deep sourced metamorphic or magmatic fluids and subsequently variably exchanged meteoric water in the other trends and districts only variably exchanged meteoric water has been detected these relationships suggest either that all of the deposits formed from deep sourced fluids and were subsequently flooded by meteoric water or that fluids from different sources evolved to produce deposits with similar charateristics

depositional and diagenetic controls on reservoir attributes within a fluvial outcrop analog upper triassic sonsela member of the chinle formation petrified forest national park arizona the upper triassic sonsela member of the chinle formation in the petrified forest national park was evaluated using sedimentologic stratigraphic paleopedologic and petrographic criteria along a continuous 0 5 km 0 3 mi outcrop the study interval consists of interbedded sandstones and mudstones and is composed of a two tiered hierarchy of cyclic alluvial deposits with bounding paleosols the succession is composed of 15 fluvial aggradational cycles facs that comprise two fac sets fac sets the fac sets are composed of architectural elements suggestive of a mixed load fluvial system that is alternately dominated by bed load deposits and suspended load deposits a thinning and fining stacking pattern within fac sets is accompanied by an upward increase in pedogenic modification suggesting that cycles systematically stack in response to a longer period decrease in the rate of accommodation gain sandstones are classified as litharenites feldspathic litharenites and lithic subarkoses and occur within recycled orogen dissected arc and transitional arc provenance fields sandstone compositional maturity increases upward through the fac sets point counts of intergranular volume as a proxy for primary porosity within channel facies and subsequent transform to syndepositional permeability provide a two dimensional depiction of the lateral variability in reservoir quality paleosols are weakly to moderately developed and have little stratigraphic variation these characteristics suggest that climatic fluctuations are not responsible for evolving fluvial depositional style or associated reservoir quality trends in sandstone compositional maturity suggest that fluvial stacking patterns and depositional style are related to pulses of tectonism sandstones are volcanogenic rich and have undergone an almost complete diagenetic loss of porosity caused by the precipitation of authigenic clays paragenetic reconstruction suggests that porosity loss occurred contemporaneous with the silicification of fossil logs in channel deposits log compaction at the time of silicification averaged 9 1 suggesting that log silicification and porosity loss occurred soon after deposition

biogeochemical indicators of buried mineralization under cover talbot vms cu zn prospect manitoba abstract results are presented of a surficial geomicrobiological investigation of glacial cover overlying buried mineralization at the talbot prospect manitoba canada where previous surficial geochemistry surveys indicated anomalous concentrations of elements above the buried mineralization the cu zn volcanogenic massive sulfide vms occurrence is overlain by 100 m of paleozoic dolomites and quaternary glacial cover the geomicrobiological investigation demonstrates that there is a distinct microbial ecology at the anomalous sampling locations especially directly overlying buried mineralization the combined geochemical and geomicrobiological analyses reveal the presence of an anomaly directly over mineralization due to oxidation of the buried ore specifically geomicrobiological analyses yield an inverse correlation between zn in the clay size

the las cruces deposit iberian pyrite belt spain abstract the las cruces deposit is located at the eastern margin of the iberian pyrite belt ipb beneath the neogene quaternary deposits of the guadalquivir basin these sediments covered and preserved the supergene profile somewhat after its generation until its recent discovering for this reason the las cruces ore deposits together with lagoa salgada in portugal are the only known deposits in the ipb that preserve the entire weathering profile including both the gossan and the enrichment zone in that sense the present study provides new data on the ipb ore deposits and their post palaeozoic evolution the primary mineralization consists of massive and semi massive polymetallic sulfides overlaying a cupriferous and pyritic stockwork the supergene enrichment extends from the primary zone to gossan and consists of a thick cementation zone characterized by intense replacement of part of the primary sulfides by cu rich supergene sulfides at present the only economic resource of las cruces is the cementation zone with initial reserves of 17 6 mt 6 2 cu but the orebody also includes significant contents of cu and zn within the primary mineralization and au ag and pb in the gossan mineralogical and geochemical data confirm that the primary mineralization at las cruces resembles other ipb deposits in terms of distribution and evolution however the gossan and cementation zone show an uncommon evolution for this kind of supergene profile the major singularity that makes the las cruces supergene mineralisation noticeably different from others in the ipb or elsewhere resides in its unusual mineralogical composition mostly comprised of newly formed siderite calcite fe sulfides and galena the genetic model proposed for the las cruces deposit includes three main stages 1 ore genesis and evolution of primary mineralization which seems to be comparable to other ipb deposits 2 genesis of cu rich secondary mineralization and gossan by weathering after miocene exhumation of the upper part of the massive sulfide deposit under oxidizing and acidic conditions and 3 late evolution of supergene profile below the carbonated rich sediments of the guadalquivir basin with the subsequent change in the redox conditions due to water rock interaction between the supergene profile and basinal fluids

geochemical modeling of zns in biofilms an example of ore depositional processes the precipitation of nearly pure nanocrystalline zinc sulfides primarily sphalerite and wurtzite within a biofilm dominated by sulfate reducing bacteria of the family desulfobacteriaceae has been observed in the flooded tunnels of an abandoned mine in southwestern wisconsin zns accumulations are limited to biofilms growing on old mine timbers zns deposits which comprise about 20 percent of the volume of the biofilm formed in less than 30 yr from solutions containing only a few milligrams per liter mg l zn 2 a model is proposed wherein sulfate reduction is followed by the formation of aqueous metal sulfide clusters that aggregate to form 1 to 3 nm diameter crystals that are transported and agglomerate to form micron scale aggregates geochemical modeling shows how reduction of sulfate leads to exclusive precipitation of zns until most of the zn 2 is consumed the model also predicts a series of discrete metal sulfide precipitation events that may be used to interpret sulfide mineral paragenesis of low temperature cu pb zn ore deposits for example the paragenesis of essentially monomineralic and mixed sulfide layers in mississippi valley type strataform and strata bound pb zn cu and sedex deposits can be predicted thermodynamically if the rate of aqueous sulfide generation does not outstrip the flux of metals into the system based on the characteristics of zns produced by sulfate reducing bacteria features of ore deposit minerals consistent with a biogenic origin can be identified these include microstructures formed by coarsening of nanophase materials the presence of micron scale spherical aggregates in organic rich microenvironments and spatially heterogeneous patterns of sulfide mineral distribution consistent with local variations in redox potential and activity of sulfate reducing bacteria

anhydrite cementation and compaction in geothermal reservoirs interaction of pore space structure with flow transport p t conditions and chemical reactions in order to analyze local clogging phenomena due to the precipitation of anhydrite in the pore space we performed a petrophysical study on cores and data from three boreholes probing the rhaetian hydrothermal aquifer in northern germany allermohe neuruppin 1 88 neuruppin 2 87 the pore size geometry of sandstones was studied using among other methods pulsed field gradient nuclear magnetic resonance pfg nmr we found two facies types with clearly different diagenetic history 1 a fine grained sand with small pores mechanically compacted during diagenesis into an average sandstone of fractal pore geometry 2 a coarser sand with larger pores almost completely cemented by anhydrite after compaction had reduced the pore space to a porosity of 30 thus no further mechanical compaction occurred and the pores remained smooth in contrast the fine grained facies was not cemented possibly because anhydrite crystal nuclei are unstable in pores of insufficient size with regard of these two facies types we developed 1 an approach for calculating vertical logs of anhydrite and permeability content from gamma density measurements in boreholes or on core 2 a chemical reaction model to calculate the amount of precipitation and dissolution of each mineral species at high temperature and salinity these petrophysical and geochemical models are integrated into the numerical simulation tool shemat for simulating coupled flow heat and species transport and chemically induced permeability changes a comparison of the diagenesis of the cemented and un cemented facies types yields an improved understanding of the geological conditions required for anhydrite cementation specifically with regard to the studied rhaetian sandstones numerical reactive flow simulations demonstrate that intense local anhydrite cementation may occur when saline formation waters mix with hot brines ascending on faults

estimating irreducible water saturation and permeability of sandstones from nuclear magnetic resonance measurements by fractal analysis abstract understanding the relationships between the pore structure and bulk properties such as irreducible water saturation swir and permeability k of rocks is a crucial problem in geoscience in this study two types of fractal dimension were determined from nuclear magnetic resonance nmr t2 relaxation time distribution and models for estimating swir and k using fractal theory were proposed in view of the data of sandstone samples from upper paleozoic formation in china we found a good agreement between the predicted swir values based on fractal analysis and the experimental measurements and the estimated k values based on the proposed model are within one order of magnitude of measured k additionally another four frequently used k estimation models were compared with our proposed model and the result support that the proposed approach has great potential in investigating k while certain limitation still exists this procedure was applied on another set of sandstone samples collected from a different location and the predicted permeability values are reliable our study suggests that the proposed swir estimation model using nmr t2 data and fractal dimensions provides useful insights into characterizing the pore space properties of sedimentary rocks our work demonstrates that we can use nmr data to infer swir directly and the estimated swir value can be well integrated in permeability prediction model which improves the applications of nmr in characterizing the properties related to rock pores

isotope fractionation by sulfate reducing natural populations and the isotopic composition of sulfide in marine sediments isotope fractionations during sulfate reduction by natural bacterial populations were measured in seven different marine sediments and compared with the isotopic composition of solid phase sulfides in the same sediments the measured fractionations during sulfate reduction could explain only between 41 and 85 of the 34s depletion in the sedimentary sulfides this result directly demonstrates that the depletion of 34s in solid sulfides is an expression of the combined activity of sulfate reducing organisms with additional fractionations accumulated during the oxidative part of the sulfur cycle the only known process to significantly augment the fractionations created during sulfate reduction is the microbial disproportionation of the intermediate sulfur compounds elemental sulfur thiosulfate and sulfite in a simple model we show how important each of these disproportionation processes could be in generating the isotopic composition of sedimentary sulfides the sulfate reduction rates in the sediments studied varied by a factor of 1000 and did not correlate with the fractionation during sulfate reduction by contrast a correlation was observed between sulfate reduction rate and the extent of 34s depletion into sedimentary sulfides the most 34s depleted sulfides found in sediments supporting the lowest rates of sulfate reduction thus the fractionations imposed during the disproportionating processes are better expressed in sediments with low sulfate reduction rates the direct phototrophic oxidation of sulfide to sulfate with minimal fractionation may have been important in the sediments that had a high sulfate reduction rate

extreme 34s depletions in zns at the mike gold deposit carlin trend nevada evidence for bacteriogenic supergene sphalerite we identified submicrometer sized framboidal sphalerite zns below the base of supergene oxidation in a carlin type gold deposit of eocene age in nevada united states where the framboidal sphalerite forms a blanket like body containing 400 000 metric tons of zinc framboidal sphalerite 0 1 mum in diameter formed in the early miocene ranges from 0 1 to 0 35 mol fes the delta 34 s values range from 25 to w 70 the lowest values measured in a marine or terrestrial environment these s isotope data demonstrate the involvement of sulfate reducing bacteria and provide the first documentation that sphalerite can form significant supergene sulfide enrichment blankets

stable isotope geochemistry of carbonate minerals in supergene oxidation zones of zn pb deposits abstract the 18 o 16 o and 13 c 12 c ratios of carbonate minerals formed by supergene oxidation of zn pb deposits and submarine alteration of ancient slags were studied in order to constrain isotope fractionation factors for smithsonite cerussite and phosgenite and to characterize conditions of nonsulfide ore formation we present new isotope data of carbonate hosted ores from the iglesiente district sardinia italy and vila ruiva portugal as well as from the silicate hosted ores of the broken hill district new south wales australia and freihung germany and review previously published isotope data the temperature dependence of oxygen isotope fractionation between pb and zn carbonate minerals and water below 240 c for cerussite and below 100 c for smithsonite and phosgenite can be expressed as 1000ln cerussite water 2 29 10 6 t 2 3 56 1000ln smithsonite water 3 10 10 6 t 2 3 50 1000ln phosgenite water 2 55 10 6 t 2 3 50 with t in kelvin the carbon isotope fractionation between smithsonite phosgenite hydrozincite and calcite is less than about 2 while cerussites are strongly depleted in 13 c by about 10 as compared to the former minerals oxygen isotope variations of individual carbonate minerals within a deposit are relatively small indicating constant formation temperatures and a single meteoric fluid source average formation temperatures of the studied deposits are calculated at 20 5 c using the estimated isotope compositions of local paleometeoric waters we observe a linear relationship between the isotope values of estimated paleometeoric waters and supergene carbonates thus base metal carbonate minerals from supergene deposits may provide paleoclimatic information the carbon isotope values are in most carbonate hosted deposits highly variable more than 10 suggesting at least two isotopically distinct carbon sources the isotopically light component can be related to oxidation of c3 plants soil derived carbon and or microbes that take active part in sulfide oxidation while the isotopically heavy component originates from carbonate carbon from wall rocks and or atmospheric carbon the 13 c enriched component is less dominant in silicate hosted deposits

permeability prediction for low porosity rocks by mobile nmr estimating permeability from nmr well logs or mobile nmr core scanner data is an attractive method as the measurements can be performed directly in the formation or on fresh cores right after drilling furthermore the method is fast and non destructive compared to t 1 relaxation times commonly measured t 2 distributions are influenced by external and internal magnetic field gradients we performed two dimensional t 1 and t 2 relaxation experiments on samples of rhaetian sandstone a rock with low porosity and small pore radii using a mobile nmr core scanner which operates within a nearly homogeneous static magnetic field because small pore sizes are associated with high internal magnetic field gradients standard methods from nmr logging in the oil industry cannot be applied for accurate permeability prediction therefore a new model theory was developed which describes the pore radius dependence of the surface relaxivity p 2 by both an analytical and a more practical empirical equation using corrected p 2 values permeability can be predicted accurately from the logarithmic mean of the t 2 distribution and the physically based kozeny carman equation additional core plug measurements of structural parameters such as porosity permeability specific inner surface area and pore radius distributions supported the nmr results

hydraulic and acoustic properties as a function of porosity in fontainebleau sandstone laboratory measurements have been made of the permeability k free porosity l compressional velocities vp or ve and compressional attenuations qp or qe in fontainebleau sandstone over a continuous range of porosities from 3 to 28 this large variation was achieved without any composition change fontainebleau sandstone is made of fine quartz grains with regular grain size 250 m permeability was measured with a falling head permeameter velocities and attenuations were obtained either through an ultrasonic experiment for frequencies around 500 khz or through a resonant bar technique experiment for frequencies around 5 khz and in both cases with varying water saturation the results show an excellent correlation between permeability k and total porosity for all our samples for low porosities 3 to 9 permeability in millidarcies is 2 75 10 5 7 33 while for high porosities 9 to 28 permeability k in millidarcies is given by 0 303 3 05 the correlation is also excellent between free porosity and total porosity on the other hand the correlation between acoustic properties and total porosity is not as clear as for hydraulic properties whatever the frequency 500 khz or 5 khz or the water saturation on the average velocity decreases and attenuation roughly increases with increasing total porosity velocity and attenuation values are related to the variation of grain contact structure and two samples with the same porosity and permeability may exhibit different velocities and attenuations the clear correlation between hydraulic properties and porosity is related to constant grain size while the lack of correlation for acoustic properties emphasizes the importance of the microstructure

micro texture and in situ sulfur isotope of pyrite from the baiyunpu pb zn deposit in central hunan south china implications for the growth mechanism of colloform pyrite aggregates abstract colloform pyrite textures have been detected in various geological bodies and have received much attention in recent years although these textures have been proved to be formed by the aggregation of micro grains with different sizes further work is needed to understand the mechanism for developing them we carried out a detailed study on the micro textures crystal preferred orientations cpos trace element and sulfur isotope compositions of colloform pyrite aggregates from the baiyunpu pb zn deposit in hunan china results showed that the inner core of colloform pyrite had an irregular outline with flattening at their contact boundaries and was commonly formed by the compaction of multiple spherical aggregates the outer layers concentrically grew around the core field emission scanning electron microscope fe sem suggested both the inner core and the outer layers were composed of a large number of nano or micron scale grains 300 nm granular crystals to acicular and elongated crystals up to 100 m in length electron backscatter diffraction ebsd revealed an initial random cpo in the core and either 1 0 0 or 1 1 0 cpos in subsequent layers in situ sulfur isotope compositions obtained by secondary ion mass spectrometry sims showed that the 34s values of colloform pyrite ranged from 8 4 to 0 2 which were interpreted to be mainly derived from thermochemical sulfate reduction tsr colloform pyrite aggregates are considered to grow from the core outward through the accretion of layers including 1 formation and aggregation of microcrystals in core a1 and 2 growth and geometrical selection of crystals in outer layers the growth and transformation of pyrite from disorderly granular microcrystals in the core to elongated crystals radiating from the aggregated center in the outer concentric zones is thought to be controlled by geometrical selection factors affecting the epitaxial relationship between the substrate and the growing crystals such as interface energy ambient temperature and degree of sulfur supersaturation may control the abrupt changes in cpo recorded in colloform pyrite aggregates

microbial sphalerite formation in carbonate hosted zn pb ores bleiberg austria micro to nanotextural and sulfur isotope evidence microglobular sphalerite 90 180 m is a major form of sphalerite in the abandoned triassic carbonate hosted zn pb deposit at bleiberg austria it is common in ores from the crest horizon and the first cardita horizon which contain about 0 5 to 3 mm thick and up to 5 cm long wavy discontinuous sphalerite rich bands composed of agglomerations of microglobular sphalerite based on comparisons with modern environments these textures are interpreted as peloids and probably represent fossil microbial mats these are inter layered with carbonate and marcasite rich as well as finely banded sphalerite layers fibrous galena and relics of oxysulfides resulting in the characteristic rhythmically banded macrotexture of these zn dominated ores microbial nanotextures made visible by field emission scanning electron microscopy fesem after etching include sphalerite nanospheres 10 90 nm and bacterial filaments the sphalerite nanospheres are identical to those previously reported for mixed calcite sphalerite peloids from bleiberg and are very similar to nanotextures observed in recent bacterial biofilms made by desulfobacteriaceae the observed sphalerite nanospheres are interpreted as in situ metabolic products of sulfate reducing bacteria micro and nanotextures suggest that the larger m sized sphalerite globules formed by agglomeration of sphalerite nanospheres as well as by replacement of peloids representing former bacterial colonies the latter are now composed of zn calcite cores surounded by serrated sphalerite rims most samples studied evidence recrystallization of sphalerite that is broadly coeval with formation of fluorite involvement of sulfate reducing bacteria in the formation of this early sphalerite mineralization is supported by sulfur isotope data sphalerite is generally characterized by isotopic light sulfur with 34 s per mil values ranging from 30 5 to 20 3 per mil the most negative sulfur isotope values are recorded from sphalerite 30 5 30 2 and galena with unusual fibrous to dendritic morphology 31 9 31 8 both are associated with oxysulfides microglobular sphalerite with well preserved sphalerite globules has a 34 s value of 28 8 to 28 2 per mil colloform sphalerite schalenblende ranges from 29 0 to 25 0 per mil microglobular sphalerite associated with fine grained fluorite and euhedral sphalerite formed through recrystallization processes show a trend to less negative values i e 26 3 to 22 2 per mil and 22 9 to 20 3 per mil respectively we suggest that the combined biogenic nano to macrotextures and sulfur isotope data are evidence that microbes played a key role in formation of alpine carbonate hosted zn pb deposits results of this study contradict the mvt model suggested for alpine pb zn deposits which calls for formation of pb zn mineralization during late diagenetic burial in the late triassic early jurassic

microbial structures and possible bacterial sulfide fossils in the giant jinding zn pb deposit yunnan sw china insights into the genesis of zn pb sulfide mineralization abstract the jinding zn pb sulfide deposit lanping yunnan china is one of the youngest sediment hosted giant zn pb deposit in the world it is also a well known deposit in china the large scale of the mineralization and especially the huge volume of h 2 s that was required to precipitate the zn pb sulfide are of great interest to ore geologists ore microscopy shows microbial structures such as framboidal sphalerite spherical aggregates of galena sphalerite oolite sphalerite dendritic colloidal sphalerite pyrite metacolloidal sphalerite pyrite multinuclear metacolloidalring like sphalerite pyrite botryoidal sphalerite pyrite framboidal pyrite and bacterial plate like of galena sphalerite detailed observations and analyses of the microbial structures at micron to nanometer scales by field emission scanning electron microscopy fesem and energy dispersive spectrometry eds reveal that the bacteria fossils are composed of sphalerite galena or pyrite or of multiple sulfide minerals with calcite and that they are distributed in bacterial colonies in the ore the individual bacteria fossils are spherical botryoidal or ring like with a diameter of 200 500 nm filamentous mucoid and tubular extracellular polymeric substances eps are commonly observed that are closely associated with and have the same composition as the bacteria fossils secondary ion microprobe analysis sims by in situ sulfur micro isotopic analysis of the microbial sulfide structures and bacteria fossils yield 34 s v cdt values varying from 48 6 to 9 5 per mil indicating that there was a high percentage of sulfate reducing bacteria in the zn pb sulfide mineralization process previous analyses have shown that the zn pb mineralization was formed at a shallow depth and low temperature with barely visible hydrothermal alteration the presence of evaporitic sulfate layers and paleo oil reservoir characteristics the authors believe that bacterial sulfate reduction might be the key h 2 s production mechanism in the jinding dome that was required to form this giant pb zn sulfide ore body

isotope geochemistry tracks the maturation of submarine massive sulfide mounds iberian pyrite belt the massive sulfide deposits of the southern iberian pyrite belt ipb occur as shale hosted exhalative mounds or shallow sub seafloor replacive bodies that formed at the devonian carboniferous boundary in anoxic bottoms the geochemistry of the mineralization and the host shale from some of the major deposits including a detailed 50 m thick section through the migollas orebody shows a marked textural and vertical zonation that is also reflected in the chemical textural and isotopic variations of pyrite and carbonates pyrite evolves from primary framboids and colloform aggregates to late euhedral crystals which accompanies a redistribution of the contained base metals and grain coarsening sims analyses depict an extreme variability of 34s values from 42 3 to 4 4 with a gradual increase that is related to the textural maturation there is also a systematic rise in the 87sr 86sr ratios 0 70846 to 0 71354 13c 12 2 to 5 2 and 18o values 14 1 to 27 8 of the associated carbonates which evolve from early dolomite to late siderite this evolution evidences the maturation of the exhalative mineralization during mixing between two fluids modified seawater enriched in biogenically derived reduced sulfur and upflowing hydrothermal fluids early sulfides precipitated in the seawater mound interface towards the core of the mounds there was an increasing influence of deep fluids that modified the early mineral textures and the isotopic signatures this evolution is similar to that observed in modern submarine hydrothermal systems and confirms the importance of mound refining in the evolution of fossil exhalative mounds and the formation of economic ores

reported supergene sphalerite rims at the chuquicamata porphyry deposit northern chile revisited evidence for a hypogene origin previous studies attributed a supergene origin to sphalerite rimming copper minerals occurring in chuquicamata in a mineral assemblage including typically chalcocite digenite cu1 85s1 12 and u1 99s1 01 covellite cus and cu1 08s0 92 and sphalerite up to 1 2 wt fe microscopic observations on samples from a central and a southern section completed by scanning electronic microscope sem backscattering electron imaging and electron microprobe analyses suggest that all sphalerite in chuquicamata is hypogene a scenario backed by observations in each step that explains the formation of the peculiar sphalerite rims is the following 1 precipitation of chalcopyrite typical of the early and main hydrothermal stages 2 precipitation of sphalerite rimming chalcopyrite and in voids and in weakness sites during the late hydrothermal stage 3 partial or total replacement of chalcopyrite by chalcocite digenite during the late hydrothermal stage and 4 formation of lamellar covellite principally at the expense of chalcopyrite suggesting increasingly oxidizing and or acidic conditions this covellite may be linked to supergene processes and or to the late hydrothermal stage the findings of the present work have implications for the position of the lower limit of the supergene enrichment in the eastern southern part of the deposit as the sphalerite rims now interpreted as hypogene were the only potential supergene sulfide in the eastern vertical section of the southern section

thermohaline fronts and baroclinic flow in the argentine basin during the austral spring of 1984 thermohaline fronts structure and baroclinic flow in the central argentine basin are investigated on the basis of a 1984 field experiment the brazil current after initial overshoot meanders northeastward toward subtropical latitudes with speeds of the order of 0 3 m s 1 the meanders have a wavelength of about 400 km and an amplitude of 200 km brazil current signatures as expressed by dynamic height are recognizable to depths of several kilometers the brazil and antarctic circumpolar currents do not meet in the central argentine basin to form common eastward flow as was expressed in classical descriptions but instead diverge sharply near 42 w this is seen also in the trajectories of satellite tracked drifters the region between the currents is marked by cyclonic and anticyclonic eddies strong thermohaline fronts accompany the boundaries of these currents the brazil current and subantarctic fronts are well separated in the central basin brazil current density fronts are deep and extend from the surface to 3000 m while the associated temperature and salinity fronts are intermittent over this depth interval temperature fronts virtually vanish at the interface between the antarctic intermediate water and the north atlantic deep water salinity fronts reverse their polarity beneath the core of the former at depths between 3000 and 4000 m abyssal temperature and salinity fronts are observed which are largely density compensating at the subantarctic and cold core eddy fronts horizontal temperature and salinity gradients in the upper mixed layer compensate each other in such a way that no density front is found deep subpycnocline mixed layers occur in the poleward lobes of the brazil current during austral spring suggestive of previous winter convection

bacterially mediated supergene alteration and redistribution of copper in mineralised rocks at the salobo iocg deposit brazil abstract the primary ore at the giant salobo iron oxide copper gold iocg deposit in brazil is dominated by magnetite and fe rich silicates with minor 1 disseminated cu fe sulphides and a distinctive absence of pyrite supergene fe silicate and sulphide oxidation has been mediated by bacteria commonly within micrometre scale acidic environments but silicate dominated acid neutralisation has maintained ambient circumneutral ph supergene cu mobility has been controlled by the highly localised fe dominated biogeochemical processes with cu redistribution on the micrometre to metre scales and negligible supergene cu enrichment silicates especially the phyllosilicates biotite and chlorite have variably altered to the clay minerals vermiculite and or smectite and ultimately to kaolinite leaching of mn fe mg and si accompanied silicate alteration with minor addition of cu to clay mineral structures and along cleavage planes iron mobilised by bacterial oxidation processes initially precipitated as ferrihydrite with up to 10 wt cu most cu and mn mobilised in localised acidic environments were precipitated nearby metre scale at circumneutral ph and reflect the immediate supergene biogeochemical environments cu carbonates pseudomalachite chrysocolla and cu mn oxides copper wad the early stages of these natural supergene processes were simulated in laboratory leaching studies using a range of fresh rocks inoculated with an endemic iron oxidising strain of acidithiobacillus ferrooxidans previously cultured from the salobo site bacterially mediated precipitation of ferrihydrite commonly cu bearing in these experiments strongly resembles that seen in the natural outcrops these leaching experiments confirmed the effectiveness of silicate dominated acid neutralisation especially when accompanied by bornite oxidation which is also acid consuming in contrast chalcopyrite oxidation is acid producing and leads to more effective localised cu mobility in solution our combination of field and laboratory observations at the salobo iocg deposit shows that the biogeochemical environment dominated by fe silicates with little sulphides typical for these systems has led to an entirely different style of supergene cu redistribution from that seen at many other cu deposits such as chalcopyrite and pyrite rich porphyry copper deposits where substantial supergene cu enrichment has occurred

variation of permeability with porosity in sandstone diagenesis interpreted with a fractal pore space model permeability is one of the key rock properties for the management of hydrocarbon and geothermal reservoirs as well as for aquifers the fundamental equation for estimating permeability is the kozeny carman equation it is based on a capillary bundle model and relates permeability to porosity tortuosity and an effective hydraulic pore radius which is defined by this equation whereas in clean sands the effective pore radius can be replaced by the specific surface or by the grain radius in a simple way the resulting equations for permeability cannot be applied to consolidated rocks based on a fractal model for porous media equations were therefore developed which adjust the measure of the specific surface and of the grain radius to the resolution length appropriate for the hydraulic process these equations are calibrated by a large data set for permeability formation factor and porosity determined on sedimentary rocks this fractal model yields tortuosity and effective pore radius as functions of porosity as well as a general permeability porosity relationship the coefficients of which are characteristic for different rock types it can be applied to interpret the diagenetic evolution of the pore space of sedimentary rocks due to mechanical and chemical compaction with respect to porosity and permeability

hypersulfidic deep biosphere indicates extreme sulfur isotope fractionation during single step microbial sulfate reduction coexisting dissolved sulfide and sulfate from hypersulfidic interstitial waters of a 380 m long sediment core show a large isotopic difference of up to 72 caused by in situ microbial sulfate reduction this is considerably larger than the assumed biological maximum of 46 derived from laboratory studies with pure cultures of sulfate reducing bacteria similar high fractionations inferred from sedimentary metal sulfides have been previously explained by a multistage process involving sulfide reoxidation and disproportionation of sulfur intermediates our data show that extreme isotopic differences between sulfate and the reduced sulfur species can also be generated during microbial single step fractionation this result indicates that the sulfate reducing communities and or their cellular metabolic activities in the deep biosphere may differ from those observed in near surface sediments or the water column

micro textures and in situ sulfur isotopic analysis of spheroidal and zonal sulfides in the giant jinding zn pb deposit yunnan china implications for biogenic processes abstract the jinding deposit in yunnan southwest china is the largest sandstone and conglomerate hosted zn pb deposit in the world in this paper we report various micro textures of spheroidal and zonal sulfides such as pellet shaped and colloform aggregates of pyrite and sphalerite from the deposit and interpret them to be possibly related to micro colonies of sulfate reducing bacteria probably supporting an in situ bsr hypothesis micro scale sulfur isotope analysis in different parts of the spheroidal and zonal sulfide aggregates using secondary ion mass spectrometry sims revealed 34s vcdt values as low as 48 4 for sulfides formed in the early main stage disseminated ores in the western part of the deposit possibly suggesting maximum sulfur isotopic fractionation through bsr relatively elevated 34s vcdt values 7 7 to 34 8 mainly from 10 to 20 for the late stage cavity filling ores in the eastern part of the deposit are interpreted to be possibly related to elevated temperatures close to the hydrothermal conduit and elevated 34s values of the remaining sulfates resulting from the preceding bsr processes the apparent discrepancy between the low temperatures required for bsr and the high temperatures indicated by fluid inclusions 120 c may be reconciled through invoking episodic influx of ore forming hydrothermal fluids into a shallow relatively cool environment it is proposed that the host rocks of the jinding deposit have not been buried to great depths 1 km which combined with the availability of hydrocarbons in the jinding dome a paleo oil and gas reservoir provides an ideal environment for bsr episodic influx of metal carrying hydrothermal fluids temporarily and locally suppressed bsr and promoted thermo chemical sulfate reduction tsr resulting in deposit and micro scale variations of 34s

ore depositional process in the navan zn pb deposit ireland the navan zn pb deposit in ireland is hosted by a lower carboniferous carbonate dominated sedimentary sequence in excess of 97 percent of the ore is hosted by a courceyan shallow water succession termed the pale beds the ore occurs as complex strata bound tabular lenses often dislocated by faulting and truncated by a submarine erosional slide structure above this surface unconformity lies the economically minor but genetically important conglomerate group ore hosted by a complex debris flow termed the boulder conglomerate timing constraints on the mineralization can be defined by the relationship to the erosion surface and style of mineralization suggesting a late chadian or early arundian age approximately 345 ma the bulk of the ore formed below the erosion surface in the semilithified to lithified pale beds ore the mineralogy of the economic ores is relatively simple being dominated by sphalerite and galena in a 5 1 ratio pyrite and marcasite are present in subordinate amounts in the majority of the pale beds ore but dominate the conglomerate group ore and the pale beds ore immediately below the erosion surface particularly lens 2 1 gangue minerals are dominated by calcite dolomite and barite the morphology of the mineralization reflects subsea floor emplacement the orebody occurs as numerous strata bound horizons ranging from intense high grade massive sulfides to lower grade sulfide layers separated by barren limestone in all cases there is strong evidence for tectonic disruption during ore deposition sulfides were dominantly deposited as open space growth and replacement of host rock open space textures include dendritic skeletal stalactitic internal sediment geopetal and coarse bladed forms the general absence of coarse euhedral cavity lining textures or substantial collapse brecciation suggests that large cavities were not present prior to mineralization replacement textures range from delicate pseudomorphs of biodasts to more destructive granular styles sulfide sulfur isotope analyses exhibit two dominant groupings of delta 34 s from around 23 to 5 and 0 to 15 per mil respectively and a third minor grouping around 32 to 28 per mil at least two sources of sulfur are invoked values around 23 to 15 per mil are considered to be the result of bacteriogenic reduction of lower carboniferous seawater sulfate approximately 20ppm with a characteristic fractionation around 35 to 45 per mil away from sulfate this is the most common range of delta 34 s in the deposit values around 8 to 15 per mil are interpreted to be hydrothermal sulfide transported with the metal bearing fluid mixing of these two components is inferred from the isotopic data and trends in the mineral paragenesis barite has a mean of delta 34 s 21 or 2 per mil which falls within the range generally recognized for lower carboniferous seawater sulfate we consider that contemporaneous seawater sulfate was the dominant source of sulfur in the barite at navan implying that seawater accessed the pale beds at the time of mineralization

modeling flow and reactive transport to explain mineral zoning in the atacama salt flat aquifer chile geochemical processes are typically neglected when modeling groundwater flow in highly saline systems in the atacama salt flat northern chile field data indicate that the main aquifer presents a mineralogical zoning consisting of carbonates sulfates and halite which is a result of precipitation and or dissolution reactions when precipitation and or dissolution of minerals are active processes in the aquifer physical properties that control groundwater flow such as porosity and permeability would also change until now groundwater flow in the atacama salt flat has been simulated with conventional constant or variable density flow models this study for the first time investigated the importance of incorporating geochemical processes in modeling the atacama salt flat aquifer in particular the impact of mineral precipitation dissolution on aquifer s physical properties and flow patterns was studied to this end the shemat code was utilized to develop a two dimensional numerical groundwater flow model in the eastern border of the atacama salt flat the shemat code solves the classic groundwater flow equation coupled to the reactive transport of ions and mineral precipitation with variable density viscosity porosity and permeability when geochemical processes were included in the simulations the model reproduced reasonably well the mineral zoning evidenced by field observations mineral precipitation was responsible of a strong permeability reduction in areas of the aquifer associated with halite and calcite formation permeability alterations were responsible of changes in the equivalent freshwater head that resulted in significant flow pattern variations compared to variable density flow models these results highlight the importance of considering geochemical processes that modify the aquifer s physical properties when modeling groundwater flow in highly saline aquifers such as the atacama salt flat aquifer

fractal model for permeability calculation from porosity and pore radius information and application to excavation damaged zones surrounding waste emplacement boreholes in opalinus clay abstract an excavation damaged zone edz around emplacement boreholes for radioactive waste represents a potential pathway for radionuclides due to its increased porosity and crack permeability as clay is one of the potential host rocks for radioactive waste disposal a methodical approach was developed for permeability calculation of damaged opalinus clay the approach was based on a permeability porosity relationship and on the theory of fractals which allows the description of rock mass properties by fractal dimensions it was calibrated against laboratory test data and provides the possibility to calculate the permeability from the pore size parameters effective porosity and pore radius as well as from the fractal dimension an application of this relationship was given in terms of calculating the edz permeability around a vertical 50 m deep emplacement borehole in opalinus clay at a german generic repository site the particle flow code pfc was applied to simulate the fissure development in the edz the results of the simulation provide the necessary pore size parameters considering the thermo mechanical impact of adjacent already filled boreholes in an emplacement field for heat generating radioactive waste the crack occurrence and evolution over time in the edz of a newly drilled borehole was calculated on a 2d horizontal plane a 3d calculation as well as a verification against in situ data is still pending

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

core flooding laboratory experiment validates numerical simulation of induced permeability change in reservoir sandstone 1 numerical simulation of reactive transport was validated in a core flooding experiment simulating conditions in a managed geothermal reservoir permeability was measured along a sandstone core prepared with anhydrite and subjected to a temperature gradient anhydrite was dissolved and precipitated in the cold upstream and hot downstream regions of the core respectively the numerical code shemat was used to simulate coupled transport and chemical reactions at the temperature front http www rwth aachen de geop shemat it comprises an extended version of the geochemical speciation code phrqpitz for calculating chemical reactions in brines of low high ionic strength and temperatures of 0 150 c permeability is updated to porosity via a novel calibrated power law based on a fractal pore space model resulting in a large exponent of 11 3 simulation results agree well with measured permeability this both validates the model and demonstrates that the fractal relationship is crucial for a successful simulation of this type of reactive transport