floating gold grains and nanophase particles produced from the biogeochemical weathering of a gold bearing ore a gold bearing ore from the san salvador vein capillitas mine argentina was exposed to an enriched iron and sulfur oxidizing bacterial consortium for two months in an experimental system that represented an oxidized acid leached weathering environment within this laboratory model the dissolution of metal sulfide minerals by the bacterial consortium liberated gold grains that floated on water surficial crevices on grains contained detrital material associated with m scale gold rich bacteriomorphic structures interpreted to be relics of gold dissolution the presence of nanophase gold particles i e colloids and octahedral platelets was attributed to gold reprecipitation these secondary gold structures suggest that gold dissolution reprecipitation i e cycling was occurring concurrently with the bacterially catalyzed dissolution of metal sulfides the flake like morphology and small size of gold grains i e high surface area to volume ratio increased by m scale surface dissolution textures would have enhanced their propensity to float the liberation of buoyant gold grains and secondary gold particles could contribute to rapid gold mobility and dispersion in natural environments

transport related mylonitic ductile deformation and shape change of alluvial gold southern new zealand abstract gold is a malleable metal and detrital gold particles deform via internal distortion the shapes of gold particles are commonly used to estimate transport distances from sources but the mechanisms of internal gold deformation leading to shape changes are poorly understood because of subsequent recrystallisation of the gold in situ in placer deposits which creates a rim zone around the particles with undeformed 10 m grains this paper describes samples from southern new zealand in which grain size reduction to submicrometer scale and mylonitic textures have resulted from internal ductile deformation these textures have been preserved without subsequent recrystallisation after deposition in late pleistocene holocene alluvial fan placers these mylonitic textures were imposed by transport related deformation on recrystallised rims that were derived from previous stages of fluvial transportation and deposition this latest stage of fluvial transport and deformation has produced numerous elongated gold smears that are typically 100 m long and 10 20 m wide these smears are the principal agents for transport induced changes in particle shape in the studied placers focused ion beam fib sectioning through these deformed zones combined with scanning electron microscopic sem imaging show that the interior of the gold particles has undergone grain size reduction to 500 nm and extensive folding with development of a ductile deformation fabric that resembles textures typical of mylonites in silicate rocks relict pods of the pre existing recrystallised rim zone are floating in this ductile deformation zone and these pods are irregular in shape and discontinuous in three dimensions micrometer scale biologically mediated deposition from groundwater of overgrowth gold on particle surfaces occurs at all stages of placer formation and some of this overgrowth gold has been incorporated into deformation zones these examples provide a rare view into the nature of the physical processes that accommodate gold particle shape change during sedimentary transport

application of microfocus computed tomography in carbonate reservoir characterization possibilities and limitations normally thin section petrography by which observations are made in two dimensions forms the basis of sedimentpetrological reservoir appraisal studies in reservoir characterization however insight in the three dimensional mineral and porosity distribution is necessary in this study microfocus computed tomography ct which is a non destructive technique has been used for 3d characterization of the mineral phases i e calcite dolomite anhydrite and porosity in carbonate reservoir rocks in order to obtain quantitative information on density and atomic number of the scanned reservoir samples as well as about their rock texture a dual energy scanning technique has been used additional beam artifact correction and a segmentation algorithm focused on differentiating calcite dolomite and anhydrite have been implemented to validate the developed methodology thin sections of scanned samples of the khuff formation oman have also been analyzed petrographically and compared to corresponding ct sections and to the results of the dual energy algorithms despite the lower resolution when compared to thin section analysis the accuracy of the dual energy technique is in the range of the standard point counting technique and estimations can be made concerning the microporosity of the samples since the developed dual energy methodology provides a fast and objective determination of the percentages of the mineralogical phases ct becomes a very powerful tool in the evaluation of the reservoir potential and in the quantification of mineralogical changes in sedimentary systems e g cycles in addition images are acquired visualizing and quantifying the spatial distribution of these phases in three dimensions which is a major advantage compared to classic 2d thin section petrography

development of a shear flow test apparatus and determination of coupled properties for a single rock joint abstract a new laboratory technique for coupled shear flow tests of rock joints was developed and used to investigate the coupled effect of joint shear deformation and dilatancy on hydraulic conductivity of rock joints this technique was used to carry out coupled shear flow tests with an artificial created granite joint sample under constant normal loads and up to residual shear deformations of 20 mm the hydraulic conductivity was estimated by using a finite difference method and an approximate equation assuming the cubic law the shear flow testing results revealed that the change of hydraulic conductivity is approximately similar to that of the dilatancy of a joint the hydraulic conductivity increases rapidly by about 1 2 1 6 orders of magnitude for the first 5 mm of shear displacement after passing the residual shear stress the hydraulic conductivity becomes gradually a constant value with increasing shear displacement on the other hand the hydraulic conductivity after shearing is about one order of magnitude larger than that prior to shearing shear flow coupling characteristics obtained from these tests have a consistent trend with barton s model prediction during the initial shear process however increasing deviation between measured and predicted hydraulic conductivity of rock joint samples has been observed with increasing shear displacement

extremely rapid and localized recharge to a fractured rock aquifer the factors that govern recharge to fractured rock aquifers with overlying soil are poorly understood the objective of this study is to determine if recharge to a fractured crystalline aquifer in a humid climate is governed by heterogeneous fracture networks and or overlying soil characteristics a 10 km2 study area is instrumented with a network of 15 bedrock wells completed to observe conditions in the shallow bedrock aquifer hydrogeological characterization detailed observation of the 2007 snowmelt freshet and numerical simulations are used snowmelt is a valuable natural tracer because it has a distinct thermal and isotopic signature and is applied simultaneously and evenly to the entire ground surface results indicate that soil thickness and bedrock transmissivity are both highly heterogeneous at the site scale but that much of the study area is underlain by silty sand with a thickness of 1 m cold 2h depleted snowmelt locally recharged the bedrock aquifer to depths of at least 20 m within two days since recharge is typically quantified and discussed as an annual flux the snowmelt event is extremely rapid however hydraulic isotopic and thermal data also indicate that most wells did not rapidly recharge numerical simulations indicate that soil thickness and hydraulic conductivity are critical parameters that controls whether the underlying bedrock aquifer rapidly recharges the vertical fracture aperture number of vertical fractures the amount of snowmelt water table gradient depth to water table and pressure saturation relations are all less significant controls on the rate and amount of rapid recharge both field results and numerical simulations indicate that the rapid recharge process is localized to areas where the soil is very thin such as the fringes of outcrops outcrops are exposed in 0 1 of the study area indicating that the process of rapid recharge is also extremely localized this poorly documented hydrogeologic phenomenon has broad implications for groundwater management and protection as well as our understanding of recharge processes in fractured rock aquifers

application of high resolution x ray computed tomography to mineral deposit origin evaluation and processing abstract high resolution x ray computed tomography ct is the industrial equivalent of medical cat scanning and provides a mechanism for non destructive studies of the three dimensional nature of geological materials hrxct produces two dimensional images slices that reveal the interior of an object as if it had been sliced open along the image plane for viewing a ct image is generated by differences in x ray attenuation that arise from differences in density and composition within the object by acquiring a contiguous set of slices volumetric data for all or part of a sample can be obtained allowing three dimensional inspection and measurement of features of interest ct is particularly effective in the study of metallic ores that commonly contain minerals spanning the range of densities of natural materials available software can produce grain shape size and orientation data from the scanned volume which can be particularly useful for oriented samples ct is particularly useful for studies of gold and other precious metal bearing minerals that typically have significant contrast even with common metallic mineral phases ct precisely defines the in situ location of mineral grains of interest within a sample which then can be studied in conventional petrographic sections and other forms of data collected e g isotope or trace element geochemistry another area of application is fluid inclusions which can be discerned even in opaque phases and fluid and vapor volumes measured for sufficiently large occurrences we summarize ct principles and review available instrumentation as well as scanning and data reduction protocols that provide unique three dimensional information for diverse ore types and applications in mineral deposits geology ct applications for economic geology and other fields will continue to expand as instruments continue to evolve and as scanning protocols and applications are extended for more precise quantification of three dimensional relationships particularly for fine grained particles and small fluid inclusions in larger volumes and for separation of minerals with limited contrast

a continuum model for water movement in an unsaturated fractured rock mass the movement of fluids in a fractured porous medium has been the subject of considerable study this paper presents a continuum model that may be used to evaluate the isothermal movement of water in an unsaturated fractured porous medium under slowly changing conditions this continuum model was developed for use in evaluating the unsaturated zone at the yucca mountain site as a potential repository for high level nuclear waste thus its development has been influenced by the conditions thought to be present at yucca mountain a macroscopic approach and a microscopic approach are used to develop a continuum model to evaluate water movement in a fractured rock mass both approaches assume that the pressure head in the fractures and the matrix are identical in a plane perpendicular to flow both approaches lead to a single flow equation for a fractured rock mass the two approaches are used to calculate unsaturated hydrologic properties i e relative permeability and saturation as a function of pressure head for several types of tuff underlying yucca mountain using the best available hydrologic data for the matrix and the fractures rock mass properties calculated by both approaches are similar

transient pulse test and morphological analysis of single rock fractures abstract transient pulse tests were performed on single rock fractures at different confining pressures a new data analysis method based on polynomial fitting was introduced to investigate the relationship between flow velocity and hydraulic gradient 3d laser scanning was used to quantify the morphological changes of the fracture surface after the transient pulse test or under the hydro mechanical coupling effect the results show that the flow velocity versus hydraulic gradient data gradient shows a nonlinear relationship at very low hydraulic possibly due to strong solid water interaction but becomes approximately linear after the hydraulic gradient is high enough the permeability of a single fracture is sensitive to the confining pressure as the confining pressure increases the permeability first remarkably decreases when the confining pressure is lower than a certain value and then decreases at a much lower speed when the confining pressure is higher than that value both mechanical and hydraulic apertures decrease at a decreasing rate with the increase in confining pressure the effect of fracture roughness on the permeability is related to the magnitude of the confining pressure rougher fractures have lower permeability at low confining pressures but the opposite can be true when the confining pressure is high enough roughness is no longer critical to permeability when the confining pressure is over a certain value

hydromechanical behavior of a deformable rock fracture subject to normal stress lbl 12297 preprint to be published in the journal of geophysical research hydromechanical behavior of a deformable rock fracture subject to normal stress y w tsang and p a witherspoon january 1981 two week loan copy this is a library circulating copy which may be borrowed for two weeks for a personal retention copy call tech info diu is ion ext 6782 prepared for the u s department of energy under contract w 7405 eng 48

biogeochemical cycling of gold transforming gold particles from arctic finland abstract bio geochemical cycling of gold au has been demonstrated in present day semi arid sub tropical and temperate environment hereby biofilms on au bearing mineral and au particle surfaces drive au dispersion and reconcentration thereby trans forming the particles however it is unknown if biogeochemical cycling of au occurs in polar environments where air temperatures can reach 40 c and soils remain frozen for much of the year therefore placer au particles soils and waters were collected at two placer mining districts in arctic finland i e the ivalojoki and lemmenjoki goldfields sites were chosen based on contrasting settings glacio fluvial vs glacial till deposits and depths surface to 5 m below current surface gold particles were studied using a combination of tagged 16s rrna gene next generation sequencing and electron microscopic micro analytical techniques across all sites a range of au particle morphologies were observed including morphotypes indicative of au dissolution and aggregation elevated au concentrations indicative of au mobility were detected in placer particle bearing soils at both districts typically au particles were coated by polymorphic biofilm layers composed of living and dead cells embedded in extracellular polymeric substances intermixed were biominerals clays and iron sulfides oxides and abundant secondary au morphotypes i e nano particles micro crystals sheet like au branched au networks and overgrowths and secondary rims biofilms communities were composed of acidobacteria 18 3 bacteroidetes 15 1 and proteobacteria 47 1 with proteobacteria 19 5 being the most abundant proteobacterial group functionally biofilms were composed of taxa contributing to biofilm establishment exopolymer production and nutrient cycling abundant taxa capable of au mobilization detoxification and biomineralization among them cupriavidus metallidurans acinetobacter spp and pseudomonas spp were detected in conclusion these results demonstrate that placer au particle transformation and au dispersion occur in cold arctic environments this corroborates the existence of biogeochemical au cycling in present day cold environments

evaluation of van genuchten mualem model on the relative permeability for unsaturated flow in aperture based fractures abstract the relative permeability versus saturation relation is fundamental for modeling unsaturated flow processes in aperture based fractures on the basis of the local cubic law and the connectivity probability of aperture distribution within single fractures an analytical relationship between the relative permeability and saturation is established when the van genuchten function on the description of the capillary pressure saturation relationship is applied an explicit mathematical expression between the relative permeability and saturation is gained similar to the form of the van genuchten mualem vg m model of porous media through the comparisons between the several series of laboratory measured data available in the literature and theoretical results good agreements are both presented and they suggest that the proposed vg m model can be successfully used for aperture based fractures as well as porous media to understand aperture variation dependence of the relative permeability properties a computational method combining fractal theory and the invasion percolation model to determine the empirical parameters associated with the spatial correlation of aperture distribution is developed simulated fractures with spatially correlated and uncorrelated aperture distributions corresponding respectively to small and large fractal dimensions are both studied according to the simulated results the residual saturation generally increases with fractal dimension increments however the value of m exhibits a weak dependence on fractal dimension the proposed model can be applied to various engineering such as seepage control for rock slopes petroleum reservoirs nuclear waste disposal and geologic storage of carbon dioxide

review of close range three dimensional laser scanning of geological hand samples abstract the morphological study of geological hand samples has a wide variety of applications in the geosciences which is conventionally accomplished by measuring the distance between features of interest on the sample s surface close range three dimensional 3d laser scanners provide an opportunity to study the form and shape of geological samples in a digital environment and have been increasingly utilized in fields such as paleontology rock mechanics and sedimentology with some uptake in planetary sciences and structural geology for paleontological studies primary applications are in quantitative analysis of fossil morphology and integration into 3d animated models for understanding species movements in the field of rock mechanics typical uses of 3d digital geological hand sample models include quantifying joint roughness coefficient jrc determining the surface roughness of rock samples and assessing morphological changes over time due to processes such as weathering in the field of sedimentology such models are incorporated to characterize the shape of sediment particles and to calculate key parameters such as bulk density this paper aims to provide a comprehensive review of established literature that includes substantial use of digital geological hand samples acquired from 3d close range

measurement of field saturated hydraulic conductivity on fractured rock outcrops near altamura southern italy with an adjustable large ring infiltrometer up to now field studies set up to measure field saturated hydraulic conductivity to evaluate contamination risks have employed small cylinders that may not be representative of the scale of measurements in heterogeneous media in this study a large adjustable ring infiltrometer was designed to be installed on site directly on rock to measure its field saturated hydraulic conductivity the proposed device is inexpensive and simple to implement yet also very versatile due to its large adjustable diameter that can be fixed on site it thus allows an improved representation of the natural system s heterogeneity while also taking into consideration irregularities in the soil rock surface the new apparatus was tested on an outcrop of karstic fractured limestone overlying the deep murge aquifer in the south of italy which has recently been affected by untreated sludge disposal derived from municipal and industrial wastewater treatment plants the quasi steady vertical flow into the unsaturated fractures was investigated by measuring water levels during infiltrometer tests simultaneously subsurface electrical resistivity measurements were used to visualize the infiltration of water in the subsoil due to unsaturated water flow in the fractures the proposed experimental apparatus works well on rock outcrops and allows the repetition of infiltration tests at many locations in order to reduce model uncertainties in heterogeneous media

quantification of sulfur and phosphorus within secondary gold rims on yukon placer gold an examination of yukon placer gold nuggets using ultrathin section 70 nm transmission electron microscopy and energy dispersive x ray spectroscopy revealed three distinct morphological and compositional regions the outer surface of the nuggets possessed silicate minerals which included electron dense particles containing gold 13 6 to 27 2 at and silver 6 7 to 13 2 at the organic composition of these particles ranged from 7 3 to 12 3 at s and 0 53 to 1 5 at p 4 4 to 5 4 at po the periphery of the nuggets also possessed crystalline gold bearing material that was enriched with gold 81 to 93 12 at 30au 1ag compared to the particulate material 2au 1ag present within the silicate minerals annealed to the nuggets surface the organic composition of this peripheral secondary gold ranged from 0 29 to 5 9 at s and from 0 63 to 5 9 at p 4 5 to 9 5 at po the internal structure of the secondary gold around the periphery of the nuggets was highlighted by the occurrence of compositional banding caused by these lighter electron translucent compounds internal regions of the nuggets were composed of gold or gold and silver indicating the presence of an original unweathered grain that served as a nucleating site these findings suggest that sulfur and phosphorus presumably of biological origin are important to placer gold formation

fully coupled poroelastic peridynamic formulation for fluid filled fractures a new fully coupled poroelastic peridynamic formulation is presented and its application to fluid filled fractures is demonstrated this approach is capable of predicting porous flow and deformation fields and their effects on each other moreover it captures the fracture initiation and propagation in a natural way without resorting to an external failure criterion the peridynamic predictions are verified by considering two benchmark problems including one and two dimensional consolidation problems moreover the growth of a pre existing hydraulically pressurized crack case is presented based on these results it is concluded that the current peridynamic formulation has a potential to be used for the analysis of more sophisticated poroelastic problems including fluid filled rock fractures as in hydraulic fracturing

preliminary evidence for the involvement of budding bacteria in the origin of alaskan placer gold lacelike networks of micrometre size filiform gold associated with alaskan placer gold particles are interpreted as low temperature pseudomorphs of a pedomicrobium like budding bacterium submicron reproductive structures hyphae and other morphological features similar to those of pedomicrobium manganicum occur as detailed three dimensional facsimiles in high purity gold in and on placer gold particles from lillian creek alaska in a scanning electron microscope survey the majority of gold particles at nine alaskan placer deposits appear to include gold that has accumulated chemically at low temperatures in and on the cells of p manganicum similar bacterioform gold from a paleozoic deposit in china and from the precambrian witwatersrand deposit in south africa may indicate that bacterioform gold is widespread

constraints for flow regimes on smooth fracture surfaces 1 in recent years significant advances have been made in our understanding of the complex flow processes in individual fractures aided by flow visualization experiments and conceptual modeling efforts these advances have led to the recognition of several flow regimes in unsaturated individual fractures subjected to different initial and boundary conditions for an idealized smooth fracture surface the most important regimes are film flow rivulet flow and sliding of droplets the existence of such significantly dissimilar flow regimes has been a major hindrance in the development of self consistent conceptual models of flow for single fracture surfaces that encompass all the flow regimes the objective of this study is to delineate the existence of the different flow regimes in individual fracture surfaces for steady state flow conditions we developed physical constraints on the different flow regimes that satisfy minimum energy configurations which enabled us to segregate the wide range of fracture flux volumetric flow rate per fracture width into several flow regimes these are in increasing order of flow rate flow of adsorbed films flow of sliding drops rivulet flow stable film flow and unstable turbulent film flow the scope of this study is limited to wide aperture smooth fractures with the flow on the opposing sides of fracture being independent

supergene gold in silcrete as a vector to the scuddles volcanic massive sulfides western australia this study reports data on the first occurrence of economic supergene au in a near surface silcrete horizon over the scuddles volcanic massive sulfide vms deposit in the golden grove district western australia a deep weathering profile was developed on dacite rhyodacite siltstone and breccia that host primary cu zn and pb sulfides with au ag ore from the base the weathering profile at scuddles is subdivided into five main zones 1 supergene sulfide enrichment zone 2 supergene oxide enrichment zone 3 ferruginous saprolite 4 leached zone of kaolinitic saprolite and silcrete and 5 lateritic zone of mottled clays ferruginous duricrust and gravels silcrete at scuddles hosts supergene au deposit that formed in two generations the first is intimately associated with ag halides during supergene enrichment of the primary vms and the second is associated with kaolinite in dissolution cavities inside ag halides during lateritic weathering these two au generations imply more than one mechanism of au remobilization and formation multiple fluid pathways and superimposed episodes of weathering under variable timing and climatic conditions gold grains are pure nanocrystalline up to 10 nm and clustered together forming microcrystalline aggregates a few au grains are residual in silcrete with ag sb rich cores and ag poor rims possibly formed during dealloying of ag and sb chemically au in silcrete is associated with a multi element concentration of ag i br cl sb sn bi hg mo w te and ge gold and ag in the supergene weathering profile were mobilized to silcrete as a halide complex under acidic and saline conditions generated during the oxidation of massive sulfides at depth the precipitation of au ag halides in the silcrete may have taken place in response to a rise in ph gold was likely remobilized with kaolinite from the surface lateritic zone facilitated by decays of plant roots and bioturbation the clustered spongy cube octahedral platy six sided dendritic and reniform like morphologies of au in cavities inside ag halides may indicate biogenic related processes in its precipitation recognizing au ag rich silcrete over the buried vms at scuddles highlights the significance of the silcrete in finding buried vms particularly if the gossan is absent

the in vitro growth of gold grains gold colloids octahedral platelets and foils directly and indirectly formed from the reduction of soluble au i thiosulfate and au iii chloride complexes by iron oxidizing bacteria cyanobacteria and sulfate reducing bacteria were combined in an experimental system this system represented simplified biogeochemical conditions occurring within a fluvial environment in which placer au could occur in this study biofilm formation and physical aggregation i e sedimentation processes were critical for the accumulation of nanometer to micrometer sized au particles into grains 4 5 mm in size characterization of grain surface textures by scanning electron microscopy in association with monitoring soluble au concentrations over time suggested that dissolution and reprecipitation processes were occurring at the au grain fluid interface this laboratory model demonstrates that the biogeochemical cycling of au can contribute to the formation of anomalous enrichments such as placer au deposits

characterizing coal cleats from optical measurements for cbm evaluation abstract in this study we apply fracture characterization techniques common to many other reservoir rocks to coals additionally the data gathered from this technique is used to determine fracture permeability and porosity based on a cubic relationship between permeability and porosity as a function of aperture and spacing however these data are in an unconfined stress state to relate this information to the subsurface which is in a confined state the results are then compared and calibrated to permeability data determined from laboratory triaxially confined samples using the same sample material a 1d scanline technique is used to gather data on cleat aperture spacing height and frequency sixteen different coals from several european basins were examined creating a large dataset 8000 individual data measurements this data was gathered from blocks of coals and from polished sections the polished sections were digitally scanned under the microscope to create an image of the whole section as a result we examined a range of scales from micrometers to centimeters maximum minimum and median values are determined for each attribute to clearly define the limits of resolution of the data a practical pore resolution is applied to a power law function of the data cleat attributes were further examined to determine a relationship with cleat type e g face or butt and lithotype power law distributions of butt cleat attributes are similar to the distributions found in lithotype it was concluded that butt cleats are more strongly related to lithotype and thus bed thickness and mechanical strength of the bed than face cleats cleat aperture and spacing depend on cleat type a face to butt cleat ratio of 5 1 given an aperture of about 12 m was found this is similar to a published anisotropy in permeability where face cleats are five times more permeable than butt cleats cleat porosity from aperture and spacing is several times greater than cleat porosity calibrated to laboratory permeability under stress the calibrated porosity ranged from 0 01 to 1 8 and agrees with published values of in situ cleat porosity thus aperture width due to an increase in stress is predicted to decrease four times this data can be used to calibrate reservoir simulators for cbm production

ct scanning and flow measurements of shale fractures after multiple shearing events abstract a shearing apparatus was used in conjunction with a hassler style core holder to incrementally shear fractured shale cores while maintaining various confining pressures computed tomography scans were performed after each shearing event and were used to obtain information on evolving fracture geometry fracture transmissivity was measured after each shearing event to understand the hydrodynamic response to the evolving fracture structure the digital fracture volumes were used to perform laminar single phase flow simulations local cubic law with a tapered plate correction model to qualitatively examine small scale flow path variations within the altered fractures fractures were found to generally increase in aperture after several shear slip events with corresponding transmissivity increases lower confining pressure resulted in a fracture more prone to episodic mechanical failure and sudden changes in transmissivity conversely higher confining pressures resulted in a system where after an initial setting of the fracture surfaces changes to the fracture geometry and transmissivity occurred gradually flow paths within the fractures are largely controlled by the location and evolution of zero aperture locations a reduction in the number of primary flow pathways through the fracture and an increase in their width was observed during all shearing tests

revisiting hydrocarbon phase mobilization of au in the au hg mclaughlin mine geysers clear lake area california abstract carbonaceous material cm enriched silica is co located with gold au mineralization at the au hg mclaughlin deposit geysers clear lake area california u s a the co location suggests that hydrocarbons hc may be involved in mineralization and metal concentration processes but little is known about the role of hc in the formation of ore deposits previous studies noted liquid oil inclusions in samples from the mclaughlin deposit and proposed that the hc were liquid at the time of ore deposition hydrocarbon materials in the mclaughlin deposit occur as solid and liquid textural evidence suggests that hydrocarbon rich and aqueous silica rich fluids were present simultaneously as well as separately in alternating pulses synchrotron x ray fluorescence microscopy of microscopic silica free carbonaceous material reveals that the cm contains abundant ore metals e g au ag hg and pb the cm could have become metal enriched by scavenging metals from other ore fluids or it could have transported metals when the cm was still liquid with subsequent in situ degradation due to hydrothermal heat gold concentrations of up to 18 ppm were measured via acid digestion of solid and liquid hc material and subsequent inductively coupled plasma mass spectrometry icp ms analyses hydrocarbon material with liquid to medium viscous properties bearing 10 8 ppm au provides evidence that au in liquid hc in the mclaughlin au hg deposit is still mobile and that remobilization and or transport of metals to the deposit by hc liquids cannot be ruled out

liquid release tests in unsaturated fractured welded tuffs ii numerical modeling abstract we have carried out a numerical modeling study in conjunction with the in situ liquid release experiment described in salve et al j hydrol 257 2001 the experiment site is a highly fractured welded tuff accessed from the exploratory studies facility an underground laboratory in the unsaturated zone at yucca mountain nevada the experiment examines the effect of the rock matrix on liquid flow and transport that occurs primarily through the fracture network the purpose of the modeling is to aid in experimental design predict experimental results and study the physical processes accompanying liquid flow through unsaturated fractured welded tuff the model uses cubic elements arranged in a regular three dimensional grid to represent a 24 m3 block of fractured tuff high permeability fracture elements located deterministically preserve the connectivity of the fracture network which is crucial to its ability to conduct fluid because element thickness is much greater than fracture aperture fracture elements are assigned properties of a fracture continuum rather than of an individual fracture the fracture network is constructed using fracture geometry data taken from a fracture map of the walls and ceiling of the alcove adjacent to the field test site the network is then refined using the results of air permeability tests model results suggest that it may not be sufficient to conceptualize the fractured tuff as consisting of high permeability fractures embedded in a low permeability matrix the need to include a secondary fracture network with distinct characteristics from the network of larger mapped fractures is demonstrated by comparison to the liquid flow observed in the field

the morphology mineralogy and behavior of u fine grained gold from placer deposits of alberta sampling and implications for mineral exploration the morphology of a large number of gold grains from stream sediments of the north saskatchewan river and the athabasca river was studied together with the partitioning of the placer gold between various size fractions two major morphological varieties of gold were observed 1 flaky scaly gold with folded and hammered edges and with crystals or crystal faces still visible on the surface and 2 sandwiched droplike particles sometimes toroidal about 5 of both types of gold were found to be coated with new secondary gold the size of the majority of the gold grains studied varies between 0 500 and 0 010 mm the most frequent size range in the north saskatchewan river is 0 125 0 250 mm whereas in the athabasca river it is 0 063 0 125 mm an important fraction of the gold from both rivers is smaller than 0 063 mm the average corey shape factor csf of the gravity recovered gold increases as the particle size decreases whereas the gold grains lost to the tailings indicate very low average sha

the deposition of elemental gold from gold i thiosulfate complexes mediated by sulfate reducing bacterial conditions the role of sulfate reducing bacteria in the precipitation of elemental gold through a geologic stratum was investigated using column experiments the mixed culture dominated by sulfate reducing bacteria was isolated from the driefontein consolidated gold mine witwatersrand basin republic of south africa bacterially mediated gold precipitation from the gold i thiosulfate complex was more efficient than the corresponding abiotic experiments in the bacterial systems sulfate reducing bacteria i e desulfovibrio sp deposited gold inside the cells as spherical nanoparticles over time these nanoparticles of gold were released from the cells and deposited at cell surfaces and in the bulk solutions ultimately these nanoparticles of gold contributed to the formation of micrometer scale octahedral gold crystals occasional framboidlike structures 1 5 m diam and millimeter scale gold foils typically surrounding the silicate grains spherical gold particles 1 m diam were precipitated in the abiotic experiments and the formation of octahedral gold framboidlike structures and gold foils were not observed in these experiments the reduction and enrichment of elemental gold by sulfate reducing bacteria occurred without the concomitant death of the bacteria suggesting that in natural systems this process could go on over geologic time scales as long as nutrients and gold i thiosulfate were provided to the system

diversity of channeling flow in heterogeneous aperture distribution inferred from integrated experimental numerical analysis on flow through shear fracture in granite 1 shear mode ii fractures with shear displacements of 1 and 5 mm were generated by direct shear on granite under normal stresses of 1 20 and 60 mpa fracture surface mapping showed that the surface roughnesses of the shear fractures decreased with increasing shear displacement and normal stress and were smaller than those of tensile fractures reported in our previous study fluid flow experiments on the shear fractures provided fracture permeabilities at a wide range of confining pressures of 10 100 mpa nonmonotonic permeability was usually observed to decrease with increasing confining pressure however the permeability changes were different between the shear fractures generated at the normal stress of 20 and 60 mpa in addition obvious permeability changes with shear displacement were observed for 60 mpa whereas no significant difference was observed for 20 mpa comparing the shear fractures with the tensile fractures having shear displacements revealed clear differences even for equivalent shear displacements numerical models that were constructed using the data of the fracture surface mapping by matching their permeabilities with the experimentally evaluated fracture permeabilities revealed the development of preferential flow paths i e channeling flows for the shear fractures providing a diversity of channeling flow in heterogeneous aperture distributions of rock fractures in the earth s crust

supergene neoformation of pt ir fe ni alloys multistage grains explain nugget formation in ni laterites ni laterites from the dominican republic host rare but extremely platinum group element pge rich chromitites up to 17 5 ppm without economic significance these chromitites occur either included in saprolite beneath the mg discontinuity or as floating chromitites within limonite above the mg discontinuity both chromitite types have similar iridium group pge ipge enriched chondrite normalized patterns however chromitites included in limonite show a pronounced positive pt anomaly investigation of heavy mineral concentrates obtained via hydroseparation techniques led to the discovery of multistage pge grains i os ru fe ir grains of porous appearance are overgrown by ii ni fe ir and ir fe ni pt phases which are overgrown by iii pt ir fe ni mineral phases whereas ir dominated overgrowths prevail in chromitites from the saprolite pt dominated overgrowths are observed within floating chromitites the following formation model for multistage pge grains is discussed i hypogene platinum group minerals pgm e g laurite are transformed to secondary pgm by desulphurization during serpentinization ii at the stages of serpentinization and or at the early stages of lateritization ir is mobilized and recrystallizes on porous surfaces of secondary pgm serving as a natural catalyst and iii at the late stages of lateritization biogenic mediated neoformation and accumulation of pt ir fe ni nanoparticles occurs the evidence presented in this work demonstrates that in situ growth of pt ir fe ni alloy nuggets of isometric symmetry is possible within ni laterites from the dominican republic

the relationship between placer gold particle shape rimming and distance of fluvial transport as exemplified by gold from the klondike district yukon territory canada a semiquantitative study of various physical features of approximately 2 700 gold particles from 21 lode deposits and 36 placer deposits in the klondike district yukon territory canada was undertaken the shape parameters of roundness and flatness were determined using a classification method there appears to be a systematic variation between these parameters and between the parameters and the distance of transport of the particle these relationships were confirmed by quantitative measurements on critical samples rim characteristics were also estimated they show a systematic relationship between one another with the particle shape and less clearly with the distance of transport gold particle shape data shows a smooth well defined relationship to distance of transport from the lode source of the gold both roundness and flatness show a rapid increase within the first 5 km from the lode source and a slower more linear increase beyond this relationship seems to apply worldwide the relationship between the shape of a gold particle and the rim characteristic supports the conclusion that rims are formed by the removal of ag hg and cu and not by the precipitation of au thus rim thickness and the associated high fineness is probably the result of the dynamic process of ag removal in stagnant sediments to create the rim and abrasion in active sediments to remove the rim the composition of the rims represents the stable composition of gold in normal surficial environments together these observations place limits on the occurrence of new gold hammering is the main cause of shape change in fluvially transported gold particles its principal effect is to flatten particles abrasion has its most marked effect on surface texture hammering and abrasion both decrease the mass size and increase the roundness of the gold particles it is therefore possible to make a connection between hydraulic conditions during gold particle transport and its shape change

measurement of capillary pressure curve of dnapl in a water saturated sandstone fracture this paper describes a methodology for the measurement of the capillary pressure curve of dense nonaqueous phase liquids dnapls in a water saturated sandstone induced fracture details of specimen preparation capillary barrier design and capillary pressure measurement setup procedure and results are given the aperture distribution of the induced fracture was estimated using the x ray com puted tomography ct technique the primary drainage or invasion of dnapls in the water saturated induced fracture was simulated using the invasion percolation ip approach it was found that the invasion process was highly dependent on the spatial distribution of the fracture apertures the ip model matched the experimentally measured entry pressure very well but deviated from the measured capillary pressure curve at the midrange and high nonwetting phase saturations the ip model tended to yield an l shaped function with a fairly flat portion at the midrange saturation and a sharp rise at the high end the measured capillary pressure curve was observed to follow the well known brooks corey porous media function these discrepancies between the measured and predicted results could be attributed to the fact that the ip model did not consider the effects of fracture surface roughness and undulation for a fracture with small apertures these two factors could make the fracture behave more as a porous medium than a parallel plate channel doi 10 1061 asce gt 1943 5606 0000590 2012 american society of civil engineers

measurement of aperture distribution capillary pressure relative permeability and in situ saturation in a rock fracture using computed tomography scanning we develop an experimental technique that uses computed tomography ct scanning to provide high resolution measurements of aperture distribution and in situ saturation along with capillary pressure and relative permeability for the same rough walled fracture we apply this technique to an induced fracture in a cylindrical basalt core undergoing water drainage we find that the sum of the water and gas relative permeabilities is much 1 at intermediate saturations and the water relative permeability shows a sharp change over a narrow range of average water saturation in situ saturation maps show channeling of gas and significant retention of the wetting phase water the capillary pressure initially increased and then decreased with decreasing water saturation although this type of capillary behavior is atypical for unsaturated flows we find that the sizes of the gas filled apertures are consistent with the measured capillary pressure

leakage of dense nonaqueous phase liquids from waste impoundments constructed in fractured rock and clay theory and case history this paper examines the behaviour of dense nonaqueous phase liquids dnapls in fractured media with an emphasis on waste disposal ponds constructed in fractured clay and rock calculations are presented to estimate the height of dnapl that may accumulate at the base of a disposal pond prior to initial entry into a water saturated fracture this height is found to be a function of the fluid densities the dnapl water interfacial tension the fracture aperture and the position of the water table a numerical model is applied to estimate the steady state rate of dnapl leakage from a disposal pond underlain by vertical fractures this rate of leakage is found to be a function of the spacing of fractures the fracture aperture the dnapl density and the height of the water table in the formation outside of the impoundment it is demonstrated that a wide range of leakage rates can occur over a relatively narrow range of parameters a conceptual analysis of two phase flow examines the conditions that lead t

on two phase relative permeability and capillary pressure of rough walled rock fractures this paper presents a conceptual and numerical model of multiphase flow in fractures the void space of real rough walled rock fractures is conceptualized as a two dimensional heterogeneous porous medium characterized by aperture as a function of position in the fracture plane portions of a fracture are occupied by wetting and nonwetting phase respectively according to local capillary pressure and accessibility criteria phase occupancy and permeability are derived by assuming a parallel plate approximation for suitably small subregions in the fracture plane for log normal aperture distributions a simple approximation to fracture capillary pressure is obtained in closed form it is found to resemble the typical shape of leverett s j function wetting and non wetting phase relative permeabilities are calculated by numerically simulating single phase flows separately in the wetted and non wetted pore spaces illustrative examples indicate that relative permeabilities depend sensitively on the nature and range of spatial correlation between apertures it is also observed that interference between fluid phases flowing in a fracture tends to be strong with the sum of wetting and nonwetting phase relative permeabilities being considerably less than 1 at intermediate saturations

low temperature sulphate reduction biological versus abiological sulphate is considered to have been a major source of sulphide in strata bound and stratiform base metal sulphide deposits many of these deposits however appear to have been formed at moderate temperatures 200 c which poses the question by what mechanism s was sulphate reduced to sulphide two modes of reduction have been established experimentally 1 catalysis by sulphate reducing bacteria which at present is only known to occur below ca 100 c and 2 abiological reduction by ferrous iron or organic matter which has only been clearly shown above ca 250 c several attempts have been made to demonstrate abiological reduction below 200 c and some new data are presented here although the results do not exclude the possibility that such a reaction may be geochemically significant there has been no unequivocal demonstration of nett sulphide formation from sulphate at these temperatures recent studies of the microbiology of hydrothermal regions have opened up the prospect of bacterial sulp

effect of physical and biogeochemical factors on placer gold transformation in mountainous landscapes of switzerland abstract in surface environments placer gold particles are re shaped by physical chemical and biogeochemical processes this study hypothesizes that in modern landscapes combinations of physical and biogeochemical factors determine placer gold transformation and the composition of biofilm communities living on particle surfaces morphology composition and biofilm communities of placer particles from eight locations in switzerland were analyzed sites reflect a variety of modern day placer environments in mountainous terrains ranging from eluvial sites in close proximity to primary sources to alluvial sites associated with both slow and fast moving streams and to distal glacio fluvial and depositional lake sediments particles are progressively physically and biogeochemically transformed with increasing distance from source variable degrees of rounding gouging and scratching from physical reshaping due to transport and sedimentation processes are evident especially on particles from high energy environments surface textures indicative of biogeochemical gold silver dissolution are common in low energy depositional environments and with increasing distance from source overgrowths of gold nano and micro particles and aggregates are abundant these form micro crystalline layers of secondary gold on particle surfaces covering them to depths of tens of micrometers biofilm communities across all sites are dominated by proteobacteria 669 operational taxonomic units otus 49 8 especially proteobacteria other important phyla include acidobacteria 172 otus 9 7 bacteroidetes 222 otus 11 6 cyanobacteria 26 otus 13 7 and planctomycetes 125 otus 7 1 canonical analysis of principal coordinates demonstrates significant links of community assemblages to biogeochemical transformation and landscape position of collected particles increasing specialization towards metallophilic phyla was recorded on particles collected with increasing distance from source suggesting that au toxicity resulting from progressing biogeochemical transformation affected bacterial communities this study ultimately shows that placer gold transformation and biofilm composition within modern landscapes is highly dependent on the interplay of physical and biogeochemical factors

numerical simulations examining the relationship between wall roughness and fluid flow in rock fractures understanding how fracture wall roughness affects fluid flow is important when modeling many subsurface transport problems computed tomography scanning provides a unique view of rock fractures allowing the measurement of fracture wall roughness without destroying the initial rock sample for this computational fluid dynamics study we used several different methods to obtain three dimensional meshes of a computed tomography scanned fracture in berea sandstone these volumetric meshes had different wall roughnesses which we characterized using the joint roughness coefficient and the fractal dimension of the fracture profiles we then related these macroscopic roughness parameters to the effective flow through the fractures as determined from navier stokes numerical models thus we used our fracture meshes to develop relationships between the observed roughness properties of the fracture geometries and flow parameters that are of importance for modeling flow through fractures in field scale models fractures with high joint roughness coefficients and fractal dimensions were shown to exhibit tortuous flow paths be poorly characterized by the mean geometric aperture and have a fracture transmissivity 35 times smaller than the smoother modeled fracture flows

a conventional straddle sliding packer system as a borehole extensometer monitoring shear displacement of a fault during an injection test abstract a constant head step injection test using a conventional straddle packer system was performed for a normal fault in siliceous mudstone the test applied a new method whereby axial displacements of isolated test sections in a borehole during injection are monitored by measuring the pressures of sliding packers and the pore pressure in the test section the measured pressures and axial displacement and the injection flow rate were used to estimate the hydraulic aperture shear displacement normal compliance normal stress shear stiffness and hydraulic dilation angle of the fault during the test the injection successfully yielded a large shear displacement during normal faulting of up to 13 3 49 5 mm including the estimation error which left residual shear displacement of 2 8 10 4 mm after a remarkable shear slip event the shear stiffness during faulting is estimated to be 2 3 107 to 8 4 107 pa m 1 considering the estimation error which is consistent with empirically predicted values based on previous studies the hydraulic dilation angle was inferred to be effectively zero as the residual shear displacement did not leave any increase in hydraulic aperture the experimental method applied here does not require specialized equipment and could aid in the investigation of the hydromechanical behavior of subsurface fractures or aquifers

a two step homogenization based permeability model for deformable fractured rocks with consideration of coupled damage and friction effects abstract the permeability variation induced by anisotropic damage of rock blocks and nonlinear deformation of fractures is modeled with a two step homogenization technique for deformable fractured rocks containing arbitrarily distributed penny shaped microcracks in rock blocks separated by multiple sets of critically orientated fractures of much large scales the proposed model accounts for the influences of the microstructural alteration of rock blocks and fractures at the laboratory scale and the development pattern of the fracture system as well as the rock fracture interaction at the field scale on the permeability of a fractured rock under mechanical loading or excavation condition the proposed model was first validated by laboratory data of compression tests with permeability measurements on the beishan granite coupled shear flow tests with hydraulic conductivity measurements on a granite fracture and anisotropic strength tests on the martinsburg slate with good agreement between the model predictions and the laboratory measurements numerical simulations were finally performed to examine the excavation induced permeability change in the surrounding granitic rock of the stripa tunnel demonstrating the importance in considering both the damage of rock blocks and the deformation of fractures for better understanding the excavation induced permeability change in the surrounding rock near the excavation surface

the use of discrete fracture network simulations in the design of horizontal hillslope drainage networks in fractured rock abstract characteristics of fracture networks are explored in a discrete fracture network framework to provide design guidelines for horizontal drainage networks in fractured rock central to the study is defining how fracture attributes relate to fracture network structure and network scale fluid flow and in turn how flow characteristics of fracture networks influence horizontal drain length and orientation multiple realizations of stochastic fracture networks generated from both synthetic and field specific data sets serve as a basis for understanding physical fracture network structure and resultant global flow and for performing intersection analyses of hillslope drains with flowing fractures study results indicate that the logarithm of the standard deviation of fracture transmissivity log t is the single most important attribute for drainage network design as higher values of log t describe heterogeneous flow patterns where only a small portion of the network conducts a significant quantity of fluid thus recommended drain lengths for intersecting significantly conductive fractures increase with increases in log t fracture trace length orientation and density also play a role albeit secondary to the distribution of transmissivity in defining drain length as a function of drain orientation relative to the mean fracture set orientation the spatially discontinuous nature of fracture networks and the wide range in transmissivity values found in natural fracture networks tend to produce high degrees of variability in computed intersection distances between drains and fractures conducting significant quantities of fluid to account for this variability a conservative approach is recommended where horizontal drain lengths along a pre defined orientation are scaled by discrete fracture network computed intersection distances equal to the upper 95th confidence interval

3d analysis of geometry and flow changes in a limestone fracture during dissolution summary the effects of reactive transport on fracture geometry and fluid flow were investigated through an integrated experimental and modelling approach a fractured limestone sample 90 calcite was injected with an acidic co2 rich solution over a period of 55 h to induce carbonate dissolution the changes in fracture geometry and related parameters are reported for six data sets obtained from synchrotron x ray micro tomography experiments a series of algorithms was used to extract the aperture and fracture walls from 3d images and allowed quantification of the geometry changes with an optical resolution of 4 91 m in addition measurement of fluid chemistry hydraulic tests and computation of navier stokes flow constrained the characterisation of the dissolution process the effects of reactive transport on fracture geometry and fluid flow were then discussed the presence of silicates in the rocks led to heterogeneous dissolution at the micro scale despite dissolution appearing to be quite homogeneous at sample scale no formation of preferential flow pathways was noticed although heterogeneous dissolution at the micro scale led to fracture walls and aperture decorrelation and to modification of the flow velocity profiles in the fracture

a random field model for surface roughness and aperture of rock fractures present constitutive models for rock fracture behaviour require information concerning the fracture geometry on which the mechanical and hydraulic properties of the rock mass are greatly dependent in this paper measurements of rock fracture surfaces and aperture using a 3 d laser scanning technique are reported in order to check the validity of a fractal model for fracture geometry this formulation incorporates fractal descriptions of roughness angularity and aperture fractal patterns can be persistent if an increasing increment implies an increase in the next increment or anti persistent if increasing increments follows decreasing increments persistence and anti persistence are recognised as descriptors of the geometrical complexity of roughness and aperture the analysis of the data also shows that the fractal models apply until stationarity occurs for sufficiently large samples which behave as random variables these sample sizes are defined as stationarity thresholds of roughness and aperture moreover the study of the cross correlation between the asperity height and aperture provides the link between fracture roughness and aperture geometry a theoretical model of fracture aperture during shearing is developed and successfully compared with experimental and numerical studies reported in the literature

gold behavior in supergene profiles under changing redox conditions the example of the las cruces deposit iberian pyrite belt the las cruces deposit is in the eastern end of the iberian pyrite belt sw spain it is currently being mined by cobre las cruces s a the main operation is focused on the supergene cu enriched zone initial reserves of 17 6 mt 6 2 cu an au ag pb rich gossan resource 3 6 mt 3 3 pb 2 5 g t au and 56 3 g t ag occurs in the upper part of the deposit the au grade ranges from 0 01 ppm to 100 ppm and occurs as three different au ore types 1 au mineralization in the upper part of the gossan linked to fe oxides lithofacies 2 au concentration in the lower part of the gossan associated with leached black shales and 3 au ore in the cementation zone related to subvertical fractures a hydroseparation device has been used to obtain heavy mineral concentrates from selected samples of different ore types reflected light microscopy scanning electron microscopy energy dispersive spectroscopy sem eds and electron probe microanalysis epma were used to study the separated au particles significant differences between the defined ore types include the au bearing lithologies mineral associations textural features particle sizes morphologies and fineness au rich minerals include native au au ag electrum and au ag hg amalgams gold bearing mineral associations include pb oxihalides fe oxides galena pyrite cinnabar and ag sulfosalts the au enrichment mechanism in the supergene profile involves 1 dissolution of au from the primary sulfides as chloride rich ionic complexes during the weathering of the deposit under subaerial exposure dissolved au is transported downward through the supergene profile under acidic and oxidized conditions 2 destabilization of the au complexes by fe controlled redox reactions as a consequence coarse grained high fineness au particles precipitated in association with fe oxyhydroxides this resulted in secondary concentration in the upper gossan and 3 after deposition of cover sediments took place a progressive change in the system conditions resulting in a later au remobilization as hydroxidehalide hydroxide thiosulfate and bisulfide complexes in the lowermost gossan and cementation zone the main pathways for migration of enriched fluids to the cementation zone are secondary permeability zones linked to alpine reactivated faults deposition of au seems to be related to fluid interaction with reductant lithologies including black shales and the primary sulfides

numerical model of water flow in a fractured basalt vadose zone box canyon site idaho a numerical model of a fractured basalt vadose zone has been developed on the basis of the conceptual model described by faybishenko et al his issue the model has been used to simulate a ponded infiltration test in order to investigate infiltration through partially saturated fractured basalt a key question addressed is how the fracture pattern geometry and fracture connectivity within a single basalt flow of the snake river plain basalt affect water infiltration the two dimensional numerical model extends from the ground surface to a perched water body 20 m below and uses an unconventional quasi deterministic approach with explicit but highly simplified representation of major fractures and other important hydrogeologic features the model adequately reproduces the majority of the field observation and provides insights into the infiltration process that cannot be obtained by data collection alone demonstrating its value as a component of field studies

stable isotopes in guano potential contributions towards palaeoenvironmental reconstruction in tabon cave palawan philippines abstract tabon cave is a key site for the understanding of modern human dispersals in the philippine archipelago and island southeast asia nestled in the karst landscape that borders the southwestern coast of palawan it has delivered the earliest confirmed homo sapiens remains in the philippines dating to the late pleistocene as far back as around 47 ka among other methods the broad characteristics of the environment in which these humans once lived may be drawn using stable isotope analysis of the rich guano deposits in the cave an approach that follows a growing number of studies indicating the potential of guano as a palaeoenvironmental archive 13 c values reveal the general prevalence of c 3 forest tempered by savannah woodland with grassland contributions both well before and slightly after a securely dated fireplace at 32 ka the lower interval would refer to ois 3 or older interglacial periods while the upper interval would refer to the transition either before or after the last glacial maximum no useful conclusions are drawn from 15 n results due to suspected ammonia fractionation pending future dating efforts for confirmation this preliminary study contributes to the development of an alternative and promising palaeoenvironmental proxy and hopes to shed further light on the prehistoric odysseys that took place across island southeast asia

seepage into drifts and tunnels in unsaturated fractured rock 1 methods for obtaining estimates of seepage into drifts and tunnels excavated in unsaturated fractured rocks are of interest for engineering and environmental applications for uniform porous media a tunnel surface may present a capillary barrier promoting water diversion around the opening through the porous matrix hence reducing seepage into the opening the presence of fractures intersecting the opening complicates flow behavior and presents a challenge to seepage prediction we present a simple and physically based model for seepage estimation that preserves key physical processes associated with fracture flow while avoiding complexity of detailed fracture network characterization the processes of film and capillary driven flows are combined with a geometrically tractable representation of the dual continuum fractured rock with two disparate populations of matrix pores and fracture apertures the large disparity in capillary forces between matrix and fractures rules out matrix seepage based on philip s theory we obtain estimates of seepage fraction for a given percolation flux from consideration of the hydraulic conductivity of the fracture domain only similar to previous studies the new model shows existence of a percolation threshold for onset of seepage the new model also exhibits a steep increase in seepage with increase in percolation flux that reflects the role of fracture film flow in addition to consideration of physically based flow processes computations for the proposed analytical model can be performed with common spreadsheet software which is a distinct advantage over numerical equivalent porous media approaches that require a powerful computational environment excessive computation time and thorough characterization of the fracture domain

formulation of strain dependent hydraulic conductivity for a fractured rock mass abstract by characterizing rock masses as anisotropic continua with one or multiple sets of critically oriented fractures a methodology is developed in this paper to address the change in hydraulic conductivity resulted from engineering disturbance material nonlinearity and anisotropy an equivalent elastic perfectly plastic constitutive model with non associated flow rule and mobilized dilatancy is developed to describe the global nonlinear response of the rockmass under complex loading conditions by separating the deformation of fractures from that of the equivalent medium a strain dependent hydraulic conductivity tensor is formulated this not only considers the normal compressive deformation of the fractures but also and more importantly integrates the effect of material nonlinearity and post peak shear dilatancy using this methodology a closed form solution is derived to describe the hydraulic behavior of a single fracture during combined normal and shear loading processes the closed form solution is validated by an existing coupled shear flow test under wide ranges of normal and shear loads numerical simulations are performed to investigate the changes in hydraulic conductivities of a cubic block of fractured rock mass under triaxial compression and shear loading as well as a circular underground excavation in a biaxial stress field at the stripa mine sweden the simulation results agree well with the in situ experimental observations and an existing elastic strain dependent analytical solution respectively the evaluation results clearly demonstrate that the proposed model is capable of predicting the changes in hydraulic properties of fractured rock masses under loading or excavation

a review of existing methods used to evaluate the hydraulic conductivity of a fractured rock mass we review the existing methods for evaluating the hydraulic conductivity of a rock mass rock mass permeability may be assessed using empirical analytical and numerical approaches empirical methods use data from in situ field tests to derive the relationship between depth and permeability by applying a curve fitting method and establishing the relationship between hydraulic conductivity and a geological index analytical methods rely on darcy and cubic laws to estimate the permeability of a rock mass by taking into account the geometrical characteristics of the joint sets analytical equations of the flow rate into underground excavations are also developed by solving the laplace equation for homogeneous and isotropic aquifers under various boundary conditions numerical modeling can evaluate the outcomes of both empirical and analytical approaches and vice versa and can provide a sensitivity analysis of the parameters that affect rock mass permeability the importance of stress and joint set characteristics is often investigated via numerical modeling as are the scale effect and directional permeability in this review paper we provide a comprehensive review of these approaches for studying rock mass permeability we summarize the advantages and disadvantages of existing methods and highlight potential future research directions

metal fixation by bacterial cell walls all biomass contains a significant quantity of metallic constituents and mineralization in living and dead biodebris may contribute to element transport from the hydrosphere into sediments the anionic cell walls of bacteria are remarkable in their ability to fix metals and provide sites for nucleation and growth of minerals results presented show the types of cell wall polymers that are responsible for metal binding in walls of gram positive and gram negative bacteria

paleoanthropological significance and morphological variability of the human bones and teeth from tabon cave abstract tabon cave is one of the few archaeological sites in island southeast asia which provided upper pleistocene homo sapiens fossils the published osteological material consists in one frontal bone and three mandibular fragments discovered during 1960 fieldworks as well as 11 new human remains unearthed during 2000 2001 excavations however recent efforts to recover and centralize the considerable amount of archaeological specimens and data from 1960s excavations revealed that an unexpected huge number of human bone remains were excavated during this period the collection preserved in the national museum of the philippines includes currently at least 483 human bone remains we propose here a preliminary review of the anatomical representation of the human bones from this collection and a first large scale comparative morphometric analysis focusing on the crown dimensions of six permanent first upper molars um1 this first overview revealed an extreme fragmentation of the bones of the collection resulting in a poorly indicative mni from the bones bearing sufficient diagnostic morphology few immature individuals are present in the assemblage refitting of specimens and observation of broken surfaces indicated that ancient human activity in the cave anterior to the excavation was likely to be an important taphonomic factor of fragmentation of the assemblage our comparative analysis including 339 um1 revealed that two um1 from tabon cave have unusual large dimensions outside the range of variation of submodern southeast asians sean molars of our sample four other um1 from tabon fall in or close to the variability of the philippines negritos we show also that the morphological disparity encountered among the um1 from tabon cave is higher than in other archaeological sites and submodern populations of our sample this confirms previous publications that emphasized important morphological variations and proposed the hypothesis of the presence of two morphotypes although chrono stratigraphic information is lacking because of the disturbed stratigraphic context in which almost the totality of the bones was unearthed unpublished reports and field documents show that robert fox head of the 1960s excavations considered that an important part of this collection might have a pleistocene age given the scarcity of the pleistocene homo sapiens fossil record in island southeast asia sea part of this collection might improve significantly our knowledge of the morphological relatedness and variability of the upper pleistocene homo sapiens in the region

considerations of the dilatancy angle in rocks and rock masses the present study responds to the poor treatment given to dilatancy in classical rock mechanics post failure problems such as tunnel or mine pillar design a comprehensive review of the literature and observations in regard to published test results would indicate that dilatancy is highly dependent both on the plasticity already experienced by the material and confining stress moreover it also appears that scale may play a non negligible role in our article we provide a detailed analysis of published test data with a view to proposing a sufficiently significant but conveniently simple formulation of the dilatancy angle that reflects these dependencies and that can be readily implemented in numerical codes the model is then tested demonstrating that it is capable of representing rock sample strain behaviour in compressive tests finally the model is applied to the resolution of ground reaction curves for tunnels in poor to average quality rock masses showing a good correlation with results obtained using practical rock engineering techniques r 2005 elsevier ltd all rights reserved

on the cubic law and variably saturated flow through discrete open rough walled discontinuities the water research commission of south africa www wrc org za for funding of project k5 2052 68 on multidisciplinary vadose zone hydrology as well as project k5 2326 on quantification of unsaturated flow in the fractured intermediate vadose zone by means of geotechnical centrifuge to be published by the wrc in 2016

nanoforms of gold from abandoned placer deposits of wądroze wielkie lower silesia poland the evidence of authigenic gold mineralization abstract being the most recently exposed gold grains from historical tailings of underground and surface workings offer the opportunity to study supergene transformations occurring over historic periods in this study gold grains were collected from the abandoned historically mined deposits of w droze wielkie at lower silesia all three distinct gold sub types of detrital gold display surface morphotypes and internal textures of au and ag dissolution indicative of supergene gold modification as well as authigenic au nanoparticle formation and aggregation the indicative morphotypes include nano particulate semispherical or bubble like gold and aggregates of bacteriomorphic gold that could be evidence for microbial gold biomineralization sem investigation of the microtopography and internal texture of gold grains revealed indications of post depositional dissolution of au ag alloys and redistribution of these components within the sediment some of seed and bubble like growths are also embedded in clayey kaolinite masses within crevices suggesting that dissolution re precipitation processes occur at the gold grain interface authigenic gold occurs as overgrowths and aggregates of nearly pure gold on a detrital au ag alloy that are readily removed during transport but are replaced by re precipitation occurring over historic rather than geological periods

secondary gold structures relics of past biogeochemical transformations and implications for colloidal gold dispersion in subtropical environments abstract biogeochemical processes are known to drive the cycling of gold via dissolution re precipitation reactions that result in the transformation of gold grain in near surface environments in this study placer gold grains were collected from west coast creek queensland australia and characterized using high resolution electron microscopy the outer surface of grains contains 98 1 mol au and 1 9 mol ag crevices occur on the surface of grains and are filled with organics and clay minerals in which nanometer size gold colloids and micrometer sized octahedral gold platelets are embedded the formation of these secondary gold structures is attributed to gold precipitation by the availability of reducing agents such as microbiota residual organics and clays bacterioform gold contains 74 7 mol au and 25 3 mol ag and is also embedded in clay minerals within crevices from sonicated gold grains grain surfaces beneath the clay minerals are striated and contain 68 5 mol au and 31 5 mol ag this data suggests that dissolution processes occur at the gold grain interface varying sizes of gold colloids on the grains suggest that five episodes of gold dissolution re precipitation processes occurred each episode was estimated to be 7 64 4 1 years therefore these grains represent 17 9 58 5 years of gold cycling and mobilization within this subtropical environment furthermore laboratory experiments involving colloidal gold dispersion demonstrated that iron oxides and organic material from west coast creek sediment adsorbed 94 5 of suspended gold colloids in conclusion this study highlights the value of nanophase gold characterization for the interpretation of biogeochemical processes affecting gold grain transformation and mobility in near surface environments importantly this study is the first to estimate the kinetics of biogeochemical gold cycling with regards to colloidal gold dispersion and re concentration

investigation of flow in water saturated rock fractures using nuclear magnetic resonance imaging nmri the application of nuclear magnetic resonance imaging nmri to the direct three dimensional measurement of flow in rough walled water saturated rock fractures is presented for the first time the study demonstrates the abilities of nmri to noninvasively measure rock water interfaces and water flow velocities in these fractures and investigates the effects of wall morphology on flow patterns inside a typical rock fracture two and three dimensional flow encoded spin echo pulse sequences were applied the stability and reproducibility of the water flow patterns were confirmed by analyzing two dimensional velocity images a variety of geometrical and hydraulic features were determined from three dimensional velocity images including the rock water interfaces the fracture aperture distribution and the critical aperture path velocity profiles and volumetric flow rates flow and stagnant regions and the critical velocity path in particular the effects of a sharp step discontinuity of the fracture walls and the applicability of the cubic law were examined as a result of the complex three dimensional geometry velocity profiles are generally parabolic but often highly asymmetric with respect to the fracture walls these asymmetric velocity profiles are clustered together with significant correlations they are not just local random phenomena however theoretical considerations indicate that the effects of the measured asymmetry on volumetric flow rates and hydraulic conductivities are insignificant in that the overall flow inside rough fractures still obeys the cubic law the features discussed in this study emphasize the strong heterogeneity and the highly three dimensional nature of the flow patterns in natural rock fractures and consequently the need for three dimensional flow analysis

the fascinating and complex dynamics of geyser eruptions geysers episodically erupt liquid and vapor despite two centuries of scientific study basic questions persist why do geysers exist what determines eruption intervals durations and heights what initiates eruptions through monitoring eruption intervals analyzing geophysical data taking measurements within geyser conduits performing numerical simulations and constructing laboratory models some of these questions have been addressed geysers are uncommon because they require a combination of abundant water recharge magmatism and rhyolite flows to supply heat and silica and large fractures and cavities overlain by low permeability materials to trap rising multiphase and multicomponent fluids eruptions are driven by the conversion of thermal to kinetic energy during decompression larger and deeper cavities permit larger eruptions and promote regularity by isolating water from weather variations the ejection velocity may be limited by the speed of sound of the liquid vapor mixture

anisotropy in capillary invasion and fluid flow through induced sandstone and shale fractures abstract understanding the physics of flows in a single fracture is the basis for modeling subsurface transport problems in fractured media capillary pressure curve and equivalent aperture have been accepted as tools for characterizing capillary invasion and single phase flow in a single fracture numerical modeling is used to determine the capillary pressure curve and the equivalent aperture for different flow directions in sandstone and shale fractures invasion percolation method is used to model the invasion process of dense non aqueous phase liquid in a water saturated sandstone fracture from different directions finite element method is applied to model the flows of brine and electric current in the fractures along different directions the numerical results are calibrated against the experimental data including capillary pressure measurement and single phase flow tests in the fractures results from the invasion percolation modeling show that the capillary pressure curve is independent of invasion direction the study on the flows of brine and electric current in the fractures illustrates that the sandstone fracture displays a higher anisotropy in hydraulic and electrical conductivities than the shale fracture furthermore it is found that the anisotropy is correlated with the directional roughness harmonic mean and range of fracture aperture

new ν type relative permeability curves for two phase flows through subsurface fractures appropriate relative permeability curves for two phase flows through subsurface fractures remain unclear we have conducted decane water and nitrogen water two phase flow experiments and simulations on real variable aperture fractures in rocks under confining stress experiments have been conducted on fractures for different combinations of rock type granite or limestone wettability contact angle of water 0 or 90 and intrinsic fracture permeability 10 11 m2 or 10 10 m2 using different combinations of shear displacement 0 or 1 mm and effective confining stress 1 or 40 mpa it has been demonstrated that nonwetting phase relative permeability depends on capillary pressure except at either a higher contact angle or higher intrinsic permeability i e bigger aperture where no influence of capillarity is expected from the young laplace equation in the absence of an influence of capillarity relations between wetting and nonwetting phase relative permeabilities agree with that of the x type relative permeability curves in order to determine the relative permeability curves under the influence of capillarity the experimental results have been analyzed by two phase flow simulations of the aperture distributions of the fractures it has been revealed that nonwetting phase relative permeability becomes zero even at a small wetting phase saturation of approximately 0 3 while wetting phase relative permeability exhibits corey type behavior resulting in shaped relative permeability curves similar curves have been reported in the literature but have not been demonstrated for real fractures it has been revealed that the new type and traditional x type relative permeability curves are appropriate for describing two phase flows through subsurface fractures

naturally occurring gold nanoparticles and nanoplates during the weathering of gold deposits exceptionally pure 200 nm diameter nanoparticulate gold plates 6 nm thick are formed the particles display controlled growth of both size and shape and signs of assembly to form belts and sheets the gold is associated and intergrown with minerals formed by evaporation and is interpreted to have been deposited rapidly from saline groundwater during a drying event the size and morphology of the gold nanoparticles and nanoplates are identical to the products of experimentally manufactured gold colloids this represents the fi rst direct observation of colloidal nanoparticulate gold in nature confi rming this as an active mechanism of gold transport during the weathering of gold deposits

effect of fracture aperture variations on the dispersion of contaminants dispersion of dissolved contaminants in fractured rocks is strongly dependent on the variability of fracture aperture large fracture aperture regions result in significant channeling of the fluid flow accelerating the movement of solutes in a particular direction which may differ locally with respect to the main flow direction from high to low hydraulic potential this may result in very early breakthrough of the contaminants significantly earlier than in the conventional parallel plate simplification of fluid flow in fractured systems in addition flow and transport in the low aperture regions can be orders of magnitude smaller which has major implications for remediating contaminated fractured media in this study we observed the transport of a nonsorbing solute in a naturally fractured rock which was characterized at very high resolution using computed tomography scanning to determine the fracture aperture distribution we compared the observed breakthrough curve of the solute at various flow rates with the predicted breakthrough curve using the fracture s geostatistics and small perturbation analysis as well as direct numerical simulation of flow through the fracture using the measured fracture aperture distribution the experimentally determined fracture transmissivity and dispersivity are within a factor of 2 of those predicted using either the small perturbation approach using the fracture geostatistics or explicit numerical modeling of breakthrough which differ by around 20 indicating that the geostatistics of the fracture aperture can be used to predict the approximate shape of the breakthrough curve for a fracture

secondary gold mineralization in the amani placer gold deposit tanzania abstract the amani placer gold deposit apgd is located in a braided river valley in southwestern tanzania and is characterised by large gold nuggets with anomalously fine macroscopic textural features as well as significant levels of silver depletion i e high fineness gold in the nugget rim the study site thus represents an ideal natural laboratory in which to explore the controls on the low temperature biogeochemical cycle of gold using x ray fluorescence xrf and inductively coupled plasma mass spectrometry icp ms geochemical data this study evaluated the sediment and pore water chemistry of the river sediment profile and using scanning electron microscopy sem coupled these results with a high resolution morphological and chemical investigation of the ambient gold nuggets collected from the auriferous gravel horizon down profile metal distributions indicate a steep redox gradient and observed oximorphic mottling textures along with slumped river terraces reveal that the redox conditions fluctuate as a function of seasonality and episodic fluvial incision events respectively fluctuating physico chemical conditions during early diagenesis result in changes to the stability of ambient gold bearing complexes e g au s2o3 23 in oxidising condition and au hs 2 in reducing conditions thereby leading to nanophase gold precipitation on clay minerals organic matter and importantly on pre existing gold nugget surfaces the diagenetic biogeochemical processes operating in the apgd thus formed supergene enriched gold nuggets characterized by delicate textures and low ag

gold nugget growth during tectonically induced sedimentary recycling otago new zealand abstract an alluvial fan 5 km wide and 3 5 km long has been derived over the past 65 000 years from an actively rising schist mountain range dunstan range in central otago new zealand the fan can be locally subdivided into four distinctive consecutively formed gravel sequences the earliest of which has been deformed along the range margin these gravels are pre dated by miocene mature fluvial sediments manuherikia group which have been recycled into the alluvial fan gravels during uplift all these sedimentary sequences contain gold which has been mined sporadically manuherikia gold grains up to 13 wt ag are well rounded and typically 300 m across typical grain size of gold becomes progressively coarser with each gravel sequence in the alluvial fan and nuggets up to 2 cm occur in younger gravel sequences gold grain size increase is due to addition of authigenic gold on to pre existing grains authigenic gold occurs as a cement between earlier detrital grains 1 4 wt ag as amorphous coatings and protrusions 0 1 wt ag and as overgrowths of lattice intergrowths 0 1 wt ag gold nuggets formed in the gravels have overgrown detrital minerals and authigenic clay minerals chemical accretion of nuggets may be still continuing today in parts of the alluvial fan

nanoparticle factories biofilms hold the key to gold dispersion and nugget formation biofilms living on gold au grains play a key role in the biogeochemical cycle of au by promoting the dispersion of au via the formation of au nanoparticles as well as the formation of secondary biomorphic au gold grains from queensland australia are covered by a polymorphic organic inorganic layer that is up to 40 m thick it consists of a bacterial biofilm containing au nanoparticles associated with extracellular polymeric substances as well as bacterioform au focused ion beam fib sectioning through the biofilm revealed that aggregates of nanoparticulate au line open spaces beneath the active biofilm layer these aggregates bacterioform au type 1 resulted from the reprecipitation of dissolved au and their internal growth structures provide direct evidence for coarsening of the au grains at the contact between the polymorphic layer and the primary au bacterioform au type 2 is present it consists of solid rounded forms into which crystal boundaries of underlying primary au extend and is the result of dealloying and ag dissolution from the primary au this study demonstrates that 1 microbially driven dissolution precipitation and aggregation lead to the formation of bacterioform au and contribute to the growth of au grains under supergene conditions and 2 the microbially driven mobilization of coarse au into nanoparticles plays a key role in mediating the mobility of au in surface environments because the release of nanoparticulate au upon biofilm disintegration greatly enhances environmental mobility compared to au complexes only

permeability tensor for discontinuous rock masses rock masses which commonly contain a large number of discontinuities are treated as homogeneous anisotropic porous media to formulate the corresponding permeability tensor this has been successfully achieved by introducing a symmetric tensor crack tensor which depends only on the geometry of the related cracks aperture size and orientation the principal directions associated with the symmetric crack tensor are coaxial with those of the permeability tensor the first invariant of the crack tensor is proportional to the mean permeability while the deviatoric part is related to the anisotropic permeability these results are well supported by numerical experiments on the permeability of cracked media by long remer wilson and witherspoon an actual rock mass moderately jointed granite was studied to see whether the crack tensor can be determined in situ stereology based on geometrical statistics provides a sound basis for determining the crack tensor in situ the crack tensor is obtained by

the great arc of dispersal of modern humans africa to australia abstract during the late pleistocene anatomically modern humans amh dispersed out of africa across the continents their routes obeyed the limitations placed on any large terrestrial mammal dependent on daily drinking water following certain climate permissive corridors amh first spread north with game across the sahara to the levant during the eemian interglacial c 125 ka but failed to continue to europe then occupied by neanderthals the savannah ecosystem in north africa and the middle east then dried up and amh vanished from the levantine fossil record being replaced there by neanderthals later amh successfully left africa as a single group by the southern route to india the added ability to make short but deliberate open water crossings allowed them first to cross the mouth of the red sea from eritrea and subsequently wallace s line to reach the isolated sahul continent at least by 48 000 years ago and possibly by 60 50 000 years ago they only finally arrived in europe from south asia around 45 50 000 years ago probably linked to climatic amelioration during ois 3

laboratory measurement of capillary pressure saturation relationships in a rock fracture a laboratory technique has been developed to measure the hysteretic relationship between capillary pressure and fluid saturation for a rough walled rock fracture under different states of normal stress the technique incorporates a loading system and a uniquely designed capillary barrier to the nonwetting phase which allows for fracture closure and provides excellent hydraulic connection of the wetting phase in the fracture with external pressure control the method is applied to a single rough walled fracture in limestone using oil and water as the nonwetting and wetting phase respectively the measured capillary pressure curves were found to be well represented by a brooks corey porous media capillary pressure function a distinct entry pressure giving rise to initial nonwetting phase invasion was observed in each test it was found that the inferred aperture distributions became less skewed with increased normal load these aperture distributions were inferred using one of three conceptual models presented for nonwetting phase invasion of a rough walled fracture under conditions of main drainage

development of a fracture network in crystalline rocks during weathering study of bishop creek chronosequence using x ray computed tomography and 14c pmma impregnation method the progressive development of porosity during subsoil weathering of granodiorite clasts was studied at the bishop creek moraine chronosequence in east central california fractures and other pores were examined using two complementary imaging techniques x ray computed tomography xrct and a 14c pmma 14c polymethylmethacrylate method the well known xrct method allows the investigation of three dimensional 3 d pore space 14c pmma is a less known method based on the complete impregnation of pore space with 14c doped pmma and subsequent autoradiograph of a rock section these imaging methods allow us to decipher the evolution of pore space in the granodiorite during the 120 k y weathering period the 14c pmma imaging technique was found to be more suitable for following the evolution of the whole sequence from intact bedrock to saprock in terms of crack density porosity and aperture working with hand specimens this method was adapted to detect both the low aperture fractures microcracks and macrocracks only a slight and progressive increase in total fracture density was observed during the whole weathering period however this trend does not hold if macrocracks and microcracks are separated microcrack density slightly decreases whereas macrocrack density increases due to a progressive expansion of microcracks the total porosity of the rock increases during weathering and is correlated to the progressive aperture increase of all types of cracks this evolution is accompanied by a change of crack morphology and connectivity and an overall increase in intragranular porosity of biotite and plagioclase aggregates

estimation of rev size and three dimensional hydraulic conductivity tensor for a fractured rock mass through a single well packer test and discrete fracture fluid flow modeling abstract a new methodology is presented to determine the representative elementary volume rev size and three dimensional 3 d hydraulic conductivity tensor for a fractured rock mass first a 3 d stochastic fracture network model was built and validated for a gneissic rock mass based on the fracture data mapped from scanline surveys at the site this validated fracture network model was combined with the fracture data observed on a borehole to generate a stochastic deterministic fracture network system in a cubic block around each packer test conducted at a different depth region in the same borehole each packer test was simulated numerically applying a developed discrete fracture fluid flow model to estimate the influenced region or effective range for the packer test a cubic block of size 18 m with the packer test interval of length about 6 5 m located at the centre of this block was found to be suitable to represent the influenced region using this block size the average flow rate per unit hydraulic gradient defined as the transmissivity multiplied by mean width of flow paths field for fractures was calibrated at different depth regions around the borehole by numerically simulating the packer tests conducted at different depth regions the average flow rate per unit hydraulic gradient of the fractures that intersect the borehole was considered to be quite different to the average flow rate per unit hydraulic gradient of the fractures that do not intersect the borehole a relation was developed to quantify the ratio between these two parameters by studying the directional hydraulic conductivity behaviour of different cubic block sizes having the validated stochastic fracture network and calibrated hydraulic parameters a rev for the hydraulic behaviour of the rock mass was estimated to be a block size of 15 m the hydraulic conductivity tensor in 3 d computed through regression analysis using the calculated directional hydraulic conductivity values in many directions was found to be significantly anisotropic the principal directions of the hydraulic conductivity tensor were found to be agreeable with the existing fracture system of the site further the geometric hydraulic conductivity calculated was found to be comparable to the hydraulic conductivity estimated through the radial flow assumption in continuum porous media

constitutive relationships and pore structure of undisturbed fracture zone samples with cohesionless fault gouge layers multiphase flow processes in fractured rocks are of major importance for the remediation of subsurface contamination for engineering petroleum reservoirs and for the safety analysis of nuclear waste repositories we developed procedures for determining the water retention curve gas permeability function and pore structure of undisturbed fracture zone samples with cohesionless fault gouge layers in the laboratory mylonitic samples were taken at grimsel test site switzerland intrinsic permeabilities of the fault gouge layers were 5 orders of magnitude higher and significant desaturation occurred at capillary pressure heads about 10 times lower than in the surrounding granodiorite thus showing that at this site gas flow would take place mainly in the fracture zone the measured water retention and gas permeability data were well represented by parametric models designed for porous media gas flow could only be detected at water saturations below about 0 8 thus showing strong phase interference at high water saturations to relate these findings to the pore structure of the samples a qualitative and quantitative description of the pore space was obtained at different scales using fluorescent resin imbibition and image analysis techniques results show that the fracture zone consists of a continuous and interconnected fracture network that is filled with a porous medium like material thus explaining the applicability of the above mentioned models and the rather strong phase interference

distribution and speciation of gold in biogenic and abiogenic calcium carbonates implications for the formation of gold anomalous calcrete abstract calcrete pedogenic ca carbonate is an important sampling medium for geochemical gold au exploration in semi arid and arid regions of australia because it is widespread easy to sample and calcium ca shows a strong positive correlation with au but not with base metals in calcrete overlying buried au mineralization in this study we show that the formation of au anomalous calcrete can be biomediated through the activity of resident microorganisms and may not simply be the result of passive nucleation on inactive cells or evapotransporative processes calcified microfossils are highly abundant in calcrete from the barns au prospect in south australia these microfossils are morphological analogues of calcified cells and biofilms formed in laboratory experiments conducted with active bacterial cultures enriched from au anomalous calcareous sand from the barns prospect calcium carbonates precipitated by these cultures consisted mostly of calcite which is the main carbonate mineral in calcrete synchrotron micro x ray fluorescence s xrf mapping was used to assess the distribution of au zn ca and other metals in ca carbonates precipitated by active bacterial cultures on a m scale the distribution of au was heterogeneous in these ca carbonates and differed from base metal distribution thus mimicking the spatial separation of these metals observed in calcrete the speciation of au in ca carbonates precipitated by active bacteria was measured using micro x ray absorption near edge structure spectroscopy xanes and resembled that observed in au anomalous calcrete closely while metallic au was observed in au hotpots ionic au was detected in the halo surrounding the hotspot in contrast the precipitates produced in the presence of dead bacterial cells or by raising solution ph or pco 2 i e hydroxylapatite portlandite and vaterite respectively did not reflect the mineralogy of calcrete gold distribution and speciation in vaterite formed by raising pco 2 were homogenous and did not reproduce the variation observed in calcrete and ca carbonates precipitated by active cells increasing the supersaturation with respect to ca in solution by incremental drying of the medium produced only x ray amorphous precipitates or hydroxylapatite in the presence heat killed cells in conclusion this study shows that active microbial processes that combine biogenic ca carbonatogenesis with au precipitation are likely to drive the formation of au anomalous calcrete

hydraulic properties of partially saturated rock fractures subjected to mechanical loading abstract this study presents a methodology for estimating the unsaturated hydraulic properties of rock fractures under deformation conditions the surface morphology of an artificial granite rock fracture was examined using a high resolution three dimensional laser scanner and the aperture distribution of the fracture was found to follow a gaussian distribution by virtue of the aperture distribution function and applying the young laplace equation to local apertures a novel model was presented to predict the capillary pressure saturation relationship and the relative hydraulic conductivity of rough walled rock fractures subjected to normal and shear loading the proposed model was partially validated against existing laboratory data on the unsaturated hydraulic properties of rock fractures and can be readily applied to various engineering practices such as transport phenomena in fractures landslide mitigation or underground oil storage

high resolution cat imaging of fractures in consolidated materials abstract high resolution measurements of fracture aperture of granite and sandstone rocks were performed using cat scanner the aperture distribution was statistically characterized for future experimental and numerical studies on single and multiphase flow and transport the fracture aperture can be measured in situ and non destructively with cat scanning the minimum pixel size is 0 27 0 27 mm but fractures as small as 35 m can be accurately measured using a calibration standard for the variation in ct number due to the missing rock mass in a given pixel a calibration standard for each rock type yields distinctly different calibration slopes about 17 greater for granite compared to sandstone indicating that each rock type should be analyzed against its own calibration standard the aperture distribution is rather heterogeneous and is best described by a lognormal function corroborated by comparing the theoretical to actual ratio of hydraulic to mechanical apertures mechanical roughness of the fractures ranged from 0 17 to 1 5 the variability in fracture aperture displayed only short range structure with correlation lengths of 0 8 mm to 7 mm which is at most one tenth of the minimum dimension width of the fracture plane potential flow channels can be deduced from the fracture aperture distribution

an equivalent continuum model for coupled stress and fluid flow analysis in jointed rock masses to provide a set of governing equations for solving the coupled stress and fluid flow a rock mass which commonly contains a large number of geological discontinuities is treated as an anisotropic elastic porous medium with the corresponding elastic compliance and permeability tensors hydro mechanical equivalents to the discontinuous mass the hydromechanical equivalents with the special emphasis on the permeability tensor are formulated on the assumption that any crack can be replaced by a set of parallel planar plates connected by two springs two dimensional numerical analyses on seepage flow networks support the validity of the permeability tensor some field evidence is analyzed to examine the applicability of the present model for the practical purpose of rock hydraulics

biological role in the transformation of platinum group mineral grains platinum group elements are strategically important metals finding new deposits is becoming increasingly difficult owing to our limited understanding of the processes that affect their mobility in surface environments microorganisms have been shown to promote the mobility of metals around ore deposits here we show that microorganisms influence the mobility of platinum group elements in mineral grains collected from brazil australia and colombia scanning electron microscopy showed biofilms covering the platinum group mineral grains the biofilms contained abundant platinum group element nanoparticles and microcrystalline aggregates and were dominated by proteobacteria many of which were closely related to known metal resistant species some platinum group mineral grains contained carbon nitrogen sulfur selenium and iodine suggesting the grains may be biogenic in origin molecular analyses show that brazilian platinum palladium grains hosted specific bacterial communities which were different in composition from communities associated with gold grains or communities in surrounding soils and sediments nano phase metallic platinum accumulated when a metallophillic bacterium was incubated with a percolating platinum containing medium suggesting that biofilms can cause the precipitation of mobile platinum complexes we conclude that biofilms are capable of forming or transforming platinum group mineral grains and may play an important role for platinum group element dispersion and re concentration in surface environments

evaluation of fully coupled strata deformation and groundwater flow in response to longwall mining a finite element poroelastic model is presented to evaluate fully coupled strata deformation and groundwater flow resulting from underground longwall mining in variably saturated fractured geologic media through an equivalent porous elastic continuum representation the explicit coupling between the groundwater flow field and the solid skeleton deformation field is achieved by simultaneously solving the governing equations for groundwater flow and solid skeleton deformation the implicit coupling between these two fields is also accomplished by considering the effects of both unsaturated water flow and solid skeleton deformation on the hydraulic properties such as water content and hydraulic conductivity in addition to the implicit coupling caused by unsaturated water flow the other implicit coupling caused by solid skeleton deformation is also important because it may produce hydraulic heterogeneity and anisotropy in a geologic medium affecting the groundwater flow field even when the system is in a fully saturated condition a physically based constitutive model is proposed to account for the deformation strain dependencies of porosity and saturated hydraulic conductivity of the fractured media to evaluate the impacts of longwall mining and to understand their hydrogeomechanical nature the numerical model is applied to a well documented case study with satisfactory results although the numerical simulation results presented in this paper will not apply to all underground longwall mines because of differences in site specific hydrogeological and geomechanical settings the methodology described herein may find some useful applications in many longwall mining projects

the immobilization of gold from gold iii chloride by a halophilic sulphate reducing bacterial consortium a consortium containing halophilic dissimilatory sulphate reducing bacteria was enriched from basque lake 1 located near ashcroft british columbia canada to evaluate the role these bacteria have on the immobilization of soluble gold the consortium immobilized increasing amounts of gold from gold iii chloride solutions under saline to hypersaline conditions over time gold iii chloride was reduced to elemental gold in all experimental systems salinity did not affect gold immobilization scanning electron microscopy and transmission electron microscopy demonstrated that reduced gold iii chloride was immobilized as c 3 10 nm gold colloids and c 100 nm colloidal aggregates at the fluid biofilm interface the precipitation of gold at this organic interface protected cells within the biofilm from the toxic effect of ionic gold analysis of these experimental systems using x ray absorption near edge spectroscopy confirmed that elemental gold with varying colloidal sizes formed within minutes the immobilization of gold by halophilic sulphate reducing bacteria highlights a possible role for the biosphere in intercepting mobile gold complexes within natural hydraulic flow paths based on the limited toxicity demonstrated in this experimental model significant concentrations of elemental gold could accumulate over geological time in natural systems where soluble gold concentrations are more dilute and presumably non toxic to the biosphere