maceral composition and origin of organic matter input in neoproterozoic lower cambrian organic rich shales of salt range formation upper indus basin pakistan abstract the appropriate thermal maturity oil window or lower of the neoproterozoic rocks is a prerequisite for preserving robust and primary biological assemblages the neoproterozoic lower cambrian organic rich shales present in the upper part of salt range formation pakistan with abundant organic matter om total organic carbon toc up to 46 at relatively low thermal maturity protobitumen reflectance bro 0 2 0 4 represents by far the lowest thermal maturity neoproterozoic lower cambrian rocks analyzed to date the detailed petrographic description of neoproterozoic lower cambrian organic matter in the current study was lacking from previous source rock studies of coeval strata from oman eastern siberia australia and elsewhere eight organic rich shales of the salt range formation from three different outcrops have been analyzed for maceral composition and source rock characterization using organic petrography scanning electron microscopy and standard source rock assessment techniques the organic petrography reveals the organic rich shales are predominantly composed of alginites lamalginite and telalginite bituminite protobitumen and mineral bituminous groundmass overall the maceral assemblages suggest the deposition of these shales took place under a salinity stratified water column in a shallow restricted basin where both oxygenic and anoxygenic modes of primary production were operative the top oxygenated part of the water column was populated with the phototropic mat forming cyanobacterium whereas the lower low dissolved oxygen zone was dominated by algal mats and sulphate reduction bacteria the rare and scattered thucholites present within the salt range formation shales were derived from the radiation induced polymerization of adjacent om by the radioactive grains the heat from the radioactive grains however found to have a negligible effect on the overall thermal maturity of these shales

problems in identifying the effects of structure and critical state in a soil with a transitional behaviour this work shows that some soils with an intermediate behaviour between clays and sands do not have a unique compression line as has also been pointed out by martins et al it has been shown here that a unique critical state line could not be determined for the remoulded soil although the results shown here are for a reconstituted residual soil similar behaviour in compressibility has been found in silts and mixtures of sand and kaolin however it has been found that the critical state framework can be applied using a family of parallel critical state lines depending on the initial specific volume one of the questions raised by this work is how the effects of structure can be quantified if the intrinsic properties of the remoulded material are not unique the compression and critical state lines of the remoulded material are not only non unique but also of a distinctly different gradient from the natural material

effect of fabric on the behaviour of reservoir sandstones a laboratory investigation was undertaken on the mechanical behaviour of two sandstones that are commonly used as analogous hydrocarbon reservoir sandstones using triaxial apparatuses with a capacity of up to 70 mpa confining pressure both materials are lightly cemented but show a mechanical behaviour at large strains that is similar to that seen in rocks with much stronger cementation at small strains however these materials behave more like uncemented sands in that they show a strong stress dependency of the shear modulus and yield takes places at relatively small strains it is believed that fabric plays a fundamental role in the observed behaviour and this is supported by the experimental evidence so that the concept of strong fabric in sandstones is introduced

peak shear strength and dilatancy of a pleistocene age sand abstractthis paper summarizes results of laboratory investigations performed to quantify the influence of diagenesis or aging processes on the peak shear strength and dilatancy of an uncemented pleistocene age sand sampled near charleston south carolina drained triaxial compression tests were performed on high quality intact specimens retrieved using the in situ freezing and sampling method and on remolded specimens prepared with matching densities the stress strain behavior of intact specimens is accompanied by dilation and a peak shear value whereas remolded specimens generally contracted throughout shearing an age dilatancy term is added to a dilatancy index equation to account for the difference between intact and remolded peak friction angles the resulting equation suggests that dilatancies due to age and density are suppressed with increasing confining pressure a profile of peak friction angle with depth is established from the results and compared with estimates from empirical relationships

engineering geology of residual soil derived from mudstone in zimbabwe abstract as increasing amounts of civil engineering work are carried out on mudstone derived residual soils it has become important to systematically assess their geological engineering properties thus the properties of mudstone derived residual soils were evaluated in this study via a series of comprehensive laboratory tests to assess physical mechanical mineralogical and microstructural variations results show that the physical properties of these soils are inadequate in terms of engineering applications these soils can be classified as highly plastic clays that are hard to compact natural mudstone derived residual soils undergo severe disintegration underwater while remolded examples are similar but tend to exhibit more stable responses natural mudstone derived residual soils behave in a structured way when subjected to shear and compression these soil types possess superior natural shear resistance but their strength decreases significantly following saturation as well as in wetting and drying cycles data show that the microstructures of mudstone derived residual soils are characterized by the presence of aggregations with fissures although iron bearing cementation between these aggregations is responsible for high soil strength bonds can be damaged or even destroyed when samples are saturated or subjected to wetting and drying cycles leading to a reduction in shear strength the results of this research provide clear parameters for related engineering applications and enhance our understanding of residual mudstone derived soils

alteration mineralogy and stable isotope geochemistry of paleoproterozoic basement hosted unconformity type uranium deposits in the athabasca basin canada unconformity type uranium deposits are characterized by mineralization developed along the contact between younger sandstone cover and underlying crystalline basement rocks mineralization may extend up to 400 m into the underlying basement rocks whereas sandstone hosted unconformity type deposits have been well studied deposits hosted primarily in the basement have not this study examines the deposits at rabbit lake dawn lake and mcarthur river in the athabasca basin of canada which are hosted by the metamorphic archean and early paleoproterozoic rocks forming the basement to younger late paleoproterozoic sandstones alteration is similar in the three deposits and is characterized by three distinct paragenetic stages 1 preore alteration involving illitization of plagioclase and amphibole followed by chloritization of biotite and illite which formed at ca 230 c 2 ore stage alteration characterized by uraninite and coarse grained illite which formed at ca 240 c 3 postore alteration comprising spherulitic dravite vein chlorite quartz calcite and fe cu co and pb sulfides which formed at ca 135 c fluid circulation associated with emplacement of later mackenzie dikes initiated partial recrystallization of uraninite a later stage of alteration includes kaolinite and iron hydroxide precipitation formed at much lower temperatures of ca 50 c stable isotope compositions of the alteration minerals in conjunction with their paragenesis indicate that oxidized basinal fluids d 43 to 21 18o 3 8 were derived primarily from evolved seawater and leached uranium from the overlying sandstones of the athabasca formation and transported it into the basement via infiltration along fracture zones associated with reverse faults graphitic units in the basement and preore alteration served as both physical fractured zones and chemical reductants traps for the uranium mineralization the basinal fluids were responsible for the preore illite chlorite synore uraninite illite and the early postore alteration events this differs from many other sandstone hosted deposits where both oxidized basinal and reduced basement derived fluids were responsible for uranium precipitation

influence of structure on the behavior of a saturated clayey loess an intensive experimental investigation by means of triaxial and oedometer tests was performed on a clayey loess that was retrieved from two depths at a location on the southern chinese loess plate

noble gases ar kr xe and halogens cl br i in fluid inclusions from the athabasca basin canada implications for unconformity related u deposits the formation of unconformity related uranium deposits in the proterozoic athabasca basin canada involved basin scale circulation of u bearing brines during high grade diagenesis 150 200 degrees c at similar to 1 6 1 5 ga the uo2 ores occur both sides of the unconformity and are associated with extensive brecciation and illite sudoite dravite alteration quartz and dolomite cementing veins and breccias are associated with alteration and mineralisation and contain a fairly uniform population of fluid inclusions characterised by variable na ca and salinities of 25 35 wt salts and high u concentrations of up to 600 ppm u in order to further constrain the origin of these u rich brines we analysed the naturally occurring isotopes of ar kr and xe together with halogens cl br and i k ca and u in irradiated quartz and dolomite samples containing representative fluid inclusions this was achieved by the noble gas method for halogen measurement extended ar 40 ar 39 methodology using a combination of noble gas extraction techniques the fluid inclusions opened by crushing quartz and dolomite samples in vacuum have similar molar br cl ratios of 5 8 x 10 3 to 10 4 x 10 3 and molar i cl ratios of 1 8 x 10 6 to 8 2 x 10 6 these compositions lie over the top half of the modern day seawater evaporation trajectory consistent with the fluids deriving the bulk of their salinity by subaerial evaporation of seawater beyond the point of halite saturation the i cl ratios are much lower than is typical of fluids that have interacted with i rich organic matter present in many sedimentary basins or fluid inclusions found in mississippi valley type mvt pb zn ore deposits this is significant because provided the u rich fluid inclusions are representative of the ore stage fluids the low i cl ratios of the fluid inclusions do not favour fluid interaction with organic matter or hydrocarbons as a major process for localising u mineralisation the majority of samples contain fluid inclusions with age corrected ar 40 ar 36 of between the modern atmospheric value of similar to 300 and 450 these values are considered representative of the fluid s initial composition and are typical of upper crustal sedimentary formation waters the fluid inclusions nonradiogenic kr 84 ar 36 and xe 129 ar 36 ratios are slightly enriched in xe 129 relative to air and the fluid inclusions are estimated to contain 0 5 17 3 x 10 10 mol g 1 ar 36 which is up to twenty times the ar 36 concentration of air saturated seawater the data are interpreted to reflect acquisition of atmospheric noble gases from sedimentary rocks and suggest acquisition of radiogenic ar 40 within k rich basement rocks that would have been an important source of excess ar 40 was limited by temperatures of less than 200 degrees c taken together the halogen and noble gas composition of the u bearing fluid inclusions are strongly controlled by subaerial evaporation and subsequent interaction with sedimentary rocks showing that low temperature evaporitic brines dominated the mineralising system mineralisation is unlikely to have been triggered by fluid interaction with organic matter or mixing with voluminous basement derived fluids however the data do not completely preclude a role for volumetrically minor fluid or gas phases introduced by deep seated basement faults preferentially located at the sites of mineralisation

radiolytic alteration of biopolymers in the mulga rock australia uranium deposit abstract we investigated the effect of ionizing radiation on organic matter om in the carbonaceous uranium u mineralization at the mulga rock deposit western australia samples were collected from mineralized layers between 53 and 58 5 m depths in the ambassador prospect containing

on the role of bond breakage due to unloading in the behaviour of weak sandstones a laboratory investigation was made of the effects of isotropic unloading on the mechanical behaviour of cemented sandstones modelling in a simple way the influence of sampling on hydrocarbon reservoir sandstones that have been cemented at depth artificial samples of sandstone were created by allowing a cement to hydrate while a sand sample was under a high confining stress in a triaxial apparatus comparisons were then made between the behaviour of samples that had been unloaded to zero confining stress with that of samples tested at stress levels around that during cementing it was found that the isotropic unloading damaged the cement which had a significant effect on the small strain and yielding behaviour but not on the strength and large strain behaviour comparisons were also made with tests on natural samples of reservoir and analogue sandstones and it was found that the artificial sandstone had reproduced the key elements of their behaviour the intrinsic properties of all of the sandstones t

role of organic matter in the proterozoic oklo natural fission reactors gabon africa of the sixteen known oklo and the bangombe natural fission reactors hydrothermally altered elastic sedimentary rocks that contain abundant uraninite and authigenic clay minerals reactors 1 to 6 at oklo contain only traces of organic matter but the others are rich in organic substances reactors 7 to 9 are the subjects of this study these organic rich reactors may serve as time tested analogues for anthropogenic nuclear waste containment strategies organic matter helped to concentrate quantities of uranium sufficient to initiate the nuclear chain reactions liquid bitumen was generated from organic matter by hydrothermal reactions during nuclear criticality the bitumen soon became a solid consisting of polycyclic aromatic hydrocarbons and an intimate mixture of cryptocrystalline graphite which enclosed and immobilized uraninite and the fission generated isotopes entrapped in uraninite this mechanism prevented major loss of uranium and fission products from the natural nuclear reactors for 1 2 b y 24 refs 4 figs

influence of cement voids ratio on stress dilatancy behavior of artificially cemented sand the addition of cement is an interesting remediation technique when the project requires improvement of the local soil for the construction of pavement base layers in slope protection of earth dams and canal linings as a support layer for shallow foundations and to prevent sand liquefaction the present study was carried out to quantify the influence of the amount of cement and the porosity in a cement voids ratio defined as the ratio between the volume of cement and the volume of voids of a mixture on the stress dilatancy behavior of an artificially cemented sand a program of triaxial compression tests considering three distinct cement voids ratios was carried out with two combinations of volumes of voids and volumes of cement at each cement voids ratio results showed that the stress dilatancy relationship is alike for a given cement voids ratio and that the stress strain behavior is also similar the cement voids ratio is therefore an appropriate parameter to assess stress dilatancy of the sand cement mixture studied doi 10 1061 asce gt 1943 5606 0000565 2012 american society of civil engineers ce database subject headings stress dilatancy cement triaxial tests voids sand soil type

organic geochemical analysis of sedimentary organic matter associated with uranium abstract samples of sedimentary organic matter from several geologic environments and ages which are enriched in uranium 56 ppm to 12 have been characterized the three analytical techniqyes used to study the samples were rock eval pyrolysis pyrolysis gas chromatography mass spectrometry and solid state c 13 nuclear magnetic resonance nmr spectroscopy in samples with low uranium content the pyrolysis gas chromatography products contain oxygenated functional groups as hydroxyl and molecules with both aliphatic and aromatic carbon atoms these samples with low uranium content give measurable rock eval hydrocarbon and organic co 2 yields and c 13 nmr values of 30 aliphatic carbon in contrast uranium rich samples have few hydrocarbon pyrolysis products increased rock eval organic co 2 contents and 70 aromatic carbon contents from c 13 nmr the increase in aromaticity and decrease in hydrocarbon pyrolysis yield are related to the amount of uranium and the age of the uranium minerals which correspond to the degree of radiation damage the three analytical techniques give complementary results increase in rock eval organic co 2 yield correlates with uranium content for samples from the grants uranium region calculations show that the amount of organic co 2 corresponds to the quantity of uranium chemically reduced by the organic matter for the grants uranium region samples

stable isotope constraints on the role of graphite in the genesis of unconformity type uranium deposits the key lake unconformity type uranium deposit occurs in a shear zone where it intersects the unconformity between archean and aphebian gneisses and the overlying proterozoic athabasca group sandstones the roots of the key lake and many other unconformity type uranium deposits in the athabasca basin are close to gneisses rich in graphite and most deposits have small amounts of carbonaceous materials bitumen and hydrocarbon buttons within and around altered basement and sandstone ore zones in many athabasca uranium deposits hydrothermal fluids have destroyed graphite disseminated in the strongly altered gneisses in the vicinity of the deposits prompting some to suggest that graphite was converted to ch4 which reduced and precipitated the uranium and partially condensed to form bitumen the 13c values of graphite collected from unaltered and altered gneisses around the key lake deposit have a limited range 25 5 and are not a function of distance from the mineralization or the intensity of alter

summary of collapsible behaviour of artificially structured loess in oedometer and triaxial wetting tests this paper summarizes experimental studies on wetting induced collapsibility in loess using single oedometer double oedometer and triaxial wetting tests artificially structural loess samples with interparticle bonding calcite caco3 and a large void ratio were tested in the laboratory to avoid sampling disturbance of natural loess the comparison between the single and double oedometer tests confirms that the wetting induced deformation is independent of the sequence of wetting and loading the conventional triaxial apparatus was enhanced for investigating the collapse deformation in response to different water content increments when subjected to different stress levels the wetting induced strain subjected to high confining pressure develops in two steps it increases with increasing water content and reaches a relatively stable plateau and then increases rapidly again until a final stable state is reached the initial collapse surface was found by plotting the wetting induced strain vectors obser

static and dynamic properties of a lightly cemented silicate grouted sand this paper describes the results of an experimental investigation on the behaviour of a lightly grouted loose medium sand under both monotonic and cyclic loading the experimental programme in the present study was carried out on both untreated and treated sand specimens stabilized with a silica based grout and comprises isotropic triaxial compression tests equipped with bender elements drained triaxial monotonic shearing tests and undrained cyclic tests in a simple shear ss apparatus the results highlight that the weak cementation level induced by chemical treatment was sufficient to moderately increase small strain stiffness and stress dilatancy of the grouted sand during drained monotonic shear a small cohesion intercept was observed in the analyzed failure envelope while cyclic liquefaction resistance exhibited a much more significant increase with a different pattern of behaviour between low and high stress levels finally undrained cyclic ss test results evidenced that silicate grout emplo

contributions to geotechnique 1948 2008 engineering geology rock mechanics and rock engineering throughout its history geotechnique has regularly published papers on the fundamentals of engineering geology the core concepts of rock mechanics and the practice of rock engineering in totality these papers provide a concise history of the development of these areas of geotechnics here a review of many of these papers is presented in terms of the specific themes of engineering geology rock slope instability behaviour of intact rock and discontinuities in rock field measurements in rock mechanics discontinuous rock masses numerical modelling and rock engineering papers covering a wide range of issues within these themes are outlined together with an indication of how they have influenced later developments the review clearly demonstrates how geotechnique has been at the forefront of rock mechanics rock engineering and engineering geology for the whole of its 60 year existence

petrography and paragenesis of organic matter associated with the natural fission reactors at oklo republic of gabon a preliminary report sixteen known uranium rich pockets in the sediment hosted uranium ore deposits in the oklo area became nuclear fission reactors 1968 50 ma ago and operated as such for up to 1 ma nuclear criticality was caused by unique and fortuitous geological environments and events these included the localized high concentrations of uranium in small pockets in the ore bodies the fact that the relative abundance of the fissile 235u isotope was five times greater in uranium 2 ga ago than present the presence of water which acted as a moderator in the natural reactors and the absence of neutron poisons which are elements that can prevent nuclear chain reactions organic matter is present in all of the oklo natural reactors but it is abundant only in reactors 7 to 16 organic matter has been studied in natural reactors 7 to 9 and at locations at various distances from these reactors bitumen in the oklo reactors is the predominant organic phase it is now solid bitumen containing dispersed cryptocrystalline graphite in crystal domains smaller than optical microscopic size its immediate precursor was liquid bitumen generated from syngenetic kerogen in organic rich sedimentary rocks in the francevillian basin of gabon and in the natural reactors themselves by hydrous reaction mechanisms prior to during and after nuclear criticality a preliminary paragenesis of organic matter at oklo may be defined through the following sequence of events a protokerogen and kerogen evolve from abundant cyanobacteria in the tidal and deltaic sediments in the basal fa formation of the francevillian series during sedimentation and burial respectively b during subsequent subsidence of the basin the first generation of bitumen and petroleum occurred c during uplift the sedimentary strata were fractured and bitumen and petroleum migrated through fractures following this oxidizing aqueous solutions carrying uranyl ions migrated through the highly fractured rocks met and were reduced by organic matter and precipitated pitchblende or uraninite at the present sites of the oklo uranium ore deposits and natural reactors the natural reactors reached nuclear criticality they were heated and produced the second generation of bitumen through hydrous reactions from the by now solid first generation bitumen and remaining kerogen finally hydrothermal effects associated with the dolerite dike swarm intrusion 750 150 ma ago produced yet another localized generation of liquid bitumen from solid organic matter possibly other bitumen generations also occurred during and following this time interval the organic matter in the natural reactors soon became a solid and was able to prevent the loss of uraninite grains enclosed in it these uraninite grains trapped and then immobilized fission products until and to an extent even after a major tectonic igneous event the intrusion of the dolerite dike swarm

the effects of weathering on the physical and mechanical properties of igneous and metamorphic saprolites abstract the present paper presents three extensive datasets of laboratory testing on weathered geomaterials which are emblematic of soil types widely found worldwide the overall dataset includes soils originating from igneous and metamorphic rocks either coarse or fine grained and having either felsic or mafic minerals in particular the data are interpreted to highlight the effects that weathering has on the physical and mechanical properties of these natural geomaterials comparing them with published data with the aim to provide a general framework of interpretation that takes into account this geological process and links soil mechanics to engineering geology generally weathering induces a reduction in the grain size both due to physical actions e g opening of grain contacts and to the chemical decomposition of minerals resulting in the formation of clay minerals as weathering proceeds and the soil becomes finer the in situ specific volume and the location of the normal compression and critical state lines move upwards in the volumetric plane on the other hand the clay minerals cause its angle of shearing resistance to reduce when analysing the behaviour of the intact soil in all cases positive effects of structure albeit small compared to some sedimentary soils were observed and these reduced as a consequence of weathering

conceptual model describing smear zone caused by mandrel action in this study the characteristics and extent of the smear zone are investigated using a large undisturbed sample the aim of using such a sample is to capture the realistic characteristics of the smear zone in relation to the in situ soil structure during the installation of prefabricated vertical drains pvds using a mandrel the extent of the smear zone for bulli clay new south wales australia is determined on the basis of normalised permeability kh khu and the reduction in the water content upon consolidation the permeability and compressibility of the soil are investigated to determine the extent to which the soil surrounding the pvd has become disturbed in laboratory testing the soil consolidation behaviour due to a pvd is studied using a large scale consolidometer apparatus the numerical results have shown that the writers solutions give excellent agreement with laboratory observations

evaluation of cyclic shear strength of two cemented calcareous soils the mechanism controlling the cyclic shear strength of cemented calcareous soils was investigated based on the results obtained from monotonic and cyclic triaxial tests on two different types of calcareous soil undrained cyclic triaxial tests performed on artificially cemented calcareous soils with different loading combinations showed that the effective stress path moved towards or away from the origin due to the generation or dissipation of pore pressure with progressive cycles previous investigations have shown that the peak strength envelope or the state boundary surface or the critical state line forms a boundary beyond which effective stress paths during cyclic loading cannot exist however in this study it was observed that the maximum stress ratio h max obtained from monotonic tests defined the boundary for the cyclic tests based on the information obtained from this study an approach for evaluating the cyclic shear strength is proposed it was observed that the modified normalized cyclic shear strength had a strong linear relationship with the logarithm of the number of cyclic to failure irrespective of confining pressure type of consolidation and stress reversal

mineral chemistry and oxygen isotopic analyses of uraninite pitchblende and uranium alteration minerals from the cigar lake deposit saskatchewan canada abstract the cigar lake unconformity type u deposit is one of the largest and highest grade u deposits in the proterozoic athabasca basin northern saskatchewan canada cigar lake has recently been the focus of an international 3 a collaborative program in which this u deposit was studied as a natural analogue for a spent nuclear fuel repository the deposit is located near the eastern margin of the athabasca basin 430 m below the surface at the intersection between hudsonian age faults and the unconformity between athabasca group sandstones and aphebian metasediments three stages of u mineralization have been identified based on cross cutting relationships and textures observed in thin section and back scattered electron bse images o isotope data and chemical compositions all stages of u mineralization have been variably altered to ca rich u hydrate minerals or uranyl oxide hydrate minerals and coffinite u pb chemical ages of the 3 stages of u mineralization from cigar lake coincide with the 3 major fluid events that precipitated clay and silicate minerals at 1500 ma 950 ma and 300 ma throughout the entire athabasca basin stage 1 and 2 uraninite and pitchblende have the lowest 18o values that range from 30 1 to 15 2 whereas stage 3 uraninite has 18o values ranging from 10 0 to 3 4 uranyl oxide hydrate minerals have 18o values that range from 11 3 to 8 2 whereas uranyl minerals have much higher 18o values based on u pb chemical ages 18o values and petrographic relationships of u alteration minerals associated with primary u mineralization the cigar lake u ore is similar to u ore from other unconformity type u deposits in the athabasca basin therefore the cigar lake ore deposit although surrounded by clay and sandstone barriers has been effected by the same fluid events that have altered other unconformity type u deposits in the athabasca basin the 3 stages of ore formation and associated alteration minerals permit the detailed study of fluids responsible for u deposition and alteration this information provides the necessary context for the evaluation of the cigar lake deposit as a natural analogue for the disposal of spent nuclear fuel in underground vaults in rocks of the canadian shield

the chemical development of a hypersaline coastal basin in the high arctic we investigated a hypersaline seasonally isolated marine basin simb in the canadian high arctic to elucidate the role of brine rejection tidal forcing and groundwater input over the formation of hypersalinity analyses of physical parameters and seasonal sampling of ionic and isotopic composition were carried out on a coastal basin near shellabear point melville island northwest territories 75 n 113 w observations reveal daily and seasonal variability in the water column due to a seasonal tidal connection during the ice free season which lasts substantially longer than the period of freshwater inflow from the catchment an ice formation model of the volume of brine rejected from surface ice formed from marine water indicates that rapid saline enrichment of the basin due to ice formation is possible from tidally replenished marine water and that the current hypersalinity may have formed in less than a decade modeled isotopic composition of brines are consistent with observations and provide an alternative to freshwater isotopic dilution suggested by other workers a tidal connection is a critical consideration in lake evolution and many hypersaline polar lakes could have developed their current chemical composition before full marine isolation by contrast in some coastal lakes marine stratification caused by ice shelves before isolation provides a setting for minimal brine formation and subsequent meromictic conditions to develop hence the marine setting at the time of isolation represents a key factor in explaining divergent lake chemical evolution in the high arctic

the mechanical behaviour of an unsaturated compacted silty clay a comprehensive experimental study has been carried out to investigate the volumetric and shear strength behaviour of a compacted silty clay which exhibited collapse on wetting behaviour the experiments consisted mainly of suction monitored triaxial tests carried out in a new apparatus the test results are interpreted on the basis of an elasto plastic framework using the conventional stress variable approach net stress and suction as well as an approach that takes into account the degree of saturation within two modified stress variables the evidence for critical states was examined based on the stress dilatancy relationships it was found that a critical state was observed experimentally in cases where the samples contracted over much of their stress paths but was not truly established in other cases relationships between the shear strength and specific volume at the ultimate state were established for samples over a wide range of degrees of saturation from fully saturated to the air dried state

on the mechanics of structured sands to date the effect of structure on the behaviour of natural sands has focused almost exclusively on the component of bonding and the effect of fabric has been largely overlooked the paper describes a detailed investigation of the behaviour of two natural sands by means of triaxial testing over a wide range of pressures one material had bonding as the principal element of its structure and the other fabric following on from a paper of cuccovillo and coop which examined the influence of the two structural elements on the small strain stiffness the current paper develops a new framework for the yielding and large strain behaviour it is suggested that structure should be considered as an element of the nature of a sand in addition to properties such as mineralogy particle shape and grading the resulting framework is then capable of encompassing the patterns of behaviour seen for both bonding and fabric dominated sands while bonding results in a cohesive mode of shearing it is demonstrated that when

the mechanics of a saturated silty loess and implications for landslides the results from an intensive experimental investigation on a loess that was retrieved from a typical silty loess zone in the north western chinese loess plateau are presented and interpreted triaxial and oedometer tests were performed on intact and reconstituted samples in a saturated condition the soil behavior was found to be strongly affected by structure the compression paths of the intact samples crossed the intrinsic compression line of the reconstituted soil and reached well defined gross yield points after which the compression paths converged towards the intrinsic compression lines two critical state lines were defined for the intact and reconstituted soils in the volumetric plane as a result of a robust element of natural structure comparisons were made with a structured clayey loess retrieved from the south eastern loess plateau it was found that the effects of structure on the behavior of the two loess soils are similar though they are very different in natural properties this indicates that their natural structures might have experienced similar forming processes perhaps related to their common origin catastrophic flowslides commonly occur in the study area and the patterns of behavior observed in the laboratory tests may create some new insights into mechanisms of landslide initiation and subsequent movement as discussed in the study

a micro finite element model for soil behaviour experimental evaluation for sand under triaxial compression this note evaluates the ability of a combined discrete finite element approach to replicate the experimental response of a dry sand under triaxial compression the numerical sample was created by v

the effects of weathering on the physical and mechanical properties of a granitic saprolite less research has been carried out on the changes induced by weathering to the mechanical properties of reconstituted and intact soils that originate from chemical decomposition of rocks saprolite

uranium bearing stratiform organic matter in paleoplacers of the lower huronian supergroup elliot lake blind river region canada the elliot lake blind river ontario paleoplacer deposits in the basal matineda formation lowermost member of the 2 25 2 45 ga old huronian supergroup contain organic matter chemically consistent with kerogen this substance is also referred to as thucholite uranium ores and some gold occur here and these minerals may be in close association with the kerogen two uraniferous and auriferous stratiform kerogens obtained from the denison mines limited s denison mine and rio algom limited s stanleigh mine have been analyzed by combined high vacuum pyrolysis gas chromatography mass spectrometry and by neutron activation the reflectances of these samples have also been determined related samples containing dispersed kerogen have been examined by backscattered scanning electron microscopy the polymer like matrix of the two stratiform kerogens consists of aromatic alkyl aromatic hydrocarbon and sulphur moieties and contains 20 and 32 uranium with gold abundances in the parts per billion range

characterization of graphite alteration and bitumen genesis in the cigar lake deposit saskatchewan canada bitumens collected in the east zone of the cigar lake deposit have been analyzed by c 13 nuclear magnetic resonance pyrolysis gas chromatography rock eval and c h and 0 methods carbon and hydrogen isotopic compositions and uranium contents have been determined results indicate that the bitumens consist mainly of aromatic structures f a almost equal to 60 and have undergone a late oxidation process similarities in carbon isotopic composition 27 5 part per thousand deltac 13 28 2 parts per thousand between barren bitumens u 300 ppm and graphite collected in the basement gneisses as well as evidence for progressive disorganization of graphite along a basement profile suggest a genetic relationship between graphite and bitumens from the mineralized areas the presence of amorphous carbon in pit structures inside graphite flakes close to the unconformity supports this assessment significant differences in geochemical and isotopic characteristics of the cigar lake barren bitumens and the cluff lake mineralized bitumens suggest that there are two possible mechanisms for their formation barren c enriched bitumens could have formed directly by hydrogenation of amorphous carbon whereas mineralized isotopically light bitumens from cluff lake deltac 13 almost equal to 48 parts per thousand may result from the polymerization of light hydrocarbons around uraninite grains

anisotropic shear strength of a residual soil of sandstone this paper discusses results of laboratory tests carried out with a residual soil originated from the weathering of eolian sandstone from southern brazil parent rock features like microfabric and particle bonding are remarkably well preserved within this residual soil stiffness and shear strength properties were evaluated with consolidated drained cid and consolidated undrained ciu triaxial compression tests undisturbed specimens were tested with two different orientations between the specimen axis and bedding surfaces i e parallel 0 or perpendicular 90 to investigate the effect of anisotropy when cid triaxial tests were performed with 0 the yield surface associated with the structure was much larger than when tests were performed with 90 coincidently ciu tests with 0 showed peak shear strengths much greater than for 90 at comparable test conditions once the peak shear strength was surpassed ciu tests followed collapse type effective stress paths not sh

characterization of insoluble organic matter from the lower proterozoic huronian supergroup elliot lake ontario abstract elliot lake organic matter falls into two main groups 1 stratiform kerogens with reflectance from 2 63 to 7 31 ro max exhibit a high level of aromaticity and low atomic h c ratios 0 41 0 60 2 less aromatic disseminated globules most resembling solid bitumen are of lower maturity with ro max from 0 72 to 1 32 and atomic h c ratios 0 71 0 81 stratiform kerogens originated from cyanobacteria have 13c values from 15 to 25 one exception with 13c 31 8 may have originated from methanogenic source biota thus two genetically distinct populations of kerogen are tentatively recognized in elliot lake metasediments globular bitumens remobilized by hydrous pyrolysis from kerogen exhibit 13c values ranging from 25 tp 33 0 the overall isotopic bimodality among elliot lake organic material is explained by analogy to petroleum generation from particulate kerogen that matured under conditions of catagenesis to metagenesis and was subjected to radiation over a long time barium u th au pt pd and ree contents of elliot lake stratiform kerogen greatly exceed of average black shales except for as pt pd and au all metals ti v cr mn fe co ni zn se rb sr ag sb cs ba hf ta w hg th and u are more concentrated in stratiform kerogens than in the derivative bitumen this signals a significant role for a low temperature transfer of noble metals to migrating bitumen

geochronology and genesis of the bong uranium deposit thelon basin nunavut canada the thelon basin nunavut shares many similarities with the uranium producing athabasca basin saskatchewan however the uranium deposits associated with the thelon basin are still poorly understood the kiggavik project area areva resources canada is located near the northeastern terminus of the thelon basin and comprises multiple uranium deposits hosted exclusively in basement rocks the bong deposit is hosted dominantly by neoarchean metagraywacke of the woodburn lake group a five phase metallogenetic model is proposed for the bong deposit with three stages of uraninite identified the premineralization phase is characterized by host rock silicification mineralization is separated into three main stages stage 1 uraninite u1 ca 1500 ma is preserved in highly fractured and altered disseminated grains that are overgrown by later stages of uraninite stage 2 uraninite u2 ca 1100 ma forms veinlets parallel to d 1 foliation and coats and fills fractures in organic matter nodules and blebs stage 2 uraninite is associated with pervasive illite that formed from 190 c fluids 18 o 6 4 2 h 97 which remobilized much of stage 1 uraninite and completely overprinted stage 1 alteration at 1000 ma an oxidizing fluid deposited uraninite along redox fronts u3 while altering and remobilizing stage 1 and 2 uraninite post uranium oxide minerals include drusy quartz calcite and illite accompanied by uranyl phases e g uranophane ca u

isotropic yielding in an artificially cemented soil cured under stress the work simulates in the laboratory the formation of a cemented sedimentary deposit in which cement bonding occurs after burial and under geostatic stresses isotropic compression tests were carried out on artificially cemented specimens made with variable cement contents after consolidating the samples to the uncemented normal compression line the specimens were allowed to cure for 48 h before testing the curing confining stresses ranged from 50 to 2000 kpa and were intended to represent soil elements at different depths in the fictitious sedimentary deposit when the cementing occurred the contribution of the cement bonds to soil compression and the changes in the isotropic yield stress as a function of void ratio and cement content were analysed the results showed the importance of the void ratio during the formation of cement bonds and also of the degree of cementation for the compressive behaviour of the cemented soil and demonstrated that the variation in yield stress with void ratio and ce

behavior of hydrocarbon reservoir sands and sandstones most new oil and gas reservoirs are discovered in sands and weak sandstones and the petroleum industry has therefore generated an extensive amount of data from laboratory tests on these materials some of these data are reexamined in this paper within the context of recent soil mechanics research of key importance to petroleum engineers is the compressibility of the sands and this is shown to be related both to the current density and stress level of the soil and to the location of its normal compression line when present the cement bonds between the particles appear to be weaker than the particles themselves so that the major yield point during compression is still associated with breakage of the particles rather than of the cement bonds the paper also examines the behavior of the sands and sandstones in shearing allowing a more general understanding of the mechanics of the materials to be developed

interpretation and modelling of deformation characteristics of a stiff north sea clay an investigation into the behaviour of north sea glaciomarine clays was carried out in which triaxial tests were conducted on both natural and reconstituted samples to assess the effects of structure although the tests were conventional cid tests high quality instrumentation was used the tests were also technically difficult both because of the very long test durations and because some of the samples were swelled back to very low effective stresses so that the effect of swelling on the influence of structure on the soil behaviour could be assessed a class a prediction of the behaviour in these tests was carried out using the brick model although the model is not designed to account for the influence of structure it was found that its effects could be simulated by allowing the soil to have artificially high overconsolidation ratios ocrs so that the high undrained shear strengths resulting from structure could be modelled making the simple assumption that the decay of stiffness could be scaled fr

geochemistry of uraniferous bitumen in the southwest athabasca basin saskatchewan canada the sediment hosted unconformity type southwest athabasca uranium mineralization in northern saskatchewan canada contains uraniferous bitumen as observed elsewhere in the athabasca basin uraninite is present either as micron sized grains dispersed in bitumen uraniferous bitumen or as larger grains situated in the pore space between bitumen globules the spatial and textural relationships between uraninite and bitumen suggest that they were co precipitated la icp ms u pb dating of uraniferous bitumen yielded an age of 1575 53 ma similar to that of other unconformity type uranium mineralization in the athabasca basin indicating that the bitumen was formed early in the history of the basin nitrogen carbon and sulfur isotope analyses of uraniferous bitumen indicate that its source material was probably kerogen produced by cyanobacteria in a clastic environment

quantifying the evolution of soil fabric during shearing using scalar parameters the packing density of a soil is typically described in terms of the scalar parameters void ratio specific volume or porosity within a critical state soil mechanics framework the response of a sand is considered to depend on its state that is the combination of void ratio and effective stress when soil is considered from a particle scale perspective the packing density is often described using the coordination number cn that is the average number of contacts per particle using particles with simple geometries discrete element method dem simulations photoelastic tests and experiments on analogue soils e g glass ballotini have all demonstrated a correlation between cn and mechanical response this study investigates whether these correlations apply to real soils using direct measurement of the fabric via micro computed tomography micro ct a variety of scalar fabric descriptors was measured during the triaxial compression of both intact and reconstituted reigate sand samples while ea

formation of the enigmatic matoush uranium deposit in the paleoprotozoic otish basin quebec canada the matoush uranium deposit is situated in the paleoproterozoic otish basin northern quebec canada and is hosted by the indicator formation sandstones its sheet like ore bodies are closely associated with the steeply dipping matoush fracture which hosts mafic dykes and minor quartz feldspar tourmaline pegmatites regional diagenesis involving oxidizing basinal fluids 2h 15 18o 8 produced mostly illite and possibly leached u from accessory phases in the indicator formation sandstones the bimodal matoush dyke intruded the indicator formation along the matoush fracture and the related metasomatism produced cr rich dravite and muscovite in both the dyke and the proximal sandstones uraninite formed when u6 in the basinal brine was reduced to u4 in contact with the mafic dyke and by fe2 in cr dravite and cr muscovite and precipitated together with eskolaite and hematite because of its unique characteristics the matoush deposit cannot be easily classified within the generally accepted classification of uranium deposits two of its main characteristics unusual reduction mechanism structural control do not correspond to the sandstone hosted group of deposits unconformity type tabular roll front in spite of uranium being derived from the otish group sandstones

on the behaviour of thanet sand an example of an uncemented natural sand an extensive laboratory investigation was made of the mechanics of thanet sand testing the soils from a number of locations and depths in the triaxial apparatus over a wide range of stress levels comparisons between tests on intact and reconstituted samples and between vertically and horizontally trimmed intact samples highlighted the effects of structure on the behaviour of this uncemented sand in particular a significant effect of anisotropy two distinct substrata have previously been identified with different fines contents and the key difference in their behaviour has been found here to be the location of their critical state line in the v lnp plane which has a significant effect on the engineering behaviour of the two substrata and can explain recent unusual observations of decreasing pile capacity with depth tests in which the glauconite content was removed from the sand showed that it did not affect its behaviour

from evaporated seawater to uranium mineralizing brines isotopic and trace element study of quartz dolomite veins in the athabasca system abstract stable isotope o h c radiogenic isotope sr nd and trace element analyses have been applied to quartz dolomite veins and their uranium u bearing fluid inclusions associated with proterozoic unconformity related uo 2 uraninite ores in the athabasca basin canada in order to trace the evolution of pristine evaporated seawater towards u mineralizing brines during their migration through sediments and basement rocks fluid inclusion data show that quartz and dolomite have precipitated from brines of comparable chemistry excepted for relatively small amounts of co 2 found in dolomite hosted fluid inclusions however 18 o values of quartz veins 18 o 11 to 18 and dolomite veins 18 o 13 to 24 clearly indicate isotopic disequilibrium between quartz and dolomite hence it is inferred that this isotopic disequilibrium primarily reflects a decrease in temperature between the quartz stage 180 c and the dolomite stage 120 c the 13 c values of co 2 dissolved in dolomite hosted fluid inclusions 13 c 30 to 4 and the 13 c values of dolomite 13 c 23 5 to 3 5 indicate that the co 2 dissolved in the mineralizing brines originated from brine graphite interactions in the basement the resulting slight increase in the fluid partial pressure of co 2 p co 2 may have triggered dolomite precipitation instead of quartz 18 o values of quartz veins and previously published 18 o values of the main alteration minerals around the u ores illite chlorite and tourmaline show that quartz and alteration minerals were isotopically equilibrated with the same fluid at 180 c the ree concentrations in dolomite produce paas normalized patterns that show some similarities with that of uo 2 and are clearly distinct from that of the other main ree bearing minerals in these environments monazite zircon and aluminum phosphate sulfate aps minerals the radiogenic isotope compositions of dolomite 87 sr 86 sr i 0 7053 to 0 7161 and e nd t 8 8 to 20 3 differ from one deposit to another reflecting both heterogeneity in the basement geology and variable preservation of the original composition of brines the previously published 87 sr 86 sr i and e nd t values of uo 2 compare with the most evolved dolomites i e dolomites precipitated from brines that exchanged the most with the basement this reinforces a close genetic link between dolomites and uo 2 deposition and implies that uo 2 deposition occurred in a cooling system during the transition from quartz to dolomite formation the 18 o and d values of the mineralizing brines 18 o 1 to 8 and d 150 to 50 are considerably shifted from that of their theoretical original values acquired during evaporation of seawater 18 o 3 and d 40 the positive 18 o shift is explained by protracted fluid rock interaction within the basin and basement rocks the negative d shift is attributed to incomplete mixing between the u mineralizing brines and low d water this low d water was likely produced during the abiogenic synthesis of bitumen by fisher tropsch like reactions involving co 2 derived from brine graphite interaction in the basement and radiolytic h 2 the resulting low d brines have been equilibrated with alteration minerals this may explain why some alteration minerals yield anomalously low d values whose significance has long been debated

a structured cam clay model a theoretical study of the behaviour of structured soil is presented a new model referred to as the structured cam clay model is formulated by introducing the influence of soil structure into th

quantifying the evolution of soil fabric during shearing using directional parameters over the past 50 years experimental studies have repeatedly demonstrated that the mechanical behaviour of sand is sensitive to the material fabric that is the arrangement of the grains up until now there have been relatively few attempts to describe this fabric quantitatively much of our understanding of the link between the particle movements and interactions and the macro scale response of granular materials including sand comes from discrete element modelling and experiments on analogue sands with simple idealised shapes this paper investigates methods of quantifying the directional fabric of a real sand and its evolution under loading statistical analyses of the distribution of fabric directional data in terms of particle contact normal branch vector and void orientations were carried out at different stages of shearing deformation the data show that the initial particle orientation fabric that develops during the deposition of the material tends to persist during shearing while in the