an experimental method for gold partitioning between two immiscible fluids brine and n dodecane abstract organic matter can be found in many different types of ore deposits but its role in ore forming processes is not yet fully understood here we present an experimental method that can be used to determine the partition coefficient dauorg aq partition coefficient of au between an hydrocarbon and an aqueous fluid of gold between two immiscible liquids and thus whether liquid hydrocarbon fluids such as petroleum can act as ore fluids and transport gold or other metals of interest to investigate liquid hydrocarbons in the presence of an aqueous liquid doped with gold we modified the hfs 340z hydrothermal flow system coretest systems inc to enable sampling at hydrothermal p t conditions 150 c and 5 bar of each of two density stratified immiscible liquids a saline aqueous solution 10 wt nacl was doped with gold and heated with n dodecane ch3 ch2 10ch3 to 105 c and 150 c each brine sample was directly followed by an organic sample until three samples of each liquid were taken aqua regia was added to the brine samples to stabilize the gold before icp ms analyses each organic sample was digested chemically with a mixture of ultra pure nitric acid and hydrogen peroxide to generate carbon free solutions prior to icp ms analysis this procedure generates reproducible partition coefficients for gold or presumably any other metal between hydrocarbon and aqueous liquids if passivation procedures of the hfs 340z hydrothermal flow system are strictly followed and error sources are monitored rigorously the preferred dauorg aq between n dodecane and the brine is 0 05 0 04

tracing tsunami signatures of the ad 551 and ad 1303 tsunamis at the gulf of kyparissia peloponnese greece using direct push in situ sensing techniques combined with geophysical studies

nd and sr isotopic ratios and trace element geochemistry of epidote from the swiss molasse basin as provenance indicators implications for the reconstruction of the exhumation history of the central alps abstract epidote is a common heavy mineral in sandstones its use as a provenance indicator however is limited because it appears in a wide range of lithologies and geological settings in order to discriminate between mantle and crust derived source rocks we measured isotopic and trace element compositions of detrital epidote from sandstones of the swiss molasse basin the compositions of the detrital epidotes were compared to epidotes from penninic metabasites and austroalpine metagranites from the present day exposures and to epidote from ophiolitic and metagranitic pebbles from the molasse basin we found that nd isotopic ratios of epidote allow a good discrimination between different types of source rocks with end values ranging between 6 1 and 8 6 for metabasic lithologies and between 9 7 and 2 8 for metagranitic lithologies sr isotope ratios reveal similar trends but do not allow such a clear discrimination ba u rb nb and th contents of epidote correlate well with the end values yielding the same provenance signal according to isotopic and trace element compositions three types of epidote bearing sandstones can be distinguished one received epidote from lower austroalpine metagranites another from penninic ophiolites and a third type of sandstone received epidote from both sources the provenance of the detrital epidote has important bearing on the exhumation history of the central alps elucidating the transition between the erosion of lower austroalpine felsic lithologies and the onset of erosion of the penninic lower plate according to our data the penninic lower plate became exposed simultaneously in the hinterland of all molasse fans at 21 20 ma at the same time the relief collapsed as reflected by a drastic decrease of sediment accumulation rates in the foreland basin the combination of both events fits well to the geodynamic scenario of large scale lateral extension processes affecting the central alps in post collisional times

archaean oil migration in the witwatersrand basin of south africa abstract the late archaean witwatersrand supergroup of south africa hosts the largest known gold uranium pyrite ore deposits oil preserved in fluid inclusions in quartz grains in siliciclastic sedimentary rocks of that supergroup implies that hydrocarbon generation and migration occurred during the archaean and may have been involved in mineralization processes through reference to phanerozoic analogues oil bearing fluid inclusions entrapped in healed microfractures in detrital quartz grains and in early syntaxial quartz overgrowths imply that the onset of oil migration coincided with early to intermediate stages of burial while intra granular porosity was still preserved multiple generations of oil migration are indicated by i oil inclusions within early diagenetic cements at different levels in the stratigraphic succession ii more than one type of oil in entrapment sites iii oil entrapment in multiple stages of the quartz paragenetic sequence oil generation and migration are considered to have occurred throughout and for some considerable time after development of the witwatersrand basin consistent with progressive burial and kerogen maturation in more than one tectonic regime oil bearing fluid inclusions within detrital sandstone fragments suggest that oil migration also occurred in a sedimentary succession on the kaapvaal craton prior to 2 9 ga oil in the witwatersrand supergroup was most likely derived from multiple source areas with the principal source probably being shales within the lower witwatersrand supergroup the hydrocarbon migration history of the basin has important implications for understanding the textural relationship between gold bituminized oil and uraninite in the giant gold uranium pyrite ore deposits

mineral chemical study of u bearing minerals from the dominion reefs south africa the neo archean dominion reefs 3 06 ga are thin meta conglomerate layers with concentrations of u and th bearing heavy minerals higher than in the overlying witwatersrand reefs ore samples from uranium one africa s rietkuil and dominion exploration areas near klerksdorp south africa were investigated for their mineral paragenesis texture and mineral chemical composition the ore and heavy mineral assemblages consist of uraninite other uraniferous minerals fe sulphides ni co sulfarsenides garnet pyrite pyrrhotite monazite zircon chromite magnetite and minor gold sub rounded uraninite grains occur associated with the primary detrital heavy mineral paragenesis u ti u th minerals pitchblende colloform uraninite and coffinite are of secondary re mobilised origin as evidenced by crystal shape and texture most of the uranium mineralisation is represented by detrital uraninite with up to 70 2 wt uo2 and up to 9 3 wt tho2 re crystallised phases such as secondary pitchblende without th coffinite u ti and u th phases are related to hydrothermal overprint during low grade metamorphism and are of minor abundance

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

coalification in the northern wildhorn nappe and adjacent units western switzerland implications for tectonic burial histories abstract vitrinite reflectance of fourteen eocene coal samples from the northern wildhorn nappe in the kander valley have been analyzed and compared to nine agewise similar coals from adjacent tectonic units the degree of coalification decreases regularly from semi anthracite in the kander valley to lignite in the plateau molasse the degree of coalification in the tertiary coals appears to be solely dependent on their tectonic history and indicates and estimated 6 km of burial by higher pennine nappes for the kander valley the rank at this locality low volatile bituminous to semi anthracite is significantly higher than in the border chain at beatenberg high volatile a bituminous the latter locality therefore was never buried deeper than about 4 km a further decrease in rank is found in the subalpine flysch and molasse high volatile b bituminous which in turn is significantly more mature than lignites from the folded plateau molasse at linden two samples of dogger coal from the pennine prealpes medianes are medium to low volatile bituminous that is intermediate between the kander valley and beatenberg their rank however was achieved before their final emplacement north of the wildhorn nappe by comparing calculated tti time temperature indices values for time depth burial curves with measured vitrinite reflectances maximum burial temperatures were estimated for the various tectonic units for the wildhorn nappe 160 180 c were obtained in the kander valley and 100 130 c in the border chain as a result of tectonic burial due to the thrusting by the pennine prealps sedimentary burial led to temperatures of 100 120 c in the subalpine molasse below the border chain prior to its thrusting

phanerozoic analogues for carbonaceous matter in witwatersrand ore deposits thoriferous bitumen nodules in quartz pebble conglomerates and pebbly sandstones of phanerozoic age in the british isles are analogues for the uraniferous bitumen nodules flyspeck in the archean witwatersrand gold uranium deposits they are comparable in morphology relationship to bedding planes replacive behavior toward quartz mineralogy fragmentation and displacement of inclusions in each case the quartz rich sedimentary host rocks represent regionally important transgressive deposits the contrast in dominant radioelement thorium or uranium probably reflects differences in mobility of the elements as a function of variable eh conditions the phanerozoic thoriferous nodules occur only in pale low eh beds which lack uranium deposits but in the archean witwatersrand deposits fractionation of uranium and thorium may not have been as marked in the phanerozoic examples there is good evidence for migration of hydrocarbons through the host rocks and the bitumen nodules can confidently be attributed a hydrocarbon origin by analogy this supports proponents of a hydrocarbon origin for the witwatersrand carbon rather than a microbial origin

1 5d inversion of lateral variation of scholte wave dispersion reliable models of in situ shear wave velocities of shallow water marine sediments are important for geotechnical applications lithological sediment characterization and seismic exploration studies we infer the 2d shear wave velocity structure of shallow water marine sediments from the lateral variation of scholte wave dispersion scholte waves are recorded in a common receiver gather generated by an air gun towed behind a ship away from a single stationary ocean bottom seismometer an offset window moves along the common receiver gather to pick up a local wavefield a slant stack produces a slowness frequency spectrum of the local wavefield which contains all modes excited by the air gun amplitude maxima dispersion curves in the local spectrum are picked and inverted for the shear wave velocity depth profile located at the center of the window as the window continuously moves along the common receiver gather a 2d shear wave velocity section is generated in a synthetic example the smooth lateral variation of surficial shear wave velocity is well reconstructed the method is applied to two orthogonal common receiver gathers acquired in the baltic sea northern germany the inverted 2d models show a strong vertical gradient of shear wave velocity at the sea floor along one profile significant lateral variation near the sea floor is observed

investigating lake sediments and peat deposits with geophysical methods a case study from a kettle hole at the late palaeolithic site of tyrsted denmark abstract kettle holes are common ice decay features in formerly glacial landscapes like those in southern scandinavia and northern germany here the kettle holes are represented either as dry depressions wetland areas or lakes however the majority of these features are silted and part of the present farmland we investigated a small kettle hole at tyrsted near the township of tyrsted south of horsens denmark with the aim to determine the extension and depth of this feature using geophysical methods a former excavation at tyrsted carried out from the horsens museum in 2017 at a neighboring site revealed late palaeolithic flint of the bromme type and worked reindeer antlers this connection in a late glacial horizon is unique not only in a danish context and it can help to improve and clarify the dating of the bromme culture we used ground penetrating radar gpr electromagnetic induction emi and electrical resistivity tomography ert to estimate the extension of the kettle hole 16 m 25 m shear wave reflection and refraction seismics sh seismics were able to detect the bottom sediment of the former lake at about 5 m depth furthermore a seismic event at about 1 30 m depth is visible which can be associated to the transition between the allerod and younger dryas sediment making the detection of the bromme horizon possible after the non invasive investigation a location for an open excavation has been chosen in a way to groundtruth the geophysical results allowing the direct comparison with the stratigraphy these results allow the archaeologists to identify key excavation areas focused on the investigation of the allerod and younger dryas layers in a way to improve the dating information about the bromme horizon collected so far furthermore geophysical investigations together with excavations will enable the archaeological and palaeoenvironmental research groups to search large scale palaeolandscapes for these very rare but highly important finds

stable isotope composition of bentonites from the swiss and bavarian freshwater molasse as a proxy for paleoprecipitation abstract the hydrogen and oxygen isotope compositions of bentonites and smectite rich tuffs from the north alpine foreland basin were measured for samples dated between 9 and 21 ma assuming clay mineral formation shortly after the deposition of the volcanic ash layers and at surface temperatures estimated from paleoclimatic studies the h and o isotope composition of water in equilibrium with the clay minerals can be calculated a comparison with values derived from other proxies of paleoprecipitation in the molasse basin such as pedogenic carbonates and mammal remains and 18 o values of carbonate in the bentonite beds suggests that the 18 o values of water estimated by this method are typical for foreland precipitation at this time and for this region therefore the 18 o value of smectite in bentonites and altered tuff layers can be a useful tool for studies of paleoclimate and topography there are however indications that the clay minerals did not retain their initial hydrogen isotopic composition but that a postformational exchange of h isotopes has occurred

occurrence and origin of ultralaminar structures in amorphous kerogens of various source rocks and oil shales abstract forty low maturity type i ii kerogens from source rocks and oil shales ranging in age from infra cambrian to miocene were examined by transmission electron microscopy tem when previously observed by light microscopy and or uv fluorescence microscopy the above samples like a very large number of kerogens seemed homogeneous and amorphous in fact tem revealed the presence of ultralaminar structures in 22 of these amorphous kerogens the abundance of ultralaminae depends on the considered sample and some of the tested kerogens are nearly exclusively composed of ultralamina accumulations based on thickness three main groups of ultralaminae can be identified parallel studies on extant algae indicated that some of the above ultralaminae likely derived from the resistant outer walls of microalgae the fossilization of such outer walls should occur via the selective preservation pathway and result in the formation of highly aliphatic ultralaminar kerogens the lack of ultralaminae in infra cambrian kerogens is consistent with a cyanobacterial origin

thermal diagenesis in the swiss molasse basin implications for oil generation clay mineral transformations during burial are indicators of the degree of diagenesis of sediments diagenetic zonations in numerous wells of the swiss molasse basin are defined by the disappearance of smectite and or the appearance of either corrensite or irregular 2 1 mixed layers the maximum level attained in the thickest molasse sections corresponds to organic matter maturation suitable for hydrocarbon generation reconstructed on the basis of the clay mineral transformation data a burial history of the basin is proposed

the contribution of geochemistry to ancient harbor geoarcheology the example of ostia antica abstract once trapped in ancient harbor basins sediments form environmental archives that have been widely studied by geoarcheologists in recent decades especially to help reconstruct fluvio marine landscapes of the last millennia in some cases classic environmental markers cannot be used for this purpose either because of their scarcity in the sedimentary deposits or because analytical costs limit the resolution that can be achieved in order to remedy these shortcomings and to complement the more commonly used proxies elemental and isotopic geochemistry has been added to the geoarcheological toolkit here we show how to read the evolution of the paleo environmental dynamics in the water column of ostia antica rome s first maritime harbor using the geochemical and isotopic record of a 3000 year old sediment core drilled in the ancient harbor basin a comparison of the results obtained from ostia antica with those of other ancient mediterranean harbors reveals the nature of the main environmental processes operating during the formation of sedimentary deposits in harbor basins from this comparative approach it appears that the respective weight of each control factor is dependent on the coastal geomorphological context of the sites where the harbors were established since the discovery of the harbor of ostia antica in 2014 this method has provided the means for the first time to identify two distinct harbor basin regimes an initial marine dominated regime from the middle of the 4th c bc to the 3rd c bc and a later freshwater dominated regime up to the 2nd c bc more generally we observe the effects of the dynamics of the deltaic progradation of the tiber which very early on was subject to a hydro climatic component on the processes of alluviation of the harbor basin additionally and also for the first time in harbor geoarcheology pb isotope compositions measured specifically on uncontaminated sediments demonstrate their utility for both identifying the geological sources of the sediments of the tiber delta and discriminating finer from larger particles the present study further provides an opportunity to test the validity of two hypotheses recently put forward 1 that a series of three tsunamis is recorded in the harbor silts and 2 that an initial lagoon type harbor was constructed at ostia antica which later evolved into a fluvial harbor neither of these hypotheses are supported by the present data

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

gold partitioning between 1 dodecanethiol and brine at elevated temperatures implications of au transport in hydrocarbons for oil brine ore systems abstract gold can be associated with hydrocarbons in hydrothermal gold deposits but the near absence of experimental data on gold hydrocarbon interactions at hydrothermal conditions prevents a quantitative interpretation of this relationship in this study we investigate the ability of liquid hydrocarbons to act as gold transporting ore fluids using experiments on the partitioning of gold between brine 10 wt nacl and 1 dodecanethiol ddt experiments were conducted at 105 c and 150 c and

uranium deposits of franceville basin gabon role of organic matter and oil cracking on uranium mineralization abstract the lower proterozoic uranium deposits in the franceville basin gabon are mainly known to have hosted natural nuclear reactors however this basin also witnessed a former petroleum system which shows major occurrences of uranium ores associated with organic matter the uranium mineralization is the result of several episodes of oil generation and migration fluid mixing and hydrofracturing during burial at around 2 0 ga black shales were heated and expelled hydrocarbons which migrated in underlying sandstones the first episode of oil migration was synchronous with a silicification event produced by a hot low salinity fluid as shown by fluid inclusions trapped in quartz overgrowths the second episode was contemporaneous with quartz dissolution and is characterized by the mixing of hydrocarbons and oxidizing u bearing brine which resulted in the precipitation of uo2 inclusions in oil then oil to gas conversion generated overpressured gas trapped in pores with uraniferous bitumen nodules changes in the stress regime probably favored radial hydrofracturing around bitumen nodules and subsequently the development of a pervasive micro fracture network there uo2 precipitated together with cu fe sulfides through thermochemical sulfate reduction favored by the presence of hydrocarbons and methane

magmatic and metamorphic uraninite mineralization in the western margin of the trans hudson orogen saskatchewan canada a uranium source for unconformity related uranium deposits the genetic model for the giant unconformity related uranium deposits of the athabasca basin is still being debated with one of the main issues being the source of the uranium concentrated by mesoproterozoic era ca 1 60 1 00 ga diagenetic hydrothermal events at the interface between the athabasca basin and the underlying archean paleoproterozoic basement rocks currently accessory minerals like monazite zircon and or apatite from the sedimentary basin and basement rocks are proposed as the primary uranium source for these high grade uranium deposits numerous occurrences of u mineralization of hudsonian age have been documented for decades all around the athabasca basin however so far these have not been regarded as viable u sources here a systematic and detailed study of two areas of basement rocks near the eastern part of the athabasca basin is presented i e the way lake property lying outside the current margin of the basin and the moore lakes property currently covered by the basin this study highlights the significant and widespread occurrence of hudsonian ca 1 81 1 76 ga uranium oxide uo2 mineralization in these zones two types of mineralization are identified and documented here magmatic uranium oxides related to granitic pegmatites and leucogranites which are more common and high temperature vein hosted uranium oxides which have the highest grades the two types were formed during the peak 1 82 1 81 ga and or postthermal peak 1 81 1 72 ga events related to the evolution of the trans hudson orogeny the magmatic uranium oxides formed by partial melting of wollaston group metasedimentary rocks the origin of the vein type occurrences is unclear but their high thorium and rare earth element ree contents suggest a high temperature process associated with ca and or na metasomatism the uranium oxides are associated with other u th and reebearing accessory minerals like u rich thorite thorite zircon and or monazite adding to the exceptional u contents 100 2 460 ppm of these uo2 bearing rocks up to 200 times more primarily enriched in u than other basement or basin rock types a 3 d model of a 1 300 630 200 m basement zone from the way lake property indicates that uraninite bearing granitic pegmatites and leucogranites represent 7 of the total volume of crystalline rock within this rock volume are approximately 8 121 assuming a mean u content of 250 ppm to 16 242 assuming a mean u content of 500 ppm tonnes u the u tonnage of this limited rock volume contained mainly by the hudsonian age uo2 corresponds to between 4 for mcarthur river and 103 for rabbit lake of the u tonnage of known unconformity related u deposits of the basin some of the studied rock samples even macroscopically fresh and located far away from any known unconformity related u deposit present clear evidence of alteration including clay minerals aluminophosphatesulfate aps minerals and uo2 dissolution indicating the percolation of the brines associated with the formation of unconformity related uranium deposits when the basin was far more geographically extensive due to geologic similarities between the studied zones and the basement domains from the eastern part of the athabasca basin i e the hearne province it is proposed that these domains hosted widespread hudsonianage uranium oxide protores these protores provided easily leachable uranium for the metal enrichment of basinal brines during their percolation within the basement and the formation of the unconformity related u deposits these observations bring new insight to the debate about the genetic model of unconformity related u deposits and reinforce the metal source potential of the basement compared to that of the sedimentary basin

metamorphism of the witwatersrand gold fields a review abstract there is widespread evidence for greenschist facies metamorphism in different rock types within all the witwatersrand gold mines the silicate mineral assemblages suggest near uniform peak metamorphic conditions equivalent to the chlorite zone in all the major witwatersrand gold fields assemblages of coexisting pyrophyllite chloritoid have been recorded in most of the gold mines and the critical assemblage of pyrophyllite chloritoid muscovite chlorite quartz tourmaline rutile pyrite is found in most gold fields kaolinite paragonite biotite pyrrhotite and arsenopyrite have more local distribution pelites shales quartzites meta conglomerates metabasalts and some dykes record these metamorphic assemblages albeit in different mineral proportions and pyrophyllite and chloritoid are recorded from many gold producing reefs andalusite kyanite garnet and or cordierite bearing assemblages indicate higher metamorphic grades in three discrete areas along the nw margin of the witwatersrand basin to the ne of the evander gold field and around the collar of the vredefort dome concentric metamorphic facies around the vredefort dome culminate in granulite facies assemblages near the centre it is important to note that there are no definitive published data constraining the temporal relationships between the granulites and amphibolites of the vredefort dome greenschist facies assemblages in the vredefort collar rocks thermal metamorphism related to intrusion of the bushveld complex and the regional greenschist facies metamorphism documented in the gold fields metamorphic conditions of 350 50 c and up to 3 kbars are inferred for the gold fields with temperatures increasing to around 700 c in granulites of the vredefort dome other geothermometric methods including illite crystallinity fluid inclusions carbon elemental ratios and vitrinite reflectance are compatible with the above estimates but are each associated with considerable temperature uncertainties fluids in equilibrium with pyrophyllite muscovite quartz pyrite paragonite are inferred during metamorphism suggesting slightly acid conditions and elevated sulphur activities regional greenschist facies metamorphism documented in the witwatersrand gold mines was accompanied by widespread deformation large fluxes of aqueous fluid and considerable element mobility the low intermediate pressure of this metamorphic terrain and the lack of large scale tectonic thickening favours underplating by mafic magmas as the likely cause of the metamorphic pattern no model for gold genesis in the witwatersrand basin is complete without accommodating post burial processes including metamorphism deformation and alteration any placer gold would be overprinted by these processes and any epigenetic gold could potentially be introduced during these periods of thermal and fluid activity it is also important to note at least two quite unusual features of the witwatersrand metamorphic assemblages the virtual absence of feldspar from the 3 km thick central rand group over 300 km and the narrow range of metamorphic grade inferred for the gold mines over this same distance

diagenetic mobilization of ti and formation of brookite anatase in early cambrian black shales south china abstract titanium ti is typically hosted in detrital minerals in marine sediments and has long been considered to be immobile during diagenesis in this study the authigenic titania minerals brookite and anatase are observed in early cambrian carbonaceous shales from the meishucun and zhajin sections of south china respectively black shales in the meishucun section have total organic carbon toc contents from 1 6 to 3 9 wt and hi hydrogen index values from 3 8 to 20 mg hc g toc whereas black shales in the zhajin section have much higher toc 7 1 15 6 wt but lower hi

preliminary study on the feasibility of co exploitation of coal and uranium abstract both coal and uranium resources are found in the dongsheng area which is located in the northern part of ordos basin china with the coal seam below the uranium deposit in this paper we attempt to study the feasibility of co exploitation of the coal seam and the uranium deposit the permeability evolution in strata around the coal seam are selected as the key parameter indexing the separate and safe concurrent recovery of two deposits and a novel strain dependent permeability model is proposed covering the full deformation range of rock the proposed model is first verified with experimental data with good fitting of the results then an upscaled numerical model is established considering the geology conditions of dongsheng area this is implemented using comsol multiphysics and the interface of comsol with matlab is used to study the damage to the rock mass we show that a compared with the stress dependent permeability model the strain dependent permeability model proposed in this work has the advantage that each strain value is associated with a unique permeability value b the feasibility of co exploitation of the coal seam and the uranium deposit depends on the relative distance between two resources when the caved and fractured zone encroaches on the uranium deposit the coal seam should be abandoned conversely when the uranium deposit lays in the constrained zone the recovery of the coal seam would benefit recovery of the uranium deposit c the feasibility of the co recovery of the two resources can be optimized by the choice of mining approach the top caving mining approach and room and pillar mining approach can reduce the height of the caved and fractured zones and make the co exploitation of the uranium and coal feasible this work provides a new approach to investigate the feasibility of co exploitation of uranium and coal

morphology of witwatersrand gold grains from the basal reef evidence for their detrital origin thousands of rounded particles of fine grained gold released from a crossbedded gold specimen of the basal reef placer in the welkom gold field after acid digestion of the host quartz arenite have revealed morphological features and abrasion textures that are characteristic of detrital gold the size range which is between 0 038 and 0 473 mm has a lognormal distribution with a mean of 2 88 phi units 0 136 mm and a standard deviation of 0 48 this is a characteristic of well sorted sediment the shapes are predominantly disclike with toroidal forms being most common a corey shape factor of 0 08 indicates extreme flattening the preponderance of these shapes is interpreted to be the result of selective sorting by entrainment of particular shapes during extensive transport a knobby surface texture similar to placer grains recovered from both recent and devonian placers and produced during laboratory controlled tumbling with sand and cobbles in water is considered distinctive of sediment abrasion secondary gold comprising 25 percent of the total gold content is finer grained has an interstitial jagged form and displays unabraded smooth to crystalline surfaces study of this remarkable specimen has produced unequivocal evidence of the detrital origin of gold in the extensive basal reef placer and led to research concerning its metamorphic overprints

relationship between detrital zircon age spectra and the tectonic evolution of the late archaean witwatersrand basin south africa abstract shrimp u pb detrital zircon age spectra for 14 samples from the west rand and central rand groups of the witwatersrand basin indicate that felsic source rocks mostly formed at 3090 3060 and 3000 2870 ma with a smaller proportion formed prior to 3100 ma provenance evaluation indicates that source rocks have largely vanished through erosion such that greenstone terrains extending from the amalia kraaipan belt in the southwest to the murchison belt in the northeast are models of but not the actual source areas analysis of detrital zircon age modes reveals that the west rand and central rand groups record different basins the west rand group is characterised by age subpopulations with a much smaller range and less complex distribution than those in the central rand group furthermore detrital zircon age spectra for the west rand group generally decrease in complexity up section whereas they become increasingly more complex in the central rand group it is concluded that the source area for the west rand group is consistent with a passive margin setting with the decrease in complexity up section of zircon age spectra being the consequence of increasing maturity of the hinterland conversely the source area of the central rand group was far more dynamic with an increasing age range of source rocks being exposed through time pulsed tectonic rejuvenation of the source area is implied contemporaneous emplacement uplift and erosion of granitoids supports a magmatic fold thrust belt as the source and a complementary retroarc basin setting detrital xenotime grains record the ages of high u granitoids emplaced in the fold thrust belt during deposition of the central rand group and are much closer to depositional ages than are detrital zircon grains change from a passive margin to a retroarc basin across the west rand central rand boundary is emphasised by change from simple to increasingly complex detrital zircon age spectra this study establishes that detrital zircon geochronology can overcome the problem of overly quartzose compositions in archaean sandstones due to severe chemical weathering and authigenic alteration thereby enabling distinction between passive margin and retroarc basin stages through systematic changes in the age complexity of the source area

metal distribution in pyrobitumen of the carbon leader reef witwatersrand supergroup south africa evidence for liquid hydrocarbon ore fluids abstract high grade gold and uranium mineralization in the witwatersrand basin is intimately associated with pyrobitumen implying that hydrocarbons may have played a role in the genesis of these ores the nature of the pyrobitumen in the carbon leader reef was therefore investigated to determine if hydrocarbons were essential to the ore forming process the relative proportions of trace elements in pyrobitumen seams and nodules are in large part similar to those of organic rich shales located within the sedimentary succession this indicates a strong genetic relationship between the pyrobitumen and the shales a network of veins and veinlets filled with pyrobitumen and the occurrence of oil inclusions in detrital and authigenic quartz grains provide compelling evidence that the pyrobitumen was derived from a mobile liquid hydrocarbon precursor that circulated in the carbon leader reef uranium au sb pb ag te th bi se and w are enriched relative to their concentrations in the shales this is particularly the case for u and au the pervasive and relatively homogeneous distribution of the uranium is consistent with the presence of ubiquitous submicroscopic uraninite in the pyrobitumen documented in an earlier study in contrast the distribution of the gold is heterogeneous indicating the presence of irregularly distributed gold micrograins these grains are concentrated mainly in the interstices between pyrobitumen nodules secondary minerals such as brannerite monazite ce and galena are also concentrated in these interstices on the basis of this study we propose that intrabasinal shale units of the witwatersrand supergroup were the source for the pyrobitumen in the carbon leader reef these shales produced and released liquid hydrocarbons during the burial of the sedimentary succession phyllosilicates enriched in trace metals were transferred from the shales into the newly produced liquid hydrocarbons and were transported stratigraphically upward by the latter into the carbon leader reef during migration the liquid hydrocarbons dissolved detrital uraninite present in the basin adding to the uranium budget the liquid hydrocarbons were converted into pyrobitumen in response to further burial and precipitated uraninite nanocrystals post depositional hydrothermal fluids interacted with the hydrocarbons and deposited gold by reduction on hydrocarbon surfaces the interaction of these fluids with the hydrocarbons may have released u th ree pb and ti from the hydrocarbons and triggered the formation of secondary brannerite monazite ce and galena the results of this study provide convincing evidence that the hydrocarbon liquids that formed the pyrobitumen seams in the carbon leader reef played an essential role in the remobilization and redeposition of uranium and gold respectively in the witwatersrand supergroup

the source of uranium within hydrothermal uranium deposits of the motianling mining district guangxi south china abstract uranium deposits are diverse as a result of their formation in a wide variety of geological environments however the source of the uranium within these deposits is difficult to identify and as a result it is usually poorly understood this study focuses on the hydrothermal sanqiliu and sanqisi uranium deposits both of which formed within ne sw striking shear zones that cross cut the sanfang batholith and low grade metasedimentary rocks of the motianling district southern china the deposits contain vein hosted pitchblende quartz pyrite chlorite mica orebodies fluid inclusions within quartz in the orebodies in the district homogenize at temperatures between 205 c and 222 c indicating the deposit formed as a result of low to intermediate temperature hydrothermal activity pitchblende associated hydrothermal pyrite within the sanqiliu and sanqisi deposits has 34s values from 24 7 to 19 7 and from 6 0 to 13 6 respectively quartz separates from the sanqiliu deposit yield 18o values of 1 4 11 5 mean of 5 8 for syn ore hydrothermal fluids these stable isotope data indicate that the fluids that formed these deposits were derived from the sanfang granites sediments of the sibao group and meteoric sources in addition uraninite from the host sanfang granite yields u pb ages of ca 732 773 ma combining these data with the geology of the ore deposits in this region suggests that these deposits were generated from deeply circulating meteoric water and the uraninite within the highly fractionated sanfang granite is the source of the uranium within the sanqiliu and sanqisi uranium deposits

the growth and concentration of uranium and titanium minerals in hydrocarbons of the carbon leader reef witwatersrand supergroup south africa abstract uranium and gold bearing pyrobitumen from the carbon leader reef in the witwatersrand basin south africa was investigated by high resolution transmission electron microscopy this study provides evidence for the in situ growth of uraninite and anatase nanocrystals in the pyrobitumen implying mobilization and concentration of uranium and titanium by formerly mobile liquid hydrocarbons individual nanocrystals of uraninite and anatase are pervasively distributed and locally isolated within the pyrobitumen matrix crystallization of uraninite and anatase led to the formation of complex nanocrystal aggregates by oriented attachment in which anatase generally provided nuclei for the growth of uraninite single nanocrystals of curite occur locally in channel ways within masses of uraninite nanocrystals consistent with later auto oxidation of uraninite and limited release of water during hydrocarbon maturation on the basis of evidence for the migration of liquid hydrocarbons in the witwatersrand basin and the presence of abundant uraninite and anatase nanoparticles in pyrobitumen a new model is proposed for the transport and concentration of uranium and titanium in the carbon leader reef according to this model liquid hydrocarbons that were circulating in the witwatersrand basin dissolved detrital u ti bearing minerals and transported the uranium and titanium until thermal degradation immobilized the hydrocarbons by solidifying them as pyrobitumen the latter process involved the release of volatiles and the destruction of bonds that may have held the uranium and titanium in solution thereby inducing the growth of individual uraninite and anatase nanocrystals and the formation of complex nanocrystal aggregates within the pyrobitumen

ree systematics in hydrothermal fluorite abstract ree patterns of fluorite from 63 post variscan hydrothermal veins of the schwarzwald area germany can be divided into two major groups type a fluorite shows roof shaped paas normalized patterns with enriched mree the turning point of the curvature is at ho or er position all patterns of type a show a distinct positive eu anomaly type b fluorite shows roof shaped patterns with enriched mree and strongly depleted hree and a characteristic steep slope between nd and sm the turning point of the curvature is at gd to dy all patterns of type b show negative or no eu anomalies laser ablation icp ms traverses through single grains combined with cathodoluminescence imagery revealed either i identical ree patterns and total ree concentrations from core to rim ii identical ree patterns but concentration gradients or iii variable ree patterns and concentration gradients from core to rim these features are explained by different degrees of supersaturation or different fluid fluorite ratios during crystallization and by complexly controlled precipitation processes under closed system conditions petrographically late fluorites from several deposits show the characteristics of new fluid batches rather than the expected remobilization features lree enrichment close to the crystal faces in some grains may result from the copreciptiation of a submicrometer sized lree enriched phase or from lree clustering in late cool fluids by comparison with literature data on natural waters from gneissic and granitic aquifers and of leachates of granites and gneisses we show that the hydrothermal vein fluorite preserves the characteristic source related ree feature of the hydrothermal fluid that migrated through either gneissic type a or granitic type b host rocks the immediate host rocks of the veins however are not the source rocks of the ree which indicates large scale fluid convection in the basement gneiss related type a fluorite shows tb ca tb la trends of primary hydrothermal crystallization whereas granite related type b fluorite indicates remobilization of possibly pegmatitic or variscan fluorite

mobilization and agglomeration of uraninite nanoparticles a nano mineralogical study of samples from the matoush uranium ore deposit the occurrence of uraninite nanoparticles in the alteration zones of uranium ore deposits suggests potential mobilization of u iv under reducing conditions which is important for understanding the mobility of uranium in contaminated sites and potential repositories for nuclear waste this study investigates the occurrence of uraninite nanoparticles in the outer alteration zone of the matoush uranium ore deposit quebec canada selected samples with finely disseminated uraninite from the outer alteration zone of the deposit are examined by x ray fluorescence spectroscopy scanning electron microscopy and high resolution transmission electron microscopy on specimens prepared using the focused ion beam milling technique uraninite nanoparticles occur as single particles in clusters and in larger aggregates in close association with the cr rich phases chromceladonite cr rich mica ideally kmgcr 3 si 4 o 10 oh 2 eskolaite ideally cr 2 3 o 3 bracewellite cr 3 ooh and an amorphous cr rich oxide matrix as well as with fluorapatite and galena nanoparticles on the surface and in the outer rim of single uraninite crystals indicate the growth of larger uraninite crystals via crystallization through particle attachment and oswald ripening the flow texture of the uraninite nanoparticles in the amorphous cr rich oxide matrix their aggregation on the surface of nanocrystals of bracewellite the absence of products of a redox reaction involving u vi and fe ii and the occurrence of amorphous fe depleted alteration layers between uraninite and eskolaite and uraninite and cr rich mica indicate that the uraninite nanoparticles have been mobilized under reducing conditions leaching of fe 2 from the alteration layer at low t amorphous character of the alteration layer after the main mineralization event from the center of the mineralization to the outer parts of the matoush dike complex these results indicate that fluids can mobilize u iv under reducing conditions in the form of uraninite nanoparticles albeit over limited distances the potential mobilization of these nanoparticles may also explain the occurrence of proximal mineralized zones in u ore deposits that lack common products resulting from the reduction of u vi by fe 2 e g hematite and other fe 3 phases

nature and origin of carbon in the archaean witwatersrand basin south africa the nature and origin of the carbonaceous matter carbon in the gold bearing reefs of the archaean witwatersrand basin of south africa has long been a subject of controversy and debate the importance of the carbon results from its direct association with the gold grade the studies reported here were directed at resolving the nature and origin of carbon techniques used include stope scale macroscopic mapping mesoscopic hand specimen examination and microscopic studies incorporating the use of optical reflectance measurement macroscopic mapping has demonstrated the braided habit of carbon bodies over tens of square metres with a close parallel to sedimentology mesoscopic observations however show the vein like carbon seams are often cross cutting sedimentary features with the carbon occupying an anastomosing set of bed parallel fractures microscopic observations show a globular form for the carbon and inclusions of uraninite particles in seam carbon the globules are generally modified into elongated spindles oriented perpendicular to bedding optical properties are dominated by generally high reflectance and anisotropy with a swirling liquid crystal structure classifying seam carbon as carbonaceous mesophase it is this fine mesophase texture that has previously been wrongly attributed to plant algal morphology highly significantly the optical anisotropy is bed perpendicular rather than bed parallel as in normal sedimentary burial indicating mesophase formation during fracture opening both reflectance and bireflectance of the seam mesophase show a range of values at all scales no stratigraphic or depth trends were apparent though geographic variation points to localization of the maximum temperature event s given high anisotropies maximum reflectance values in the 4 8 r o range and minima in the 1 2 r o range give arithmetic mean reflectance values of about 4 0 r o kinetic modelling equates these values with short term 50 000 years temperature events of c 400 c or burial temperatures of c 280 c lower reflectance values of c 2 0 r o obtained from the shales suggests thermal detachment of permeable and impermeable beds a characteristic of pulsed hydrothermal flux the included uraninite grains influence the orientation of the surrounding anisotropic mesophase demonstrating that uraninite predated the mesophase formation event regional palaeo stress frozen into the mesophase anisotropy indicates a nw se deviatoric stress the combination of hydrocarbon radiation and hydrothermal fluid flow marks witwatersrand basin pyrobitumens out as being different from conventional oil putative source rocks for the oil are identified in the intra basinal witwatersrand shale units lithological control in carbon seams is explained by the poro perm and mechanical properties of the unconformity sequence of footwall reef conglomerates and hanging wall quartzites favouring fracture along the unconformity surfaces an overpressured oxidizing fluid created the fracture network that hosted the oil and also introduced uranium as uranyl ion on meeting a reducing agent oil uraninite precipitated stabilizing the oil by polymerization further hotter hydrothermal flux then coked the bitumen to often fibrous spindle shaped mesophase continued flow deposited gold in the available pore spaces most notably those formed by lateral contraction between mesophase spindles the speculative role of methane in the reductive precipitation of gold is indicated by the presence of gold in any co eval porosity largely independent of the mineral matrix

mineralogical characterization and origin of uranium mineralization in witwatersrand like metaconglomerate of the moeda formation quadrilatero ferrifero brazil abstract the moeda formation is the basal unit of the minas supergroup in the quadrilatero ferrifero brazil and has quartz pebble metaconglomerate that hosts au u mineralization commonly assumed to be detrital in origin the au u mineralization occurs immediately above an unconformity with the underlying archean rio das velhas greenstone sequence in this work we focus on the moeda metaconglomerate in its u bearing portions in the gandarela syncline the southern sector near the syncline axis and the western limb near the palmital gold deposit the metaconglomerate has mica seams that host zircon xenotime rutile nodules of organic matter and sulfide minerals the sulfide assemblage includes four generations of pyrite along with fe ni cu co zn pb mo sulfides a sb as sulfosalt assemblage of gersdorffite stibnite and ullmannite is late in relation to pyrite and other sulfides gold is argentiferous with minor hg uranium minerals include uraninite coffinite brannerite and uranyl arsenates an early generation of uraninite and brannerite occurs as inclusions in organic matter nodules mainly in the southern sector a late generation of uraninite formed due to a low temperature hydrothermal overprint coffinite and late stage brannerite are products of hydrothermal alteration of zircon and rutile respectively uranyl arsenates have ni as the prevalent cation they formed as replacement of arsenic minerals such as gersdorffite by oxidized fluids containing u microstructural data and mineral chemistry favor a hydrothermal hypothesis analogous to an unconformity related setting rather than a detrital placer deposit model for the occurrence of u in the moeda metaconglomerate

the origin of the gold and uranium ores of the black reef formation transvaal supergroup south africa abstract the black reef formation is a laterally extensive sedimentary succession at the base of the transvaal supergroup the quartz pebble conglomerates host erratic concentrations of gold and uranium however in areas that are located spatially above the gold and uranium bearing reefs of the witwatersrand supergroup the concentrations can reach ore grade although the depositional environment was similar to that of the witwatersrand supergroup the processes that lead to the high gold and uranium concentrations in the black reef were quite different the black reef experienced intense post depositional hydrothermal alteration by circulating aqueous and hydrocarbon fluids oils that deposited large volumes of native gold uranium minerals and pyrobitumen the gold which is filamentous is concentrated along as ni rich surfaces of pyrite and with uraninite in pyrobitumen in both environments the gold is interpreted to be the product of chemically triggered precipitation from hydrothermal fluid s the uraninite occurs either as precipitates in pyrobitumen or is invisible in the pyrite occurring as nanoparticles in this mineral this indicates that conditions were sufficiently oxidizing for the hydrothermal transport of uranium and contrasts with the case for the witwatersrand reefs where much of the uranium is detrital luminescent radiation damage associated with vein quartz and pyrobitumen as well as the diffuse distribution pattern of uranium in the pyrobitumen may indicate that some uranium was transported by liquid hydrocarbons pyrite in the black reef sedimentary detrital and hydrothermal pyrite is highly enriched in gold uranium and other redox sensitive trace elements provenance analyses using the trace element compositions of the pyrite show that it was not the result of erosional reworking of the underlying witwatersrand reefs however the close spatial association of high gold and uranium concentrations in the black reef with ore bearing witwatersrand reefs suggests strongly that gold and uranium whether in pyrite or occurring as native gold and uraninite were hydrothermally recycled uranium may have been recycled by hydrocarbon fluids from the witwatersrand reefs

two dimensional geomorphological characterization of a filled abandoned meander using geophysical methods and soil sampling abstract using geophysical methods for the geomorphological characterization of subsurface features has numerous advantages over traditional exploration methods because of their noninvasive and rapid nature in this study we compared the results of four geophysical methods with each other we also discuss their possibilities and limitations in a geomorphological investigation electrical resistivity tomography ert refraction seismic rs ground penetrating radar gpr and multichannel analysis of surface waves masw methods were applied at an abandoned meander in northern saxony to map a predefined structure by combining these methods we were able to characterize and delineate subsurface features of the abandoned meander including a point bar a channel and a cutbank core samples obtained from sonic drilling were used to validate the findings of both seismic methods however we found that electrical resistivity tomography and ground penetrating radar lacked penetration depth and could only be used to resolve shallower subsurface layers the ert gpr rs and masw can be used to gather images of subsurface structures the masw in particular provides supplementary information about the channel s internal structure with respect to lateral and vertical resolution besides fluvial morphological features we also detected inverse velocity structures within the channel this allowed us to characterize the abandoned meander using information about its layer distribution and material composition however we were only able to characterize and delineate the subsurface features of the abandoned meander by combining all of the aforementioned methods

organic maturation in the french subalpine chains regional differences in burial history and the size of tectonic loads the french subalpine chains of southeastern france are the foreland fold thrust belt of the western alps formed in the mid to late tertiary as a result of the continental collision between the european and italian north african plates with the change from passive margin to destructive margin certain areas of the subalpine chains experienced enhanced temperatures through being buried to greater depths burial of these areas has been investigated using vitrinite reflectance r o levels of organic maturity of mesozoic and tertiary horizons have been established using vitrinite reflectance r o and spore fluorescence in the southwestern part of the chain values of r o for mesozoic units from the vercors and chartreuse massifs are generally low with all cretaceous units having values r o older jurassic horizons have higher values up to 1 25 for the mid jurassic oxfordian when compared to values from the same horizons and from younger tertiary units published data from the northeastern part of the chain it is clear that this part of the belt has encountered higher temperatures produced by greater depth of burial in the haut giffre and aravis massifs mesozoic units have r o values as high as 2 7 and in terms of hydrocarbon generation can be considered mature or overmature two causes of greater depth of burial of the northeastern part of the belt are indicated by field studies and by burial history modelling of specific localities of the subalpine chains first the earlier initiation of the tertiary foredeep in the northeast compared to the southwest and second differences in the size of tectonic loads emplaced onto the subalpine chains during the final stages of alpine compression with the greater structural deformation of the subalpine chains occurring in the northeast

rare earth elements and hydrothermal ore formation processes abstract the geochemical behaviour of ree is influenced by nearly all important hydrothermal ore formation processes including fluid rock interactions fluid precipitations adsorption and scavenging onto particles and changes in fluid temperature pressure ph eh alkalinity and ligand concentration destabilization of ree complexes in response to these physicochemical changes and possible chemical crystallographic controls determine the concentration and distribution of ree within hydrothermal minerals mineraloids and amorphous phases alteration assemblages of intrusive related mineralisations may exhibit a wide range of ree distributions and ree fractionation trends the ree distribution within these hydrothermally altered lithologies will depend on the ree concentration in the rock and the fluid the partitioning behaviour of the ree between the rock phases and the fluid and the types of alteration reactions which take place reactive rocks such as carbonate rich lithologies of skarn deposits may gain or loose significant amounts of ree during fluid rock interactions ree geochemical investigations combined with fluid inclusion and stable isotope studies may point to the origin of alteration products and the source s of ore fluids ancient massive sulphide ores commonly exhibit anomalous eu concentrations similar to many recent submarine hydrothermal precipitates the recognition of hydrothermal fluid seawater sedimentary or volcanically derived ree distributions within ores chemical sediments and hydrothermally altered lithologies may help to constrain genetic modelling of massive sulphide deposits care should be taken with the interpretation of ree distributions from metamorphosed hydrothermal ore deposits becase metamorphic and diagenetic alteration reactions may change the ree distributions mobility of ree may occur during diagenesis of carbonate rich rocks and during the development of shear zones and migmatites in contrast very large fluid rock ratios are necessary to cause significant changes in ree patterns of silicate rich rocks during diagenesis and regional metamorphism

rare earth element distributions in uraninites implications for ore genesis abstract analysis of the rare earth element ree distributions in uraninites from a variety of hydrothermal mineral deposits indicates that wide variations are to be anticipated although crystal structure must exert a fundamental influence upon ree substitution in uraninite the present study suggests that other factors in particular hydrothermal fluid chemistry may be of equal importance total ree ree contents range from 15 000 ppm in uraninites from ultrametamorphic deposits to eu eu lree hree 0 08 1 10 they are interpreted to result from variations in the oxygen fugacity and the nature of the anionic complexes in the hydrothermal fluids responsible for ore transport additionally in uraniferous quartz pebble conglomerates the ree patterns of the detrital uraninites provide direct evidence regarding the provenance of these sedimentary u ores

cenozoic oxidation episodes in west africa at the origin of the in situ supergene mineral redistribution of the primary uranium orebodies imouraren deposit tim mersoi basin northern niger uranium u deposits can undergo oxidizing events subsequent to which the u may be redistributed or precipitated under distinct mineralogical forms occurrences of u6 minerals can be the result of either i in situ oxidation and alteration of previous u4 minerals or ii direct precipitation from u6 rich solutions samples from imouraren the largest u6 ore deposit known in the world located in the tim mersoi basin northern niger have been studied to determine the nature distribution and timing of occurrences of u and related minerals the host rock is composed of sandstones and analcime rich siliciclastic rocks of jurassic age the u ore is largely dominated by acicular hexavalent u minerals and by a very small amount of uraninite a comprehensive geochemical model that describes the origin and geochemical setting of this style of economically important mineralization has been developed the petrographic and mineralogical studies show evidence of in situ uraninite alteration into uranophane and metatyuyamunite documented by textural relationships and chemical analyses using sem and electron microprobe the textural relationship between the u4 and u6 minerals is supported by the near identical ree signatures of the primary uraninite and related secondary u minerals ion microprobe u pb dating from 21 to 1 ma confirms that primary uraninites were altered to u6 minerals under supergene conditions during cenozoic oxidation events in western africa in relation with the well known stages of intense continental weathering that have affected western africa from the early cenozoic to recent times

detrital origin of hydrothermal witwatersrand gold a review the witwatersrand basin is the largest known gold province in the world the gold deposits have been worked for moren than 100 years but there is still controversy about the ore forming process detailed petrographic studies often reveal that the gold is late in the paragenetic sequence which has led many researchers to propose a hydrothermal origin for the gold however observations such as the occurrence of rounded disc like gold particles next to irregularly shaped or idiomorphic secondary gold particles in the same sample suggest an initial detrital gold source within the witwatersrand strata mineral chemical and isotopic data together with sem cathodoluminescence imaging and fluid inclusion studies provide evidence for small scale variations in the fluid chemistry a requirement for the short range mobilization of the gold the existing data and observations on the witwatersrand rocks support a model of hydrothermally altered metamorphosed placer deposits with at least two subsequent gold mobilization events hydrothermal infiltration in early transvaal time 2 6 2 5 ga and during the 2 020 ga vredefort impact event

o and pb isotopic analyses of uranium minerals by ion microprobe and u pb ages from the cigar lake deposit we apply a rapid and accurate in situ technique to make u pb isotopic measurements of complexly intergrown uranium minerals and oxygen isotopic analyes of uraninite from the unconformity type cigar lake uranium deposit secondary uranium minerals intergrown with uraninite such as coffinite usio4 nh2o and calciouranoite cau2o7 5h2o were identified by highresolution transmission electron microscopy hrtem in situ u pb results from three stages of uraninite and coffinite define well correlated arrays on concordia with upper intercepts of 1461f47 1176f9 and 876f14 ma f1r these ages are interpreted as the minimum ages of mineralization correlate with the timing of clay mineral alteration f1477 ma associated with these unconformity type uranium deposits the ages of magnetization events at 1600 1450 and 900 ma from the athabasca basin and the grenvillian orogeny at f1100 ma in situ u pb isotopic analyses of uraninite and coffinite can document the pb u heterogeneities that occur on the scale of 15 30 am thus providing relatively accurate information regarding the timing of fluid interactions associated with the evolution of these deposits the high spatial resolution and precision of the ion microprobe allow us to measure d 18 o values of 20 100 am unaltered portions of uraninites from cigar lake the range of d 18 o values 33 9 to 20 4x are among the lowest reported for unconformity type deposits confirming that conventional fluorination analyses of material sampled at the mm scale are insufficient to avoid contamination from isotopically heavier coffinite and calciouranoite d 2002 elsevier science b v all rights reserved

coalification shale diagenesis and thermal modelling in the alpine foreland basin the western molasse basin switzerland france abstract the analysis of coalification and shale diagenesis in oligocene and lower miocene sediments in the western part of the molasse basin western switzerland and haute savoie france shows a close relationship between the very low temperature metamorphism in the foreland and the tectonic history in the orogenic belt the degree of thermal maturation generally increases towards the alpine front isomaturity lines however run slightly oblique to today s alpine front this is probably due to the tectonic burying under the alpine nappes in early miocene time second order variations of the coalification pattern are explained as resulting from a regional discharge of warm fluids controlled by tectonic structures

chemical evidence of kerogen formation in source rocks and oil shales via selective preservation of thin resistant outer walls of microalgae origin of ultralaminae abstract new structures termed ultralaminae were recently observed by transmission electron microscopy usually in high amounts in a number of kerogens from oil shales and source rocks morphological similarities were noted between ultralaminae and the thin ca 15 nm resistant outer walls composed of non hydrolyzable macromolecules algaenans commonly occurring in extant chlorophyceae especially in the cosmopolitan genus scenedesmus identification of the pyrolysis products of s quadricauda algaenan showed i a highly aliphatic structure based on a macromolecular network of long up to c32 polymethylenic chains probably cross linked by ether bridges and ii a close correlation based on the formation of n alkylnitriles between this algaenan and two ultralaminar kerogens the rundle oil shale mainly composed of ultralamina accumulations and the green river shale ultralaminae dispersed within an amorphous matrix these fossil ultralaminae therefore likely originated from the selective preservation of the thin algaenan containing outer walls of scenedesmus and or of other chlorophyceae containing outer walls of a similar morphology and composition relative distributions of n alkylnitriles and of n alkanoic acids in the pyrolysates of s quadricauda algaenan and of the rundle oil shale indicated that nitriles are not derived from secondary reactions of carboxylic acids but originate from preexisting nitrogen functions likely amides previous evidence of kerogen formation via selective preservation of algaenans was restricted to rather uncommon kerogens the present results added to ultralamina common occurrence and abundance point to a wide involvement and to a large contribution of the selective preservation of algaenan containing thin outer walls of chlorophyceae in the formation of kerogens in a number of lacustrine source rocks and oil shales all the available information suggest that the three way correlation selective preservation of algaenans from thin resistant chlorophycean outer walls formation of fossil ultralaminae presence of n alkylnitriles with a typical distribution in the pyrolysates of ultralaminar kerogens observed in this study might be of a general character

geochemistry and chemical dating of uraninite in the samarkiya area central rajasthan northwestern india implication for geochemical and temporal evolution of uranium mineralization abstract in the samarkiya area located at the central part of the aravalli delhi fold belt adfb uranium mineralization is hosted both by the basement mangalwar complex and the overlying supracrustal rocks of the pur banera belt the present study aims to appraise the geochemical and temporal evolution of uranium mineralization from the basement and the adjoining supracrustals in the samarkiya area integrating textural features geochemistry and in situ u th pb total dating of uraninite uraninite occurs as inclusions in the major rock forming minerals viz plagioclase quartz biotite and chlorite based on the shape location in the host mineral well inside at the grain boundary along or connected to micro cracks etc and association with other secondary uranium minerals uraninites are classified into different groups which are compositionally distinct barring some exceptions integrating texture geochemistry and in situ electron probe dating we propose that in addition to an old event at 1 88 ga in the basement rocks there are two major events of uraninite formation at 1 24 1 20 ga and 1 01 0 96 ga in both the basement and supracrustal rocks although none of the pristine unaltered uraninites that formed during the above mentioned events contain significant intrinsic minor or rare earth elements the basement uraninites are consistently much enriched in thorium compared to those from the supracrustal based on the compositions we propose that the basement uraninites formed from a high temperature magmatic metamorphic fluid whereas those in the supracrustal rocks crystallized from a low temperature presumably oxidized fluid back scattered electron images x ray elemental mapping of selected elements and epma spot analysis of large uraninite grains both from the basement and the supracrustals collectively demonstrate that subsequent to the major mineralizing event at 1 24 1 20 ga the mineralized rocks were subjected to fluid mediated alteration which resulted in ree y and si ca enrichment of existing 1 24 1 20 ga uraninites in the basement and supracrustal rocks respectively we cannot constrain the exact timing of this alteration event however as this event altered the 1 24 1 20 ga uraninites and as spot ages of the altered grains yield ages largely between 1 24 and 0 96 ga it is reasonable to place this event between the second and third stages of uranium mineralization mobilization at 1 20 ga and 1 01 ga respectively the last event that took place at 1 01 0 96 ga most likely represent an episode of recrystallization alteration of existing uraninite leading to complete pb loss and resetting of the isotopic clock however we do not entirely reject the possibility of neo mineralization the discrete events deciphered from uraninite in the samarkiya area can also be broadly linked to some major magmatic metamorphic events identified from other independent studies in the adfb for example the earliest 1 88 ga event displayed by basement uraninite is most likely related to a pervasive magmatic metamorphic event 1 86 1 82 ga that affected the basement whereas the last latest event 1 01 0 96 ga can be linked to a pervasive metamorphic event that affected perhaps the entire adfb this last episode can also be linked to the tectono thermal event related to the rodinian amalgamation the 1 24 1 20 ga event appears to be somewhat enigmatic in the context of well known geological events in the area however based on some very recently published data we interpret this to be a post peak metamorphic 1 37 1 35 ga hydrothermal event or even a new metamorphic event hitherto unknown

zircon ion microprobe studies bearing on the age and evolution of the witwatersrand triad abstract the ventersdorp and witwatersrand supergroups and the dominion group collectively referred to as the witwatersrand triad represent some of the oldest and economically most important volcano sedimentary basins within the kaapvaal craton of southern africa precise age constraints which are vital to models aimed at understanding the formation mineralisation and evolution of these basins have been hampered by analytical and geological problems these problems have been overcome by this ion microprobe study on zircons from volcanic rocks within the three basins felsic and mafic volcanics from the ventersdorp supergroup yield ages of 2709 4 ma and 2714 8 ma respectively constraining the timing of the closure of the witwatersrand basin a maximum age for the witwatersrand basin is indicated by the age of 3074 6 ma for volcanics from the underlying dominion group thus a period of c 350 ma was available for the accumulation of the full witwatersrand basin succession unfortunately dating within the witwatersrand basin itself is not complete and future work could show that extended time breaks may exist within the basin these new data show that previous age determinations on the ventersdorp witwatersrand and dominion basins were inaccurate and that the economically important witwatersrand basin must now be recognised as archaean

gold and uranium concentration by interaction of immiscible fluids hydrothermal and hydrocarbon in the carbon leader reef witwatersrand supergroup south africa highlights aggregates of uraninite nanocrystals host inclusions of native gold oil droplets triggered precipitation of gold precipitated from hydrothermal fluids hydrocarbon inclusions in native gold contain in situ grown uraninite nanocrystals water oil emulsions were responsible for the in situ growth of gold and uraninite lanarkite formed in local oxidation zones on galena uraninite interfaces high resolution scanning and transmission electron microscopy of pyrobitumen hosted uraninite reveal that uraninite grains are highly porous aggregates of uniformly sized nanocrystals and that many of their pores are filled by native gold these texturally late gold grains in turn contain small pores occupied by former oil droplets that were converted to pyrobitumen during burial and metamorphism the pyrobitumen in the pores of the gold grains contains in situ formed uraninite nanocrystals galena also occupies the pores of the uraninite aggregates in addition this study reveals the first occurrence of rare lanarkite that engulfs the galena in the pores of the uraninite on the basis of the nature of the uraninite and the filling of some of its pores with native gold we propose a mineralization model for the deposition of the uranium and gold in the carbon leader reef that calls upon the interaction of oil and aqueous hydrothermal fluids to form micro emulsions according to this model uraninite nanocrystals precipitated from uranium bearing hydrocarbon liquids and flocculated to form porous uraninite aggregates these liquids interacted with auriferous hydrothermal fluids in the carbon leader reef leading to the formation of a micro emulsion at the interface between the two fluids gold precipitated as native metal around droplets of the oil owing to a reduction in oxygen fugacity which destabilized the bisulfide species responsible for gold dissolution commonly this process went hand in hand with the flocculation of the uraninite nanocrystals causing entrapment of the native gold in the pores of the uraninite aggregates the hydrocarbon liquid which occurs as droplets in the gold and is the host to the uraninite aggregates was transformed to pyrobitumen as a result of this process a thin pyrobitumen seam containing uraninite nanocrystals formed along the inner walls of the pores in the native gold lead introduced by the hydrocarbon liquid precipitated as galena interaction of the uraninite with hydrothermal fluids or radiolysis of the pore water facilitated the development of local zones of oxidation between galena and uraninite which led to the crystallization of rare lanarkite

geochemistry of archean shales from the witwatersrand supergroup south africa source area weathering and provenance with a few exceptions shales from the archean witwatersrand supergroup 2800 ma in south africa are depleted in na ca lile ree and hfse compared to phanerozoic shales cr co and ni are enriched in all witwatersrand shales and fe and mg are high in shales from the west rand groups wrg and lower central rand group crg shales from the crg and uppermost wrg are enriched in na al lile ree hfse and transition metals relative to shales from the lower wrg chondrite normalized ree patterns for all witwatersrand shales are enriched in light ree and exhibit small to moderate negative eu anomalies a positive correlation of ree and al2o3 contents in the shales suggests that ree are contained principally in clay minerals relative to shales from the crg shales from the wrg exhibit depletions of na ca and sr a feature probably reflecting intense chemical weathering of their source rocks cia indices in witwatersrand shales are variable chiefly 70 98 even within the same shale unit such variations reflect chiefly variable climatic zones or rates of tectonic uplift in source areas with perhaps some contribution from provenance and element remobilization during metamorphism compared to present day upper continental crust all but the orange grove roodepoort and k8 shales appear to have been derived from continental sources depleted in lile ree and hfse and enriched in transition metals computer mixing models based on six relatively immobile elements th hf yb la sc co and four source rocks indicate that the relative proportions of granite basalt and komatiite increased with time in sediment source areas at the expense of tonalite the contributions of basalt and komatiite appear to reach a maximum during deposition of the booysens shale and granite during deposition of the k8 shales and possibly during deposition of the orange grove shales

geochemical evolution and timing of uranium mineralization in the khetri copper belt western india abstract the khetri copper belt kcb located in the northwestern part of the aravalli delhi fold belt western india is famous for cu mineralization and known for au ag co fe ree u p occurrences the present study conducted in and around the madan kudan kolihan chandmari cu deposits of the kcb integrates the mode of occurrence mineralogical association textural relation and chemistry of hydrothermal minerals and in situ chemical dating of uraninite we propose that the u mineralization represented by type 1 to type 6 uraninites has evolved through six successive stages u mineralization type 1 uraninite of uncertain origin u mineralization type 2 uraninite during fe mg alteration u mineralization type 3 uraninite during ca na alteration cu fe co ree u mineralization type 4 uraninite during na ca k alteration u mineralization type 5 uraninite during chloritization fe mg alteration cu co ree u mineralization type 6 uraninite during k fe mg alteration the chemical ages of uraninite suggest that the hydrothermal mineralization associated with type 2 to type 5 uraninites formed during a hitherto unknown older event compared to the previously reported age of the mineralization in the kcb i e 850 ma which initiated during the second phase of metamorphism of 1 40 1 30 ga m2 and terminated well before the third phase of metamorphism of 985 920 ma m3 the k fe mg alteration and the associated mineralization most likely is time equivalent of the known alteration mineralization event of 850 ga the chlorite and biotite thermometry in tandem with u th ratios of uraninite suggest that uraninites crystallized at high temperature 390 c in all the hydrothermal stages the common presence of magnetite and ilmenite the occasional presence of graphite and the fe3 fe3 fe2 ratios of the co genetic gangue minerals such as amphibole biotite and chlorite suggest reduced environment below the haematite magnetite buffer during the crystallization of uraninite in all the hydrothermal stages based on the composition of gangue minerals apatite amphibole biotite chlorite and scapolite in alteration assemblages veins and physicochemical characters of the fluids we discuss the possibility of transportation of u as u4 chloride and fluoride complexes the high temperature and reduced nature of the fluids high th contents and low u th ratios of most of the uraninites similar age of mineralization type 2 to type 5 uraninite and m2 metamorphism and the absence of concomitant magmatic activity collectively suggest that hydrothermal mineralization related to type 2 to type 5 uraninites took place from metamorphic fluids we report for the first time a unique uraninite graphite association in the kcb which can be best explained by their co precipitation from a hydrothermal fluid during the earliest fe mg alteration

the river harbour of ostia antica stratigraphy extent and harbour infrastructure from combined geophysical measurements and drillings abstract we performed a combined geophysical and geoarchaeological survey of the harbour of ancient ostia italy to investigate the extent of the former harbour basin the sedimentary infill and possible building remains around the harbour besides geoarchaeological results the paper highlights the advantage of combining vibracore drilling with different geophysical prospection methods which are sensitive to different physical soil parameters geophysical methods applied were electrical resistivity tomography ert ground penetrating radar gpr and seismics with shear and compressional waves the extent and shape of the harbour basin were determined by ert profiling the ert profiles were compiled into a 3d model showing that the early lagoonal harbour basin was at least 100 m 50 m wide its southern border was confirmed by gpr measurements clearly imaging the former land water transition and the onset of ancient onshore building construction at its eastern border a consolidated horizon could be mapped in 2 3 m depth by compressional wave tomography this horizon most likely represents a cemented ramp a small part of which had been excavated in a previous study the sedimentary fill of the former harbour basin was investigated by a combination of vibracoring ert and seismics the ert profiles serve for inter and extrapolating the vibracore stratigraphy from the coring locations over the whole harbour area it turned out that one sedimentary unit which is important for the harbour development could not be resolved by ert but clearly shows up in seismic velocity depth profiles instead it is a thin coarse grained high energy layer in 1 2 m depth which was caused by a tsunami according to a previous study this layer separates two harbour phases an older lagoonal harbour phase underneath and a younger fluvial harbour phase above it the high energy layer represents a thin band of 100 increased shear wave velocity compared to the more fine grained layers in which it is embedded this study is the first to show that tsunami type sedimentary layers may be mapped by shear wave profiling

uraniferous paleoplacers of the mesoarchean mahagiri quartzite singhbhum craton india depositional controls nature and source of 3 0 ga detrital uraninites abstract the quartz pebble conglomerate qpc hosted detrital uranium mineralization is unique in character in terms of their restricted distribution before 2 2 ga atmosphere during pre great oxidation event pre goe such qpc paleoplacer deposits over the world are good targets for moderate to high tonnage and low grade uranium deposits and more importantly for their gold content the mahagiri quartzite dated c 3 02 ga for their youngest detrital zircon population is developed unconformably over the mesoarchean singhbhum granite 3 44 ga to 3 1 ga the mahagiri quartzite includes a conglomerate pebbly sandstone dominated subaerial alluvial fan to coastal braided plain sequence in the lower parts and shallow marine mature quartz arenite in the upper parts the alluvial fan braided plain deposits in the lower parts host a number of pyritiferous and uraniferous conglomerate and pebbly sandstone beds the uraninite grains are rounded to subrounded in outline suggesting mechanical transport and detrital origin together with detrital pyrite and uraninite constitute the example of 3 0 ga paleoplacer closely comparable to the witwatersrand au u deposits epma and sem eds studies suggest that the uraninite grains are rich in th 4 wt s and ree y chemical formula calculations from epma analyses suggest uraninite grains belong to two populations with different oxidation states as revealed from y ree and cation u4 u6 apfu ratios the u contents of the detrital uraninite grains from mahagiri are significantly lower than that of the ideal stoichiometric composition of uo2 this is mainly due to higher amount of heterovalent cationic substitution by th ree y pb and ca in mahagiri qpc uraninite structures and partial alteration and metamictization of uraninites alteration due to metamictization resulted in elevated concentration of si al p and ca in more altered and metamict uraninite grains the ree pattern is typically flat with comparable lree hree concentration the high th content flat ree pattern suggests that the uraninitere presents high temperature phases 350 c and are magmatic in origin the mahagiri detrital uraninite grains suggest existence of highly felsic and k rich richer than ttg granodiorite granite monzogranite suites ggm of rocks older than 3 1 ga in the singhbhum craton

u redox fronts and kaolinisation in basement hosted unconformity related u ores of the athabasca basin canada late u remobilisation by meteoric fluids proterozoic basement hosted unconformity related uranium deposits of the athabasca basin saskatchewan canada were affected by significant uranium redistribution along oxidation reduction redox fronts related to cold and late meteoric fluid infiltration these redox fronts exhibit the same mineralogical and geochemical features as the well studied uranium roll front deposits in siliclastic rocks the primary hydrothermal uranium mineralisation 1 6 1 3 ga of basement hosted deposits is strongly reworked to new disseminated ores comprising three distinctly coloured zones a white green zone corresponding to the previous clay rich alteration halo contemporaneous with hydrothermal ores a uranium front corresponding to the uranium deposition zone of the redox front brownish zone rich in goethite and a hematite rich red zone marking the front progression the three zones directly reflect the mineralogical zonation related to uranium oxides pitchblende sulphides iron minerals hematite and goethite and alumino phosphate sulphate aps minerals the zoning can be explained by processes of dissolution precipitation along a redox interface and was produced by the infiltration of cold 50 c meteoric fluids to the hydrothermally altered areas u fe ca pb s ree v y w mo and se were the main mobile elements in this process and their distribution within the three zones was for most of them directly dependent on their redox potential the elements concentrated in the redox fronts were sourced by the alteration of previously crystallised hydrothermal minerals such as uranium oxides and light rare earth element lree rich aps the uranium oxides from the redox front are characterised by lree enriched patterns which differ from those of unconformity related ores and clearly demonstrate their distinct conditions of formation uranium redox front formation is thought to be linked to fluid circulation episodes initiated during the 400 300 ma period during uplift and erosion of the athabasca basin when it was near the equator and to have been still active during the last million years a major kaolinisation event was caused by changes in the fluid circulation regime reworking the primary uranium redox fronts and causing the redistribution of elements originally concentrated in the uranium enriched meteoric related redox fronts

basin internal derivation of hydrocarbons in the witwatersrand basin south africa evidence from bulk and molecular δ13c data abstract gold in the quartz pebble conglomerates of the late archean witwatersrand basin south africa is often intimately associated with carbonaceous matter of organic biogenic origin which occurs in the form of stratiform carbon seams and paragenetically late bitumen nodules both carbon forms are believed to be formed by solidification of migrating hydrocarbons this paper presents bulk and molecular chemical and stable carbon isotope data for the carbonaceous matter all of which are used to provide a clue to the source of the hydrocarbons these data are compared with those from intra basinal shales and overlying dolostone of the transvaal supergroup the 13c values of the extracts from the witwatersrand carbonaceous material show small differences up to 2 4 compared to the associated insoluble organic matter this suggests that the auriferous rocks were stained by mobile hydrocarbons produced by thermal and oxidative alteration of indigenous bitumens a contribution from hydrocarbons derived from intra basinal witwatersrand shales cannot be excluded individual aliphatic hydrocarbons of the various carbonaceous materials were subjected to compound specific isotope analysis using on line gas chromatography combustion stable isotope ratio mass spectrometry gc c irms the limited variability of the molecular parameters and uniform 13c values of individual n alkanes 31 1 1 7 and isoprenoids 30 7 1 1 in the witwatersrand samples exclude the mixing of oils from different sources carbonaceous matter in the dolostones shows distinctly different bulk and molecular isotope characteristics and thus cannot have been the source of the hydrocarbons in the witwatersrand deposits all the various forms of witwatersrand carbon appear indigenous to the witwatersrand basin and the differences between them are explained by variable in general probably short centimeter to meter scale hydrocarbon migration during diagenesis and subsequent hydrothermal infiltration

rare earth element speciation in geothermal fluids from yellowstone national park wyoming usa abstract elevated concentrations 20 1133 nmol kg of rare earth elements ree are present in acid sulphate and acid sulphate chloride hydrothermal waters of the yellowstone national park ynp we used recently estimated thermodynamic data haas et al 1995 to speciate seventeen ynp hydrothermal fluids with the eq3nr code the fluids show a range in ph 2 0 4 0 and temperature 70 93 c and are of varied chemistry with tds 155 2 075 ppm sulphate 100 10 325 mol kg chloride 190 24 580 mol kg fluoride 26 1 790 mol kg and so 4 f 0 8 323 field temperature and ph measurements were used in the modelling and saturation with kaolinite and quartz was assumed although quartz was actually supersaturated where possible oxygen fugacity was calculated from the analytical sulphate sulphide ratios otherwise it was set above the hematite magnetite buffer and pyrite saturation although speciation calculations show that this is not critical carbonate and phosphate levels were set at the analytical detection limit with the exception of 4 waters for which analytical data for phosphate existed the waters show little fractionation of ree relative to their host rhyolitic volcanics it appears that the ree abundances of hydrothermal fluids resulting from alteration of ynp rhyolites are unaffected by the presence of potential complexing species i e that acid alteration completely strips ree from the portion of the rocks that it affects without any fractionation across the ree series the main control over ree speciation is the relative abundances of potential complexing agents however ph and absolute abundances are also important in the most acidic waters ph 2 0 the free ion is the major species when salinity and so 4 cl are low 60 80 of each ree and ree complexes with chloride can be significant up to 5 for higher so 4 cl values sulphate complexes dominate 80 90 for less acid waters ph 2 8 4 0 fluoride is the main complexing agent in low so 4 f fluids but as the so 4 f ratio increases the sulphate species become dominant especially for the light ree lree

dating of anatase forming diagenetic reactions in rotliegend sandstones of the north german basin diagenetic conditions controlling authigenic formation of anatase and in situ la icp ms u pb isotope dating of this phase are studied in upper rotliegend ii sandstones from two wells in nw germany anatase grew after breakdown of detrital ti phases e g ilmenite although local scale ti transport and mobilization from detrital clay hematite coats or condensed hydrocarbons cannot be ruled out the anatase forming reaction marks the change from a regime of reducing conditions imposed by first hydrocarbon generation to oxidizing conditions probably caused by influx of a fluid from evaporitic zechstein rocks this change in fluid influx is interpreted as response to enhanced normal faulting and halokinesis during accelerated burial in triassic times isotope data of u and pb indicate incorporation of crustal common pb from mesozoic pore fluids but precisely mark diagenetic growth of anatase at 224 3 5 1 5 6 ma in a tera wasserburg plot locally u pb isotope signatures are consistent with either additional incorporation of u and pb from detrital precursor phases or with uptake of uranogenic pb from hydrocarbons generated prior to 224 ma anatase is shown to be a valuable authigenic phase suitable for u pb chronometry of diagenetic events which appears to be unaffected by protracted burial and temperatures exceeding temperatures of crystallization

origin of uranium deposits revealed by their rare earth element signature uranium deposits form in a wide range of geological settings including deep magmatic to surficial conditions and range in age from archaean to recent these temporal and spatial variations have given rise to an extreme diversity of ore deposits however understanding their conditions of formation has remained challenging this article reports rare earth element ree abundances measured by microbeam methods in uranium oxides for a series of worldwide uranium occurrences the ree patterns are very specific to each deposit type and directly reflect the conditions of their genesis we propose an evaluation of the first order parameters controlling the ree behaviour in each mineralised system this study demonstrates that the ree pattern is the most efficient tool for constraining the geological models of uranium deposits and for genetically discriminating new uranium discoveries this approach may form the starting point for a new procedure in the fight against nuclear trafficking

a major archean gold and crust forming event in the kaapvaal craton south africa the 2 89 to 2 76 gigayear old conglomerates of the central rand group of south africa host an immense concentration of gold the gold and rounded pyrites from the conglomerates yield a rhenium osmium isochron age of 3 03 0 02 gigayears and an initial 187 os 188 os ratio of 0 1079 0 0001 this age is older than that of the conglomerates thus the gold is detrital and was not deposited by later hydrothermal fluids this middle archean gold mineralization event corresponds to a period of rapid crustal growth in which much of the kaapvaal craton was formed and is evidence for a significant noble metal flux from the mantle

key factors controlling volcanic related uranium mineralization in the xiangshan basin jiangxi province south china a review abstract the xiangshan basin hosts the largest volcanic related uranium deposits in china despite several decades of extensive research the key factors controlling volcanic related uranium mineralization in the xiangshan basin remain unclear in this paper we present a review of previous studies and highlight the critical features that are closely related to the uranium mineralization in the xiangshan basin with focus on the geological feathers host rocks ore controlling structures alterations mineralization fluid inclusions and geochronological and geochemical data of the uranium deposits based on these reviews a comprehensive genetic model is proposed to better explain the uranium mineralization mechanism the uranium mineralization at xiangshan is mainly hosted in felsic volcanic and sub volcanic rocks and spatially close to the cretaceous tertiary redbeds the mineralization mainly took place from 125 to 70 ma which is much younger than the ages of host volcanic rocks 135 ma and broadly contemporaneous with the development of the redbed basins and mafic magmatism the uranium mineralization occurs mainly as veins controlled by brittle structures such as fractures faults and volcanic structures the extensional reactivation of preexisting structures and development of new fractures created permeability for the circulation of the ore forming fluids and provided spaces for uranium precipitation the ore forming fluids are characterized by basinal brines with a meteoric water origin possibly mixed with mantle derived fluids the uranium was mostly contributed by the host volcanic and sub volcanic rocks the precipitation of uranium is related to redox reactions with reductants such as fe2 h2s and ch4 as well as other mechanisms related to change of physical and chemical conditions due to fluid boiling the comprehensive review of the geological characteristics related to uranium mineralization reveals that the key factors controlling the uranium mineralization in the xiangshan volcanic basin are related to the coupling of shallow development of oxidizing fluids in the redbeds and brittle structures in the volcanic rocks and deep seated thermal activities related to mafic magmatism geological processes it is proposed that meteoric water infiltrated into the high permeability redbed basins and evolved to oxidizing basinal fluids the oxidizing fluids further circulated into the volcanic basin along brittle structures and extracted uranium from the volcanic rocks the heat provided by mafic magmatic activities accompanying upward flowing deep source hot fluids promoted the uranium extraction and transportation

assessing the role of bitumen in the formation of stratabound cu ag deposits insights from the lorena deposit las luces district northern chile abstract stratabound cu ag deposits located in north central chile have been grouped into two ns parallel belts according to the age of their volcanic and volcanoclastic host rocks deposits from the cretaceous belt are characterized by an unusual assemblage of cu sulfides with migrated hydrocarbons whereas the presence of organic matter has not yet been recognized in deposits from the jurassic belt here we report the first evidence of pyrobitumen in a jurassic stratabound cu ag deposit and evaluate its role in ore formation we present a micro analytical study of pyrobitumen associated with cu fe sulfides in the lorena deposit located in northern chile our approach involved a combination of surface and drill core sample characterization fe sem observations empa and xrf mapping of pyrobitumen in addition we determined the speciation of sulfur in pyrobitumen by using synchrotron xanes two main events of hypogene mineralization were identified at lorena deposit i e a pre ore and a main cu ore stage the pre ore stage is characterized by globularly shaped pyrobitumen and minor pyrite and a widespread albite alteration of the andesite host rock pre ore pyrite was replaced by chalcopyrite bornite and chalcocite providing evidence for a late cu inception in the main cu ore stage chalcocite is often associated with sharp edged angular pyrobitumen most likely indicating remobilization or a later pulse of hydrocarbons empa data show that pyrobitumen at lorena is enriched in fe 0 02 1 74 wt cu 0 02 0 87 wt s 0 01 0 43 wt and cl 0 01 0 4 wt other elements detected include v co ni cr sb as ag and au both ag and au were only detected in a few spots with au reaching up to 600 ppm desktop and synchrotron xrf mapping shows that s is homogeneously distributed within pyrobitumen with lower s concentrations observed at grain rims on the other hand empa wds x ray maps show that cu precipitated on pyrobitumen grain surfaces filling fractures and forming veinlets in addition textures showing the presence of micro to nano sized pyrobitumen inclusions within both pre ore pyrite and main ore chalcocite grains point unequivocally to the interaction of hydrothermal fluids with hydrocarbons during the formation of this deposit the high s concentrations measured in pyrobitumen and the presence of organosulfur compounds detected by xanes can be attributed to an organic source the pre ore assemblage is interpreted as formed from a petroleum aqueous fluid connate waters mixture that migrated from the sedimentary source rock into the jurassic host rocks where pyrite and pyrobitumen precipitated in the andesite late cu bearing hydrothermal fluids interacted with this pyrobitumen pyrite assemblage to form cu sulfides either by replacement of pyrite or precipitation we conclude that some of the s contained in pyrobitumen could have been released during interaction with the cu bearing hydrothermal fluid contributing at least partially to the s budget required for sulfide mineralization in the main ore stage our results provide evidence supporting pyrobitumen fluid interaction as a key process in the formation of the lorena deposit and possibly other stratabound cu ag deposits in chile

hydrothermal mineralization in the sandstone hosted hangjinqi uranium deposit north ordos basin china abstract tabular type uranium ore deposits the hangjinqi and daying deposits have recently been found in the middle jurassic zhiluo formation north of the ordos basin china petrographic observations the chemical composition of u minerals determined by empa and fs la icp ms whole rock geochemistry and the microthermometric study of fluid inclusions have been integrated to characterize the genetic conditions of the u mineralization in the hangjinqi sandstone hosted deposit two different groups of u minerals have been identified one group includes coffinite i associated with vanadium rich micas coffinite i is enriched in vanadium v and devoid of iron fe and yttrium y and has a lree enriched chondrite normalized ree pattern the u minerals of this group are similar to meteoric fluid infiltration related deposits the second group has coeval coffinite ii and coarsely crystalline calcite cement coffinite ii is enriched in y and fe and depleted in v and is marked by a flat chondrite normalized ree pattern which is compatible with typical hydrothermal genetic deposits with high salinity mineralizing fluids the temperature and salinity of the primary aqueous inclusions in the ore stage calcite are 120 180 c and 8 00 16 34 eq wt nacl respectively these mineral assemblages temperatures and salinities indicate that the hangjinqi deposit was affected by two distinct types of ore bearing fluids low salinity meteoric waters and high salinity hydrothermal fluids the meteoric fluids event began at 97 5 ma with the titling of the northern ordos basin and the uplift of the hetao region to the north hydrothermal u mineralization occurred since 39 2 ma with the rifting of the hetao graben thus the previous biogenic model for the u mineralization should be modified in the uraniferous region of the north ordos basin

the origin of uraninite bitumen nodules and carbon seams in witwatersrand gold uranium pyrite ore deposits based on a permo triassic analogue permo triassic dongara sandstones from the perth basin of western australia contain solitary bitumen nodules that are analogous to uraniferous bitumen nodules or fly speck carbon in late archean witwatersrand gold uranium pyrite ore deposits nodules in both contain cores of radioactive minerals and occupy depositional sites where heavy minerals were concentrated solitary bitumen nodules in the dongara sandstone formed during burial by radiation induced polymerization of liquid hydrocarbons migrating through primary porosity around detrital monazite grains similar bitumen nodules in witwatersrand ore deposits are likewise interpreted to have formed during burial although the radiation emitting detrital grains were uraninite carbon seams in witwatersrand ore deposits are stratiform bodies of coalesced bitumen nodules by analogy with solitary nodules individual nodules in carbon seams formed during burial as liquid hydrocarbons migrated through primary porosity past detrital uraninite grains but they differ from solitary nodules in that many have been stretched perpendicular to bedding to form an ellipsoidal or columnar structure although a columnar structure is consistent with deformation by vertical extension that deformation clearly postdated nodule formation in some seams elongated nodules are associated spatially with framework hosted bedding parallel microfractures which are commonly filled with fibrous secondary minerals again bedding parallel microfracturing clearly postdated nodule formation columnar textured bitumen and bedding parallel fractures are interpreted to be postdiagenetic structural fabrics whereas carbon seams appear to have been a microfocus of a compressive deformation neither columnar textured bitumen nor bedding parallel fractures are present in the dongara sandstone and they are not present in every witwatersrand carbon seam either supporting the contention that columnar textured bitumen and bedding parallel fractures are focused structural fabrics that postdate nodule formation recognition that solitary bitumen nodules and carbon seam hosted bitumen nodules of witwatersrand ore deposits are analogous in origin to bitumen nodules in the dongara sandstone supports historical mineralogical observations that the witwatersrand basin contained uraninite placers indeed carbon seams are most likely the former sites of heavy mineral uraninite strands given the chemical instability of uraninite under oxidizing conditions detrital uraninite in witwatersrand strata supports the long held contention that the archean atmosphere contained significantly less oxygen than the modern atmosphere

mafic dikes displacing witwatersrand gold reefs evidence against metamorphic hydrothermal ore formation the process responsible for the gold mineralization in the witwatersrand basin south africa remains controversial the debate is between a detrital placer enrichment in laterally extensive conglomerate layers and hydrothermal introduction by metamorphic fluids long after sedimentation while textural and geochronological data may be ambiguous a first order geological observation severely delimits the mechanism and timing of gold emplacement the individual gold reefs are cut and displaced by numerous mafic dikes which based on geochemical data presented here are feeders to flood basalts immediately overlying the witwatersrand the displacements preclude fracture controlled fluid focusing over tens of kilometers along a single conglomerate horizon during or after regional metamorphism instead basin scale gold enrichment occurred during sedimentation or early diagenesis well before local redistribution by metamorphic fluids

climate induced rebound and exhumation of the european alps foreland basins record the regional isostatic compensation of mountain belts during periods of crustal thickening they subside and when erosion unloads the mass of the mountains the basins rebound and are eroded in order to evaluate this mechanism for rebound it is critical that the timing and magnitude of erosion are documented we present data estimating the timing and magnitude of late orogenic or postorogenic erosion in the north alpine foreland basin of switzerland mineral cooling ages demonstrate that the basin underwent 1 3 km of erosion soon after 5 ma this erosion coincided with a decline in structural deformation in the swiss alps and a doubling of sediment accu mulation rates in surrounding depocenters we propose that accelerated erosional un roofing of the swiss alps triggered isostatic rebound and erosion of the foreland basin after 5 ma a projection of the isostatic rebound of the basin into the mountains suggests that at least 6 5 km of erosion should have occurred in the high topography of the aar massif accelerated erosion in the swiss alps at that time is explained by an increase in atmospheric moisture driven by an intensification of the atlantic gulf stream at 4 6 ma consequently we propose that the changing erosional capacity of the climate triggered late orogenic to postorogenic mass reduction and isostatic rebound of the swiss alps and their neighboring foreland basin

mineralogical and geochemical evidence for biogenic and petroleum related uranium mineralization in the qianjiadian deposit ne china abstract the sandstone hosted qianjiadian uranium deposit hosted in the upper cretaceous yaojia formation in the qianjiadian area songliao basin ne china has been studied for over twenty years however there exists debate on whether mineralization fluid is low temperature groundwater in favor of biogenic mineralization or diabase related magmatic hydrothermal fluid for this deposit and other adjacent geologically linked sandstone hosted uranium deposits baixingtu baolongshan and huitianzhao deposits in the north china this study provided new data from petrographic and geochemical analyses geochronology of uranium minerals the empa chemical dating method and petroleum hydrocarbon biomarkers in host sandstones two types of host sandstone were recognized in calcareous sandstones pitchblende coexists with colloform pyrite and poikilitic calcite cement while quartz and feldspars were extensively corroded in non calcareous sandstones coffinite coexists with colloform pyrite and only feldspars were slightly corroded this suggests that pitchblende formed in high ph ph 9 fluid while the ph of ore forming fluid for coffinite was lower ph 7 9 besides empa chemical dating revealed two stages of uranium mineralization stage a occurred in 43 28 ma with pitchblende as the only uranium mineral species stage b occurred in 19 3 ma with the formation of both pitchblende and coffinite the uranium mineralization was biogenic under low temperature groundwater condition and thus not from a diabase related mafic magmatic hydrothermal fluid based on the following lines of evidence i some coffinite occurs as phosphorus rich microorganism like microspherules structure ii pyrite aggregates were generated from bacterial sulfate reduction as indicated by the 34s values as low as 41 4 iii calcite cement in calcareous sandstone contains only single phase aqueous inclusions and have 13c values as low as 11 2 indicating that part of the carbon was derived from organic matter oxidation iv the organic matter oxidation is further supported by hydrocarbons extracted from petroleum inclusions within calcite cement showing occurrence of c26 c31 17 21 25 norhopanes typically resulting from heavy biodegradation

evidence for an intrabasinal source and multiple concentration processes in the formation of the carbon leader reef witwatersrand supergroup south africa laser ablation inductively coupled plasma mass spectrometer la icp ms trace element maps of pyrite and gold from the carbon leader reef in the witwatersrand basin provide new evidence that a significant proportion of the pyrite and gold was intrabasinal derived from the west rand group or equivalent shales stratigraphically below this reef rounded detrital pyrite grains in the carbon leader reef vary from compact to porous to sooty with similar textures and composition to diagenetic pyrites reported from sedimentary rocks in the west rand group detrital porous and sooty pyrites contain 0 4 to 11 3 ppm solid solution gold sulfur isotope 34s values from 17 to 16 and high levels of as and te plus a wide range of other trace elements in decreasing order ni co sb cr cu u pb bi mo zn and ag the sooty pyrite is the most au te and mo rich and is intergrown with alumino silicates and organic matter the detrital pyrite textures s isotopes and geochemistry resemble diagenetic pyrite developed under suboxic to anoxic bottom water conditions the laicp ms maps also show that the detrital pyrite grains have euhedral hydrothermal pyrite overgrowths containing micro inclusions of gold brannerite and ni as sulfides the pyrite overgrowths are also enriched in solid solution gold tellurium and other trace elements including in decreasing order as co ni cr cu mn pb bi and ag fractured and brecciated pyrite associated with brittle bedding parallel fracture zones in the carbon leader reef are also enriched in these elements due to alteration of pyrite surrounding the fractures laser icp ms pb isotope determinations on the cores of detrital pyrite indicate an age between 2750 and 2950 ma with hydrothermal overgrowths originating between 2100 and 2020 ma incorporating highly radiogenic pb this study demonstrates that both of the two competing theories for the origin of the witwatersrand gold reefs are likely to be correct we suggest that the hydrothermal event was widespread kilometer scale and involved basinal fluids that scavenged gold tellurium arsenic and trace elements co ni cr cu mn pb bi ag from gold bearing sedimentary units in the central rand group 2013 society of economic geologists inc

hydrothermal gold mineralization in the witwatersrand basin the origin of the gold mineralization in the witwaterstrand basin of south africa the largest known gold province has been controversial for decades with arguments favouring detrital1 2 placer modified placer3 4 and hydrothermal5 6 origins here we present the results of an extensive geological study of witwatersrand rocks which show that the gold and associated uranium mineralization is hydrothermal in origin and postdates a regional high temperature alteration event alteration processes identified on a small scale can be mapped out regionally as roughly strata bound zones of acid metasomatism extending far into the basin the fluid flow responsible for this alteration was concentrated in small scale structures localized along lithological boundaries we find that the gold precipitated as a consequence of interactions of the fluid with shale derived hydrocarbons present within the basin

hydrothermal rare earth element xenotime mineralization at maw zone athabasca basin canada and its relationship to unconformity related uranium deposits a reply

evolution of uranium fractionation processes through time driving the secular variation of uranium deposit types uranium deposit types have evolved considerably from the archean to the present the major global drivers were 1 change of geotectonic conditions during the late archean 2 strong increase of atmospheric oxygen from 2 4 to 2 2 ga and 3 development of land plants during the silurian other significant variations of uranium deposit types are related to unique conjunctions of conditions such as those during phosphate sedimentation in the cretaceous earth s uranium fractionation mechanisms evolved through four major periods the first from 4 55 and 3 2 ga corresponds to formation of a thin essentially mafic crust in which the most fractionated trondheimite tonalite granodiorite ttg rocks attained uranium concentrations of at most a few parts per million moreover the uranium being essentially hosted in refractory accessory minerals and free oxygen being absent no uranium deposit could be expected to have formed during this period the second period from about 3 1 to 2 2 ga is characterized by several widespread pulses of highly fractionated potassic granite strongly enriched in u th and k late in this period peraluminous granite was selectively enriched in u and to a lesser extent k these were the first granite and pegmatite magmas able to crystallize high temperature uraninite the erosion of these granitic suites liberated thorium rich uraninite which would then be concentrated in placer deposits along with pyrite and other heavy minerals e g zircon monazite fe ti oxides within huge continental basins e g witwatersrand south africa and bind river canada the lack of free oxygen at that time prevented oxidation of the uraninite which formed the oldest economic uranium deposit types on earth but only during this period the third period from 2 2 to 0 45 ga records increased oxygen to nearly the present atmospheric level tetravalent uranium from uraninite was oxidized to hexavalent uranium forming highly soluble uranyl ions in water uranium was extensively trapped in reduced epicontinental sedimentary successions along with huge quantities of organic matter and phosphates accumulated as a consequence of biological proliferation especially during the late paleoproterozoic a series of uranium deposits formed through redox processes the first of these developed at a formational redox boundary at about 2 0 ga in the oklo area of gabon all known economically significant uranium deposits related to na metasomatism are about 1 8 ga in age the high grade large tonnage unconformity related deposits also formed essentially during the late paleoproterozoic to early mesoproterozoic the last period 0 45 ga present coincided with the colonization of continents by plants the detrital accumulation of plants within continental siliciclastic strata represented intraformational reduced traps for another family of uranium deposits that developed essentially only during this period basal roll front tabular and tectonolithologic types however the increased recognition of hydrocarbon and hydrogen sulfide migration from oil or gas reservoirs during diagenesis suggests potential for sandstone hosted uranium deposits to be found within permeable sandstone older than the silurian large uranium deposits related to high level hydrothermal fluid circulation and those related to evapotranspiration calcretes are only known during this last period of time probably because of their formation in near surface environments with low preservation potential

the last erosional stage of the molasse basin and the alps we present a synoptic overview of the miocene present development of the northern alpine foreland basin molasse basin with special attention to the pattern of surface erosion and sediment discharge in the alps erosion of the molasse basin started at the same time that the rivers originating in the central alps were deflected toward the bresse graben which formed part of the european cenozoic rift system this change in the drainage direction decreased the distance to the marine base level by approximately 1 000 km which in turn decreased the average topographic elevation in the molasse basin by at least 200 m isostatic adjustment to erosional unloading required ca 1 000 m of erosion to account for this inferred topographic lowering a further inference is that the resulting increase in the sediment discharge at the miocene pliocene boundary reflects the recycling of molasse units we consider that erosion of the molasse basin occurred in response to a shift in the drainage direction rather than because of a change in paleoclimate climate left an imprint on the alpine landscape but presumably not before the beginning of glaciation at the pliocene pleistocene boundary similar to the northern alpine foreland we do not see a strong climatic fingerprint on the pattern or rates of exhumation of the external massifs in particular the initiation and acceleration of imbrication and antiformal stacking of the foreland crust can be considered solely as a response to the convergence of adria and europe irrespective of erosion rates however the recycling of the molasse deposits since 5 ma and the associated reduction of the loads in the foreland could have activated basement thrusts beneath the molasse basin in order to restore a critical wedge in conclusion we see the need for a more careful consideration of both tectonic and climatic forcing on the development of the alps and the adjacent molasse basin

palaeotsunami deposits at the tiber river mouth ostia antica italy do they really exist abstract in this paper we test the recent hypothesis of the occurrence of five to seven tsunami generations that would have struck the ancient harbour basin of ostia italy and the lower channel of the tiber river during the last three millennia because these steady disaster events would have deep implications on our knowledge of the history of rome we reviewed the pluridisciplinary data available at the tiber river mouth considering sedimentological geomorphological micropalaeontological geochemical chronological and historical evidence there is currently no conclusive palaeoenvironmental evidence to suggest past tsunami inundations near ostia river mouths are not the best context in which to identify tsunami deposits high fluvial and coastal mobility generated by regular floods and storms hardly record single high energy events hee from floods storms or tsunamis sediments are regularly reworked at the river mouth both in the river channel and on the close shoreface mixed fluvial and marine influences and the seasonal formation of a salt wedge at the mouth of the tiber create specific estuarine assemblages for micro and macrofauna the layer called high energy event 1 hee 1 on the palaeo shoreface close to the river mouth and hee 4 5 in the point bars of the tiber channel are most probably layers reworked several times by fluvio coastal events storms and or floods hee 3 sealing the republican harbour of ostia is clearly related to flood deposits complementary analyses would be necessary to definitively identify the origins of the hee 2 and hee 7 in the harbour and hee 6 in the palaeochannel or floodplain based on the data available we show how other processes than tsunami inundations could be just as accountable for these coarse grained sediment layers storm deposit flood deposit or riverbank deposit this review puts into question the use of pluridisciplinary proxies to identify palaeotsunami deposits in addition we demonstrate how high pb concentrations constitute a robust proxy to definitively refute the presence of palaeotsunami deposits as such this study will be beneficial to a large community of specialists in coastal research

petrographic evidence for emplacement of carbon into witwatersrand conglomerates under high fluid pressure abstract much gold in the witwatersrand conglomerates is directly associated with seams of carbon that are generally parallel with bedding some seams locally crosscut bedding and form anastomosing fracture patterns showing that emplacement of liquid hydrocarbons in those seams was postdepositional and infilled fractures that are generally parallel to bedding seams that are not observed to crosscut bedding are nonetheless petrographically identical and are believed to have a common postdepositional origin carbon also occurs along sets of bedding parallel microfractures through individual quartz pebbles in mineralized conglomerates planes of fluid inclusions parallel to the microfractures in pebbles show further evidence for the importance of bedding parallel fluid flow the occurrence of carbon seams on sedimentary discontinuity surfaces may reflect preferential emplacement of carbon along planes of weakness brittle extensional fracturing in pebbles indicates high fluid pressures which may relate to hydrocarbon generation bedding parallel minealization by quartz clays metamorphic chlorite pyrophyllite and gold which reflect a complex multistage paragenesis indicate repeated reactivation of bedding plane permeability previous arguments against a hydrocarbon origin for the carbon seams have been based upon the low intergranular permeability of the rocks however the present study shows that this condition actually caused focusing of hydrocarbon fluid flow along discontinuity surfaces and facies boundaries interaction with uranium could have caused fixation of fluid hydrocarbon by radiolytic polymerization the columnar nature of carbon in many of the seams interpreted by others as a biogenic structure could instead reflect polymer swelling normal to bedding in the direction of least confining stress

kerogen facies and maturity of the kimmeridge clay formation in southern and eastern england abstract the upper jurassic kimmeridge clay formation of southern and eastern england was deposited under anoxic or dysaerobic conditions in a stratified shelf sea anoxic conditions developed in the intra shelf weald and central channel basins of southern england and the cleveland basin of eastern england with generally dysaerobic conditions in the flanking shelf areas only in the basin margins such as in northern scotland were oxic bottom water conditions prevalent the maturity and distribution of the kerogen facies which can be explained in terms of the palaeogeography and burial history of the upper jurassic of southern and eastern england are discussed along with the effects of their variation on commonly used geochemical parameters relationships to clay mineralogy are also examined kerogens are largely type ii amorphous sapropels of marine origin with variable amounts of terrestrially derived type iii material type iii kerogens predominate in the basin margin areas whereas type ii kerogens are restricted to the basin centres over the intermediate shelf areas mixed type ii type iii kerogens are prevalent both the sedimentation rate and differential organic matter preservation can be demonstrated to be the major controls on the kerogen facies of the kimmeridge clay formation variations in the kerogen facies appear to be responsible for the often spurious and scattered maturity measurements from the kimmeridge clay formation using vitrinite reflectance spore coloration and rock eval pyrolysis parameters the results often conflicting with geological models for the post jurassic burial history this appears to be due to the highly variable content of terrestrial and recycled type iii kerogens from older sediments in the mudstones causing the conventional maturity indices to often not reflect the true maturity of the autochthonous marine type ii kerogens

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

trace element distribution in uraninite from mesoarchaean witwatersrand conglomerates south africa supports placer model and magmatogenic source the first systematic analyses of the trace and rare earth element ree distribution in uraninite from various gold bearing conglomerates of the mesoarchaean central rand group in south africa s witwatersrand basin by in situ laser ablation inductively coupled plasma mass spectrometry confirms a placer origin for the uraninite and a magmatogenic provenance thereof the chemistry of commonly rounded to sub rounded uraninite is highly variable from grain to grain but generally marked by elevated th w bi mo ta y ree contents and unusually high au concentrations especially the high th contents and the chondrite normalised ree patterns are incompatible with post sedimentary hydrothermal genetic models for the u mineralisation and point to derivation of the detrital uraninite from a high temperature magmatogenic presumably granitic to pegmatitic source the elevated au concentrations of as much as 67 ppm in this uraninite are unique to the witwatersrand and hint at a granitic hinterland that was enriched in both u and au thus presenting a potential source domain for some of the detrital gold in the witwatersrand conglomerates minute fracture fills of brannerite in close proximity to the larger rounded uraninite grains are devoid of detectable bi mo ree and au and have only very low concentrations of th w ta and y this is explicable by crystallisation from a low temperature hydrothermal fluid thus witwatersrand u phases show analogous to many other ore constituents such as pyrite and gold clear evidence of partial short range mobilisation of originally detrital particles by post sedimentary fluids

rare earth element geochemistry and the tetrad effect abstract the tetrad effect is found in the rare earth elements la lu and results from increased stability at quarter half three quarter and complete filling of the 4f electron shell suggestions that this effect is observed in ree patterns of seawater and other geological samples marine phases the mineral kimuraite late stage granitic rocks the mineral uraninite and siliciclastic sediments are not compelling in the cases of seawater and the carbonate mineral kimuraite a discontinuity at gd may be attributed to the tetrad effect but the complexity of the overall controls on these ree distributions leaves such an interpretation uncertain at best unusual ree patterns in leucogranites and pegmatites are best explained by fractionation of trace minerals notably apatite apparent tetrad anomalies in uraninite rees disappear when normalised to upper crustal i e shale abundances analytical difficulties probably explain apparent tetrad effects in some seawater limestone and siliciclastic ree patterns

significance of aluminum phosphate sulfate minerals associated with u unconformity type deposits the athabasca basin canada aluminum phosphate sulfate aps minerals formed around the athabasca unconformity type deposits and those from their australian counterparts are chemically very similar showing the same continuum between the diagenetic sr rich aps minerals of the barren sandstones and the lree rich composition of the aps minerals in the hydrothermally altered sandstone the p and lree rich compositions were controlled by the transport and the redistribution of p and lree elements released from the dissolution of phosphate minerals principally monazite in the basement rocks and in the basin during the syn ore alteration processes the s sr ratio measured in the aps minerals from unaltered sandstone away from the unconformity and any mineralization is preserved during the syn ore alteration processes suggesting that the fluids involved in both the deep burial diagenetic processes and the syn ore alteration system were derived from a similar diagenetic reservoir in both the athabasca and kombolgie regions the trioctahedral chlorite host rock alteration around the australian basement hosted u deposits as compared to the illite and sudoite associated with the athabasca basement hosted along with the more lree rich aps compositions in the australian deposits suggests that the ph and oxygen fugacity f o 2 of the syn ore fluids differed in the alteration systems of the two regions at the time of the u deposition