mesozoic structural evolution of the hangjinqi area in the northern ordos basin north china abstract this study analyzes the structural evolution of the hangjinqi area in the northern ordos basin based on seismic sections and exploration well data this area shows excellent examples of the relationship between tectonics and sedimentation three tectonic sequences separated by four erosional surfaces have been recognized overlying a paleoslope surface t9 in this area 1 the late carboniferous permian and triassic tectonic sequence ts 1 sedimentation of the lowest part of this succession is strongly controlled by the hangjinqi fault zone hfz whereas the rest of the sequence indicates much less fault control 2 the middle jurassic tectonic sequence ts 2 3 the late early cretaceous tectonic sequence ts 3 and the ts 2 and ts 3 sequences are more extensive than the ts 1 sequence throughout the hangjinqi area the structural framework displayed by the ts 2 sequence is very different from that displayed by the ts 3 sequence more specifically the general structure beneath the unconformity t3 between the late jurassic strata and the early cretaceous strata consists of an e w trending transtensional fault system this resulted from a multi stage dextral phase which was caused by oblique subduction of the paleo pacific plate under the eurasian plate and dextral movement of the hfz and a subsequent inversion event which caused significant reverse movement along previous transtensional structures the study area which underlies the unconformity t2 between the late jurassic strata and the early cretaceous strata has been deformed since the late cretaceous when tectonic inversion occurred possibly due to changes in the strike slip motion from dextral to sinistral of the hfz late cretaceous erosion was responsible for an important and unequal denudation the timing of the transition from extension to uplift cannot be determined due to continuous erosion but this uplift finally marked the end of the structural evolution of the hanjinqi area and even the ordos basin

geochemistry of vanadium in an epigenetic sandstone hosted vanadium uranium deposit henry basin utah the epigenetic tony m vanadium uranium orebody in south central utah is hosted in fluvial sandstones of the morrison formation upper jurassic although the deposit is mined for uranium vanadium has a higher average abundance in the ore thus the geochemistry of vanadium in the orebody was studied to characterize ore forming processes within the inferred ground water flow regime measurements of the relative amounts of v super 3 and v super 4 in ore minerals show that v super 3 is more abundant thermodynamic calculations show that vanadium was more likely transported to the site of mineralization as v super 4 the ore formed as v super 4 was reduced by hydrogen sulfide followed by hydrolysis and precipitation of v super 3 in oxide minerals e g montroseitc or paramontroseite or chlorite uranium was transported as uranyl ion u super 6 or some complex thereof and reduced by hydrogen sulfide forming coffinite detrital organic matter in the rocks served as the carbon source for sulfate reducing bacteria it was this bacteriogenic h 2 s that reduced the metals in the mineralization process possible sources for the v and u in this deposit have been identified previously vanadium most likely was derived from the dissolution of iron titanium oxides which liberated fe as well as v a zone of titanium rich remnants is observed updip and up the hydrologic gradient from the deposit m goldhaber and r l reynolds unpub data uranium probably was derived from the overlying brushy basin member of the morrison formation northrop 1982 a preliminary age date for the deposit of 115 ma k ludwig 1986 pers commun indicates that the ore formed after deposition of the brushy basin member previous studies have shown that the ore formed at the density stratified interface between a basinal brine and dilute meteoric water the mineralization processes described above occurred within the mixing zone between these two fluids stable isotope analyses of ore stage dolomite show a progressively heavier carbon and oxygen isotope signature with increasing depth through an ore horizon consistent with the two solution interface model

mineralogy geochemistry and fluid action process of uranium deposits in the zhiluo formation ordos basin china abstract some controversies still exist regarding the genesis of sandstone type uranium deposits in the northeastern ordos basin herein based on boreholes and well logging data we selected sandstone samples representing different epigenetic alteration environments as the research object and comprehensively utilized polarizing microscopy scanning electron microscopy electron probe analysis elemental analysis and other test methods to research sandstone genesis the main altered minerals in the sandstone of this area include limonite pyrite achavalite carbonate sulfate clay and uranium minerals the complex characteristics of alteration minerals indicate multi stage fluid mixed mineralization in this area according to the relationship between the major elements in different types of sand bodies the components were classified into three groups the first is the reduction media group including cao mno total oxygen carbon toc s u and burning loss the second is the detrital particle group including sio2 k2o and na2o and the third contains the clay and volcano component group including fe2o3 p2o5 tio2 feo mgo and al2o3 among these the content of reduction media is positively correlated with uranium enrichment whereas detrital particles and clay components reflect the influence of alteration on the sand body composition which indirectly affects the uranium adsorption and precipitation through the normalization of rare earth element ree chondrites we find that the distribution patterns of rees in rocks with different geochemical environments show a fractionation of light and heavy rare earth elements hrees a right leaning enrichment of light rare earth elements lrees and relatively flat hree further via the post archean australian shale paas normalization we observe that the mudstone of the zhiluo formation exhibits a relatively flat curve whereas the sandstones have strongly positive eu anomalies the difference in ree values for different types of sand bodies indicates that although all types of rocks have a similar sedimentary environment their original sediments underwent fluid alterations such as oxidation and reduction based on the uranium mineralization evolution history in the study area the water rock reaction process and mineral alteration sequence were determined on the basis of alteration types and elemental concentrations our findings provide new insight into the petrological significance mineralogy and geochemical composition of uranium deposits in the ordos basin

occurrence of pyrites in sandstone type uranium deposits relationships with uranium mineralization in the north ordos basin china abstract large quantities of pyrite have been discovered near the ore bearing segments of the sandstone type uranium deposits in the north ordos basin in this study the electron probe microanalysis scanning electron microscopy and isotope geochemical analysis were used to systematically investigate the morphology composition and s isotopes of the pyrites in these deposits and their genetic order relative to the other main altered minerals based on the regional tectonic evolutionary sequence of the basin the relationships between the pyrites and uranium mineralization are discussed macroscopically the pyrites were found to occur in lumpy banded disseminated star like or sheet like form microscopically they exist either as detrital grains or inside detrital grains as idiomorphic grains in colloidal or framboidal form inside mica minerals in banded or petaloid form and in other forms related to biological cells or microorganisms the 34s values in the pyrites are highly variable 7 3 to 37 2 but principally in the proximity of 30 and display obvious biogenic origin taking into consideration the extremely low u contents in the pyrites and achavalites iron selenide the genetic order of the main altered minerals is determined as follows detrital pyrites clay mineral overgrowths micritic calcites during the diagenetic stage and achavalites pyrites coffinite pitchblende vanadium oxides sparry calcites during the metallogenic stage the broad presence of pyrites in the jurassic yan an formation during the basin s evolution provided detrital pyrites and organic detritus for the overlying formations the zhiluo formation host of the uranium mineralization is also home to some primary spherical colloidal or framboidal pyrites the cretaceous was the main epigenetic uranium metallogenetic period as well as the main pyrite development period of the area the pyrites which are typically colloidal have cemented the earlier framboidal pyrites and other minerals and are closely associated with the redox reaction related to uranium mineralization in the paleogene uranium mineralization mainly occurred by the redox migration of early shallow deposits to and fresh pyrites forming in deeper levels

coupled uranium mineralisation and bacterial sulphate reduction for the genesis of the baxingtu sandstone hosted u deposit sw songliao basin ne china the baxingtu deposit is a typical redox front tabular shaped uranium deposit hosted in sandstones of the late cretaceous yaojia formation deposited within a braided river environment during the post rift stage of the songliao basin in northeast china this study proposes the first metallogenic model for the baxingtu deposit and provides new data on genetic processes involved in the uranium mineralisation of sandstone type deposits that were characterised through petrographic observations whole rock geochemistry and geochemical and or mineralogical study of iron disulphide uranium minerals fe ti oxides epma la icp ms and organic matter rep the 34s value has been measured in situ by sims on the different generations of iron disulphide within regional primary reduced sandstones pre ore uranium enrichment umean 7 6 ppm in whole rock was identified on altered fe ti oxides along with minor concentrations on organic matter respectively 26 3 and 1 3 of the whole rock u content which together represent a significant source of uranium for the mineralisation additional pre ore uranium concentrations may also be associated with clay minerals petrographic observations and rep data indicate that organic matter occurring in the host sandstone is mainly inherited from land plants and corresponds to type iii or type iv kerogens ore stage iron disulphides largely occur as framboids and in replacement of organic matter or also as sub idiomorphic to idiomorphic cement and crystal trace element signatures detected within framboids are likely indicative of formation mainly from a single event framboids and iron disulphide in replacement of organic matter have a light sulphur isotope signature characterised by 34s values from 72 0 to 6 2 suggesting that sulphur originated from bacterial sulphate reduction which was mainly responsible for 1 the liberation of u from fe ti oxides and organic matter 2 the generation of ore stage iron disulphides 3 the bioreduction of uranium and 4 the production of a secondary h2s rich reducing barrier also involved in uranium reduction uranyl and sulphate ions were transported through the host sandstone by low temperature oxygenated groundwater and u iv was precipitated at the redox interface as nano to microcrystals of pitchblende and coffinite dominantly associated with bacterial substrate and as intergrowth with biogenic iron disulphide or directly associated with organic matter and residual ti fe oxides the uranium mineralisation does not replace ore stage iron disulphides therefore the combined mineralogical geochemical and isotopic characteristics of the baxingtu tabular uranium deposit characterise dominantly biogenic processes for the genesis of the uranium mineralisation

a growing sandstone type uranium district in south yili basin nw china as a result of extension of tien shan orogen evidences from geochronology and hydrology abstract the mesozoic yili basin of nw china represents the largest known concentration of u deposits in china and contains five major deposits namely from west to east the 512 kujie ertai 513 511 510 mengqiguer and 509 deposits pre mining resources within the explored sandstone type uranium deposits in this area are reportedly as much as 20 000 t contained u the mineralization is hosted by the middle lower jurassic shuixigou group which from base to top is divided into the badaowan sangonghe and xishanyao formations the u pb isotopic analysis of ores from the kujie ertai and mengqiguer deposits indicate that they contain high and variable amounts of initial common pb meaning that the only possible way to date these deposits is by using u pb isochrons two major stages of uranium mineralization have been identified by the u pb isotope dating of uranium ores in this region the kujie ertai deposit apparently formed between 23 4 3 3 and 20 18 0 49 ma corresponding to a period of crustal thickening and uplift within the tien shan orogen this event 35 21 ma accommodated the majority of the strain generated by the northward collision of the indian plate with the asian plate however the dating of samples from the mengqiguer deposit yielded much younger ages between 0 61 0 24 and 0 347 0 0048 ma the western tien shan mountains expanded until the pliocene as a result of the far field influence of continuous penetration of the indian plate into the asian plate this activated reverse faults and folds in the piedmont of the tien shan mountains and caused the continuous uplift of the southern flank of the yili basin the uplift caused the erosion of anticline hinge zones introducing significant amounts of oxidizing water into the shuixigou group generating a second stage of uranium mineralization hydrological sampling also suggests that the mengqiguer deposit continues to grow indicating a possible third stage of uranium mineralization 0 ma this also indicates that the u within these deposits is derived not only from u bearing sediments but from the tien shan mountains as a result of groundwater cycling the evolution of the u contents of groundwater that was initially derived from cold springs that flow into the mineralized units indicates that these cold springs have an essential role in mobilizing u from the tien shan mountains with rivers flowing through areas of outcropping mineralized units acting as a source of mineralizing fluids during the formation of the mengqiguer deposit

the effect of hydrothermal fluids on ordovician carbonate rocks southern ordos basin china abstract hydrothermal processes have an important influence on the spatial distribution and formation of carbonate reservoirs and play a critical role in certain deep reservoirs where hydrothermal fluid rock interaction may result in permeability creation due to carbonate dissolution or permeability destruction due to the deposition of cementing minerals this study analyzed certain hydrothermal indicator minerals quartz celestite multi stage calcareous fillings in carbonate rocks from the ordovician majiagou formation southern ordos basin china the petrological and geochemical characteristics of these indicator minerals imply that the majiagou formation was affected by two metasomatic events related to the hercynian indosinian and yanshanian orogenies and linked to magmatic hydrothermal fluids derived from basaltic melts most of the ce and eu values obtained from matrix dolomite samples were lower than one but u th and v c ratios showed positive anomalies the 13c and 18o values of the matrix dolomite were concentrated between 12 8 and 6 0 whereas 13c showed a bipolar distribution at the same depth elemental geochemistry results showed that the ordovician carbonate rocks were subjected to freshwater leaching followed by evaporation and widespread hydrothermal dissolution successively as a result of the multi episodic hydrothermal activity that affected the southern ordos basin and the path of migration channel a parental magmatic hydrothermal fluid fluid 1 that had been generated during the underplating of the southern north china craton by mesozoic alkaline basalt melts separated into two types of fluids with different chemical properties an acidic hydrocarbon bearing fluid fluid 2a mixed with cambrian oil and gas and a weakly to moderately alkaline brine fluid 2b not in contact with hydrocarbons both fluids 2a and 2b then interacted with the ordovician carbonate rocks with fluid 2a having undergone hydrothermal sulfate reduction with so42 in the layers in which gypsum was developed and convection of fluid 2a having resulted in brine formation the reaction products of h2s and co2 together with organic acid co dissolved carbonate minerals in the ordovician strata played a major role in the formation of a high porosity reservoir conversely owing to the progressive reduction of temperature and solubility during fluid ascent fluid 2b precipitated quartz calcite fillings in the residual pore spaces resulting in the localized destruction of the original reservoir permeability in summary this study analyzed the petrological and geochemical characteristics of 60 carbonate rock drill core samples established the likely formation mechanism of fluids 2a and 2b and determined the effects of these hydrothermal fluids on the ordovician majiagou formation carbonate reservoir

structure and chemistry of zircon and zircon group minerals zircon zrsio4 is a common accessory mineral in nature occurring in a wide variety of sedimentary igneous and metamorphic rocks known to incorporate an assortment of minor and trace elements zircon has the ability to retain substantial chemical and isotopic information leading to its use in a wide range of geochemical investigations including studies on the evolution of earth s crust and mantle e g hanchar et al 1994 bowring 1995 vervoort et al 1996 hoskin and schaltegger this volume valley this volume as well as age dating e g gibson and ireland 1995 bowring et al 1998 solar et al 1998 bowring and schmitz this volume ireland and williams this volume parrish et al this volume the physical and chemical durability of zircon is a major factor in it being the mineral by which many of earth s oldest known rocks have been dated bowring et al 1989 maas et al 1992 buick et al 1995 bowring and williams 1999 wilde et al 2001 and is also an important factor in zircon being proposed as a candidate waste form for the geologic disposal of excess plutonium from dismantled nuclear weapons ewing and lutze 1997 ewing 1999 burakov et al 2002 burakov et al 2003 ewing et al this volume the chemical and physical properties of zircon and its ability to incorporate and retain trace elements are largely determined by its crystal structure the zircon structure is adopted by numerous minerals and synthetic compounds with the general formula at o4 in which high field strength t site cations occupy isolated tetrahedra and a site cations occupy larger eight coordinated structural sites zircon type compounds share many physical properties as well as displaying variable degrees of solid solution among end members

multifrequency turam measurements over a sulfide deposit a six frequency electromagnetic em system has been developed and used for a turam type survey over the sulfide deposit of mailaram copper belt in andhra pradesh india turam field strength ratio fsr and phase difference pd are measured in the range 84 to 2688 hz sulfides in this belt occur as thin concentrated lodes which grade into disseminations soil covers a major part of the area interpretation of the results is carried out using a thin sheet model in free space however an attempt has been made to account for finite resistivity of the normal ground by computing turam response of a conducting half space appropriate for the area and subtracting the same from the observed response the results of the survey confirm the known advantage of the turam method viz its greater depth of investigation compared to a method like slingram the normal ground at mailaram is only mildly conducting so that the free air approximation is valid at low frequencies a correction for the finite resistivity of t

a quantitative model of ground water flow during formation of tabular sandstone uranium deposits tabular sandstone uranium deposits constitute the largest uranium resource type in the united states a major point of contention has been the nature and direction of the ground water flow this paper presents a quantitative simulation of regional ground water flow during uranium deposition in the westwater canyon member and jackpile sandstone member of the upper jurassic morrison formation in the san juan basin input for the four layer finite difference model was from thicknesses and sandstone mudstone ratios in each layer from 1 600 drill holes and 100 measured sections and from palcotopographic reconstructions topographic slope shoreline position and density contrasts in the lake and pore fluids controlled the directions of flow and recharge discharge areas the most important results for uranium ore deposit formation are that regional ground water discharged throughout the basin regional discharge was concentrated along the shore line or playa margin flow was dominantly gravity driven and compaction dewatering was negligible a strong association is found between the tabular sandstone uranium deposits and major inferred zones of mixed local and regional ground water discharge the results of ground water modeling favor the brine interface model over the lacustrine humate model for uranium deposition

systematic variations of h o c isotopes in different alteration zones of sandstone hosted uranium deposits in the southern margin of the yili basin xinjiang china a review and implications for the ore forming mechanisms abstract the meso cenozoic yili basin in northwestern china hosts important uranium and coal resources the uranium deposits are mainly hosted by sandstones and are characterized by clay and carbonate alterations within and surrounding the orebodies h o c isotopes of clay minerals and carbonate cement in the different alteration zones of the uranium deposits in the southern margin of the yili basin are summarized to examine the mechanisms of uranium mineralization the alteration zones associated with the uranium mineralization include an intensely oxidized zone a weakly oxidized zone a transitional mineralization zone and a reduced zone the d and 18o values of the parent fluids calculated from clay minerals from the different alteration zones show a linear trend that intersects the global meteoric line at a point with a 18ov smow of ca 5 and a dv smow of ca 30 which coincide with the upper end of the d 18o trend along the meteoric line of formation waters in the basin suggesting that the uranium mineralizing fluid was of meteoric origin the general trends of decreasing d and 13c and increasing 18o from the intensely oxidized zone to the reduced zone together with the fact that calculated dv smow values of the mineralizing fluids are lower than the original meteoric fluid and that the 13c values of the calcite cement overlap with those of organic matter in sedimentary rocks suggest that hydrocarbons were involved in uranium mineralization the hydrocarbons may have been important reducing agents causing precipitation of uranium minerals the hydrogen ion released from oxidation of the hydrocarbons may have been buffered by the formation of clay minerals which favors co development of clay alteration and calcite cement deviation of h o c isotopes from the general variation trends as expected from the above redox mechanism likely resulted from the dynamic nature of the redox front which changed its position in response to hydrodynamic balance between a downward flow of uranium bearing oxidizing fluid and an upward flow of reductants bearing reducing fluid from the lower part of the basin

hydrogeochemical characteristics of the sandstone hosted uranium mineralization in northern ordos basin china abstract the northern ordos basin is one of the biggest uranium resource production areas in china however the hydrogeochemical mechanism for the formation of uranium deposits remains poorly understood despite that interlayer oxidation hydrothermal fluid mineralization and gas reduction were proposed in order to provide a more comprehensive knowledge on their formation mechanism the investigation was carried out by analyzing hydrogeochemistry and environmental isotopes of waters from river lakes shallow private wells boreholes over the period from 2015 to 2016 the results showed that the analysed samples exhibited a hydrochemical heterogeneity confirmed by a large range of ph eh main cation and anion concentrations and uranium concentration in surface water quaternary shallow groundwater cretaceous confined water and jurassic confined water the piper and durov diagrams highlighted that hydrochemical facies changed with groundwater flow from shallow to deep with hco3 ca mg and hco3 ca in quaternary shallow groundwater hco3 cl ca na in cretaceous confined water and cl na and hco3 na in jurassic confined water aqueous geochemistry indicated that the jurassic ore bearing confined waters originated from the cretaceous confined waters involving both leaching processes and desulfidation nonetheless the cretaceous confined waters originated from quaternary shallow groundwater and mainly have experienced leaching processes gibbs plot indicated that with an accumulation of ions in the groundwater during runoff calcite and uraninite minerals would be oversaturated and precipitation tended to occur the variation of tds along depth indicated desulfurization occurrence in ore bearing aquifer and a decrease in migrating ability of uo22 leading to u precipitation isotopic results showed that the ore bearing confined waters were depleted in 18o and d and were located along the global meteoric water line gmwl most ore bearing confined waters plotted on or near the meteoricwater line showing their deep circulating meteoric origin uranium species study indicated that dissolved uranium was dominated by uo2 oh 3 and uo2 co3 34 which have a high migrating ability saturation index of uraninite in all water samples were determined to be below 0 indicating that this uranium deposit was currently not under mineralization the ph and eh values of the samples were located in the migration area suggesting that uranium is in a migration state under current groundwater conditions only when ph 5 8 and eh

late triassic tuff intervals in the ordos basin central china their depositional petrographic geochemical characteristics and regional implications abstract tuff intervals of upper triassic yanchang formation are laterally widespread in the ordos basin central china this paper focuses on magmatic origins and potential source regions of these tuff intervals through detail depositional petrographic and geochemical analyses most of the tuff intervals are well documented at the bottom of the chang7 oil reservoir unit and can be correlated laterally and certain tuff beds are reworked by turbidity current or seismic activity petrographic studies of the chang7 tuffs indicate that they are composed of crystal shards lithic shards and altered glass shards and the crystal shards include plagioclase quartz and biotite alteration of the chang7 tuffs is ubiquitous thus most of these tuffs transformed into illite smectite i s mixed layers which are identified by scanning electron microscopy sem and x ray diffraction xrd less common minerals are also detected in the chang7 tuffs such as zircon hematite siderite anatase major elements are determined by the x ray fluorescence xrf analysis the results indicate that the chang7 tuffs are enriched in k2o average 4 21 the ratio of sio2 al2o3 ranges from 1 73 to 2 85 average 2 17 and the ratio of tio2 al2o3 varies between 0 006 and 0 032 average 0 017 which imply that the chang7 tuffs originated from a felsic parental magma trace elements are determined by inductively coupled plasma mass spectrometry icp ms indicating the total rare earth element ree concentrations are variable and range from 117 46 to 466 83 ppm average 251 88 ppm ree distribution pattern of the chang7 tuffs presents a lree rightward incline with flat hree curve the value of eu ranges from 0 151 to 0 837 average 0 492 suggesting a strong to weak negative eu anomaly the chang7 tuffs show positive anomalies in rb th and u and negative anomalies in nb sr and eu on a primitive mantle normalized spidergram a preliminary analysis of the geochemical composition of the chang7 tuffs suggests a parental magma origin of rhyodacite dacite which came from volcanic arc related setting along an active continental margin combined with the chronology and geochemical studies of the synchronous tianshui rhyolite in the west qinling mountains we propose that the west qinling mountains is one of the potential source regions of these tuffs and the middle late triassic terminal closure of eastern tethys provided the arc related magma

ore characteristics of the sandstone type daying uranium deposit in the ordos basin northwestern china the ordos basin is one of the top oil gas and coal producing basins in china and is increasingly recognized as an important uranium mineralization province uranium deposits occur near the margin of the basin and are mainly hosted in the sandstones of the jurassic zhiluo formation the daying uranium deposit in the ordos basin is one of the most important large sandstone type uranium deposits in china based on thin section analysis and electron microprobe measurements we used analytical chemical data to study the characteristics of the daying uranium deposit including the type structure particle size material composition chemical composition form and valence state of the uranium the uranium mainly exists in three forms an absorbed form independent minerals and uranium bearing minerals most of the uranium in the ore is u4 and the proportion of u6 ranges from 18 to 55 with an average of 33 the proportion of u6 is relatively high in the cores containing low grade ore this study pr

electromagnetic sounding of the kapurdi lignite deposit in western rajasthan india in the kapurdi block of the barmer lignite field in western rajasthan india lignite occurs as a number of discontinuous seams of varying thickness up to a few m the country rock is a succession of clay sand and various members of the clay sand family the overburden comprising sand fuller s earth bentonitic clay clayey sand sandy clay and clay is thick and electrically highly conductive both its thickness 40 90 m and conductivity 0 5 1 0 s m are highly variable the lignite seams may occur anywhere in the clay sand sequence below this overburden a ten layered electrical model of the kapurdi area was parameterized on the basis of galvanic resistivity sounding and core drilling results this model was then validated by electromagnetic sounding measurements made with a 200 200 m square loop transmitter and energizing current of variable frequency 80 hz to 11 khz using central induction sounding techniques with a loop of this size only formations in the overburden could be mapped subsequent computer modeling has shown that a larger loop of size say 800 m and a frequency band of 30 500 hz are required to map formations below as well as those within the overburden even then only various clay sand interfaces can be mapped i e only over burden thickness and the likely depth range of lignite seams if they occur can be estimated direct mapping of lignite seams is not feasible in practice this is true of loop dipole as well as central induction sounding it is interesting that skin depth need not always be a factor limiting depth of exploration in electromagnetic prospecting

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

enzymatic iron and uranium reduction by sulfate reducing bacteria abstract the potential for sulfate reducing bacteria srb to enzymatically reduce fe iii and u vi was investigated five species of desulfovibrio as well as desulfobacterium autotrophicum and desulfobulbus propionicus reduced fe iii chelated with nitrilotriacetic acid as well as insoluble fe iii oxide fe iii oxide reduction resulted in the accumulation of magnetite and siderite desulfobacter postgatei reduced the chelated fe iii but not fe iii oxide desulfobacter curvatus desulfomonile tiedjei and desulfotomaculum acetoxidans did not reduce fe iii only desulfovibrio species reduced u vi u vi reduction resulted in the precipitation of uraninite none of the srb that reduced fe iii or u vi appeared to conserve enough energy to support growth from this reaction however desulfovibrio desulfuricans metabolized h2 down to lower concentrations with fe iii or u vi as the electron acceptor than with sulfate suggesting that these metals may be preferred electron acceptors at the low h2 concentrations present in most marine sediments molybdate did not inhibit fe iii reduction by d desulfuricans this indicates that the inability of molybdate to inhibit fe iii reduction in marine sediments does not rule out the possibility that srb are important catalysts for fe iii reduction the results demonstrate that although srb were previously considered to reduce fe iii and u vi indirectly through the production of sulfide they may also directly reduce fe iii and u vi through enzymatic mechanisms these findings as well as our recent discovery that the so reducing microorganism desulfuromonas acetoxidans can reduce fe iii demonstrate that there are close links between the microbial sulfur iron and uranium cycles in anaerobic marine sediments

characterization of the ebre and rhone estuaries a basis for defining and classifying salt wedge estuaries river discharge is the main factor controlling the hydrologic dynamics of the ebre and rhone estuaries the topography of the estuary bed also influences the extent advance and retreat of the salt wedge tides have little influence because of the low tidal range mean annual river discharge is close to the critical value determining the formation and breakup of the salt wedge this is related to the fact that river flow controls the sedimentary dynamics of the estuary including the sandbar at the mouth when discharge is lower than the mean annual river flow the salt wedge is established and the estuary becomes a depositional environment with higher flows the salt wedge is washed away and erosive conditions prevail on the basis of the conditions in which the salt wedge is formed two types of highly stratified estuaries can be identified in the first one a salt wedge regime is established during low river flows whereas during high flows the wedge is washed away and the estuary becomes a river this circulation pattern corresponds to the salt wedge estuary or type 4 of the hansen rattray classification typical of riverdominated estuaries in microtidal seas in the second one a salt wedge is established during high river flows whereas a partially mixed estuary occurs during low flows this pattern corresponds to types 3b and 2b of the hansen rakray classification

extension in the graben systems around the ordos china and its contribution to the extrusion tectonics of south china with respect to gobi mongolia the graben basins around the ordos block are major tectonic features of late cenozoic extension in north china this paper gives a synthetic view of the basic characteristics of the graben basins and of the kinematics of the graben bounding faults this view is based on the available geological data spot imagery analysis field observations and focal mechanisms of earthquakes from this region these graben basins have been grouped into two major systems the yinchuan hetao graben system along the northern and northwestern margins of the ordos and the weihe shanxi graben system along the southern and eastern margins of the ordos crustal deformation along these graben systems involves normal slip on ne sw striking graben bounding faults normal right lateral and normal left lateral slip on nne ssw and wnw ese striking faults respectively this fault pattern is consistent with nw se trending extension the amount and rate of deformation resulting from this extension have been estimated from geological data using a cross sectional area balance and the extensional factor method deduced from the tilt of faulted blocks the results of these estimates show that the uppermost pliocene quaternary extension rate in a nw se direction is in the order of 1 6 mm yr 1 across the weihe graben 0 5 mm yr 1 across the central shanxi graben on the southeastern margin of the ordos block and 3 1 mm yr 1 across the linhe graben on the northwestern margin of the ordos block the extension across these graben systems is accompanied with counterclockwise rotation of continental blocks in north china ordos taihang shan north china plain a kinematic model is proposed in which the late cenozoic extension and block rotation in north china are interpreted as the effect of the eastward termination of the left lateral slip haiyuan fault and kunlun taibai fault system the ordos block rotates counterclockwise as a result of the push of tibet through the left lateral strike slip haiyuan fault and the liupan shan thrust and fold belt the extension along the weihe shanxi graben system may represent the effect of the left lateral slip on the kunlun taibai qinling fault system the rough estimates of the extensional deformation around the ordos block indicate that this contributes to about 5 2 mm yr 1 of left lateral movement in a n125 e direction between south china and gobi mongolia this motion adds to the left lateral slip on the qinling fault zone about 7 2 mm yr 1 in a n90 e direction between the qinling shan and the hua shan north china thus the eastward motion of south china with respect to gobi mongolia is partitioned between normal faulting around the ordos and strike slip faulting in the qinling shan it is estimated to be in the order of 12 4 mm yr 1 in a n105 e direction during the quaternary

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

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

mineralogical and geochemical evidence for coupled bacterial uranium mineralization and hydrocarbon oxidation in the shashagetai deposit nw china unusual mineral structures have recently been found in a sandstone hosted roll type uranium deposit in the middle jurassic zhiluo formation in the shashagetai deposit the northern ordos basin nw china the structures possess a chemical composition and crystal structure characteristic of mineral coffinite usio4 1 x oh 4x which occurs as nanoparticles with size ranging from 5 to 25 nm these structures are interpreted to be fossilized microorganisms based on mineralogical biosignatures including morphology size occurrence of biogenic coffinite as nano crystals and biological elements such as p the intimate intergrowth of coffinite with secondary pyrite of bacterial origin as defined by low 34 s values and calcite cements with petroleum derived carbon supports its biogenic origin oil inclusions in the host sandstone are characterized by abundant n alkanes slightly increased pr nc17 and ph nc18 ratios significant amounts of demethylated hopanes and tricyclic terpanes and the existence of unresolved complex mixtures these characteristics are interpreted to be a result of mixing of an earlier heavily degraded oil with a later charged fresh oil subsequently the oils were slightly degraded these lines of evidence lead to the proposal that the reduction of sulfate and oxidization of petroleum are likely synchronous with reduction of hexavalent u vi to tetravalent u iv uranium by sulfate reducing bacteria srb the discovery of a natural association of microorganism like structures a uranium mineral and biodegraded petroleum has implications for uranium biomineralization and fossil fuel exploration

mobility and immobility of redox sensitive elements in deep sea turbidites during shallow burial during the first few tens of thousands of years after an organic rich turbidite is emplaced on an abyssal plain surficial oxidation of the unit occurs by downwards diffusion of bottom water o2 from work on piston cores it is known that a suite of redox sensitive elements form characteristic relocation peaks in such units around the deepest reaches upper few dm achieved by oxidation fossil oxic post oxic boundaries four individual turbidites now buried at depths of 130 230 m below seafloor mbsf obtained by odp leg 157 drilling on the madeira abyssal plain map have been investigated to determine the effects of burial diagenesis on these geochemical signals over 3 7 my porewater data indicate that post oxic conditions persist to around 130 mbsf on the map below which sulphate reduction predominates all four units have retained high total organic carbon corg contents 1 4 in their lower reaches despite the fact that bottom waters have previously oxidised this same organic matter in the turbidite tops to 0 2 the apparent inertness of the turbidite corg contrasts with the reactivity of organic matter observed in hemipelagic sediment from other odp investigations in all four cases low initial caco3 contents have been quantitatively removed along with corg oxidation with additional dissolution of carbonate by undersaturated bottom waters diagenetic fractions of the elements se cd sb tl and v are present in highly localised peaks and show no evidence of migration in different combinations the elements cu co ni and zn appear to have migrated over short 5 cm distances in thin mm dark coloured sulphide bands probably sourced by reduction of a mn oxyhydroxide host phase during early 70 ky burial two examples of local diagenetic pyritisation up to 20 wt fes2 are observed in the bodies of the two turbidites buried to 130 mbsf confirming that sulphate reduction is active at this level this diagenetic pyrite is associated with high concentrations of as and lesser enrichments of ni zn co se sb and possibly mo

petroleum related origin for uraniferous organic rich nodules of southwestern oklahoma geologic field relations and geochemical analyses imply a petroleum related origin for the organic matter of uraniferous nodules in the permian hennessey group red beds in kiowa county oklahoma the local presence of crude oil in the shallow subsurface and the absence of local occurrences of plant debris suggest a hydrocarbon related origin for these nodules several oil seeps in the general vicinity of the study area indicate that major steep reverse faults near the nodule site may have provided vertical conduits for petroleum migration from deeper zones geochemical analyses of the uraniferous nodules including infrared spectroscopy and elemental analysis reveal characteristics of both coal and petroleum carbon isotopic analyses favor a petroleum related origin a model incorporating field and geochemical evidence is suggested whereby crude oil migrating from depth is initially altered near the surface to a more viscous material concurrently migrating uranium bearing ground water is then stripped of its uranium by the degraded petroleum therefore presence of such nodules in the shallow subsurface may suggest buried petroleum deposits confirmation of this model must await further study of the effects of radiation damage on organic matter

electromagnetic sounding near a large square loop source of current an electromagnetic sounding experiment with a large square loop as source was carried out on the dried up bed of a water reservoir near the town of dharmavaram in andhra pradesh the sounding was performed in both geometric and parametric modes and involved measurements of phase as well as amplitude of the vertical magnetic field inside and outside the loop the six frequency em system used for the experiment was found to be a workable system for electromagnetic sounding the results of the experiment more or less confirm the conclusions from theoretical modeling they also show that even though the earth is not always electrically horizontally layered over a sufficiently large lateral extent for the one dimensional model to be strictly valid it is still possible to apply such modeling to sounding curves taken one part at a time and obtain layer parameters which check qualitatively with the layer parameters obtained from direct current resistivity sounding

biogenic and petroleum related ore forming processes in dongsheng uranium deposit nw china abstract sandstone hosted roll type u deposits has recently been found in the middle jurassic zhiluo formation in the dongsheng area north of the ordos basin in order to assess the origin of the uranium mineralization the host sandstone has been investigated with emphasis on 34s values of ore stage pyrite 13c of calcite fluid inclusion oil biomarkers x ray diffraction icp ms as well as studies by electron microprobe and scanning electron microscope the mineralization consists mainly of coffinite some of the coffinite is intimately intergrown with ore stage pyrite indicating co precipitation ore stage pyrite has 34s values from 34 to 17 suggesting the pyrite sulfur originated from bacterial sulfate reduction in the host sandstone calcite cement exhibits 13c values from 27 6 to 2 1 and fluid inclusion oils show evidence of biodegradation these lines of evidence indicate petroleum was likely oxidized by sulfate reducing bacteria srb and thus supplied a source of some of the carbon in the calcite microbial degradation of petroleum is partially supported by the low temperature diagenetic environment

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

the rhone river plume in unsteady conditions numerical and experimental results surface current maps obtained in the plume of the rhome river by two vhf radars gave rise to comparisons with simulations produced by a primitive equation model two situations were investigated one in steady conditions the other with a variable wind the model gives a good estimation of current direction and velocity not only in the plume itself but also in the surrounding water the model reveals the mechanisms involved in the plume dilution and more generally in the renewal of surface water near the coast when the wind changes direction the sensitivity of the model results to the upper boundary condition for turbulent kinetic energy is also shown

a new model for tabular type uranium deposits tabular type uranium deposits occur as tabular originally subhorizontal bodies entirely within reduced fluvial sandstones of late silurian age or younger this paper proposes that belts of tabular type uranium deposits formed in areas of mixed local and regional ground water discharge shortly after deposition of the host sediments the general characteristics of tabular type uranium deposits especially the most studied deposits those in the uravan mineral belt henry basin and grants uranium region indicate that their essential feature was the formation at a density stratified ground water interface in areas of local and regional ground water discharge reconstruction of the paleohydrogeology is the key to understanding the formation of these deposits gravity driven ground water recharged in major highlands and discharged in lowlands at major concave changes in paleotopographic slope shallow local and deep regional ground water systems were characterized by dilute and saline water respectively typically underlying marine rocks especially evaporites provided the solutes to the deep regional ground water a density stabilized interface existed at the ground water divide between local and regional flow systems tabular type uranium deposits formed where these divides or interfaces intersected pockets of reduction where organic matter accumulated the precipitation of humate and uranium at an interface accounts for the tabular shape and the tendency of deposits to rise stratigraphically into the basin geologic ground water controls that favor discharge such as the pinch out of major aquifers are also favorable for uranium ore the combination of topographic and geologic features that both cause discharge is most favorable for ore deposition

selective crystallization and precipitation of authigenic pyrite during diagenesis in uranium reservoir sandbodies in ordos basin abstract the occurrence characteristics of authigenic pyrite during diagenesis in uranium reservoir sandbodies of zhiluo formation in ordos basin are investigated based on outcrop area investigations and drilled cores observations the pyrite is closely related to carbonaceous debris microscopically the host components for pyrite consist of carbonaceous debris clay minerals biotite the earlier pyrite and ilmenite by emphasizing on 34s values via la icp ms as well as observing through optical microscope and scanning electron microscope equipped with energy dispersive spectroscope three kinds of distribution pattern of pyrite are classified as i periphery ii infilling iii the combined form of the above two in situ micrometer scale sulfur isotope analyses of pyrite demonstrated that broad scale isotopes are heterogeneous from 52 5 to 35 4 of 34s and sulfur is derived from more than a single source significant differences of host components effects on authigenic pyrite formation are discussed the carbonaceous debris can supply the energy for the bacterial sulfate reduction process and the biotite can provide the source of iron for pyrite precipitation the ferrous ion can be adsorbed on the surface of the clay minerals meanwhile the authigenic pyrite is distributed in or around the earlier pyrite and ilmenite by the indirect adsorption of ferrous ion and the ilmenite may also provide the source of iron futhermore the uranium minerals are mainly associated with the authigenic pyrite relevant to carbonaceous debris and clay minerals which indicates there exists constraints of authigenic pyrite during diagenesis on the uranium mineralization

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

the multiple roles of sulfate reducing bacteria and fe ti oxides in the genesis of the bayinwula roll front type uranium deposit erlian basin ne china the bayinwula roll front type uranium deposit is hosted in sandstones of the early cretaceous saihan formation deposited during the postrift stage of the erlian basin in northeast china the present study aims to characterize 1 the roles of sulfate reducing bacteria and 2 the roles of fe ti oxides in the genesis of the bayinwula deposit drill cores of the host sandstone have been investigated with emphasis on petrographic observations whole rock geochemistry and geochemical and or mineralogical study of fe ti oxides iron disulfide uranium minerals emp la icpms and organic matter rock eval pyrolysis the 34 s value has been measured in situ by sims on the different generations of iron disulfide within regional sandstones preore uranium enrichment u mean 30 4 ppm in whole rock was identified on altered fe ti oxides 38 5 of the whole rock u content and constitutes a major source of uranium for the mineralization petrographic observations and rock eval data indicate that organic matter occurring in the host sandstone is mainly inherited from land plants and corresponds to type iii or type iv kerogens organic matter fragments disseminated in sandstones may also contain significant preore uranium concentration framboidal and collomorph ore stage iron disulfides have moderate to high concentrations of as ni and co and have a light sulfur isotope signature characterized by 34 s values from 30 5 to 7 5 suggesting that sulfur originated from bacterial sulfate reduction which was mainly responsible for 1 the liberation of u from fe ti oxides and organic matter 2 the generation of ore stage iron disulfides and 3 the production of a secondary h 2 s rich reducing barrier involved in the reduction of u vi and the precipitation of u iv uranyl and sulfate ions were transported through the host sandstone by low temperature oxygenated groundwater and u iv was precipitated at the redox front as p rich coffinite and ningyoite dominantly as replacement of ore stage iron disulfides which have partly to totally replaced organic matter and fe ti oxides therefore the combined mineralogical geochemical and isotopic characteristics of the bayinwula roll front uranium deposit support the theory that biogenic processes have widely contributed to the genesis of the uranium mineralization

a combined chemical isotopic and microstructural study of pyrite from roll front uranium deposits lake eyre basin south australia abstract the common sulfide mineral pyrite is abundant throughout sedimentary uranium systems at pepegoona pepegoona west and pannikan lake eyre basin south australia combined chemical isotopic and microstructural analysis of pyrite indicates variation in fluid composition sulfur source and precipitation conditions during a protracted mineralization event the results show the significant role played by pyrite as a metal scavenger and monitor of fluid changes in low temperature hydrothermal systems in situ micrometer scale sulfur isotope analyses of pyrite demonstrated broad scale isotopic heterogeneity 34 s 43 9 to 32 4 vcdt indicative of complex multi faceted pyrite evolution and sulfur derived from more than a single source preserved textures support this assertion and indicate a genetic model involving more than one phase of pyrite formation authigenic pyrite underwent prolonged evolution and recrystallization evidenced by a genetic relationship between archetypal framboidal aggregates and pyrite euhedra secondary hydrothermal pyrite commonly displays hyper enrichment of several trace elements mn co ni as se mo sb w and tl in ore bearing horizons hydrothermal fluids of magmatic and meteoric origins supplied metals to the system but the geochemical signature of pyrite suggests a dominantly granitic source and also the influence of mafic rock types irregular variation in 34 s coupled with oscillatory trace element zonation in secondary pyrite is interpreted in terms of continuous variations in fluid composition and cycles of diagenetic recrystallization a late stage oxidizing fluid may have mobilized selenium from pre existing pyrite subsequent restoration of reduced conditions within the aquifer caused ongoing pyrite re crystallization and precipitation of selenium as native selenium these results provide the first qualitative constraints on the formation mechanisms of the uranium deposits at beverley north insights into depositional conditions and sources of both sulfide and uranium mineralization and an improved understanding of pyrite geochemistry can also underpin an effective vector for uranium exploration at beverley north and other sedimentary systems of the lake eyre basin as well as in comparable geological environments elsewhere

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

paleo environmental constraints on uranium mineralization in the ordos basin evidence from the color zoning of u bearing rock series abstract color zoning of strata of mesozoic continental basins in north china is closely correlated with the sedimentary environments of sandstone type uranium deposits systematic research has been conducted on the colors of u bearing rock series within the ordos basin by using data of several ten thousands of drill holes from coal and oil fields taking an ore cluster as the unit well tie sections of deposit areas were compiled to analyze the vertical and lateral spatial variations in different color zones of rocks taking the basin as the unit two typical well tie sections in the central northern basin were compiled in order to summarize the rock color zoning laws of u bearing rock series within ore clusters and the entire basin lithogeochemical characteristics of different color zones in deposit areas and ore barren areas were studied especially variations in trace elements in different color zones and the paleo sedimentary environments they reflect were discussed within the ordos basin from the basin margin to the center and from the u ore clusters to the ore barren areas colors of the zhiluo formation u bearing rock series generally display vertical zoning i e from up downwards red green gray grayish black and show no lateral zoning characteristics u ore beds mostly occur in the lower part of the green zone and the upper part of the gray zone this conclusion differs greatly from the understanding on rock color zoning related to classic interlayer oxidation zone metallogenic theory hence a correct understanding on color zoning of u bearing rock series within the ordos basin is of great significance not only to u mineralization exploration but also to research on sandstone type u mineralization theory

intrusion of rhone river diluted water into the bay of marseille generation processes and impacts on ecosystem functioning the rhone river provides the largest inputs of terrestrial freshwater and nutrients into the mediterranean sea the rhone river diluted water intrusions into the bay of marseille were investigated examining their physical generation processes and associated biogeochemical impact by using in situ observations remote sensing data and a three dimensional physical biogeochemical coupled model during our study period from 2007 to 2011 rhone river intrusions occurred on average 7 6 times per year and affected more frequently the northern part of the bay a classification of intrusion events in three categories is proposed short lived big and small as a function of their duration and spatial extent the intrusions appeared to be driven by i wind forcing ii the presence of a mesoscale eddy iii the rhone river discharge volume and iv the variation in thermocline depth typically a combination of these favorable factors was necessary to induce an intrusion an intrusion strongly impacts the biogeochemical functioning of the bay of marseille by bringing large quantities of nutrients into the bay mass balances were computed allowing us to quantify this impact on the bay of marseille the results show that the ecological impact depends very much on the type of intrusion with big intrusions having the highest impact

age dating of individual grains of uraninite in rocks from electron microprobe analyses it is shown that an electron microprobe analysis of the u th and pb content of a single uraninite uo2 grain may be used to calculate the age of formation of that grain this is known as a chemical age examples are shown for a range of natural samples with a wide range of ages comparison with ages derived from isotopic measurements shows the results to be valid approximate formulae which have been proposed for the calculation of the chemical age are not sufficiently reliable especially where the th content is high and for older ages a method for calculating the age by iteration is presented this uses the full and exact formula and is shown to produce a reliable age for the uraninite compared to isotopic measurements the method is particularly useful for samples where the minerals and mineral textures record information on more than one event two examples of samples recording information on dual ages are discussed to show how these ages can be related to events in the formation of the host rocks in one example an alluvial heavy mineral concentrate is shown to contain uraninites from two distinct sources with significantly different ages in the other example two phases of u mineralisation are distinguished in the same rock sample one phase relates to the genesis of the sediments from which the rock was formed the second phase records remobilisation of the u during later tectonic movement

evidence of uranium biomineralization in sandstone hosted roll front uranium deposits northwestern china we show evidence that the primary uranium minerals uraninite and coffinite from high grade ore samples u3o8 0 3 in the wuyiyi wuyier and wuyisan sandstone hosted roll front uranium deposits xinjiang northwestern china were biogenically precipitated and psuedomorphically replace fungi and bacteria uranium vi which was the sole electron acceptor was likely to have been enzymically reduced post mortem accumulation of uranium may have also occurred through physio chemical interaction between uranium and negatively charged cellular sites and inorganic adsorption or precipitation reactions these results suggest that microorganisms may have played a key role in formation of the sandstone or roll type uranium deposits which are among the most economically significant uranium deposits in the world

precise electron microprobe age determination in altered uraninite consequences on the intrusion age and the metallogenic significance of the kirchberg granite erzgebirge germany an integral method of data evaluation for chemical dating of accessory uraninite by electron microprobe analysis and electron microscopy is proposed the internal structure of uraninite grains the contents of si ca and fe and tests for loss or gain of pb and u are suitable criteria to decide whether or not a given crystal area was affected by secondary alteration the method was applied to uraninite from the kirchberg granite erzgebirge germany and an age of 330 5 ma 2 was constrained this result supports earlier assumptions that there were at least two events of hercynian granite magmatism separated by a time gap of about 40 ma and that the magmatic evolution of the kirchberg granite is not related to the formation of the w mineralisation developed in the endocontact of this granite secondary alteration of uraninite is probably closely related to the formation of u deposits in the vicinity of the kirchberg massif which was extensively mined in the past

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

occurrence of analcime in the middle jurassic coal from the dongsheng coalfield northeastern ordos basin china abstract this paper describes the occurrence of significant authigenic analcime naalsi2o6 h2o in the middle jurassic coal from the northeastern ordos basin and discusses its origin twelve coal samples from borehole zk31 19 in the dongsheng coalfield were collected and analyzed the coals are characterized by a low medium ash yield high volatile matter and low sulfur contents the major element oxides in the studied coals are mostly at similar or much lower concentrations compared to the averages for chinese coals similarly most trace elements are depleted or in concentrations close to the respective averages for world low rank coals based on seredin dai s classification the rey rare earth elements and y in the coal mainly display n and h type distribution patterns with no ce and eu anomalies coal sample zk31 19 12 from the lower zhiluo formation contains analcime up to 23 wt with a high na2o concentration of 1 23 both on a whole coal basis the analcime occurs as lath as subhedral granular crystals in fissures or pores and as anhedral crystals in the organic matrix furthermore significant analcime has also been observed by sem in coal from the upper yan an formation sample zk31 19 10 which mainly occurrs as anhedral crystals no evidence of analcime forming from precursors of volcaniclastic material alkali zeolites or other silicates was detected therefore it is deduced that the analcime in the studied coals formed by authigenic precipitation the na2o content in the studied coal seams displays a vertical variation different from that of the ash yield ad and those of the detrital dominated elements such as sio2 al2o3 tio2 zr nb and th indicating a different origin of na compared with other detrital materials of terrigenous origin combined with the evidence of the obvious na peak in authigenic amorphous material and gypsum mineral by sem it can be inferred that the source of na may derive from the fluids the paleoclimatic change from subtropical warm and humid to semi arid and arid hot during the deposition period of the yan an to the zhiluo formation may provide favorable conditions for analcime authigenesis leading to its abundant precipitation in the lower zhiluo formation and its limited occurrence in the upper yan an formation such paleoclimatic change is also significant for the u mineralization in the lower zhiluo formation

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

genetic models and exploration implication of the paleochannel sandstone type uranium deposits in the erlian basin north china a review and comparative study abstract since the bayanwula uranium deposit was discovered several paleochannel sandstone type uranium deposits have been found in the manite and wulanchabu sub basins of the erlian basin the paleochannel sandstone type uranium deposits in the erlian basin represent important uranium sources in north china the regional geological settings depositional facies and sequences ore bearing sand bodies and uranium source rocks e g granite and sandstones play important roles in the formation of these deposits three styles of paleochannel sandstone type uranium deposits occur in the erlian basin 1 interlayer oxidation style deposit hosted in the braided river sand bodies of the saihan formation and characterized by laterally zoned mineralization 2 phreatic oxidation style deposits hosted in meandering river sand bodies of the saihan formation showing vertically zoned oxidized mineralization 3 superimposed mineralization style deposits hosted in braided river sand bodies of the saihan formation characterized by an oxidized zone from fluvial channel center to margin which was then overprinted by hydrothermal fluids these three styles of the uranium deposits depend on depositional microfacies and development of deep seated faults which can be used to locate the mineralization and exploration targets within the erlian basin

evolution and origins of pyrite in sandstone type uranium deposits northern ordos basin north central china based on micromorphological and compositional analysis abstract pyrite is an abundant mineral throughout the uranium bearing middle jurassic zhiluo formation northern ordos basin three different morphologies of pyrite are identified framboidal euhedral and cement based on textural and geochemical results from optical microscopy secondary electron se and back scattered electron bse imaging energy dispersive spectroscopy eds electron probe microanalysis epma and laser ablation multi collector inductively coupled plasma mass spectrometry la mc icpms three evolutionary models are proposed as follows aggregation of framboids to form polyframboids as a result of the bacterial sulfate reduction bsr processes the formation of cement pyrite under the addition of thermal fluids with numerous framboids and microcrystals inside and euhedral pyrite evolving from framboids the analytical data show that there is a minor increase in major and trace element contents in transformed pyrite and each pyrite morphology has a distinct sulfur isotopic composition 9 9 to 8 0 for framboids 19 1 to 14 2 for polyframboids 18 7 to 20 3 for euhedral pyrite and 15 7 to 21 2 for cement pyrite this indicates that the sulfur was derived from more than one source compared with the original framboids the association between uranium and different types of pyrite indicates that different processes e g bsr and thermogenic sulfate reduction tsr were involved in the precipitation of uranium mineralization and are important to the formation of the precipitation of uranium in the zhiluo formation northern ordos basin

impact of an intrusion by the northern current on the biogeochemistry in the eastern gulf of lion nw mediterranean abstract we present the results from the rhoma2011 leg2 campaign that took place in the eastern gulf of lion from 7 to 17 oct 2011 and combine them with remote sensing observations and results from a 3d coupled hydrodynamic biogeochemical model to study an intrusion event of the northern current nc onto the continental shelf in the gulf of lion nw mediterranean our analysis shows that during the intrusion the previously upwelled nutrient rich water present on the shelf is replaced by warmer and mostly oligotrophic nc water within a matter of 2 3 days this has a marked impact on the local biogeochemistry in the gulf with pre intrusion chl a concentrations in the surface layer of over 0 5 mg m 3 dropping to near the detection limit within less than 72 h the intrusion event leads to a dramatic albeit short lived regime shift in the limiting nutrient for primary production prior to the intrusion most of production on the shelf is nitrogen limited while the intrusion induces a shift to phosphorous limitation the relatively high frequency of occurrence of these intrusions in combination with their impact on the local ecosystem make them primary targets for future study

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

the sandstone hosted beverley uranium deposit lake frome basin south australia mineralogy geochemistry and a time constrained model for its genesis the sandstone hosted beverley uranium deposit is located in terrestrial sediments in the lake frome basin in the north flinders ranges south australia the deposit is 13 km from the u rich mesoproterozoic basement of the mount painter inlier which is being uplifted 100 to 200 m above the basin by neotectonic activity that probably initiated in the early pliocene the mineralization was deposited mainly in organic matter poor miocene lacustrine sands and partly in the underlying reductive strata comprising organic matter rich clays and silts the bulk of the mineralization consists of coffinite and or uraninite nodules growing around co rich pyrite with an s isotope composition 34 s 1 0 0 3 suggestive of an early diagenetic lacustrine origin in contrast authigenic sulfides in the bulk of the sediments have a negative s isotope signature 34 s ranges from 26 2 to 35 5 indicative of an origin via bacterially mediated sulfate reduction minor amounts of zn bearing native copper and native lead also support the presence of specific reducing microenvironments in the ore zone small amounts of carnotite are associated with the coffinite ore and also occur beneath a paleosoil horizon overlying the uranium deposit provenance studies suggest that the host miocene sediments were derived from the reworking of early cretaceous glacial or glaciolacustrine sediments ultimately derived from paleozoic terranes in eastern australia in contrast the overlying pliocene strata were in part derived from the mesoproterozoic basement inlier mass balance and geochemical data confirm that granites of the mount painter domain were the ultimate source of u and ree at beverley u pb dating of coffinite and carnotite suggest that the u mineralization is pliocene 6 7 3 4 ma the suitability of the beverley deposit for efficient mining via in situ leaching and hence its economic value are determined by the nature of the hosting sand unit which provides the permeability and low reactivity required for high fluid flow and low chemical consumption these favorable sedimentologic and geometrical features result from a complex conjunction of factors including deposition in lacustrine shore environment reworking of angular sands of glacial origin deep pliocene weathering and proximity to an active fault exposing extremely u rich rocks

occurrence of microplastics in surface waters of the gulf of lion nw mediterranean sea abstract between 2014 and 2016 a total of 43 microplastic samples were collected at six sampling stations in the eastern section of the gulf of lion located in the northwestern mediterranean sea as well as upstream of the rhone river microplastics were found in every sample with highly variable concentrations and masses concentrations ranged from 6 103 items km 2 to 1 106 items km 2 with an average of 112 103 items km 2 and mass ranged from 0 30 g km 2 to 1018 g km 2 dw mean 61 92 178 03 g km 2 the samples with the highest and lowest microplastic count originate both from the bay of marseille for the bay of marseille it is estimated that the total microplastic load consist of 519 103 101 106 items weighing 0 07 118 kg estimations for daily microplastic transport by the northern current and the rhone river two important hydrologic features of the northwestern mediterranean sea range from 0 18 to 86 46 t and from 0 20 to 21 32 kg respectively particles