an energy dispersive miniprobe multielement analyzer emma for direct analysis of trace elements and chemical age dating of single mineral grains abstract an energy dispersive miniprobe multielement analyzer emma was designed and constructed for the analysis of trace elements as cr cu fe ga ge hf mn ni pb rb se sr th y u zn in small individual mineral grains such as apatite garnet monazite sphene zircon and other accessory minerals the instrument is sensitive ppm for most elements rapid 3 6 min per analysis non destructive and essentially no sample preparation is required with respect to single zircon grains as small as 50 m with mass as low as a few g for example the detection limits for u th and pb are on the order of 10 ppm 5 10 times better than the electron microprobe here the emma is used to illustrate the variation in hf and y concentrations in single zircon grains from pegmatites granites basalts carbonatites and kimberlites also the instrument is used for chemical age dating u th total pb of 1 single zircon grains from the berdyshevsky intrusive complex ukraine and 2 single monazite grains from a small placer deposit within the transition zone between the saxothuringikum and moldanubikum bavaria germany the average age of the single zircon grains from berdyshevsky granite determined using emma 2 19 0 17 ga 1 is consistent with the u pb zircon intrusion age of this complex 2 14 0 07 ga and monazite data ranging from 1 95 to 2 48 ga with respect to the pegmatite from this complex the average age of 1 93 0 09 ga found with emma is geologically consistent with zircon and monazite ages ranging from 1 90 to 2 29 ga regarding the monazite grains from the placer the age dates obtained using emma 328 28 ma are comparable to the isotopic ages conventional u pb and pb pb step leaching which yielded ages of 312 3 and 324 12 ma respectively

early permian peak metamorphism recorded in u pb system of black slates from the ogcheon metamorphic belt south korea and its tectonic implication abstract we report pb pb whole rock and uraninite chemical th u total pb isochron method chime ages of carbonaceous black slates from the ogcheon metamorphic belt south korea the pb isotopic data of whole rock samples yield 207 pb 206 pb ages of 283 33 and 291 13 ma for two outcrops from the northeastern part of the belt the uraninite chime age is estimated at 283 26 and 281 27 ma for the northeastern and the middle part of the belt respectively all of the above ages are identical within error ranges and represent the timing of peak metamorphism after the late precambrian intraplate rifting on the other hand the 207 pb 206 pb whole rock age for the southwestern part of the belt is estimated at 194 27 ma probably representing the timing of contact thermal metamorphism associated with the intrusion of jurassic granitic plutons rb sr isotopic data of the black slates do not define any meaningful isochron the early permian metamorphic age of this study does not support any tectonic scheme in favor of major tectonometamorphism at either the silurian devonian or the triassic time instead it corroborates the probability that the two zones in the ogcheon belt the ogcheon metamorphic belt and the taebaegsan zone were separated from each other before the development of major structural framework in the former our data do not support an idea that the ogcheon belt corresponds to the continuation of the triassic collision belt in east central china

u pb dating of single grain uraninite by isotope dilution thermal ionization mass spectrometry abstract uraninite can be used to measure u pb ages due to its high uranium and low common lead content accurate in situ u pb dating of uraninite by secondary ion mass spectrometry sims or laser ablation inductively coupled plasma mass spectrometry la icp ms requires a matrix matched external standard as a result of the different pb u fractionation behavior in varied matrices however being lack of the suitable uraninite standard in situ u pb dating technique of uraninite is hardly carried out in many laboratories in this paper a method with a detailed analytical procedure is proposed for u pb age determination of single grain uraninite by isotope dilution thermal ionization mass spectrometry id tims this method not only avoids the difficulty of looking for the ideal uranium mineral standards because of no need to make matrix effect calibration but also gives high precision ages with a small amount of sample used

microprobe monazite geochronology understanding geologic processes by integrating composition and chronology abstractmonazite is a light rare earth element lree bearing phosphate mineral that is present in a wide variety of rock types has an extremely variable composition reflecting host rock conditions and is a robust geochronometer that can preserve crystallization ages through a long history of geological events monazite crystals typically contain distinct compositional domains that represent successive generations of monazite which in turn can provide a detailed record of the geologic history of its host rocks the electron microprobe can be used to characterize the geometry of compositional domains analyze the composition of each domain and when carefully configured determine the u th total pb age for domains as small as 5 m in width these data allow the monazite to be linked with and place timing constraints on silicate processes in the host rocks current applications span a broad range of geologic processes in igneous metamorphic hydrothermal and sedimentary rocks

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

depositional environments and tectonic controls on the coal bearing lower to middle jurassic yan an formation southern ordos basin china the ordos basin of north central china is well known for vast energy resources this nonmarine interior basin developed on the north china korean platform following the late triassic indochina orogeny and for a time contained a large freshwater lake prior to being uplifted into its present form at the close of the mesozoic lower to middle jurassic coal occurs in the fluviolacustrine yan9an formation along the southern margin of the basin in the huanglong coalfield in the northeast part of the field the formation ranges from 0 to 180 m in thickness and is divided into five fining upward members each representing a regressive transgressive lacustrine cycle low sulfur high volatile bituminous coal is complexly distributed in the lowest member of the yan9an formation deposition of this member was influenced by two tectonic events that controlled coal occurrence first regional uplifts were produced by the late triassic indochina orogeny and left as highlands on the pre yan9an triassic land surface in the lowest member coal beds thin toward and pinch out against these highlands second syndepositional tectonism of the jurassic through cretaceous yanshan orogeny created a series of northeast trending folds that were topographically expressed as evolving highs and lows swamps and resulting peat accumulation preferentially occupied the subsiding paleodepressions because of the tectonic influence on peat accumulation coal beds thin and merge toward anticlines and thicken and split toward synclines in addition coal quality is documented to be less variable along a northeast trend than along a northwest trend

cerium anomaly and th u fractionation in the 1 85 ga flin flon paleosol clues from ree and u rich accessory minerals and implications for paleoatmospheric reconstruction the 1 85 ga paleosol at flin flon manitoba canada was one of the first paleoweathering profiles taken as evidence for a dramatic rise in the oxygen content of the paleoproterozoic atmosphere diagenesis and greenschist facies metamorphism have modified the abundances of some major elements e g k and fe in the flin flon paleosol inductively coupled plasma mass spectrometry icp ms analyses reveal a positive ce anomaly on both chondrite and amisk basalt normalized ree patterns and marked th u fractionation in the uppermost maroon paleosol the ce anomaly is confirmed by the occurrence of cerianite and by the compositions of other ree and u rich accessory minerals i e secondary monazite and uraninite in the uppermost maroon paleosol th u fractionation is supported by the presence of uraninite in both the paleosol and overlying missi sedimentary rocks chemical ages of uraninite 1 85 to 1 0 ga suggest that this mineral might have formed during weathering or diagenesis but was susceptible to disturbance although igneous monazite and zircon are well preserved in even the uppermost maroon paleosol primary fluorapatite exhibits variable degrees of weathering in the basal green paleosol and has been obliterated completely in the upper maroon paleosol published paleomagnetic data suggest a tropical paleolatitude for the flin flon region at the time of formation of the paleosol the positive ce anomaly in the flin flon paleosol confirms previous studies for an oxic atmosphere p o 2 10 1 5 to 10 2 pal at 1 85 ga however extreme caution must be exercised in the interpretation of th u fractionation in paleosols moreover this study demonstrates the advantage of a detailed characterization of ree and u rich accessory minerals in the application of trace element geochemistry of paleosols for paleoatmospheric reconstruction eh ph diagrams for the stabilities of cerianite and uraninite in their respective systems ce p c h o and up c h o at 25 c and 1 bar reveal the importance of phosphate complexes in the formation of ce anomalies and th u fractionation in both modern and ancient weathering environments

association of gold with uraninite and pyrobitumen in the metavolcanic rock hosted hydrothermal au u mineralisation at rompas perapohja schist belt northern finland the perapohja schist belt comprises a supracrustal sequence of quartzites mafic volcanics and volcaniclastics carbonate rocks black shales mica schists and greywackes which were deposited from ca 2 44 to 1 91 ga during the rifting of the archaean basement in the eastern part of the fennoscandian shield metamorphism and multiple folding of the basin fill took place during the svecofennian orogeny 1 9 1 8 ga followed by intrusions of late orogenic 1 84 1 80 ga and post orogenic granitoids 1 79 1 76 ga the rompas au u mineralisation is hosted by deformed calcsilicate veins in mafic volcanic rocks and locally contains very high grade 10 000 g t au gold pockets with strict spatial association of gold minerals to uraninite and pyrobitumen chemical ages from the unaltered domains in the structure of uraninite indicate a 1 95 1 90 ga age for the deposition of the primary high temperature e g u th 100 in uraninite hydrothermal uranium mineralisation these data are in agreement with the results of previous u pb dating of uraninite by sims textural evidence suggests that metamorphic recrystallisation of the uraninite bearing quartz dolomite veins into calcsilicate mineral assemblages during the svecofennian orogeny 1 9 1 8 ga was followed by a hydrocarbon bearing fluid flow event and radiolytic polymerisation of hydrocarbons around grains of uraninite gold precipitated during a subsequent hydrothermal process in the fractures of uraninite as well as in the cracks and on the botryoidal surfaces of uraninite pyrobitumen nodules remobilisation and redeposition of uranium by these hydrothermal events produced secondary uraninite grains with chemical ages between 1 85 and 1 65 ga native gold is associated with galena altaite hunchunite nickeline and rare cobaltite pb bearing maldonite pyrite pyrrhotite chalcopyrite molybdenite and titanite raman spectra show disordered structure of undeformed pyrobitumen nodules in contrast with the well ordered graphite in calcsilicate veins mean random reflectance data for pyrobitumen indicate 270 340 c maximum temperature of thermal maturation this temperature range is also considered as the temperature of gold deposition results of multiple sulphur isotope analyses of organic material pyrite and acid volatile bound sulphur show distinct ranges of 34s values for sorg and scrs in uraninite pyrobitumen from 6 99 to 3 55 and from 10 02 to 4 41 respectively and uraninite pyrobitumen native gold mineral associations from 1 36 to 6 87 and from 0 42 to 9 7 respectively 33s data indicate local occurrence of nonmass dependent sulphur isotope fractionation owing to interaction of fluids with organic material concentration of lead in uraninite is depleted along the gold mineral filled fractures whereas the uranogenic lead isotope contents of galena altaite and hunchuite deposited in the same fractures are extremely high suggesting that the dominant source of lead for the crystallisation of these minerals was the radiogenic lead content of uraninite taking into account this source of radiogenic lead the calculated pb pb model ages for the lead minerals are between 1 75 and 1 70 ga sulphur and tellurium removal from the fluid by reaction with radiogenic lead released by uraninite appears to be an important mechanism in the strongly localised deposition of gold minerals scavenging of sulphur by pyrobitumen nodules from gold transporting fluids was an additional process triggering precipitation of gold carbon particles and organic functional groups in pyrobitumen probably acted as nucleation and adsorption centres for gold minerals

regional setting geology and paragenesis of the centennial unconformity related uranium deposit athabasca basin saskatchewan canada the centennial unconformity related uranium deposit represents the first significant uranium mineralization along the snowbird tectonic zone in the south central part of the athabasca basin the deposit is associated with a steeply wnw dipping contact between the virgin schist group and mylonitic granite of uncertain age virgin schist group rocks in the deposit area include phyllites impure quartzite and quartzite medium to coarse grained microcline augen porphyroclasts characterize the granite the quartzite being resistant to weathering forms a paleotopographic high flanked by a paleotalus which formed prior to athabasca group sedimentation diabase petrographically and geochemically similar to the 1 27 ga mackenzie dikes intrudes the mineralized trend along brittle structures in the basement rocks and athabasca group a detailed paragenetic study of the deposit area reveals a protracted history that is related to the episodic reactivation of brittle structures and associated fluid movement along this significant structural corridor retrograde metamorphism converted biotite to chamosite at temperatures between 335 to 350 c weathering caused the breakdown of microcline and the dissolution of quartz prior to erosion and deposition of the athabasca group which started at about 1750 ma compaction and diagenesis resulted in quartz overgrowths and development of a diagenetic clay assemblage of illite and sudoite at temperatures between 150 and 200 c which was broadly synchronous with primary mineralization clinochlore euhedral quartz carbonate and pyrite was developed after the intrusion of the diabase under reducing conditions primarily at temperatures between 270 to 320 c uranium remobilization and alteration of uraninite to coffinite appears to have taken place after the emplacement of the diabase dikes kaolinite and uranophane form last in the paragenetic sequence and probably form at relatively low temperatures

the petrology and origin of the tertiary lundy granite bristol channel uk the british tertiary volcanic province btvp comprises within plate central igneous complexes associated with plateau lavas and regional dyke swarms lundy is the southernmost complex of the btvp and comprises granite small tilde90 emplaced into deformed devonian sedimentary rocks within the hercynian cornubian granite province of southwest england the complex is intruded by a northwest southeast trending dyke swarm in common with other btvp igneous complexes lundy is associated with positive gravity and magnetic anomalies which are interpreted in terms of the presena of an underlying basic intrusion at shallow depth with a volume exceeding that of the overlying granite the lundy intrusion is a coarse grained megacrystic granite containing up to 20 alkali feldspar megacrysts in a coarse grained groundmass composed of alkali feldspar quartz lithium bearing muscovite and biotite lithian siderophyllite with a range of aaxssory minerals the main granite has a coarse grained locally miarolitic pegmatitic facies and is intruded by thin sheets and veins of fine grained aplite and microgranite the mineralogy indicates crystallization of the lundy granite from a highly fractionated h2o and halogen rich magma at a relatively shallow crustal level the main lundy granite is a peraluminous leucogranite with na2o 3 4 k2osmall tilde5 low tio2 meo cao zr and sr and high rb and rb sr in comparison with many other peralurninous granites including those from the cornubian batholith and the btvp a new rb sr whole rock isochron for the granite yields an age of 58 7 1 6 ma with an initial 87sr 86sr of 0 715 0 006 nd values for the granite i 0 9 to 1 9 plot between contemporaneous mantle positive nd and cornubian granites nd ca i 11 the trace element data rb y nb show affinities with syn collision and within plate granites as the sr isotope data indicate a major crustal component and the nd isotope data suggest both mantle and crustal components we propose that the lundy granite is derived from a parental magma comprising crustal components derived from a similar source to that of the cornubian granite batholith and a mantle derived component derived from a differentiate of contemporaneous basaltic magma this magma experienced fractional crystallization of plagioclase alkai feldspar fe mg minerals and ree bearing accessory minerals before emplacement and the lundy granite experienced further in situ fractional crystallization associateded with crustal contamination by the devonian shale after emplacement

significance of alteration assemblages for the origin and evolution of the proterozoic nabarlek unconformity related uranium deposit northern territory australia the proterozoic nabarlek unconformity related uranium deposit in the alligator rivers uranium field is hosted by paleoproterozoic amphibolite grade metamorphosed semipelitic sedimentary rocks and amphibolite schist high grade ore is confined to the nabarlek fault a reverse fault shear zone that crosscuts a series of interbedded muscovite quartz biotite schists and amphibolite petrographic studies on polished thin sections combined with electron microprobe analyses x ray diffraction fluid inclusion data o h and u pb isotope values as well as 40 ar 39 ar dating have identified up to eight significant fluid events beginning with the precipitation of early quartz veins during uplift of the myra falls metamorphics at 1830 ma and ending with limited uraninite recrystallization during reactivation of the nabarlek fault between 1380 and 750 ma quartz veins that likely formed toward the end of the top end orogeny represent the earliest recorded fluid event fluid inclusion data and 18 o and d values indicate that these veins formed from basement derived fluids that may have been heated by a cooling nabarlek granite during circulation through reverse faults shear zones the next fluid event represented by fine grained sericite and chlorite occurred when fluids passed into these faults and altered the metamorphic minerals following the exhumation of the basement and deposition of the kombolgie subgroup at ca 1760 ma the intrusion of the oenpelli dolerite at ca 1720 ma resulted in the local remobilization of silica and the precipitation of quartz associated with minor pyrite and dolomite around the reverse faults uranium mineralization is associated with an inner and outer alteration halo that extends as far as 1 km from the nabarlek fault alteration in the outer halo began as early as 1700 ma and is dominated by chlorite and sericite which formed when a 200 c fluid flowed into the nabarlek fault from the overlying kombolgie subgroup u pb and 207 pb 206 pb dating reveals that massive uraninite precipitated at ca 1640 ma and formed together with illite and hematite at ca 200 c chlorite was not coeval with uraninite precipitation stable isotope values indicate that the pre and synore alteration assemblage formed from basinal brines with 18 o fluid and d fluid values of 2 2 and 25 10 per mil respectively reactivation of the nabarlek fault at ca 1360 1100 and 900 ma is indicated by u pb and 207 pb 206 pb dating of uraninite these ages correlate with the intrusion of the maningkorrirr phonolitic dikes and the derim derim dolerite at ca 1316 40 and 1324 4 ma respectively the amalgamation of australia and laurentia during the grenville orogen at ca 1140 ma and the breakup of rodinia between 1000 and 750 ma fluid incursions associated with these events precipitated much of the chlorite that has previously been related to uraninite precipitation drusy quartz veins that host high salinity fluid inclusions and sulfides particularly galena also formed after the initial uraninite forming event finally erosion of the kombolgie subgroup and subsequent weathering of the deposit resulted in the recent formation of kaolinite and numerous secondary uranium minerals these data constrain individual events more precisely than previous studies and thus advance the current genetic model to a level that takes into account the multiple stages of fluid overprinting that occurred over a period of at least 800 m y

analytical perils and progress in electron microprobe trace element analysis applied to geochronology background acquisition interferences and beam irradiation effects electron probe microanalysis epma of accessory minerals such as monazite xenotime and thorite for minor and trace element concentrations and geochronology requires consideration of beam irradiation effects increasing heat and charge as higher current densities and lengthy counting times are employed and requires careful detailed assessment of background intensities and interferences a carbon coat 250 a thickness is generally inadequate for prevention of absorbed current s uctuation and beam damage when using the high current densities applied for high precision e g 200 na focused beam beam irradiation effects include element mobility in monazite resulting in p loss relative to ree coating materials of higher electrical and thermal conductivity are indicated and use of gold 100 a is strongly suggested systematic compositional and therefore age variability can result simply from analytical effects requiring evaluation of all aspects of data acquisition the spectra relevant to measurement of y th pb and u are complex especially in ree bearing minerals acquisition of detailed spectral wavelength scans allows recognition of background and peak interferences as well as curvature background intensities can be extracted directly from scan data by regression x ray mapping allows delineation of domains guiding background acquisition and detailed quantitative analysis minor substitution or s uorescence of unexpected elements can compromise analyses one documented effect being the s uorescence of k in monazite adjacent to or hosted by k feldspar or micas this effect clearly evident within 10 micrometers from k feldspar can result in erroneous u concentrations leading to misinterpretation of rim ages as younger overgrowths absorption edges associated with th also become relevant to the measurement of u at high th concentrations because background intensity is sensitive to variation in average atomic number backgrounds must be acquired from each identi ed domain with particular attention being paid to th variation misapplication of background intensities can result in large age discrepancies for example application of backgrounds obtained from a high th domain in monazite to measurement of a low th domain 1 3 of the amount in the high th domain results in an overestimation of the um background intensity of 0 008 cps na and an overall increase in age of 70 m y

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

identification of discrete low temperature thermal events in polymetamorphic basement rocks using high spatial resolution fe sem edx u th pb dating of uraninite microcrystals

natural uranium in forsmark sweden the solid phase u bearing solid phases from forsmark sweden a proposed host for radioactive waste repositories havebeen identified and characterized elevated dissolved u was found in some groundwater samples d

uraninite from the olympic dam iocg u ag deposit linking textural and compositional variation to temporal evolution the olympic dam iocg u ag deposit south australia the world s largest known uranium u resource contains three main u minerals uraninite coffinite and brannerite four main classes of uraninite have been identified uraninite occurring as single grains is characterized by high pb and ree y rey but based on textures can be classified into three of these classes typically present in the same sample primary uraninite class 1 is smallest 10 50 m displays a cubic euhedral habit and both oscillatory and sectorial zoning zoned uraninite class 2 is coarser sub euhedral and combines different styles of zonation in the same grain cobweb uraninite class 3 is coarser still up to several hundred micrometers has variable hexagonal octagonal morphologies varying degrees of rounding and features rhythmic intergrowths with sulfide minerals in contrast the highest grade u in the deposit is found as micrometer sized grains to aphanitic varieties of uraninite that form larger aggregates up to millimeter and vein fillings massive class 4 and have lower pb and rey but higher ca nanoscale characterization of primary and cobweb uraninite shows these have defect free fluorite structure both contain lattice bound pb rey which for primary uraninite is concentrated within zones and for cobweb uraninite is within high pb rey domains micro fractured low pb rey domains sometimes with different crystal orientation to the high pb rey domains in the same cobweb grain contain nanoscale inclusions of galena cu fe sulfides and rey minerals the observed pb zonation and presence of inclusions indicates solid state trace element mobility during the healing of radiogenic damage and subsequent inclusion nucleation recrystallization during formula 1 driven percolation of cu bearing fluid tetravalent lattice bound radiogenic pb is proposed based on analogous evidence for u bearing zircon calculating the crystal chemical formula to uo2 stoichiometry the sum of cations m is 1 for most classes but the presence of mono di and trivalent elements rey ca etc drive stoichiometry toward hypostoichiometric m o2 x in the absence of measured o and constraints of hypostoichiometric fluorite structure charge balance calculations showing o deficit in the range 0 15 0 36 apfu is compensated by assumption of mixed u oxidation states crystal structural formulas show up to 0 20 apfu pb and 0 25 apfu rey in classes 1 3 while for class 4 these are an order of magnitude less low pb and rey subcategories of classes 2 and 3 are similar to massive uraninite with 0 2 apfu ca other elements si na mn as nb etc show two distinct geochemical trends 1 across classes 1 3 and 2 class 4 whereby low pb rey sub populations of classes 2 and 3 are part of trend 2 for certain elements plots of alteration factor cao sio2 fe2o3 vs pb u suggest two uraninite generations early high pb rey classes 1 3 and late massive class 4 there is evidence of pb loss from diffusion leaching and or recrystallization for classes 2 3 low pb rey domains micro analytical data and petrographic observations reported here including nanoscale characterization of individual uraninite grains support the hypothesis for at least two main uraninite mineralizing events at olympic dam and multiple stages of u dissolution and reprecipitation early crystalline uraninite is only sparsely preserved with the majority of uraninite represented by the massive aphanitic products of post 1590 ma dissolution reprecipitation and possibly addition of uranium into the system coupled dissolution reprecipitation reactions are suggested for early uraninite evolution across classes 1 to 3 the calculated oxidation state u6 u4 u6 of the early and late populations point to different conditions at the time of formation charge compensation for rey rich early fluids rather than auto oxidation of uraninite late uraninites may have formed hydrothermally at lower temperatures t 250 c 1 embed mml math 1 gif

improving u th pb electron microprobe dating using monazite age references abstract this article proposes an improved approach to monazite dating by electron microprobe that includes a monazite age reference correction marc during analysis a set of differing monazite standard reference materials with established isotopic ages are measured at the start of the session these measurements are used to test the analytical set up and if necessary to calculate marc factors that can be applied to monazite samples the marc is not intended as a way to correct systematic errors due to problems in set up but rather as a fine scale adjustment for factors that cannot be readily assessed during single sessions long term multi session calculation of marc factors allows for precise monitoring of anomalous behavior among monazite age reference materials during individual sessions the method can also assist in the identification of chemical inhomogeneity in monazite such as that commonly produced by interaction with metasomatic fluids a representative set of electron microprobe monazite age reference materials are presented including two reference monazites that are good examples of monazite with age disturbance induced by metasomatism additional modifications to analytic protocols are proposed including a corrections for count rate increases during long beam dwell times and b improved estimation of background values at line positions by accounting for the effect of mean atomic number

uraninite recrystallization and pb loss in the oklo and bangombe natural fission reactors gabon abstract the oklo and bangombe natural fossil fission reactors formed ca 2 ga ago in the franceville basin gabon the response of uraninite in the natural reactors to different geological conditions has implications for the disposal of the uo 2 in spent nuclear fuel uraninite and galena from two reactor zones rz16 at oklo and rzb at bangombe were studied to clarify the chronology and effect of alteration events on the reactor zones in addition ion microprobe u pb analysis of zircons from a dolerite dyke in the oklo deposit were completed to better constrain the age of the dyke and thereby testing the link between the dyke and an important alteration event in the reactor zones the analyzed uraninite from rz16 and rzb contains ca 6 wt pbo indicating a substantial loss of radiogenic pb transmission electron microscopy showed that microscopic uraninite grains in the reactor zones consist of mainly defect free nanocrystalline to microcrystalline aggregates however the nanocrystalline regions have elevated si contents and lower pb contents than coarser uraninite crystallites single stage model ages of large millimeter sized galena grains at both rz16 and rzb correlate well with the age of the oklo dolerite dyke 860 39 ma 2 thus the first major pb loss from uraninite occurred at both oklo and bangombe during regional extension and the intrusion of a dyke swarm in the franceville basin 860 890 ma ago uraninite pb isotopes from rz16 and rzb give lower ages of ca 500 ma these ages agree with the chemical ages of the uraninite and show that an ancient pb loss occurred after the intrusion of the dolerite dykes the presence of nanocrystallites in the reactor uraninite indicates internal recrystallization which may have occurred around 500 ma resulting in the 6wt pbo uraninite it is suggested that leaching by fluid interaction triggered by the pan african orogeny was important during this second pb loss event thus there are indications that uraninite at both the oklo and bangombe natural reactors has experienced at least two ancient episodes of pb loss associated with internal recrystallization these recrystallization events have occurred without significantly depleting the 2 ga fission products compatible with the uraninite structure

a three dimensional method for calculating independent chemical u pb and th pb ages of accessory minerals abstract previous theoretical considerations on the chemical u th total pb dating method failed to distinguish between thorogenic and uranogenic lead however it can be shown that the data points are located on a plane in the three dimensional tho2 pbo uo2 space the calculation of the best fit plane yields a slope in the tho2 pbo and uo2 pbo coordinate projections and an initial pbo value from the two slopes th pb and u pb ages can be calculated independently the method described in this paper is applied to monazites from the hercynian g4 granite of the fichtelgebirge germany th pb and u pb ages were calculated at 323 20 ma and 304 15 ma respectively the intercept value close to zero indicates that no significant amounts of common lead are present in the monazites studied

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

carbon disulfide in the north atlantic and pacific oceans carbon disulfide cs2 was determined in surface waters of the north atlantic and pacific oceans the mean concentrations and ranges of cs2 in open ocean waters were 13 4 7 8 26 1 pm s picomol sulfur per liter for the north atlantic and 14 6 7 2 27 5 pm s for the pacific the concentrations in the coastal waters of the north atlantic averaged 26 4 pm s and ranged from 17 9 to 40 4 pm s warm waters generally contained higher levels of cs2 than did cold waters all the study areas were found to be supersaturated in cs2 relative to the atmosphere based on calculations from published cs2 mixing ratios in the marine boundary layer and their henry s law constants sea to air fluxes of cs2 were estimated using exchange velocities for spot and climatological wind speeds the global oceanic flux extrapolated from this study is 0 18 tg cs2 yr 1 and in the range 0 13 0 24 tg cs2 yr 1 it is suggested that microbial processes photochemical reactions and phytoplankton activity are potential sources for oceanic cs2

tracing the palaeoredox conditions at forsmark sweden using uranium mineral geochronology abstract u pb isotope systems have been used to constrain the timing of formation alteration and oxidation of u minerals from the meta granitic bedrock at forsmark eastern sweden secondary ion mass spectrometry sims has been used to collect u pb data from uraninite discordant data suggest a 1 8 ga emplacement of uraninite bearing pegmatites and an event of uraninite alteration at 1 6 ga the latter age is contemporaneous with the gothian orogeny in scandinavia which was associated with hydrothermal fluid circulation in the fennoscandian shield ca uranyl silicates haiweeite and uranophane predominately formed 1 3 1 2 ga contemporaneous with the emplacement of the satakunta complex of the central scandinavian dolerite group a palaeozoic group of ca u vi silicates is also present which indicates that the geochemical composition of geologic fluids was heterogeneous throughout the fracture network during this time low pb concentrations in the u vi silicates of several samples are compatible with a recent

migration of biogenic hydrocarbons into granites a review of hydrocarbons in british plutons abstract the occurrence of hydrocarbons bitumens senso lato in granite plutons and other basement rocks is not per se evidence of an abiogenic origin for the hydrocarbons on the contrary plutons are thermal foci and often highly fractured and therefore are hosts to the migration of fluids from outside the plutons including water and biogenic hydrocarbons hydrocarbons are associated with several british granites in all cases they can be attributed to biogenic sedimentary source rocks the occurrences are particularly related to hydrothermal mineralized veins in granites including the cornish hercynian granites the mountsorrel granodiorite and the weardale granite

uranium enrichment in the lala cu fe deposit kangdian region china a new case of uranium mineralization associated with an iocg system abstract elevated uranium concentrations have been reported in many iocg deposits but detailed information about the occurrences of uranium minerals and their relationships with other minerals remains scarce which hinders understanding of the mineralization mechanisms and the nature of the association of these metals this paper reports a new case of uranium enrichment in an iocg system the lala cu fe deposit in the kangdian region sw china whole rock analyses of ores and barren rocks yielded highly variable u concentrations ranging from 0 76 to 266 ppm uranium shows a strong positive correlation with mo broadly positive correlations with cu and ree and a vague negative correlation with th four uranium minerals uraninite uo2 uranothorite th u sio4 polycrase y ca ce u th ti nb ta 2o6 and coffinite u sio4 1 x oh 4x were identified the uraninite is divided into two phases phase 1 ur1 characterized by corroded or irregular crystal shapes and phase 2 ur2 showing well developed subhedral to euhedral crystal shapes ur1 is interpreted to be formed in the primary cu fe mo ree u mineralization together with the bulk of cu and other metal sulfides as well as other u and ree minerals including uranothorite polycrase bastnasite and xenotime and accompanied by k alteration k feldspar and biotite ur2 is interpreted to be formed in a secondary hydrothermal event characterized by introduction of fluorite and carbonates in which u and mo and to lesser extent cu and ree were remobilized while th remained relatively stable the primary mineralization is inferred to have taken place in a period from ca 1086 to 1053 ma based on previous re os geochronology and the secondary mineralization remobilization likely took place from ca 888 to 828 ma as suggested by uraninite chemical ages obtained in this study and other published geochronological data these ages correspond to tectonomagmatic events taking place in generally extensional environments in the western margin of the yangtze block during the meso to neoproterozoic time the lala cu fe deposit represents a new case of iocg deposits with u and ree enrichment the economic potential of which warrants further examination

the proterozoic albitite hosted valhalla uranium deposit queensland australia a description of the alteration assemblage associated with uranium mineralisation in diamond drill hole v39 the valhalla uranium deposit located 40 km north of mount isa queensland australia is an albitite hosted mesoproterozoic u deposit similar to albitite hosted uranium deposits in the ukraine sweden brazil and guyana uranium mineralisation is hosted by a thick package of interbedded fine grained sandstones arkoses and gritty siltstones that are bound by metabasalts belonging to the ca 1 780 ma eastern creek volcanics in the western succession of the mount isa basin alteration associated with u mineralisation can be divided into an early main and late stage the early stage is dominated by laminated and intensely altered rock comprising albite reibeckite calcite titano magnetite brannerite the main stage of mineralisation is dominated by brecciated and intensely altered rocks that comprise laminated and intensely altered rock cemented by brannerite apatite uranoan zircon uraninite anatase albite reibeckite calcite and hematite the late stage of mineralisation comprises uraninite red hematite dolomite calcite chlorite quartz and pb fe cu sulfides brannerite has u pb and pb pb ages that indicate formation between 1 555 and 1 510 ma with significant pb loss evident at ca 1 200 ma coincident with the assemblage of rodinia the oldest ages of the brannerite overlap with 40ar 39ar ages of 1 533 9 ma and 1 551 7 ma from early and main stage reibeckite and are interpreted to represent the timing of formation of the deposit these ages coincide with the timing of peak metamorphism in the mount isa area during the isan orogeny lithogeochemical assessment of whole rock data that includes mineralised and unmineralised samples from the greater mount isa district reveals that mineralisation involved the removal of k ba and si and the addition of na ca u v zr p sr f and y u th ratios indicate that the ore forming fluid was oxidised whereas the crystal chemistry of apatite and reibeckite within the ore zone suggests that f and text po 3 4 were important ore transporting complexes 18o values of co existing calcite and reibeckite indicate that mineralisation occurred between 340 and 380 c and involved a fluid having 18ofluid values between 6 5 and 8 6 reibeckite d values reveal that the ore fluid had a dfluid value between 98 and 54 the mineral assemblages associated with early and main stages of alteration plus 18ofluid and dfluid values and timing of the u mineralisation are all very similar to those associated with na ca alteration in the eastern succession of the mount isa basin where a magmatic fluid is favoured for this style of alteration however isotopic data from valhalla is also consistent with that from the nearby mount isa cu deposit where a basinal brine is proposed for the transport of metals to the deposit based on the evidence to hand the source fluids could have been derived from either or both the metasediments that underlie the eastern creek volcanics or magmatism that is manifest in the mount isa area as small pegmatite dykes that intruded during the isan orogeny

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

production of 210pb from a slochteren sandstone gas reservoir abstract recently precipitates of metallic pb and galena in gas production facilities have been reported to contain 210 pb in the north sea area u bearing kupferschiefer or carboniferous coal measures have been suggested as a possible source of 210 pb through coproduction of formation water with natural gas 210 pb may enter production facilities together with non radioactive pb and precipitate as metallic pb or galena in this study bituminous sandstones with up to 2 8 wt organic c from a 210 pb producing permian slochteren formation gas reservoir have been found to contain up to 330 ppm u the sandstones show a complex diagenetic history during which migrating oil was trapped in secondary pores continuing enlargement of pore space and the wetting characteristics of the reservoir fluids lead to a preferred distribution of oil rims around quartz grains creating fluid filled voids between the grains syngenetic precipitation of finely grained u oxide occurred along the bitumen fluid boundaries u pb chemical age dating of u oxide grains provides an age of 246 ma for the influx of the oil and the close association of abundant anhydrite with the bitumen impregnations points to a zechstein source for both bitumen and u one of the bituminous sandstones shows a marked depletion of 210 pb with respect to 238 u and 226 ra probably caused by the production of natural gas from the reservoir production started at the end of the 1960s and induced fluid flow throughout the reservoir this enabled transport of 222 rn and its decay product 210 pb away from the u oxide grains the observed u concentrations and permeabilities make the bituminous sandstones in this reservoir probably a more important source of 210 pb than the overlying kupferschiefer or underlying carboniferous coal measures

chime dating of monazite xenotime zircon and polycrase protocol pitfalls and chemical criterion of possibly discordant age data abstract this paper outlines the chime chemical th u total pb isochron method dating method which is based on precise electron microprobe analyses of th u and pb in th and u bearing accessory minerals such as monazite xenotime zircon and polycrase the age mapping technique that is applicable to young monazite and zircon is also described chime dating consists of analyzing multiple spots within homogeneous age domains that show sufficient compositional variation and then these data are used to construct a pseudo isochron from which an age can be obtained via regression this method when coupled with discrimination of possibly concordant age data by chemical criteria such as the ca si th u pb s ratio for monazite and ca and s contents for zircon has the potential advantage of significant precision and the ability to work with minerals that have a significant initial common pb component this technique can identify two or more homogeneous domains that are separated by age gaps smaller than the error on individual spot age analysis many features that are insignificant in major element analysis can have major impact in the acquisition of trace element data critical factors include the roles of collimator slit detector gas background estimation accelerating voltage probe current x ray interferences and count rate in affecting the accuracy and a way to apply the th and u interference correction without pure th and u oxides or synthesized pure thsio4 the age mapping procedure for young monazite and zircon includes acquiring pbm or pbm intensity of individual pixels with multiple spectrometers correcting background with background maps computed from a measured background intensity by the intensity relationships determined in advance of the measurement calibrating of intensity with standards and calculating of ages from the th u and pb concentrations this technique provides age maps that show differences in age domains on the order of 20 ma with in monazite as young as 100 ma the effect of sample damage by irradiation of intense and prolonged probe measurement is also described

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

improved u th total pb dating of zircons by electron microprobe using a simple new background modeling procedure and ca as a chemical criterion of fluid induced u th pb discordance in zircon abstract we present a simple new background modeling method particularly for the determination of trace concentrations of pb u and th to date zircons chemically by electron microprobe this method reduces the acquisition time considerably and at the same time increases the precision of a single pb u and th analysis depending on the analytical conditions theoretical detection limits down to 45 ppm 99 confidence level for u th and pb could be obtained the final precision on age for a single measurement was between 8 and 35 l at pb concentrations between 100 and 200 ppm in proterozoic zircons precise u th and pb analyses however do not necessarily facilitate a straightforward chemical age calculation u th total pb data of zircons from four granites could not be objectively interpreted because of a severe disturbance of the u th pb system however it is shown that chemical ages derived only from zircon areas containing less than 0 2 wt cao agree very well with published conventional radiometric ages of these rocks we propose a model which explains the ca gain and pb loss of zircons which have not undergone any metamorphism after emplacement to be the result of a hydration of radiation damaged zircon domains through low temperature aqueous solutions it is suggested that the ca content can be used independently from u th and pb analyses as a chemical criterion to discriminate between altered zircon domains having suffered a low temperature fluid induced pb loss and non altered zircon domains for which there is a high probability that they will give concordant u th pb ages 2000 elsevier science b v all rights reserved

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

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

fate of trace elements during alteration of uraninite in a hydrothermal vein type u deposit from marshall pass colorado usa alteration of uraninite from a hydrothermal vein type u deposit in marshall pass colorado has been examined by electron microprobe analysis in order to investigate the release and migration of trace elements w as mo zr pb ba ce y ca ti p th fe si al during alteration under both reducing and oxidizing conditions the release of trace elements from uraninite is used to establish constraints on the release of fission product elements from the uo2 in spent nuclear fuels uraninite occurs with two different textures 1 colloform uraninite and 2 fine grained uraninite the colloform uraninite contains 1 04 1 75 wt of wo3 0 16 1 70 wt of as2o3 0 06 0 88 wt of moo3 whereas the fine grained uraninite retains 2 25 4 93 wt of wo3 up to 5 76 wt of moo3 and 0 26 0 60 wt of as2o3 the near constant concentration of incompatible w in the colloform uraninite suggests w incorporation into the uraninite structure or homogeneous distribution of w rich nano domains incorporation of w and mo into the uraninite and subsequent precipitation of uranyl phases bearing these elements are critically important to understanding the release and migration of cs during the corrosion of spent nuclear fuel as there is a strong affinity of cs with w and mo zoning in the colloform texture is attributed to variation in the amount of impurities in uraninite for unaltered zones the calculated amount of oxygen ranges from 2 08 to 2 32 apfu atom per formula unit and defines the stoichiometry as uo2 x and u4o9 whereas for the altered zones of the colloform texture the oxygen content is 2 37 2 48 apfu which is probably due to the inclusion of secondary uranyl phases mainly schoepite the supergene alteration resulted in precipitation of secondary uranyl minerals at the expense of uraninite four stages of colloform uraninite alteration are proposed i formation of an oxidized layer at the rim ii corrosion of the oxidized layer iii precipitation of u6 phases with well defined cleavage and iv fracture of the uraninite surface along the cleavage planes of the u6 phases

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

geochronological constraints on meso and neoarchean regional metamorphism and magmatism in the dharwar craton southern india this contribution addresses the time framework of the regional metamorphism in the three crustal provinces making the archean dharwar craton we present results of texturally controlled in situ epma chemical dating of monazites chemical dating of monazite separates as well as sm nd garnet whole rock isochrons and shrimp u pb zircon ages for pelites amphibolites and granitoids over target areas typical of the various crustal levels of the provinces the western dharwar craton has undergone a major thermal pulse at 2 52 ga followed by slow cooling to ca 2 4 ga and recorded earlier thermal events around 3 0 ga and 3 1 ga the central dharwar craton records a major high grade thermal imprint at ca 2 55 2 51 ga followed by cooling up to 2 45 ga and earlier thermal events at ca 2 62 and 3 20 ga in the eastern dharwar craton the widespread thermal pulse between 2 55 and 2 52 ga is best recorded from 2 52 ga on the entire craton ultimately and contemporaneously undergoes the main event of regional ht lp metamorphism the contrasted thermal records of the three provinces reflect their accretion age s and their degree of involvement in a wide latest archean hot orogen which sets the capacity of these lithospheric segments to be impact by deformation and mantle fluxes the tectonic setting of latest archean hot orogeny is compatible with active plate margin processes having interacted with mantle instabilities i e plumes the tectonic setting of pre 2 5 ga thermal pulses is difficult to assess but considering their systematic links with documented magmatic pulses they may have been generated in contexts comparable that of latest archean hot orogeny where lateral constrictional flow of hot orogenic crust achieves gravity driven flow 3d mass redistribution of viscous lower crust submitted to convergence

newly discovered uranium mineralization at 2 0 ma in the menggongjie granite hosted uranium deposit south china abstract the southeastern part of the nanling metallogenic province south china contains numerous economically important granite hosted hydrothermal vein type uranium deposits the miao ershan mes uranium ore field is one of the most important uranium sources in china hosts the largest chanziping carbonaceous siliceous pelitic rock type uranium deposit and several representative granite hosted uranium deposits the geology and geochemistry of these deposits have been extensively studied however accurate and precise ages for the uranium mineralization are scarce because uranium minerals in these deposits are usually fine grained and may have formed in several stages thus hindering the understanding of the uranium metallogenesis of this province the menggongjie mgj uranium deposit is one of the largest granite hosted uranium deposits in the mes ore field uranium mineralization in this deposit occurs at the central part of the mes granitic complex accompanied with silicification fluorination k metasomatism and hematitization the ore minerals are dominated by uraninite occurring in quartz or fluorite veinlets along fractures in altered granite in situ sims u pb dating on the uraninite yields the u pb isotopic age of 1 9 0 7 ma which is comparable to the chemical u th pbtol uraninite age of 2 3 0 1 ma such ages agree well with the eruption ages of the extension related quaternary volcanics 2 1 1 2 ma in south china suggesting that the uranium mineralization have formed at an extensional setting possibly related to the quaternary volcanic activities therefore our robust new dating results of the mgj uranium deposit make it the youngest granite hosted uranium deposit reported so far in south china and the mineralization event represents a newly identified mineralization epoch