decoupling of o and pb isotope systems of uraninite in the early proterozoic conglomerates in the elliot lake district abstract both isotopic pb and o and chemical compositions were measured by two in situ techniques sims and epma for 20 m diameter areas of over forty eight individual grains of uraninite in the early proterozoic quartz pebble conglomerate uranium deposits in the elliot lake district in order to constrain the origin of uraninite and its post mineralization history together with textural observation by sem pb isotope analyses and chemical compositions of brannerite and uranothorite our data revealed a protracted uranium remobilization history for the uranium deposits in the elliot lake district all grains of uraninite examined show consistently high th contents supporting detrital origin of uraninite derived from pegmatitic rocks the unimodal distribution of th concentration of uraninite excludes the possibility that uraninite formed by multiple pathways where some grains are detrital and some are later diagenetic hydrothermal in origin the measured uraninite grains yield u pb discordia age of 1 8 ga which is much younger than the depositional age of the host huronian basin 2 45 to 2 2 ga this age closely corresponds with the age of peak metamorphism in the huronian basin suggesting that all uraninite grains completely lost its pb during this time the least texturally and chemically altered grains of uraninite yield 18 o smow values of 10 to 22 this range of 18 o value is lower than that expected for uraninite from granitic pegmatitic rocks by 10 it is concluded that the oxygen isotope ratios of uraninite is completely reset during the peak metamorphism and or by interaction with recent meteoric water the 18 o of uraninite however do not show systematic variation with th u pb u and 207 pb 206 pb ratios indicating uraninite exchanged its o isotopes without much disturbance in its chemical composition among the various geochemical signatures in uraninite high th content is the only original signature preserved since detrital deposition of uraninite both pb and o isotope systems have been disturbed in various degrees by later events the coupling decoupling of the composition pb and o isotope systematics of uraninite reflect the protracted mineralization remobilization history of the oldest uraninite

on cyclonic tracks over the eastern mediterranean abstract in this study an updated and extended climatology of cyclonic tracks affecting the eastern mediterranean region is presented in order to better understand the mediterranean climate and its changes this climatology includes intermonthly variations classification of tracks according to their origin domain dynamic and kinematic characteristics and trend analysis the dataset used is the 1962 2001 2 5 2 5 40 yr european centre for medium range weather forecasts ecmwf re analysis era 40 the identification and tracking of the cyclones was performed with the aid of the melbourne university algorithm it was verified that considerable intermonthly variations of track density occur in the eastern mediterranean consistent with previous studies for the entire mediterranean while further interesting new features have been revealed the classification of the tracks according to their origin domain reveals that the vast majority originate within the examined area itself mainly in the cyprus

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

stratigraphy diagenesis and geological evolution of the paleoproterozoic roraima basin guyana links to tectonic events on the amazon craton and assessment for uranium mineralization potential abstract the paleoproterozoic roraima supergroup is a siliciclastic succession exposed in guyana venezuela and brazil that filled the extensive roraima basin on the amazon craton sequence stratigraphy mineral geochemistry and geochronology are integrated to understand the evolution of the basin within the tectonic framework of the amazon craton and fluid flow events to evaluate its uranium resource potential three depositional sequences comprise the roraima supergroup in guyana these are bounded by laterally extensive sequence boundaries marking both fluvial incision and source area uplift followed by aggradation and basin subsidence the roraima supergroup experienced at least three major fluid events following deposition associated with 1 early burial 1820 ma 2 metasomatism during intrusion of the avanavero suite mafic sills 1799 9 ma to 1779 10 ma and 3 late burial diagenesis 1756 5 ma to 1723 10 ma the events are identified based on petrography 207pb 206pb and 40ar 39ar ages of fluorapatite and white mica and the isotopic compositions of h c o and sr in white mica and calcite despite having multiple characteristics indicating that it could host unconformity related u deposits the roraima basin suffered extensive permeability loss during early burial and then with avanavero suite intrusion as a result the probability that high grade unconformity related u deposits formed in the study area is unlikely

measurement of u pb ages of uraninite and davidite by laser ablation hr icp ms laser ablation high resolution inductively coupled plasma mass spectrometry la hr icp ms is a rapid accurate and inexpensive technique for making in situ u pb isotopic measurements of uraninite and davidite the advantages of this method include 1 mineral separation and chemical digestion are not required 2 measurements on complex samples are feasible because significant isobaric interferences can be resolved and 3 accurate u pb and 207pb 206pb dates on 10 25 m spots can be obtained rapidly the la hr icp ms method is applied to u oxide minerals from four deposits and prospects from northern australia and the new dates are compared to previously published conventional thermal ionization mass spectroscopy tims dates and to known ages of geologically important events these comparisons permit us to assess elemental fractionation of u and pb for uraninite and davidite of the new method relative to zircon as well as its geochronological accuracy and precision u pb apparent ages measured previously agree well with our measurements for el sherena palette and mt isa additionally the upper intercept 207pb 206pb dates for adelaide river 701 190 ma 1 and palette 841 94 ma 1 uraninite measured here are similar to those previously obtained for palette 730 ma nabarlek 920 ma and koongarra 870 ma and the upper intercept date for el sherena uraninite 1573 160 ma is within error of that previously determined for ranger 1550 15 and 1472 40 ma such apparent age agreement for uraninite and similarly for davidite indicates that u and pb fractionations are within error of that for zircon whereas the inherent imprecision of our dates and their associated mswd values greater than 2 5 probably indicate that multiple resetting events affected our samples analytically these results demonstrate that the la hr icp ms technique provides excellent spatial resolution while also removing argide phosphide sulfide and halide interferences that can otherwise lead to erroneous data when using quadrupole icp ms geologically the individual 207pb 206pb and upper intercept u pb dates of uraninite from adelaide river and palette are ca 800 ma possibly reflecting recrystallization of uraninite during the break up of rodinia

feldspar diagenesis in the frio formation brazoria county texas gulf coast tremendous quantities of detrital feldspar have been dissolved or albitized below about 14 000 ft 4 267 m in the frio formation oligocene chocolate bayou field brazoria county texas some sandstones no longer contain any unmodified detrital feldspar grains material transfer involved in these reactions is immense affecting at least 15 of the rock volume thus albitization has important implications for several other diagenetic processes that involve feldspars or their components these processes include formation of secondary porosity precipitation of quartz and carbonate cements and the evolution of na ca cl formation water

geomorphic analysis in areas of low rate neotectonic deformation south epirus greece as a case study abstract river morphology and the distribution of river deposits reliably reflect the neotectonic activity of a region in relation to rock resistance and climatic changes geomorphic indices have been used to identify landscape evolution and active faults particularly in areas of high rate tectonic deformation in areas of low rate deformation the influence of neotectonic activity on landscape evolution is less apparent although it is important the aim of this study is to examine the region of south epirus greece a region where the rates of active tectonic processes are low because rock resistance is low and the sediment supply is intense in this region the fault surfaces are either not well preserved or they are covered for the purposes of this paper geomorphic analysis including the drainage basin asymmetry factor the basin hypsometric curve and integral the valley floor width to height ratio longitudinal river profiles the stream length gradient index normalized by the graded river gradient and the mountain front sinuosity index was used to evaluate neotectonic activity and to identify covered potentially active faults in places where fault surfaces could be observed geological mapping and tectonic analysis were applied to determine the fault characteristics the first result of this work is that important active or potentially active faults extend for a significant distance into the alluvial plains of south epirus in this case study we considered that geomorphic indices constitute a valuable tool for identifying neotectonic activity in regions of low rate deformation furthermore geomorphic analysis reveals the location of covered fault structures contributes to evaluating fault capability and therefore to estimating seismotectonic hazard

geochronology of unconformity related uranium deposits in the athabasca basin saskatchewan canada and their integration in the evolution of the basin the importance of geochronology in the study of mineral deposits in general and of unconformity type uranium deposits in particular resides in the possibility to situate the critical ore related processes in the context of the evolution of the physical and chemical conditions in the studied area the present paper gives the results of laser step heating 40ar 39ar dating of metamorphic host rock minerals pre ore and syn ore alteration clay minerals and laser ablation inductively coupled plasma mass spectrometer la icp ms u pb dating of uraninite from a number of basement and sediment hosted unconformity related deposits in the athabasca basin canada post peak metamorphic cooling during the trans hudson orogen of rocks from the basement occurred at ca 1 750 ma and gives a maximum age for the formation of the overlying athabasca basin pre ore alteration occurred simultaneously in both basement and sandstone hosted mineralizations at ca 1 675 ma as indicated by the 40ar 39ar dating of pre ore alteration illite and chlorite the uranium mineralization age is ca 1 590 ma given by la icp ms u pb dating of uraninite and 40ar 39ar dating of syn ore illite and is the same throughout the basin and in both basement and sandstone hosted deposits the mineralization event older than previously proposed as well as several fluid circulation events that subsequently affected all minerals studied probably correspond to far field continent wide tectonic events such as the metamorphic events in wyoming and the mazatzal orogeny ca 1 6 to 1 5 ga the berthoud orogeny ca 1 4 ga the emplacement of the mckenzie mafic dyke swarms ca 1 27 ga the grenville orogeny ca 1 15 to 1 ga and the assemblage and break up of rodinia ca 1 to 0 85 ga the results of the present work underline the importance of basin evolution between ca 1 75 ga basin formation and ca 1 59 ga ore deposition for understanding the conditions necessary for the formation of unconformity type uranium deposits

diagenesis of the aphebian mistassini regolith quebec canada abstract a well developed regolith is preserved beneath early proterozoic aphebian rocks of the otish and mistassini groups in central quebec canada the regolith is covered by fluviatile clastic rocks otish group in the north and by a thick sequence of stromatolitic and sandy dolomite mistassini group in the south where preserved beneath clastic rocks the regolith exhibits the structures and textures of its crystalline parent rocks tonalite gneiss and amphibolite despite the alteration of feldspars to clay minerals and the partial oxidation of biotite a later event recrystallized the clay minerals to muscovite while conserving the original outline of the feldspars beneath the dolomite the regolith was largely replaced by dolomite but retains many original textures dolomite replaced first the clay minerals then quartz and unaltered feldspars and finally biotite repeated crustifications of dolomite with intervals of chert and minor anthraxolite surround unaltered blocks of crystalline rock within the regolith profile and similar complex veins fill many master joints these veins are identical in composition to vug fillings throughout the overlying carbonate formations clasts of partly dolomitized regolith included in non dolomitic sands filling channels and scours dug deep into the profile suggest that dolomitization commenced very early possibly related to a sabkha environment developed during the transgression

40ar 39ar geochronology of the eocene green river formation wyoming the deposits of eocene lake gosiute that constitute the green river formation of wyoming contain numerous tuff beds that represent isochronous correlatable stratigraphic markers tuff beds selected for 40ar 39ar analysis occur within laminated mudstone are matrix supported and lack evidence of reworking these tuffs contain 2 15 euhedral phenocrysts of quartz plagioclase sanidine biotite and minor amphibole pyroxene and zircon encased in a matrix of altered glassy ash air abrasion and handpicking under refractive index oils were required to obtain clean unaltered phenocrysts of sanidine 40ar 39ar age determinations from single crystal and 1 mg multigrain aliquots of sanidine and biotite allowed the identification and exclusion of xenocrystic contamination laser fusion experiments on phenocrysts from the rife firehole c bed grey main sixth and analcite tuff beds from the tipton wilkins peak and laney members yielded weighted mean ages 2 analytical uncertainties of 51 25 0 31 ma 50 70 0 14 ma 50 56 0 26 ma 50 39 0 13 ma 49 96 0 08 ma 49 70 0 10 ma and 48 94 0 12 ma respectively ages for sanidine and biotite from the main tuff are indistinguishable when presumably xenocrystic contaminants are excluded from the age calculation moreover the 40ar 39ar ages are consistent with the stratigraphic order of the tuff beds and with provenance in the absaroka and challis volcanic fields our 40ar 39ar based age model indicates that sediment accumulated three times more rapidly 327 86 m yr during the evaporative wilkins peak phase than the freshwater to saline tipton 88 34 m yr and laney 104 18 m yr phases the much lower accumulation rates for the tipton and laney members are permissive of an annual origin for 1 mm thick laminae and precessional forcing of 1 3 m thick depositional cycles in these units however previously described cycles in the wilkins peak member have average durations that are significantly shorter than the 19 23 k y precessional modes the green river formation encompasses an 5 m y period between ca 53 5 and 48 5 ma spanning magnetic chrons 24n through 21r the green river formation was therefore deposited during the warmest period of the cenozoic corresponding to the early eocene climatic optimum as defined by the global marine o isotope record deposition of bedded evaporites trona of the wilkins peak member began at ca 51 ma or 2 m y after the onset of the highest inferred temperatures of the climatic optimum the bridgerian wasatchian faunal turnover occurred subsequently during wilkins peak time at ca 50 6 ma thus our 40ar 39ar ages strongly suggest that wilkins peak evaporite deposition and the turnover from wasatchian to bridgerian fauna were not directly caused by the initiation of maximum greenhouse conditions

a review of the superior province of the canadian shield a product of archean accretion abstract the superior province consists of northern and southern high grade gneiss subprovinces and a central region of alternating granite greenstone and metasedimentary belts subprovinces are commonly fault bounded and display contrasting lithological assemblages metamorphic and structural styles geophysical characteristics and ages they are comparable to phanerozoic suspect terranes the middle and late archean rocks of the superior province are of mantle and juvenile crustal origin with little evidence of inheritance of components older than ca 3 1 ga high grade gneiss subprovinces are mainly deeper level equivalents of the supracrustal rich belts but one minnesota river valley is part of an older ca 3 6 ga terrane that was juxtaposed late in the tectonic history granite greenstone terranes are characterized by low grade volcano sedimentary sequences tholeiitic komatiitic submarine lava plain tholeiitic calc alkalic submarine to subaerial central complexes early platform type quartz arenite stromatolitic carbonate late timiskaming type shoshonitic alkalic volcanic fluvial sediment that range in age from ca 3 0 ga to 2 7 ga the volcanics represent oceanic island arc and continental arc volcanism the quartz arenite carbonate sequences deposition on relatively stable early formed ca 3 0 ga crust and the timiskaming type sequences deposition in pull apart basins developed along strike slip faults late archean ca 2 75 2 70 ga greenstone sequences occur throughout the superior province middle archean ca 3 0 2 8 ga sequences are common in northern and central superior province rare or absent in the south volcanism was accompanied by mafic to trondhjemitic plutonism the metasedimentary belts consist of variably metamorphosed volcanogenic turbidites with detrital zircons ranging in age from ca 3 0 ga to 2 7 ga the metasediments were deposited after major volcanism and probably represent accretionary prisms late archean orogenesis accompanied and followed by calc alkalic plutonism youngs southward from about 2 73 2 72 ga to 2 70 2 68 ga it involved large scale north south compression and dextral transpression and displays thin to thick skinned transitions the contemporaneity of events along the lengths of the belts and their southward younging coupled with the evidence of major compression are consistent with subduction driven oblique accretion of oceanic and continental volcanic arcs accretionary sedimentary wedges older microcontinental fragments etc in a convergent margin setting analogous to parts of the pacific rim differences eg abundance of komatiites and tonalitic plutonic suites are attributable to a hotter archean mantle

a basin system and fluid flow analysis of the zn pb ag mount isa type deposits of northern australia identifying metal source basinal brine reservoirs times of fluid expulsion and organic matter reactions paleoproterozoic rocks of northern australia host one of the world s largest base metal repositories and are the world s most important zinc repository the mcarthur mount isa cloncurry mineral belt contains several world class zn pb ag u cu and cu au deposits ewers and fergusson 1980 williams 1998 betts et al 2003 large et al 2005 fig 1 the province has the potential to host additional base metal and uranium reserves advances in exploration techniques in the 1980s led to the discovery of several major new zn and cu au deposits including cannington century ernest henry and osborne however recent exploration results have been disappointing and new exploration strategies are required if the region is to further its growth potential and if new resources are to be realized beneath shallow cover fig 1 map of northeastern australia showing the principal tectonostratigraphic subdivisions for the region the map highlights the areas of study covered by the thematic papers in this volume and the location of the principal zn pb ag cu and cu au deposits the locations of profiles p1 and p2 the comalco seismic grid and deep boreholes including desert creek 1 are shown in the inset map bottom left between 1975 to 1995 geoscientists from geoscience australia the geological survey of queensland and the northern territory geological survey mapped the paleoproterozoic outcrop belt of northern australia at a scale of 1 100 000 subsequently researchers at monash university undertook detailed studies of the deformation history of the mount isa block placing the ore deposits within a tectonic context e g o dea et al 1997 betts et al 1998 2003 betts and lister 2002 researchers at james cook university carried out structural metamorphic and mineralization studies across the mount isa block with their principal focus concentrating on the deposits and their immediate environs bell et al 1988

world wide delivery of river sediment to the oceans new data and new estimates from old data show that rivers with large sediment loads annual discharges greater than about 15 times 10 6 tons contribute about 7 times 10 9 tons of suspended sediment to the ocean yearly extrapolating available data for all drainage basins the total suspended sediment delivered by all rivers to the oceans is about 13 5 times 10 9 tons annually bedload and flood discharges may account for an additional 1 2 times 10 9 tons about 70 of this total is derived from southern asia and the larger islands in the pacific and indian oceans where sediment yields are much greater than for other drainage basins

petrogenesis of the proterozoic athabasca basin northern saskatchewan canada and its relation to diagenesis hydrothermal uranium mineralization and paleohydrogeology abstract in the athabasca basin proterozoic sandstones unconformably overlie archean and aphebian rocks multiple fluid events involving isotopically and chemically distinct fluids which have migrated laterally for considerable distances and along fault zones have produced a paragenetically identifiable assemblage of clay silicate and oxide minerals in the basin and basement rocks altered sandstones and the underlying metasedimentary rocks proximal to fault zones host high grade u ni co unconformity type uranium ore deposits and contain an alteration assemblage of highly crystalline 2m 3t illite 1m kaolinite clinochlore and sudoite hematite dravite and euhedral quartz in the sandstones 18o values of coeval quartz hematite quartz illite quartz dravite illite hematite and kaolinite hematite fluid inclusion temperatures in diagenetic quartz and d values of 1m kaolinite 2m 3t illite dravite and in fluid inclusions in the quartz indicate formation from a basinal fluid that had d values of 60 10 and which underwent salinity temperature and 18o increases from 5 to 34 wt nacl 120 to 240 c and 5 to 3 respectively as a result of increasing burial depth and sustained water rock interactions with the basinal sediments over substantial time periods 18 o 16 o and d h ratios of sudoite and clinochlore in meta sedimentary basement rocks within the alteration haloes indicate formation from a basement derived fluid with 18o and d values of 4 4 and 30 10 respectively that was isotopically distinct from the basinal fluids 18o and d values of late kaolinites in reactivated fault zones indicate formation mainly from low temperature 50 25 c fluids having 18o and d values of 16 and 130 respectively similar to relatively modern meteoric waters in the area some kaolinites have 18o and d values which suggest they formed from meteoric waters at mid latitudes and have experienced varying degrees of oxygen and hydrogen isotope exchange with relatively modern meteoric waters in the re activated faults illite sudoite and dravite have d values that vary by 100 without concurrent changes to their 18o values indicating preferential hydrogen isotope exchange with relatively modern meteoric waters at low temperatures and under conditions of high integrated water rock ratios rb sr isochron and model ages of 1477 57 and 952 ma respectively for the crystalline 2m 3t illites indicate the timing of the high temperature basinal fluid events associated with fluid mixing rb sr and k ar ages on illites with the lowest d values are as young as 300 ma and indicate late stage resetting of their radiogenic isotope systematics as a result of substantial interactions with relatively modern meteoric waters the evolution of sr isotopic compositions of fluids in the basin and basement rocks as reflected by the 87 sr 86 sr ratios of chlorite illite and dravite indicates that mixing of two isotopically distinct fluids in the vicinity of faults was the process by which uranium was precipitated similar to that suggested by oxygen and hydrogen isotope systematics in the clays and silicate minerals nd ratios in the high temperature diagenetic and hydrothermal clay and silicate minerals and the cogenetic uranium ores suggest they all have formed from similar fluids which have interacted substantially with the basin sediments in general the isotopic chemical microthermometric and petrologic data indicate that the athabasca basin has had a protracted fluid history comparable to that documented for more modern sedimentary basins the data clearly show that the major sandstone aquifers have been affected by widespread lateral flow of diagenetic fluids over distances of hundreds of kilometers and also that these fluid migration paths have been modified by cross formational fluid flow near active fault zones

basin evolution and unconformity related uranium mineralization the camie river u prospect paleoproterozoic otish basin quebec the paleoproterozoic otish basin quebec hosts several uranium prospects that until recently remained underexplored and poorly understood in this study the camie river u prospect which shows similar charac teristics to high grade unconformity related u deposits is the focus of an integrated basin analysis in the western otish basin conglomerate and sandstone of the indicator formation which were deposited in at least six depositional sequences were affected by insignificant early diagenetic compaction and cementation this allowed the for mation of regional peak diagenetic aquifers which became muscovite altered due to interaction with fluids having 18 o and 2h values similar to those of seawater influenced basinal brines at 250 c u mineralization at camie river occurred at 1721 20 ma based on a 207 pb 206 pb date obtained by laser ablation of uraninite which coincides with a phase of the otish gabbro intrusion that has been dated at ca 1730 ma the intrusive event promoted circulation of u bearing basinal brines triggering u mineralization at several locations in the western otish basin interaction of basinal brines with the otish gabbro produced coarse grained chlorite tourmaline and phengitic muscovite which decreased the fluid conducting capabilities of diagenetic aquifers and resulted in fault zone and fracture dominated fluid flow subsequent fluid alteration events produced limited u remobilization sulfides sudoite and siderite between ca 1670 and 1410 ma based on mineral paragenesis and 40 ar 39 ar dates of muscovite metamorphic fluids having high 18 o values and temperatures around 300 c accompanied 1 2 to 1 0 ga grenville orogene sis and subgreenschist grade metamorphism in the otish basin but were present at low water rock ratios at camie river and therefore produced little alteration post grenville uplift of the otish basin likely produced late low temperature alteration minerals that have been influenced by recent meteoric water suggesting that the fault zones and fractures the minerals occupy remain as preferential fluid flow pathways to the present day radiogenic pb and the characteristic trace elements mo w nb have also preferentially dispersed from the mineralization along fault zones fractures and depositional sequence boundaries and can be used to explore for camie river style u mineralization

geomorphic controls on andean denudation rates abstract to predict erosion rates throughout the andes we conducted a multiple regression analysis of the sediment discharge from 47 drainage basins in the bolivian andes and various topographic climatologic and geologic parameters these mountainous basins are typically large 17 81 000 km2 documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage pifont usepackage stmaryrd usepackage textcomp usepackage portland xspace usepackage amsmath amsxtra usepackage ot2 ot1 fontenc newcommand cyr renewcommand rmdefault wncyr renewcommand sfdefault wncyss renewcommand encodingdefault ot2 normalfont selectfont declaretextfontcommand textcyr cyr pagestyle empty declaremathsizes 10 9 7 6 begin document landscape mathrm mean 11 000 end document km2 often have decades of measurement data on daily water and sediment discharge and display an extraordinary range of denudation 0 01 6 9 mm yr

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

chloritization of the hydrothermally altered bedrock at the igarape bahia gold deposit carajas brazil the igarape bahia gold deposit has developed from weathering of a near vertical hydrothermal cu au mineralization zone the unweathered bedrock composed of chlorite schists is mainly metamorphosed basalts pyroclastic and clastic sedimentary rocks and iron formation contents and fe fe mg ratios of chlorites increase from distal country rock towards the mineralization zone which can be attributed to different water rock ratios and locations in a hydrothermal system in the hydrothermal system high salinity fluids convected through basin floor rocks stripping metals from the recharge zones with precipitation in discharge zones the chlorite with lower fe fe mg ratios indicates alteration by relatively unreacted mg rich fluids occurring within recharge zones by contrast the chlorite with higher fe fe mg ratios in the mineralization zone formed from solutions rich in fe mn au cu h2s and sio2 within a discharge zone the iron formation could also be formed within the discharge zone or on the basin floor from the fe rich fluids the distal country rock with less chlorite content is a hydrothermal product at low water rock ratios whereas the proximal country rock and the host rock with more chlorite content formed at high water rock ratio conditions the al iv contents of chlorites indicate that the formation temperatures of these rocks range from 204 to 266 c with temperatures slightly increasing from distal country rock towards the mineralization zone

porosity reduction in sandstone by quartz overgrowth a mathematical model for predicting porosity histories due to quartz overgrowth in quartz rich sandstone reservoirs has been developed the model neglects secondary dissolution porosity and other diagenetic processes such as compaction and precipitation of carbonate and clay minerals nevertheless the model is straightforward and easy to use to calculate porosity the calculated porosity corresponds to measured porosity of simple quartz cemented sandstones in 27 wells in north and south america the model is based on fluid flow through initially porous unlithified sands in which the fluid phase is saturated with si oh 4 and is always in equilibrium with quartz as the continuously circulating fluid migrates updip toward the basin edge it cools and quartz precipitates into the pore spaces causing a loss of porosity basinal fluid velocities may be calculated assuming 1 thermal convection and 2 hydrostatic pressure due to recharge at the edge of the basin porosity diagrams relating porosity to geothermal gradient burial rate and depth of burial are compared to thermal maturation models of source rocks fluid flow history and grain size distribution the rate of porosity reduction depends on the following variables in decreasing order of significance buria rate age initial porosity basin size dip angle fluid dynamics initial permeability and geothermal gradient

the sediment delivery problem abstract the linking of on site rates of erosion and soil loss within a drainage basin to the sediment yield at the basin outlet and improved knowledge and representation of the associated processes of sediment delivery represent a major research need within the field of erosion and sedimentation and also an important scale problem in drainage basin studies this paper reviews the limitations of the sediment delivery ratio concept by considering the problems of temporal and spatial lumping and its blackbox nature some recent advances in our understanding of the sediment delivery system and its modelling are described and the lack of detailed empirical investigations is highlighted the significance of recent concern for the role of sediments in the transport of nutrients and contaminants to sediment delivery studies is introduced and the need for further work in this field is emphasised

the tectonic significance of some basic dyke swarms in the canadian superior province with special reference to the geochemistry and paleomagnetism of the mistassini swarm quebec canada the mistassini dykes extend northwest from the mistassini embayment and comprise both tholeiitic and komatiitic suites they are probably 2000 ma old and yield two major paleomagnetic components one of these with a pole at 131 w 13 s is thought to be an overprint related to the elsonian disturbance 1400 1500 ma ago a very steeply down and reversed component may be primary and has a pole at 080 w 50 n these spacial chemical and age relationships between the mistassini molson marathon and payne river dyke swarms and the aphebian supracrustal fold belts on the perimeter of the superior province suggest a genetic relationship between the dyke swarms and the fold belts the supracrustal belts are evidence of the opening and closing of oceans and the dyke swarms are evidence of early stage failed arms related to these openings more rarely for example the payne river dykes early stage dyke swarms are developed and preserved parallel to the edges of newly developed spreading plate boundaries

geomorphic tectonic control of sediment discharge to the ocean the importance of small mountainous rivers analysis of data from 280 rivers discharging to the ocean indicates that sediment loads yields are a log linear function of basin area and maximum elevation of the river basin other factors controlling sediment discharge e g climate runoff appear to have secondary importance a notable exception is the influence of human activity climate and geology on the rivers draining southern asia and oceania sediment fluxes from small mountainous rivers many of which discharge directly onto active margins e g western south and north america and most high standing oceanic islands have been greatly underestimated in previous global sediment budgets perhaps by as much as a factor of three in contrast sediment fluxes to the ocean from large rivers nearly all of which discharge onto passive margins or marginal seas have been overestimated as some of the sediment load is subaerially sequestered in subsiding deltas before the proliferation of dam construction in the latter half of this century rivers

uplift and active tectonics of southern albania inferred from incision of alluvial terraces abstract in albania the osum and vjoje rivers cross the active graben system and the active frontal thrust system of the albanides the effects of climatic and geodynamic forcing on the development of these two rivers were investigated by the means of field mapping topographic surveying and absolute exposure age dating we established the chronology of terraces abandonment from the compilation of new dating 14c and in situ produced 10be and previously published data we identified nine fluvial terraces units developed since marine isotope stage 6 up to historic times from this reconstituted history we quantified the vertical uplift on a time scale shorter than the glacial climatic cycle regional bulging produces an overall increase of the incision rate from the west to the east that reaches a maximum value of 2 8 m ka in the hinterland local pulses of incision are generated by activation of normal faults the most active faults have a sw ne trend and a vertical slip rate ranging from 1 8 to 2 2 m ka this study outlines the geodynamic control in the development of rivers flowing through the albanides on the scale of 103 105ka

oxygen isotope studies of diagenesis and pore water evolution in the western canada sedimentary basin evidence from the upper cretaceous basal belly river sandstone alberta abstract the oxygen isotope compositions and paragenetic sequence of diagenetic minerals from the upper cretaceous basal belly river sandstone southwestern alberta have been used to identify changes in pore water composition during diagenesis these changes can be related to major geologic events within the western canada sedimentary basin low 18o meteoric water has played an important role in the diagenesis of these upper cretaceous rocks on a basinwide scale during deposition and early diagenesis and following uplift of the basin in early eocene time diagenetic phases include early chlorite 18o 6 1 to 8 3 and calcite 18osmow 21 0 13cpdb 1 6 followed by quartz overgrowths 18o 13 1 to 18 0 calcite 18osmow 10 4 to 14 4 13cpdb 10 6 to 1 2 and then kaolinite 18o 7 8 to 11 9 illite smectite 18o 10 9 to 13 1 and smectite 18o 12 6 to 13 7 the interpretation of these results is that shallow diagenesis early in the burial history chlorite calcite occurred in the presence of brackish or fresh water with burial the 18o value of the pore water increased due to water rock interaction burial diagenesis was terminated in the early eocene by uplift laramide orogeny recharge of the basin by low 18o meteoric water occurred at this time the meteoric water then became involved in the formation of diagenetic quartz and calcite at or near maximum burial temperatures and in the crystallization at lower temperatures of kaolinite illite smectite and smectite as post eocene cooling and erosion progressed

models for sediment yield in mountainous greek catchments abstract in this study we explore the controls over suspended sediment yield in 11 stations situated along six major rivers of western northern greece arachthos achelooos evinos aoos kalamas and aliakmon values of area specific sediment yield for these stations come from reanalysis of existing records by adaptation of the broken rating curve concept and range from 140 to 2300 t km 2 y 1 we investigate the correlations among suspended sediment yield values and many geomorphic topographic morphometric textural tectonic geological lithological and climatic precipitation runoff characteristics of the corresponding basins along with land cover variables and rusle factors ls r k and c rusle from maps of the european soil data center we find the principal controls to be slope and lithology followed by precipitation runoff and landslide frequency factors such as ground cover percentage of barren land within the basin and alluviation of the river have also some relevance with the use of stepwise multiple regression analysis we build a model that employs three variables slope in percent precipitation mean annual in mm and lithology as percentage of the easily erodible geological formations within the catchment where the contribution of lithology is an additive term to the slope precipitation power relationship the proposed model achieves good statistics nse 0 84 from the other models tested with our data set bqart performs well while rusle2015 of the esdc performs poorly

the transition from dyke to sill in the otish mountains quebec relations to host rock characteristics the otish gabbro sills intrude aphebian clastic rocks lying uncanformably on the archean rocks of the superior province close to its juncture with the grenville province the sills are undated but by inference may be ca 1750 ma two dyke swarms are known in the vicinity the 1950 ma northwest trending mistassini dykes and a northeast trending swarm of unknown age extending 600 km from senneterre to the otish mountains and possibly another 300 km to the northeast the trends of feeder dykes to the otish sills are physically compatible with the dominant northeast dykes which are therefore considered to be the feeders and should be called the otish dykes the otish sills appear to be a unique occurrence along the 900 km dyke trend possibly but not entirely because of the chances of preservation the general form of the otish sill complex is a triangle bounded on the north by the east west lip of the sedimentary basin on the southwest by a northwest trending otish feeder dyke and on the southeast by the

stable isotope geochemistry of alteration associated with the key lake uranium deposit canada the key lake uranium deposit occurs within a shear zone that intersects the unconformity between early proterozoic basement gneiss and overlying middle proterozoic athabasca group sandstone uranium is concentrated near the unconformity and is associated with intense illite chlorite and kaolinite alteration the delta d and delta 18 o values of the clay minerals suggest that several different fluids have affected the ores and surrounding host rocks alteration of the basement gneisses associated with the uranium mineralization consists mainly of mg chlorite that equilibrated about 200 degrees c with a fluid having a delta d value near 20 per mil and a delta 18 o value near 5 per mil an illite rich sandstone alteration halo preserved only locally above the deposit equilibrated about 200 degrees c with a basinal brine having a delta d value near 65 per mil and a delta 18 o value near 5 per mil the uranium was concentrated near the unconformity by the mixing of these two distinct fluids the delta 18 o values of coexisting quartz and illite sampled from the shear zone hosting the uranium mineralization yield equilibration temperatures of 190 degrees to 230 degrees c which is postulated to be the temperature of the ore forming event fracturing in the sandstone above the deposit controlled late low temperature 50 degrees c kaolinitization of preexisting hydrothermal illite and chlorite by meteoric waters having delta d values of 50 or 30 per mil and delta 18 o values of 7 or 3 per mil the youngest event to affect the key lake deposit is related to the influx of modern meteoric waters that have lowered the delta d values but not greatly affected the delta 18 o values of some of the clay minerals associated with the shear and breccia zones this latest event has recrystallized much of the hydrothermal mg chlorite associated with the uranium to produce an fe mg chlorite with delta d values as low as 170 per mil

sediment yield variability in spain a quantitative and semiqualitative analysis using reservoir sedimentation rates an existing dataset of area specific sediment yield ssy for 60 catchments in spain that was retrieved from sediment deposition rates in reservoirs avendano salas c sanz montero e rayan c gomez montana 1997 sediment yield at spanish reservoirs and its relationship with the drainage basin area in proceedings of the 19th symposium of large dams florence 1997 icold international committee on large dams pp 863 874 reveals that catchment area alone explains only 17 of the variability in ssy in this study an attempt to explain the remaining variability in ssy was made using a quantitative and a semiqualitative approach for 22 catchments during a field survey the 22 selected catchments were characterised by topography vegetation cover lithology shape and the presence of gullies in the broad vicinity of the reservoir this information was used to develop a factorial scoring index model that provides a fairly accurate and reliable prediction of ssy a classical multiple regression model using climatic topographic and land use properties derived from regional datasets could not explain as much variance as the qualitative index model nor did it appear to be as reliable the same conclusion could be drawn when using the corine soil erosion risk map of southern europe the low prediction capability of the multiple regression models and the corine soil erosion risk map could be attributed mainly to the fact that these methods do not incorporate gully erosion and that the land cover data are not a good representation of soil cover both variables have been shown to be of great importance during the field surveys future assessments of ssy could be quickly and efficiently made using the proposed factorial scoring index model in comparison with other models which demand more data the index model offers an alternative prediction tool d 2002 elsevier science b v all rights reserved

a 2169 ma u pb baddeleyite age for the otish gabbro quebec implications for correlation of proterozoic magmatic events and sedimentary sequences in the eastern superior province otish gabbro sills intrude sedimentary rocks in the otish basin of the southeastern superior province here deposition of otish supergroup sediments had previously been thought to be older than k ar and sm nd ages of ca 1750 1710 ma for otish gabbro sills and younger than ca 2515 2500 ma u pb ages of underlying mistassini dykes however a much older u pb baddeleyite age of 2169 0 1 4 ma is presented here for an otish sill indicating that they are coeval with and likely genetically related to the giant 2172 2167 ma biscotasing dyke swarm to the southwest and or the cramolet sills and payne river dykes to the north the new date also indicates that the age of the otish supergroup falls between ca 2515 ma and ca 2169 ma only a little different from the ca 2450 2217 ma bracket for the huronian supergroup of the southern province and is consistent with both supergroups spanning the oxy atmo inversion the otish supergroup could also be coeval with the sakami formation to the north but is like

river sediment discharge to the oceans present day controls and global budgets empirical relationships between river sediment yields and a large number of hydroclimatic biological and geomorphological parameters are investigated at the global scale for a set of 60 major world river basins the environmental characteristics were extracted from various global computer data sets and natural river sediment fluxes were taken from the literature it is found that sediment yields can be best correlated by forming the products of hydroclimatic and geomorphological factors that is runoff intensity basin slope an index characterizing rock hardness and an index characterizing rainfall variability over the year the best parameter combination varies to some extent when the rivers are grouped according to their average climatic situation but it is always a combination of the above mentioned parameters that yields the most significant models in arid climates however regression coefficients are greater than in humid climates indicating that erodibility is much greater than in arid climates when extrapolated to the total continental area on the basis of the corresponding data sets the empirical models result in a total sediment flux of about 16 gigatons discharged to the oceans every year which is in good agreement with previous estimates derived from compilations of world wide river data consequently two global maps are proposed showing the spatial distributions of river sediment yields on the continents as well as the inputs of these sediments to the oceans in a grid point scale by far most of the sediments originate from the young orogenic belts of the continents mainly due to a combination of steep morphologies and high runoff intensities

geology geography and humans battle for dominance over the delivery of fluvial sediment to the coastal ocean abstract sediment flux to the coastal zone is conditioned by geomorphic and tectonic influences basin area and relief geography temperature runoff geology lithology ice cover and human activities reservoir trapping soil erosion a new model termed bqart in recognition of those factors accounts for these varied influences when applied to a database of 488 rivers the bqart model showed no ensemble over or underprediction had a bias of just 3 across six orders of magnitude in observational values and accounted for 96 of the between river variation in the long term 30 years sediment load or yield of these rivers the geographical range of the 488 rivers covers 63 of the global land surface and is highly representative of global geology climate and socioeconomic conditions based strictly on geological parameters basin area relief lithology ice erosion 65 of the between river sediment load is explained climatic factors precipitation and temperature account for an additi

formation and destabilization of the high pressure assemblage garnet phengite paragonite krusne hory mountains bohemian massif the significance of the tschermak substitution in the metamorphism of pelitic rocks abstract the metamorphism of low alumina metapelites along high pressure gradients involves only a few continuous and discontinuous reactions that produce minor variations in modal mineralogy this is the case with metamorphic rocks forming the para autochthonous sequence in the vicinity of the village of m d nec krusne hory mts bohemian massif metamorphic reactions taking place among micas garnets and feldspars can be described using tschermak exchange and nak 1 exchange pressure temperature conditions for some of these continuous reactions were calculated from mineral compositions these calculations suggest that the tschermak and nak 1 exchanges are sensitive monitors of pressure and temperature conditions in these rocks the mineral assemblages of which are unsuitable for experimentally calibrated thermobarometers the results show metamorphic temperatures of 580 630 c at a pressure of 13 15 kbar during metamorphism of pre variscan basement beneath a nappe sequence

late paleoproterozoic climate tectonics and metamorphism in the southern lake superior region and proto north america evidence from baraboo interval quartzites abstract red supermature quartzites of the baraboo interval of the lake superior region contain detrital zircon that ranges in age from 1782 to 1712 ma deposition clearly occurred after the geon 18 penokean orogeny these late paleoproterozoic sedimentary rocks consist largely of quartz kaolinite or pyrophyllite and hematite detrital feldspar and muscovite are rare or absent their chemical index of alteration ranges from 96 8 to 98 6 among the most chemically mature clastic sediments in the geological record the quartzites are underlain by mature feldspar free paleosols accounting for the absence of feldspar in the overlying sediments and indicating the presence of first cycle quartzose detritus such physical and chemical characteristics imply that late paleoproterozoic deposition in the lake superior region occurred in a stable tectonic setting with subdued topographic relief in a warm humid climate folding and low grade metamorphism of the quartzites is thought to reflect 1630 ma foreland

the millennium uranium deposit athabasca basin saskatchewan canada an atypical basement hosted unconformity related uranium deposit the millennium uranium basement hosted unconformity related deposit is one of the most recent discoveries of basement hosted deposits and may hold as much as 46 8 million pounds 18 000 metric tonnes u at an average grade of 4 53 percent u3o8 the alteration zone associated with the deposit is atypical as it consists predominantly of muscovite rather than the chlorite and muscovite commonly found in the other basement hosted deposits of the athabasca basin the preore stage consists of early minor clinochlore alteration at temperatures of about 275 c interpreted to result from retrograde metamorphism of the basement rocks prior to the deposition of the athabasca basin this clinochlore event is followed by an extensive 1mc muscovite alteration of the basement rocks by na k fe rich basinal brines at temperatures of about 250 c creating up to 25 percent void space in the basement rocks subsequently a weak chamoisite alteration resulted from fe mg ca rich fluids with temperatures of about 300 c that evolved from reactions between the basinal brines and the basement rocks ore stage uraninite has an extrapolated chemical age of 1590 ma and is contemporaneous with synore 1mc muscovite and iron oxide deposited at temperatures near 250 c from fluids with similar 18o but lower d values to preore basinal fluids the low d values indicate postdepositional exchange of h isotopes with cenozoic fluids postore alteration consists of dravite and sudoite precipitated from mg ca rich fluids from the same evolved basinal brines that precipitated preore chamoisite at temperatures of about 185 c filling voids created during the preore stage our results indicate that the pre and synore minerals were formed dominantly by basinal fluids with no contribution from basement fluids which differ from some other basement hosted deposits in the athabasca basin where basement derived fluid influx was more significant several u pb and ar ar resetting events recorded on preore muscovite and on uraninite are coincident with fluid flow induced by distal orogenies remobilizing radiogenic pb from the deposit the radiogenic pb remobilization events were not widespread as the presence of radiogenic pb is restricted to basement rocks proximal to the deposit and along the unconformity

the role of sandstone diagenesis and aquifer evolution in the formation of uranium and zinc lead deposits southern mcarthur basin northern territory australia the paleo to mesoproterozoic mcarthur basin in the northern territory australia is filled with mixed carbonate siliciclastic successions and felsic and mafic volcanic units that contain authigenic minerals that formed during burial diagenesis petrographic investigations indicate that some of these lithologic units were cemented early by quartz overgrowths and became diagenetic aquitards whereas secondary porosity was developed in others that became diagenetic aquifers for basinal brines the authigenic minerals in both lithology types preserve geochemical information about the types of fluids that occurred in the basin with those that resided in the diagenetic aquifers having similar geochemical composition to those indicated by alteration minerals in the mcarthur river pb zn deposit and the westmoreland u deposits quartz overgrowths formed early during shallow burial in all clastic lithologic units and are particularly common in the well sorted marine sediments these became diagenetic aquitards due to the porosity occluding cement in the calcareous units early dolomite replaced calcite and aragonite at shallow burial depths fluid inclusion microthermometry indicates that most quartz overgrowths formed between 80 and 125 c from a fluid with a salinity between 0 and 13 1 wt percent nacl equiv the isotopic composition of dolomite indicates 18ofluid of 4 5 1 5 per mil and 13cfluid of 6 9 1 0 per mil suggesting formation from a mixed marine and meteoric fluid illite cemented by early quartz has a 40ar 39ar age of 1738 10 ma in one diagenetic aquitard which reflects the age when the host sediment was deposited and confirms that quartz cementation occurred early during burial with increased burial the poorly sorted sandstones and conglomerates that were initially poor aquifers at or near the surface experienced framework grain dissolution and the creation of secondary porosity at depth as a result the sediments of the westmoreland conglomerate the lower yiyintyi sandstone significant proportions of the warramana sandstone and most of the sandstone interbeds of the gold creek volcanics became diagenetic aquifers and conduits for basinal brines illite dolomite and chlorite formed late in the paragenesis and filled the secondary porosity quartz veins formed last and primarily in faults and fractures the dolomite and quartz veins contain fluid inclusions that have low eutectic temperatures indicative of ca2 and na dominated brines and salinities between 18 5 and 30 9 wt percent nacl equiv illite crystallinity data and chlorite chemical compositions indicate formation between 150 and 250 c the isotopic compositions of illite and chlorite indicate 18ofluid values between 2 9 and 9 1 per mil and dfluid values between 61 and 25 per mil which suggest formation from a mixed meteoric and marine fluid these 18ofluid values are indistinguishable from those determined from the isotopic composition of alteration minerals at the mcarthur river pb zn deposit 5 5 or synore illite at the westmoreland uranium deposit 4 2 suggesting that the diagenetic aquifers and the deposits may be linked argon ages of illite from the diagenetic aquifers indicate that fluid migration began as early as 1680 ma and continued to approximately 1541 ma coinciding with and extending past the time when the mcarthur river pb zn deposit 1640 ma and the westmoreland u deposits 1655 1606 ma formed the results presented in this study show that clastic sediments dominated by poorly sorted sandstone and conglomerate facies evolved through burial diagenesis to become aquifer lithologic units that hosted basinal brines with chemical characteristics and ages similar to those that are reported from the pb zn and u deposits of the southern mcarthur basin

variations in the uranium isotopic compositions of uranium ores from different types of uranium deposits abstract variations in 238u 235u and 234u 238u ratios were measured in uranium minerals from a spectrum of uranium deposit types as well as diagenetic phosphates in uranium rich basins and peraluminous rhyolites and associated autunite mineralisation from macusani meseta peru mean 238u values of uranium minerals relative to nbl crm 112 a are 0 02 for metasomatic deposits 0 16 for intrusive 0 18 for calcrete 0 18 for volcanic 0 29 for quartz pebble conglomerate 0 29 for sandstone hosted 0 44 for unconformity type and 0 56 for vein with a total range in 238u values from 0 30 to 1 52 uranium mineralisation associated with igneous systems including low temperature calcretes that are sourced from u rich minerals in igneous systems have low 238u values of ca 0 1 near those of their igneous sources whereas uranium minerals in basin hosted deposits have higher and more variable values high grade unconformity related deposits have 238u values around 0 2 whereas lower grade unconformity type deposits in the athabasca kombolgie and otish basins have higher 238u values the 234u values for most samples are around 0 in secular equilibrium but some samples have 234u values much lower or higher than 0 associated with addition or removal of 234u during the past 2 5 ma these 238u and 234u values suggest that there are at least two different mechanisms responsible for 238u 235u and 234u 238u variations the 234u 238u disequilibria ratios indicate recent fluid interaction with the uranium minerals and preferential migration of 234u fractionation between 235u and 238u is a result of nuclear field effects with enrichment of 238u in the reduced insoluble species mostly uo2 and 235u in oxidised mobile species as uranyl ion uo22 and its complexes therefore isotopic fractionation effects should be reflected in 238u 235u ratios in uranium ore minerals formed either by reduction of uranium to uo2 or chemical precipitation in the form of u6 minerals the 238u values of uranium ore minerals from a variety of deposits are controlled by the isotopic signature of the uranium source the efficiency of uranium reduction in the case of uo2 systems and the degree to which uranium was previously removed from the fluid with less influence from temperature of ore formation and later alteration of the ore uranium isotopes are potentially superb tracers of redox in natural systems

estimating accumulation rates and physical properties of sediment behind a dam englebright lake yuba river northern california 1 studies of reservoir sedimentation are vital to understanding scientific and management issues related to watershed sediment budgets depositional processes reservoir operations and dam decommissioning here we quantify the mass organic content and grain size distribution of a reservoir deposit in northern california by two methods of extrapolating measurements of sediment physical properties from cores to the entire volume of impounded material englebright dam completed in 1940 is located on the yuba river in the sierra nevada foothills a research program is underway to assess the feasibility of introducing wild anadromous fish species to the river upstream of the dam possible management scenarios include removing or lowering the dam which could cause downstream transport of stored sediment in 2001 the volume of sediments deposited behind englebright dam occupied 25 5 of the original reservoir capacity the physical properties of this deposit were calculated using data from a coring campaign that sampled the entire reservoir sediment thickness 6 32 m at six locations in the downstream 3 4 of the reservoir as a result the sediment in the downstream part of the reservoir is well characterized but in the coarse upstream part of the reservoir only surficial sediments were sampled so calculations there are more uncertain extrapolation from one dimensional vertical sections of sediment sampled in cores to entire three dimensional volumes of the reservoir deposit is accomplished via two methods using assumptions of variable and constant layer thickness overall the two extrapolation methods yield nearly identical estimates of the mass of the reservoir deposit of 26 106 metric tons t of material of which 64 7 68 5 is sand and gravel over the 61 year reservoir history this corresponds to a maximum basin wide sediment yield of 340 t km2 yr assuming no contribution from upstream parts of the watershed impounded by other dams the uncertainties and limitations of the estimates of overall sediment quantities are discussed implications for watershed management and future reservoir sedimentation studies are also presented

on why gravel bed streams are paved bedload transport in poorly sorted gravel bed streams downstream of dams is considered bedload and typical bed material subpavement size distributions are observed to be similar it follows that the coarse half of the subpavement moves through a reach at a rate near that of the fine half since coarser grains are intrinsically less mobile than fine grains it follows that some mechanism must act to nearly equalize mobility it is hypothesized that the pavement seen in gravel bed streams at low flow is in fact in place during typical transport events capable of moving all available sizes this pavement can provide the equalizing mechanism by exposing proportionally more coarse grains to the flow field data are used to quantify this concept and to develop a predictive relation for river pavement the model indicates that pavement should be absent in most sand bed streams in agreement with observation

structural controls on basin evolution neogene to quaternary of the ionian zone western greece turbidite deposition of oligocene to early miocene age occurred in the foreland basin to the pindus mountains which formed the nnw trending hellenide thrust front deposition was interrupted by the migration of the deformation front westwards through the foreland basin itself the kalamitsi thrust exposed in west levkas became active in late early miocene times a miocene to pliocene piggy back basin developed fed both from the thrust front to the west and the mountain belt to the east during the mid late miocene deformation remained confined to the ionian and gavrovo zones possibly related to the presence of lubricating evaporites which terminate in the pre apulian zone to the west during the late plio quaternary inner arc extension trenchward of the hellenic arc caused a system of ene and wnw basins to open under the n s tensional regime these were linked by nnw and ne transtensional faults and the system is still active in the lake trikhonis and gulf of corinth areas today in the west of the study area however post pliocene nw se compressional faults dissected the piggy back basin this compressional phase must have been either contemporaneous with or interrupted the extension active in the east from late pliocene times

contrasting patterns of alteration at the wheeler river area athabasca basin saskatchewan canada insights into the apparently uranium barren zone k alteration system previous studies on athabasca basin unconformity related uranium deposits have focused on major deposits and have not investigated sites with barren alteration systems that could clarify some of the critical factors controlling mineralization processes a paragenetic study of the wheeler river area reveals the presence of minerals that formed during the diagenetic the main hydrothermal which is subdivided into early mid and late hydrothermal substages and the late alteration stages the diagenetic stage consists of early quartz overgrowths siderite rutile hematite and abundant dickite in the pore spaces of the manitou falls formation the early hydrothermal alteration substage is characterized by pervasive 1mc muscovite alteration and minor goyazite clusters which formed from oxidizing basinal fluids at temperatures around 240 c prior to 1550 ma based on ar ar dates the mid hydrothermal alteration substage comprises dravite and sudoite in the basal 200 m of the manitou falls formation which are interpreted to have formed at temperatures around 175 c from fluids chemically distinct but isotopically similar to the basinal fluids involved during the early hydrothermal alteration substage the late hydrothermal substage was observed only at zone k of the wheeler river area and is characterized by the precipitation of clinochlore copper sulfides and florencite from reducing basement fluids emerging into the manitou falls formation at temperatures around 230 c creating a 250 m high by 250 m wide reducing halo oxidized uranium bearing basinal fluids interacted with the manitou falls formation during the early hydrothermal substage prior to the arrival of the reducing fluids during the mid and late hydrothermal substages and this precluded uranium precipitation the post hydrothermal alteration stage is characterized by formation of kaolinite after late hydrothermal clinochlore near fractures by meteoric waters a minimal amount of leachable radiogenic pb with a pb pb model age of 1907 ma that is older age than both the athabasca basin and the main mineralization event of 1590 ma was encountered at zone k indicating low probability of this area to host uranium mineralization however areas of possible unconformity related uranium deposits were identified outside zone k wherein significant amounts leachable radiogenic pb were observed

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

critical geochemical and mineralogical factors for the formation of unconformity related uranium deposits comparison between barren and mineralized systems in the athabasca basin canada the spring point barren alteration system and the maurice bay subeconomic uranium deposit situated on the northwest rim of the athabasca basin northern saskatchewan are hosted by the sandstones and conglomerates of the fair point formation of the athabasca group macroscopic observations indicate two different styles of alteration for the two systems chlorite dominated partly reduced alteration at spring point and illite dominated strongly oxidized alteration at maurice bay the paragenetic sequences developed for each area are similar but the crystal chemistry of the alteration minerals differs markedly indicating that the alteration fluids at spring point were richer in mg and ca than at maurice bay this is consistent with a predominantly basement origin for the former stable isotope analyses of clay alteration minerals indicate that in particular the chlorite related fluids from spring point have a basement signature 18 o 3 5 and d 13 whereas chlorite from maurice bay is more consistent with a mixture of basement and basinal fluids 18 o 5 2 and d 28 the absence of uranium transporting basinal fluids at the critical time when reducing basement fluids were producing chlorite alteration is likely the single most important cause for the lack of uranium mineralization at spring point

a low variance mineral assemblage with talc and phengite in an eclogite from the saxonian erzgebirge central europe and its p t evolution a light coloured fine grained eclogite sample from near the village of hammerunterwiesenthal in the erzgebirge nw bohemian massif preserves the low variance mineral assemblage of garnet omphacite phengite talc amphibole clinozoisite quartz rutile and accessory phases porphyroblasts of amphibole clinozoisite and phengite formed during a late stage iii of metamorphism paragonite joined the assemblage late in this stage iiib the chemical zonation of the minerals was carefully studied various geothermobarometric methods were applied especially involving phengite and talc the constrained p t path for the eclogite starts at about 480 c and 25 kbar stage ib followed by a significant temperature rise stage ii at slightly increasing pressure at the peak p t conditions of 720 c and 27 kbar blastesis of amphibole clinozoisite and phengite was caused by infiltrating hydrous fluids the resulting density reduction may have allowed buoyant uplift of the eclogite subsequently significant cooling occurred at high pressures stage iiib is characterized by p t conditions around 520 c and 18 kbar at reduced water activities this unusual late p t evolution might explain the freshness of the eclogite including the preservation of chemical zonation on the micrometre scale

a 6 year westward rotary motion in the earth detection and possible micg coupling mechanism abstract seeking geophysical explanations for the periodic six year oscillation syo previously found in the earth s length of day variation lod we analyze the global gps displacement and geomagnetic data using the array processing technique of ose optimal sequence estimation and find clear evidences of the 6 yr signals which manifest as a westward rotary propagating wave of the sectoral spherical harmonic pattern of degree 2 order 2 y 22 based on the period the spatial pattern and the amplitudes and the estimated phases that exhibit consistent synchronicity among the three datasets we propose the following scenario the mantle inner core gravitational micg coupling gives rise to a 6 yr axial torsional libration of the inner core controlled by the sectoral y 22 density anomalies or the equatorial ellipticities in the inner core and the lower mantle the angular momentum exchange between which manifests as the syo in lod it forces into action a pressure wave 2 cyclic in 6 yr through the fluid outer core which in turn produces the corresponding gps and geomagnetic variations our findings provide insight into the dynamics of the deep earth and corroborate a positive density anomaly for the lower mantle large low shear velocity provinces

age and origin of uranium mineralization in the camie river deposit otish basin quebec canada abstract the camie river uranium deposit is located in the southeastern part of the paleoproterozoic otish basin quebec the uranium mineralization consists of disseminated and vein uraninite and brannerite precipitated close to the unconformity between paleoproterozoic fluviatile pervasively altered sandstones and conglomerates of the matoush formation and the underlying sulfide bearing graphitic schists of the archean hippocampe greenstone belt diagenetic orange pink feldspathic alteration of the matoush formation consists of authigenic albite cement partly replaced by later orthoclase cement with the na2o content of clastic rocks increasing with depth basin wide green muscovite alteration affected both the matoush formation and the top of the basement tichegami group uraninite with minor brannerite is mainly hosted by subvertical reverse faults in basement graphitic metapelites sulfides and overlying sandstones and conglomerates uranium mineralization is associated with chlorite veins and alteration with temperatures near 320 c that are paragenetically late relative to the diagenetic feldspathic and muscovite alterations re os geochronology of molybdenite intergrown with uraninite yields an age of 1724 0 4 9 ma whereas uraninite yields an identical although slightly discordant 1724 29 ma sims u pb age uraninite has high concentrations in ree with flat ree spectra resembling those of uraninite formed from metamorphic fluids rather than the bell shaped patterns typical of unconformity related uraninite paragenesis and geochronology therefore show that the uranium mineralization formed approximately 440 million years after intrusion of the otish gabbro dykes and sills at 2176 ma which constrains the minimum age for the sedimentary host rocks the post diagenetic stage of uraninite after feldspathic and muscovite alterations the paragenetic sequence and the brannerite uraninite assemblage the relatively high temperature for the mineralizing event 320 c following the diagenetic na and k dominated alteration lack of evidence for brines typical of unconformity related u deposits the older age of the otish basin compared to worldwide basins hosting unconformity related uranium deposits the large age difference between basin fill and mineralization the older age of the uranium oxide compared to ages for worldwide unconformity related u deposits and the flat ree spectra of uraninite do not support the previous interpretation that the camie river deposit is an unconformity associated uranium deposit rather the evidence is more consistent with a paleoproterozoic higher temperature hydrothermal event at 1724 ma whose origin remains speculative