distribution characterization and geochemical controls of elements of concern in uranium mine tailings key lake saskatchewan canada abstract the distribution of as mo ni and se in the aqueous and solid phases of u mine tailings in the deilmann tailings management facility dtmf located at the key lake mine in northern saskatchewan canada was defined using as discharged tailings samples collected monthly starting in 1996 and core samples collected from the dtmf from 3 locations on 3 occasions between 2004 and 2009 these data indicated that the dtmf can be divided into two geochemical zones tailings generated from the deilmann ore body between 1996 and 2000 and tailings from the mcarthur river ore body mined after july 2000 the deilmann tailings solids are generally characterized by greater elemental concentrations than those in the mcarthur river tailings particularly for as co and ni these elevated concentrations are attributed to the abundance of ni co as s minerals in this ore the mean aqueous concentrations of as mo ni and se are 3 7 23 2 0 14 and 0 02 mg l 1 respectively in the deilmann porewaters and 0 20 4 16 0 06 and 0 03 mg l 1 respectively in the mcarthur river porewaters similarly the mean as mo ni and se solid phase concentrations are 5 89 10 3 69 9 3 20 10 3 and 17 4 g g 1 respectively for the deilmann tailings and 440 13 6 551 and 3 03 g g 1 in the mcarthur river tailings statistically ph remained unchanged from the time of discharge while eh values have remained oxic with no significant change between the two tailings types over 15 a of residence time results from sequential extractions thermodynamic modeling and results of complimentary research indicated that ferrihydrite solubility is the dominant control on aqueous as concentrations and also plays a role in controlling dissolved mo ni and se

late quaternary vegetation dynamics in a biodiversity hotspot the uluguru mountains of tanzania abstract late quaternary vegetation history and environmental changes in a biodiverse tropical ecosystem are inferred from pollen charcoal and carbon isotope evidence derived from a 48 000 yr sedimentary record from the uluguru mountains a component of the eastern arc mountains of kenya and tanzania results indicate that eastern arc forest composition has remained relatively stable during the past 48 000 yr long term environmental stability of the eastern arc forests has been proposed as a mechanism for the accumulation and persistence of species during glacial periods thus resulting in the diverse forests observed today the pollen and isotope data presented here indicate some marked changes in abundance but no significant loss in moist forest taxa through the last glacial maximum thereby providing support for the long term environmental stability of the eastern arc anthropogenic activities including burning and forest clearance were found to play a moderate role in shaping the mosaic of forest patches and high altitude grasslands that characterise the site today however this influence was tempered by the inaccessibility of the mountain

the kashiru pollen sequence burundi palaeoclimatic implications for the last 40 000 yr b p in tropical africa abstract a continuous pollen record from a central african highland site 3 28 s 29 34 e with 15 radio carbon dates spans at least the last 40 000 yr both modern and fossil pollen have been investigated a clear pattern of changes in vegetation and climate is suggested prior to 30 000 yr b p the occurrence of the montane conifer forest including the upper forest limit indicates climatic conditions colder and drier than now but more humid than in late glacial time between 30 000 and 15 000 yr b p grassland with afroalpine indicators expanded down to 2500 2000 m altitude as a result of dry and most probably cool climate the montane forest persisted in refuges although much reduced forest vegetation with the same floristic composition as today appeared after 13 250 200 yr b p suggesting more humid conditions the occurrence of a possible short term humid episode about 21 500 yr b p is correlated with some high lake level stages in east africa and with organic deposits in deep sea cores from the mediterranean and the atlantic ocean

mineralogy and u pb pb pb and sm nd geochronology of the key lake uranium deposit athabasca basin saskatchewan canada the key lake deposit is one of several large high grade unconformity related uranium deposits located at the eastern margin of the athabasca basin in northern saskatchewan canada the deposit consists of the gaertner orebody now mined out and the deilmann orebody which is presently being mined in the past radiometric dating efforts yielded an age of oldest ore forming event of 1250 34 ma at the gaertner orebody and 1350 4 ma at the deilmann orebody this unlikely age difference called for further investigation innovative preparation techniques were used to separate the paragenetically oldest u mineral an anisotropic uraninite ore microscopy and u pb isotopic data show that the oldest event of uranium emplacement occurred simultaneously at the two orebodies at 1421 49 ma the primary ore forming phase was followed by younger generations of u mineralization and periods of remobilization sm nd data of key lake uraninite form an isochron corresponding to an age of 1215 ma this is interpret

vegetation history in western uganda during the last 1200 years a sedimentbased reconstruction from two crater lakes pollen plant macrofossil and charcoal records from two neighbouring crater lakes lake wandakara and lake kasenda in lower montane altitude 1200m western uganda 0 5dn 30 reveal major changes in local and regional vegetation over the last 1200 years which can be related to regional variations in climate especially effective precipitation and human impact the biological signals are supplemented by evidence from physical sedimentary analyses magnetic susceptibility loss on ignition dry mass accumulation rate for major catchment changes in a wider regional context from ad 750 to 900 medium altitude moist forest existed around lake kasenda which was largely replaced by grassland by ad 1000 coincident e with evidence for increased catchment erosion and fire events linked to human impact during a brief arid phase despite wetter conditions from ad 1000 to 1200 and in the 1400s grassland prevailed around both sites until c ad 1700 1750 with increased catchment disturbance from ad 1600 t

vegetation response to rainfall variation and human impact in central kenya during the past 1100 years pollen data from a 625 cm sediment core from crescent island crater a subbasin of lake naivasha kenya provide an 1100 year record of vegetation change at a mean time resolution of 15 years earlier data from the same core show a record of lake depth and thus inferred rainfall variation in the form of changing sedimentary facies supported by salinity inferences based on diatom and chironomid assemblages stratigraphic variation in the abundances of aquatic and semi aquatic plants and chlorophyte algae generally supports the reconstructed lake depths woody afromontane and woodland plant taxa decreased relative to poaceae grasses during low rainfall periods and increased during high rainfall periods a decrease in the extent of lower montane forest coincident with favourable climatic conditions after about ad 1700 was probably caused by kikuyu immigration and population expansion around that time as indicated by simultaneous appearance of the food crop zea mays maize increases in ruderal herbaceous and exotic tree pollen during the twentieth century indicate increased local landscape disturbance during the colonial period there is little direct pollen evidence for accelerating clearance of the montane forest during recent decades

late quaternary vegetation reconstruction from the eastern arc mountains tanzania abstract pollen spore macrofossil and stable isotope c and n analyses from a 266 cm sediment core collected from a swamp on the eastern arc mountains tanzania are used to reconstruct vegetation and environmental history an estimated time scale based on five 14c ages records approximately 38 000 yr this palaeorecord is the first from this biodiversity hotspot and importantly extends through the last glacial maximum lgm the altitudinal transition from montane to upper montane forest shifted from 1700 1800 m 38 000 14c yr bp to 1800 1900 m 35 000 29 000 14c yr bp from 29 000 to 10 000 14c yr bp it shifted from 1850 1950 m across the lgm to 1750 1800 m during 10 000 3500 14c yr bp and to present day elevations at 2000 m during the last 3500 14c yr bp the relative ecosystem stability across the lgm may be explained by the indian ocean s influence in maintaining continuous moist forest cover during a period of east african regional climate aridity during the late holocene presence of abundant coprophilous fungi and algal blooms demonstrates increasing human impact neurospora spores indicate frequent fires coinciding with clear signals of decline in podocarpus and psychotria trees that possibly represent selective logging

human environment interactions in an agricultural landscape a 1400 yr sediment and pollen record from north pare ne tanzania abstract a sediment and pollen record from the north pare mountains in north eastern tanzania provides evidence for strong anthropogenic landscape transformations since the 7th century ad and demonstrates that shortly after the arrival of early iron age farmers agricultural land use became the main driving force of vegetation and landscape change predominating over external climatic factors the absence of pollen characteristic for the corresponding altitudinal submontane forest implies widespread forest clearance and agriculture land use prior to the onset of the sedimentary record land clearance soil erosion and corresponding accumulation of colluvial slope deposits on the valley floor triggered paludification and the establishment of the lomwe palaeowetland in the 7th century ad accelerated soil erosion and rapid alluvial burial of the palaeowetland between ad 1200 and ad 1500 represent an environmental tipping point with important repercussions for present day land degradation and resource restraints age control is complicated by radiocarbon date reversals and draws on introduced forest taxa cupressus and eucalyptus as biostratigraphic markers of the 20th century geoarchives from agricultural landscapes that are shaped by long term settlement and land use such as the pare mountains can enhance archaeological occupation histories and provide crucial information for both the identification of ecological thresholds and for the reconstruction of environmental transitions during anthropogenic landscape transformations

lake level history of lake tanganyika east africa for the past 2500 years based on ostracode inferred water depth reconstruction assemblages of ostracodes from sediment cores illuminate lake level history at decadal to centennial timescales during the late holocene at lake tanganyika east africa the ostracode based lake level curves for several cores resemble both each other and the only previously published lake level record of comparable resolution for lake tanganyika during this interval successfully reconstructing known highstands improving the chronology of known lowstands and contributing new information on late holocene lake level variability at this important tropical african location in agreement with other late holocene records from east africa the surface level at lake tanganyika reflects predominantly arid conditions throughout this interval interrupted by relatively brief episodes of higher precipitation and lake level the most pronounced lowstand in the record occurs at v200 0 bc with other significant lowstands dating to the intervals v200 500 ad v700 850 ad the medieval warmperiod mwp v1050 1250 ad at lake tanganyika and the latter part of the little ice age lia v1550 1850 ad the most important wet intervals in the lake level record are centered on v500 ad v1500 ad and v1870 ad the highstands and lowstands reported here for lake tanganyika appear to be fairly coherent with other records of rainfall throughout east africa during the mwp and the lia prior to the mwp paleoclimate records are apparently less coherent although this may be a reflection of the resolution and abundance of recent paleoclimatic data available for this climatically complex region

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

pollen based vegetation changes in southern tanzania during the last 4200 years climate change and or human impact the age constrained pollen data of a sedimentary sequence from the crater lake masoko southern tanzania 9 20ps 33 45pe 770 m display a continuous record of vegetation for the past 4200 years this record provides evidence that wetter zambezian woodlands always occupied this area during the late holocene reaching a maximum extent between 2800 and 1650 cal yr bp related to increase in summer monsoon intensity however three main episodes of decline have been detected between 3450 and 2800 cal yr bp between 1650 and 1450 cal yr bp and from 1200 to 500 cal yr bp for which a climatic interpretation decrease in the summer monsoon strength was preferentially advanced the first is synchronous with lowstand of many tropical african lakes and so mainly induced by increased aridity in contrast the abrupt change in the pollen record at 1650 1550 cal yr bp is marked by a large extension of grasslands at the expense of arboreal cover further by an increase in ricinus communis and an intensification of burning it could thus indicate local clearance of vegetation by man however at the same time the decline of montane forest suggests the impact of a more regional change during the last episode between 1200 and 500 cal yr bp dry climatic conditions are inferred from a combination of pollen diatom and magnetic proxies although the occurrence of late iron age settlements in the region means that local human interference cannot be excluded this study illustrates the difficulties in deciphering ecological and anthropological changes from pollen data in african tropical regions a 2003 elsevier b v all rights reserved

evaluation of rammelsbergite nias2 as a novel mineral for 187re 187os dating and implications for unconformity related u deposits abstract rammelsbergite nias2 is often present in ore deposits worldwide in association with other arsenides sulphides and sulfarsenides this work demonstrates the value of the application of the re os isotopic system to the dating of rammelsbergite using the example of the cigar lake uranium deposit athabasca basin saskatchewan canada our results show that rammelsbergite concentrates significant and variable amounts of re when crystallizing up to 1 6 g g 1 while incorporating minimal common os such characteristics make this mineral an ideal target for re os isotopic dating by both isochron and model age methods remarkable agreement of the re os age of the rammelsbergite with the u pb age of the uranium oxide grains found inside one of the massive rammelsbergite veins confirms the applicability of the method the selected rammelsbergite samples from the cigar lake uranium deposit yield a 187re 187os isochron age of 1239 33 20 ma these results challenge a long standing petrogenetic model which postulates contemporaneous u oxide and ni co arsenide deposition in unconformity related uranium deposits the new re os age of rammelsbergite veins indicates that arsenide crystallization postdated the deposition of the primary uranium oxides at 1461 1341 ma implying that uranium oxides and nickel arsenides as well as other sulphides and sulfarsenides were not precipitated contemporaneously during a single hydrothermal event as previously proposed the 187re 187os data suggest that crystallization of rammelsbergite and co genetic sulphides arsenides and sulfarsenides was linked to the ca 1270 ma mackenzie magmatic event marked by the emplacement of mafic dikes throughout the canadian shield including in the area of the athabasca basin this study therefore suggests a new hypothesis for the origin of nickel cobalt sulfur and arsenic in unconformity related u deposits of the athabasca basin more broadly the successful application of the 187re 187os rammelsbergite chronometer in this geological context suggests that its application in other ore deposit environments worldwide is likely to provide similar insights in this respect the 187re 187os chronometer applied to rammelsbergite and potentially to other arsenides and sulfarsenides represents a valuable complement to molybdenite dating because it can be used in systems that lack molybdenite

palynological evidence of climate change and land degradation in the lake baringo area kenya east africa since ad 1650 abstract paleoenvironmental records derived from pollen fungal spores and microscopic charcoal from lake baringo kenya reveal a largely dry environment in the east african region since ad 1650 the dry environment is punctuated by a succession of centennial to decadal scale wet and dry episodes disjointed by sharp transitions including two intense dry episodes that led to drying of the lake at ca ad 1650 and ad 1720 which coincide with the little ice age lia period in europe the baringo record shows that land degradation in the area began prior to the colonial period in east africa and has persisted to the present land degradation and increased soil erosion in the lake baringo drainage basin was severe enough to significantly age the lake sediments due to influx of old carbon resulting in the dating inversion

little ice age drought in equatorial africa intertropical convergence zone migrations and el nino southern oscillation variability high resolution analyses of the mg concentration in authigenic calcite in five cores from lake edward provide a water balance history of central equatorial africa spanning the past 1400 yr a high ratio of mg to ca mg indicates strong droughts in central africa during the little ice age a d 1400 1750 in contrast to records from lake naivasha kenya which suggest a wet little ice age this spatial pattern in africa likely arose due to coupled changes in the high latitudes the position of the intertropical convergence zone and the el nino southern oscillation enso system our results further suggest that the patterns and variability of twentieth century rainfall in central africa have been unusually conducive to human welfare in the context of the past 1400 yr

the 1992 nicaragua earthquake a slow tsunami earthquake associated with subducted sediments the 1992 nicaragua earthquake was a tsunami earthquake that is it generated tsunamis disproportionately large for its surface wave magnitude m s the moment magnitude m w determined from long period 250 s surface waves was 7 6 significantly larger than the 20 s m s of 7 this m s m w disparity is also characteristic of tsunami earthquakes the nicaragua earthquake is the first tsunami earthquake to be captured by modern broadband seismic networks allowing us to present here seismograms of sufficiently high quality to make inferences about the rupture mechanisms we conclude that the nicaragua earthquake was a slow thrust earthquake which occurred on the subduction interface between the cocos and north american plates and because of the absence of sediments on the trench floor offshore of nicaragua the slip propagated up dip all the way to the ocean bottom exciting large tsunamis the occurrence of slip on a plate interface filled with soft subducted sediments caused the rupture process to be slower than in ordinary subduction zone thrust earthquakes our results reinforce the idea that tsunami warning systems using long period 100 s waves are necessary to reduce the hazard from this type of earthquake

paleoenvironmental change in tropical africa during the holocene based on a record from lake kifuruka western uganda a 10 000 year palynological record of vegetation and environmental changes in tropical africa is presented based on sediment data from a 230 cm long core recovered from lake kifuruka in western uganda the lake kifuruka record provides new sedimentary and paleoecological data for human environment interactions and anthropogenic disturbance in the tropical african region during the holocene the record shows evidence for prolonged dry conditions in the region at the terminus of the last glaciation period and the onset of the holocene period the early holocene and mid holocene periods were characterized by largely warm and wet climatic conditions the pollen record shows evidence of forest disturbance that is probably associated with agricultural activities near lake kifuruka shortly after ca 4300bp cal a bp coinciding with a time of increased desiccation in the region the forest disturbance in the record appears to have intensified and continued into the modern period but with no significant change in the overall vegetation diversity suggesting quick environmental recovery the lake kifuruka record is largely devoid of the abrupt climatic changes that have been observed from a couple of sites in the east african region which implies that the changes may be site specific rather than regional scale

palaeolimnological evidence for widespread late 18th century drought across equatorial east africa abstract the sediment records of three shallow climate sensitive lakes in equatorial east africa chibwera and kanyamukali in western uganda and baringo in central kenya contain clear lithological evidence of an episode of complete desiccation in the relatively recent past quantitative stratigraphic analyses of bulk sediment composition texture sand and coarse organic detritus the c n ratio of bulk organic matter and magnetic susceptibility allowed us to define a common succession of sedimentary units in all three lakes this common stratigraphy includes a basal unit of dry and stiff low organic clays capped by a horizon of peaty mud or peat overlain by organic lake sediment we interpret this stratigraphy to represent an episode of nearly complete desiccation of these lake basins this was followed first by an early phase of modest lake refilling during which time extensive littoral and submerged vegetation developed producing peaty lake deposits mostly higher lake levels later on resulted in deposition of fine grained lake muds using 210 pb and 137 cs activity profiles combined with four ams 14 c dates on single terrestrial plant macrofossils or multiple charred grass particles indicate that in all three lakes the episode of most recent complete desiccation occurred in the late 18th and early 19th century these results add to an accumulating body of palaeoenvironmental data revealing a prolonged period of extreme drought in equatorial east africa about 200 years ago also documented in the cultural history of the african great lakes region given the geographical spread of the study lakes across the east african plateau these results indicate that the climatic anomaly of reduced rainfall responsible for this drought was at least sub continental in scale

quiet zone within a seismic gap near western nicaragua possible location of a future large earthquake a 5700 square kilometer quiet zone occurs in the midst of the locations of more than 4000 earthquakes off the pacific coast of nicaragua the region is indicated by the seismic gap technique to be a likely location for an earthquake of magnitude larger than 7 the quiet zone has existed since at least 1950 the last large earthquake originating from this area occurred in 1898 and was of magnitude 7 5 a rough estimate indicates that the magnitude of an earthquake rupturing the entire quiet zone could be as large as that of the 1898 event it is not yet possible to forecast a time frame for the occurrence of such an earthquake in the quiet zone

the age of unconformity related uranium mineralization in the athabasca basin northern saskatchewan age data are presented for major athabasca basin uranium deposits at cigar lake cluff lake collins bay dawn lake eagle point mcarthur river midwest and rabbit lake as well as for several minor or undeveloped deposits including hughes lake and nisto the best constrained data indicate that almost all the deposits formed in a restricted time interval between about 1330 and 1380 ma this range of ages is believed to be real and not the result of uncertainties in the calculation of ages based on discordant data the one major exception is the recently discovered nias free deposit at mcarthur river for which a well determined age of 1514 18 ma 2 has been obtained even this deposit yields an age in the1330 1380 ma range for some material periods of reworking redeposition occurred at 1280 1000 575 and 225 ma these may be basin wide affecting to some degree all the deposits that we have studied other times of redeposition are less well determined but may be present as well no ages tha

farmers smelters and caravans two thousand years of land use and soil erosion in north pare ne tanzania abstract slope deposits in north pare provide evidence of two millennia of anthropogenically driven land clearance soil erosion and land degradation drawing on deposit stratigraphy soil magnetic parameters stable carbon isotope composition and radiocarbon dating three phases of soil erosion are distinguished characterized by distinct surface processes and increasing levels of agricultural land use onset of slope deposit formation in pare since about 300 bc documents soil erosion as an immediate consequence of new land use practices associated with the spread of agriculture and iron working across northern tanzania by ad 500 slope deposits extended into valley bottoms and to middle slopes suggesting catchment wide land clearance and soil erosion in the 15th century ad progressive anthropogenic soil erosion had exhausted the topsoil resource and material changes of the slope deposits reflect widespread subsoil erosion the exposure of subsoils represents an ecological tipping point and triggered the transition to a new morphodynamic framework dominated by runoff based erosion processes that are recorded as sand lenses and sand layers the most recent deposits show ongoing accelerated erosion and severe land degradation whilst cessation of sand lens preservation indicates pre colonial intensification of agricultural land use land use changes and socioeconomic transitions associated with the establishment of the ugweno chiefdom and the 19th century caravan trade are discussed as possible responses to imperceptible long term land degradation in pare the study demonstrates that anthropogenic soil erosion and not external climatic drivers shaped landscape development in pare and shows that the identification of environmental thresholds is essential for the assessment of resilience in human dominated ecosystems

monte carlo slip inversion in the frequency domain application to the 1992 nicaragua slow earthquake the spatio temporal complexity of moment release of the 1992 nicaragua slow earthquake mw 7 7 is estimated by simulated annealing contrary to linearized inversions monte carlo techniques do not make assumptions about a priori features of the model in particular large variations in rupture velocities can be imaged relative spectra between the main shock and an empirical green s function were obtained from 4 44 mhz using first and second orbit fundamental mode rayleigh waves the spectra were inverted for the moment distribution on a 2d horizontal fault under the physical constraints of slip positivity and causality the non linear inversion revealed two main regions of slip one centered 20 km to the nw of the epicenter the other 160 km to the se but delayed by 70 s rupture velocities in the slipping patches were found to be low around 1 km s large amount of slip occurred trench ward of the epicenter accounting for the large tsunami excitation analysis of the slip distribution suggests that the slow and smooth nature of the 1992 nicaragua event may be related to the frictional properties at the plate interface

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