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

numerical simulation of strain localization and its relationship to formation of the sue unconformity related uranium deposits eastern athabasca basin canada abstract unconformity related uranium deposits in the athabasca basin canada are spatially associated with reactivated basement faults that cut the unconformity surface between archean to paleoproterozoic basement and paleoproterozoic to mesoproterozoic sedimentary rocks of the athabasca group the sue deposits sue a b c d and e are located in the eastern athabasca basin along a 2 km long north northeast trending structural corridor and have both sandstone hosted sue a and sue b to the north and basement hosted sue c sue d and sue e to the south orebodies all the deposits are structurally controlled by north northeast trending basement faults that demonstrate different degrees of reverse displacements of the unconformity surface however it is not clear why the mineralization is distributed in such a pattern along the corridor in this study both 2 dimensional 2d and 3 dimensional 3d numerical modeling of deformation were conducted to examine the relationship between the distribution of strain and uranium mineralization the modeling shows that dilation positive volumetric strain thought to correlate with the development of extensional fracture systems and dilational jogs that represent potential mineralization sites is primarily controlled by the rheological contrasts in basement rocks and the degree of deformation the presence of faulted graphitic pelitic gneiss associated with the sandstone hosted sue a and sue b deposits favours dilation localized within the sandstone at low degrees of deformation mainly due to the overlying competent hangingwall granitic gneiss in contrast the basement hosted sue c sue d and sue e deposits are associated with dilation zones localized along the contact between the faulted graphitic pelitic gneiss and competent footwall silicified gneiss at higher degrees of deformation the modeling results highlight the importance of both graphitic basement structures and strong rheological contrasts between basement rocks in uranium exploration in the athabasca basin

metal rich fluid inclusions provide new insights into unconformity related u deposits athabasca basin and basement canada the paleoproterozoic athabasca basin canada hosts numerous giant unconformity related uranium deposits the scope of this study is to establish the pressure temperature and composition p t x conditions of the brines that circulated at the base of the athabasca basin and in its crystalline basement before during and after uo2 deposition these brines are commonly sampled as fluid inclusions in quartz and dolomite cementing veins and breccias associated with alteration and u mineralization microthermometry and laser ablation inductively coupled plasma mass spectrometry la icp ms data from five deposits rabbit lake p patch eagle point millennium and shea creek complement previously published data for the mcarthur river deposit in all of the deposits investigated fluid inclusion salinity is between 25 and 40 wt nacl equiv with compositions displaying a continuum between a nacl rich brine end member cl na ca mg k and a cacl2 rich brine end member cl ca mg na k the cacl2 rich brine has the highest salinity and shows evidence for halite saturation at the time of trapping the continuum of compositions between the nacl rich brine and the cacl2 rich brine end members combined with p t reconstructions suggest anisothermal mixing of the two brines nacl rich brine 180 30 c and 800 400 bars cacl2 rich brine 120 30 c and 600 300 bars that occurred under fluctuating pressure conditions hydrostatic to supra hydrostatic however because the two brines were u bearing and therefore oxidized brine mixing was probably not the driving force for uo2 deposition several scenarios are put forward to account for the cl na ca mg k composition of the brines involving combinations of seawater evaporation halite dissolution mixing with a halite dissolution brine mg ca exchange by dolomitization na ca exchange by albitization of plagioclase na k exchange by albitization of k feldspar and mg loss by mg rich alteration finally the metal concentrations in the nacl rich and cacl2 rich brines are among the highest recorded compared to present day sedimentary formation waters and fluid inclusions from basin hosted base metal deposits up to 600 ppm u 3000 ppm mn 4000 ppm zn 6000 ppm cu 8000 ppm pb and 10 000 ppm fe the cacl2 rich brine carries up to one order of magnitude more metal than the nacl rich brine though the exact origin of major cations and metals of the two brines remains uncertain their contrasting compositions indicate that the two brines had distinct flow paths and fluid rock interactions large scale circulation of the brines in the athabasca basin and basement was therefore a key parameter for metal mobility including u and formation of unconformity related u deposits

crustal evolution and age of thermotectonic reworking in the western hinterland of the trans hudson orogen northern saskatchewan abstract the hearne province in northern saskatchewan forms the western hinterland of the trans hudson orogen it is a fault bounded terrane lying structurally and geographically between the rae province to its west and the wathaman batholith and orogenic internides to its east the hearne province is comprised primarily of high grade metamorphic archean rocks structurally overlain by archean or proterozoic metasedimentary rocks and intruded by paleoproterozoic granites whereas the rae terrane on its west boundary is comprised primarily of still higher grade archean rocks the calc alkaline wathaman batholith was intruded at ca 1 855 ga and the orogenic internides to the east of it include mostly high grade mafic and intermediate volcanic rocks crystallized between 1 92 and 1 86 ga terminal collision and orogenesis in the internides have been constrained to be later than 1 82 ga and earlier than 1 78 ga mineral u pb data presented here unequivocally demonstrate that high grade metamorphism and large volume anatexis across the southern hearne province were approximately synchronous with terminal collision and high grade metamorphism across the trans hudson orogen zircon data for most samples form complex arrays in concordia space but demonstrate a high grade metamorphic overprint at 1810 1800 ma zircons typically have inherited components of archean age suggesting the presence of extremely old material in the hearne and a potential archean connection with the rae province sm nd data indicating ca 3500 ma model ages for similar parageneses in both terranes further support the proposed archean connection between hearne and rae province and the great antiquity of hearne crust sm nd data also elucidate the similarity of the ca 1 80 ga anatectic granites of the hearne to the 1 82 ga junction granite which intruded the virgin river shear zone and constrains the timing of final motion on that structure monazite 207 pb 206 pb ages are not older than 1812 ma or younger than 1769 ma and rutile 207 pb 206 pb ages and u pb ages are tightly constrained at about 1750 ma these data in combination with results of standard thermobarometric analysis permit determination of post orogenic cooling and denudation rates high cooling 7 c ma and denudation 240 m ma rates suggest fault accomodated uplift during post orogenic collapse

geochemical isotopic and geochronlologic constraints on the formation of the eagle point basement hosted uranium deposit athabasca basin saskatchewan canada and recent remobilization of primary uraninite in secondary structures the athabasca basin hosts many world class unconformity related uranium deposits recently uranium reserves for the eagle point basement hosted deposit have increased with the discovery of new mineralized zones within secondary structures a paragenetic study of eagle point reveals the presence of three temporally distinct alteration stages a pre athabasca alteration a main alteration and mineralization comprised of three substages and a post main alteration and mineralization stage that culminated in remobilization of uraninite from primary to secondary structures the pre athabasca alteration stage consists of minor amounts of clinochlore followed by dolomite and calcite alteration in the hanging wall of major fault zones and kaolinitization of plagioclase and k feldspar caused by surface weathering the main alteration and uranium mineralization stage is related to three temporally distinct substages all of which were produced by isotopically similar fluids a major early alteration substage characterized by muscovite alteration and by precipitation ca sr lree rich aluminum phosphate sulfate minerals both from basinal fluids at temperatures around 240 c prior to 1 600 ma the mineralization substage involved uraninite and hematite precipitated in primary structures the late alteration substage consists of dravite uranophane beta veins calcite veins and sudoite alteration from mg ca rich chemically modified basinal fluids with temperatures around 180 c the post main alteration and mineralization stage is characterized by remobilization of main stage uraninite from primary to secondary structures at a minimum age of ca 535 ma u pb resetting events recorded on primary and remobilized uraninites are coincident with fluid flow induced by distal orogenies remobilizing radiogenic pb to a distance of at least 225 m above the mineralized zones

fluid p t x characteristics and evidence for boiling in the formation of the phoenix uranium deposit athabasca basin canada implications for unconformity related uranium mineralization mechanisms abstract the phoenix uranium deposit in the southeastern athabasca basin canada is a typical unconformity contact hosted uranium deposit characterized by an association with reactivated basement faults graphite rich rocks in the underlying basement and a pervasive clay alteration halo surrounding the mineralized zones petrographic results suggest that the mineralizing hydrothermal system was characterized by alternating desilicification and silicification events uraninite and clay size minerals tourmaline kaolinite illite and minor chlorite mainly precipitated in the desilicification periods whereas hydrothermal quartz mainly drusy quartz formed during the silicification periods primary fluid inclusions in the hydrothermal quartz are inferred to represent the ore forming fluids even though quartz did not co precipitate with uraninite the coexistence of multiple types of fluid inclusions liquid dominated biphase vapor dominated biphase vapor only and halite bearing triphase within individual fluid inclusion assemblages is interpreted to indicate fluid boiling and heterogeneous trapping bulk fluid inclusion volatile analysis by mass spectrometry indicates h2o as the dominant species with less than 1 mol non aqueous volatiles that show a compositional trend typical of fluid boiling microthermometric and cryogenic raman spectroscopic analyses indicate that the mineralizing fluids are of h2o nacl cacl2 mgcl2 composition with salinities ranging mainly from 23 4 to 31 1 wt the liquid dominated biphase inclusions excluding those interpreted to have resulted from heterogeneous trapping have homogenization temperatures from 90 to 157 c these data are generally consistent with the classical diagenetic hydrothermal model in which basinal brines that extracted uranium from the basin or the basement were channeled along reactivated basement faults and precipitated uraninite near the unconformity through reaction with reducing agents however the relatively low fluid inclusion homogenization temperatures documented in this paper together with fluid boiling inferred from fluid inclusion assemblages suggest that the deposit may have formed in a shallower environment 2 5 km than assumed in the conventional diagenetic hydrothermal model 5 km abrupt fluid pressure drops during episodic faulting may have resulted in fluid boiling flash vaporization changing the fluid ph and promoting uraninite precipitation with the alternating liquid vapor conjugates of the boiling system resulting in alternating precipitation of quartz and uraninite respectively

topographic features of the sub athabasca group unconformity surface in the southeastern athabasca basin and their relationship to uranium ore deposits topographic features of the sub athabasca unconformity surface such as paleovalleys topographic highs and fault scarps have been documented locally in the eastern athabasca basin and available data indicate that they are spatially associated with mineralization however the mechanisms by which such topographic features were generated their size and distribution at the regional scale as well as their relationship to mineralization are still not completely understood a 100 by 60 square kilometre area of the southeastern athabasca basin encompassing the mcarthur river phoenix and key lake deposits was selected to study the relationship between these topographic features and u mineralization in this region three dominant sets of sub vertical faults were identified on the basis of aeromagnetic data northeast trending north northwest trending and northwest trending a detailed three dimensional 3 d model of this part of the basin was constructed using data from more than 1200 drill holes th

intraformational fluid flow in the thuringian syncline germany evidence from stable isotope data in vein mineralization of upper permian and mesozoic sediments abstract vein mineralization observed in boreholes quarries and outcrops of upper permian and mesozoic sediments in the thuringian syncline germany was investigated for the first time by petrography electron microprobe analysis and stable isotope analysis the objective was a characterization of paleo fluid systems within this basin veins are mostly restricted to nw se trending fault systems and comprise carbonates calcite dolomite minor sulfates gypsum anhydrite celestite barite and rarely sulfides they are variably distributed within the late paleozoic to mesozoic succession calcite vein mineralization occurs in almost all triassic strata though dominating in the lower muschelkalk subgroup mu gypsum anhydrite veins occur in the middle keuper subgroup km middle muschelkalk subgroup mm middle and upper buntsandstein subgroup sm so as well as in the upper permian zechstein sulfate and carbonate isotope analyses indicate that most vein mineralization dominantly crystallized from intraformational fluids within the upper permian and triassic sediments crystallization from descending meteoric waters was observed especially for calcite veins in the lower muschelkalk but also for gypsum anhydrite veins in the upper buntsandstein mineralization from ascending carbonate ph buffered warm waters was restricted to individual parts of the southern deep reaching main border fault zone of the thuringian syncline mixing and fault crossing fluid movements are subordinate within the thuringian syncline we conclude that no large scale cross formational fluid flow occurred in thuringian syncline over the last millions of years

brine rock interaction in the athabasca basement mcarthur river u deposit canada consequences for fluid chemistry and uranium uptake terra nova 22 303 308 2010 abstract the nature of uranium source rocks transport conditions and deposition processes are still highly controversial for world class unconformity related u deposits this article presents the first detailed chemistry of brines associated with the giant mcarthur river u deposit canada la icp ms analysis of individual fluid inclusions suggests mixing between a na ca mg k sr ba brine and a ca mg na k sr ba brine the brines share a common origin evaporated seawater and show evidence for contrasting interaction with basement rocks the na rich brine lost mg and k in alteration haloes around u ores while the ca rich brine results from na ca exchange and sr ba gain u concentrations 0 3 530 g g 1 are anomalously high compared with usual basinal fluids this indicating that u uptake occurred within basement rocks the two brine end members have mixed within the main u deposit area which could be one of the major driving forces for u deposition

new insights from 2 and 3 d numerical modelling on fluid flow mechanisms and geological factors responsible for the formation of the world class cigar lake uranium deposit eastern athabasca basin canada the cigar lake uranium deposit in the athabasca basin is the world s second largest high grade unconformity related uranium deposit its distinct geological architecture includes heterogeneous basement lithologies a local basement high and sub vertical faults the sub vertical faults are classified further into two sub types faults that are restricted to the basement termed basement faults and faults that are distinctly related to post athabasca fault reactivation in that they extend upward into the sandstone termed extended basement faults this study aims to evaluate the effects of the aforementioned geological factors on the fluid flow patterns under two different driving forces buoyancy due to variation of fluid density or thermal convection and deformation or a combination of them and to determine the most probable fluid flow scenarios for the formation of the deposit the numerical results show that fluid flow is strongly affected by the two types of faults while the basement faults represent fluid paths with complex fluid flow patterns depending on the driving forces providing favourable physical conditions for different chemical processes such as fluid fluid and fluid rock interactions the extended basement faults enhance the permeability of an e w corridor within the sandstone and significantly strengthen the overall upwelling flow above the basement faults promoting sandstone hosted mineralization the numerical results also suggest that the main deposit likely formed via fluid convection during tectonically quiet periods although faulting played a critical role in increasing permeability in turn enhancing thermal convection

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

the 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

laboratory measurements on turbulent pressure fluctuations in and above gravel beds the statistics of pressure fluctuations above and within three types of porous granular beds such as in gravel bed streams rivers and man made canals are investigated by data gained via laboratory flume experiments the flow conditions examined include a diversity of hydrodynamic loads that increase up to the point where single grains are moving from time to time without causing severe modification to the bed texture and the related positions of the pressure sensors analysis is performed by means of histograms and spectral techniques and vertical intensity profiles two simplified equations are found that describe the vertical decrease for the standard deviation of the measured fluctuations indicating drag and lift respectively nondimensionalized by the mean bed shear stress the former fluctuation is described by a crude linear fit whereas the latter clearly shows that the lift intensity decreases exponentially in the porous bed with a decay distance of one to two times the equivalent grain roughness within the subsurface layer the standard deviation reaches a nonzero constant mainly dominated by long wave pressure fields that are convected in the outer flow these findings can be used in future sediment transport models that use force balance approaches to determine incipient motion conditions

structural constraints and localization of gold mineralization in leather jacket lodes ballarat victoria australia gold mineralization at the ballarat east deposit central victoria australia is hosted in lodes that are historically known as leather jackets these are quartz dominant vein arrays related to low displacement w dipping faults 45 that transect the core and or eastern limb of tight asymmetric n s trending anticlines the leather jacket lodes typically have dip extents from 5 to 65 m widths of 20 m and strike lengths up to hundreds of meters but their along strike continuity is disrupted by oblique low displacement listric faults known as cross courses the gold lodes are characterized by distinct phases of sulfide paragenesis with minor gold arsenopyrite pyrite defining the early sulfide stage late stage coarse gold was precipitated with galena sphalerite pyrrhotite chalcopyrite late pyrite also occurs the gold mineralization events are linked to low strain mineralized fracture networks which are closely related to the final deformation stages and the amplification of the major folds enclosing the lodes this amplification produced domal fold culminations with plunges 30 and localized minor parasitic folds with shallower plunges 10 a network of dilation sites on the w dipping faults preferentially developed in the cores of anticlines particularly in zones where there are changes in strike of bedding or fault bifurcation and refraction through contrasting sandstone and interbedded packages of sandstone and shale numerical three dimensional simulations were undertaken to test our geologic observations and replicate conditions controlling the emplacement of the leather jacket lodes two different scenarios were investigated first to determine how changes in the local stress field orientation influences dilation and fluid infiltration secondly to test variations in fault geometry during the last stages of deformation that is within the final 2 of shortening when most of the mineralized sites were created results show that strain and fluid flow localized along refracted sections of faults and around changes in dip specifically on the shallower dipping sections within subvertical sandstone units this is consistent with the observation that high grade gold bearing quartz is associated with localized changes in fault dip in thicker sandstone and sandstone shale packages there was also a component of strike slip motion and near field nw to se or n to s stress fields which can be attributed to the development of a component of out of plane motion during the development of fold culminations the preferred model for the distribution of the high grade auriferous vein arrays defining the leather jacket lodes is one of fold amplification and extension parallel to the fold axes which produced an increasing out of plane relaxation the main fluid conduits responsible for the leather jacket style of mineralization involve infiltration along steep bedding parallel faults and veins that link up with the arrays of low displacement w dipping faults

mixing of sodic and calcic brines and uranium deposition at mcarthur river saskatchewan canada a raman and laser induced breakdown spectroscopic study of fluid inclusions the richest u deposit in saskatchewan canada occurs in the mcarthur river area in the vicinity of the unconformity between the athabasaca sandstones and an archean to lower proterozoic basement paleofluids related to the silicification of the sandstones and the formation of pre and postore cements in breccias were studied using microthermometry raman microspectroscopy and laser induced breakdown spectroscopy libs on individual fluid inclusions a detailed reconstruction of the fluid composition in the system na ca mg cl shows that two types of brines are responsible for the main quartz cements an nacl rich brine 25 wt nacl up to 14 wt cacl 2 and up to 1 wt mgcl 2 which is interpreted as a primary formation water that was expelled from bedded evaporites and a cacl 2 rich brine 5 8 wt nacl 20 wt cacl 2 and up to 11 wt mgcl 2 which is considered to have formed during the interaction between the nacl rich brine and ca rich minerals in the basement and was introduced into the fault system and mixed with the nacl rich brine during the critical stage of u deposition the pressure temperature conditions of formation of the quartz cements are estimated to be 1 200 to1 400 bars and 190 to 235 c for the silicification events during the preore stage and 500 to 900 bars after a pressure decrease from lithostatic conditions and slightly lower temperatures due to the mixing of the nacl rich brine with the cooler approx 140 c cacl 2 rich brine during the main stage of breccia sealing temperature and pressure drops combined with the effects of brine mixing appear to be key factors for the main stages of quartz cementation and u deposition at the mcarthur deposit

synchronous egress and ingress fluid flow related to compressional reactivation of basement faults the phoenix and gryphon uranium deposits southeastern athabasca basin saskatchewan canada previous studies on unconformity related uranium deposits in the athabasca basin canada suggest that egress flow and ingress flow can develop along single fault systems at different stages of compressional deformation this research aims to examine whether or not both ingress and egress flow can develop at the same time within an area under a common compressional stress field as suggested by the reverse displacement of the unconformity surface by the basement faults the study considers the phoenix and gryphon uranium deposits in the wheeler river area in the southeastern part of the athabasca basin two dimensional numerical modeling of fluid flow coupled with compressional deformation and thermal effects was carried out to examine the fluid flow pattern the results show that local variations in the basement geology under a common compressional stress field can result in both egress and ingress flow at the same time the fault zone at phoenix underwent a relatively low degree of deformation as reflected by minor reverse displacement of the unconformity and egress flow developed whereas the fault zone at gryphon experienced a relatively high degree of deformation as demonstrated by significant reverse displacement of the unconformity and ingress flow was dominant the correlation between strain development and location of uranium mineralization as exemplified by gryphon and phoenix uranium deposits suggests that the localization of dilation predicted by numerical modeling may represent favourable sites for uranium mineralization in the athabasca basin

structural controls on fluid flow during compressional reactivation of basement faults insights from numerical modeling for the formation of unconformity related uranium deposits in the athabasca basin canada the unconformity related uranium deposits in the athabasca basin canada are generally associated with reactivated basement faults crosscutting the basin basement unconformity two dimensional 2 d numerical modeling of coupled compression and fluid flow in a reverse fault system was carried out with varying dip angles preexisting offsets and degrees of deformation the results indicate that the fluid flow pattern associated with structural reactivation is sensitive to the degree of bulk shortening at a low bulk shortening stage fluid is driven up along the fault zone into the sandstone in the basin whereas at a relatively high bulk shortening stage fluid tends to flow down into the fault zone and the basement this is interpreted to indicate that the fluid pressure within the fault zone increases at the early stage of deformation due to pore volume decreases in relation to shortening whereas the fluid pressure within the fault zone decreases at later stages of deformation due to dilation in relation to fracturing and reverse displacement variation of the dip angles and preexisting offsets of the faults shows little effect on the strain distribution and fluid flow patterns the simulation results demonstrate that both unconformity contact and basement hosted orebodies may be generated at different stages of deformation within the same fault system under a unified compressional stress regime

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

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 u rich mineralizing fluids through basinal brine migration within basement hosted shear zones a large scale study of the fluid chemistry around the unconformity related cigar lake u deposit saskatchewan canada abstract the evolution of basinal brines through percolation into basement rocks is studied in the paleo to mesoproterozoic athabasca basin and its underlying basement this specific geological context includes the evolution of a nacl rich basinal brine to a u mineralizing cacl2 rich brine that is of particular importance for the understanding of the formation of giant u deposits the objective of this study is to determine the physico chemical parameters p t x of the basinal brines and their changes both within the athabasca group sandstones and the underlying basement lithologies on the scale of several km around the world class unconformity related cigar lake u deposit particularly this study focuses on the basement hosted fault systems that are considered to be the main fluid flow pathways a comprehensive study including microthermometry raman spectroscopy and la icp ms analyses was carried out on fluid inclusions as was a semi quantitative estimation of the microfracture paleoporosity based on the surface density of fluid inclusion planes initial nacl rich brines were trapped during early diagenesis c a 1 7 1 65 ga in dickite rich sandstones under a three to seven kilometers thick sedimentary cover at around 90 to 150 c under hydrostatic pressure or at 120 210 c assuming lithostatic conditions at the time of u deposits formation ca 1 46 1 29 ga these brines percolated through the entire basement but preferentially within the damage zones of some graphite rich faults formed during the ca 1 8 ga trans hudson orogeny and active during the subsequent retrograde metamorphism and exhumation ca 1 8 1 72 ga the circulation of the basinal brines into these structures was enhanced and structurally controlled by the microfracture network inherited from earlier brittle reactivation during basement uplift the resulting high microfracture paleoporosity in the vicinity of some but not all of these structures favored intense interaction between the brines and basement rocks that induced the formation of illite sudoite alteration haloes in the basement the percolating brines scavenged mn k ba sr and especially u and evolved from the original nacl dominant composition toward a higher salinity cacl2 rich composition the resulting u bearing brine mixed with the unmodified diagenetic nacl rich brine in above and all along the reactivated faults either during thermal convection in isobaric settings and higher temperatures 110 200 c or through episodic tectonic reactivation in isothermal settings through episodic pressure fluctuation in direct vicinity of the u deposits the interactions between the brines and the basement rocks were the strongest which is marked by the highest intensity of alteration of the host rocks thus the formation of ore forming fluids resulted from the interaction between nacl rich basinal brines and highly microfractured basement rocks this study reinforces the hypothesis that interaction with basement rocks enhanced by strong fluid flow in cataclastic zones can significantly modify the physico chemical characteristics of basin derived brines leading to the formation of mineralizing fluids and the genesis of giant ore deposits such as the unconformity related u deposits

modelling of deformation around magmatic intrusions with application to gold related structures in the yilgarn craton western australia abstract this study simulates rock deformation around high temperature granite intrusions and explores how gold bearing shear zones near intrusions were developed in the yilgarn using a new continuum damage mechanics algorithm that considers the temperature and time dependent elastic visco plastic constitutive behaviour of crustal materials the results demonstrate that strain rates have the most significant effects on structural patterns for both extensional and compressional cases smaller strain rates promote the formation of narrow high strain shear zones and strong strain localisation along the flank or shoulder areas of the intrusion and cold granite dome wider diffuse shear zones are developed under higher strain rates due to strain hardening the cooling of the intrusion to background temperatures occurred over a much shorter time interval when compared to the duration of deformation and shear zones development strong strain localisation near the intrusion and shear zone development in the crust occurred under both extensional and compressional conditions there is always clear strain localisation around the shoulders of the intrusion and the flanks of the cold granitic dome in early deformation stages in the models containing a pre existing fault strain localisation near the intrusion became asymmetric with much stronger localisation and the development of a damage zone at the shoulder adjacent to the reactivated fault at higher deformation stages the models produced a range of structural patterns including graben and half graben basin extension pop up wedge structures compression tilted fault blocks and switch of shear movement from reverse to normal on shear zones the model explains in part why a number of gold deposits e g wallaby and paddington deposits in the yilgarn were formed near the flank of granite cored domes and deep tapping faults and shows that the new modelling approach is capable of realistically simulating high strain localisation and shear zone development

thermal profiles inferred from fluid inclusion and illite geothermometry from sandstones of the athabasca basin implications for fluid flow and unconformity related uranium mineralization abstract the proterozoic athabasca basin and underlying basement host numerous unconformity related uranium deposits that were formed from extensive fluid circulation near the basement cover interface although it is generally agreed that the mineralizing fluids were basinal brines it is still unclear what driving forces were responsible for the circulation of the basinal fluids because different fluid flow driving forces are associated with different thermal profiles knowing the basin scale distribution of paleo fluid temperatures can help constrain the fluid flow mechanism this study uses fluid inclusions entrapped in quartz overgrowths and authigenic illite in sandstones from three drill cores wc 79 1 bl 08 01 and dv10 001 in the central part of the athabasca basin as thermal indicators of paleo fluids in the basin a total of 342 fluid inclusions in quartz overgrowths were studied for microthermometry the homogenization temperatures t h range from 50 to 235 c recording the minimum temperatures in various diagenetic stages temperatures estimated from illite geothermometry 121 points range from 212 to 298 c which are systematically higher than partly overlapping the t h values suggesting that illite was precipitated in hotter fluids following the formation of quartz overgrowths neither the fluid inclusion t h values nor the illite temperatures show systematic increase with depth in individual drill cores this together with the high illite temperatures that cannot be explained by burial at a normal geothermal gradient 35 c km is interpreted to indicate that basin scale fluid convection took place during the diagenetic history of the basin prolonged fluid convection is inferred to be responsible for delivering uranium extracted from the basin or the upper part of the basement to the unconformity where uranium mineralization took place due to redox reactions associated with fluid rock interaction or structurally controlled fluid mixing

mechanical controls on fluid flow during regional metamorphism some numerical models the control of fluid flow by plastic deformation during metamorphism is critical to our understanding of metamorphic processes various geological observations and field studies demonstrate the consequences of fluid flow control by deformation so that the concept appears to be accepted at least for small scale public for example faults and vein public however the concept appears to be less well recognized at regional scales considered here are examples of simple conceptual models based on fully coupled mechanical fluid flow concepts they include deformation of a section of fluid saturated crust containing a block or a layer of material of different properties from its surrounds in particular rheological and permeability contrasts between rock types during deformation associated with regional metamorphism are sufficient to control the form of fluid flow over the range of a few kilometres low contrasts and small strains allow pervasive fluid flow whereas greater contrasts and increasing strains cause focusing of the flow such focusing is generally associated with localization of the deformation especially for a strongly dilatant elastic plastic material however a rate of fluid flow much greater than the rate of deformation may result in pervasive flow although for most models pervasive flow is difficult to attain over regional distances furthermore lateral and downward fluid flow may occur demonstrated here by simple models for folding and for deformation of regions containing plutons therefore such modelling may be used as a means of testing the various hypotheses concerning the volumes of fluid predicted to have passed through some rock volumes numerical models of the future will become increasingly complex and powerful allowing greater coupling of thermal mechanical chemical and fluid flow effects and based more on the physical processes involved combined field and laboratory studies will provide correspondingly greater understanding and will permit the determination of the timing of fluid flow and structural controls on fluid flow patterns

fluid flow in extensional environments numerical modelling with an application to hamersley iron ores the mechanical feasibility of focusing both surface and basinal derived fluids towards sites of iron ore genesis during proterozoic deformation in the hamersley province is tested here by computer simulation finite difference modelling of porous media flow during extensional deformation of a mountain range shows that surface fluids are drawn towards areas of failure and focus into the centre of the mountain the addition of permeable structures such as a normal fault provides focused fluid pathways in which mechanical and geological conditions are particularly conducive to both upward and downward flow upward flow from the base of the fault within the model overall is favoured by low permeability basement materials and supra hydrostatic pore pressures downward migration of fluids becomes more prominent as extension progresses and upward fluid flow from the base diminishes the introduction of sedimentary layering into the models allows lateral fluid flow such that sites of potential fluid mixing may then occur within permeable iron formation units close to the fault zone allowing parts of the stratigraphy to become more permeable as a function of high fluid flux simulates permeability enhancement by silica dissolution as a mechanism for iron ore genesis the involvement of both basinal and surficial fluids in the genesis of the ore deposits is supported by the mechanical models and in addition provides an explanation for a progression from relatively reduced to oxidised conditions at the mt tom price deposit and possibly other large deposits with time