the karpinka lake uranium prospect saskatchewan a possible metamorphosed middle precambrian sandstone type uranium deposit the karpinka lake prospect is a strata bound uranium deposit hosted by aphebian meta sediments located just to the south of the important unconformity type deposits at key lake in northern saskatchewan the uranium occurs as disseminated uraninite and brannerite in sillimanite bearing quartz feldspar biotite gneisses which on the basis of major element data are interpreted to represent metamorphosed arkoses sulfides predominantly pyrrhotite occur in amounts up to 10 volume percent in the uraniferous gneisses these zones are flanked by sulfide poor gneisses containing over 10 percent titanomagnetite and ilmenite the uraninite is commonly in contact with sillimanite and the brannerite is commonly rimmed by sulfides both minerals have similar u th ratios of approximately 35 1 bulk chemical analyses suggest that the host rocks were leached of sodium prior to metamorphism the mineralized rocks show higher than background concentrations of copper molybdenum and vanadium u pb isotopic analyses of the uraniferous phases indicate that the deposit is at least 1 800 m y in age this age is approximately the same as that of the hudsonian orogeny and is interpreted to reflect metamorphic resetting of the isotopic clock the 1 800 m y age for the karpinka lake mineralization is at least 500 m y greater than the oldest dates obtained for the nearby unconformity type deposits it is proposed that the karpinka lake deposit represents a metamorphosed epigenetic sand stone type uranium deposit a model is presented which involves sulfidation of iron titanium oxide rich arkoses and subsequent alteration of these rocks by uranium bearing solutions uraninite is inferred from its association with sillimanite to have formed by uranium adsorption on precursor kaolinitc produced by alteration of detrital feldspar or felsic volcanic fragments brannerite is considered to have formed by uranium adsorption on titania sponges created by the alteration of iron titanium oxides the demonstrable existence of aphebian strata bound uranium mineralization and the observation that the saskatchewan unconformity type deposits are controlled by faults parallel to the aphebian gneissosity lend support to previous suggestions that the basement supplied the uranium for the younger unconformity type deposits

an abyssal carbonate compensation depth overshoot in the aftermath of the palaeocene eocene thermal maximum the palaeocene eocene thermal maximum was associated with a massive release of carbon marine sediments suggest a temporary deepening of the calcite compensation depth indicating extensive silicate weatheringin the aftermath of the event the palaeocene eocene thermal maximum was associated with a massive release of carbon marine sediments suggest a temporary deepening of the calcite compensation depth indicating extensive silicate weatheringin the aftermath of the event during the palaeocene eocene thermal maximum petm about 56 million years ago thousands of petagrams of carbon were released into the atmosphere and ocean in just a few thousand years followed by gradual sequestration over approximately 200 000 years if silicate weathering is one of the key negative feedbacks that removed this carbon a period of seawater calcium carbonate saturation greater than pre event levels would be expected during the event s recovery phase in marine sediments this should be recorded as a temporary deepening of the depth below which no calcite is preserved the calcite compensation depth ccd previous and new sedimentary records from sites that were above the pre petm ccd show enhanced carbonate accumulation following the petm a new record from an abyssal site in the north atlantic that lay below the pre petm ccd shows a period of carbonate preservation beginning about 70 000 years after the onset of the petm providing the first direct evidence for an over deepening of the ccd this record confirms an overshoot in ocean carbonate saturation during the petm recovery simulations with two earth system models support scenarios for the petm that involve a large initial carbon release followed by prolonged low level emissions consistent with the timing of ccd deepening in our record our findings indicate that sequestration of these carbon emissions was most likely the result of both globally enhanced calcite burial above the ccd and at least in the north atlantic an over deepening of the ccd

the kivalliq igneous suite anorogenic bimodal magmatism at 1 75ga in the western churchill province canada abstract the kivalliq igneous suite 1 77 1 73 ga includes the nueltin granite intrusions gabbro and anorthosite intrusions three swarms of mafic dykes and basalt rhyolite and pyroclastic rocks of the pitz formation wharton group middle dubawnt supergroup it was emplaced in the reworked archaean hinterland of the trans hudson orogen in the central western churchill province wcp of the canadian shield the nueltin granites have field relations mineral assemblages and compositions typical of metaluminous to peraluminous proterozoic to recent rapakivi granites and the suite comprises a classic bimodal anorogenic province kivalliq rhyolites granites were erupted emplaced in a n s band the nueltin corridor about 700 km long and 300 km wide with volcanic rocks and dykes concentrated at the north end and coarse plutonic rocks to the south the mcrae lake dyke swarm originates among three prominent gabbro anorthosite intrusions inside the corridor and forms a narrow array extending a minimum of 600 km to the ne along the central axis of the wcp early mafic rocks intrusions and some lavas 1 77 ga had an alkali basalt parent with subalkaline basalts sills dykes and mafic enclaves present at the peak time of granite emplacement 1 75 ga average initial nd of basaltic rocks at 1 75 ga is 4 0 indicating a significant crustal component sm nd depleted mantle model ages of granites and rhyolites average initial nd 8 7 range from 2 2 to 3 ga consistent with melted archaean crust variably mixed with juvenile basalt metallogenic prospects of the kivalliq suite include u th zr y ree enriched granite and syenite epithermal ag au at silicic centres including mafic felsic ring complexes and pb cu sulphides associated with mafic intrusions topaz rhyolites are present but sn enriched rocks have not been observed the kivalliq suite is one of about 15 prominent anorogenic provinces and dyke swarms which erupted within the nuna supercontinent at ca 1 75 ga and the thermal effects of the kivalliq event are recorded in u pb and k ar data throughout most of the western churchill province

collisional snowbird tectonic zone resurrected growth of laurentia during the 1 9 ga accretionary phase of the hudsonian orogeny the 2800 km long snowbird tectonic zone is one of the most controversial tectonic features of the canadian shield metamorphic and in situ geochronologic data reported here reveal that a 1 9 ga medium to high pressure belt extends along most of this tectonic zone in contrast to recent interpretations a collisional origin is indicated by the length of this metamorphic belt tectonic thickening documented in parts of it geological contrasts across it and subduction type microdiamonds within it this collisional event marks a pre 1 865 ga phase of the hudsonian orogeny involving microcontinent accretion that was fundamental to the growth of laurentia

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

fluorapatite in the paleoproterozoic thelon basin structural stratigraphic context in situ ion microprobe u pb ages and fluid flow history fluorapatite cements have been documented at more than 18 localities in the thelon basin canada occupying stratigraphic positions from the paleosol below the unconformity to well within the upper parts of depositional sequence of the fluvial siliciclastic thelon formation ion microprobe analyses targeted using cathodoluminescence images to areas of higher uranium content on petrographically characterized cements provide the most precise pin on the timing of mesodiagenesis in the northeastern part of the thelon basin at 1667 5 ma expulsion of phosphate rich basinal brines was associated with development of faults and local breccias in the lower strata where extensive quartz cementation took place before the apatite event the new data do not support previous interpretations for multiple episodes of fluorapatite cementation within the basin despite the wide range of stratigraphic positions and variations in style of occurrence the tectonic cause remains speculative as does the relationship of the fluorapatite cements to the unconformity style uranium mineralization thelon fluorapatite cements are older than those reported in the athabasca basin suggesting distinct fluid flow histories occurred within the two basins the difference in timing indicates that the basinwide events that generated the fluids with the chemistry capable of producing fluorapatite cement took place independently but under similar conditions within the thelon and athabasca basins

basin related uranium mineral systems in australia a review of critical features abstract this paper reviews critical features of basin related uranium mineral systems in australia these mineral systems include proterozoic unconformity related uranium systems formed predominantly from diagenetic fluids expelled from sandstones overlying the unconformity sandstone hosted uranium systems formed from the influx of oxidised groundwaters through sandstone aquifers and calcrete uranium systems formed from oxidised groundwaters flowing through palaeochannel aquifers sand and calcrete the review uses the so called source pathway trap paradigm to summarise critical features of fertile mineral systems however the scheme is expanded to include information on the geological setting age and relative timing of mineralisation and preservation of mineral systems the critical features are also summarised in three separate tables these features can provide the basis to conduct mineral potential and prospectivity analysis in an area such analysis requires identification of mappable signatures of above mentioned critical features in geological geophysical and geochemical datasets the review of fertile basin related systems shows that these systems require the presence of at least four ingredients a source of leachable uranium and vanadium and potassium for calcrete uranium deposits suitable hydrological architecture enabling connection between the source and the sink site of accumulation physical and chemical sinks or traps and a post mineralisation setting favourable for preservation the review also discusses factors that may control the efficiency of mineral systems assuming that world class deposits result from more efficient mineral systems the review presents a brief discussion of factors which may have controlled the formation of large deposits in the lake frome region in south australia the chu sarysu and syrdarya basins in kazakhstan and calcrete uranium deposits in the yilgarn region western australia

tectonic entrapment and its role in the evolution of continental lithosphere an example from the precambrian of western canada new geophysical data acquired over the buried crystalline basement of western canada provide constraints on the history of tectonic assembly of the western canadian shield in the interval 1 75 1 85 ga specifically these data provide new perspectives on the evolution of an archean continental fragment heame province that was trapped in a tectonic vise between coeval orogenic belts that dipped beneath the hearne province the trans hudson orogen developed along the southeastern margin of the hearne province as a series of ocean floor oceanic arc and arc marginal basins were telescoped and thrust obliquely beneath the hearne along the northwest edge of the hearne collapse and subduction of a narrow marginal basin now marked by the subsurface extension of the snowbird tectonic zone led to formation of magmatic arc and collision of older proterozoic terranes the hearne province itself is characterized by regional granulite grade metamorphism and evidence of extensive and pervasive partial melting of the crust the internal character of the hearne province seen on crustal seismic reflection profiles is that of a crustal scale structural fan with reflection fabrics that verge toward the bounding orogens the deformation of the hearne is predominantly of paleoproterozoic age and constitutes a thorough reworking of this formerly archean crustal domain over a distance of more than 600 km across strike entrapment and thermal weakening of the hearne resulted from mechanical coupling of inferred buoyant subduction collision zones and removal of or modification of archean lithospheric mantle that may have originally formed the keel to the hearne long period magnetotelluric profiles show that anomalously conductive mantle lithosphere underlies the present day hearne province which is attributed to metasomatic modification of the subcontinental lithosphere following collisional thickening and delamination convective removal of thickened lithosphere in the proterozoic tectonic entrapment as illustrated by the proterozoic structural and thermal evolution of the hearne province crust and subcontinental mantle may be an example of the lithospheric consequences of opposing collisional polarity during assembly of continents

simulating brittle fault growth from linkage of preexisting structures many researchers have proposed conceptual models of fault development that are based on the linkage of preexisting structures such as isolated faults joints or veins to date such models largely use theoretical mechanics to explain the detailed damage zone geometries observed in linkage structures in this paper we present the first numerical simulations of the temporal and spatial development of geometrically complex fault linkage structures using the finite element model for fault damage zone evolution mopedz simulations show spatial and temporal fault zone evolution for a range of preexisting joint or fault geometries and stress conditions simulations show that linkage geometries are governed by three key factors the stress ratio the original joint geometry such as contractional or dilational configurations and the orientation of the principal stress simulated linkage structures display close correspondence to field observations of fault zone geometry with all secondary and tertiary damage features being reproduced the research also demonstrates that given information on the regional stress conditions numerical modeling can be used to predict fault zone geometries and hence identify the most and least likely structures for promoting fluid flow

clay mineralogy and isotope geochemistry of the alteration halo at the cigar lake uranium deposit the clay size fraction of the alteration halo associated with the cigar lake uranium deposit consists of illite with subordinate kaolinite sudoite al chlorite fe chlorite hematite and traces of an illite chlorite mixed layer mineral the kubler index of illite crystallinity ranges from 2 0 to 6 7 the most altered samples average 4 0 these data indicate that high grade diagenetic to anchizonal conditions have been reached within the alteration halo intensity ratios of the 002 and 001 illite reflections i 002 i 001 are generally greater than 0 4 the phengite muscovite boundary reflecting aluminum rich illites illite composition approaches hydromuscovite whereas 1m and 2m polytypes prevail regionally the presence of 3t and 2m polytypes in the alteration halo suggests that locally higher temperatures have been attained than the regional estimates of 180 220 c k ar dates for illite rich samples from 1255 to 1148 ma could reflect variable resetting of the k ar system during hydrothermal f

giant uranium deposits formed from exceptionally uranium rich acidic brines the athabasca basin canada is home to some of the world s largest uranium deposits analysis of preserved ore forming fluids and experimental measurement of uranium solubility in analogous solutions show that the giant deposits could have formed relatively rapidly from extremely uranium rich brines under acidic conditions

radiation damage rims in quartz from uranium bearing sandstones abstract using cathodoluminescence cl mode of a scanning electron microscope sem radiation damage in quartz is made visible in uranium vanadium bearing sandstones located in the salt wash member of the morrison formation jurassic from the colorado plateau u s a detrital quartz grains surrounded by uranium minerals display radiation damage rims three concentric rims with thicknesses of 37 m 24 m and 16 m have been observed the rims are similar to halos surrounding uranium and thorium rich accessory minerals observed by owen 1988 they are due to alpha particles which create damage when penetrating a medium the width of the rims agrees well with the bragg kleeman rule and corresponds to the most energetic alpha particles in the 238u decay series sandstones entirely cemented by vanadium clays also exhibit radioactive rims which demonstrates that uranium has been removed during diagenesis these results have important implications for the uranium ore genesis in the salt wash sandstones because they imply an ancient episode of uranium leaching prior to recent weathering therefore cathodoluminescence in sandstones may be useful in recognizing ancient zones or episodes of accumulation and leaching of alpha emitting nuclides from the uranium series

a model for the structure and development of fault zones cross sections of fault zones commonly show two sub parallel slip surfaces which bound more or less deformed rock this characteristic geometry can be explained by a combination of 9tip line9 and 9asperity9 bifurcation processes fault tip line bifurcation is due to irregular tip line propagation resulting in leading edge segmentation fault overlap and eventual duplex formation asperity bifurcation removes a fault surface irregularity by the generation of a new slip surface which by passes the original slip surface repetitions of either or both bifurcation processes give rise to a fault zone with a complex and unpredictable internal geometry these processes are described mainly on the basis of observation of normal faults hut can be applied to other fault types fault zone thickening by bifurcation is intermittent rather than progressive and localised fault zone thinning may occur

ar ar and u pb geochronology of a late paleoproterozoic rift basin support for a genetic link with hudsonian orogenesis western churchill province nunavut canada abstract the baker lake group baker sequence represents the record of the formative stage of baker lake basin a series of generally elongate northeast striking half graben and fault bounded troughs filled with continental redbeds and coeval voluminous ultrapotassic volcanic rocks an estimate for the time of basin initiation is given by a u pb zircon age of 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 1833 pm 3 end document ma obtained from a basal volcanic flow at the western end of the basin which is in agreeme

the cora lake shear zone athabasca granulite terrane an intraplate response to far field orogenic processes during the amalgamation of laurentia the cora lake shear zone clsz is a 4 6 km wide localized high strain zone that bisects the polydeformed athabasca granulite terrane northern saskatchewan it also coincides with the geophysical trace of the snowbird tectonic zone the clsz represents a major lithotectonic and thermobarometric discontinuity within the exposure of 20 000 km2 of high pressure granulites most rocks have a strong mineral lineation plunging moderately to the southwest the northwestern subdomain hangingwall is characterized by ca 2 6 ga plutonic rocks that contain an early subhorizontal gneissic layering ca 2 57 ga that was overprinted by large amplitude folds and a partitioned but pervasive axial planar dextral shear fabric at ca 1 9 ga thermobarometry suggests metamorphic conditions of 0 9 gpa and 750 c during both of the phases of tectonism the footwall is predominantly underlain by the ca 3 3 3 0 ga chipman tonalite layers of intercalated mafic and felsic granulite and the widespread 1 9 ga chipman

geochronological constraints on metamorphism magmatism and exhumation of deep crustal rocks of the kramanituar complex with implications for the paleoproterozoic evolution of the archean western churchill province canada u pb and sm nd geochronology establishes an important paleoproterozoic 1 9 ga history for the kramanituar complex located in the interior of the archean western churchill province and provides further insight into the snowbird tectonic zone a crustal scale 2000 km feature whose role during precambrian time remains controversial the kramanituar complex is a window of deep crustal rocks dominated by a granulite facies metagabbroic suite of 1902 ma age with minor supracrustal rocks and charnockite these yield peak equilibrium conditions of 12 15 kbar and 850 900 c which are bracketed between 1910 ma the age of prograde metamorphic monazite in sillimanite and kyanite bearing paragneiss and 1901 ma the cooling ages of titanite and rutile in gabbroic and paragneissic rocks although mineral assemblages reflecting peak metamorphic conditions are widespread some rocks record near isothermal decompression to 8 kbar and 800 c the timing of uplift and exhumation is tightly bracketed between magmatic crystallization of gabbroic anorthosite under granulite facies conditions at 1902 ma and widespread rutile cooling ages of 1901 ma time averaged cooling rates of 100 c ma are estimated for gabbroic anorthosite and leucogranite rocks surrounding the kramanituar complex are mainly amphibolite facies archean plutonic and supracrustal rocks those to the north were at deep crustal conditions coeval with the complex whereas those to the south appear to preserve a record of older mainly neoarchean tectonometamorphic assemblages and fabrics the southern boundary of the complex is inferred to be a normal fault that accommodated tectonic unroofing of the kramanituar complex at 1 9 ga this geochronological data set highlights the protracted history of a segment of the geophysically defined snowbird tectonic zone a structure along which latest significant magmatism and tectonometamorphism has been interpreted as either 2600 or 1800 ma penetrative 1900 ma activity in the east trending chesterfield segment as documented at the kramanituar complex suggests that the complex may have represented a favorably oriented segment of a crustal scale archean fault that was reactivated during paleoproterozoic time possibly in response to collision between the slave and churchill cratons thelon orogen at 1 97 1 9 ga

thermobarometry and geochronology of the uvauk complex a polymetamorphic neoarchean and paleoproterozoic segment of the snowbird tectonic zone nunavut canada the uvauk complex is an ultramylonite bounded granulite facies suite of anorthosite gabbro that forms part of the chesterfield inlet segment of the snowbird tectonic zone following initial anorthosite gabbro magmatism at ca 2 71 ga and a cryptic 2 62 2 60 ga event marked by zircon and monazite growth the uvauk complex experienced two high grade tectonometamorphic events at 2 56 2 50 and 1 91 1 90 ga similar to the 2 56 2 50 ga development of other shear zones in the region the upper amphibolite facies to granulite facies moderately high pressure 8 4 11 0 kbar and 705 760 c 1 kbar 100 mpa m1 event is interpreted to have involved the structural emplacement of ca 2 71 ga uvauk complex rocks on ca 2 68 ga tonalitic rocks to the south granulite facies high pressure 11 2 14 7 kbar and 695 865 c m2 metamorphism gabbroic magmatism and mylonite development within the complex at ca 1 9 ga culminated with 3 5 kbar decompression at high temperature clockwise pressure temperature time p t t

sequence stratigraphy and evolution of the paleoproterozoic intracontinental baker lake and thelon basins western churchill province nunavut canada abstract the baker lake and thelon basins lie along the border between the rae and hearne domains of the western churchill province basin fill comprises the dubawnt supergroup a ca 1 85 1 70 ga succession of predominantly continental clastic and intercalated volcanic rocks that nonconformably and unconformably overlies granitic and supracrustal rocks most of late archean age the dubawnt supergroup comprises three second order sedimentary sequences that record deposition within a rift basin a modified rift basin and a thermal sag basin respectively the baker sequence is inferred to represent the principal phase in the development of baker lake basin a series of generally elongate northeast striking half graben and fault bounded troughs filled with continental redbeds and coeval voluminous ultrapotassic volcanic rocks faults parallel to the basin margin exhibit evidence for strike slip ca 1 83 1 81 ga the nature and timing of basin development and associated magmatism allows that it may be a transtensional basin that formed by lateral escape in response to crustal thickening during the trans hudson orogeny similar to the formation of mesozoic and cenozoic strike slip and associated rift basins on the margins of the tibetan plateau the overlying whart sequence was deposited in small basins formed by block faulting and tilting of the baker sequence basin fill comprises eolian and alluvial redbeds with intercalated rhyolite flows and epiclastic rocks distribution of facies and stratigraphy suggest that faulting occurred throughout deposition of the whart sequence but ceased before deposition of the overlying barrens sequence ca 1 72 ga deformation and basin formation can be linked to a regional episode of granite emplacement and associated thermal metamorphism ca 1 76 1 75 ga the barrens sequence represents deposition over a broader area primarily in thelon basin strata generally are thinner and flatter than underlying sequences and display lateral continuity indicating minimal influence from syndepositional faulting the depositional record reflects progressive upward fining and eventually the first record of marine transgression within the dubawnt supergroup these features suggest that the barrens sequence was deposited over a broad region of thermal subsidence likely related to cooling of previously attenuated continental lithosphere the barrens sequence may be a remnant of a huge cratonic sand sheet that included the thelon athabasca amundsen and elu basins a regional subsidence mechanism to account for these basins may be mantle downwelling linked to the late stage amalgamation of laurentia the tripartite sequence evolution of the baker lake and thelon basins represents a framework for future sequence correlation among late paleoproterozoic basins in laurentia and shares characteristics with the evolution of contemporaneous intracontinental basins from north central australia and southeastern brazil

early paleoproterozoic supracrustal assemblages of the rae domain nunavut canada intracratonic basin development during supercontinent break up and assembly abstract the basal paleoproterozoic supracrustal succession of the churchill province in northern canada comprises sedimentary basins overlying the archean rae and hearne domains the rae domain supracrustal succession e g amer ketyet river chantrey and montresor groups comprises four lithotectonic assemblages which include in ascending stratigraphic position 1 shallow marine fluvial quartzarenite with mainly neoarchean detrital zircons of local provenance 2 shallow marine quartzarenite with mainly local provenance that locally includes carbonates mafic volcanic flows 3 abrupt but conformable transition to basinal dark shales and overlying platformal carbonates that pass upward into siltstones and sandstones that record gradual emergence of the platform sandstones within this assemblage display a substantially different detrital zircon provenance signature dominated by early paleoproterozoic zircons with grains as young as 1 95 ga 4 unconformably to conformably overlying immature marine sandstones including turbidites with a significant component of 2 0 1 9 ga detritus probably derived from a combination of local and distal sources the thickness and relative compositional maturity of the basal lithotectonic assemblage 1 records a protracted period of enhanced weathering on a slowly subsiding but stable supercontinent e g kenorland this was followed by mafic volcanism and marine transgression consistent with partial rifting of the rae domain and crustal extension attending supercontinent break up lithotectonic assemblage 2 strata of lithotectonic assemblage 3 record basin flooding and deepening followed by platformal sedimentation along the margins of extended continental blocks assemblage 4 is interpreted to represent deposition in foreland basins during early amalgamation of laurentia part of nuna at ca 1 9 ga the stratigraphy and detrital zircon geochronology of the hurwitz group which overlies the hearne domain is broadly similar to the supracrustal sequence of the rae domain but differs through the presence of basal diamictites and lack of 2 5 ga detritus a major local source in the rae our data suggest that the rae and hearne domains were assembled together by max 1 91 ga i e max age of deposition of the uppermost hurwitz and amer groups the paleoproterozoic stratigraphic assemblage framework for the churchill province compares well with that of other cratons derived from break up of kenorland and ultimately amalgamated in nuna examples from laurentia include supracrustal rocks that overlie the southern margin of the superior province southern province e g huron supergroup animikie group marquette range supergroup whitewater group and mistassini otish group the paleoproterozoic assemblages of the southern and churchill provinces exhibit first order stratigraphic similarities that indicate a shared history of stable continental sedimentation followed by rifting basin opening and basin closure

spatial distribution and compositional variation of aps minerals related to uranium deposits in the kiggavik andrew lake structural trend nunavut canada the kiggavik andrew lake structural trend consists of four mineralized zones partially outcropping lying 2 km south of the erosional contact with the unmetamorphosed sandstone and basal conglomerates of the paleoproterozoic thelon formation the mineralization is controlled by a major e w fault system associated with illite and sudoite alteration halos developed in the archean metagraywackes of the woodburn lake group aluminum phosphate sulfate aps minerals from the alunite group crystallized in association with the clay minerals in the basement alteration halo as well as in the overlying sandstones which underwent mostly diagenesis aps minerals are sr and s rich svanbergite end member in the sedimentary cover overlying the unconformity whereas they are light rare earth elements lree rich florencite end member in the altered basement rocks below the unconformity the geochemical signature of each group of aps minerals together with the petrography indicates three distinct generations of aps minerals related to the following 1 paleoweathering of continental surfaces prior to the basin occurrence 2 diagenetic processes during the burial history of the lower unit of the thelon sandstones and 3 hydrothermal alteration processes which accompanied the uranium deposition in the basement rocks and partially overlap the sedimentary diagenetic mineral parageneses in addition the association of a first generation of aps minerals with both detrital cerium oxide and aluminum oxy hydroxide highlights the fact that a part of the detrital material of the basal thelon formation originated from eroded paleolaterite allochthonous regolith the primary rare earth element ree bearing minerals e g monazite ree carbonates and allanite of the host rocks were characterized to identify the potential sources of ree the ree chemical composition highlights a local re incorporation of the ree released from the alteration processes in the aps minerals of hydrothermal origin the distinctive geochemical signatures between diagenetic or sedimentary and hydrothermal aps minerals suggest a different source material in the thelon basin than in the athabasca basin

geological environment of the cigar lake uranium deposit the cigar lake uranium deposit occurs within the athabasca basin of northern saskatchewan canada like other major uranium deposits of the basin it is located at the unconformity separating helikian sandstones of the athabasca group from aphebian metasediments and plutonic rocks of the wollaston group the athabasca group was deposited in an intra continental sedimentary basin that was filled by fluviatile terrestrial quartz sandstones and conglomerates the group appears undeformed and its actual maximum thickness is about 1500 m on the eastern side of the basin the detrital units correspond to the manitou falls formations where most of the uranium deposits are located the lower pelitic unit of the wollaston group which lies directly on the archean basement is considered to be the most favourable horizon for uranium mineralization during the hudsonian orogeny 1800 1900 ma the group underwent polyphase deformation and upper amphibolite facies metamorphism the hudsonian orogeny was followed by

in situ u pb sims in sims micro baddeleyite dating of mafic rocks method with examples abstract an in situ u pb sims in sims method to date micro baddeleyite crystals as small as 3 m is presented with results from three samples that span a variety of ages and geologic settings the method complements id tims geochronology by extending the range of dateable crystals to sizes smaller than can be recovered by physical separation x ray mapping and bse imaging are used to locate target grains in thin section followed by sims analysis on a cameca ims 1270 using the field aperture in the transfer column to screen out ions from host phases internal age precisions for the method are anticipated to range from 0 1 for precambrian rocks to 3 7 for phanerozoic rocks results establish a 2689 5 ma age for mafic dikes in the wyoming craton usa a 1540 30 ma age for a subaerial lava flow from the thelon basin of northern canada and a 457 34 ma age for mafic dikes in the platform sequence of southeastern siberia the method is ideal for relatively non destructive dating of small samples such as extraterrestrial rocks and precious terrestrial samples

structural control of uranium mineralization at the dominique peter deposit saskatchewan canada the dominique peter deposit is part of a cluster of unconformity related uranium deposits that have been exploited since 1980 at the cluff lake mine in northern saskatchewan it is located on the south side of the 18 km basement core of the 39 km diameter circular carswell structure the metamorphic basement cylinder has risen at least 1 200 m through the mesoproterozoic sandstones underground structural study at dominique peter resulted in a revision of the understanding of the succession of tectonic events controlling mineralization emplacement and deformation the main premineralization ductile deformation d 1 and d 2 produced a flat lying gneissosity and subsequent development of foliation conformable mylonites and exhibits some contrasts with the eastern athabasca trans hudsonian tectonics east west to northwest southeast general extension ca 1 3 ga resulted in the formation of a set of 015 degrees to 050 degrees listric normal faults the latter controlled the opening of quartz then uraninite veins and induced a general tilting of fault blocks to the east mechanisms of mineralization emplacement are described in detail foliation reactivation in mylonite and aluminous gneiss is favorable to vein opening the postmineralization formation of the carswell circular structure ca 480 ma displays a centrifugal deformation with a symmetry axis located in the center of the basement dome a suite of pseudotachylyte veins breccias and shatter cones accompanies this deformation overall geometry of the carswell dome and surrounding rings as well as the nature of associated breccias presents strong similarities with those of other impact related structures

clay alteration associated with proterozoic unconformity type uranium deposits in the east alligator rivers uranium field northern territory australia clay minerals associated with the unconformity type uranium deposits of the east alligator rivers uranium field have been used to determine the spatial distribution of hydrothermal alteration and the conditions of uranium deposition within the altered basement underlying the kombolgie unconformity alteration develops a similar pattern at regional and smaller scales with a close relationship between the degree of alteration and the amount of structural discontinuities observed on both sides of the unconformity e g faults fractures breccias these discontinuities were mechanically active during the hydrothermal activity the hydrothermal clay minerals partly to totally replace diagenetic dickite and illite in the kombolgie sandstones and metamorphic phengite and chlorite in the basement rocks the time space alteration sequence established in this study can be summarized as follows 1 early crystallization of illite illite smectite i s mixed layer minerals lree sr bearing aluminum phosphate sulfates aps in sandstones above the unconformity illite i s mixed layer minerals sudoite aps on both sides of the unconformity and in fault gouges and illite i s mixed layer minerals chlorite apatite deeper in the basement and 2 late precipitation of chlorite in the open fracture network mainly centered below the unconformity the main stage of uranium deposition was associated with chloritization in the basement rocks smaller particle size lath shaped or flaky morphology common interstratification with expandable layers lower crystallinity and mg rich chemical compositions can be used to distinguish the hydrothermal clays from the other diagenetic and metamorphic illite and or chlorite hydrothermal illite can be distinguished from diagenetic and metamorphic illite phengite by its poor crystallinity along the c axis interstratification with minor amounts of smectite layers and a 1m polytype in which trans vacant octahedral sites predominate 1 mt chemically the hydrothermal illite differs from diagenetic illite by a lower interlayer charge and a higher mg content the hydrothermal chlorite is distinguished from the metamorphic chlorite by its smaller particle size spherulitic habit poor crystallinity along the c axis and common association with corrensite and or chlorite corrensite mixed layers most of the hydrothermal chlorite is mg rich and has a structural formula close to that of clinochlore xfe 0 20 near the uranium deposits the spherules of hydrothermal chlorite are chemically zoned from xfe 0 10 to xfe 0 40 which is interpreted as the result of a change in the oxidation state of the hydrothermal solution during the chlorite crystallization the space time alteration sequence established for clay minerals and the observed transition of aps to apatite are interpreted as the result of an increasing degree of interaction of the basement rocks with infiltrating acidic and oxidizing sub basinal brines in turn these fluids tend to be neutralized and reduced by their ongoing interaction with ferrous iron bearing phyllosilicates fe chlorite and biotite and iron sulfides of metamorphic origin the ore deposits are surrounded by zones in which the degree of fluid rock interaction was very high and chloritization is most abundant the octahedral mg content of the associated hydrothermal illite from the sandstone can be used as a guide to indicate the possible presence of uranium orebodies in the basement rocks tens to hundreds of meters below the crystal structures of the hydrothermal illite and chlorite suggest that these minerals crystallized at temperatures approximatively 30 to 50 c lower than those expected at the peak diagenesis of the kombolgie sandstones near the unconformity

framework geophysical modelling of granitoid versus supracrustal basement to the northeast thelon basin around the kiggavik uranium camp nunavut the northeast thelon basin in the kivalliq region of nunavut is prospective for uranium deposits recently discovered basement hosted unconformity associated prospects west of kiggavik are restric

comparison of diagenetic fluids in the proterozoic thelon and athabasca basins canada implications for protracted fluid histories in stable intracratonic basins the paleoproterozoic thelon basin located on the border between nunavut and the northwest territories of canada is a contemporaneous analog of the uranium rich paleoproterozoic athabasca basin in canada early diagenesis resulted in precipitation of extensive hematite on the surfaces of detrital quartz grains throughout the thelon formation and minor hydroxy phosphate in veins locally continued diagenesis then resulted in syntaxial quartz cementation of detrital quartz at 130 c from fluids having ca 17 wt equivalent nacl similar to the athabasca basin cementation of this type is most pronounced in fine grained sequences in the thelon basin a period of extensive desilicification during continued burial was followed by formation at ca 200 c of peak diagenetic illite having ar ar ages of ca 1400 1690 ma in the thelon formation this illite was associated with fluids with 18 oa nd d values of ca 6 and 50 respectively similar to those during peak diagenesis of the athabasca basin although the timing salinity and isotopic composition of the peak diagenetic fluids in the thelon and athabasca basins are similar the peak diagenetic mineral assemblage in the athabasca formation is dickite and illite with minor dravite and goyasite rather than simply illite consequently the fluids at peak diagenesis which in the athabasca basin are synchronous with formation of world class unconformity type uranium deposits had different compositions in each basin post peak diagenesis in the thelon basin was quite distinct from that in the athabasca basin in that illite was replaced in the central portion of the basin by k feld spar and then sudoite which crystallized from saline brines at ca 1000 ma and 100 c evidence for later infiltration of these brines is absent in the athabasca basin although uranium mobilization at ca 900 ma from fluids having the same characteristics as those at peak diagenesis was pronounced in the athabasca basin recent incursion of meteoric waters along reactivated structures into the athabasca basin has variably affected hydrous and uraniferous minerals but evidence for this is lacking in the thelon basin the thelon basin reflects less intensive fluid rock interaction in its early history than that recorded in the basal units of the athabasca basin 132

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 influence of layering and pre existing joints on the development of internal structure in normal fault zones the lodeve basin france this paper examines the role of mechanical stratigraphy on the evolution of normal fault geometry and fault zone internal structure using a well exposed normal fault system from the permian lodeve basin southern france faults formed early during the syn deformation tilting history of the basin tend to have steeper segments in the competent sandstone layers due to refraction assisted by pre existing early bedding perpendicular joints where displacement remained on the order of bed thickness faults which continued to slip during tilting have a more complex structure of splays due both to the space incompatability problem of slip at fault bends of this irregular geometry and because tilting favours the generation of new splays at a different angle to the earlier faults experiencing rotation continued deformation between faults and their splays often causes both distributed deformation in between the two and reconnection of splays to the main fault forming isolated lenses thus fault zone complexity increases greatly as slip exceeds competent bed thickness owing both to the presence of the mechanical layering and the fact that this layering is being tilted

origins of calcite in a boiling geothermal system the formation of hydrothermal calcite relates to the movement of carbon dioxide in a geothermal system as governed by boiling dilution and condensation in this paper we show how these processes control the occurrence distribution and stable isotope composition of calcite based on a study at broadlands ohaaki the two principal calcite occurrences in the broadlands ohaaki geothermal system are 1 as replacement of rock forming minerals and volcanic glass and 2 as platy crystals infilling voids both are stable over a broad temperature range from 160 degrees c to 300 degrees c replacement calcite is widespread and forms through hydrolysis reactions involving calcium alumino silicates and sub boiling liquids that contain 0 3 to 0 75 m co 2 platy calcite in contrast forms over a restricted vertical interval of a few hundred meters within the upflow zone it precipitates from boiling fluids through exsolution of carbon dioxide as indicated by coeval liquid rich and vapor rich fluid inclusions and its formation in the two phase zone fluid inclusion data help to define the boiling paths of fluids from which platy calcite formed homogenization temperatures range from 160 degrees c to 310 degrees c and are consistent within the present geothermal regime ice melting temperatures range from 0 0 to 1 0 degrees c and indicate the presence of up to 0 5 m dissolved carbon dioxide model boiling curves calculated to match these data show how the concentration of dissolved carbon dioxide in the preboiled fluid dictates the depth of first boiling most fluid inclusion data lie along a model boiling path characteristic of the centre of the upflow zone in which the rising fluid initially containing 0 75 m co 2 begins to boil at approximately 320 degrees c and approximately 2000 m depth data from well br 18 instead matches a curve in which the rising fluid initially containing 0 53 m co 2 begins boiling at approximately 245 degrees c and approximately 900 m depth the shallowing of the depth of first boiling likely results from dilution of dissolved carbon dioxide in the parent chloride water as it rises and mixes with marginal waters calcite precipitates from both shallow formed steam headed groundwater and deeply derived chloride water and these waters are isotopically distinct at broadlands ohaaki the delta 18 0 values of calcite at 200 degrees c range from 0 5 to 7 5 per mil whereas delta 18 0 values of calcite at 200 degrees c range from 4 to 10 per mil taking appropriate temperature dependent fractionation factors into account these data indicate equilibration with chloride water delta 18 0 h2o 4 5 per mil and steam heated groundwater delta 18 o h2o 7 0 per mil respectively oxygen isotopes of hydrothermal calcites in the nearby wairakei and waiotapu geothermal systems show similar patterns consistent with the occurrence of both chloride and steam heated waters there calcite formation is explained by a model that describes the distribution of two phase conditions and aqueous carbon dioxide concentrations in a column of hydrothermal fluid rising through a rock matrix of isotropic permeability in this ideal situation platy calcite forms along the inner margin of the two phase zone having the shape of an inverted cone whereas replacement calcite mostly forms in the surrounding one phase liquid only zone the sparse occurrence of calcite at less than or equal to 800 m depth in the central upflow of the ohaaki sector at broadlands ohaaki is compatible with this model and appears related to the exsolution of dissolved carbon dioxide through boiling deeper in the system

the contact uranium prospect kiggavik project nunavut canada tectonic history structural constraints and timing of mineralization uranium mineralization in the kiggavik area on the eastern border of the thelon basin nunavut canada hosts significant uranium resources within the basement and its understanding is critical to comprehending the genesis of unconformity related deposits structural controls and therefore exploration of these types of deposits in this prospective district this article deciphers the complex multiphase fracture network associated with uranium mineralization of the most recently discovered basement hosted prospect in the kiggavik area named contact the contact prospect is located along the andrew lake fault alf a major ne sw fault corridor in the area this study combines field work drillcore logging sampling and macro to micro petro structural analyses key results from this study highlight that the ne trending alf along with the ene trending thelon tf and judge sissons jsf faults formed early during intracratonic rifting and deposition of the baker lake and wharton groups ca 1850 1750 ma in response to the thelon and trans hudsonian orogeny the alf was affected by a strong silicification brecciation event that likely developed at ca 1750 ma and partitioned later deformation and fluid circulation in the contact prospect the alf was reactivated multiple times and mineralized in three stages with distinctive secondary fracture patterns alteration and mineralization types ten fracture stages have been identified at the contact prospect f1 to f10 the first stage of mineralization coeval with f5 is related to fluids of unconstrained origin that circulated through e w faults in the area that locally reactivated quartz veins of the brecciation event at the intersection with the alf mineralization at this stage is polymetallic and associated with weak clay alteration the second stage of uranium mineralization occurred coeval with transtensional reactivation of the ne sw trending alf f6c and in relation to circulation of oxidizing basinal brines within the fault zone mineralization at this stage is monometallic and associated with illite and sudoite alteration later reactivation of the inherited fracture network f8 led to strong illitization and bleaching of the host rock with local reworking of the ore body finally reactivation of the fracture network during f9 and 10 lead to circulation of meteoric fluids that remobilized mineralization in a third stage of uranium re concentration along redox fronts with strong illitization and bleaching of the host rock unlike the classic unconformity related uranium deposits in the athabasca basin where clay alteration halos occur around the ore bodies related to mineralizing processes in the contact prospect the strongest clay alteration event f8 postdates both main stages of mineralization along with uranium remobilization the basement hosted contact prospect is likely a relict of what was once a larger deposit

geochronology and genesis of the bong uranium deposit thelon basin nunavut canada the thelon basin nunavut shares many similarities with the uranium producing athabasca basin saskatchewan however the uranium deposits associated with the thelon basin are still poorly understood the kiggavik project area areva resources canada is located near the northeastern terminus of the thelon basin and comprises multiple uranium deposits hosted exclusively in basement rocks the bong deposit is hosted dominantly by neoarchean metagraywacke of the woodburn lake group a five phase metallogenetic model is proposed for the bong deposit with three stages of uraninite identified the premineralization phase is characterized by host rock silicification mineralization is separated into three main stages stage 1 uraninite u1 ca 1500 ma is preserved in highly fractured and altered disseminated grains that are overgrown by later stages of uraninite stage 2 uraninite u2 ca 1100 ma forms veinlets parallel to d 1 foliation and coats and fills fractures in organic matter nodules and blebs stage 2 uraninite is associated with pervasive illite that formed from 190 c fluids 18 o 6 4 2 h 97 which remobilized much of stage 1 uraninite and completely overprinted stage 1 alteration at 1000 ma an oxidizing fluid deposited uraninite along redox fronts u3 while altering and remobilizing stage 1 and 2 uraninite post uranium oxide minerals include drusy quartz calcite and illite accompanied by uranyl phases e g uranophane ca u

proterozoic low sulfidation epithermal au ag mineralization in the mallery lake area nunavut canada the mallery lake area contains pristine examples of ancient precious metal bearing low sulfidation epithermal deposits the deposits are hosted by rhyolitic flows of the early proterozoic pitz formation but are themselves apparently of middle proterozoic age gold mineralization occurs in stockwork quartz veins that cut the rhyolites and highest gold grades up to 24 g t over 30 cm occur in the chalcedonic stockwork zone quartz veining occurs in two main types barren a veins characterized by fine to coarse grained comb quartz with fluorite calcite and or adularia and mineralized b veins characterized by banded chalcedonic silica and fine grained quartz locally intergrown with fine grained gold or electrum a third type of quartz vein c which crosscuts b veins at one locality is characterized by microcrystalline quartz intergrown with fine grained hematite and rare electrum fluid inclusions in the veins occur in two distinct assemblages assemblage 1 inclusions represent a moderate temperature th 150 to 220 c low salinity 1 eq wt nacl with trace co2 locally boiling fluid this fluid type is found in both a and b veins and is thought to have been responsible for au ag transport and deposition assemblage 2 inclusions represent a lower temperature th 90 to 150 c high salinity calcic brine 23 to 31 wt cacl2 nacl which occurs as primary inclusions only in the barren a veins assemblage 1 and 2 inclusions occur in alternating quartz growth bands in the a type veins where they appear to represent alternating fluxes of dilute fluid and local saline groundwater no workable primary fluid inclusions were observed in the c veins the a vein quartz yields 18o values from 8 3 to 14 5 average 10 9 1 7 1 n 30 whereas 18o values for b vein quartz range from 11 2 to 14 0 average 13 0 0 9 n 12 calculated 18oh2o values for the dilute mineralizing fluid from b veins range from 2 6 to 0 2 average 0 8 0 9 n 12 and are consistent with a dominantly meteoric origin no values could be calculated for the brine however because all a vein quartz samples contain mixed fluid inclusion populations however the fact that a vein quartz samples extend to lower 18o values than the b veins suggests that the brine had a lighter isotopic signature relative to the dilute fluid hydrogen isotopic ratios of fluid inclusion waters extracted from eleven quartz samples of both vein types range from dfi 56 to 134 but show no particular correlation with vein type in most respects the mineralogical and fluid characteristics of the mallery lake system are comparable to those of phanerozoic low sulfidation deposits and although the presence of high salinity brines is unusual in such deposits it is not unknown e g creede colorado in addition one of the few other examples of well preserved precambrian low sulfidation epithermal deposits from the central pilbara tectonic zone australia contains a similarly bimodal fluid assemblage the significance of these saline brines is not clear but from this study we infer that they were not directly involved with au ag transport or deposition

striding athabasca mylonite zone implications for the archean and early proterozoic tectonics of the western canadian shield study of the northern saskatchewan district of mackenzie segment of the snowbird tectonic zone suggests that fragments of relatively stiff mid archean crust possibly arc related have controlled the localization shape and complex kinematics of the multistage striding athabasca mylonite zone during the archean as well as the geometry of the early proterozoic rifted margin of the western churchill continent by the late archean the striding athabasca mylonite zone was located in the interior of the western churchill continent well removed from the contemporaneous plate margins except for the alberta segment the snowbird tectonic zone was not the site of an early proterozoic plate margin we suggest that the geometry of the archean early proterozoic boundary in the western canadian shield represents a jagged continental margin composed of a pair of reentrants defined by rifted and transform segments these segments were inherited from early proterozoic breakup and controlled by the archean structure

u pb detrital zircon geochronology and provenance of the late paleoproterozoic dubawnt supergroup linking sedimentation with tectonic reworking of the western churchill province canada u pb sensitive high resolution ion micro probe shrimp analysis of detrital zircon in 11 sandstone samples from the late paleo proterozoic dubawnt supergroup of the baker lake and thelon basins are presented here alluvial fan and braided stream facies of the ca 1 84 1 78 ga baker sequence yield age spectra with significant groupings at 2 70 and 2 60 ga reflecting provenance chiefly from local sources in the northwestern hearne domain of the western churchill province age spectra are consistent with sed imentological and stratigraphic information which indicate provenance from the proximal uplifted shoulders of an intracontinental rift that developed in response to inboard effects of the hudsonian orogeny collision of superior craton into western churchill province the unconformably overlying 1 76 1 74 ga whart sequence exhibits a more varied provenance and has an abundance of 2 0 1 9 ga detrital zircon these ages match those of synorogenic plutons in the taltson thelon orogen collision of slave craton into the western churchill province provenance from the taltson thelon orogen is supported by easterly paleocurrents and rb sr cooling ages from mafic dikes that indicate reactivated collision of the slave craton and related uplift and denudation coeval with deposition of the whart sequence the depositional age of the whart sequence is constrained by intercalated rhyolite flows with conventional 207 pb 206 pb crystallization ages of 1757 6 3 4 ma and 1753 0 1 7 ma 2 the thermal effects of this collision also are recorded in isotopic data from basement rocks throughout the western churchill province and in syndepositional to postdepositional faults that parallel the main boundary faults of the slave indentor late reactivation and associated metamorphism faulting and basin development could be the result of the inboard effects of subduction and related collision along the southern margin of laurentia the detrital zircon geochronology of the barrens sequence supports recycling of local supracrustal sequences and weathering of underlying granitic gneisses zircons of hudsonian affinity ca 1 9 1 8 ga are nearly absent which argues against a distant eastern source region for the barrens sequence the dubawnt supergroup detrital zircon age data set shows concentrations ca 2 75 2 6 ga 2 1 1 9 ga and 1 85 1 75 ga which are concordant with the known ages of major juvenile crust forming events leading up to final amalgamation of late archean and paleoproterozoic supercontinents detritus of this age was shed cratonward and captured by interior basins such as the baker lake and thelon basins during major collisional events that reworked the margins of the western churchill province e g hudsonian and thelon taltson orogenies

petrology and geochronology of paleoproterozoic intrusive rocks kiggavik uranium camp nunavut we investigated the age and petrology of paleoproterozoic granitic intrusions in the area of the kiggavik uranium exploration camp near the southeast margin of the aberdeen subbasin of the thelon basin a subset of these intrusions e g the lone gull stock is spatially associated with and mineralized by basement hosted unconformity related uranium deposits surface outcrop samples have field relations textures and compositions consistent with hudson suite granitoids and mixtures of monzogranite with minette we obtained u pb zircon ages ranging from ca 1818 to 1840 ma within the known range of the hudson suite and cogenetic minettes of the baker lake group 1 80 1 84 ga core samples of granitic rocks adjacent to mineralized zones are more complex and indicate an influence from the younger nueltin granite kivalliq igneous suite ca 1 77 1 73 ga one sample from the lone gull stock contains two zircon populations in texturally distinctive domains one at 1806 41 ma and the other at 1748

geology of the nabarlek uranium deposit northern territory australia the nabarlek deposit is an unusually high grade uranium orebody 1 84 u 3 o 8 12 000 metric tons hosted by amphibolite and semipelitic schist of lower proterozoic age it is unusual in the alligator rivers uranium field in being hosted by amphibolite the disposition of the ore is controlled by a prominent reverse fault which is part of a larger zone of reverse faulting the fault zone is nearly perpendicular to prominent metamorphic s 2 and s 3 fabrics a geometry which might enhance the fluid rock ratio a striking feature of the deposit is the extent and intensity of hydrothermal alteration which extends more than 1 km from the ore alteration remote from the ore resulted in pseudomorphous replacement of metamorphic biotite amphibole and feldspar under conditions of a low fluid rock ratio and mass transfer ore is associated with a small desilicification zone within and superimposed on this larger envelope the fluid rock ratio and mass transfer resulting mainly in silica loss were high within this interior zone and produced intense pervasive alteration leading to an assemblage of phengitic white mica magnesian chlorite and hematite large volumes of fluid were required to effect the massive desilicification and deposit such a volume of uranium given the current knowledge of the solubility of quartz and uraninite ore deposition predominantly as uraninite postdated intense phengitic white mica alteration chlorite however is the main gangue mineral possibly reflecting a change in redox conditions accompanying ore deposition a redox control on ore deposition is supported by the sparse ocurrence of host rock graphite which evidently participated in ch 4 forming reactions abundant hematite in the alteration halo suggests the presence of an oxidized fluid log f sub o 2 approx 35 at 200 degrees c which was thus suitable for transporting ore forming quantities of uranium probably as chloride complexes primary mineralization underwent incongruent dissolution to coffinite in equilibrium with a vanadian illite kaolinite and secondary hematite assemblage residual ore weathering of primary and residual ore produced yellow and green secondary uranium minerals both pseudomorphous after earlier ore types and as crusting of open goethite lined fractures

implications for mechanical properties of brittle faults from observations of the punchbowl fault zone california field observations of the punchbowl fault zone an inactive trace of the san andreas are integrated with results from experimental deformation of naturally deformed punchbowl fault rocks for a qualitative description of the mechanical properties of the fault and additional information for conceptual models of crustal faulting the punchbowl fault zone consists of a single continuous gouge layer bounded by zones of extensively damaged host rock fault displacements were not only localized to the gouge layer but also to discrete shear surfaces within the gouge deformation in the exposure studied probably occurred at depths of 2 to 4 km and was dominated by cataclastic mechanisms textural data also suggest that significant amounts of pore fluids were present during faulting and that fluid assisted mechanisms such as dissolution diffusion and precipitation were operative the experimental data on specimens collected from the fault zone suggest that there is a gradual decrease in strength and elastic modulus and an increase in relative ductility and permeability toward the main gouge zone the gouge layer has fairly uniform mechanical properites and it has significantly lower strength elastic modulus and permeability than both the damaged and the undeformed host rock for the punchbowl fault and possibly other brittle faults the variations in loading of the gouge zone with time are primarily governed by the morphology of the fault and the mechanical properties of the damaged host rock in addition the damaged zone acts as the permeable unit of the fault zone and surrounding rock it appears that the gouge primarily governs whether displacements are localized and it therefore may have a significant influence on the mode of slip

hydraulic properties of closely spaced dipping open fractures intersecting a fluid filled borehole derived from tube wave generation and scattering fluid filled fractures and fissures often determine the pathways and volume of fluid movement they are critically important in crustal seismology and in the exploration of geothermal and hydrocarbon reservoirs we introduce a model for tube wave scattering and generation at dipping parallel wall fractures intersecting a fluid filled borehole a new equation reveals the interaction of tube wavefield with multiple closely spaced fractures showing that the fracture dip significantly affects the tube waves numerical modeling demonstrates the possibility of imaging these fractures using a focusing analysis the focused traces correspond well with the known fracture density aperture and dip angles testing the method on a vsp data set obtained at a fault damaged zone in the median tectonic line japan presents evidences of tube waves being generated and scattered at open fractures and thin cataclasite layers this finding leads to a new possibility for imaging characterizing and monitoring in situ hydraulic properties of dipping fractures using the tube wavefield