apatite feldspar u pb thermochronometer a reliable mid range 450 c diffusion controlled system the u pb systematics of apatite are commonly dominated by simple volume diffusion without secondary growth and recrystallization that can affect u pb systematics of sphene monazite and zircon although apatite is a relatively low u mineral both u and pb are lattice bound and thus the u pb systematics are not controlled by micro inclusions as appears to be the case for other low u minerals such as garnet and staurolite closure temperature estimates from both experimental and empirical studies range from 425 c to as high as 500 c for typical diffusion radii 25 m and cooling rates 2 100 c ma respectively this range can be exploited to constrain cooling and exhumation histories of both igneous and metamorphic rocks in addition the closure temperature for pb diffusion in apatite fills a gap between that for pb diffusion in sphene 650 c and diffusion of ar in hornblende 500 c muscovite 350 c and biotite 300 325 c apatite is a common accessory phase in many rock types and u pb apatite dating can be a reliable and powerful thermochronometer as it combines mid range cooling ages with the strength of the u pb system in testing for isotopic closure precisions of u pb apatite dates can range from 1 2 to as low as 0 3 for proterozoic or archean dates the main limitation to accuracy of u pb apatite dates is a moderate to low ratio of u to pb and corresponding dependence of concordia coordinates on the choice of initial pb isotopic composition for proterozoic aged samples with measured 206pb 204pb of 100 the range of geologically reasonable initial pb isotopic compositions can shift the calculated u pb age by 60 ma fortunately even though the diffusion rate of pb in alkali feldspar is less than in apatite it appears that the isotopic composition of pb in coexisting feldspar is a good approximation of the initial isotopic composition in apatite for many geologic settings examples are given from an archean terrane in se wyoming that was unroofed and cooled during proterozoic uplift and from proterozoic terranes in sw us that have contrasting thermal histories

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

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

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

geochronology of the narakay volcanic complex implications for the age of the coppermine homocline and mackenzie igneous events u pb isotope analysis of four zircon separates from a rhyolite porphyry that is part of the bimodal narakay volcanic complex dease arm great bear lake yields an age of 1663 8 ma east trending feldspar phyric dykes that cut the complex yield zircons that are within analytical error the same age as the porphyry the narakay volcanic complex occurs in the upper part of the hornby bay group the lowermost group of the coppermine homocline and the stratigraphic position of the dated rocks indicates that 1663 ma is the depositional age of the upper hornby bay group this is the first u pb zircon age determined from rocks of the coppermine homocline and has important implications for previous geochronology and extrabasinal correlation earlier rb sr dates from the conformably overlying coppermine river group basalts of ca 1200 ma when taken together with the new data suggest that the dismal lakes group which conformably overlies the hornby bay group was deposited during a period of more than 400 ma

sources of sulphur for the proterozoic kiggavik uranium deposit nunavut canada the thelon basin is temporally and spatially related to the athabasca basin in saskatchewan canada which hosts the highest grade unconformity related uranium deposits in the world several uraniu

high closure temperatures of the u pb system in large apatites from the tin mountain pegmatite black hills south dakota usa abstract the cores of several large 1 2 cm apatites from the early proterozoic tin mountain pegmatite black hills south dakota have concordant u pb ages the age uncertainties of these samples are less than 5 ma the lead isotopic compositions of muscovite and k feldspar coexisting with the apatites were used for initial lead isotopic corrections the resulting u pb concordia ages agree well with u pb and pb pb isochron ages based solely on multiple fragments from single apatites this agreement justifies the use of coexisting muscovite and k feldspar for initial lead corrections the precision of these u pb ages is comparable to those of the u pb systems of more commonly analyzed minerals such as zircon monazite and sphene the estimated u pb closure temperature t c of these apatites is about 620 c this t c is in close agreement with the t c calculated for 0 5 cm diffusion radii and published data for diffusivity and activation energy of lead diffusion in apatite apatite can therefore yield high precision u pb ages that are close to its crystallization age in igneous rocks

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

alteration of monazite and zircon and lead migration as geochemical tracers of fluid paleocirculations around the oklo okelobondo and bangombe natural nuclear reaction zones franceville basin gabon abstract large scale light rare earth element lree uranium lead and phosphorus migration has been evidenced in the fa lower proterozoic sandstones of the franceville basin gabon hosting oklo natural nuclear reaction zones rz in relation with extensive accessory mineral alteration by highly saline diagenetic brines 28 7 wt nacl eq to 30 wt cacl2 eq at about 140 c and 1 kbar monazite is the most severely altered accessory mineral in the coarse grained sandstones of the basal fa formation detrital monazite crystals are altered to th oh silicate microcrystalline phase with very low concentrations of u and lree the th la ratio increase from non altered th la 0 27 to altered sandstones th la 1 14 shows that about 76 of the lree was leached this corresponds to the leaching of 2 01 109 metric tons at the scale of the fa formation in the franceville basin similarly the th u increase from monazite th u 18 6 to the th silicate phase th u 88 7 is interpreted as a result of an alteration by oxidizing brines with leaching of u together with lree and p it corresponds to the leaching of 9 06 106 metric tons of uranium this amount of uranium largely exceeds the known uranium reserves from the franceville basin in zircon crystals the cores are generally homogeneous weakly fractured and well preserved as attested by the archean ages 2867 24 and 2865 51 ma obtained by ionic microprobe analysis on zircon of the fa formation respectively from the marginal and central parts of the basin their composition corresponds to the pure end member zr hf sio4 poor in th and u th u 1 at the contrary their rims which present several growth zones with cracks fillings are enriched in ree p th and u with higher th u ratios 5 10 both altered monazite and altered zircon contain galena as numerous inclusions in the outer growth zones and as crack fillings for example in zircon the pb of galena crystals 3 23 wt largely exceeds the amount of pb maximum 0 1 wt that would have been produced in situ by radioactive decay in this mineral nearly all the lead were introduced into altered zones of accessories dissolution of accessory minerals occurred at 2000 ma producing a porous and distorted crystal structure which has allowed a later incorporation of pb galena inclusions in altered zircons located in the vicinity of reactor zones have radiogenic lead compositions altered zircon rims and galena inclusions in altered zircon located far from reactor zones have non radiogenic pb isotopic compositions confirming the external origin of lead pb isotopic evolution models indicate a crystallization age sometime after 1000 ma both for galena located close to and far from u mineralizations and reactor zones which may be synchronous with a regional extension event contemporaneous with intrusion of dolerite dyke swarms between 1000 and 750 ma at the scale of the franceville basin the present study also illustrates the different retention capacities of accessory mineral for elements representing analogs of the radiotoxic nuclides in the relatively extreme natural conditions created by the circulation of moderately hot and chloride rich fluids during the diagenesis of a sedimentary basin

diagenetic fluorapatite and aluminum phosphate sulphate in the paleoproterozoic thelon formation and hornby bay group northwestern canadian shield in the northwestern part of the canadian shield fluorapatite and a rare earth element bearing hydrated aluminum phosphate sulphate mineral aps occur as cements in continental successions near the base of the paleoproterozoic thelon formation thelon basin and hornby bay group hornby bay basin these minerals occupy interstitial sites form euhedral crystals display micro scale zonation make up part of an unmetamorphosed paragenetic assemblage and are distributed in correlative units across thousands of square kilometres suggesting a diagenetic origin stratigraphy geochronology and other lines of evidence suggest that the thelon formation and hornby bay group containing these phosphatic cements as well as the ellice formation and athabasca group are correlative and may have been originally interconnected the evidence suggests that the basal thelon formation and the hornby bay group underwent similar and approximately coeval diagenetic mineral paragenesis furthermore the diagenetic fluid

ion microprobe u pb dating of apatite abstract to illustrate in situ sensitive high resolution ion microprobe shrimp analysis of apatites pb isotopes and pb u ratios of five apatite samples with different ages have been measured using shrimp ii ion microprobe at hiroshima university the prap apatite from a carbonatite complex at prairie lake ontario with a 207 pb 206 pb age of 1156 45 ma 2 was used as the standard for 206 pb 238 u 238 u 16 o 238 u calibration apatites from the poohbah lake alkaline complex give 204 pb 206 pb 238 u 206 pb and 204 pb 206 pb 207 pb 206 pb isochron ages of 2726 145 ma 2 and 2701 86 ma 2 in agreement with a conventional tims 207 pb 206 pb age of 2667 10 ma 2 and a k ar isochron age of 2706 46 ma 2 for the remaining three apatite samples the 204 pb 206 pb 238 u 206 pb and 204 pb 206 pb 207 pb 206 pb isochron ages obtained by shrimp are consistent with radiometric and geological ages in the literature

geochemistry and geochronology of the kiggavik uranium deposit nunavut canada the thelon basin nunavut canada is similar in age size and geology to the u producing athabasca basin in saskatchewan the kiggavik project area located immediately south of the aberdeen sub basin of the thelon basin contains u deposits and showings along a 30 km long ne sw structural trend the basement hosted kiggavik deposit comprising three separate mineralized zones main centre and east is located at the northern end of this trend multiple styles of u mineralization and alteration were identified at the kiggavik deposit disseminated euhedral uraninite u1 1284 53 ma has elevated pb contents up to 14 wt pbo and is associated with illite and hematite alteration vein style uraninite u2 284 19 ma forms along fractures contains lower pb contents 3 9 wt pbo and is partly altered to ca si rich 4 5 wt cao and 3 3 wt sio2 uraninite highly altered u2 is associated with galena late u minerals u3 have biogenic textures and are pb free indicating that they formed recently 1 ma based on sims in situ u pb geochronology the minimum age of uraninite at the kiggavik deposit is 1284 53 ma however this is likely a reset age associated with the mackenzie dyke event 1267 ma oxygen and hydrogen stable isotope compositions of illite and muscovite suggest that the kiggavik deposit has been overprinted by high latitude surficial fluids derived from snowmelt

bushveld aged fluid flow peak metamorphism and gold mobilization in the witwatersrand basin south africa constraints from in situ shrimp u pb dating of monazite and xenotime in situ u pb dating of monazite and xenotime in gold reefs and unmineralized greenschist facies sedimentary rocks from the witwatersrand basin south africa reveals two episodes of tectonothermal activity a major event between 2 06 and 2 03 ga is recorded in the wit watersrand and transvaal supergroups in the northwestern and central basin and broadly coincides with the ca 2 06 ga bushveld event in the central and southern basin a previously unrecognized event has been dated between 2 14 and 2 12 ga the widespread geographic and stratigraphic occurrence of bushveld aged monazite and xenotime including both auriferous reefs and unmineralized strata indicates that metamorphism and fluid flow associated with magmatism was pervasive affecting most of the succession 10 km thick in the central and northern parts of the basin the metamorphic phosphate dates which are younger away from the complex indicate a lag of 20 30 m y between emplacement and phosphate growth in the central basin 100 km south suggesting that heat related to magmatism was transferred southward at an average rate of 3 5 mm yr 1 the absence of 2 06 2 03 ga phosphates in the welkom goldfield at the southern end of the basin implies that bushveld related heating and fluid flow did not affect this part of the basin the intergrowth of ca 2 045 ga monazite with gold in quartz pebble conglomerate from the west rand goldfield indicates that fluid flow related to the bushveld event caused mobilization of gold in the witwatersrand basin

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

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

mineralogy geochronology and genesis of the andrew lake uranium deposit thelon basin nunavut canada the thelon basin located in nunavut canada shares many similarities with the u producing athabasca basin in saskatchewan the kiggavik project area located near the northeastern edge of the thelon basin contains u deposits and showings along the 30 km long ne sw kiggavik andrew lake structural trend the andrew lake deposit is near the southern end of this trend pre mineralization is characterized by quartz carbonate veins that occupy fault systems later reactivated as conduits for u mineralizing fluids a four phase genetic model is proposed for the andrew lake deposit phase 1 comprises vein style uraninite u1 1031 23 ma that is associated with illite and hematite and contains variable pbo contents 0 2 9 5 wt phase 2 is characterized by altered uraninite u2 530 ma that is associated with coffinite altered uraninite u3 1 ma characterizes phase 3 and occurs as centimetre scale roll fronts in phase 4 all three uraninite stages and coffinite are altered to boltwoodite al

intracratonic indentation of the archean slave province into the early proterozoic thelon tectonic zone of the churchill province northwestern canadian shield some time between 1735 and 1840 ma an intracratonic compression resulted in the indentation and consequent underthrusting of the eastern thelon tectonic zone by the central slave province and part

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

dynamic effective pressure coefficient calibration abstractpore pressure prediction provides an important risk assessment in the oil and gas industry most predrill pore pressure prediction methods from seismic and or well log sonic velocities are based on the effective stress principle which relates velocity variation to the combined effect of overburden stress and pore pressure in the current practice of pore pressure prediction the effective stress coefficient n is often assumed as unity which is not always the case especially when sediments are deeply buried and consolidated to understand the variation of n with depth i analyzed density and velocity trends from more than 100 gulf of mexico wells near the louisiana continental shelf edge in the study area overpressure zones are present in most wells and compaction disequilibrium is the dominant overpressure mechanism normal compaction trends for velocity and density were built the overburden pressure model was refined by taking into account that the density gradient approaches zero at the on

diagenetic apatite character and in situ ion microprobe u pb age keeseville formation potsdam group new york state an occurrence of diagenetic fluorapatite cement is documented within the cambro ordovician keeseville formation potsdam group near chateaugay in new york state the fluorapatite cement occurs as stratiform layers within ephemeral fluvial quartz arenites which have been reworked by aeolian processes prior to burial the paragenetic sequence includes the following compaction of dust rimmed grains quartz cementation minor kaolinite fluorapatite cementation followed by secondary dissolution porosity and telogenetic hematite cementation mesogenetic illitization of kaolinite may have taken place prior to or following fluorapatite cementation the fluorapatite occurs as elongated bladed crystals that characteristically contain ladder like inclusion rich cores running parallel to crystal length surrounded by clearer rims and larger blocky crystals towards the middle of interstices in situ shrimp analyses of blocky fluorapatite crystals yield a u pb age of 486 29 ma indicating that the cement for

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

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

petrography fluid inclusion analysis and geochronology of the end uranium deposit kiggavik nunavut canada the end deposit is one of several uranium deposits in the kiggavik area near the proterozoic thelon basin which is geologically similar to the athabasca basin known for its unconformity related uranium deposits the mineralization occurs as uraninite and coffinite in quartz veins and wall rocks psammopelitic gneisses in the sub thelon basement and is associated with clay and hematite altered fault zones fluid inclusions were studied in quartz cementing unmineralized breccias formed before mineralization q2 quartz veins that were formed before mineralization but spatially associated with uranite q4 and calcite veins that were formed after mineralization four types of fluid inclusions were recognized namely liquid dominated biphase liquid vapor vapor dominated biphase vapor liquid monophase vapor only and triphase liquid vapor halite inclusions the first three types were found in q2 whereas all four types were found in q4 and calcite the coexistence of these different types of inclusions within individual fluid inclusion assemblages is interpreted to indicate fluid immiscibility and heterogeneous trapping based on microthermometry the fluids associated with q2 are characterized by low salinities 0 4 to 6 6 wt and moderate temperatures from 148 to 261 c and the fluids associated with calcite show high salinities 26 8 to 29 3 wt and relatively low temperatures from 146 to 205 c whereas the fluids associated with q4 have a wide range of salinities from 0 7 to 38 8 wt and temperatures from 80 to 332 c microthermometric and cryogenic raman spectroscopic studies indicate that the high salinity fluids in q4 and calcite belong to the h2o nacl cacl2 mgcl2 system with some dominated by nacl and others by cacl2 the fluid inclusions in q2 are interpreted to be unrelated to mineralization whereas those in q4 and calcite reflect the mineralizing fluids the fluid inclusion data are consistent with a genetic link of mineralization with basinal brines derived from the thelon basin however unlike the conventional deep burial 5 km diagenetic hydrothermal model proposed for the unconformity related uranium deposits the uranium mineralization in the end deposit is inferred to have formed in a shallow environment probably 2 km based on fluid immiscibility and low fluid pressures obtained in this study the u pb age of uraninite 1295 12 ma is interpreted to reflect isotopic resetting after the primary mineralization

ontogenetic effects on stable carbon and oxygen isotopes in tests of live rose bengal stained benthic foraminifera from the pakistan continental margin abstract we determined the stable oxygen and carbon isotopic composition of live rose bengal stained tests belonging to different size classes of two benthic foraminiferal species from the pakistan continental margin samples were taken at two sites with water depths of about 135 and 275 m corresponding to the upper boundary and upper part of the core region of the oxygen minimum zone omz for uvigerina ex gr uvigerina semiornata and bolivina aff bolivina dilatata 13c and 18o values increased significantly with increasing test size in the case of uvigerina ex gr u semiornata 13c increased linearly by about 0 105 for each 100 m increment in test size whereas 18o increased by 0 02 to 0 06 per 100 m increment for bolivina aff b dilatata the relationship between test size and stable isotopic composition is better described by logarithmic equations a strong positive linear correlation is observed between 18o and 13c values of both taxa with a constant ratio of 18o and 13c values close to 2 1 this suggests that the strong ontogenetic effect is mainly caused by kinetic isotope fractionation during co2 uptake our data underline the necessity to base longer 18o and 13c isotope records derived from benthic foraminifera on size windows of 100 m or less this is already common practice in down core isotopic studies of planktonic foraminifera

provenance of the proterozoic thelon basin nunavut canada from detrital zircon geochronology and detrital quartz oxygen isotopes abstract the paleoproterozoic thelon basin in nunavat canada is one of several large quartz dominated sedimentary basins developed on paleoproterozoic and archean rocks of the canadian shield coarse grained quartz to sub feldspathic sandstones and conglomerates of the thelon formation comprise the basin fill detrital zircons from the thelon formation have lam icp ms 207 pb 206 pb ages ranging from 3 94 to 1 78 ga but most are neoarchean 2 70 2 50 ga the 18 o values of quartz range from 7 7 to 13 9 and are typically 10 12 ages u zr ratios and oxygen isotopic compositions of detrital quartz are consistent with a predominantly neoarchean metasedimentary source such as surrounds the eastern thelon basin and comprises the bulk of basement rocks within the rae domain the three stratigraphic sequences of the thelon formation have 18 o ranges for detrital quartz and zircon ages that further constrain the source areas and support previous sequence stratigraphic interpretations the lower sequence contains reworked siltstone and sandstone clasts and 2 50 1 85 ga zircons indicating a contribution from paleoproterozoic terranes detrital quartz 18 o values range from 9 8 to 13 9 indicating a metamorphic source also which is consistent with a proximal source for the lower sequence the middle sequence contains zircons exhibiting the widest range of ages 3 94 1 78 ga a 3 4 ga paleoarchean zircon population cannot be correlated to the immediately surrounding basement and therefore indicates a distal source possibly in the order of 1000 2000 km away the upper sequence contains relatively few zircons due to extensive alteration but ages are predominantly early paleoproterozoic and neoarchean the upper sequence strata contain the lowest 18 o values of quartz indicating an influx of granitic material late in the depositional history of the basin the geochronology and geochemistry of detrital grains within the thelon formation indicate that the source areas evolved from predominantly proximal to distal and back to proximal as the basin filled

asymmetric extension of the middle proterozoic lithosphere mount isa terrane queensland australia abstract the middle proterozoic mount isa basin of the mount isa terrane hosts several large pb zn ag deposits and is arguably one of the richest mineral provinces in the world the deformed remnants of this basin extend from the eastern margin of the leichhardt river fault trough through to the murphy tectonic ridge in the far north of the terrane the mount isa basin initially evolved in response to nw se directed extension during the mount isa rift event this event began before 1708 ma and had ceased by 1653 ma a sag basin continued to evolve thereafter until 1595 ma regional analysis of the highest level cover rocks of the mount isa basin reveals a notable difference in the locus of syn rift sedimentation syn rift magmatism and post rift subsidence although crustal extension was widespread across the mount isa basin tectonic subsidence was focussed along the n s oriented mount isa rift approximately 3 5 km of fluvial to shallow marine clastic sediments were deposited into isolated rift basins bimodal volcanism and emplacement of shallow level plutons occurred along the western and northwestern margins of the mount isa rift magmatic provinces mark the locus of significant subcrustal lithospheric thinning asthenospheric upwelling and mafic underplating within these magmatic provinces the syn rift sequences are fewer and thinner 750 2000 m and were dominantly deposited in subaerial environments suggesting a relatively stable uplift and subsidence history the position of maximum subcrustal lithospheric extension is determined by the position of greatest post rift subsidence this occurred beneath the northern mount isa terrane where the thickest post rift sequences are preserved and the depositional history is more protracted we propose that the evolution of the mount isa basin is a consequence of asymmetric extension of the middle proterozoic lithosphere

3d geophysical inversions of the north east amer belt and their relationship to the geologic structure the amer lake area is located within the churchill structural province in the kivalliq region of nunavut approximately 160 km north west of baker lake two distinct geophysical geological entities are structurally intercalated an archean mixed granitoid gneiss metasedimentary metavolcanic basement and the unconformably overlying paleoproterozoic amer group metasediments from east of amer lake stretching toward the south west these two entities form the amer fold and thrust belt at the north east end of this belt high resolution aeromagnetic data define a distinctive oval shape that has been interpreted as a south west trending doubly plunging synform the outcrop within the interior of this structure is sparse resulting in limited structural data and speculative geological interpretations with multiple geometries possible the high resolution aeromagnetic data compiled through an industry government consortium and newly acquired detailed gravity profiles were modelled to provide constraints on the geometry of this synform we document a geophysical geological feedback process whereby the available geological and geophysical data were used to derive constraints on inversion models for the synform starting with available limited litho structural data the presence of a double plunging synform was directly inferred from the aeromagnetic data segments of the aeromagnetic data have 2d morphology and so can be modelled using a simple parametric 2d dipping slab inversion approach models of profiles extracted from the aeromagnetic data were used to provide preliminary dip and magnetic susceptibility constraints for the three lakes mudstone with iron formation and the five mile lake basalt landsat imagery outlined the spatial limits of the stratigraphically underlying non magnetic ayagaq quartzite incorporating these outputs as bounds in the input reference model for a ubc gif 3d magnetic inversion helped to accentuate the geological structure in the output mesh an enhanced inversion that incorporates both geological and geophysical constraints the validity of the resulting inversion model was tested by computing 2d forward models of the gravity profile data the inversion model generated by this study emphasizes the importance of integrating information from as many knowledge sources as one can find more trust can be placed on forward and inversion models where there is agreement among all data sets and a coherency of structural style

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

unconformity related rare earth element deposits a regional scale hydrothermal mineralization type of northern australia rare earth element ree orebodies are typically associated with alkaline igneous rocks or develop as placer or laterite deposits here we describe an economically important heavy h ree mineralization type that is entirely hydrothermal in origin with no demonstrable links to magmatism the mineralization occurs as numerous xenotime rich vein and breccia orebodies across a large area of northern australia but particularly close to a regional unconformity between archean metasedimentary rocks of the browns range metamorphics and overlying proterozoic sandstones of the birrindudu group the deposits formed at 1 65 to 1 61 ga along steeply dipping faults there is no known local igneous activity at this time depletion of hrees in the browns range metamorphics together with the similar nonradiogenic nd isotope composition of the orebodies and the browns range metamorphics indicates that ore metals were leached directly from the browns range metasedimentary rocks we propose an ore genesis model that involves fluid leaching hrees from the browns range metamorphics and subsequently mixing with p bearing acidic fluid from the overlying sandstones in fault zones near the unconformity the union of p and hrees via fluid mixing in a low ca environment triggered extensive xenotime precipitation this mineralization is unlike that of any other class of ree ore deposit but has a similar setting to unconformity related u deposits of australia and canada so we assign it the label unconformity related ree further discoveries of this ree mineralization type are expected near regional unconformities within proterozoic intracontinental sedimentary basins across the globe

the proterozoic thelon paleosol northwest territories canada abstract beneath the 1 72 ga thelon formation in the northwestern part of the canadian shield an unmetamorphosed and undeformed paleosol is preserved on a variety of paleoproterozoic and archean protoliths this paper documents the paleosol referred to as the thelon paleosol in four localities where it developed on leucocratic schist gneiss and granite the thelon paleosol is characterized by these ascending changes from fresh protolith through paleosol to the unconformity a saprolitic disruption of the protolith resulting in ped and ferran formation b reddening of the paleosol as a consequence of hematitization c increase in dissolution of feldspar plagioclase alkali feldspar increase in the degree of iron oxidation in biotite chlorite and garnet and an increase in the abundance of neoform kaolinite illite and hematite cement d a loss of tio2 fe2o3 total feo mno mgo cao na2o k2o p2o5 u zr rb sr ba e a gain of fe2o3 and f an increase in cia values the fabric of the parent material appears to be the only soil forming factor that locally influenced paleosol development in comparison to thin profiles developed on massive relatively impervious protoliths thick profiles have developed on metamorphic protoliths in which the fabric has allowed deeper penetration of paleoweathering fluids the behaviour of iron in the profiles particularly profile 2 with a granite protolith and an increase in hematite towards the top of the profiles suggests that the thelon paleosol formed under an oxidizing atmosphere subsequent deposition of quartzose conglomerate and sandstone of the thelon formation has caused compaction of the thelon paleosol and this compaction probably was responsible for the formation of stylocumulates in the paleosol during diagenesis of the thelon formation the influx of diagenetic fluids into the paleosol produced veinlets of quartz and hematite a newly recognized microcrystalline hydrated alumino phosphate sulphate mineral and widespread pseudomorphs of illite after pedogenic vermiform kaolinite

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

comparing 1800 1600 ma accretionary and basin processes in australia and laurentia possible geographic connections in columbia abstract we focus on potential pinning points on the southern and eastern margins of australia and the southern and western margins of laurentia and interpret a convergent plate boundary along the southern margin of the proto australian continent during the palaeo to mesoproterozoic 1800 1600 ma specific geological events within the southern australian margin can be correlated with events preserved along the medicine bow yavapai mazatzal belt in southwestern laurentia these belts were characterised by southward continental growth with varying degrees of crustal reworking and accretion of juvenile material in australia crustal reworking appears to have been the dominant process from 1800 to 1670 ma with more juvenile material accreted at 1620 ma in contrast the southern laurentian terranes were dominated by accretion of juvenile material from 1800 to 1620 ma although reworked continental crust was also accreted to the margin in the interior of both continents basins developed with comparable histories from 1800 to 1670 ma thereafter the evolution of the interior basins diverged with sag phase processes dominant in northern australia and a protracted depositional hiatus in laurentia the geologic evolution is consistent with palaeomagnetic data and provides further evidence for geographic links between eastern australia and western laurentia from 1800 to 1600 ma

long lived deformation history recorded along the precambrian thelon and judge sissons faults northeast thelon basin nunavut the ene striking thelon and judge sissons faults of south central nunavut are well preserved and record long lived dextral transcurrent movement with complex reactivation and fluid flow histories

predrill prediction of subsalt pore pressure from seismic impedance abstract a target oriented predrill pore pressure prediction method using seismically estimated acoustic impedance is applied to recently acquired and processed dual coil data in the green canyon and walker ridge areas of the gulf of mexico three deepwater subsalt wells are used in the study one was used as a calibration well and the other two were used as blind wells for comparing prediction results with the measured pore pressure and mud weight data all three wells are in the green canyon area penetrating thick salt bodies a new seismic inversion method is used for inversion of seismic impedance the pore pressure method uses a direct transform of the inverse of acoustic impedance with two adjustable parameters the optimization of the parameters is done through an iterative process to match the pore pressure gradient obtained from the well acoustic impedance with those of pore pressure measurements and mud weights within a tolerable range of those data for the calibration well the optimized p

stability of detrital heavy minerals on the norwegian continental shelf as a function of depth and temperature abstract petrographic analysis of 1931 thin sections from sandstones of pliocene to devonian age on the norwegian continental shelf indicate that the heavy minerals zircon tourmaline rutile apatite and spinel survive to depths exceeding 5000 m and to temperatures of around 200 c without showing signs of intrastratal dissolution on the other hand the maximum depth and temperature of occurrence for amphibole are 841 m and 40 c around 1500 m and 55 c for sphene when 0 5 km of probable uplift is taken into account 2231 m and 92 c for kyanite 2559 m and 95 c for epidote 2810 m and 109 c for staurolite and 4589 m and 175 c for garnet initial signs of garnet dissolution occur at around 2000 m depth and all garnets are partially dissolved at depths greater than 3500 m monazite is present down to 4858 m and 182 c and chloritoid to 3811 m and 149 c it is however uncertain whether this is due to the low number of samples deeper than 4858 m and to the rare occurrence of chloritoid or to intrastratal dissolution the same sequence of heavy mineral stability is found when volume of quartz cement is used as a proxy for time temperature exposure quartz cement is not found in samples containing amphibole or detrital sphene a maximum of a fraction of a percent quartz cement is found in samples containing kyanite up to 1 together with epidote up to 6 with staurolite up to 24 with chloritoid up to 25 with garnet whereas maximum values of 25 35 are present together with zircon tourmaline rutile patite spinel and monazite the sequence of persistence of heavy minerals versus depth found in this study is very similar to results from several previous studies although unstable heavy minerals survive to greater depths in very young and rapidly buried sandstones and there are some differences regarding the stability of sphene and epidote heavy mineral dissolution has created secondary pores and possibly has contributed to precipitation of kaolinite illite quartz and carbonates in the studied sandstones but these reactions are of very limited volumetric importance

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

basement geology beneath the northeast thelon basin nunavut insights from integrating new gravity magnetic and geological data current models for unconformity associated uranium deposits predict fluid flow and ore deposition along reactivated faults in 1 76 ga basement beneath mesoproterozoic siliciclastic basins in frontier regions such as the thelon basin in the kivalliq region of nunavut little is known about the sub basin distribution of units and structures making exploration targeting very tenuous we constructed a geological map of the basement beneath the unconformity by extrapolating exposed features into the subsurface the new map is constrained by detailed geological geophysical and rock property observations of outcrops adjacent to the basin and by aeromagnetic and gravity data over the geophysically transparent sedimentary basin from rock property measurements it is clear that the diverse magnetic and density characteristics of major rock packages provide quantitative three dimensional constraints gravity profiles forward modelled in four cross sections define broad synforms of the amer belt and archean volcanic rocks that are consistent with the structural style outside the basin major lithotectonic entities beneath the unconformity include supracrustal rocks of the archean woodburn lake group and marjorie hills meta sedimentary gneiss and associated mixed granitoid and amphibolitic gneiss the amer mylonite zone and inferred mafic intrusions oriented parallel and sub parallel other igneous intrusions of 2 6 ga 1 83 ga and 1 75 ga vintage and the 1 84 ga amer group four main brittle regional fault arrays 040 060 075 90 120 and 150 controlled development and preservation of the basin the reactivated intersections of such faults along fertile basement units such as the rumble assemblage marjorie hills assemblage nueltin igneous rocks and pitz formation are the best targets for uranium exploration

estimation of formation fluid pressure using high resolution velocity from inversion of seismic data and a rock physics model based on compaction and burial diagenesis of shales accurate assessment and prediction of formation fluid pressure and fracture gradient form an essential part of the planning process during various phases of hydrocarbon exploration and exploitation these include regional basin analysis and basin high grading prospect identification analysis and drilling campaign to lift hydrocarbons while the literature is full of activities in this field that are linked to the need for drilling safety by providing help with casing and mud weight program and quite justifiably so very little discussion addresses another and very important need seal integrity and trap configuration analysis

hydrothermal alteration of monazite in the precambrian crystalline basement of the athabasca basin saskatchewan canada implications for the formation of unconformity related uranium deposits microanalytical studies of basement rocks below the athabasca sandstone basin indicate that monazite is the dominant uranium bearing mineral in the study area drill core samples of hydrothermally altered basement show that monazite is commonly altered to a th silicate phase and uranium has been significantly mobilized on average 75 of the uranium bound to monazite is leached out during monazite alteration in contrast no substantial mobilization of uranium from detrital minerals e g zircon has yet been observed in the athabasca sandstones it is suggested that hydrothermal alteration of granitic rocks especially potassic pegmatoids and potassic orthogneisses of the sub athabasca basement represents the most important uranium source for the unconformity type deposits

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

structural controls and metallogenic model of polyphase uranium mineralization in the kiggavik area nunavut canada the kiggavik area is located on the eastern boundary of the paleo to mesoproterozoic thelon basin nunavut canada and hosts uranium mineralization in archean basement rocks the major fault fracture network in the kiggavik area is mainly oriented ene wsw and ne sw consisting of polyphased fault zones initiated during the thelon and trans hudsonian orogenies ca 1900 1800 ma these faults were subsequently mineralized in four stages referred to as u0 u1 u2 and u3 the first event u0 is inferred to be of magmatic origin and is related to microbrecciation and weak clay alteration under a wsw ene 1 u0 is a ca 1830 event which predates intense quartz brecciation qb and veining at ca 1750 ma qb is associated with emplacement of the kivalliq igneous suite and caused pervasive silicification of former fault zones which in turn controlled subsequent fracture development and behaved as barriers for later u mineralizing fluids u1 to u3 u1 u2 and u3 postdate deposition of the thelon basin u1 and u2 occurred under a regional strike slip stress regime with the direction of 1 evolving from wnw ese u1 to ne sw ene wsw u2 both formed at 1500 1330 ma and are related to circulation of thelon derived uranium bearing basinal brines a post u2 but pre mackenzie dykes ca 1270 ma extensional transtensional stress regime with 3 oriented ne sw caused normal dextral offset of the orebodies by reactivating nnw sse and e w trending faults this fracturing event triggered circulation of hot 300 c probably acidic fluids that dissolved quartz and caused illitization and bleaching of the host rocks finally u3 records remobilization of the previous mineralization along redox fronts through percolation of low temperature meteoric fluids during two main tectonic events at ca 550 and 350 ma this study provides evidences for the presence of a primary pre thelon basin uranium stock within the kiggavik prospects and a strong structural control on mineralization in the kiggavik area our study also shows a nearly similar evolution of uranium mineralization in this area compared to the world class uranium district of the athabasca basin saskatchewan canada

u pb pb pb and k ar isotopic study and petrography of uraniferous phosphate bearing rocks in the thelon formation dubawnt group northwest territories canada the thelon formation uppermost unit of the dubawnt group overlies a regionally extensive paleoweathered zone developed on a wide range of lithochronological units including formations in the lower dubawnt group authigenic uraniferous phosphate minerals fluorapatite and goyazite cementing thelon conglomerate sandstone and filling fractures in the underlying paleoweathered zone were dated in an attempt to better constrain the age of thelon sedimentation and diagenesis the oldest age 1720 6 ma derived from phosphate cemented sediments is interpreted as a minimum age for diagenesis and therefore brackets initial thelon sedimentation between emplacement of fluorite bearing granites at 1753 ma and authigenic phosphate cementation at 1720 ma additional ages of 1685 4 and 1647 ma are interpreted as remobilization or subsequent cementation events k ar ages on illite 1386 37 and 1266 31 ma from the paleoweathered zone and basal conglomerate respectively are significantly younger than ages de

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

geology lithogeochemistry and u pb geochronology of the aberdeen lake area nunavut new insights into the neoarchean tectonic evolution of the central rae domain abstract the aberdeen lake supracrustal belt is one of several neoarchean greenstone belts preserved within the rae domain of the western churchill province we divide the belt into 1 a lower sequence of ca 2750 ma komatiite ttg tonalite trondhjemite granodiorite intrusions and ttg contaminated fe tholeiitic mafic gneiss 2 a middle sequence of ca

experimental study of igneous and sedimentary apatite dissolution control of ph distance from equilibrium and temperature on dissolution rates apatite dissolution experiments were conducted using both a fluidized bed and stirred tank reactor over a range of ph temperature solution saturation state and on non carbonated and carbonated apatite compositions igneous fluorapatite fap and sedimentary carbonate fluorapatite cfa respectively from 2 8 5 were not possible due to detection limits of the analytical techniques used in this study and the high insolubility of fap for the cfa compositions studied the dissolution rate decreased with increasing ph from 4 ph 7 during early stages of the dissolution reaction for both fap and cfa mineral components were released in non stoichiometric ratios with reacted solution ratios of dissolved ca p and ca f being greater than mineral stoichiometric ratios suggesting that ca was preferentially released compared to p and f from the mineral structure during the early stages of dissolution an increase in reacted solution ph accompanies this early elevated release of ca as the dissolution reaction proceeded to steady state dissolution became congruent when normalized to bet measured surface area fap dissolved faster from 4 ph 7 compared to cfa the apparent arrhenius activation energy ea of fap dissolution over the temperature range of 25 55 c at ph 3 0 i 0 1 and pco2 0 is 8 3 0 2 kcal mol 1 both the apparent exchange of solution h for solid bound ca at low ph in the early stage of dissolution and the ea of dissolution suggest a surface and not a diffusion controlled dissolution reaction for fap and cfa the degree of undersaturation of the solution gr with respect to fap was important in determining the dissolution rate at ph 3 0 i 0 1 and pco2 0 the dissolution rate of fap was 5 greater in the far from equilibrium region compared to the near equilibrium slope region a simple apatite weathering model incorporating the experimental results from this study was constructed and numerical calculations suggest that during the phanerozoic both the surface area of igneous rock available for weathering and the average global temperature were important factors in determining the p weathering flux from apatite dissolution it is possible that elevated global temperatures coupled with relatively high surface area of igneous rock during the early to mid paleozoic resulted in elevated p weathering fluxes which along with climatic evolutionary pressures of the neoproterozoic facilitated the radiation of multicellular organisms large scale phosphorite deposition and abundance of calcium phosphate shelled organisms during the early cambrian

new insights from geophysical data on the regional structure and geometry of the southwest thelon basin and its basement northwest territories canada detailed analysis of gravity and aeromagnetic data covering the southwest thelon basin northwest territories canada has provided insight into basement geology that has significance to exploration for uranium and possibly other economic metals in a remote frontier region interpretation of basement geology has been constrained by the calibration of gravity and magnetic signatures with precambrian geology adjacent to the basin and sparse seismic data within the basin creating the first basement geologic map of the southwest thelon basin the basement to the overlying sedimentary units is dominated by magnetic felsic and mafic bodies variably overlying and intruding the gneissic crystalline basement supracrustal belts located outside the basin margins are interpreted to continue below the basin fill major structures have been delineated geophysically including the howard lake shear zone and the bathurst and mcdonald fault systems northwest trending structures forming part of the bathurst fault system appear to control the unconformity surface morphology and the location of basin depocenters the geologic interpretations are corroborated by joint gravity and magnetic modeling of profiles that reveal the deepest part of the thelon basin reaches depths of 2100 m in an area of subdued magnetic and gravimetric response to the north the basin is a focus of active exploration for uranium and we have found that areas along the south and eastern margins underlain by u rich granitoid rocks may have significant potential where intersected by reactivated faults

lead diffusion in apatite and zircon using ion implantation and rutherford backscattering techniques abstract ion implantation was used to introduce pb into the minerals zircon and apatite diffusion profiles were obtained using rutherford backscattering and the results were fitted with a model to determine the diffusion coefficients this approach is both simple and useful in studying diffusion over a temperature range of geologic interest without inordinate annealing times results for apatite over the temperature range 600 900 c are in good agreement with earlier results obtained for higher temperatures watson et al 1985 and are described by the following arrhenius law d 1 27 10 4 cm 2 s 1 exp 54 6 1 7 kcl mol 1 rt this suggests that radiation damage induced by ion implantation has little effect on pb diffusion in this case due to rapid annealing of induced damage at low temperatures the activation energy stated above is somewhat smaller than that previously determined 70 kcal mol 1 reflecting the larger range in 1 t sampled by the present results closure temperatures calculated with these diffusion parameters are in good agreement with those inferred from geochronologic data diffusion coefficients for pb in zircon determined in this study are greater than those obtained from a single experimental measurement and estimates of pb diffusion based on geochronologic data and u pb zoning in natural zircons the differing results for zircon and apatite obtained in this study appear to be related to each mineral s ability to anneal the radiation damage induced by ion implantation

age geological setting and paragenesis of heavy rare earth element mineralization of the tanami region western australia metasedimentary rock hosted heavy rare earth element hree mineralization occurs as numerous orebodies distributed across a large district of the tanami region of central australia close to a regional unconformity between archean metasedimentary rocks of the browns range metamorphics brm and overlying proterozoic birrindudu group sandstones the orebodies consist predominantly of quartz xenotime and minor florencite and occur along steeply dipping structures within a stockwork of hydrothermal veins and breccias paragenetic stages of the mineralization include 1 a pre ore stage of a greenschist facies overprint of detrital minerals including quartz alkali feldspar plagioclase and muscovite aligned in the premineralization foliation 2 syn ore quartz and white mica alteration associated with a multistage mineralization of the ore minerals primarily in breccias and veins and 3 a post ore stage of veining and brecciation forming several generations of quartz plus hematite barite anhydrite and pyrite in situ u pb dating of xenotime from several deposits prospects yielded an age range for mineralization of 1 65 to 1 60 ga this timeframe lacks local magmatism or orogeny and is significantly younger than the ca 1 72 ga 40ar 39ar age of the pre ore muscovite far field stresses associated with the distal isan and liebig orogenies are invoked as drivers of large scale fluid flow and fault re activation in the region we propose that ore formation was achieved via fluid leaching of ree from the brm followed by fluid mixing in fault zones especially in the vicinity of the unconformity between the brm and overlying birrindudu group sandstones this mineralization style shares many features with unconformity related u deposits and there is significant potential for discovery of further ree orebodies of this style especially in the vicinity of regional unconformities in intercontinental sedimentary basins