timing and thermochemical constraints on multi element mineralisation at the nori ra cu mo u prospect great bear magmatic zone northwest territories canada the timing of cu mo u mineralisation at the nori ra prospect in the paleoproterozoic great bear magmatic zone has been investigated using re os molybdenite and 40ar 39ar biotite geochronology the re os molybdenite ages presented are the first robust sulphide mineralisation ages derived from the great bear magmatic zone cu mo u mineralisation is hosted in early to syn deformational hydrothermal veins consisting of quartz and k feldspar or more commonly tourmaline biotite quartz k feldspar with associated wall rock alteration assemblages being predominantly biotite sulphide and oxide minerals consist of chalcopyrite molybdenite and uraninite with lesser pyrite and magnetite elevated light rare earth elements and tungsten concentrations associated with the cu mo u mineralisation have also been reported at the prospect by previous workers molybdenite and uraninite occur intimately in dravitic tourmaline growth zones and at grain margins attesting to their syngenetic nature with respect to hydrothermal veining two molybdenite separates yield re os model ages of 1 874 4 8 7 2 and 1 872 4 8 8 ma 2 with a weighted average model age of 1 873 4 6 1 ma 2 laser step heating of biotite from the marginal alteration of the wall rock adjacent to the veins yields a 40ar 39ar maximum cooling age of 1 875 8 ma mswd 3 8 2 indistinguishable from the re os molybdenite model age and a previously dated syn tectonic aplitic dyke in the region dravitic tourmaline hosts abundant primary liquid vapour solid bearing fluid inclusions analytical results indicate liquid vapour homogenisation at 260 c constraining the minimum temperature of mineralisation the solids which are possibly trapped did not homogenise with the liquid vapour by 400 c salinities in the inclusions are variable raman spectra identify that at least some of the solids are calcite and anhydrite raman spectra also confirm the vapour phases contain some co2 whereas clathrates or ch4 was not observed or detected quartz grains only host secondary fluid inclusions which fluoresce under ultraviolet light indicating trapped hydrocarbons we speculate that these resulted from phanerozoic fluid circulation through the proterozoic basement the collective interpretation of the age hydrothermal character and associated metals high temperature and variable salinity suggests that the nori ra cu mo u mineralisation can be linked with the earliest stages of plutonism in the great bear magmatic zone from a regional perspective the mineralisation may pre date the extensive multi element mineralisation now recognised as part of the iron oxide copper gold iocg spectrum of deposits as iocg provinces generally contain a variety of mineralisation styles we interpret this as the earliest phase of the extensive mineralising system

shrimp u pb geochronology of detrital zircons from the treasure lake group new evidence for paleoproterozoic collisional tectonics in the southern hottah terrane northwestern canadian shield the recently defined treasure lake group is a platformal sedimentary sequence more than 3 km thick that was deformed and metamorphosed prior to formation of the great bear continental arc during 1875 1845 ma the group is exposed as remnants in the southern part of the arc its basement is not exposed but is interpreted to comprise the paleoproterozoic hottah terrane which is exposed at hottah lake in the northern part of the arc studies in that region show that the hottah terrane collided with the archean slave craton to the east ca 1883 ma following reversal of subduction polarity from west to east continued eastward subduction under the collision zone formed the great bear arc the present study was undertaken to determine the age and provenance of the treasure lake group thirty nine detrital zircon grains from a sample of a quartz arenite unit in the middle part of the treasure lake group were analyzed by shrimp sensitive high resolution ion microprobe they show an age range from ca 2729 to

parentage of archean basement within a paleoproterozoic orogen and implications for on craton diamond preservation slave craton and wopmay orogen northwest canada the wopmay orogen is a paleoproterozoic accretionary belt preserved to the west of the archean slave craton northwest canada reworked archean crystalline basement occurs in the orogen and new bedrock mapping u pb geochronology and sm nd isotopic data further substantiate a slave craton parentage for this basement detrital zircon results from unconformably overlying paleoproterozoic supracrustal rocks also support a slave craton provenance rifting of the slave margin began at ca 2 02 ga with a second rift phase constrained between ca 1 92 and 1 89 ga resulting in thermal weakening of the archean basement and allowing subsequent penetrative deformation during the calderian orogeny ca 1 88 1 85 ga the boundary between the western slave craton and the reworked archean basement in the southern wopmay orogen is interpreted as the rifted cratonic margin which later acted as a rigid backstop during compressional deformation age isotopic characteristics of plutonic phases track the extent and evolu

thermo tectonic evolution of a metamorphic internal zone documented by axial projections and petrological p t paths wopmay orogen northwest canada axial projections of the transversely folded 1 9 ga wopmay orogen document stratigraphic and structural relations in a metamorphic internal zone having more than 30 km of structural relief the greater part of the metamorphic belt is separated from underlying autochthonous archean basement and thin early proterozoic cover by a sole thrust coextensive with that beneath the external thrust fold belt site specific metamorphic pressure temperature p t paths are derived from core to rim microprobe analyses of large zoned poikiloblastic garnets that contain abundant inclusions of biotite plagioclase quartz and in some cases aluminosilicate for garnet absent units qualitative p t paths are deduced from overprinting mineral assemblages the structural and metamorphic data combined with the results of geochronological and contiguous external belt studies show that regional metamorphism in the internal zone is the result of three overlapping thermally additive thermotectonic regimes 1 onset of metamorphism during crustal thinning 2 plutonic heat advection during crustal shortening and 3 thermal relaxation concurrent with uplift as a consequence of crustal thickening

influences of chemical degradation on mechanical behaviour of a limestone this paper is devoted to the experimental investigation of chemical degradation effects on mechanical behaviour of a porous limestone hydrostatic and triaxial compression tests are first performed respectively on sound and chemically degraded samples it is found that the chemical degradation induces the diminution of pore collapse limit stress elastic modulus and material cohesion coupled triaxial creep chemical degradation tests are also performed the chemical degradation enhances time dependant deformation and can generate significant increase in permeability through the formation of wormholes networks

tectonomagmatic evolution of the southern great bear magmatic zone northwest territories canada implications for the genesis of iron oxide alkali altered hydrothermal systems the great bear magmatic zone in northwestern canada is a paleoproterozoic volcano plutonic belt of high k calc alkaline to shoshonitic affinity interpreted as a continental arc that formed between 1 87 and 1 85 ga following the short lived calderian orogeny tectonomagmatic evolution of this magmatic zone favored the formation of multiple iron oxide and alkali alteration systems within a time frame of 10 m y as constrained geochronologically within error between 1875 and 1865 ma this illustrates a temporal and genetic relationship between shoshonitic to high k calc alkaline continental arc magmatism and the formation of iron oxide rich deposits and alkali alteration associated with iron oxide copper gold iocg mineralization early rhyolitic magmatism formed the basal sequence of the lou assemblage under a compressive or transpressive tectonic regime between 1872 and 1867 ma an apparent higher magmatic production is linked to a marked change in composition of the volcanic and plutonic rocks from rhyolite to intermediate felsic and locally mafic compositional homogeneity of the intrusive and volcanic rocks of the mazenod and bea assemblages termination of ductile to brittle ductile deformation along the main deformation zones and transition to widespread brittle fracturing and breccia formation are interpreted to reflect a change in the regional stress regime from compressional transpressional to extensional transtensional this change in stress regimes is associated with iron oxide rich mineralization that initially formed the nico au bi co deposit followed by iocg mineralization in the nico and sue dianne deposits as well as albitite hosted u mineralization in the southern breccia

the effect of thermal cycling on the seismic quality factor q of some sedimentary rocks changes in q in rocks in response to thermal cycling can result from the removal of physisorbed water an increase in the crack density and therfore the internal surface area at temperatures greater than 400 sup 0 c the removal of chemisorbed oh groups which are the adsorption sites for physisorbed water and the dehydration of clays when rocks are heated to temperatures of 100 sup 0 200 sup 0 c the change is q is reversible and is due to the removal of physisorbed water sioux quartzite and berea sandstone were thermally cycled to 657 sup 0 c and 385 sup 0 c respectively the q of both rocks increased when measured over a broad range of relative humidities but decreased at low humidities 10 25 measurements of adsorption isotherms for the berea sandstone showed no loss of adsorptive capacity of the clays although the surface area of thermally cracked rocks increased the number of sites where adsorbed water molecules contribute to attenuation decreased

test of thermoluminescence dating of loess from new zealand and alaska abstract the accuracy of thermoluminescence tl ages for loess and sediments in general greater than 100 ka is disputed we tested the accuracy of three common tl sediment dating techniques applied to 4 11 m sized polymineral grains from known age loess using 16 samples from north island and south island new zealand and 2 samples from central alaska estimated sample ages range from 20 26 to 800 ka we varied the optical bleaching spectrum the selected window of the emission spectra ultraviolet or uv blue and green wavelengths the pre readout heat treatment and the tl equivalent dose measurement technique most of the 20 26 ka samples gave tl age underestimates of 3 6 ka that may be attributed to post burial open system behavior for the older samples the partial bleach tl method gave expected ages up to 300 ka and the total bleach tl method produced expected ages above 100 ka the partial bleach regeneration tl method gave significant age underestimates for samples older than 100 ka with a maximum tl age of 250 ka for samples having expected ages up to 350 ka two 300 360 ka samples which gave total bleach age underestimates with use of uv tl and green tl gave expected ages with use of blue tl these results demonstrate that reliable tl ages for loess from new zealand and alaska up to 800 ka can be obtained if uv and green emissions and the various regeneration methods are avoided this age range is well above the former putative 80 100 ka upper age limit for tl dating of loess from other regions which was thought to be a global limit application of our successful procedures to such loess is encouraged

a special issue devoted to proterozoic iron oxide apatite ree and iron oxide copper gold and affiliated deposits of southeast missouri usa and the great bear magmatic zone northwest territories canada preface this special issue is focused on the geology and mineral deposits in the mesoproterozoic st francois mountains terrane of southeast missouri united states and in the paleoproterozoic great bear magmatic zone of northwest territories canada contributions in this special issue emphasize iron oxide apatite ioa rare earth element ree and iron oxide copper gold iocg and affiliated deposits e g hitzman 2000 barton 2014 the volume includes results of studies by the u s geological survey usgs and geological survey of canada gsc derived from research done for the usgs mineral resources program and from gsc research completed under auspices of the geomapping for energy and minerals and targeted geoscience initiative programs these studies took advantage of extensive historic drilling at and near ioa and iocg deposits in missouri and of exceptional field exposures in the great bear magmatic zone collectively results of this cumulative body of work provide new insights into the geological geochemical geophysical and temporal characteristics of ioa ree iocg and affiliated deposits leading to enhanced understanding of diverse magmatic hydrothermal systems and refining of genetic models and exploration strategies for such deposits within these terranes and elsewhere in the world both north american terranes contain iron oxide alkali alteration zones that formed during predominantly i type calc alkaline including s type and shoshonitic in the great bear zone volcano plutonic magmatism later magmatism in both terranes was mainly of a type affinity locally the ioa deposits are spatially associated with high ree concentrations the iocg and affiliated deposits include co and birich variants skarns polymetallic veins and albitite hosted u deposits are also present within the footprints of the regional iron oxide alkali alteration systems mineralization occurred contemporaneously with mafic to felsic volcanism and local volcanogenic sedimentation including within or marginal to large ash flow calderas proterozoic rocks in both the st francois mountains terrane and the great

gold refining by bismuth melts in the iron oxide dominated nico au co bi cu w deposit nwt canada the nico au co bi cu w deposit is located in the great bear magmatic zone nwt canada where numerous polymetallic iron oxide dominated mineralized systems have been recognized petrographic electron microprobe analysis empa and laser ablation inductively coupled plasma mass spectrometry la icp ms studies of host rock alteration and ore mineralogy together with sulfarsenide geothermometry have been carried out to constrain the nature of alteration and or mineralization assemblages in this deposit metasedimentary rocks of the treasure lake group host nico and are pervasively altered to an assemblage of ferrohornblende i actinolite i biotite i magnetite i orthoclase which is cut by barren veins composed of quartz ferrohornblende orthoclase calcite set 1 these alteration events are overprinted by metasomatic prograde and retrograde mineralized assemblages and both brittle and ductile deformation accompanied the metasomatism the prograde assemblage 400 c consists of cobaltite co rich loellingite and co rich arsenopyrite stage i magnetite ii ferrohornblende ii actinolite ii biotite ii pyrite and minor scheelite and orthoclase the earliest retrograde mineralization consists of arsenopyrite stages ii and iii which contains variable amounts of co together with native bi bismuthinite and au with lesser magnetite marcasite pyrite hastingsite and minor quartz the preservation of solidified native bi droplets suggests a temperature range of 270 to 400 c for precipitation of this assemblage the final stage of retrograde mineralization consists of a chalcopyrite bismuthinite hematite chlorite assemblage together with hastingsite emplectite which formed at temperatures of less than 270 c textural and trace element evidence indicates that the au and bi present within arsenides and sulfarsenides in the nico system resulted from the initial partitioning of structurally bound au and or invisible nanometer sized particles of au and bi into the prograde sulfarsenide and arsenide phases which contain up to 81 ppm au the au and bi were remobilized following retrograde alteration of those minerals to arsenopyrite ii molten bi droplets are interpreted to have scavenged au insitu resulting in the formation of the bi au inclusions observed in arsenopyrite ii the second mechanism of gold refining is explained by the occurrence of contemporaneous bi te melt and hydrothermal fluids that also could have fractionated gold during transport in solution and deposited it in fractures interstitially to earlier mineral grains and as disseminations within ca fe amphibole magnetite biotite altered rocks overall the gold upgrading at nico is consistent with the liquid bismuth collector model suggesting that this process was an important control on gold concentration in this and potentially other au bi te fe as s rich iron oxide copper gold iocg deposits

element mobility patterns in magnetite group iocg systems the fab iocg system northwest territories canada this paper documents element mobility patterns from a magnetite group iron oxide copper gold iocg prospect in the northwest territories of canada and explores implications for space time chemical evolution of metasomatic systems hosting iocg deposits the fab system located in the great bear magmatic zone gbmz of the northwest territories canada contains numerous fe cu u showings associated with high temperature ht potassic iron alteration overprinting extensive zones of sodic to ht calcic iron alteration each hydrothermal alteration assemblage is associated with distinct element mobility patterns that record evolving physico chemical properties of the hydrothermal fluids new geochronological data constrain the alteration and iocg mineralization in the fab system to a 3 m y window between 1870 1867 ma which is broadly contemporaneous with extensive high level intrusive activity across the gbmz regional to local scale element mobility patterns characteristic of the sodic and sodic calcic iron alteration type record leaching combined with weak to strong mass losses pure sodic alteration depleted the rocks in ca co cu fe mg th u and v conversely sodic calcic iron alteration records significant depletions of nb ree ta ti th and u these element mobility patterns differ from intense ht calcic iron alteration that is enriched in ca co f fe mg mn ni and v with modest enrichments to locally significant mineralization in th u and ree ht calcic iron alteration is also characterized by substantial mass gains that translate into volume gains in stockwork zones and mass volume gains in zones of intense host rock replacement ht potassic iron alteration is characterized by enrichments in ba k ni u and v along with locally co and cu the temporal and spatial association of the fab system alteration and the emplacement of the porphyritic dacite are indicative of the predominant involvement of magmatic hydrothermal fluids the high f and cl contents of the porphyritic dacite and of the ht calcic iron alteration zones as well as nb ree ta th and ti mobility provide strong evidences of high halogen activities f and cl in the hydrothermal fluids high f and cl activities in the hydrothermal fluid are interpreted to have facilitated the mobilization of normally immobile nb ta ti th or weakly mobile elements as well as some metals e g v ni co the formation of ree fluorocarbonates and calcite in the early and incipient ht calcic iron alteration zones indicates the presence of co2 in the hydrothermal fluids weaker hfse hree and ti mobility during later ht potassic iron alteration is interpreted to reflect decreasing temperatures pressures f activities and increasing fo2 as the fluids evolved and interacted with the host rocks

genesis of the paleoproterozoic nico iron oxide cobalt gold bismuth deposit northwest territories canada evidence from isotope geochemistry and fluid inclusions abstract the nico deposit is located in the southern portion of the paleoproterozoic great bear magmatic zone northwest territories canada the majority of the mineralization lies within the bowl zone hosted by the treasure lake group tlg where heavily altered precursor rocks are interpreted to be carbonate rich wackes and siltstones these rocks are crosscut by a set of pre ore quartz calcite amphibole k feldspar veins s1 the co au bi w cu mo mineralization at nico is contained in stratabound ore lenses within the bowl zone and comprises a prograde assemblage of co rich arsenopyrite arsenopyrite i and loellingite cobaltite pyrite actinolite ferrohornblende biotite and rare scheelite molybdenite along with minor magnetite and amphibole retrograde assemblages resulted from re crystallization of the co bearing phases to form arsenopyrite ii and iii along with precipitation of marcasite pyrite hastingsite native bi au te and minor bismuthinite and magnetite the latest stage of retrograde mineralization comprises chalcopyrite hastingsite chlorite and hematite emplectite two sets of barren quartz dolomite amphibole k feldspar chalcopyrite veins s2 and s3 post date the mineralization the southern breccia zone hosts minor u cu mo mineralization and is interpreted to be the deepest portion of the nico system two molybdenite samples from the bowl zone and the southern breccia yielded re os ages of 1865 9 and 1877 8 ma respectively consistent with the interpreted ca 1870 ma age of the nico deposit this age is also synchronous with the onset of magmatism in the great bear magmatic arc ca 1875 1850 ma ore mineral 34s values 3 3 6 7 sulfides indicate that crustal sulfur was assimilated by upwelling felsic magmatic melts the 18o values of the fluids precipitating magnetite and co rich arsenopyrite 6 and 8 and from pre and syn mineralization magnetite 0 8 to 1 5 support a magmatic hydrothermal origin of the fluids two out of three calcite samples from pre s1 and post ore s3 veins have also 13c values consistent with a magmatic origin 5 5 to 3 6 however one calcite sample from the s3 veins has a value that indicates a reduced sulfur source 15 6 this value is similar to those of the much younger secondary trails of native bi in s1 vein quartz are associated with liquid vapor lv and liquid vapor halite lvs inclusions which indicates that bi and possibly au were transported in saline to hyper saline brines lv bi 2 16 wt nacl equiv 8 22 wt cacl2 equiv lvs bi 37 wt nacl equiv with homogenization temperatures of 137 216 c and 192 to 350 c for lv bi thl v l and lvs bi thl s l respectively the presence of calcium rich fluids might indicate extensive equilibration of those solutions with the host tlg rocks if a pressure correction is applied to the lv inclusions using a minimum entrapment temperature of 271 4 c the bi melting point a minimum crystallization depth of between approximately 5 and 8 km is indicated trace element analyses carried out in this study and compiled from acosta gongora et al 2014 show that the least altered metasedimentary tlg rocks contain up to six times more as carbonate unit 30 5 ppm than the average upper continental crust conversely concentrations of au

strain dependent attenuation observations and a proposed mechanism the measured attenuation q 1 of a rock is a function of a number of parameters one of those being the applied strain amplitude it is important to understand the effect that strain amplitude has on q 1 for several reasons different measurement techniques use differing strain amplitudes and may measure a dissimilar q 1 near source large strain wave propagation may behave highly non linearly and the strain amplitude dependence can provide insight into the attenuation mechanism a physical model based on the contact friction between crack surfaces in the rock has been developed to describe rock deformation and dissipation under large applied strain the three dimensional crack surfaces are characterized by a statistical distribution of asperity heights the sliding contact of these spherically tipped asperities dissipates frictional energy hertzian theory is applied to the average asperity contact and predicts that the large strain attenuation is given by q 1 k e p4 3 where k is a constant consisting of the matrix elastic parameters is the crack density e is the strain amplitude and p is the confining pressure the total attenuation measured appears to be the sum of this strain dependent term and a strain independent term the results of ultrasonic pulse transmission experiments are compared with the model s prediction both p and s waves with strain amplitudes from 10 8 to 10 5 were employed frequencies from 0 4 to 1 5 mhz were used in conjunction with rock confining pressures of 2 to 580 bars on dry berea sandstone and lucite samples the spectral ratio method and rise time technique were applied to deduce the q 1 values the observed data and other observations from the literature compare well with the model s prediction for the dependence of q 1 on large strain amplitude crack density and pressure

great slave lake shear zone canadian shield reconstructed vertical profile of a crustal scale fault zone abstract the great slave lake shear zone gslsz of the northwestern canadian shield a 25 km wide early proterozoic transcurrent dextral mylonite zone is a type example of a crustal scale fault zone profile with time 1 1 the metamorphic grade decreased from granulite to greenschist facies 2 2 the locus of high strain narrowed and jumped laterally abandoning relatively older mylonites progressively younger mylonites represent both cooler temperatures and lower pressures thus the sequence of narrowing mylonite belts represents a series of progressively shallower seated sections through the gslsz 3 3 deformation evolved through the brittle ductile transition initially producing non dilational penetrative breccias followed first by discrete non dilational faulting and subsequently by dilational quartz stockworks developing crustal scale shear zones grow to an optimum width dictated by the requirement of minimum geologically reasonable strain rates for given conditions of wall rock rheology and displacement rate independent of variations in relative plate motion mature shear zones change width and migrate laterally as a function of inferred thermally activated rheological changes within the wall rocks

crustal recycling by slab failure models for crustal recycling are based upon estimates of the amount of material being returned to the mantle today thus a better understanding of those processes will help to constrain the models we suggest through the use of an early proterozoic example in the wopmay orogen that failure of the subducting slab during collision leads to large quantities of crustal material being recycled into the mantle that this process has been active since the early proterozoic and that it may explain the paucity of rift deposits in other orogens

magmatic evolution of the southern great bear continental arc northwestern canadian shield geochronological constraints the calc alkaline great bear continental arc in the wopmay orogen developed after a collision ca 1890 ma of the archean slave craton with the paleoproterozoic hottah terrane to the west u pb zircon dating of three volcanic and six intrusive rocks from the southern part of the arc shows four stages of development i intrusion of a few small sodic leucogranite plutons at 1873 2 ma into a previously folded metasedimentary sequence ii abundant calc alkaline felsic volcanism and subvolcanic intrusions during the period 1870 1866 ma bracketed by five ages iii intrusion of large calc alkaline granitic plutons including the marian river batholith dated by zircon and titanite from two samples at 1866 2 3 ma and iv emplacement of the potassic faber lake rapakivi granite at 1856 2 3 ma the arc was developed on the hottah terrane due to easterly subduction of an oceanic plate under the amalgamated slave craton hottah terrane the oldest exposed rocks in the southern part of the arc are remnants

geochemistry of hydrothermal tourmaline from iocg occurrences in the great bear magmatic zone implications for fluid source s and fluid composition evolution abstract tourmaline crystallized during iron oxide and alkali calcic alteration and iocg mineralization in the great bear magmatic zone canada within the samples analyzed tourmaline occurs as small crystals in the groundmass of hydrothermal breccias southern breccia and contact lake or as large prismatic crystals in quartz ore mineralogy veins contact lake devries lake and nico the tourmaline from these localities is predominantly shorlitic in composition with minor dravitic uvitic and feruvitic components the boron isotopic composition ranges from 15 to 5 with the majority of values between 15 and 10 the lack of variation among samples supports a common fluid source across the belt for the metasomatic hydrothermal systems these results are isotopically similar to global magmatic and non marine evaporitic reservoirs and lighter than seawater and marine sedimentary rocks the 11b results support a single fluid iocg deposit model for the systems studied wherein metasomatic hydrothermal fluids derived by magmatism ascend and evolve over time through fluid rock interactions

result from a comparison of uv and sunlight bleaching of feldspar and quartz abstract the influence of artificial uv light and sunlight on natural glow curves were compared for k feldspar and quartz from a fluvial and an aeolian deposit the results for feldspar grains show that the use of a uv lamp for bleaching instead of sunlight does not influence the accumulated dose plateau results on the quartz sample on the other hand show clear differences this fact makes dating using quartz grains more complicated the problem of finding the correct residual reached at sedimentation by using the regenaration technique starting from different artificial residuals is also discussed

short lived 1 9 ga continental margin and its destruction wopmay orogen northwest canada a 1 9 ga continental margin in the northwest of the canadian shield evolved in less than 15 m y from a zone of crustal stretching through a phase of passive margin subsidence to attempted subduction beneath an exotic microcontinent reversal of subduction polarity and generation of a major episutural magmatic arc occurred within 15 m y following microcontinental accretion terminal collision occurred 90 m y at most after initial rifting certain differences in detail between this collided margin and those of phanerozoic age may be related to subduction of newly rifted lithosphere rapid evolution of the orogen the contracted passive margin phase in particular is consistent with but does not prove more rapid recycling of oceanic plates at that time

formation of albitite hosted uranium within iocg systems the southern breccia great bear magmatic zone northwest territories canada uranium and polymetallic u mineralization hosted within brecciated albitites occurs one kilometer south of the magnetite rich au co bi cu nico deposit in the southern great bear magmatic zone gbmz canada concentrations up to 1 wt u are distributed throughout a 3 by 0 5 km albitization corridor defined as the southern breccia zone two distinct u mineralization events are observed primary uraninite precipitated with or without pyrite chalcopyrite molybdenite within magnetite ilmenite biotite k feldspar altered breccias during high temperature potassic iron alteration subsequently pitchblende precipitated in earthy hematite specular hematite chlorite veins associated with a low temperature iron magnesium alteration the uraninite bearing mineralization postdates sodic albite and more localized high temperature potassic iron biotite magnetite k feldspar alteration yet predates potassic k feldspar boron tourmaline and potassic iron magnesium hematite k feldspar chlorite alteration the southern breccia zone shares attributes of the valhalla australia and lagoa real brazil albitite hosted u deposits but contains greater iron oxide contents and lower contents of riebeckite and carbonates potassium ni and th are also enriched whereas zr and sr are depleted with respect to the aforementioned albitite hosted u deposits field relationships geochemical signatures and available u pb dates on pre syn and post mineralization intrusions place the development of the southern breccia and the nico deposit as part of a single iron oxide alkali altered ioaa system in addition this case example illustrates that albitite hosted u deposits can form in albitization zones that predate base and precious metal ore zones in a single ioaa system and become traps for u and multiple metals once the tectonic regime favors fluid mixing and oxidation reduction reactions

shear modulus and internal friction of calcite rocks at seismic frequencies pressure frequency and grain size dependence abstract the shear modulus g and associated internal friction q 1 have been measured at seismic frequencies for a suite of four essentially monomineralic calcite rocks with grain sizes ranging from 4 to 1000 m the measurements are based on a previously described technique for the observation of forced torsional oscillations of a series combination of a rock cylinder and a steel standard under high confining pressure at room temperature the behaviour of each rock has been studied as a function of strain amplitude 10 8 10 6 maximum at surface pressure 0 300 mpa and oscillation period 1 300 s no evidence is found of any departure from linearity in the range of strain amplitudes studied corrections which are significant only at the shortest periods 1 3 s have been applied to the raw data to account for the influence of torques exerted on the specimen assembly by the gas pressure medium up to about 100 mpa increase in pressure results in a marked increase in g and decrease in q 1 attributable to the closure of crack porosity except in the fine grained solnhofen limestone in which both g and q 1 are insensitive to change in pressure indicative of the virtual absence of crack porosity at higher pressures g is much less pressure sensitive and q 1 is essentially pressure independent with values less than 0 001 in all four rocks since the rock specimens were jacketted under conditions of normal humidity these relatively low values of q 1 indicate a diminished role for adsorbed water in the anelasticity of rocks at high effective pressures within the pressure independent regime q 1 is essentially independent of frequency for periods of 3 100 s and increases by only 30 as the grain size decreases from 1000 to 4 m thus within this regime it is concluded that the observed value of q 1 results to a large degree from an intracrystalline mechanism with a broad range of relaxation times the possibility of significant dislocation damping will be discussed

evidence from ophiolites blueschists and ultrahigh pressure metamorphic terranes that the modern episode of subduction tectonics began in neoproterozoic time comment and reply comment i agree with my friend bob stern that the onset of actualistic plate tectonics is an unsolved problem and that the answer must ultimately come from geological evidence and not from model calculations there are simply too many unknown factors e g eclogitization oceanic crustal delamination

alteration facies linkages among iron oxide copper gold iron oxide apatite and affiliated deposits in the great bear magmatic zone northwest territories canada high temperature metasomatism driven by ascent of voluminous saline fluid columns in the upper crust plays a major role in the genesis of iron oxide alkali alteration ore systems but fundamental questions remain on genetic linkages among iron oxide copper gold iocg iron oxide apatite ioa albitite hosted uranium and skarn deposits that they produce excellent surface exposures of such systems in the great bear magmatic zone of northernwestern canada record the depth to paleosurface prograde evolution of iron oxide alkali alteration facies and mineralization across the belt albitite corridors that are tens of kilometers in length record the earliest reactions between highly saline fluids and host rocks along fault zones and subvolcanic intrusions pervasive albitization partitioned metals from the host rocks into the ascending fluid column leaving behind structurally weakened corridors of porous albitite these corridors were cut replaced and overprinted by amphibole and magnetite bearing calcic iron alteration assemblages in extreme cases the discharge of calcium iron and specialized metals formed iron oxide apatite deposits vanadium rare earth elements while recharging the outgoing fluids in sodium potassium and base and precious metals as temperatures declined and fluid chemistry evolved through fluid rock reactions the formation of potassic iron alteration assemblages breccias and sulfides resulted in magnetite and hematite group iocg mineralization within carbonate units skarns formed prior to are replaced by and evolved to calcic iron alteration facies skarns can locally host base metal mineralization tectonically uplifted albitite breccias replaced by potassic iron alteration assemblages became a preferential host for uranium mineralization the results of this study also illustrate that permutations and cyclical build up of alteration products can arise from a combination of faulting differential uplift and renewed magmatism framed within an alteration facies deposit model alteration zones and mineral occurrences play a pivotal role in predicting the mineral potential of iron oxide and alkali altered systems at district to deposit scales

u pb zircon ages and field relationships of archean basement and proterozoic intrusions south central wopmay orogen nwt implications for tectonic assignments new field and u pb zircon data from the south central wopmay orogen south of 65 n establish crystallization ages of basement and plutonic phases and bring to the forefront questions on the architecture of the orogen the complex and extensive 3300 2575 ma basement domain was derived from the adjacent slave craton paleoproterozoic supracrustal rocks dominated by an extensive pelitic psammitic sequence with basal arenite conglomerate and carbonate unconformably overlie this basement pre to post kinematic paleoproterozoic plutons intrude both basement and overlying strata and crystallized at 1877 1867 1862 and 1858 1850 ma the first pulse of plutonism constrains an early generation of metamorphism and deformation to younger than 1877 ma and is corroborated by metamorphic zircon in archean basement the interval from 1867 to 1862 ma brackets ductile deformation in granite and granodiorite intrusions although corresponding structure in the metasedimentary strata is equivocal post kinematic ca 1

trace element geochemistry of magnetite and its relationship to cu bi co au ag u w mineralization in the great bear magmatic zone nwt canada the paleoproterozoic great bear magmatic zone is the focus of ongoing exploration for iron oxide copper gold iocg deposits and also hosts iron oxide apatite occurrences examples of iocg deposits in the great bear magmatic zone include sue dianne and nico and other smaller prospects including damp fab and nori ra the past producing terra mine property hosts significant iocg like alteration that contains dome shaped iron oxide apatite bodies petrographic study has identified multiple generations of magnetite at nico fab and nori ra and for the most part a single generation of magnetite at sue dianne damp and terra laser ablation inductively coupled plasma mass spectrometry la icp ms documents important geochemical differences in v ni cr and co concentrations within the magnetite variations of trace elements in magnetite from the great bear magmatic zone could be a result of 1 host rock fluid equilibration during regional metamorphism 2 postmetamorphic hydrothermal metasomatism of treasure lake group metasedimentary rocks 3 preferential solubility of co over ni within the fe rich fluids 4 changes in oxygen fugacity f o2 and 5 partitioning of elements into coprecipitating sulfides regionally the cr co ratio is higher in barren and pre ore magnetite compared to magnetite coprecipitated with ore minerals and or present in ore rich veins and breccias locally at the nori ra prospect the v ni ratio in magnetite differentiates between barren and ore related magnetite and at damp and sue dianne the co ni ratio is extremely high and clearly different from that of other great bear magmatic zone magnetite samples these results provide the first database for geochemically characterized magnetite from different stages of iocg alteration and illustrate the potential use of magnetite as an indicator mineral in the exploration for iocg deposits

on the relationship between alteration facies and metal endowment of iron oxide alkali altered systems southern great bear magmatic zone canada the great bear magmatic zone in northern canada hosts large iron oxide and alkali altered systems that developed within a 10 m y period during the paleoproterozoic in the eastern treasure lake and duke sectors and at the nico deposit early albitization associated with magmatism was followed by tungsten mineralization that was spatially associated with extensive skarn and fe skarn alteration subsequent fluid rock reactions led to substantial iron enrichment that culminated in iron oxide apatite mineralization at the transition from compressional transpressional to extensional transtensional stress regimes changes in magma composition increased the metal budget of exsolved magmatic hydrothermal fluids and played a key role in the formation of au co bi mineralization at the nico deposit and its satellite showings in the duke zone this process happened as the systems regionally transitioned to magnetite bearing potassic iron alteration the continued evolution of magmatism and fluid chemistry then contributed to the formation of iron oxide copper gold iocg and variant mineralized zones in the sue dianne and nico deposits and other showings and albite hosted uranium mineralized zones elsewhere the great bear magmatic zone illustrates that the evolution of magmatically derived fluids during a transition between different stress regimes can play a significant role in metal endowment and the ability of metasomatic systems to form skarn iron oxide apatite iocg and albitite hosted uranium mineralization

origin of sulfur and crustal recycling of copper in polymetallic cu au co bi u ag iron oxide dominated systems of the great bear magmatic zone nwt canada the great bear magmatic zone in northwest canada contains numerous polymetallic mineral occurrences prospects and deposits of the iron oxide copper gold deposit iocg family the mineralization is hosted by the treasure lake group and igneous rocks of the great bear arc and was deposited concomitantly with the arc magmatism ca 1 88 to 1 87 ga in situ 34s n 48 and 65cu n 79 analyses were carried out on ore related sulfides from a number of these systems the 34s values mainly vary between 0 and 5 consistent with derivation of sulfur from the mantle lower 34s values 7 7 to 1 4 from the sue dianne breccia may indicate so2 disproportionation of a magmatic hydrothermal fluid the 65cu values vary between 1 2 and 0 3 and are lower than the igneous 65cu range of values 0 0 0 27 the s and cu isotopic data are decoupled which suggests that cu and possibly some s was dissolved and remobilized from supracrustal rocks during early stages of alteration e g sodic alteration and then precipitated by lower temperature more oxidizing fluids e g ca fe k alteration a limited fluid inclusion dataset and 13c and 18o values are also presented the 18ofluid values are consistent with a magmatic origin or a host rock equilibrated meteoric water source whereas the 13cfluid values support a marine carbonate source combined the s and cu isotopic data indicate that while the emplacement of the great bear magmatic bodies may have driven fluid convection and may be the source of fluids and sulfur metals such as cu could have been recycled from crustal sources

chronostratigraphy of the hottah terrane and great bear magmatic zone of wopmay orogen canada and exploration of a terrane translation model the paleoproterozoic hottah terrane is the westernmost exposed bedrock of the canadian shield and a critical component for understanding the evolution of the wopmay orogen thirteen new high precision u pb zircon crystallization ages are presented and support field observations of a volcano plutonic continuum from hottah terrane through to the end of the great bear magmatism from 1950 to 1850 ma the new crystallization ages new geochemical data and newly published detrital zircon u pb data are used to challenge hitherto accepted models for the evolution of the hottah terrane as an exotic arc and microcontinent that arrived over a west dipping subduction zone and collided with the slave craton at ca 1 88 ga although the hottah terrane does have a tectonic history that is distinct from that of the neighbouring slave craton it shares a temporal history with a number of domains to the south and east domains that were tied to the slave craton by ca 1 97 ga it is interpreted herein that hottah terra

characterization of the paleoproterozoic hottah terrane wopmay orogen using multi isotopic u pb hf and o detrital zircon analyses an evaluation of linkages to northwest laurentian paleoproterozoic domains abstract the paleoproterozoic wopmay orogen is modeled as a simple arc continent collision involving the archean slave craton and an enigmatic continental arc terrane termed the hottah terrane hottah is a composite terrane that includes a juvenile 2 6 2 1 ga basement and a younger 1 93 1 90 ga continental arc the extent and crustal age structure of the terrane is poorly known which limits interpretations as to its origin and eventual role in the development of the orogen multi isotopic u pb hf o analyses of detrital zircon from rocks of the hottah terrane and its cover sequence are used to indirectly evaluate its age and crustal characteristics the data confirm that ca 2 6 2 1 ga crust is an important component of the terrane but hf isotopic data indicate mostly non juvenile compositions consistent with recycled neoarchean crust sources ages of detrital zircon are distinct from those expected of the slave craton but are similar to adjacent 2 0 1 90 ga paleoproterozoic terranes of northwestern laurentia the similarity to terranes such as the ksituan buffalo head and taltson thelon magmatic zones south and east of the wopmay orogen indicate that hottah could represent a terrane that initially evolved adjacent to the earliest assembled parts of the nuna continent between 2 0 and 1 9 ga and was rifted prior to the collision with the slave margin that produced the calderian orogeny

the geochronology of uranium deposits in the great bear batholith northwest territories the oldest uranium mineralisation found in the great bear batholith during this study may be hydrothermal pitchblende hematite veins at hottah lake their apparent age of 2058 34 ma can also be explained by the contamination of deposits only 440 57 ma old which is the age of pitchblende veins nearby numerous pendants of metamorphosed uraninite bearing black sand placers in a north trending belt west of the wopmay fault are 1860 20 ma old the age of the granites that intrude them mineralisation at echo bay is from 1500 10 to 1424 29 ma old and extends up to 30 km north and 40 km south of echo bay the jd claims contain small quartz vein deposits dated at 535 164 and 1092 115 ma at mountain lake pitchblende in helikian sandstones overlying the batholith is 1076 96 ma old polymetallic veinlets at mazenod lake are 457 26 ma old pitchblende in a giant quartz vein at the rayrock mine is 511 86 ma old small pitchblende veins east of the batholith along the coppermine river are be

geophysical signature of the nico au co bi cu deposit and its iron oxide alkali alteration system northwest territories canada models of the three dimensional physical property variation of the nico au co bi cu deposit northwest territories and the southern breccia albitite hosted uranium occurrences and their iron oxide alkali alteration envelopes were derived from inversion of high resolution aeromagnetic gravity and magnetotelluric mt data at deposit to regional scales in turn integration of the geophysical results with physical property measurements and geologic observations leads to a new understanding of the geometry of the deposit adjacent mineralized and altered zones and potential cogenetic links within the host metasomatic system nico which is a variant of the magnetite group iron oxide copper gold iocg class of deposit is spatially associated with a discrete zone of lower electrical resistivity occurring within a broader ne dipping zone of higher density the high density zone overlaps a ne dipping zone of higher magnetic susceptibility and is truncated to the southwest by a nw striking geophysical discontinuity interpreted as a major fault zone this inferred fault divides the magnetite altered metasedimentary rocks hosting the nico deposit from the albite altered rocks within the southern breccia corridor to the southwest that host the uranium mineralization having been active during development of the metasomatic system this fault influenced the formation of these distinct but complementary deposit types

nd isotopic evidence from wopmay orogen for 2 0 2 4 ga crust in western north america abstract nd isotopic data from the 1 9 ga wopmay orogen n w t canada strongly suggest the involvement of crust in the range of 2 0 2 4 ga remnants of three compositionally diverse magmatic arcs 1940 1902 ma 1890 1880 ma and 1875 1840 ma are preserved in wopmay orogen each of the three arcs originated west of the limit of exposed archean crust nineteen samples of plutonic and volcanic rocks from the three arcs yield a narrow range of initial e nd from 1 8 to 0 3 there is no apparent correlation between e nd and geographic distribution nor with whole rock chemistry sio 2 54 75 two basalt samples from west of the archean have initial e nd s between 2 and 3 two 1 87 ga granites which intrude through archean crust have much lower initial e nd s of 5 9 and 8 6 the data from the three magmatic arcs are best interpreted in terms of a source region which had a very limited range of e nd at 1 9 ga which we interpret as 2 0 2 4 ga crust presumably hottah terrane basement wopmay fault zone is therefore the surface manifestation of a suture between 2 0 2 4 ga hottah terrane and the archean slave craton there is a growing body of data which suggests that much of western north america may be underlain by 2 0 2 4 ga crust geochronologic and isotopic data from other precambrian cratons also suggest that 2 0 2 4 ga crust may be much more widespread than previously thought models of crustal growth which interpret 1 9 1 7 ga crust as mixtures of archean crust and proterozoic depleted mantle may be overestimating the amount of juvenile material added to the crust in this time period

the role of aqueous fluids in the internal friction of rock the effects of water on elastic energy dissipation in rock under upper crustal conditions are considered briefly in this paper experimental evidence indicates that in dry rock the energy dissipation process involves water adsorbed on the surfaces of very thin cracks in one mechanism the adsorbed water is regarded as a viscoelastic film portions of this layer are forced to relax as crack thickness changes with the passing elastic wave a second possible mechanism involves the relaxation of electrostatic repulsion stresses between oriented polar water molecules on opposing crack faces when water is present as a bulk fluid attenuation can be explained by the flow of a viscous fluid into and out of very thin cracks in response to dynamic stresses associated with a passing elastic wave

hepburn intrusive suite peraluminous plutonism within a closing back arc basin wopmay orogen canada within the hepburn metamorphic plutonic internal zone of the wopmay orogen northwest territories canada there are two chronologically and petrologically distinct plutonic associations the more voluminous of the two the older 1 885 ga hepburn intrusive suite includes rocks ranging in composition from gabbro to granite peraluminous granite dominating the younger 1 855 ga neighboring bishop intrusive suite also gabbro to granite represents the waning stages of a well documented calc alkaline arc the great bear magmatic zone the petrological distinctions between the two suites are all late acquired features imposed primarily by contrasting environments of emplacement hepburn magmas were intruded within a closing dominantly sedimentary back arc basin magma emplacement was synchronous with crustal imbrication regional metamorphism and translation of the basin fill units onto archean crust significant assimilation of sedimentary host rocks by the rising hepburn magmas occurred whereas the postregional metamorphism emplacement of the bishop magmas precluded similar assimilation the gabbroic contribution observed in the hepburn intrusive suite is interpreted to reflect a mantle derived precursor inherited from the back arc rifting event that immediately preceded emplacement of the suite

dating of fluvial sediments from the amazon lowland in peru abstract tl dating was attempted on sediments from surficial alluvial formations of the peruvian amazon a huge area for which there are few pleistocene age determinations the samples were collected from several locations of erosional banks carved in older alluvial deposits in order to date the quaternary stratigraphy the major part of the time scale falls beyond the range of the radiocarbon method a complex resedimentation also makes the use of this method difficult here tl dating can provide an approximate idea of the age and history of sedimentation some preliminary results are presented and problems due to sample characteristics are discussed

lead isotopic study of early proterozoic wopmay orogen nw canada role of continental crust in arc magmatism lead isotopes are sensitive indicators of crustal interaction in arc magmatism because of the large contrast in lead concentration between mantle derived magmas and continental crust and the three independent decay paths in the u th pb system preserved within wopmay orogen 1 94 to 1 84 ga are the remnants of three magmatic arcs the isotopic composition of lead in alkali feldspars separated from a diverse suite of samples from all three arcs fall in a relatively tight cluster with 206 pb 204 pb 15 59 15 88 207 pb 204 pb 15 27 15 36 and 208 pb 204 pb 35 15 35 54 except for samples from the only plutonic suite within wopmay orogen observed to intrude archean crust plutons intruding archean crust have 206 pb 204 pb 15 29 15 49 206 pb 204 pb 15 23 15 31 and 208 pb 204 pb 35 21 35 30 lead isotopic compositions do not correlate with rock composition both diorites and peraluminous granites have the same lead isotopic composition this isotopic composition