determination of recent 238u 234u and 230th mobility in granitic rocks application of a natural analogue to the high level waste repository environment abstract the isotope activity ratios 234u 238u and 230th 234u have been investigated in drill core samples up to 1300 m depth in three granitoids from australia to identify the nature of possible recent 1 0 which has generated excess 230th these enriched ground waters do not appear to have penetrated below 530 m depth and 230th excess indicates bulk loss of u the observed disequilibria indicate that significant radionuclide mobilisation has occurred in these rocks during the recent past

gold metallogeny and the copper gold association of the australian proterozoic australian proterozoic gold producing deposits emplaced mainly at 1 55 2 00 ga are divided into the following categories 1 iron oxide dominated brecciahosted cu u au replacement deposits spatially associated with felsic intrusions 273t au 2 stratabound au cu bearing iron formations 152 4t au 3 unconformity style u cu pgm au deposits 53t au 4 iron oxide dominated au cu mineralisation hosted within elements of ductile deformation 146 7t au 5 broken hill and volcanic hosted massive sulphides 150t au 6 iron sulphide dominated veins and replacement zones spatially related to felsic intrusions 150 7t au and 7 iron sulphide dominated veins and replacement zones spatially related to elements of regional deformation 159 9t au categories 1 to 4 are mainly confined to proterozoic rocks constituting an association in which au and cu are commonly present together with variable amounts of u bi co w se te and ree most examples in categories 1 4 fall into either of two groups cu aumagnetite hematite types formed at relatively high temperature 300 450 c and cu u au hematite types formed at 150 300 c we postulate that these ores formed from a common high salinity 15 35 wt nacl equiv low total sulphur a s 10 3 to 10 2 high fo2 fluid type in which metal transport was dominated by chloride complexing the most effective method of metal deposition was fluid mixing achieving a synchronous decrease in fo2 and temperature this unusual oxidised fluid association was favoured in high heat flow extensional settings containing oxidised and or oxidised evaporitic sedimentary sequences the intrusion of oxidised fractionated granites which are commonly temporally associated with metal emplacement acted in some places to heat and focus basinal fluids and in others was the ultimate source of metals

wavelet analysis for the regional residual and local separation of potential field anomalies a method based on the discrete wavelet transform was applied to the regional residual separation of potential fields and to the filtering of local anomalies a specific space scale wavelet analysis called multiresolution analysis allowed decomposition of the signal with respect to a vast range of scales different analysing wavelets were applied to anomalies in both synthetic and real cases but the more appropriate basis needed to be chosen by requiring the maximum compactness for the multiresolution analysis moreover since such analysis was found not to be shift invariant the same criterion was applied to choosing the best signal shift application of the technique to both synthetic and real cases produced an optimal space scale representation of the fields and a consistent regional residual separation furthermore the space localization allowed a variety of filtered signals to be obtained each one with a specific scale and local area content fourier and wavelet analyses were both applied to the filtering out of the intense etna anomaly from the aeromagnetic field of sicily the wavelet method was more powerful suppressing only the etna volcano anomaly and leaving the rest of the map practically unchanged

fission track analysis of uranium distribution in granitic rocks abstract the natural uranium concentration and distribution in three granitoids from australia has been used to develop an understanding of the geochemical processes which control its behaviour in the natural environment and the potential behaviour of some analogue elements within a crystalline high level radioactive waste hlw repository environment in the coles bay granite olympic dam granite and the kambalda granodiorite fission track micromapping has been used to identify primary and secondary distribution between four main mineralogical locales 1 background u 2 resistate u 3 secondary u and 4 fracture u minor concentrations of total u are present as background u in the major rock forming minerals whereas resistate u contributed by the accessory minerals comprises up to 60 of total u two modes of redistribution of primary u are evident 1 in the secondary minerals particularly fe and ti hydroxides and 2 on alteration minerals which infill microfractures the association of u with these secondary and fracture infilling minerals indicates that it has been redistributed during post magmatic hydrothermal alteration and possibly by recent groundwater rock interaction the most important geochemical processes involved in this u redistribution include mobilisation and fixation through complex decoupling and redox reactions and retention by secondary minerals through adsorption and ionic exchange the effect of these processes upon natural u redistribution may be considered as an analogue of geochemical processes around a hlw repository this work shows that a degree of post magmatic alteration of a granite increases the proportion of secondary minerals of high sorption capacity present which may thus enhance the radionuclide retardation capability of the granitoids

neodymium isotopic constraints for the origin of mesoproterozoic felsic magmatism gawler craton south australia mesoproterozoic felsic magmatism of the gawler range volcanics and hiltaba suite granites occurred at 1585 1595 ma across much of the gawler craton south australia nd isotopic analysis of this felsic magmatism combined with petrological and geochemical arguments suggest derivation by partial melting of both paleoproterozoic and archean crust the majority of samples analyzed have nd isotopic and geochemical characteristics compatible with the involvement of paleoproterozoic crust stabilized during the 1 85 1 71 ga kimban orogeny as sources for the mesoproterozoic magmatism others require derivation from sources dominated by archean rocks this cycle of paleoproterozoic crustal stabilization followed by involvement of this crust mesoproterozoic felsic magmatism is one previously documented from many parts of mesoproterozoic laurentia on the basis of models proposing east australia antarctica to be the conjugate landmass at the rifted margin of western north america it appears that the voluminous mag

inactive and relict rock glaciers of the deboullie lakes ecological reserve northern maine usa lobate talus slopes in the deboullie lakes ecological reserve dler of northern maine exhibit parabolic profiles characteristic of inactive and relict talus derived rock glaciers vegetated rock glacier surfaces suggest that the landforms are no longer active and lobes comprising two dler rock glaciers document periods of past growth observations of perennial subsurface ice are supported by datalogger temperature measurements indicating that sporadic permafrost exists throughout the dler we compare the dler rock glaciers along with similar features elsewhere in new england and adjacent quebec to the modern alpine permafrost distribution results indicate that a mean annual temperature cooling of 68c is required to promote active rock glacier growth ages of plant remains recovered from the basal sediments of a local pond constrain deglaciation to before 11 320 14 c a bp and core stratigraphy and organic content reveal that a periglacial environment persisted during the early postglacial era thus we hypothesise that the dler rock glaciers were active during lateglacial time despite the lack of glacier activity in the region we take this to suggest that north eastern us rock glaciers formed in response to mean annual temperatures skewed towards the frigid winters of the younger dryas chronozone copyright 2009 john wiley sons ltd

zircon u pb dating in the vicinity of the olympic dam cu u au deposit roxby downs south australia isotopic data are presented for granitoids and felsic volcanics from the stuart shelf of south australia some of which are spatially associated with the olympic dam cu u au deposit relatively unaltered quartz monzodiorite more extensively altered quartz syenite and felsic volcanics yield zircon u pb ages of 1 590 super 5 sub 4 1 613 super 20 sub 19 and 1 576 super 22 sub 19 m y respectively the zircons from this group of rocks the olympic dam suite have similar morphologies and similar 206 pb 208 pb ratios suggesting an intimate genetic relationship their ages are comparable to the gawler range volcanics cropping out approximately 130 km to the southwest in the gawler orogenic domain close to the olympic dam deposit the zircon u pb system of olympic dam suite quartz syenite was contaminated by barite precipitated from hydrothermal fluids associated with the mineralization the barite is readily removed by air abrasion which restores the reversely discordant and spuriously young zircons to more normally discordant positions on the concordia diagram the abraded zircons then have u pb ages similar to uncontaminated olympic dam suite zircons the barite lead must be enriched in 206 pb which is concluded to be derived from radium extracted from u bearing rocks and admitted to the ba crystal lattice site deformed and altered basement granitoids on the stuart shelf have complex zircons with discrete cores and overgrowths which yield complicated u pb isotope systematics the cores are estimated to be about 1 800 m y old and the overgrowths probably less than 1 730 m y old these granitoids are temporally correlated with basement rocks of the gawler orogenic domain comparable apatite u pb and biotite rb sr isotope dates from all the granitoids and from thin veins in the acropolis prospect suggest regional cooling through the respective blocking temperatures about 350 degrees 400 degrees and 300 degrees c between 1 602 or 7 and about 1 542 m y the acropolis apatite date suggests at least some stuart shelf mineralization was emplaced at or before about 1 602 m y a maximum age for the olympic dam mineralization is set by the olympic dam suite quartz syenite zircon age 1 613 super 20 sub 19 m y our data do not place minimum age limits on the mineralization

uraninite from the olympic dam iocg u ag deposit linking textural and compositional variation to temporal evolution the olympic dam iocg u ag deposit south australia the world s largest known uranium u resource contains three main u minerals uraninite coffinite and brannerite four main classes of uraninite have been identified uraninite occurring as single grains is characterized by high pb and ree y rey but based on textures can be classified into three of these classes typically present in the same sample primary uraninite class 1 is smallest 10 50 m displays a cubic euhedral habit and both oscillatory and sectorial zoning zoned uraninite class 2 is coarser sub euhedral and combines different styles of zonation in the same grain cobweb uraninite class 3 is coarser still up to several hundred micrometers has variable hexagonal octagonal morphologies varying degrees of rounding and features rhythmic intergrowths with sulfide minerals in contrast the highest grade u in the deposit is found as micrometer sized grains to aphanitic varieties of uraninite that form larger aggregates up to millimeter and vein fillings massive class 4 and have lower pb and rey but higher ca nanoscale characterization of primary and cobweb uraninite shows these have defect free fluorite structure both contain lattice bound pb rey which for primary uraninite is concentrated within zones and for cobweb uraninite is within high pb rey domains micro fractured low pb rey domains sometimes with different crystal orientation to the high pb rey domains in the same cobweb grain contain nanoscale inclusions of galena cu fe sulfides and rey minerals the observed pb zonation and presence of inclusions indicates solid state trace element mobility during the healing of radiogenic damage and subsequent inclusion nucleation recrystallization during formula 1 driven percolation of cu bearing fluid tetravalent lattice bound radiogenic pb is proposed based on analogous evidence for u bearing zircon calculating the crystal chemical formula to uo2 stoichiometry the sum of cations m is 1 for most classes but the presence of mono di and trivalent elements rey ca etc drive stoichiometry toward hypostoichiometric m o2 x in the absence of measured o and constraints of hypostoichiometric fluorite structure charge balance calculations showing o deficit in the range 0 15 0 36 apfu is compensated by assumption of mixed u oxidation states crystal structural formulas show up to 0 20 apfu pb and 0 25 apfu rey in classes 1 3 while for class 4 these are an order of magnitude less low pb and rey subcategories of classes 2 and 3 are similar to massive uraninite with 0 2 apfu ca other elements si na mn as nb etc show two distinct geochemical trends 1 across classes 1 3 and 2 class 4 whereby low pb rey sub populations of classes 2 and 3 are part of trend 2 for certain elements plots of alteration factor cao sio2 fe2o3 vs pb u suggest two uraninite generations early high pb rey classes 1 3 and late massive class 4 there is evidence of pb loss from diffusion leaching and or recrystallization for classes 2 3 low pb rey domains micro analytical data and petrographic observations reported here including nanoscale characterization of individual uraninite grains support the hypothesis for at least two main uraninite mineralizing events at olympic dam and multiple stages of u dissolution and reprecipitation early crystalline uraninite is only sparsely preserved with the majority of uraninite represented by the massive aphanitic products of post 1590 ma dissolution reprecipitation and possibly addition of uranium into the system coupled dissolution reprecipitation reactions are suggested for early uraninite evolution across classes 1 to 3 the calculated oxidation state u6 u4 u6 of the early and late populations point to different conditions at the time of formation charge compensation for rey rich early fluids rather than auto oxidation of uraninite late uraninites may have formed hydrothermally at lower temperatures t 250 c 1 embed mml math 1 gif

sources of mineralising fluids for the olympic dam deposit south australia smnd isotopic constraints abstract the olympic dam cu u au ag deposit south australia is hosted by the olympic dam breccia complex a high level hematite rich hydrothermal breccia system the deposit is characterised by extreme enrichments of ree which are a product of the ore forming process therefore making the sm nd isotopic system an ideal tool for clarifying the complex relationships between the different ore and breccia types pyrite chalcopyrite and bornite chalcocite rich hematitic ores share an initial end signature of 2 5 which suggests that these ore types are cogenetic these ores together with sulphide poor hematitic breccias yield a 14 point sm nd isochron age of 1572 99 ma the host roxby downs granite has an initial nd of 5 and therefore cannot alone have been the source of the mineralising fluids for the hematitic ores in contrast to hematitic rocks volumetrically minor magnetite rich assemblages have the same initial nd signature as the host granite suggesting that they are cogenetic assuming that both hematite and magnetite were precipitated from solution their contrasting isotopic signatures require that ore deposition involved two distinct fluids the isotopic data do not allow the distinction between a model involving concurrent activity of such fluids in a mixing regime and a model involving temporally separate overprinting of magnetite by hematite cu sulphides the ore signature of nd 2 5 cannot have been derived solely from pre existing crustal rocks of the gawler craton it must have involved a contribution from a mantle derived source rock or magma the most likely source of this nd component are the mantle derived rocks produced during the gawler range volcanics event e g altered alkaline mafic ultramafic dykes within the deposit which have initial isotopic signatures as high as nd 4 assuming end member compositions equivalent to these dykes and the roxby downs granite the ore signature implies that 30 of the nd in the ores was derived from the mafic ultramafic source if nd was leached from source rocks rather than derived from magmatic volatiles the inferred rock fractions contributing ree to the deposit are 13 mafic ultramafic rocks and 87 roxby downs granite or its volcanic equivalent massbalance calculations indicate that 13 rock fraction of mafic ultramafics can account for 50 of the cu contained in the deposit the involvement of mafic ultramafic rocks is therefore inferred to have been crucial to the genesis of the cu enriched ores at olympic dam

an example of reverse discordance during ion microprobe zircon dating an artifact of enhanced ion yields from a radiogenic labile pb abstract sample 74459 contains 204pb rich zircons which when analyzed by ion microprobe yield u pb ages that are exceptionally older than their 207pb 206pb ages the 64 ion microprobe measurements define an age of 2681 6 ma 1 for the zircons with individual analyses giving dilution analyses were conducted on 12 single grains previously analyzed by shrimp the idtims measurements yielded radiogenic 238u 206pb ratios between 2 0 and 8 5 whereas the 34 ion microprobe analyses on the same 12 grains gave systematically lower values between 0 6 and 2 5 the discrepancy between the shrimp and idtims data has been traced to the labile pb by plotting the 204pb vs 206pb concentrations observed by the ion microprobe an unusually low 204pb 206pb ratio of 0 02 has been defined for the labile component apparently the secondary ion emission yield of the labile pb was significantly greater than that of in situ radiogenic pb thereby invalidating shrimp s interelement calibration and leading to inaccurate u pb ages these data provide important insights into the geochemistry of labile pb in 74459 the labile pb was locally derived and was well mixed at the kilogram scale prior to becoming housed within the zircon grains high resolution tem data suggest that the labile pb is contained within amorphous microdomains which are intimately associated with crystalline zircon another feature of the labile pb is its ubiquitous presence in the zircons whereas it was not taken by the coexisting feldspar this labile component has an age of 0 ma

uranium bearing hematite from the olympic dam cu u au deposit south australia a geochemical tracer and reconnaissance pb pb geochronometer abstract uranium bearing hematite containing up to several wt u also containing al mo w and radiogenic pb is described from olympic dam south australia these elements are present in grains that display both oscillatory zonation and porous structures laser ablation inductively coupled mass spectrometry la icp ms element mapping confirms oscillatory and sectorial zoned domains in hematite grains are enriched in 238u and 206pb and are distinct from those of w and mo the crystal structure and absence of inclusions within zoned hematite was assessed by transmission electron microscopy on foils obtained by in situ slicing across zonation patterns using the scanning electron microscope focused ion beam technique satellite reflections on the electron diffraction patterns obtained from banded zones in hematite are attributable to long range superstructure ordering that is inferred to assist metal incorporation via the substitution 2fe3 me6 vacancy where me u w mo the suitability of u bearing hematite for pb pb geochronology as a first pass was tested on both zoned and porous hematite grains via la icp ms using the gj 1 zircon as the primary external standard only pb pb ages were considered and resulted in 207pb 206pb ages of 1590 8 ma and 1577 5 ma for oscillatory and sector zoned hematite from two samples although reconnaissance in nature these ages potentially support the supposition that mineralization is coeval with emplacement of the gawler range volcanics and associated hiltaba intrusive suite the geochronological application utilizing an abundant refractory mineral represents a new tool for dating iron bearing ores

hematite geochemistry and geochronology resolve genetic and temporal links among iron oxide copper gold systems olympic dam district south australia abstract the wirrda well and acropolis prospects 25 km south from the olympic dam deposit are among several dozen examples of iron oxide copper gold iocg mineralisation forming a 600 km long province in the eastern gawler craton south australia iocg systems across the province differ in terms of host lithology iron oxide mineral associations intensity of brecciation and grade of cu u au mineralisation previous efforts to provide a geochronological framework for mineralisation and correlate this with igneous activity were inhibited by a lack of clear crosscutting features particularly in breccia hosted systems and a scarcity of reliable hydrothermal mineral geochronometers the earliest generation of hematite characterised by enrichment in u w sn mo and previously reported from olympic dam provides confident u pb dates and insights into hydrothermal fluid signatures similar hematite is recognised from wirrda well and acropolis allowing direct comparison between the three iocg systems relationships between early silician wirrda well and titaniferous acropolis magnetite and u bearing hematite at the two prospects differ inferred martitisation of magnetite at acropolis has generated zoned hematite with u w mo enrichment at constant sn concentration but with a marked loss of ree y rey and ti whereas at wirrda well single crystal zoned hematite resembling that from olympic dam retains high rey and sn concentrations although morphologies textures and compositions of u bearing hematite at olympic dam wirrda well and acropolis vary significantly a common u pb laser ablation inductively coupled plasma mass spectrometry age of 1590 ma is obtained from the most reliable data 207pb 206pb 1598 9 6 3 ma at wirrda well and 1590 6 6 5 ma at acropolis the geochemical signatures of iron oxides from the two prospects share common trends for u w sn mo high field strength and siderophile elements comparable with signatures of fe oxides from the outer shell of the olympic dam deposit given that datable iron oxides would seem to be ubiquitous phases throughout the eastern gawler craton the commonality in geochemistry and age of u bearing hematite from the olympic dam district is significant as it provides a single traceable mineral to compare iocg systems across the province

mesoproterozoic gold in the central gawler craton south australia geology alteration fluids and timing similarities in mineralization and alteration style host rocks fluid compositions and alteration related 40ar 39ar ages from several recently discovered gold prospects support the existence of a significant mesoproterozoic gold province spanning an arcuate region at least 300 km in length in the central gawler craton south australia at the recently discovered prospects of tunkillia nuckulla hill barns and weednanna as well as at the historically mined au deposit at tarcoola gold occurs as disseminated and veinlet hosted mineralization focused in brittle to brittle ductile faults and shear zones host rocks are principally 1715 to 1680 ma granites but also include hutchison group 2000 1860 ma and tarcoola formation 1650 ma metasedimentary rocks hydrothermal alteration is characteristically zoned around gold mineralization with intense sericite pyrite alteration and quartz veining proximal to gold mineralization and chlorite epidote hematite alteration distal from mineralization alteration was either synchronous with or in some cases continued after deformation gold is associated with pyrite and minor to trace galena sphalerite and chalcopyrite iron oxides are low in abundance in mineralized zones which correspond to demagnetized zones fluid inclusion analyses suggest that multiple fluids were present in some systems but one key fluid type occurs in each of the gold prospects a low to moderate salinity up to 10 wt nacl equiv fluid with homogenization temperatures mostly in the range of 150 to 300 c and commonly containing co2 or associated with co2 rich inclusions several features of the prospects are similar to those of orogenic and intrusion related gold deposits but neither the prospect scale geology nor the regional geologic setting in the central gawler craton is sufficiently well understood to establish a genetic model or to confidently classify the mineralizing system hydrothermal white micas from several of the central gawler craton gold prospects yield reproducible 40ar 39ar plateau ages of between 1567 and 1583 ma these ages together with u pb zircon ages of granitic host rocks constrain the timing of mineralization to the interval 1690 to 1570 ma although we interpret the 40ar 39ar results to indicate a narrower mineralizing interval at 1580 10 ma this age range overlaps with and is indistinguishable from the range of u pb zircon ages reported from regional hiltaba suite granites and gawler range volcanics although igneous rocks of this age have not been identified locally at each of the prospects

timing of iron oxide cu au u hydrothermal activity and nd isotope constraints on metal sources in the gawler craton south australia the eastern gawler craton hosts australia s premier uranium bearing iron oxide copper gold iocg belt the 500 km long olympic cu au u province in addition to the olympic dam cu u au and prominent hill cu au deposits numerous barren and weakly mineralized iocg prospects are present in the province new geochronological data for hydrothermal minerals combined with constraints from host rock ages demonstrate that alteration and associated iocg mineralization formed between 1570 and 1600 ma in three districts of the province this iocg hydrothermal activity temporally overlaps with magmatism of the hiltaba suite and gawler range volcanics titanites in paragenetically early magnetite bearing alteration in the olympic dam and prominent hill districts yield u pb ion probe ages of 1576 5 and 1567 10 ma respectively molybdenite in veins crosscutting magnetite biotite and albitic alteration in the moonta wallaroo district have re os ages of 1574 6 and 1599 6 ma respectively these represent minimum ages of the iocg alteration assemblages in this district a muscovite 40ar 39ar age of 1575 11 ma provides a minimum age of paragenetically later hematitic alteration in the olympic dam district neodymium isotope compositions were determined for 44 whole rock samples from barren and weakly mineralized cu au prospects and host rocks in the olympic dam and prominent hill districts the new geochronological framework enables comparison of the nd isotope data across two iocg districts at the time of formation of the olympic dam deposit ca 1590 ma magnetite rich weakly cu mineralized alteration from five prospects yields a relatively narrow range end 1590 values of 5 8 to 4 1 both hematite and magnetite rich alteration yield generally similar end 1590 values that match values from fresh and weakly altered paleoproterozoic metasedimentary and metagranitic rocks 6 6 to 3 5 as well as from most felsic hiltaba suite intrusions and gawler range volcanics in the eastern gawler craton ca 6 to 4 these data are consistent with crustal sources for ree and by implication for associated copper in the barren and weakly mineralized prospects mineralization and alteration in these minor iocg systems can be geochemically discriminated from the giant olympic dam deposit where greater inputs of mantle derived ree and other ore components are evident 2007 society of economic geologists inc

re os dating of molybdenite within hematite breccias from the vulcan cu au prospect olympic cu au province south australia the vulcan prospect is a newly discovered cu au prospect located within the eastern gawler craton south australia the prospect is entirely subsurface and defined by a geophysical anomaly intersected by diamond drilling eight drill holes have all intersected hematite rich alteration and cu au mineralization within a variety of breccia types ranging from those composed entirely of hydrothermal hematite sericite chlorite to those dominated by altered rock in which clasts of protolith rock are preserved the highest grade zones of mineralization at vulcan occur within hematite dominant breccias molybdenite within hematite rich brecciated granite samples has been dated via the re os method and yields a crystallization age of 1586 8 ma including decay constant uncertainties shrimp zircon u pb analyses show that a sample of hematite sericite chlorite altered and brecciated granite was emplaced at 1743 7 ma the new data from vulcan confirm that hematite breccia related cu au mineralization formed during a widespread alteration and mineralization event between ca 1600 and 1570 ma broadly coeval with the voluminous felsic large igneous province of the gawler range volcanics hiltaba suite and are consistent with most interpretations of the geology of the olympic cu au province

fluid evolution and origins of iron oxide cu au prospects in the olympic dam district gawler craton south australia geologic observations suggest two stages of hydrothermal activity at a number of presently subeconomic iron oxide copper gold systems in the olympic dam district eastern gawler craton they contain high and moderate to low temperature fe oxide rich hydrothermal alteration the mineral assemblages include magnetite calc silicate alkali feldspar fe cu sulfides and hematite sericite chlorite carbonate fe cu sulfides u ree minerals in all documented prospects the minerals of the hematitic assemblages replace the minerals of the magnetite rich assemblages the bulk of the subeconomic cu au mineralization is associated with the hematitic alteration assemblages microanalysis by proton ion probe pixe of hypersaline fluid inclusions in magnetite rich assemblages however demonstrates that significant amounts of copper 500 ppm were transported by the early stage high temperature 400 c fluids responsible for the magnetite rich alteration these brine inclusions contain multiple solid phases liquid vapor multiple solids including chalcopyrite in some cases in comparison inclusions of the hematitic stage are relatively simple liquid vapor types with homogenization temperatures of 200 to 300 c and containing 1 to 8 wt percent nacl equiv the br cl ratios of the magnetite forming fluids measured by pixe lie beyond the range of typical magmatic and or mantle values allowing for the possibility that the fluids originated as brines from a sedimentary basin or the crystalline basement sulfur isotope compositions of chalcopyrite and pyrite demonstrate that sulfur in both alteration assemblages was derived either from cooling magmas and or crystalline igneous rocks carried by relatively oxidized fluids so42 h2s 34ssulfides from 5 to 2 or from crustal sedimentary rocks 34ssulfides from 5 to 10 oxygen and hydrogen isotope compositions of waters calculated for minerals of the magnetite rich assemblage have 18o values of 7 7 to 12 8 per mil and d values of 15 to 21 per mil the only available 18o and dfluid values for the hematitic assemblage are 4 7 and 9 per mil respectively the isotopic compositions of both fluids coupled with the available literature data can be explained in terms of fluid reequilibration with felsic gawler range volcanics or other felsic igneous rocks in the region and with metasedimentary rocks of the wallaroo group at low water to rock ratios prior to their arrival at the mineralization sites the lack of significant copper mineralization associated with magnetite forming fluids that carried copper suggests that there was no effective mechanism of saturation of copper minerals or the quantity of these fluids was not sufficient to produce appreciable copper mineralization association of the copper gold mineralization with the hematitic alteration in the subeconomic prospects can be explained by a two stage model in which preexisting hydrothermal magnetite with minor associated copper gold mineralization was flushed by late stage oxidized brines that had extensively reacted with sedimentary or metamorphic rocks the reduction of these brines driven by conversion of magnetite to hematite resulted in precipitation of copper and gold the oxidized brines may have contributed additional copper and gold to the system in addition to upgrading preexisting subeconomic cu au mineralization when compared to published models for the olympic dam deposit the new data for fluids in subeconomic fe oxide cu au prospects of the olympic dam district indicate the diversity of origins of iron oxide copper gold systems even within the same geologic region

direct dating of fe oxide cu au mineralization by u pb zircon geochronology we present results for direct dating of fe oxide cu au iron oxide copper gold iocg mineralization by u pb zircon geochronology constraining the timing of mineralization has important geodynamic implications for the processes involved in the genesis of these types of deposits and the tectonic evolution of rocks associated with these deposits hydrothermal zircon crystals were separated from four iocg type ore deposits associated with the lyon mountain granite in the adirondack mountains united states zircon grains from these low ti magnetite deposits reveal at least two periods of mineralization one episode ca 1039 ma and a second between ca 1015 and 1000 ma previous age determinations of these deposits were constrained by the age of the altered host granitoids and the assumption that fe mineralization was directly related to pluton emplacement zircon crystals extracted from the ore yield ages that show that ore mineralization was episodic and younger than pluton emplacement

rejuvenation vs recycling of archean crust in the gawler craton south australia evidence from u pb and hf isotopes in detrital zircon abstract zircon grains from modern and ancient drainages of the gawler craton south australia have been analysed to define the relative contributions of juvenile sources and recycled crust to magmatic activity as a function of time and to constrain the role of mantle inputs during the proterozoic rejuvenation of the archean gawler craton the integration of hf isotope data with u pb age spectra shows that the crustal evolution was dominated by long periods of crustal reworking and that crust generated in the paleoarchean 3 2 3 5 ga was largely reworked during proterozoic time four periods of juvenile mantle input can be recognised at ca 2540 ma 1853 ma 1595 ma and 1169 ma the 1169 ma event is not previously recognised in the gawler craton but the absence of other important age peaks argues against the transport of these zircons from the musgrave block only minor proportions of the magmatic zircons with paleoproterozoic to mesoproterozoic ages have strongly juvenile signatures e hf 4 indicating that crustal reworking was the dominant process with relatively minor mantle input comparison of the crustal evolution with that of nearby australian terranes suggests that although the gawler craton shows some similarities with the mount isa block and the georgetown inlier in neoarchean paleoproterozoic time it evolved independently between ca 1800 and 1550 ma

the significance of titanite and apatite u pb ages constraints for the post magmatic thermal hydrothermal evolution of a batholithic complex berens river area northwestern superior province canada abstract titanite apatite and in one case rutile from a suite of twenty seven samples representing the major phases of an extensive and well dated archean plutonic domain of the northwestern superior province have been dated by u pb to determine the temporal progress of thermal and hydrothermal events accompanying and following major plutonism and to assess the isotopic behaviour of these geochronometers most samples contain 1 dark brown titanite with 350 20 ppm u showing shapes and textural relationships indicative of a primary magmatic origin and yielding ages corresponding either to the time of magmatic crystallization or to that of secondary metamorphic or magmatic events known in the area 2 pale titanite with 30 2 ppm u showing textural evidence for a secondary origin by breakdown of biotite hornblende oxide or older titanite and yielding ages that in general post date the major plutonic and metamorphic events in the area 3 apatite containing 30 5 ppm u occasionally up to 150 ppm u showing igneous shapes and textural relationships but yielding post magmatic ages similar to those of coexisting pale titanite 4 rutile in one sample postdating the ages of coexisting titanite and apatite the common coexistence of two noncoeval titanite generations demonstrates that the often invoked mechanism of pb diffusion during slow cooling in this case has no general validity the distribution of primary dark titanite ages however could be explained by late closure to diffusion or alternatively as the result of resetting by the thermal or hydrothermal effects caused by younger plutonic activity the ages of the secondary pale titanites probably reflect crystallization during discrete retrogressive events promoted by moderate heating or enhanced fluid activity the correspondence between pale titanite and apatite ages suggests that the same processes also caused the isotopic resetting of apatite on a regional scale the data pattern permits the identification of domains characterized by differences in the length and intensity of the thermal and hydrothermal processes the most protracted activity is recorded in northern domains of the berens river area whereas the gold mineralized red lake area in the south underwent a very rapid decline of the thermal hydrothermal activity these data also highlight important differences between the red lake and other gold camps of the superior province such as hemlo and val d or where hydrothermal activity locally associated with mineralization occurred as much as 30 80 m y after the major orogenic developments

petrogenesis of a mesoproterozoic quartz latite granitoid suite from the roxby downs area south australia abstract mesoproterozoic granitoids from the roxby downs area south australia show a range in composition from mafic quartz monzodiorites 56 sio 2 to felsic granites 71 sio 2 and are interpreted as consanguineous on the basis of similar age isotopic composition and mineralogical and geochemical characteristics these granitoids have geochemical similarities with other mesoproterozoic granitoids the world over including enrichments in k 2 o rb ba th u rare earth elements ree nb y zr and depletions in mgo cao sr cr ni v sc relative to typical phanerozoic calc alkaline granitoids the mafic granitoids have mineralogical textural and geochemical features consistent with an origin as cumulates from a more felsic primary magma and the felsic granites likely represent the fractionated residual melt to this accumulation process none of the granitoids from the batholith preserve the primary magma composition which is deduced to be similar to abundant quartz latite volcanic rocks of the region it is estimated by geochemical modeling that about 27 fractionation of observed phenocrysts from a primary quartz latite is required to produce a typical felsic granite 71 sio 2 production of the primary quartz latite magma was likely the result of partial melting of existing paleoproterozoic crust in response to intrusion into the crust of mantle derived magmas the combination of widespread crustal melting contemporaneous granulite facies metamorphism and mantle derived magmatism suggests involvement of large scale tectonothermal processes in the origin of these granitoids the petrogenesis of these rocks and similar occurrences in laurentia and baltica indicates that processes involving reworking of existing paleoproterozoic crust were similar throughout many continental areas during the mesoproterozoic

characterization of geological boundaries using 1 d wavelet transform on gravity data theory and application to the himalayas we investigate the use of the continuous wavelet transform for gravity inversion the wavelet transform operator has recently been introduced in the domain of potential fields both as a filtering and a source analysis tool here we develop an inverse scheme in the wavelet domain designed to recover the geometric characteristics of density heterogeneities described by simple shaped sources the 1 d analyzing wavelet we use associates the upward continuation operator and linear combinations of derivatives of any order in the gravity case we first demonstrate how to localize causative sources using simple geometric constructions both the upper part of the source and the whole source can be studied when considering low or high altitudes respectively the homogeneity degree of the source is deduced without prior information and allows us to infer its shape introducing complex wavelets we derive analytically the scaling behavior of the wavelet coefficients for the dyke and the step sources the modulus term is used in an inversion procedure to recover the thickness of the source the phase term provides its dip this analysis is performed on gravity data we measured along a profile across the himalayas in nepal good agreement of our results with well documented thrusting structures demonstrates the applicability of the method to real data also deeper less constrained structures are characterized

preserved initial in apatite from altered felsic igneous rocks a case study from the middle proterozoic of south australia abstract strontium isotope data from a suite of hydrothermally altered middle proterozoic granitoids and a related felsic volcanic rock show that the total rock systems have been disturbed as a result of hydrothermal alteration as such unambiguous determination of initial 87 sr 86 sr is not possible using total rock data with consequent loss of valuable petrogenetic information in contrast initial 87 sr 86 sr values derived from apatite are uniform when compared with the discordant total rock analyses evaluation of strontium diffusion kinetics in apatite together with geological and isotopic evidence presented here suggest that initial 87 sr 86 sr derived from apatite preserves the igneous initial 87 sr 86 sr and that 87 sr 86 sr in apatite is unlikely to have been modified as a result of igneous cooling or hydrothermal alteration this study shows that under some conditions apatite is resistant to 87 sr 86 sr modification and can yield petrogenetic information not attainable from total rock analyses data presented here together with data obtained in other studies indicate that the strontium isotope system in apatite is more resistant to modification than feldspar and biotite this approach may be of widespread application in determining initial 87 sr 86 sr of similarly altered ancient igneous rocks