petrochemical features of miocene volcanism around the cubukludag graben and karaburun peninsula western turkey implications for crustal melting related silicic volcanism abstract widespread neogene volcanism mainly intermediate and rarely mafic and felsic in composition was controlled by the extensional tectonic regime in western turkey the karaburun and cumaovasi volcanics are the cases for understanding the magma source s and petrological processes producing the extension related mafic and felsic volcanism the karaburun volcanics kv are mainly oriented north to south in the karaburun peninsula and span a wide spectrum from basalt 20 ma to rhyolite 16 ma and younger trachyte and trachydacites 13 ma the products of the subaerial silicic volcanism the cumaovasi volcanics cv 17 ma which are represented by cluster of rhyolite domes related pyroclastics occur within the ne sw trending cubukludag graben and intermediate and mafic volcanic rocks are lack in this area the lavas of the cumaovasi volcanics are high silica rhyolites and rare dacites which are calc alkaline peralumious and enriched significantly in lile extremely low sr ba values extremely eu depletions and very low la n yb n ratios are typical for the rhyolites of cv similar to the topaz rhyolites the karaburun volcanics with the exception of the minor alkaline basaltic and trachytic lavas are mainly calc alkaline and metaluminous intermediate lavas 87 sr 86 sr ratios of the kv and dacitic samples of cv are close to each other and range from 0 708 to 0 709 while sr isotopic ratios of the rhyolites are significantly high and variable 0 724 0 786 143 nd 144 nd ratios of the cv and kv except for the alkaline samples are similar for both sequences vary from 0 51230 to 0 51242 geological geochemical isotopic and radiochronologic data reveal that the kv and cv were formed in extensional tectonic setting but evolved by different petrological processes in different magma chambers during the neogene underplated mafic magma was injected into the crust and hybridized by mantle and crustal derived materials geochemical features and trace element modeling for the mafic members of the kv indicate that they were derived from enriched lithospheric mantle and modified by fractional crystallization from basalt to rhyolite helvaci et al 2009 unexpectedly the felsic lavas from cumaovasi region have a unique chemical composition and similar to the extension related rhyolites formed from small magma bodies our data reveal that extension related mafic inputs caused crustal anatectic melting and formed felsic melts that rapidly ascended into the upper crust the cumaovasi felsic rocks were differentiated into the highly evolved silica rich melts within the magma chambers trapped near the surface

fluid compositions and p t conditions of vein type uranium mineralization in the beaverlodge uranium district northern saskatchewan canada the beaverlodge district in northern saskatchewan is known for vein type uranium mineralization most of the uranium deposits are spatially related to major structures and hosted by ca 3 2 1 9 ga granitic rocks and albitite derived from them and by ca 2 33 ga murmac bay group amphibolite all of which are unconformably overlain locally by deformed but unmetamorphosed redbeds of the ca 1 82 ga martin group and by the flat lying ca 1 75 1 5 ga athabasca group the uranium mineralization is mainly hosted in fault rocks breccias and carbonate quartz albite veins referred to as breccia style and vein style mineralization respectively with the latter being the focus of this study most of the mineralized veins occur in the basement rocks although some crosscut the martin group this study examines the field petrographic fluid inclusion and c o isotope characteristics of mineralized and non mineralized veins from 19 deposits occurrences as well as from the martin group with an aim to better understand the mineralizing environment and processes the coexistence of liquid dominated l v vapour dominated v l and vapour only v fluid inclusions within individual fluid inclusion assemblages fias in the veins suggests fluid immiscibility and heterogeneous trapping the l v inclusions with the lowest homogenization temperatures th within individual fias are interpreted to represent homogeneous trapping of the liquid phase which yield th values from 78 to 330 c mainly 100 to 250 c and salinities from 0 2 to 30 8 wt nacl equivalent mass spectrometric analysis of bulk fluid inclusions shows that the volatiles are dominated by h2o average 97 2 mol with minor amounts of co2 ch4 h2 o2 n2 ar and he fluid pressures were estimated to be 200 bars based on the inference of fluid immiscibility fluid temperatures of 100 to 250 c and low concentrations of non aqueous volatiles 3 mol the 18ovpdb and 13cvpdb of carbonate minerals associated with mineralization range from 20 5 to 8 9 and 10 1 to 0 9 respectively the 18ovsmow values of the parent fluids calculated using the th values range from 9 6 to 17 0 with the majority from 0 to 5 0 o isotopes of paired equilibrium quartz and calcite analyzed by secondary ion mass spectrometry sims yield temperatures from 161 to 248 c which are consistent with the fluid inclusion data the new fluid inclusion and stable isotope data are inconsistent with a metamorphic or magmatic hydrothermal model as proposed in some previous studies for breccia style and vein style mineralization but rather support a model in which the vein type uranium mineralization took place at relatively low temperature 100 to 250 c and shallow 2 km conditions with fluid pressure fluctuating between hydrostatic and sub hydrostatic regimes possibly related to episodic faulting the mineralizing fluids were mainly sourced from the martin lake basin and uraninite was precipitated as a result of mixing between this basin derived fluid and fluids carrying reducing agents fe2 ch4 derived from the basement although fluid rock reactions and fluid immiscibility may have also played a role

residence of ree y th and u in granites and crustal protoliths implications for the chemistry of crustal melts a systematic study with laser ablation icp ms scanning electron microscopy and electron microprobe revealed that 70 95 wt of ree except eu y th and u in granite rocks and crustal protoliths reside within reeythu rich accessories whose nature composition and associations change with the rock aluminosity the accessory assemblage of peraluminous granites migmatites and high grade rocks is composed of monazite xenotime in low ca varieties apatite zircon thorthosilicate uraninite and betafite pyrochlore metaluminous granites have allanite sphene apatite zircon monazite and thorthosilicaie peralkaline granites have aeschinite fergusonite samarskite bastnaesite fluocerite allanite sphene zircon monazite xenotime and th orthosilicate granulite grade garnets are enriched in nd and sm by no less than one order of magnitude with respect to amphibolite grade garnets granulitegrade feldspars are also enriched in lree with respect to amphibolite grade feldspars accessories cause non henrian behaviour of ree y th and u during melt solid partitioning because elevated fractions of monazite xenotime and zircon in common migmatites are included within major minerals their behaviour during anatexis is controlled by that of their host settling curves calculated for a convecting magma show that accessories are too small to settle appreciably being separated from the melt as inclusions within larger minerals biotite has the greatest tendency to include accessories thereby indirectly controlling the geochemistry of ree y th and u we conclude that ree y th and u are unsuitable for petrogenetical modelling of granitoids through equilibrium based trace element fractionation equations

error analysis for the determination of tectonic rotation from paleomagnetic data appendix b is available with entire article on microfiche order from american geophysical union 2000 florida avenue n w washington d c 20009 document b83 001 2 50 payment must accompany order recent determinations of tectonic rotation and flattening from paleomagnetic data have exaggerated the size of the confidence limits or error bars by about 25 this has been caused by the misuse of conventional error propagation formulas to derive one degree of freedom error bars from a two dimensional cone of confidence 95 an analytical calculation which is valid when error bars are small shows that the correct error bars are 75 to 80 of the values derived in previous studies i have used numerical integration to check on the applicability of the analytical solution and to calculate error bars when the analytical approximation cannot be used the analytical approximation may be used whenever 95 is less than 10 and the mean inclination is not too close to vertical confidence limits given for tectonic rotation and flattening in recent literature are too large and should be reduced by 20 25 narrowing the error bars in this way permits a more accurate interpretation of paleomagnetic data

structure and emplacement of a rhyolitic obsidian flow little glass mountain medicine lake highland northern california many rhyolitic obsidian flows show consistent stratigraphic relations among textural units exposed in the flow fronts of undissected flows and in cross sections of older flows the stratigraphy of the holocene little glass mountain rhyolitic obsidian flow consists of from bottom to top air fall tephra deposits basal breccia coarsely vesicular pumice obsidian finely vesicular pumice and surface breccia slightly crystalline rhyolite occurs near the vent areas a model of obsidian flow emplacement based on these textural relations is presented this stratigraphy may reflect the distribution of volatiles within the magma source region with the interlayered contact between coarsely vesicular pumice and overlying obsidian indicating stratification of volatiles in the magma body the distribution of pumiceous and glassy zones along with the orientations of flow banding can be used to map the surface structure of rhyolitic obsidian flows this complex structure as mapped on the little glass mountain flow reflects both the initial flow stratigraphy and subsequent deformational processes during emplacement of the lava three processes disrupt the initial flow configuration the rise of coarse pumice diapirs from the base of the flow the inward propagation of fractures in areas of extension and surface folding in sites of flow parallel compression subvertical flow banding in vent areas indicates that fracturing accompanies the emergence of lava most of the observed upper surface of a dome originates as a fracture plane the structure of domes that form over vent areas may reflect the orientation of dike like conduits as well as the local state of stress during extrusion

the contribution of the precambrian continental lithosphere to global h 2 production the production of hydrogen gas from the precambrian continental lithosphere has been underestimated taking into account hydrogen from serpentinization and radiolysis may double estimates previously based on marine systems alone molecular hydrogen produced by interactions between water and rocks in the earth s subsurface and at deep ocean vents can sustain microbial ecosystems it was thought that global h2 production originates mainly from the marine lithosphere with a negligible contribution from precambrian rocks but here the authors present a global compilation of h2 concentration data that identifies the fracture waters in the precambrian continental subsurface as a domain of the terrestrial hydrosphere that produces h2 at a rate comparable to estimates from marine systems this finding revises our understanding of the production of reduced gases in the earth s subsurface and may aid in the exploration of life in deep habitat locations microbial ecosystems can be sustained by hydrogen gas h2 producing water rock interactions in the earth s subsurface and at deep ocean vents1 2 3 4 current estimates of global h2 production from the marine lithosphere by water rock reactions hydration are in the range of 1011 moles per year5 6 7 8 9 recent explorations of saline fracture waters in the precambrian continental subsurface have identified environments as rich in h2 as hydrothermal vents and seafloor spreading centres1 2 and have suggested a link between dissolved h2 and the radiolytic dissociation of water10 11 however extrapolation of a regional h2 flux based on the deep gold mines of the witwatersrand basin in south africa11 yields a contribution of the precambrian lithosphere to global h2 production that was thought to be negligible 0 009 1011 moles per year 6 here we present a global compilation of published and new h2 concentration data obtained from precambrian rocks and find that the h2 production potential of the precambrian continental lithosphere has been underestimated we suggest that this can be explained by a lack of consideration of additional h2 producing reactions such as serpentinization and the absence of appropriate scaling of h2 measurements from these environments to account for the fact that precambrian crust represents over 70 per cent of global continental crust surface area12 if h2 production via both radiolysis and hydration reactions is taken into account our estimate of h2 production rates from the precambrian continental lithosphere of 0 36 2 27 1011 moles per year is comparable to estimates from marine systems

monazite xenotime garnet equilibrium in metapelites and a new monazite garnet thermometer prograde suites of pelitic rocks were examined with electron microprobe introduction and laser ablation inductively coupled plasma mass spectrometry to monazite ce la th po4 plays an important role in determine the systematics of element partitioning between coexisting studies of igneous and metamorphic petrogenesis foremonazite xenotime and garnet monazite grains that grew in most monazite is used to date specific events in a equilibrium with xenotime are enriched in y and dy compared with petrogenetic sequence e g parrish 1990 harrison et al monazite that grew in xenotime absent assemblages y and heavy 1997 hawkins bowring 1999 foster et al 2000 rare earth element contents of monazite coexisting with xenotime monazite may contain a large percentage of the sample increase with rising temperature monazite xenotime y gd and rare earth element ree budget and thus exert an y dy partitioning is systematic within a metamorphic grade and important influence on the evolution of melt composition increases slightly with increasing metamorphic grade suggesting wark miller 1993 bea 1996 the thermobarometric that monazite xenotime pairs approached partitioning equilibrium potential of monazite coexisting with xenotime has been garnet and monazite in both xenotime bearing and xenotime absent recognized leading to calibration of monazite geoassemblages show a strong r 0 94 systematic relationship thermometers gratz heinrich 1997 1998 heinrich between inverse temperature and ln keq for the net transfer equiet al 1997 andrehs heinrich 1998 in addition the librium yag oh ap 25 4 qtz 5 4 grs 5 4 an recognition that nearly all lead in monazite is radiogenic 3ypo4 mnz 1 2h2o suggesting that garnet and monazite parrish 1990 montel et al 1994 has led to development crystallized in compositional equilibrium the following temand application of electron microprobe monazite dating perature keq relationship for the equilibrium above has been derived techniques suzuki adachi 1991 montel et al 1996 williams et al 1999 t c 1 45p bars 447772 32052 567 40 rln keq 273 15 full realization of monazite as a thermochronometer requires detailed understanding of the specific reactions responsible for its formation previous studies of monazite with a precision of some 30 c for temperature estimates our petrogenesis have focused on monazite compositional observations suggest that major and accessory phases interact in a zonation zhu o nions 1999a 1999b monazite coupled fashion during metamorphism and also approach a state growth kinetics ayers et al 1999 behavior of monazite of compositional equilibrium as reactions proceed during hydrothermal alteration poitrasson et al 1996 crowley ghent 1999 and melting events watt 1995 or to a limited extent the influence of major phase mineral assemblage in monazite reactivity zhu

obtaining diagenetic ages from metamorphosed sedimentary rocks u pb dating of unusually coarse xenotime cement in phosphatic sandstone the depositional age of nonfossiliferous metamorphosed sedimentary rocks is commonly bracketed between the age of the youngest detrital mineral and the age of the oldest metamorphic mineral the technique of dating diagenetic xenotime by ion microprobe can provide robust minimum ages for sediment deposition however in most cases xenotime is only a few microns m in size and rarely exceeds 10 m the minimum size for in situ ion microprobe analysis phosphatic sandstone in the greenschist facies mount barren group in southwestern australia contains unusually abundant xenotime occurring as exceptionally coarse 200 m pore filling cement that nucleated on detrital zircon grains the optimum environmental site for the formation of the cement was sand beds within a black shale condensed section analysis of xenotime by sensitive high resolution ion microprobe yields two age populations 1696 7 ma for cement adjacent to detrital zircon grains and 1646 8 ma for outer zones preserved textures show that initial xenotime growth was early diagenetic establishing the ca 1700 ma age as a proxy for the depositional age of the mount barren group the younger age ca 1650 ma is regarded as burial related the xenotime data reduce considerably the previous limits on the age of the succession i e between ca 1850 ma youngest zircon population and ca 1200 ma peak metamorphism the significant achievement of our results is establishing that early diagenetic xenotime retains its physical form and u pb isotopic age despite greenschist facies metamorphism and penetrative deformation

geochronology of unconformity related uranium deposits in the athabasca basin saskatchewan canada and their integration in the evolution of the basin the importance of geochronology in the study of mineral deposits in general and of unconformity type uranium deposits in particular resides in the possibility to situate the critical ore related processes in the context of the evolution of the physical and chemical conditions in the studied area the present paper gives the results of laser step heating 40ar 39ar dating of metamorphic host rock minerals pre ore and syn ore alteration clay minerals and laser ablation inductively coupled plasma mass spectrometer la icp ms u pb dating of uraninite from a number of basement and sediment hosted unconformity related deposits in the athabasca basin canada post peak metamorphic cooling during the trans hudson orogen of rocks from the basement occurred at ca 1 750 ma and gives a maximum age for the formation of the overlying athabasca basin pre ore alteration occurred simultaneously in both basement and sandstone hosted mineralizations at ca 1 675 ma as indicated by the 40ar 39ar dating of pre ore alteration illite and chlorite the uranium mineralization age is ca 1 590 ma given by la icp ms u pb dating of uraninite and 40ar 39ar dating of syn ore illite and is the same throughout the basin and in both basement and sandstone hosted deposits the mineralization event older than previously proposed as well as several fluid circulation events that subsequently affected all minerals studied probably correspond to far field continent wide tectonic events such as the metamorphic events in wyoming and the mazatzal orogeny ca 1 6 to 1 5 ga the berthoud orogeny ca 1 4 ga the emplacement of the mckenzie mafic dyke swarms ca 1 27 ga the grenville orogeny ca 1 15 to 1 ga and the assemblage and break up of rodinia ca 1 to 0 85 ga the results of the present work underline the importance of basin evolution between ca 1 75 ga basin formation and ca 1 59 ga ore deposition for understanding the conditions necessary for the formation of unconformity type uranium deposits

ore genesis constraints on the idaho cobalt belt from fluid inclusion gas noble gas isotope and ion ratio analyses a reply the idaho cobalt belt is a 60 km long alignment of deposits composed of cobaltite co pyrite chalcopyrite and gold with anomalous nb y be and rare earth elements rees in a quartz biotite tourmaline gangue hosted in mesoproterozoic metasedimentary rocks of the lemhi group it is the largest cobalt resource in the united states with historic production from the blackbird mine all of the deposits were deformed and metamorphosed to upper greenschist lower amphibolite grade in the cretaceous they occur near a 1377 ma anorogenic bimodal plutonic complex the enhanced solubility of fe co cu and au as chloride complexes together with gangue biotite rich in fe and cl and gangue quartz containing hypersaline inclusions allows that hot saline fluids were involved the isotopes of b in gangue tourmaline are suggestive of a marine source whereas those of pb in ore suggest a u th enriched source the ore and gangue minerals in this belt may have trapped components in fluid inclusions that are distinct from those in post ore minerals and metamorphic minerals such components can potentially be identified and distinguished by their relative abundances in contrasting samples therefore we obtained samples of co and cu sulfides gangue quartz biotite and tourmaline and post ore quartz veins as well as cretaceous metamorphic garnet and determined the gas noble gas isotope and ion ratios of fluid inclusion extracts by mass spectrometry and ion chromatography the most abundant gases present in extracts from each sample type are biased toward the gas rich population of inclusions trapped during maximum burial and metamorphism all have co 2 ch 4 and n 2 ar ratios of evolved crustal fluids and many yield a range of h 2 ch 4 co 2 h 2 s equilibration temperatures consistent with the metamorphic grade cretaceous garnet and post ore minerals have high r h and r s values suggestive of reduced sulfidic conditions most extracts have anomalous 4 he produced by decay of u and th and 38 ar produced by nucleogenic production from 41 k in contrast some ore and gangue minerals yield significant so 2 and have low r h and r s values of a more oxidized fluid three extracts from gangue quartz have high helium r r a values indicative of a mantle source and neon isotope compositions that require nucleogenic production of 22 ne in fluorite from u th decay two extracts from gangue quartz have estimated 40 k 40 ar that permit a precambrian age extracts from gangue quartz in three different ore zones are biased toward the hypersaline population of inclusions and have a tight range of ion ratios na k nh 4 cl br f suggestive of a single fluid their na cl br ratios suggest this fluid was a mixture of magmatic and basinal brine na k ca temperatures 279 347 c are similar to homogenization temperatures of hypersaline inclusions the high k na of the brine may be due to albitization of k silicate minerals in country rocks influx of k rich brines is consistent with the k metasomatism necessary to form gangue biotite with high cl an extract from a post ore quartz vein is distinct and has na cl br ratios that resemble metamorphic fluids in cretaceous silver veins of the coeur d alene district in the belt basin the results show that in some samples for certain components it is possible to see through the cretaceous metamorphic overprint of great import for genetic models the volatiles trapped in gangue quartz have 3 he derived from a mantle source and 22 ne derived from fluorite both of which may be attributed to nearby 1377 ma basalt rhyolite magmatism the brine trapped in gangue quartz is a mixture of magmatic fluid and evaporated seawater the former requires a granitic intrusion that is present in the bimodal intrusive complex and the latter equatorial paleolatitudes that existed in the mesoproterozoic the results permit genetic models involving heat and fluids from the neighboring bimodal plutonic complex and convection of basinal brine in the lemhi group while the inferred fluid sources in the idaho cobalt belt are similar in many respects to those in iron oxide copper gold deposits the fluids were more reduced such that iron was fixed in biotite and tourmaline instead of iron oxides

fluid inclusion and stable isotope constraints on the heavy rare earth element mineralisation in the browns range dome tanami region western australia this study reports on fluid inclusion and oxygen isotope compositions of mineralised and barren hydrothermal quartz veins and hosting metasedimentary rocks associated with the heavy rare earth element hree mineralisation in the browns range dome of the tanami region western australia the hree mineralisation consists of quartz and xenotime bearing hydrothermal veins and breccias that occurs along sub vertical faults within archean to paleoproterozoic metasedimentary rocks based on analysis of nearly 550 quartz hosted primary fluid inclusions three fluid inclusion types were identified in the mineralised samples type i low salinity h2o nacl largely 5 wt nacl consistent with meteoric water type ii medium salinity h2o nacl 12 18 wt nacl and type iii low to high salinity h2o cacl2 nacl 1 to ca 24 wt nacl cacl2 homogenisation temperatures of all fluid inclusion types vary over a relatively wide range from 100 to 250 c barren quartz veins contain only type i low salinity h2o nacl fluid inclusions with homogenisation temperatures extending from 170 to 350 c raman analyses of all three fluid inclusion types confirmed their aqueous nature with no carbon bearing fluid species identified the three fluid inclusion types indicate mixing of three hydrothermal fluids a low salinity h2o nacl meteoric fluid 5 wt nacl a medium salinity h2o nacl 12 18 wt nacl fluid and a high salinity h2o cacl2 nacl ca 24 wt nacl cacl2 fluid limited la icp ms analysis found detectable y ce u and cl only in the type iii fluid inclusions which indicates that transport of ore metals was at least partly by cl complexes in the type iii fluid the 18ofluid values calculated from quartz from mineralised samples are in the range defined by the archean metasedimentary host rocks of the browns range metamorphics 18ofluid 1 8 to 5 2 and the unconformably overlying paleoproterozoic birrindudu group sandstones 18ofluid 8 collectively our fluid inclusion and oxygen isotope data together with other field mineralogical and geochemical data support an ore genesis model involving mixing of the three hydrothermal fluids in fault zones and along unconformity surfaces in and around the browns range dome the meteoric low salinity h2o nacl fluid potentially carried p from the birrindudu group sandstones and the high salinity h2o cacl2 nacl fluid leached hree y from metasedimentary rocks of the browns range metamorphics ore deposition occurred following mixing of the p bearing and hree y bearing fluids and was associated with a widespread white mica alteration the temperature and pressure during the fluid fluid mixing and mineralisation was between 100 and 250 c and 0 4 and 1 6 kbar respectively

numerical model to determine the composition of h2o nacl cacl2 fluid inclusions based on microthermometric and microanalytical data natural fluids approximated by the h2o nacl cacl2 system are common in a wide range of geologic environments including sedimentary basins associated with hydrocarbon occurrences and mvt deposits submarine hydrothermal systems and other metamorphic magmatic and hydrothermal environments we present a comprehensive numerical model and microsoft excel based computer program to determine the compositions of fluid inclusions in the h2o nacl cacl2 system based on microthermometric and microanalytical data the model consists of six polynomial correlation equations that describe liquid salinity as a function of nacl cacl2 ratio and melting temperature on each of the ice hydrohalite halite antarcticite cacl2 4h2o and cacl2 2h2o vapor saturated liquidus surfaces the cotectic and peritectic boundaries are determined from the intersections of the liquidus surfaces the model is implicitly internally consistent and topologically correct the model expands upon the compositional range of applicability and the data types that can be used for compositional determination it reproduces experimental data for all compositions that lie within the h2o nacl cacl2 4h2o compositional triangle in the h2o nacl cacl2 system and yields accurate reproductions of the h2o nacl and h2o cacl2 binaries furthermore in comparison to previously published models the one presented here eliminates systematic errors wavy isotherms and cotectic and peritectic curves with local bumps

water geochemistry of the seferihisar geothermal area izmir turkey abstract the na cl thermal waters of seferihisar have measured temperatures of 30 153 c and conductivities of 7400 55200 s cm they issue from upper cretaceous to paleocene bornova melange rocks which are made up of sandstone shale intercalations conglomerate mafic submarine volcanics limestone lenses serpentinite and limestone bodies and their complexes through the intersection of faults the clay rich zones of the overlying neogene terrestrial sediments cap the system the heat source is the high geothermal gradient caused by graben tectonics of the area na and cl ions mainly dominate the chemistry of thermal waters thus thermal waters of the seferihisar area appear to be mixtures of groundwaters and seawater the seawater contribution in thermal waters varies from 10 to 80 assessments from empirical chemical geothermometers mineral equilibria and silica mixing model applied on the thermal waters of the seferihisar geothermal area suggest that the temperatures of the reservoir systems vary between 60 and 180 c the seferihisar geothermal area has been physically divided into five main groups and estimated reservoir temperatures provided by the entire methods give the increase as doganbey burnu karakoc spa doganbey tuzla and cumali spa areas in ascending order of reservoir temperature hydrogeochemical assessments indicate that thermal waters were mixed with cold waters before and or after heating at depth in different proportions the results of mineral equilibrium modeling indicate that the thermal waters of seferihisar are undersaturated with respect to gypsum and amorphous silica oversaturated with respect to calcite dolomite and aragonite and undersaturated or oversaturated with respect to quartz chalcedony and anhydrite

depositional mechanics and sequences of base surges songaksan tuff ring cheju island korea the songaksan mount in the southwestern part of cheju island korea is a taalian tuff ring produced by phreatomagmatic explosions at an aquifer a detailed analysis of proximal to distal facies changes reveals that the tuff ring sequence can be represented by 21 sedimentary facies one lateral facies sequence lfs and three vertical facies sequences vfs the vfs 1 and 2 are representative of facies relationships in horizontal near vent deposits the vfs 1 comprises scour fill bedded tuff inversely graded tuff massive tuff and laminated tuff from base to top the vfs 2 is a variant of the vfs 1 replaced by an inversely graded lapilli tuff unit at the base the sequences suggest traction carpet suspension and minor traction sedimentation from a high concentration near vent base surge the lfs 1 and the vfs 3 are distilled from outward dipping flank deposits both sequences begin with disorganized lapilli tuff followed successively by stratified lapilli tuff dune bedded lapilli tuff very thinbedded tuff and accretionary lapilli they are suggestive of waning base surge which decreases in particle concentration suspended load fall out rate and flow regimes with an increase in traction and sorting these facies sequences suggest that a base surge experiences flow transformation with its flow characters changing with time and space a near vent base surge is turbulent uniformly mixed and highly concentrated and produces scour fill bedded tuff as capacity decreases the surge transforms into a dense and laminar underflow and a dilute and turbulent upper part gravity transformation depositing inversely graded massive and normally graded lapilli tuff ensuing loss of sediment load and mixing of ambient air result in flow dilution surface transformation stratified and dune bedded units are produced by tractional processes of turbulent and low concentration surge further dilution causes deceleration and cooling and results in precipitation of moistened ash and accretionary lapilli from suspension

petrogenesis of the proterozoic athabasca basin northern saskatchewan canada and its relation to diagenesis hydrothermal uranium mineralization and paleohydrogeology abstract in the athabasca basin proterozoic sandstones unconformably overlie archean and aphebian rocks multiple fluid events involving isotopically and chemically distinct fluids which have migrated laterally for considerable distances and along fault zones have produced a paragenetically identifiable assemblage of clay silicate and oxide minerals in the basin and basement rocks altered sandstones and the underlying metasedimentary rocks proximal to fault zones host high grade u ni co unconformity type uranium ore deposits and contain an alteration assemblage of highly crystalline 2m 3t illite 1m kaolinite clinochlore and sudoite hematite dravite and euhedral quartz in the sandstones 18o values of coeval quartz hematite quartz illite quartz dravite illite hematite and kaolinite hematite fluid inclusion temperatures in diagenetic quartz and d values of 1m kaolinite 2m 3t illite dravite and in fluid inclusions in the quartz indicate formation from a basinal fluid that had d values of 60 10 and which underwent salinity temperature and 18o increases from 5 to 34 wt nacl 120 to 240 c and 5 to 3 respectively as a result of increasing burial depth and sustained water rock interactions with the basinal sediments over substantial time periods 18 o 16 o and d h ratios of sudoite and clinochlore in meta sedimentary basement rocks within the alteration haloes indicate formation from a basement derived fluid with 18o and d values of 4 4 and 30 10 respectively that was isotopically distinct from the basinal fluids 18o and d values of late kaolinites in reactivated fault zones indicate formation mainly from low temperature 50 25 c fluids having 18o and d values of 16 and 130 respectively similar to relatively modern meteoric waters in the area some kaolinites have 18o and d values which suggest they formed from meteoric waters at mid latitudes and have experienced varying degrees of oxygen and hydrogen isotope exchange with relatively modern meteoric waters in the re activated faults illite sudoite and dravite have d values that vary by 100 without concurrent changes to their 18o values indicating preferential hydrogen isotope exchange with relatively modern meteoric waters at low temperatures and under conditions of high integrated water rock ratios rb sr isochron and model ages of 1477 57 and 952 ma respectively for the crystalline 2m 3t illites indicate the timing of the high temperature basinal fluid events associated with fluid mixing rb sr and k ar ages on illites with the lowest d values are as young as 300 ma and indicate late stage resetting of their radiogenic isotope systematics as a result of substantial interactions with relatively modern meteoric waters the evolution of sr isotopic compositions of fluids in the basin and basement rocks as reflected by the 87 sr 86 sr ratios of chlorite illite and dravite indicates that mixing of two isotopically distinct fluids in the vicinity of faults was the process by which uranium was precipitated similar to that suggested by oxygen and hydrogen isotope systematics in the clays and silicate minerals nd ratios in the high temperature diagenetic and hydrothermal clay and silicate minerals and the cogenetic uranium ores suggest they all have formed from similar fluids which have interacted substantially with the basin sediments in general the isotopic chemical microthermometric and petrologic data indicate that the athabasca basin has had a protracted fluid history comparable to that documented for more modern sedimentary basins the data clearly show that the major sandstone aquifers have been affected by widespread lateral flow of diagenetic fluids over distances of hundreds of kilometers and also that these fluid migration paths have been modified by cross formational fluid flow near active fault zones

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

composite tuff ring cone complexes in jeju island korea possible consequences of substrate collapse and vent migration hydromagmatic volcanoes tuff rings and tuff cones in jeju island korea are divided into holocene volcanoes that were constructed upon rigid plateau forming lavas and early to middle pleistocene volcanoes that underlie the lavas and were constructed upon fragile unconsolidated sediments the older volcanoes are distinguished from the holocene volcanoes in that the former have irregular morphologies the irregular morphologies resulted from superposition or juxtaposition of multiple rim deposits of partial tuff rings and or tuff cones that have contrasting lithofacies characteristics bed attitudes and paleoflow directions the rim deposits are bounded by laterally persistent truncation surfaces which suggest large scale collapse of the substrate together with the overlying tephra piles and or erosion during a break in eruptive activity collapse was probably caused by the instability of the friable sedimentary substrate removal of lateral support because of downward quarrying of volcanic conduits and liquefaction of the water saturated substrate by volcanic seismicity the path of magma supply was diverted in some cases after collapse giving rise to migration of the active vent in other cases the eruption style changed abruptly from cone forming fallout dominated to ring forming surge dominated eruptions after collapse the resultant volcanic edifices thus consist of multiple rim beds of partial tuff rings and or tuff cones commonly with non circular morphologies substrate collapse and lateral vent migration as observed in jeju island appears to be an important phenomenon in hydromagmatic volcanoes because they are commonly constructed upon unstable sedimentary substrates substrate collapse and vent migration needs to be taken into account as an important control on volcano morphology and structures and as a means of lateral enlargement of terrestrial submarine or extraterrestrial volcanoes

the origin of an unusual tuff ring of perlitic rhyolite pyroclasts the last explosive phase of the ramadas volcanic centre andean puna salta nw argentina a thick sequence of bedded pyroclastic deposits comprised largely of crystal poor partially flow banded perlite fragments defines the remains of a tuff ring around the eastern margin of the miocene ramadas volcanic centre rvc central andes nw argentina in numerous quarry exposures planar bed forms dominate but low angle cross stratification lensoidal truncations and lateral pinching and swelling of cm dm scale bed forms occur consistent with pyroclastic surge as the dominant transport and depositional mechanism intercalated are mantling very fine grained well sorted mm cm scale planar ash layers that represent deposition from pyroclastic fall out and are most likely the products of co surge ash clouds also observed are thick m scale laterally continuous poorly sorted horizons that are interpreted as pyroclastic flow deposits grainsize variations within the 70 m thick succession range from fine ash to coarse lapilli with occasional large blocks reaching 20 cm clast vesicularities are typically very low the sequence constitutes a rhyolitic tuff ring around the proximal margins of the rvc stratigraphic relationships indicate that the tuff ring was developed following cessation of the major plinian eruption phase of the rvc a series of pyroclastic density currents and associated ash clouds is inferred to have resulted in the construction of the rhyolitic tuff ring with deposition focussed on the eastern and southern margins of the central vent the fine grained nature of the deposits and low clast vesicularity are consistent with some degree of magma water interaction during fragmentation pervasive perlitic fracturing of clasts found within the tuff deposits also indicates hydration and an extended post depositional hydration of the pyroclastic sequence due to the influence of meteoric water is likely to have occurred with deposit permeability clast specific surface and climate influential in facilitating additional textural modification of pyroclasts

spherulites and thundereggs from pitchstones of the deccan traps geology petrochemistry and emplacement environments spherulites and thundereggs are rounded typically spherical polycrystalline objects found in glassy silicic rocks spherulites are dominantly made up of radiating microscopic fibers of alkali feldspar and a silica mineral commonly quartz they form due to heterogeneous nucleation in highly supercooled rhyolitic melts or by devitrification of glass associated features are lithophysae stone bubbles which have an exterior sometimes concentric shells of fine quartz and feldspar and internal cavities left by escaping gas when filled by secondary silica these are termed thundereggs here we describe four distinct occurrences of spherulites and thundereggs in pitchstones mostly rhyolitic some trachytic of the deccan traps india the thundereggs at one locality were previously misidentified as rhyolitic lava bombs and products of pyroclastic extrusive activity we have character ized the thundereggs petrographically and geochemically and have determined low contents of magmatic water 0 21 0 38 wt in them using fourier transform infrared spectros copy we consider that the spherulite bearing outcrops at one of the localities are of lava flows but the other three represent subvolcanic intrusions based on the structural disposition of the deccan sheet intrusions studied here and considerations of regional geology we suggest that they are cone sheets emplaced from a plutonic center now submerged beneath the

an empirical oxygen and hydrogen isotope geothermometer for quartz tourmaline and tourmaline water abstract oxygen isotope equilibration temperatures of coexisting quartz muscovite illite chlorite and biotite from a variety of geologic environments have been used in conjunction with the 18o and d values of associated tourmaline to formulate empirical quartz tourmaline and tourmaline water isotope fractionation factors over temperatures from 200 to 600 c the fractionation factors determined using this method are as follows 1 1 1000 in quartz tourmaline 1 0 0 17 10 6 t 2 0 39 0 44 oxygen 2 2 1000 in tourmaline water 27 2 4 4 10 6 t 2 28 1 9 8 hydrogen 350 600 c the isotopic properties of tourmaline are nearly identical to those of muscovite and illite despite the significant differences in their crystal structures similarities in the oxygen and hydrogen isotope systematics of tourmalines and micas imply that the dominant controls on the isotopic properties of these minerals are the vibrational energies of the al si o and si o bonds however the bo3 groups in the tourmalines may have some effect on oxygen isotopic properties as there are minor differences between the 18o values of coexisting tourmalines and micas d values of coexisting tourmalines and micas are generally concordant to within 10 chemical compositions indicate that varying fe mg ratios in the tourmalines appear to have only a minor control on their d values there is a discontinuity in the 1000 in tourmaline water values for hydrogen at temperatures between 200 c and 300 c suggesting that the hydroxl groups in tourmaline are affected by hydrogen bonding and changes in the properties of water near its critical point as are some other hydrous minerals

miocene geochronology and stratigraphy of western anatolia insights from new ar ar dataset abstract understanding the dynamic evolution of orogenic belts and intra continental basins depend on field based tectono stratigraphic observations paired with geochronologic data such as 40ar 39ar analyses independent dating of tectono stratigraphic units is a crucial tool to place them in a broader framework in this study we focus on the geodynamic development of western anatolia with an emphasis on the timing and progression of volcanism along the izmir balikesir transfer zone ibtz we present 36 new 40ar 39ar ages of both volcanic complexes domes and volcanic rocks coevally emplaced within miocene sediments from western anatolian extensional basins in combination with existing ages from the literature and paleontological records from miocene basin in fills we build an improved and integrated stratigraphic framework for the region our results show a remarkable break in volcanism from this area during the langhian 15 97 13 82 ma encompassing a major unconformity in the ibtz and a pulse in the exhumation of metamorphic core complexes in western anatolia hence we attribute this magmatic pause to the tectonic reorganization and change in the partitioning of extensional deformation between cycladic and menderes core complexes facilitated by the acceleration of roll back of african oceanic lithosphere below western anatolia

u pb ages and hf isotopic compositions of zircon from the early miocene kestanbol magmatic complex in nw anatolia turkey implications for crustal contribution in the post collisional magmatism abstract the tertiary post collisional magmatic activity in nw anatolia occurred after the late cretaceous to early tertiary collision of the sakarya and anatolide tauride blocks and the closure of the izmir ankara ocean the magmatism resulted in coeval emplacement of granitic plutons and andesitic volcanic rocks along the izmir ankara erzincan suture zone iaesz the kestanbol magmatic complex kmc on the biga peninsula w of the iaesz is one of the representative magmatic complexes in the sakarya zone situated north of the iaesz monzo dioritic syeno diorite plutonic rocks show close relationships with dacitic trachyandesitic and rhyolitic rocks in space and time which are characterized by enrichment in large ion lithophile elements lile and depletion in nb ta p and ti interpreted as reflecting an arc related origin trace element concentrations and isotope data indicate that the kmc the kestanbol pluton and the ayvacik and the balabanli volcanic rocks was formed by differentiation of mantle derived mafic melts via assimilation of ancient continental materials coupled with mineral fractionation the zircon ages for the kestanbol pluton and the ayvacik volcanic rocks are 22 24 and 21 58 ma respectively whereas zircon u pb age data suggest that the balabanli volcanic rocks 19 33 0 30 ma is 3 million years younger than the kestanbol pluton and the ayvacik volcanic rocks hf isotopes in zircon ehf t ranging from 5 7 to 0 7 combined with u pb ages support the hypothesis that the mantle source of the kestanbol magmatism was severely modified by crust derived metasomatic fluids during the previous subduction

depositional processes of the suwolbong tuff ring cheju island korea the suwolbong pyroclastic sequence in the western part of cheju island korea comprises partly preserved rim beds of a quaternary basaltic tuff ring whose vent lies about 1 km seaward of the present shoreline the sequence consists of breccia lapillistone lapilli tuff and tuff eighteen sedimentary facies are established and organized into six lateral facies sequences lfs and seven vertical facies sequences vfs the lfs 1 4 and 5 begin with massive lapilli tuff which transforms downcurrent into either planar bedded lfs 1 undulatory bedded lfs 4 or climbing dune bedded lfs 5 lapilli tuff units they are representative of relatively dry base surge whose particle concentration decreases downcurrent with a progressive increase in both tractional processes and sorting the lfs 2 begins with disorganized and massive lapilli tuff and transforms into crudely stratified units downcurrent it results from relatively wet base surge in which sorting is poor due to the cohesion of damp ash the lfs 3 comprises well sorted lapilli tuff and stratified tuff further downcurrent suggestive of deposition from combined fall and surge of relatively dry hydroclastic eruption all seven vertical facies sequences generally comprise two facies units of coarse grained fines depleted lapilli tuff and an overlying fine grained tuff these sequences are suggestive of deposition from base surge that consists of a turbulent head and a low concentration tail depositional processes in the suwolbong tuff ring were dominated by a relatively dry base surge the base surge comprises turbulent and high concentration suspension near the vent whose deposits are generally unstratified due to the lack of tractional transport as the base surge becomes diluted downcurrent through fallout of clasts and mixing of ambient air it develops large scale turbulent eddies and is segregated into coarse grained bedload and overlying fine grained suspension forming thinly stratified units further downcurrent the base surge may be either cooled and deflated or pushed up into the air depending on its temperature the suwolbong tuff ring comprises an overall wet to dry cycle with several dry to wet cycles in it suggestive of overall decrease in abundance of external water and fluctuation in the rate of magma rise

hydrothermal transport and deposition of the rare earth elements by fluorine bearing aqueous liquids new technologies particularly those designed to address environmental concerns have created a great demand for the rare earth elements ree and focused considerable attention on the processes by which they are concentrated to economically exploitable levels in the earth s crust there is widespread agreement that hydrothermal fluids played an important role in the formation of the world s largest economic ree deposit i e bayan obo china until recently many researchers have assumed that hydrothermal transport of the ree in fluorine bearing ore forming systems occurs mainly due to the formation of ree fluoride complexes consequently hydrothermal models for ree concentration have commonly involved depositional mechanisms based on saturation of the fluid with ree minerals due to destabilization of ree fluoride complexes here we demonstrate that these complexes are insignificant in ree transport and that the above models are therefore flawed the strong association of h and f as hf and low solubility of ree f solids greatly limit transport of the ree as fluoride complexes however this limitation does not apply to ree chloride complexes because of this the high concentration of cl in the ore fluids and the relatively high stability of ree chloride complexes the latter can transport appreciable concentrations of ree at low ph the limitation also does not apply to sulphate complexes and in some fluids the concentration of sulphate may be sufficient to transport significant concentrations of ree as sulphate complexes particularly at weakly acidic ph this article proposes new models for hydrothermal ree deposition based on the transport of the ree as chloride and sulphate complexes

silicic phreatomagmatism in the snake river plain the deadeye member non welded rhyolitic pyroclastic units in the central snake river plain are interbedded with the much better exposed large volume snake river type rheomorphic welded rhyolitic ignimbrites and rhyolite lavas we document one such unit to investigate why it is so different from the interbedded welded ignimbrites the newly recognised deadeye member of southern idaho is a soil bounded eruption unit that comprises ashfall layers and a 4 m thick ignimbrite that extends for 35 km the ignimbrite is non welded lithic clast poor and varies from massive to diffuse low angle cross bedded it contains abundant angular clasts of non vesicular black glass and upper parts contain accretionary lapilli the ashfall layers above it contain coated ash pellets and ash clumps which record moist aggregation of fine ash the magmas of the deadeye eruption were closely similar in composition and temperature to those that generated the intensely welded rheomorphic ignimbrites of the central snake river plain we infer that the marked contrast in physical appearance of the deadeye ignimbrite compared to the other more typical snake river type welded ignimbrites was the result of emplacement at relatively low temperatures during an eruption in a lacustrine environment magmatic volatile driven fragmentation of the rhyolitic magma was influenced by interaction with lake water that also led to cooling the deadeye member is the first recorded example of explosive silicic phreatomagmatism in the central snake river plain

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

flash vaporization during earthquakes evidenced by gold deposits fluids flowing through cavities in earth s crust can deposit gold thermo mechanical modelling of a fluid filled cavity that expands suddenly during an earthquake shows that the drop in pressure would cause the fluid to vaporize and deposit the gold almost instantaneously

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

pyroclastic phases of a rhyolitic dome building eruption puketarata tuff ring taupo volcanic zone new zealand the 14 ka puketarata eruption of maroa caldera in taupo volcanic zone was a dome related event in which the bulk of the 0 25 km3 of eruption products were emplaced as phreatomagmatic fall and surge deposits a rhyolitic dike encountered shallow groundwater during emplacement along a ne trending normal fault leading to shallow seated explosions characterised by low to moderate water magma ratios the eruption products consist of two lava domes a proximal tuff ring three phreatic collapse craters and a widespread fall deposit the pyroclastic deposits contain dominantly dense juvenile clasts and few foreign lithics and relate to very shallow level disruption of the growing dome and its feeder dike with relatively little involvement of country rock the distal fall deposit representing 88 of the eruption products is despite its uniform appearance and apparently subplinian dispersal a composite feature equivalent to numerous discrete proximal phreatomagmatic lapilli fall layers each deposited from a short lived eruption column the puketarata products are subdivided into four units related to successive phases of a shallow lava intrusion and initial dome growth b rapid growth and destruction of dome lobes c slower sustained dome growth and restriction of explosive disruption to the dome margins and d post dome withdrawal of magma and crater collapse phase d was phreatic phases a and c had moderate water magma ratios and phase b a low water magma ratio dome extrusion was most rapid during phase b but so was destruction and hence dome growth was largely accomplished during phase c the puketarata eruption illustrates how vent geometry and the presence of groundwater may control the style of silicic volcanism early activity was dominated by these external influences and sustained dome growth only followed after effective exclusion of external water from newly emplaced magma

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

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

paleogene history of the kula plate offshore evidence and onshore implications paleocene to middle eocene magnetic anomalies were mapped over oceanic crust that accreted at the kula pacific spreading center and is now obliquely entering the western aleutian trench between 179 e and 168 e the strike of anomalies and the pattern of abyssal hills and fracture zones changed abruptly during 56 55 ma when north south spreading veered to northwest southeast 310 130 kula pacific spreading ceased in 43 ma a 75 km long section of the fossil kula rift axis has avoided subduction although it now intersects the trench axis almost orthogonally near 171 5 e a narrow remnant of the former kula plate northwest of this fossil spreading center is bounded by a fossil kula pacific transform with a high transverse ridge alongside a sediment filled transform valley anomalies on this remnant show that eocene kula pacific spreading was highly asymmetric 2 1 the 56 55 ma change in kula plate rotation inferred from the change in spreading direction coincided with birth of the aleutian subduction zone and was probably a consequence of the resulting change in slab pull stresses on the oceanic lithosphere the change in direction of kula north american motion is a plausible explanation for the detachment of continental terranes from the pacific northwest and their migration around the gulf of alaska and for the early eocene demise of alaska range are volcanism the cessation of kula pacific spreading coincides with a major change in pacific plate rotation and the subsequent direction of convergence of the pacific plate with the aleutian arc was similar to the 55 43 ma direction of kula plate convergence

fluid evolution in the strange lake granitic pluton canada implications for hfse mobilisation abstract strange lake is a mid proterozoic peralkaline granite pluton quebec labrador canada that underwent extreme enrichment in high field strength elements hfse including the rare earth elements ree the hfse mineralisation is confined to highly altered pegmatites and the most altered parts of the granites implying a genetic association between hydrothermal fluids and hfse enrichment this study uses analyses of fluid inclusions to investigate the hydrothermal evolution of the strange lake pluton and the role of hydrothermal processes in concentrating the hfse to potentially exploitable levels five groups of inclusions were distinguished from earliest to latest these groups are primary aqueous inclusions 25 wt nacl eq associated with melt inclusions group 1 primary aqueous inclusions 13 23 wt nacl eq associated with ch 4 inclusions groups 2a and b primary aqueous inclusions 9 wt nacl eq associated with co 2 inclusions group 3 primary aqueous inclusions 9 wt nacl eq which contain no carbonic component group 4 and finally secondary aqueous inclusions 19 wt nacl eq including inclusions that outline mineral pseudomorphs also with no detectable carbonic component group 5 most of the inclusions except those in group 5 have conspicuous implosion haloes evident as numerous tiny voids this indicates that the inclusions re equilibrated most likely during isobaric cooling fluid evolution commenced with the exsolution of a saline aqueous liquid 25 wt nacl eq and an immiscible ch 4 h 2 gas from the pegmatitic melt at temperatures of 450 500 c and a pressure of 1100 bars during isobaric cooling the gas component of the fluid was gradually oxidised evolving from being ch 4 dominant to a ch 4 fluid with a significant proportion of higher order hydrocarbons due to oxidative coupling of methane induced by the consumption of o 2 through the alteration of arfvedsonite to aegirine 325 360 c and finally to a co 2 dominated fluid at 300 c the apparent salinity of the aqueous fluid decreased from 25 to 4 5 wt nacl eq due to fluid rock interaction the latter also caused precipitation of nahcolite as a result of the reaction of newly formed co 2 with sodium from decomposing minerals formation of pseudomorphs after primary na zirconosilicates and na titanosilicates and replacement of primary ree silicates by bastnasite ce owing to this interaction the carbonic component of the fluid was consumed which together with the consumption of h 2 o to form al k and fe phyllosilicates contributed to an increase in the fluid salinity up to 19 wt nacl eq light rare earth elements lree were remobilised over 10s to 100 s of metres by the high temperature high salinity fluid preserved as group 1 and 2a inclusions whereas heavy rare earth elements hree were remobilised on a much smaller scale by a late low temperature high salinity fluid trapped as inclusion group 5 fluid preserved as inclusion group 3 may have been responsible for remobilisation of zr and ti

experimental diffusion of hydrogen into synthetic fluid inclusions in quartz quartz hosted synthetic co2 h2o fluid inclusions behave as open systems with respect to diffusional transfer of hydrogen during laboratory simulated metamorphic re equilibration at 650 750 and 825 c and 1 5 kbar total pressure with fo2 defined by the c ch4 buffer microthermometry and raman spectroscopy show that the initial co2 h2o inclusions become co2 ch4 h2 h2o inclusions after diffusive influx of hydrogen from the reducing confining medium measurable changes are observed in inclusion compositions after only 15 days of re equilibration implying significant hydrogen mobility at still lower temperatures over geological time spans results of synthetic inclusion re equilibrium experiments have profound implications for the interpretation of natural fluid inclusion data failure to account for potential hydrogen migration in inclusions from high temperature geological environments may lead to erroneous estimates of p t and or the compositions of metamorphic fluids

improved calibration procedures and new standards for u pb and th pb dating of phanerozoic xenotime by ion microprobe abstract xenotime is a widely occurring mineral that is amenable to u pb and th pb dating but often is found as micrometre sized crystals that can only be dated by in situ microanalytical techniques determining accurate ages for phanerozoic samples and assessing concordance in older samples requires accurate determination of pb u and pb th however ion microprobe data for these ratios are affected by the highly variable trace element composition of xenotime we have identified calibration procedures including matrix corrections for the effects of the dominant trace elements u th and ree that provide an accuracy of 1 for pb u and

fluid inclusion and stable isotope constraints on ore genesis of the zajkan epithermal base metal deposit tarom hashtjin metallogenic belt nw iran in the zajkan pb zn cu au ag deposit of the tarom hashtjin metallogenic belt thmb northwest iran mineralization occurs as quartz base metal sulfide veins hosted by eocene volcanic and volcaniclastic rocks of the karaj formation four stages of ore formation are identified at zajkan 1 quartz chalcopyrite pyrite veins 2 quartz galena sphalerite chalcopyrite pyrite veins and breccias 3 quartz hematite veins and breccias and 4 barren quartz carbonate veinlets the primary metallic minerals are pyrite chalcopyrite sphalerite galena and trace amounts of hematite gangue minerals are mainly quartz sericite chlorite and calcite the main wall rock alteration is silicification and intermediate argillic and propylitic alteration the coexistence of different types of fluid inclusions lv vl and v in individual fluid inclusion assemblages in quartz and sphalerite suggests boiling and heterogeneous trapping excluding the heterogeneously entrapped fluid inclusions the microthermometric measurements of primary lv fluid inclusion assemblages in quartz and sphalerite indicate that the veins were formed at temperatures between 217 and 273 degrees c from fluids with salinities between 1 7 and 6 4 wt nacl equiv the oxygen isotopic compositions delta o 18 water vsmow of 3 7 to 1 1 parts per thousand indicate that the ore forming fluids were mainly derived from magmatic water with the input of meteoric water in the later ore stages sulfur isotopic values of sulfide minerals vary over a narrow range from 5 0 to 0 9 parts per thousand vcdt averaging 2 2 parts per thousand vcdt suggesting that sulfur was derived from a homogeneous magmatic source the fluid inclusion and stable isotope data indicate that fluid boiling and mixing facilitated hydrothermal alteration and mineralization at zajkan our data suggest that the zajkan deposit is an intermediate sulficiation style epithermal mineralization the estimated ore formation depth of zajkan indicates minor denudation in the region and may imply a great prospecting potential for other epithermal mineralization in the thmb

shrimp u pb ages of diagenetic and hydrothermal xenotime from the archaean witwatersrand supergroup of south africa shrimp dating of xenotime overgrowths on detrital zircon grains can constrain maximum durations since diagenesis and therefore provide minimum dates of sediment deposition thus xenotime dating has significant economic application to precambrian sediment hosted ore deposits such as witwatersrand au u for which there are no precise depositional ages the growth history of xenotime in the witwatersrand supergroup is texturally complex with several phases evident the oldest authigenic xenotime 207pb 206pb age obtained in sandstone underlying the vaal reef is 2764 5 myr 1 and most likely represents a mixture of diagenetic and hydrothermal growth nevertheless this represents the oldest authigenic mineral age yet recorded in the sequence and provides a minimum age of deposition other xenotime data record a spread of ages that correspond to numerous post diagenetic thermotectonic events including a ventersdorp event at 2720 ma up to the 2020 ma vredefort event

hydrothermal dolomite a product of poor definition and imagination abstract the latest dolomite bandwagon is the hydrothermal dolomite model in its present form this bandwagon is doomed or at least very much overstated for at least two reasons 1 there are several definitions of hydrothermal and hardly any author specifies which one s he is using 2 very few of the dolomites hitherto called hydrothermal have been demonstrated to be hydrothermal according to any definition except the worst as presently applied the term hydrothermal dolomite is confusing and or meaningless we suggest to use white s geol soc amer bull 68 1957 1637 time honored definition of hydrothermal as aqueous solutions that are warm or hot relative to its surrounding environment with no genetic implications regarding the fluid source hence a dolomite should be called hydrothermal only if it can be demonstrated to have formed at a higher than ambient temperature regardless of fluid source or drive furthermore this definition does not carry a lower or upper temperature limit even a dolomite formed at 40 c could be hydrothermal by extension dolomites formed at temperatures lower than ambient are not hydrothermal even if they formed at a rather high temperature for example groundwater may penetrate a rock sequence through a highly permeable pathway such that it is heated to 150 c at a depth where the surrounding rock has a temperature of 250 c we suggest to call dolomite formed from this water hydrofrigid dolomite formed in or near thermal equilibrium with the surrounding rocks may be called geothermal furthermore not all saddle dolomite formation requires advection fluid flow to transport mg saddle dolomite can be formed in at least three ways i e from advection local redistribution of older dolomite during stylolitization and as a by product of thermochemical sulfate reduction in a closed or semi closed system only the first and the last of these three possibilities have a chance of being hydrothermal almost all dolomites and dolostones in the western canada sedimentary basin have recently been re interpreted as hydrothermal applying the rationale outlined above reveals however that this basin contains very little hydrothermal dolomite rather most dolomites in this basin and almost all dolostones south of the peace river arch are geothermal and or the proof of a hydrothermal origin has not been made this has important implications beyond the various case studies at hand as attempts to tie dolomitization to orogenic events become moot at least in the southern part of the basin

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

geochemical modeling of the formation of an unconformity type uranium deposit petrologic studies of alteration associated with uranium mineralization in unconformity type uranium deposits have established a detailed paragenetic sequence of the preore and synore alteration in addition fluid inclusion studies have determined the presence of two distinct fluids and thermodynamic analysis of the alteration assemblages has defined their basic characteristics these fluids were probably basinal brines derived from the overlying sandstones and have been distinguished by their different salinities fluids responsible for alteration and ore formation were na ca cl brines speciation calculations suggest that the hydrothermal fluids responsible for the formation of unconformity type uranium deposits were distinguished by their high oxygen fugacity and relatively low ph uranium was transported mainly as uranyl chloride complexes reconstruction of the reactions associated with the formation of the deposits employing chemical mass transfer calculations helps unravel the geochemical processes operating during their genesis reaction path calculations indicate that fe present in aluminosilicates in the host rocks is the principal reductant of oxidized uranium present in the ore forming fluids the use of variable host rock lithologies results in the reproduction of mineralogical features unique to each deposit along with the characteristics common to all unconformity related uranium deposits the calculations show that the observed paragenesis is a function not only of the fluid chemistry but also of the host rock lithologies the modeling indicates that although an orebody can be produced with or without graphite as a reactant its presence leads to a better agreement with the observed alteration paragenesis

effusive eruptions from a large silicic magma chamber the bearhead rhyolite jemez volcanic field nm abstract large continental silicic magma systems commonly produce voluminous ignimbrites and associated caldera collapse events less conspicuous and relatively poorly documented are cases in which silicic magma chambers of similar size to those associated with caldera forming events produce dominantly effusive eruptions of small volume rhyolite domes and flows the bearhead rhyolite and associated peralta tuff member in the jemez volcanic field new mexico represent small volume eruptions from a large silicic magma system in which no caldera forming event occurred and thus may have implications for the genesis and eruption of large volumes of silicic magma and the long term evolution of continental silicic magma systems 40ar 39ar dating reveals that most units mapped as bearhead rhyolite and peralta tuff the main group were erupted during an 540 ka interval between 7 06 and 6 52 ma these rocks define a chemically coherent group of high silica rhyolites that can be related by simple fractional crystallization models preceding the main group minor amounts of unrelated trachydacite and low silica rhyolite were erupted at 11 9 and 8 ma respectively whereas subsequent to the main group minor amounts of unrelated rhyolites were erupted at 6 1 and 1 5 ma the chemical coherency apparent fractional crystallization derived geochemical trends large areal distribution of rhyolite domes 200 km2 and presence of a major hydrothermal system support the hypothesis that main group magmas were derived from a single large shallow magma chamber the 540 ka eruptive interval demands input of heat into the system by replenishment with silicic melts or basaltic underplating to maintain the bearhead rhyolite magma chamber although the volatile content of main group magmas was within the range of rhyolites from major caldera forming eruptions such as the bandelier and bishop tuffs eruptions were smaller volume and dominantly effusive bearhead rhyolite domes occur at the intersection of faults and are cut by faults suggesting that the magma chamber was structurally vented preventing volatiles from accumulating to levels high enough to trigger a caldera forming eruption

preliminary palaeomagnetic results from the subbetic zone betic cordillera southern spain kinematic and structural implications abstract we present palaeomagnetic evidence from jurassic limestones and basic submarine volcanic rocks sills pillow lavas and intrusive material from the central part of the subbetic zone of the betic cordillera isothermal remanent magnetization acquisition experiments performed on limestones and thermomagnetic curves and measurements of the magnetic susceptibility determined for the volcanic rocks demonstrate strong dependence of rock magnetic properties on lithology in most cases a stable magnetization could be isolated after thermal and or alternating field demagnetization locally declinations of the characteristic remanent magnetization from interbedded limestones and volcanics are similar but inclinations tend to vary regionally declinations for both limestones and volcanics show significant clockwise rotation these results cannot be explained by the anticlockwise rotation of iberia during the cretaceous opening of the bay of biscay considering the long and complex history of large scale shear between africa and europe accommodated in southern spain the anomalous declinations can be explained by a model with rotation of crustal blocks within a zone of wrench tectonics

hydrothermal rare earth element xenotime mineralization at maw zone athabasca basin canada and its relationship to unconformity related uranium deposits a discussion

uraniferous diagenetic xenotime in northern australia and its relationship to unconformity associated uranium mineralisation stratabound uraniferous diagenetic xenotime cements provide a minimum depositional age of 1 632 3 ma for the sedimentary birrindudu group in the killi killi hills tanami region in northern australia the age of xenotime formation is broadly coeval with that recently proposed 1 650 1 600 ma for uranium mineralisation in the unconformity associated deposits of the pine creek inlier northern australia and athabasca basin canada the geological setting and formation model for the uraniferous xenotime crystals are similar to those widely proposed for unconformity associated uranium deposits suggesting a genetic link between the two however xenotime formation in the birrindudu group occurred during an apparently earlier stage of diagenesis compared to late diagenetic formation of unconformity associated uranium deposits this could be explained by variations in the thickness of sediment cover and diachronous diagenesis across the basin at the time of the basin wide uranium mobilisation event herein dated at ca 1 630 ma in such a scenario stratabound uraniferous xenotime cements could represent the remote distal zones of a more deeply buried uranium mineralising system alternatively the xenotime layer represents a precursor to or a source for later unconformity associated ore deposition in this case the presence of diagenetic uraniferous xenotime in an area prospective for unconformity associated uranium mineralisation would be an indication of and still provide an approximate age for uranium mobilisation within the cover sequence xenotime is a far more robust mineral than uraninite for u pb geochronology and can potentially provide a more reliable and precise timeframe for uranium mineralisation and subsequent recrystallisation events if present in the immediate uranium ore environment

uranium in iron oxide copper gold iocg systems the olympic dam iron oxide copper gold iocg deposit is currently the world s largest producer of uranium other iocg deposits generally have anomalous though uneconomic uranium grades the fluids that generate iocg deposits are thought to be saline and highly oxidized and would be capable of leaching and transporting significant uranium the reasons for uranium enrichment in certain iocg deposits remain speculative but could include the composition of mineralization related magmas of the wall rocks altered by hydrothermal fluids or of the fluids mixing at the site of mineralization there is sparse data available on uranium abundance in iocg ores there is even less reliable data on the uranium content of unaltered wall rocks for the deposits however the data that is available suggest that the uranium grade of iocg deposits may be primarily related to the uranium content of their unaltered host rocks many iocg deposits appear to have approximately 10 to 40 times enrichment in the ore compared to unaltered host rocks this suggests that exploration for uranium rich iocg deposits should focus on areas with anomalously high uranium contents in host rock sequences

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

matrix effects and calibration limitations in ion probe u pb and th pb dating of monazite abstract monazite can be used for u pb and th pb dating of a wide variety of rocks and geological processes particularly metamorphism in many instances ion microprobe analysis is the preferred method for dating monazite combining good analytical precision with m scale spatial resolution however ion microprobe dates can be compromised by matrix effects on the ionisation efficiencies of different secondary ionic species which can bias monazite pb tho n and pb uo n data by as much as 40 and 30 respectively for known monazite compositions these effects appear to be entirely attributable to the sputtering process in which case similar effects exist in data from all ion probes the effects on data ratios are modified sometimes exacerbated or reversed when data are subjected to the correlation based pb th and pb u calibrations that are now commonly used one dimensional calibrations of 206 pb 270 uo 2 and 208 pb 264 tho 2 are recommended corrections derived from data for a suite of reference materials with diverse compositions can reduce biases in 208 pb 232 th ages to 206 pb 238 u ages to 204 pb can be addressed without iterative data reduction

origin and evolution of hydrothermal fluids in the marshoun epithermal pb zn cu ag deposit tarom hashtjin metallogenic belt nw iran abstract the marshoun epithermal pb zn cu ag deposit is located in the tarom hashtjin metallogenic belt thmb northwest iran the epithermal base metal veins are mainly hosted in eocene volcanic and volcaniclastic rocks of the karaj formation and late eocene pyroxene quartz monzodiorite the mineralization process can be divided into five stages 1 quartz chalcopyrite pyrite veins and breccias 2 quartz calcite sphalerite galena chalcopyrite pyrite veins and breccias 3 barren post ore quartz veinlets 4 barren post ore calcite veinlets and 5 supergene mineral assemblages the primary metallic minerals are pyrite chalcopyrite sphalerite and galena gangue minerals are mainly quartz calcite sericite and chlorite the main wall rock alteration is silicification intermediate argillic carbonate and propylitic alteration microthermometric measurements of primary lv fluid inclusion assemblages in quartz and sphalerite indicate that the veins were mainly formed at temperatures between 173 and 285 c from fluids with salinities between 3 4 and 6 3 wt nacl equiv coexisting lv vl and v inclusions in quartz and sphalerite provide evidence for boiling in ore stage breccia and veins additionally the occurrence of bladed calcite as well as plumose and colloform crustiform banded quartz in the ore zones and the presence of hydrothermal breccias are consistent with boiling obtained oxygen and sulfur isotope compositions 18owater 9 2 to 1 5 34sh2s 10 0 to 5 7 indicate there was a major contribution from a magmatic component to metallogenesis the fluid inclusion and stable isotope data indicate that fluid boiling and mixing facilitated hydrothermal alteration and mineralization at marshoun the marshoun deposit is interpreted as an intermediate sulfidation style of epithermal mineralization our data suggest that the epithermal mineralization in the thmb are related to late eocene ca 36 37 ma shallow magmatic hydrothermal activity the altered eocene volcanic subvolcanic rocks particularly at the intersection of subvolcanic rocks with faults were the most favorable locus for exploration targeting of epithermal ores at thmb

origin of uranium deposits revealed by their rare earth element signature uranium deposits form in a wide range of geological settings including deep magmatic to surficial conditions and range in age from archaean to recent these temporal and spatial variations have given rise to an extreme diversity of ore deposits however understanding their conditions of formation has remained challenging this article reports rare earth element ree abundances measured by microbeam methods in uranium oxides for a series of worldwide uranium occurrences the ree patterns are very specific to each deposit type and directly reflect the conditions of their genesis we propose an evaluation of the first order parameters controlling the ree behaviour in each mineralised system this study demonstrates that the ree pattern is the most efficient tool for constraining the geological models of uranium deposits and for genetically discriminating new uranium discoveries this approach may form the starting point for a new procedure in the fight against nuclear trafficking

textural and geochemical discrimination between xenotime of different origin in the archaean witwatersrand basin south africa abstract xenotime ypo4 of detrital diagenetic and hydrothermal origin within siliciclastic rocks of the archaean witwatersrand basin south africa has been identified on the basis of petrography and in situ ion microprobe shrimp age data the chemical composition of xenotime determined by in situ electron microprobe analysis can be correlated with its origin this allows the origin of any xenotime grain to be assessed by a non destructive microanalytical method prior to ion microprobe geochronology the main chemical discriminators are mree hree abundance normalised hree slope and eu anomaly and in some cases u and th contents igneous detrital xenotime 2800 ma is distinguished from diagenetic 2780 ma and hydrothermal

hydrothermal formation of heavy rare earth element hree xenotime deposits at 100 c in a sedimentary basin most rare earth element deposits form from magmatic fluids but there have also been discoveries of heavy rare earth element hree enriched hydrothermal xenotime deposits within sedimentary basins as xenotime is notoriously insoluble the question arises as to whether these lesser known deposits form at typical basin temperatures or by influx of much hotter magmatic hydrothermal fluids the browns range district in northern western australia hosts deposits of xenotime that are enriched in hrees and also uranium the ore bodies consist of fault controlled hydrothermal quartz xenotime breccias that crosscut archean basement rocks and overlying paleoproterozoic sandstones analyses of fluid inclusions show that the xenotime precipitated at remarkably low temperatures between 100 and 120 c in response to decompression boiling the inclusions contain high excess concentrations of yttrium 10 3 mol kg rees 1 7 10 5 mol kg and uranium 4 10 5 mol kg in equilibrium with xenotime at these low temperatures showing that availability of phosphate limited the amount of xenotime precipitated the analyses further identify so4 2 and cl as the ligands that facilitated the elevated ree and uranium solubilities these findings establish that significant ree transport and deposition is feasible at basin temperatures and hence they raise the potential of unconformity settings for ree exploration moreover the aqueous metal contents support a genetic link between this type of ore fluid and world class proterozoic unconformity related uranium deposits elsewhere

origin of accretionary lapilli within ground hugging density currents evidence from pyroclastic couplets on tenerife aggregation of airborne particles is an important way in which the atmosphere is cleansed of fine dust particles such as following explosive eruptions and meteorite impacts we identify successive stages in the growth history of particle aggregates based upon well preserved ash aggregate bearing pyroclastic layers on tenerife the layers are persistently organized into couplets made up of a lower ignimbrite layer and an upper widespread coignimbrite ash fall layer the upper part of each ignimbrite contains whole and fragmented concentric laminated accretionary lapilli whereas the overlying coignimbrite ash fall layer lacks accretionary lapilli and is composed of framework supported smaller and nonlaminated ash pellets sometimes slightly deformed or partly disaggregated the pellets resemble the cores of the larger accretionary lapilli in the underlying ignimbrite layer these field relations are repeated numerous times in several different successions and they indicate that ash pellets not accretionary lapilli form within the coignimbrite ash plumes some pellets fell directly to the ground producing coignimbrite ash fall layers but others settled into pyroclastic density currents where they accreted successive concentric laminations of fine ash as they circulated through the variously turbulent levels of the stratified current and heat of the lower part of the current dried and partly lithified them into brittle accretionary lapilli the fully formed whole and broken accretionary lapilli were then deposited from the current along with ash and pumice lapilli numerous ignimbrite veneers on tenerife have the form of ash layers a few centimeters thick that drape topography and locally contain matrix supported accretionary lapilli most volcanoes lack laterally continuous field exposure and such accretionary lapilli bearing layers might be mistaken for ash fall deposits we highlight the value of careful distinction between different types of ash aggregate facies when interpreting the origin of pyroclastic deposits for example during hazard assessments

neotectonic structures in the area offshore of alacati doganbey and kusadasi western turkey evidence of strike slip faulting in the aegean extensional province abstract about 400 km of new seismic reflection data has been acquired in the study region offshore of alacati doganbey and kusadasi which enables investigation of the active crustal deformation in this region the deformation onshore in western turkey is dominated by crustal extension and clear evidence of this process is also now available from this offshore area however in the onshore area adjacent to this study region evidence of active right lateral strike slip faulting has also previously been observed this strike slip faulting has previously been thought only to accommodate variations in extension between adjacent normal faults however in the offshore area there is considerable evidence of zones of deformation some of which may link to the strike slip faulting onshore suggesting that strike slip faulting may be of greater importance in this region than previously thought

new paleomagnetic data from the aleutian islands implications for terrane migration and deposition of the zodiac fan sedimentary rocks of late eocene to early oligocene age from the aleutian islands have been paleomagnetically studied to determine the paleolatitude of this island arc samples were collected from gently dipping thin bedded laminated siltstone mudstone and very fine grained sandstone of marine origin after demagnetization samples from each locality showed both polarities of a remanent magnetization that thermal isothermal remanent magnetization and js t experiments suggest is carried by magnetite after tectonic correction the 95 decreases in both localities suggesting magnetization was acquired before folding of the beds the characteristic magnetization shows that no significant poleward motion of the aleutian arc has occurred with respect to the north american plate since the early oligocene amlia f 4 f 5 umnak f 0 8 f 3 5 but the declinations are rotated significantly clockwise amlia r 70 r 23 umnak r 36 7 r 11 2 using these paleomagnetic data relevant euler poles and hotspot locations we propose a new model for the formation of the zodiac fan in this model the start of zodiac fan deposition corresponds to accretionary igneous and erosional events in the pacific northwest and fragmentation of the farallon plate along the margin of the north american plate into small plates fan deposition on the pacific plate was controlled by the geometry of the bowie and cobb seamount chains which prevented sediment from being dispersed over the bathymetrically lower oceanic crust to the west and by the bathymetry of the pacific plate which focused sedimentation in the magnetic bight region of the plate our model suggests that the present day zodiac fan is only a remnant of a much larger fan system

paleomagnetism of paleogene rocks of the central east kamchatka and komanorsky islands tectonic implications abstract paleomagnetic investigation of paleocene eocene to miocene rocks has been carried out at five localities in the eastern kamchatka and komandorsky islands after thermal and af cleanings consistent paleomagnetic directions were isolated for a number of formations data from the kronotsky peninsula and medny island passed both the fold and reversal tests and thus can be considered as reliable other results are of lower quality all the results were derived from sedimentary rocks and thus the corresponding paleolatitudes may be biased due to inclination errors a limited collection of basalts yielded inclination values systematically lower than those in sediments this anomaly was tentatively explained by shape anisotropy the correctness of paleolatitude estimations was thus left unproved several models of the northern pacific tectonic evolution were suggested and analyzed but the authors failed to find a model that was fully compatible with paleomagnetic kinematic and geological data

early diagenetic ree phosphate minerals florencite gorceixite crandallite and xenotime in marine sandstones a major sink for oceanic phosphorus

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

hydrothermal rare earth element xenotime mineralization at maw zone athabasca basin canada and its relationship to unconformity related uranium deposits a reply

reconstructing eruption processes of a miocene monogenetic volcanic field from vent remnants waipiata volcanic field south island new zealand the miocene waipiata volcanic field new zealand is an eroded phreatomagmatic intracontinental volcanic field formed during a period of weak lithospheric extension the field includes remnants of at least 55 volcanoes in an area of 5000 km2 vent filling deposits comprising predominantly lava e g plugs necks lava flows or dykes often associated with thin basal phreatomagmatic pyroclastic deposits were classified as type 1 vents and are inferred to be the remnants of scoria cones vents represented by predominantly pyroclastic infill are classified as type 2 vents and are inferred to have been the substructures of phreatomagmatic tuff ring and or maar volcanoes type 3 vent complexes are groups of closely spaced or overlapping vents with voluminous preserved lava flows they are inferred to be the remnants of volcanoes comprising adjoining to coalescing maars and tuff rings with magmatic explosive and effusive products pyroclastic rocks of most of the waipiata vents record initial phreatomagmatic explosive activity fuelled by groundwater followed by strombolian style eruptions aligned and clustered vents are accommodated to structural features of the regional basement rock otago schist

melting behavior of fluid inclusions in laboratory grown halite crystals in the systems naclh2o naclkclh2o naclmgcl2h2o and naclcacl2h2o abstract the chemical composition of aqueous fluid inclusions in crystals of halite can be accurately determined from observed melting behaviors of ice hydrohalite and sylvite some fluid inclusion melting behaviors observed in laboratory grown halite crystals systems nacl h 2 o nacl kcl h 2 o nacl mgcl 2 h 2 o and nacl cacl 2 h 2 o differ from predicted stable equilibrium relations in the nacl h 2 o and nacl kcl h 2 o systems observed first melt temperatures are up to 15 c below the equilibrium eutectic temperatures of 21 2 and 22 9 c respectively the final melting temperature of ice in the presence of hydrohalite and the final melting temperature of hydrohalite are reproducible and match predicted melting temperatures the limit of detection of sylvite daughter crystals in the nacl kcl h 2 o system is approximately 5 wt 1 molal kcl final melting temperatures of sylvite match published equilibrium data to within 0 3 c in the nacl kcl h 2 o system at halite saturation m kcl can be determined from the final sylvite dissolution temperature or from the final melting temperature of hydrohalite fluid inclusions in the nacl mgcl 2 h 2 o and nacl cacl 2 h 2 o systems that form stable salt hydrates mgcl 2 12h 2 o and cacl 2 6h 2 o during freezing first melt within 3 c of predicted eutectic temperatures 37 and 52 c however fluid inclusions with mgcl 2 or cacl 2 may also start melting at temperatures as low as 80 c such low first melt temperatures indicate the presence of metastable salt hydrates presumably mgcl 2 8h 2 o mgcl 2 6h 2 o or cacl 2 4h 2 o the formation of metastable phases during freezing of fluid inclusions can lead to misinterpretation of the chemical composition of fluid inclusions in natural samples this is especially true for fluid inclusions with first melt temperatures below 37 c which may be erroneously interpreted as being rich in cacl 2 the final melting of ice in the presence of hydrohalite may vary by more than 15 c in fluid inclusions of different size but identical bulk composition and occurs at lower temperatures than predicted in fluid inclusions from the nacl mgcl 2 h 2 o and nacl cacl 2 h 2 o systems however the final melting temperature of ice in inclusions which fail to nucleate hydrohalite and the final melting temperature of hydrohalite are reproducible to within 0 1 c and can be used to determine mgcl 2 and cacl 2 molalities

volcano stratigraphy of the extension related silicic volcanism of the cubukludag graben western turkey an example of generation of pyroclastic density currents western turkey9s extension related cumaovasi volcanic rocks lower miocene 17 ma are excellent examples of silicic eruptions the sub aerial silicic volcanism at cubukludag graben between izmir and kusadasi in west central anatolia is mainly in the form of rhyolite domes lava flows and pyroclastic deposits the initial features of volcanism derived from phreatomagmatic explosive eruptions from silicic magma that came into contact with lake waters during neogene times most of the volcanic succession represents pyroclastic density currents pdcs known as the kuner ignimbrite the deposits are fine grained and laminated at the base and pass laterally and vertically into deposits displaying well developed traction structures soft sediment deformation and or erosion channels in the ne part of the region alternate deposits of massive diffusely stratified lapilli and ash are the main products of the later explosive stage massive lithic breccias forming the top of the sequences are the proximal facies of the pdcs the lava phase mainly consists of rhyolite extruded as dome and fissure eruptions of lavas aligned along ne sw trending faults as well as from extensional cracks that are nearly perpendicular to the main graben faults considering the tectono stratigraphical aspects and geochemical nature of the study area we propose that the cumaovasi silicic volcanism was produced by extension related crustal melting during the late early miocene period 17 ma

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

from evaporated seawater to uranium mineralizing brines isotopic and trace element study of quartz dolomite veins in the athabasca system abstract stable isotope o h c radiogenic isotope sr nd and trace element analyses have been applied to quartz dolomite veins and their uranium u bearing fluid inclusions associated with proterozoic unconformity related uo 2 uraninite ores in the athabasca basin canada in order to trace the evolution of pristine evaporated seawater towards u mineralizing brines during their migration through sediments and basement rocks fluid inclusion data show that quartz and dolomite have precipitated from brines of comparable chemistry excepted for relatively small amounts of co 2 found in dolomite hosted fluid inclusions however 18 o values of quartz veins 18 o 11 to 18 and dolomite veins 18 o 13 to 24 clearly indicate isotopic disequilibrium between quartz and dolomite hence it is inferred that this isotopic disequilibrium primarily reflects a decrease in temperature between the quartz stage 180 c and the dolomite stage 120 c the 13 c values of co 2 dissolved in dolomite hosted fluid inclusions 13 c 30 to 4 and the 13 c values of dolomite 13 c 23 5 to 3 5 indicate that the co 2 dissolved in the mineralizing brines originated from brine graphite interactions in the basement the resulting slight increase in the fluid partial pressure of co 2 p co 2 may have triggered dolomite precipitation instead of quartz 18 o values of quartz veins and previously published 18 o values of the main alteration minerals around the u ores illite chlorite and tourmaline show that quartz and alteration minerals were isotopically equilibrated with the same fluid at 180 c the ree concentrations in dolomite produce paas normalized patterns that show some similarities with that of uo 2 and are clearly distinct from that of the other main ree bearing minerals in these environments monazite zircon and aluminum phosphate sulfate aps minerals the radiogenic isotope compositions of dolomite 87 sr 86 sr i 0 7053 to 0 7161 and e nd t 8 8 to 20 3 differ from one deposit to another reflecting both heterogeneity in the basement geology and variable preservation of the original composition of brines the previously published 87 sr 86 sr i and e nd t values of uo 2 compare with the most evolved dolomites i e dolomites precipitated from brines that exchanged the most with the basement this reinforces a close genetic link between dolomites and uo 2 deposition and implies that uo 2 deposition occurred in a cooling system during the transition from quartz to dolomite formation the 18 o and d values of the mineralizing brines 18 o 1 to 8 and d 150 to 50 are considerably shifted from that of their theoretical original values acquired during evaporation of seawater 18 o 3 and d 40 the positive 18 o shift is explained by protracted fluid rock interaction within the basin and basement rocks the negative d shift is attributed to incomplete mixing between the u mineralizing brines and low d water this low d water was likely produced during the abiogenic synthesis of bitumen by fisher tropsch like reactions involving co 2 derived from brine graphite interaction in the basement and radiolytic h 2 the resulting low d brines have been equilibrated with alteration minerals this may explain why some alteration minerals yield anomalously low d values whose significance has long been debated

evidence against the core cover interpretation of the southern sector of the menderes massif west turkey the menderes massif in western anatolia has been described as a lithological succession comprising a basal precambrian gneissic core of sedimentary origin overlain in sequence by palaeozoic schist and mesozoic cenozoic marble forming the envelope the boundary between core and schist envelope was interpreted as a major unconformity the supra pan african unconformity by contrast our field observations and geochemical data show that around the southern side of besparmak mountain north of selimiye milas the protoliths of highly deformed mylonitized augen gneisses are granitoid rocks intrusive into the adjacent palaeozoic metasedimentary schists the field relationships indicate the age of intrusion to be younger than late permian and there is no evidence for the existence of either an exposed precambrian basement or the supra pan african unconformity in this sector of the menderes massif