iceberg calving flux and mass balance of the austfonna ice cap on nordaustlandet svalbard 1 satellite radar interferometry 60 mhz airborne ice penetrating radar data and visible band satellite imagery were used to calculate the velocity structure ice thickness and the changing ice marginal extent of austfonna 8000 km2 and 2500 km3 the largest ice cap in the eurasian arctic ice cap motion is generally less than about 10 m a 1 except where faster flowing curvilinear features with velocities of several tens to over 200 m a 1 are present most drainage basins of austfonna have undergone ice marginal retreat over the past few decades at an average of a few tens of meters per year integrating margin change around the whole ice cap gives a total area loss of about 10 km2 a 1 iceberg flux from the marine margins of austfonna is about 2 5 0 5 km3 a 1 water equivalent about 45 of the total calving flux from the whole svalbard archipelago when mass loss by iceberg production is taken into account the total mass balance of austfonna is negative by between about 2 5 and 4 5 km3 a 1 this iceberg flux represents about 33 5 of total annual mass loss from austfonna with the remainder lost through surface ablation iceberg flux should be included in calculations of the total mass balance of the many large arctic ice caps including those located in the russian and canadian arctic that end in tidewater the neglect of this term has led to underestimates of mass loss from these ice caps and thus to underestimates of the contribution of arctic ice caps to global sea level rise

the giant dexing porphyry cu mo au deposit in east china product of melting of juvenile lower crust in an intracontinental setting the dexing porphyry cu mo au deposit in east china 1 168 mt at 0 45 cu is located in the interior of the south china craton scc made up of two lithospheric blocks the yangtze and cathaysia blocks the cu mo au mineralization is associated with mid jurassic granodioritic porphyries with three high level intrusive centers controlled by a series of lineaments at the southeastern edge of the yangtze block available age data define a short duration 172 170 ma of the felsic magmatism and the mineralization 171 1 ma the deposit shows broad similarities with deposits in volcanoplutonic arcs although it was formed in an intracontinental setting porphyries associated with mineralization are mainly granodiorites which contain abundant phenocrysts 40 60 and carry contemporaneous microgranular mafic enclaves mmes they are mainly high k calc alkaline and show geochemical affinities with adakite characterized by relatively high mgo cr ni th and th ce ratios the least altered porphyries yielded relatively uniform end t values from 0 9 to 0 6 and wide 87sr 86sr i range between 0 7046 and 0 7058 partially overlapping with the sr nd isotopic compositions of the mmes and mid jurassic mafic rocks in the scc zircons from the porphyries have positive ehf t values 3 4 to 6 9 and low 18o values 4 7 to 6 3 generally close to those of depleted mantle all data suggest an origin by partial melting of a thickened juvenile lower crust involving mantle components e g neoproterozoic mafic arc magmas triggered by invasion of contemporaneous mafic melts at dexing the mmes show textural mineralogical and chemical evidence for an origin as xenoliths formed by injection of mafic melts into the felsic magmas these mmes usually contain magmatic chalcopyrite and have original variable contents of cu up to 500 ppm their geochemical characteristics suggest that they were derived from an enriched mantle source metasomatized by proterozoic slab derived fluids and supplied a part of cu au and s for the dexing porphyry system during their injection into the felsic magmas the 171 1 ma magmatic hydrothermal event at dexing is contemporaneous with the mid jurassic extension in the scc followed by 160 90 ma arc like magmatism in southeastern china with respect to the tectono magmatic evolution of the scc the emplacement of cu bearing porphyries and the associated cu mineralization occurred in response to the transformation from a tensional regime related to mid jurassic extension to a transpressional regime related to the subduction of the paleo pacific oceanic lithosphere

magmatic anhydrite in plutonic rocks at the el teniente cu mo deposit chile and the role of sulfur and copper rich magmas in its formation anhydrite occurs along with biotite feldspars quartz fe oxides and sulfides in fine grained igneous rocks that form the small porphyry a stock at el teniente these minerals crystallized together in the space generated by the intrusion of this stock and they do not replace preexisting phases planar crystal boundaries between anhydrite and other phases as well as the fact that plagioclase and biotite are fresh and unaltered also suggest that anhydrite is an igneous phase and not the product of secondary hydrothermal alteration plagioclase is unusually na rich ranging from oligoclase in mafic varieties of these rocks with 20 percent biotite to albite in more felsic samples with 20 percent these unusual anhydrite bearing plutonic rocks which contain up to 3 wt percent s and 0 5 wt percent cu are isotopically similar to all other igneous rocks related to the deposit these rocks formed during a late miocene period of regional compressive deformation with no coeval volcanic activity in the area of the deposit which prevented devolitalization of the oxidized parent magma in the large productive magma chamber inferred to have underlain el teniente at 4 km below the paleosurface this allowed igneous fractionation involving the recharge of mantle derived mafic magmas into the base of the chamber as well as volatile transfer and concentration near its roof to produce the cu and s rich magmas that formed the anhydrite bearing intrusive rocks

u pb dating of zircon and 40ar 39ar dating of biotite at bingham utah uranium lead dating of zircon and 40ar 39ar dating of biotite provide a new estimate of the age of the bingham hydrothermal system the u pb age of zircon from the last chance monzonite establishes the age of crystallization of this intrusion at 38 55 0 19 ma 2 mswd 2 08 the oldest hydrothermal event in the monzonite is dated at 38 40 0 16 ma and is based on a 40ar 39ar determination plateau age of primary igneous biotite this age is indistinguishable from the u pb zircon age of emplacement of the monzonite petrographic and fluid inclusion data show that the biotite bearing sample was propylitically altered at 400 c which would reset the 40ar 39ar age within 115 ka thus the concordance of the biotite age with the intrusion age of the monzonite suggests that propylitic alteration was essentially contemporaneous with monzonite emplacement the 40ar 39ar ages from three hydrothermal biotites sampled within the 0 35 percent cu isopleth in the monzonite overlap within uncertainty and indicate that potassic alteration in monzonite occurred at 37 57 0 11 ma the youngest hydrothermal activity is identified from a biotite sample 37 07 0 21 ma correlation age in potassically altered quartz monzonite porphyry within the central mos2 zone hydrothermal biotite within the bingham deposit was produced over a time period of approximately 0 50 0 32 ma

iceberg trajectory modeling and meltwater injection in the southern ocean this is the first large scale modeling study of iceberg trajectories and melt rates in the southern ocean an iceberg model was seeded with climatological iceberg calving rates based on a calculation of the net surface accumulation from each snow catchment area on the antarctic continent in most areas modeled trajectories show good agreement with observed patterns of iceberg motion though discrepencies in the weddell sea have highlighted problems in the ocean general circulation model output used to force the iceberg model the coriolis force is found to be important in keeping bergs entrained in the coastal current around antarctica and topographic features are important in causing bergs to depart from the coastal regions the modeled geographic distribution of iceberg meltwater joining the ocean has been calculated and is found in many near coastal regions to be comparable in magnitude to the excess of precipitation over evaporation p e

a helium based model for the effects of radiation damage annealing on helium diffusion kinetics in apatite abstract widely used to study surface processes and the development of topography through geologic time u th he thermochronometry in apatite depends on a quantitative description of the kinetics of 4he diffusion across a range of temperatures timescales and geologic scenarios empirical observations demonstrate that he diffusivity in apatite is not solely a function of temperature but also depends on damage to the crystal structure from radioactive decay processes commonly used models accounting for the influence of thermal annealing of radiation damage on he diffusivity assume the net effects evolve in proportion to the rate of fission track annealing although the majority of radiation damage results from recoil while existing models adequately quantify the net effects of damage annealing in many geologic scenarios experimental work suggests different annealing rates for the two damage types here we introduce an alpha damage annealing model adam that is independent of fission track annealing kinetics and directly quantifies the influence of thermal annealing on he diffusivity in apatite we present an empirical fit to diffusion kinetics data and incorporate this fit into a model that tracks the competing effects of radiation damage accumulation and annealing on he diffusivity in apatite through geologic time using time temperature paths to illustrate differences between models we highlight the influence of damage annealing on data interpretation in certain but not all geologic scenarios the interpretation of low temperature thermochronometric data can be strongly influenced by which model of radiation damage annealing is assumed in particular geologic scenarios involving 1 2 km of sedimentary burial are especially sensitive to the assumed rate of annealing and its influence on he diffusivity in cases such as basement rocks in grand canyon and the canadian shield u th he ages predicted from the adam can differ by hundreds of ma from those predicted by other models for a given thermal path involving extended residence between 40 80 c

mineral chemical and isotopic studies of namaqualand granulites south africa a grenville analogue the northwestern part of south africa and southern south west africa namibia is amongst the most extensive granulite terranes in africa this work reports the results of electron microprobe studies of minerals from two pyroxene cordieriteorthopyroxene gedrite sapphirine and garnet and or cordierite parageneses from namaqualand in the n w cape province of south africa determined pt conditions of prograde metamorphism based on thermodynamic calculations are 800 900 c and ca 6 7 kb and it is argued that rocks of unusual composition notably cordierite orthopyroxene rocks are restites after the extraction of granitic liquid from former argillites this interpretation is consistent with previously published data on similar rocks and with mccarthy s 1976 suggestion of extensive partial melting in the quartzofeldspathic rocks in the area

rate of fluvial incision in the central alps constrained through joint inversion of detrital 10be and thermochronometric data abstract we integrate constraints from published detrital thermochronometry and detrital 10 be concentrations in a single catchment to infer how erosion is shaping alpine topography we apply this analysis to the codera watershed in the bergell intrusion central european alps where rivers have incised into a glacial valley because thermochronometric ages of bedrock samples increase with elevation a distribution of detrital ages in river sediment provides a tracer for the source elevations of sediment within the catchment while detrital 10 be concentrations provide constraints on rates of erosion we find that modern erosion rates within the fluvial portion of the landscape are too low to permit the inferred 500 m of incision during the most recent interglacial based on the spatial pattern of modern erosion rates we predict that if the incised fluvial valley was formed during interglacial periods only it has formed over the last approximately 400 000 years

a new approach to thermal history modelling with detrital low temperature thermochronological data abstract we present an inverse modelling strategy to infer thermal history information from detrital low temperature thermochronological data from modern sediment sampling the outlet of a single catchment as presented the method relies on the assumption that the geological timescale thermal history was the same across the catchment the detrital sample is assumed to represent a mixture of grains originating from a potentially unknown sampling of the present elevation range in the catchment the approach also implements a method to infer a function describing the topographic sampling represented in the detrital sample in practice this may reflect variations in erosion with elevation but also lithological differences in the catchment fertility and the nature of erosion transport processes in the catchment a combination of detrital and in situ bedrock data are recommended to improve the resolution of the topographic sampling function we demonstrate the application of the approach to a set of fission track data from the fundacion catchment in the sierra nevada de santa marta in northern colombia the inferred thermal history suggest a period of rapid cooling initiated around 50 30 ma followed by slower cooling to the present day consistent with the regional geological history the topographic sampling function estimates suggest that the hypsometric distribution is not appropriate in terms of the contributions from different elevations to the detrital sample rather the data imply a higher proportion of sampling from lower elevations close to the location of the outlet where the detrital sample was collected

the origin of cu sulfide deposits in the curaca valley bahia brazil evidence from cu ni se and platinum group element concentrations the curaca valley of bahia brazil is a high grade granulite facies granite gneiss terrane that hosts numerous sill like mafic ultramafic intrusive bodies of variable size of particular interest are the orthopyroxenites which contain economically important cu sulfides the ore is generally interpreted to be of primary magmatic origin mainly because of the almost exclusive association of the mineralization with the orthopyroxenites however the ore is highly atypical of magmatic deposits in that it contains up to 50 percent magnetite the sulfide assemblage consists of bornite and chalcopyrite yielding an average cu ni ratio of 40 and the host orthopyroxenites contain abundant phlogopite and locally apatite and zircon this has raised questions about an alternative mechanism of ore formation in addition to cu ni and se we have determined noble metal contents in 90 samples from several bodies along a strike length of some 80 km in order to constrain the ore forming processes most orthopyroxenites contain between 100 and 500 ppb platinum group elements but individual samples may contain up to 2 700 ppb mantle normalized noble metal patterns are relatively fractionated with pd ir ratios of approximately 70 hydrothermal cu sulfide ores typically show much more pronounced noble metal fractionation caused by the relatively high mobility in low temperature fluids of au pd and pt compared to os ir ru and rh this supports an originally magmatic origin of the ore to explain the high cu ni and other unusual features of the curaca valley ores we suggest that the orthopyroxenites may represent restitites of a sulfide magnetite phlogopite and apatite bearing dioritic protolith which underwent anatexis and effective melt extraction the sulfides may have been molten but could have remained in the restite due to their relatively high density partial dissolution of the sulfide melt by the s undersaturated silicate melt would cause enrichment of the excess sulfide melt in the highly chalcophile cu and se potentially followed by the crystallization of bornite and chalcopyrite this interpretation is supported by the absence of differentiated lithologies that may represent residual liquids and by the fact that the curaca valley deposits as well as the okiep deposits and several other minor cu sulfide ores described from elsewhere are located in high grade metamorphic terranes

nickeliferous sulfides in xenoliths olivine megacrysts and basaltic glass the composition of olivine and nickeliferous sulfide inclusions from a selection of mafic and ultramafre rocks xenoliths and megacrysts including picritic basalts from kilauea volcano hawaii kimberlite from fayette county pennsylvania and megacrysts from mount shasta california are compared with the mean experimental value of the distribution coefficient for ni fe exchange kd3 32 only nine of the forty five olivipe bulk sulfide pairs investigated have compositions consistent with equilibration at high temperature yielding calculated kd3 values in the range 22 to 41 the remaining pairs have calculated kd3 values which range from 0 to 19 bulk sulfides in disequilibrated assem blages are consistently depleted in nickel and within both indivudual associations and individual petrographic sections they exhibit a wide variation in nis content the bulk copper contents of olivine and groundmass hosted sulfides from kilauea volcano range from 0 5 to 43 at and samples from the kilauea iki lava lake are more fe and cu rich and generally have lower kd3 values than those from the eruption itself as with magmatic ni cu sulfide deposits most nickeliferous sulfide inclusions in mantle related rocks and xenoliths and in volcanic rocks do not have pristine early magmatic bulk compositions and it would seem to be premature to attribute these sulfides solely to either a mantle or an early magnatic origin

contributions from mafic alkaline magmas to the bingham porphyry cu au mo deposit utah usa the bingham porphyry cu au mo deposit utah may only be world class because of substantial contributions of sulfur and metals from mafic alkaline magma to an otherwise unremarkable calc alkaline system volcanic mafic alkaline rocks in the district are enriched in cr ni and ba as well as cu au platinum group elements pge and s the bulk of the volcanic section that is co magmatic with ore related porphyries is dacitic to trachytic in composition but has inherited the geochemical signature of high cr ni and ba from magma mixing with the mafic alkaline rocks the volcanic section that most closely correlates in time with ore related porphyries is very heterogeneous containing clasts of scoriaceous latite latitic and minette and flows of melanephelinite shoshonite and olivine latite in addition to volumetrically dominant dacite trachyte bingham ore related porphyries show ample evidence of prior mixing with mafic alkaline magmas intrusive porphyries that have not been previously well studied have several chemical and mineralogical indications of magma mixing these mixed lithologies include the hybrid quartz monzonite porphyry biotite porphyry and minette dikes even some of the more silicic latite and monzonite porphyries retain high cr and ba contents indicative of mixing and contain trace amounts of sapphire 1 mm the heterogeneous block and ash flow deposits also contain sapphire and are permissively correlated with the intrusions based on chemical mineralogical and isotopic data magma mixing calculations suggest about 10 of the monzonitic latitic ore related magma may have been derived from mafic alkaline magma similar to the melanephelinite if the original s content of the mafic magma was about 2 000 4 000 ppm comparable with similar magmas then the mafic magma may have been responsible for contributing more than half of the s and a significant portion of the cu au and pge in the bingham deposit

atmospheric forcing on the barents sea winter ice extent abstract the atmospheric forcing on the barents sea ice extent during winter december february djf has been investigated for the period 1967 2002 the time series for the sea ice extent is updated and includes the winter of 2005 which marks a new record low in the wintertime barents sea ice extent and a linear trend of 3 5 decade 1 in the ice extent was found covariability between the barents sea ice extent and the atmospheric mean seasonal flow and the synoptic cyclones has been discussed separately for the mean flow linear correlations and regression analysis reveal that anomalous northerly southerly winds prevail in the nordic seas during winters with extensive sparse barents sea ice extent some of the variability in the mean flow is captured by the north atlantic oscillation nao however the wintertime link between the barents sea ice extent and the nao is moderate by studying the cyclone activity in the high latitude northern hemisphere using a dataset of individual cyclones two

precious metals assemblages at the mikheevskoe porphyry copper deposit south urals russia as proxies of epithermal overprinting abstract mineral assemblages and formation conditions of precious metals au ag pge in ores of the mikheevskoe porphyry copper deposit south urals are the subject of our study three mineralization types can be distinguished 1 gold silver telluride mineralization overlapping porphyry style bornite chalcopyrite ores includes native gold fineness 863 873 electrum fineness 593 672 galena hessite coloradoite and more rarely petzite stutzite au ag ditellurides native tellurium tellurobismuthite tetradymite kawazulite altaite and extremely rare melonite nite2 merenskyite pdte2 and sopcheite ag4pd3te4 2 gold arsenopyrite base metal mineralization within quartz tetrahedrite sphalerite veinlets cutting porphyry style mineralization 3 gold telluride mineralization with argillic alteration and mineralogically similar to that of type 1 but distinct because of the presence of au ag ag and pb selenides textural relationships supported by fluid inclusions data and chlorite geothermometry provide evidence that occurrence of precious metals minerals at the mikheevskoe deposit is mostly linked to epithermal overprint of the porphyry mineralization and was deposited at ca 300 200 c from moderately saline fluids ca 5 10 wt eq nacl it is suggested that the observed variability in au and ag minerals results from small fluctuations of s2 and or te2 fugacity

unusually cu rich magmas associated with giant porphyry copper deposits evidence from bingham utah mass balance constraints indicate that formation of giant porphyry copper deposits pcds requires either highly efficient collection of cu from large volumes of magma or unusually cu rich parent magmas support for the second of these possibilities has been discovered in the form of mafic enclaves with abundant bornite and chalcopyrite in the last chance stock one of the parent intrusions of the giant bingham pcd utah united states mineral assemblages and compositions indicate that the last chance enclaves are autoliths consisting of phases that crystallized from the intrusion and that the intrusion was unusually enriched in cu one possible mechanism for generating cu rich magmas is fractional crystallization during pyrrhotite undersaturated conditions the high fo 2 conditions observed for the last chance stock may have allowed such an evolution alternatively if the magma has not undergone significant fractionation early crystallization of chalcopyrite and bornite from the magma would indicate that the lower crustal source region for the magma probably contained cu fe sulfides possible cu rich source regions are a subcrustal mafic intrusion with sulfide cumulates or a deeply buried metamorphic terrane containing cu deposits such as those in the curaca valley brazil or okiep south africa heterogeneous distribution of cu fe sulfides in an okiep type source terrane would produce local pcds such as bingham or large accumulations of cu fe sulfides possibly in the form of cumulates in subcrustal intrusions at convergent margins could produce giant pcd provinces such as those in indonesia papua new guinea and central chile

geochronology and geochemistry of porphyritic intrusions in the duolong porphyry and epithermal cu au district central tibet implications for the genesis and exploration of porphyry copper deposits abstract the duolong district in central tibet hosts a number of porphyry as well as high sulfidation epithermal copper gold deposits and prospects associated with voluminous calc alkaline volcanism and plutonism in this study we present new geochronological geochemical isotopic and mineralogical data for both economically mineralized and barren porphyritic intrusions from the duobuza and naruo porphyry cu au deposits zircon u pb analyses suggest the emplacement of economically mineralized granodiorite porphyry and barren granodiorite porphyry at naruo deposit took place at 119 8 1 4 ma and 117 2 0 5 ma respectively four molybdenite samples from the naruo deposit yield an isochron re os age of 119 5 3 2 ma indicating mineralization occurred synchronously with the emplacement of the early granodiorite porphyry at duobuza deposit the barren quartz diorite porphyry intruded at 119 5 0 7 ma and two economically mineralized intrusions intruded at 118 5 1 2 ma granodiorite porphyry and 117 5 1 2 ma quartz diorite porphyry respectively petrographic investigations and geochemical data indicate that all of the porphyritic intrusions were oxidized water rich and subduction related calc alkaline magmas zircons from the porphyritic intrusions have a wide range in the ehf 0 11 1 indicating that they were sourced from mixing of mantle derived mafic and crust derived felsic melts moreover the variation of trace element content of plagioclase phenocrysts indicates that the magma chambers were recharged by mafic magmas comparison of the composition of amphibole phenocrysts indicates the porphyry copper gold mineralization at duolong was generated in magma chambers at low crystallization temperatures and pressures 754 to 791 c 59 m to 73 mpa n 8 and under highly oxidizing conditions nno 2 2 to 2 7 n 8 in contrast barren intrusions were sourced from the magma chambers with higher crystallization temperatures and pressures 816 to 892 c 111 to 232 mpa n 22 that were less oxidizing nno 0 6 to 1 6 n 22 the requirement for a thermal contrast is supported by the declining of ti content in magnetite crystals in barren intrusions 12 550 to 34 200 ppm versus those from economically mineralized intrusions 600 to 3400 ppm moreover the v content in magnetite crystals from economically mineralized intrusions 990 to 2510 ppm is lower than those recorded from barren intrusions 2610 to 3510 ppm which might reflect the variation in oxidation state of the magma the calculated water solubility of the magma forming the economically mineralized intrusions 3 2 3 7 wt is lower than that of magma forming the barren intrusions 4 6 6 4 wt based on the chemical physical characteristics of economically mineralized magma our study suggests that the development of porphyry cu au mineralization at duolong was initiated by shallow level emplacement of a magma that crystallized at lower temperatures and pressures experimental studies show that copper and water solubilities in silicate melts decrease with falling temperatures and pressures indicating metals and ore forming fluids are more likely to be released from a magma reservoir emplaced at shallow crustal levels we propose the magnetite might be a convenient exploration tool in the search for porphyry copper mineralization because the variations in ti and v content of mineral concentrates and rock samples are indicative of barren versus mineralized intrusions

origin and tectonic setting of the giant duolong cu au deposit south qiangtang terrane tibet evidence from geochronology and geochemistry of early cretaceous intrusive rocks abstract we constrain the origin and tectonic setting of the giant duolong porphyry epithermal cu au deposit in the south qiangtang terrane of northern tibet based on new zircon u pb ages and hf isotopic data as well as whole rock major and trace element data from poorly studied ore associated intrusions in the duolong area the la icp ms zircon u pb dating indicates that the ore associated rocks formed between 121 and 126 ma these ore associated rocks are geochemically similar to low k tholeiitic m type granitoids and to mid to high k calc alkaline i type granitoids they have variable and predominantly positive zircon e hf t values 1 4 to 15 6 and variable crustal model ages t c dm hf 176 1122 ma taking into account previous data and the regional geology of the study area we propose that the ore associated rocks originated from fractional crystallization of mantle derived mafic melts and magma mixing of mantle derived mafic and hybrid lower crust derived felsic melts and the hybrid lower crust included a mix of juvenile and older continental material the duolong porphyry epithermal cu au deposit formed within an ensialic forearc of an active continental margin as a result of the northwards subduction of the bangong nujiang ocean crust beneath the south qiangtang terrane

geologic setting depths of emplacement and regional distribution of fluid inclusions in intrusions of the central wasatch mountains utah nine mid tertiary calc alkaline stocks a subvolcanic porphyry system and coeval volcanic rocks are exposed in a 45 km long east trending belt across the central wasatch mountains utah the intrusions vary systematically from west to east in texture style of emplacement extent of contact metamorphism hydrothermal alteration and mineralization pressure depth estimates based on metamorphic mineral assemblages stratigraphic reconstructions and fluid inclusion data indicate a regular variation in paleodepths ranging from about 11 km on the west to less than 1 km on the east these data indicate that the central wasatch mountains have been tilted down to the east about 20 degrees during the late cenozoic fluid inclusion populations in igneous quartz also vary systematically with paleodepth high salinity halite saturated fluid inclusions are present in the eastern porphyry stocks and in the upper parts of the alta and clayton peak stocks in the center of the belt but are absent in the deeper parts of the alta and clayton peak stocks and in the little cottonwood stock on the west side of the belt in the alta and clayton peak stocks nearly planar high paleosalinity horizons presently dipping 15 degrees to 20 degrees east separate rocks containing high salinity fluid inclusions above the high paleosalinity horizon from those lacking such fluid inclusions comparison of fluid inclusion populations in igneous and vein quartz in the alta and clayton peak stocks indicates that high salinity fluids predated most of the vein forming hydrothermal activity and provide the earliest record of fluids to circulate in these stocks high salinity fluids probably formed either by boiling of fluids released during the late stages of crystallization in the parts of the intrusions where pressure was less than about 1 300 bars or by exsolution of immiscible high salinity brines from the crystallizing magmas most hydrothermal mineralization associated with the intrusions including ag pb zn ores in the park city district are associated spatially with parts of the intrusions where high salinity fluids were present the major exception is the porphyry molybdenum system in the eastern part of the little cottonwood stock which probably was at too great a depth approximately 7 km to form high salinity brines and is dominated by low salinity co 2 rich fluids

vertical tectonics at a continental crust oceanic plateau plate boundary zone fission track thermochronology of the sierra nevada de santa marta colombia 1 the topographically prominent sierra nevada de santa marta forms part of a faulted block of continental crust located along the northern boundary of the south american plate hosts the highest elevation in the world 5 75 km whose local base is at sea level and juxtaposes oceanic plateau rocks of the caribbean plate quantification of the amount and timing of exhumation constrains interpretations of the history of the plate boundary and the driving forces of rock uplift along the active margin the sierra nevada province of the southernmost sierra nevada de santa marta exhumed at elevated rates 0 2 km my during 65 58 ma in response to the collision of the caribbean plateau with northwestern south america a second pulse of exhumation 0 32 km my during 50 40 ma was driven by underthrusting of the caribbean plate beneath northern south america subsequent exhumation at 40 25 ma 0 15 km my is recorded proximal to the santa marta bucaramanga fault more northerly regions of the sierra nevada province exhumed rapidly during 26 29 ma 0 7 km my further northward the santa marta province exhumed at elevated rates during 30 25 ma and 25 16 ma the highest exhumation rates within the sierra nevada de santa marta progressed toward the northwest via the propagation of nw verging thrusts exhumation is not recorded after 16 ma which is unexpected given the high elevation and high erosive power of the climate implying that rock and surface uplift that gave rise to the current topography was very recent i e 1 ma and there has been insufficient time to expose the fossil apatite partial annealing zone

generation of metal rich felsic magmas during crustal anatexis we show that partial melting of a preexisting mineral deposit during regional anatexis is likely to lead to incorporation of sulfide melt into silicate melt simple dissolution of metals in silicate melt during anatexis leads to minor metal addition to escaping magma but physical entrainment of sulfide melt can lead to extreme enrichment and higher total metal incorporation metal enrichment is enhanced if melt segregation is structurally driven only dissolved metal is incorporated if initial segregation is driven by buoyancy alone however once encapsulated within a larger volume of silicate melt immiscible globules of sulfide melt are physically carried by buoyantly rising magma gradual dissolution of entrained sulfide melt globules is expected as the silicate magma migrates from the lower crust this process may lead to significant variations in metal contents of silicate magmas above regions that underwent anatexis

tungsten deposits in the wolfram schist namaqualand south africa strata bound versus granite related genetic concepts several tungsten deposits from which ca 1 800 metric tons t of concentrate at 65 3 percent w03 was produced occur in the okiep copper district south africa which is part of a high temperature low pressure granulite terrane m 2 750 degrees 850 degrees 5 7 kbars the 1 2 to 1 0 ga high grade metamorphism of proterozoic supracrustal and older intrusive rocks is polymetamorphic and was accompanied by crustal melting resulting in formation of several early to postorogenic granitoid suites the w mo deposits are spatially and genetically associated with the 1 1 ga concordia granite a silica rich 70 76 wt peraluminous leucogranite with subalkaline monzonitic magma characteristics more fractionated cogenetic intrusions are interpreted as separated residual granitic liquids they are enriched in large ion lithophile k 2 o rb and some high field strength w nb etc elements mineralized pegmatites replacement orebodies strongly silicified granitic rocks and exo and endogranitic veins are distinguished ferberite and minor scheelite are associated with mo cu and bi sulfides and u th nb ree silicates oxides and phosphates metapelites wolfram schist hosting s 2 subparallel exogranitic veins are characterized by m 2 upper amphibolite lower granulite facies assemblages biotite sillimanite or garnet or cordierite plus quartz alkali feldspar and plagioclase schistose host rocks were derived from normal clastic sedimentary material slightly peraluminous lithologies probably from more pelitic kaolinite rich precursors the facts that late to postorogenic granites and the w mo deposits are deformed metamorphic ore textures e g garnet coronas around ore minerals are preserved and ore deposit specific hydrothermal low temperature alteration is absent suggest that the second m 3 late kibaran metamorphic overprint postdated mineralization oxygen isotope temperatures of ca 600 degrees to 660 degrees c for coexisting garnet and quartz from mineralized veins and host rocks indicate that high grade conditions were again reached during this late kibaran overprint retrograde greenschist facies metamorphism is of pan african age ca 560 590 ma and is unrelated to mineralizing processes the w mo deposits are interpreted as metamorphosed deep seated granitic ore deposits occurring in a polymetamorphic high grade terrane two high grade events of kibaran age m 2 and m 3 and a low grade event of pan african age m 4 are distinguished

spatiotemporal reconstruction of late mesozoic silicic large igneous province and related epithermal mineralization in south china insights from the zhilingtou volcanic intrusive complex silicic large igneous provinces slips generally reflect large scale melting of lower crustal materials and represent significant metal reservoirs the south china block coastal region scb cr slip hosts several large epithermal deposits to better understand these deposits we document the spatio temporal framework of the host slip across the scb cr using zircon u pb dating and geochemical and isotopic analysis we identify four stages of emplacement stage 1 felsophyre ca 149 ma shows a chemical affinity to highly fractionated i type granites stages 2 and 3 of low mg felsic volcanics ca 128 to 111 ma and stage 4 felsite ca 100 ma have higher ehf t and end t values than stage 1 felsophyre suggesting a significant contribution of newly underplated juvenile crust to the magma sources stage 4 diabase ca 101 ma was likely produced by melting of subduction metasomatized asthenospheric mantle together with reliable published data we build a new spatio temporal framework of volcanics and infer that the majority of the scb cr slip was related to the gradual northwestward subduction of the izanagi plate beneath south china in a continental arc setting during ca 170 to 110 ma and minor contribution was from the eastward retreat of the subducting slab in a back arc setting during ca 110 to 90 ma we conclude that the large scale epithermal mineralization was generated by melting of the metal rich thin 30 40 km newly underplated hydrous juvenile crust during the tectonic transition from arc to back arc settings

the relationship between track shortening and fission track age reduction in apatite combined influences of inherent instability annealing anisotropy length bias and system calibration abstract the relationship between reduced track density 0 and reduced mean confined track length l l 0 during annealing has been studied for both spontaneous and induced tracks in four apatite samples with different chemical composition compositional range and origin and with spontaneous tracks giving mean confined track lengths varying from 14 5 m down to 12 3 m in all four apatites induced tracks show a relationship between l l 0 and 0 composed of two regions at higher values the two appear to be equal while at lower values l l 0 is greater than 0 this can be understood qualitatively in terms of the anisotropy of annealing and the bias against revelation of short tracks data from three apatites of uniform composition show near identical relationships in a sample showing a range of apatite compositions the point of divergence from the 1 1 relationship is somewhat higher than in the uniform composition apatites because individual grains anneal at different rates and the presence of highly annealed grains affects the track density more strongly than the mean track length spontaneous tracks show similar relationships to those observed for induced tracks in each sample when the data are renormalised to allow for the natural annealing present in the spontaneous tracks previous studies which led to the idea of length reduction without density reduction for spontaneous tracks did not renormalise density data as well as length data thereby distorting the apparent relationship data for the multi compositional apatite sample where annealing has taken place in geological conditions also agrees with the laboratory annealing data for both spontaneous and induced tracks this consistency suggests that a single process is responsible in all three cases implying that a laboratory based description of annealing can be applied to geological conditions with confidence recognition that spontaneous tracks in apatite are commonly annealed suggests that in general the fission track age should be interpreted as a reflection of both the time over which tracks have been retained and the distribution of etchable track lengths since the latter is a manifestation of the thermal history the fission track age should be interpreted in similar terms

modeling dynamics and thermodynamics of icebergs in the barents sea from 1987 to 2005 1 a modeling study of iceberg drift characteristics in the barents and kara seas for the period 1987 2005 is presented maps of iceberg density and potential locations subject to grounding complement sparse existing oceanographic and aerial field survey campaigns the model suggests preferential pathways from the most important calving sources icebergs originating from franz josef land have the largest spread over the domain simulations confirm the previously observed seasonal cycle of the southernmost extent of the icebergs strong interannual variability of the iceberg extent with a weak decreasing trend occurs similar to the observed sea ice extent analysis of the atmospheric forcing reveals that years with anomalous northerly winds enhance the southward iceberg extension northerly winds also have a positive delayed impact on the iceberg extent they limit the inflow of atlantic water into the barents sea and therefore its heat content the following year increasing the mean age of icebergs and thus their potential extension finally the model is able to reproduce the observed extreme iceberg extension southeast of the barents sea in may 2003

recycling of metal fertilized lower continental crust origin of non arc au rich porphyry deposits at cratonic edges recent studies argue that subduction modified cu fertilized lithosphere controls the formation of porphyry cu deposits in orogenic belts however it is unclear if and how this fertilization process operates at cratonic edges where numerous large non arc au rich deposits form here we report data from lower crustal amphibolite and garnet amphibolite xenoliths hosted by cenozoic stocks that are genetically related to the beiya au rich porphyry deposits along the western margin of the yangtze craton china these xenoliths are thought to represent cumulates or residuals of neoproterozoic arc magmas ponding at the base of arc at the edge of the craton that subsequently underwent high pressure metamorphism ca 738 ma the amphibolite xenoliths are enriched in cu 383 445 ppm and au 7 12 ppb and a few garnet amphibolite xenoliths contain higher au 6 16 ppb with higher au cu ratios 2 10 4 to 8 10 4 than normal continental crust these data suggest that metal fertilization of the base of an old arc at the edge of the craton occurred in the neoproterozoic via subduction modification and has since been preserved the whole rock geochemical and zircon hf isotopic data indicate that melting of the neoproterozoic cu au fertilized low crustal cumulates at 40 30 ma provided the metal endowment for the au rich porphyry system at the cratonic edge we therefore suggest that the reactivated cratonic edges triggered by upwelling of asthenosphere have the potential to host significant au ore forming systems especially non arc au rich porphyry deposits

evaluating magmatic fertility of paleo tethyan granitoids in eastern tibet using apatite chemical composition and nd isotope abstract the paleo tethyan granitoids in eastern tibet are generally cu barren and only a few can generate porphyry cu deposits it is still unclear what magmatic differences cause these coeval granitoids to have different mineralization potentials in this study the major minor and trace element abundances and nd isotope in the apatites from four triassic granitoids from eastern tibet have been determined using epma la icp ms and la mc icp ms the following are the selected plutons the pulang pluton which is associated with the porphyry type cu deposit and the coeval cuojiaoma dongcuo and daocheng plutons three of which do not generate any cu mineralization our study reveals that ga ce s cl and cu in apatite are effective indicators for both magmatic oxidation states and the abundances of volatiles and ore forming metals the nd isotope of apatite can be used to trace the magma source according to the above chemical compositions of apatite and ce4 ce3 ratio of zircon the parental magma of the pulang pluton is identified to be more fertile for cu mineralization than those of the other three plutons i e cuojiaoma dongcuo and daocheng because it is more oxidized and richer in cu cl and s the aforementioned differences in magmatic physical and chemical conditions among the plutons investigated are ascribed to the different sources and natures of magmas as revealed by both the nd isotope and eu sr y and la yb values of apatite generally the results indicate that magmatic fertility mainly governs the cu mineralization potential of paleo tethyan granitoids in eastern tibet and that apatite is a robust probe for magmatic fertility

effect of alpha damage annealing on apatite u th he thermochronology recent data on he diffusion challenge the temperature sensitivity of apatite u th he thermochronology the damage induced by recoil of u and th decay series during emission of particles recoil damage has been proposed to modify he diffusion properties through time however we propose that annealing of these irradiation defects may be an important phenomenon and may be significant in case of slowly cooled or reheated basement rocks to test this hypothesis we developed a quantitative model including an explicit treatment of recoil damage annealing and their effect on he diffusion kinetics and calibrate it against literature data our model is based on two hypotheses 1 helium is in equilibrium between an apatite crystal and its defects and 2 alpha recoil damage annealing can be described analogously to fission track annealing this model has been embedded into a monte carlo simulation of helium production ejection diffusion and applied to data from the french massif central a complex slowly cooled terrain with burial reheating where the thermal history has been constrained by previous fission track ft data including ft length distributions u th he ages are close to the ft ages from the same samples and are generally reproducible among replicates but some samples present he age dispersion that is not correlated with crystal size our model reproduces the massif central data very well except for three samples where he ages are older than corresponding ft ages we show that annealing of irradiation damage has an important impact on retentivity of helium and that the he content he is only a rough approximation of the damage level in particular our results show that independence of he ages on crystal sizes in case of reheated samples is a clear indication of the higher he retentivity induced by recoil defects and that an explicit treatment of defect annealing is required for a correct interpretation of u th he ages in such a case more generally a correlation with the crystal size can bring information on the thermal path only if the age of defects well represented by the fission track age is available due to the dependence of the partial retention zone on damages conversely in case of rapid cooling or for samples having low u and th contents damage effects can be ignored without significant effects on he ages

uplift and denudation of the central alaska range a case study in the use of apatite fission track thermochronology to determine absolute uplift parameters apatite fission track thermochronology aftt on granitic samples collected in the central alaska range in conjunction with geologic constraints from basins to the north nenana basin and south cook inlet of the range is used to constrain the timing amount rate and pattern of surface uplift rock uplift and denudation since the late miocene the conversion from a thermal frame of reference apatite fission track data to an absolute frame of reference with respect to mean sea level which requires constraining the paleoland surface elevation the paleomean annual temperature and the paleogeothermal gradient is evaluated and shown to be viable in the context of an exhumed apatite partial annealing zone paz apatite ages at denali mount mckinley range from 16 ma near the summit 6 km elevation to 4 ma at 2 km elevation a distinctive break in slope in the apatite age profile at an elevation of 4 5 km also marked by a change in confined track length distributions marks the base of an exhumed apatite paz rock uplift and denudation are greatest at denali decreasing southward away from the mckinley strand of the denali fault system as shown by progressively older apatite ages 7 35 ma from a suite of samples along the kahiltna glacier a correlative decrease in topography occurs southward from the fault the central alaska range lies within an arc defined by the denali fault with the highest peaks including denali concentrated at the arc apex patterns of rock uplift and denudation within the central alaska range mimic topography between early and late miocene and possibly earlier the central alaska range was most likely an area of relative tectonic and thermal stability rock uplift denudation and mean surface uplift of the denali region began by the late miocene 5 6 ma being 8 5 km 5 7 km and 2 8 km respectively at average rates of 1 5 km m y 1 km m y and 0 5 km m y the amount of rock uplift denudation and surface uplift decreases to 3 km 2 km and 1 km at little switzerland some 45 km south of the denali fault we conclude that the topographic and rock uplift patterns of the central alaska range the shape and proximity of the mckinley strand of the denali fault to these patterns the timing of the onset of rock uplift and denudation at 5 6 ma and a significant change in relative plate motion between north america and the pacific plates circa 5 6 ma are all inherently related

a comparative study of detrital mineral and bedrock age elevation methods for estimating erosion rates traditional age elevation method using detrital and bedrock 40 ar 39 ar muscovite data sets from a single river catchment in the annapurna range nepal himalaya a nominal erosion rate estimate of 0 6 km myr for the 5 0 2 5 ma period was calculated from the bedrock data presented here for the first time this result agrees with the 0 7 km myr maximum estimate from the detrital data set which was derived from the dmt variant that emphasizes the range of single grain ages for a detrital sample in this case 11 2 5 ma however the other dmt variant which emphasizes the mean of the sample age distribution yields an erosion rate estimate of 2 3 km myr the simplest explanation for this discrepancy is that erosion rate increased significantly after 2 5 ma a scenario that is supported by apatite fission track data from the catchment

detrital thermochronology reveals major middle miocene exhumation of the eastern flank ofthe andes that predates the pampeanflat slab 33 33 5 s fil lossada ana clara consejo nacional de investigaciones cientificas y tecnicas oficina de coordinacion administrativa ciudad universitaria instituto de estudios andinos don pablo groeber universidad de buenos aires facultad de ciencias exactas y naturales instituto de estudios andinos don pablo groeber argentina universidad de buenos aires facultad de ciencias exactas y naturales departamento de geologia argentina

the role of strain localization in the segregation and ascent of anatectic melts namaqualand south africa granulite facies gneisses of the late proterozoic okiep copper district of the namaqua province in south africa preserve evidence of a range of anatectic melt features that reflect the initial stages of segregation and ascent of crustally derived magmas during high grade metamorphism these melt bodies include both in situ and sharply transgressive subvertical pipe like bodies that show vertical dimensions of several hundreds of metres and horizontal dimensions of tens to hundreds of metres migmatite bodies are spatially closely linked with narrow upright zones characterized by intense high strain fabrics locally referred to as steep structures they display a progressive textural development from diktyonitic textures in in situ bodies via schollen and raft textures to largely homogeneous intrusive granites that have migrated vertically for distances of several hundreds of metres or more the intimate association of the migmatite bodies with the steep structures reflects strain induced melt segregation facilitated by increased permeabilities in these ductile deformation zones and migration of melts into sites of strain incompatibility at the intersections between the regional subhorizontal gneissosity and the superimposed high strain zones subsequent melt migration was focused along the network of subvertical structural anisotropies provided by the steep structures melt migration was controlled by a combination of buoyancy shear enhanced melt compaction during ongoing deformation melt compaction due to the settling of wall rock fragments from higher stratigraphiclevels and subordinate brittle fracturing the unusual geometry of the steep structures and the intensely heterogeneous nature of the strain and the absence of similar strain features and voluminous melt bodies elsewhere in the granulite facies terrane suggest a positive feed back mechanism between melt generation and strain localization in steep structures the structural development of the migmatite bodies illustrates that the efficiency of melt segregation and migration in a mid crustal segment is dependent not only on the fertility of its lithologies but also on its deformational style

the aurora volcanic field california nevada oxygen fugacity constraints on the development of andesitic magma the aurora volcanic field located along the northeastern margin of mono lake in the western great basin has erupted a diverse suite of high k and shoshonitic lava types with 48 to 76 wt sio2 o ver the last 3 6 million years there is no correlation between the age and composition of the lavas three quarters of the volcanic field consists of evolved 4 wt mgo basaltic andesite and andesite lava cones and flows the majority of which contain sparse euhedral phenocrysts that are normally zoned there is no evidence of mixed hybrid magmas the average eruption rate over this time period was 200 m 3 ykm 2 yyear which is typical of con tinental arcs and an order of magnitude lower than that for the slow spreading mid atlantic ridge all of the au rora lavas display a trace element signature common to subduction related magmas as exemplified by baynb ratios between 52 and 151 pre eruptive water contents ranged from 1 5 wt in plagioclase rich two pyroxene andesites to 6 wt in a single hornblende lamprophyre and several biotite hornblende andesites calculated oxygen fugacities fall within 0 4 and 12 4 log units of the ni nio buffer the aurora potassic suite follows a classic calc alkaline trend in a plot of feo t ymgo vs sio 2 and displays linear decreasing trends in feo t and tio2 with sio2 content suggesting a prominent role for fe ti oxides during differentiation however develop ment of the calc alkaline trend through fractional crys tallization of titanomagnetite would have caused the residual liquid to become so depleted in ferric iron that its oxygen fugacity would have fallen several log units below that of the ni nio buffer nor can fractionation of hornblende be invoked since it has the same effect as titanomagnetite in depleting the residual liquid in ferric iron together with a thermal stability limit that is lower than the eruption temperatures of several andesites 1040 10808c derived from two pyroxene ther mometry unless some progressive oxidation process occurs fractionation of titanomagnetite or hornblende cannot explain a calc alkaline trend in which all erupted lavas have oxygen fugacites the ni nio buffer in con trast to fractional crystallization closed system equi librium crystallization will produce residual liquids with an oxygen fugacity that is similar to that of the initial melt however the eruption of nearly aphryic lavas ar gues against tapping from a magma chamber during equilibrium crystallization a process that requires crys tals to remain in contact with the liquid a preferred model involves the accumulation of basaltic magmas at the mantle crust interface which solidify and are later remelted during repeated intrusion of basalt as an end member case closed system equilibrium crystallization of a basalt followed by equilibrium partial melting of the gabbro will produce a calc alkaline evolved liquid namely high sio 2 and low feo t ymgo with a relative fo2 corrected for the effect of changing temperature that is similar to that of the initial basalt differentiation of the aurora magmas by repeated partial melting of previous underplates in the lower crust rather than by crystal fractionation in large stable magma chambers is consistent with the low eruption rate at the aurora vol canic field

platinum group elements in cu sulphide ores at carolusberg and east okiep namaqualand south africa cu sulphide ores at carolusberg and east okiep have cu ni ratios of up to 80 an order of magnitude higher than most magmatic sulphide ores elsewhere in contrast se s ratios 500 1700 10 6 and pge tenors up to 5 ppm of the sulphides are in the range of more typical magmatic sulphide ores the observed metal patterns may be explained by a process of monosulphide solid solution mss fractionation of a magmatic sulphide melt at depth but this model is currently considered unlikely due to the paucity of refractory ores in the district assimilation of cu rich country rocks during ascent of the koperberg magmas proved difficult to test with the available data but this provides no explanation for the common high grade metamorphic setting of similar ores elsewhere a restitic origin of the pyroxenites appears to explain many of the observed ore features and is presently favoured here desulphidization of a primary magmatic sulphide ore could not have yielded the observed metal patterns and is therefore considered to be of relatively minor importance in ore genesis

giant ore deposits formed by optimal alignments and combinations of geological processes giant ore deposits are priority targets for mining companies a review of the characteristics of several giant porphyry and epithermal deposits worldwide suggests that they formed from ordinary processes that were fortuitously operating at maximum efficiency

apatite u th he thermochronometry using a radiation damage accumulation and annealing model helium diffusion from apatite is a sensitive function of the volume fraction of radiation damage to the crystal a quantity that varies over the lifetime of the apatite using recently published laboratory data we develop and investigate a new kinetic model the radiation damage accumulation and annealing model rdaam that adopts the effective fission track density as a proxy for accumulated radiation damage this proxy incorporates creation of crystal damage proportional to production from u and th decay and the elimination of that damage governed by the kinetics of fission track annealing the rdaam is a version of the helium trapping model hetm shuster d l flowers r m and farley k a 2006 the influence of natural radiation damage on helium diffusion kinetics in apatite earth planet sci lett 249 148 161 calibrated by helium diffusion data in natural and partially annealed apatites the chief limitation of the hetm now addressed by rdaam is its use of he concentration as the radiation damage proxy for circumstances in which radiation damage and he are not accumulated and lost proportionately from the crystal by incorporating the rdaam into the hefty computer program we explore its implications for apatite u th he thermochronometry we show how u th he dates predicted from the model are sensitive to both effective u concentration eu and details of the temperature history the rdaam predicts an effective he closure temperature of 62 c for a 28 ppm eu apatite of 60 m radius that experienced a 10 c ma monotonic cooling rate this is 8 c lower than the 70 c effective closure temperature predicted using commonly assumed durango diffusion kinetics use of the rdaam is most important for accurate interpretation of u th he data for apatite suites that experienced moderate to slow monotonic cooling 1 0 1 c ma prolonged residence in the helium partial retention zone or a duration at temperatures appropriate for radiation damage accumulation followed by reheating and partial helium loss under common circumstances the rdaam predicts u th he dates that are older sometimes much older than corresponding fission track dates nonlinear positive correlations between apatite u th he date and eu in apatites subjected to the same temperature history are a diagnostic signature of the rdaam for many but not all thermal histories observed date eu correlations in four different localities can be explained with the rdaam using geologically reasonable thermal histories consistent with independent fission track datasets the existence of date eu correlations not only supports a radiation damage based kinetic model but can significantly limit the range of acceptable time temperature paths that account for the data in contrast these datasets are inexplicable using the durango diffusion model the rdaam helps reconcile enigmatic data in which apatite u th he dates are older than expected using the durango model when compared with thermal histories based on apatite fission track data or other geological constraints it also has the potential to explain at least some cases in which u th he dates are actually older than the corresponding fission track dates

zoning of mineralization in hypogene porphyry copper deposits insight from comb microfractures within quartz chalcopyrite veins in the hongshan porphyry cu deposit western yunnan sw china abstract the origin of zonal mineralization in porphyry copper deposit is important for understanding the mineralization processes we propose a new modified orthomagmatic genetic model for mineralization zoning in hypogene porphyry copper deposits this new model is based on the features and formation mechanism of comb microfractures in quartz chalcopyrite veins within pyrite vein from the hongshan porphyry copper deposit in zhongdian county western yunnan province sw china the main evidence for this model is volume expansion related to crystallization of chalcopyrite magnetite and k metasomatism in the deposit comb microfractures are well developed in quartz chalcopyrite veins and are present as comb quartz veinlets consisting of a zone of central longitudinal quartz overprinted by laterally grown quartz combs chalcopyrite fragments lie perpendicular to the central quartz veinlet and were dismembered by the quartz combs the combed microfractures are typical tensional hydrofractures the formation of the comb microfractures is related to volume expansion that was induced by crystallization of chalcopyrite from a chalcopyrite melt that resulted in the subsequent increase of volumetric pressure in the confined residual silica melt the formation mechanism of the comb microfractures including volume expansion induced by crystallization increases volumetric pressure hydrofracturing and fluid expulsion and was the most likely process for zoning of minerals in hypogene porphyry copper deposits fabrics in the veins and veinlets are consistent with overpressuring and injection and are common structures that are directly related to volumetric pressure and crystallization of chalcopyrite and magnetite and k metasomatism in hypogene porphyry copper deposits the volume expansion ratio of chalcopyrite mineral to melt and that of magnetite mineral to melt are approximately 19 vol and 20 vol respectively the volume expansion rate of a monomolecular lattice is 8 vol for orthoclase replacing plagioclase we suggest that zoning of mineralization in hypogene porphyry copper deposits is mainly related to hydrofracturing migration and distribution of ore forming fluids including 1 the enclosure and formation of a mush core 2 concentration of ore forming fluids in the orthoclase shell 3 k metasomatism and pressure building 4 hydrofracturing and migration of ore forming fluids and 5 prior crystallization of magnetite and chalcopyrite that will expel residual fluids upwards and outwards due to the change in volumetric pressure

natural age dispersion arising from the analysis of broken crystals part i theoretical basis and implications for the apatite u th he thermochronometer abstract over the last decade major progress has been made in developing both the theoretical and practical aspects of apatite u th he thermochronometry and it is now standard practice and generally seen as best practice to analyse single grain aliquots these individual prismatic crystals are often broken and are fragments of larger crystals that have broken during mineral separation along the weak basal cleavage in apatite this is clearly indicated by the common occurrence of only 1 or no clear crystal terminations present on separated apatite grains and evidence of freshly broken ends when grains are viewed using a scanning electron microscope this matters because if the 4 he distribution within the whole grain is not homogeneous because of partial loss due to thermal diffusion for example then the fragments will all yield ages different from each other and from the whole grain age here we use a numerical model with a finite cylinder geometry to approximate 4 he ingrowth and thermal diffusion within hexagonal prismatic apatite crystals this is used to quantify the amount and patterns of inherent natural age dispersion that arises from analysing broken crystals a series of systematic numerical experiments were conducted to explore and quantify the pattern and behaviour of this source of dispersion using a set of 5 simple thermal histories that represent a range of plausible geological scenarios in addition some more complex numerical experiments were run to investigate the pattern and behaviour of grain dispersion seen in several real data sets the results indicate that natural dispersion of a set of single fragment ages defined as the range divided by the mean arising from fragmentation alone varies from c 7 even for rapid c 10 c ma monotonic cooling to over 50 for protracted complex histories that cause significant diffusional loss of 4 he the magnitude of dispersion arising from fragmentation scales with the grain cylindrical radius and is of a similar magnitude to dispersion expected from differences in absolute grain size alone spherical equivalent radii of 40 150 m this source of dispersion is significant compared with typical analytical uncertainties on individual grain analyses c 6 and standard deviations on multiple grain analyses from a single sample c 10 20 where there is a significant difference in the u and th concentration of individual grains eu the effect of radiation damage accumulation on 4 he diffusivity assessed using the rdaam model of flowers et al 2009 is the primary cause of dispersion for samples that have experienced a protracted thermal history and can cause dispersion in excess of 100 for realistic ranges of eu concentration i e 5 100 ppm expected natural dispersion arising from the combined effects of reasonable variations in grain size radii 40 125 m eu concentration 5 150 ppm and fragmentation would typically exceed 100 for complex thermal histories in addition to adding a significant component of natural dispersion to analyses the effect of fragmentation also acts to decouple and corrupt expected correlations between grain ages and absolute grain size and to a lesser extent between grain age and effective uranium concentration eu considering fragmentation explicitly as a source of dispersion and analysing how the different sources of natural dispersion all interact with each other provides a quantitative framework for understanding patterns of dispersion that otherwise appear chaotic an important outcome of these numerical experiments is that they demonstrate that the pattern of age dispersion arising from fragmentation mimics the pattern of 4 he distribution within the whole grains thus providing an important source of information about the thermal history of the sample we suggest that if the primary focus of a study is to extract the thermal history information from u th he analyses then sampling and analytical strategies should aim to maximise the natural dispersion of grain ages not minimise it and should aim to analyse circa 20 30 grains from each sample the key observations and conclusions drawn here are directly applicable to other thermochronometers such as the apatite rutile and titanite u pb systems where the diffusion domain is approximated by the physical grain size

constraints on the formation of the baogutu reduced porphyry copper deposit west junggar nw china assessing the role of mafic magmas in mineralization abstract the baogutu porphyry copper deposit is a typically reduced porphyry copper deposit rpcd characterized by reduced calc alkaline felsic shallow intrusions a newly discovered gabbro which contains 1182 1260 ppm cu provides an ideal window to reveal the genesis and formation of the baogutu rpcd a combined study of the petrological geochronological geochemical and isotopic characteristics of the cu bearing gabbro and granitoids in the baogutu rpcd has been completed the laser ablation inductively coupled plasma mass spectrometry la icp ms u pb dating of zircons from a gabbro diorite and porphyritic diorite are 318 2 0 8 ma mswd 0 01 n 16 315 8 1 0 ma mswd 1 50 n 16 and 314 9 0 6 ma mswd 0 12 n 20 respectively the geochemical and isotopic characteristics of the gabbro diorite and porphyritic diorite at baogutu rpcd are all metaluminous calc alkaline series rocks with depletion in nb ta and ti and enrichment in light rare earth elements lree and large ion lithophile elements consistent with an arc related setting the relatively high nd and hf isotopes end t 6 9 to 7 5 ehf t 8 8 to 14 4 and wide variations of major and trace elements suggest that the gabbro and diorite in the baogutu rpcd were all derived from a mixture of melts of metasomatized mantle wedge the hydrous slab and old crustally derived materials the high mg andesites hma sanukite features high mg cr and ni content of the gabbro suggest it was derived mainly from a metasomatized mantle hydrous slab derived melt source with only slightly contamination by the old crustal materials whereas adakitic features of the diorite high al2o3 and sr contents and sr y ratios suggest a greater role the melting of residual subducted oceanic crust with juvenile mantle materials the porphyritic diorite which inherited the geochemical characteristics of diorite was probably derived from a similar parental magma but the low end t of 1 4 old t2dm nd age of 961 ma and enrichment in zr and hf suggest a greater degree of crustal contamination the high content of cu and high oxidation state of the gabbro is consisted with it having formed early from an unusually cu rich parental magma this magma would have provided abundant metal and sulfides which would have been mobilized and reconcentrated by later ore bearing fluids linked to the intermediate to acid porphyry intrusions in the baogutu rpcd

modeling giant iceberg drift under the influence of sea ice in the weddell sea antarctica the drift trajectory of giant iceberg c 7 traversing the weddell sea antarctica for 2 years was successfully simulated application of the classical driving forces like wind and ocean currents resulted in a significant discrepancy between modeled and observed iceberg velocities in the western weddell sea the most realistic drift pattern in space and time was achieved by adding a sea ice force which represents the ability of a dense sea ice cover 90 to lock in icebergs and collect the momentum of the wind over an area much larger than the area of the iceberg proper this process was parameterized using a sea ice strength p which depends on sea ice concentration and thickness both having highest values in winter and in the western weddell sea which is covered with multi year sea ice as a consequence of the sensitivity to sea ice the timing of the iceberg drift becomes important revealing the region off brunt ice shelf eastern weddell sea as a location where bergs either continue westward with the coastal current or follow a southern branch onto the shallow continental shelf

magmatic sulfides and au cu ratios in porphyry deposits an experimental study of copper and gold partitioning at 850 c 100 mpa in a haplogranitic melt pyrrhotite intermediate solid solution gold metal assemblage at gas saturation abstract the behavior of copper and gold in the phase assemblage pyrrhotite po intermediate solid solution iss haplogranitic melt gold metal capsule at 850 c 100 mpa and gas saturation ah2o 0 9 has been investigated the results are presented as nernst partition coefficients the partition coefficient dcupo melt 2 6 0 3 103 1 was determined for po and melt in equilibrium with an iss of composition cu 19 1 fe 30 1 s 51 1 2 for gold the partition coefficients are dauiss melt 5 7 2 2 103 1 between iss and melt and daupo melt 140 40 1 between po and melt these imply dauiss po 42 9 1 between iss and po the oxygen fugacity for the experiments log f o 2 13 2 0 3 1 was determined by using the hydrogen sensor technique the sulfur fugacity log f s 2 1 0 0 7 1 was calculated from the composition of po in our experiments melts at iss saturation have cu fe by weight of ca 1 100 the results indicate that crystallization of iss may deplete a melt in gold and crystallization of po may deplete a melt in copper however a melt saturated with iss at a given bulk composition temperature pressure oxygen and sulfur fugacity and feo concentration will have a fixed concentration of cu preventing strong depletion of the melt in cu until iss is fractionated from the melt or changes in environmental conditions destabilize iss a thermodynamic model for the partitioning of cu and au between po and melt in terms of oxygen and sulfur fugacity indicates that dcupo melt and daupo melt may increase greatly with increasing sulfur fugacity and decreasing oxygen fugacity within the po stability field the model also suggests that destabilization of both iss and po relative to magnetite due to changes in oxygen and sulfur fugacities can result in the release of cu and au from the sulfides to the melt

geology fluid inclusion and isotope constraints on ore genesis of the post collisional dabu porphyry cu mo deposit southern tibet abstract the dabu cu mo porphyry deposit is situated in the southern part of the lhasa terrane within the post collisional gangdese porphyry copper belt gpcb it is one of several deposits that include the qulong and zhunuo porphyry deposits the processes responsible for ore formation in the dabu deposit can be divided into three stages of veining stage i quartz k feldspar biotite chalcopyrite pyrite stage ii quartz molybdenite pyrite chalcopyrite and stage iii quartz pyrite molybdenite three types of fluid inclusions fis are present liquid rich two phase l type vapor rich two phase v type and solid bearing multi phase s type inclusions the homogenization temperatures for the fis from stages i to iii are in the ranges of 272 475 c 244 486 c and 299 399 c and their salinities vary from 2 1 to 49 1 1 1 to 55 8 and 2 9 to 18 0 wt nacl equiv respectively the coexistence of s type v type and l type fis in quartz of stage i and ii with similar homogenization temperatures but contrasting salinities indicate that fluid boiling is the major factor controlling metal precipitation in the dabu deposit the ore forming fluids of this deposit are characterized by high temperature and high salinity and they belong to a h2o nacl magmatic hydrothermal system the h o s pb isotopic compositions indicate that the ore metals and fluids came primarily from a magmatic source linked to miocene intrusions characterized by high sr y ratios similar to other porphyry deposits in the gpcb the fluids forming the dabu deposit were rich in na and cl derived from metamorphic dehydration of subducted oceanic slab through which nacl brine or seawater had percolated the inheritance of ancient subduction associated arc chemistry without shallow level crustal assimilation and or input of the meteoric water was responsible for the generation of fertile magma as well as co2 poor and halite bearing fis associated with post collisional porphyry deposits the estimated mineralization depths of qulong dabu and zhunuo deposits are 1 6 4 3 km 0 5 3 4 km and 0 2 3 0 km respectively displaying a gradual decrease from eastern to western gangdese deep ore forming processes accounted for the generation of giant sized qulong deposit because the exsolution of aqueous fluids with large fraction of water and chlorine in deep or high pressure systems can extract more copper from melts than those formed in shallow systems however the formation of small sized dabu deposit can be explained by a single magmatic event without additional replenishment of s metal or thermal energy in addition the ore forming conditions of porphyry cu mo deposits in gpcb are comparable to those of porphyry cu au mo deposits formed in oceanic subduction related continental or island arcs but differ from those of porphyry mo deposit formed in the dabie qinling collisional orogens the depth of formation of the mineralization and features of primary magma source are two major controls on the metal types and ore fluid compositions of these porphyry deposits

apatite u th he signal of large magnitude accelerated glacial erosion southwest british columbia alpine glaciers are efficient agents of erosion and capable of significantly modifying topography despite recent advances in theoretical and field studies that quantify glacial erosion processes few studies have documented glacial erosion rates over long 10 6 yr or large more than tens of kilometers scales we use apatite u th he ahe and apatite fission track aft cooling ages to address the late miocene to holocene erosion history across two 60 km long transects of the heavily glaciated southern coast mountains british columbia observed ahe cooling ages from equal elevation samples range between 1 5 and 8 ma and suggest that thick alpine glaciers resulted in a 16 km shift of the highest point in the topography in the past 1 5 4 0 m y we evaluated temporal and spatial variations in erosion rates using a three dimensional thermal kinematic model that predicted ahe and aft ages at the surface for different erosion histories comparison of model predicted and observed cooling ages suggests an increase in erosion rates of as much as 300 over the past 1 5 7 m y coincident with the onset of glaciation of this range

velocity field of the western entrance to the barents sea 1 by the use of 4 year long records from moored current meters between 71 30 n and 73 30 n of the western entrance to the barents sea the velocity field of the atlantic inflow is examined the mean velocity field shows the atlantic inflow as a wide core that occupies most of this section but the general picture is a velocity field that is dominated by large and frequent fluctuations the key parameter that to a large degree determines the spatial distribution of the velocity field is sea level changes within the section that are induced by the local wind field the main process is the ekman transport through its ability to accumulate water thereby creating strong gradients of barotropic pressure and associated currents southwesterly winds along the norwegian coast and southeasterly winds farther north will in general create wide inflows while northerly winds will result in wide outflows these flow regimes may be persistent for up to 2 3 weeks and are related to the relative strength and lateral extension of the icelandic low and the arctic high although the alignment of the local isobars must be considered in order to be able to describe the details of the flow

the magnetite crisis in the evolution of arc related magmas and the initial concentration of au ag and cu the association of large au cu ag ore deposits with convergent margins is commonly attributed to the higher content of chalcophile elements in the parental magmas generated at subduction zones compared with mid ocean ridges we present new geochemical data for arc like relatively oxidized mantle derived basalt to rhyolite magmas from the pual ridge and vicinity eastern manus basin which show that the initial abundances of base and precious metals in the parental basalts are similar to those of mid ocean ridge basalt morb the contents of au cu and ag are built up in the evolving pual ridge liquids to levels considerably in excess of those in morb because unlike morb they are not saturated in a sulfide phase which is a consequence of their being more oxidized than morb the behaviour of s during the evolution of the pual ridge magmas is obscured by late stage so2 loss during eruption but we show that it may be inferred by using se as a proxy because this element follows s closely during magmatic evolution except it is not lost during low pressure near sea floor degassing the onset of magnetite fractionation at 60 wt sio2 and an mg number of 40 is accompanied by an abrupt decrease in the contents of au cu and ag previously attributed to separation of cu au rich fluid which is also shown by se implying that magnetite fractionation triggers sulfide saturation petrological modelling reveals that the amount of magnetite fractionation involved is sufficient to convert most of the s originally dissolved in the magma as sulfate so42 to sulfide s2 triggering saturation in a cu rich sulfide phase tentatively identified as bornite cu5fes4 this sulfide phase sequesters au and ag elements with the same valence as cu in sulfides but not other potentially chalcophile elements such as ni re and pt which suggests that the phase is crystalline rather than an immiscible sulfide melt the relatively high contents of cu and au characteristic of evolved convergent margin magmas requires no enrichment from subducted material instead the association of major cu au deposits with convergent margin magmatism results specifically from the process of magmatic evolution under oxidizing conditions this same property also leads to early magnetite fractionation triggering the abrupt saturation in the cu rich sulfide hence the easily recognizable trend of magmatic evolution under oxidizing conditions i e the sharp drop in chalcophile element concentrations may be an exploration guide to economic au ag cu provinces or a crucial pre enrichment step in the formation of such deposits the decrease in p2o5 and sr at the same stage in the fractionation sequence 60 wt sio2 indicates that saturation in apatite is concomitant with magnetite sulfide saturation in the eastern manus basin

episodic rapid uplift in the himalaya revealed by 40ar 39ar analysis of detrital k feldspar and muscovite bengal fan detrital k feldspar and muscovite samples from ocean drilling program leg 116 cores have been dated by the sup 40 ar sup 39 ar technique and have depositional ages from 0 to 18 ma from 4 to 13 individual k feldspars and 1 to 12 individual muscovites have been dated from 7 stratigraphic levels in every level at least one k feldspar and one muscovite yielded a minimum age identical within uncertainty to the age of deposition these results indicate that a significant portion of the material in the bengal fan is first cycle detritus derived from the himalaya therefore the substantial amount of sediment deposited in the distal fan in early to middle miocene time can be ascribed to a significant pulse of uplift and erosion in the collision zone at this time moreover these data indicate that throughout the neogene some part of the himalayan orogen was undergoing rapid erosion 1 to 10 mm yr this erosion must have been less than or equal to uplift relative to sea level the lack of granulite facies rocks in the eastern himalaya and tibetan plateau suggests to us that very rapid uplift must have been distributed in brief pulses over different parts of the mountain belt these datamore are incompatible with tectonic models in which the himalaya and tibetan plateau are uplifted either uniformly over the past 40 m y or mostly within the past 2 to 5 m y less

form and flow of the academy of sciences ice cap severnaya zemlya russian high arctic 1 the 5 575 km2 academy of sciences ice cap is the largest in the russian arctic a 100 mhz airborne radar digital landsat imagery and satellite synthetic aperture radar sar interferometry are used to investigate its form and flow including the proportion of mass lost through iceberg calving the ice cap was covered by a 10 km spaced grid of radar flight paths and the central portion was covered by a grid at 5 km intervals a total of 1 657 km of radar data digital elevation models dems of ice surface elevation ice thickness and bed elevation data sets were produced cell size 500 m the dems were used in the selection of a deep ice core drill site total ice cap volume is 2 184 km3 5 5 mm sea level equivalent the ice cap has a single dome reaching 749 m maximum ice thickness is 819 m about 200 km or 42 of the ice margin is marine about 50 of the ice cap bed is below sea level the central divide of the ice cap and several major drainage basins in the south and east of the ice cap and of up to 975 km2 are delimited from satellite imagery there is no evidence of past surge activity on the ice cap sar interferometric fringes and phase unwrapped velocities for the whole ice cap indicate slow flow in the interior and much of the margin punctuated by four fast flowing features with lateral shear zones and maximum velocity of 140 m yr 1 these ice streams extend back into the slower moving ice to within 5 10 km of the ice cap crest they have lengths of 17 37 km and widths of 4 8 km mass flux from these ice streams is 0 54 km3 yr 1 tabular icebergs up to 1 7 km long are produced total iceberg flux from the ice cap is 0 65 km3 yr 1 and probably represents 40 of the overall mass loss with the remainder coming from surface melting driving stresses are generally lowest 40 kpa close to the ice cap divides and in several of the ice streams ice stream motion is likely to include a significant basal component and may involve deformable marine sediments

inversion of thermochronological age elevation profiles to extract independent estimates of denudation and relief history i theory and conceptual model abstract we determine to what extent low temperature thermochronology data in particular from age elevation profiles provide independent and quantitative estimates on denudation rates and relief development thermochronological age elevation profiles have been widely used to infer exhumation histories however their interpretation has remained inherently one dimensional neglecting potential effects of lateral offsets between samples furthermore the potential effects of transient topography on crustal isotherms and consequently on thermochronological data have not yet been addressed in detail we investigate this problem with the aim of deriving independent estimates of both denudation rates and relief history from low temperature thermochronometers measuring the relative uncertainties on these parameters and finally constraining the timing of potential variations in denudation rate and or relief development we adopt a non linear inversion method combining the three dimensional thermal kinematic model pecube which predicts thermal histories and thermochronological ages from an input denudation and relief history with an inversion scheme based on the neighbourhood algorithm we use synthetic data predicted from imposed denudation and relief histories and quantitatively assess the resolution of thermochronological data collected along an age elevation profile our results show that apatite fission track aft ages alone do not provide sufficient quantitative information to independently constrain denudation and relief histories multiple thermochronometers apatite u th he ahe ages and or track length measurements combined with aft ages are generally successful in constraining denudation rates and timing of rate changes the optimum combination of thermochronometers varying with the input scenario relief change or varying denudation rates however relief changes can only be quantified and precisely constrained from thermochronological age elevation profiles if the rate of relief growth is at least 2 3 times higher than the background denudation rate this limited resolution is due to the depth of the closure isotherm between 70 and 110 c for the aft and ahe systems which only partly record topographic change new thermochronometers such as 4 he 3 he or osl that are sensitive to lower temperatures may be the key for resolving this issue

magmatic process recorded in plagioclase at the baogutu reduced porphyry cu deposit western junggar nw china abstract despite the fact that porphyry cu deposits contain large amounts of cu in one or more small stocks few studies have discussed evidence for significant magma recharge in porphyry cu deposits a systematic elemental and sr isotopic study of plagioclase crystals from mineralized diorite and granodiorite porphyry constrains the processes of crystallization and magma recharge at the baogutu reduced porphyry copper deposit western junggar nw china large compositional changes in an 12 24 mol are observed along with strong positive correlations between an and feo significant resorption textures are also preserved in plagioclase crystals as well as repeated oscillatory zoning in an and feo and complex sr isotope variations three types of crystals with different core to rim sr isotope variations are recognized type i crystals have core to rim increases in 87sr 86sr i that could be explained by diffusion for example sr isotope variations recorded in bck2 1 2 crystal could be generated by diffusion with simulated maximum crystal residence times of 100 500 years with the proximate value of 300 years type ii crystals with different variation trends in 87sr 86sr i on opposite sides of the core could be produced either by multi stage crystallization or by analytical uncertainty whereas type iii crystals with complex core to rim variations in 87sr 86sr i may record repeated magma recharge events all these results suggest repeated recharging of the magma chamber by hotter more mafic and less radiogenic sr isotope melts therefore more mafic melt injection recorded in plagioclase profiles may provide significant metal contributions to the magma chamber which ultimately results in cu mineralization at the baogutu reduced porphyry copper deposit

downstream evolution of the thermochronologic age signal in the brahmaputra catchment eastern himalaya implications for the detrital record of erosion the namche barwa massif in the eastern himalayan syntaxis is characterized by very rapid exhumation and provides a significant proportion of the sediment flux carried by the brahmaputra river we present new detrital zircon fission track zft and muscovite 40ar 39ar mar data from modern sediments of rivers draining the eastern himalaya the cooling age populations for both thermochronometers contain a characteristic 2 ma signature related to the rapid exhumation of namche barwa which can be traced hundreds of kilometers downstream from their source into the brahmaputra foreland despite dilution from downstream tributary catchments to estimate present day erosion in the catchments we apply a mixing model based on linear inversion of the binned age distributions the inversion predicts relative erosion rates in the syntaxial region that are an order of magnitude higher than those in upstream catchments and about twice as high as those in the southern himalayan catchments consistent to first order with previous estimates of erosion rate patterns in the eastern himalaya a comparison of the observed downstream evolution of age distributions with a sediment flux model suggests that the zft signal can be explained by dilution from himalayan tributaries only whereas the mar signal is also affected by selective sequestering possibly through winnowing of micas as they are transported downstream nevertheless thermochronological ages 2 ma provide a diagnostic signal of syntaxial exhumation in the sedimentary record of the eastern himalaya this study suggests the most robust signal to be recorded in the most proximal deposits with respect to the syntaxis

can economic porphyry copper mineralization be generated by a typical calc alkaline melt numerical simulation of chlorine and copper partitioning between a crystallizing melt and exsolving aqueous fluids indicates that typical calc alkaline magmas contain sufficient copper chlorine and water to produce economic porphyry copper mineralization neither an elevated copper content in the magma nor an additional large volume of magma are required to provide metals or volatiles the most important variables that determine the volume of melt necessary to produce sufficient copper are the degree of compatible behavior displayed by copper the ratio of initial water in the melt to the water saturation level and the initial chlorine water ratio of the melt the absolute values for initial water in the melt and water content at saturation are relatively unimportant in determining the required melt volume the bulk salinity of the exsolved fluid may vary from 2 0 wt nacl to saturation levels 84 wt nacl at 700 c indicating that boiling is not necessary to produce high salinity brines at appropriate p t xnacl conditions the magmatic aqueous fluid separates into a saline liquid which transports most of the copper and a low salinity vapor the salinities of the two immiscible phases are governed by the p t conditions while the bulk fluid salinity determines the mass fractions of liquid and vapor formed pressure quenching causes rapid crystallization of the aplitic groundmass in porphyritic rocks associated with copper mineralization and significantly reduces the amount of chlorine and copper partitioning to the aqueous fluid this results in abrupt and possibly large reductions in fluid salinity and causes copper to become concentrated in the melt as copper is transported from the melt by the earliest exsolving fluids in deep 2 0 kbar systems and by late exsolving fluids in shallow 0 5 kbar systems the relative timing of pressure quenching aplite formation and fluid transport of copper from the melt can vary significantly in systems produced under different confining pressures model results incorporating petrologic constraints determined for yerington nevada are in good agreement with observed mineralization

low temperature thermochronology and modeling strategies for multiple samples 1 vertical profiles abstract low temperature thermochronology is a powerful method for constraining the time temperature history of rocks and provides constraints on denudation chronologies landscape evolution and tectonic history of geological terrains we present a strategy for modelling thermal histories constrained by thermochronological data from multiple samples in vertical profiles the thermal history is specified to be similar in form for each sample and we include extra parameters to determine the offset temperature between the uppermost and lowermost samples we combine the likelihood from each sample to produce a joint likelihood for all samples together and using initially stochastic search then directed search methods we try to identify a maximum likelihood solution we also implement a test bayesian information criterion which allows us to assess whether we have overparameterised the thermal history and potentially introduced unwarranted complexity this test allows us to simplify the thermal history model without compromising the acceptable data fit subsequently we use a sampling approach to determine the uncertainty or resolution of the thermal history markov chain monte carlo is straightforward to implement and is used to produce joint and marginal probability distributions and from these we can infer credible intervals on the model parameters we demonstrate that combining the samples is preferable in that the final model is easier to interpret and generally has smaller uncertainties than the case where we model all samples independently we consider both synthetic and real data examples focusing on apatite fission track analysis but the general approach is applicable to other analytical methods such as u th he dating and 40ar 39ar analysis and in principle it is straightforward to combine these different data types into one joint thermal history model

separation of molybdenum and copper in porphyry deposits the roles of sulfur redox and ph in ore mineral deposition at bingham canyon the giant bingham canyon porphyry cu mo au deposit utah is associated with eocene subvolcanic intrusions it shows a distinct metal zonation above a barren core with dominantly shallow cu au mineralization cu stage following the early quartz monzonite porphyry qmp intrusion and spatially deeper mo mineralization mo stage occurring in a separate vein set exclusively after a late quartz latite porphyry qlp intrusion that truncates earlier cu au veins to understand this metal separation and the geochemical process of molybdenite mineralization we investigated fluid inclusions by microthermometry raman spectroscopy and laser ablation inductively couple plasma mass spectrometry la icp ms microanalysis in low and high grade quartz veins of both mineralization stages in deep low grade quartz veins interpreted to represent the root zone of the cu stage we found high concentrations of cu s and mo in the fluid inclusions whereas in low grade mo stage veins we found lower cu but similar concentrations of s and mo compared to the inferred input fluids to the cu stage sulfur and copper concentrations were similar in intermediate density type fluid inclusions in deep low grade cu stage samples whereas intermediate density type inclusions in low grade mo stage veins have s contents that exceed their cu contents in high grade mo stage vein we found large variations of mo concentrations in coexisting brine and vapor inclusions compared to the p t conditions of the cu precipitation stage 90 260 bars and 320 430 c the mo precipitating fluids were trapped at higher pressures and temperatures of 140 to 710 bars and 360 to 580 c mass balance calculation based on the compositions of intermediate density inclusions and brine vapor assemblages interpreted to be derived by phase separation during decompression of the ascending single phase intermediate density fluid indicate that the mass of vapor phase exceeded that of brine by about 9 1 in both mineralization stages combining this mass balance with the analyzed vapor brine partitioning data indicates that more than 70 of mo and s by mass in the deposit were deposited from the vapor phase earlier cu au deposition was similarly dominated by vapor but recently published data about postentrapment cu diffusion in and out of fluid inclusions cast doubt on previous quantifications suggesting that almost none of the copper was deposited by brine mo is less likely to be modified by selective diffusion and high mo contents max 0 0054 mo na in intermediate density 380 g g mo in brine in the hydrothermal fluids were maintained from the early cu stage to the late mo stage this indicates that mo concentration was not the decisive factor for separate precipitation of late mo ore at bingham canyon instead the metal separation may be explained by a reduction in redox potential and an increase in acidity in the evolving source region of the fluids i e a large subvolcanic magma reservoir this is indicated by the stoichiometry of chalcopyrite and molybdenite precipitation reactions a tentative difference in the fe mn ratio in fluids of both veining stages incipient muscovite alteration along high temperature molybdenite veins and an increasing tendency for mo to fractionate from brine to vapor we suggest that the early cu stage fluids were slightly more oxidized and neutral allowing cu fe sulfides to saturate first while molybdenite saturation was suppressed and mo was lost from the early ore stage by contrast during the later mo stage the fluids were more reduced and acidic thereby allowing selective saturation of molybdenite as the first precipitating sulfide in the cooling and expanding two phase fluid consistent with textural observations this interpretation may imply more generally that small differences in redox potential and acid base balance of the magmatic source of porphyry mineralizing systems may be decisive in the temporal and spatial separation of the two metals

triggers for the formation of porphyry ore deposits in magmatic arcs porphyry ore deposits supply much of the copper molybdenum gold and silver used by humans a review of the main processes that trigger porphyry ore formation suggests that sulphide saturation of the magmas that supply the metals could be the overriding mechanism that helps control the temporal and spatial distribution of the ore deposits

sulfide mineral in intrusive and volcanic rocks of the bingham park city belt utah we report here the results of a reconnaissance study of sulfide inclusions in some intrusive and volcanic rocks from the bingham park city belt in central utah the study was undertaken to determine whether primary sulfides were preserved in these rocks and if so to assess their role in the geochemistry of copper in the magmas numerous samples were studied from the alta clayton peak and flagstaff stocks and a few samples were also studied from the little cottonwood last chance and soldier canyon stocks as well as from the phoenix dike and the keetley volcanics our results show that sulfides are present in unaltered intrusive and volcanic rocks although most of these inclusions lack hematite and pyrite that are typical products of degassing at least some inclusions appear to have been modified possibly by reaction with enclosing iron bearing host minerals measurements of the sizes of inclusions suggest that sulfides contain only 20 to 50 percent of the copper in the rock whereas sulfide selective analyses suggest that all of the copper in the rock is hosted by sulfides despite this uncertainty compositions of sulfides vary systematically from unit to unit the distribution of sulfide inclusions in different minerals suggests that mafic intrusions were saturated with sulfur over a longer period of time during their crystallization history than were felsic intrusions although there are exceptions chalcopyrite is most abundant in intrusions emplaced at deeper levels bornite is found in intrusions emplaced at intermediate levels and pyrrhotite is found in the shallowest intrusions and volcanic rocks finally apparently unaltered samples of the last chance soldiers canyon and phoenix bodies contain talnakhite a copper bearing sulfide mineral that was not observed in the other intrusive rocks in view of the close association of the last chance and phoenix bodies with the bingham porphyry copper deposit this relationship could be of use in evaluation of the mineral potential of felsic intrusive rocks