u pb evidence for abitibi gold mineralization postdating greenstone magmatism and metamorphism two widely held theories for the origin of archaean lode gold deposits the magmatic1 and metamorphic replacement2 models predict that gold emplacement should have occurred near the end of late syn kinematic greenstone magmatism here we report that at the camflo mine in the abitibi subprovince of canada u pb ages for rutile and titanite in auriferous alteration 2 625 7 myr are much younger than the age of the host quartz syenite 2 680 4 myr and ages for regional magmatism 2 670 myr 3 and metamorphism 2 680 myr 4 mineral associations and pb pb systematics indicate that the hydrothermal minerals record crystallization ages that are probably coeval with the gold mineralization these ages and others from the abitibi subprovince4 6 rule out a direct connection between gold and magmatism or metamorphism associated with regional folding of the greenstone belt they are broadly contemporaneous with metamorphism at deep crustal levels7 and may record late devolatilization of the lower crust

geochronological constrains on the timing of magmatism deformation and mineralization at the karouni orogenic gold deposit guyana south america abstract the karouni deposit is located in central guyana 35 km to the w of the former producing 5 moz omai mine and is interpreted to be an orogenic gold deposit it is hosted in rhyacian aged 2 2 to 2 1 ga volcano sedimentary and intrusive rocks metamorphosed to greenschist facies detailed structural and crosscutting relationships coupled with robust new u pb geochronology on intermediate to felsic intrusive rocks and hydrothermal minerals from the karouni camp have constrained the structural evolution of the deposit and provided a new age for gold mineralization with important implications for the structural framework and timing of gold mineralization throughout the region magmatism within the 200 km2 of the karouni camp progressed from early synvolcanic intermediate composition dikes at 2147 ma to a major voluminous pulse of felsic magmatism coeval with regional deformation during the trans amazonian orogeny between 2120 and 2088 ma a late pulse of granitic magmatism at 1950 ma may be related to a post orogenic event inherited zircons within the felsic intrusive rocks indicate assimilation of crust as old as 2223 32 ma gold mineralization associated with camp scale d2 deformation has been dated to 2084 15 ma on the basis of u pb geochronology of hydrothermal titanite these results show gold mineralization is coeval with felsic magmatism and contemporaneous with a major pulse of orogenic gold mineralization in the birimian province of west africa

rare earth element geochemistry of the metamorphosed volcanogenic massive sulfide deposits of the manitouwadge mining camp superior province canada a potential exploration tool trace and rare earth element bee geochemistry indicates that rocks in the manitouwadge mining camp were derived from three major lithological units mafic volcanic rocks acid volcanic tuffs and dacites the geco willroy willecho and big nama creek cu zn ag deposits are contained within the 2720 ma acid volcanic tuffs our study suggests that the thickness of the felsic volcanic unit acid tuffs and volcaniclastics may be significantly underestimated in the area medium to high grade metamorphism upper amphibolite lower granulite gave rise to specific alteration assemblages which crystallized during several episodes of deformation and plutonism because major element geochemistry of the rocks was modified during ore forming processes and later by several episodes of metamorphism and tectonism the present alteration minerals merely reflect the cumulative effect s of these episodes and are often misleading in the identification of the protoliths thus due to extensive alteration the protoliths of various lithological units can be positively identified only from trace and rare earth element geochemistry extensive up to 97 light ree depletion was observed in the felsic volcanic rocks around the geco willroy and willecho deposits the positive correlation between bee mobility and mineralization suggests that ree geochemistry can be successfully used in the exploration for volcanogenic massive sulfide deposits around the manitouwadge mining camp the absence of a well defined discordant alteration pipe at geco and localized enrichment in fe al or k at the willroy willecho big nama creek and geco deposits implies that they may be highly metamorphosed equivalents of mattabi type deposits where the original iron rich carbonates have recrystallized to calc silicate or amphibole rich assemblages during regional metamorphism localized enrichment in fe al and k in the felsic tuffs could be used to identify possible alteration pipes or semicomformable alteration zones associated with mineralization

the link between the north pacific climate variability and the north atlantic oscillation via downstream propagation of synoptic waves abstractthe north atlantic oscillation nao response to the northeast pacific climate variability is examined using the era 40 dataset the main objective is to validate a mechanism involving downstream wave propagation processes proposed in a recent idealized companion study a low frequency planetary scale ridge trough anomaly located in the eastern pacific north american sector induces more equatorward poleward propagation of synoptic scale wave packets on its downstream side which favors the occurrence of anticyclonic cyclonic wave breakings in the atlantic sector and the positive negative nao phase the mechanism first provides an interpretation of the canonical impact of the el nino southern oscillation on the nao in late winter the wintertime relationship between the pacific north american oscillation pna and the nao is also investigated for out of phase fluctuations between the pna and nao indices i e the most recurrent situation in late winter the eastern pacific pna ridge trou

geochemical behavior under tropical weathering of the barama mazaruni greenstone belt at omai gold mine guiana shield abstract mineralogical petrographical and geochemical studies of the weathering profile have been carried out at omai au mine guyana the area is underlain by felsic to mafic volcanic and sedimentary rocks of the barama mazaruni supergroup part of the paleoproterozoic greenstone belts of the guiana shield tropical rainy climate has favoured extensive lateritization processes and formation of a deeply weathered regolith the top of the weathering profile consists of lateritic gravel or is masked by the pleistocene continental deltaic berbice formation mineralogical composition of regolith consists mainly of kaolinite goethite and quartz and subordinately sericite feldspar hematite pyrite smectite heavy minerals and uncommon mineral phases nacrite ephesite corrensite guyanaite a specific feature of the weathering profile at omai is the preservation of fresh hydrothermal pyrite in the saprolith horizon chemical changes during the weathering processes depend on various physicochemical and structural parameters consequently the depth should not be the principal criterion for comparison purposes of the geochemical behavior within the weathering profile but rather an index that measures the degree of supergene alteration that has affected each analyzed sample independently of the depth of sampling thus the mineralogical index of alteration mia can provide more accurate information about the behavior of major and trace elements in regolith as opposed to unweathered bedrock it can also aid in establishing a quantitative relationship between intensity of weathering and mobility leaching or accumulation of each element in each analyzed sample at omai some major and trace elements that are commonly considered as immobile ex tio2 zr etc during weathering could become mobile in several rock types and cannot be used to calculate the mass and volume balance in addition due to higher immobile element ratios the weathered felsic volcanic rocks plotted in identification diagrams are shifted towards more mafic rock types and a negative adjustment of 20 units is necessary for correct classification in contrast these elements could aid in defining the material source in sedimentary rocks affected by weathering generally the rare earth element ree patterns of the bedrock are preserved in the saprolith horizon this can represent a potentially useful tool for geochemical exploration in tropical terrains strong negative ce and tb anomalies are displayed by weathered pillowed andesites which are explained by the influence of the water rock ratio

understanding the contrasting north atlantic oscillation anomalies of the winters of 2010 and 2014 the present study investigates the two contrasting winters of 2010 and 2014 during which the north atlantic oscillation nao was mainly negative and positive respectively in the north pacific contrasting anomalies were also present with a straight zonal pacific jet in 2010 and a strong poleward deviation of the pacific jet in its exit region in 2014 using reanalysis data sets and adopting a nonlinear initial value approach with a quasi geostrophic model we show that the pacific north american anomalies are responsible for shaping synoptic wave trains propagating across north america this in turn largely determines the nature of wave breaking and the synoptic eddy feedback onto the mean flow in the north atlantic and finally the nao phase in such a proposed mechanism synoptic wave activity forms the cornerstone of the dynamical relationship between the north pacific and north atlantic large scale anomalies during the contrasting winters of 2010 and 2014

the role of synoptic waves in the formation and maintenance of the western hemisphere circulation pattern abstractprevious studies have demonstrated that the nao the leading mode of atmospheric low frequency variability over the north atlantic could be linked to northeast pacific climate variability via the downstream propagation of synoptic waves in those studies the nao and the northeast pacific climate variability are considered as two separate modes that explain the variance over the north atlantic sector and the east pacific north american sector respectively a newly identified low frequency atmospheric regime the western hemisphere wh circulation pattern provides a unique example of a mode of variability that accounts for variance over the whole north atlantic north american north pacific sector the role of synoptic waves in the formation and maintenance of the wh pattern is investigated using the ecmwf reanalysis datasets persistent wh events are characterized by the propagation of quasi stationary rossby waves across the north pacific north american north atlantic regions and by associated s

a new perspective toward cataloging northern hemisphere rossby wave breaking on the dynamic tropopause abstractrossby wave breaking rwb events are a common feature on the dynamic tropopause and act to modulate synoptic scale jet dynamics these events are characterized on the dynamic tropopause by

crust and mantle evolution in the late archean evidence from a sm nd isotopic study of the north spirit lake greenstone belt northwestern ontario canada sm nd data are presented for volcanic plutonic and sedimentary rocks from the late archean north spirit lake greenstone belt in northwestern ontario the greenstone belt is divided into six lithotectonic assemblages emplaced between 2700 and 3000 ma the earliest assemblage indicative of an island arc setting is characterized by positive initial nd values 0 to 3 whereas shales and granitoids in succeeding assemblages yield increasingly negative nd values as low as 3 this argues strongly that the assemblages formed in close proximity to each other because the younger assemblages likely include recycled crustal material from earlier assemblages through erosion into younger basins and remelting however even the earliest assemblage exhibits decreasing nd values from basaltic to intermediate felsic volcanic strata within the same assemblage this suggests that the initial arc was itself contaminated by either a sedimentary component or remelting of older oceanic crust granitoid samples yield nd values similar to the shales in the belt indicating a common evolutionary history these granitoids may thus represent the roots of the greenstone belt mantle derived rocks such as basalts and komatiites are derived from a variably depleted mantle source with values as high as 3 8 at 2925 ma a 2925 10 8 ma u pb zircon age obtained for a tonalitic pluton on the northern margin of the north spirit lake belt is similar to the age of a volcanic plutonic cycle in the adjacent favourable lake greenstone belt implying that the two belts may have had common orogenic episodes the north spirit lake greenstone belt appears to have nucleated from an initial primitive volcanic arc and through continued volcanism was transformed into a stable platform exhibiting continental features such as intracrustal differentiation and sedimentary recycling to produce the current array of assemblages in this respect the evolution of the north spirit lake greenstone belt resembles the evolution of proterozoic and phanerozoic continents and suggests that archean microcontinents grew in much the same fashion as present day continents

zircon upb ages of guyana greenstone gneiss terrane abstract isotopic u pb studies of zircons collected from weathered metagreywackes of the barama mazaruni supergroup of northern guyana south america demonstrate an age of origin of ca 2250 ma this is the best estimate for the age of the associated metavolcanic rocks zircons from weathered gneiss of the bartica complex adjacent to the volcanic sedimentary belts yield a similar age the contiguous greenstone gneiss terrane of eastern venezuela is also of similar age and comparable greenstone gneiss terranes of eastern suriname and french guiana are probably also of this age continental crust formation of a style closely comparable to that of the canadian archean occurred on a very widespread scale in the lower proterozoic of the guiana shield the lead losses from the weathered zircons are comparable to those from zircons from fresh rock from the adjacent terrane of venezuela and the advantages of field concentration from numerous saprolite exposures warrant use of such material in future geochronological studies of the region

in situ 87sr 86sr of scheelite and calcite reveals proximal and distal fluid rockinteraction during orogenic w au mineralization otago schist new zealand

elemental and multiple isotopic evidences of enriched lithospheric mantle origin of the xiadian gold deposit in the jiaodong peninsula east china abstract the jiaodong peninsula is the largest gold concentration district in china and the third largest one in the world it covers no 0 2 of china s total landmass yet accounts for 30 of the total national gold reserves with total proved resources near 5000 t au one wonders where all this gold comes from here we present detailed whole rock element and sr nd pb isotope quartz h o isotope and pyrite he ar isotope geochemical data for the xiadian gold deposit a large jiaojia type gold deposit in the jiaodong district which furnishes new constrains on the sources of ore forming fluids and metals the results indicate that the ore and alterated rock have much higher hree e g yb and y hfse e g nb ta zr and hf and transition elements e g sc ti v cr co and ni than the host granites but similar to the lithospheric mantle derived lamprophyres suggesting an enriched lithospheric mantle origin the h o isotopes dv smow 93 9 to 102 3 18oh2o 0 2 to 1 6 of fluid inclusions in quartzs collected from auriferous pyrite sericite quartz altered rocks are distinctly different from either primary magmatic water and metamorphic water or meteoric water in the jiaodong district but similar to the local enriched mantle derived fluids the he ar isotopes 3he 4 he 0 58 10 6 to 1 90 10 6 0 42 1 36 ra 40ar 36ar 725 1358 of fluid inclusions in pyrites collected from auriferous pyrite sericite quartz altered rocks are also similar to the local enriched mantle derived fluids the ore and alterated rock have distinct nd pb isotopic compositions either from the host linglong granites or from the asthenosphere derived mafic dikes but similar to the lithospheric mantle derived mafic dikes their sr isotopic compositions show a mix trend between the lithospheric mantle derived mafic dikes and neoarchaean basement all the elemental and multiple isotopic features support a metallogenic model that the ore forming fluids and metals were derived from the local previously enriched lithospheric mantle and such deeply sourced fluids may have interacted with neoarchaean basement along their flow path and mixed with a little meteoric water when they arrived high levels in the crust

adjustment of the atmospheric circulation to tropical pacific sst anomalies variability of transient eddy propagation in the pacific north america sector nas a pattern that is shifted southward northward compared with climatology paths of coherent phase propagation of transient eddies and of the propagation of wave packets are analyzed a coherent path of propagation across the pacific towards north america is identified that is more zonal during el niwinters and during la nihas a dominant path heading northeastward to the pacific northwest a second path heading southeastward from the central pacific to the tropical east pacific is more accentuated during la ni nas than el ni nos these changes in wave propagation are reproduced in an ensemble of seasonal integrations of a general circulation model forced by a tropical pacific sea surface temperature pattern confirming that the changes are forced by changes in the mean atmospheric state arising from changes in tropical sea surface temperature a simplified model with a specified basic state is used to model the storm tracks for el ni no and la ni na winters the results suggest that the changes in transient eddy propagation and the eddy statistics can be understood in terms of the refraction of transient eddies within different basic states copyright c 2010 royal meteorological society

rb sr sm nd and pb isotope systematics of pyrite implications for the age and genesis of lode gold deposits lode gold deposits commonly consist of pyrite and lesser amounts of lead and zinc sulfides accompanied by quartz and calcite their exact origin remains controversial mainly because of the scarcity of reliable geochronological data here we present direct rb sr dating of pyrite from a lode gold deposit and propose the method as a useful geochronological technique for gold mineralization for which age data are poor a positive correlation between present day 87 sr 86 sr and 87 rb 86 sr ratios of pyrite fes 2 subsamples from the linglong gold mine of china corresponds to an age of 122 123 ma which dates the age of gold mineralization the sr nd and pb isotopic compositions of pyrites and the associated rocks suggest that the hydrothermal fluids responsible for the pyrite and gold mineralization were probably derived from a mixed source i e degassing of mafic magmas and meteoric water that had leached the country rocks

sm nd systematics of hydrothermal scheelite from the mount charlotte mine kalgoorlie western australia an isotopic link between gold mineralization and komatiites

nd isotopic evidence for juvenile crust in the carolina terrane southern appalachians nd isotopic analyses of whole rock samples from the older portion of the carolina terrane one of the largest terranes in the appalachian orogen demonstrate that part of this terrane is composed of juvenile mantle derived crust these data suggest that the terrane may not have originally been built upon old evolved basement material but rather may have been built upon oceanic crust a recent study by other workers demonstrates a more crustally evolved nd isotopic signature for younger components of the carolina terrane these data may indicate that the terrane interacted with evolved crust at a later time possibly by amalgamation with a more evolved crustal fragment before final accretion to laurentia rather than indicating a primary old basement a juvenile nature for the older portion of the terrane contrasts with models that suggest it is an evolved crustal fragment that formed in a continental margin setting a scenario proposed to explain the high proportion of felsic volcanic rocks within the terrane it is herein suggested that carolina is a chemically evolved but isotopically juvenile crustal fragment because it remained in an oceanic setting for an unusually long time in this regard the carolina terrane is similar to some of the large accreted terranes in the canadian cordillera such as wrangellia and alexander the presence of juvenile crust in the carolina terrane documents that at least part of the southern appalachian orogen is not composed solely of reactivated pre existing continental crust the importance of this part of the orogen in terms of the volume of juvenile phanerozoic crustal material in north america may be larger than previously thought however until additional major appalachian terranes have been isotopically characterized the volume of juvenile crust in the whole orogen remains unknown the isotopic make up of a terrane can be an important aspect of terrane analysis as different terranes may have significantly different isotopic compositions while even widespread pieces of a single terrane should have very similar isotopic characteristics the nd isotopic data for the carolina terrane form the beginning of an isotope database for terranes in the southern appalachians

annular modes in the extratropical circulation part i month to month variability the leading modes of variability of the extratropical circulation in both hemispheres are characterized by deep zonally symmetric or annular structures with geopotential height perturbations of opposing signs in the polar cap region and in the surrounding zonal ring centered near 458 latitude the structure and dynamics of the southern hemisphere sh annular mode have been extensively documented whereas the existence of a northern hemisphere nh mode herein referred to as the arctic oscillation ao has only recently been recognized like the sh mode the ao can be defined as the leading empirical orthogonal function of the sea level pressure field or of the zonally symmetric geopotential height or zonal wind fields in this paper the structure and seasonality of the nh and sh modes are compared based on data from the national centers for environmental prediction national center for atmospheric research reanalysis and supplementary datasets the structures of the nh and sh annular modes are shown to be remarkably similar not only in the zonally averaged geopotential height and zonal wind fields but in the mean meridional circulations as well both exist year round in the troposphere but they amplify with height upward into the stratosphere during those seasons in which the strength of the zonal flow is conducive to strong planetary wave mean flow interaction midwinter in the nh and late spring in the sh during these active seasons the annular modes modulate the strength of the lagrangian mean circulation in the lower stratosphere total column ozone and tropopause height over mid and high latitudes and the strength of the trade winds of their respective hemispheres the nh mode also contains an embedded planetary wave signature with expressions in surface air temperature precipitation total column ozone and tropopause height it is argued that the horizontal temperature advection by the perturbed zonal mean zonal wind field in the lower troposphere is instrumental in forcing this pattern a companion paper documents the striking resemblance between the structure of the annular modes and observed climate trends over the past few decades

crustal scale detachment in the himalayas a reappraisal summary according to the most popular tectonic model of the himalayas proposed by a number of scientists the indian crustal material underthrusts the himalayas at a low angle and is relatively free of deformation compared to the overlying accreted material that makes up the himalayan mountainchain inthisworkwehavecarriedoutlocalearthquaketomographyforthegarwhalkumaun himalayas to estimate p and s wave velocity variations vp and vs respectively and variation in their ratio vp vs that would indicate the structure of the himalayas and the underlying indian crust in this part of the himalayas the results indicate that there is crustal level folding and faulting in this region indicating that the underlying indian crustal material has also undergone deformation unlike what was postulated for the entire himalayas by some workers before by comparing our tomographic result with that for the eastern nepal southern tibet region it is concluded that there is variation in mode of deformation along the trend of the himalayas this observation matches well with the observed velocity variation in the upper mantle of these two regions reported by others the area under investigation falls within a region where there is more oblique convergence between india and eurasia compared to the nepal himalayas region this may explain why such variation in mode of deformation is observed the ratio vp vs gets affected by strength of material presence or absence of fluid filled fractures or molten material affects it most strongly in the crustal region the variation in vp vs in the study area shows that almost the entire crust here have enough rheological strength such that it can store strain energy that can be released through earthquakes a zone of low vp vs beginning at the higher himalayas and dipping towards sw is observed this zone also has high vp and vs and is observed even when inversion is carried out with very high damping value these observations do not suggest that seismic hazard will be less in the study area

lithostratigraphy geochronology and gold metallogeny in the northern guiana shield south america a review abstract with a surface area of nearly 900 000 km 2 the guiana shield represents the northern segment of the amazonian craton in south america lying for the most part between the amazon and orinoco river basins most of the guiana shield formed during protracted periods of intense magmatism metamorphism and deformation culminating with the trans amazonian tectono thermal event bracketed between 2 1 and 1 9 ga the guiana shield is among the least known precambrian terranes because it is relatively inaccessible lacks bedrock exposure due to intense weathering and is poorly documented in the international geological literature this situation has significantly improved during the last 20 years when shallow in situ gold occurrences attracted exploration and mining companies to initiate geological programs aimed at better understanding the geology and the mineral deposits of the shield the only archean terrane ca 3400 ma known to date in the guiana shield is the imataca complex in venezuela the paleoproterozoic low grade volcano sedimentary greenstone sequences and associated granitoid intrusions have yielded ages between 2 25 and 2 08 ga recent u pb age determinations of the granitoid greenstone belts suggest protracted magmatic cycles from pre to post peak regional metamorphism the younger terranes comprise anorogenic sedimentary sequences of the roraima formation as well as felsic volcanic rocks and associated intrusions of the uatuma formation mafic dikes of the avanavero suite and rapakivi type and alkali intrusions several large scale ductile shear zones have been documented in the guiana shield in northcentral venezuela the most outstanding structure documented to date the ne sw trending guri fault juxtaposes the archean imataca complex against paleoproterozoic terranes the central guiana shear zone cgsz extends from french guiana westerly towards central suriname and further west towards northcentral guyana where it matches with the makapa kuribrong shear zone mksz in french guiana the north guiana trough ngt is interpreted as a sinistral strike slip formed during the trans amazonian orogeny most gold deposits and occurrences discovered to date in the guiana shield are sited in close proximity to major structures in addition they are linked with low to medium metamorphic grade granitoid greenstone belts similar to other better explored precambrian terranes at a local scale the gold deposits are hosted within or in close proximity to quartz veins that are syn to late tectonic and to a lesser extent in stockworks breccias and lenses they are commonly located in units that behaved in a more brittle manner than the country rocks available information suggests that gold deposits are mainly epigenetic although some are associated with specific lithostratigraphic units pyrite pyrrhotite chalcopyrite galena sphalerite scheelite molybdenite and tellurides are the main metallic minerals associated with gold non metallic minerals are mainly quartz and carbonates ankerite calcite siderite associated with minor chlorite epidote albite muscovite and fuchsite silica carbonate propylitic and potassic alteration is common high erosion rates expected after the creation of an orogenic belt did not occur in the northern guiana shield shallow level deposits preserved in many settings suggest that the granitoid greenstone belts represent first order exploration targets for large tonnage low grade gold deposits

pyrite rb sr sm nd and fe isotopic constraints on the age and genesis of the qingchengzi pb zn deposits northeastern china abstract sr nd fe isotopes are reported for pyrites and whole rocks of ores and associated rocks for the qingchengzi pb zn deposits in the northeasern china to investigate the age sources and processes of the pb zn mineralization rb sr leaching isotopic dating of pyrites that crystallized coeval with galena and sphalerite from five subsamples of ores yields isochron ages of 143 12 ma to 159 12 ma with a weighted mean age of 151 8 5 2 ma this age can be interpreted to be the timing of pb zn mineralization coeval with the emplacement of late jurassic granites in the region the pyrites have negative end 152 ma values of 17 6 to 22 0 among the neoarchean ttg rocks paleoproterozoic meta sedimetary rocks i e wall rocks and granites and mesozoic mafic dykes and granites however the initial 87sr 86sr ratio of 0 7188 0 0004 is similar to those of late jurassic granites and paleoproterozoic rocks 0 7082 0 7183 distinct from those of mafic dykes 0 7069 0 7110 indicating the ore forming materials i e pb and zn were mainly derived from wall rocks and late jurassic granites combined with the previously published h o isotopes the new age and sr nd isotopic data indicate that the mineralizaing fluids were mainly derived from dehydration of granitic magmas interacted with meteoric water that extracted pb and zn from the wall rocks the 56fe values of pyrites in the pb zn ores and paleoproterozoic meta sedimentary rocks range from 0 23 to 1 09 and 0 49 to 0 17 respectively distinct from those of paleoproterozoic basement rocks and mesozoic rocks 0 03 to 0 28 combined with nd isotopes the large range of 56fe values for pyrites would be the result of rapid precipitation of pyrites in the wall rocks and contemperal deposition of pyrites in the residual fluids during interaction between wall rocks and ore forming fluids collectively our new sr nd fe isotopes of pyrites not only constrain the age and sources of pb and zn mineralization but also reveal the detailed mineralization processes providing a new method to constrain the genesis of hydrothermal pb zn deposits

the north atlantic oscillation response to large scale atmospheric anomalies in the northeastern pacific abstractingredients in the north pacific flow influencing rossby wave breakings in the north atlantic and the intraseasonal variations of the north atlantic oscillation nao are investigated using both reanalysis data and a three level quasigeostrophic model on the sphere first a long term run is shown to reproduce the observed relationship between the nature of the synoptic wave breaking and the phase of the nao furthermore a large scale low frequency ridge anomaly is identified in the northeastern pacific in the days prior to the maximum of the positive nao phase both in the reanalysis and in the model a large scale northeastern pacific trough anomaly is observed during the negative nao phase but does not systematically precede it then short term linear and nonlinear simulations are performed to understand how the large scale ridge anomaly can act as a precursor of the positive nao phase the numerical setup allows for analysis of the propagation of synoptic waves in the eastern pacific in the p

strontium isotope systematics of hydrothermal minerals from epigenetic archean gold deposits in the yilgarn block western australia strontium isotope compositions are presented for samples of hydrothermal scheelite and tourmaline from one granitoid hosted and 14 greenstone hosted archean gold deposits in the yilgarn block western australia the direct measurement of the 87 sr 86 sr ratios of rb poor minerals such as scheelite and tourmaline which show an intimate paragenetic relationship to gold allows an accurate estimate of the local strontium isotope composition of the archean gold bearing hydrothermal fluids the population of greenstone hosted gold deposits is sub divided according to gangue mineralogy into gold skarns with garnet pyroxene biotite and amphibole biotite calcite wall rock alteration which formed in the lower parts of the green stone belts at depths of 10 to 15 km and medium temperature gold deposits with biotite or sericite ankerite albite wall rock alteration which formed in the upper parts of the belts at depths of 3 to 7 km the 87 sr 86 sr ratios of the fluids vary from 0 7020 to 0 7035 in skarns with garnet pyroxene biotite alteration from 0 7020 to 0 7043 in skarn quartz orebodies with amphibole biotite calcite alteration and from 0 7014 to 0 7028 in the medium temperature gold deposits the variations in the strontium isotope composition of scheelite from the same mining district are interpreted to reflect mixing between radiogenic strontium introduced by the hydrothermal fluid and nonradiogenic strontium released from the wall rocks during interaction with this fluid the greenstone host rocks of all deposits mainly metamorphosed ultramafic or mafic volcanic rocks and their intrusive equivalents are characterized by the low initial 87 sr 86 sr ratio 0 7007 0 7012 and low rb sr ratio of the archean mantle on the other hand the initial 87 sr 86 sr ratios of granodiorite and granite plutons in the batholiths which underlie and border the greenstone belts vary from 0 7023 to 0 7044 the strontium isotope data indicate that the deep seated gold skarns formed predominantly from fluids which evolved from or interacted with anatectic magmas in the granitoid batholiths the data do not as clearly constrain the origin of the fluids in the higher level medium temperature hydrothermal systems they are however inconsistent with models involving predominantly metamorphic fluids generated by the devolatilization of the lower parts of the greenstone belts

scheelite geochemistry in porphyry skarn w mo systems a case study from the gaojiabang deposit east china abstract scheelite cawo4 a hydrothermal mineral commonly displaying enrichment in mo up to 16 and or rare earth elements ree is the main economic mineral in the gaojiabang porphyry skarn type w mo deposit east china based on microscopic observations and in situ la icp ms and la mc icp ms analysis three groups of scheelite each with different geochemical characteristics can be recognized this evidence provides a good basis for considering the behavior of some trace elements in scheelite and how they may constrain ore genesis in porphyry skarn systems p group scheelite occurs inside the porphyry rocks in the form of vein hosted or disseminated scheelite these have the lowest 87sr 86sr i values 0 7089 0 7108 lowest mo concentration mean 213 ppm n 51 lree hree ratios of 16 33 84 91 and highest ree concentration 191 405 ppm with downwards sloping ree fractionation trends s group scheelite occurs in skarns coexists with skarn minerals garnet diopside epidote etc and has the highest 87sr 86sr i values 0 7103 0 7113 highest mo concentration mean 1 323 ppm n 29 highest lree hree ratio 62 6 164 and lowest ree concentrations 68 5 112 ppm also with strongly downwards sloping ree fractionation trends h group scheelite occurs within veins hosted by hornfels and displays moderate 87sr 86sr i 0 70104 0 70122 mo mean 806 ppm n 17 lree hree ratio 16 32 42 55 and ree concentration 98 3 167 6 ppm during hydrothermal precipitation of scheelite changing redox state plays a major role in controlling mo behavior both the precipitation of early skarn minerals and changing redox states of ore forming fluids likely result in an increase in mo and corresponding decrease of hree in scheelite particularly in s group scheelite the sr isotope study indicates that crustal materials provided the main source for w mo bearing ore forming fluids furthermore both fluid mixing and fluid rock interaction played an important role in the evolution of ore forming fluids formation water or groundwater was likely involved in ore formation a geochemical model is described combining data for the different types of scheelite and the behavior of mo rees and sr isotopes to constrain the evolution of ore forming fluids and constrain ore genesis in the porphyry skarn system at gaojiabang this study contributes to the fingerprinting of ore deposits using scheelite geochemistry

general equations for modeling fluid rock interaction using trace elements and isotopes abstract general equations for modeling open and closed system fluid rock interaction using trace elements and isotopes are presented taylor s 1977 open system equation for stable isotopes is extended to account for a change in the value between rock and fluid during interaction it is shown that hydrothermal systems in which fractionation factors vary during fluid rock interaction will significantly alter the isotopic ratios of rocks compared to equivalent systems with invariant fractionation factors the equations for modeling trace element exchange are analogous to the stable isotope equations and permit the calculation of fluid rock ratios using changes in trace element concentrations in the rock similarly to stable isotope exchange the change of the trace element concentration in a rock during infiltration is a function of the trace element concentration in the fluid the fluid rock partition coefficient and the fluid rock ratio rather than simply the concentration of the trace element in the fluid

scheelite elemental and isotopic signatures implications for the genesis of skarn type w mo deposits in the chizhou area anhui province eastern china scheelite is well developed in hydrothermal deposits providing a window into genetic processes and facilitating comparative studies however few studies have focused on characterizing scheelite in skarn type w mo deposits the primary ore mineral in the jitoushan and baizhangyan skarn type w mo deposits anhui province eastern china scheelite was analyzed for major trace and rare earth element ree abundance and for sr nd isotopes the analysis revealed two unique geochemical characteristics that distinguish the scheelite from skarn type w mo deposits to that from vein type au w and porphyry type w mo deposits higher mo content with a negative correlation between moo 3 and wo 3 and a strong hree depletion skarn type scheelite mainly inherited ree signatures from ore forming fluids and the early precipitation of skarn minerals e g garnet diopside and amphibole has most likely resulted in the observed strong hree depletion in scheelite and the decoupling of lrees and hrees of the numerous substitution mechanisms suggested by previous workers 3ca 2 2ree 3 ca where ca is a ca site vacancy is preferred for the substitution of ree 3 for ca 2 and in this study particularly given the low salinity of ore fluids as the scheelite eu anomalies were inherited from ore forming fluids with variable redox conditions and ph the complex deu mo correlation indicates that mo increasingly entered the scheelite under oxidizing conditions and reached a maxim at deu values of 0 8 to 1 in contrast under reducing conditions mo contents in scheelite decrease gradually and mo is precipitated as molybdenite as a result of the change in dominant valence state unlike the sr nd isotope compositions of scheelite from vein type au w and w sb au deposits the scheelite from skarn type w mo deposits has low 143 nd 144 nd t most 87 sr 86 sr t values most between 0 708 and 0 715 the end t values of the scheelite varied from 16 to 12 3 in the baizhangyan deposit and from 9 5 to 9 1 in the jitoushan deposit indicating that the ore forming materials in the two w mo deposits were mainly derived from crustal sources

nd and sr isotope study of hydrothermal scheelite and host rocks at omai guiana shield implications for ore fluid source and flow path during the formation of orogenic gold deposits omai is a high tonnage low grade world class gold deposit located in the paleoproterozoic guiana shield it is the second most important gold deposit in the guiana shield after las cristinas venezuela and one of the largest in south america 4 0 million oz sm nd and sr isotope data are presented for host rocks and for scheelite from auriferous quartz carbonate scheelite sulfide telluride veins from the omai deposit gold bearing veins are hosted by the paleoproterozoic barama mazaruni supergroup a greenstone belt sequence consisting of mafic volcanic rocks interbedded with sedimentary rocks that are intruded by quartz feldspar porphyry and rhyolite dikes this lithologic sequence was folded and metamorphosed to lower greenschist facies during the paleoproterozoic trans amazonian orogeny the volcano sedimentary unit was intruded by a post tectonic quartz monzodiorite diorite hornblendite stock initial nd isotope ratios for the omai volcanic rocks range from nd 2 1 to 4 2 these values suggest that this part of the guiana shield was a site of new crust formation during the paleoproterozoic and was not contaminated by older archean reworked continental crust initial nd isotope ratios for the omai stock range between 0 5 and 2 3 which suggest limited contamination with previously formed continental crust although the nd isotopic ratios of gold related scheelites overlap with those of the host rocks particularly the tholeiitic basalts at the interpreted time of vein emplacement the lack of both isotopic mixing and significant nd movement during the hydrothermal process suggest that the nd isotope composition can be used to determine the isotopic characteristics of the ore fluid source area at omai the ore fluid is largely derived from a radiogenic nd source represented by mantle or lower crustal reservoirs strontium isotope ratios for the scheelites cluster tightly between 0 7019 and 0 7021 the sr isotope data suggest that unlike nd sr was significantly mobile during the hydrothermal process the fluids responsible for the omai deposit may have picked up sr along the flow path the constant low sr isotope values of scheelites probably reflect the key role that the local tholeiitic basalts played as the main source of sr in the fluids whereas nd isotopes identify the fluid source area the sr isotopes map the fluid flow paths

is the north atlantic oscillation a breaking wave abstract given the recent observational evidence that the positive negative phase of the north atlantic oscillation nao is the remnant of anticyclonic cyclonic wave breaking this study uses a multilevel primitive equation model to investigate important dynamical attributes of the above wave breaking behavior for this purpose a hierarchy of different basic states two and three dimensional and initial perturbations are used with the three dimensional climatological flow as the basic state it is found that initial perturbations located equatorward poleward and upstream of the climatological atlantic jet lead to wave breaking similar to that of the positive negative nao phase consistently analysis of observational data indeed shows that the pacific storm track is displaced equatorward poleward prior the onset of the positive negative nao phase this result suggests that the latitudinal position of the pacific storm track plays an important role for determining the phase of the nao sen

surface water influx in shallow level archean lode gold deposits in western australia archean shallow level lode gold deposits in western australia are located in rocks of prehnite pumpellyite to lower greenschist facies and are characterized by 1 predominantly brittle shear zones that formed well after volcanism and late in the structural history 2 breccia hosted lodes 3 low temperature ore and gangue minerals such as silver sulfosalts stibnite and precursor chalcedony and 4 vertical metal zonation of the orebodies ore fluid temperatures ranged from 150 to 325 c and a depth of em placement of 5 km is inferred isotopic analyses of alteration minerals such as quartz sericite and chlorite indicate higher dfluid 6 9 relative to smow 1 n 19 and lower 18ofluid 4 4 2 3 relative to smow 1 n 167 values compared to such values for hydrothermal fluids that deposited au in other archean lode gold deposits with similar structural timing the fluid inclusion and stable isotope data and the presence of chalcedony in this deposit style are best explained by the influx of surface water at shallow levels and interaction of that water with advecting metamorphic magmatic fluids

are the winters 2010 and 2012 archetypes exhibiting extreme opposite behavior of the north atlantic jet stream abstractthe atmospheric circulation over the north atlantic european sector experienced exceptional but highly contrasting conditions in the recent 2010 and 2012 winters november march with the year dated by the relevant january evidence is given for the remarkably different locations of the eddy driven westerly jet over the north atlantic in the 2010 winter the maximum of the jet stream was systematically between 30 and 40 n south jet regime whereas in the 2012 winter it was predominantly located around 55 n north jet regime these jet features underline the occurrence of either weak flow 2010 or strong and persistent ridges throughout the troposphere 2012 this is confirmed by the very different occurrence of blocking systems over the north atlantic associated with episodes of strong cyclonic anticyclonic rossby wave breaking in 2010 2012 winter these dynamical features underlie strong precipitation and temperature anomalies over parts of europe with detrimental impacts on many soc

sm nd dating of scheelite and tourmaline implications for the genesis of archean gold deposits val d or canada sm nd analyses of 19 scheelite samples from auriferous quartz carbonate tourmaline scheelite gold veins from three mines in the val d or gold camp in the abitibi greenstone belt in western quebec the sigma pascalis north and siscoe extension mines yield a linear array on an isochron diagram with a mean square weighted deviation mswd of 3 6 corresponding to an age of 2596 or 33 ma and epsilon sub nd 1 2 5 eight scheelite samples from the pascalis north mine alone define an excellent linear array with an mswd 0 31 an age of 2593 or 18 ma and epsilon sub nd 1 2 7 these ages are interpreted to represent the age of quartz carbonate tourmaline scheelite vein hosted gold mineralization in the three mines sampled sm nd analyses of tourmaline suggest that this mineral may also be useful for sm nd dating of hydrothermal mineralization the sm nd scheelite age of ca 2600 ma is in good agreement with u pb ages obtained from mineralization related rutile and titanite in the val d or area these results indicate that the quartz carbonate tourmaline scheelite vein hosted gold mineralization was emplaced approximately 70 m y later than the youngest observed premineralization magmatic activity and approximately 60 m y later than peak regional metamorphism in the val d or area these ages do not support hypotheses for deposit formation which involve fluids derived from spatially related intrusive rocks or metamorphism although they do not preclude an earlier stage of introduction of gold into the val d or area the scheelite sm nd age and depleted mantlelike epsilon sub nd 1 and the mineralogy and alteration of the quartz carbonate tourmaline veins are consistent with the derivation of the mineralizing fluids from a relatively homogeneous external source and introduction into the upper crust as part of a single large hydrothermal system the formation of the val d or gold deposits also appears to be broadly synchronous with the growth of zircon in high grade metamorphic rocks of the lower crust underlying the greenstone belt material suggesting that these may be related processes

structural mineralogical and geochemical studies of the paleoproterozoic omai gold deposit guyana the granitoid and greenstone hosted omai gold deposit is located in the paleoproterozoic barama mazaruni greenstone belt guiana shield at regional scale the emplacement of the deposit was controlled by the makapa kuribrong crustal shear zone at local scale the gold bearing quartz veins are associated mainly with a quartz monzodioritic intrusion omai stock fennell pit and subvolcanic quartz feldspar porphyry and rhyolite dikes and subordinately with intermediate volcanic flows and metasedimentary rocks wenot pit six gold bearing undeformed subhorizontal and subvertical vein sets can be distinguished in the two ore zones on the basis of their internal structures and textures the veins can be classified as crack and seal laminated breccia and open space filling veins the geometrical and textural relationships between the vein sets suggest that they are broadly contemporaneous the formation of most veins can be summarized by two filling stages and a late fracture filling stage related to a protracted hydrothermal process although the metallic minerals represent less than 1 percent of the vein volume their mineralogy is complex and consists of various sulfides together with tungstates native elements tellurides and sulfosalts the metallic paragenesis is defined by the au ag te w bi pb zn cu hg mo assemblage the nonopaque gangue includes mainly quart and subordinately carbonates albite sericite chlorite tourmaline rutile and epidote wall rocks of gold bearing veins are affected by synmineralization alteration the dominant alteration assemblages include carbonates sericite silica chlorite albite epidote argillic minerals pyrite and pyrrhotite there is an obvious association between the alteration assemblages the vein internal textures and the chemical nature of the host rocks vein forming scheelite has 87 sr 86 sr ratios between 0 7019 and 0 7021 and delta 18 o values between 3 8 and 4 3 per mil which suggest both consistent temperature and isotopic composition of the hydrothermal solutions during its deposition oxygen isotopes measured in vein quartz vary between 13 2 and 14 per mil similar to the delta 18 o values of carbonates avg 13 8ppm for calcite and 14 4ppm for ankerite the carbon isotopes of carbonates range between 1 7 and 4 7 per mil the delta 18 o values of the mineralizing fluids vary between 5 6 and 2 7 per mil and the delta d values between 52 and 18 per mil the isotopic composition of the hydrothermal fluids plots outside both magmatic and metamorphic water boxes therefore suggesting a significant component of surface derived water the omai deposit is late orogenic and its emplacement was controlled by the last brittle to brittle ductile stages of the trans amazonian orogeny it can be considered as a paleoproterozoic equivalent of the archean epizonal orogenic deposits described in the yilgarn wiluna racetrack and zimbabwe shamwa commoner cratons

propagation of the arctic oscillation from the stratosphere to the troposphere geopotential anomalies ranging from the earth s surface to the middle stratosphere in the northern hemisphere are dominated by a mode of variability known as the arctic oscillation ao the ao is represented herein by the leading mode the first empirical orthogonal function of low frequency variability of wintertime geopotential between 1000 and 10 hpa in the middle stratosphere the signature of the ao is a nearly zonally symmetric pattern representing a strong or weak polar vortex at 1000 hpa the ao is similar to the north atlantic oscillation but with more zonal symmetry especially at high latitudes in zonal mean zonal wind the ao is seen as a north south dipole centered on 40 45 n in zonal mean temperature it is seen as a deep warm or cold polar anomaly from the upper troposphere to 10 hpa the association of the ao pattern in the troposphere with modulation of the strength of the stratospheric polar vortex provides perhaps the best measure of coupling between the stratosphere and the troposphere by examining separately time series of ao signatures at tropospheric and stratospheric levels it is shown that ao anomalies typically appear first in the stratosphere and propagate downward the midwinter correlation between the 90 day low pass filtered 10 hpa anomaly and the 1000 hpa anomaly exceeds 0 65 when the surface anomaly time series is lagged by about three weeks the tropospheric signature of the ao anomaly is characterized by substantial changes to the storm tracks and strength of the midtropospheric flow especially over the north atlantic and europe the implications of large stratospheric anomalies as precursors to changes in tropospheric weather patterns are discussed

rare earth element systematics in hydrothermal fluids abstract rare earth element concentrations have been measured in hydrothermal solutions from geothermal fields in italy dominica valles caldera salton sea and the mid atlantic ridge the measured abundances show that hydrothermal activity is not expected to affect the ree balance of either continental or oceanic rocks the ree enrichment of the solutions increases when the ph decreases high temperature solutions 230 c percolating through different rock types may show similar ree patterns

in situ sr isotopic measurement of scheelite using fs la mc icpms abstract scheelite is one of the main ore minerals in tungsten deposits and sr isotopic compositions of scheelite can be used to examine the petrogenesis of igneous rocks and fluid metasomatism in mineralization processes both thermal ionization mass spectrometer tims and femsecond laser ablation multi collector inductively coupled plasma mass spectrometer fs la mc icp ms have been applied to analyze sr isotopic compositions in scheelite here we describe a la mc icp ms technique which can obtain in situ accurate high precision 87sr 86sr ratios from 20 to 50 m scheelite in line mode without requiring time consuming mineral separation and pre chemical procedures we found that ca dimers and ca argides do not detectably affect the obtained 87sr 86sr ratios and the adopted protocol overcomes interferences from kr rb er2 and yb2 the results of three mpi ding reference glasses kl2 g ml3b g and sths6 80 g are consistent with the recommended values here we show that the values of 87sr 86sr are relatively homogeneous for two scheelites from quartz veins and are comparable to the values determined by a traditional solution method hence these two scheelite samples have the potential to be reference materials for sr isotopic determination by la mc icp ms to illustrate the utility of the technique sr isotopes of scheelites from three different types of tungsten deposits of south china are documented the 87sr 86sr of scheelite from granite related veinlet disseminated and porphyry tungsten deposits varies systematically showing a positive correlation between sr content and 87sr 86sr ratios these micrometer scale inhomogeneities could be explained by mixing of two components reflecting intense fluid metasomatism during mineralization processes high 87sr 86sr ratios were obtained for the scheelite samples from a quartz vein type tungsten deposit indicating that the late stage ore forming fluid was mainly derived from the surrounding strata these examples show that in situ sr isotopic measurement of scheelite is a powerful tool to decipher the degree of fluid rock interaction in ore forming processes

nd sr pb isotopic constraints on metal and fluid sources in w sb au mineralization at woxi and liaojiaping western hunan china this paper presents nd sr pb isotope data on scheelite inclusion fluids and residues of gangue quartz and sulfides from the w sb au ore deposits at woxi and liaojiaping ljp in the xuefeng uplift belt xub western hunan china sm and nd concentrations in scheelite from woxi are much lower than in scheelite from ljp and can be distinguished by their high 147sm 144nd ratios of 1 25 from the much lower ratios around 0 26 in scheelites from the ljp end values compared to values at 200 ma which is the average timing of granitoid emplacement during the indosinian yanshanian periods in the xub are around 10 for the ljp and compare well with the range of 5 to 11 defined by the granitoids whereas they are around 27 for scheelite from woxi this might indicate that rees in the mineralizing fluids at ljp originated from granitoids that are concentrated along the southern border of the xub whereas in the case of woxi the original fluids might have been masked by rees released during intense high temperature wall rock alteration of unexposed precambrian basement rocks at depth sr isotopes of scheelite from these two deposits show similar relations to host nearby rocks in that 87sr 86sr t 200 ma ratios of 0 721 for ljp scheelite agree with values ranging between 0 718 0 726 for granitoids whereas these ratios are much higher i e 0 745 for scheelite from woxi and correspond to the 87sr 86sr t 200 ma ratio range of 0 743 0 749 for precambrian host slates crushing experiments to release inclusion fluids from gangue quartz and sulfides deposited during later stages of ore deposition in both deposits failed to provide accurate and geologically meaningful two point fluid residue tie lines in rb sr isochron diagrams however sr released from fluid inclusions generally reveals lower initial 87sr 86sr ratios than the respective residues and shows affinities to 87sr 86sr t 200 ma values of indosinian yanshanian granitoids both at woxi and ljp pb stepwise leaching of scheelite and sulfides did not result in sufficient spreads in pb isotope diagrams and therefore no information regarding exact mineralization ages in the two deposits could be deduced overall ore pb isotopes reveal upper crustal signatures and are compatible with pb isotope signatures of the predominant precambrian slates in the woxi area steep trajectories through late stage quartz sulfide mineralization in pb isotope diagrams may hint at mixing scenarios involving pb from the host rocks and a component with lower 207pb 204pb and 208pb 204pb ratios relative to 206pb 204pb ratios which cannot be linked to any known reservoir in the xub mining district sr isotopes of four out of seven residual sulfide samples from woxi plot along a paleomixing line at an age of 199 8 ma supporting a mixing scenario for the fluids indicated by the pb isotopes and pointing to a possible genetic relationship with the emplacement of indosinian yanshanian granitoids the budgets of rees rb sr and pb in the original fluids were severely affected by contamination of these elements apparently during intense wall rock alteration but after sealing of the major pathways the mineralizing fluids tend to have better preserved their original signatures these attest a genetic relationship between the metallogeny in the xub w sb au province and the emplacement of indosinian yanshanian granitoids during mesozoic intracontinental tectonic uplift and thrusting

thermochronology of the camflo gold deposit malartic quebec implications for magmatic underplating and the formation of gold bearing quartz veins the dominant ore host at camflo is a small monzonite pluton cut by main stage gold bearing quartz veins containing hydrothermal titanite and k feldspar main stage veins are spatially and temporally related to brittle ductile faults emplaced into most faults are younger transitional stage quartz pyrite lodes with sericite rutile alteration halos titanite in main stage gold quartz veins is replaced by rutile calcite quartz where overprinted by transitional stage sericitic alteration a u pb zircon age from the camflo monzonite indicates that the stock was emplaced at 2685 or 10 ma a u pb age of 2621 or 4 ma for hydrothermal titanite and a pb pb isochron age of 2621 or 7 ma defined by seven titanite and two k feldspar samples indicate that the gold quartz veins formed approximately 60 m y later which precludes a direct genetic link between these two events rutile analyses plot below the titanite feldspar pb pb isochron and so support field and petrographic evidence suggesting rutile did not precipitate from the same fluid that formed the titanite and k feldspar incremental heating and total fusion 40 ar 39 ar ages of hydrothermal micas related to gold quartz veins and quartz pyrite lodes are 70 to 170 m y younger than the hydrothermal u pb ages in addition 40 ar 39 ar ages of micas on the 1650 level are approximately 10 to 15 m y older than like micas on the 3475 level the younger 40 ar 39 ar ages are interpreted as cooling and not recrystallization or reset ages 40 ar 39 ar ages indicate cooling rates of approximately 1 degrees c m y for 2600 to 2550 ma rutile vein muscovite approximately 0 6 degrees c m y for 2550 to 2511 ma vein muscovite wall rock muscovite and approximately 0 3 degrees c m y for 2507 to 2452 ma large biotite small biotite an apparent uplift rate of approximately 0 04 km m y for 2520 to 2478 ma is calculated by comparing biotite and white mica ages from the 1650 and 3475 levels the u pb and 40 ar 39 ar thermochronology is consistent with an accretionary tectonic setting for camflo during the terminal stages of tectonic construction of the superior province a critical feature of this setting is large volumes of mantle derived basalt underplating the lower crust during peak granulite formation at approximately 2648 to 2640 ma co 2 rich fluids liberated by solidification of ponded mafic magma after peak granulite formation interacted with other fluids magmas and rock either at their source or during migration in shear zones to upper crustal levels where they deposited significant quantities of gold at camflo at approximately 2621 ma slow cooling and slow apparent uplift at camflo ensued for 150 m y after magmatic under plating resulting in the young 40 ar 39 ar cooling ages recorded by hydrothermal minerals this model is consistent with ages for granulite facies metamorphism in the kapuskasing structural zone postpeak metamorphic ages for co 2 h 2 o fluid inclusions in regional granulite terranes and geochronological data from other gold deposits and may have widespread implications for the formation of gold deposits in the southern superior province

re os and sr nd pb isotope constraints on source of fluids in the zhifang mo deposit qinling orogen china abstract the zhifang mo deposit is located in the northeastern qinling orogen along the southern margin of the north china craton the deposit represents a quartz vein system hosted in the mesoproterozoic xiong er group volcanic rocks we identify three hydrothermal stages early middle and late characterized by veinlets of quartz pyrite quartz molybdenite pyrite chalcopyrite galena sphalerite and quartz carbonate assemblages respectively five molybdenite samples from the zhifang deposit yield re os ages ranging from 241 2 1 6 ma to 247 4 2 5 ma with an isochron age of 246 0 5 2 ma 2 mswd 7 4 and a weighted mean age of 243 8 2 8 ma 2 mswd 5 5 the re os age shows that the mo mineralization occurred during the indosinian orogeny and suggests that the mineralization is unrelated to the yanshanian magmatism or the paleo mesoproterozoic volcanic hydrothermal event this study also reports a new sr nd pb isotope dataset from ore sulfides in an attempt to constrain the source of the ore forming fluids ten sulfide samples from middle stage of the zhifang mo deposit yield i sr t ratios of 0 710286 0 711943 with an average of 0 711004 e nd t values between 19 5 and 14 8 with an average of 16 7 and 206 pb 204 pb i 207 pb 204 pb i and 208 pb 204 pb i ratios of 17 126 17 535 15 374 15 466 and 37 485 37 848 with averages of 17 380 15 410 and 37 631 respectively one pyrite from the early stage yield i sr t of 0 722711 0 722855 with an average of 0 722783 which is higher than those of the middle stage sulfides and suggests equilibration with wallrocks the e nd t values are in the range of 17 3 to 16 6 with a mean at 17 0 and 206 pb 204 pb i 207 pb 204 pb i and 208 pb 204 pb i ratios are 17 386 15 405 and 37 622 respectively the ore sulfides show higher pb isotope ratios higher e nd t and lower i sr t values than the host rocks the results suggest that the ore forming fluids had lower i sr t and higher e nd t values than the ore sulfides and were possibly sourced from the dengfeng complex the southward subduction of the north china craton beneath the huaxiong block during the triassic was possibly responsible for the formation of the waifangshan orogenic mo system

how rossby wave breaking over the pacific forces the north atlantic oscillation 1 anticyclonic rossby wave breaking rwb over a well defined limited area region of the east pacific leads to the positive polarity of the north atlantic oscillation nao by locally piling up wave activity where it may be advected downstream resulting in increased wave activity flux and anticyclonic rwb over the subtropical atlantic a composite time series shows that pacific rwb occurs several days prior to the atlantic rwb and the peak of the nao index following pacific rwb a channel of increased pseudomomentum flux extends from the pacific wave breaking region northeastward toward midlatitudes of eastern north america where pseudomomentum density accumulates for several days prior to moving eastward and leading to anticyclonic rwb over the atlantic

an assessment of the impact of transient eddies on the zonal flow during a blocking episode using localized eliassen palm flux diagnostics abstract the eliassen palm e p flux applied to zonal men flows is an indicator of both the flux of eddy activity and the eddy forcing of the zonal mean flow for time mean flows a localized e p flux is derived and used diagnostically to assess the impact of transient eddies on a major blocking episode that occurred over the south pacific during the southern hemisphere winter of 1979 in contrast to previous studies that have focused on the mean quasi geostrophic potential vorticity equation the focus here is on the mean momentum equations eddy transports and the associated induced meridional circulation and other internal adjustments necessary to maintain the thermal wind balance are gathered together allowing the residual circulation and the effects of the eddies to be determined the time mean equations of motion are thus transformed to consist of mean terms the residual circulation and the divergence of a localized e p flux vector the latter is a measure of the eddy forcing of the mean flow

contributions of downstream eddy development to the teleconnection between enso and the atmospheric circulation over the north atlantic abstractthe spatiotemporal evolution of various meteorological phenomena associated with el nino southern oscillation enso in the north pacific north american north atlantic sector is examined using both ncep ncar reanalyses and output from a 2000 yr integration of a global coupled climate model particular attention is devoted to the implications of downstream eddy developments on the relationship between enso and the atmospheric circulation over the north atlantic the el nino related persistent events are characterized by a strengthened pacific subtropical jet stream and an equatorward shifted storm track over the north pacific the wave packets that populate the storm tracks travel eastward through downstream development the barotropic forcing of the embedded synoptic scale eddies is conducive to the formation of a flow that resembles the negative phase of the north atlantic oscillation nao the more frequent and higher persistence of those episodes during el nino winters contribute to the prevale

north pacific north atlantic relationships under stratospheric control 1 based on a linear regression correlation analysis of monthly mean atmospheric sea level pressure slp data from the national centers for environmental prediction ncep reanalysis 1948 2000 we find a significant anticorrelation between pressure in the northern north atlantic and north pacific only if the stratospheric circulation is in the strong polar vortex regime but not when the vortex is weak since some general circulation models gcms e g european center hamburg echam4 are biased toward the strong vortex regime svr they tend to reproduce this anticorrelation already in the mean the pattern of the arctic oscillation ao is shown to be consistent with the mean surface pressure differences between the two stratospheric regimes the typical sw ne tilt of the node line of the north atlantic oscillation nao found with linear analyses i e with such that do not take the regime character of the stratospheric circulation into account in northern hemisphere winter is due to a superposition of correlation patterns based on physical processes working in the troposphere a strictly meridional dipole and the pattern resulting from planetary wave refraction in the strong vortex regime and those produced by the rapid transition from one stratospheric regime to the other with subsequent downward propagation of the signal this result underlines the necessity of the application of nonlinear statistics or the restriction of linear statistics to variations in the stable quasi linear environment of natural regimes

late archean granitoid hosted lode gold deposits yilgarn craton western australia deposit characteristics crustal architecture and implications for ore genesis granitoid hosted lode gold deposits constitute a sub group of late archean lode gold deposits in the yilgarn craton of western australia they share a number of common characteristics including 1 a strong structural control on a variety of scales 2 in most instances the presence of mineralisation in adjacent supracrustal sequence 3 wallrock alteration and vein assemblages consistent with the addition of sio2 k2o co2 s na2o but dependent on the p t conditions of the host environment and ore fluid 4 a metal association comprising au ag as bi te w mo and low concentrations of cu pb and zn and 5 deposition from a low moderate salinity near neutral h2o co2 ch4 fluid over a temperature and pressure range from 250 to 600 c and 1 to 4 kbar which corresponds to a range of crustal environments from lower greenschist to upper amphibolite facies these characteristics suggest that the granitoid hosted lode gold deposits represent a coherent genetic group that is equivalent to the more abundant greenstone hosted lode gold deposits of the craton in combination lode gold deposits irrespective of their host rocks and host terrane formed over a range of crustal levels and developed late in the tectonic sequence of the craton granitoids which host lode gold mineralisation are older than the inferred age of mineralisation by at least 10 million years and in combination with thermodynamic and isotope studies indicate that the host granitoids are not the dominant source of the ore fluid however the host granitoids do provide a structural and to a lesser extent chemical trap for gold bearing fluids in combination trace element and isotope studies of greenstone and granitoid hosted deposits suggest that the ore fluid originated from a deep mid to lower crustal source and at least interacted with granitic rocks at some stage the ore fluid composition is quite constant over the range of crustal levels from deep to shallow implying that the extent of modification by interaction with fluid conduit rocks is variable but not substantial

nd and sr isotope study of hydrothermally altered granite at san manuel arizona implications for element migration paths during the formation of porphyry copper ore deposits a study of the nd and sr isotope composition of the late cretaceous monzogranite stock at san manuel arizona and its mineralized alteration halo was undertaken in order to assess the transport of nd and sr that accompanied the hydrothermal alteration sampling was along a 1 km transect perpendicular to the alteration zones extending from the potassically altered core to the propylitically altered fringe of the system large isotopic differences between the stock and the enclosing 1 4 b y old granitic wall rock coupled with the original homogeneity of the latter provide optimal conditions for detecting evidence of chemical transport the mineralizing porphyry stock has a lower 87 sr 86 sr ratios 0 708 and a higher epsilon nd 6 than the precambrian granite wall rock 0 782 11 the 87 sr 86 sr ratios of the altered wall rock decrease regularly from 0 782 to 0 715 from the propylitic alteration zone to the stock contact indicating that material flow was primarily from the stock into the wall rock consistent with an orthomagmatic model for porphyry copper ore genesis the sr in the ore zone is 75 percent stock derived and evidence of stock derived sr is found up to 700 m into the wall rock the sr and rb concentration variations are mainly controlled by the alteration mineralogy and do not correlate with the isotopic variations the epsilon nd values and the sm and nd concentrations of the altered wall rock show subtle changes that are mostly confined to the potassically altered zone only one wall rock sample located 0 5 m from the stock contact is strongly disturbed the results suggest that sr isotopes may provide a useful tool for studying or locating fossil hydrothermal systems whereas the relatively immobile nd isotopes are reliable indicators of the magmatic provenance of altered intrusions

pb sr isotopic evidence for contribution of deep crustal fluid to the hishikari epithermal gold deposit southwestern japan abstract the gold bearing quartz adularia veins of the world class hishikari mine in southwestern japan occur in a geological regime where the rocks of the upper to middle crust are simple and their chemical and sr nd pb isotopic compositions are well studied detailed comparison of pb and sr isotopic data of the hishikari veins with those of all possible source materials demonstrates that metals in the veins were essentially derived from a mixture of magmatic fluid with a deep crustal fluid that originated near the boundary between the shimanto middle crust and the underlying subcontinental crustal materials we propose that the release of the deep crustal fluid was triggered by intrusion of the shishimano rhyodacite magma related to timing of the mineralization this fluid mixture carried metals to the brittle upper crust along fissures created by extensional stress forming the ore deposits although the deep crustal fluid has not been paid much attention it may be distributed over a large scale in the deep crust from the continent to the arc system and play an important role in the genesis of magmatic hydrothermal ore deposits and in the generation of flow induced deep tremor

the archean proterozoic transition evidence from the geochemistry of metasedimentary rocks of guyana and montana abstract chemical and isotopic compositions of ancient sedimentary rocks have in some cases provided evidence of first order changes yin the composition and extent of continental crust from the archean to the proterozoic we reversed the typical sampling pattern comparing metapelites and carbonates from proterozoic greenstone belts with those from an archean continental margin sequence and found the reverse of the typical age composition relations metapelites and volcaniclastic metagreywackes from the early proterozoic greenstone belts of northern guyana resemble those of many archean greenstone belts in ree trace and major element compositions mean ratios la sm 5 0 la th 5 1 eu eu 0 80 th u 3 4 median k 2 o na 2 o 0 8 schists from an archean continental marginal sequence in montana have compositions like many post archean metapelites derived from continental sources mean ratios la sm 6 8 la th 2 7 eu eu 0 67 th u 5 2 median k 2 o na 2 o 1 7 other archean continental basin sediments also resemble their post archean counterparts implying that upper continental crusts of these eras may not have differed significantly in these respects however temporal change may have occurred in upper crustal contents of ni and cr many archean clastic metasedimentary rocks of both continental and greenstone belt provenance have contents of these compatible elements higher than in their post archean equivalents dolomitic limestone from a greenstone belt of northern guyana has a very low 87 sr 86 sr ratio of 0 7007 such low values may reflect the local influence of mantle derived volcanic rocks during carbonate deposition diagenesis or metamorphism and they may not be reliable indicators of the evolution of sr in seawater archean dolomitic marbles from the continental marginal sequence of montana have 87 sr 86 sr ratios of 0 7065 and higher significantly more radiogenic than many accepted values for carbonates of archean greenstone belts

the evolution of the southern abitibi greenstone belt in light of precise u pb geochronology this paper summarizes u pb zircon ages for the archean southern abitibi greenstone belt and integrates them together with zircon and baddeleyite data for three new samples into a general framework for the evolution of the region new ages are reported for the ghost range gabbroic complex 2713 super 7 sub 5 ma and for a pyroclastic volcanic rock of the gauthier group 2700 or 3 ma a previously determined age of 2701 super 3 sub 2 ma for the felsic volcanic skead group is confirmed by magmatic zircons from a second sample that also contains a xenocrystic component or 2720 ma indicating that the skead volcano was built on top of an older volcanic sequence the compiled ages show that the southern abitibi greenstone belt developed between 2750 and 2670 ma the earliest ages date remnants of volcanic complexes that occur at the periphery of the belt major preorogenic magmatism was confined mainly to the period 2720 to 2700 ma in general each episode was characterized by the essentially coeval formation of komatiitic tholeiitic and calc alkalic igneous rocks taking into consideration the known geologic geochemical and isotopic data this association is consistent with evolution in paired active are and back are systems older crust was absent from the region but it may have interacted with these arcs and rift systems farther to the west the extensional regime was followed by a period of compression that caused folding and thrusting emplacement of calc alkalic plutons and deposition of turbidites between 2700 and 2688 ma the magmatism became predominantly alkalic during the main timiskaming period between 2681 and 2676 ma this event was accompanied by the deposition of alluvial fluvial sequences and was followed by renewed compression that caused polyphase folding and thrusting probably between approximately 2676 and 2670 ma lamprophyre dikes were associated with these final stages of deformation postorogenic activity includes faulting and episodes of hydrothermal activity locally associated with gold mineralization ages in the range 2630 to 2580 ma for hydrothermal minerals e g titanite and rutile camflo suggest a correlation of these events with lower crustal magmatism and metamorphism as recorded for example in the adjacent kapuskasing zone

the molybdenite re os isotope chronology in situ scheelite and wolframite trace elements and sr isotope characteristics of the chuankou tungsten ore field south china abstract the chuankou tungsten ore field situated in the central area of the qing hang ancient suture zone in south china is characterized by predominantly quartz vein type tungsten mineralization that formed near the contact between the chuankou granite and slightly metamorphosed silt bearing sericite slate based on field work cathodoluminescence molybdenite re os dating and in situ laser ablation inductively coupled plasma mass spectrometry la icp ms analysis the chuankou tungsten ore was formed at 230 6 2 9 ma to 229 4 2 6 ma in a typical indosinian metallogenic event in addition three distinct generations of scheelite and two types of wolframite can be clearly distinguished type 1 wolframite has a semiautomorphic grain or brecciated vein structure with a high heavy rare earth element hree content and an obvious negative eu anomaly type 2 wolframite grains are strongly altered as residual pseudomorphic structures by ore forming fluids and have relatively low ree contents sch 1 scheelite is present in the interior of the type 2 wolframite grains the sch 1 scheelite grains have an elevated ree content and low 87sr 86sr ratios with a strongly negative eu anomaly which suggests an inheritance signal of the host rocks comparatively sch 2 and the altered sch 1 scheelite have characteristic extremely low ree contents and remarkably strong positive eu anomalies these scheelites also have increased 87sr 86sr ratios and low 88sr signals sch 3 is idiomorphic with perfect oscillating zoning the ree content of sch 3 which typically has the lowest 87sr 86sr ratios is higher than those in sch 1 and sch 2 and the extremely high 88sr signals indicate a distinct thermal fluid event that was directly derived from the host rock the correlations between the ree and nb of scheelite imply a type b substitution of sch 1 and sch 2 but a type c substitution for sch 3 the correlation of eun and eun shows an eu3 substitution process for stages sch 1 and sch 2 and an eu2 substitution process for stage sch 3 thus we confirm that ore bearing hydrothermal rocks must undergo early stage metasomatism and filling middle stage fluid mixing between wall rocks and magmatic hydrothermal activity and refilling of late stage magmatic hydrothermal activity during the metallogenic process during the indosinian period the mineralization stages of polymetallic deposits in the indosinian were composed of stage 1 240 to 220 ma and stage 2 220 to 200 ma the chuankou tungsten ore field can be considered as the typical representation of the stage 1 metallogenic event in south china this ore field is derived from remelting of the ancient basement and was reduced by regional extension under the dominant compression regime in the south china block

assessing the origin of sr and nd isotopes and ree y in middle upper pleistocene travertines from the acquasanta terme area marche central italy and implications for neotectonics abstract pleistocene bedded travertines from acquasanta terme display ranges of sr and ree y contents 462 1576 mg kg and 250 13 789 ng g respectively which are consistent with an evaporitic rock source paas normalized ree y patterns may support the origin of travertine bearing fluids from marine rocks travertines exhibit a very narrow range of 87sr values from 1 9 to 1 84 or 87sr 86sr ratios from 0 70782 6 to 0 70786 6 indicating an unchanged rock source throughout the travertine depositional time from about 350 to 26 ka likely represented by burano evaporites upper triassic as suggested by previous authors no sr contribution from magmatic sources has been detected travertines also display a very narrow range of nd values from 9 1 to 7 8 or 143nd 144nd ratios from 0 51217 to 0 51224 indicating an unchanged source also for ree y through time likely the same one providing sr lastly chemical and isotopic data of acquasanta travertines have been compared with those of bedded travertines from semproniano tuscany of similar age in particular 87sr values clearly distinguish between the two groups in agreement with their different rock sources as a whole these new geochemical and isotopic data on acquasanta travertines have provided a deeper insight into the origin of their parent hydrothermal fluids which upwelling from significant depth circulated through an area still affected by major seismic activity in particular the application of nd isotopes has resulted useful as unlike sr isotopes of fluid which tend to re equilibrate rather quickly with rocks along upwelling pathways nd isotopes sluggishly do so thus better reflecting the fluid source

synoptic view of the north atlantic oscillation abstract this article investigates the synoptic characteristics of individual north atlantic oscillation nao events by examining the daily evolution of the potential temperature field on the nominal tropopause the 2 pvu surface this quantity is obtained from the national centers for environmental prediction national center for atmospheric research ncep ncar reanalysis dataset for the winter season for both phases the nao is found to originate from synoptic scale waves as these waves evolve into the low frequency nao pattern they break anticyclonically for the positive phase and cyclonically for the negative phase the results of this analysis suggest that it is the remnants of these breaking waves that form the physical entity of the nao throughout the nao events for both phases the nao is maintained by the successive breaking of upstream synoptic scale waves when synoptic scale disturbances are no longer present mixing processes play an important role in the nao decay as in other recent

late archean and early proterozoic gold tungsten mineralization in the zimbabwe archean craton rb sr and sm nd isotope constraints the sm nd technique has been successfully used to date scheelites from lode gold and tungsten deposits in the archean midlands greenstone belt zimbabwe two phases of mineralization have been established which correlate with late archean and early proterozoic magmatic events in the region the gold deposits are mainly structurally controlled and are spatially associated with high strain zones and internal synvolcanic to late tectonic tonalite plutons most gold bearing structures can be categorized into one of two preferred orientations parallel to acutely oblique with the main s1 fabric or crosscutting s1 at a high angle and striking parallel to locally developed d2 structures or fabrics sm nd dating of scheelite demonstrates that these two structural populations are characterized by discrete phases of gold mineralization the main s1 parallel gold deposition dated at 2 66 0 05 ga correlates with the late archean trondhjemite tonalite granodiorite event in zimbabwe the s1 discordant phase has yielded an age of 2 41 0 07 ga broadly corresponding to the timing of emplacement of the great dyke and reactivation of the late archean high strain zones sr isotope data provide important constraints on the evolution of the hydrothermal fluids

archaean au ag mineralisation at racetrack near kalgoorlie western australia a high crustal level expression of the archaean composite lode gold system the racetrack au ag deposit in the archaean yilgarn block western australia is hosted by a porphyritic basalt in a low greenschist facies setting and is associated with a brittle strike slip fault system three distinct and successive stages of hydrothermal activity and late quartz carbonate veining resulted in multiple veining and or brecciation stages i and ii are au bearing whereas stage iii and late veins are barren the ore shows features of both classic epithermal and mesothermal deposits alteration assemblages typified by sericitization carbonization silicification and chloritization are similar to those of mesothermal gold deposits wheras the quartz vein textures including comb rosette plumose and banded ore mineralogyof arsenopyrite pyrite chalcopyrite sphalerite galena freibergite tetrahedrite tennantite fahlore electrum and gold and metal associations cu as ag sn sb w au and pb are more characteristics of epithermal deposits fluid inclusions related to stage ii are two phase and aqueous with 1 8 average 4 wt nacl equiv and co2 content of 0 85 molal pressure corrected homogenisation temperatures range from 190 c to 260 c mineral assemblages indicate that ore fluid ph ranged between 4 2 and 5 3 fo 2 between 10 38 8 and 10 39 6 bars and m s between 10 3 2 and 10 3 6 calculated chemical and stable isotope compositions require a component of surface water in the ore fluid depositing the mineralisation but evidence for deep crustal pb indicates that deeply sourced fluids were also involved the deposit is interpreted to have formed in a shallow environment via mixing of deeply sourced fluids from at least as deep as the base of the greenstone belt with surface waters it therefore represents the upper crustal end member of the crustal depth spectrum of archaean lode gold mineralisation

garnet and scheelite as indicators of multi stage tungsten mineralization in the huangshaping deposit southern hunan province china abstract the huangshaping w mo pb zn deposit in southern hunan province south china contains multiple generations of garnet and scheelite in skarn and sulfide carbonate altered rocks optical characteristics and chondrite normalized rare earth element reen patterns obtained by in situ laser ablation inductively coupled plasma mass spectrometry analysis were used to distinguish different generations of garnet and scheelite these data show a clear correspondence of garnet reen patterns to major element zonation with hrees e g gd lu being depleted overall coarse grained garnets in the huangshaping deposit have extreme hree depletions and significant lree e g la eu enrichment particularly for ce pr and nd this indicates that rees in these garnets are the result of coupled substitutions ca2 viii 1 ree3 viii 1 and fe2 iv 1 al3 iv 1 medium grained garnets have reen patterns showing significant lree enrichment and depleted hrees with high sn contents this suggests that substitution of rees in these garnets occurs as ca2 viii 1 ree3 viii 1 sn4 iv 1 al3 iv 1 the fact that medium grained garnets have high sn contents indicates mineralizing fluids were oxidizing which is consistent with significant positive eu anomalies however hump shaped reen patterns for garnet rims suggest substitution by ca2 viii 2 na viii 1 ree3 viii 1 where nd tb are preferentially incorporated into the garnet lattice over other rees group 1a scheelite has black cores in cathodoluminescence images and reen patterns showing extreme lree enrichment and hree depletion group 1b scheelite has cores with fine oscillatory zoning and enriched lrees with depleted hrees similar to the reen patterns of group 2a scheelite that occur as rims with bright cl surrounding both group 1a and 1b scheelite the substitution mechanism for rees in these three types of scheelite is ca2 viii 3 viii 1 ree3 viii 2 with being a ca site vacancy the influence of ree speciation in the hydrothermal fluid dominates the reen patterns of these types of scheelite however for group 2b bright rims of scheelite rees are incorporated as ca2 viii 2 na viii 1 ree3 viii 1 similar to the garnet rims finally scheelite mo contents and eu values that decrease from group 1a to 2b support a temporal decrease in oxygen fugacity of the mineralizing fluids ratios of y ho and mo contents that decrease from group 1a and 1b to group 2a and 2b scheelites are similar to those in porphyry related skarn w mo and quartz vein au w deposits respectively our studies also suggest that all these scheelites in this deposit formed from magmatic fluids at the huangshaping deposit medium grained garnets associated with group 1a scheelite precipitated from evolved magmatic fluids during prograde metamorphism as indicated by their complementary y ho ratios paragentically younger scheelite particularly group 2b may have formed from dilute magmatic fluids that underwent large scale hydrothermal circulation the characteristics of group 1b and 2a scheelite likely reflect a transitional environment and fluid mixing during tungsten mineralization in the polymetallic huangshaping deposit

pacific sea surface temperature and the winter of 2014 it is shown from historical data and from modeling experiments that a proximate cause of the cold winter in north america in 2013 2014 was the pattern of sea surface temperature sst in the pacific ocean each of the three dominant modes of sst variability in the pacific is connected to the tropics and has a strong expression in extratropical sst and weather patterns beginning in the middle of 2013 the third mode of sst variability was two standard deviations positive and has remained so through january 2015 this pattern is associated with high pressure in the northeast pacific and low pressure and low surface temperatures over central north america a large ensemble of model experiments with observed ssts confirms that sst anomalies contributed to the anomalous winter of 2014

a review of the geochronology of the amazonian craton tectonic implications abstract the available geochronological data for the amazonian craton permit delineation of its main age provinces and their respective tectonic development demarcation of the boundaries of each age province is primarily based on rb sr whole rock isochrons supported by k ar determinations on minerals some u pb results on zircons pb pb whole rock isochrons and sm nd model ages complement these data in key areas at the center of the amazonian craton lies the archean age central amazonian province bounded in its northern part by the maroni itacaiunas mobile belt which developed during early proterozoic times the western and southern margins of the archean core are bordered by three tectonic provinces 1 the rio negro juruena magmatic arc 2 the rondonian mobile belt and 3 the sunsas mobile belt each belt borders the western margin of the preceding belt and each records a successively younger middle proterozoic orogeny within the central amazonian province 2 7 ga age determinations have been obtained from the serra dos carajas area although the maroni itacaiunas belt includes several reworked archean nuclei rock units formed during the 2 2 1 9 ga trans amazonian orogeny predominate the isotopic evidence suggests that a mantle derived component constituted a significant portion of the crust accreted at that time the rio negro juruena province is of mid proterozoic age 1 75 1 50 ga and includes almost entirely mantle derived material juxtaposed with the pre existent continental mass along a series of successive magmatic arcs the rondonian and sunsas provinces both exhibit older sialic basements 1 5 ga the former is characterized by important tectonomagmatic events in the 1 45 1 25 ga interval whereas the latter records tectonic reworking at 1 1 0 9 ga finally the amazonian craton is bordered to the east by the late proterozoic paraguai araguaia or araguaia tocantins fold belt

a classification scheme for epigenetic archaean lode gold deposits recent research has shown that archaean lode gold deposits occur in environments that range in their metamorphic grade from prehnite pumpellyite to lower granulite facies based on this data a new classification is proposed for these deposits in this classification shallow level gold deposits are classed as epizonal the so called mesothermal deposits are mesozonal and the deeper deposits commonly in mid amphibolite or lower granulite terrains are hypozonal

the role of dynamic tropopause rossby wave breaking for synoptic scale buildups in northern hemisphere zonal available potential energy abstractzonal available potential energy az measures the magnitude of meridional temperature gradients and static stability of a domain here the role of northern hemisphere dynamic tropopause 2

sm nd and rb sr isotope systematics of scheelites possible implications for the age and genesis of vein hosted gold deposits a positive correlation between present day sup 143 nd sup 144 nd and sup 147 sm sup 144 nd ratios from scheelite samples from the hollinger mcintyre coniaurum gold deposit of ontario canada corresponds to an age of 2403 plus minus 47 ma and may date the age of gold mineralization initial isotope ratios of scheelites suggest that the fluid responsible for the scheelite and gold mineralization was probably of mantle origin and that it subsequently interacted with continental crust

lead isotope signature of early proterozoic ore deposits in western africa comparison with gold deposits in french guiana lead isotope analyses of samples from ore deposits of the west african shield trace the metallogenic evolution of the early proterozoic or birimian period the selected deposits which include the loulo poura and banora gold deposits the faleme iron deposit and the perkoa gan hanhui and pilimpikou base metal deposits are representative of each stage of the so called eburnean evolution the study was completed by an analysis of gold deposits in the french guianan shield which is a rifted remnant correlative of the west african craton the isotopic compositions of most of the galenas cluster in a narrow field 206 pb 204 pb 14 60 15 15 207 pb 204 pb 14 96 15 23 208 pb 204 pb 34 34 34 71 corresponding to the initial lead isotopic composition of birimian mineralization secondary isochrons obtained on cogenetic lead depleted sulfides all converge toward the same narrow field it is likely that they reflect an in situ addition of radiogenic lead to older lead from the eburnean event the calculated ages 2236 2741 ma have no clear geologic significance the elongated field of initial lead compositions requires a mixing between juvenile mantle derived lead as expressed in the syngenetic deposits perkoa mu 9 11 and a more radiogenic component such as old 2 150 ma crustal lead as expressed in the late orogenic deposits dorlin thr stockwork mu 10 06 this increase in mu values reflects a gradual increase in the older recycled crustal lead component favored by the tectonic change from d 1 thrusting to d 2 gold bearing vertical strike slip faulting the age of the old recycled crust would almost certainly be earliest proterozoic 2300 2145 ma dabakalian no perceptible archcan lead influx is required to explain the genesis of these deposits geochronological data from other sources bracket most of the eburnean metallogenesis between 2153 or 13 ma 2sigma age of the dabakalian metamorphism and 1949 or 55 ma 2sigma age of the last post tectonic granites pb pb model ages respectively 2113 ma for the early so called syngenetic ore deposits and 2014 ma for the late orogenic mesothermal gold deposits are consistent with these independent geochronologieal data and probably reflect fairly well the approximate geologic ages of these deposits

effect of latitudinal variations in low level baroclinicity on eddy life cycles and upper tropospheric wave breaking processes abstract an analysis of the potential vorticity gradient and the refractive index in quasigeostrophic qg flows on the sphere reveals that the absolute vorticity and the stretching parts have two contradictory effects on the horizontal shape of the baroclinic waves when the full variations of the coriolis parameter are taken into account in each term the absolute vorticity effect favors the anticyclonic southwest northeast tilt and anticyclonic wave breaking awb and is stronger in the upper troposphere in contrast the stretching effect promotes the cyclonic northwest southeast tilt and cyclonic wave breaking cwb and is more efficient at lower levels a positive eddy feedback acting on the latitudinal variations of the zonal winds is deduced because the absolute vorticity and the stretching effects are respectively more and less efficient with increasing latitude a more northward southward jet renders awb more less probable and cwb less more probable the jet is pushed or maintained mor

ore genesis of the zhuxi supergiant w cu skarn polymetallic deposit south china evidence from scheelite geochemistry abstract scheelite is the main ore mineral in skarn type tungsten deposits which can be used to track the ore forming processes and sources the zhuxi w cu deposit 3 44 mt wo3 at 0 54 and 0 10 mt cu at 0 57 located in the northern part of the jiangnan orogen is one of the largest tungsten deposits in the world skarn and orebodies occur mainly within the contact zone between the mesozoic highly fractionated intrusions and carboniferous carbonate sediments huanglong and chuanshan formations our data reveal that the rees of scheelite are mainly controlled by the substitution mechanism 3ca2 2ree3 ca scheelites from the zhuxi deposit show negative eu anomalies in the prograde skarn stage but positive eu anomalies in the retrograde skarn stage in the chondrite normalized ree patterns variation of eu anomalies recorded the ore forming processes the negative eu anomalies were inherited from the mesozoic granites and the positive ones formed under more reduced redox conditions the decrease of mo concentrations along with increase of eu and ce of scheelite from prograde to retrograde skarn stage support a temporal decrease in oxygen fugacity of the mineralization fluids the scheelites from the zhuxi deposit are characterized by low end t values 10 1 to 7 0 and high initial 87sr 86sr ratios 0 71231 0 72371 which are different from the scheelites hosted in vein type au w deposits contributed mainly by mantle the nd sr isotopes of scheelites are consistent with the results of the three mesozoic granites indicating their genetic relationship however the scheelites show variable nb ta compositions which straddle between the values of mesozoic granites and the country rock of shuangqiaoshan group meta sedimentary rocks indicating the shuangqiaoshan group also has contributed to mineralization this is different from a commonly accepted model that the ore forming fluids and metals were exsolved exclusively from the granite plutons

comparative fe and sr isotope study of nephrite deposits hosted in dolomitic marbles and serpentinites from the sudetes sw poland implications for fe as au bearing skarn formation and post obduction evolution of the oceanic lithosphere abstract nephrites belonging to both the dolomite related and serpentinite related genetic types from the zloty stok deposit and jordanow l ski and naslawice prospects in the leza ophiolite respectively were analyzed for fe and sr isotope compositions these deposits in the central sudetes sw poland are unusually situated relatively close to each other this study is a first attempt to perform combined fe and sr isotope study of nephrites our results show that fe in the fe as au bearing skarn samples from zloty stok 2 77 7 00 wt fe 56fe 0 07 to 0 14 and 57fe 0 12 to 0 21 to which the dolomite related nephrite belongs is not inherited from the host dolomitic marbles ca 0 4 wt fe 56fe 0 08 to 0 07 and 57fe 0 12 to 0 09 but derived from the nearby ca 340 ma granite intrusion 2 64 5 64 wt fe in contrast iron in the serpentinite related nephrites 2 06 3 88 wt fe 56fe 0 41 to 0 45 and 57fe 0 59 to 0 66 was likely inherited from host serpentinites 5 27 4 81 wt fe rather than metasomatically derived from adjacent granite intrusions 0 13 0 45 wt fe moreover both the marble transformation into a dolomite related nephrite and fe as au bearing skarn and the abyssal serpentinite through ophiolite towards serpentinite related nephrite transformation are accompanied by a progressive increase of 56fe and 57fe this increase is regardless of changes in the bulk fe content increasing during the dolomite related nephrite formation and decreasing during serpentinite related nephrite formation this phenomena may be caused by one of the below listed factors or combinations a preferential incorporation of heavy iron by tremolite and diopside b preferential incorporation of the heavy iron in the fe3 bearing phases crystallizing during nephrite formation c preferential incorporation of the heavy fe from migrating granite derived fluids positive fractionation between aqueous fe bearing fluid and tremolite diopside d positive isotope fractionation between dolomite antigorite precursor and newly formed amphibole clinopyroxene e change of the fe oxidation state furthermore fe in the rock forming tremolite from the serpentinite related nephrites is isotopically heavier than fe in tremolite from the dolomite related ones in contrast to the iron the isotopic composition of strontium combined with its content and structural evidence suggest multiple sources for this element in the case of the dolomite related nephrite ca 3 4 ppm sr initial 87sr 86sr 0 7085 sr inheritance from the host dolomitic marble ca 90 ppm sr initial 87sr 86sr 0 7081 as well as its derivation from intrusions of both the syn to late tectonic ca 340 ma granites ca 400 440 ppm sr and post tectonic 305 ma granites 86 4 ppm sr is suggested in the case of the serpentinite related nephrite 6 3 61 7 ppm sr initial 87sr 86sr 0 7037 to 0 7081 the situation is similar i e sr in the most primitive samples tends to be sourced from ophiolitic rocks up to 2 4 ppm sr in serpentinite whereas in the more evolved types it was likely delivered from the adjacent ca 340 ma 8 8 102 6 ppm sr partially rodingitized granites as well as 305 ma granites ca 80 ppm sr moreover these granites caused the fluid flow responsible for sr bearing clinozoisite vein formation these veins are likely related with nephrite formation and with a metallic mineralization

the anomalous merging of the african and north atlantic jet streams during the northern hemisphere winter of 2010 the north atlantic jet stream during winter 2010 was unusually zonal so the typically separated atlantic and african jets were merged into one zonal jet moreover the latitude height structure and temporal variabilityofthe northatlanticjet duringthis winterweremore characteristic ofthe northpacific this work examinesthe possibility of aflow regime changefrom an eddy driven to a mixed eddy thermally drivenjet a monthly jet zonality index is defined which shows that a persistent merged jet state has occurred in the past both at the end of the 1960s and during a few sporadic months the anomalously zonal jet is found to be associated with anomalous tropical pacific diabatic heating and eddy anomalies similar to those found during a negative north atlantic oscillation nao state a lagrangian back trajectory diagnosis of eight winters suggests the tropical pacific is a source of momentum to the atlantic and african jets and that this source was stronger during the winter of 2010 the results suggest that the combination of weak eddy variance and fluxes in the north atlantic along with strong tropical heating act to push the jet toward a merged eddy thermally driven state the authors also find significant sst anomalies in the north atlantic which reinforce the anomalous zonal winds particularly in the eastern atlantic

sm nd sr c and o isotope systematics in hydrothermal calcite fluorite veins implications for fluid rock reaction and geochronology article i nfo the 147 sm 143 nd isotope system may be used to determine the age of hydrothermal vein growth for single veins or sets of veins providing that the minerals in these veins formed from a hydrothermal fluid with initially homogeneous 143 nd 144 nd in this study we determined the 147

characteristics of the atlantic storm track eddy activity and its relation with the north atlantic oscillation abstract this study focuses on feedbacks of the high frequency eddy activity onto the quasi stationary circulation particularly with regard to the north atlantic oscillation nao the methodology consists of analyzing ncep ncar reanalysis data and sensitivity runs from a high resolution nonhydrostatic regional model consistent with recent studies results show that the jet displacement characteristic of the nao phenomenon depends strongly on the dynamics of the synoptic scale waves and the way they break positive and negative phases of the nao are closely related to anticyclonic and cyclonic wave breaking respectively indeed the high frequency momentum flux whose sign is directly related to the type of wave breaking is correlated with the nao index over the atlantic the peak of the momentum flux signal precedes that of the nao by a few days suggesting that wave breaking is triggering nao events two examples illustrate the significant impact of single storms in particular those occurring in the e

rb sr k ar and stable isotope evidence for the ages and sources of fluid components of gold bearing quartz veins in the northern sierra nevada foothills metamorphic belt california gold bearing quartz veins occur in and near major fault zones in deformed oceanic and island arc rocks west of the main outcrop of the sierra nevada composite batholith veins typically occupy minor reverse faults that crosscut blueschist to amphibolite grade metamorphic rocks whose metamorphic ages range from early paleozoic to jurassic vein micas and carbonate quartz mica assemblages that formed by hydrothermal metasomatism of ultramafic wall rocks in the alleghany grass valley washington and mother lode districts yield concordant k ar and rb sr ages the dated veins are significantly younger than prograde metamorphism penetrative deformation and accretion of their host rocks to the continental margin new and previously published mineralization ages from 13 localities in the sierra foothills range from about 140 to 110 m y ago with mean and median between 120 and 115 m y the age relations suggest that mineralizing fluids were set in motion by deep magmatic activity related to the resumption of east dipping subduction along the western margin of north america following the late jurassic nevadan collision event co 2 bearing fluids responsible for metasomatism and much of the vein mica carbonate albite and quartz deposition in several northern mines were isotopically heavy delta 18 o asymp 8 14ppm delta d between about 10 and 50ppm and do not resemble seawater magmatic or meteoric waters metasomatic and vein filling mica dolomite magnesite and quartz in altered ultramafic rocks generally formed from fluids with similar sr and o isotope ratios at a given locality consistent quartz mica delta 18 o fractionations delta 18 o sub q m 4 5 4 9ppm from various localities imply uniform equilibration temperatures probably between 300 degrees and 350 degrees c on a local mine scale fluids responsible for both carbonate alteration of mafic and ultramafic wall rocks and albitic alteration of felsic and pelitic rocks had similar sr isotope ratios samples from three veins in the central alleghany district fit a 115 7 or 3 m y rb sr isochron with a 87 sr 86 sr i value of approximately 0 7119 inferred 87 sr 86 sr ratios of metasomatic fluids from mines in different parts of the foothills region vary considerably 0 704 0 718 suggesting that sr was derived from sources ranging from western assemblage mesozoic ophiolitic or arc volcanic rocks to early paleozoic continent derived clastic rocks of the shoo fly complex systematic geographic variations in both sr and o isotopes can be rationalized by assuming extensive fluid interaction with rocks similar to the ones that are exposed within a few kilometers of the veins but the ultimate sources of the fluids and of au and other constituents may be independent of these isotopically lighter meteoric fluids deposited some late quartz overgrowths and occupied secondary fluid inclusions in earlier vein quartz