alaskan type nature and pge mineralization of the wuxing mafic ultramafic complex in eastern part of the central asian orogenic belt abstract the wuxing mafic ultramafic complex is located in the eastern part of the central asian orogenic belt caob it consists of hornblende olivine clinopyroxenite hornblende clinopyroxenite clinopyroxenite gabbro and diorite hornblende occurs in all the rock types of the complex and is pargasite in composition clinopyroxene is diopsidic in composition with high cao and low tio2 contents the flat ree and sub parallel trace element patterns of both clinopyroxene and hornblende suggest that these rocks were formed by fractional crystallization from common magma with no significant crustal contamination enrichment in large ion lithophile elements relative to high field strength elements of the silicate minerals together with the variable sulfur isotope compositions 34s 2 55 11 01 of the sulfides indicate the involvement of subducted oceanic materials into the mantle source these petrological mineralogical and geochemical features strongly suggest the alaskan type nature of the wuxing complex the hydrous parental magma of the wuxing complex was derived from partial melting of the mantle wedge which had been metasomatized by subducted melts fluids the wuxing complex is a unique pt pd rich ni cu sulfide deposit in the caob the ore minerals which are dominated by pyrite pyrrhotite pentlandite chalcopyrite and platinum group mineral pgm mainly occur in clinopyroxenite and hornblende clinopyroxenite the sulfide ores are predominantly present as net textured and disseminated textures pentlandite and chalcopyrite associated with pyrrhotite commonly occur in the marginal zone of the pyrrhotite grains the pgms occur as interstitial grains at the contact between base metal sulfides and silicate minerals or along the crack of pyrrhotite or clinopyroxene or as inclusions in pyrrhotite the occurrences of sulfides and pgms in the wuxing complex together with sulfur isotope compositions and pge patterns reveal that the pge enrichment of the alaskan type complexes can be attributed to the high degree partial melting of the mantle source sulfur involvement in the source and pge transportation of hydrous melts

experimental calibration of the aluminum in hornblende geobarometer with application to long valley caldera california volcanic rocks a new geobarometer based on the al content of igneous hornblendes in equilibrium with melt fluid biotite quartz sanidine plagioclase sphene and magnetite or ilmenite has been calibrated experimentally the calibration was performed by equilibrating the required phase assemblage over the pressure range 2 8 kbar at 740 780c and then analyzing euhedral hornblendes in equilibrium with glass melt experiments were performed on natural samples of both volcanic and plutonic rocks earlier empirical calibrations of this geobarometer relied on analyzing natural hornblendes from plutons with the required phase assemblage and inferring pressure from nearby metamorphic country rocks the experimental calibration differs from the empirical calibrations especially above 5 kbar and shows that the al content of hornblendes in equilibrium with the required phase assemblage is greater for a given total pressure than previously thought the geobarometers uncertainty is dramatically reduced the derived equation is p plus minus 0 5 kbar 3 minus 3 46 plus minus 0 24 4 23 plus minus 0 13 al sup t the geobarometer is applied to post bishop tuff volcanic rocks from long valley caldera california and reveals that most rhyodacites in this complex erupted from depths of about 6 km these eruptions occurred over 500 000 yr suggesting that the rhyodacitic magma reservoir beneath longmore valley had reached a steady p depth t state less

geochemistry and chronology of the early paleozoic diorites and granites in the huangtupo volcanogenic massive sulfide vms deposit eastern tianshan nw china implications for petrogenesis and geodynamic setting abstract the eastern tianshan orogen contains many late paleozoic porphyry cu and magmatic cu ni deposits recent studies demonstrate that several early paleozoic volcanogenic massive sulfide vms cu polymetallic and porphyry cu deposits were discovered in the northern part of eastern tianshan this study presents zircon u pb whole rock geochemical and sr nd isotopic data for granites and diorites from the huangtupo vms cu zn deposit northern part of the eastern tianshan our results can provide constraints on the genesis of intermediate and felsic intrusions as well as early paleozoic geodynamic setting of the northern part of eastern tianshan la icp ms zircon u pb analyses suggest that the granites and diorites were formed at 435 2 ma and 440 2 ma respectively geochemical characteristics suggest that the huangtupo granites and diorites are metaluminous rocks exhibiting typical subduction related features such as enrichment in lile and lree and depletion in hfse the diorites have moderate mg positive end t values 6 4 to 7 3 and young nd model ages indicative of a depleted mantle origin the granites exhibit mineral assemblages and geochemical characteristics of i type granites and they have positive end t values 6 7 to 10 2 and young nd model ages suggesting a juvenile crust origin the early paleozoic vms cu polymetallic and porphyry cu deposits in the northern part of eastern tianshan were genetically related the formation of the early paleozoic magmatic rocks as well as vms and porphyry cu deposits in the northern part of eastern tianshan was due to a southward subduction of the junggar oceanic plate

sm nd and sr isotope systematics of scheelite from the giant au w deposit muruntau uzbekistan implications for the age and sources of au mineralization the application of the sm nd isotope system of scheelite to dating of low sulfide quartz vein hosted au mineralization is still under discussion in the present work new sm nd and rb sr data for scheelite from the giant muruntau myutenbai au deposit kyzylkum western uzbekistan are discussed based on the geological relationship mineralogical properties and trace element characteristics two types of scheelite can be distinguished within the deposit the first one is represented by early bluish luminescent and weakly coloured scheelite generation 1 found within strongly deformed flat quartz veins the apparent isochron defined by this scheelite 351 22 ma is interpreted as a mixing line typically brownish to orange and yellowish luminescent scheelite from steeply dipping veins generation 2 defines a sm nd isochron age of 279 18 ma end 9 5 0 3 mswd 1 5 no evidence for mixing or disturbance by late alteration were found for these scheelites this sm nd isochron age agrees with the rb sr and k ar age range for wall rock alteration in this deposit reported previously the age of 280 ma is interpreted to date the high grade ore formation in the muruntau deposit there are currently no reliable age data available on the magmatic events in the muruntau region probably there is some overlap in time of the hercynian gold deposition with the intrusion of lamprophyric dykes the nd and sr isotopic signatures of scheelite define the wall rocks mainly metasiltstones and metasandstones as the most probable sources for these elements in scheelite

relationships between meso cenozoic denudation in the eastern tian shan and uranium mineralization in the turpan hami basin nw china constraints from apatite fission track study abstract the eastern tian shan tectonic belt located in the southern domain of the central asian orogenic belt consists of the bogda mountain range turpan hami tuha basin and choltagh mountain range from north to south understanding the meso cenozoic denudation history of the eastern tian shan is critical to unravel the genesis of sandstone type uranium u mineralization in the tuha basin in this paper thirteen granite and sandstone samples were collected along two north south transects in the west of the eastern tian shan for apatite fission track thermochronological study the apatite fission track ages obtained in this study in combination with the thermal history modeling results and previous thermochronological data indicate three main episodes of denudation in the eastern tian shan since the mesozoic i e late jurassic to early cretaceous 160 135 ma late cretaceous to early eocene 100 50 ma and late eocene to early miocene 35 20 ma the late cretaceous denudation events are related to the kohistan dras arc accretion collision that affects the tian shan mountain range extensively whereas the cenozoic ones are related to the india asia collision regional distribution of apatite fission track ages in the eastern tian shan and comparison with u mineralization ages in the tuha basin suggest that the choltagh mountain range began to denudate in the late jurassic exposing high u bearing volcanic rocks on the surface and resulting in significant u mineralization in the southern part of the tuha basin in the cretaceous whereas the bogda mountain range in the north did not experience significant denudation until the late eocene due to the relatively low exhumation of the bogda mountain range and limited exposure of u bearing rocks u mineralization in the tuha basin is minor during the cenozoic but the newly deposited sediments helped the preservation of the u deposits that were formed in the cretaceous

the brittle plastic transition in experimentally deformed quartz aggregates deformation experiments have been conducted to provide constraints on the processes responsible for the brittle plastic transition in quartz aggregates a correlation between mechanical behavior and distinctive microstructural characteristics indicates that the brittle plastic transition in nonporous quartzite involves at least three transitions in deformation mechanism that occur with increasing temperature and or pressure first there is a transition from cataclastic faulting to semibrittle faulting microstructural observations indicate that this transition occurs due to the activation of dislocations in addition faulting is more stable in the semibrittle faulting regime due to the blunting of the stresses at the advancing fault tip by dislocation glide second there is a transition from semibrittle faulting to semibrittle flow this transition corresponds to a change from localized to distributed deformation microstructural observations indicate that microcracks nucleate in response to stress concentrations at dislocation pileups in the semibrittle flow regime we conclude that the transition to semibrittle flow occurs when the stress intensity at crack tips is insufficient to allow propagation across grain boundaries third there is a transition from semibrittle flow to dislocation creep microstructural observations suggest that this transition occurs as a result of an increase in grain boundary mobility with increasing temperature in addition microstructural observations indicate that a transition from dominantly mode i axial to mode ii shear microcracking occurs with an increase in confining pressure from 0 4 to 0 8 gpa regardless of temperature the differential stresses supported by the experimentally deformed samples are higher than those expected under geologic conditions however a comparison of the experimentally produced microstructures to those reported from natural fault zones suggests that similar processes are operative in the laboratory and in the earth the results of this study provide further evidence to indicate that the brittle plastic transition in the continental crust occurs over a relatively wide range of conditions

hydrothermal alteration and associated mineralization in the freda rebecca gold deposit bindura district zimbabwe the freda rebecca mine is currently the largest gold producer in zimbabwe the ore deposit is hosted by two main shear systems crosscutting the rebecca diorite and bindura granodiorite 2 65 ga as well as shamvaian metasediments which are affected by contact metamorphism following the intrusion of the bindura granodiorite intensive hydrothermal alteration developed preferentially in the dioritic part of the igneous complex rebecca diorite the hydrothermal alteration started with an extensive k dominated hydrothermal metasomatism in the whole rebecca diorite it was followed by less penetrative hydrothermal alteration developed preferentially near shear zones and veinlets hydrothermal metasomatism caused microcline and biotite formation prevailing in the rebecca diorite two main stages of post metasomatic hydrothermal alteration and mineralization were distinguished based on spatial relationships between different minerals and some geochemical aspects in the first stage an actinolite tourmaline arsenopyrite mineralization formed which is characterized by ni co arsenopyrite associated with actinolite tourmaline and quartz the second lower temperature stage gave a polyphase gold rich mineralization that developed in four phases which are distinguished by different parageneses including phase 1 actinolite chlorite clinozoisite epidote quartz calcite arsenopyrite pyrite pyrrhotite chalcopyrite phase 2 chlorite epidote calcite gold native bi bi pb sulfides galena chalcopyrite fahlore pyrite fe gersdorffite phase 3 epidote calcite ni co fe as s phases co fe gersdorffite phase 4 chlorite calcite quartz the gold mineralization is exclusively associated with phase 2 and developed in three sulfide parageneses gold bi pb sulfides bismuth chalcopyrite galena associated with chlorite au 1 gold galena pyrite associated with calcite and chlorite au 2 gold pyrite fe gersdorffite associated with epidote chlorite and calcite au 3 the hydrothermal alteration and mineralization formed after the consolidation of the rebecca diorite and bindura granodiorite most probably in the postmagmatic cooling stage the mineralization was emplaced either synchronously or subsequently to the shear zones which crosscut the consolidated pluton not all shear zones are mineralized and different shear zones show different amounts of mineralization and hydrothermal alteration thus it is suggested that during the cooling stage of the pluton and subsequent to the formation of the k metasomatic zone microcline biotite hydrothermal fluids preferentially followed just forming or pre existing shear zones it cannot be excluded that this process developed in a plutonic porphyry copper like environment in which the classically hydrothermal zonation did not form due to synchronous tectonic disturbance which preferentially drives the hydrothermal flow along shear zones mineral parageneses and data from chlorite geothermometry indicate that the different stages and phases of hydrothermal alteration reflect cooling stages of the hydrothermal system from 300 c in the first stage to about 150 c in the last phases

ocean science hiatus heat in the indian ocean global surface warming has slowed since the start of the twenty first century while pacific heat uptake was enhanced analyses of ocean heat content suggest that the warm water was transferred to the indian ocean through the indonesian straits

geology and geochemistry of listwaenite related gold mineralization in the sayi gold deposit xinjiang nw china abstract the sayi gold deposit is part of the sartohay ophiolitic melange in west junggar xinjiang china and is hosted by listwaenite which was transformed from serpentinite in a shear zone via fluid rock reaction gold mineralization is hosted by mylonitized listwaenites and quartz veins within listwaenite lenses formed during shearing our study demonstrates that fluid concentrated au ag as sb cu cr ni and co during transformation from serpentinite to listwaenite and ductile deformation deformation due to shearing played an important role in focusing ore forming fluid along the shear zone gold mineralization accompanied formation of hydrothermal minerals in the following stages carbonate quartz pyrite cqp stage i mariposite gersdorffite gold mgg ii quartz carbonate pyrite qcp iii gold bearing quartz iv and dolomite calcite stage v geological characteristics of mgg in mylonitized listwaenite demonstrate that gold mineralization formed during the transition from ductile to brittle deformation which was followed by gold bearing quartz veins filling brittle fractures the au contents show a positive correlation with ag as cu and sb contents in mylonitized listwaenite samples consistent with the coexistence of native gold gersdorffite arsenian pyrite and chalcopyrite in mylonitized listwaenite pressure decrease due to hydraulic fracturing during the transition from ductile to brittle deformation induced gold deposition in the sayi deposit

the post collisional cihai iron skarn deposit eastern tianshan xinjiang china abstract the cihai iron skarn deposit is located in the southern part of the eastern tianshan xinjiang northwestern china the major iron orebodies are banded and nearly parallel to each other the iron ores are hosted in an early diabase dike and in skarn post ore diabase dikes cut the iron ores and their hosting diabase hydrothermal activity can be divided into four stages based on geological and petrographic observations initial k na alteration stage i skarn minor magnetite event ii retrograde skarn magnetite main ore event iii and quartz calcite sulfide veining iv zircon u pb dating yields ages of 286 5 1 8 ma for early diabase and 275 8 2 2 ma for post ore diabase dikes amphibole separated from massive magnetite ore gives a 40ar 39ar plateau age of 281 9 2 2 ma and is the time of ore formation formation of the cihai iron deposit is closely related to post collisional magmatism and associated cu ni au polymetallic mineralization in the eastern tianshan

laser 40ar39ar ages of tephra from indian ocean deep sea sediments tie points for the astronomical and geomagnetic polarity time scales tephra layers within deep sea sediment cores are valuable stratigraphic markers which can be radiometrically dated with high precision by the laser 40ar39ar technique two neogene ash layers from ocean drilling program odp site 758 have been dated these layers are located within detailed oxygen isotope and paleomagnetic stratigraphies which have previously been assigned ages based on the astronomically derived geomagnetic polarity time scale adgpts 7 10 28 we use the radiometric dates from the ash layers to independently evaluate the ages assigned to oxygen isotope stage 19 1 and the paleomagnetic reversals marking the brunhes matuyama boundary and the termination of the nunivak event ash d 20 21 yields an age of 800 20 ka which is consistent with an adgpts age of 780 ka for the overlying brunhes matuyama transition and with the astronomical age for oxygen isotope stage 19 1 ash i located near the top of the nunivak subchron bears evidence of excess 40ar an error weighted mean of five plateau ages gives an apparent age of 4 519 012 ma but an errorchron through a subset of the data suggests a possible eruption age of 4 43 03 ma the plateau age is in agreement with the adgpts 7 10 28 and the errorchron age is in agreement with the time scale of baksi 29 the laser 40ar39ar ages of both ashes are significantly older than the ages from the radiometrically derived time scale rdgpts of mankinen and dalrymple 3 which is primarily based upon a large dataset of k ar dated paleomagnetic poles it is essential to reconcile the adgpts with the rdgpts because radiometric age tie points are the best hope of extending the adgpts to times before 5 ma an analysis of the expected and actual variance for the astronomical and mankinen and dalrymple 3 time scales suggests that only a handful of low k ar ages may have biased the original gpts it is not necessary to invoke general systematic errors in the ar dating system to explain the discrepancies between the rdgpts and adgpts

evidence for diachronous archean lode gold mineralization in the yilgarn craton western australia a shrimp u pb study of intrusive rocks the currently accepted model for the archean lode gold deposits of the yilgarn craton postulates that they represent a coherent group of epigenetic deposits the majority of which formed during a craton scale broadly synchronous hydrothermal event late in the tectonothermal evolution of the granite greenstone terranes at ca 2640 to 2630 ma felsic rocks from the southern eastern goldfields which host or are cut by gold mineralization have shrimp ii u pb zircon ages of 2673 or 3 ma at mount charlotte 2669 or 17 ma at mount percy 2663 or 3 ma at racetrack and 2657 or 8 ma at porphyry all these ages are consistent with gold mineralization at ca 2640 to 2630 ma intermediate to felsic dikes cut typical syn to postmetamorphic lode gold mineralization at the mount mcclure and jundee deposits in the yandal greenstone belt in the north of the kurnalpi terrane the dikes give ages of 2656 or 4 2663 or 4 and 2668 or 10 ma from mount mcclure and 2656 or 7 ma from jundee requiring that mineralization and peak regional metamorphism in the belt occurred prior to ca 2660 ma however both the characteristics of the jundee and mount mcclure deposits and the relative timing of mineralization with respect to the metamorphic and structural history of the belt are similar to that seen for gold deposits elsewhere in the yilgarn craton this implies that mineralization at jundee and mount mcclure was produced prior to 2660 ma by similar processes to those seen elsewhere in the yilgarn at 2640 to 2630 ma peak metamorphism in the western higher metamorphic grade terranes of the yilgarn was not reached until ca 2630 ma some 10 to 30 m y after peak metamorphism in the kalgoorlie terrane and more than 30 m y after metamorphism in the yandal belt in addition almost all of the published robust ages supporting gold mineralization at ca 2640 to 2630 ma are from the west of the craton consideration of the new data from the yandal belt in conjunction with previously published geochronology throws doubt on the hypothesis that lode gold mineralization occurred approximately synchronously across the yilgarn craton rather it suggests that mineralization along with regional metamorphism is earlier by at least 30 m y in the northeastern yilgarn craton

new 40ar 39ar age constraints on the late palaeozoic tectonic evolution of the western tianshan xinjiang northwestern china with emphasis on permian fluid ingress laser probe dating of mylonite whole rock samples from the north tianshan main tianshan fault zone that cross cuts the north tianshan domain s southern margin yielded 40ar 39ar spectra with 255 285 ma ages biotite from an undeformed early carboniferous granite which cuts the steep mylonitic foliation in the proterozoic basement of the yili arcs s southern margin gave a 263 4 0 6 ma plateau age 1 pre carboniferous metasediments overlying this basement yielded plateau ages 1 of 253 3 0 3 muscovite and 252 3 0 3 biotite ma the permian ages of mylonites date movement on these ductile dextral strike slip shear zones whereas the mica ages are interpreted by recrystallisation as a result of fluid flow around such transcurrent faults we propose that the tianshan s permian syn tectonic bimodal magmatism was created in a non plume related yellowstone like extensional transtensional tectonic regime gold mineralisation tracing aqueous flow in the crust peaked in permian time and continued locally into the triassic the picture is emerging that a convective fluid system partly driven by magmatic heat existed in a strongly fractured and weakened crust with an elevated heat flow leading to regional scale isotope resetting we suggest that surprisingly young isotopic ages in the literature for early orogenic ultra high pressure metamorphism are similarly due to fluid mediated recrystallisation

ore genesis of the saridala gold deposit western tianshan nw china constraints from fluid inclusion s pb isotopes and 40ar 39ar dating abstract the saridala gold deposit is located in the western tianshan xinjiang nw china southwestern part of the central asian orogenic belt caob the deposit is mainly hosted in precambrian metamorphic rocks and early paleozoic granites and is structurally controlled by the shenglidaban ductile shear zone the gold orebodies consist of gold bearing quartz veins and altered mylonite the mineralization comprises three stages quartz pyrite veins early stage sulfide quartz veins middle stage and quartz carbonate veins veinlets late stage ore minerals and native gold were mainly formed in the middle stage four fluid inclusion types in quartz veins were identified pure co2 pc type co2 h2o c type aqueous w type and daughter mineral bearing s type inclusions hydrothermal fluids related to the mineralization are composed of co2 h2o nacl n2 fluids 115 307 mpa with th total values of 256 475 c peak at 320 380 c and salinities

gold mineralisation and alteration of penakacherla schist belt india constraints on archaean subduction and fluid processes abstract in the dharwar craton southern india gold deposits are found mostly along the six arcuate shear zones passing through late archaean greenstone belts 2 7 ga one such shear zone complex extends for about 400 km within and along the ramagiri hungund schist belt the penakacherla sector of this shear zone is excellently exposed enabling a detailed investigation of synorogenic gold mineralisation and its relationship to associated hydrothermal alteration metamorphism and deformation under ne sw compression associated with archaean subduction processes converted mafic volcanic rocks into amphibolites and intermediate to felsic volcanic rocks into quartz mica schists continued compression generated a 50 100 m wide shear zone complex consisting of mafic phyllonites advection of hydrothermal fluids through this shear zone and reaction between fluids and the mafic phyllonites resulted in a silicified k metasomatic assemblage mainly consisting of chlorite amphibole k mica plagioclase ankerite quartz fe oxides pyrite chalcopyrite and arsenopyrite networks of quartz and carbonate veinlets a few millimeters to a few centimeters thick formed along the foliation planes giving rise to microscopic alteration envelope in which individual veinlet systems are merged into one another to form a composite alteration system gold is found within these quartz veinlets mafic phyllonites and at their mutual contacts hydrothermal fluids have modified the primary major minor trace and lree compositions of host rocks such that their mutual behaviour became non systematic some hfse and hree also show minor mobility but the overall ree pattern generally resembles that of the precursor mafic volcanic rocks mass and volume loss gain by si and ca has made significant impact on al ti and zr abundances which are generally immobile during hydrothermal alteration however element pairs such as zr hf v sc and nb ta maintain primary inter element ratios although their absolute abundances are drastically diluted similarly ree in highly silicified and carbonatised samples are reduced but patterns remain similar to those of relatively least altered mafic phyllonites with la n yb n between 1 and 3 in some samples lree enrichment is observed elevating in la n yb n from 3 to 11 pathfinder elements and base metals such as as cd cu pb zn and sb have been added along with the au and ag 13 c of carbon varies from 16 to 21 suggesting a biogenic origin whereas coexisting pyrite 34 s ranges from 1 to 3 pointing towards the involvement of magmatic or average crustal sulphur overall concentrations of k rb sr ba nb ta ti cs cr co v y and sc and many of the ratios such as k rb la sc la yb indicate that metamorphism devolatilisation and dehydration of an oceanic subducting slab might have partially contributed the mineralising fluids and generated the alteration assemblage observed in the host rocks fluid sources were mantle and greenstone belt dehydration and devolatilisation generating observed compositional and alteration diversity

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

gold mineralization without quartz veins in a ductile brittle shear zone macraes mine otago schist new zealand greenschist facies schist which hosts the macraes mine in east otago new zealand has been pervasively altered by post metamorphic lower greenschist facies fluids over a 120 m thick section perpendicular to foliation metamorphic titanite has been replaced by rutile and epidote has been replaced by a variety of metamorphic minerals including siderite chlorite muscovite and calcite the early stages of this alteration occurred during development of a ductile cleavage associated with kilometre scale recumbent folding the cleavage was widely overprinted by a subparallel set of spaced mm scale microshears which are locally enriched in rutile and hydrothermal graphite strain was then concentrated into narrow m scale zones where more intensely deformed portions of the rock are crossed and highly disrupted by closely spaced 100 m scale microshears the highly strained rocks show a combination of mylonitic and cataclastic microstructures including crystal plastic grain size reduction and recrystallization of micas to form a new foliation muscovite has grown at the expense of albite in the mylonitic cataclasites hydrothermal alteration was accompanied by addition of pyrite arsenopyrite and gold without development of quartz veins gold precipitated with sulphides during reduction of the fluid by hydrothermal graphite the whole altered rock sequence was later cut sporadically by mesothermal quartz veins which contain gold scheelite rutile pyrite and arsenopyrite this deposit displays a continuum of post metamorphic processes and hydrothermal fluid flow which occurred during uplift of the schist belt

round hill shear zone hosted gold deposit macraes flat otago new zealand evidence of a magmatic ore fluid the 0 8 moz round hill shear zone hosted gold deposit is one of several located on or near the hyde macraes shear zone macraes flat new zealand field relationships show stockwork veins are the oldest part of the hydrothermal system followed by flat and ramp veins hanging wall shear veins formed early but have been modified by late deformation fluid inclusion microthermometric results for dominant type i inclusions show that flat and ramp veins have the same average wt percent nacl equiv values 2 2 0 6 and were precipitated from the same fluid salinity data for these veins overlap with those from hanging wall veins average 1 3 0 3 and stockwork veins 1 6 0 6 for vein margins 0 9 0 3 for vein centers although both of the latter trend toward lower overall wt percent nacl equiv values suggesting mixing between relatively dilute and more saline end members all of the above veins have similar temperatures of homogenization t h ranging between 110 and 188 c fluid inclusion trapping temperatures are considered to be 300 c equating to a 10 km depth of formation carbon dioxide dissolved in the hydrothermal fluid is responsible for up to one third of fluid inclusion apparent salinities stockwork and hanging wall veins thus have true salinities of 1 wt percent nacl equiv 0 17 molal and flat and ramp veins have true salinities of fluid inclusion volatiles from round hill and other macraes deposits are dominated by h 2 o 99 02 99 69 mol with lesser co 2 0 14 0 76 mol n 2 0 03 0 32 mol and ch 4 0 06 0 17 mol noticeable concentrations of hydrocarbons occur in many of the samples fluid inclusion cation and anion data show few components of relatively low concentration are dissolved in the hydrothermal fluid consistent with co 2 corrected microthermometric measurements a range in fluid inclusion d h 2 o values obtained for the round hill deposit is coincident with the different vein types and also indicates mixing between two fluids one fluid is considered to be o isotope shifted meteoric water as trapped by the early stockwork veins and has the lowest d h 2 o values of 80 per mil the other fluid is represented by flat and or ramp and hanging wall veins that have d h 2 o values up to 40 per mil the macraes d h 2 o data show a trend toward the magmatic water end member for geothermal systems associated with convergent plate boundaries and are consistent with a 25 to 50 percent magmatic component in the macraes hydrothermal system

provenance constraints on the xishanyao formation southern yili basin northwest china evidence from petrology geochemistry and detrital zircon u pb geochronology we conducted petrographic geochemical and new u pb laser ablation inductively coupled mass spectrometry analyses of detrital zircons in the sandstone samples from the important mengqiguer sandsto

calculated phase relations in high pressure metapelites in the system nkfmash na2o k2o feo mgo al2o3 sio2 h2o using an internally consistent thermodynamic dataset and updated models of activity composition relation for solid solutions petrogenetic grids in the system nkfmash na2o k2o feo mgo al2o3 sio2 h2o and the subsystems nkmash and nkfash have been calculated with the software thermocalc 3 1 in the p t range 5 36 kbar and 400 810 c involving garnet chloritoid biotite carpholite talc chlorite kyanite sillimanite staurolite phengite paragonite albite glaucophane jadeite with quartz coesite and h2o in excess these grids together with calculated afm compatibility diagrams and p t pseudosections are shown to be powerful tools for delineating the phase equilibria and p t conditions of na bearing pelitic assemblages for a variety of bulk compositions from high p terranes around the world these calculated equilibria are in good agreement with petrological studies moreover contours of the calculated phengite si isopleths in p t pseudosections for different bulk compositions confirm that phengite barometry is highly dependent on mineral assemblage

geochronological and geochemical constraints on the genesis of the huanren skarn cu zn deposit northeast china abstract the huanren skarn cu zn deposit is located in southeastern liaoning on the eastern edge of the north china craton ncc in this paper we present a study on the geochronologic geochemical and sr nd hf and s isotopic data for the magmatic rocks and sulfide minerals exposed in the deposit laser ablation inductively coupled plasma mass spectrometry la icp ms dating of zircon grains from two mining pits in the monzodiorite yields ages of 128 2 1 1 ma and 128 6 1 5 ma these results indicate that the magmatism in the huanren cu zn deposit might have occurred in the early cretaceous geochemically the huanren monzodiorite belongs to the high k calc alkaline and shoshonitic series is enriched in rb ba and k and is depleted in nb ta and ti the rocks also have relatively high 87sr 86sr i 0 7091 0 7099 and low end t 13 2 to 10 3 and ehf t values 14 3 to 7 8 the sr nd hf isotopic data for the monzodiorite indicate that the magma may be derived from mixed sources of the crust and mantle the 34s values of chalcopyrite galena and pyrite range from 4 4 to 5 8 with an average of 5 1 indicating that the sulfur in the deposit was mainly derived from a magmatic source the huanren cu zn deposit resulted from the magmatism and mineralization induced by the rollback of the paleo pacific plate

characteristics and genesis of kanggur gold deposit in the eastern tianshan mountains nw china evidence from geology isotope distribution and chronology abstract the kanggur gold deposit lies in east tianshan mountains eastern section of central asia orogenic belt the gold mineralization occurs on the northern margin of the aqishan yamansu island arc in the tarim plate it is mainly hosted in lower carboniferous volcanic rocks and controlled by syn tectonic intrusions and the ductile shear zone the host rock is a calc alkaline volcanic rock series consisting of andesite dacite tuff and subvolcanic rocks the gold ore bodies were distributed in transition zone from strong ductile deformation to weak deformation ore controlling structure is ew trending normal brittle ductile shear zone the gold ore bodies are composed of au bearing altered rocks and a few au bearing sulfide quartz veins the mineralization shows vertical zonation in which au was enriched in the upper orebodies au pb zn were enriched in the middle and au cu were enriched in the lower orebodies according to mineral assemblages and alteration intensity hydrothermal alteration could be divided into three zones silicification chloritization pyritization and magnetization zone major ore body pyrite phyllic rock and or sericite alteration zone and sericite chlorite alteration zone five mineralization stages are identified on the basis of mineral assemblage and crosscutting relationship of veins the 34 s values of sulfide in the ores range from 0 9 to 3 3 similar to those of the volcanic and subvolcanic rocks 3 21 1 3 indicating that the sulfur isotope composition is characterized by unfractionated mantle sulfur the lead isotope compositions of ores are between those of the volcanic rocks and subvolcanic rocks the initial 87 sr 86 sr ratios of the ores vary between 0 7077 and 0 7106 similar to those of the host rocks 0 7079 0 7125 according to the sr s and pb isotopic data it is indicated that the ore forming materials were derived from the surrounding volcanic rocks and feature deep source the 18 o values of the ore fluids vary from 3 83 to 1 77 and the d values from 46 to 66 the 18 o vs d and 18 o vs 87 sr 86 sr diagrams indicate that ore fluids were derived from dynamic metamorphic water magmatic water and meteoric water the ore forming ages of kanggur gold deposit are determined by rb sr and sm nd isochron methods the results show that the main ore forming stages of kanggur gold deposit are 290 282 ma secondary mineralization stages are 275 254 ma studies on regional geology ore geology isotope geochemistry and ore forming ages have proved that the kanggur gold deposit was formed in the compression extension transition stage during the latest paleozoic continental collision and is characterized by orogenic gold deposits

geology and structural evolution of the muruntau gold deposit kyzylkum desert uzbekistan abstract the muruntau gold deposit in the kyzylkum desert of uzbekistan is the largest single deposit 1100 tonnes of gold of the class of low sulfide syndeformation synigenous gold deposits formed in the brittle ductile transition zone of the crust within transpressional shear zones hosted by the cambrian to ordovician besopan suite the ores were deposited in pre existing thrust fault and metamorphism related permeabilities and in synmineralization dilational zones created in a large fault related fold the besopan suite is a 5 000 m thick sequence of turbiditic siltstones shales and sandstones the ore is primarily localized at the base of the besopan 3 unit which is a 2 000 m thick series of carbonaceous shales siltstones sandstones and cherts initial gold deposition took place within the sangruntau tamdytau shear zone which was developed along the stratigraphic contact between the besopan 3 and besopan 4 units during the mineralization process folding of the besopan suite and a left step adjustment in the sangruntau tamdytau shear zone were caused by two concurrent events 1 the activation of the left lateral muruntau daugyztau shear zone that developed at nearly a 90 angle to the preceding shear zone and 2 the intrusion of granitoid plutons these structural events also resulted in the refocusing of hydrothermal fluid flow into new zones of permeability

geology and fluid evolution of the wangfeng orogenic type gold deposit western tian shan china abstract the wangfeng gold deposit is located in western tian shan and the central section of the central asian orogenic belt caob the deposit is mainly hosted in precambrian metamorphic rocks and caledonian granites and is structurally controlled by the shenglidaban ductile shear zone the gold orebodies consist of gold bearing quartz veins and altered mylonite the mineralization can be divided into three stages quartz pyrite veins in the early stage sulfide quartz veins in the middle stage and quartz carbonate veins or veinlets in the late stage ore minerals and native gold mainly formed in the middle stage four types of fluid inclusions were identified based on petrography and laser raman spectroscopy co 2 h 2 o inclusions c type pure co 2 inclusions pc type nacl h 2 o inclusions w type and daughter mineral bearing inclusions s type the early stage quartz contains only primary co 2 h 2 o fluid inclusions with salinities of 1 62 to 8 03 wt nacl equivalent bulk densities of 0 73 to 0 89 g cm 3 and homogenization temperatures of 256 c 390 c vapor bubbles are composed of co 2 the middle stage quartz contains all four types of fluid inclusions of which the co 2 h 2 o and nacl h 2 o types yield homogenization temperatures of 210 c 340 c and 230 c 300 c respectively the co 2 h 2 o fluid inclusions have salinities of 0 83 to 9 59 wt nacl equivalent and bulk densities of 0 77 to 0 95 g cm 3 with vapor bubbles composed of co 2 ch 4 and n 2 fluid inclusions in the late stage quartz are nacl h 2 o solution with low salinities 0 35 3 87 wt nacl equivalent and low homogenization temperatures 122 c 214 c the coexistence of inclusions of these four types in middle stage quartz suggests that fluid boiling occurred in the middle stage mineralization trapping pressures estimated from co 2 h 2 o inclusions are 110 300 mpa and 90 250 mpa for the early and middle stages respectively suggesting that gold mineralization mainly occurred at depths of about 10 km in general the wangfeng gold deposit originated from a metamorphic fluid system characterized by low salinity low density and enrichment of co 2 depressurized fluid boiling caused gold precipitation given the regional geology ore geology fluid inclusion features and ore forming age the wangfeng gold deposit can be classified as a hypozonal orogenic gold deposit

paleozoic early mesozoic gold deposits of the xinjiang autonomous region northwestern china the late paleozoic early mesozoic tectonic evolution of xinjiang autonomous region northwestern china provided a favorable geological setting for the formation of lode gold deposits along the sutures between a number of the major eastern asia cratonic blocks these sutures are now represented by the altay shan tian shan and kunlun shan ranges with the former two separated by the junggar basin and the latter two by the immense tarim basin in northernmost xinjiang final growth of the altaid orogen southward from the angara craton is now recorded in the remote mid to late paleozoic altay shan accreted early to middle devonian oceanic rock sequences contain typically small precious metal bearing fe cu zn vms deposits e g ashele orogenic gold deposits are widespread along the major irtysh e g duyolanasayi saidi taerde kabenbulake akexike shaerbulake and tuergen hongshanzui e g hongshanzui fault systems as well as in structurally displaced terrane slivers of the western junggar e g hatu and eastern junggar areas geological and geochronological constraints indicate a generally late carboniferous to early permian episode of gold deposition which was coeval with the final stages of altaid magmatism and large scale right lateral translation along older terrane bounding faults the tian shan an exceptionally gold rich mountain range to the west in the central asian republics is only beginning to be recognized for its gold potential in xinjiang in this easternmost part to the range northerly and southerly directed subduction accretion of early to mid paleozoic and mid to late paleozoic oceanic terranes respectively to the precambrian yili block central tian shan was associated with 400 to 250 ma arc magmatism and carboniferous through early permian gold forming hydrothermal events the more significant resulting deposits in the terranes of the southern tian shan include the sawayaerdun orogenic deposit along the kyrgyzstan border and the epithermal and replacement deposits of the kanggurtag belt to the east in the chol tagh range gold deposits of approximately the same age in the yili block include the axi hot springs epithermal deposit near the kazakhstan border and a series of small orogenic gold deposits south of urumqi e g wangfeng gold rich porphyry copper deposits e g tuwu define important new exploration targets in the northern tian shan of xinjiang the northern foothills of the kunlun shan of southern xinjiang host scattered small placer gold deposits sources for the gold have not been identified but are hypothesized to be orogenic gold veins beneath the icefields to the south they are predicted to have formed in the tianshuihai terrane during its early mesozoic accretion to the amalgamated tarim qaidam kunlun cratonic block

la icp ms zircon u pb age of longwang gabbro of shanmen silver deposit in siping city and its geological significance in the mining area of the large size shanmen silver deposit in siping of southern jilin province ni cu sulfide mineralization was also found besides ag au mineralization however no reliable isotopic dating result was available for the deposit based on the interior structure of zircons from the ore bearing longwang gabrro intrusion and the results of cl analysis the authors performed in situ zircon u pb dating by means of la icp ms and as a result obtained reliable age data the results show that the gabbro intrusion was formed at 225 1 ma mswd 2 7 consistent with the age of the no 1 intrusion in the hongqiling cu ni sulfide deposit of central jilin province the comparability of the ages between the shanmen silver deposit in southern jilin and the hongqiling cu ni sulfide deposit in central jilin provides the evidence for the previous argument that both dunhua mishan and yilan yitong faults are northern extensions of the well known tanlu fault zone and that the two types of mineralization belong to different stages of tanlu fault evolution it is concluded that the two types of mineralization probably have the same derivation which could serve as an reliable guide to the exploration of these two types of mineralization in this area

paleozoic tectonic evolution of the tianshan orogen northwestern china abstract the chinese tianshan orogenic belt which extends west east for about 1500 km is one of the most important paleozoic orogenic belts in central asia it includes parts of the tarim yili central tianshan and junggar plates which are microcontinental blocks with precambrian basements and meso cenozoic depositional covers the tarim plate is separated from the yili central tianshan plate by the southern central tianshan suture early carboniferous ophiolitic melanges and blueschists are widespread in this suture and are believed to be produced by the collision between a passive continental margin on the north side of the tarim plate and an active continental margin on the south side of the yili central tianshan plate the collision occurred at the end of early carboniferous the yili central tianshan and the junggar plates are separated by the northern central tianshan suture also considered as an early carboniferous collisional zone along which the middle ordovician ophiolitic melanges blueschists and late devonian early carboniferous ophiolites are exposed in early paleozoic times the subduction of the paleo junggar ocean took place in an active margin on the north side of the yili central tianshan plate along the northern central tianshan suture at the end of early carboniferous the north side of the yili central tianshan plate collided with the north tianshan arc along this suture the paleo oceanic crust in the tianshan and adjacent region was entirely consumed at the end of early carboniferous meanwhile the tarim yili central tianshan and junggar plates were accreted to eurasia epicontinental sediments were then deposited throughout the tianshan region during the middle late carboniferous times in the early permian tianshan began to uplift with accompanying volcanic eruption and granitic intrusion the uplift was accelerated in the late permian and continental molasse was extensively deposited

early jurassic porphyry copper mineralization in ne china a case study of the yanghuidongzi deposit abstract the yanghuidongzi cu deposit is located in the southeastern part of heilongjiang province in ne china and represents one of the few known early jurassic porphyry cu deposits within the eastern edge of the xing an mongolia orogenic belt here we present new whole rock major and trace element and sr nd isotopic data zircon u pb and hf isotopic data and molybdenite re os data for units associated with the deposit laser ablation inductively coupled plasma mass spectrometry la icp ms dating of zircons from the granodiorite porphyry in the study area yielded ages of 191 0 1 1 and 191 2 1 0 ma that are interpreted to be the emplacement age of this intrusion the molybdenite re os dating undertaken during this study yielded model ages of 192 7 187 0 ma an isochron age of 188 2 3 8 ma and a weighted mean model age of 190 2 2 6 ma representing the timing of formation of the cu mineralization in this area the yanghuidongzi granodiorite porphyry contains relatively high concentrations of sio 2 68 88 72 49 wt al 2 o 3 15 37 16 31 wt and sr 230 479 ppm but relatively low concentrations of y 7 97 9 87 ppm and yb 0 72 0 85 ppm suggesting that this intrusion has an adakitic affinity combining this with the positive end t 0 7 1 1 and ehf t values 4 0 6 9 low mg values 41 50 and the low concentrations of mgo 0 86 1 22 wt cr 3 17 4 37 ppm and ni 2 11 4 20 ppm within this intrusion suggests it formed from a magma generated by the partial melting of juvenile lower crustal material during the early jurassic subduction of the paleo pacific plate

the tianger bingdaban shear zone hosted gold deposit west tianshan nw china petrographic and geochemical characteristics abstract the wangfeng tianger saridala ore district consists of over 20 orebodies with total proven gold reserves exceeding 15 tonnes the district is located on the ew striking tianger bingdaban shear zone in west tianshan mountains northwest china the lensoid orebodies are distributed along the shear zone in a region about 25 km in length and 1 km in width enhanced fluid flow and fracturing controlled location and orientation of mineralized zones during deformation along narrow shear bands oriented oblique to the overall shear zone margins fabrics in fractures and strain shadow overgrowths generally plunge steeply parallel to the lineation in the surrounding cataclasite matrix consisting of new grains of quartz and minor amounts of micas native gold occurs in mylonitized granites or mylonitized sulfide mica quartz veins gold grade is closely related with the occurrence of sulfide quartz veins pyrite and pyrrhotite in gold bearing sulfide quartz veins contain inclusions of native gold chondrite normalized rare earth element ree distribution patterns for pyrite from the orebodies show light ree enrichments and negative eu anomalies relationships between gold contents and th u zr hf and la yb n values for pyrites imply that gold rich pyrites are different from gold poor pyrites thus indicate that the pyrites in the orebodies have a different origin compared with those in wall rocks a rb sr isochron for the mylonitized au bearing quartz veins indicates an age of 224 14 ma with an initial 87 sr 86 sr ratio of 0 7294 0 0089 mswd 1 1 this age is conformed by 40 ar 39 ar dating on muscovites 220 9 to 222 5 ma which is interpreted as the age of ore formation in the tianger deposit high initial 87 sr 86 sr ratios 0 7294 high 34 s values 11 2 to 16 5 low 18 o h2o values 1 67 to 3 07 and low d values 84 to 104 indicate that the ore forming fluid was unrelated to any magmatic process

deformation mechanisms in the mylonite ultramylonite transition abstract the deformation mechanisms and controls that operate in the mylonite ultramylonite transition are interpreted from microstructural observation the investigated mylonites and ultramylonites were derived from a granitic protolith which was deformed under greenschist facies conditions and in the presence of fluid in a regional scale shear zone from northwest argentina several deformation mechanisms were recognized to operate simultaneously in different domains of the microstructure at each particular stage of the microstructural evolution this continuously mobile deformation partitioning present throughout the microstructural evolution ceases abruptly in the ultramylonite stage where a stable state microstructure is achieved domainal quartz c axis fabrics indicate that quartz deforms by crystal plastic processes at the initial and intermediate stages of deformation but solution transfer processes become predominant in the ultramylonite stage plagioclase is progressively transformed into muscovite through retrograde softening reactions k feldspar is progressively transformed into fine grade aggregates via cataclastic flow and incipient recrystallization mica deforms by kinking and basal slip with progressive development of fine grained morphologically oriented aggregates plagioclase disappearance as well as the development of intrafolial microfolds characterize the transition between the mylonitic and ultramylonitic domains disruption of these microfolds is interpreted to represent the ultimate control on the localization of the ultramylonite bands

synchronous deformation and hydrothermal activity in the shear zone hosted high sulphidation au cu deposit at peak hill nsw australia altered and mineralised rocks at peak hill are confined to a 300 500 m wide north south striking steeply dipping shear zone that is flanked by the mingelo volcanics along its western side and cotton formation siltstones along its eastern side this shear zone is defined by extensive zones of cataclasite and strongly foliated micaceous schists in marked contrast to the largely undeformed nature of the adjacent rocks advanced argillic assemblages quartz kaolinite pyrite alunite illite occur throughout the core of the peak hill deposit propylitic assemblages including albite quartz interlayered chlorite smectite illite and ankerite and a narrow discontinuous zone of argillic quartz illite pyrite alteration are developed in the mingelo volcanics along the western side of the deposit propylitic argillic and advanced argillic assemblages are overprinted by an internally zoned phase of phyllosilicate alteration that grades inwards from a peripheral sericite clay chlorite assemblage through phyllic assemblages muscovite illite pyrite paragonite to a pyrophyllite pyrite diaspore andalusite altered core au cu mineralisation is hosted by barite pyrite veins that cut the advanced argillic assemblage but pre date the phyllosilicate dominated alteration native au lacking ag calaverite te rich tennantite tetrahedrite goldfieldite chalcopyrite covellite and chalcocite occur in the barite pyrite veins no ore bearing minerals were detected in any of the alteration assemblages the total gold content of the peak hill deposit is currently 720 k ounces and this includes 100 k ounces of unmined reserves within the shear zone phyllosilicate minerals are developed in strain shadows and partly define the stretching lineation associated with dip slip movement the zonation within the phyllosilicate assemblages mimics the geometry of bends in the shear zone and minor internal structures these textures indicate that the phyllosilicate alteration developed synchronous with movement on the shear zone earlier advanced argillic alteration and mineralisation are developed in rocks derived from both sides of the shear zone hydrothermal activity associated with the earlier advanced argillic alteration was therefore either synchronous with juxtaposition of these distinct rock units or occurred during a later phase of movement on the shear zone cross cutting fibrous textures in the auriferous barite pyrite veins indicate that repeated fracturing of the advanced argillic altered rocks accompanied development of successive generations of auriferous veins concentrations of auriferous veins are localised in steeply plunging shoots that are oriented parallel to the stretching lineation in the shear zone these features all indicate movement on the host shear zone accompanied each phase of hydrothermal activity in the peak hill deposit the location alteration zonation and distribution of mineralised veins within the deposit are intimately controlled by deformation on the host shear zone synchronous with hydrothermal activity the development of high sulphidation hydrothermal systems synchronous with deformation along brittle ductile shear zones is a predictable consequence of intrusive activity during deformation in areas characterised by a high geothermal gradient the close relationship between tectonism and hydrothermal activity indicates that these deposits are likely to be located in the vicinity of regional scale shear zones deposits are likely to be aligned parallel to the regional scale structural grain and restricted to areas of conspicuous deformation as is the case at peak hill and temora nsw aluminous alteration zones concentrated in the vicinity of regional scale structures in the carolina slate belt may be a further example of this style of hydrothermal activity

zircon u pb and muscovite 40ar 39ar geochronology of the gold bearing tianger mylonitized granite xinjiang northwest china implications for radiometric dating of mylonitized magmatic rocks abstract this study focuses on zircon u pb and muscovite 40ar 39ar geochronology of gold bearing mylonitized granite in the north tianshan of china all zircon samples have euhedral hydrothermal rims which have replaced their igneous mantles igneous zircon mantles with narrow hydrothermal rims in sample ts06 give a weighted average u pb age of 403 7 5 6 ma 1 standard error mswd 1 5 n 18 zircons in ts277 show a complex texture with core detrital origin 1276 2215 ma indicating igneous mantle and a hydrothermal rim the igneous mantles give a weighted average u pb age of 443 4 3 3 ma mswd 3 1 n 10 two younger ages 394 and 400 ma have been obtained on hydrothermal rims the mantles plus rims of all zircons have positive ehf t values with an average of 3 99 0 86 mswd 2 8 n 23 the positive ehf t values suggest that the granite magma is derived from melting of juvenile crustal rocks the shearing deformation post dated granite intrusion and introduced fluid which replaced igneous zircons via dissolution and reprecipitation however the age data for zircon hydrothermal rims do not represent the time of the dissolution re precipitation the zircons crystallized in granite in the early silurian 443 ma have been replaced on their rims during middle triassic deformation 248 238 ma which was followed by brittle deformation accompanied by gold deposition at 220 ma based on 40ar 39ar dating of muscovite

petrological and geochemical features of the early paleozoic granitic gneisses and iron ores in the tianhu iron deposit eastern tianshan nw china implications for ore genesis abstract this paper reports whole rock geochemical zircon u pb and hf isotopic data for ore hosted granitic gneisses mineral compositions of oxides and sulfur isotopic data for sulfides in iron ores from the tianhu deposit central part of the eastern tianshan our results can provide crucial constraints on the genesis of granitic gneisses and early paleozoic tectonic setting of the eastern tianshan la icp ms u pb dating on magmatic zircons yielded weighted mean 206pb 238u ages of 463 to 438 ma interpreted as the crystallization ages of the granitic protoliths and the formation ages of the tianhu group zircon u pb age of ore hosted granitic gneiss ca 459 ma can provide reliable constrains on upper limit for iron mineralization age in the tianhu deposit geochemical characteristics suggest that the protoliths of the tianhu granitic gneisses are metaluminous to weakly peraluminous high k calc alkaline granitic rocks exhibiting typical subduction related features such as strong enrichment in lree and lile and depletion in hfse zircon hf isotopic compositions show a positive trend from 463 to 438 ma indicating that 460 ma magmas came from both ancient and juvenile sources whereas 438 ma magmas involved more juvenile material some early paleozoic granitoids were recently identified in the eastern tianshan with the ages between ca 475 and ca 425 ma the formation of these early paleozoic granitoids was in response to subduction processes suggesting that subduction of junggar ocean probably began in the early ordovician and lasted until late silurian pyrite and pyrrhotite in iron ores have 34scdt values from 4 6 to 15 7 which are consistent with the marine source but inconsistent with the magmatic source or those involved evaporites in skarn iron deposit geological geochemical and isotopic data suggest that the tianhu iron ores were formed by volcano sedimentary processes in a subduction environment during the early paleozoic time and tianhu is a metamorphosed volcano sedimentary iron deposit rather than a skarn iron deposit as previously proposed

evidence for dominant grain boundary sliding deformation in greenschist and amphibolite grade polymineralic ultramylonites from the redbank deformed zone central australia abstract microstructural and textural investigations by scanning sem and transmission electron microscopy tem techniques have been performed on samples taken across two quartzo feldspathic mylonite zones from the redbank deformed zone central australia one has been deformed at greenschist facies gs the second at amphibolite facies am conditions with increasing strain the rock type changes from protomylonite to mylonite to ultramylonite the protomylonites and mylonites consist of alternating quartz and polymineralic quartz feldspar bands at the highest strains a homogeneous fine grained polymineralic ultramylonite occurs shear zone geometry and microscale structures indicate that these ultramylonites experienced higher strains and were weaker than the encapsulating protomylonites and mylonites tem and sem studies of the ultramylonites reveal a rectangular to square grain shape a continuous alignment of grain and interphase boundaries across several grain diameters a grain size gs 0 5 m am 5 11 m less than the equilibrium subgrain size and open and void containing grain and interphase boundaries analysis of local textures by electron back scatter diffraction ebsd in the sem showed a very weak crystallographic preferred orientation cpo for the quartz the grain misorientation relationships are not consistent with dislocation creep being the dominant deformation mechanism all structures are of the type expected if grain boundary sliding processes had contributed significantly to the deformation consequently the deformation of such quartzo feldspathic rocks and by implication the rheology of the redbank deformed zone must have been controlled by the mechanical properties of these fine grained polymineralic ultramylonites deforming by grain boundary sliding processes this is in contrast to the pure quartz bands which deformed by dislocation creep mechanisms and were less important in the rheology of the redbank deformed zone

sims u pb rutile age of low temperature eclogites from southwestern chinese tianshan nw china article i nfo the geological evolution in the southwestern chinese tianshan orogen in nw china is poorly understood because of controversial geochronological results of the low temperature eclogites it is likely due to sm nd and rb sr isotopic disequilibrium in different mineral fractions excess 40 ar in the high pressure k bearing minerals and multi stage growths of zircon in u pb system rutile as a typical eclogite facies mineral with high u pb ratio is a feasible candidate to constrain the eclogite facies metamorphic event in this study we measured u pb rutile age data using sims cameca ims 1280 for low temperature eclogites from southwestern chinese tianshan orogen nw china we demonstrate that sims is a powerful technique for in situ u pb dating of rutile with u content as low as 1 ppm sims u pb rutile dating yielded an age of 318 7 ma which may record the time when the rocks cooled down to the closure temperature of pb in rutile ca 500 c but should be very close to the time of eclogite facies metamorphism in terms of common fast exhumation of coesite bearing eclogite this new proof strongly suggests a late carboniferous collision between kazakhstan yili block and central tianshan microcontinent

late kinematic timing of orogenic gold deposits and significance for computer based exploration techniques with emphasis on the yilgarn block western australia abstract orogenic gold deposits are a widespread coherent group of epigenetic ore deposits that are sited in accretionary or collisional orogens they formed over a large crustal depth range from deep seated low salinity h2o co2 ch4 n2 ore fluids and with au transported as thio complexes regional structures provide the main control on deposit distribution in many terranes first order faults or shear zones appear to have controlled regional fluid flow with greatest ore fluid fluxes in and adjacent to lower order faults shear zones and or large folds highly competent and or chemically reactive rocks are the most common hosts to the larger deposits focusing of supralithostatic ore fluids into dilatant zones appears to occur late during the evolutionary history of the host terranes normally within d3 or d4 in a d1 d4 deformation sequence reactivation of suitably oriented pre existing structures during a change in far field stress orientation is a factor common to many deposits and repeated reactivation may account for multiple mineralization episodes in some larger deposits absolute robust ages of mineralization support their late kinematic timing and in general suggest that deposits formed diachronously towards the end of the 100 to 200 m y long evolutionary history of hosting orogens for example in the yilgarn block a region specifically emphasised in this study orogenic gold deposits formed in the time interval between 40 and 90 m y with most about 60 to 70 m y after the youngest widespread basic ultrabasic volcanism and towards the end of felsic magmatism the late timing of orogenic gold deposits is pivotal to geologically based exploration methodologies this is because the present structural geometries of i the deposits ii the hosting goldfields and iii the enclosing terranes are all essentially similar to those during gold mineralization at least in their relative position to each other thus interpretation of geological maps and cross sections and three dimensional models can be used to accurately simulate the physical conditions that existed at the time of ore deposition it is particularly significant that the deposits are commonly related to repetitive and predictable geometries such as structural heterogeneities within or adjacent to first order structures around rigid granitoid bodies or in specific locked up fold thrust structures importantly the two giant greenstone hosted goldfields kalgoorlie and timmins show a remarkably similar geometry at the regional scale computer based stress mapping and gis based prospectivity mapping are two computer based quantitative methodologies that can utilize and take advantage of the late timing aspect of this deposit type to provide important geological aids in exploration both in broad regions and more localized goldfields both require an accurate and consistent solid geology map stress mapping requires knowledge of the far field stresses during mineralization and the empirical prospectivity mapping requires data from a significant number of known deposits in the terrane the kalgoorlie terrane in the yilgarn block meets these criteria and illustrates the potential of these methodologies in the exploration for orogenic gold deposits low minimum stress anomalies interpreted to represent dilational zones during gold related deformation coincide well with the positions of known goldfields rather than individual gold deposits in the terrane and there are additional as yet unexplained anomalies the prospectivity analysis confirms that predictable and repetitive factors controlling the siting of deposits are i proximity to and orientation and curvature of granitoid greenstone contacts ii proximity to segments of crustal faults which strike in a preferred direction iii proximity to specific lithological contacts which have similar preferred strike iv proximity to anticlinal structures and v the presence of preferred reactive host rocks e g dolerite the prospectivity map defines a series of anomalous areas which broadly conform to those of the stress map 78 correspondence the most prospective category on this map covers less than 0 3 of the greenstone belts and yet hosts 16 of the known deposits which have produced 80 of known gold thus it discriminates in favour of the larger economically more attractive deposits in the terrane the successful application of stress mapping and prospectivity mapping to geology based exploration for orogenic gold deposits indicates that more quantitative analysis of geological map data is a profitable line of research the computer based nature of these methodologies is ideal for the production of an ultimate integrated deposit target map which can be compared to other more conventional targeting parameters such as geophysical and geochemical anomalies such an integrated strategy appears the way forward in the increasingly difficult task of cost effective global exploration for orogenic gold deposits in poorly exposed terranes

geochemistry of the rare metal bearing pegmatite no 3 vein and related granites in the keketuohai region altay mountains northwest china abstract the chemical composition of a barren biotite granite a two mica granite and a rare metal bearing pegmatite the no 3 vein in keketuohai altay mountains northwest china along with mineral separates of apatite and mica were analyzed and compared in the present work bulk chemistries of biotite granite two mica granite and pegmatite rim are consistent with fractional crystallization trend from granites toward pegmatite changes in pegmatite composition can be explained mainly by fractional crystallization of biotite rb sr isochrons yield 248 8 7 5 ma for the biotite granite 247 8 6 3 ma for the two mica granite and 218 4 5 8 ma for the pegmatite rim similar geochemical characteristics including initial e nd t values ranging from 0 76 to 3 04 for apatites similar initial e nd t values for whole rock samples of studied granites and pegmatite ranged from 1 40 to 3 21 and for biotites from granites ranged from 2 75 to 3 15 suggest that these rocks were derived from a common magma source old continental crust may have played a significant role in magma generation based on these data we interpret the evolution of the keketuohai granite pegmatite by magma differentiation from a common source biotite granite was the first to crystallize followed by two mica granites the residual melt was probably stored in a granitic batholith the pegmatite veins were injected 30 m y later during another episodic tectono magmatic event in the altay mountains

deformation of granitoids at low metamorphic grade ii granular flow in albite rich mylonites abstract the high strain deformation at low metamorphic grades of three investigated granitoids is dominated by the granular flow of albite rich polyphase aggregates these aggregates formed by retrograde breakdown reactions from intermediate plagioclase and k feldspar the predominant deformation mechanism changes in granitoids as the grain size is reduced coarse grained low strain examples are deformed by a combination of intracrystalline plasticity quartz and fracturing feldspar in the mylonites intracrystalline plasticity of quartz plays only a minor role and the dominant deformation mechanism is a non cataclastic granular flow of polyphase aggregates consisting largely of albite and quartz deformation appears to be stable probably because grain growth in albite quartz mixtures is inhibited these fine grained aggregates are mechanically weaker than pure quartz aggregates thus the change in deformation mechanism mainly due to feldspar breakdown reactions appears to be important for the localization of high shear strain deformation at low metamorphic grades in granitoids and other lithologies modally dominated by feldspar the rheological behaviour of albite dominated mineral aggregates may have two consequences for middle to upper crustal deformation of modally feldspar dominated lithologies 1 feldspar in the presence of aqueous fluids can be an important mineral controlling the rheology at low metamorphic grades that is below amphibolite facies p t conditions 2 the occurrence of granular flow of fine grained polyphase aggregates in low grade granitoids is probably common and calls for great care in the modelling of middle to upper crustal rheology based on flow laws for intracrystalline plasticity of single minerals such as quartz

u pb hf zircon study of two mylonitic granite complexes in the talas fergana fault zone kyrgyzstan and ar ar age of deformations along the fault abstract a 2000 km long dextral talas fergana strike slip fault separates eastern terranes in the kyrgyz tien shan from western terranes the aim of this study was to constrain an age of dextral shearing in the central part of the fault utilizing ar ar dating of micas we also carried out a u pb hf zircon study of two different deformed granitoid complexes in the fault zone from which the micas for ar dating were separated two samples of the oldest deformed neoproterozoic granitoids in the area of study yielded u pb zircon shrimp ages 728 11 ma and 778 11 ma characteristic for the cryogenian bolshoi naryn formation and zircon grains analyzed for their lu hf isotopic compositions yielded ehf t values from 11 43 to 16 73 and their calculated thfc ages varied from 2 42 to 2 71 ga thus varying cryogenian ages and noticeable heterogeneity of meso to paleoproterozoic crustal sources was established for mylonitic granites of the bolshoi naryn formation two samples of mylonitized pegmatoidal granites of the kyrgysh complex yielded identical 206 pb 238 u ages of 279 5 ma corresponding to the main peak of late paleozoic post collisional magmatism in the tien shan seltmann et al 2011 and zircon grains analyzed for their lu hf isotopic compositions yielded ehf t values from 11 43 to 16 73 and calculated thfc ages from 2 42 to 2 71 ga indicating derivation from a paleoproterozoic crustal source microstructural studies showed that ductile brittle deformation of pegmatoidal granites of the kyrgysh complex occurred at temperatures of 300 400 c and caused resetting of the k ar isotope system of primary muscovite deformation of mylonitized granites of the bolshoi naryn formation occurred under high temperature conditions and resulted in protracted growth and recrystallization of micas the oldest ar ar muscovite age of 241 ma with a well defined plateau from a pegmatoidal granite of the kyrgysh complex is considered as a minimum age of dextral motions along this section of the fault in the triassic while younger ages varying from 227 ma to 199 ma with typical staircase patterns indicate protracted growth and recrystallization of micas during ductile deformations which continued until the end of the triassic

alder creek sanidine acs 2 a quaternary 40ar 39ar dating standard tied to the cobb mountain geomagnetic event accurate 40ar 39ar dating of quaternary and holocene samples requires a standard neutron fluence monitor of appropriate age this standard should be isotopically homogenous at the scale of analysis and should be well intercalibrated with other standards several such standards have been proposed including sanidine from the 1 19 ma alder creek rhyolite acs turrin et al 1994 turrin b d donnely nolan j m hearn b c jr 1994 40ar 39ar ages from the rhyolite of alder creek california age of the cobb mountain normal polarity subchron revisited geology 22 251 254 this sanidine is satisfactorily homogeneous well intercalibrated with fish canyon sanidine fcs renne et al 1998 renne p r swisher c c deino a l karner d b owens t l depaolo d j 1998 intercalibration of standards absolute ages and uncertainties in 40ar 39ar dating chem geol 145 117 152 and is linked to the astronomically calibrated magnetic polarity time scale since the alder creek rhyolite lava is the type occurrence of the cobb mountain event cm we collected 408 kg of this rock from which we anticipate being able to extract more than 8 kg of 425 m sanidine crystals analyses of sanidine phenocryts from the acs 2 from three separate irradiations and two distinct grain sizes yield ages ranging from 1 190 0 004 to 1 194 0 003 ma1 with a weighted mean age of 1 193 0 001 ma mswd 0 74 n 225 based on fcs 28 02 ma renne et al 1998 renne p r swisher c c deino a l karner d b owens t l depaolo d j 1998 intercalibration of standards absolute ages and uncertainties in 40ar 39ar dating chem geol 145 117 152 the value of the intercalibration factor renne et al 1998 renne p r swisher c c deino a l karner d b owens t l depaolo d j 1998 intercalibration of standards absolute ages and uncertainties in 40ar 39ar dating chem geol 145 117 152 is rfcsacs 2 0 04229 0 00012 n 8 identical with that of the original acs measurements 0 04229 0 00012 renne et al 1998 renne p r swisher c c deino a l karner d b owens t l depaolo d j 1998 intercalibration of standards absolute ages and uncertainties in 40ar 39ar dating chem geol 145 117 152 the age of acs 2 is in agreement with the recent astronomical calibration of the cm event 1 215 to 1 190 ma channell j e t mazaud a sullivan p turner s raymo m e 2002 geomagnetic excursions and paleointensities in the matuyama chron at ocean drilling program sites 983 and 984 iceland basin j geophys res 107 6 10 1029 2001jb000491 the apparent absence of xenocrysts and excess argon suggests that multigrain analyses are feasible and therefore the amount of material can be tailored to experimental requirements aliquots from various grain sizes will be available upon request zircon is also potentially available which may be of interest to u th he researchers