late miocene environmental change in nepal and the northern indian subcontinent stable isotopic evidence from paleosols neogene sediments belonging to the siwalik group crop out in the himalayan foothills along the length of southern nepal carbon and oxygen isotopic analyses of siwalik paleosols from four long siwalik sections record major ecological changes over the past 11 m y the carbon isotopic composition of both soil carbonate and organic matter shifts dramatically starting ca 7 0 ma marking the displacement of largely c3 vegetation probably semi deciduous forest by c4 grasslands by the beginning of the pliocene all the flood plains of major rivers in this region were dominated by monsoonal grasslands the floral shift away from woody plants is also reflected by the decline and final disappearance of fossil leaves and the decrease in coal logs in the latest miocene a similar carbon isotopic shift has been documented in the paleosol and fossil tooth record of pakistan and in terrigenous organic matter from the bengal fan showing that the floral shift was probably continentwide the latest miocene also witnessed an average change of 4 in the oxygen isotopic composition of soil carbonate as observed previously in pakistan the reasons for this are unclear if not diagenetic a major environmental change is indicated perhaps related to that driving the carbon isotopic shift recently described pollen and leaf fossils from the surai khola section show that evergreen forest was gradually displaced by semi deciduous and dry deciduous forest between 11 and 6 ma the gradual nature of this floral shift which culminated in the rapid expansion of c4 grasses starting 7 0 m y ago is difficult to explain by a decrease in atmospheric pco2 alone cerling et al 1993 but fits well with a gradual onset of monsoonal conditions in the late miocene in the northern indian subcontinent himalayan uplift driving both monsoonal intensification and consumption of co2 through weathering may be the common cause behind major late miocene environmental change globally however the decline of effective moisture associated with monsoon development has probably slowed not increased the rate of consumption of co2 by chemical weathering of himalayan sediments

synthetic fluid inclusions xvii pvtx properties of high salinity h2o nacl solutions 30 wt nacl application to fluid inclusions that homogenize by halite disappearance from porphyry copper and other hydrothermal ore deposits fluid inclusions that homogenize by disappearance of the halite crystal after the vapor bubble has disappeared have been reported from a wide range of ore forming systems while this inclusion type is most commonly observed in porphyry copper and similar magmatichydrothermal ore deposits they have also been reported from iron oxide copper gold iocg mississippi valley type orogenic lode greenstone gold massive sulfide unconformity u and mantotype deposits as well as from non ore associated granitoids and oceanic crust the lack of experimental data to interpret microthermometric data from these inclusions combined with poor petrographic characterization of inclusion origin has led to a wide range of inferred pt trapping conditions for the inclusions the relationship between liquid vapor homogenization temperature thl v halite dissolution temperature tmhalite and pressure has been determined using synthetic h2o nacl fluid inclusions that homogenize by halite disappearance the experimental data cover the range thl v 150 to 500 c and tmhalite 275 to 550 c an empirical equation describing the relationship between pressure thl v and tmhalite has been developed to estimate formation pressures from microthermometric data and is valid from pressures along the liquid vapor halite curve to 300 mpa a detailed literature review reveals that the results of this study cannot be applied retroactively to estimate pressures of previously reported inclusions that homogenize by halite dissolution for several reasons first most workers have not collected and reported the data in a manner that allows one to determine if the inclusions have trapped a single homogeneous phase and have not leaked or changed volume following trapping thus it is not possible to determine if the inclusions show consistent microthermometric behavior within a group of coeval inclusions additionally many published studies provide only summaries of results from numerous samples or present the data graphically precluding application of our results to individual inclusions however based on our review it appears that much of the published data for inclusions that homogenize by halite dissolution represent inclusions that have either trapped a halite crystal along with the liquid or have reequilibrated by necking and or stretching results from this study have been used to estimate minimum formation pressures for inclusions from the ditrau alkaline massif transylvania romania the musoshi stratiform copper deposit zaire the bismark skarn deposit northern mexico the naica chimneymanto deposit mexico the questa porphyry molybdenum deposit new mexico and the bingham canyon porphyry cu mo deposit utah in each case pressures estimated using results from the present study are in good agreement with previous pressure estimates however in some cases estimated pressures both our estimates as well as those of other authors appear to be unreasonably high based on the geologic setting at the time of formation these results highlight the currently limited understanding concerning pressures depths of ore formation

scheelite malayaite and axinite bearing skarns from el hammam central morocco in the el hammam fluorite mining district central morocco 50 km southwest of meknes interlayered pelite and limestone beds have been metamorphosed into banded calc silicate rocks under the influence of a hidden granitic pluton of variscan age various calc silicate bands occur in the following zonal relationship 1 pelitic hornfels quartz muscovite biotite and plagioclase 2 pyroxene feldspar band salitic pyroxene anorthite k feldspar and titanite 3 grossularite band grossularite accessory diopside and idocrase and 4 marble or wollastonite band field relationships suggest that at least part of the calc silicate rocks predated the skarns and were not genetically linked to them mineral assemblages indicatethat the conditions of formation were 525 degrees t 580 degrees c and x sub co 2 0 15 at p total 2 kbars assumed skarns replaced the calc silicate rocks but not the marble beds based on crosscutting and replacement relationships a sequence of three successive skarn formation stages has been recognized scheelite bearing skarns formed during the first stage they occur as unzoned conformable bodies and consist of salite to ferrosalite anorthite scheelite titanite and k feldspar malayaite bearing skarns formed during the second stage they occur conformably to the banding and display different zonal patterns along strike where the replaced calc silicate band is a wollastonite band the succession of zones is zone 1 tin bearing andradite variable tin content up to 1 6 wt sno 2 and wollastonite zone 2 tin bearing andradite variable tin content up to 5 6 sno 2 and malayaite casnsio 5 and zone 3 hedenbergite and malayaite where the replaced rock is a pyroxene feldspar band or a scheelite bearing skarn malayaite bearing skarns consist of hedenbergite and malayaite where the replaced rock is a grossularite band the zonal pattern is disseminated malayaite and disseminated tin bearing andradite and malayaite axinite bearing skarns formed during the third stage as veins and pods in calc silicate rocks and scheelite and malayaite bearing skarns they consist of ferroaxinite and datolite and in places tin bearing manganaxinite up to 1 7 sno 2 wt malayaite bearing skarns formed at t 480 degrees c log f sub o 2 25 and f sub co 2 100 bars assuming p total 2 kbars the temperature was probably higher for scheelite bearing skarns and lower for axinite bearing skarns late alteration of skarns involved partial silicification sulfidation recarbonation and hydration

isotopic reconstructions of habitat change surrounding the extinction of sivapithecus a miocene hominoid in the siwalik group of pakistan abstract this research presents an isotopic study of a wide range of mammalian taxa from the miocene siwalik group of pakistan with a focus on two time intervals 9 3 9 2 ma when the hominoid sivapithecus was present and 8 1 8 0 ma shortly after sivapithecus became extinct the purpose of this investigation is to reconstruct the vegetation mosaic at both time levels in order to determine what sivapithecus habitat was like and what changes in habitat and climate may have taken place by the time sivapithecus went extinct both carbon and oxygen stable isotopes were sampled from inorganic carbonate in tooth enamel results indicate a vegetation mosaic of both closed and open habitat at both time intervals but a decrease in forest accompanied by an increase in open habitat including c 4 grasses during the younger interval individuals from many species cluster with each other with respect to both carbon and oxygen isotope values indicating a spectrum of feeding adaptations exploiting different parts of the habitat isotopic values for sivapithecus suggest that it fed in the forest upper canopy taxa feeding in the most closed wet habitat become extinct by 8 1 ma furthermore higher 18 o values over time suggest a change in climate with a reduction in annual rainfall perhaps accompanied by changes in precipitation sources or rainfall regime as well these results suggest that forests became fragmented over time while still present in the younger level much of the forest was replaced by open habitat including patches of c 4 grass forest loss and fragmentation is a likely cause of the extinction of sivapithecus

fluid chemistry structural setting and emplacement history of the rosario cu mo porphyry and cu ag au epithermal veins collahuasi district northern chile the rosario cu mo ag deposit is located in the collahuasi district of northern chile it comprises high grade cu ag au epithermal veins superimposed on the core of a porphyry cu mo orebody rosario has mining reserves of 1 094 million metric tons mt at 1 03 percent copper an additional 1 022 mt at 0 93 percent copper occurs in the district at the nearby ujina and quebrada blanca porphyry deposits the rosario reserve contains over 95 percent hypogene ore whereas supergene sulfide ores dominate at ujina and quebrada blanca mineralized veins are hosted within lower permian volcanic and sedimentary rocks lower triassic granodiorite and late eocene porphyritic quartz monzonite the rosario fault system a series of moderate southwest dipping faults has localized high grade cu ag au veins at cerro la grande similar high grade cu ag au veins are hosted in north northeast trending sinistral wrench faults normal movement in the rosario fault system is interpreted to have been synchronous with sinistral strike slip deformation at la grande hydrothermal alteration at rosario is characterized by a k feldspar core focused in the rosario porphyry that grades out to a secondary biotite albite magnetite assemblage paragenetic relationships indicate that magnetite was the earliest formed alteration product but has been replaced by biotite albite vein crosscutting relationships indicate that k feldspar formed during and after biotite albite alteration chalcopyrite and bornite were deposited in quartz veins associated with both k feldspar and biotite albite assemblages the early hydrothermal fluid was a hypersaline brine 40 45 wt nacl that coexisted with vapor between 400 degrees and 600 degrees c weakly mineralized illite chlorite intermediate argillic alteration of the early k and na silicate assemblages was caused by moderate temperature 250 degrees 350 degrees c moderate salinity brines 10 15 wt nacl molybdenite was precipitated in quartz veins that formed between the potassic and intermediate argillic alteration events these fluids were 350 degrees to 400 degrees c with salinities between 10 and 15 wt percent nacl porphyry style ore and alteration minerals were overprinted by structurally controlled quartz alunite pyrite pyrophyllite dickite and muscovite quartz phyllic alteration assemblages the quartz alunite pyrite alteration formed at 300 degrees to 400 degrees c from fluids with a salinity of 10 wt percent nacl the pyrophyllite dickite assemblage formed between 250 degrees and 320 degrees c from dilute 5 wt nacl fluids an upward flared zone of muscovite quartz pyrite altered rocks surrounds the fault controlled domain of advanced argillic alteration thick veins 0 5 2 m wide of fault hosted massive pyrite chalcopyrite and bornite precipitated brines with a salinity of 30 wt percent nacl at temperatures of 250 degrees to 300 degrees c pressure depth estimates indicate that at least 1 km of rock was eroded at rosario between formation of the k na silicate and advanced argillic assemblages this erosion was rapid occurring over a period of 1 8 m y the rosario porphyry intruded immediately after the incaic tectonic phase implying that it was emplaced as the domeyko cordillera underwent gravitational collapse expressed as normal faults in the upper crust gravitational sliding potentially accelerated exhumation and helped to promote telescoping of the high sulfidation environment onto the rosario porphyry the hydrothermal system responsible for porphyry cu mineralization at rosario was partially exhumed prior to the formation of high sulfidation ore and alteration assemblages this implies that emplacement of a second blind intrusion occurred somewhere beneath the rosario and cerro la grande high sulfidation vein systems and is supported by the fault geometry and zoning of precious metals and sulfosalts at the district scale

late miocene upward and outward growth of eastern tibet and decreasing monsoon rainfall over the northwestern indian subcontinent since 10 ma 1 many geologic observations suggest that the eastern portion of the tibetan plateau has expanded eastward and grown in height over the past 15 10 ma and other observations suggest that climate over the northwestern indian subcontinent nw india became more arid between 11 and 7 ma we suggest that they are linked higher terrain increased orographic precipitation over eastern tibet which diabatically heated the atmosphere there that heating then forced subsidence to the west via the mechanism proposed by rodwell and hoskins and subsidence suppressed rainfall simple gill model calculations for a heat source displaced from the equator show such subsidence and a regression of july august outgoing long wave radiation olr over southeastern tibet with rainfall shows a negative relationship between eastern tibet and nw india consistent with the proposed link between growth of eastern tibet and diminished south asian monsoon rainfall over the northwestern indian subcontinent

advent of strong south asian monsoon by 20 million years ago abstractthe monsoonal paleoclimate of india has been critical for understanding the tectonic history of himalayan and tibetan uplift over the past 60 my monsoonal circulation in deep time has been inferred from variation in stable isotopes of tooth enamel diatom blooms and dust influx in the indian ocean and the advent of c4 grasses but these proxies are compromised by temperature biotic and source effects our study uses a proxy of carbonate distribution within paleosol profiles to infer appearance of monsoonal circulation of modern strength in the himachal pradesh segment of the himalayan foreland by at least 20 my ago cued to high himalayan deformation and ongoing tibetan plateau uplift and retreat of the paratethys sea paleosol records also demonstrate declining chemical weathering with himalayan and tibetan uplift which was a force for global warming rather than cooling over the past 20 my

a two stage evolution model for the amantaytau orogenic type gold deposit in uzbekistan a lithogeochemical mineral chemical isotopic and fluid inclusion study of barren low and high grade au mineralized samples from the shear zone hosted amantaytau gold deposit uzbekistan shows that the local host rocks late ordovician earlz silurian carbonacous shales are likely to have been an important source of au as ni and s in the formation of the deposit syn depositional pyrite in these shales contains on average 0 23 ppm au 1 083 ppm as and 861 ppm ni the distribution of rare earth elements ree indicates a homogeneous source of light ree whereas the heavy ree distribution reflects most likely primary variations in the sediments the mineralized zone is marked by a positive eu anomaly which supports reducing conditions during the mineralization a hydrothermal overprint by an aqueous carbonic fluid is reflected in a high grade au mineralized sample by 13c values of 13 0 v pdb the 34s values in pyrite 0 13 to 7 30 cdt from barren and mineralized samples are consistent with marine sulfate being the principal source of the ore sulfur assuming a formation temperature of between 300 and 400 c for the main stage of mineralization as indicated by the alteration mineral assemblage the calculated 18ofluid is between 9 5 and 13 4 v smow which points at a metamorphic origin of the ore fluid

possible source dichotomy of contemporaneous post collisional barren i type versus tin bearing a type granites lying on opposite sides of the south tien shan suture abstract two granitoid complexes in the eastern kyrgyz tien shan situated north and south of the southern tien shan suture were studied the suture formed as a result of the closure of the turkestan ocean and collision of the tarim microcontinent in the south with the middle tien shan in the north the timing of collision is still disputed the deformed calc alkaline terektinsky complex situated immediately north of the suture represents one of the largest shear zone related intrusions in the tien shan 130 5 15 km in size small stocks of evolved a type granites of the inylchek complex hosting economic tin mineralization were emplaced immediately south of the suture opposite the terektinsky complex two samples from the terektinsky complex and 3 samples from three a type stocks were collected for u pb zircon shrimp ii geochronology the ages at 2 level obtained for the terektinsky complex north of the suture 294 5 ma and 291 5 ma and ages of the small granite bodies south of the suture 299 4 ma 295 4 ma 289 6 ma tashkoro inylchek and maida adir intrusions respectively are nearly identical within error limits they show that the southern tien shan suture in the eastern kyrgyz tien shan had already formed by 295 ma and had evolved into a transcrustal mega shear zone controlling emplacement of granitoids geochemical distinction between the two magmatic systems is based on 10 original bulk and trace analyses of rocks from this study and on a large dataset extracted from previously published research and unpublished reports geochemically the rocks of the terektinsky complex comprise calc alkaline high potassium i type series while the granites of the inylchek complex are typical a type granites with an elevated alumina saturation index and higher boron contents compared to a standard a type rapakivi granite contrasting metallogenic features of the two granitoid complexes south and north of the southern tien shan suture are defined by their sources a fertile fore arc complex and or passive margin sediments of tarim to the south and barren metamorphic precambrian basement of the middle tien shan to the north

late cretaceous granitic magmatism and mineralization in the yingwuling w sn deposit south china constraints from zircon and cassiterite u pb geochronology and whole rock geochemistry abstract numerous late cretaceous w sn deposits associated with granitic rocks were developed in the southern part of south china however the relationship among granitic magma mineralization and tectonic setting remains disputed the yingwuling w sn deposit is spatially associated with k feldspar granite and biotite granite in the southwestern part of guangdong province south china la icp ms zircon u pb dating of k feldspar granite biotite granite and weathered ore bearing granites yielded ages of 79 ma which agree well with la icp ms cassiterite u pb age of 79 6 0 9 ma indicating a close genetic link between the yingwuling pluton and w sn mineralization geochemically both k feldspar granite and biotite granite show high sio 2 na 2 o k 2 o and low cao p 2 o 5 contents and they belong to shoshonitic series and high k calc alkaline series respectively high rb sr ratios and low nb ta and zr hf ratios of the yingwuling pluton indicate strong magmatic differentiation compared with k feldspar granite biotite granite experienced a higher degree of fractional crystallization as indicated by lower fe 2 o 3 tio 2 lree sr eu ba and zr contents and higher sio 2 hree rb cs and y contents their sr and nd isotope compositions initial 87 sr 86 sr 0 7027 and 0 7097 e nd t 5 6 and 5 7 are less radiogenic than that of the south china basement thus it is likely that some juvenile materials were involved in the formation of these granitic intrusions this is also favored by the wide range of zircon hf isotope values e hf t 6 6 to 0 8 which indicates mixing processes a type granite affinity of the yingwuling pluton shows that it was possibly formed in an extensional setting late cretaceous w sn deposits constitute an ew trending belt from guangdong to yunnan provinces which was compatible with the northward subduction of the neo tethys plate rather than the northwestward subduction of the pacific plate during late cretaceous combined with previous studies on magmatic rocks and tectonic activities during late cretaceous in south china this study suggests that the subduction of the neo tethys plate was most possibly responsible for the late cretaceous yingwuling granitic intrusion and associated w sn mineralization

late neogene environmental changes in the central himalaya related to tectonic uplift and orbital forcing the linkage between tectonic forces and climate evolution remains a matter of much debate and speculation here we present high resolution oxygen and carbon isotope data from an ancient lake basin in the central himalaya these data together with sedimentologic evidence reveal major changes in drainage systems and depositional settings at 7 2 5 5 and 3 2 ma these environmental changes appear to be driven by regional scale tectonics the oxygen isotope record also reveals alternating wet and dry climates with periodicities of 24 and 100 kyr that were likely controlled by orbital forcing paleo temperatures estimated using a fossil based oxygen isotope paleo thermometer are 21 6 ca t 7 ma which is 19 6 c higher than the present day mean annual temperature in the same area the much warmer environment inferred here is consistent with fossil mammalian and pollen assemblages and sediment clay mineralogy as well as carbon isotope data from fossil tooth enamels and paleosol carbonates the estimated temperature difference would require the study area to have been raised by 2 2 5 km since 7 ma to its current elevation of 4100 4500 m above sea level this result can be interpreted as either indicating the presence of a low altitude intermountain basin in the hanging wall of the already formed main central thrust or a protracted development of a north trending rift basin that has experienced changes in drainage system and depositional environment through time

peraluminous i type granites abstract s type granites always contain more al than the amounts of na ca and k in the rock required to form feldspars primarily owing to their derivation from source components that had previously been weathered those rocks are therefore always saturated in al or peraluminous many i type granites are also peraluminous despite i type source rocks typically not being saturated in al it has previously been suggested that this may result from the fractional crystallisation of amphibole however data from compositionally zoned high temperature plutons in the lachlan fold belt show that it is difficult to generate large quantities of peraluminous melt by removal of amphibole most of the i type granites 95 in the lachlan fold belt formed at lower temperatures and almost half of those rocks for which bulk chemical compositions are available are peraluminous among these granites there are 98 separate suites for which there are chemical data for two or more samples with 47 suites that include both metaluminous more mafic and peraluminous more felsic compositions the origin of those peraluminous compositions is fundamental to any understanding of i type granite petrogenesis in this region compositional variations caused by the assimilation or by partial melting of supracrustal rocks are very small as the isotopic variations within these rocks are dominantly between different suites not within suites the partial melting of more mafic source rocks rather than the fractional crystallisation of more mafic magmas is favoured for the origin of these rocks partial melting is the most likely process involved in the petrogenesis of felsic granites where broadly granodioritic monzogranitic batholiths are associated with lesser amounts of tonalite and very minor amounts of mafic rock experimental studies have shown that the melts generated by the partial melting of basaltic to andesitic rocks under crustal conditions are mostly peraluminous during the dehydrational melting of i type granite source rocks at pressures below the garnet stability field biotite and amphibole melt incongruently to yield pyroxenes the excess al is incorporated into the felsic liquid resulting in the generation of peraluminous melts in this instance the excess al in felsic i type granites is a function of the melting process and unrelated to the bulk composition of the source the observed gradation from peraluminous felsic granites to metaluminous compositions in less felsic rocks in largely isotopically closed systems could happen in two ways at higher temperatures of partial melting ca and other components of clinopyroxene could dissolve in the melt with the melt eventually becoming metaluminous alternatively minerals residual from partial melting dominantly pyroxenes and plagioclase could be incorporated in suspension in the melt so that the resulting bulk magma is metaluminous examples of these two extremes and of intermediate cases are well developed among the granites of southeastern australia

the savage lode magnesian skarn in the marvel loch gold silver mine southern cross greenstone belt western australia part 2 pressure temperature estimates and constraints on fluid sources the savage lode gold skarn orebody in the marvel loch mine southern cross greenstone belt western australia replaces foliated metakomatiites in a subvertical ductile shear zone and is located within the broad metamorphic aureole of the ghooli dome granodiorite granite batholith pressure estimates based on metamorphic as well as alteration mineral parageneses indicate that skarn formation took place at p 4 1 kbar 1 kbar 100 mpa corresponding to a burial depth of about 13 km metamorphism reached temperatures of 550 630 c in the mine area and preceded skarn formation pressure temperature calculations constrain the maximum temperature of the hydrothermal fluid in the savage lode to 640 20 c during the formation of early olivine calcite and diopside amphibole rocks and to 500 600 c during the formation of phlogopite chlorite calcite schists and quartz diopside veins lower fluid temperatures 500 to 400 c are recorded by retrograde serpentine after olivine talc after tremolite a

the geology and geochemistry of the zoned sn w f be skarns at mt lindsay tasmania australia the following discrete mineral associations occur 1 f vesuvianite ti sn garnet or fe pyroxene or stanniferous sphene or scheelite stage ib 2 cassiterite magnetite ilmenite siderite k feldspar or danalite or scheelite or rutile or ankerite or fluorite stage ia 3 sn amphibole or pyrrhotite or stanniferous sphene or magnetite or ilmenite or fluorite stage iia 4 is like 3 except the sn ilvaite occurs stage iib 5 is like 4 except that pyrite and arsenopyrite occur as matrix minerals stage iic and 6 fe biotite fluorite quartz pyrite ilmenite stage iid modified journal abstract

permian a type granites in tarim and western part of central asian orogenic belt caob genetically related to a common permian mantle plume abstract zircon u pb ages whole rock geochemical and zircon hf isotope data are reported for the permian a type quartz syenites granites in western tarim block northwest china zircon u pb dating indicates these alkali plutons were emplaced at 270 277 ma elemental geochemistry shows their typical a type signatures i e high total alkali hfse ree contents and ga al feo tot feo tot mgo and nb y ratios isotopically their epsilon nd values vary from 2 6 to 2 0 based on zircon hf isotope compositions they could be divided into two sub groups group i exhibits high positive ehf t ranging from 3 to 11 mostly within the range of 5 to 9 which is highly comparable with the syenites in bachu area located just south of these plutons group ii has ehf t ranging from 3 to 2 the second group exhibits comparable nd hf isotope compositions with the spatially and temporally related piqiang ultramafic mafic complex integrating geological geochemical and nd hf isotope data we suggest that the a type syenite granites were formed via intensive crystal fractionation from a common plume derived parental mafic magma coupled with variable extent of crustal contamination moreover the extent of the crustal contamination increase from inner tarim towards south tianshan collisional belt a comprehensive synthesis of the coeval a type granites in the western part of the central asian orogenic belt caob shows that they exhibit distinct geochemical features e g large range of end t and 87 sr 86 sr i values high y nb yb ta and low nb la ratios all these features argue that they were derived from juvenile mafic crust with variable addition of the mafic materials from mantle sources and some old crustal materials or mixing of mantle derived mafic magma with precambrian crustal components we suggest that both the permian a type granites from tarim and western section of caob were genetically linked to the permian tarim mantle plume which is concurrent with the two mantle domains for the permian tarim large igneous province lip

geology mineralization and fluid inclusion characteristics of the koitash redox intermediate w mo skarn and w au stockwork deposit western uzbekistan tien shan the koitash w mo skarn deposit in the tien shan gold belt contained resources of 60 kt wo3 in altered skarn averaging 0 56 wo3 and 0 029 mo and an additional 42 kt wo3 in separate zones of phyllic alteration averaging 0 30 wo3 0 97 g t au 0 67 cu and 0 02 bi it is related to an early permian multiphase granodiorite granite leucogranite pluton that is composed of medium to high k transitional metaluminous to peraluminous weakly oxidized weakly reduced ilmenite titanite series granitoids the pluton was emplaced in a tectonic domain with inferred ancient continental crust the latter coupled with possible ascent of hot asthenospheric material has likely defined a distinct w mo au metallogenic assemblage forming in a post collisional environment the deposit includes redox intermediate prograde and retrograde pyroxene garnet skarns partially overprinted by propylitic and phyllic alteration assemblages comprising scheelite molybdenite cu bi ag te sulfides and sulfosalts as well as native bi and au compositional similarities between w mo deposits containing au w cu bi mineralization in late alteration assemblages and coeval intrusion related au dominant with minor w bi etc deposits in the region support their possible genetic links fluid inclusion data indicate the involvement of carbonic free moderately saline 10 5 15 0 to 8 0 11 7 wt nacl eq high pressure 2000 to 1500 bars hot 550 600 c aqueous fluid which was sourced from crystallizing magma and formed prograde calcic skarn this fluid was followed by moderately saline ca rich 14 16 wt nacl 19 21 wt cacl2 lower pressure 800 bars fluids toward the retrograde skarn stage with the deposition of scheelite in association with pyrrhotite and molybdenite locally with minor fluorite propylitic quartz amphibole chlorite oligoclase calcite with scheelite pyrrhotite locally molybdenite assemblages formed from boiling high methane aqueous carbonic fluids at temperatures of 370 400 c and pressures of 950 1000 bars phyllic quartz sericite fe carbonate locally with albite fluorite chlorite scheelite molybdenite and other sulfides also bi and au minerals alteration assemblages initially formed from homogeneous and then from boiling aqueous carbonic low salinity fluids at temperatures of 365 370 to 300 315 c and pressures of 2000 bars 34s increases from retrograde skarn 34s 2 0 to 2 3 through propylitic 34s 3 0 to 3 4 to phyllic alteration 34s 4 2 to 4 7 stages

fault controlled carboniferous a type magmatism in the proto andean foreland sierras pampeanas argentina geochemical constraints and petrogenesis abstract the intrusion of granitoids into the eastern sierras pampeanas in the early carboniferous took place after a long period of mainly compressional deformation that included the famatinian ordovician and achalian devonian orogenies these granitoids occur as small scattered plutons emplaced in a dominant extensional setting within older metamorphic and igneous rocks and many of them are arranged along a reactivated large shear zone a set of 46 samples from different granitic rocks huaco granitic complex san blas pluton and the la chinchilla stock from the sierra de velasco zapata granitic complex from sierra de zapata and the los arboles pluton from sierra de fiambala display high and restricted sio 2 contents between 69 2 and 76 4 wt on both feo feo mgo vs sio 2 and na 2 o k 2 o cao vs sio 2 plots the samples plot in the ferroan and alkaline calcic to calco alkaline fields feo feo mgo 0 88 1 0 na 2 o k 2 o cao 6 3 8 3 thus showing an a type granitoid signature the high concentrations for the high field strength elements hsfe such as y nb ga ta u th etc and flat ree patterns showing significant negative eu anomalies are also typical features of a type granites our petrogenetic model supports progressive fractional crystallization with dominant fractionation of feldspar and a source mineral assemblage enriched in plagioclase biotites have distinctive compositions with high feo mgo ratios 7 8 61 5 f 360 5610 ppm and cl 120 1050 ppm the feo mgo ratios together with the f and cl content of igneous biotites seem to reflect the nature of their parental host magmas and may be useful in identifying a type granitoids the isotopic data rb sr and sm nd confirm that the a type granites represent variable mixtures of asthenospheric mantle and continental crust and different mixtures lead to different subtypes of a type granite illustrating the lack of consensus about a type magma origin we conclude that prominent shear zones play an important role in providing suitable conduits for ascending asthenospheric material and heat influx in the crust a hypothesis that is in accord with other recent work on a type granites

an experimental study of sulfidation reactions involving andradite and hedenbergite three sulfur buffering sulfide silicate reactions which limit the stabilities of the skarn silicates andradite garnet and hedenbergite pyroxene under sulfidizing conditions were studied hydrothermally at a pressure of 2 kb over the temperature range 700 degrees to 350 degrees c reaction 1 andradite s 2 wollastonite anhydrite quartz pyrite or pyrrhotite reaction 2 andradite magnetite s 2 anhydrite quartz pyrite or pyrrhotite andreaction 3 hedenbergite s 2 andradite quartz pyrrhotite the equilibrium value of the sulfur fugacity f sub s 2 for each reaction assemblage at any given temperature was calculated from the measured composition of a coexisting sulfur fugacity indicator pyrrhotite or sphalerite as appropriate the log f sub s 2 data were adequate for the determination of the log f sub s 2 1 t relations for each of the andradite sulfidation reactions owing to excessive scatter in the data for the hedenbergite sulfidation reaction however the log f sub s 2 1 t relation for this reaction derived from the log f sub o 2 data of burton et al 1982 is preferred to the one developed by gamble 1976 1978 the log f sub s 2 1 t relations for the three sulfidation reactions were combined with equilibrium data available in the literature for other reactions in the model system ca si fe o s and used to construct quantitative isothermal isobaric log f sub s 2 log f sub o 2 phase diagrams applicable to the formation of ca si fe skarns the quantitatively derived phase relations were found to be consistent in all major respects with the schematic phase relations deduced by burt 1972a and b the influence of diopside component on the stability of hedenbergitic pyroxene was also studied diopside was found to enlarge the stability field of hedenbergitic pyroxene increasing the temperature at which pyroxene becomes stable with pyrite from 288 degrees c for end member hedenbergite burton et al 1982 to 395 degrees c for 50 mole percent diopside diopside was found to be less effective than the johannsenite component in stabilizing hedenbergitic pyroxene

geology mineralization and fluid inclusion characteristics of the meliksu reduced tungsten skarn deposit alai tien shan kyrgyzstan insights into conditions of formation and regional links to gold mineralization abstract the meliksu w skarn deposit 10kt wo3 with average grade of 6 6 wo3 in the alai segment of the southern tien shan is related to an early permian granitoid pluton that comprises ilmenite series to ilmenite titanite bearing medium k metaluminous to peraluminous i type granitoid monzonite diorite tonalite granodiorite to granite rocks there is a regional scale continuum from these intrusions to transitional weakly reduced to weakly oxidized metaluminous i type granitoid suites accompanied by reduced intrusion related au deposits magmatic evolution also included coeval high k to shoshonitic suites and younger early permian post collisional to within plate alkaline from monzogabbro to nepheline syenite and carbonatite intrusions indicative of an extensional tectonic regime consistent with this evolution toward an extensional environment reduced w skarns and associated reduced intrusion related au mineralization in the region may evolve toward sb hg as au w mineralization exhibiting the carlin type affinity the deposit bears signatures of reduced w skarn deposits with dominant pyroxene hedenbergite rich prograde and retrograde skarns scheelite was mostly deposited during the propylitic amphibole chlorite calcite quartz with abundant pyrrhotite and minor chalcopyrite and phyllic quartz sericite albite fe carbonate with sulfides bi ag and au minerals alteration stages silver mineralization is particularly abundant that together with very high w grades low au grades intense calcic sodic and sodic alteration and coarse grained sericite muscovite quartz aggregate possibly reveal a root level of reduced w skarn deposits fluid inclusions data indicate formation of retrograde mainly pyroxene quartz amphibole skarn from aqueous dominantly magnesian sodic chloride moderately saline 16 18 wt nacl eq high pressure 1 9 0 7 kbar moderately hot 400 500 c fluid propylitic alteration assemblages were formed from slightly less saline 11 13 wt nacl eq high pressure 1 8 0 5 kbars lower temperature 370 450 c ca enriched fluid phyllic alteration assemblages were formed from high pressure 2 2 0 1 kbars boiling methane rich carbonic aqueous cooling from 350 to 335 c to 275 265 c fluid high fluid pressures at different hydrothermal stages are consistent with a deep level of mineralization at a lithostatic depth of 9 0 km a strong enrichment in heavy sulfur isotope 34sfluid varies from 6 5 0 4 to 8 0 0 3 can reflect sulfur sourcing from sedimentary rocks enriched in seawater sulfate with sulfur isotope homogenization in a magmatic chamber

mixed geothermal and shallow meteoric origin of opal and calcite beds in pliocene lower pleistocene axial fluvial strata southern rio grande rift rincon hills new mexico u s a abstract exposed in upper pliocene fluvial strata in the eastern rincon hills and adjacent jornada del muerto basin southern rio grande rift new mexico usa are five laterally continuous beds 0 2 to 1 0 m thick of opal ct which straddle the east rincon hills normal fault four of these opal beds change basinward over 1 km or less to white friable lithofeldspathic sand with opal glaebules and then to microcrystalline calcite the opal and calcite generally replaced fine sand at shallow depths although two beds locally precipitated from standing water 87sr 86sr values 0 71301 to 0 71724 of the opal beds are consistent with precipitation from an advecting high temperature geothermal fluid that flowed through bedrock and or from a high temperature geothermal fluid derived from a deep crustal source carbon and oxygen isotopic values 13cpdb 7 1 to 0 6 18opdb 9 1 to 5 6 of the calcite beds lie between and overlap those of paleozoic carbonate and pliocene paleosol calcite suggesting precipitation from a mixture of a high temperature geothermal fluid that interacted with paleozoic carbonates and shallow meteoric groundwater for which paleosol calcite is a proxy the geothermal fluids are interpreted to have upwelled along the east rincon hills fault flowed laterally at or just below the surface and precipitated opal in response to rapid cooling and evaporation downflow precipitation of opal glaebules occurred as a result of decreasing silica concentrations and perhaps by mixing with shallow meteoric groundwater from which calcite precipitated probably by co2 degassing

tectonics or climate what drove the miocene global expansion of c4 grasslands investigations into the most plausible causes which triggered the late miocene global expansion of c4 grasslands have reached no consensus and are still being debated the global decline in co2 levels in the late miocene has been thought to be the most common driver although c4 grassland expansion was largely confined to the late miocene their first appearance varied significantly in different parts of the old and new world and therefore emphasizes role of local and or regional factors may or may not be in combination with one or more global factors the dynamic himalayan orogen constitutes a significant global tectonic event that is believed to have affected global climate hence a study of the himalayan foreland basin sediments could help in gleaning out possible causes behind this major paleoecologic event which could perhaps be directly or indirectly related stable carbon isotope analyses of a total of 141 pedogenic carbonates in the mio pleistocene siwalik paleosols of the ramnagar sub basin are coherent providing a better insight into paleovegetational changes across the sub basin on temporal and spatial scales furthermore paleovegetational history during oligocene is reconstructed from dagshai paleosols exposed in the subathu sub basin the isotopic results show dominance of c3 vegetation pre 7 ma and dominance of c4 vegetation post 5 ma percentage abundance of c4 vegetation was less than 20 pre 7 ma but increased to more than 40 post 5 ma reaching up to 100 in the youngest analyzed sediments there is exclusive dominance of c3 vegetation during oligocene these results conform to the pattern of change in vegetation documented in other parts of the himalayan belt the global expansion of c4 grasslands largely during late miocene have long been linked with then climate changes particularly brought by declining atmospheric co2 level large scale fires intensification of monsoon seasonality and aridity as demonstrated by various researchers these major hypotheses explaining expansion of c4 grasslands during late miocene are not very convincing due to significant shortcomings associated with them for example expansion of c4 grasslands in non monsoonal regions put serious constraints on the monsoonal intensification hypothesis likewise aridity as being the primary driver of c4 grassland expansion seems hard to support since there is no substantial evidence that could suggest global onset of arid conditions at about same geologic time and some most arid periods like the triassic show no evidence of c4 plants we suggest that the initial lowering of co2 below 450 ppmv created an environment for the beginning of c4 vegetation but the persistence of this threshold value for a considerable time during late miocene appears to be the probable cause of the late miocene global expansion of c4 grasslands irrespective of their time of first appearance it has been deduced through the correlation of himalayan tectonic events with atmospheric co2 levels and paleovegetational changes since upper miocene times that it was indeed the late miocene continuous intense tectonic instability of the himalayas that significantly decreased atmospheric co2 levels and which perhaps played a key role in changing the nature of photosynthetic pathways

sr c and o isotopes in carbonate nodules from the ganga plain evidence for recent abrupt rise in dissolved 87sr 86sr ratios of the ganga abstract the evolution of 87 sr 86 sr ratio of the ganga water during the past 100 ka has been reconstructed in this study the 87 sr 86 sr 13 c and 18 o values have been measured in carbonate nodules from different depths of two sediment cores raised from the indian institute of technology kanpur iitk campus 50 m long and jagdishpur jp 25 m long respectively the 87 sr 86 sr ratios of the carbonate nodules range from 0 7142 to 0 7189 in the iitk and 0 7142 to 0 7367 in the jp cores the nodules in general display significantly lower 87 sr 86 sr ratio compared to contemporary ganga river water at kanpur however values of 87 sr 86 sr ratio are observed in the nodules of the jp core near the surface are consistent with that of the present day ganga water at kanpur as well as groundwater samples from adjacent areas indicate recent abrupt increase in 87 sr 86 sr ratio of the ganga these findings are also consistent with the concomitant increase in 87 sr 86 sr ratio of silicates in contemporary sediments of the ganga at kanpur compared to that of past 100 ka the sudden rise of 87 sr 86 sr ratio of the ganga is probably due to increase in the relative proportion of sr from the lesser himalaya containing silicates and carbonates with higher 87 sr 86 sr ratio the cause for the recent increase in sr contribution from the lesser himalaya is not clear this could be due to enhanced agricultural activities and deforestation and or climatic variability during recent times resulting in more erosion in the lesser himalaya the 13 c and 18 o measured in the nodules from the iitk core vary from 6 8 to 1 6 and 8 3 to 5 4 respectively the co variation of 13 c and 18 o suggest the impact of paleoclimate paleovegetation petrography and chemical composition of carbonate nodules indicate little or no diagenetic alteration

postcollisional granites in the south tien shan variscan collisional belt kyrgyzstan abstract two major types of the potassium rich postcollisional granites of permian age were studied in the south tien shan variscan collisional belt the first type metaluminous granites of the jangart complex are located along the southeastern boundary of this belt with the precambrian tarim block the plagioclase rims on k feldspar megacrysts rapakivi texture extremely high feot feot mgo ratio indications of the low h2o and o2 fugacities high concentrations of the incompatible elements especially light rare earth elements lree ba nb along with heightened contents of the compatible elements especially ni cr and moderately initial 87sr 86sr ratio sr0 0 7075 make those granites similar to other rapakivi granites the second type peraluminous granites of the inylchek complex is located along the northwestern boundary of the belt with the caledonian kazakh microcontinent those granites are rich in f b li rb cs sn ta and heavy rare earth elements hree but are poor in ba sr ni and cr and are characterized by the relatively high initial 87sr 86sr ratio sr0 0 7098 li mica granites are distributed widely among them the granites of a transitional type uchkoshkon complex occupy an intermediate geographic position between major granite types the initial sr isotopic composition of the transitional granites varies widely sr0 from 0 7080 to 0 7256 the variation in chemical composition of the coeval postcollisional granites across the collisional belt together with the variability of initial sr isotopic ratios of the transitional granites are thought to indicate basement heterogeneity this heterogeneity in turn is probably related to thrusting of the tarim block under south tien shan during the collision

geology mineralization and fluid inclusion characteristics of the kashkasu w mo cu skarn deposit associated with a high potassic to shoshonitic igneous suite in kyrgyzstan tien shan toward a diversity of w mineralization in central asia abstract the kashkasu deposit is part of the subduction related late paleozoic late carboniferous metallogenic belt of tien shan it is associated with a multiphase monzodiorite monzonite granodiorite granite pluton of the magnetite series high k calc alkaline to shoshonitic igneous suite the deposit contains zones of w mo cu oxidized prograde and retrograde skarns with abundant andraditic garnet magnetite locally scapolite and k feldspar as well as scheelite chalcopyrite and molybdenite skarns are overprinted by quartz carbonate sericite phyllic alteration zones with scheelite and sulfides prograde calcic skarn and initial retrograde skarns were formed from a high temperature 650 c to 450 550 c high pressure 2000 bars to 600 900 bars magmatic hydrothermal low to high salinity aqueous chloride fluid the gradual fluid evolution was interrupted by the intrusion of granodiorite and likely associated release of low salinity 7 8 wt nacl equiv fluid ascent of this fluid to shallower levels and or its cooling to 400 500 c has resulted in phase separation into low salinity 2 1 3 1 wt nacl equiv vapor and coexisting brine 35 40 wt nacl equiv the boiling was coincident with most intense scheelite deposition in retrograde skarn later retrograde skarn assemblages were formed from a gaseous low to moderate salinity 3 4 8 1 wt nacl equiv fluid and then from high salinity 37 42 wt nacl equiv aqueous chloride fluids the latter being enriched in ca 17 20 wt cacl2 that could also affect scheelite deposition another cycle of fluid exsolution from crystallizing magma corresponded to quartz carbonate sericite scheelite sulfide phyllic alteration stage with the early low salinity 5 3 8 4 wt nacl equiv fluid followed by later high salinity 33 5 38 2 wt nacl equiv fluid the sulfur isotope data 34s 5 1 to 9 0 suggest significant sulfur sourcing from sedimentary rocks enriched in seawater sulfate possibly evaporites

the detrital record of orogenesis a review of approaches and techniques used in the himalayan sedimentary basins the sediment archive of material eroded from an active tectonic region and stored in adjacent basins can provide a valuable record of hinterland tectonism especially when information in the source region itself is obscured by later metamorphism or removed by tectonism or erosion using the sediment record to document tectonism is a well established approach but more recently there has been a burgeoning of the number of isotopic techniques which can be applied to detrital material in particular single grain analyses thus the scope for application of detrital studies to a number of different tectonic problems has widened considerably in this review the example of sediments eroded from the himalayan orogen and preserved in the suture zone basin foreland basin remnant ocean basins and deep sea fans is used to illustrate the approach techniques as diverse as petrography heavy mineral xrf and sr nd studies single grain dating by ar ar u pb and fission track methodologies and single grain sm nd and pb isotopic analyses are described the paper documents how the sediment record can be used to determine the thermal and tectonic evolution of the orogen constrain mechanisms of continental deformation exhumation rates and palaeodrainage

architecture and mineral deposit settings of the altaid orogenic collage a revised model abstract the altaids are an orogenic collage of neoproterozoic paleozoic rocks located in the center of eurasia this collage consists of only three oroclinally bent neoproterozoic early paleozoic magmatic arcs kipchak tuva mongol and mugodzhar rudny altai separated by sutures of their former backarc basins which were stitched by new generations of overlapping magmatic arcs in addition the altaids host accreted fragments of the neoproterozoic to early paleozoic oceanic island chains and neoproterozoic to cenozoic plume related magmatic rocks superimposed on the accreted fragments all these assemblages host important many world class late proterozoic to early mesozoic gold copper molybdenum lead zinc nickel and other deposits of various types in the late proterozoic during breakup of the supercontinent rodinia the kipchak and tuva mongol magmatic arcs were rifted off eastern europe siberia and laurentia to produce oceanic backarc basins in the late ordovician the siberian craton began its clockwise rotation with respect to eastern europe and this coincides with the beginning of formation of the mugodzhar rudny altai arc behind the kipchak arc these earlier arcs produced mostly cu pb zn vms deposits although some important intrusion related orogenic au deposits formed during arc arc collision events in the middle cambrian and late ordovician the clockwise rotation of siberia continued through the paleozoic until the early permian producing several episodes of oroclinal bending strike slip duplication and reorganization of the magmatic arcs to produce the overlapping kazakh mongol and zharma saur valerianov beltau kurama arcs that welded the extinct kipchak and tuva mongol arcs this resulted in amalgamation of the western portion of the altaid orogenic collage in the late paleozoic its eastern portion amalgamated only in the early mesozoic and was overlapped by the transbaikal magmatic arc which developed in response to subduction of the oceanic crust of the paleo pacific ocean several world class cu mo porphyry cu pb zn vms and intrusion related au mineral camps which formed in the altaids at this stage coincided with the episodes of plate reorganization and oroclinal bending of magmatic arcs major pb zn and cu sedimentary rock hosted deposits of kazakhstan and central asia formed in backarc rifts which developed on the earlier amalgamated fragments major orogenic gold deposits are intrusion related deposits often occurring within black shale bearing sutured backarc basins with oceanic crust after amalgamation of the western altaids this part of the collage and adjacent cratons were affected by the siberian superplume which ascended at the permian triassic transition this plume related magmatism produced various deposits such as famous ni cu pge deposits of norilsk in the northwest of the siberian craton in the early mesozoic the eastern altaids were oroclinally bent together with the overlapping transbaikal magmatic arc in response to the northward migration and anti clockwise rotation of the north china craton the following collision of the eastern portion of the altaid collage with the siberian craton formed the mongol okhotsk suture zone which still links the accretionary wedges of central mongolia and circum pacific belts in the late mesozoic a system of continent scale conjugate northwest trending and northeast trending strike slip faults developed in response to the southward propagation of the siberian craton with subsequent post mineral offset of some metallogenic belts for as much as 70 400 km possibly in response to spreading in the canadian basin india asia collision rejuvenated some of these faults and generated a system of impact rifts

the jc tin skarn deposit southern yukon territory ii a carbon oxygen hydrogen and sulfur stable isotope study the jc tin deposit is a stanniferous skarn hosted within mississippian sediments intruded by the mid cretaceous seagull batholith the stable isotope compositions of silicate carbonate and sulfide minerals have been used to interpret the evolution of fluid sources during sequential stages of skarn formation the delta 13 c and delta 18 o values of remnant calcite from the earliest contact metamorphic stage 0 rocks are the result of decarbonation of the protolith marble coupled with infiltration of variable amounts of meteoric water garnet pyroxene skarn stage i was produced by predominantly magmatic fluids during initial skarn forming metasomatism stage ii amphibole rich skarn was formed by magmatic water mixed with up to 50 percent meteoric water this meteoric water had undergone stable isotope exchange with the jc granite at a low water to rock ratio as it moved upward along the contact of the granite with the surrounding wall rock the magmatic water component of stage ii fluids is inferred to have moved vertically through the solid cap of the granite before mixing with the exchanged meteoric water stage iii epidote quartz calcite skarn formed in the presence of a fluid consisting of magmatic water which had reequilibrated with the granite cap at temperatures between 350 degrees and 500 degrees c and subsequently mixed with up to 45 percent meteoric water the delta 13 c and delta 13 o values of stage iii calcite suggest the presence of an additional fluid component which had equilibrated with the protolith marble at similarly high temperatures these observations reinforce the hypothesis that originally highly saline stage iii fluids were diluted by low salinity meteoric water at the periphery of the skarn replacement zone and suggest that the surrounding marble horizon may have provided a pathway by which such fluids entered the skarn during formation of stage iv biotite quartz fluorite cassiterite skarn the fluid was predominantly magmatic with no detectable involvement of meteoric water this stage represented a renewed influx of magmatic fluid following the increased involvement of meteoric water during stages ii and iii and may have been related to a discrete episode of aqueous fluid separation from the underlying granitic magma the return to a predominantly magmatic fluid at stage iv is concomitant with an increase in both fluid temperature and salinity relative to stage iii fluids during the fracturing and formation of breccia zones which accompanied formation of stage vi pyrite marcasite carbonate skarn meteoric water which had initially equilibrated at low temperature 13 s values for all skarn sulfide minerals 1 0 to 2 5ppm is consistent with a magmatic source for sulfur throughout skarn formation stage iii and iv mineral pairs which remained in isotopic equilibrium after their initial crystallization yield oxygen isotope geothermometric temperatures consistent with those determined by fluid inclusion microthermometry

hercynian post collisional magmatism in the context of paleozoic magmatic evolution of the tien shan orogenic belt abstract the hercynian tien shan tianshan orogen formed during late palaeozoic collision between the karakum tarim and the kazakhstan paleo continents in order to constrain timing of hercynian post collisional magmatism 27 intrusions were sampled for u pb zircon dating along a ca 2000 km long profile in uzbekistan and kyrgyzstan the samples were dated utilizing sensitive high resolution ion microprobe shrimp ii the obtained ages together with previously published age data allowed the timing of hercynian post collisional magmatism to be constrained and interpreted in the context of the paleozoic magmatic evolution of the region apart from hercynian post collisional magmatism two older magmatic episodes have been recognized and the following sequence of events has been established 1 approximately 10 ma after cessation of continuous caledonian magmatism a number of late silurian early devonian intrusions were emplaced in the middle and northern tien shan terranes between 420 and 390 ma the intrusions probably formed in an extensional back arc setting during coeval subduction under the margins of caledonian paleo kazakhstan continent 2 the next relatively short late carboniferous episode of subduction under paleo kazakhstan was registered in the kurama range of the middle tien shan calc alkaline volcanics and granitoids with ages 315 300 ma have distinct metallogenic affinities typical for subduction related rocks and are not found anywhere outside the middle tien shan terrane west of the talas farghona fault 3 the early permian hercynian post collisional magmatism culminated after the closure of the paleo turkestan ocean and affected the whole region across terrane boundaries the post collisional intrusions formed within a relatively short time span between 295 and 280 ma the model for hercynian post collisional evolution suggests that after collision the tien shan was affected by trans crustal strike slip motions which provided suitable conduits for ascending asthenospheric material and heat influx in the crust this produced both granitoid magmas and hydrothermal fluid flow as a result post collisional intrusions and orogenic au deposits known in the region formed coevally and were tectonically controlled 4 between 240 and 220 ma a triassic thermal event affected the region resulting in resetting and growth of new zircon grains which is detected on a regional scale probably the influx of heat into the crust during the triassic was tectonically focused and varied significantly in different terranes in the region under investigation the triassic thermal event was not accompanied by any significant magmatic activity thus after cessation of hercynian post collisional magmatism ca 280 ma ago there was a long magmatically quiet period in the tien shan

geodynamic evolution of the western tien shan uzbekistan insights from u pb shrimp geochronology and sr nd pb hf isotope mapping of granitoids sr nd pb hf isotope mapping combined with u pb zircon shrimp ages of granitoids from four sampling profiles across terrane boundaries in uzbekistan reveal distinct reservoir types cratonic and accretionary witnessed by the diverse nature and origin of the predominant paleozoic granitic magmatism that provided hosts for major ore bodies the study region comprises four major terranes including 1 the sultan uvais terrane 2 the kyzylkum nurata segment and 3 the gissar segment of the south tien shan and 4 the chatkal kurama terrane of the middle tien shan sr nd isotope analyses show a wide range of endt 5 to 7 and 87sr 86sr t of 0 704 0 707 indicating involvement of both mantle derived material and older crustal sources a wide range of hf isotope compositions found in zircons of chatkal kurama granites middle tien shan ehf mainly 5 to 5 could be due to recycling of older crustal protolith s in particular the earliest silurian granites may be directly derived from 1 5 to 1 7 ga lower crust in the southern tien shan some involvement of subducted oceanic crust is evidenced by strongly juvenile ehft values of up to 14 and 16 sultan uvais teskuduk kyzylkum permo carboniferous granitoids which occur across all terranes also exhibit a wide range of isotope signatures corresponding to mesoproterozoic neoproterozoic crustal protoliths with a westward increase in juvenile contributions pb isotopes whole rock imply the dominance of a crustal component and crust mantle mixing processes new age data confirmed 1 old age of the turkestan ocean 505 ma in sultan uvais 2 fragments of silurian island arcs in the accretionary complex of the chatkal kurama terrane granites of 429 416 ma and in the upper allochthon of the south tien shan gabbro 438 ma in tamdytau and 3 a significant volume of granitoid magmatism of subduction or early collisional stages around 320 310 ma in the chatkal kurama segment and especially in the gissar segment the westernmost part of the tien shan is characterized by multiple subduction processes responsible for 300 million years of geodynamic evolution history accretionary collage crustal growth with the pre mesozoic crust formation concluded by permian post collisional extensional magmatism

on ferroan a type granitoids their compositional variability and modes of origin we recognize eight types of ferroan granitoid that can be distinguished on the basis of major element chemistry these include alkalic granitoids that may be metaluminous or peralkaline alkali calcic granitoids that may be metaluminous peraluminous or peralkaline calc alkalic granitoids that may be metaluminous or peraluminous and rare calcic ferroan granitoids these granitoids may form by two distinct end member processes extreme differentiation of basaltic melts results in ferroan granitoids that are either peralkaline alkalic and alkali calcic or metaluminous alkalic alkali calcic and calc alkalic with alkalinity increasing with increasing pressure of differentiation partial melting of tonalitic to granodioritic crust produces alkali calcic to calc alkalic granitoids that are metaluminous at low pressures and peraluminous at high pressures it is likely that a combination of these two processes plays some role in the formation of most ferroan granitoids most granitoids that are referred to as ferroan however the term has become more confusing than edifying because it has been applied to a broad spectrum of granitoid compositions with varying petrogenesis for this reason we recommend that the term be discontinued and ferroan used in its stead

geology mineralization and fluid inclusion characteristics of the kumbel oxidized w cu mo skarn and au w stockwork deposit in kyrgyzstan tien shan the kumbel deposit is located within a metallogenic belt of w mo cu mo au w and au deposits along the late paleozoic active continental margin of tien shan the deposit is related to a late carboniferous multiphase pluton with successive intrusive phases from early olivine monzogabbro through monzonite quartz monzonite to granodiorite and granite with the latest monzogabbro porphyry dikes the deposit represents an example of a complex w cu mo au magmatic hydrothermal system related to magnetite series high k calc alkaline to shoshonitic igneous suite it contains large bodies of w cu mo oxidized prograde and retrograde skarns with abundant andradite garnet magnetite and especially hematite as well as k feldspar molybdoscheelite chalcopyrite and molybdenite with transitions to zones of intense quartz k feldspar with minor andradite and hematite veining the skarns are cut by quartz carbonate adularia sericite veins locally sheeted and stockworks bearing scheelite and minor cu zn pb sulfides as well as au bi te and as mineralization the association of these veins with the oxidized skarns and magnetite series intrusion is consistent with the general oxidized intrusion related w mo cu au type of deposit with an affinity to the alkalic silica saturated cu au mo porphyry deposits the fluid inclusion data show the predominance of magmatic hydrothermal aqueous chloride fluid during the formation of skarns and quartz carbonate scheelite sulfide veins the high fluid pressures 1 750 bars together with their high temperature up to 600 c and high salinity 50 60 wt nacl equiv suggest the formation of skarns and quartz k feldspar andradite hematite veins under conditions typical of magmatic hydrothermal transition depth of 4 5 km of intrusion related mineralized system possibly by exsolution of the fluids from crystallizing magma the auriferous quartz carbonate scheelite sulfide veins formed from high to moderate salinity from 40 to 20 wt nacl equiv and high pressure from 1 200 bars to 850 900 bars aqueous chloride fluids under decreasing temperature from 370 to 120 c the massive deposition of molybdoscheelite in retrograde skarn and scheelite in quartz carbonate scheelite sulfide veins could correspond to enrichment of fluids in ca up to 18 25 wt cacl2 likely from crystallizing magma

geological characteristics tectonic setting and preliminary interpretations of the jilau gold quartz vein deposit tajikistan the southern tien shan metallogenic province of central asia hosts a number of important gold resources including the jilau gold quartz vein system in western tajikistan these deposits were formed at the late stages of continent continent collision in association with subduction related magmatism metamorphism and continental margin deformation attributed to the central asian hercynian orogeny jilau is hosted by a hercynian syntectonic granitoid intrusive that was emplaced into bituminous dolomite country rocks economic mineralisation is associated with a dilational jog within a high angle oblique dextral reverse slip shear zone that was undergoing brittle ductile deformation the orebody takes the form of shear zone subparallel quartz veins and lenses that emanate from a steeply plunging ore shoot of veins and stringers within a silicified and sulphidised granodiorite core it is thought to have formed by a dynamic process in which fluid flow was governed by a fault valve mechanism numerous cycles of fluid pressure build up fault failure jog dilation fluid flow phase separation of low salinity h2o co2 ch4 n2 fluids and sealing took place gold appears together with scheelite and bismuth minerals predominantly as inclusions in arsenopyrite in quartz veins and altered wall rock and is mainly associated with quartz containing fluid inclusions enriched in ch4 the correlation between high gold grades and high ch4 concentrations suggests that components of the mineralising fluids were derived from or passed through the reducing carbonaceous rocks in the contact aureole of the intrusive the occurrence of au and w in an adjacent hercynian skarn deposit and in the jilau orebody infers that the ore metals in both these systems were ultimately derived from a magmatic source

geology mineralization and fluid inclusion characteristics of the lermontovskoe reduced type tungsten cu au bi skarn deposit sikhote alin russia abstract the lermontovskoe deposit 48 kt wo 3 average 2 6 wo 3 0 24 cu 0 23 g t au is situated in a w sn au metallogenic belt that formed in a collisional tectonic environment this tungsten skarn deposit has a w au as bi te sb signature that suggests an affinity with reduced intrusion related au deposits the deposit is associated with an intrusion that is part of the ilmenite series high k peraluminous granitoid granodiorite to granite suite these rocks formed via mantle magma induced melting of crustal sources the deposit comprises reduced type pyroxene dominated prograde and retrograde skarns followed by hydrosilicate amphibole chlorite pyrrhotite scheelite quartz and phyllic muscovite sericite carbonate albite quartz scheelite sulfide with abundant apatite alteration assemblages fluid inclusions from the skarn assemblages indicate high temperature 500 c high pressure 1400 1500 bars and high salinity 53 60 wt nacl equiv magmatic hydrothermal fluids they were post dated by high carbonic methane dominate low salinity fluid at the hydrosilicate alteration stage these fluids boiled at 360 380 c and 1300 1400 bars the subsequent phyllic alteration started again with a high temperature 450 c high pressure 1000 1100 bars and high salinity 42 47 wt nacl equiv fluid with further incursion of high carbonic methane dominated low salinity fluid that boiled at 390 420 c and 1150 1200 bars the latest phyllic alteration included the lower temperature 340 360 c lower pressure 370 400 bars high carbonic methane dominated but with higher co 2 fraction low salinity fluid and then the low temperature 250 300 c h 2 o co 2 ch 4 nacl fluid with both fluids boiled at the deposit level the high salinity aqueous fluids are interpreted to have come from crystallizing granitoid magma whereas the reduced high carbonic fluids probably came from a deeper mafic magma source both of these fluids potentially contributed to the w au as bi te sb metal budget decreasing temperatures coupled with high aca 2 and fluid boiling promoted scheelite deposition at all post skarn hydrothermal stages the deposit is characterized by limited downdip extent of mineralized zones and abundant coarse grained muscovite quartz apatite scheelite aggregates that formed at the phyllic alteration stage together with presence of high temperature high pressure and high salinity fluids directly exsolving from crystallizing magma this suggests a root level of the mineralized magmatic hydrothermal system of reduced w skarn deposits

a geotraverse across two paleo subduction zones in tien shan tajikistan abstract we present first la icp ms u pb zircon ages as well as geochemical and sr nd pb isotope data for 14 magmatic rocks collected along ca 400 km profile across the chatkal kurama terrane in the mogol tau and kurama ranges and the gissar segment of the tien shan orogen in tajikistan these new data from supra subduction and post collisional magmatic rocks of two late paleozoic active margins constrain a tectonic model for terrane motions across two paleo subduction zones 1 the 425 ma old muzbulak granite of the mogol tau range formed in a supra subduction setting at the northern margin of the turkestan ocean the north dipping plate was subducted from the early silurian to the earliest middle devonian thereafter the northern side of the turkestan ocean remained a passive margin until the early carboniferous 2 in the early carboniferous subduction under the northern margin of the turkestan ocean resumed and the 315 to 305 ma old kara kiya muzbek and karamazar intrusions formed in a supra subduction setting in the mogol tau and kurama ranges 3 at the same time in the early carboniferous rifting of the southern passive margin of the turkestan ocean formed the short lived gissar basin separated from the turkestan ocean by the gissar micro continent north dipping subduction in the gissar basin is documented by the 315 ma kharangon plagiogranite and the voluminous ca 321 312 ma andean type supra subduction gissar batholith the kharangon and khanaka gabbro plagiogranite intrusions of the southern gissar range have geochemical and sr nd isotopic compositions 87sr 86sr t 0 7047 0 7056 end of 1 5 to 2 3 compatible with mantle derived origin typical for plagiogranites associated with ophiolites the supra subduction rocks from the gissar batholith and from the mogol tau kurama ranges have variably mixed sr nd pb isotopic signatures 87sr 86sr t 0 7057 0 7064 end of 2 1 to 5 0 typical for continental arcs where mantle derived magmas interact with continental crust 4 in the latest carboniferous the turkestan ocean and the gissar basin were closed the early permian chinorsay 288 ma and dara i pioz 267 ma post collisional intrusions emplaced in the northern part of the gissar micro continent after a long period of amagmatic evolution have intraplate geochemical affinities and isotopic sr nd pb isotopic compositions 87sr 86sr t 0 7074 0 7086 end of 5 5 to 7 4 indicating derivation from precambrian continental crust which is supported by old nd model ages 1 5 and 1 7 ga and by the presence of inherited zircon grains with ages 850 500 ma in the chinorsay granodiorite the post collisional intrusions in the southern gissar and in the mogol tau and kurama ranges 297 286 ma emplaced directly after supra subduction magmatic series have geochemical and isotopic signatures of arc related magmas the distinct shoshonitic affinities of post collisional intrusions in the mogol tau and kurama ranges are explained by the interaction of hot asthenospheric material with subduction enriched wedge of lithospheric mantle due to slab break off at post collisional stage despite origination from different tectonic environments all magmatic rocks have relatively old nd model ages 1 7 1 0 ga indicating a significant proportion of paleoproterozoic or older crustal material in their sources and their model ages are similar to those of post collisional intrusions from the alai and kokshaal segments of the south tien shan

geology mineralization and fluid inclusion study of the kuru tegerek au cu mo skarn deposit in the middle tien shan kyrgyzstan the kuru tegerek cu au mo deposit is situated in a system of late carboniferous subduction related magmatic arcs of the middle tien shan which together constitute a metallogenic belt of cu au mo w porphyry with local skarns deposits the deposit is related to magnetite series gabbro diorite to tonalite intrusion it contains prograde magnesian and calcic skarns with abundant magnetite associated with gabbro diorite and retrograde skarn with cu mineralization formed after intrusion of tonalite subsequent propylitic alteration introduced abundant chalcopyrite and pyrrhotite and native au culminating in zones overprinting magnetite and garnet skarn later quartz muscovite carbonate veins formed after intrusion of late mafic quartz monzogabbro dikes contain chalcopyrite pyrite arsenopyrite and other sulfides and sulfosalts tellurides and native au the earliest retrograde skarn garnet contains gaseous low salinity 1 7 3 4 wt nacl eq fluid inclusions homogenizing at 460 500 c into vapor indicating that the early fluid released from crystallizing magma was a low density vapor it was followed by more saline 4 0 5 0 wt nacl eq high temperature 400 440 c aqueous fluid as fluid release from the magma progressed boiling of this fluid at temperatures of 420 to 370 c and a pressure of 350 300 bar produced a low salinity 0 6 1 2 wt nacl eq essentially gaseous and high salinity from 39 to 31 wt nacl eq brine with possible metal including cu partitioning into both gaseous and aqueous saline phases boiling was coeval with sulfide deposition in the retrograde skarn the latest episode of the retrograde skarn stage included direct separation of saline 40 42 wt nacl eq fluid from crystallizing magma the separation of saline 40 to 14 wt nacl eq fluids from a crystallizing magmatic melt continued during the propylitic stage when fluid cooling from 370 to 320 c together with decreasing fo2 caused cu and especially au precipitation a new influx of possibly magma derived low salinity 4 5 6 7 wt nacl eq aqueous and then nacl co2 h2o fluids corresponds to the phyllic quartz muscovite carbonate sulfide stage these fluids may have a deeper source associated with the late mafic quartz monzogabbro dikes fluid cooling from 340 to 255 c and boiling of the nacl co2 h2o fluid together with increased fs2 increased the au endowment

opening of the kuril basin deduced from the magmatic history of central hokkaido north japan abstract the kuril basin is a fan shaped back arc basin in the northwestern pacific rim the basin is separated by the kuril arc from the pacific ocean to the southeast and is bounded by the subsided okhotomorsk block to the north and by the late eocene to early miocene hidaka magmatic arc to the west the clastic sediments constituting the late cretaceous to early eocene proto kuril arc which underlies the modern kuril arc were transported from the okhotomorsk block between them the kuril basin now intervenes this suggests that the kuril basin had not opened and that the proto kuril arc had been located in the southern margin of the okhotomorsk block at least until early eocene time it also indicates that the kuril basin was not entrapped by the proto or modern kuril arc the tertiary hidaka magmatic arc in central hokkaido was formed along a n s trending subduction zone where the pacific plate was subducting beneath the eurasian plate therefore the kuril basin was not yet present on the east of central hokkaido during the period when the hidaka magmatism was taking place based on the fact that the hidaka arc magmatism ceased at 17 16 ma and coevally along its n s trending extension it is suggested that the kuril basin opened just after 16 ma by the southward retreat of the proto kuril arc trench system in central hokkaido an extensional stress regime during the middle miocene is inferred from the occurrence of a type magmatism and graben like sedimentary basins this stress field can be attributed to subsidence of the pacific slab covered by the retreated proto kuril arc during the opening of the kuril basin the occurrence of an undeformed and horizontal sedimentary cover on the rugged basement of the kuril basin is consistent with rather rapid opening at 16 15 ma during the middle miocene the kuril basin and japan basin were formed by a similar process i e rotation and oceanward retreat of an arc trench system opening of the two back arc basins along different plate boundaries i e the pacific north american boundary for the kuril basin and the pacific eurasian boundary for the japan basin may have been caused by the migration of a hot region across the overriding plate boundary

formation of anhydrous and hydrous skarn in cu au ore deposits by magmatic fluids most skarn ore deposits are characterized by two distinctly different alteration styles an early prograde stage with anhydrous minerals such as garnet and pyroxene forms from relatively high temperature hypersaline liquid a later retrograde stage with hydrous minerals such as epidote amphibole and chlorite plus sulfide ore minerals forms from lower temperature lower salinity fluids these two alteration stages commonly have been thought to reflect a dominance of magmatic and meteoric water respectively with relevance to the source of ore metals we report data from two different skarn systems one being part of the world s largest cu au resource stable isotope compositions of anhydrous and hydrous alteration minerals from both deposits indicate a magmatic source for both the prograde and retrograde stages 18o averages 5 0 per mil for garnet range 3 4 7 2 6 5 per mil for pyroxene 4 3 8 2 and 7 1 per mil for amphibole 4 3 8 7 the d values of late amphibole are more complex with magmatic values 77 to 78 for one deposit and both magmatic and lighter values for another deposit that could be explained either by magmatic degassing or by limited mixing with meteoric water we conclude that the differences in fluid composition prograde versus retrograde stages resulted from a magmatic fluid that intersected its solvus during the early stage creating vapor and hypersaline liquid whereas in the later stage this magmatic fluid did not intersect its solvus because it followed a different cooling path this late low salinity liquid only boiled once its vapor pressure curve was reached causing sulfide ore to precipitate during the retrograde stage

tungsten mineralization in the tien shan gold belt geology petrology fluid inclusion and stable isotope study of the ingichke reduced tungsten skarn deposit western uzbekistan abstract the ingichke reduced w skarn deposit 100kt wo 3 with the average grade of 0 58 wo 3 is the largest one among w deposits known in the tien shan gold belt it is associated with an early permian multiphase granitoid pluton that comprises ilmenite series to ilmenite titanite bearing medium to high k metaluminous to peraluminous i type granitoid monzodiorite granodiorite to granite leucogranite rocks the pluton is related to crustal accretionary type reservoirs of granitoid magma likely formed in response to an ascent of asthenospheric material at the post collisional stage it is part of the continuum of plutonic suites related to reduced w au polymetallic deposits with further links to reduced intrusion related au deposits the deposit comprises abundant pyroxene mainly hedenbergitic skarn and a minor garnet skarn mostly grossular rich garnet with elevated almandine and spessartine contents hydrosilicate propylitic alteration amphibole chlorite calcite quartz with abundant pyrrhotite and minor chalcopyrite partially overprints skarn and is in turn overprinted by zones of phyllic alteration quartz sericite fe carbonate locally with albite scheelite and sulfides bi and au minerals prograde and retrograde skarns were formed from aqueous dominantly magnesian sodic chloride moderately saline 10 14 to 4 7 wt nacl eq hot fluid with its progressing enrichment in ca hydrosilicate propylitic and phyllic alteration assemblages were formed from boiling low salinity carbonic aqueous magnesium sodic calcic fluids at moderate 330 355 c to lower 250 265 c temperatures respectively with separation of carbonic with varying co 2 ch 4 ratio and aqueous chloride fluids trapping pressures ranged from 2000 to 1500 bars indicating a lithostatic depth of some 6 to 8 km i e a lower intermediate level in an integrated model of reduced w skarn deposits the stable isotope data indicate an influence of a sedimentary limestone source of oxygen and carbon at the retrograde skarn stage 18 o h2o 8 1 to 9 0 13 c co2 2 5 to 0 3 and a dominantly magmatic mantle to crustal derived source of water 18 o h2o 7 0 0 5 at the hydrosilicate propylitic and phyllic alteration stages and carbon 13 c co2 7 8 to 4 7 at the hydrosilicate propylitic stage at the phyllic alteration stage a strong enrichment in the light carbon isotope 13 c co2 10 1 to 9 4 indicates a possible influence of a reduced organic carbon source a magmatic source of sulfur is envisioned for the hydrosilicate propylitic 34 s 2 0 0 5 and phyllic 34 s 1 0 0 3 alteration stages

mineralization and fluid inclusion study of the shizhuyuan w sn bi mo f skarn deposit hunan province china the shizhuyuan deposit china is a world class w sn bi mo f skarn deposit hosted by devonian limestone in the thermal aureole of the qianlishan granite complex the qianlishan complex comprises five separate intrusions including fine grained porphyritic biotite granite 182 187 ma granite 1 medium grained biotite k feldspar granite 158 163 ma granite 2 fine grained biotite and k feldspar granite granite 3 granitic porphyry 144 146 ma granite 4 and diabase 142 ma the upper part of the granite complex is characterized by extensive greisen alteration skarn zones distributed around the intrusions are mainly calcic consisting of garnet garnet pyroxene vesuvianite garnet and wollastonite vesuvianite progressively outward from the intrusion following the primary skarn formation some of the skarn zones underwent retrograde alteration the high garnet pyroxene ratio and the diopside rich and andradite rich compositions of the pyroxene and garnet indicate that the skarn belongs to the oxidized type mineralization consists of sn be veinlet ore type i in marble and porphyry massive w bi mo sn skarn ore type ii stockwork w sn bi mo f ore type iii and w sn mo bi greisen ore type iv mainly associated with granite 2 emplacement of granite 2 was accompanied by late intense fracturing characterized by stockwork mineralization type iii which was superimposed on massive skarn and greisen zones the stockwork ore consists mainly of greisen and skarn veins and veinlets with scheelite wolframite molybdenite cassiterite bismuthinite and fluorite the sm nd method has been used to analyze the sm nd concentration and data for pyroxene and garnet in the massive skarn type ii ore associated with granite 2 yields an isochron age of 157 ma this age corresponds closely to the age of granite 2 fluid inclusion studies of four types of ore samples reveal four types of inclusions aqueous two phase inclusions h2o co2 inclusions gas rich inclusions and daughter mineral bearing inclusions containing halite or calcite homogenization temperatures of fluid inclusions in skarn minerals range from 350 to 535 c the homogenization temperatures of fluid inclusions in greisen and stockwork are lower than that in skarn and range from 200 to 360 c the fluid inclusion data indicate that there are two types of fluids associated with the massive skarn and greisen having salinities from 26 to 41 wt percent nacl equiv and from 1 to 21 wt percent nacl equiv respectively the high salinity inclusions are daughter mineral bearing whereas the low salinity inclusions are dominantly aqueous with a few gas rich inclusions the results suggest the evolution of the ore forming fluids either by immiscibility or by mixing between a high temperature high salinity magmatic water and a low temperature low salinity fluid such as meteoric water consistent with previously published isotopic studies the shizhuyuan deposit is a multi element skarn highly enriched in w sn bi mo and f this is interpreted to reflect multiple sources and stages of mineralization which in turn may account for the large size of the shizhuyuan deposit

early permian intrusions of the alai range understanding tectonic settings of hercynian post collisional magmatism in the south tien shan kyrgyzstan abstract we present geochemical and sr nd pb hf isotope data as well as the results of single grain u pb zircon dating for ten granitoid and alkaline intrusions of the alai segment of kyrgyz south tien shan sts the intrusions comprise four geochemically contrasting series or suites including 1 i type and 2 shoshonitic granitoids 3 peraluminous granitoids including s type leucogranites and 4 alkaline rocks and carbonatites closely associated in space new geochronological data indicate that these diverse magmatic series of the alai segment formed in a post collisional setting five single grain u pb zircon ages in the range 287 281 ma in combination with published ages define the main post collisional magmatic pulse at 290 280 ma which is similar to ages of post collisional intrusions elsewhere in the sts an age of 287 4 ma obtained for peraluminous graniodiorite of the liayliak massif emplaced in amphibolite facies metamorphic rocks of the zeravshan alai block is indistinguishable from ca 290 ma age of peraluminous granitoids emplaced coevally with barrovian type metamorphism in the garm block located ca 40 km south west of the research area the sr nd pb hf isotopic compositions of the studied intrusions are consistent with the reworking of crustal material with 1 6 1 1 ga average crustal residence times indicating the formation of the alai segment on a continental basement with mesoproterozoic or older crust the pattern of post collisional magmatism in the alai segment characterized by emplacement of i type and shoshoninitic granitoids in combination with coeval barrovian type metamorphism is markedly different from the pattern of post collisional magmatism in the adjacent kokshaal segment of the sts with predominant a type granitoids that formed on a former passive margin of the tarim craton we suggest that during the middle late carboniferous the alai segment probably comprised a microcontinent with precambrian basement located between the turkestan ocean to the north and an inferred oceanic basin to the south where the evidence of supra subduction magmatism was largely destroyed by subsequent tectonic processes in this scenario after collision the position of the alai microcontinent between two major sutures enabled delamination of its lithospheric mantle which resulted in production of diverse post collisional magmatic series by interaction of ascending asthenospheric material with lithospheric mantle and various crustal protoliths

metallogeny of the saryjaz ore district eastern kyrgyz tien shan abstract the saryjaz ore district relates to the tien shan metallogenic belt in the eastern part of the kokshal segment of the tien shan collisional belt the regional structure is known as the saryjaz syntaxis also partially capturing the middle and south tien shan the ore district was formed during multiple changes of tectonic regimes in relation to subduction of the turkestan ocean in the silurian to the carboniferous to the collision of the kazakh and tarim continents in the late carboniferous to the early permian and to postcollisional permian geological events a distinctive feature of the tectonic evolution of the region is the transition from the subduction of the oceanic crust to the continental subduction of the tarim continent under the kazakh continent followed by the impact of the tarim mantle plume after the collision sinistral strike slip tectonics caused by oblique collision between the tarim and kazakh continents led to formation of postcollisional transcrustal fault zones of great importance as the main magma and ore controlling conduits these fault zones penetrated into the mantle and controlled the distribution of heat and fluid flows as well as localization of granite plutons and mineralization in the consolidated crust the metallogenic zoning of the ore district reflects its geological and structural heterogeneity relationship features of mineralization and magmatism and the varying depth of formation of mineral deposits within the south tien shan portion of the district mineralization is associated with late postcollisional permian a type granites related to a one petrogenetic series namely granite rapakivi biotite leucogranite li mica leucogranite rapakivi granites of the jangart suite were formed in the course of exhumation and melting of overheated continental slabs of the tarim craton previously subducted into the mantle leucogranite uchkoshkon complex and leucogranite li mica granite inylchek complex were formed during complex interaction of the rapakivi magma fractionation with further melting of the continental crust under the influence of the tarim mantle plume at the bottom of the collisional edifice the megamelange terrain includes togolok gold deposit and several rare tin occurrences associated with rapakivi granites of the jangart complex within the lower and middle thrust sheets the leucogranite plutons of the uchkoshkon complex control a large uchkoshkon tin deposit and a medium sized sarybulak tin polymetallic deposit within the upper thrust sheet the leucogranite li mica granite plutons of the inylchek complex control a large trudovoe tungsten tin deposit and a small atjailau tin deposit within the middle tien shan portion of the district neoproterozoic carbonaceous shales intensively deformed in a thick thrust zone accommodated a giant kumtor orogenic gold deposit it has no proven links with granites it is structurally controlled by a system of postcollisional transcrustal fault zones the spatial proximity and synchronism of permian magmatic activity in tarim 300 272 ma and a types granites in the saryjaz ore district 299 269 ma as well as the age of kumtor gold deposit 288 284 ma support a hypothesis about the influence of the tarim mantle plume upon the formation of the ore district

magmatic hydrothermal evolution at the lyangar redox intermediate tungsten molybdenum skarn deposit western uzbekistan tien shan insights from igneous petrology hydrothermal alteration and fluid inclusion study abstract the lyangar w mo skarn deposit is situated in a metallogenic belt of w mo cu mo w au and au deposits and is related to an early permian multiphase monzodiorite granodiorite granite leucogranite pluton that was emplaced in a tectonic domain with possible ancient continental crust the latter coupled with an inferred ascent of hot asthenospheric material has defined an enrichment in mo and fluorine together with w and au to form a distinct metallogenic assemblage in a post collisional environment the parental moderately to high k transitional metaluminous to peraluminous weakly oxidized weakly reduced ilmenite titanite series granitoids are accompanied by hydrothermal alteration and mineralization that formed in redox intermediate environment the deposit incorporates prograde and retrograde pyroxene and garnet skarns composed of hedenbergitic pyroxene and grossular to almandine spessartine rich garnet respectively fluorite is present in the retrograde skarn together with scheelite and sulfides the latter including most abundant pyrrhotite and molybdenite hydrosilicate amphibole epidote chlorite quartz locally with albite sulfides and scheelite assemblage has limited development phyllic quartz sericite fe carbonate locally with albite fluorite scheelite and sulfides also bi and au minerals alteration assemblage partially overprints altered skarns and extends over much larger areas overall the deposit represents a superposition of the early w mo mineralization related to retrograde skarn and hydrosilicate alteration and the late au w cu bi mineralization in phyllic alteration assemblages prograde and retrograde skarns were formed from dominantly magnesian sodic chloride moderately saline 11 7 13 9 wt to 8 6 10 5 wt nacl eq high pressure 1500 to 1350 bars hot aqueous fluids that were followed by moderately saline 12 3 14 5 wt nacl eq ca rich lower pressure 600 bars fluids during deposition of most scheelite hydrosilicate propylitic assemblages were formed from boiling fluids at the temperatures of 380 430 c and pressures of 600 300 bars whereas phyllic alteration assemblages from boiling carbonic aqueous low salinity fluids at the temperatures of 300 320 c and pressures of 1000 bars 18oh2o values range from 7 8 to 8 6 for retrograde skarn and from 6 6 to 7 0 for phyllic alteration whereas 13cco2 from 3 3 to 0 5 for retrograde skarn and from 5 5 to 4 5 for phyllic alteration 34s increases from retrograde skarn 34s 2 0 to 2 3 to phyllic alteration 34s 4 3 to 4 6 stages

stable isotope paleoaltimetry a critical review stable isotope paleoaltimetry makes use of systematic trends in the distribution and isotopic composition of modern precipitation with climate and topography and of the potential to estimate the isotopic composition of paleoprecipitation from authigenic in situ formed minerals to illustrate the usefulness as well as potential limitations of this method we review 1 processes controlling the isotopic composition of modern precipitation 2 stable isotope data from modern precipitation across regions of high topography and 3 stable isotope data from authigenic minerals that have been used to infer paleotopography from this we conclude that stable isotope studies of authigenic minerals can permit useful inferences on paleotopography with uncertainties that critically depend on a detailed understanding of local to global scale paleoclimate during the time interval of interest

trace element and fluid inclusion geochemistry constraint for genesis of gold polymetallic mineralization in the songhung deposit dpr korea abstract the songhung deposit is located in the southwestern part of the yangdok metamorphic core complex ymcc in the northern portion of the pyongnam basin the eastern part of the sino korean craton in this paper we present a detailed study on the magma sources of the granitoids yangdok and hoechang graintic intrusions genesis of pyrite and fluid inclusion characteristics for sufficient and additional understanding of tectonic events petrogenesis of the granitoids and mineralization in the study deposit the yangdok granite has lower al2o3 tio2 ratios mean value of 60 58 than the hoechang granite mean value of 994 46 indicating the higher temperature magma source of the former on the rb ba vs rb sr and cao tfeo mgo tio2 vs cao tfeo mgo tio2 discriminant diagrams the magma source of the yangdok granite belongs in the plagioclase rich and clay poor source rocks while those of the hoechang granite plots either in the plagioclase rich and clay poor source rocks for granite and fine grained granite or in the plagioclase poor and clay rich source rocks for granite porphyry and felsite on the nb vs y ta vs yb rb vs y nb and rb vs yb ta tectonomagmatic discrimination diagrams these two granites are connected with the volcanic arc related setting and plot in post collision setting moreover some data of the hoechang granite fall in wpg field suggesting that the volcanic arc setting may be changed to an intraplate setting from middle cretaceous the pyrite trace element geochemistry showing the high co ni ratio than one with an average of 8 2 and high co content and low ni content suggests that its formation was closely linked with i type granitic magma derived hydrothermal fluid mixed with meteoric water it could also be assumed by the co and as contents in pyrite indicating a certain degree of meteoric water in the ore forming fluid it is consonant to the pb s c and o isotope geochemistry in the previous study suggesting that ore forming fluids and metals could be derived from both the yangdok granite and the proterozoic and paleozoic meta sedimentary rocks exposed in the study area all of the pyrite grains have not compositional zoning and the similar distribution patterns of co and ni are appeared in single pyrite grain from core to rim suggesting the stable crystallization environment of pyrites and same ore forming fluid source in pyrite grains the positive correlation between gold and arsenic is appeared the au exists either as a micro and nano size inclusion in pyrite and other minerals or as a solid solution in pyrite lattice based on the petrological and microthermometric characteristics of the fluid inclusions in ore bearing quartz we suggest that the ore forming fluid is represented as nacl h2o or nacl kcl h2o systems with low salinity the absence of co2 enriched phase and vapor only or liquid only primary inclusions in quartz indicates the homogenous magma derived ore forming fluids and a lack of boiling during ore forming process the formation temperature and pressure of this deposit approximately vary from 317 to 326 c and from 105 46 to 111 69 105 pa respectively exhibiting the hydrothermal deposit origin in conclusion the songhung deposit is originated from i type granitic magma source derived hydrothermal fluid which was mixed with meteoric water

mio pleistocene zanda basin biostratigraphy and geochronology pre ice age fauna and mammalian evolution in western himalaya article i nfo the pliocene 5 3 2 6 ma of tibet witnessed the drying of the northern tibetan plateau and the approach to the pleistocene ice age within the background of intensifying indian and east asian monsoons yet little is known about pliocene mammals living on the high tibetan plateau despite the fact that fossil mammals elsewhere consti tute an important knowledge base for terrestrial environments the late miocene to pleistocene zanda basin at the northern foothills of the himalayas affords a welcome opportunity to evaluate the biological response to environ mental change at high elevations abundant well preserved fossil mammals and fish from an 800 m continuous section of fine to coarse grained sediments thus open a rare window into a past biological world for example the discovery of an ancestral wooly rhino from zanda basin that was the precursor of its late pleistocene megafaunal descendants leads to our out of tibet hypothesis suggesting that the high tibetan plateau was a pliocene cradle for ice age cold adaptations in this paper we document in detail the mammalian biostratigraphy chronology and paleozoogeography based on zanda basin fossil mammals our high resolution biostratigraphy and biochronology offer for the first time independent constraints that both support and modify recent magnetostratigraphic correlations using charac teristic pliocene and pleistocene mammals particularly the small mammal assemblages in the lower part of the section and monodactylid equus from the upper section we propose a correlation to c1n to c3an 1r with an age range of 400 ka to 6 4 ma within the 800 m zanda section the lower 0 150 m is of latest miocene age spanning 6 4 5 3 ma sparsely fos siliferous the lower section has produced five taxa so far ochotona panthera qurliqnoria palaeotragus a nd hipparion all are consistent with a late miocene age the middle 150 620 m section spans the entire pliocene this section is by far the most fossiliferous including such typical pliocene small mammals as prosiphneus mimomys apodemus a ndtrischizolagus as well as large mammals such as coelodonta thibetana hipparion zandaense chasmaporthetes nyctereutes meles antilospira and others in the upper 620 800 m section the fos sils are rare but do include characteristic pleistocene taxa such as equus zoogeographically zanda basin mammals are a mixture from two major sources taxa such as mimomys prosiphneus trischizolagus chasmaporthetes nyctereutes meles a ndxenocyon are commonly found in north china or east asia in contrast several forms such as unique species of pikas ochotona squirrels aepyosciurus and ancestral tibetan antelope qurliqnoria seem to belong to an indigenous tibetan fauna evolved within the plateau a lack of shared taxa with the oriental realm suggests a formidable barrierby the himalayas despite a short distance 100 km between zanda basin and the indian subcontinent

geodynamics and metallogeny of the central eurasian porphyry and related epithermal mineral systems a review abstract major porphyry cu au and cu mo deposits are distributed across almost 5000 km across central eurasia from the urals mountains in russia in the west to inner mongolia in north eastern china these deposits were formed during multiple magmatic episodes from the ordovician to the jurassic they are associated with magmatic arcs within the extensive subduction accretion complex of the altaid and transbaikal mongolian orogenic collages that developed from the late neoproterozoic through the palaeozoic to the jurassic intracratonic extension the arcs formed predominantly on the palaeo tethys ocean margin of the proto asian continent but also within two back arc basins the development of the collages commenced when slivers of an older proterozoic subduction complex were rifted from an existing cratonic mass and accreted to the palaeo tethys ocean margin of the combined eastern europe and siberian cratons subduction of the palaeo tethys ocean beneath the karakum and altai tarim microcontinents and the associated back arc basin produced the overlapping late neoproterozoic to early palaeozoic tuva mongol and kipchak magmatic arcs contemporaneous intra oceanic subduction within the back arc basin from the late ordovician produced the parallel urals zharma magmatic arc and separated the main khanty mansi back arc basin from the inboard sakmara marginal sea by the late devonian the tuva mongol and kipchak arcs had amalgamated to form the kazakh mongol arc by the mid palaeozoic the two principal cratonic elements the siberian and eastern european cratons had begun to rotate relative to each other drawing in the two sets of parallel arcs to form the kazakh orocline between the two cratons during the late devonian to early carboniferous the palaeo pacific ocean began subducting below the siberian craton to form the sayan transbaikal arc which expanded by the permian to become the selanga gobi khanka arc by the middle to late permian as the kazakh orocline continued to develop both the sakmara and khanty mansi back arc basins were closed and the collage of cratons and arcs were sutured by accretionary complexes during the permian and triassic the north china craton approached and docked with the continent closing the mongol okhotsk sea an embayment on the palaeo pacific margin to form the mongolian orocline subduction and arc building activity on the palaeo pacific ocean margin continued to the mid mesozoic as the indosinian and yanshanian orogens significant porphyry cu au mo and au cu deposits were formed during the ordovician in the kipchak arc e g bozshakol cu au in kazakhstan and taldy bulak porphyry cu au in kyrgyzstan silurian to devonian in the kazakh mongol arc e g nurkazgan cu au in kazakhstan and taldy bulak levoberezhny au in kyrgyzstan devonian in the urals zharma arc e g yubileinoe au cu in russia devonian in the kazakh mongol arc e g oyu tolgoi cu au and tsagaan suvarga cu au in mongolia carboniferous in the kazakh mongol arc e g kharmagtai au cu in mongolia tuwu yandong cu au in xinjiang china koksai cu au kounrad cu au and the aktogai group of cu au deposits in kazakhstan carboniferous in the valerianov beltau kurama arc e g kal makyr dalnee cu au in uzbekistan benqala cu au in kazakhstan late carboniferous to permian in the selanga gobi khanka arc e g duobaoshan cu au in inner mongolia china triassic in the selanga gobi khanka arc and jurassic in the selanga gobi khanka arc e g wunugetushan cu mo and jiguanshan mo in inner mongolia china in addition to the tectonic geologic and metallogenic setting and distribution of porphyry cu au mo mineralisation within central eurasia the setting geology alteration and mineralisation at each of the deposits listed above is described and summarised in table 1

the jc tin skarn deposit southern yukon territory i geology paragenesis and fluid inclusion microthermometry the jc tin deposit is one of several stanniferous skarns associated with the mid cretaceous seagull batholith at jc a ridgelike lobe of the seagull batholith granite has intruded a thick sequence of mississippian quartzite containing a 30 to 35 m carbonate horizon skarn has replaced this carbonate along its elongate contact with the granite ridge for a distance of more than 850 m the paragenetic sequence in the jc skarn is contact metamorphic skarnoid stage 0 grossularite diopside quartz calcite early skarn stage i andradite hedenbergite stage iia fe amphibole magnetite stage iib fe amphibole pyrrhotite or chalcopyrite or sphalerite stage iii epidote quartz calcite or axinite or sn al sphene late skarn stage iv early veins beryl quartz or tourmaline or danalite stage iv main stage biotite quartz fluorite or arsenopyrite or chalcopyrite or cassiterite stage v fe chlorite muscovite calcite stage vi veins breccias calcite pyrite or marcasite the sequential stages of skarn development display a progression from massive skarn replacement of the protolith calcite marble stages i and ii to more diffuse or veinlike replacement of earlier skarn assemblages stages iii to vi many of the early skarn silicates contain appreciable tin especially andradite up to 0 79 wt sno 2 fe amphibole 0 07 0 61 wt sno 2 epidote 0 12 1 56 wt sno 2 and the sn al sphene the replacement of earlier stage iia skarn at stage iv was an important ore forming process precipitating tin as cassiterite in a narrow zone above the skarn granite contact microthermometric measurements of primary fluid inclusions in epidote and axinite yield a temperature range for stage iii skarn formation of 410 degrees to 500 degrees c at an estimated pressure of 750 bars stage iii fluids ranged in salinity from 20 to 27 wt percent 4 5 6 5 molal total cl and had high cacl 2 nacl ratios 11 these fluids are interpreted to be the result of mixing of originally more saline magmatic fluids with meteoric water during the latest stage of early skarn formation low salinity pseudosecondary inclusions in epidote may represent a relatively unmixed sample of this meteoric water component stage iii fluids appear to have become cacl 2 enriched as a consequence of skarn forming reactions primary fluid inclusions in cassiterite imply a temperature range of 430 degrees to 560 degrees c and salinities of 25 to 43 wt percent 6 12 molal total cl for stage iv fluids these fluids contained predominantly cacl 2 nacl h 2 o and a lesser component of kcl with cacl 2 nacl kcl ranging from 0 6 to 7 7 the apparent increase in both fluid temperature and salinity at stage iv is attributed to a renewed episode of fluid release from the underlying granite with concomitant greisen alteration of the upper part of the jc granite ridge a trend toward very high cacl 2 nacl kcl ratios in the stage iv fluids may be attributable to the progress of cacl 2 producing kcl consuming replacement reactions within the skarn however variations in the overall salinity and other compositional characteristics of these fluids may have been largely controlled by the process of aqueous phase separation from the jc granite the high salinity of the stage iv fluids implies derivation from a granitic melt which exsolved a subcritical two phase aqueous fluid the observation of extremely saline two phase fluids in greisens and other types of granite hosted deposits provides more direct evidence of such a process the relatively low salinity observed in some other examples of granite related sn and w mineralization may be a direct consequence of supercritical rather than subcritical aqueous fluid separation from the associated magmas

geology and mineralization of the uchkoshkon tin deposit associated with a breccia pipe eastern kyrgyzstan abstract the uchkoshkon tin deposit is one of the largest deposits in the sn w saryjaz ore district of eastern kyrgyzstan the district coincides spatially with the saryjaz syntaxis which is the narrowest portion of the south tien shan collisional belt the syntaxis is distinguished by collisional thrust tectonics and postcollisional a type granite magmatism of permian age the uchkoshkon deposit is in the exocontact zone of a 260 km 2 273 279 ma ilmenite series high heat production biotite granite pluton a satellite granite stock 400 250 m and an explosive breccia pipe 450 150 m crosscutting the stock are the central structural features of the deposit area the main stock accompanied by li f felsite dykes controlled early stage mo w and sn w greisen stockwork mineralization that surrounds the apical portion of the stock the breccia pipe postdates the emplacement of the li f felsite dykes and greisen stockwork mineralization the pipe is rooted in main pluton and has been traced by a borehole to a depth of 800 m the breccia was injected by a swarm of tree like branching dykes with diffuse contours consisting of k and b rich rhyolite porphyry cementing the breccia fragments the main breccia body has been intruded by a much smaller 150 100 m hydrothermal breccia pipe with quartz tourmaline matrix which immediately preceded main stage lode mineralization the majority of the lodes occur outside the breccia pipe within a zone of pervasive scapolitization that surrounds the main pluton the main stage lodes are represented by quartz tourmaline cassiterite veins with minor sulfides which occupy a series of steeply dipping near parallel north northeast trending shear fractures that are related to postcollisional strike slip tectonics where quartz tourmaline cassiterite veins crosscut moderately dipping skarn deposits the latter are commercially mineralized with cassiterite nordenskioldine and borosilicate minerals the formation of both explosive breccia and main stage lode mineralization was related to the evolution of b and h 2 o rich residual magma deep within the main pluton the suggested formation model of the uchkoshkon tin deposit is generally applicable to other major sn and sn w deposits in the saryjaz ore district

genesis of the maikhura tungsten tin skarn deposit tajik tien shan insights from petrology mineralogy and fluid inclusion study abstract the maikhura w sn skarn deposit is situated in the gissar segment of the southern tien shan it associates with a late carboniferous early permian composite granitoid pluton which includes earlier ilmenite series transitional metaluminous to peraluminous i type granodiorite and later magnetite series biotite to biotite tourmaline granite leucogranite the oxidized granitic intrusions exhibit a type granite affinity and define a geochemically and genetically distinct group of w sn deposits the deposit incorporates both pyroxene and garnet dominant prograde and retrograde skarns with scheelite and locally magnetite overprinted by highly reduced pyrrhotite stable post skarn mineral assemblages of hydrosilicate and phyllic alteration stages containing scheelite cassiterite and sulfides the fluid inclusions data indicate the involvement of carbonic free aqueous moderately saline 9 9 16 wt nacl eq high pressure 2 1 0 5 kbar hot fluid which was sourced from crystallizing magma and formed prograde calcic skarn this fluid evolved into a sodic chloride slightly less saline 8 6 11 wt nacl eq lower pressure 1 7 0 5 kbar cooler fluids toward the retrograde skarn stage this stage was characterized by deposition of scheelite in association with magnetite the hydrosilicate propylitic alteration was formed from a low salinity ca enriched homogenous aqueous carbonic methane rich fluid at lower temperatures 350 400 c with precipitation of scheelite and cassiterite particularly in phlogopite chlorite oligoclase quartz assemblage corresponding ph decrease explains the trend toward overlapping fields of insoluble cassiterite and scheelite the phyllic alteration assemblages were formed from a boiling aqueous carbonic co2 dominated low salinity fluid at temperatures of 310 250 c and pressure of 1 85 0 1 kbar the alteration evolving from chlorite through muscovite to albite dominant paragenesis indicates a trend toward higher ph less acidic conditions and was accompanied by precipitation of scheelite and cassiterite with further deposition of sulfides a homogeneity of 34s values suggests sulfur isotope homogenization in a magmatic chamber whereas their proximity to the meteorite standard supports a magmatic source of sulfur the depletion in heavy sulfur isotope of sulfides from hydrosilicate propylitic alteration 34s 1 8 to 0 7 to sulfides from phyllic alteration 34s 0 1 to 0 8 is consistent with the evolution from ilmenite series to magnetite series magmatic source

geology mineralization stable isotope and fluid inclusion characteristics of the vostok 2 reduced w cu skarn and au w bi as stockwork deposit sikhote alin russia abstract the large 180 kt wo 3 and at least 10 15 t au vostok 2 deposit is situated in a metallogenic belt of w sn w au and au w deposits formed in late to post collisional tectonic environment after cessation of active subduction the deposit is related to an ilmenite series high k calc alkaline plutonic suite that by its petrologic signatures is transitional between those at w dominant and au dominant reduced intrusion related deposits consistently besides large w cu skarns of the reduced type the deposit incorporates quartz stockworks with significant au w bi mineralization also formed in a reduced environment the hydrothermal stages include prograde and retrograde essentially pyroxene skarns hydrosilicate amphibole chlorite quartz alteration and phyllic quartz sericite albite apatite and carbonate alteration assemblages these assemblages contain abundant scheelite associated with pyrrhotite chalcopyrite and at the phyllic stage also with bi minerals as bi sb te pb zn sulfides and sulfosalts as well as au mineralization the fluid evolution included hot high pressure 420 460 c 1 1 1 2 kbar low salinity 5 4 6 0 wt nacl equiv aqueous fluids at the retrograde skarn stage followed by lower temperature cyclic releases of high carbonic low salinity to non carbonic moderate salinity aqueous fluids at the hydrosilicate stage a high carbonic ch 4 dominated hot 350 380 c low salinity fluid was followed by cooler 300 350 c non carbonic moderate salinity 5 7 14 9 wt nacl equiv fluid at the phyllic stage a high carbonic co 2 dominated moderately hot 330 355 c 0 9 kbar low salinity fluid was followed by cooler 230 265 c non carbonic moderate salinity 6 6 12 0 wt nacl equiv fluid a homogenized magmatic source of water 18 o h2o 8 3 to 8 7 and a sedimentary source of sulfur 34 s 6 9 to 6 2 and carbon 13 c fluid 20 1 to 14 9 at the hydrosilicate stage are suggested a magmatic source of water 18 o 8 6 to 9 2 and a sedimentary source of sulfur 34 s 9 3 to 4 1 but a magmatic mantle to crustal derived source of carbon 13 c fluid 6 9 to 5 2 are envisaged for fluids that formed the early mineral assemblage of the phyllic stage then the role of sedimentary carbon again increased toward the intermediate 13 c fluid 16 4 to 14 5 and late 13 c fluid 16 3 to 14 7 phyllic mineral assemblages the magmatic differentiation was responsible for the fluid enrichment in w whereas au and bi could also have been sourced from mafic magma the decreasing temperatures together with elevated ca content in non boiling fluids promoted scheelite deposition at the early hydrothermal stages the most intense scheelite deposition at the phyllic stage was caused by co 2 removal due to boiling of co 2 rich fluids further cooling of non boiling fluids favoured joint deposition of scheelite bi and au

geology geochemistry and genesis of tungsten tin deposits in the baiganhu district northern kunlun belt northwestern china mineralized occurrences in the baiganhu district were discovered in 2002 after extensive exploration in the eastern kunlun domain in the kunlun terrane tungsten sn deposits in the area contain total resources of 174 913 metric tons t of wo3 and 79 091 t of sn which makes the baiganhu field a new large w sn metallogenic province after the nanling region of southern china the w sn mineralization in the baiganhu field is spatially associated with monzogranite that yielded a 238u 206pb zircon age of 430 5 1 2 ma n 25 cassiterite yielded a 206pb 207pb 238u 207pb isochron age of 427 13 ma n 32 which confirms a close relationship of the early silurian intrusion and the w sn mineralization the timing of the mineralization indicates another important w sn metallogenic event in china in addition to the period of late jurassic from 160 150 ma in the nanling region the mineralization is divided into three stages i scheelite bearing skarn stage ii wolframite and scheelite bearing greisenization stage and iii wolframite and cassiterite bearing quartz veining stage quartz in the wolframite and cassiterite bearing quartz veins shows two types of fluid inclusions liquid rich two phase aqueous inclusions and co2 rich and ch4 bearing three phase inclusions inclusions have medium salinity 10 14 wt nacl equiv low density 0 60 1 06 g cm3 and moderate homogenization temperatures 240 270 c the co2 phase in three phase inclusions shows a large variation from 10 to 70 vol which is attributed to immiscible separation of a co2 rich phase from saline aqueous fluids the immiscible separation likely contributed to the mineralization in quartz veins the formula 1 values of the mineralizing fluids calculated from quartz and d of inclusion fluids in quartz vary from 4 5 to 6 4 and 65 to 43 respectively supporting that the mineralizing fluids originated from the parental magmas 1 embed mml math 1 gif

from seamount accretion to tectonic erosion formation of osa melange and the effects of cocos ridge subduction in southern costa rica 1 the costa rica portion of the middle america trench mat is characterized by active tectonic erosion a process that causes the removal of material from the base of the upper plate as the plate boundary migrates upward offshore studies demonstrate accelerated subduction erosion starting at the miocene pliocene boundary as the result of subduction of thickened galapagos related crust as presently represented by the cocos ridge the subduction of the cocos ridge also caused uplift and exposure of the outer forearc on the osa peninsula which offers a window to explore the tectonic evolution of the area the rocks outcropping on osa peninsula are a middle eocene middle miocene melange dominated by basalt chert and limestone resulting from accretion of seamounts the accretion dominated period of the mat evolution ended at the miocene pliocene boundary when thickened crust a paleo cocos ridge produced at the galapagos hot spot arrived at the trench the thick crust caused uplift and severe tectonic erosion of the accretionary edifice allowing exhumation of the osa melange the change from accretion to erosion caused the outer forearc to be offset along subvertical faults that define small kilometer to tens of kilometers size blocks that are going through differential vertical movements in response to the morphology of the subducting ridge subduction accretion and erosion are two processes that can alternate in time and space or coexist along the same margin so that mass removal can develop on a previously growing margin and completely remove an accretionary prism

birth life and demise of the andean syn collisional gissar arc late paleozoic tectono magmatic metamorphic evolution of the southwestern tian shan tajikistan the amalgamation of the central asian orogenic belt in the southwestern tian shan in tajikistan is represented by tectono magmatic metamorphic processes that accompanied late paleozoic ocean closure and collision between the karakum tarim and kazakh kyrgyz terranes integrated u pb geochronology thermobarometry pseudosection modelling and hf geochemistry constrain the timing and petro tectonic nature of these processes the gissar batholith and the garm massif represent an eastward along strike increase in paleodepth from upper batholith 21 7 km to arc root 36 19 km levels of the andean syn collisional gissar arc which developed from 323 288 ma in two stages i andean i type granitoid magmatism from 323 306 ma due to northward subduction of the gissar back arc ocean basin under the gissar microcontinent which was immediately followed by ii syn collisional i s type granitoid magmatism in the gissar batholith and the garm massif from 304 288 ma due to northward subduction underthrusting of karakum marginal continental crust under the gissar microcontinent a rapid isotopic pull up from 288 286 ma signals the onset of juvenile alkaline syenitic post collisional magmatism by 280 ma which was driven by delamination of the gissar arclogite root and consequent convective asthenospheric upwelling whereas m ht lp prograde metamorphism in the garm massif 650 750 c 6 7 kbar from 310 288 ma was associated with subduction magma inundation and crustal thickening ht lp heating and decompression to peak metamorphic temperatures 800 820 c 6 4 kbar at 288 6 ma was driven by the transmission of a post collisional mantle derived heat wave through the garm massif crust

formation of a rain shadow o and h stable isotope records in authigenic clays from the siwalik group in eastern bhutan we measure the oxygen and hydrogen stable isotope composition of authigenic clays from himalayan foreland sediments siwalik group and from present day small stream waters in eastern bhutan to explore the impact of uplift of the shillong plateau on rain shadow formation over the himalayan foothills stable isotope data from authigenic clay minerals 2 m suggest the presence of three paleoclimatic periods during deposition of the siwalik group between 7 and 1 ma the mean 18o value in paleometeoric waters which were in equilibrium with clay minerals is 2 5 lower than in modern meteoric and stream waters at the elevation of the foreland basin we discuss the factors that could have changed the isotopic composition of water over time and we conclude that a the most likely and significant cause for the increase in meteoric water 18o values over time is the amount effect specifically a decrease in mean annual precipitation b the change in mean annual precipitation over the foreland basin and foothills of the himalaya is the result of orographic effect caused by the shillong plateau s uplift the critical elevation of the shillong plateau required to induce significant orographic precipitation was attained after 1 2 ma c by applying scale analysis we estimate that the mean annual precipitation over the foreland basin of the eastern bhutan himalayas has decreased by a factor of 1 7 2 5 over the last 1 3 million years 2018 american geophysical union all rights reserved

multiple sources for mineralizing fluids in the charmitan gold tungsten mineralization uzbekistan mineral assemblages present within the charmitan gold tungsten quartz vein mineralization have been investigated for their cathodoluminescence behaviour chemical composition and noble gas isotope systematics this inventory of methods allows for the first time a systematic reconstruction of the paragenetic relationships of quartz scheelite sulphides and native gold within the gold mineralization at charmitan and provides the basis to utilise noble gas data in the discussion of sources and evolution of ore forming fluids the vein quartz is classified into four generations based on microscopic and cathodoluminescence investigations quartz i shows intense brittle deformation as associated scheelite i undeformed scheelite ii overgrows scheelite i and has lower light rare earth element and higher intermediate rare earth element contents as well as higher strontium concentrations scheelite ii is associated with the economic gold mineralization and formed during re crystallisation and re precipitation of material which was partly re mobilised from early scheelite i during infiltration of gold bearing fluids early stage native gold inclusions are often associated with stage 2 sulphides scheelite ii and bismuth tellurides and contain ag 3 6 24 4 wt hg 1 0 wt and bi 0 2 wt later stage electrum grains occur in association with stage 3 sulphides and sulphosalts and contain hg 0 8 wt and elevated sb concentrations up to 3 0 wt noble gas isotope data 3he 4he 0 2 0 4 ra for hydrothermal ore fluids trapped in the gold related sulphides and sulphosalts stage 2 pyrite and arsenopyrite stage 3 pyrite sphalerite galena and lead sulphosalts suggest that diverse fluid sources were involved in the formation of the charmitan gold deposit these data are indicative of a small but significant input of fluids from external deep seated mantle and possibly lower crust sources a decrease in the input of mantle helium and an increasing role of crustal helium from early to later stages of the mineralization is suggested by the measured 3he 4he and 40ar 4he ratios sulphides from ore veins in meta sedimentary rocks contain higher portions of meteoric fluids than those in intrusive rock types as indicated by their lower 3he 36ar ratios the 3he 36ar ratios in the meta sedimentary rocks agree well with ratios typical of gold mineralizations in the tien shan gold province completely hosted by meta sedimentary sequences indicating intense fluid wall rock interaction