hydrothermal alteration and fluid chemistry of the endako porphyry molybdenum deposit british columbia hydrothermal alteration and fluid chemistry data of the early cretaceous endako porphyry molybdenum deposit british columbia provide new information on the hydrothermal fluids associated with low fluorine molybdenite mineralization molybdenite mineralization and hydrothermal alteration occur as early quartz molydenite stockwork veins with k feldspar bearing selvages and paragenetically later quartz molybdenite ribbon veins with sericite bearing selvages late hydrothermal alteration is associated with the development of kaolinite and postore tertiary age calcite veins fluid inclusions in early formed quartz molybdenite stockwork veins with k feldspar bearing alteration assemblages are dominated by moderate salinity 5 to 15 wt nacl equiv liquid rich type 1 and rare high salinity 30 to 45 wt nacl equiv halite bearing type 3 fluid inclusions type 1 and type 3 fluid inclusions in early veins homogenize between 390 and 430 c and 375 and 420 c respectively secondary fluid inclusions type 2 of low salinity 1 to 5 wt nacl equiv in these early veins are minor and homogenize between 130 and 285 c fluid inclusions in quartz molybdenite ribbon veins with sericite bearing alteration assemblages are dominated by moderate salinity liquid rich type 1 inclusions with minor type 2 fluid inclusions type 1 fluid inclusions of ribbon veins homogenize between 360 and 400 c fluid inclusions in postore calcite veins are of only type 2 fluid inclusions which homogenize at 209 c hydrothermal fluids recorded by type 1 and type 3 fluid inclusions in early veins were trapped under lithostatic to hydrostatic conditions between 0 3 and less than or equal to 2 0 kbar and 360 and 560 c postore fluids recorded by type 2 fluid inclusions were trapped under conditions less than or equal to 0 5 kbar and between 190 and 300 c quartz stockwork and ribbon veins possess 18o values of 8 4 0 2 n 9 and 8 4 0 6 n 13 respectively hydrothermal k feldspar and biotite from k feldspar alteration assemblages possess 18o values of 6 8 0 4 n 7 and 3 5 0 8 n 8 respectively oxygen isotope geothermometry of quartz biotite and quartz k feldspar pairs from k feldspar alteration assemblages yield temperatures between 200 and 490 c which is similar to the trapping temperatures of hydrothermal fluids determined from fluid inclusion studies associated with molybdenite mineralization the development of kaolinite and calcite veins the oxygen isotope temperatures of the quartz biotite and quartz k feldspar pairs suggest that k feldspar and biotite either record the approximate 18o composition of hydrothermal fluids associated with k feldspar alteration or have undergone 18o exchange with late stage hydrothermal fluids hydrogen isotope composition of quartz stockwork and ribbon veins fluid inclusion waters range between 105 and 173 per mil solute chemistry studies of fluid inclusion waters indicate that ore forming fluids from endako have low br cl and br na ratios and high i cl and i br ratios in comparison to porgera epithermal babine lake porphyry cu and st austell capitan pluton vein deposits associated with magmatic processes na k ratios of fluid inclusion waters yield temperatures 308 to 429 c similar to those determined from type 1 and type 3 fluid inclusions and stable isotope thermometry results from fluid inclusion and solute chemistry studies indicate the involvement of hydrothermal fluids exsolved from a crystallizing melt in the formation of the endako molybdenum deposit however oxygen and hydrogen isotope values deviate from the generally accepted magmatic compositions which suggests the early involvement of meteoric water in the ore forming fluids and ore genesis

geochemical and sr nd isotopic constraints on the genesis of the cenozoic linzizong volcanic successions southern tibet abstract the linzizong volcanic successions that crop out in the lhasa terrane southern tibet have been conventionally regarded as the products of northward subduction of the neotethyan oceanic slab beneath south asia this study reports geochemical data of 100 volcanic rocks from the lhasa terrane to better constrain the temporal spatial distribution and petrogenesis of the linzizong volcanism the linzizong volcanic successions consist dominantly of calc alkaline rocks that erupted from ca 69 to 43 ma and show typical arc lava geochemical features marked with lile enrichment and hfse depletion in the spidergram their sr and nd isotope ratios e nd t 3 3 to 2 4 i sr 0 7048 0 7072 are generally similar to those of the associated gangdese i type granitoids the linzizong volcanism is characterized by a flare up period ca 50 ma that shows significant geochemical variations manifested by the coexistence of five types of volcanic rocks 1 the main suite of calc alkaline rocks sio 2 45 80 wt la 12 45 ppm e nd t 3 8 to 4 9 i sr 0 7037 0 7105 that could be interpreted by partial melting of the mantle wedge followed by assimilation and fractional crystallization afc processes with 10 crustal contamination and or magma mixing 2 the low k low ree suite sio 2 48 61 wt k 2 o 0 5 1 1 wt la 7 10 ppm that has the highest nd isotope ratios e nd t 5 9 to 3 5 suggesting a juvenile mantle origin possibly related to decompression melting of the asthenosphere 3 the shoshonitic suite sio 2 53 71 wt k 2 o 3 8 6 7 wt e nd t 2 8 to 6 1 from small degree melting of the metasomatized lithospheric mantle 4 the high ree suite sio 2 61 75 wt la 36 87 ppm e nd t 2 6 to 3 2 originating from remelting of a newly underplated basaltic lower crust and 5 the evolved suite of rhyolitic flows and ignimbrites sio 2 65 wt that have the lowest e nd t values of 14 to 18 representing remelting products of the basement or continental crust of the lhasa terrane such geochemical heterogeneities are attributed to breakoff of the subducted neotethyan slab under southern tibet that occurred in the early stage of the india asia collision

origin of mesozoic and tertiary granite in the western united states and implications for pre mesozoic crustal structure 2 nd and sr isotopic studies of unmineralized and cu and mo mineralized granite in the precambrian craton in the cordilleran region of the western united states mesozoic and tertiary peraluminous granitic rocks display regional variations in initial 143nd 144nd end end 10 to 12 in southern arizona 17 to 19 in the northern great basin ngb and 30 in the northern rocky mountains initial 87sr 86sr values are between 0 710 and 0 721 and show no regional pattern metaluminous granitic rocks have a wider range of end values extending from values similar to those of the peraluminous granites to much higher values the 87sr 86sr values are mostly fairly low between 0 705 and 0 710 except in the ngb where values as high as 0 7157 are observed no systematic differences between the end or 87sr 86sr values of cu or mo mineralized and unmineralized granite were discerned except for cu mineralized granite in eastern nevada and mo mineralized granite in colorado which have end values higher 0 and lower 10 0 respectively than unmineralized granite in the same region comparison to end values of exposed precambrian rock suggests that the peraluminous granite and the mo granite in colorado were derived exclusively from felsic precambrian basement rocks and that the regional variations in the end values reflect the regional variation in the average crustal age the nd data confirm that the precambrian basement underlying the ngb and eastern california is isotopically distinct from precambrian crust in the remainder of the western united states the similarity between the end values of peraluminous granite and precambrian crust also suggests that the high 147sm 144nd 0 13 and the low total light rare earth element lree abundances characteristic of peraluminous granite in southern arizona were imposed during the chemical evolution of the magmas metaluminous granite are interpreted to have formed via mixing of mantle derived magma and large proportions of low 87sr 86sr granulite facies lower crust except in the eastern ngb where the mantle magmas mixed with a lower crustal source with a significantly higher 87sr 86sr ratio ree abundance patterns for metaluminous granite in the ngb are characterized by extreme lree enrichment which supports the proposed origin for these rocks by mantle crust mixing or by remelting of the lower crust alone no systematic difference exists between the sources of cu or mo mineralized and unmineralized metaluminous granite but the data suggest that the cu sources are in the mantle and the mo sources are in preexisting crust overall the nd data indicate that continental interior granite in the western united states was primarily derived from preexisting crust and although changes in the thermal structure of the continental mantle may have triggered magma formation the resulting granites do not represent significant juvenile additions to the continental crust

adakites from continental collision zones melting of thickened lower crust beneath southern tibet adakites are geochemically distinct intermediate to felsic lavas found exclusively in subduction zones here we report the first example of such magmas from southern tibet in an active continental collision environment the tibetan adakites were emplaced from ca 26 to 10 ma and their overall geochemical characteristics suggest an origin by melting of eclogites and or garnet amphibolites in the lower part 50 km of thickened tibetan crust this lower crustal melting required a significantly elevated geotherm which we attribute to removal of the tectonically thickened lithospheric mantle in late oligocene time the identification of collision type adakites from southern tibet lends new constraints to not only the himalayan tibetan orogenesis how and when the indian lithosphere started underthrusting asia can be depicted but also the growth of the early continental crust on earth that consists dominantly of the tonalite trondhjemite granodiorite suites marked by adakitic geochemical affinities

tibetan tectonic evolution inferred from spatial and temporal variations in post collisional magmatism cenozoic magmatism on the tibetan plateau shows systematic variations in space and time that must be considered in models concerning tibetan tectonic evolution after the india asia collision which started in the early tertiary and terminated the gangdese arc magmatism in the lhasa terrane made of the southern tibetan plateau widespread potassium rich lavas and subordinate sodium rich basalts were generated from f50 to 30 ma in the qiangtang terrane of northern tibet subsequent post collisional magmatism migrated southwards producing ultrapotassic and adakitic lavas coevally between f26 and 10 ma in the lhasa terrane then potassic volcanism was renewed to the north and has become extensive and semicontinuous since f13 ma in the western qiangtang and songpan ganze terranes such spatial temporal variations enable us to elaborate a geodynamic evolution model which depicts when and how the indian continental lithospheric mantle started thrusting under asia by involving rollback and breakoff of the subducted neo tethyan slab followed by removal of the thickened lhasa lithospheric root we propose that only after the lithospheric removal which occurred at f26 ma could the indian mantle lithosphere have commenced its northward underthrusting and henceforth served as a pivotal control to the himalayan tibetan orogenesis consequently the tibetan plateau is suggested to have risen diachronously from south to north whereas the southern part of the plateau may have been created and maintained since the late oligocene the northern plateau would have not attained its present day elevation and size until the mid miocene when the lower part of the western qiangtang and songpan ganze lithospheres began to founder owing to the push of the underthrust indian mantle lithosphere d 2004 elsevier b v all rights reserved

neotectonic fault mapping at the gibraltar strait tunnel area bolonia bay south spain abstract a map of fault activity has been developed for preliminary engineering planning related to the construction of an underwater fixed link route between africa and europe at the gibraltar strait sector in south spain the gibraltar tunnel main criteria used in fault activity evaluation have been seismicity surface faulting geomorphology of fault traces identification of paleoseismic ground failures and evaluation of differential uplift rates on coastal segments separated by large scale inland faults the aim of this work is the development of comprehensive methodology for the graphic representation chart format of geo hazards related to ground conditions seismicity and fault activity the criteria management is mainly focused on the establishment of the seismic or aseismic character of individual fault traces for this the age of the last deformational event and slip rates where possible are taken into account but their classification as active or inactive structures is avoided from this study the cabo de gracia strike slip fault ne sw can be catalogued as active during at least the last 128 ka bp and as a probable seismic source of moderate events mb

country rock contamination of magmas associated with the baogutu porphyry cu deposit xinjiang china abstract the baogutu porphyry cu deposit located in the west junggar region xinjiang china has the reduced mineralization features baogutu is associated with a late carboniferous intrusive complex that was emplaced into lower carboniferous volcano sedimentary sequences the complex consists of a main stage diorite stock and late stage diorite porphyry dikes the former hosts the most of the cu mineralization the main stage stock has a wide range of composition from minor gabbro through dominant diorite to tonalite porphyry these are all inhomogeneous over a few meters with no distinct boundary between the gabbro diorite and tonalite porphyry some felsic microgranular enclaves and heterogeneous phenocrysts occur in these rocks the latter is a single mineral with a range of compositions the elemental and sr nd compositions of the tonalite porphyry have a transitional character from the gabbro and diorite to the country rocks these findings suggest possible country rock contamination mineral composition data suggest that the primary magma at baogutu is oxidized i type magma the gabbro and diorite have high positive e nd t 3 3 to 6 0 and low initial 87 sr 87 sr ratios 0 7035 0 7038 and are characterized by moderately fractionated rare earth element ree patterns pronounced nb depletion and weak negative eu anomalies these observations suggest that the baogutu magmas were derived from partial melting of a metasomatized mantle wedge and underwent significant country rock contamination after emplacement the contamination process involved the felsic components and reduced materials e g carbonaceous sediment which caused the chemical variation of the baogutu rocks and the reduced mineralization features in the baogutu deposit thus contamination played an important role in the formation of the host rocks and associated mineralization at baogutu

geochronology and geochemistry of the max porphyry mo deposit and its relationship to pb zn ag mineralization kootenay arc southeastern british columbia canada the max porphyry mo deposit is located at the northern end of the kootenay arc in southeastern british columbia canada molybdenum mineralization is genetically related to the variably altered trout lake granodiorite stock which has lithogeochemical affinities to the low fluorine calc alkaline granodiorite hosted porphyry mo deposit type three molybdenite samples from early and late mo bearing veins yield re os dates that overlap within analytical error with a weighted average age of 80 3 0 2 ma these dates are in close agreement with two 206pb 238u weighted average zircon ages for phases of the trout lake stock at 80 3 1 6 and 79 2 1 0 ma indicating that crystallization of the stock and hydrothermal molybdenite formation were coeval and likely cogenetic 40ar 39ar plateau ages for primary biotite in igneous dikes secondary biotite in early potassic alteration and muscovite in late phyllic alteration range from 80 to 76 ma the younger 40ar 39ar plateau ages may reflect unusually slow cooling of the magmatic hydrothermal system or a late thermal disturbance pb zn ag vein deposits are common throughout the kootenay arc and several such veins are located within and proximal to the max porphyry mo deposit the presence of rare molybdenite associated with sphalerite and argentiferous galena in some of these pb zn ag veins suggests that they represent a late stage event related to the max magmatic hydrothermal system fluid inclusions in quartz from mo and pb zn ag veins are similar and can be divided into two compositional groups type 1 aqueous liquid rich fluid inclusions and type 2 aqueous carbonic liquid rich fluid inclusions pressure corrected 1 4 1 7 kbar trapping temperatures of typical type 1 inclusions from mo bearing veins range from 430 to 460 c and for pb zn ag veins from 335 to 365 c the ranges of salinity 0 12 wt nacl equiv in fluid inclusions from both vein types are almost identical and type 2 inclusions from both vein types contain similar amounts of co2 avg xco2 0 08 with traces of ch4 the similarity of chemistry in the two vein types suggests a genetic link between porphyry mo mineralization and adjacent pb zn ag deposits however muscovite from the alteration halo around a pb zn ag vein within the max deposit yielded a 40ar 39ar plateau age of 72 2 0 5 ma this date is significantly younger than the 80 ma age of porphyry magmatism and mo mineralization suggesting either that this event is in fact unrelated to porphyry mo mineralization at 80 ma or that the k ar isotope system has been disturbed by a later thermal event

petrogenesis of paleocene eocene porphyry deposit related granitic rocks in the yaguila sharang ore district central lhasa terrane tibet abstract the paleocene eocene ore deposits in the gangdese metallogenic belt tibet are thought to have been formed during the main period of india asia continental collision this paper reports the whole rock major element trace element and sr nd hf isotopic compositions and zircon trace element contents of volcanic and intrusive rocks from the paleocene yaguila skarn pb zn ag deposit and adjacent eocene sharang porphyry mo deposit in the central lhasa terrane tibet geochemical signatures and nd hf isotopic compositions indicate that the yaguila cretaceous rhyolitic rocks were formed by the melting of ancient continental crust whereas the paleocene causative granite porphyry may have resulted from the interaction between mantle derived and crustal derived materials when continental collision was initiated the dramatic increase of end t values between emplacement of the granite porphyry and later porphyritic biotite granite suggests a greater involvement of mantle materials during the crystallization of the barren biotite granite stock the post ore miocene granodiorite porphyry has a similar geochemical signature to the sharang miocene dykes suggesting they were both generated from melting of enriched lithospheric mantle nd hf mixing calculations indicate an increasing contribution of mantle materials in paleocene to eocene intrusions consistent with the regional tectonic model of neo tethyan oceanic slab roll back and break off zircons from both the yaguila and sharang ore related porphyries have higher ce anomalies than those from the barren granitoids suggesting that mo mineralization was closely related to highly oxidized and differentiated magma the fertile intrusions in the yaguila sharang district contain eun eun values from 0 3 to 0 6 higher than the non mineralized intrusions the processes of early crystallization of plagioclase and or so2 degassing from underlying magma can explain the observed negative eu anomalies in zircon

the remarkable re os chronometer in molybdenite how and why it works the re os rhenium osmium chronometer applied to molybdenite mos2 is now demonstrated to be remarkably robust surviving intense deformation and high grade thermal metamorphism successful dating of molybdenite is dependent on proper preparation of the mineral separate and analysis of a critical quantity of molybdenite unique to each sample such that recognized spatial decoupling of 187re parent and 187os daughter within individual molybdenite crystals is overcome highly precise accurate and reproducible age results are derived through isotope dilution and negative thermal ion mass spectrometry id ntims spatial decoupling of parent daughter precludes use of the laser ablation icp ms microanalytical technique for re os dating of molybdenite the use of a reference or control sample is necessary to establish laboratory credibility and for interlaboratory comparisons the rb sr k ar and 40ar 39ar chronometers are susceptible to chemical and thermal disturbance particularly in terranes that have experienced subsequent episodes of hydrothermal magmatic activity and therefore should not be used as a basis for establishing accuracy in re os dating of molybdenite as has been done in the past re os ages for molybdenite are almost always in agreement with observed geological relationships and when available with zircon and titanite u pb ages for terranes experiencing multiple episodes of metamorphism and deformation molybdenite is not complicated by overgrowths as is common for some minerals used in u pb dating e g zircon monazite xenotime nor are re and os mobilized beyond the margins of individual crystals during solid state recrystallization moreover inheritance of older molybdenite cores incorporation of common os and radiogenic os loss are exceedingly rare whereas inheritance common pb and pb loss are common complications in u pb dating techniques therefore molybdenite ages may serve as point in time markers for age comparisons

zircon u pb and hf isotopic constraints on the onset time of india asia collision the time of initial collision between india and asia has been extremely controversial despite the fact that it is vital to constraining the orogenesis and subsequent evolution of the himalayas and tibetan plateau here we report u pb and hf isotope analysis of detrital zircons from two principal foreland basins that is the sangdanlin and gyangze basins respectively in the western and central parts of southern tibet our data suggest that asian derived clastic sediments started contributing to sedimentation on the indian continental margin earlier than generally thought at 60 ma in both basins near the yarlung zangbo suture zone in southern tibet no evidence for the existence of an intra oceanic arc within the neotethys is observed we conclude that 60 ma can be used to constrain the onset time of the india asia collision at least in central tibet after this initial collision closure of the neotethys propagated both westward and eastward with the final closure occurring at 50 and 45 ma in northwestern and eastern himalayas respectively our conclusion differs significantly from the previous view that the india asia collision may have started in northwestern himalaya and propagated eastward with diachronous suturing

geology and genesis of the post collisional porphyry skarn deposit at bangpu tibet abstract bangpu deposit in tibet is a large but poorly studied mo rich 0 089 wt and cu poor 0 32 wt porphyry deposit that formed in a post collisional tectonic setting the deposit is located in the gangdese porphyry copper belt gpcb and formed at the same time 15 32 ma as other deposits within the belt 12 18 ma although it is located further to the north and has a different ore assemblage mo pb zn cu compared to other porphyry deposits cu mo in this belt two distinct mineralization events have been identified in the bangpu deposit which are porphyry mo cu and skarn pb zn mineralization porphyry mo cu mineralization in the deposit is generally associated with a mid miocene porphyritic monzogranite rock whereas skarn pb zn mineralization is hosted by lower permian limestone clastic sequences coprecipitated pyrite and sphalerite from the bangpu skarn yield a rb sr isochron age of 13 9 0 9 ma in addition the account of garnet decreases and the account of both calcite and other carbonate minerals increases with distance from the porphyritic monzogranite suggesting that the two distinct phases of mineralization in this deposit are part of the same metallogenic event four main magmatic units are associated with the bangpu deposit namely a paleogene biotite monzogranite and miocene porphyritic monzogranite diabase and fine grained diorite units these units have zircon u pb ages of 62 24 0 32 14 63 0 25 14 46 0 38 and 13 24 0 04 ma respectively zircons from porphyritic monzogranite yield e hf t values of 2 2 8 7 with an average of 5 4 whereas the associated diabase has a similar e hf t value averaging at 4 7 the geochemistry of the miocene intrusions at bangpu suggests that they were derived from different sources the porphyritic monzogranite has relatively higher heavy rare earth element hree concentrations than do other ore bearing porphyries in the gpcb and plots closer to the amphibolite lithofacies field in y zr sm and y sm yb diagrams the bangpu diabase contains high contents of mgo 7 92 wt feot 8 03 wt but low k 2 o the bangpu deposit has alteration zonation ranging from an inner zone of biotite alteration through silicified and phyllic alteration zones to an outer propylitic alteration zone similar to typical porphyry deposits some distinct differences are also present for example k feldspar alteration at bangpu is so dispersed that a distinct zone of k feldspar alteration has not been identified hypogene mineralization at bangpu is characterized by the early stage precipitation of chalcopyrite during biotite alteration and the late stage deposition of molybdenite during silicification fluid inclusion microthermometry indicates a change in ore forming fluids from high temperature 320 c 550 c and high salinity 17 wt 67 2 wt fluids to low temperature 213 c 450 c and low salinity 7 3 wt 11 6 wt fluids the deposit has lower d v smow 107 1 to 185 8 values compared with other porphyry deposits in the gpcb suggesting that the bangpu deposit formed in a shallower setting and is associated with a more open system than is the case for other deposits in this belt sulfides at bangpu yield 34 s v cdt values of 2 3 to 0 3 indicative of mantle derived s implying that coeval mantle derived mafic magma e g diabase simultaneously supplied s and cu to the porphyry system at bangpu in comparison the pb isotopic compositions 206 pb 204 pb 18 79 19 28 207 pb 204 pb 15 64 15 93 208 pb 204 pb 39 16 40 45 of sulfides show that other metals e g mo pb zn were likely derived mainly from an ancient crustal source therefore the formation of the bangpu deposit can be explained by a two stage model involving 1 the partial melting of an ancient lower crust triggered by invasion of asthenospheric mantle derived mafic melts that provide heat and metal cu and 2 the formation of the bangpu porphyry mo cu system formed by magmatic differentiation in the overriding crust in a post collisional setting

u pb and re os geochronological evidence for the jurassic porphyry metallogenic event of the xiongcun district in the gangdese porphyry copper belt southern tibet prc abstract two large copper gold porphyry deposits no i and no ii were discovered in the last decade within the xiongcun district which is located along the south margin of the gangdese porphyry copper belt these two deposits are hosted by two porphyries that were emplaced into the early jurassic volcano sedimentary rock sequences of the xiongcun formation the porphyries are both quartz diorite bodies with one of these distinguished by its large quartz eyes our new molybdenite re os and zircon u pb dates for no i and no ii deposits and host intrusions reveal the presence of two middle jurassic ore forming episodes in the xiongcun district the no ii deposit is related to the 181 175 ma quartz diorite porphyry and formed ca 172 6 2 1 ma the no i deposit is related to the 167 161 ma quartz diorite porphyry with large quartz eyes and formed ca 161 5 2 7 ma geochronological and geochemical features of the jurassic ore bearing porphyries in the xiongcun district indicate that the porphyry copper gold mineralization formed in an island arc setting which is related to the northward subduction of the neo tethys oceanic plate these observations in combination with geochronological data reported at gangdese porphyry copper belt indicated four major metallogenic events existed in the gangdese porphyry copper belt at 172 161 ma 65 48 ma 40 23 ma and 20 12 ma we have identified two mineralization episodes comprise middle jurassic metallogenic event 172 161 ma in the xiongcun district which provides new constrains for the middle jurassic metallogenic event in the gangdese porphyry copper belt

new insights into the hydrothermal evolution of skarn deposits a case study of the dongzhongla pb zn deposit in tibet sw china abstract revealing hydrothermal evolution from the early quartz sulfide to the late fluorite carbonate sulfide stages of skarn sulfide deposits is significant for understanding their ore formation processes but the detailed studies are rare in this study we choose the dongzhongla skarn pb zn deposit 0 38 mt pb zn located in central lhasa tibet as a case study and present detailed ore deposit geology and dataset of in situ chemical compositions of quartz in situ pb isotopic ratios of galena sulfur isotopic compositions of sulfides and c o isotopic compositions of hydrothermal calcite and wall rocks to address this issue there are two types of hydrothermal quartz in the early stage 1 the early phase euhedral quartz qz1 crosscut by quartz sulfide veins and 2 the late phase subhedral quartz qz2 coexisting with sulfides titaniq thermometer of qz1 and qz2 limits the two phases with a temperature range of 336 427 c mean 373 c and 357 461 c mean 386 c respectively the decreasing al concentrations of qz1 from core to rim suggest that magmatic fluids mixed with acidic meteoric water prevented the precipitation of sulfides during the early phase the increasing al and decreasing sulfur concentrations of qz2 indicate that the increasing ph values of hydrothermal fluids made principal sulfides precipitate during the late phase in addition fluid inclusions and c o isotopic studies reveal that the late stage minerals were deposited from low salinity

zircon u pb chronology of the nyingtri group southern lhasa terrane tibetan plateau implications for grenvillian and pan african provenance and mesozoic cenozoic metamorphism abstract the nyingtri group of the lhasa terrane in southern tibet consists dominantly of metasedimentary rocks and orthogneiss these rocks have a similar mineral paragenesis of plagioclase k feldspar biotite quartz sillimanite garnet staurolite muscovite amphibole indicating amphibolite facies metamorphic conditions inherited detrital zircons from the metasedimentary rocks show magmatic features and yield widely variable 206pb 238u ages ranging from 3300 to 50 ma the data define two prominent age populations 1200 1000 and 600 500 ma indicating that the source of the nyingtri group preserves the records of both grenville and pan african magmatic thermal events inherited magmatic zircon cores from the orthogneiss yield a crystallization age of 496 ma limiting the depositional age of the metasedimentary sequence to cambrian or older overgrowth rims on the detrital zircons from one metasedimentary rock yield a metamorphic age of 32 ma on the basis of these results together with the

geochronology and geochemistry of the bangpu mo cu porphyry ore deposit tibet abstract we have determined the ages of the ore bearing bangpu porphyries and the age of formation of an associated mo cu ore deposit using the la icpms zircon u pb and the molybdenite re os methods zircons from two adamellite porphyries give ages of 14 07 0 08 ma and 14 96 0 16 ma and zircons from a diorite porphyry give an age of 15 30 0 25 ma the ages of three molybdenite samples are 14 96 0 23 ma 15 08 0 23 ma and 16 61 0 23 ma light rare earth elements lree are enriched in the ore bearing adamellite which is shoshonitic and peraluminous while heavy rare earth elements hree and y are strongly depleted indicating an adakitic affinity in contrast to other deposits formed in the post collisional gangdese belt the rb sr ratio in bangpu is high demonstrating more crustal contamination the geochemistry of the ore bearing diorite porphyry differs significantly from that of the ore bearing adamellite the diorite porphyry displays a reverse slope in its ree rare earth element pattern and is shoshonitic and metaluminous the geochronology and geochemistry of both ore bearing rocks indicate that the bangpu ore deposit is related to two different source regions in a post collisional environment the metallic minerals formed mainly during the older diorite porphyry stage but they were recycled and reactivated during adamellite magmatism the sources of the mineralising fluids and the evolution of the northern gpcb gangdese porphyry copper belt where the bangpu ore deposit is located are more complex than in the southern gpcb

metallogenesis and the minerogenetic series in the gangdese polymetallic copper belt abstract the gangdese is a newly explored porphyry cu ore belt in china in fact except for the porphyry cu deposits there are a lot of other deposits forming a polymetallic copper belt in the southern gangdese sg i e southern lhasa terrane and gangdese back arc fault uplift belt gbafub also called lungar nyainqentanglha arc the gangdese polymetallic copper belt contains porphyry cu mo au cu au and mo cu skarn cu mo au w pb zn ag fe cu and mo w breccia type and hydrothermal vein type pb zn ag deposits the porphyry cu au mineralization occurred at the xiongcun area of sg during the middle jurassic 175 160 ma and was associated with island arc magmatism related to the northward subduction of the neo tethyan oceanic slab the cretaceous ca 112 ma skarn fe cu mineralization appeared at the nixiong area of gbafub and was generated in a back arc extensional setting related to the neo tethyan oceanic subduction beneath the lhasa terrane the paleocene eocene 65 51 ma porphyry mo cu skarn mo w and skarn pb zn ag deposits are located in the eastern part of gbafub and related to granitoids originating from the partial melting of the old crust with contributions from the mantle in contrast the paleocene eocene 60 45 ma porphyry cu skarn breccia and hydrothermal vein type pb zn ag and skarn fe cu deposits at the namling area were associated with granitoids derived from the partial melting of the mantle with some input of the old crust the oligocene 30 23 ma porphyry skarn cu mo w au mineralization occurred at the zedong area adjacent to north of the indus yarlung zangbo suture zone in a post collisional setting the intensified miocene 21 13 ma porphyry skarn cu mo au and skarn hydrothermal vein type pb zn ag deposits formed in the sg whereas the porphyry mo cu and skarn hydrothermal vein type pb zn ag deposits formed in the gbafub the porphyry mo cu mineralization have more substantial contributions from the old crust in addition to the mantle than those with porphyry cu mo au mineralization the source region of the high sr y intrusions associated with post collisional porphyry cu mo au mineralization is probably the arc magmas that were generated at the subduction stage and have remained stalled at the boundary between the crust and mantle since the neo tethyan ocean closed the early subduction of the neo tethyan oceanic lithosphere played a crucial role in the generation of ore deposits formed in collisional and post collisional settings six minerogenic series or groups can be recognized in the gangdese polymetallic copper belt 1 jurassic porphyry cu au minerogenic series related to island arc magmatism 2 cretaceous skarn fe cu minerogenic series in back arc extensional setting 3 paleocene eocene granitoids related polymetallic minerogenic series in collisional setting 4 oligocene porphyry skarn cu w mo au minerogenic series in post collisional setting 5 miocene cu mo au pb zn ag minerogenic series related to granitoids with substantial contributions from the mantle in post collisional setting and 6 miocene mo cu pb zn minerogenic series related to granitoids with significant contributions from the old crust in post collisional setting during mineralization some deposits underwent superimposed mineralization such as the jiru porphyry cu deposit where the eocene and miocene porphyry type cu mineralization occurred the minerogenic series can be applied to ore prospecting for example when either pb zn ag veins or porphyry skarn mo w cu orebodies are known in an area one of them could provide a useful exploration vector for the other

relative oxidation states of magmas inferred from ce iv ce iii in zircon application to porphyry copper deposits of northern chile major and trace element compositions of zircons and whole rocks from 14 barren and seven ore bearing calc alkaline intrusions from the chuquicamata el abra porphyry copper belt of northern chile have been measured in situ by excimer laser ablation ela icp ms these data permit the ce iv ce iii ratio within zircon to be calculated using a lattice strain model for mineral melt partitioning of ce iv and ce iii zircon ce iv ce iii and eun eun ratios and by inference magmatic oxidation states generally increase from older mafic to younger felsic units within this sequence porphyry copper mineralization is directly associated only with intrusions with zircon ce iv ce iii 300 and eun eun 0 4 such trends can be understood in terms of interdependent relations between oxygen fugacity sulfur speciation and solubility and chalcophile element partitioning in silicate magmas because zircon occurs in most calc alkaline intrusions and is resistant to subsolidus alteration zircon ce iv ce iii ratios provide a useful tool for evaluating the economic potential of such rocks for magmatic hydrothermal cu au mineralization the approach is general and may provide a means to infer relative oxidation state in a wide range of intermediate to felsic igneous rocks

variation of copper isotopes in chalcopyrite from dabu porphyry cu mo deposit in tibet and implications for mineral exploration abstract the study presents copper cu isotope data of mineral separates of chalcopyrite from four drill core samples in the miocene dabu porphyry cu mo deposit formed in a post collisional setting in the gangdese porphyry copper belt southern tibet copper isotope values in hypogene chalcopyrite range from 1 48 to 1 12 displaying a large variation of up to 2 60 which demonstrates cu isotope fractionation at high temperature during hydrothermal evolution the majority of measured chalcopyrite isotopic compositions show a gradual increasing trend from 1 48 to 1 12 with the increase of drilling depth from 130m to 483m as the alteration assemblages change from potassic to phyllic similarly the other 65 cu values 65 cu 65 cu 63 cu sample 65 cu 63 cu standard 1 1000 of the chalcopyrite show a gradual increasing trend from 1 48 to 0 59 with the decrease of drilling depth from 130 m to 57 m as the alteration assemblages change from potassic phyllic through argillic to relatively fresh these observations suggest a genetic link between cu isotope variation and silicate alteration assemblages formed at different temperatures indicative of a rayleigh precipitation process resulting in the large variation of 65 cu values at dabu in general samples closest to the center of hydrothermal system dominated by high temperature potassic alteration are isotopically lighter whereas samples dominated by low temperature phyllic alteration peripheral to the center are isotopically heavier the predicted flow pathways of hydrothermal fluids are from no 0 to no 3 exploration line and the lightest 65 cu values are the most proximal to the hydrothermal source finally we propose that the northwest side of the no 0 exploration line has high potential for hosting undiscovered orebodies the pattern of cu isotope variation in conjunction with the features of silicate alteration in porphyry system can be used to trace the hydrothermal flow direction and to guide mineral exploration

the fault controlled skarn w mo polymetallic mineralization during the main india eurasia collision example from hahaigang deposit of gangdese metallogenic belt of tibet abstract the hahaigang w mo polymetallic skarn deposit is located in the central eastern part of gangdese tectono magmatic belt in lhasa terrane tibet the deposit was discovered in 2007 with currently proven 46 million tons of wo 3 ores 12 million tons of mo ores and 1 31 million tons of combined cu pb zn ores at an average grade of 0 20 wo 3 0 07 mo 0 026 cu 0 49 pb and 3 1 zn ore bodies occur in veins or disseminations and are confined within the ne striking dalong fault zone which is hosted by the lower permian pangna group of dominantly quartz sandstone and slate several granitic plutons are exposed in the area or known from drill holes ages of these granitic plutons are determined by using zircon u pb la icp ms method for example the biotite monzogranite yields a 206 pb 238 u 207 pb 238 u concordia age of 58 66 0 90 ma and a weighted mean 206 pb 238 u age of 57 02 0 42 ma the granite porphyry yields a 206 pb 238 u 207 pb 238 u concordia age of 109 1 8 9 ma and a weighted mean 206 pb 238 u age of 114 0 2 6 ma the biotite monzogranite yields a weighted mean 206 pb 238 u age of 56 1 1 1 ma re os isochron age of 63 2 3 2 ma from 5 molybdenite samples collected from the w mo skarn ores is also obtained in this study the zircon u pb and molybdenite re os geochronological data suggest that the w mo mineralization was not temporally associated with any of the dated igneous plutons however the molybdenite re os age of 63 2 3 2 ma indicates that the w mo mineralization might have occurred during the main india eurasia collision that was initiated around 65 ma microprobe analysis of ilvaite that occurs in two generations in the w mo skarn ores reveals a close relationship to ca fe f rich hydrothermal fluids which were probably derived from deeply seated magmas we suggest that ascent of the fluids was strictly controlled by the ore controlling dalong fault zone and that chemical interaction and metasomatism between the fluids and the lower permian pangna quartz feldspathic host rocks produced the ilvaite and the w mo polymetallic skarn deposit during the main india eurasia collision although the majority of the polymetallic deposits in the gangdese belt are reported to be either pre or post main collision it is evident from this study that the main collision also produced w mo polymetallic mineralization within the belt

metallogeny of the northeastern gangdese pb zn ag fe mo w polymetallic belt in the lhasa terrane southern tibet abstract the northeastern gangdese pb zn ag fe mo w polymetallic belt ngpb characterized by skarn and porphyry deposits is one of the most important metallogenic belts in the himalaya tibetan continental orogenic system this belt extends for nearly four hundred kilometers along the luobadui milashan fault in the central lhasa subterrane and contains more than 10 large ore deposits with high potential for development three major types of mineralization system have been identified skarn fe systems skarn breccia pb zn ag systems and porphyry skarn mo cu w systems in this study we conducted a whole rock geochemical u pb zircon geochronological and in situ zircon hf isotopic study of ore forming rocks in the ngpb specifically the jiangga jiaduopule and rema skarn fe deposits and the yaguila pb zn ag deposit although some of these deposits porphyry mo systems formed during the post collisional stage 21 14 ma the majority these three systems developed during the main soft collision stage of the india asia continental collision 65 50 ma the skarn fe deposits are commonly associated with granodiorites monzogranites and granites and formed between 65 and 50 ma the ore forming intrusions of the pb zn ag deposits are characterized by granite quartz porphyry and granite porphyry which developed in the interval of 65 55 ma the ore forming porphyries in the sharang mo deposit formed at 53 ma the rocks from fe deposits are metaluminous and have relatively lower sio2 and higher cao mgo feo contents than the intrusions associated with mo and pb zn ag mineralization while the pb zn ag deposits are peraluminous and have high sio2 and high total alkali concentrations they all exhibit moderately fractionated ree patterns characterized by lower contents of heavy ree relative to light ree and they are enriched in large ion lithophile elements and relatively depleted in high field strength elements ore forming granites from fe deposits display 87sr 86sr i 0 7054 0 7074 and end t 4 7 to 1 3 whereas rocks from the yaguila pb zn ag deposit have 87sr 86sr i 0 7266 0 7281 and end t 13 5 to 13 3 in situ lu hf isotopic analyses of zircons from fe deposits show that ehf t values range from 7 3 to 6 6 with tdm hf c model ages of 712 to 1589 ma and yaguila pb zn ag deposit has ehf t values from 13 9 to 1 3 with tdm hf c model ages of 1216 to 2016 ma combined with existing data from the sharang mo deposit we conclude that the ore forming intrusions associated with the skarn fe and porphyry mo deposits were derived from partial melting of metasomatized lithospheric mantle and rejuvenated lower crust beneath the central lhasa subterrane respectively melting of the ancient continental material was critical for the development of the pb zn ag system therefore it is likely that the source rocks play an important role in determining the metal endowment of intrusions formed during the initial stage of the india asia continental collision

ore genesis of skarn mineralization in continental collision orogens a case study from the pusangguo co bearing cu pb zn deposit in tibet abstract the gangdese belt in southern tibet is renowned for hosting numerous collision related porphyry cu mo deposits the recent discovery of pusangguo co bearing cu pb zn skarn deposits is the first reported co bearing deposit in gangdese belt as well as in tibet researches on the geological and metallogenic characteristics of pusanguo indicate that this co bearing cu pb zn deposit was formed in a collisional setting we document mineralogy fluid inclusion studies and h o s pb isotope systematics of the skarns and ores of the pusangguo deposit intense endoskarn alteration dominated by green and pink epidote and quartz is widely disseminated throughout the host granodiorite as well as in veinlets exoskarn alteration is characterized by the presence of prograde grandite andradite32 100 and grossular0 68 with minor pyroxene diopside0 46 hedenbergite38 74 and johannsenite1 62 retrograde epidotes from both the endoskarn and exoskarn show a narrow range of fe3 fe3 al ratios 0 25 0 34 ore minerals include chalcopyrite sphalerite and galena with lesser pyrite pyrrhotite bornite co minerals and falkmanite four paragenetic stages of skarn formation and ore deposition are recognized in the pusangguo cu pb zn deposit prograde stage i retrograde stage ii early sulfide stage iii and late sulfide stage iv fluid inclusions in all stages are dominated by two phase liquid rich type l inclusions during the major phase of mineralization stage iii fluid inclusions formed at low temperatures 180 240 c and with low salinities 0 5 8 6 wt nacl equiv this is in contrast to other skarn deposits within the gangdese porphyry copper belt e g the zhibula jiama and bangpu deposits that formed from highly saline fluids at high temperatures hydrogen oxygen isotopic values obtained from garnet epidote quartz and calcite are dh2o 179 to 213 and 18oh2o 9 1 to 9 3 whereas s pb isotopic values for sphalerite chalcopyrite pyrite and galena are 34s 1 0 to 1 2 estimated 34sfluid 0 05 such data are indicative of ore forming fluids and metals that originated from a magmatic hydrothermal source related to granodiorite emplacement during the miocene post continental collision extensive mixing between the magmatic hydrothermal and meteoric fluids led to the co precipitation of cu pb and zn minerals from low salinity fluids at relatively low temperatures the pusangguo co bearing cu pb zn skarn deposit shows consistent features with other porphyry related skarn deposits in the gangdese belt except for relatively low temperature and salinity the research is of great significance for understanding cobalt as an associated mineral in the gangdese sulfide skarn deposit in tibet

india s hidden inputs to tibetan orogeny revealed by hf isotopes of transhimalayan zircons and host rocks abstract to better understand tibetan orogenesis which involves complex tectonic processes here we report the first integrated analysis of hf isotopes of zircon separates and their host rocks from the transhimalayan batholiths the rocks studied include 19 granitoids from different parts of the gangdese batholith the largest transhimalayan intrusive complex and five postcollisional adakites that occurred as plugs or dikes cutting the gangdese batholith in the southern lhasa terrane southern tibet published zircon hf isotope data from other transhimalayan granitoids and the linzizong volcanic rocks are also synthesized the magmatic zircons crystallizing between ca 200 and 15 ma show depleted mantle type hf isotopic characteristics throughout the mesozoic but shift markedly in the paleogene the hf isotopic shift is interpreted as tracking the evolving progress of himalayan sediment subduction driven by the approaching indian continent and thus signals the initiation of the india asia collision that we infer to have occurred by 55 ma our data furthermore indicate that southern tibet underwent significant crustal thickening during ca 45 and 30 ma before emplacement of the postcollisional adakites that exhibit hf nd isotopic systematics suggesting binary mixing of melts from the juvenile gangdese mafic crust and incorporated himalayan sediments in the petrogenesis

high sr y magmas reflect arc maturity high magmatic water content and porphyry cu mo au potential examples from the tethyan arcs of central and eastern iran and western pakistan the temporal and geochemical evolution of arc magmatism that culminated in porphyry cu mo au deposit formation has been studied in three separate neo tethyan arc systems in central and eastern iran and western pakistan porphyry cu au deposits in the lut block of eastern iran formed in the middle eocene at the end of a period of extensive paleocene eocene volcanism porphyry cu mo deposits in the kerman belt of central iran formed in the middle miocene at the end of a period of voluminous eocene oligocene volcanism and porphyry cu au deposits in the chagai belt of western pakistan formed in four pulses during the eocene early miocene middle late miocene and late miocene pliocene after a prolonged period of arc magmatism that began in the late cretaceous and is still active in each region the late porphyry related magmas are more geochemically evolved and more hydrous as evidenced by the presence of hornblende phenocrysts than the preceding volcanic rocks we suggest that this reflects maturation of the arc magmatic system over a period of tens of millions of years leading to the generation of more evolved volatile rich magmas at later stages of the arc s history high magmatic water contents are a prerequisite for the shallow crustal emplacement of arc magmas and the subsequent generation of potentially ore forming subvolcanic magmatic hydrothermal systems it is thus suggested that the fertility of arc magmas within a given arc terrane can be assessed by observing the relative timing of plutonic suites later suites are more prospective noting the common presence of hornblende or biotite phenocrysts indicating high magmatic water contents and through lithogeochemical fingerprinting of magmatic fractionation processes relatively high sr y and la yb ratios and eun eu ratios 1 indicating abundant early hornblende fractionation and suppression of plagioclase crystallization in hydrous magmas

a genetic linkage between subduction and collision related porphyry cu deposits in continental collision zones the genesis of continental collision related porphyry cu deposits pcds remains controversial the most common hypothesis links their genesis with magmas derived from subduction modified arc lithosphere however it is unclear whether a genetic linkage exists between collision and subduction related pcds here we studied jurassic subduction related cu au and miocene collision related cu mo porphyry deposits in south tibet the jurassic pcds occur only in the western segment of the jurassic arc which has depleted mantle like isotopic compositions e g 87 sr 86 sr i 0 7041 0 7048 e nd t as high as 7 5 and e hf t as high as 18 by contrast no jurassic pcds have been found in the eastern arc segment which is isotopically less juvenile e g 87 sr 86 sr i 0 7041 0 7063 e nd t 4 5 and e hf t 12 these results imply that incorporation of crustal components during underplating of jurassic magma induced copper accumulation as sulfides at the base of the eastern jurassic arc inhibiting pcd formation at this time miocene pcds are spatially confined to the jurassic arc and the giant miocene pcds cluster in its eastern segment where no jurassic pcds occur this suggests that the arc segment barren for subduction related pcds could be fertile for collision related pcds miocene ore forming porphyries have young hf model ages and sr nd hf isotopic compositions overlapping with those of the jurassic rocks in the eastern segment whereas contemporaneous barren porphyries outside the jurassic arc have abundant zircon inheritance and crustlike sr nd hf isotopic compositions these data suggest that remelting of the lower crustal sulfide bearing cu rich jurassic cumulates triggered by cenozoic crustal thickening and or subsequent slab break off led to the formation of giant miocene pcds the spatial overlap and complementary metal endowment between subduction and collision related magmas may be used to evaluate the mineral potential for such deposits in other orogenic belts

metallogeny during continental outgrowth in the columbia supercontinent isotopic characterization of the zhaiwa mo cu system in the north china craton abstract the eastern qinling molybdenum belt eqmb in central china represents the largest mo province in the world located at the southern margin of the north china craton this mo province is largely associated with mesozoic granitoids here we report re os isochron age of 1761 33 ma 2 mswd 2 9 from molybdenite in the recently discovered zhaiwa porphyry mo cu system within the eqmb this age coincides with the peak eruption period 1 78 1 75 ga of the xiong er group volcanic rocks which unconformably overlie the taihua supergroup and are interpreted to have developed on a continental arc the re concentrations 1 to 43 ppm of the zhaiwa molybdenites are similar to those of typical porphyry cu mo au systems developed on continental arcs the 34 s values of the zhaiwa ores 2 7 7 3 average 5 2 suggest that the sulfur was mainly sourced from a magmatic system the sulfides from the ores yield sr i average of 0 70533 similar to that of the xiong er group 0 70547 albeit higher than that of the kuanping group 0 70334 and lower than the taihua supergroup 0 70763 suggesting a mixed source the average e nd 1 76 ga of the sulfides from the ores 0 9 falls between the averages of the taihua supergroup ca 6 8 and the kuanping group ca 7 4 the pb isotope ratios of the ores are similar to but slightly higher than those of the taihua supergroup reflecting preferential leaching of radiogenic pb from the taihua supergroup by magmatic fluids integrated data and interpretations constrain the zhaiwa mo cu deposit to be a porphyry mineral system developed within a ca 1 76 ga continental arc related to oceanic plate subduction beneath the southern margin of the north china craton a correlation between tectonic settings and metallogenic types clearly indicate that the xiong er group was formed in a volcanic arc confirming paleo mesoproterozoic continental outgrowth along the margins of the columbia supercontinent the isotopic characterization of the zhaiwa deposit provides new insights into the enigma of the widespread distribution of large and super large mo deposits of eqmb along the southern margin of the north china craton

timing of the yuchiling giant porphyry mo system and implications for ore genesis the yuchiling mo deposit is a recently discovered giant porphyry system in the east qinling mo belt china its apparent causative intrusion i e the yuchiling granite porphyry is the youngest intrusion phase 4 of the heyu multiphase granite batholith which was emplaced between 143 and 135 ma new robust constraints on the formation of the yuchiling porphyry mo system are provided by combined zircon u pb biotite 40ar 39ar and molybdenite re os dating zircon grains from the mo mineralized granite porphyry yield weighted 206pb 238u age of 134 0 1 4 ma n 19 2 error mswd 0 30 magmatic biotite from the same sample yield a 40ar 39ar plateau age of 135 1 1 4 ma 2 error and an inverse isochron age of 135 6 2 0 ma n 7 2 error mswd 10 8 which are effectively coincident with the zircon u pb age within analytical error three pulses of mineralization can be deduced from the molybdenite re os ages namely 141 137 and 134 ma which agree well with the zircon u pb ages of granitic phases 1 2 and the yuchiling porphyry phase 4 respectively these well constrained temporal correlations indicate that mo mineralization was caused by pulses of granitic magmatism and that the ore forming magmatic hydrothermal activity responsible for the yuchiling porphyry mo system lasted about 8 ma the yuchiling mo deposit represents a unique style of porphyry mo system formed in a post collision setting and associated with f rich high k calc alkaline intrusions which differ from convergent margin associated porphyry mo deposits

zircon u pb and hf isotope constraints on the mesozoic tectonics and crustal evolution of southern tibet the first in situ hf and u pb isotope analyses of zircon separates from mesozoic granites in southern tibet identify a significant previously unknown stage of magmatism igneous zircons n 34 from a granite within the gangdese batholith show a weighted mean 206 pb 238 u age of 188 1 1 4 ma and e hf t the parts in 10 4 deviation of initial hf isotope ratios between the zircon sample and the chondritic reservoir values between 10 4 and 16 8 suggesting predominantly early jurassic intrusive activity with a juvenile mantle contribution of 40 inherited zircons from two cretaceous s type granites in the northern magmatic belt 23 delineate a slightly older 206 pb 238 u age cluster between 188 and 210 ma these zircons have e hf t values from 3 9 to 13 7 yielding crustal hf model ages from ca 1 4 to 2 1 ga suggesting a major episode of crustal growth in proterozoic time and remelting of this crust in early jurassic time combining these with literature data we interpret the jurassic gangdese magmatism as an early product of the neo tethyan subduction that played a long lasting role in the tectonic evolution of southern tibet prior to the india asia collision

geology of the post collisional porphyry copper molybdenum deposit at qulong tibet porphyry deposits are usually thought to form from subduction related calc alkaline magmas in magmatic arc settings although some porphyry deposits also occur in post collisional extensional settings the post collisional deposits remain poorly understood here we describe the igneous geology alteration mineralogy and mineralization history of qulong a newly discovered porphyry cu mo deposit in southern tibet that belongs to the post collisional class the deposit is associated with miocene monzogranite granodiorite intrusions and is hosted partly by jurassic andesitic dacitic volcanic rocks the deposit contains 7 1 mt cu and 0 5 mt mo metal the 19 5 ma granodioritic monzogranitic rongmucuola pluton with diorite enclaves is the earliest miocene intrusive unit it was intruded by a regularly shaped stock p porphyry and then thin dikes x porphyry of monzogranite at about 17 7 ma the main cu mo mineralization is associated with the p porphyry a barren diorite porphyry intruded the p and x porphyries around 15 7 ma petrologic trends of the intrusions suggest that the miocene intrusions have similar origins and probably formed by fractionation of a deeper magma chamber emplacement of miocene porphyries controlled by the qulong anticline is in direct response to the rapid uplift erosion of the gangdese arc batholiths in southern tibet miarolitic cavities and unidirectional solidification textures key evidence for volatile separation have been recognized in the p and x porphyries respectively early potassic alteration characterized by quartz k feldspar anhydrite pervades the p porphyry and rongmucuola pluton laterally this alteration grades into quartz biotite anhydrite k feldspar which affects all miocene intrusions except the latest dioritic porphyry wall rocks of rongmucuola pluton and jurassic andesitic dacitic volcanics within 1 1 5 km of the porphyries are dominated by pervasive potassic alteration an outer halo of propylitic alteration epidote chlorite calcite extends up to 2 km away from the deposit feldspar destructive alteration sericite chlorite clay minerals has overprinted most of the potassic and part of the propylitic alteration the alteration is strongly pervasive in the interior of the porphyry bodies and occurs as vein halos away from the porphyry bodies the earliest quartz k feldspar alteration and veins are barren whereas approximately 60 of the cu reserves is associated with slightly later quartz biotite anhydrite alteration barren assemblages are related to irregular quartz k feldspar anhydrite veins which are truncated by the x porphyry cu sulfide bearing assemblages are associated with discontinuous chalcopyrite biotite and continuous quartz anhydrite chalcopyrite molybdenite veins deposition of cu mo with abundant anhydrite occurred during or between emplacement of closely related porphyries from high temperature magmatically derived fluids and was probably caused by the disproportionation of so

mo total organic carbon covariation in modern anoxic marine environments implications for analysis of paleoredox and paleohydrographic conditions 1 sedimentary molybdenum mo s has been widely used as a proxy for benthic redox potential owing to its generally strong enrichment in organic rich marine facies deposited under oxygen depleted conditions a detailed analysis of mo s total organic carbon toc covariation in modern anoxic marine environments and its relationship to ambient water chemistry suggests that 1 mo s while useful in distinguishing oxic from anoxic facies is not related in a simple manner to dissolved sulfide concentrations within euxinic environments and 2 patterns of mo s toc covariation can provide information about paleohydrographic conditions especially the degree of restriction of the subchemoclinal water mass and temporal changes thereof related to deepwater renewal these inferences are based on data from four anoxic silled basins the black sea framvaren fjord cariaco basin and saanich inlet and one upwelling zone the namibian shelf representing a spectrum of aqueous chemical conditions related to water mass restriction in the silled basin environments increasing restriction is correlated with a systematic decrease in mo s toc ratios from 45 5 for saanich inlet to 4 5 1 for the black sea this variation reflects control of mo s by mo aq which becomes depleted in stagnant basins through removal to the sediment without adequate resupply by deepwater renewal the basin reservoir effect the temporal dynamics of this process are revealed by high resolution chemostratigraphic data from framvaren fjord and cariaco basin sediment cores which exhibit long term trends toward lower mo s toc ratios following development of water column stratification and deepwater anoxia mo burial fluxes peak in weakly sulfidic environments such as saanich inlet owing to a combination of greater mo aq availability and enhanced mo transport to the sediment water interface via fe mn redox cycling and are lower in strongly sulfidic environments such as the black sea and framvaren fjord these observations demonstrate that at timescales associated with deepwater renewal in anoxic silled basins decreased sedimentary mo concentrations and burial fluxes are associated with lower benthic redox potentials i e more sulfidic conditions these conclusions apply only to anoxic marine environments exhibiting some degree of water mass restriction e g silled basins and are not valid for low oxygen facies in open marine settings such as continent margin upwelling systems

increasing magmatic oxidation state from paleocene to miocene in the eastern gangdese belt tibet implication for collision related porphyry cu mo au mineralization in the gangdese belt of southern tibet paleocene eocene magmas record the final stage of neo tethyan subduction and are associated with few economic porphyry deposits in contrast magmas formed during later stages of the india asia collision in the oligo miocene are associated with several large porphyry cu mo au deposits especially in the eastern part of the belt 89 e 93 e in a previous study we showed that these oligocene miocene magmas were more hydrous than the earlier paleocene eocene magmas in this study we show that the later magmas were also more oxidized paleocene eocene rocks from the eastern gangdese belt are characterized by low zircon ce4 ce3 ratios mostly 50 32 3 141 9 average 74 3 30 1 n 33 and higher f o2 values fmq 0 8 2 9 average 1 8 0 8 n 6 estimated from magnetite ilmenite pairs estimates of magmatic oxidation state from amphibole compositions also show an increase from fmq 1 2 to 2 1 average 1 6 0 2 n 40 in the paleocene eocene to 2 0 to 2 8 average 2 5 0 2 n 58 in the miocene sparse whole rock fe3 fe2 ratios show the same general trend the amphibole results are systematically shifted to higher fmq compared to data from magnetite ilmenite pairs but their trend is internally consistent the higher oxidation states and water contents of miocene igneous rocks from the eastern gangdese belt may explain their unique association with large porphyry deposits in tibet because it has been shown from other studies that the potential for hydrous calc alkaline magmas to transport au is maximized near fmq 1 0 and cu at higher f o2 fmq 1 0 in comparison the somewhat less oxidized and less hydrous paleocene eocene magmas would have been less fertile for the formation of such deposits we suggest that these differences reflect the tectonomagmatic evolution of the cenozoic gangdese collisional orogen from early collision related magmatism in the paleocene eocene to late collisional magmatism in the miocene asthenospheric upwelling following slab breakoff in the miocene caused interaction between mantle derived magmas and previously subduction modified tibetan lithosphere the resultant evolved magmas had high oxidation states and water contents which are favorable properties for the subsequent formation of magmatic hydrothermal porphyry cu mo au deposits

collision related genesis of the sharang porphyry molybdenum deposit tibet evidence from zircon u pb ages re os ages and lu hf isotopes article i nfo sharang is a low fluorine calc alkaline porphyry mo deposit hosted mainly in a granite porphyry of a multi stage plutonic complex in the northern gangdese metallogenic belt largely with stockwork and ribbon textured mineralization the observed age estimates suggest that the formation of the magmatic host complex 52 9 51 6 ma and the ore deposit itself 52 3 ma occurred during the main stage of the india asia collision the host rocks are characterized by lower zircon ehf t values than those of the pre ore and post ore rocks this suggests that the lhasa terrane basement might play an important role in the formation of sharang ore forming intrusions in view of the framework of magmatic metallogenic events we suggest that slab roll back may have induced melting of juvenile crust and ancient continental complexes during the india asia collision this proposal focuses exploration for additional molybdenum deposits on the collision zone

geochronology petrogenesis and tectonic implications of granites from the fuxin area western liaoning ne china article i nfo new geochemical and sr nd isotopic data from the ping andi granitic pluton in the fuxin area which straddles the north china craton ncc and the central asian orogenic belt caob border are presented here to discuss the geochronology petrogenesis and tectonic implications petrographically the ping andi granites contain monzogranites to minor granodiorites they are high k calc alkaline series silica rich sio2 66 78 wt peraluminous a cnk 0 98 1 10 with enrichment in lree lan ybn 6 51 8 53 moderately negative eu anomalies eu eu 0 33 0 90 with enrichment in lile rb and k and with depletion in hfse nb ti and p they also have slightly negative and positive end t 1 1 0 4 low initial isr 0 70587 0 70620 and young depleted mantle model ages tdm2 911 1027 ma the emplacement of the ping andi granites took place at 150 ma as revealed by whole rock rb sr isochron age the petrography geochemistry and isotopic compositions indicate that they are i type and were the result of partial melting of mixed sources composed of a juvenile component and a pre existing crust coupled with plagioclase dominated fractionation and that there was a significant crustal growth in the phanerozoic in the northern margin of the ncc the formation of the ping andi granites was related to the tectonic transformation from the convergent tectonic regime of paleo asian ocean to that of the paleo pacific ocean which also induced

first field identification of the cuonadong dome in southern tibet implications for ew extension of the north himalayan gneiss dome the cuonadong dome exposes in east southern margin of the north himalayan gneiss domes nhgd which is reported first time in this study the cuonadong dome is located at the southern part of the zhaxikang ore concentration area which is divided into three tectono lithostratigraphic units by two curved faults around the dome geometry from upper to lower or from outer to inner the upper unit middle unit and lower unit and the outer fault is nading fault while the inner fault is jisong fault the cuonadong dome is a magmatic orthogneiss and leucogranite mantled by orthogneiss and metasedimentary rocks which in turn are overlain by jurassic metasedimentary and sedimentary rocks the grades of metamorphism and structural deformation increase towards the core which is correspondence with the ridang formation low metamorphic schist tourmaline granitic biotite gneiss garnet mica gneiss and mylonitic quartz mica gneiss the cuonadong dome preserves evidences for four major deformational events firstly top to s thrust d1 early approximately n s extensional deformation d2 main approximately e w extensional deformation d3 and late collapse structural deformation d4 around the core of the cuonadong dome which are consistent to three groups lineation approximately n s trending lineation including l1 and l2 e w trending l3 and l4 with plunging towards outside of the dome respectively the formation of the cuonadong dome was probably resulted from the main e w extensional deformation which is a result of eastward flow of middle or lower crust from beneath tibet accommodated by northward oblique underthrusting of indian crust beneath tibet the establishment of the cuonadong dome enhanced the e w extension of the nhgd which is further divided into two structural dome zones according to the different extensional directions approximately n s extensional north himalayan gneiss domes ns nhgd and e w extensional north himalayan gneiss domes ew nhgd the ns nhgd developed by a dominantly n s contraction and locally extensional regime and keep a close relationship to the south tibetan detachment system whereas the ew nhgd formed by an e w extensional deformation along the north south trending rifts

eocene neotethyan slab breakoff in southern tibet inferred from the linzizong volcanic record abstract formation of the linzizong volcanic successions in the lhasa terrane southern tibet has long been related to northward subduction of the neotethyan oceanic slab under asia here we report new 40ar 39ar age results for the volcanic rocks recovered from a large area 29 n to 32 n and 85 e to 93 e that together with literature data delineate two discrete stages of volcanism these are a widespread cretaceous stage and an intense but spatially confined paleogene stage the latter occurring only in the southern part of the lhasa terrane resulted in the linzizong volcanic successions our data furthermore suggest southward migration and intensification of the volcanism in the lhasa terrane with magmatic flare ups at ca 50 ma while the volcanic successions consist dominantly of calc alkaline rocks typical of arc lava geochemistry those formed during the flare up period show significant compositional variations from low k tholeiitic through calc alkaline to shoshonitic magma suites these observations enable us to interpret the volcanic southward migration and following flare ups as the consequences of rollback and breakoff of the subducted neotethyan slab that occurred ahead and in the early stage respectively of the india asia collision our interpretation that involves a major eocene tectonomagmatic activity and concomitant topographic uplift in southern tibet is consistent with himalayan metamorphic constraints regional sedimentary records and seismic tomography

geochemistry and nd isotopes of the francois lake plutonic suite endako batholith host and progenitor to the endako molybdenum camp central british columbia the endako low f granodiorite type porphyry mo deposit is hosted by the triassic to eocene endako batholith which comprises five temporally distinct plutonic suites only one of which is mineralized pre mineralization suites range in composition from diorite to granodiorite the synmineralization jurassic cretaceous francois lake suite includes two granodiorite to monzogranite bearing subsuites postmineralization phases include the eocene sam ross creek monzogranite the batholith spans a silica range of 44 80 wt and consists of metaluminous to slightly peraluminous low to high k i type granitoids the sam ross creek phase is an a type granite positive e nd t values 1 1 to 7 2 indicate derivation predominately from juvenile source materials but with variable input from an older crustal component evidence suggests generation of older plutonic suites in a juvenile arc type setting and younger k rich felsic suites via recycling of juvenile arc crust without significant mantle derived contrib

sulfide saturation in mafic magmas is external sulfur required for magmatic ni cu pge ore genesis the importance of externally derived sulfur in the genesis of sulfide rich magmatic ni cu platinum group element pge deposits remains a key yet unresolved issue calculations utilizing a variety of mafic magma types indicate that in general sulfide saturation by fractional crystallization occurs after ni has been depleted due to olivine crystallization cu and pge rich layers may form during relatively later stages of closed system crystallization but unless the collection of the cotectic proportion of immiscible sulfide is extremely efficient the mass of sulfide is too small to produce an economic deposit we show that there are numerous processes that may lead to early sulfide saturation in mafic ultramafic magmas contamination of mantle derived magmas by siliceous country rocks or their partial melts will lower the sulfur content needed to induce sulfide liquid saturation typically by amounts ranging from 200 to 700 ppm the mixing of magmas particularly if the result is to lower the liquidus temperature of the mixed magma may also lower the sulfur content needed to attain sulfide saturation by similar amounts an increase in magma fo2 related to the addition of volatiles such as h2o and co2 is less effective in decreasing the sulfur concentration needed to achieve sulfide liquid saturation contamination processes that lead to an increase in the activity of sio2 in the melt and hence may promote orthopyroxene rather than olivine crystallization aid in generating relative ni enrichment in remaining liquid as a result of the lower dni mineral melt value of orthopyroxene relative to olivine although contamination and magma mixing may produce early sulfide saturation without the addition of externally derived sulfur ni rich sulfide deposits can form in such cases only from large volume open systems where the efficiency of sulfide collection is high no matter what the liquidus minerals may be without the addition of country rock derived sulfur the mass of sulfide necessary to generate economic ni cu pge concentrations requires efficient sulfide collection from large but not necessarily unrealistic volumes of magma small deposits 4 30 mt of sulfide may form from the collection of cotectic proportions of sulfide from less than 50 km3 of magma larger deposits such as those at noril sk could involve more than 200 km3 of magma this volume of magma is not unreasonable particularly in rift plume related settings despite such possibilities sulfur isotope data clearly indicate that externally derived sulfur has been involved in the formation of many large deposits and that collection of mantle derived sulfide in sufficient quantities to produce orebodies is a rare process we propose that magmatic ni cu pge sulfide ore formation normally requires significant sulfide supersaturation and that the addition of sulfur derived from xenoliths is the most viable mechanism for producing sulfide well above the cotectic proportion in mafic ultramafic magmas

geochronology and petrogenesis of miocene granitic intrusions related to the zhibula cu skarn deposit in the gangdese belt southern tibet abstract the zhibula cu skarn deposit 19 5 mt ore 1 64 near the qulong porphyry cu mo deposit is located in the gangdese porphyry copper belt in southern tibet the deposit is a typical metasomatic skarn that is related to the interaction of magmatic hydrothermal fluids and calcareous host rocks stratiform skarn orebodies are mainly distributed in the contact between tuff and marble in the lower part of the jurassic yeba formation endoskarn zonations for an outward trend are observed in the granodiorite which grade from a fresh granodiorite to a weakly chlorite altered granodiorite a green diopside bearing granodiorite and a dark red brown garnet bearing granodiorite the zhibula granodiorite and monzogranite have similar secondary ion mass spectrometry sims zircon u pb ages of 16 9 0 3 ma and 17 0 0 2 ma respectively they exhibit different fractional crystallization from granodiorite sio 2 64 8 69 3 wt to monzogranite sio 2 72 3 76 8 wt both the granodiorite and monzogranite are characterized by high al 2 o 3 12 6 16 7 wt and k 2 o 1 5 5 5 wt contents high sr y 35 151 and la yb 19 48 ratios and variable mgo 0 16 3 91 and mg 31 61 values they display features of enrichment in large ion lithophile elements liles e g rb ba sr and k depletion in high field strength elements hfses e g nb ta ti and p and moderate negative eu anomalies eu 0 58 0 98 they show restricted in situ zircon hf isotopic compositions 6 7 to 8 8 only one sample is 4 5 and consistent 18 o values 6 0 to 6 6 the geochemical data indicated that the miocene zhibula granitic intrusions formed by the magma that were characterized by high sr y ratios and were derived from the partial melting of the thickened juvenile lower crust which may have been metasomatized by the slab melts during subduction of the neo tethyan oceanic crust and were induced by the convective removal of the thickened lithosphere in addition the zhibula cu skarn deposit and the qulong cu mo deposit form a significant porphyry skarn ore system

new 40ar 39ar and u th he dating for the zhunuo porphyry cu deposit gangdese belt southern tibet implications for pulsed magmatic hydrothermal processes and ore exhumation and preservation understanding the magmatic hydrothermal cooling and exhumation history is fundamental for investigating porphyry deposit formation and preservation in the zhunuo porphyry copper deposit of southern tibet hydrothermal biotite related to early potassic alteration likely formed from 14 7 0 3 ma zircon u pb age to 14 23 0 13 ma molybdenite re os age and cooled below the closure temperature for 40ar 39ar system at 13 91 0 05 ma hydrothermal biotite 40ar 39ar plateau age the 40ar 39ar spectra of another hydrothermal biotite sample that was selectively replaced by chlorite record the timing of late phyllic alteration at 13 53 0 08 ma zhunuo hydrothermal alteration and mineralization likely ceased at 13 09 0 07 ma based on the 40ar 39ar plateau age of the fresh magmatic biotite crystals the biotite 40ar 39ar systematics have not been reset by 12 0 ma post mineralization granite porphyry within ore district which is likely due to rapid cooling and or absence of fluid exsolution for the granite porphyry in combination with previous zircon u pb and molybdenite re os data two pulses of magmatic hydrothermal activity from 14 78 0 11 to 14 44 0 05 ma and from 14 23 0 13 to 13 53 0 08 ma can be recognized at zhunuo u th he thermochronological data on zircon and apatite from the inter mineralization monzogranite porphyry suggest three cooling events characterized by first stage magmatic cooling at a rate of 1850 c m y and two later phases of uplift and exhumation at 70 c m y and 10 c m y approximately 1 4 km thickness of materials have been removed from the zhunuo miocene monzogranite porphyry during uplift and erosion including a large volume of ore

genesis of luobuzhen pb zn veins implications for porphyry cu systems and exploration targeting at luobuzhen dongshibu in western gangdese belt southern tibet abstract porphyry systems are known to form in magmatic arc environment and commonly include porphyry cu epithermal pb zn au ag skarn polymetallic mineralization etc the systems are rarely reported in collisional zones such as the gangdese belt in southern tibet where many postcollisional porphyry copper deposits occurred in addition other types of mineral systems are rarely present except porphyry copper mineralization in the gangdese belt in this study we present pb zn bearing quartz veins at luobuzhen in the western gangdese belt the luobuzhen pb zn veins cross cut dacite of the linzizong group with zircon u pb age of 50 1 0 2 ma and monzogranite with zircon u pb age of 17 1 0 1 ma ore minerals include sphalerite galena chalcopyrite and pyrite gangue minerals are quartz with minor chlorite and sericite primary fluid inclusions of quartz are liquid rich aqueous and two phase inclusions the homogenization temperatures of these primary inclusions are moderate to high 267 400 c and salinities range from 8 9 to 18 4 wt nacl equiv quartz has 18 o smow values of 6 2 9 3 while sulfides have 34 s v cdt values of 5 1 to 0 1 206 pb 204 pb of 18 722 18 849 207 pb 204 pb of 15 640 15 785 and 208 pb 204 pb of 39 068 39 560 these data suggest that magmatic fluids with contribution from meteoric water magmatic sulfur and lead derived from upper crust and metasomatized mantle by indian continental materials would be critical for the luobuzhen base metal mineralization the dongshibu area located at 2 km east of the luobuzhen is characterized by high concentrations of cu up to 1450 ppm and mo up to 130 ppm of stream sediments which is quite different from high concentrations in pb zn ag and au shown in the luobuzhen area in addition porphyry copper mineralization related alteration and veins veinlets occur in the miocene monzogranite at dongshibu the monzogranite is characterized by high sr y ratios which are also shown on ore forming intrusions in the gangdese postcollisional porphyry copper deposits and shows similar zircon hf isotopes to the ore related high sr y intrusions from the zhunuo porphyry copper deposit which is located 20 km northeast of the luobuzhen dongshibu a comprehensive analysis allows us to infer that the base metal veins at luobuzhen are components of a porphyry cu system with porphyry cu mineralization likely present at dongshibu and epithermal au ag veins possibly occurring at luobuzhen which are indicative of the existence of porphyry copper systems in collisional zones the potential porphyry cu mineralization and epithermal au ag veins should be targeted in future exploration at luobuzhen dongshibu

immiscibility of magmatic fluids and their relation to mo and cu mineralization at the bangpu porphyry deposit tibet china abstract the coexistence of aqueous fluid inclusions and silicate melt inclusions in quartz phenocrysts from porphyrites at the bangpu porphyry mo cu deposit tibet china were examined to characterize the immiscibility processes during the magmatic to hydrothermal transition the physical and chemical environment during crystallization of the magmas has been reconstructed on the basis of microthermometric experiments and trace element microanalysis compositions of melt and brine fluid phases are determined using synchrotron radiation x ray fluorescence analysis sem eds and laser raman spectroscopy analyses brine fluids were directly exsolved by a crystallizing melt and the simultaneous entrapment of volatile rich brine fluid and volatile poor immiscible phases silicate melt occurred at 670 700 c and 1 6 1 95 kbar when the magma had h2o contents between 5 and 6 wt and crystal contents of 60 80 a later low density fluid with a higher mo concentration exsolved after about 80 90 crystallization had occurred this fluid contained significant concentrations of cl na k ca fe cu zn rb and small amounts of mn br and pb immiscibility of magmatic fluids can lead to different metal partitioning behaviors between residual melt and volatile phases which generate variable metal ratios copper was partitioned preferentially into the brine phase in contrast to the behavior observed in other porphyry cu deposits ore deposition by a dense brine could explain the partially deep cu mineralization condensation of brine from a later low density parental fluid could be an efficient mechanism to concentrate shallow cu mineralization and broadly distributed mo mineralization the source of the mo mineralizing fluids probably was a particularly large magma chamber that crystallized and fractionated at depth greater than upper continental crust level

fluid inclusion study of the nannihu giant porphyry mo w deposit henan province china implications for the nature of porphyry ore fluid systems formed in a continental collision setting abstract the nannihu mo w deposit located in the henan province of china is a giant porphyry deposit formed in the qinling orogen during the jurassic continental collision between the north china and yangtze cratons mo w mineralization is associated with the nannihu porphyritic monzogranite occurring as numerous stockwork veinlets in the altered wallrocks and the causative porphyry both the porphyry stock and wallrocks underwent intense hydrothermal alteration ranging outwardly from potassic to phyllic alteration and to carbonation zones with increasing distance from the intrusion the hydrothermal ore forming process can be divided into four stages characterized by veinlets from early to late 1 quartz potassic feldspar molybdenite pyrite 2 quartz molybdenite veins containing minor pyrite and chalcopyrite 3 quartz polymetal sulfide and 4 quartz carbonate fluorite most of the ores are formed during stages 2 and 3 four types of fluid inclusions fis are distinguished in this study based on petrographic and microthermometric criteria i e pure co 2 nacl h 2 o co 2 h 2 o and daughter mineral bearing fluid inclusions all of the four types of fis can be observed in the hydrothermal quartz formed in stages 1 2 and 3 while the stage 4 minerals contain only nacl h 2 o fluid inclusions fluid inclusions of stage 1 are mainly homogenized between 350 and 460 c with salinities ranging from 5 7 to 17 9 wt nacl equiv the stage 2 fis yield homogeneous temperatures of 300 380 c and salinities of 3 5 16 9 wt nacl equiv fis of stage 3 are homogenized between 250 and 370 c with salinities of 1 8 14 3 and 28 6 39 1 wt nacl equiv fis of stage 4 are homogenized at temperatures of 115 to 265 c yielding salinities of 0 5 to 1 2 wt nacl equiv daughter minerals such as halite chalcopyrite and some unknown minerals are frequently present in stage 3 fis which probably represent a reducing and oversaturated fluid system resulting from fluid boiling the daughter mineral bearing fis coexist with vapor and liquid rich nacl h 2 o fis that have contrasting salinities these fis are homogenized in divergent ways at similar temperatures suggesting that fluid boiling took place in stages 2 and 3 the estimated pressures range from 70 to 270 mpa in stage 1 through 30 150 mpa in stage 2 to 30 85 mpa in stage 3 corresponding to a depth of no less than 3 km in other words the ore forming fluids are characterized by high temperature high salinity high f o 2 and high co 2 content and fluid boiling resulted in co 2 release f o 2 decrease and ore mineral precipitation we suggest that the co 2 rich fluid is a distinctive feature of porphyry systems developed in continental collision setting in transitional compressional to extensional regime contrasting to the co 2 poor nacl h 2 o fluids observed in volcanic arcs

zircon ce4 ce3 ratios and ages for yulong ore bearing porphyries in eastern tibet yulong ore bearing porphyries along the northwestern extension of the red river ailao shan fault system in eastern tibet consist of five porphyry deposits containing a total of more than 8 million tons of copper resources u th pb laser inductively coupled plasma mass spectrometry dating of zircon shows that the porphyries were emplaced in early tertiary 41 2 36 9 ma covering a period of 4 3 ma with formation ages decreasing systematically from northwest to southeast the start of porphyry magmatism coincided with the onset of transpressional movement along the red river ailao shan fault system implying a close link between these two events age sequence in intrusions can be plausibly explained by assuming that a region of melting in the lower northwestern plate moved southeasternward along the tuoba mangkang fault relative to the upper plate zircon grains from the yulong ore bearing porphyries have higher ce4 ce3 than those from barren porphyries in the region this suggests that the ore bearing porphyries crystallized from a relatively oxidized magma which has important implications for future ore exploration in the region and other cu deposits in convergent margin environments in general

genesis of the yaguila pb zn ag mo skarn deposit in tibet insights from geochronology geochemistry and fluid inclusions abstract the yaguila skarn deposit with reserves of 52 mt at 4 pb 2 zn and 64 3 g t ag is located in the eastern segment of the central lhasa subterrane tibet the stratabound skarn pb zn ag orebodies are hosted in the upper carboniferous lower permian laigu formation which consists of meta quartz sandstone slate and marble molybdenum occurs as quartz molybdenite pyrite veinlets veins and partial disseminations in the paleocene quartz porphyry slate and garnet skarn zircon u pb dating suggests that three major magmatic events occurred in the yaguila area producing cretaceous rhyolitic rock ca 128 ma paleocene quartz porphyry 65 6 1 2 ma and miocene granite porphyry 17 8 0 4 ma combined with the published data the quartz porphyry has variable ehf t values of 13 9 to 12 1 87sr 86sr i values of 0 71718 0 72805 and end t values of 5 2 to 13 5 whereas the granite porphyry displays relatively restricted ehf t values of 2 3 to 6 5 87sr 86sr i values of 0 70798 0 71678 and end t values of 2 8 to 5 5 geochemical and isotopic sr nd pb hf signatures indicate that the cretaceous rhyolitic magma was derived from the melting of continental lower crust of the ancient lhasa subterrane with a strong fractional crystallization the emplacement of the paleocene quartz porphyry probably resulted from the magma mixing process between the dominant lhasa middle upper crust derived magma and varying contributions of mantle derived materials during the collision and neo tethyan subduction slab rollback the miocene granite porphyry was likely formed by the melting of thickened lhasa lower crust which was triggered by upwelling of hot asthenosphere our molybdenite re os data from garnet skarn together with published data from quartz porphyry and slate display an excellent isochron age of 64 3 1 6 ma fluid inclusion data from this study reveal that the ore forming fluids associated with diverse types of molybdenum mineralization were a common magmatic hydrothermal fluid with moderate to high temperatures 290 400 c and moderate salinities 9 22 wt nacl equiv our study suggests that the yaguila pb zn ag and mo mineralization occurred under the same ore system associated with the paleocene quartz porphyry

the nature and timing of crustal thickening in southern tibet geochemical and zircon hf isotopic constraints from postcollisional adakites abstract rising as the roof of the world the tibetan plateau is now underlain with the thickest continental crust on earth how and when was this crust formed which would have exerted pivotal controls to the formation of the plateau has long been an issue of hot debates this paper reports zircon u pb ages and hf isotope data for postcollisional 30 9 ma adakites in the southern lhasa terrane southern tibet a comparative analysis of whole rock rare earth element geochemistry and zircon hf isotopes between the adakites and associated gangdese igneous rocks suggests that the tibetan crust underwent a major phase of tectonic thickening between ca 45 and 30 ma in the region the lower part of the thickened crust consisted prevailingly of mafic lithologies which we argue to have resulted from intense basaltic underplating and subsequent remelting that took place during the late cretaceous and eocene time related to the neotethyan subduction processes including breakoff of the subducted slab at ca 50 ma in the early stage of the india asia collision these processes were responsible for not only the juvenile crust formation but also for the creation of a thermally softened lithosphere in the southern lhasa terrane the indentation of india consequently caused distributed lithospheric thickening with formation of an orogenic root beneath southern tibet root foundering during the oligocene gave rise to the adakitic magmatism regional topographic uplift and onset of northward underthrusting of the indian plate that has since played a key role in forming the entire tibetan plateau

tethys tectonic evolution and its bearing on the distribution of important mineral deposits in the sanjiang region sw china abstract the sanjiang region in se tibet plateau and nw yunnan is known to have formed by amalgamation of gondwana derived continental blocks and arc terranes as a result of oceanic subduction followed by continental collision from paleozoic to mesozoic in this paper we provide a synthesis of tectonic evolution magmatism and metallogeny in the region based on data from literatures early paleozoic ophiolites 473 439 ma in the changning menglian belt indicate the existence of a proto tethys ocean in this region two episodes of subduction related magmatism in the early paleozoic one occurred in the baoshan and tengchong blocks at 502 455 ma and the other occurred in the simao block at 421 401 ma are regarded as evidence for two different events of subduction of the proto tethys ocean at different locations the proto tethys was succeeded in early devonian by the paleo tethys which comprised the main ocean and three branches ailaoshan jinshajiang and garze litang the changning menglian main ocean existed from middle devonian to middle triassic the remnants of the oceanic crust are preserved in a few places in the longmu tso shuanghu suture as well as in the changning menglian ophiolite belt the eastward subduction of the main oceanic plate from early permian to early triassic formed a prominent arc terrane stretching 1500 km from yunnan to eastern tibet from the waning stage of subduction to post subduction numerous s type granite plutons with ages varying between 230 and 219 ma such as the lincang batholith in yunnan were emplaced at or close to the suture this event produced several hydrothermal w sn deposits in the region the tectonic evolution and associated magmatism of the jinshajiang and ailaoshan branch oceans are generally comparable to those of the main ocean however the branch oceans were subducted westward instead the garze litang branch ocean also underwent westward subduction from middle devonian to late triassic arc related high sr y porphyry intrusions and associated porphyry skarn cu mo au deposits are common in the jinshajiang ailaoshan region especially in the yidun arc which formed prior to jurassic the vms deposits in the sanjiang region formed in diverse tectonic settings including middle silurian back arc basins carboniferous oceanic islands paleozoic subduction zones and triassic post subduction rifting environments the mesozoic and early cenozoic evolution of the baoshan and tengchong blocks was largely influenced by eastward oceanic subduction of the meso and neo tethys from late permian to middle cretaceous and from late cretaceous to 50 ma respectively abundant early cretaceous granitoids and associated skarn type pb zn and sn fe deposits in the baoshan and tengchong blocks were produced in the background of the shan boundary oceanic slab subduction to the west and the break off of the nujiang bitu oceanic slab to the north the subduction of the neo tethys oceanic plate beneath the tengchong block from late cretaceous to paleogene formed abundant s type granitoids and many skarn type and greisen type sn w deposits granitoids formed at 105 to 81 ma and contemporaneous hydrothermal w mo ag and au deposits which temporally coincided with the subduction of the neo tethys are common in the yidun arc terrane

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

genesis of the 1 76 ga zhaiwa mo cu and its link with the xiong er volcanics in the north china craton implications for accretionary growth along the margin of the columbia supercontinent abstract the east qinling molybdenum belt hosting numerous mesozoic magmatic hydrothermal mo deposits is one of the largest molybdenum provinces in the world the recently discovered zhaiwa mo cu deposit luoning county henan province occurs within the xiong er terrane of the east qinling orogenic belt the mo cu mineralization is associated with widespread stockworks or veinlets occurring within altered amphibolite here we investigate the characteristics of the ore mineralization through systematic fluid inclusion petrography microthermometry and laser raman spectroscopy the typical inclusions in the veins and stockworks are aqueous daughter mineral bearing and a subordinate co2 rich type the homogenization temperatures of the aqueous inclusions in quartz molybdenite veins are up to 370 c which together with some daughter mineral bearing inclusions homogenized by dissolution of halite at 500 c indicates that the ore forming fluids were derived from a hypothermal fluid system the daughter mineral bearing inclusions assign high salinities for the ore forming fluids correlating the ore deposit to a magmatic hydrothermal system we also present h o isotope systematics which support this interpretation the recently reported re os molybdenite age of 1 76 0 03 ga from this deposit is coeval to the xiong er group andesite dominated volcanic sequence 1 8 1 45 ga based on which we propose that the zhaiwa deposit represents the upper domain of a porphyry system developed within a subduction related setting with accretion to the southern margin of the north china craton our study provides new constraints on the outgrowth of the columbia supercontinent during paleoproterozoic

zircon u pb geochronology and hf isotopic constraints on petrogenesis of the gangdese batholith southern tibet abstract during the mesozoic cenozoic northward neotethyan subduction and subsequent india asia collision gave rise to the extensive transhimalayan magmatism that stretches from burma and western yunnan through southern tibet to the ladakh and kohistan complexes to understand the age distribution and petrogenesis of the gangdese batholith the largest intrusive exposure along the transhimalayan magmatic belt fifty granitic samples were selected for in situ zircon u pb and hf isotopic analyses the u pb data suggest four discrete stages of magmatic activity i e 205 152 109 80 65 41 and 33 13 ma respectively with the 65 41 ma stage being the most prominent the hf isotopic data indicate that the gangdese batholith is overwhelmed by positive e hf t values which are comparable to those of the kohistan ladakh batholiths in the west but differ markedly from those of the chayu burma batholiths in the east most of the gangdese granites show similar and young hf model ages 1000 300 ma indicating their derivation from juvenile crust however those formed in the 65 41 ma stage exhibit more heterogeneous hf isotopic ratios with negative e hf t values being observed in some granites younger than 50 ma suggesting the involvement of old indian continental crust in their petrogenesis this age may thus mark the onset of the india asia collision the newly established zircon u pb age and hf isotope database of the gangdese batholith can be used as a powerful tracer or fingerprint when studying the source to sink relation of the sediments eroded from the southern tibetan plateau

origin of the ore forming fluids and metals of the bangpu porphyry mo cu deposit of tibet china constraints from he ar h o s and pb isotopes abstract the bangpu porphyry mo cu deposit is a representative mo dominated deposit besides the sharang porphyry mo deposit in the gangdese metallogenic belt the mo cu mineralization has a close relationship with the monzogranite porphyry and diorite porphyrite we identify three stages during the ore formation a pre ore stage a main ore stage with mo cu deposited dominantly and a post ore stage in this study he ar h o s and pb isotopic compositions of the bangpu deposit were determined based on these determinations integrated isotope geochemistry studies were performed to constrain the possible sources of the ore forming fluids and metals the 3 he 4 he and 40 ar 36 ar ratios of fluid inclusions exhibit a range of 0 12209 0 36370 ra and 275 6 346 1 respectively the 4 he and 40 ar concentrations vary from 1 51 to 3 57 10 7 cm 3 stp g 1 and 0 49 to 9 31 10 7 cm 3 stp g 1 respectively he ar isotopic compositions suggest dominantly crustal derived fluid with minor amount of meteoric water in the main ore stage the 18 o fluid and d fluid values vary from 1 3 to 3 9 and 140 5 to 73 7 respectively indicating that magma fluids mixed with meteoric water the average 34 s value of the sulfides 0 3 in the main ore stage is close to the ore forming porphyries indicating a magmatic source the lead isotopic components of ore sulfides exhibit restricted ranges with 206 pb 204 pb 207 pb 204 pb and 208 pb 204 pb ratios of 18 450 18 728 15 602 5 672 and 38 715 39 211 respectively and values in the range of and 9 46 9 58 indicating ore forming metals of primarily an upper crust source with a small amount of mantle materials compared to the bangpu deposit the ore metals derived from mantle are even greater in the jiama and qulong deposits which leads to cu being the dominant mineralization in the jiama and qulong deposit

metallogenesis and ore controls of cenozoic porphyry mo deposits in the gangdese belt of southern tibet abstract the gangdese is a newly explored porphyry copper ore belt in china except for the cu mo au porphyry deposits there are some mo cu w porphyry and skarn deposits in this belt two pulses of molybdenite mineralization are recognized in the central lhasa subterrane with ancient continent crust including the paleocene eocene 65 52 ma porphyry mo and skarn mo w deposits formed during the rollback of neo tethyan oceanic slab in collisional setting and miocene 21 15 ma porphyry mo cu deposits generated in the postcollisional setting the gangdese copper deposits also occur during these two periods but are distributed in the southern lhasa subterrane dominated by juvenile crust through mantle derived magmatism resulting from neo tethyan ocean lithosphere subduction the intrusions related to molybdenite mineralization have relatively lower bulk rock e nd t and higher 87 sr 86 sr i values lower zircon e hf t values and older hf model ages lower molybdenite re contents and more radiogenic pb isotopes than the coeval copper related porphyries in the gangdese belt in addition the miocene mo cu related intrusions generally have lower zircon ce 4 ce 3 ratios than the miocene cu mo related intrusions these data indicate that more contributions from mature continental crustal materials play crucial role in the generation of mo than cu porphyry mineralization in the gangdese belt the eocene mo related intrusions are characterized by high sio 2 68 76 and k 2 o 5 1 5 9 concentrations enrichment of large ion lithophile elements lile depletion of high field strength elements hfse and low sr y 7 5 23 8 ratios their sr nd isotope compositions e nd t 3 4 to 4 6 87 sr 86 sr i 0 70622 0 70679 indicate that they are associated with partial melting of mantle wedge mixing with significant amounts 55 65 of middle upper crustal materials the miocene mo cu related intrusions have relatively high sio 2 64 73 and k 2 o 1 9 4 8 contents and are characterized by enrichment of lile depletion of hfse and high sr y ratios 55 189 their sr nd isotope compositions e nd t 4 6 to 3 4 87 sr 86 sr i 0 70622 0 70679 are indicative of derivation from remelting of previously subduction modified tibetan lithosphere with significant amounts 50 70 of middle upper crustal materials for the gangdese mo cu porphyry mineralization mo metal was suggested to be derived from the middle upper crustal materials particularly the carbonaceous permian marine sedimentary whereas cu metal to be sourced from the gangdese miocene cu fertile magmas the exploration targeting of the gangdese molybdenite deposits should be focused on southern part of the central lhasa subterrane where the carbonaceous permian strata occur the occurrence of mo cu porphyry deposits could provide clue for targeting cu mo porphyry deposits in the gangdese belt the gangdese molybdenite deposits share many similarities with the east qinling molybdenite deposits such as type of ore deposits geodynamic setting of their formation variable mo grades and high f contents

extent of underthrusting of the indian plate beneath tibet controlled the distribution of miocene porphyry cu mo au deposits miocene igneous rocks in the 1 600 km long e w gangdese belt of southern tibet form two groups separated at longitude 89 e the eastern group is characterized by mainly intermediate felsic calc alkaline plutons with relatively high sr y ratios 23 to 342 low 87sr 86sr i ratios 0 705 to 0 708 and high endi values 5 5 to 6 1 in contrast the western group is characterized by mainly potassic to ultrapotassic volcanic rocks with relatively high th and k2o contents low sr y ratios 11 to 163 high 87sr 86sr i ratios 0 707 to 0 740 and low endi values 4 1 to 17 5 the eastern plutonic group is associated with several large porphyry cu mo au deposits whereas the western group is largely barren we propose that the sharp longitudinal distinction between magmatism and metallogenic potential in the miocene gangdese belt reflects the breakoff of the greater india slab and the extent of underthrusting by the indian continental lithosphere at that time magmas to the east of 89 e were derived by partial melting of subduction modified tibetan lithosphere mostly lower crust triggered by heating of hot asthenospheric melt following slab breakoff these magmas remobilized metals and volatile residual in the crustal roots from prior arc magmatism and generated porphyry cu mo au deposits upon emplacement in the upper crust in contrast magmas to the west of 89 e were formed by smaller volume partial melting of tibetan lithospheric mantle metasomatized by fluids and melts released from the underthrust indian plate they are less hydrous and oxidized and did not have the capacity to transport significant amounts of metals into the upper crust

fluid flux melting generated postcollisional high sr y copper ore forming water rich magmas in tibet miocene postcollisional porphyry cu deposits in southern tibet are genetically associated with dacitic rhyolitic intrusions with unusually high sr y ratios 40 which have been attributed to dehydration melting of garnet amphibolite in a thickened lower crust to test this hypothesis and examine the hydration state of copper ore forming high sr y magmas we utilize a geohygrometer for granitoid rocks entailing zircon saturation thermometry and h 2 o dependent phase equilibria the results show that these tibetan high sr y magmas had dissolved h 2 o contents 10 wt which considerably exceeds the water supply by dehydration melting of basaltic amphibolites maximum of 6 7 1 4 wt our results indicate that high sr y dacitic rhyolitic magmas cannot be produced by dehydration melting of basaltic amphibolites while h 2 o added melting of basaltic amphibolites can produce high sr y dacitic rhyolitic melts it does not yield high enough mg 50 to match the tibetan ore forming porphyries we propose an alternative model for the genesis of copper ore forming high sr y magmas in tibet and suggest that the high sr y dacitic rhyolitic porphyries in southern tibet are residually h 2 o enriched high pressure differentiation products of hydrous mafic partial melts of tibetan mantle this hypothesis is based on the previous investigation of miocene mafic microgranular enclaves mantle derived melts which define a fractionation trend with and have sr nd hf isotopic compositions similar to the host tibetan ore forming porphyries

ore geology fluid inclusions and four stage hydrothermal mineralization of the shangfanggou giant mo fe deposit in eastern qinling central china article i nfo the eastern qinling central china containing more than 20 mesozoic porphyry skarn systems is the most important mo province in the world the shangfanggou giant mo deposit luanchuan county henan province is a porphyry skarn system hosted in a lithologic association comprising carbonaceous sandstone shale carbon ate and chert within the neoproterozoic luanchuan group mo ores are mainly altered porphyry skarn and hornfels with minor altered gabbro the mineralization process includes four stages potassic alteration of the porphyry and skarnization of dolomite marble in stage 1 stockworks of quartz molybdenite sulfide stage 2 pyrite quartz sulfides stage 3 and carbonate quartz fluorite stage 4 respectively mo mineralization was generally associated with strong silicification and or phyllic alteration the fluid inclusions in minerals include three compositional types i e co2 bearing c type aqueous w type and daughter mineral bearing s type minerals formed in stages 1 to 3 contain all the three types of fis but the stage 4 minerals only contain the w type fis oxides and cu phosphate are recognized as daughter minerals in s type inclusions in minerals of stage 1 whereas the daughter sulfide and reducing gases such as co ch4 h 2 sa nd c2h6 can be observed in quartz of stages 2 and 3 suggesting that the ore forming fluids were initially oxidizing and then evolved to reducing boiling fluid inclusion assemblages can be observed in minerals formed in stage 2 or earlier but not in stage 3 or later fluid boiling caused co2 escape oxygen fugacity decrease and rapid precip itation of ore minerals and was a key factor causing mo mineralization at shangfanggou data and interpreta tions presented in this contribution show that the fluids forming the shangfanggou mo deposit evolved from co2 rich high salinity hypothermal to co2 poor low salinity epithermal low t the mo mineralization at theshangfanggoudepositmainlyoccurredatdepthof6 6 7 0 km deeperthanthemajorityofporphyrysystems in volcanic arcs which resulted from a co2 rich magma fluid system originating from partial melting of thick ened lower crust the shangfanggou mineral system developed during 158 134 ma when the yangtze north china continental collision began to evolve from compression to extension magmatic hydrothermal deposits developed in a continental collision regime are generally formed by co2 rich high salinity fluids

the lhasa terrane record of a microcontinent and its histories of drift and growth article i nfo the lhasa terrane in southern tibet has long been accepted as the last geological block accreted to eurasia before its collision with the northward drifting indian continent in the cenozoic but its lithospheric architecture drift and growth histories and the nature of its northern suture with eurasia via the qiangtang terrane remain enigmatic using zircon in situ u pb and lu hf isotopic and bulk rock geochemical data of mesozoic early tertiary magmatic rocks sampled along four north south traverses across the lhasa terrane we show that the lhasa terrane has ancient basement rocks of proterozoic and archean ages up to 2870 ma in its centre with younger and juvenile crust phanerozoic accreted towards its both northern and southern edges this finding proves that the central lhasa subterrane was once a microcontinent this continent has survived from its long journey across the paleo tethyan ocean basins and has grown at the edges through magmatism resulting from oceanic lithosphere subduction towards beneath it during its journey and subsequent collisions with the qiangtang terrane to the north and with the indian continent to the south zircon hf isotope data indicate significant mantle source contributions to the generation of these granitoid rocks e g 50 90 0 70 and 30 100 to the mesozoic magmatism in the southern central and northern lhasa subterranes respectively we suggest that much of the mesozoic magmatism in the lhasa terrane may be associated with the southward bangong nujiang tethyan seafloor subduction beneath the lhasa terrane which likely began in the middle permian or earlier and ceased in the late early cretaceous and that the significant changes of zircon ehf t at 113 and 52 ma record tectonomagmatic activities as a result of slab break off and related mantle melting events following the qiangtang lhasa amalgamation and india lhasa amalgamation respectively these results manifest the efficacy of zircons as a chronometer u pb dating and a geochemical tracer hf isotopes in understanding the origin and histories of lithospheric plates and in revealing the tectonic evolution of old orogenies in the context of plate tectonics

paleocene eocene record of ophiolite obduction and initial india asia collision south central tibet 1 uppermost cretaceous to eocene marine sedimentary sequences occur both to the south and north of the yarlung zangbo suture in south central tibet they consist of indian margin strata of the northern tethyan himalaya and asian margin strata of the gangdese forearc both assemblages are characterized by major changes in depositional environment and sedimentary provenance at 65 ma and an appearance of detrital chromium rich spinel of ophiolite affinity tio2 generally 0 1 wt during the paleocene ophiolitic melange exposed along the suture could have provided a source for detrital spinel the melange occurs in the hanging wall of a north dipping south directed mylonitic shear zone which includes a tectonic sliver of mafic schist amphibole from the schist yields 40ar 39ar ages of 63 ma which we attribute to cooling during slip along the shear zone and southward obduction of the melange melange obduction was coeval with the development of an angular unconformity within the gangdese forearc basin to the north between late maastrichtian time and 62 ma upper paleocene to middle eocene sandstones in the northern tethyan himalaya yield 200 120 ma u pb detrital zircon ages and 190 170 ma 40ar 39ar detrital mica ages these detrital grains were most likely sourced from regions north of the yarlung zangbo suture suggesting that onset of india asia collision in south central tibet is middle eocene or older in age collectively our results support previous suggestions that oceanic rocks were obducted onto the northern margin of india during latest cretaceous earliest tertiary time coeval changes in gangdese forearc sedimentation raise the possibility that this obduction event marks onset of tectonic interaction between india and asia at 65 ma alternatively in concert with the conventional view of eocene collision initiation the obducted oceanic rocks may be of intraoceanic origin while coeval changes in gangdese forearc sedimentation may be a consequence of an increase in the rate of ocean continent convergence following the demise of the intraoceanic subduction zone

episodic growth of the gondwana supercontinent from hafnium and oxygen isotopes in zircon it is thought that continental crust existed as early as 150 million years after planetary accretion but assessing the rates and processes of subsequent crustal growth requires linking the apparently contradictory information from the igneous and sedimentary rock records for example the striking global peaks in juvenile igneous activity 2 7 1 9 and 1 2 gyr ago imply rapid crustal generation in response to the emplacement of mantle super plumes rather than by the continuous process of subduction yet uncertainties persist over whether these age peaks are artefacts of selective preservation and over how to reconcile episodic crust formation with the smooth crustal evolution curves inferred from neodymium isotope variations of sedimentary rocks detrital zircons encapsulate a more representative record of igneous events than the exposed geology and their hafnium isotope ratios reflect the time since the source of the parental magmas separated from the mantle these model ages are only meaningful if the host magma lacked a mixed or sedimentary source component but the latter can be diagnosed by oxygen isotopes which are strongly fractionated by rock hydrosphere interactions here we report the first study that integrates hafnium and oxygen isotopes all measured in situ on the same precisely dated detrital zircon grains the data reveal that crust generation in part of gondwana was limited to major pulses at 1 9 and 3 3 gyr ago and that the zircons crystallized during repeated reworking of crust formed at these times the implication is that the mechanisms of crust formation differed from those of crustal differentiation in ancient orogenic belts

the miocene gangdese porphyry copper belt generated during post collisional extension in the tibetan orogen abstract the mid miocene gangdese orogenic belt in southern tibet contains porphyry cu deposits that developed after the indian asian continental collision in the early cenozoic field work confirms that these porphyry cu deposits are temporally and spatially associated with mid miocene monzogranitic and quartz monzonitic stocks which intruded mesozoic cenozoic gangdese granitoid batholiths and surrounding triassic tertiary volcano sedimentary sequences in the lhasa terrane and formed a 50 km wide 400 km long e w belt magmatism occurred during the interval 11 2 to 19 7 ma peaking at 16 ma for the porphyry stocks this is consistent with the age 10 to 18 ma of the east west extension and subsequent ns striking normal fault systems 13 5 ma in the tibetan orogen the stocks typically occur as multiple small diameter intrusions 50 km breakdown of hornblende in the juvenile lower crust source during melting is regarded as fundamental for the formation of the fertile adakite and porphyry cu systems in south tibet the gangdese belt contains four large and three intermediate and small sized porphyry cu mo deposits and shows a continuous spectrum from typical porphyry type cu mo to skarn type zn pb mineralization twenty three samples collected from four deposits yielded a limited range of molybdenite re os isochron ages from 15 2 to 16 0 ma similar to previously reported re os ages 13 8 to 14 9 ma for other porphyry cu mo deposits in the belt suggesting that cu mo mineralization in the belt occurred in a post collisional extension environment the characteristics of porphyry cu mo deposits in the collisional zone are similar in many aspects to those in arc settings i e mineralization style alteration zoning and metal association preliminary fluid inclusion studies indicate that the early hydrothermal fluids are preserved as high temperature 450 c high salinity 40 to 47 wt nacl equiv and high pressure 1100 to 1500 bar fluid inclusions these fluids are interpreted to represent an orthomagmatic fluid that boiled episodically due to fluid overpressuring and hydrofracturing resulting in potassic alteration and precipitation of chalcopyrite molybdenite assemblages on the basis of comparison with porphyry cu deposits in arc settings we proposed that melting of thickened newly formed basaltic crust resulted in generation of cu bearing magmatic systems in the tibetan collision zone and both orogen transverse normal faults and orogen parallel thrust zones during the miocene post collisional extension constrain the temporal and spatial localization of the porphyry cu systems in the collision zone

hot paleocene eocene gangdese arc growth of continental crust in southern tibet abstract the 1600 km long gangdese magmatic belt features extensive paleocene eocene i type intrusive rocks and coeval volcanic successions which can be divided into group i 69 53 ma group ii 53 49 ma and group iii 49 43 ma corresponding to neo tethyan slab rollback neo tethyan slab breakoff and ongoing indian asian collision respectively the magmas from these three groups show significant variations in geochemical and isotopic compositions which provide the information of the growth of continental crust in southern tibet the most voluminous magmatism in the gangdese belt occurred during 53 49 ma high zircon saturation temperature up to 800 c and ti in zircon temperature up to 980 c estimations suggest there is a period of thermal anomaly during 53 49 ma starting from 53 ma magmas have increased k2o contents and their zircons have decreased th u ratios and y and yb contents zircons from group ii have the most heterogeneous hf isotopic compositions ehf t 5 3 to 15 1 these are evident of ingress of asthenosphere mantle in the arc extensive crustal melting and magma mixing magma underplating during this time is the main mechanism for the growth of continental crust with the indian asian collision going on the magmas in group iii show high th y and la yb ratios and k2o contents but significantly low tzr and t ti zr values mostly below 750 c these features suggest the water fluxed melting of early arc residues occurred in the late stage of growth of continental crust the crust has been thickened and nearly mature at this stage this study has great implication on understanding of growth of continental crust in orogenic belts

re os isotopic dating of molybdenites in the xiaoliugou w mo deposit in the northern qilian mountains and its geological significance abstract the xiaoliugou is a large scale w mo deposit newly explored in the northern qilian mountains caledonian fold belt northwestern china it is a vein and skarn type deposit genetically associated with the xiaoliugou caledonian granodiorite stock re os isotopic dating for the molybdenite in the deposit yields an isochron age of 462 13 ma 2 and model ages of 436 to 496 ma these results suggest that w mo mineralization occurred before the collision of plates and mineralized substances mainly originated from the crust

the gulf stream influence on wintertime north atlantic jet variability in this paper we investigate the influence of the gulf stream sst front on the north atlantic eddy driven jet and its variability by analysing the ncep cfsr dataset and a pair of agcm simulations forced with realistic and smoothed gulf stream sst boundary conditions the gulf stream sst front acts to generate stronger meridional eddy heat flux in the lower troposphere and an eddy driven jet over the eastern north atlantic that is located further polewards compared to the simulation with smoothed sst the strong gulf stream sst gradient is found to be crucial in more accurately capturing the trimodal distribution of the eddy driven jet latitude with the more poleward climatological jet being the result of the jet occupying the northern jet position more frequently in the simulation forced with observed ssts the more frequent occurence of the northern jet location is associated with periods of high eddy heat flux over the gulf stream region composite analysis of high eddy heat flux events reveals that the significantly higher heat flux is followed by larger and more persistient poleward jet excursions in the simulations with realistic ssts compared to the simulation with smoothed ssts with upper tropospheric eddy momentum fluxes acting to maintain the more poleward eddy driven jet periods of high eddy heat flux over the gulf stream region are also shown to be associated with increased blocking frequency over europe which are clearly distinct from periods with a northern jet position

mantle contributions to crustal thickening during continental collision evidence from cenozoic igneous rocks in southern tibet the tibetan crust is twice as thick as average continental crust crustal compression and shortening as a result of indian asian collision isoftenconsideredtobetheprimarycauseforthecrustalthickening inthispaper weshowthatmagmaticcontributionisalsoimportant we come to this conclusion by documenting the paleogene linzizong volcanic succession lvs its coeval granitoid batholiths and the miocene adakitic rocks along the gangdese magmatic belt in southern tibet it has been widely accepted that the indian asian collision proceeded from a soft phase at 65 70 ma to a hard phase at 45 40 ma followed by continued post collisional convergence to the present in response to the collision and post collision convergence are a series of tectono magmatic events recorded in the gangdese magmaticbelt theseinclude 1 thesyn collisionallvsvolcanism 65 40ma andtheemplacementofsoutherngangdesebatholiths a peakageof 50ma 2 aperiod 40mato25ma thatismagmaticallyquiescent yettectonicallydominatedbyactivecompressionand crustal shortening and 3 the emplacements of post collisional adakitic rocks 25 12 ma potassic ultrapotassic volcanics 25 10 ma and peraluminous muscovite bearing granites between 24 and 18 ma these three major events contribute in different ways to the crustal thickness phase i formation of the lower juvenile crust from 65 ma to 50 ma with crustal thickening largely concentrated at 50 40maviainputofmantle derivedmagmas phaseii crustalthickeningbytectonicshorteningat 40 25ma andphaseiii retaining crustal thickness but thinning of the lithospheric mantle since 25 ma in response to crustal extension and upwelling and lateral flow of asthenosphericmantle weemphasizethatcollision inducedcrustalthickeningtookplacemainlyintheperiodof 50 40maand 25ma i e the period between the late stage of the lvs volcanism and the beginning of the adakitic rock emplacement most of the lvs rocks and the collision related granitoids in southern gangdese have end 0 attesting to the significance of mantle input most likely through remelting of mantle derived basaltic rocks including the subducted neo tethyan ocean crust the petrologic and geochemical characteristics of the miocene potassic adakitic rocks support the idea that the lower portion of the thickened tibetan crust is mafic and is genetically associated with the earlier lvs magmatism we estimate that the mantle material input contributed about 30 of the total thickness of the present day tibetan crust by assuming a pre collision crustal thickness of 35 km then the tectonic contribution would be about 20 km

discovery of late triassic mineralization in the gangdese metallogenic belt tibet the banduo pb zn deposit somdo area abstract the newly discovered banduo pb zn deposit in the somdo area of tibet is hosted by a late triassic granodiorite a combination of zircon u pb dating hf isotopic compositions sulfide rb sr dating and whole rock geochemistry was used to determine the age of the mineralization and characterize the metallogenesis of the deposit the weighted mean u pb ages of zircon from the granodiorite 203 8 1 7 ma mswd 0 53 206 1 0 4 ma mswd 0 098 and the weighted mean rb sr isochron age of sulfides from the pb zn mineralization 202 7 2 3 ma mswd 1 3 suggest that the timing of mineralization was close to that of granodiorite crystallization during the late triassic the average 87sr 86sr i value of 0 71026 implies that the ore forming metals were sourced from a mixture of mantle and crustal material the weakly altered granodiorite of the deposit is characterized by sio2 66 78 67 85 wt k2o 2 57 3 37 wt al2o3 13 53 15 15 wt and mg 45 5 51 3 it is enriched in lrees and liles and depleted in hrees and hfses and it exhibits a negative eu anomaly the granodiorite has positive and negative ehf t values 2 5 to 1 7 and crustal model ages tc dm of 1 14 1 40 ga hf isotopic analyses and whole rock geochemistry indicate that the late triassic granodiorite was likely sourced from of a mixture of mantle and ancient lower crust material that had undergone variable degrees of fractional crystallization based on regional data the banduo deposit is the oldest pb zn deposit in the gangdese belt and likely formed as a result of the northward subduction of the neo tethys ocean the metallogenic epoch indicates that deposits related to the northward subduction of the neo tethys oceanic crust exist in this area the late triassic age of granitoid hosted mineralization provides additional prospects for exploration in the gangdese metallogenic belt

mesozoic molybdenum deposits in the east qinling dabie orogenic belt characteristics and tectonic settings abstract the east qinling dabie orogenic belt accommodates the largest mo ore district in the world it contains 8 43 mt of proven mo metal reserves which accounts for 66 of the total proven chinese mo reserves the mo ore district includes 24 deposits and 12 occurrences with four major types of mo mineral systems i e porphyry porphyry skarn skarn and hydrothermal veins the latter can be further subdivided into quartz vein and carbonatite vein types although mo mineralization in the belt began in the paleoproterozoic 1680 24 to 2044 14 ma all economically significant deposits were formed during the mesozoic re os dating of molybdenite has shown that there are three episodes of mo mineralization i e late triassic 233 221 ma late jurassic to early cretaceous 148 138 ma and early to middle cretaceous 131 112 ma late triassic mo deposits developed as molybdenite quartz veins and carbonatite vein types stable isotope systematics c o s and high contents of re and sr indicate that the carbonatite mo veins are mantle derived porphyry and porphyry skarn mo mineral deposits were formed in the late jurassic to early cretaceous and early to middle cretaceous the late jurassic to early cretaceous granite porphyries that are associated with the mo deposits usually occupy less than 1 5 km2 at the surface and are situated in the east qinling area far west of china s continental margin on the other hand the early to middle cretaceous batholiths and granite porphyries with associated mo deposits are located in the dabieshan area and eastern part of the east qinling area the late jurassic to early creataceous granitoids and related mo deposits possibly formed in a back arc extensional setting of the eurasian continental margin which was probably triggered by the oblique subduction of the izanagi plate the early to middle cretaceous batholiths and granite porphyries are linked to the tectonic regime of lithospheric thinning asthenospheric upwelling and partial melting of the crust induced by a change in izanagi plate motion parallel to the continent margin in the east qinling dabie belt there are vein type pb zn ag deposits surrounding porphyry and or porphyry skarn mo w deposits forming well defined ore clusters the same spatial arrangement i e porphyry mo stockworks and outlying pb zn ag ore veins is also observed at the deposit scale thus mo porphyry stockworks and distal polymetallic veins belong to the same ore system and may reflect an outward temperature decrease from the highly fractionated granite plutons both porphyry stockworks and polymetallic veins can be used as vectors for further prospecting

mount st helens potential example of the partial melting of the subducted lithosphere in a volcanic arc mount st helens 50 km to the west of mount adams and the main cascade volcanic chain is only 80 km above the subducting oceanic lithosphere the elevated temperatures off the subducting slab because of the close proximity of the juan de fuca ridge to the trench may induce slab melting at a depth of 80 km dacites from mount st helens have geochemical compositions off magmas that are derived by direct partial melting of metamorphosed basalts at high pressure i e relatively high ai al2o3 15 at 70 sio2 low y and yb because of garnet and amphibole stability in the source low sc and high sr and eu trace element modeling of the partial melting of mid oceanic ridge basalt morb from the juan de fuca ridge that yields a hornblende eclogite residue can reproduce the mount st helens data results off the model are quite distinct from data derived from the mount adams volcanic rocks in contrast mount adams is 135 km above the subducting slab and is associated with normal arc magmatism believed to be derived from the mantle above the subducting plate the cascade are has been active in its present locality because of oblique subduction for the past 7 m y the major volcanoes along the arc have existed for at least 500 ka but mount st helens has existed for 40 ka we suggest that the subducting plate may have reached elevated temperatures because of the approach of north america to the juan de fuca ridge at 40 ka which initiated melting of the slab

geodynamic settings of mineral deposit systems mineral deposits represent extraordinary metal concentrations that form by magmatic magmatic hydrothermal or hydrothermal processes in geodynamic environments typified by anomalously high thermal and or mechanical energy near plate boundaries as they require the conjunction of specific environmental conditions to form particular mineral deposit types tend to occupy specific geodynamic niches the temporal distributions of mineral deposit types reflect both formational and preservational processes in the archaean and palaeoproterozoic these were linked because of preservation in continental crust connected to thick buoyant subcontinental lithospheric mantle sclm but were decoupled by the neoproterozoic and phanerozoic as a result of evolution to thinner increasingly dense sclm the transition marks a change from mantle plume influenced plate tectonics to modern style plate tectonics with broadly coincident environmental changes and a major impact on the nature and abundance of preserved mineral deposit types as mineral deposits represent an integral part of tectonic process they are essential indicators of that process and geodynamic settings and should be incorporated into any holistic tectonic terrane analysis their distribution also provides a particularly critical test on ancient continental reconstructions derived from palaeomagnetic data conversely such reconstructions provide a first order targeting tool for the conceptual exploration required to discover new mineral provinces and deposits under cover

postsubduction porphyry cu au and epithermal au deposits products of remelting of subduction modified lithosphere porphyry cu mo au and some epithermal au deposits are formed from hydrothermal fluids exsolved from cooling water rich calc alkaline magmas emplaced in volcanoplutonic arcs above subduction zones these magmas originate by partial melting of the metasomatized asthenospheric mantle wedge however there is increasing evidence for the existence of a suite of porphyry cu au and epithermal au deposits related to magmas generated after subduction beneath the arc has ceased associated magmas tend to be mildly alkaline relatively sulfur poor and emplaced as isolated complexes rather than in voluminous volcanoplutonic arcs they are likely formed by remelting of previously subduction modified arc lithosphere triggered by postsubduction lithospheric thickening lithospheric extension or mantle lithosphere delamination metasomatized mantle lithosphere or hydrous lower crustal cumulates residual from first stage arc magmatism contain small amounts of chalcophile and siderophile element rich sulfides and constitute a fertile source for hydrous au rich but relatively sulfur poor magmas during later remelting the recognition that porphyry cu au and related epithermal au systems can also form in postsubduction and collisional tectonic settings expands the range of geological environments and geographical terranes that are prospective for such deposits

syn collisional magmatism at the longgen pb zn deposit western nyainqentanglha belt tibet petrogenesis and implications for regional polymetallic metallogeny abstract syn collisional orogeny generally lacks adequate fluids and has a low potential to form magmatic hydrothermal ore deposits however some syn collisional pb zn deposits have been recognized in the nyainqentanglha polymetallic belt npb central lhasa subterrane and ore related magma petrogenesis and the metallogenic geodynamic setting is limited in this study detailed petrology geochemical and geochronological data of ore related syn collisional granite porphyries are evaluated to constrain the timing of mineralization and discuss the genesis and evolution of ore related magma using the longgen skarn pb zn deposit as a case study zircon u pb dating of ore related porphyries provides a weighted mean age of 61 2 0 8 ma which is slightly earlier than the sphalerite rb sr age of 59 1 3 0 ma indicating that a paleocene pb zn mineralization event occurred during syn collisional orogeny the porphyries have high sio2 k2o na2o and are enriched in rb th u pb lrees and a cnk 0 94 1 15 but have low p2o5 and are depleted in nb ta and ti this suggests that the longgen granite porphyries are metaluminous to weakly peraluminous high k calc alkaline arc like granites these porphyries have highly radiogenic isotopic compositions with 87sr 86sr i 0 709513 0 713587 207pb 204pb i 15 657 15 713 and 208pb 204pb i 38 964 39 163 but low end t values from 6 7 to 6 0 as well as negative zircon ehf t values from 5 1 to 3 2 corresponding to tdm2 nd ages of 1 37 to 1 42 ga and zircon hf tdmc ages of 1 30 to 1 42 ga this demonstrates that the longgen granite porphyries may have been generated by the partial melting of mesoproterozoic basement continental crust materials with significant amounts 30 50 of mantle derived melt input paleocene eocene 65 45 ma magmatic rocks associated with pb zn and fe cu deposits are compiled in the npb the pb zn ore related granitoids have relatively lower whole rock end t and zircon ehf t values higher 87sr 86sr i values and older tdmc ages than the coeval granitoids associated with fe cu mineralization this indicates that mantle material is more critical for the development of fe cu ore related granitoids than granitoids associated with pb zn mineralization the final results show that different sources of paleocene eocene syn collisional magma in the npb are beneficial for different mineralization events during the syn collisional orogeny of the indian and asian plates