miocene high sr y magmatism south tibet product of partial melting of subducted indian continental crust and its tectonic implication abstract post collisional 26 10 ma high sr y and hree depleted intrusive rocks occur in an e w trending belt paralleling the yarlung zangbo suture in south tibet their petrogenesis has been a subject of debate here we present chronological geochemical and sr nd hf isotopic data for two newly discovered large volume high sr y granitoids the pagu granodiorite and the nanmuqie granite and three high sr y porphyries intruding the granitoids in the lhasa terrane la icp ms zircon u pb dating for the pagu granodiorite and nanmuqie granite yielded identical magma crystallization ages of 14 0 14 4 ma which is indistinguishable from their associated high sr y porphyries 14 2 14 6 ma the granitoid was intruded at middle crust depth whereas the porphyry was intruded at upper crust depth indicating that the lhasa terrane has experienced a rapid crustal uplift during the high sr y magma emplacement zircon hf isotopic and whole rock sr nd isotopic compositions for these granitoids and porphyries suggest that their magmas were dominantly derived from partial melting of crustal materials the granitoids and porphyries have ehf t values overlapping with the mafic granulites in the himalayan terrane indian plate their sr nd isotopic compositions show two endmember mixing between the himalayan mafic lower crust and the ultrapotassic lavas the lhasa lower crust we suggest that the high sr y magmas in the lhasa terrane could be derived from partial melting of subducted indian mafic lower crust with incorporation of the ultrapotassic lava and or the lhasa lower crust components our study suggests a new model for the high sr y magma generation in the lhasa terrane and provides a line of geochemical evidence that the indian continental crust was subducted beneath the southern lhasa terrane in the early middle miocene

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

age and genesis of the pusangguo skarn cu dominated polymetallic deposit gangdese metallogenic belt tibet abstract the pusangguo skarn cu polymetallic deposit is a newly discovered deposit in the western gangdese porphyry copper belt gpcb the orebodies are hosted along the contact between limestone of the early cretaceous takena formation and a biotite granodiorite intrusion the mineralization is associated with the biotite granodiorite intrusion and is divided into four stages 1 a prograde skarn stage 2 a pre ore retrograde skarn stage 3 a quartz sulfides stage and 4 a post ore carbonate stage these skarns have the characteristics of both calcareous and manganese skarns the mineral compositions of the garnets and pyroxenes indicate that the ore forming environment gradually evolved from a high temperature oxidative and alkaline environment into a low temperature and reductive environment the sulfur and lead isotopic compositions of the ore sulfides suggest a magmatic source for the sulfur and a crust dominated source for the ore forming metals the hydrogen and oxygen isotopic compositions of the quartz and garnets in the ores indicate that the ore forming fluids may have originated from a mixture of magmatic and meteoric fluids the geochronological data show that both the magmatism 14 8 0 4 ma and mineralization 13 2 0 7 ma occurred during the miocene in a post collisional tectonic setting the ore forming biotite granodiorite is a high k calc alkaline i type granite and has an adakitic geochemical affinity similar to the gangdese miocene adakites which were generated from thickened lower crust in a post collisional tectonic setting the low positive ehf t values 0 to 2 6 young two stage hf model zircon ages and whole rock geochemical and lead isotopic compositions indicate that the magma of the ore related biotite granodiorite may have originated from the thickened lower crust in the lhasa terrane

ages and petrogenesis of the late triassic andesitic rocks at the luerma porphyry cu deposit western gangdese and implications for regional metallogeny abstract the tibetan plateau is one of the most significant cu poly metallic mineralization regions in the world and preserves important information related to subductional and collisional porphyry cu mineralization this study investigates a new occurrence of cu mineralization related andesitic porphyries in the western domain of the gangdese magmatic belt and assesses its petrologic zircon u pb geochronology whole rock chemistry and sr nd hf pb isotope data zircon u pb dating of three ore related porphyries yields crystallization ages of 212 211 ma these ages are consistent with previous molybdenite re os dating indicating a late triassic magmatic and cu mineralization event in the western gangdese magmatic belt nb ta and ti depletion th and lree enrichment and high la yb and th yb ratios in addition to high u yb ratios from zircons suggest that the magma was generated in an active continental arc setting the porphyries have radiogenic isotopic compositions with 87sr 86sr i 0 70431 0 70473 end t 1 1 to 3 8 207pb 204pb i 15 601 15 622 and 208pb 204pb i 38 450 38 693 as well as high positive zircon ehf t values from 6 2 to 10 6 mean value 8 3 corresponding to model ages tdm ranging from 509 ma to 819 ma mean 646 ma this suggests that the andesitic magmatism was dominantly sourced from depleted mantle materials that were modified by subducted oceanic sediment derived melts during the subduction of the neo tethys ocean the mineralization related porphyries contain amphibole and epidote as well as high whole rock fe2o3 feo and zircon ce4 ce3 ratios suggesting hydrous and highly oxidized parent magmas considering the existing cu mineralization and highly oxidized magma of the well preserved triassic andesitic igneous rocks in the western gangdese belt the subduction related continental arc magma system is favorable for subduction related porphyry cu deposits the existence of luerma porphyry mineralization demonstrates that there are at least five generations of porphyry cu mo au mineralization in the gangdese magmatic belt which advances the timeframe of porphyry mineralization to the late triassic

melt components derived from a subducted slab in late orogenic ore bearing porphyries in the gangdese copper belt southern tibetan plateau abstract a porphyry type cu mo au polymetallic ore belt extends in an e w direction for 400 km along the gangdese magma arc in the southern tibetan plateau extensive field investigations and systematic geochemical study combined with s and pb isotopic tracing indicate that cu polymetallic mineralization of the copper belt is genetically related to late orogenic granitic porphyries formed in a late himalayan crustal extension stage 18 14 ma geochemistry of the porphyries shows the essential characteristics of adakite and suggests a dominant role of subduction related components in their genesis the genesis of these ore bearing porphyries is mainly related to melt components derived from subducted slabs and has little relationship with fluids released from them pb isotopes show a clear linear array in the plumbotectonics model and are manifested by a progressive variation from orogenic pb in the east segment of the copper belt to mantle pb in the west segment forming a mixing line of indian oceanic morb and indian oceanic sediments this suggests that the porphyry magma dominantly originated from partial melting of subducted oceanic crust and was mixed with a minor melts of sediments and mantle wedge components

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

contribution of mantle components within juvenile lower crust to collisional zone porphyry cu systems in tibet most porphyry cu mo au deposits are found in magmatic arcs worldwide and are associated with hydrous high fo2 calc alkaline magmas derived from a mantle wedge that was metasomatized by the fluids from a subducted oceanic slab recently such deposits have been documented as occurring widely in collisional settings where they are associated with potassic magmas generated during the collisional process but the genesis of the fertile magmas and the mechanism of metallic enrichment remain controversial here we present new geochemical and sr nd hf isotopic data from the post collisional fertile and barren porphyries of the miocene gangdese porphyry belt in the tibetan orogen an orogen formed by the collision of india and asia in the early cenozoic both types of porphyry are characterized by high k2o contents and have geochemical affinities with adakite but the fertile magmas were most likely derived from the melting of a thickened juvenile mafic lower crust formed by the underplating of earlier asthenospheric melts at the base of crust whereas the derivation of the barren magmas involved variable amounts of old lower crust in tibet the melting of sulfide bearing phases in the juvenile mantle components of the tibetan lower crust probably provided cu au and s to the fertile magmas the breakdown of amphibole during melting at the source released the fluids necessary for the formation of the porphyry cu deposits in tibet the thickened crust up to 70 80 km due to collision is thought to be responsible for a decrease in the fo2 of the fertile magmas during their ascent to the upper crust thus preventing the generation of more porphyry cu au and epithermal au deposits in this collisional zone

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

metallogenic regularity and minerogenetic series of ore deposits in inner mongolia and adjacent areas in the discipline of ore deposits minerogenetic series is a kind of academic thought of studying regional metallogeny it advocates using system theory and activity theory to study ore forming process and ore deposit association that have been developed in various stages of geological history and in specific tectonic environment in this study based on the new understanding of tectonic evolution of inner mongolia the new progresses in geosciences of its adjacent areas especially a large number of precise mineralization ages data and the new understanding of the sources of rock forming and ore forming materials the authors divided the ore deposits in inner mongolia into 11 metallogenic series the archaean anshan type metamorphic sedimentary iron deposit metallogenic series consisting of the middle archaean and the late archaean series the middle proterozoic submarine exhalative type lead zinc copper sulfur deposit metallogenic series the mesoproterozoic bayan obo ree fe nb deposit metallogenic series the ordovician silurian porphyry copper deposit metallogenic series the devonian ophiolite related chromite deposit metallogenic series the late permian triassic granite related molybdenum gold polymetallic deposit metallogenic series the triassic middle jurassic porphyry copper deposit metallogenic series the late jurassic early cretaceous granite related epithermal type lead zinc polymetallic deposit metallogenic series in de erbugan area the late jurassic early cretaceous granite related lead zinc tin molybdenum gold polymetallic deposit metallogenic series in the da hinggan mountains and adjacent areas the cenozoic lacustrine sedimentary evaporation related salt deposit metallogenic series furthermore on the basis of such division the ore deposit metallogenic series distribution map was drawn up with a brief discussion on their ore forming geological background mineralization characteristics ore deposits association and spatia l temporal distribution patterns the metallogenic series division in this study emphasizes the importance of tectonic events and highlights the coupling between the major tectonic events and the large scale m i neralization with the purpose of recognizing the geological background of the mineralization episode on a larger scale for example the authors set the two coeval deposits of duobaoshan and bainaimiao as a metallogenic series though it is not clear whether they belonged to the same intermittent arc chain or whether they were split by later tectonic movement it is worth noting that a lot of minerogenetic series in inner mongolia show signif i cant diachronism for example the metallogenic events related to the closure of paleo pacifc ocean lasted from late carboniferous through permian to triassic and those related to the subduction of mongo l okhotsk ocean lasted from triassic to middle jurassic

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

economic geology copper conundrums the metal content of magmas erupted at subduction zone arcs is thought to be derived from the mantle a correlation between crustal thickness and copper content in arc magmas worldwide however reveals an important role for the crust in the upper plate

adakitic rocks from slab melt modified mantle sources in the continental collision zone of southern tibet abstract major trace element and sr nd pb isotopic data are presented for newly discovered adakitic rocks in the western gangdese belt southern tibet the miocene 26 10 ma adakitic rocks from the southern tibetan continental collision zones exhibit distinct differentiation trends typical of arc magmas these rocks display geochemical affinities similar to those of cretaceous 136 80 ma adakitic rocks derived from the partial melting of subducted neotethyan slab in southern tibet the whole rock geochemical and isotope characteristics of the post collision adakitic rocks reveal that their magmas likely originated from an upper mantle region previously metasomatized by slab melts during the cretaceous subduction event an interesting observation is that the e w trending belt of adakitic rocks along the yarlung tsangpo suture zone occupies a fore arc position reflecting a geotectonic setting compatible with the genesis of adakitic magmas the widespread occurrences of cretaceous adakitic rocks in this region are interpreted to testify to the former location of the adakite metasomatized mantle our favoured interpretation is that the spatial isotopic variation in the post collision adakitic rocks is mostly linked to a westward increase in sediment input in the tibetan mantle region under the framework of our paleo subduction model a slab break off event that initiated at around 25 ma would have allowed an asthenospheric upwelling beneath southern tibet which was instrumental in generating the post collision adakitic magmatism in southern tibet

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

an exploration model for jiama copper polymetallic deposit in maizhokunggar county tibet the jiama copper polymetallic deposit in tibet is a significant ore deposit serving as a nonferrous metal base in central tibet this paper deals emphatically with the ore bodies in such aspects as its metallogenic geological conditions prospecting indicators geochemical exploration model geophysical exploration model and spatial framework studies show that the ore controlling strata are sandy slate and hornfels of linbuzong formation k1l and marble and limestone of duodigou formation j3d and that hornfels controls the distribution of hornfels type ore bodies and inter layer structure between hornfels and marble controls skarn type ore bodies due to the good trap formed by the hornfels which caused good magmatic hydrothermal mineralization there are nine types of exposed magmatic rocks such as granite porphyry biotite monzonite granite porphyry granite diorite porphyrite quartz diorite porphyry and diorite porphyryp granite of high k calc alkaline series is related to the passive filling of mineralization into the collapse space caused by the structure the ore forming structure is the niumatang complex anticline in the center of the jiama kajunguo nappe structure controlling the generation of skarn and porphyry type ore bodies the geochemical exploration model at the scale of 1 10 000 indicates that cu mo au ag bi sn and mo are concentrated in the anomaly center bi and sn as the high temperature elements exist in the internal circle and as sb hg pb zn co and ni as the lower temperature elements are present in the external circle co and ni anomalies suggest that the original rocks were carbonaceous and argillaceous sandy slate as sb and hg anomalies imply the wide distribution of pyrite in hornfels and represent the external alteration of porphyry metallogenic system cu mo au ag sn and bi assume m shaped distribution along the cross section the geophysical exploration model at the scale of 1 10 000 indicates that the high precision magnetic anomaly and apparent resistance anomaly assume w shaped distribution along the cross section whereas the apparent chargeability anomaly shows the wave shape the areas with intense mineralization of the porphyry metallogenic system show low magnetic anomalies t values being 0 200 nt and the orbicular contact zone has intermediate high magnetic anomalies t value being 200 1 500 nt with the features of porphyry mineralization the polarizability in the distributive areas of hornfels skarn and porphyry type ore bodies is 4 10 and the apparent resistivity is 50 700 m the other significant prospecting indicators are huge limonite coverage and hydrothermal alteration and concentrate rock bodtes at the surface in addition to the indicators of geophysical and geochemical anomalies on the basis of the above data the systematic drilling to the depth of 145 000 m has confirmed the typical porphyry metallogenic system in the jiama copper polymetallic deposit the zoning of wall rock hornfels type mo cu au ag skarn type cu mo pb zn au ag porphyry mo cu au ag along the section has constituted an integrated porphyry metallogenic system forming porphyry type mo cu ore bodies in the porphyry network cu mo ore bodies in the hornfels and veinlet disseminated and massive cu mo and pb zn cu ore bodies in the skarn

late cretaceous gangdese intrusions of adakitic geochemical characteristics se tibet petrogenesis and tectonic implications article i nfo the gangdese batholith emplaced from the cretaceous to eocene in southern tibet has been widely regarded as the major constituent of an andean type convergent margin resulting from northward subduction of the neo tethyan oceanic lithosphere under asia while the gangdese batholith consists predominantly of calc alkaline rocks we identify from the eastern part of the batholith a suite of epidote bearing granodiorites that shows adakitic geochemical characteristics marked with apparently higher la yb and sr y and lower y and hree than other gangdese rocks and common arc magmas shrimp zircon u pb analyses of two of the samples yielded 206 pb 238 u dates of 80 4 1 1 and 82 7 1 6 2 ma which constrain the emplacement ages of the adakitic rocks trace element modeling suggests that these rocks originated from partial melting of a garnet amphibolite source that on the basis of the sr and nd isotope data isr 0 7044 0 7048 end t 3 2 to 0 9 we interpret to be a newly underplated mafic lower crust rather than the subducted neo tethyan oceanic crust this juvenile crust was produced by cretaceous basaltic underplating above the mantle wedge and then thickened by the tectonic contraction owing to flattening of the neo tethyan subduction a process that also led to the adakitic magmatism our interpretation involving a late cretaceous flat slab subduction and related orogenesis in southern tibet is consistent with petrographic data such as the occurrence of magmatic epidote and muscovite rimmed with resorption texture in the granodiorites which indicate deep seated emplacement followed by rapid tectonic exhumation

tectonic evolution of the qinghai tibet plateau abstract the qinghai tibet plateau composed of several continental slivers within the eastern tethyan domain is one of the pivotal sites to examine to better understand the theory of plate tectonics and the orogenic evolution on earth this plateau is generally inferred to be a collage of several continental blocks that rifted from gondwanaland and subsequently accreted to the asian continent however recent recognition of over twenty ophiolite melange zones and their associated island arcs indicates that the traditional model of tectonic evolution requires revision based on 177 recently finished 1 250 000 scale geological maps and related studies we summarize the main tectonic context of the qinghai tibet plateau and propose a new integrated model to account for the new findings the complex orogen of the immense qinghai tibet plateau consisting of multiple island arc basin systems that developed at different stages while surrounded by the north china yangtze tarim and indian plates is emphasized the entire orogen surrounded by suture zones that mark the locations of oceanic closure is investigated by examining i the first order tectonic units and ophiolitic melanges including arc arc continent collision zones and ii their internally enclosed blocks as the second order tectonic units therefore the qinghai tibet plateau is divided into three major orogenic systems namely from northeast to southwest the early paleozoic qinling qilianshan kunlunshan qin qi kun the late paleozoic triassic qiangtang sanjiang and the late paleozoic to cenozoic gangdese himalaya orogenic systems which are separated by the kangxiwa muzitagh maqin mianxian and the bangong shuanghu changning menglian sutures respectively we propose that the formation and evolution of the qinghai tibet plateau to have been intrinsically related to those of the eastern tethys recorded by the longmu co shuanghu ophiolite melange zone the southern qiangtang paleozoic accretionary arc basin system the bangong nujiang suture zone and their associated composite island arc basin systems the present day bangong shuanghu changning menglian suture system marks the final closure of the tethyan ocean the yarlung zangbo ocean opened as a back arc basin in response to the southward subduction of the tethyan ocean lithosphere in the middle triassic and closed as a result of the india asia collision at the end of cretaceous followed by the northward indention of the indian plate that resulted in significant intra continental deformation and plateau uplift in the cenozoic

differential exhumation histories between qulong and xiongcun porphyry copper deposits in the gangdese copper metallogenic belt insights from low temperature thermochronology abstract the qulong and xiongcun porphyry deposits in the gangdese copper molybdenum metallogenic belt gcmb are both giant porphyry deposits they were located in the eastern and the central gcmb about 400 km apart and were generated in the miocene and the jurassic respectively in order to reveal why the two asynchronous deposits could occur in the same metallogenic belt the in situ zircon u pb zircon and apatite fission track zft and aft and apatite u th he ahe dating were conducted their associated exhumation amounts and histories were compared and finally the prospecting significance was evaluated ahe ages of the qulong deposit indicate it underwent an amount of at least 1 3 2 8 km exhumation since 13 8 13 1 ma however aft data and modeling results reveal that the xiongcun deposit experienced two stages of rapid cooling at 20 13 ma and 13 8 ma respectively the temperature decreases from 160 c to 40 c after 20 ma and the corresponding exhumation amount is about 4 6 km integrated the regional thermochronological data exhumation amounts of 4 6 km and

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

jurassic u pb and re os ages for the newly discovered xietongmen cu au porphyry district tibet prc implications for metallogenic epochs in the southern gangdese belt the gangdese belt in southern tibet includes the cretaceous to early eocene gangdese continental magmatic arc a newly recognized middle jurassic magmatic arc and post gangdese arc magmatism of miocene age that is well known for its association with important copper molybdenum deposits although the tectonic history of the gangdese continental arc is relatively well constrained the tectonomagmatic setting of the jurassic and miocene magmatic events was poorly constrained previously geochronological analysis of samples from the xietongmen copper gold porphyry district has identified a previously unknown metallogenic event related to middle jurassic arc magmatism the occurrence of several metallogenic epochs within the southern gangdese belt highlights the importance of systematic metallogenic studies of this belt

molybdenite re os dating of jiama and zhibula polymetallic copper deposits in gangdese metallogenic belt of tibet and its significance the origin of the jiama and the zhibula polymetallic copper deposits in the gangdese metallogenic belt southern tibet is a problem of long controversy this paper gives for the first time the highly precise re os age of molybdenite from these two polymetallic copper deposits the re os model ages of 7 molybdenite samples from the jiama deposit vary from 15 4 0 2 ma to 15 5 0 2 ma yielding an isochron age of 15 18 0 98 ma the re os model ages of 5 molybdenite samples from the zhibula deposit vary from 16 88 0 28 ma to 17 06 0 27 ma yielding an isochron age of 16 90 0 64 ma these ages are much younger than the ages of the gangdese inter arc sedimentary basin development and the ages of collisional granitic intrusive rocks in the gangdese belt but are obviously consistent with the ore forming ages of the near by porphyry copper deposits such as qulong lakang e chongjiang and tingguan in the gangdese metallogenic belt these re os ages suggest that the jiama and the zhibula polymetallic copper deposits were formed in the same porphyry skarn ore forming system in a post collisional extensional tectonic setting of miocene epoch the porphyry copper deposits and the skarn type polymetallic copper deposits in the gangdese metallogenic belt were formed by different ore forming processes of the magmatic hydrothermal system in different wall rocks

remnants of a cretaceous intra oceanic subduction system within the yarlung zangbo suture southern tibet extensive field investigations along the yarlung zangbo suture zone in southern tibet reveal the presence of now fragmented remnants of a south facing intra oceanic subduction system this system developed within tethys during the cretaceous the associated arc forearc ophiolite and subduction complex were emplaced onto the leading edge of india at the end of the cretaceous rapid sedimentation in oblique slip basins and disruption of water saturated sediments into melange was widespread and concomitant with ophiolite emplacement we describe the tectonic entities that developed during this previously unrecognized phase of tethys tibet evolution and present a new model for the evolution of this portion of tibet

geological characteristics and ore forming epoch of ri a copper deposit related to bimodal rock series in coqen county western tibet lying southeast of coqen county in western tibet and tectonically within lhasa terrain the ri a copper deposit is a skarn copper deposit related to an adamellite porphyry stock the 40ar 39ar mineralization age of phlogopite in the ri a copper deposit is 87 69 0 64 ma mswd 0 42 which is in accordance with the u pb shrimp age of zircon 90 1 ma moreover the diabase prophyrite in the ore district is accompanied by disseminated copper mineralization whose age 87 2 ma and rock geochemical characteristics are close to those of the adamellite porphyry they together constitute a copper bearing bimodal rock assemblage representing a copper mineralization event under the middle late cretaceous extensional tectonic environment in lhasa terrain researches show that the bimodal rock series resulting in copper mineralization was formed during the extensional period after the southward subduction of bangonghu nujiang oceanic crust the discovery of the deposit shows that besides the porphyry copper deposits in yulong gangdese and bangonghu nujiang porphyry type copper ore belts related to the plate suture zone there existed a porphyry skarn copper ore forming event related to the bimodal rock series in lhasa terrain

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

time limit for formation of main geological bodies in xiongcun copper gold deposit xietongmen county tibet evidence from zircon u pb ages and re os age of molybdenite the xiongcun copper gold deposit is a superlarge copper and gold deposit the main mineralization occurs in quartz augen diorite porphyry and exo contact zone of strongly altered fine grained tuff and is composed of veinlet disseminations in the porphyry and veinlet disseminations and veins in the tuff the genetic types of the ore deposit include porphyry ore type epithermal ore type sedex type fracture controlled altered rock type and structure altered rock type much controversy still exists concerning the rock forming and ore forming age based on zircon dating of ore bearing rocks intrusions and penetrating ore bodies as well as detailed geological mapping the authors carried out chronologic studies of ore bearing wall rocks of no and ore bodies the oldest hornblende quartz diorite porphyry j2 1 quartz augen diorite porphyry j2 biotite granodiorite e2 lamprophyre and molybdenite of no ore body according to the results of zircon u pb isotopic dating the weighted average age of 9 analytical data from ore bearing tuff zk5036 68 m is 175 5 ma with mswd being 0 63 the weighted average age of 16 analytical data from quartz augen diorite porphyry zk5036 303 m is 173 3 ma with mswd being 1 16 and the weighted average age of 14 analytical data from diorite granodiorite zk6187 335 m is 46 5 1 1 ma with mswd being 0 83 all the zircons have characteristics of magmatic origin zircon u pb isotopic dating data suggest that the ore bearing wall rocks were formed in early middle jurassic the mineralized intrusions were formed in middle jurassic and the batholiths were formed in eocene the dating results of four molybdenite re os isotope samples from xiongcun no ore body show that the content of 187re is 1 269 1 354 g g and the content of 187os is 3 587 3 993 ng g model ages of molybdenite are around 169 5 176 8 ma and model ages are consistent within the error range mswd 5 6 implying that mineralization took place in middle jurassic ar ar dating of the magmatic body and dyke show that 39ar 40ar plateau age of biotite from lamprophyre is 49 59 0 58 ma and 39ar 40ar plateau age of biotite from biotite granodiorite is 46 96 0 42 ma combined with the results obtained by other researchers it is thought that retrograde metamorphism is the cause for the ar ar dating of mica minerals around 46 50 ma the xiongcun copper gold deposit is an island arc porphyry copper gold deposit as evidenced by the study of petrologic and geochemical characteristics and the analysis of ore bearing features ore mineral assemblage element assemblages and chronology the discovery exploration and chronologic studies of the xiongcun island arc porphyry copper gold deposit have provided the information concerning the tethys subduction ore forming stage and also widened the new prospecting direction in the gangdese metallogenic belt of tibet

la icp ms u pb zircon age of intermediate acidic intrusive rocks in jiama of tibet and its metallogenic significance this paper deals with the emplacement timing of the intermediate acidic intrusive rocks in jiama of tibet and its metallogenic significance based on the measured geological data and la icp ms u pb zircon ages of the four intermediate acidic intrusive rocks the authors preliminarily regularized the timing sequence which is from early to late in order of porphyry granite 15 31 ma 16 27 ma quartz diorite porphyrite adamellite porphyry 14 81 ma granodiorite porphyry exemplified by molybdenum the jiama ore deposit assumes three periods of metallogenesis i e the ore forming processes corresponding respectively to different degrees of magmatic activities of porphyry granite or quartz diorite porphyrite adamellite porphyry and granodiorite porphyry the jiama ore deposit resulted from the superposition of the three periods of magma mineralization

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

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

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

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

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

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

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

k ar dating and 18o d characterization of nanometric illite from ordovician k bentonites of the appalachians illitization and the acadian alleghenian tectonic activity nanometric 0 02 0 02 0 05 0 05 0 1 0 1 0 2 m illite fractions were separated from k bentonite samples from northwestern georgia and studied by x ray diffraction oxygen and hydrogen isotope geochemistry and k ar dated to more tightly constrain the tectono thermal history of the appalachian orogeny their xrd patterns are very similar for a given sample with respect to the peak shapes and positions they are ordered illite smectite mixed layers with only small variations in the relative proportions of illite and smectite interlayers the illite crystal thickness distributions also are very homogeneous across the various size fractions of the same sample but crystallite thickness varies from sample to sample it can be concluded from the 2 diagram that illitization occurred in all fractions by simultaneous nucleation and crystal growth except for one sample in that sample a period of growth without nucleation was detected on top of the nucleation and growth episode the k ar ages organize into two isochrons the first at 319 9 2 0 ma with an initial 40ar 36ar ratio of 271 66 ma and the second at 284 9 1 2 ma with an initial 40ar 36ar ratio of 310 44 one data point above the older isochron and three between the two isochrons suggest a detrital contamination for the former separate and a possible further generation of nanoparticles for the three others the samples with the older crystallization age consist of illite and illite rich mixed layers and those with the younger age contain smectite rich mixed layers without illite or illite enriched illite smectite mixed layers the k ar ages fit the age trends published previously for similar k bentonites with regional age patterns between 240 and 270 ma in the southwestern region between 270 and 300 ma in the central zone and the southern appalachians and between 315 and 370 ma in the northernmost each of the two generations of illite crystals yields very consistent 18o v smow values at 17 1 for the older and at 21 1 for the younger if crystallization temperatures of the nanometric illite were between 100 and 200 c as suggested by microthermometric determinations the hydrothermal fluids had 18o values of 4 1 in the dalton district and of 8 1 in the lafayette trenton and dirtseller districts at 100 c and of 11 1 and 15 1 in the same locations at 200 c probably because the water rock isotope exchanges at elevated temperature occurred in rock dominated systems the 18o of the fluids remained unchanged during local crystal growth but varied depending on the geographic location of the samples and timing of illitization the d v smow values of the different size fractions do not provide consistent information they range from 70 to 45 for most nanometric and micrometric fractions v smow but with no apparent coherent pattern nanometric illite rich crystals from k bentonite that underwent tectono thermal alteration yield constant ages constant clay mineralogy constant crystallite size distributions for all of the nucleating and growing illite type crystals of each sample as well as constant 18o values implying constant fluid chemistry all pointing to geologically sudden crystallization

internal kinematics of salt diapirs discussion iklbot and jackson 1987 presented a very good sum mary of several aspects of salt stock configuration and emplacement as applied to the united states gulf coast one aspect of this emplacement is a process they describe as nested toroidal stream surfaces iklbot and jack son 1987 p 1083 their figure 11 or toroidal flow the concept may have been originally suggested by the over turned and even convoluted salt structures observed at the boulby mine in england a highly deformed beddedsalt deposit concepts about these structures have been expanded upon by experiments hydrodynamic theory and further observations toroidal type swirl struc tures develop early and are best displayed in salt in the early stages of deformation and diapir rise my main purpose here is to note that tiilbot and jack son 1987 have apphed these toroidal shapes where they do not seem to apply the mature high rise diapirs of the five island salt stocks of south central louisiana as a result iklbot and jackson have suggested an unlikely origin for the spines in these stocks they further infer that these toroidal structures should be present in mature type salt diapirs of the gulf coast coastal prov ince these diapirs have been well explored for petroleum tklbot and jackson 1987 p 1068 stated that mature diapirs can form crestal bulbs i suggest that these are unlikely assumptions i have emphasized for example kupfer 1970a p 43 p 55 56 1988 p 14 the distinctly different structural styles within low rise salt diapirs exemplified by north german diapirs with toroidal structures for example iklbot and jackson s 1987 figures 5 and 15 and the high rise diapirs of coastal louisiana the five islands from north to south jefferson avery weeks cote blanche belle isle are over the deepest part of the gulf coast basin 60 000 ft or 18 km and represent an extreme case of high rise above the present mother salt hori zon as iklbot and jackson have noted 1987 p 1074 1084 the salt at the top of these stocks has moved about 19 mi 30 km is highly refolded and the flow inside the diapirs is neither homogeneous nor simple these stocks are complex and have lost or distorted nearly all of their early formed structures much of tklbot and jackson s experience and evi dence cited in their paper has been with salt glaciers early diapirism and with the intermediate rise diapirs of eastern texas and northern louisiana these interme diate stocks as might be expected retain much of the

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

giant porphyry deposits characteristics distribution and tectonic controls more than half of the 25 largest known porphyry copper deposits defined in terms of contained copper metal formed during three time periods the paleocene to eocene eocene to oligocene and middle miocene to pliocene these giant deposits are clustered within three provinces central chile northern chile and southwest arizona northern mexico other giant deposits occur in montana utah panama peru argentina irian jaya mongolia and iran compressive tectonic environments thickened continental crust and active uplift and erosion were associated with the formation of many of these deposits calc alkalic magmas are most favorable for the formation of giant porphyry copper deposits although several of the largest systems are associated with high k calc alkalic intrusions the 25 largest gold rich porphyry deposits are concentrated in the southwest pacific and south america with other occurrences in eurasia british columbia alaska and new south wales many of the deposits formed in the last 13 m y the largest of the deposits are associated with high k calc alkalic intrusions many calc alkalic porphyritic intrusions have also produced giant gold rich porphyries in the last 20 m y the formation of giant porphyry copper molybdenum and copper gold deposits in the circum pacific region has been closely associated with subduction of aseismic ridges seamount chains and oceanic plateaus beneath oceanic island and continental arcs in several examples these tectonic perturbations have promoted flat slab subduction crustal thickening uplift and erosion and adakitic magmatism coeval with the formation of well endowed porphyry and or epithermal mineral provinces similar tectonic features are inferred to be associated with the giant porphyry copper molybdenum provinces of northern chile eocene oligocene and southwest united states cretaceous paleocene topographic and thermal anomalies on the downgoing slab appear to act as tectonic triggers for porphyry ore formation other factors such as sutures in the overriding plate permeability architecture of the upper crust efficient processes of ore transport and deposition and in some cases formation and preservation of supergene enrichment blankets are also vital for the development of high grade giant ore deposits a low grade geochemical anomaly may be the final product of mineralization if ore forming processes do not operate efficiently even in the most favorable geodynamic settings

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

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

cenozoic volcanism in tibet evidence for a transition from oceanic to continental subduction geochronological k ar or ar ar major and trace element sr nd pb isotopic and mineral chemical data are presented for newly discovered cenozoic volcanic rocks in the western qiangtang and central lhasa terranes of tibet alkali basalts of 65 45ma occur in the western qiangtang terrane and represent primitive mantle melts as indicated by high mgnumbers 100 mg mg fe 54 65 cr 204 839 ppm and ni 94 218 ppm contents and relatively low ratios of sr sr 0 7046 0 7061 pb pb 18 21 18 89 pb pb 15 49 15 61 and pb pb 38 42 38 89 and high ratios of nd nd 0 5124 0 5127 in contrast younger volcanic rocks in the western qiangtang terrane 30ma and the central lhasa terrane 23 13 and 8ma are potassic to ultrapotassic and interpreted to have been derived from an enriched mantle source they are characterized by very high contents of incompatible trace elements negative ta nb and ti anomalies and radiogenic pb isotopic compositions pb pb 18 43 19 10 pb pb 15 64 15 83 pb pb 39 14 39 67 sr sr 0 7088 0 7092 and nd nd 0 5122 ratios of the western qiangtang terrane potassic lavas are similar to those of 45 29ma potassic volcanic rocks in the north central qiangtang terrane whereas sr sr 0 7167 0 7243 and nd nd 0 5119 ratios of central lhasa terrane lavas are similar to those of 25 16ma ultrapotassic volcanic rocks in the western lhasa terrane the 65 45ma alkali basalts in the western qiangtang terrane along with widespread calc alkaline volcanic rocks of this age in the lhasa terrane may be related to roll back of a previously shallow north dipping slab of tethyan oceanic lithosphere beneath tibet subduction as opposed to convective thinning of continental lithosphere is favored to explain potassic volcanism in tibet because of its occurrence in distinct east west trending belts 45 29ma in the qiangtang terrane 25 17ma in the northern lhasa terrane 16 8ma in the southern lhasa terrane and temporal and spatial relationships with major thrust systems

age and petrogenesis of magmatic rocks from jiaduobule skarn fe cu deposit in tibet evidence from zircon shrimp u pb dating hf isotope and ree located in the central part of the lhasa terrane the jiaduobule skarn fe cu deposit occurs in the contact zone between a biotite monzogranitic body and the marble of permian xiala formation the zircons from biotite monzogranite are typical magmatic zircons which can be divided into four groups based on their characteristics shrimp u pb dating of the fourth group zircons yields the age of 50 9 1 8 ma which represents the crystallization age of biotite monzogranite showing that the rock was formed in the main collisional period of indo asia continental collision process the fourth group zircons have intermediate 176hf 177hf of 0 282 523 0 282 864 ehf t of 7 72 4 29 model age of crust tcdm from 851 to 1 618 ma high ree of 351 2 198 g g varying yb nd cn from 11 to 506 and ce of 1 21 65 58 and low eu 0 09 0 33 indicating that the rock was formed from a mixed magma between the partial melting materials of the mesoproterozoic upper crust of indian continent and asthenospheric mantle these data suggest that the magma was derived from a mixing process between the asthenospheric mantle fluid and the partial melting material of the upper crust which was motivated by the asthenospheric mantle upwelling through the break off of the tethyan oceanic slab from the indian continental crust after the steep and deep subduction of indian continental crust with tethyan oceanic slab into lhasa terrane in the main collisional orogenic epoch of the indo asia continental collision the mixed magma produced fractional crystallization in the magma chamber and then intruded upward to form the biotite monzogranite

geodynamic settings and tectonic model of skarn gold deposits in china an overview seventy skarn type gold deposits including 1 super large 19 large and 24 medium sized are known from different geotectonic units of china they contain a total resource of approximately 1000 t of gold 625 t in south china and account for 20 of china s gold reserves these skarn deposits are sited in collisional orogenic belts fault controlled magmatic belts and reactivated cratonic margins all of the chinese skarn gold provinces were affected by phanerozoic collisional orogenesis the timing of the metallogenic events and the spatial temporal distribution of the chinese skarn gold deposits indicates that they were formed during ore forming processes linked to the transition from shortening to extension in the geodynamic evolution of a collision orogen and not to subduction systems as is commonly advocated for porphyry copper systems around the pacific rim

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

distribution of porphyry deposits in the eurasian continent and their corresponding tectonic settings in the eurasian continent there are three huge metallogenic belts of cu and mo porphyry deposits comprising the paleozoic central asian ore belt in the north the tethyan eurasian ore belt of jurassic to cenozoic age in the southwest and the east margin ore belt of the eurasian continent of jurassic to cretaceous age in the east the latter is considered to be part of the vast circum pacific ore belt some of the main features of the spatial temporal distribution of cu and mo porphyry systems and related geodynamic processes of the three metallogenic belts are described in particular the key role of postsubduction related porphyry ore systems is emphasized comprising collisional and post collisional cu mo porphyry deposits during the geological history of the eurasian continent the recurrent feature of these ore systems and related felsic rocks is their derivation from partial melting of stagnant or residual oceanic slabs and mixing with a variable amount of crustal material during magma ascent to shallower levels 2013 published by elsevier ltd

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

la icp ms zircon u pb dating of ore bearing monzogranite porphyry in bangpu molybdenum copper deposit tibet and its significance the bangpu porphyry mo cu deposit is located about 30 km northeast of the jiama copper polymetallic deposit the rocks related to molybdenum mineralization in this ore deposit are mainly monzogranite porphyry with minor granodiorite porphyry and diorite porphyrite the age of the ore forming rock was obtained through la icp ms precise determination of the zircon u pb age for the molybdenite bearing monzogranite porphyry 26 zircons from the monzogranite porphyry yielded the weighted average 206pb 238u age of 16 23 0 19 ma mswd 2 0 n 26 suggesting miocene granitic magma emplacement in the gangdese belt the previous dating of the molybdenite from this ore deposit had yielded a re os isochron age of 15 32 0 79 ma which is about 1 ma later than the time of rock cooling thus the authors work has improved the constraint of mineralization in time regional minerogenetic regularity shows that the bangpu porphyry mo cu polymetallic deposit has an uniformity with the regional porphyry skarn deposits such as jiama qulong and other ore deposit in this region in the age of petrogenesis and mineralization which shows that this ore deposit has the same tectonic and magmic geochemical dynamic background as other ore deposits in this region and that this ore deposit was a product of mineralization explosion during the extension phase after india asia continental collision

petrogenesis and geological implications of the oligocene chongmuda mingze adakite like intrusions and their mafic enclaves southern tibet abstractthe oligocene to the miocene was a critical period for the growth of the tibetan plateau this growth is commonly considered to have been controlled by deep geodynamic processes the ultrapotassic and adakite like igneous rocks that developed during this period offer constraints on these deep seated processes in southern tibet whole rock geochemistry u pb zircon geochronology and in situ zircon hf isotopes have been determined for the mafic enclaves and host adakite like granitoids in the oligocene chongmuda mingze intrusive complex of southern tibet the host rocks including granodiorite and monzogranite are mainly high k and calc alkaline in composition their whole rock geochemistry low mgo ni and cr contents negative end t values 2 5 to 3 4 and low 87sr 86sr i values 0 7061 0 7066 and in situ zircon ehf t values 0 6 6 1 indicate that they were derived by partial melting of a juvenile lower crust implying that the southern tibetan crust was already thickened to up to 50 k