major types and time space distribution of mesozoic ore deposits in south china and their geodynamic settings the ore deposits of the mesozoic age in south china can be divided into three groups each with different metal associations and spatial distributions and each related to major magmatic events the first event occurred in the late triassic 230 210 ma the second in the mid late jurassic 170 150 ma and the third in the early mid cretaceous 120 80 ma the late triassic magmatic event and associated mineralization is characterized by peraluminous granite related w sn nb ta mineral deposits the triassic ore deposits are considerably disturbed or overprinted by the later jurassic and cretaceous tectono thermal episodes the mid late jurassic magmatic and mineralization events consist of 170 160 ma porphyry skarn cu and pb zn ag vein deposits associated with i type granites and 160 150 ma metaluminous granite related polymetallic w sn deposits the late jurassic metaluminous granite related w sn deposits occur in a ne trending cluster in the interior of south china such as in the nanling area in the early mid cretaceous from about 120 to 80 ma but peaking at 100 90 ma subvolcanic related fe deposits developed and i type calc alkaline granitic intrusions formed porphyry cu mo and porphyry epithermal cu au ag mineral systems whereas s type peraluminous and or metaluminous granitic intrusions formed polymetallic sn deposits these cretaceous mineral deposits cluster in distinct areas and are controlled by pull apart basins along the south china continental margin based on mineral assemblage age and space time distribution of these mineral systems integrated with regional geological data and field observations we suggest that the three magmatic mineralization episodes are the result of distinct geodynamic regimes the triassic peraluminous granites and associated w sn nb ta mineralization formed during post collisional processes involving the south china block the north china craton and the indo china block mostly along the dabie sulu and songma sutures jurassic events were initially related to the shallow oblique subduction of the izanagi plate beneath the eurasian continent at about 175 ma but i type granitoids with porphyry cu and vein type pb zn ag deposits only began to form as a result of the breakup of the subducted plate at 170 160 ma along the nne trending qinzhou hangzhou belt also referred to as qin hang or shi hang belt which is the neoproterozoic suture that amalgamates the yangtze craton and cathaysia block a large subduction slab window is assumed to have formed in the nanling and adjacent areas in the interior of south china triggering the uprise of asthenospheric mantle into the upper crust and leading to the emplacement of metaluminous granitic magma and associated polymetallic w sn mineralization a relatively tectonically quiet period followed between 150 and 135 ma in south china from 135 ma onward the angle of convergence of the izanagi plate changed from oblique to parallel to the coastline resulting in continental extensional tectonics and reactivation of regional scale ne trending faults such as the tan lu fault this widespread extension also promoted the development of ne trending pull apart basins and metamorphic core complexes accompanied by volcanism and the formation of epithermal cu au deposits granite related polymetallic sn w deposits and hydrothermal u deposits between 120 and 80 ma with a peak activity at 100 90 ma

geochronology petrogenesis and tectonic significance of the jitang granitic pluton in eastern tibet sw china abstract the jitang granitic pluton which is situated in the southern margin of the north qiangtang block in eastern tibet may provide critical information about the source and derivation of the north qiangtang block during gondwana breakup and dispersion in this paper we report relevant data such as zircon u pb age whole rock major and trace element abundances and sr nd isotopes for the jitang pluton the major rock types of the pluton are granodiorite and biotite granite whole rock major element data reveal that the jitang pluton is a peraluminous s type granitic pluton the u pb age of zircons from the pluton is 219 1 1 7 ma which is 10 ma younger than the age of high pressure metamorphism in the longmu co shuanghu collisional suture between the north and south qiangtang blocks the jitang granitoids show pronounced negative ba eu sr anomalies high initial 87sr 86sr ratios from 0 7266 to 0 7389 and low end t values for from 11 1 to 13 2 which are remarkably similar to the gneisses and meta sedimentary rocks from the indian craton as well as the north qiangtang block the results from this study indicate that the jitang granitoids formed by melts derived from a crustal source with sr nd isotopic compositions similar to those of the indian cratonic crust we concur with the previous interpretation based on detrital zircon records that the north qiangtang block was derived from the indian gondwana

oxidized and reduced mineral assemblages in greenstone belt rocks of the st ives gold camp western australia vectors to high grade ore bodies in archaean gold deposits hydrothermal sulfide oxide gold mineral assemblages in gold deposits in the archaean st ives gold camp in western australia indicate extremely variable redox conditions during hydrothermal alteration and gold mineralization in space and time reduced alteration assemblages pyrrhotite pyrite occur in deposits in the southwest of the camp e g argo junction deposits and moderately to strongly oxidized assemblages magnetite pyrite hematite pyrite occur in deposits in the central corridor in the northeast e g north orchin revenge deposits reduced mineral assemblages flank the central corridor of oxidized deposits and locally cut across it along e w trending faults oxidized mineral assemblages in the central corridor are focused on gravity lows which are interpreted to reflect abundant felsic porphyritic intrusions at about 1 000 m below present surface hydrothermal magnetite predates and is synchronous with early phases of gold associated albite carbonate pyrite biotite chlorite hydrothermal alteration later stage gold associated pyrite is in equilibrium with hematite the spatial distribution and temporal sequence of iron sulfides and oxides with gold indicate the presence of at least two spatially restricted but broadly synchronous hydrothermal fluids with contrasting redox states sulfur isotope constraints support the argument that the different mineral assemblages reflect differences in redox conditions the 34s values for pyrite for the st ives gold camp range between 8 4 and 5 1 with the negative values occurring in oxidized magnetite rich domains and slightly negative or positive values occurring in reduced pyrrhotitic domains preliminary spatial and paragenetic analysis of the distribution of iron sulfides and oxides in the st ives camp suggests that gold grades are highest where the redox state of the hydrothermal alteration assemblages switches from relatively reduced pyrrhotite pyrite to relatively oxidized magnetite pyrite and hematite pyrite both in space and time gold deposition is inferred to have occurred where fluids of contrasting redox state mixed

ore genesis of the late cretaceous larong porphyry w mo deposit eastern tibet evidence from in situ trace elemental and s pb isotopic compositions abstract the late cretaceous ca 92 ma larong porphyry w mo deposit 39 44 mt wo3 0 1541 a newly discovered deposit in the easternmost bangong nujiang metallogenic belt bnmb is located in eastern tibet the w mo mineralization occurs as veins and stock works hosted in monzogranite porphyry granodiorite porphyry and surrounding quartz schist and can be divided into two main paragenetic stages the w mineralization stage stage i consists of various k feldspar quartz scheelite veins and the quartz sulfide stage stage ii is dominated by molybdenite and pyrite of which the latter can be further subdivided into three sub stages here we present la icpms in situ trace elements and s pb isotopes of sulfides from the larong deposit in order to constrain the sources of ore forming elements and the processes of mineralization our study shows that pyrite is rich in co and as molybdenite is rich in w pb and bi and chalcopyrite has high sn contents these results are consistent with the mineralization characteristics of the larong deposit where the main metallogenic elements are w and mo accompanied by bi sn and cu overall sulfides from the larong deposit have calculated 34svcdt values ranging from 0 25 to 6 37 suggesting a predominantly magmatic origin for sulfur from stage ii 1 to stage ii 2 to stage ii 3 the average 34svcdt values of pyrite change from 0 33 to 1 88 to 5 34 showing a progressive and gradual change in redox and temperature conditions molybdenite has high pb isotopic ratios 208pb 204pb 39 356 39 908 207pb 204pb 15 747 15 928 206pb 204pb 18 843 20 120 but low re contents and pyrite has low ni contents implying that the ore forming materials were mainly derived from the crust we propose that the w mo mineralization is genetically related to the late cretaceous monzogranite porphyry with the mineralization of w and mo occurring as a result of decreases in temperature and oxygen fugacity of the ore forming fluid exsolved from the magma in combination with previous studies our study led to the identification of three w dominated polymetallic metallogenic events and mineralization potential of igneous rocks in the bnmb

petrogenesis of ore bearing porphyries from the duolong porphyry cu au deposit central tibet evidence from u pb geochronology petrochemistry and sr nd hf o isotope characteristics abstract the duolong porphyry cu au deposit 5 4 mt at 0 72 cu 41 t at 0 23 g t au which is related to the granodiorite porphyry and the quartz diorite porphyry from the bangongco copper belt in central tibet formed in a continental arc setting here we present the zircon u pb ages geochemical whole rock sr nd whole rock and zircon in situ hf o isotopic data for the duolong porphyries secondary ion mass spectrometry sims zircon u pb analyses for six samples yielded consistent ages of 118 ma indicating a cretaceous formation age the duolong porphyries sio2 of 58 81 68 81 wt k2o of 2 90 5 17 wt belong to the high k calc alkaline series they show light rare earth element lree enriched distribution patterns with la yb n 6 1 11 7 enrichment in large ion lithophile elements e g cs rb and ba and depletion of high field strength elements e g nb with negative ti anomalies all zircons from the duolong porphyries share relatively similar hf o isotopic compositions 18o 5 88 7 27 ehf t 3 6 7 3 indicating that they crystallized from a series of cogenetic melts with various degrees of fractional crystallization this along with the general absence of older inherited zircons rules out significant crustal contamination during zircon growth the zircons are mostly enriched in 18o relative to mantle values indicating the involvement of an 18o enriched crustal source in the generation of the duolong porphyries together with the presence of syn mineralization basaltic andesite the mixing between silicic melts derived from the lower crust and evolved h2o rich mafic melts derived from the metasomatized mantle wedge followed by subsequent fractional crystallization fc and minor crustal contamination in the shallow crust could well explain the petrogenesis of the duolong porphyries significantly the hybrid melts possibly inherited the arc magma characteristics of abundant f cl cu and au elements and high oxidation state which contributed to the formation of the duolong porphyry cu au deposit

trace element and sulfur isotopic evidence for redox changes during formation of the wallaby gold deposit western australia abstract wallaby is a major gold deposit of the st ives gold field of western australia with an estimated resource of 8 million ounces of gold it has a well established paragenesis across five vein sets that displays macroscopic evidence of changing redox through time from hematite to magnetite micro analysis of pyrite from each vein generation shows a progressive and gradual change in redox conditions the sulfur isotope composition has a 34 s range of 7 7 to 9 8 using 3 m spots on the sensitive high resolution iron micro probe stable isotope shrimp si negative values indicative of an oxidized sulfur signature are found in the earliest generation of pyrite which coexists with hematite that also contains high concentrations of as ni zn ag sb cu and pb conversely positive values representative of reduced sulfur are found in later generations of pyrite with lower concentrations of as ni sb cu zn and pb these later pyrite crystals display higher as ni as sb and as bi and lower cu te these geochemical trends are the result of redox controlled transport and partitioning into pyrite of minor and trace elements now within the pyrite structure previous studies suggested a single orogenic event formed the wallaby deposit this is not supported by the present study trace element ratios such as as ni clearly delineate the high au generations and could be used as an exploration tool it is suggested that pyrite from the wallaby gold deposit formed via desulfidation and a gradual change in redox conditions within an evolving fluid and did not result from mixing of two separate fluids as previously advocated utilizing pyrite to link the entire fluid history of wallaby demonstrates the general use of pyrite as a valuable mineral tracer in gold bearing fluid systems

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

geology geochemistry and origin of lanuoma pb zn sb deposit in changdu area tibet the lanuoma pb zn sb polymetallic deposit is located 10 km north of jitang in changdu basin hosted by carbonate of triassic bolila group t3b the ore deposit occurs in an ore district which is considered to be a part of the sanjiang base metal ore forming belt along the lancang river it is unique in metallic composition of the ores different from the lead zinc deposits in the lanping basin and other major sedimentary rock hosted lead zinc deposits both in china and abroad the lanuoma ore deposit is characterized by mineralization of sb associated with pb zn ore composition analysis and electron microprobe analysis of ore minerals show that sb is closely associated with pb and occurs as robinsonite the ore deposit was formed at intermediate low to epithermal temperatures fluid inclusions in hydrothermal quartz and calcite veins are mainly in the two phase l v state at room temperature and are homogenized to the liquid phase between 140 and 350 their salinities w nacleq range from 2 to 10 results of bulk analysis of the fluid inclusions show that na and cl are most abundant components in liquid phase co2 and trace ch4 c2h6 were detected by bulk analysis and laser raman spectrometry in vapor phase of the fluid inclusions these data indicate that the ore forming fluid is nacl type co2 rich and hydrocarbon bearing fluid brine 13cv pdb values of hydrothermal calcite range from 3 5 to 1 8 and 18ov smow values of hydrothermal calcite range from 11 to 16 suggesting the characteristics between marine carbonate rocks and granite related fluids and the mixing of magmatic components with hydrothermal dissolution of marine carbonate the sulfide minerals have a restricted range of 34s values from 1 6 to 2 6 around zero indicating that the sulfur is of deep crustal derivation the authors hold that the mineralization was related to cenozoic magmatism associated with indo asian collision the sulfur and metals were derived mainly from igneous source or leached from crustal rocks related to tectono magmatic activity and partly from the triassic strata the fluid driven mechanism included topography driven fluid flow in cover sequences and deep magmatic heat source driving for large scale ore forming fluid flow

sanjiang tethyan metallogenesis in s w china tectonic setting metallogenic epochs and deposit types abstract tectonically the sanjiang tethyan metallogenic domain stmd is located within the eastern himalayan tibetan orogen in the sanjiang tethys southwestern china although this metallogenic domain was initiated in the early palaeozoic extensive metallogenesis occurred in the late palaeozoic late triassic and himalayan tertiary epochs corresponding tectonic settings and environments in the domain are an arc basin system related to the subduction of the palaeo tethyan oceanic slabs a post collision crustal extension setting caused by the lithospheric delamination or slab breakoff underneath the sanjiang tethys during the late triassic large scale strike slip faulting and thrusting systems due to the indo asian continent collision since the palaeocene in this metallogenic domain important gold copper base metals rare metals and tin ore belts incorporating a large number of giant deposits were developed the main types of deposits include 1 porphyry copper deposits controlled by a large scale strike slip fault system 2 vhms deposits mainly occurring in intra arc rift basins and post collision crustal extensional basins 3 shear zone type gold deposits in the ophiolitic melange zone along the thrusting shearing system 4 hydrothermal silver polymetallic deposits in the triassic intra continental rift basins and tertiary strike slip pull apart basins and 5 himalayan granite related greisen type tin and rare metallic deposits within the metallogenic epochs of the late palaeozoic to cenozoic the styles and types of the ore deposits changed from vhms types in the late palaeozoic through exhalative sedimentary type deposits in the late triassic to porphyry type copper deposits shear zone type gold deposits hydrothermal vein type silver polymetallic deposits greisen type tin and rare metal deposits in the cenozoic correspondingly ore forming metals also changed from a pb zn cu ag association through ag cu pb zn fe ag pb and ag au hg associations to ag cu pb zn cu mo au sn and li rb cs nb zr hf y ce sc associations

cretaceous magmatism and metallogeny in the bangong nujiang metallogenic belt central tibet evidence from petrogeochemistry zircon u pb ages and hf o isotopic compositions abstract porphyry cu au and porphyry skarn cu au mo deposits are widely distributed in the bangong nujiang metallogenic belt central tibet zircon u pb dating has revealed that cretaceous ore bearing intrusions related to cu au mo mineralization formed in two periods 118 115 ma and 90 88 ma these primarily high k calc alkaline series intrusions show light rare earth element enrichment lan ybn 6 06 20 2 and negative to no eu anomaly eu eu 0 39 1 02 on primitive mantle normalized diagrams all the intrusions show strong enrichments in large ion lithophile elements e g cs rb and k depletions in nb ta and ti and negative ba anomalies characteristic of arc magma these intrusions show a wide range of zircon ehf t values from 6 3 to 10 9 and 18o values from 5 82 to 10 82 suggesting variable contributions from mantle and crustal sources considering the 100 ma lhasa qiangtang collision the 118 115 ma magmas and related deposits were likely formed by melting of subduction metasomatized mantle wedge in a continental arc setting during northward subduction of the bangong nujiang ocean and then further evolved in the upper crust as a result of mash processes the younger 90 88 ma ore bearing magmas were potentially derived from melting of previously metasomatized lithospheric mantle during slab tear and break off after the lhasa qiangtang collision

evolution of the bangong nujiang tethyan ocean insights from the geochronology and geochemistry of mafic rocks within ophiolites abstract the bangong nujiang suture zone bnsz is located in the central tibetan plateau and represents the relict of the bangong nujiang tethyan ocean bnto this paper presents zircon u pb ages and whole rock geochemical and sr nd isotope data for the ophiolitic rocks from the rutog dongco dongqiao amdo and dengqen areas from west to east in the bnsz zircon u pb ages obtained from five gabbros and one leucogabbro from the five areas are 169 2 167 2 187 2 184 2 177 3 and 164 2 ma respectively mafic rocks gabbros and basalts in the bnsz can be divided into morb like and oib type based on geochemical data the morb like rocks are tholeiitic and can be further divided into n and e morb subtypes marked by depleted and flat ree patterns respectively all morb like rocks show supra subduction zone ssz geochemical affinities such as mild enrichment in the large ion lithophile elements and depletion in the high field strength elements coupled with high and positive whole rock e nd t values 8 1 to 5 4 the oib type rocks which formed in the early cretaceous 132 108 ma are exposed in the dongco dongqiao and tarenben areas and they consist mostly of alkali basalts with within plate geochemical characteristics and positive e nd t values 5 9 to 4 5 on the basis of these new data combined with information from the literature we further support that the bnto was an intra oceanic arc backarc basin that existed between the north lhasa subterrane nlt and the south qiangtang subterrane sqt during the early middle jurassic this basin may have been active until the early cretaceous when the oib type basalts erupted

origin and tectonic setting of the giant duolong cu au deposit south qiangtang terrane tibet evidence from geochronology and geochemistry of early cretaceous intrusive rocks abstract we constrain the origin and tectonic setting of the giant duolong porphyry epithermal cu au deposit in the south qiangtang terrane of northern tibet based on new zircon u pb ages and hf isotopic data as well as whole rock major and trace element data from poorly studied ore associated intrusions in the duolong area the la icp ms zircon u pb dating indicates that the ore associated rocks formed between 121 and 126 ma these ore associated rocks are geochemically similar to low k tholeiitic m type granitoids and to mid to high k calc alkaline i type granitoids they have variable and predominantly positive zircon e hf t values 1 4 to 15 6 and variable crustal model ages t c dm hf 176 1122 ma taking into account previous data and the regional geology of the study area we propose that the ore associated rocks originated from fractional crystallization of mantle derived mafic melts and magma mixing of mantle derived mafic and hybrid lower crust derived felsic melts and the hybrid lower crust included a mix of juvenile and older continental material the duolong porphyry epithermal cu au deposit formed within an ensialic forearc of an active continental margin as a result of the northwards subduction of the bangong nujiang ocean crust beneath the south qiangtang terrane

fluid rock interaction is decisive for the formation of tungsten deposits tungsten mineralization is typically associated with reduced granitic magmas of crustal origin while this type of magmatism is widespread economic tungsten deposits are highly localized with 90 produced from only three countries worldwide therefore the occurrence of reduced magmatism while necessary for tungsten enrichment seems to be insufficient to form such rare deposits here we explore the mechanisms that lead to wolframite precipitation and evaluate whether they may exert a decisive control on tungsten global distribution tungsten differs from other rare metals enriched in magmatic hydrothermal ore deposits because it is transported as an anionic species precipitation of the main tungstate minerals scheelite cawo 4 and wolframite fe mn wo 4 thus depends on the availability of calcium iron or manganese we demonstrate quantitatively that magmatic fluids at panasqueira portugal provide tungsten in solution whereas the host rock contributes the iron required to precipitate wolframite the combination of special source conditions with specific reactive host rocks explains why major wolframite deposits are rare and confined to a few ore provinces globally

gold mineralization in gaize area tibet gaize area is located in the western part of bangongcuo nujiang plate suture zone in tibet where original gold mineralization was poorly explored and studied and therefore the prospecting orientation was not clear based on the study of the metallogenic background characteristics and ages this paper discusses the model of gold mineralization in gaize area for the purpose of finding out some clues to gold prospecting studies show that gold deposits are mainly distributed in jurassic yanshiping group and mugagangri group both of which are typical epimetamorphic volcano sedimentary formations the yanshiping group occurs in tiegeshan area on the southern margin of qiangtang plate chip whereas the mugagangri group is present in dacha area and belongs to mugagangri block within the suture zone it is clearly known from tectonic and geochemical studies that the yanshiping group and mugagangri group were jurassic metastable flysch sedimentary rocks formed in the continental rift valley and marginal sea along the suture zone the formation of the strata was accompanied by large scale ophiolite and basic volcanic eruption as well as hydrothermal fluid activities on the ocean floor these processes concentrated such mantle derived materials as au and cu in the strata and hence the strata became the primary source bed of the gold ore deposits in the process of collision and amalgamation between the gangdise block and the qiangtang block at the late stage of early cretaceous the i type intermediate acidic magma rich in mantle derived components such as au and cu moved upward and heated the downward infiltrated marine water this caused the marine water to mix with the magmatic water thus forming the effective media such media extracted au from the primary source bed ophiolite basic and intermediate acidic magmatic rocks and carried au through various cracks in the rocks to form gold orebodies of transitional type between the altered rock type and the quartz vein type in late cretaceous the ocean basin came to a closure and the differential orogenic uplift took place as a result the top part of the original deposit was eroded resulting in the rebirth of the gold deposit and the formation of placers

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

simultaneous measurement of sulfur and lead isotopes in sulfides using nanosecond laser ablation coupled with two multi collector inductively coupled plasma mass spectrometers abstract we herein report the coupling of a nanosecond laser ablation system with a large scale multi collector inductively coupled plasma mass spectrometer nu1700 mc icpms np 1700 and a conventional nu plasma ii mc icpms np ii for the simultaneous laser ablation and determination of in situ s and pb isotopic compositions of sulfide minerals we found that the required aerosol distribution between the two spectrometers depended on the pb content of the sample for example for a sulfide containing 100 3000 ppm pb the aerosol was distributed between the np 1700 and the np ii spectrometers in a 1 1 ratio while for lead contents 3000 and

jurassic cretaceous granitoids and related tectono metallogenesis in the zapug duobuza arc western tibet abstract the zapug duobuza magmatic arc zdma located along the southern edge of the south qiangtang terrane in western tibet extends east west for 400 km small scattered granite and porphyry intrusions crop out in the zdma but a large amount of granite may be buried by late cretaceous to paleogene thrusting two stages of magmatism have been identified at 170 150 ma and 130 110 ma the widely distributed middle late jurassic granite intrusions in the zdma exhibit sr nd isotopic characteristics similar to those of ore bearing porphyries in the duolong giant cu au deposit and their ehf t values mostly overlap those of other porphyry cu mo deposits in the zdma and the gangdese zone the sr nd hf isotopic geochemistry suggests variable contributions of mantle and qiangtang crustal sources and indicates the presence of two new ore districts with potentials for cu au fe and pb zn ores located in the jiacuo liqunshan and larelaxin caima areas except for the duolong ore forming porphyries which show significant contributions of mantle components intruded into an accretionary melange setting the early cretaceous granites in other areas of the belt are of mostly crustal origin from sources in qiangtang felsic basement and permo carboniferous strata indicating the weak ore forming potential of skarn type fe and pb zn deposits the ephemeral but deep bangong co nujiang ocean in the early jurassic evolved into a shallow compressional marine basin in the middle late jurassic possibly transitioning to northward flat subduction of oceanic crust at this time the subducted slab broke off in the early cretaceous initiating a peak in arc magmatism and metallogenesis at 125 110 ma

petrogenesis and metallogenic setting of porphyries of the duobuza porphyry cu au deposit central tibet china abstract given that the duobuza deposit was the first porphyry cu au deposit discovered in central tibet the mineralization and mineralized porphyry in this area have been the focus of intensive research yet the overall porphyry sequence associated with the deposit remains poorly understood new geological mapping logging and sampling of an early granodiorite porphyry an inter mineralization porphyry and a late mineralization diorite porphyry were complemented by la icp ms zircon dating whole rock geochemical and sr nd isotopic analyses and in situ hf isotopic analyses for both inter and late mineralization porphyry intrusions all of the porphyry intrusions are high k and calc alkaline and were emplaced at ca 120 ma the geochemistry of these intrusions is indicative of arc magmatism as all three porphyry phases are enriched in light rare earth elements and large ion lithophile elements and depleted in heavy rare earth elements and high field strength elements these similar characteristics of the intrusions when combined with the relatively high 87 sr 86 sr i negative e nd t and positive e hf t values suggest that the magmas that formed the porphyries were derived from a common source region and shared a single magma chamber the magmas were generated by the mixing of upwelling metasomatized mantle wedge derived mafic magmas and magmas generated by partial melting of amphibolite within the lower crust the inter mineralization porphyry has the lowest e nd t and highest 87 sr 86 sr i values suggesting that a large amount of lower crust derived material was incorporated into the melt and that metals such as cu and au from the enriched lower crust were scavenged by the parental magma the relative mafic late mineralization diorite porphyry phase was formed by the residual magma in the magma chamber mixing with upwelling mafic melt derived from metasomatized mantle the magmatic hydrothermal evolution of the magma in the chamber released ore forming fluid that was transported mainly by the inter mineralization porphyry phase during the mineralization stage which ultimately formed the duobuza porphyry cu au deposit these porphyritic intrusions of the duobuza deposit have high mg and low la yb n values and show some high lile hfse ratios indicating the magma source was enriched by interaction with slab derived fluids combined with age constraints on the regional tectonic evolution these dating and geochemical results suggest that the duobuza porphyry cu au deposit formed in a subduction setting during the final stages of the northward subduction of the neo tethyan ocean

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

tectonic implications from re os dating of mesozoic molybdenum deposits in the east qinling dabie orogenic belt abstract the east qinling dabie molybdenum belt is part of a larger east west trending metallogenic belt in eastern china most of the molybdenum deposits occur as porphyry or porphyry skarn type but there are also some vein type deposits following systematic re os dating of molybdenite from 13 deposits and comparisons with two previously dated deposits we have recognized that the molybdenum mineralization in the east qinling dabie belt was developed during hydrothermal activity linked to magmatism and the emplacement of granitoid stocks three pulses of granitoid magmatism and mo mineralization are recognized corresponding to significant tectonic events in the east qinling dabie belt vein type deposits dated at 233 221 ma were formed in detachment fractures indicating localized extension within the collisional setting of the north china and yangtze cratons i type and transitional i and s type granites and related mineralization dated at 148 138 ma may have formed part of a continental magmatic arc with widespread magmatism and back arc extension caused by subduction of the izanagi or paleopacific plate beneath the eurasian continent in a wnw ese direction in the late jurassic early cretaceous both s type and transitional s and i type granite associated porphyry molybdenum deposits dated at 131 112 ma are part of an extensive mineralization event throughout east china that can be ascribed to regional large scale lithospheric thinning delamination and thermal erosion

subduction of a spreading ridge within the bangong co nujiang tethys ocean evidence from early cretaceous mafic dykes in the duolong porphyry cu au deposit western tibet abstract the intrusion of mafic dykes into a near trench accretionary prism and continental margin magmatism with characteristics that differ from those of adjacent arc magmatism are direct manifestations of the subduction of a spreading ocean ridge and the formation of a slab window in this paper we investigated mafic dykes intruded into the accretionary prism that hosts the duolong porphyry cu au deposit dcad of western tibet la icp ms analysis of u pb in zircon indicates that the dykes formed during the early cretaceous 126 127 ma the dykes are characterized by ehf t values from 2 44 to 11 8 twenty nine mafic dyke samples were divided into three groups based on their locations and geochemical compositions group i has nb 8 31 10 2 ppm nb la 0 71 1 20 and nb u 21 4 37 9 group ii has nb 40 5 52 6 ppm nb la 0 84 1 58 and nb u 18 8 47 8 and group iii has nb 65 7 105 ppm nb la 1 35 2 08 and nb u 36 5 73 8 group i is classified as nb enriched basalts enbs whereas groups ii and iii are classified as high nb basalts hnbs both the enbs and hnbs were derived from an adakite metasomatized mantle wedge that subsequently underwent crystallization of olivine and clinopyroxene the compositional variations of the studied dykes resulted mainly from mantle source heterogeneity the volume of the slab melts gradually increases from group i enbs to group ii hnbs and group iii hnbs leading to gradually increasing incompatible element concentrations considering their geochemical characteristics and field relationships as well as the unique characteristics of continental margin magmatism in the dcad we propose that the dykes emplaced in an extensional accretionary prism were derived from the northward subduction of a spreading ridge in the bangong co nujiang tethys ocean during the early cretaceous the ridge subduction event was also responsible for the generation of coeval adakites intermediate felsic intrusions the maierze bimodal volcanic rocks as well as the metallogenesis of the dcad

molybdenite re os and shrimp zircon u pb dating of duobuza porphyry copper deposit in tibet and its geological implications the duobuza porphyry copper deposit the first large size porphyry copper deposit discovered along the bangong nujiang suture zone is situated in the duobuza tectonic magmatic zone on the southern margin of the qiangtang sanjiang massif the main mineralized porphyry in the ore deposit is a granodiorite porphyry whose sio2 content varies from 61 37 to 67 73 65 16 on the average its ree content is 41 4 94 10 6 and the lree content is higher than the hree content suggesting the enrichment of lree as for trace elements the porphyry shows enrichment of rb k th ba la ce sr and depletion of nb ta p ti the major rare earth and trace elements of the mineralized porphyry have characteristics of volcanic rocks formed in the island arc the zircon shrimp dating 14 samples of duobuza granodiorite porphyry gave 206pb 238u concordant ages from 116 5 4 6 ma to 125 3 4 7 ma with a weighted mean age of 120 9 2 4 ma which indicates the age of the copper mineralized porphyry rock meanwhile the 187re and 187os content of molybdenite from the ore deposit was determined by inductively coupled plasma mass sperctrometry icp ms and the results show that the re os model ages of the deposit are from 117 6 1 3 to 118 5 1 4 ma and its isochron age 118 0 1 5 ma which have accurately determined the timing of mineralization the age of the ore deposit is consistent with the evolution of the bange nujiang archipelagic arc basin system in early cretaceous implying that the duobuza copper deposit was formed in an archipelagic are basin system similar to the system of southeast asia

the nadun cu au mineralization central tibet root of a high sulfidation epithermal deposit abstract a new high sulfidation epithermal cu au occurrence nadun has been discovered adjacent to the cretaceous duolong porphyry cu au deposit within the bangong nujiang metallogenic belt central tibet the nadun cu au mineralization is hosted in a tectonic hydrothermal breccia with advanced argillic alteration which occurs above sandstone associated with quartz pyrite veins the granodiorite porphyry with strong argillic alteration yields a zircon u pb age of 119 1 1 3 ma whereas the weakly argillic granodiorite porphyry intruded into the breccia has a younger age of 116 1 1 3 ma this indicates that cu au epithermal mineralization likely occurred between 116 ma and 119 ma consistent with the duration of magmatic hydrothermal activity at duolong 115 118 ma and providing evidence that nadun and duolong were formed during the same event moreover the nadun and duolong porphyries have similar hf isotopic compositions ehf t values ranging from 8 8 to 8 1 mean 5 0 1 1 n 32 likely indicating that the deposits are comagmatic in addition boiling assemblages in vapor rich inclusions coexisting with brines occur in early stage quartz pyrite veins and likely record phase separation at a temperature of 550 300 c and pressure of 700 110 bars most liquid rich fluid inclusions formed at the breccia stage show similar salinity 1 7 19 3 wt nacl equiv to vapor rich inclusions from the underlying quartz pyrite veins likely indicating vapor contraction during cooling at elevated presssure this suggests that quartz pyrite veins may act as conduits for ore forming fluid traveling from the porphyry to the epithermal hydrothermal system o and h isotopic compositions 18ofluid 0 42 9 71 and d 102 to 66 suggest that ore forming fluids are dominantly from a magmatic source with a minor addition of meteoric water at a later stage the s and fe isotope compositions of sulfides 34s 5 9 to 0 5 and 57fe 2 15 to 0 17 decrease from the quartz pyrite vein to breccia ore indicating that ore forming fluids gradually become so42 enriched and relatively oxidized this body of evidence suggests that the nadun cu au mineralization may represent the root of a high sulfidation epithermal deposit

tectono magmatic evolution of late jurassic to early cretaceous granitoids in the west central lhasa subterrane tibet abstract there is ongoing debate as to the subduction direction of the bangong nujiang ocean during the mesozoic northward southward or bidirectional subduction arc related intermediate to felsic intrusions could mark the location of the subduction zone and more importantly elucidate the dominant geodynamic processes we report whole rock geochemical and zircon u pb and hf isotopic data for granitoids from the west central lhasa subterrane e80 to e86 all rocks show metaluminous to peraluminous calc alkaline signatures with strong depletion of nb ta and ti enrichment of large ion lithophile elements e g cs rb k a negative correlation between sio 2 and p 2 o 5 and a positive correlation between rb and th all these features are indicative of i type arc magmatism new zircon u pb results together with data from the literature indicate continuous magmatism from the late jurassic to the early cretaceous 160 to 130 ma zircon u pb ages for samples from the northern part of the west central lhasa subterrane e80 to e82 30 yielded formation ages of 165 to 150 ma whereas ages of 142 to 130 ma were obtained on samples from the south this suggests flat or low angle subduction of the bangong nujiang ocean consistent with a slight southward decrease in zircon ehf t values for late jurassic rocks considering the crustal shortening the distance from the bangong nujiang suture zone and a typical subduction zone melting depth of 100 km the subduction angle was less than 14 for late jurassic magmatism in the central lhasa interior consistent with flat or low angle subduction compared with late jurassic rocks main ehf t values of 16 to 7 early cretaceous rocks 145 to 130 ma show markedly higher ehf t values mainly 8 to 0 possibly indicating slab roll back likely caused by slab foundering or break off combined with previously published works on arc magmatism in the central lhasa and west part of the southern qiangtang subterranes our results support the bidirectional subduction of the bangong nujiang ocean along the bangong nujiang suture zone and indicates flat or low angle southward subduction 165 to 145 ma followed by slab roll back 145 to 130 ma

temporal variability in spatial correlation of daily rainfall composite correlation fields based on a 5 year record of daily rainfall at 67 stations throughout tunisia were used to investigate spatial and temporal properties of rainfall fields the composite correlation fields had in general banded or elliptical patterns and with the elongations generally along the coastline or the topographical ridges the banded patterns occurred usually during the rainy season and the elliptical patterns occurred toward the summer or early autumn the ratio of width to length of the elongated correlation fields varied in general between 0 1 and 0 4 the composite correlation fields defined as the area within the 0 7 correlation isoline were usually less than about 8 000 km2 the mean monthly rainfall was moderately correlated with the size of the composite correlation fields the major orientation of the coastline seems to be a more important factor for the rainfall generation than are local irregularities in the coastal orientation and local topographical differences

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

gold telluride nanoparticles revealed in arsenic free pyrite pyrite the most abundant sulfide on earth and a common component of gold deposits can be a significant host for refractory gold this is the first documentation of pore attached composite au telluride nanoparticles in arsenic free pyrite trace elements mapping in pyrite from an intrusion hosted au deposit with orogenic overprint dongping china shows trails of tellurides overlapping co ni zonation intragranular microfracturing anomalous anisotropy and high porosity are all features consistent with devolatilization attributable to the orogenic event the pyrite hosted nanoparticles are likely the frozen solid expression of te rich au ag pb bearing vapors discharged at this stage nanoparticle formation as presented here provides the smallest scale tool to fingerprint au trapping during crustal metamorphism

pyrite compositions from vhms and orogenic au deposits in the yilgarn craton western australia implications for gold and copper exploration abstract the archaean yilgarn craton western australia is a world class metallogenic province hosting considerable resources of au ag ni cu zn and fe here we present trace element compositions of pyrite from 30 orogenic au and 5 volcanic hosted massive sulphide vhms deposits across the yilgarn pyrites from vhms deposits tend to have higher sn se cu pb bi and lower ni relative to orogenic deposits vhms deposit pyrites commonly have co ni as 100au te au se te orogenic gold deposits could be subdivided based on association of au with as or te pyrites from au as ores generally have pb bi 5 se te 5 pb sb 100 and the majority of au is refractory in pyrite structure at the same time au te association pyrites are characterised by lower values of pb bi se te and tl te higher values of ag au pb sb and au generally resides in inclusions of different compositions our data can be used at the exploration stage to distinguish between vhms vs orogenic au signatures for all studied deposits inclusion populations are summarised with implications for au and ag deportment orogenic au deposits from the yilgarn mostly have multistage formation histories reflected in the presence of multiple generations of pyrites however only some deposits record multiple high au mineralisation events

temporal and spatial variations of late mesozoic granitoids in the sw qiangtang tibet implications for crustal architecture meso tethyan evolution and regional mineralization abstract the western segment of the south qiangtang terrane w sqt is an ideal place to investigate the late mesozoic crustal architecture tectonomagmatic evolution and regional mineralization of this terrane where the emplacement of voluminous late mesozoic granitoids provides favorable conditions to form some world class porphyry cu au mineral deposits as well as a series of fe pb zn and w mineral deposits or occurrences here we synthesize the spatial distribution geological geochronological geochemical and isotopic data of the late mesozoic granitoids and associated mineral deposits or occurrences in w sqt these data suggest that the granitoid magmatism in w sqt lasted from ca 170 ma to ca 110 ma with two magmatic flare ups at ca 170 150 ma and ca 130 110 ma in particular the granitoids formed between ca 170 ma and ca 120 ma are generally younger from north to south indicating a southward migration of magmatism during this period the compositions of the granitoids vary considerably across w sqt becoming more reduced and evolved from the ancient coastal area i e the area close to the bangong nujiang suture zone to the continental interior area moreover the zircon ehf t values of the granitoids also gradually decrease from the ancient coastal area to the interior area indicating the ancient crustal components in the source of the granitoids increase continentward we therefore concluded that an ancient crustal basement with archean to paleoproterozoic ages must exist beneath the interior of the south qiangtang terrane i e the south qiangtang terrane has been an older microcontinent based on this conclusion a comprehensive model involving the flat subduction break off rollback and complete detachment of the bangong nujiang oceanic slab was proposed for the late mesozoic tectonomagmatic and metallogenic evolution of w sqt in particular the thickening of w sqt crust during late jurassic and the occurrence of magmatic gap ca 140 130 ma were interpreted to be associated with the flat subduction of bangong nujiang oceanic slab the development of regional extension recorded by early cretaceous 127 122 ma mafic dikes and bimodal volcanic rocks and the southward migration of granitoid magmatism were attributed to the break off and rollback of bangong nujiang oceanic slab our study also shows that the early cretaceous mantle derived juvenile crust derived highly oxidized and less evolved granitoids are most favourable for the generation of significant porphyry cu au deposits while the middle late jurassic mature crust derived relatively reduced and highly evolved granitoids are highly prospective for pb zn and w mineralisations in addition the granitoids generated by a mixture of mantle derived and mature crust derived components have high potential for skarn fe cu deposits for the w sqt magmatic belt as a whole cu au prospective granitoids fe cu prospective granitoids and pb zn w prospective granitoids exist in the south the middle and the north respectively

origin of the luping pb deposit in the beiya area yunnan province sw china constraints from geology isotope geochemistry and geochronology abstract the luping pb deposit a newly discovered pb fe au ag zn polymetallic deposit close to the cenozoic beiya porphyry related au fe cu pb zn ag deposit is located in the central sanjiang three rivers jinshajiang lancangjiang and nujiang region western yangtze block in southwestern china ore bodies of the luping deposit are mainly stratiform type host in the middle triassic beiya formation limestone and lower triassic qingtianbao formation sandstone and occur along nnw trending bedding plane faults within axis of beiya qinghe syncline three ore types namely the pb au sulfide fe au and au ores can be discerned regarding their ore metal association with reserves of 2 7 million tonnes mt average grade 3 06 wt pb 0 66 g t au 41 g t ag and 0 82 wt zn 3 mt average grade 30 wt fe 0 96 g t au and 31 g t ag and 0 67 mt average grade 2 16 g t au and 13 g t ag respectively pb au sulfide ores contain mainly galena siderite native gold sphalerite and pyrite with minor chalcopyrite pyrrhotite and arsenopyrite and gangue minerals such as quartz calcite and dolomite sulfide ore textures include mainly brecciated banded and vein and minor massive and disseminated la icp ms zircon u pb dating of alkali rich quartz syenite porphyry from drill holes yielded a late eocene priabonian age 36 2 0 4 ma broadly coeval to the zircon u pb ages ca 38 ma 31 ma of alkaline porphyries and molybdenite re os age 36 9 0 3 ma from the beiya deposit near luping calcite separates have 13cpdb and 18osmow values ranging from 5 8 to 5 1 average 5 6 and 13 2 to 14 7 mean 13 6 respectively suggesting association with the mantle the sulfides have a narrow range of 34scdt values 0 8 2 8 mean 1 8 which is similar to that of mantle derived s 0 3 206pb 204pb 207pb 204pb and 208pb 204pb values of the sulfides range from 18 62 to 18 69 15 66 to 15 70 and 38 92 to 39 08 respectively similar to those of the porphyry whole rock 206pb 204pb 36 ma 18 61 18 71 207pb 204pb 36 ma 15 64 15 77 and 208pb 204pb 36 ma 38 88 39 32 ore deposit geology and c o s pb isotopic data suggest that the sources of metals and ore forming fluids were likely to be derived from the alkali rich porphyries in the beiya area we propose that the luping deposit is best classified as an epithermal pb polymetallic deposit associated with the beiya alkaline porphyries ca 36 ma 31 ma similar to other deposits related to the cenozoic alkaline porphyries in the jinshajiang red river ailaoshan metallogenic belt the luping deposit may have been formed in the india eurasia post collisional setting when partial melting occurred in the triassic stagnant slab that thickened the lower crust and the upper mantle producing the alkaline magmatism and its associated mineralization

late triassic granitic magmatism in the eastern qiangtang eastern tibetan plateau geochronology petrogenesis and implications for the tectonic evolution of the paleo tethys abstract triassic granites are widely exposed in the central qiangtang northern tibetan plateau they therefore made an important contribution to the growth of the tibetan plateau in this paper we present zircon u pb dating and hf isotopic results and whole rock elemental and sr nd isotopic analyses of the dongdashan dds batholith in the central qiangtang in order to understand their petrogenesis and tectonic setting la mc icp ms zircon u pb results show that the dds batholith was emplaced at 220 3 0 7 ma all the granites in the dds possess high a cnk values 1 0 and display peraluminous characteristics similar to s type granite their strongly fractionated ree patterns la yb n 6 98 13 9 with conspicuous negative eu anomalies eu eu 0 51 0 67 together with negative e nd t and e nd t values and depleted nd and hf model ages suggest that the dds granitic magma had a dominantly crustal source likely the paleoproterozoic basement i e the ningduo and caoqu group metasediments in the area in combination with regional studies our new geochemical data and geochronological results demonstrate that the late triassic magmatism was generated in a post collisional tectonic setting the spatial distribution pattern of the mesozoic igneous rocks coupled with the exhumation of high pressure metamorphic rocks in the central qiangtang favors a slab breakoff model which resulted in post collisional extension and asthenospheric upwelling that induced large scale partial melting of the middle lower crust to produce voluminous amounts of felsic magma therefore the occurrence of the late triassic post collisional magmatism and particularly the exhumation of high pressure eclogites and blueschists as well as their presence in the lowermost portion of the late triassic volcanoclastics in the qiangtang basin clearly indicate that the final closure of the of paleo tethys ocean and associated continent continent collision between the gondwana derived western qiangtang and eastern qiangtang terranes had not been completed until the early mid triassic

petrogenesis and tectonic implications of late cretaceous highly fractionated i type granites from the qiangtang block central tibet abstract the tectonic evolution of the lhasa and qiangtang collision zone is poorly understood due to a lack of pivotal magmatic records and complex geology in central tibet in this study we present zircon u pb ages whole rock major and trace elements and sr nd pb isotopic data for the newly discovered chuburi pluton in the southern qiangtang block zircon u pb data reveal that the chuburi pluton was emplaced during the late cretaceous ca 73 ma bulk rock analyses show that this intrusion is characterized by high sio2 na2o and k2o but low mgo cao and p2o5 the granites are enriched with large ion lithophile elements and light rare earth elements with marked eu anomalies and there are few heavy rare earth elements and high field strength elements these geochemical features indicate that the chuburi pluton is a highly fractionated i type granite the nine granitic samples show high 87sr 86sr i ratios 0 7064 0 7089 negative end t values 1 94 to 5 59 and have nd isotopic model ages ranging from 0 76 to 0 97 ga the initial pb isotopic ratios of the chuburi pluton is uniform 206pb 204pb t 18 774 18 884 207pb 204pb t 15 695 15 713 208pb 204pb t 39 362 39 613 based on geochemical characteristics of the chuburi pluton and consideration of the region geological setting we suggest that the parent magma was generated by magmatic mixing of mantle and lower crust and then undergoing extensive fractional crystallization with removal of k feldspar plagioclase mafic mineral and minor accessory mineral the crust beneath the central tibet may have been significantly thickened following the final lhasa qiangtang amalgamation we argue the generation of the chuburi pluton can be interpreted as a result of regional lithospheric delamination

pyrite as a record of hydrothermal fluid evolution in a porphyry copper system a sims empa trace element study porphyry copper deposits are currently the world s largest source of copper and molybdenum and are also among the largest reservoirs of gold in the upper crust despite the fact that pyrite is a ubiquitous mineral phase in these deposits and secondary cu enrichment processes are commonly controlled by the abundance of this sulfide the major and trace element chemistry of pyrite from porphyry systems remains unconstrained in this study we report the first comprehensive trace element database of pyrite from the dexing deposit china s largest porphyry cu deposit by combining high spatial resolution and x ray mapping capabilities of electron microprobe analysis empa with low detection limits and depth profiling capabilities of secondary ion mass spectrometry sims in a suite of samples from the dexing deposit we show that the concentrations of precious metals e g au ag metalloids e g as sb se te and heavy metals e g cu co ni zn hg in pyrite from porphyry systems are more significant than previously thought among the elements analyzed cu as au and ni are the most abundant with concentrations that vary from sub ppm levels to a few wt i e 6 wt cu 3 wt as 0 25 wt au and 0 2 wt ni detailed wavelength dispersive spectrometry wds x ray maps and sims depth vs isotope concentration profiles reveal that pyrite from the dexing deposit is characterized by complex chemical zoning where the studied elements occur in different mineralogical forms while as occurs as a structurally bound element in pyrite cu and au can occur as both solid solution and micro to nano sized particles of chalcopyrite and native au or au tellurides respectively indicating that pyrite can control metal speciation and partitioning during porphyry cu mineralization the well developed oscillatory zoning detected in pyrite where cu rich as depleted growth zones alternate with cu depleted as rich layers indicates that cu is geochemically decoupled from as suggesting that this selective partitioning of metals into pyrite is most likely the result of changes in hydrothermal fluid composition

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

gold and trace element zonation in pyrite using a laser imaging technique implications for the timing of gold in orogenic and carlin style sediment hosted deposits laser ablation icp ms imaging of gold and other trace elements in pyrite from four different sedimenthosted gold arsenic deposits has revealed two distinct episodes of gold enrichment in each deposit an early synsedimentary stage where invisible gold is concentrated in arsenian diagenetic pyrite along with other trace elements in particular as ni pb zn ag mo te v and se and a later hydrothermal stage where gold forms as either free gold grains in cracks in overgrowth metamorphic and or hydrothermal pyrite or as narrow goldarsenic rims on the outermost parts of the overgrowth hydrothermal pyrite compared to the diagenetic pyrites the hydrothermal pyrites are commonly depleted in ni v zn pb and ag with cyclic zones of co ni and as concentration the outermost hydrothermal pyrite rims are either as au rich as in moderate to highgrade deposits such as carlin and bendigo or co ni rich and as au poor as in moderate to low grade deposits such as sukhoi log and spanish mountain the early enrichment of gold in arsenic bearing syngenetic to diagenetic pyrite within black shale facies of sedimentary basins is proposed as a critical requirement for the later development of carlin style and orogenic gold deposits in sedimentary environments the best grade sediment hosted deposits appear to have the gold climax event toward the final stages of deformation related hydrothermal pyrite growth and fluid flow

northward subduction of bangong nujiang tethys insight from late jurassic intrusive rocks from bangong tso in western tibet abstract new zircon la icpms u pb age data whole rock major and trace elements and zircon hf isotopic data of intrusive rocks from larelaxin and caima plutons in the southern margin of the western qiangtang subterrane provide important evidence of northward subduction of the bangong nujiang tethyan ocean lithosphere host granitoids including quartz diorites granodiorites and syenogranites and associated mafic varieties including gabbroic enclaves dioritic dikes and enclaves and quartz dioritic enclaves are investigated in this study five host granitoid samples are dated at 163 160 ma and one dioritic dike and three dioritic enclave samples are dated at 162 158 ma which indicates that these rocks were contemporaneous the quartz diorites and granodiorites are normal calc alkaline i type granitoids the syenogranites are characterized by high sio 2 74 77 wt and differentiation index di 92 97 and marked depletion in ba nb ta sr p ti and eu thus indicating that they are highly fractionated i type granitoids the host granitoids exhibit uniform zircon e hf t values 1 4 to 1 9 considering the current data and their negative whole rock e nd t values 4 7 to 3 5 reported in recent studies these rocks can be interpreted to have resulted from the partial melting of ancient mafic lower crust with varying contributions from mantle derived or juvenile crust derived components one gabbroic enclave sample exhibits high al 2 o 3 18 3 wt low mgo 3 3 wt high tio 2 1 4 wt and high nb 24 ppm and is geochemically similar to high alumina basalt hab and high nb basalt hnb this indicates that the gabbroic enclave originated from the partial melting of mantle wedge peridotite that was metasomatized by slab melting and subsequently experienced significant fractional crystallization of olivine and clinopyroxene the dioritic dike and enclave samples yield e hf t values 1 6 to 3 1 similar to those of the host granitoids they most likely originated from magma mixing between mantle derived and crust derived melts at or close to the moho the intrusive rocks with geochemical diversity of the larelaxin and caima plutons from bangong tso in western tibet can be interpreted to have resulted from melting assimilation storage and homogenization a mash process above subduction zones thus indicating that the bangong nujiang tethyan ocean lithosphere was subducted northward beneath the western qiangtang subterrane during the late jurassic

pyrite and pyrrhotite textures and composition in sediments laminated quartz veins and reefs at bendigo gold mine australia insights for ore genesis the various types textures and compositional zoning of pyrite in the gold bearing saddle reefs quartz veins and surrounding sedimentary rocks provide new information on the potential source and timing of gold and arsenic and related fluid processes responsible for mineralization at bendigo nodular diagenetic pyrite in the black shale tops to sandstone turbidites is enriched in invisible gold and arsenic with mean values of 0 61 ppm au 1 300 ppm as and au ag 1 based on la icpms analyses other elements enriched in the diagenetic pyrite within the organic rich shales are mn zn mo cu v ba ag cd tl co ni bi pb and te in contrast euhedral and growth zoned hydrothermal pyrite in the turbidites and bedding parallel laminated quartz veins contains lower contents of most trace elements but has higher contents of invisible au and as especially on the outermost rim of the pyrite the gold rich pyrite rims generally become thicker a few to hundreds of microns in proximity to the gold bearing saddle reefs pyrite in the reef commonly has the highest levels of invisible au and as and the lowest levels of other trace elements it is characterized by au ag 1 and au pb 0 01 in the deepest stratigraphic levels below known productive gold reefs diagenetic pyrite in the most carbonaceous shales has been replaced by pyrrhotite during metamorphism la icpms analyses reveal that the disseminated pyrrhotite contains similar levels of ni and co to the diagenetic pyrite but is strongly depleted in as and au the spatial relationships between organic rich shales folded bedding parallel laminated quartz veins and gold arsenic bearing saddle reefs combined with the consistent trends in the trace element composition of pyrite hosted by these three geological elements is interpreted to indicate that the black shales were an initial source of au and as and the laminated quartz veins acted as the initial pathways for hydrothermal fluid flow carrying au and as from the source shales to the saddle reefs maximum gold and arsenic input into the reefs principally as free gold plus arsenopyrite occurred late during deformation toward the end of the hydrothermal cycle and is expressed by the au as rich rims to hydrothermal pyrite in the sedimentary host rocks laminated quartz veins and reefs this corresponds with final fold lockup and the development of through going fault arrays linking adjacent anticlines the source of au and as for this final and most economically important fluid flow event is considered to be from carbonaceous shales deeper in the basin where original gold bearing diagenetic arsenian pyrite reacts with organic matter and is converted to pyrrhotite with release of au as and s to the metamorphic fluid

late cretaceous transition from subduction to collision along the bangong nujiang tethys new volcanic constraints from central tibet abstract this study deals with arc type and subsequent bimodal volcanic rocks interbedded with late cretaceous sedimentary formations near gaize central tibet that shed new light on the tethyan evolution along the bangong nujiang suture unit i consists of trachyandesites interbedded with fine grained sandstone slate and limestone zircon dating on a trachyandesite sample yields a 206pb 238u age of 99 1 ma the trachyandesites are characterized by strong enrichment in lile but depletion in hfse low zircon saturation temperatures tzr 642 727 c and high oxygen fugacity fmq 0 67 0 73 indicating their arc affinities unit ii comprises a bimodal basalt rhyolite suite interbedded with coarse grained sandstone and conglomerate zircon dating on two rhyolitic samples yield 206pb 238u ages of 97 1 87 0 ma in contrast with unit i trachyandesites unit ii basalts and rhyolites exhibit oib like trace element patterns high temperatures t 1298 1379 c for basalts tzr 855 930 c for rhyolites and low oxygen fugacity fmq 3 37 0 43 suggesting that unit ii bimodal volcanic rocks probably formed in an extensional setting the sr nd isotopes of both unit i 87sr 86sri 0 7052 0 7074 end t 2 21 1 02 and unit ii 87sr 86sri 0 7057 0 7098 end t 3 22 0 88 rocks are similar to mantle wedge derived volcanic rocks within the southern qiangtang block the parental magma of unit i trachyandesites was formed by fluid induced melting of the mantle wedge above the subducted bangong nujiang tethyan slab and contaminated by crustal materials during mash process within a deep crustal hot zone and unit ii bimodal volcanic rocks were derived by melting of upwelling asthenosphere and a mildly metasomatized mantle wedge during the lhasa qiangtang collision we propose that the transition from the bangong nujiang tethyan subduction to the lhasa qiangtang collision occurred during the late cretaceous in central tibet

geochemical investigation of early cretaceous igneous rocks along an east west traverse throughout the central lhasa terrane tibet article i nfo bulk rock major and trace element sr nd isotope zircon u pb and hf isotope data are reported for early cretaceous igneous rocks sampled along an east west traverse through the central lhasa subterrane e80 00 e89 in southern tibet these results offer new insights into the pre cenozoic geology and tectonomagmatic evolution of the lhasa terrane and provide boundary conditions for the origin and evolution of the tibetan plateau our new data together with data from the literature indicate that the early cretaceous magmatism in the central lhasa subterrane lasted for a long period 143 102 ma with a magmatic flare up at 110 ma the latter is accompanied by mafic magmatism in this terrane the silicic rocks are metaluminous to peraluminous and enrichedinrb th and u and depleted inba nb ta sr p and ti withvarying initial 87

the origin and pre cenozoic evolution of the tibetan plateau different hypotheses have been proposed for the origin and pre cenozoic evolution of the tibetan plateau as a result of several collision events between a series of gondwana derived terranes e g qiangtang lhasa and india and asian continent since the early paleozoic this paper reviews and reevaluates these hypotheses in light of new data from tibet including 1 the distribution of major tectonic boundaries and suture zones 2 basement rocks and their sedimentary covers 3 magmatic suites and 4 detrital zircon constraints from paleozoic metasedimentary rocks the western qiangtang amdo and tethyan himalaya terranes have the indian gondwana origin whereas the lhasa terrane shows an australian gondwana affinity the cambrian magmatic record in the lhasa terrane resulted from the subduction of the proto tethyan ocean lithosphere beneath the australian gondwana the newly identified late devonian granitoids in the southern margin of the lhasa terrane may represent an extensional magmatic event associated with its rifting which ultimately resulted in the opening of the songdo tethyan ocean the lhasa northern australia collision at similar to 263 ma was likely responsible for the initiation of a southward dipping subduction of the bangong nujiang tethyan oceanic lithosphere the yarlung zangbo tethyan ocean opened as a back arc basin in the late triassic leading to the separation of the lhasa terrane from northern australia the subsequent northward subduction of the yarlung zangbo tethyan ocean lithosphere beneath the lhasa terrane may have been triggered by the qiangtang lhasa collision in the earliest cretaceous the mafic dike swarms ca 284 ma in the western qiangtang originated from the panjal plume activity that resulted in continental rifting and its separation from the northern indian continent the subsequent collision of the western qiangtang with the eastern qiangtang in the middle triassic was followed by slab breakoff that led to the exhumation of the qiangtang metamorphic rocks this collision may have caused the northward subduction initiation of the bangong nujiang ocean lithosphere beneath the western qiangtang collision related coeval igneous rocks occurring on both sides of the suture zone and the within plate basalt affinity of associated mafic lithologies suggest slab breakoff induced magmatism in a continent continent collision zone this zone may be the site of net continental crust growth as exemplified by the tibetan plateau c 2012 international association for gondwana research published by elsevier b v all rights reserved

geochronology geochemistry and zircon hf isotopic compositions of mesozoic intermediate felsic intrusions in central tibet petrogenetic and tectonic implications abstract mesozoic intermediate felsic intrusions are widely distributed in the southern qiangtang terrane central tibet zircon u pb dating shows that these intrusions formed in two periods in the jurassic 169 150 ma and cretaceous 127 113 ma they mostly belong to the high k calc alkaline series and show strong enrichments in large ion lithophile elements e g cs rb and k depletions in nb ta and ti and negative ba anomalies on primitive mantle normalized diagrams p 2 o 5 contents decrease with increasing sio 2 content and th contents increase with increasing rb content consistent with the evolution trend of i type magmas these intrusions show a wide range of zircon ehf t values from 19 4 to 11 2 including in rocks with similar sio 2 contents suggesting variable contributions from mantle and qiangtang crustal sources fine grained mafic to intermediate igneous enclaves in jurassic intrusions have similar zircon u pb ages and similar or slightly higher zircon ehf t values to the host rocks suggesting that the enclave magmas were derived from mixed magmas at depth and injected into more evolved magmas in upper crustal magma chambers magma mixing is also supported by the wide range of zircon hf isotopic compositions ehf t 19 4 to 2 5 from within individual jurassic and cretaceous intrusions and jurassic enclaves the jurassic cretaceous magmas likely formed in a continental arc setting during subduction of the bangong nujiang ocean between 170 and 110 ma and evolved in the upper plate crust by mash processes

in situ trace element and sulfur isotope of pyrite constrain ore genesis in the shapoling molybdenum deposit east qinling orogen china abstract the early cretaceous ca 128 ma shapoling vein type molybdenum mo mineralization associated with the huashan intrusion is a newly discovered deposit in the xiong ershan district east qinling china where pyrite is a ubiquitous mineral phase here we present results from an integrated study on the texture in situ trace element chemistry from laser ablation inductively coupled plasma mass spectrometry la icp ms and sulfur isotopic composition using secondary ion mass spectrometry sims with a view to understand the geochemical variation genesis of mo mineralization and ore forming process the distinct textural patterns as revealed by petrographic observations suggest three types of pyrites py1 is composed of coarse grained euhedral pyrite in the wall rock and early barren quartz vein at stage i py2 is represented by subhedral anhedral grains coexisting with molybdenite in quartz veins at stage ii and py3 forms irregular interstitial grains in the quartz k feldspar molybdenite dominated veins at stage iii the mo enrichment mainly occurred in py3 with co ni ratios 1 and 34s values mainly