fluid inclusion h o s pb and noble gas isotope studies of the aerhada pb zn ag deposit inner mongolia ne china abstract the aerhada pb zn ag deposit is located in the western segment of the great hinggan range ag pb zn cu mo au fe metallogenic belt in ne china orebodies occur mainly as vein type and are hosted by sandstone and siliceous slate three stages of primary mineralization including an early arsenopyrite pyrite quartz a middle polymetallic and silver sulfides quartz and a late sphalerite pyrite calcite fluorite are recognized four types of fluid inclusions have been identified in the ore bearing quartz and fluorite veins i e liquid rich gas rich three phase co 2 aqueous inclusions and pure gas or liquid aqueous inclusions microthermometric studies on fluid inclusions reveal that homogenization temperatures from early to late stages range from 253 to 430 c 195 to 394 c and 133 to 207 c respectively fluid salinities range from 2 9 to 14 0 wt nacl equiv the vapor composition of the ore fluid is dominated by h 2 o co 2 and ch 4 with minor proportions of n 2 the fluid 18 o h2o and d h2o values vary from 1 6 to 9 3 and 122 to 56 respectively and reflect a magmatic fluid and a meteoric fluid dominant hydrothermal system for the early and late stages of mineralization respectively the calculated 34 s h2s values of hydrothermal fluids in equilibrium with sulfides range from 5 2 to 7 1 suggesting a mixed source for sulfur i e the local magmatic and sedimentary rocks the pb isotope compositions of sulfides are similar to those of the local magmatic and sedimentary rocks implying that lead and possibly silver relate to these sources the noble gas isotope compositions of fluid inclusions hosted in ore minerals suggest that the ore forming fluids were dominantly derived from a deep mantle source fluid mixing and dilution are inferred as the dominant mechanisms for ore deposition the aerhada pb zn ag deposit can be classified as a medium to low temperature hydrothermal vein type deposit

lead isotopic signatures of porphyry copper deposits in oceanic and continental settings colombian andes abstract three discrete sub belts of porphyry copper type mineralization are recognized in the colombian andes a western eocene sub belt an eastern jurassic to early cretaceous sub belt and between them a central miocene sub belt the western sub belt is part of an oceanic domain constituted by oceanic crust and overlying immature island arc rocks the eastern sub belt is within a continental domain underlain by the leading edge of the guayana shield and the central sub belt spans the faulted boundary between them the thicker continental crust includes important granulitic rocks which crop out locally as in the vicinity of the mocoa porphyry copper deposit pb isotopic ratios were determined for pyrite samples collected from 6 porphyry copper centers 3 in the western sub belt 2 in the eastern sub belt and one in the central sub belt ratios fall into 3 discrete populations the most radiogenic values represent the western sub belt the least radiogenic represent the eastern sub belt and an intermediate value corresponds to the central sub belt ratios therefore become progressively less radiogenic from the western oceanic domain to the eastern cratonic domain comparison of the pb isotopic ratios with those given in the literature for possible source materials for colombian porphyry copper leads enables the subcontinental mantle wedge subducted oceanic crust and subducted metalliferous sediments to be discounted as principal sources the relatively radiogenic signatures of 5 of the porphyry copper centers appear to be broadly compatible with either a subducted pelagic sediment source or an upper continental crust source whereas the sixth center mocoa is characterized by a distinctly less radiogenic 206 pb 204 pb ratio an admixture of a relatively small percentage of non radiogenic pb from granulitic material in the upper crust with the more radiogenic pb typical of the western sub belt centers could account for the mocoa data because much of the upper crustal section in the region of mocoa is thought to be dominated by granulitic material the radiogenic pb component could be best derived from subducted pelagic sediments if this is the case then a subducted pelagic sediment source could dominate the pb isotopic signatures of all colombian porphyry copper mineralization with some of the pb isotopic differences being produced by selective contamination with upper crustal leads of variable character if this conclusion is correct then the fundamental metal budgets of colombian porphyry copper systems are probably largely independent of upper crustal influences

amplitude preservation of radon based multiple removal filters this study examines the effect of filtering in the radon transform domain on reflection amplitudes radon filters are often used for removal of multiple reflections from normal moveout corrected seismic data the unweighted solution to the radon transform reduces reflection amplitudes at both near and far offsets due to a truncation effect however the weighted solutions to the transform produce localized events in the transform domain which minimizes this truncation effect synthetic examples suggest that filters designed in the radon domain based on a weighted solution to the linear parabolic or hyperbolic transforms preserve the near and far offset reflection amplitudes while removing the multiples whereas the unweighted solutions diminish reflection amplitudes which may distort subsequent amplitude versus offset avo analysis

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

evidence for tibetan plateau uplift before 14 myr ago from a new minimum age for east west extension important changes in south asian climate occurred in the late miocene epoch 8 myr ago 1 2 and these have been attributed by some researchers to uplift of the tibetan plateau at about the same time3 5 unfortunately this link has been difficult to test because the timing of plateau uplift remains poorly constrained by independent evidence one way to determine the minimum age of uplift is to establish the initiation age of the north striking normal fault systems in southern tibet that are widely regarded6 10 as being related to gravitational collapse of the tibetan plateau here we report an40ar 39ar age of 14 myr for hydrothermal mica from an extensional fracture belonging to such a fault system in north central nepal this age implies that east west extension began before 14 myr ago in at least some parts of the tibetan plateau suggesting that the plateau attained its high mean elevation well before late miocene time

dipping interface mapping using mode separated rayleigh waves multichannel analysis of surface waves masw method is a non invasive geophysical technique that uses the dispersive characteristic of rayleigh waves to estimate a vertical shear s wave velocity profile a pseudo 2d s wave velocity section is constructed by aligning 1d s wave velocity profiles at the midpoint of each receiver spread that are contoured using a spatial interpolation scheme the horizontal resolution of the section is therefore most influenced by the receiver spread length and the source interval based on the assumption that a dipping layer model can be regarded as stepped flat layers high resolution linear radon transform lrt has been proposed to image rayleigh wave dispersive energy and separate modes of rayleigh waves from a multichannel record with the mode separation technique therefore a dispersion curve that possesses satisfactory accuracy can be calculated using a pair of consecutive traces within a mode separated shot gather in this study using synthetic models containing a dipping layer with a slope of 5 10 15 20 or 30 degrees and a real world example we assess the ability of using high resolution lrt to image and separate fundamental mode rayleigh waves from raw surface wave data and accuracy of dispersion curves generated by a pair of consecutive traces within a mode separated shot gather results of synthetic and real world examples demonstrate that a dipping interface with a slope smaller than 15 degrees can be successfully mapped by separated fundamental waves using high resolution lrt

geology and geochronology of naruo large porphyry breccia cu deposit in the duolong district tibet abstract the duolong district is located in the south qiangtang terrane of tibet and is the most significant ore cluster within the bangongco nujiang metallogenic belt duolong contains one giant three large and two medium to small sized porphyry epithermal breccia copper deposits and several other mineralized porphyry bodies all deposits are closely associated with early cretaceous 123 115 ma intermediate felsic intrusions naruo is a poorly studied porphyry breccia copper deposit in the north of the duolong district hydrothermal alteration surrounding the ore bearing granodiorite at naruo is characterized by an inner potassic zone and an outer propylitic zone overlapped locally by minor phyllic and argillic alteration assemblages a detailed paragenetic study has identified five distinct hydrothermal veins m a b c d within the porphyry system hydrothermal b veins are strongly related to copper mineralization strong propylitic alteration is also observed throughout the hydrothermal breccias identified at naruo sandstone breccia diorite bearing breccia and granodiorite bearing breccia were identified according to the distribution and composition of clasts u pb zircon dating has determined the ages of the ore bearing granodiorite 121 6 1 3 ma and a barren intrusion 115 5 1 1 ma within the porphyry system diorite clasts 122 3 0 9 ma and later diorite matrix 120 5 1 0 ma in the hydrothermal breccia system suggesting that with the exception of the late barren intrusion they all belong to the same mineralizing event at duolong the geological and geochemical evidence presented in this study suggest that the porphyry and breccia systems may have originated from the same magma source but are now spatially independent

structure and evolution of the himalaya tibet orogenic belt the 1981 french chinese expedition to tibet focused on the lhasa block extending earlier coverage 400 km north of the tsangpo suture the lhasa block stood between 10 and 15 n latitude over most of the upper cretaceous and eocene and if gondwanian in origin had detached from gondwana by early permian seismic profiles reveal a complex moho topography resulting both from multiple continental thrusting and large scale strike slip faulting subduction related granitoids representing mixtures of mantle and crustal components and anatectic granitoids have been analysed and dated this study emphasizes the role of smaller blocks in the accretion of the continental mosaic

age and composition of dikes in southern tibet new constraints on the timing of east west extension and its relationship to postcollisional volcanism controversy exists over whether east west extension in southern tibet is related to plateau uplift or to the accommodation of plate boundary forces relationships between the onset of extension plateau uplift and the thermal state of the lithosphere are critical to this debate we present new data on postcollisional north south trending dikes in southern tibet their ages range from 18 3 2 7 ma to 13 3 0 8 ma and define the onset of regional east west extension in southern tibet dikes are compositionally indistinguishable from postcollisional lavas in southern tibet being either ultrapotassic having a source in the subcontinental lithospheric mantle or calc alkaline with a dominantly crustal origin the ultrapotassic dikes demonstrate that east west extension and subcontinental lithospheric mantle derived magmatism were temporally and spatially linked supporting models that relate the latest phase of plateau uplift to subcontinental lithospheric mantle thinning thus the onset of extension by 18 3 2 7 ma represents the time at which the potential energy of the plateau exceeded convergent boundary forces this places a new age limitation on the attainment of high elevation in southern tibet with implications for models that relate cenozoic monsoon intensification to plateau uplift

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

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

origin of the ore forming fluids and metals of the hetai goldfield in guangdong province of south china constraints from c h o s pb he ar isotopes abstract the hetai goldfield located in the southern segment of the qinzhou bay hangzhou bay juncture orogenic belt qhjb is one of the largest gold mining districts in south china although the goldfield shares some similarities in ore geology and geochemistry to orogenic gold deposits there has been controversy on the origin of the ore forming fluids and metals an integrated analysis on c h o s pb he ar isotopes has been carried out to trace the origins of the ore fluids and metals thereby to evaluate the genesis of the hetai goldfield the 3 he 4 he and 40 ar 36 ar ratios of fluid inclusions in sulfides from the hetai ores exhibit a range of 0 27 0 62 ra and 932 4 6324 2 with the 4 he and 40 ar concentrations varying from 1 99 to 96 80 10 7 cm 3 stp g and 0 51 7 75 10 7 cm 3 stp g respectively this suggests a dominant crust derived fluid mixed with significant mantle derived fluids for the hetai gold mineralization the calculated 18 o h2o vsmow and measured d h2o vsmow values of fluid inclusions in gold bearing quartz range from 0 5 to 10 4 and from 83 1 to 52 4 respectively the 13 c pdb and 18 o pdb of calcite range from 3 53 to 1 91 and 21 21 to 19 67 respectively suggesting a deep seated source of the c bearing portion of the fluid the 34 s cdt values of sulfides intergrown with native gold range from 4 0 to 1 3 with an average of 2 8 indicating that the majority of the sulfur came from granitic magma by partial melting of the host rocks but likely with minor input from the mantle the pb isotopic components of sulfides from the hetai ores have 206 pb 204 pb 207 pb 204 pb and 208 pb 204 pb ratios of 18 044 19 404 15 568 15 793 and 38 426 39 597 respectively indicating a main upper continental crust source of ore metals but probably with minor contribution from the mantle linked to the ore geology and regional tectonomagmatic events the integration of the isotopic compositions obtained in this study with previously published fluid inclusion and geochronologic data suggests that the ore fluids and metals may have undergone two stages of evolution i e from the indosinian metamorphic water dominated fluids mixed with minor magmatic waters to the yanshanian magmatic water dominated fluids mixed with mantle derived fluids and meteoric waters

ore geology and fluid inclusions of the hucunnan deposit tongling eastern china implications for the separation of copper and molybdenum in skarn deposits abstract the hucunnan ore deposit is a representative skarn cu mo deposit in the tongling district an important ore district of the renowned middle lower yangtze river metallogenic belt of china the deposit shows distinct zonation of metals with cu mineralization distributed mainly in the exoskarn zone at shallow depths and mo mineralization occurring chiefly in the endoskarn zone located at deeper depths field evidence and petrographic observations indicate that the ore forming processes can be divided into the skarn quartz molybdenite quartz chalcopyrite and carbonate stages five types of fluid inclusions fis are present in the deposit solid bearing type 1 liquid rich type 2 vapor rich type 3 pure vapor type 4 and co 2 bearing type 5 the skarn stage contains mainly type 1 and 2 but also minor type 3 and 4 fis the fis display homogenization temperatures of 434 570 c and salinities of 2 07 66 0 wt nacl equiv the existence of hematite daughter minerals in the type 1 inclusions together with the presence of magnetite in skarn implies that the skarn stage fluid was oxidizing the skarnization of the granodiorite porphyry is commonly accompanied by potassic alteration suggesting that the fluids were rich in alkali similar to the skarn stage the quartz molybdenite stage contains type 1 and 2 and minor type 3 and 4 fis which yield homogenization temperatures of 280 458 c and salinities of 1 40 54 2 wt nacl equiv the presence of sulfide instead of hematite daughter minerals in the type 1 inclusions in quartz molybdenite veins associated with sericitization indicates that the fluids of the quartz molybdenite stage were more reducing and more acidic than the fluids in the skarn stage the decrease in oxygen fugacity and increase in acidity could have resulted from magnetite crystallization and the consumption of alkali cations and oh respectively during the skarn stage the quartz chalcopyrite stage contains all types of fis which show homogenization temperatures of 203 392 c and salinities of 1 22 46 6 wt nacl equiv observations of hematite bearing type 1 fis in quartz chalcopyrite veins containing anhydrite associated with biotitization suggest that the fluids of the quartz chalcopyrite stage were oxidizing and alkali rich probably on account of the inflow of meteoric water and boiling in an open system in the carbonate stage only type 2 fis are present these fis yield the lowest homogenization temperatures of 156 276 c and the lowest salinities of 1 05 12 3 wt nacl equiv microthermometry and h o isotope data indicate that the ore forming fluids were dominated by magmatic water in the early stages skarn and quartz molybdenite stages and that the magmatic water gradually mixed with circulating meteoric water during the late stages quartz chalcopyrite and carbonate stages the coexistence of saline and vapor rich fis as internal trails or clusters within individual crystals with similar homogenization temperatures but contrasting salinities and homogenization modes to the liquid and vapor respectively in the first three stages strongly suggests that three episodes of fluid boiling occurred in these stages as further supported by the hydrogen isotopic compositions of the fluids which are lower than those of magmatic water based on the above data we conclude that temporal changes in redox conditions acidity and temperature in the mineralizing fluids resulted in the temporal separation of cu and mo by selective sulfide precipitation in the hucunnan skarn deposit the competition among metals e g mo and cu for sulfur in magmatic fluids along with vapor brine immiscibility fluid boiling are major factors that contributed to the spatial separation of cu and mo in the deposit

stable isotope s o h and c studies of the phyllic and potassic phyllic alteration zones of the porphyry copper deposit at sungun east azarbaidjan iran abstract the porphyry copper deposit pcd at sungun is located in east azarbaidjan nw of iran the magmatic suites in the sungun area are a part of the nw se trending cenozoic magmatic belt of iran the sungun porphyries occur as stocks and dikes the stocks are divided into two groups i and ii porphyry stock ii ranging in composition from quartz monzonite through granodiorite to granite hosts the sungun pcd four distinct types of hypogene alterations were recognized at sungun 1 potassic 2 potassic phyllic 3 phyllic and 4 propylitic stable isotope s o h and c studies were restricted to within the phyllic and potassic phyllic alteration zones where numerous cross cutting quartz sulfides carbonates and sulfate veinlets are present the objective of these studies was to determine the origin of the ore forming solutions and their important components e g sulfur and carbon twenty sulfide and four sulfate samples were taken from sulfide and gypsum veinlets within porphyry stock ii and the associated skarn zone for sulfur isotopic analyses the 34 s values of sulfides pyrite chalcopyrite molybdenite galena sphalerite and sulfate gypsum range from 4 6 to 0 2 mean of 1 5 and from 10 9 to 14 4 mean of 12 9 respectively these values are almost analogous to those from el salvador chile and ajo arizona and twin buttes arizona and strongly suggest a magmatic source for the sulfur at sungun twenty eight fluid inclusion rich quartz samples from quartz veinlets beneath the supergene zones of the porphyry stock ii were chosen for o and h isotopic analyses the 18 o of quartz and d of fluid inclusions in quartz values range from 8 3 to 10 2 mean of 9 2 and 58 to 75 mean of 66 relative to standard mean ocean water smow respectively the calculated 18 o values of the fluids range from 4 4 t 375 c to 7 6 t 570 c with a mean of 6 4 the 18 o and d values of the fluids lie within the typical range of magmatic waters based upon the lowest obtained d values the calculated maximum exchangeable meteoric water that might be involved in the phyllic and potassic phyllic alteration processes was 20 fourteen calcite samples from carbonate veinlets in the porphyry stock ii and two samples from associated marble aureole were collected for carbon and oxygen isotopic analyses the 13 c calcite from porphyry stock ii and associated marble aureole varies from 0 4 to 2 9 and 0 06 to 2 relative to the pdb standard of the university of chicago respectively the corresponding 18 o calcite values range from 6 to 13 2 relative to smow the 13 c values lie within the sedimentary range suggesting that there was little or almost no magmatic carbon in the hydrothermal system in contrast the 18 o calcite values are far lower than that of cretaceous sedimentary carbonates which suggest that the values were influenced by those of magmatic fluids through isotopic re equilibration these isotopic investigations demonstrated that 1 in contrast to some well known pcds about 80 of the fluids involved in the phyllic and potassic phyllic alterations at sungun had a magmatic o and h isotopic signature 2 the upper cretaceous limestone was the potential source of c and 3 the sulfur had a magmatic origin

zircon hf isotopic characteristics and constraints on petrogenesis of mesozoic cenozoic magmatic rocks in nyainqentanglha region tibet in this paper the mesozoic cenozoic magmatic rocks in yaguila sharang dongzhongla ore forming area serve as the object for zircon hf isotope study by means of la mc icp ms hf isotopic compositions of the zircons from yanshanian yaguila quartz porphyry 35 show that the ratio of 176hf 177hf is 0 282 090 0 282 480 the ehf t value is 7 750 21 449 and the tdm2 value is 1 679 2 543 ma hf isotopic compositions of the zircons from himalayan yaguila quartz porphyry 16 show that the ratio of 176hf 177hf is 0 282 413 0 282 805 the ehf t value is 11 463 2 46 and the tdm2 value is 980 1 864 ma hf isotopic compositions of the zircons from himalayan yaguila granite 35 show that the ratio of 176hf 177hf is 0 282 601 0 282 800 the ehf t value is 2 279 2 182 and the tdm2 value is 996 1 279 ma hf isotopic compositions of the zircons from late himalayan yaguila granite porphyry show that the ratio of 176hf 177hf is 0 282 600 0 282 830 the ehf t value is 5 676 3 128 and the tdm2 value is 900 1 461 ma hf isotopic compositions of the zircons from himalayan sharang hornblende diorite show that the ratio of 176hf 177hf is 0 282 700 0 282 790 the ehf t value is 1 536 1 618 and the tdm2 value is 1 019 1 219 ma hf isotopic compositions of the zircons from yanshanian dongzhongla quartz porphyry show that the ratio of 176hf 177hf is 0 282 142 0 282 396 the ehf t value is 19 744 10 620 and the tdm2 value is 1 857 2 430 ma based on a comparison with the hf isotopic compositions of the zircons from porphyry of the qulong ore deposit and linzizong volcanic rock the authors have reached some conclusions the characteristics of hf isotope of two intrusion stages of yaguila quartz porphyry 35 16 are different from each other the characteristics of hf isotope of yanshanian yaguila 35 and dongzhongla quartz porphyries are similar to each other suggesting that the rocks were formed by the crust base materials the hf isotope of yaguila and sharang himalayan igneous rocks 16 16 36 k linzizong volcanic rock and qulong quartz porphyry shows the rock is the combination of the crust base materials and the depleted mantle the different ehf t value of these igneous rocks may because of the different proportion of the crust base materials or the depleted mantle during the hybridization of them

atmospheric variability over the 14 7 kyr bp stadial interstadial transition in the north atlantic region as simulated by an agcm the echam4 t42 atmospheric general circulation model was applied to study the change in atmospheric variability in the north atlantic region over the similar to14 7 kyr cal bp climatic transition from greenland stadial 2a gs 2a end of pleniglacial to greenland interstadial le gi le start late glacial the following three climates are simulated 1 present day 2 gs 2a and 3 gi le we focus on climatic parameters near the earth s surface temperature precipitation and sea level pressure results on two different temporal scales are analysed seasonal and daily the seasonal fields show that the main change over the 14 7 kyr bp transition occurred in winter we calculated daily standard deviations of temperature and pressure about the seasonal means and the high pass filtered less than six days variability of pressure the largest change in atmospheric variability occurred in northwest europe here the daily temperature variability decreased by 50 whereas storm activity also decreased substantially these changes are related to a northward shift of the atlantic sea ice margin at 14 7 kyr bp leading to a northward relocation of the atlantic storm track in the gs 2a experiment a strong storm track was located over northwest europe where frequent depressions produced alternations of northerly air flow below 30 degreesc and southerly air flow close to 0 degreesc this strong daily atmospheric variability decreased in gi le because the storm track had a sw ne orientation over the atlantic towards iceland the decrease in atmospheric variability at 14 7 kyr bp probably contributed to landscape stabilization for instance through decreasing eolian transport

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

helium neon and argon systematics of the european subcontinental mantle implications for its geochemical evolution in this study we present a comprehensive noble gas study of mantle xenoliths from various european cenozoic volcanic provinces the main body of samples is from the massif central france and the eifel germany smaller subsets of samples are from spitsbergen and the graz basin austria in all the helium neon and argon isotopic abundances of a total of forty five mantle xenoliths phenocrysts and xenocrysts were determined the 3he 4he ratios within each volcanic province are very uniform irrespective of the diverse lithologies and p t conditions which are represented by our sample suite mean 3he 4he ratios of the massif central eifel spitsbergen and kapfenstein are 6 53 25 6 03 14 6 65 25 and 6 1 7 1 times the atmospheric ratio ra respectively the strontium and neodymium isotopic composition of some of the cpx separates are highly variable and therefore in contrast to the uniform he signature we thus conclude that he and probably also the other noble gases in the xenoliths are effectively decoupled from the non volatile elements therefore the he signature that is preserved in the xenoliths is actually that of their host magmas published strontium neodymium and lead isotope data of the unevolved host magmas of the xenoliths correlate well with our xenolith he data the position of the fields of the investigated volcanic provinces in hesr hend and hepb variation diagrams depict ternary mixtures between dmm em himu endmembers as the source the host magmas and their volatiles the neon isotopic composition of the gases released from the xenoliths is in most cases atmospheric and probably reflects atmospheric contamination only a few samples reveal indications for morb type ne or evidence of mass fractionation the 40ar 36ar ratios of the xenoliths are mostly radiogenic with the highest ratio being 17 000 however all samples have suffered a certain degree of atmospheric contamination we calculate that the uncontaminated 40ar 36ar ratio of the european subcontinental mantle is 30 000 the4he 40ar ratios have been fractionated since with values around 0 25 they are below both the current production ratio and the morb ratio they cannot be explained by atmospheric contamination as the samples with high 40ar 36ar ratios also have low 4he 40ar ratios helium and ar were probably fractionated during initial closed system degassing of the host magma we calculate the original unfractionated 4he 40ar ratios of the massif central and eifel magma source which are 2 56 18 and 2 71 17 respectively the noble gas systematics are compatible with the notion that addition of crustal material has modified a former morb source signature we use our mean 3he 4 he ratios and reconstructed 4he 40ar ratios to model the time and degree of contamination of a morb like source with crustal material combining our model with evidence from published oxygen strontium neodymium and lead isotope data we judge that the source of the massif central and eifel magmas became enriched in k u and th shortly prior or during the variscan orogeny pre collisional collisional in this case the enrichment in these elements is therefore most probably related to subduction of crustal material in a destructive continental margin setting

qulong superlarge porphyry cu deposit in tibet geology alteration and mineralization although some porphyry deposits are seen in post collisional extensional settings and seemingly have no relationship to subduction such deposits commonly occur in arc settings in association with subduction related calc alkaline magmas and their characteristics remain poorly understood in this paper the authors describe igneous geology alteration mineralogy and mineralization history of qulong deposit a newly discovered post collisional type porphyry cu deposit in southern tibet it is associated with miocene monzogranite granodiorite intrusions and hosted partly in jurassic andesitic dacitic volcanics a 19 5 ma granodiorite pluton with diorite enclaves seem to be the earliest miocene intrusive unit into which a regularly shaped stock p porphyry and then a thin dike x porphyry of monzogranite intruded about 17 7 ma ago the main copper molybdenum mineralization is associated with the p porphyry a barren diorite porphyry intruded into the p and x porphyries around 15 7 ma petrologic trends of the intrusions suggest that the miocene intrusions had similar origin and were probably formed by fractionation of a rather deep magma chamber emplacement of miocene porphyries controlled by qulong anticline was a direct response to the rapid uplift erosion of gangdese arc batholiths in southern tibet miarolitic cavities and unidirectional solidification textures the key evidence for volatile separation were recognized in the p and x porphyries respectively early potassic alteration characterized by quartz k feldspar anhydrite pervades the p porphyry and granodiorite laterally this alteration grades into quartz biotite anhydrite k feldspar which has affected all miocene intrusions except the latest dioritic porphyry wall rocks of granodiorite and jurassic andesitic dacitic volcanics within 1 1 5 kilometers from the porphyries are dominated by potassic alteration an outer halo of propylitic alteration epidote chlorite calcite extends up to 2 km 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 porphyries and occurs as vein halos away from the porphyries the earliest quartz k feldspar alteration and veins are barren whereas approximately 60 percent of the 7 million tons of copper they contain have to do 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 molybdenum veins deposition of cu mo with abundant anhydrite occurred during or between emplacements of closely related porphyries from high temperature magmatically derived fluids and was probably caused by hydrolysis of so2

sulfur isotope evidence for penetration of mvt fluids into igneous basement rocks southeast missouri usa previous studies of galena and sphalerite from paleozoic mvt deposits in the viburnum trend southeast missouri documented large variations in 34s values throughout the ore forming event the present study of cu fe sulfides reveals a similar 34s variation that reflects two end member sulfur reservoirs whose relative importance varied both temporally and spatially more 34s enriched sulfides 34s approaching 25 indicate introduction of sulfur from basinal sedimentary sources whereas more 32s enriched sulfides 34s 600 m vertically through underlying precambrian igneous rocks such basement involvement has been suggested for other carbonate hosted base metal districts e g irish base metal deposits and should be considered an integral part of the ore forming process in southeast missouri

investigation of structural heterogeneity at the spe site using combined p wave travel times and rg phase velocities we present analyses of the 2d seismic structure beneath source physics experiments spe geophone lines that extended radially at 100 m spacing from 100 to 2000 m from the source borehole with seismic sources at only one end of the geophone lines standard refraction profiling methods cannot resolve seismic velocity structures unambiguously in previous work we demonstrated overall agreement between body wave refraction modeling and rg dispersion curves for the least complex of the five lines a more detailed inspection supports a 2d reinterpretation of the structure we obtained rg phase velocity measurements in both the time and frequency domains then used iterative adjustment of the initial 1d body wave model to predict rg dispersion curves to fit the observed values our method applied to the most topographically severe of the geophone lines is supplemented with a 2d ray tracing approach whose application to p wave arrivals supports the rg analysis in addition midline sources will allow us to refine our characterization in future work

metallogenesis of continental collision setting part i gangdese cenozoic porphyry cu mo systems in tibet giant porphyry deposits are generally found in magmatic arcs and continent collisional belt metallogenic theory of the porphyry copper deposit under the magmatic arc condition has been well established while that in the continental collision setting has not been formed a large number of porphyry deposits were formed in tibetan plateau as the result of collision between the india and the lhasa plates three different porphyry deposit belts have been found in the lhasa terrene the sharang type porphyry mo deposit and the yaguila type porphyry skarn pb zn cu deposit distributed along the north margin of the gangdese belt the central lhasa terrane were formed in the main collisional period 65 41 ma the mingze type porphyry mo deposit and the nuri type porphyry skarn cu wu mo deposit in the central part of the gangdese belt southern lhasa terrane were formed in late collisional period 40 26 ma whereas the qulong type porphyry cu mo deposits developed in the zedong arc belt was formed in the post collisional period 25 13 ma the fertile gangdese porphyry systems are generally composed of multistage hypergenic intrusive complexes these complexes are generally characterized by high k and most of them are k calc alkali and shoshonitic in composition the cu bearing porphyries are dominated by monzogranite and generally show geochemical affinity to adakites while the mo bearing porphyry deposits are mainly associated with granite which was most likely derived from continental crust whole rock geochemistry and sr nd hf isotopic data indicate that the cu bearing magmas were most probably derived from the thickened juvenile mafic lower crust beneath south tibet the melting of sulfide bearing phases in the juvenile mantle components of the tibetan lower crust probably provided parts of cu au and s for the fertile magmas however the mo bearing magmas were likely derived from partial melting of the ancient tibetan lower crust while mo was also mainly derived from the ancient crust large amounts of micro mafic enclaves mme with varied components have been found in the porphyry magmas these mmes which were derived from the enriched lithosphere mantle probably represent the addition of the remnants of a mafic component to the host magma these cu and h2o enriched mantle derived magmas experienced underplating at the base of the gangdese crust supplied heat and h2o to inducing partial melting of the thickened lower crust and were partly injected into the lower crust derived felsic melts probably providing heat and some fluids rich in h2o metals and s and playing an important role in generating the hydrous high f o2 fertile porphyry magmas the gangdese porphyritic hydrothermal systems were commonly controlled by the settings of the crust where they intruded in the granitoid batholiths setting the impermeable wall rocks would result in the spreading of the hydrothermal fluid around the porphyry stocks core which would form the concentric circle alteration zones and generate cu mo mineralization in the potassium silicate alteration zone in the clastic limestone setting carbonate was likely to be altered by skarn and then induced the precipitation of metals while impermeable fine grained clastic rocks would prohibit the penetration of the hydrothermal fluids and thus porphyry mo and skarn pb zn mo or mo w cu ore bodies were commonly developed around the porphyry bodies in the bedding volcano sediment setting the impermeable overlying strata probably led to lateral migration of the hydrothermal fluids for a long distance and intense mixing with meteotic water these processes could develop widespread hydrothermal alteration zones and finally resulted in the development of epithermal au cu and porphyry cu mo deposits at the shallow and deep level respectively combined with the regional tectonic magmatic evolution the authors have concluded that the three stages of mantle derived magamas underplating partial melting of lower crust hypergenic emplacement of magama porphyritic minerlization system might have been controlled by various deep processes in the three periods of india eurasia continental collision various geodynamic models have been established by the authors for the three types of porphyry deposits within the continental collision setting

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

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

formation and evolution of multistage ore forming fluids in the miocene bangpu porphyry skarn deposit southern tibet insights from la icp ms trace elements of quartz and fluid inclusions abstract the large bangpu mo cu pb zn deposit is a mo rich 0 089 cu poor 0 32 porphyry skarn deposit located in the northeastern gangdese porphyry copper belt gpcb southern tibet in this study la icp ms data for fluid inclusions and quartz formed during different stages of the mineralization are used to 1 constrain changes in fluid composition during mineralization 2 infer the origin transport pathways and conditions of ore precipitation and 3 explore the influence of magma chamber on fluid exsolution and shallow mineralization the cu content of the vapor rich vl inclusions is higher than that of the halite bearing lvh inclusions while the mo pb and zn contents of the vl and lvh inclusions are similar indicating that mo cu pb and zn had a common source which is inferred to be the intermediate level magma chamber the metal contents of fluid inclusions in the early stage potassic alteration related vein a vein and later stage sericitic alteration related vein b vein are similar but variable implying the intermediate level magma chamber was too small to form a large stable fluid system the enrichment of mo pb and zn in the bangpu deposit relative to other porphyry deposits in the gpcb is related to the participation of ancient crustal material a comparison of our results with those from super large porphyry cu deposits elsewhere indicates that metal rich fluids are not the sole factor to form ore deposits and the variability of metal contents in the early exsolved fluids is a better predictor of mineralization potential than absolute metal concentrations

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

u pb geochronology geochemistry and h o s pb isotopic compositions of the leqingla and xin gaguo skarn pb zn polymetallic deposits tibet china abstract the leqingla and xin gaguo deposits are two representative skarn pb zn polymetallic deposits of the gangdese pb zn polymetallic belt tibet china la icp ms zircon u pb dating of the mineralization related biotite granites from both the leqingla and xin gaguo deposits yielded weighted mean ages of 60 8 ma and 56 5 ma respectively which can be inferred as their mineralization ages the leqingla biotite granite is characterized by high al 2 o 3 total fe na 2 o and low k 2 o in comparison the xin gaguo biotite granite is characterized by relative higher k 2 o but lower al 2 o 3 total fe and na 2 o geochemical and mineralogical characteristics indicate that the leqingla and xin gaguo biotite granites are calc alkaline i type granite and high k calc alkaline i type granite respectively both the leqingla and xin gaguo biotite granites are enrichment in lree and liles and depletion in hfses and they were formed at the india asia collision stage 18 o and d values for the leqingla and xin gaguo deposits are 8 8 to 5 3 and 140 4 to 90 1 4 5 to 7 0 and 117 3 to 81 0 respectively indicating magma fluids mixed with meteoric water in ore forming fluids 34 s values 11 6 to 0 3 of ore sulfides from the leqingla deposit show characteristics of biogenetic sulfur isotope compositions suggesting sulfur for the leqingla deposit were sourced from wall rocks of the mengla and luobadui formation which are rich in organic materials 34 s values of ore sulfides from the xin gaguo deposits show bimodal distribution 5 0 to 1 6 and 1 6 2 1 indicating sulfur in the xin gaguo deposit were derived from both wall rocks and magma in the leqingla deposit most ore sulfides have the similar pb isotopic compositions with that of the mineralization related biotite granite suggesting the biotite granite supplied most of the ore forming metals pb isotopic compositions of ore sulfides and hf isotopic compositions of biotite granite show that the majority of ore forming metals are derived from mantle components of partial melting of the neo tethys ocean slab with some upper crust materials of the lhasa terrane pb isotopic compositions of ore sulfides from the xin gaguo deposit are similar to that of the leqingla deposit indicating they have the similar sources of ore forming metals

lead isotope signatures of the igneous rocks and porphyry copper deposits from the kerman cenozoic magmatic arc se iran and their magmatic metallogenetic implications abstract copper deposits in the kerman cenozoic magmatic arc kcma of iran are genetically related to miocene porphyries the porphyries and their associated cu deposits were intruded and emplaced into eocene volcanic sedimentary successions lead isotope compositions of the eocene volcanic rocks exhibit homogeneous non radiogenic values 206 pb 204 pb 18 40 to 18 49 207 pb 204 pb 15 41 to 15 48 and 208 pb 204 pb 38 15 to 38 36 in contrast the miocene ore hosting porphyries and associated sulfide minerals also show a relatively radiogenic and homogenous pb isotopic values with orogen character 206 pb 204 pb 18 52 to18 60 207 pb 204 pb 15 58 to 15 64 and 208 pb 204 pb 38 57 to 38 80 the shift in the pb isotopic composition of igneous rocks with time towards higher pb isotopic values precludes derivation of the ore hosting porphyries from a reservoir of similar composition to those in the eocene volcanic rocks the non radiogenic pb isotope signature of the eocene volcanic rocks indicates an origin from subduction related mantle derived magmas whereas the higher pb isotopic values of the miocene ore hosting porphyries suggest an increasing involvement of crustal materials with lower u pb ratios than the upper crust in the source region of these rocks combining the pb isotope data with petrogenetic considerations suggests derivation of the middle miocene ore hosting porphyries from a mixed reservoir with slightly radiogenic pb values such as a hybridized lower continental crustal source this source probably formed because of the involvement of cretaceous oligocene subduction related mantle derived mafic magmas at the base of arc crust the contribution of the miocene collision related mantle derived mafic magma in melting of the hybridized lower continental crust caused generation of the middle miocene porphyries hosting large copper deposits with the least 206 pb 204 pb ratios among other porphyries the higher 206 pb 204 pb ratios of the late miocene pliocene porphyries hosting small copper deposits as well as barren porphyries may reflect a decreasing involvement of collision related mantle derived mafic magma in the source of the late miocene pliocene porphyries the overall similarity in pb isotope values between sulfide minerals and ore hosting porphyries suggests a magmatic source for most of the pb and possibly other metals the more radiogenic isotopic ratios of some late sulfide minerals suggest an insignificant metal contribution from an external source such as local country rocks during hydrothermal circulation

fluid inclusion noble gas and halogen evidence on the origin of cu porphyry mineralising fluids the naturally occurring noble gas isotopes 40ar 36ar 84kr and 129xe and halogens cl br i have been determined simultaneously in irradiated quartz vein samples by noble gas mass spectrometry quartz vein samples were collected from the potassic and propylitic alteration zones of six porphyry copper deposits pcd bingham canyon utah and silverbell ray mission pinto valley and globe miami in arizona in addition analyses of 3he 4he have been obtained from sulphide minerals hosted by the quartz veins at silverbell ray pinto valley and globe miami the majority of pcd fluids studied have br cl and i cl ratios that overlap those of fluids included in mantle diamond suggesting that the salinity had a juvenile origin the high i cl 121 10 6 mole m in samples from the propylitic zone of silverbell is attributed to the presence of sedimentary formation water 3he 4he ratios have r ra values in the range 0 3 to 1 72 and provide evidence for the involvement of a crustal component in addition to mantle volatiles 40ar 36ar ratios vary from meteoric values of 317 in the propylitic zone of bingham canyon and 323 in the skarn alteration of mission up to 3225 in the potassic zone of pinto valley fluids in both the potassic and propylitic alteration zones of every deposit are a mixture of a low salinity end member comprising meteoric water and air and a high salinity end member consisting of a mixed mantle and crustal fluid the 40ar cl ratio of fluid inclusions at pinto valley 10 4 m is similar to values obtained previously for mantle fluids the 40ar cl value is two orders of magnitude lower at bingham canyon where a depleted 36ar concentration 0 2 10 6 cm3 g below that of air saturated water asw and a range of highly fractionated noble gas compositions f84kr 13 and f129xe 160 indicate that boiling and pulsed fluid flow have occurred

re os systematics of sulfides chalcopyrite bornite pyrite and pyrrhotite from the jiama cu mo deposit of tibet china abstract the jiama cu mo deposit one of the largest skarn porphyry deposits in china currently being mined is located in the eastern part of the gangdese porphyry cu belt tibet china chalcopryite and bornite concentrate in the skarn ore zone at jiama with molybdenite concentration whereas molybdenite occurs in the porphyry ore zone and hornfels ore zone relatively by itself cu and mo have different distributions in the porphyry ore zone with cu concentrating above the porphyry and with mo inside of porphyry intrusion the direct re os dating on cu sulfides will be helpful for us to understand the cu and mo mineralization at jiama this study is the first attempt to use the re os isotope system to directly date chalcopyrite bornite pyrite and pyrrhotite at jiama the contents of re common os and 187 os in these four sulfides are 0 145 32 9 ppb 0 0022 0 0669 ppb and 0 0003 0 0118 ppb respectively they have very low ratios of 187 os to common os 0 09 0 55 therefore they are different from low level highly radiogenic llhr sulfides the plot of 187 re 188 os and 187 os 188 os did not yield an isochron age based on the scatter points even if age of 15 ma based on molybdenite re os age is used to calculate the initial 187 os 188 os the ratios show a wide range and low ratios of 187 re 188 os 187 os 188 os the geology suggests the cu and mo mineralizations at jiama are both related to porphyry intrusions and the cu mineralization should also have occurred in miocene based on the molybdenite re os age and porphyry zircon u pb ages

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

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

interferometric multichannel analysis of surface waves imasw abstract refraction microtremor remi and multichannel analysis of surface waves masw are effective approaches to estimate shallow shear wave velocity v s structure often needed to estimate ground motions using recent ground motion prediction relations interferometric masw imasw uses slowness frequency slant stack analyses combined with interferometric time domain dispersion analyses to improve resolution of lower frequency rayleigh wave dispersion to better constrain v s cross correlation interferometry is used to obtain deterministic correlation green s function cgf imasw seismograms from ambient noise and or active source wave fields contained in remi and or masw data the cgfs are processed using the multiple filter technique to estimate phase and group dispersion in the imasw approach active seismic sources ensure that the stationary phase contributions to cross correlations dominate cgf responses in a single imasw profile each geophone represents a virtual source and the imasw approach stacks cgf common offset data from all virtual sources to obtain a single averaged forward and reverse record section cgf time domain and slowness frequency phase slowness estimates are combined with cgf time domain group slowness estimates for a consistency check on dispersion picks a multistate monte carlo approach is used to estimate mean slowness depth and slowness uncertainties imasw is evaluated with passive remi data from two sites and active source imasw at six sites with independent downhole velocity depth logs comparison of six p s suspension log imasw profile pairs across the van norman complex in northern san fernando valley shows that on average 30 m depth shear wave velocity estimates between the two methods differed by p s suspension log measurements of v s were made at the imasw profile midpoint the imasw v s depth inversions resolve 3 m thickness v s variations accurately to the bottom of one borehole at 40 m depth and to 100 m depth at a 200 m deep borehole site

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

improved parameterization to invert rayleigh wave data for shallow profiles containing stiff inclusions inversion of shear wave velocity profiles from phase velocity measurements of rayleigh wave energy for sites containing stiff layers can be erroneous if such layers are not characterized in the starting or reference model incorporation of a priori knowledge then is key for converging upon a realistic or meaningful solution resolving soil profiles in desert regions where stiff layers cemented with calcium carbonate are intermixed with softer uncemented media is an application for which locating shallow stiff inclusions has important implications identification of the stiff layers is critical for foundation design and cost estimating of excavations a parameterization that seems adequate for this problem is to solve for anticipated high stiffness layers embedded in a coarser background profile that captures the general shear wave velocity trend of the study area the optimization is accomplished by using simulated annealing uncertainty measures resulting from the inversion are helpful for describing the influence of the parameterization on final model estimates

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

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

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

characteristics and metallogenic potential of skarn copper lead zinc polymetallic deposits in central eastern gangdese the skarn copper lead zinc polymetallic deposits are distributed in an ew striking metallogenic belt some 450 km long and 90 km wide the metallogenic belt can be divided into three sub belts i e lhasa xietongmen in the western part of gandese jiama linzhou in the northeast and gongga zalang zhedang in the southern part along the brahmaputra river with most of the ore deposits located in jiama linzhou sub belt the ore deposits show apparent regional zonal distribution there exist various kinds of polymetallic deposits such as iron copper copper lead zinc gold silver copper molybdenum lead zinc copper gold deposits and independent copper lead zinc and iron deposits the ore bearing strata consist mainly of jurassic cretaceous marine carbonate strata and carbonate bearing marine volcanic detrital strata the ore controlling stocks are dominated by small granitic stocks or porphyries belonging to calcic alkaline high k calcic alkaline series orebodies mainly occur in stock contact zones and tectonic zones beside stocks the main ore controlling structures include interlaminar tectonic zones stock contact zones and fracture zones the ore formation shows notable multistage mineralization characteristics the copper lead and zinc sulfides must have been precipitated mainly at the retrograde skarn stage and the favorable temperatures for ore precipitation range from 160 to 380 sulfur hydrogen and oxygen isotope studies indicate that the ore forming fluids and materials were mainly derived from magmatic fluids the re os isochronic ages of ore deposits in jiama linzhou region are concentrated in a narrow range of 15 17ma coincident with the stretching period in the crust after the formation of the main collision belt in tibet plateau this implies that the formation of skarn deposits was related to the partial melting at depth and the fluid concentration resulting from the stretching after indian asia plate collision the skarn deposits and the porphyry copper deposits in this region have similar magmatic tectonic and metallogenic geodynamic conditions these two types of ore deposits were formed in the same period and belong to the same metallogenic series the skarn deposits are characterized by polymetallic association high grade great size and high economic value central gangdese has favorable geological and geochemical environments for the formation of skarn deposits it is concluded that jima linzhou basin along leqingla qulong jiama and bangpu might constitute a potential metallogenic area dominated by skarn type copper lead zinc polymetallic deposits

multichannel analysis of surface waves to map bedrock in many geologic settings topographic variations and discontinuities in the surface of bedrock can influence the transport and eventual fate of contaminants introduced at or near the ground surface determining the nature and location of anomalous bedrock can be an essential component of hydrologic characterization preliminary analysis of the hydrologic characteristics of a site in olathe kansas u s based primarily on borehole data alone suggested that a cluster of fractures and or an unmapped buried stream channel may influence fluid movement along the drill defined bedrock surface

helium isotopes as tracers of trapped hydrothermal fluids in ocean floor sulfides helium isotopes have been measured in fluids trapped in minerals from three mid ocean ridge hydrothermal systems at bare rock sites and at the sediment covered site at middle valley northern juan de fuca ridge fluid inclusion 3 he 4 he ratios from the bare rock sites are indistinguishable from those of the vent fluids and are close to the local basalt values values for 34 s of the host sulfide are consistent with variable contributions of seawater sulfate s to the basalt derived s in the hydrothermal fluids this does not affect inclusion hosted 3 he 4 he because of the high he concentration of the hydrothermal fluids relative to seawater fluid inclusion 3 he 4 he ratios from middle valley are a mixture of basalt derived he and radiogenic he acquired from pore fluids in the overlying pleistocene turbidite sediments after seawater basalt interaction the radiogenic he accompanies isotopicalty heavy s demonstrating that he isotopes may be used to distinguish pore fluids from seawater in hydrothermal systems

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

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

mantle crustal and atmospheric noble gases in ailaoshan gold deposits yunnan province china abstract helium and argon isotopic and elemental compositions of fluids released by crushing pyrite grains are reported from the ailaoshan gold province china the province is a series of gold deposits hosted on a 200 km segment of a major normal fault formed during eocene extension the deposits have been well characterised using conventional geochemical and microthermometric techniques the results of which are consistent with a predominantly high temperature magmatic fluid present in the ore minerals in contrast analyses of noble gases from three gold deposits demonstrate the palaeofluids were a mixture between a mantle derived magmatic fluid and two different low temperature fluids similar to modern groundwaters the specific isotopic and abundance characteristics of helium and argon allow unequivocal identification of both a mantle derived component and a surface derived component to these fluids the magmatic fluid dominates deposits from the northern end of the fault the second groundwater is present only in deposits in the south of the province by assuming fluid inclusion homogenisation temperatures in coexisting quartz are representative of fluid temperature 3he heat ratios can be estimated the 3he heat ratios vary systematically along the fault from 30 10 12 cm3 stp j 1 in the northern deposits to

characteristics and genesis of gangdese porphyry copper deposits in the southern tibetan plateau preliminary geochemical and geochronological results porphyry type cu mo au deposits have been discovered along the gangdese magmatic arc in the southern tibetan plateau extensive field investigations and systematic studies of geochemistry s pb isotopic tracing together with re os and 40ar 39ar isotopic dating indicate that the mineralisation of the copper belt is genetically related to emplacement of late orogenic granitic porphyries during the post collisional crustal relaxation period of the late himalayan epoch these porphyries are petrochemically k enriched and belong to shoshonitic to high k calc alkaline series they display enrichment of large ion lithophile elements lile rb k u th sr pb and depletion of high field strength elements hfse nb ta ti and the heavy rare earth elements hree and y without eu anomalies these characteristics demonstrate that subduction played a dominant role in their petrogenesis and residual garnet was left in the magma sources pb isotope data show a linear correlation in the plumbotectonic framework diagram ranging from orogenic pb in the eastern segment of the copper belt to mantle pb in the western segment these constitute a mixing line of the indian oceanic morb with indian oceanic sediments and suggest that the porphyry magmas were dominantly derived from partial melting of subducted oceanic crusts mixed with a minor quantity of sediments and mantle wedge components the gangdese porphyry copper polymetallic belt has alteration characteristics and zonation typical of porphyry type copper deposits which include potassic alteration k feldspathisation and biotitisation silicification sericitisation and propylitisation mineralisation mainly occurs in strongly altered granitic cataclasite at the exo contact with veinlet disseminated textures the porphyries themselves are weakly mineralised with disseminated pyrite and chalcopyrite the copper deposits contain simple ore mineral associations consisting of chalcopyrite pyrite bornite molybdenite sphalerite and oxidised minerals of malachite covellite and molybdite during supergene oxidation primary ores underwent secondary enrichment to form economic orebodies with cu grade ranging from 1 to 5 ore sulphides of the copper belt display s and pb isotopic compositions identical to the ore bearing porphyries their 34s values vary between 3 8 and 2 4 and are typical of mantle sulphur the 206pb 204pb 207pb 204pb and 208pb 204pb ratios vary in the ranges 18 106 to 18 752 15 501 to 15 638 and 37 394 to 39 058 respectively and yielded radiogenetic lead enriched signatures twelve molybdenite samples from the copper belt yielded isochron ages of 14 76 0 22 ma and 13 99 0 16 ma for the nanmu and chongjiang deposits and model ages of 13 5 to 13 6 ma for the lakang e deposit meanwhile 40ar 39ar isotopic dating of two biotite phenocrysts from the chongjiang and lakang e deposits give plateau ages of 13 5 1 0 ma and 13 42 0 10 ma respectively during the geodynamic evolution of the gangdese collision orogenic belt intrusion of the ore bearing porphyries took place just before the rapid uplift and e w extension of the southern plateau and the ore forming process may have occurred simultaneously with the uplift and extension 14 0 1 ma

resolving mantle and crustal contributions to ancient hydrothermal fluids hear isotopes in fluid inclusions from dae hwa wmo mineralisation south korea abstract helium and argon isotopes from fluid inclusions in individual colour zones b c d and e of a large scheelite crystal from the 88 ma dae hwa w mo deposit south korea trace the source and history of the ore fluids a gradual decrease of the fluid 3 he 4 he 3 he 36 ar and 40 ar 36 ar from the core to the edge of the scheelite reflects the progressive dilution of a magmatic fluid by meteoric water and is consistent with the previously observed decrease of 18oh2o and fluid inclusion homogenisation temperatures th shelton et al 1987 the covariation of fluid inclusion he ar isotope systematics with 18o and th defines a magmatic component with 3 he 4 he 1 2 10 6 3 he 36 ar 0 01 and 40 ar 36 ar 1000 anomalously high helium and argon isotope ratios in zone d fluids represents undiluted magmatic noble gases this may reflect local variation in the magmatic gas flux or gas loss due to boiling of the hydrothermal fluids prior to mixing with magmatic gas helium and argon isotope systematics constrain mantle and crustal components in the hydrothermal fluids 40 ar 3 he 4 5 104 are close to the mid ocean ridge basalt value implying that 40ar is mantle in origin radiogenic isotope ratios of the mantle endmember 40 ar 4 he 0 69 0 06 are similar to contemporary geothermal fluids the coincidence of mantle derived he and ar in the fluids is strong evidence that mantle melting during late cretaceous subduction triggered the crystal melting responsible for granite formation 40 ar 4 he of the meteoric fluid 0 007 0 001 is far lower than the crystal production ratio 0 2 implying an origin in crust below 200 c

mineral chemistry of magmatic and hydrothermal biotites from the bangpu porphyry mo cu deposit tibet abstract the bangpu deposit located in the eastern part of the gangdese porphyry copper belt tibet is a porphyry mo cu deposit in a continental collisional orogenic belt the mo cu mineralization occurs mainly in monzogranite porphyry whereas the cu mo mineralization occurs mainly in diorite porphyry most magmatic and hydrothermal biotites from the bangpu deposit are mg rich plotting in the phlogopite and mg biotite compositional fields the bangpu magmatic biotite has high bao 0 1 wt and tio2 3 wt while the hydrothermal biotite has low bao

normal faulting in central tibet since at least 13 5 myr ago tectonic models for the evolution of the tibetan plateau interpret observed east west thinning of the upper crust to be the result of either increased potential energy of elevated crust1 or geodynamic processes that may be unrelated to plateau formation2 3 4 5 6 a key piece of information needed to evaluate these models is the timing of deformation within the plateau the onset of normal faulting has been estimated to have commenced in southern tibet between about 14 myr ago7 and about 8 myr ago8 and in central tibet about 4 myr ago9 here however we report a minimum age of approximately 13 5 myr for the onset of graben formation in central tibet based on mineralization ages determined with rb sr and 40ar 39ar data that post date a major graben bounding normal fault these data along with evidence for prolonged activity of normal faulting in this and other tibetan grabens support models that relate normal faulting to processes occurring beneath the plateau thinning of the upper crust is most plausibly the result of potential energy increases resulting from spatially and temporally heterogeneous changes in thermal structure and density distribution within the crust and upper mantle beneath tibet this is supported by recent geophysical and geological data10 11 12 13 14 15 16 17 which indicate that spatial heterogeneity exists in both the tibetan crust and lithospheric mantle

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