multiple sulfur isotopes monitor fluid evolution of an archean orogenic gold deposit abstract the evolution of a gold bearing hydrothermal fluid from its source to the locus of gold deposition is complex as it experiences rapid changes in thermochemical conditions during ascent through the crust although it is well established that orogenic gold deposits are generated during time periods of abundant crustal growth and or reworking the source of fluid and the thermochemical processes that control gold precipitation remain poorly understood in situ analyses of multiple sulfur isotopes offer a new window into the relationship between source reservoirs of au bearing fluids and the thermochemical processes that occur along their pathway to the final site of mineralisation whereas 34s is able to track changes in the evolution of the thermodynamic conditions of ore forming fluids 33s is virtually indelible and can uniquely fingerprint an archean sedimentary reservoir that has undergone mass independent fractionation of sulfur mif s we combine these two tracers 34s and 33s to characterise a gold bearing laminated quartz breccia ore zone and its sulfide bearing alteration halo in the 6 moz au structurally controlled archean waroonga deposit located in the eastern goldfields superterrane of the yilgarn craton western australia over 250 analyses of gold associated sulfides yield a 34s shift from what is interpreted as an early pre mineralisation phase with chalcopyrite pyrrhotite 34s 0 7 to 2 9 and arsenopyrite cores 34s 0 5 to a syn mineralisation stage reflected in au bearing arsenopyrite rims 34s 7 6 to 1 5 this shift coincides with an unchanging 33s value 33s 0 3 both temporally throughout the au hosting hydrothermal sulfide paragenesis and spatially across the au ore zone these results indicate that sulfur is at least partially recycled from mif s bearing archean sediments further the invariant nature of the observed mif s signature demonstrates that sulfur is derived from a homogeneous mif s bearing fluid reservoir at depth rather than being locally sourced at the site of au precipitation finally by constraining the mif s bearing sulfur source to a fixed reservoir we are able to display the thermochemical evolution of the ore fluid in 34s space and capture the abrupt change in oxidation state that causes au precipitation our results highlight the importance of constraining multiple sulfur isotopes in space and time in order to elucidate the source and evolution of any given au bearing fluid

gold remobilisation and formation of high grade ore shoots driven by dissolution reprecipitation replacement and ni substitution into auriferous arsenopyrite abstract both gold rich sulphides and ultra high grade native gold oreshoots are common but poorly understood phenomenon in orogenic type mineral systems partly because fluids in these systems are considered to have relatively low gold solubilities and are unlikely to generate high gold concentrations the world class obuasi gold deposit ghana has gold rich arsenopyrite spatially associated with quartz veins which have extremely high localised concentrations of native gold contained in microcrack networks within the quartz veins where they are folded here we examine selected samples from obuasi using a novel combination of quantitative electron backscatter diffraction analysis ion microprobe imaging synchrotron xfm mapping and geochemical modelling to investigate the origin of the unusually high gold concentrations the auriferous arsenopyrites are shown to have undergone partial replacement 15 by au poor nickeliferous arsenopyrite during localised crystal plastic deformation intragranular microfracture and metamorphism 340 460 c 2 kbars our results show the dominant replacement mechanism was pseudomorphic dissolution reprecipitation driven by small volumes of an infiltrating fluid that had relatively low s 2 and carried aqueous nicl 2 we find that arsenopyrite replacement produced strong chemical gradients at crystal fluid interfaces due to an increase in s 2 during reaction which enabled efficient removal of gold to the fluid phase and development of anomalously gold rich fluid potentially 10 ppm or more depending on sulphur concentration this process was facilitated by precipitation of ankerite which removed co 2 from the fluid increasing the relative proportion of sulphur for gold complexation and inhibited additional quartz precipitation gold re precipitation occurred over distances of 10 m to several tens of metres and was likely a result of sulphur activity reduction through precipitation of pyrite and other sulphides we suggest this late remobilisation process may be relatively common in orogenic belts containing abundant mafic ultramafic rocks which act as a source of ni and co scavenged by chloride bearing fluids both the preference of the arsenopyrite crystal structure for ni and co rather than gold and the release of sulphur during reaction can drive gold remobilisation in many deposits across broad regions

new insights into the origin of two contrasting himalayan granite belts the two parallel belts of miocene granite that extend along much of the himalaya differ in age petrogenesis and emplacement style we suggest that their origin is linked to shear heating on a continuously active decollement that cuts through previously metamorphosed indian supracrustal rocks that were transformed into basement during the initial stages of the indian asian collision numerical simulations assuming a shear stress of 30 mpa indicate that initiation of slip on the himalayan thrust at 24 ma could trigger discontinuous melting reactions leading to formation of the high himalayan granite chain from 24 to 20 ma and the north himalayan belt from 18 to 12 ma this model result agrees well with observation as do model predictions regarding emplacement style and location

gold bearing arsenian pyrite and marcasite and arsenopyrite from carlin trend gold deposits and laboratory synthesis invisible gold in natural and synthetic arsenian pyrite and marcasite correlates with anomalous as content and fe deficiency and high contents of invisible gold in most natural and all synthetic arsenopyrite correlate with excess as and fe deficiency as rich fe deficient arsenopyrite synthesized hydrothermally contains up to 3 0 wt au uniformly distributed in growth zones of light backscattered electron contrast at the deep star gold deposit carlin trend nevada the sulfide compositions apparently span the full range of metastability from fesz to near feass 40 at s arsenian pyrite contains up to 0 37 wt au but arsenopyrite has excess s and is relatively au poor observed minimum fe contents are 29 1 at in arsenian pyrite and marcasite from the deep star deposit and 31 3 at in synthetic arsenopyrite we suggest that invisible gold in arsenian pyrite and marcasite and arsenopyrite from sediment hosted gold deposits represents au removed from ore fluids by chemisorption at as rich fe deficient surface sites and incorporated into the solids in metastable solid solution however the oxidation state of invisible gold aua au1 remains uncertain because the chemisorption process is intrinsically nonsystematic in terms of crystal chemical parameters and does not result in definitive atomic substitution trends

shisha pangma leucogranite south tibetan himalaya field relations geochemistry age origin and emplacement the shisha pangma pluton forming most of the xixabangma 8027 m massif in south tibet is one of the 20 larger leucogranite intrusives that mark the highest structural levels of the himalayan metamorphic core the pluton occurs immediately below the shisha pangma detachment a strand of the south tibetan detachment std system a low angle 30 north dipping normal fault placing paleozoic black slates atop sillimanite grade pelites and calc silicate rocks k feldspar augen gneisses containing fibrolite and sillimanite paragneisses along the footwall show strong internal s c fabrics indicative of down to the north extension the shisha pangma leucogranite is a heterogeneous polyphase intrusion with an earlier foliated biotite rich phase and a later tourmaline muscovite rich phase typically containing the assemblage kfs pl qtz ms tur gt bt sil ap the highly peraluminous granites have high 87sr 86sr ratios 0 738 0 750 typical of pelite derived anatectites nd depleted mantle model

relationships between gold and pyrite at the xincheng gold deposit jiaodong peninsula china implications for gold source and deposition in a brittle epizonal environment the xincheng gold deposit hosted by the early cretaceous 132 to 123 ma guojialing type granitoids in northwest jiaodong peninsula southeast north china craton formed about 2 billion years later than regional metamorphism of the archean jiaodong basement rocks the xincheng deposit comprises mineralized zones with three types of hydrothermal pyrite associated with gold tellurides and a variety of sulfides py1 as disseminated euhedral to subhedral grains in altered granitoids around quartz veins py2 as subhedral grains with brittle cataclastic textures and fractures in quartz pyrite veins and py3 as subhedral partially corroded crystals in sulfide rich veins or veinlets all three generations of pyrite are unzoned and have low trace element contents including very low lattice bound gold contents py1 0 180 ppm py2 0 053 ppm py3 0 060 ppm given that there is 10 to 15 pyrite in the ore zone at xincheng its very low gold content indicates that it contributes 0 2 of gold to the 7 75 g t gold in the orebody instead over 99 of the gold is present as discrete electrum and or gold total range 0 02 59 silver grains which are largely sited in fractures at all scales in pyrite other ore minerals and quartz importantly visible gold in py3 is also sited on solution corroded pyrite grains the pyrite textural and geochemical data indicate that it is impossible to derive the high gold grade orebodies through local remobilization of originally lattice bound gold in pyrite instead the gold is interpreted to have been deposited through sulfidation reactions and phase separation of a h2o co2 ore fluid during progressive brittle cataclastic deformation associated with seismic activity and regional sinistral transtensional shear movement this concomitant fluid infiltration and deformation caused episodic deposition and fracturing and corrosion of earlier formed pyrite and deposited visible gold in dilational cracks the coupled development of the transtensional rather than normal transpressional setting and precipitation of gold within dilational veins and wall rock alteration facilitated the deposition of visible gold and an exceptionally high gold tenor all deposit characteristics indicate that the xincheng gold deposit is a member of the epizonal orogenic deposit class

structure and geochronology of the southern xainza dinggye rift and its relationship to the south tibetan detachment system abstract the xainza dinggye rift is one of several north south trending rifts in central and southern tibet created by cenozoic east west extension during indo asian convergence the southern part of the rift cuts through the tethyan and high himalayas in the tethyan himalaya this rift consists of an early domal structure and a late normal fault developed during the progressive deformation the dome is cored by leucogranitic plutons that intruded during extension muscovite 40ar 39ar ages of the mylonitic leucogranite indicate that extension in the tethyan himalaya began at 8 ma or before in the high himalaya the rift is controlled by a normal fault dipping to the southeast this fault has a structural constitution similar to a detachment fault its lower block is made up of mylonitic high himalayan gneiss intruded by early mylonitic leucogranite sills and late less deformed biotite bearing leucogranite dikes mica 40ar 39ar ages of these leucogranites and the retrograded metamorphosed gneiss of the lower block range from 13 to 10 ma in the study area the south tibetan detachment system stds is a ductile shear zone composed of mylonitic leucogranite that is intruded by less deformed leucogranite and overlain by low grade metamorphic rocks mica 40ar 39ar ages of leucogranites in the shear zone and schist from the detachment hanging wall indicate a protracted deformation history of the stds from 19 to 13 ma the xainza dinggye rift is younger than the stds because it offsets the stds this north south trending rift belongs to a different tectonic system from the east west striking stds and may be caused by geological process related to india asia convergence this temporal and spatial relationship of the stds to the rift may indicate an important change in tectonic regime at 13 ma in the building of the plateau

mesoscopic faults in the bregaglia bergell massif central alps abstract the strike direction of dip and pitch of the striae along mesoscopic faults in the oligocene granodiorite tonalite of val masino val bregaglia bergell are analysed most fault planes are steeply dipping and show strike slip or oblique slip motion dominant strikes are nnw or nne a relative chronology of fault sets is suggested based on the presence of different minerals chlorite and epidote on fault planes the pattern of mesoscopic faults in the val masino val bregaglia massif does not follow the earlier tectonic trends of the pennidic nappe edifice nor even the trend of the nearby section of the insubric line considered at both regional and mesoscopic scales the mesoscopic analysis of the val masino val bregaglia massif thus reveals a fault system largely oblique to the major alpine lineaments the observed fault pattern does not reveal traces of thrusting referable to late alpine orogenic phases and can be related to subsequent deformation dominated by strike slip movements this pattern does not match the traditional schemes of extensional dip slip faulting following orogenesis it records a stage of tectonic evolution which follows nappe emplacement yet it precedes vertical or extensional post orogenic tectonics

indian continental subduction and slab break off during tertiary collision high wavespeed seismic anomalies in the transition zone and uppermost lower mantle beneath the india asia collision zone imaged by body wave seismic tomography have been interpreted as subducted fragments of continental material in this study we focus on the prominent anomaly located beneath india between depths of about 450 and 900 km by combining the location of this anomaly with palaeogeographical positions of india we constrain the timing of the subduction event probably related to this anomaly we infer that a large portion of the north western margin of india initiated subduction at 35 5 ma along a 1500 km long wnw ese striking zone and ended with a progressive slab break off process this break off started most probably around 25 ma at the western end of the slab and propagated eastwards until complete break off around 15 ma this study helps to constrain better the amount of convergence between india and asia absorbed by continental subduction

direct stratigraphic dating of india asia collision onset at the selandian middle paleocene 59 1 ma the collision of india with asia had a profound influence on cenozoic topography oceanography climate and faunal turnover however estimates of the time of the initial collision when indian continental crust arrived at the transhimalayan trench remain highly controversial here we use radiolarian and nannofossil biostratigraphy coupled with detrital zircon geochronology to constrain firmly the time when asian derived detritus was first deposited onto india in the classical sangdanlin section of the central himalaya which preserves the best paleocene stratigraphic record of the distal edge of the indian continental rise deep sea turbidites of quartzarenite composition and indian provenance are replaced upsection by turbidites of volcano plutoniclastic composition and asian provenance this sharp transition occurs above abyssal cherts yielding radiolaria of paleogene radiolarian zones rp 4 6 and below abyssal cherts containing radiolaria of zone rp6 and calcareous shales with nannofossils of the paleocene calcareous nannofossil zone cnp 7 constraining the age of collision onset to within the middle paleocene selandian the youngest u pb ages yielded by detrital zircons in the oldest asia derived turbidites indicate a maximum depositional age of 58 1 0 9 ma collision onset is thus mutually constrained by biostratigraphy and detrital zircon chronostratigraphy as 59 1 ma this age is both more accurate and more precise than those previously obtained from the stratigraphic record of the northwestern himalaya and suggests that within the resolution power of current methods the india asia initial collision took place quasi synchronously in the western and central himalaya

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

identifying geochemical anomalies associated with sb au pb zn ag mineralization in north himalaya southern tibet abstract the north himalaya is a prospective area for sb sb au au pb zn ag and sb pb zn ag mineralization geochemical anomalies for mineralizing elements and element associations were identified using concentration area c a fractal model together with statistical analyses including the mean 2 standard deviation mean 2std and the median 2 median absolute deviation median 2mad the results show that the mean 2std for log transformed data and c a model could well identify the geochemical anomalies associated with mineralization in the north himalaya sb au anomalies show a better spatial association with sb sb au and sb pb zn ag deposits than those of single sb element au anomalies are associated with all deposits and pb zn ag anomalies are associated with pb zn and sb pb zn ag deposits in addition weak anomalies associated with sb mineralization can be identified by the singularity method with the utilization of the sb au sb au and pb zn ag anomalies identified by c a fractal model and mean 2std for log transformed data as well as the singularity method we can facilitate the exploration targeting of various deposits in the north himalaya in addition our results also show that principal component analysis pca of centered logratio clr transformed data can accurately recognize three different geochemical assemblage compositions representing three different types of mineralization i e au pb zn ag and sb in the north himalaya

the geology and tectonics of central bhutan lithotectonic mapping metamorphic observations and u pb zircon ages underpin a substantial revision of central bhutan geology notably a more extensive and continuous outcrop of the tethyan sedimentary series tss than previously mapped metamorphic grade in the tss increases downward towards a basal north vergent tectonic contact with the underlying greater himalayan series ghs interpreted as a southward continuation of the south tibetan detachment std miocene c 17 20 ma leucogranite sheets are associated with the std in this region but appear to diminish southwards two leucogranite dykes that cross cut tss structures yield ages of 17 8 0 2 and 17 9 0 5 ma a 500 4 ma u pb zircon metamorphosed ash bed in the pele la group within the psammite dominated lower tss yields the first direct isotopic age for the tss in the eastern himalaya confirming existing age constraints from detrital zircon and fossil studies a continuation of the paro metasedimentary unit underlying the ghs was mapped near wangdue phodrang our observations notably the exposure of a wholly ductile std so far south and the significance of large nappe like structures in the tss prompt a major revision to the geological map of the bhutan himalaya and require a reassessment of tectonic interpretations of the bhutan himalaya supplementary materials zircon u pb geochronological data sample locations and descriptions features of analysed zircons sample processing method and detailed analytical conditions are available at http www geolsoc org uk sup18876

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

new insight into the south tibetan detachment system not a single progressive deformation 1 low angle normal faults lanf typically regarded as accommodating crustal or lithospheric extension may also form during lithospheric shortening the best studied system of syn contractional lanfs is the south tibetan detachment system a network of low angle normal sense faults and shear zones that formed coevally with and parallel to south vergent thrusts during lithospheric shortening accompanying development of the himalayan orogen in the eastern himalaya there are several across strike exposures of the south tibetan detachment system we present new structural and thermometry data from the eastern himalaya that demonstrate that the south tibetan detachment system cannot have formed as a single progressive structure we characterize and distinguish two distinct structural and tectonic components within the currently recognized system 1 an extensive diffuse sheared layer that formed the boundary between strong upper crust and weak southward flowing middle crust and 2 a network of brittle ductile lanfs that locally exhume partly excise and overprint the earlier mylonite zone at the topographic break between the himalayan orogen and the tibetan plateau the sheared layer not a lanf formed the boundary between upper and middle crust during ductile flow of the middle crust and is extensively exposed in the himalaya at the base of klippen of upper crustal rocks preserved in bhutan along the crest of the himalaya where it has been excised and exhumed by the brittle ductile extrusion lanfs and bounding the cores of the north himalayan gneiss domes citation kellett d a and d grujic 2012 new insight into the south tibetan detachment system not a single progressive deformation tectonics 31 tc2007 doi 10 1029 2011tc002957

sedimentary history of the tethyan basin in the tibetan himalayas after an epicontinental phase the sedimentary rocks in the tibetan himalayas document a complete wilson cycle of the neo tethyan tethys ill evolution between the gondwana supercontinent and its northward drifting margin lhasa block from the late permian to the eocene during the triassic rift stage the basin was filled with a huge clastic dominated sediment wedge with up to 5 000 m of flysch in the northern zone widespread deltaic clastics and shallow water carbonates of late norian to earliest jurassic age in the southern zone mark in conjunction with decreasing tectonic subsidence the transition to the drift stage some 4 500 m of jurassic and early cretaceous shallow water carbonates and siliciclastics accumulated on the tethyan indian passive margin deepening upward sequences with condensed beds at their tops alternate with repeated progradational packages of shelf sediments extensive abyssal sediments with basaltic volcanics in the northern deep water zone reflect continued ocean spreading and thermal subsidence paleomagnetic data gained separately for the northern indian plate and the lhasa block indicate that the neo tethys reached its maximum width about 110 ma ago with a spreading rate of 4 8 cm year before it commenced to close again during the remnant basin stage in the late cretaceous and paleogene a shallowing upward megasequence capped by a carbonate platform developed in the southern inner shelf realm in the northern slope basin plain zone turbidites and chaotic sediments derived from both the acretionary wedge and the steepening slope of the passive margin accumulated the depositional center of the remnant basin shifted southward as a result of flexural subsidence and southward overthrusting the sediments from the triassic to the paleogene are tentatively subdivided into five mega sequences which are controlled mainly by regional tectonics climatic influence e g carbonate deposition due to northward plate motion is partially subdued by terrigenous input and or increased water depth during the oligocene and miocene crustal shortening led to rapid uplift and the deposition of fluvial molasse in limited basins

application of aromatic compounds as maturity indicators in source rocks and crude oils concentration ratios of aromatic compounds such as naphthalenes phenanthrenes and dibenzothiophenes are at present attracting increasing attention as maturity indicators in sedimentary rocks and crude oils generally these indicators rely either on an increase with maturity in the degree of alkylation of a given parent compound or a shift in the isomer distribution of alkyl aromatic homologues towards thermally more stable isomers a combination of both concepts in the methylphenanthrene index mpi resulted in an excellent maturity parameter as demonstrated for rock extracts by an improved correlation with mean vitrinite reflectance rm between 0 65 and 1 4 i e in the zone of oil formation in cases that rm measurements were ambiguous this empirical relationship has proved useful in the calculation of theoretical vitrinite reflectance rc values from the mpi on the other hand for potential petroleum source rocks reaching maturity at relatively low temperatures the influence of the organic matter type on the aromatic distributions cannot be neglected consequently organic facies effects should be taken into account in the interpretation of aromatic distributions of such source rocks and related crude oils since the impact of the organic facies is strongly reduced with increasing maturity aromatic maturity parameters are particularly useful in the maturity evaluation of post mature crude oils and condensates in contrast to biological markers substantially higher concentrations of the key alkyl aromatics persist at elevated maturation levels thus aromatic maturity parameters should be considered as versatile tools in organic maturation studies and can complement established maturity indicators based on steranes and terpanes

distributed deformation in southern and western tibet during and after the india asia collision field and radiometric data are used to describe and date strain and stress states in southern longitude 88 o to 91oe latitude 28 o to 30on and western tibet longitude 79 o to 82oe latitude 30 o to 34on we factorize deformation into syncollisional and postcollisional and we present stretching lineation and displacement orientation maps two sections across the indian shelf sequence and stress orientations calculated from mesoscale fault slip data in southern tibet syncollisional stretching and displacement directions trend 90 46 o and displacement is top to south synkinematic low grade metamorphism is dated at 50 ma at one locality in the indian shelf sequence underlying the main mantle thrust of the indus yarlung suture this implies paleocene onset of continental collision for the investigated section postcollisional structures comprise a backthrust group which includes foreland and hinterland directed thrusts reverse and strike slip faults and folds it dominates postcollisional deformation is concentrated along the indus yarlung suture and portrays n s compression otrend of 8o 17 o o2 of 97o 17o a strike slip group consists of conjugate strike slip faults is concentrated in east trending narrow highly deformed zones and indicates that n s compression is locally compensated by e w extension oof 15o 29 o o3 of 103o 30o synkinematic muscovite dates postcollisional deformation as late early miocene 17 5 ma at one locality at the suture strike slip and oblique normal 03 of 600 23 o oof 144o 21 o and normal o3 114o 16 o faulting dated between late miocene and recent and including active deformation represents dominant e w and minor n s extension due to e w stretching of southern tibet and oroclinal bending along the himalayan arc restoring syncollisional and postcollisional deformation yields a minimum of 67 258 km shortening across the indian shelf sequence incorporating recently published contraction estimates across the eastern himalaya yields minimum shortening between undeformed india and the indus yarlung suture of 66 536 km the himalaya tibet orogenic system south of the indus yarlung suture had an initial width of 811 km in the southern tibetan section in western tibet imbrication of an ophiolite sequence of the bangong nujiang suture is top to south stretching lineation trend of 15o 18o and o3 of active deformation trends ese faulting along the shiquanhe fault zone which transfers displacement from the northern part of the karakorum fault to a system of rifts in western central tibet indicates dextral strike slip alternating with sinistral oblique normal faulting and block rotations around vertical axes during a prolonged shearing history the indian shelf sequence south of mount kailas shows top to south imbrication stretching lineation trend of 52o 60o both indian shelf rocks and oligocene miocene kailas conglo merates record backthrusting and backfolding oof 33 o and recent e w extension 03 of 85o 28o

stratigraphy of the upper cretaceous and lower tertiary strata in the tethyan himalayas of tibet tingri area china the 1500 m thick marine strata of the tethys himalaya of the zhepure mountain tingri tibet comprise the upper albian to eocene and represent the sedimentary development of the passive northern continental margin of the indian plate investigations of foraminifera have led to a detailed biozonation which is compared with the west tethyan record five stratigraphic units can be distinguished the gamba group upper albian lower santonian represents the development from a basin and slope to an outer shelf environment in the following zhepure shanbei formation lower santonian middle maastrichtian outer shelf deposits continue pebbles in the top layers point to beginning redeposition on a continental slope intensified redeposition continues within the zhepure shanpo formation middle maastrichtian lower paleocene the series is capped by sandstones of the jidula formation danian deposited from a seaward prograding delta plain the overall succession of these units represents a sea level high at the cenomanian turonian boundary followed from the turonian to danian by an overall shallowing upward megasequence this is followed by a final transgression regression cycle during the paleocene and eocene documented in the zhepure shan formation upper danian lutetian and by upper eocene continental deposits the section represents the narrowing and closure of the tethys as a result of the convergence between northward drifting india and eurasia the plate collision started in the lower maastrichtian and caused rapid changes in sedimentation patterns affected by tectonic subsidence and uplift stronger subsidence and deposition took place from the middle maastrichtian to the lower paleocene the final closure of remnant tethys in the tingri area took place in the lutetian

synchronous oligocene miocene metamorphism of the pamir and the north himalaya driven by plate scale dynamics gneiss domes in the pamir central asia and the himalaya provide key data on mid to deep crustal processes operating during the india asia collision laser ablation split stream inductively coupled plasma mass spectrometry lass icp ms data from monazite in these domes yield a time record from u th pb dates and a petrologic record from rare earth element ree abundances seven samples from the pamir and six samples from the north himalayan gneiss domes yield almost identical monazite dates of ca 28 15 ma most monazite has invariant heavy ree hree abundances two samples however have older monazite that records progressive hree depletion and two samples have younger monazite that records progressive hree enrichment these variations in hree are compatible with increasing garnet abundance prograde metamorphism until ca 20 ma and decreasing garnet abundance thereafter the change from hree depletion to enrichment may record a transition from crustal thickening and heating to dome exhumation and cooling this documentation of synchronous barrovian metamorphism within domes of indian crust along the margin of the orogen himalaya and within domes of asian crust within the core of the orogen pamir is best explained by a plate scale driving force rather than by local events we propose that widespread synchronous thickening was initiated by the resumption of indian subduction following slab breakoff and then terminated by a second slab tearing event both plate scale events inferred from tomography

extreme variation of sulfur isotopic compositions in pyrite from the qiuling sediment hosted gold deposit west qinling orogen central china an in situ sims study with implications for the source of sulfur high spatial resolution textural scanning electron microscope sem chemical electron microprobe emp and laser ablation inductively coupled plasma mass spectrometry la icp ms and sulfur isotopic secondary ion mass spectrometry sims analyses of pyrite from the qiuling sediment hosted gold deposit 232 4 ma in the west qinling orogen central china were conducted to distinguish pyrite types and gain insights into the source and evolution of sulfur in hydrothermal fluids the results reveal an enormous variation 27 1 to 69 6 in sulfur isotopic composition of pyrite deposited during three paragenetic stages pre ore framboidal pyrite which is characterized by low concentrations of as au cu co and ni has negative 34s values of 27 1 to 7 6 that are interpreted in terms of bacterial reduction of marine sulfate during sedimentation and diagenesis of the paleozoic carbonate and clastic sequences the predominant lithologies in the deposit area and the most important hosts of many sediment hosted gold deposits throughout the west qinling orogen the ore stage hydrothermal pyrite contains high concentrations of au as cu sb tl and bi and has a relatively narrow range of positive 34s values ranging from 8 1 to 15 2 the sulfur isotope data are comparable to those of ore pyrite from many triassic orogenic gold deposits and paleozoic sedimentary exhalative sedex pb zn deposits in the west qinling orogen both being hosted mainly in the devonian sequence this similarity indicates that sulfur responsible for the auriferous pyrite at qiuling was largely derived from the metamorphic devolatization of paleozoic marine sedimentary rocks post ore stage pyrite which is significantly enriched in co and ni but depleted in au and as has unusually high 34s values ranging from 37 4 to 69 6 that are interpreted to result from thermochemical reduction of evaporite sulfates in underlying cambrian sedimentary rocks with very high 34s values the variations in au content and sulfur isotopic compositions across a single ore stage pyrite grain may reflect displacement of indigenous groundwater with low 34s values by auriferous metamorphic fluids with high 34s values the very low grade metamorphism of the host rocks and the metamorphic derivation of sulfur for the ore pyrite indicate that the qiuling sediment hosted gold deposit is an epizonal manifestation of an orogenic gold system in the west qinling orogen

la icp ms trace element analysis of pyrite from the chang an gold deposit sanjiang region china implication for ore forming process abstract the chang an gold deposit yunnan province is one of five large gold deposits in the ailaoshan gold belt that is the most important ore belt of the sanjiang tethyan metallogenic domain geochemical study of pyrite in the deposit was conducted using laser ablation inductively coupled plasma mass spectroscopy three types of hydrothermal pyrite were identified in the ores and wall rocks i e the coarse euhedral crystals in syenite py1 the coarse grains disseminated in altered sandstones or sandstone ores py2 and the fine grained euhedral pyrite in sandstone ores py3 their trace elements exhibit different concentrations associations and rim core zoning implying different geneses and crystallization processes the cores of py1 were formed by magmatic fluids and have the lowest concentrations of au as cu and zn the cores of py2 were formed by metamorphic fluids and have relatively high au ag ni pb and cu concentrations the py3 grains and the growth rims of py1 and py2 show consistently high contents of au as pb and co suggesting that all of them were rapidly deposited from a mixing fluid system that was probably composed of fluids of metamorphic and magmatic origins this interpretation is supported by the observation that the high grade ores generally contain lots of py2 and py3 hence we consider that the deposit was formed during india asia collision slightly postdate the 33 35 ma tectono magmatism

arsenopyrite pyrite association in an orogenic gold ore tracing mineralization history from textures and trace elements laser ablation inductively coupled plasma mass spectrometry la icp ms spot analysis and element mapping coupled with high resolution focused ion beam scanning electron microscopy fib sem imaging has been performed on au hosting sulfides from a proterozoic orogenic gold deposit tanami gold province north central australia gold distribution patterns in the arsenopyrite pyrite assemblage which probably crystallized toward the end of the au forming event suggest a process of initial scavenging of au into arsenopyrite and subsequent remobilization of that au following brittle fracture gold expelled from the sulfide lattice during the remobilization event is reconcentrated around the margins of the same arsenopyrite grains and within swarms of crosscutting microfractures the distribution of pb bi and ag closely mimic au indicating that these elements were also reconcentrated preservation of oscillatory zonation patterns for co ni sb se and te in arsenopyrite imply however that no significant degree of sulfide recrystallization took place residual concentrations of invisible gold in grain centers are 5 ppm in arsenopyrite and 1 ppm in coexisting pyrite the presence of submicron sized pores is suggestive of a fluid driven process rather than solid state diffusion micron scale 2 10 m remobilized gold is accompanied by fine particles 200 nm 2 m and nanoparticles 200 nm of gold the extensive variation of au concentrations within single arsenopyrite grains underlines the significance of textures when using trace element data to understand how gold ores evolved

bimodal distribution of gold in pyrite and arsenopyrite examples from the archean boorara and bardoc shear systems yilgarn craton western australia this study investigates the microstructures geochemistry and hydrothermal evolution of gold bearing pyrite and arsenopyrite from six orogenic gold deposits in the archean eastern goldfields province western australia scanning electron microscope sem electron microprobe emp and laser ablation inductively coupled plasma mass spectroscopy la icp ms analyses show that the gold bearing minerals possess a number of similar textural features including the occurrence of invisible gold within initial phases of growth and later stage visible gold associated with alteration rims the alteration rims are characterized by a higher than average atomic mass mainly owing to arsenic enrichment and are preferentially located along fractures and grain boundaries in the pyrite and arsenopyrite these observations suggest that visible gold formation is associated with hydrothermal alteration of preexisting pyrite and arsenopyrite textural observations and la icp ms data suggest that some invisible gold was remobilized from early formed pyrite and arsenopyrite to form visible gold during development of these alteration rims gold may also have been added by hydrothermal fluids during a later stage of mineralization in situ geochemistry and phase relationships of alteration rims are used to further constrain the hydrothermal process responsible for formation of alteration rims and visible gold in fractures based on sulfide stability relations our data indicate that development of arsenopyrite alteration rims associated with late stage visible gold formation was related to an increase in temperature maximum increase from 310 to 415 c and up to of sic orders of magnitude increase in sulfur fugacity whereas changes in oxygen fugacity were less important la icp ms analyses show that the relative and absolute variations in selected trace element au ag sb bi ba te pb co and mo concentrations can also be used to distinguish between unaltered and altered pyrite and arsenopyrite in general trace elements within pyrite and arsenopyrite have a relatively uniform distribution whereas later stage alteration rims have more variable trace element distributions although the observed textures are typical of prograde metamorphic coronae we suggest that they are the consequence of variations in fluid conditions and chemistry and that mineralization occurred in response to syn and or postpeak metamorphic fluid infiltration

fluid inclusion geochemistry and ar ar geochronology of the cenozoic bangbu orogenic gold deposit southern tibet china abstract located along the southern part of the yarlung zangbo suture zone in southern tibet bangbu is one of the largest gold deposits in tibet auriferous sulfide bearing quartz veins are controlled by second or third order brittle fractures associated with the regional qusong cuogu zhemulang brittle ductile shear zone fluid inclusion studies show that the auriferous quartz contains aqueous inclusions two phase and three phase co2 bearing inclusions and pure gaseous hydrocarbon inclusions the co2 bearing inclusions have salinities of 2 2 9 5 nacleq and homogenization temperatures th of 167 336 c the d 18o and 13c compositions of the bangbu ore forming fluids are 105 5 to 44 4 4 7 to 9 0 and 5 1 to 2 2 respectively indicating that the ore forming fluid is mainly of metamorphic origin with also a mantle derived contribution the 3he 4he ratio of the ore forming fluids is 0 174 to 1 010 ra and 40ar 36ar ranges from 311 9 to 1724 9 calculations indicate that the percentage of mantle derived he in fluid inclusions from bangbu is 2 7 16 7 these geochemical features are similar to those of most orogenic gold deposits dating by 40ar 39ar of hydrothermal sericite collected from auriferous quartz veins at bangbu yielded a plateau age of 44 8 1 0 ma with normal and inverse isochronal ages of 43 6 3 2 ma and 44 3 ma respectively this indicates that the gold mineralization was contemporaneous with the main collisional stage between india and eurasia along the yarlung zangbo suture which resulted in the development of near vertical lithospheric shear zones a deep metamorphic fluid was channeled upward along the shear zone mixing with a mantle fluid the mixed fluids migrated into the brittle structures along the shear zone and precipitated gold sulfides and quartz because of declining temperature and pressure or fluid immiscibility the bangbu is a large scale cenozoic syn collisional orogenic gold deposit

north south extension in the tibetan crust triggered by granite emplacement we combine zircon sensitive high resolution ion microprobe u pb spot dating and mica 4 0 ar 3 9 ar plateau ages with field geological and geochemical constraints from the malashan area of southern tibet to show that the deformed granite core of the north himalayan metamorphic domes in this area is not indian basement but was intruded and deformed during the himalayan orogeny microstructural observations reveal that a transition from top to the south thrust related to top to the north extension related deformation occurred during granite intrusion and related metamorphism this suggests that intrusion triggered the onset of extensional tectonics in the tibetan middle to upper crust expected positive feedback mechanisms between decompression melting leading to more intrusion and more extensional deformation suggest that this mechanism may have been important on a regional scale

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

sulfide replacement processes revealed by textural and la icp ms trace element analyses example from the early mineralization stages at cerro de pasco peru the large cerro de pasco cordilleran base metal deposit in central peru is the result of three successive mineralizing stages comprising both low and high sulfidation mineral associations a several pyrrhotite pipes grading outward to sphalerite and galena replacement bodies b a massive funnel shaped pyrite quartz replacement orebody and c e w trending cu ag au zn pb enargite pyrite veins and well zoned zn pb bi ag cu carbonate replacement orebodies this superposition of hydrothermal events leads to complex replacement textures and crosscutting relationships a detailed study of the textures and mineral composition of the up to 15 m wide replacement front existing between the pyrrhotite pipes and the pyrite quartz body allows for clarification of the relative chronology of the hydrothermal events the results show that in contrast to previous interpretations the emplacement of the pyrrhotite pipes and their zn pb mineralized rims precedes that of the pyrite quartz body the replacement textures affecting pyrrhotite and arsenopyrite and the nature of the newly formed minerals have been used as a qualitative way to track the evolution of fs2 fo2 and ph of the mineralizing fluids two steps of pyrrhotite replacement have been recorded the first one takes place under moderate acidity and relatively reduced to moderately oxidized conditions and is marked by replacement of pyrrhotite by euhedral nonporous pyrite the second step occurs under more acidic and oxidized conditions and is characterized by replacement of pyrrhotite by porous marcasite and replacement of arsenopyrite by pyrite subsequently marcasite is partly replaced by fine grained euhedral nonporous pyrite la icp ms trace element analyses of the replaced pyrrhotite and arsenopyrite and of the newly formed marcasite and pyrite support dissolution reprecipitation as the main mechanism for replacement positive correlations between some of the elements e g pb sb pb ag are indicative of the possible presence of nanoscale solid inclusions as main carriers for those elements however coupled substitutions and incorporation of some of the elements at a ppm level into the pyrite and marcasite structures cannot be excluded the obtained as sb pb and bi values in pyrite are systematically higher than published data of pyrite in epithermal and porphyry systems nature and trace element content of the newly formed minerals yield information on the physicochemical conditions during their precipitation the initial trace element content of replaced minerals and the subsequently dissolved neighboring phases the results show that the metal concentration of the fluid is locally influenced by the composition of the dissolved minerals this study leads to a simpler interpretation of the fluid evolution than previously proposed with a progressive increase of fs2 fo2 and ph as a result of decreasing wall rock buffering during the three successive mineralizing stages at cerro de pasco

oil filling history of the ordovician oil reservoir in the major part of the tahe oilfield tarim basin nw china abstract the ordovician oil reservoir in the tahe oilfield northern tarim basin is so far the largest marine oil reservoir in china ordovician oil was sampled from 73 exploration production wells in the oilfield according to oil oil correlation all the ordovician oil samples belong to the same oil population of mature to high mature phase based on the coexisting intact n alkane series evident ucm and 25 norhopanes in the oil as well as the bimodal distribution pattern of homogenization temperatures t h ranging from 80 to 100 c and from 115 to 135 c respectively in fluid inclusions within the reservoir rocks it is concluded that the oil reservoir has been twice charged during its oil filling history by means of 1d basin modeling the measured t h values can be related to relevant geological ages of 429 415 ma and of 8 2 ma respectively i e the middle to late silurian and the miocene to pliocene representing two phases of oil filling and entrapment using independent molecular parameters e g the 4 1 mdbt ratio and total concentrations of pyrrolic n compounds as indicators to reconstruct the oil filling process in the reservoir oil filling pathways can be traced and mapped the general orientation of oil filling is from south to north in the oil reservoir therefore it can be predicted that its source kitchen should be on the south side of the oilfield most probably at the shuntuoguole uplift between the awati and manjiaer depressions

tectonics of the northern himalaya since the india asia collision abstract the india asia collision resulted in the construction of the vast himalayan orogen the northern himalayan domain began to experience extensional tectonics since eocene oligocene transition eot when the himalayan orogeny was still in progress major structures generated by the extension in the northern himalaya include the south tibet detachment system stds the north himalayan gneiss domes nhgd and the north south trending rifts nstr the earliest emplacement of syn deformational leucogranite at 36 32 ma along the stds marks the initial transformation from thickening to thinning in the northern himalayan domain at eot the thickening before eot caused crustal partial melting which formed the weak root of the thickened orogen or the so called channel flow this channel flow triggered the collapse of the orogen extrusion of the greater himalayan crystalline complex ghc and the onset of extensional tectonics of the stds the similarities in tectono thermal history and geochemistry of rocks between the stds and nhgd suggest that the formation of the nhgd has a direct relationship to the activity of the stds the extension of stds and the resultant thinning caused further partial melting of the crust leading to the larger scale emplacement of leucogranite during miocene 27 13 ma diapirism of these plutons shaped the domes in nhgd exposing the ghc and the shear zones of the stds in the northern himalaya in gyirong another tectonic transform from extension to shortening occurred after 18 7 ma in dinggye region the stds was offset by the nstr culminating the deformation at 13 ma when the nstr began to be active this indicates another tectonic transform in the northern himalaya at 13 ma when the n s extension of the stds ceased and gave way to e w extension of the nstr marking the end of the peak granitic magmatism in northern himalaya multiple episodes of deformation in the major structures such as the stds mct and nstr and superposition of different structures indicate a multiphase orogenic process in the himalayas in which mountain building and collapse occurred alternately with the formation of nstr and conjugate shear zones in tibet this tectonic scenario was possibly controlled by the india asia convergent rate we propose that the extension was an integral part of the orogenic process rather than a simple marker of the culmination of the orogeny

uncloaking invisible gold use of nanosims to evaluate gold trace elements and sulfur isotopes in pyrite from carlin type gold deposits one hundred nm resolution secondary ionizing mass spectrometry nanosims was used to determine the distribution of au cu as sb and s and stable isotopes of s 34s 32s in gold bearing pyrite from two refractory carlin type gold deposits west banshee northern carlin trend and turquoise ridge getchell trend located in northern nevada nanosims maps reveal that gold occurs in two discrete episodes in each deposit elevated gold concentrations correlate with elevated concentrations of as sb cu te and lower 34s 32s ratios compared to periods when gold was not deposited precipitation of elevated gold and trace elements at west banshee was followed by precipitation of pyrite with lower gold concentrations whereas at turquoise ridge precipitation of trace element rich pyrite was followed by precipitation of late ore stage minerals these nanosims results are consistent with formation of the deposits by the episodic incursion of gold rich fluids into hydrothermal systems otherwise dominated by gold poor fluids such gold rich fluid pulses may be related to incursions of magmatic fluid which have been shown to have high concentrations of gold arsenic and copper in porphyry and high sulfidation epithermal systems

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

e w extension at 19 ma in the kung co area s tibet evidence for contemporaneous e w and n s extension in the himalayan orogen abstract active faulting in southern tibet consists of n s trending extensional faults and linked strike slip faults which are an expression of regional e w extension a second type of extensional deformation associated with n s movement is also recognized this extension is expressed as a series of shear zones and normal faults in the high himalayas the southern tibetan detachment system and mid crustal rocks exposed in metamorphic domes reported constraints on the timing of movements associated with these two phases of extension indicate that n s extension predates the onset of e w extension however only a few studies have provided clear constraints on the timing of e w extension and the extent to which the two kinematically distinct domains of extension were contemporaneous is unclear the kung co fault in southern tibet is a major n s trending normal fault the associated e w extension is locally expressed as high strain ductile deformation both field and microstructural observations show that this deformation occurred synchronously with granite intrusion previously reported u pb zircon dating shows granite crystallization took place at around 19 ma implying that ductile e w extension in the kung co area was also active at around 19 ma this is the oldest documented example of e w extension in tibet and shows that e w extension was at least locally contemporaneous with n s extension to the south at shallower crustal levels simultaneous mid crustal n s extension and upper crustal e w extension may be explained by southward flow of tibetan crust with a divergent radial component

activation of the nyainqentanghla shear zone implications for uplift of the southern tibetan plateau neogene extension of the tibetan plateau is manifested as a series of north south trending graben the most prominent of which is the yadong gulu rift the nyainqen tanghla shan a ne sw trending mountain range 100 km nw of lhasa bounds the western margin of the yangbajian graben the central segment of the yadong gulu rift the eastern edge of the nyainqentanghla massif is marked by a low angle 25 o detachment fault shear zone of amphibolite grade mylonites the noar 3 ar thermal history results from samples collected along two deeply incised valleys within the massif reveal that a rapid cooling event propagated from 8 ma in the core of the range to 4 ma within the high strain zone at the eastern boundary assuming that faulting initiated at high angle 60o thermal histories were fit to a numerical simulation of slip on a normal fault to yield estimates of both the age of fault initiation and the slip rate history the form of the isotopically derived thermal histories are similar to general form predicted by the thermal model and suggests that significant movement began at 8 1 ma in the southern valley goring la and proceeded at an average slip rate of 3 mm yr between 8 and 3 ma a more complex history is required to fit the data from the northern valley balum chun but the timing of initiation and average slip rate are similar to the goring la result numerical simulations in which the fault angle is varied indicate that the isotopically derived temperature histories are inconsistent with slip occurring at low angle 40o because the extension direction of the yangbajian graben is representative of most rifts on the southern tibetan plateau our data suggest that crustal thickness and elevation reached close to their present values by 8 1 ma a carbon isotopic shift in pedogenic carbonates from the siwalik formation at about 7 5 ma appears to reflect intensification of the asian monsoon and by inference that the plateau had attained an important threshold elevation by that time formation of a diffuse plate boundary in the indian oceanic lithosphere beginning at 7 5 8 0 ma is also consistent with this history we suggest that the plateau had attained a threshold area and elevation by 8 1 ma sufficient to trigger these three independent manifestations

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

genesis of the bangbu gold deposit in the southern tibet evidenced from in situ sulfur isotopes and trace element compositions of pyrite abstract the bangbu orogenic gold deposit in the north himalaya of the southern tibet contains more than 40 t au at an average grade of 7 0 g t in this deposits gold bearing quartz veins were controlled by nearly e trending qusong cuogu zhemulang shear zone and occurred within the secondary faults which crosscut late triassic greenschist facies rocks to further understand the sulfur source and ore forming process we have conducted a compressive study of in situ sims sulfur isotopes and la icp ms trace element compositions of two stages of pyrite at bangbu early stage pyrite py1 is coarse grained mostly 0 2 2 mm and euhedral and has gold concentrations of less than 0 3 54 ppm mean of 20 ppm and 34s values of 1 6 5 1 mean of 3 2 late stage pyrite py2 is generally fine grained mostly

deposystem architectures and lithofacies of a submarine fan dominated deep sea succession in an orogen a case study from the upper triassic langjiexue group of southern tibet abstract over thirty stratigraphic sections of the himalaya orogen upper triassic langjiexue group in southern tibet china were studied to interpret the environments and lithofacies the facies associations channel a lobe b levee interchannel c and basin plain d with nine facies a1 3 b1 3 and c1 3 were distinguished they form six architectural elements channel interchannel overbank levee crevasse splay outer fan lobe fan fringe and basin plain taking into account the facies analysis sub deposystem correlation paleocurrent dispersal pattern and restoration of primary stratal width the langjiexue group displays the architecture of a coalescing submarine fan dominated deep sea deposystem measuring about 400 500 km 600 700 km in size or even more one of the largest pre cenozoic submarine fans ever reported subdivisionally four fans lacking inner fans could have coalesced laterally within the submarine fan deposystem and at least six submarine fan developments were vertically succeeded by mid to outer fan deposits with progradational to retrogradational successions according to the range of 30 70 of sandstone content the fan deposystem is mud and sand rich suggesting a medium far over 400 600 km transport of sediment from the source area

early palaeozoic orogenesis along the indian margin of gondwana tectonic response to gondwana assembly abstract shrimp u pb dating of zircons from a peralkaline s type lesser himalayan granite from the kathmandu region nepal indicate an age of emplacement of 475 ma the granites along with metasedimentary xenoliths show a similar signature of inherited detrital zircon ages ranging from archaean to early palaeozoic with prominent late mesoproterozoic grenvillian and neoproterozoic pan african age peaks and have a maximum age of 500 ma based on the youngest detrital grains deformation structures in xenoliths are truncated by the granite and along with the granites are assigned to a cambro ordovician orogenic event herein termed the bhimphedian orogeny that can be traced across the himalaya from pakistan to the eastern himalaya and possibly extends west into afghanistan we interpret the orogeny as being related to andean type orogenic activity on the northern margin of the indian continent following gondwana assembly the magmatic arc was associated with andesitic and basaltic volcanism and was active from c 530 to 490 ma the arc activity overlaps with and is succeeded by regional deformation crustal melting and s type granite emplacement that extended to 470 ma orogenic activity was driven by coupling across the plate margin either during on going subduction or through accretion of microcontinental ribbons possibly represented by the lhasa and qiangtang blocks it represents the termination of an orogenic cycle termed the north indian orogen that commenced with neoproterozoic rifting and passive margin development and terminated with the bhimphedian orogeny this was succeeded by a return to passive margin setting along the northern indian margin of gondwana which continued until the cenozoic himalayan orogeny

the coupled geochemistry of au and as in pyrite from hydrothermal ore deposits the ubiquity of au bearing arsenian pyrite in hydrothermal ore deposits suggests that the coupled geochemical behaviour of au and as in this sulfide occurs under a wide range of physico chemical conditions despite significant advances in the last 20years fundamental factors controlling au and as ratios in pyrite from ore deposits remain poorly known here we explore these constraints using new and previously published empa la icp ms sims and pixe analyses of as and au in pyrite from carlin type au epithermal au porphyry cu cu au and orogenic au deposits volcanogenic massive sulfide vhms witwatersrand au iron oxide copper gold iocg and coal deposits pyrite included in the data compilation formed under temperatures from 30 to 600 c and in a wide variety of geological environments the pyrite au as data form a wedge shaped zone in compositional space and the fact that most data points plot below the solid solubility limit defined by reich et al 2005 indicate that au1 is the dominant form of au in arsenian pyrite and that au bearing ore fluids that deposit this sulfide are mostly undersaturated with respect to native au the analytical data also show that the solid solubility limit of au in arsenian pyrite defined by an au as ratio of 0 02 is independent of the geochemical environment of pyrite formation and rather depends on the crystal chemical properties of pyrite and post depositional alteration compilation of au as concentrations and formation temperatures for pyrite indicates that au and as solubility in pyrite is retrograde au and as contents decrease as a function of increasing temperature from 200 to 500 c based on these results two major au as trends for au bearing arsenian pyrite from ore deposits are defined one trend is formed by pyrites from carlin type and orogenic au deposits where compositions are largely controlled by fluid rock interactions and or can be highly perturbed by changes in temperature and alteration by hydrothermal fluids the second trend consists of pyrites from porphyry cu and epithermal au deposits which are characterised by compositions that preserve the au as signature of mineralizing magmatic hydrothermal fluids confirming the role of this sulfide in controlling metal ratios in ore systems

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

onset of mid crustal extensional flow in southern tibet evidence from u pb zircon ages new ion microprobe u pb dates from zircon in deformed orthogneiss and migmatite and an undeformed granite in mabja dome are the first to constrain the timing of peak metamorphism and onset and duration of mid crustal ductile extension in southern tibet at 35 0 0 8 ma and 12 19 million years the structural metamorphic and intrusive his tories in mid crustal rocks exposed in these north himalayan gneiss domes are similar to those recorded in the greater himalayan sequence suggesting that middle crust was continuous from beneath southern tibet southward to the high himalaya strain compatibility indicates that 35 ma ductile extension in mid crustal rocks of southern tibet was accommodated to the south at shallow crustal levels via normal slip along the southern tibetan detachment system the oldest age estimate for slip along this normal fault zone and extrusion of its footwall if gravitational collapse is an additional important process driving extension then southernmost tibet may have been at or near maximum elevation by late eocene early oligocene time

dibenzothiophenes and benzo b naphthothiophenes molecular markers for tracing oil filling pathways in the carbonate reservoir of the tarim basin nw china abstract dibenzothiophenes dbts and benzo b naphthothiophenes bnts are the main sulfur containing heterocyclic aromatic compounds in crude oils and sedimentary rock extracts because of the relatively higher electronegativity and an unshared pair of electrons in the outer shell orbital of the sulfur atom hydrogen bonds can be formed between the sulfur and hydrogen atoms of the surrounding medium in carrier beds therefore dbts and bnts are potential geochemical markers for tracing oil filling pathways a correlation of oils in the halahatang oilfield of the tabei uplift in the tarim basin nw china shows that the molecular marker compositions of all oils are quite similar implying that these oils have been sourced from the same source kitchen and belong to a same oil family using molecular indicators relative to dbts and bnts namely 4 1 mdbt 4 1 methyldibenzothiophene 4 6 1 4 1 6 dmdbt 4 6 1 4 1 6 dimethyldibenzothiophene 2 6 3 6 1 4 1 6 dmdbt 2 6 3 6 1 4 1 6 dimethyldibenzothiophene and 2 1 bnt 2 1 bnt 1 2 bnt benzo b naphtho 2 1 d thiophene benzo b naphtho 2 1 d thiophene benzo b naphtho 1 2 d thiophene this paper traces the oil migration orientation and filling pathways in this oilfield the isopleth maps of these molecular indicators unequivocally reveal an overall oil migration filling points and preferred filling pathways orientation from south to north based on this a potential source kitchen is predicted in the southern part of the halahatang depression most probably at the manxi shuntuoguole low uplift just between the awati and manjiaer depressions the southern part of the halahatang depression along the oil charging pathways is predicted to be the most promising region for oil exploration

genesis of bangbu orogenic gold deposit in tibet constraints from fluid inclusions and isotopic composition the bangbu quartz vein type gold deposit is located in jiacha county southern tibet lying in the southeastern segment of the langjiexue accretionary wedge on the south side of the yarlung zangbo suture muscovite ar ar geochronological study indicates that it was formed at 49 5 0 5 ma consistent with the period of the onset of the indo asian collision the gold ore bodies are jointly controlled by the jindi lunong synclinorium and cuogu zhemulang large scale brittle ductile shear zone as well as its secondary structures the mineralization of gold was mainly associated with quartz veins in the mining area according to the attitudes the quartz veins can be divided into three types namely the pre metallogenic hook like veins the metallogenic large quartz veins and the post metallogenic ns striking quartz veins the authors made microthermometric measurement laser raman analysis of fluid inclusions and h o isotopic analysis of the three types of the quartz veins microthermometric measurements indicate that the three types of fluid inclusions in the bangbu gold deposit are characterized by low salinity low temperature and low density laser raman analysis indicates that the inclusions in the pre metallogenic hook like quartz veins are dominated mainly by liquid and h o isotope analyses of these quartz veins indicate that the fluids trapped in the quartz were derived from regional metamorphism in the early phase inclusions in the mineralized large quartz veins are mainly vl inclusions characterized by larger volume analysis indicates that these inclusions mainly contain h2o co2 ch4 n2 and h o isotopic data indicate that the ore forming fluids were mainly derived from metamorphic fluids which were interacted with organic materials during their passing through the regional sedimentary strata fluid inclusions in the post metallogenic quartz veins associated with stds are chiefly vl inclusions in small volume and mainly contain h2o co2 and h o isotopes suggesting that these fluids might have resulted from post ore metamorphism the main mineralizing fluid was derived from the deep metamorphic fluid and the main factor responsible for the deposition of au was probably the boiling process

geology s pb isotopes and 40 ar 39 ar geochronology of the zhaxikang sb pb zn ag deposit in southern tibet implications for multiple mineralization events at zhaxikang several au sb sb au pb zn and sb pb zn ag deposits are present throughout the north himalaya in southern tibet china the largest sb pb zn ag deposit is zhaxikang 18 mt at 0 6 wt sb 2 0 wt pb 3 5 wt zn and 78 g t ag zhaxikang veins are hosted within n s trending faults which crosscut the early middle jurassic ridang formation consisting of shale interbedded with sandstone and limestone deposited on a passive continental margin ore paragenesis indicates that zhaxikang mineralization occurred in two main phases composed of six total stages the initial phase was characterized by assemblages of fine grained mn fe carbonate arsenopyrite pyrite sphalerite stage 1 followed by relatively coarse grained mn fe carbonate fe rich sphalerite galena pyrite stage 2 the second phase was marked by assemblages of quartz pyrite fe poor sphalerite and ag rich galena tetrahedrite sericite stage 3 quartz sb pb sulfosalt minerals mainly composed of boulangerite and jamesonite stage 4 quartz stibnite cinnabar stage 5 and quartz calcite stage 6 sulfides of stage 2 have 34sv cdt of 8 4 12 0 206pb 204pb ratios of 19 648 to 19 659 207pb 204pb ratios of 15 788 to 15 812 and 208pb 204pb ratios of 40 035 to 40 153 sulfides of stage 3 have similar 34sv cdt of 6 1 11 2 and relatively more radiogenic lead isotopes 206pb 204pb 19 683 19 792 stage 4 sb pb sulfosalt minerals have 34sv cdt of 5 0 7 2 and even more radiogenic lead 206pb 204pb 19 811 19 981 by contrast stibnite of stage 5 has 34sv cdt of 4 5 7 8 and less radiogenic lead 206pb 204pb 18 880 18 974 taken together with the geological observations that the pb zn bearing mn fe carbonate veins were crosscut by various types of quartz veins sphalerite and galena of stage 2 underwent dissolution and remobilization and that sb pb fe sulfosalts formed at the expense of pb from stage 2 galena and of fe from stage 2 sphalerite we argue that the early pb zn veins were overprinted by later sb rich fluids stage 2 fluids were likely acidic and oxidized and leached lead from high grade metamorphic rocks of the greater himalayan crystalline complex ghc and sulfur from reduced rocks such as slate of the ridang formation along n s trending faults leading to precipitation of pb zn sulfides and mn fe carbonate and formation of solution collapse breccias later sb rich fluids leached pb from the ghc and the pre existing sulfides and deposited fe poor sphalerite ag rich galena tetrahedrite sb pb sulfosalts and stibnite in quartz veins that cut pre existing pb zn bearing mn fe carbonate veins the sb rich fluids also likely leached pb from early cretaceous gabbro and formed stibnite at shallow levels where early pb zn bearing mn fe carbonate veins are absent a sericite 40ar 39ar plateau age of 17 9 0 5 ma from stage 3 veins represents the timing of the onset of stage 3 mineralization

the occurrence of ultra deep heavy oils in the tabei uplift of the tarim basin nw china abstract deeply buried heavy oils from the tabei uplift of the tarim basin have been investigated for their source origin charge and accumulation time biodegradation mixing and thermal cracking using biomarkers carbon isotopic compositions of individual alkanes fluid inclusion homogenization temperatures and authigenic illite k ar radiometric ages oil source correlation suggests that these oils mainly originated from middle upper ordovician source rocks burial history coupled with fluid inclusion temperatures and k ar radiometric ages suggests that these oils were generated and accumulated in the late permian biodegradation is the main control on the formation of these heavy oils when they were elevated to shallow depths during the late hercynian orogeny a pronounced unresolved complex mixture ucm in the gas chromatograms together with the presence of both 25 norhopanes and demethylated tricyclic terpanes in the oils are obvious evidence of biodegradation the mixing of biodegraded oil with non biodegraded oil components was indicated by the coexistence of n alkanes with demethylated terpanes such mixing is most likely from the same phase of generation but with accumulation at slightly different burial depths as evidenced by overall similar oil maturities regardless of biodegradation level and or amount of n alkanes although these ordovician carbonate reservoirs are currently buried to over 6000 m with reservoir temperatures above 160 c no significant secondary hydrocarbon generation from source rocks or thermal cracking of reservoired heavy oil occur in the study area this is because the deep burial occurred only within the last 5 ma of the neogene and there has not been enough heating time for additional reactions within the middle upper ordovician source rocks and reservoired heavy oils