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

direct dating of sulfides by rbsr a critical test using the polaris mississippi valley type znpb deposit abstract the rb sr dating of sphalerites is a powerful method for directly determining the age of base metal deposits and testing models for large scale fluid flow however the uncertainty over the exact host phases for the trace amounts of rb and sr and the causes of variability in rb sr have caused concern over the reliability of the method here we show that the polaris mvt deposit with a geologically well constrained age of formation confirmed by paleomagnetic measurements and hosted in significantly older sedimentary rocks yields a consistent rb sr age of 366 15 ma providing the first unequivocal vindication of the reliability of the method

a 1 78 ga large igneous province in the north china craton the xiong er volcanic province and the north china dyke swarm abstract the 1 78 ga xiong er volcanic province xvp and coeval north china giant mafic dyke swarm ncds are the most important magmatic events occurring after the amalgamation of the north china craton ncc the xvp consists of 3 7 km of extrusive volcanics and some feeder dykes sills located along the southern margin of the ncc and extending over an area 0 06 m km2 compositions vary from basalt to rhyolite but are predominantly intermediate in terms of silica content there are also minor sedimentary intercalations and pyroclastic units the sedimentary interlayers indicate an environment changing from continental facies to oceanic facies up section the xvp is characterized by fractional crystallization from an em i type mantle source and both continental arc andean type and rift environments have been proposed the ncds is widespread in the central ncc with an outcrop area 0 1 m km2 and are exposed at variable depths up to 20 km deepest in the north dyke compositions vary from basalt to andesite and dacite but are dominantly mafic and comprise two series of magmatism previous studies revealed that the ncds recorded assimilation and fractional crystallization of an em i type magma source with a minor dm contribution in the younger magmas both syn collisional and intra continental anorogenic environments have been proposed spatial and petrogenic correlations suggest a cogenetic relationship between the ncds and xvp and considered together they define a large igneous province lip of 0 1 m km2 in area and 0 1 m km3 in volume which is also notable for its continuous compositional range from mafic to felsic with no gap at intermediate compositions the petrology is explained by a common magma source that undergoes a silica poor and iron enriched fractionation trend at depth followed by a silica rich and iron poor fractionation trend in shallow level magma conduits dykes and surface lavas a mantle plume is favored as the cause of this 1 78 ga north china lip

genesis of the dianfang breccia hosted gold deposit western henan province china constraints from geology geochronology and geochemistry abstract the dianfang gold deposit located in songxian western henan province china is one of two breccia hosted gold deposits in the xiong ershan waifangshan region previous studies suggest that the breccia and host volcanic rocks of the xiong er group formed coevally the deposit consists of seven vein type orebodies occurring within the southern and hanging wall margins of the breccia pipe as well as in fractures in the rhyolites of the jidanping formation and are structurally controlled by ene trending faults their mineral assemblage includes k feldspar quartz sericite chlorite epidote carbonate adularia and sulfides formed from hydrothermal alteration related to mineralization pyrite is the dominant ore mineral and is associated with minor galena sphalerite and chalcopyrite the trace minerals include magnetite rutile cervelleite matildite and bismuthinite gold occurs as native gold and electrum inclusions in pyrite or along microfractures in sulfides and quartz four stages of hydrothermal mineralization have been identified quartz k feldspar i quartz pyrite ii polymetallic sulfide iii and carbonate adularia iv zircon u pb geochronology of the granitic matrix of the breccia constrains the timing of breccia pipe formation to 145 8 ma indicating it formed at the end of the late jurassic rather than the paleoproterozoic as suggested by previous studies hydrothermal sulfides from the main orebody yield a rb sr isochron age of 121 5 1 7 ma placing gold mineralization at the end of the early cretaceous the sulfur and lead isotope data suggest that the ore forming materials have a close connection with magmatic fluid the initial 87 sr 86 sr value of the sulfides is 0 71056 0 00012 suggesting an ancient crustal source likely the archean taihua group mixed with a juvenile mantle component the trace element characteristics of pyrite indicate the mineralizing fluid was magmatic in origin sourced from a magma derived from the partial melting of the taihua complex and may have been affected by water rock interaction at high temperatures under reducing conditions geological geochronological and geochemical data suggest the dianfang ore deposit is genetically related to a hidden late mesozoic granite and forms part of an intrusion related auriferous system gold deposits of similar ages are widespread at the southern margin of the north china craton and are coeval with the emplacement of felsic and mafic intrusions exhumation of a metamorphic core complex and formation of extensively faulted basins this suggests that the dianfang gold deposit formed under conditions of lithospheric extension caused by crustal thinning and the destruction of the lithosphere mantle beneath the craton during the late jurassic to early cretaceous

textures and in situ chemical and isotopic analyses of pyrite huijiabao trend youjiang basin china implications for paragenesis and source of sulfur many carlin like au deposits occur within the late paleozoic and triassic youjiang basin of southwest china the huijiabao trend in guizhou province contains over 300 metric tons t 10 6 moz of au at an average grade of 7 to 18 g t in a narrow corridor that is about 20 km long and 5 km wide petrographic and sem studies of pyrite in barren host rocks and high grade orebodies led to the recognition of four stages of pyrite py1 consists of fine grained framboidal crystals in black mudstone py2 is comprised of coarser grained euhedralsubhedral clusters that are spatially related to organic matter py3 is coarse grained euhedral and occurs as overgrowths on py1 and py2 py3 s porous texture inclusion of randomly oriented detrital minerals and association with quartz recrystallization suggest it was deformed during late triassic orogenesis with py1 and py2 py4 generally occurs as rims on py1 to py3 and is intergrown with arsenopyrite sensitive high resolution ion microprobe shrimp 34s analyses of each pyrite type and arsenopyrite show that py1 is related to py2 and that py3 is related to py4 and arsenopyrite the s isotope compositions of py1 7 5 to 5 9 and py2 5 3 to 7 9 are bimodal which suggests that h2s was generated by biogenic sulfate reduction in open marine and sulfate limited systems during sedimentation and or diagenesis the compositions of py3 2 6 to 1 5 py4 1 2 to 1 5 and arsenopyrite 0 8 to 0 9 are homogeneous and have an intermediate range of values near 0 that suggest that h2s was derived either from average pyrite 0 2 in sedimentary rocks or from a concealed magmatic source laser ablation inductively coupled plasma mass spectrometer la icp ms trace element analyses as ni co cu ag se v support different origins and show that py3 and py4 are ore related the lower w co w ni and w s w se ratios of py1 and py2 are consistent with formation during sedimentation or diagenesis whereas the higher ratios of py3 py4 and arsenopyrite are consistent with a hydrothermal origin the lower concentrations of au in py1 0 23 2 5 ppm and py2 0 06 12 ppm show that little au was added during sedimentation or diagenesis the higher concentrations of au in hydrothermal py3 1 1 110 ppm and py4 0 34 810 ppm indicate that most of the au was introduced during subsequent hydrothermal fluid flow the low au contents of arsenopyrite 0 09 0 52 ppm suggests they formed from au depleted fluids the au as ratios of py1 and py2 are typical of diagenetic pyrite whereas py3 and py4 have ratios that approach those of ore stage pyrite in nevada carlin type deposits the fracturing of py3 and its cementation by py4 suggests that ore fluid movement was associated with deformation published isochron ages on arsenopyrite re os 200 ma and late calcite realgar veinlets sm nd 135 ma in the huijiabao trend are older than mafic dikes 84 ma exposed 20 km to the east if the 200 and 135 ma ages are valid h2s and au may be derived from a sedimentary source because igneous intrusions of this age have not been found if these ages are not valid and the gold deposits are actually late cretaceous in age then h2s and au may be derived from a magmatic source additional geochronology and isotopic tracer studies are needed to resolve this uncertainty

low oxygen and high inorganic carbon on the vancouver island shelf 1 recently independent concerns about declining oxygen and ph conditions in the coastal ocean have emerged in coastal upwelling regions hypoxia can be driven by onshore advection of oxygen depleted offshore waters as well as by local biological consumption triggered by high productivity as both mechanisms can also decrease ph and carbonate saturation states coupled studies of oxygen and carbon are imperative a quasi two dimensional model coupling carbon oxygen and nitrogen was developed for the summer wind driven upwelling region off southern vancouver island using the regional ocean modeling system the physical model is coupled to an ecosystem module that tracks 11 state variables and allows nonfixed c n ratios for detritus and dissolved organic matter given uncertainties in sediment parameterizations in biophysical models three sediment models are compared and discussed results demonstrate that sediment associated processes play a dominant role in consuming oxygen from and releasing inorganic carbon to the bottom waters over the shelf this study also examines the unique characteristics of the southern vancouver island shelf two key features distinguish this region from other shelves in the california current system and protect inner shelf waters from severe hypoxia and corrosive i e undersaturated in aragonite conditions first the near shore vancouver island coastal current provides a source of oxygen and nutrients and forms a barrier that prevents upwelled waters depleted in oxygen and rich in carbon from penetrating the inner shelf second the greater width of the shelf dilutes these upwelled offshore waters and reduces their penetration onto the shallower shelf region

potential and timescales for oxygen depletion in coastal upwelling systems a box model analysis a simple box model is used to examine oxygen depletion in an idealized ocean margin upwelling system near bottom oxygen depletion is controlled by a competition between flushing with oxygenated offshore source waters and respiration of particulate organic matter produced near the surface and retained near the bottom upwelling supplied nutrients are consumed in the surface box and some surface particles sink to the bottom where they respire consuming oxygen steady states characterize the potential for hypoxic near bottom oxygen depletion this potential is greatest for faster sinking rates and largely independent of production timescales except in that faster production allows faster sinking timescales for oxygen depletion depend on upwelling and productivity differently however as oxygen depletion can only be reached in meaningfully short times when productivity is rapid hypoxia thus requires fast production to capture upwelled nutrients and fast sinking to deliver the respiration potential to model bottom waters combining timescales allows generalizations about tendencies toward hypoxia if timescales of sinking are comparable to or smaller than the sum of those for respiration and flushing the steady state will generally be hypoxic and results indicate optimal timescales and conditions exist to generate hypoxia for example the timescale for approach to hypoxia lengthens with stronger upwelling since surface particle and nutrient are shunted off shelf in turn reducing subsurface respiration and oxygen depletion this suggests that if upwelling winds intensify with climate change the increased forcing could offer mitigation of coastal hypoxia even as the oxygen levels in upwelled source waters decline

geological geochronological pyrite geochemical and stable isotope studies of the tantou gold deposit in central china abstract the tantou au deposit is a large scale gold deposit in the xiong ershan area a geochemical study of pyrite was conducted using laser ablation inductively coupled plasma mass spectrometry two types of hydrothermal pyrite were identified in the ores and wall rocks i e the fine euhedral pyrite in brecciated ores py1 and coarse grains disseminated in the quartz sulfide veins py2 the trace elements of the two pyrite types exhibit different concentrations associations and rim core zoning implying different geneses and crystallization processes both pyrites of the two mineralization stages were hydrothermal pyrite however the au as co ni and zn were more rich in py1 while ag cu mo sb and pb were favored in py2 the growth rims of py1 suggest several pulses of fluid activities hydrothermal sulfides from the main ore forming stage have a rb sr isochron age of 124 2 3 1 ma placing the gold mineralization in the early cretaceous the initial 87sr 86sr value of the sulfides is 0 71124 0 00010 suggesting an ancient crust source the paleoproterozoic xiong er group in situ s isotope data acquired from the main sulfides suggest that the ore forming materials underwent isotopic fractionation because of oxidation of the ore forming fluids during the hydrothermal process the c o isotope values of calcite from the postore stage indicate that magmatic fluids were likely the principle sources of carbon and that low temperature alteration has had a significant effect on the levels of co2 and carbonate ions together these results suggest that the tantou au deposit is genetically related to the destruction of the north china craton as a result of lithospheric thinning during the early cretaceous

timing of collision of the sino korean and yangtse cratons u pb zircon dating of coesite bearing eclogites the suture zone between the sino korean and yangtse cratons in central china is marked by a series of fault bounded belts composed of crustal protoliths in the dabie mountains some of these blocks contain coesite and diamond indicating subduction to minimum depths of 120 km as a result of continental collision the blocks range from the structurally lowest ultrahigh pressure metamorphic belt and decrease in metamorphic grade upsection to the structurally highest low greenschist facies belt furthermore the faults mark large contrasts in metamorphic grade these features form a structure that is similar to metamorphic core complexes indicating extension as part of the exhumation process timing of the continental collision has previously been inferred as late triassic from regional geologic relations or caledonian from 40 ar 39 ar dating of the adjacent and possibly related qinling metamorphic belt u pb dating of zircon from ultra high pressure eclogites yields a metamorphic age of 209 2 ma this age coincides with later stages of collision and is therefore a minimum estimate of the time of collision

modeling the generation of the juan de fuca eddy 1 numerical simulations with the regional ocean modeling system are used to study the generation of the cyclonic juan de fuca eddy located off the entrance of juan de fuca strait in summer an initial simulation forced with average summer upwelling favorable winds tides and buoyancy boundary conditions that maintain an estuarine flow in juan de fuca strait produces an eddy and currents that are in reasonable agreement with observations sensitivity studies are then carried out to explore the importance of these three forcing mechanisms the relative proximity of dense water in the bottom estuarine flow entering the strait is shown to lead to enhanced upwelling off cape flattery when either wind or tidal forcing is applied this upwelled water then mixes with the estuarine outflow and is advected offshore the tidal upwelling arises through three mechanisms m2 vertical excursions of nearly 20 m at 50 m depth west of the cape on the flood tide strong tidally rectified vertical velocities west of the cape and the spilling of denser bottom water over the western wall of juan de fuca canyon on the ebb tide the cyclonic eddy is a consequence of geostrophic adjustment to the doming isopycnals that arise from the upwelling these model simulations refute an earlier hypothesis that the eddy is generated when california undercurrent water is drawn up tully canyon and onto the vancouver island shelf suggesting instead that these canyon dynamics play only a secondary role in maintaining the eddy once it is formed

geochemical implications of rare earth element patterns in hydrothermal fluids from mid ocean ridges abstract rare earth element data are reported for vent fluids collected from eight deep sea hydrothermal areas including samples from sediment hosted and bare rock hydrothermal systems the morb normalized ree patterns from these diverse settings are remarkably similar to each other but distinctly different than seawater or basalt being lree enriched and possessing a strikingly positive eu anomaly the ree concentrations making up these patterns vary widely however both on a spatial and temporal basis when plotted against ionic radii these fluid trends are remarkably linear and show the same fractionation patterns exhibited by plagioclase during magma segregation this analysis suggests that the partitioning of the ree between fluid and rock during high temperature hydrothermal alteration of morb is dominated by crystochemical exchange during dissolution and recrystallization reactions at the exposed surfaces of plagioclase phenocrysts a comparison of ree ionic radii in eight coordination indicate that the partitioning of 3ree and 2eu are dominated by chemical substitution for ca 2 and sr 2 respectively these considerations predict that the total 3ree content of vent fluid varies in a systematic way during the transition from an rich morb plagioclase to ab rich hydrothermal plagioclase and that these parameters can be used as indicators of the average extent of alteration inside active hydrothermal systems

geochronology and petrogenesis of gray gneisses from the taihua complex at xiong er in the southern segment of the trans north china orogen implications for tectonic transformation in the early paleoproterozoic the taihua complex in the xiong er area along the southern segment of the trans north china orogen tnco consists of gray gneisses with minor amphibolites zircon u pb dating of the gray gneisses reveals at least two episodes of early paleoproterozoic magmatism 2 30 2 32 ga and 2 07 2 19 ga each with distinct geochemical features the tieluping ttg gneisses of the early suite have very low hree ybn 0 58 4 75 and y contents 2 05 13 2 ppm with moderate to high la yb n 14 3 192 6 and sr y ratios 38 5 220 1 pronounced negative ta nb and ti anomalies but positive sr and pb anomalies the protoliths of these gneisses were most likely derived from partial melting of thickened lower crust with residual garnet and amphibole and underwent garnet amphibole fractionation plagioclase accumulation and or fractionation the tieluping ttg gneisses have variable zircon hf model ages tdm hfc 2 48 3 06 ga and whole rock end t values 4 89 4 98 and the youngest whole rock depleted mantle nd model age tdm 2 32 ga is close to the crystallization age of the ttg 2318 8 ma the protolith of the gneisses formed from a combination of pre existing continental crust and juvenile materials implying an andean type continental margin arc environment it is suggested that crustal thickening was the result of accretionary orogenesis accompanied by basaltic underplating the ganshugou potassium rich gneisses of the later suite have low na2o and high k2o and show fractionated lree and nearly flat hree patterns with strong negative ta nb and ti anomalies they are characterized by negative end t values 5 01 to 2 33 and heterogeneous zircon ehf t values 10 65 2 10 with decoupling of zircon hf model ages tdm hfc 2 64 3 23 ga and whole rock nd model ages tdm 2 55 2 81 ga the protolith of the ganshugou gneisses was a potassium rich igneous rock which was likely the result of partial melting of pre existing crustal materials at shallow depth compatible with a post collisional setting there is therefore a tectonic transformation from an accretionary orogenesis to an extensional regime as a consequence of post collisional uplift in the southern segment of the tnco in the early paleoproterozoic

a hydrocarbon biomarker record for the last 40 kyr of plant input to lake heqing southwestern china multi proxy records relating to climate and vegetation have been obtained for a core spanning the last 40 kyr from the heqing lake basin 26 n 100 e 2200 m asl yunnan province of southwestern china compound specific carbon isotope records for the vascular plant leaf wax hydrocarbons the c23 c33 n alkanes and for the algal hydrocarbons the c23 and c25 n alkenes and a c30 cyclobotryococcatriene all show a shift of circa 3 in d 13 c values from mis 3 to the end of mis 2 followed by a rapid return to lighter values this shift from 32 to 29 for the n alkanes and n alkenes most likely derives from bicarbonate utilization by aquatic plants in the lake rather than increased c4 photosynthesis thus both pollen data and hydrocarbon data appear to reveal a rise and fall in the contributions of submerged and or floating plants during mis 2 2004 elsevier ltd all rights reserved

the role of a longshore pressure gradient in pacific northwest coastal dynamics abstract in this paper we demonstrate the importance of the seasonal barotropic longshore pressure gradient force to pacific northwest coastal dynamics values of the seasonal longshore pressure gradient corrected for gauge height relative to a level surface hickey and pola 1982 and for year to year variations enfield and alien 1980 were included in the two dimensional time dependent baroclinic finite difference model of hamilton and rattray 1978 as an external force observed wind stress stratification and bottom topography were included in the model and comparisons were made with current meter data in each of the three seasonal situations observed in the northwest pressure gradient force southward opposing local wind stress winter pressure gradient force northward opposing local wind stress summer and pressure gradient force and local wind stress both southward spring three important features of the seasonal circulation are shown to depend on the existence of the pressure gradient

precise determination of phanerozoic zircon pb pb age by multicollector sims without external standardization 1 zircon has long been recognized as the best geochronometer and the most important timekeeper in geosciences modern microbeam techniques such as sims and la icpms have been successfully applied to in situ u pb zircon age determinations at spatial resolutions of 20 30 m or less matrix matched calibration by external standardization of well characterized natural zircon references is a principal requirement for precise microbeam u pb zircon age determination due to fractionation effects between pb and u which usually result in an external age error exceeding 1 alternatively zircons with a closed u pb system can be directly dated by measurement of 207pb 206pb isotopic ratio without external standardization which has been a common practice for zircons older than 1 0 ga but not for relatively young 1 0 ga and particularly phanerozoic ones because of limitations of analytical precision we describe in this paper a method of 207pb 206pb measurement on phanerozoic zircons using a new generation of large radius magnetic sector multicollector cameca ims 1280 sims in combination with multicollector mode a nuclear magnetic resonance nmr magnet controller and oxygen flooding techniques we achieve precisions of 207pb 206pb ratio of 0 1 and 0 1 0 2 propagating to pb pb age errors 0 4 and 1 3 excluding u decay constant uncertainties for zircons of latest neoproterozoic and late paleozoic to mesozoic age respectively therefore the multicollector sims is capable of direct determination of zircon pb pb ages as young as mesozoic age with uncertainties of geological significance this technique is useful for direct dating of zircons in thin sections moreover it has significance for dating of some other u rich minerals i e baddeleyite and zirconolite that are not suitable for sims u pb dating by external standardization

timing of the formation of the changba lijiagou pb zn ore deposit gansu province china evidence from rb sr isotopic dating of sulfides abstract the giant changba lijiagou pb zn deposit is located in the north of the xihe chengxian abbreviated as xicheng ore cluster in gansu province china the orebodies in the deposit are mainly hosted in the marble dolomitic marble and biotite calcite quartz schist of the middle devonian anjiacha formation the genesis of the deposit has previously been argued to be of sedex type sedimentary exhalative type or of epigenetic hydrothermal type this paper reports results of rb sr isotopic dating on sphalerite and pyrite taken from the main orebody which yield an isochron age of 222 3 2 2 ma for eight sphalerite samples and 222 0 3 0 ma for the eight sphalerite samples combined with four pyrite samples indicating that the deposit formed during the late triassic the 87sr 86sri value of the sphalerite is 0 71370 0 00013 and that of the sphalerite and pyrite is 0 71371 0 00014 which are identical within experimental error suggesting that the ore metals are derived mainly from the continental crust by integrating the present results with the regional geology we propose that the changba lijiagou pb zn deposit is a product of regional hydrothermal mineralization processes forced by tectono magmatic activities which took place in the xicheng ore cluster during triassic orogenic processes

rb sr dating of sphalerites from tennessee and the genesis of mississippi valley type ore deposits mississippi valley type mvt ore deposits commonly consist of some combination of lead zinc and iron sulphides accompanied by barite fluorite dolomite and calcite they are thought to form by fluid expulsion from sedimentary successions1 3 but their exact origin has remained controversial because of the scarcity of reliable geochronological data in a recent and widely quoted model the mvt deposits of the central and eastern united states formed as a result of large scale lateral fluid flow driven by the tectonic squeezing of sedimentary successions during the late palaeozoic alleghenian orogeny 330 250 myr 4 here we report the first direct rb sr dating of sphalerites from an mvt deposit and propose this as a useful geochronological technique for sulphide mineralization with poor age control rb sr data for sphalerites from coy mine east tennessee define an isochron age of 377 29 myr ruling out any genetic connection with the alleghenian orogeny instead mvt mineralization in the eastern united states was apparently generated from fluids expelled during thrusting associated with the older acadian orogeny 380 350 myr

carbon and oxygen cycles sensitivity to changes in environmental forcing in a coastal upwelling system 1 biogeochemical cycles in the coastal ocean are changing and will continue to change in response to a changing climate effects on the oxygen and carbon cycles are particularly important as either episodic or permanent shifts toward lower oxygen and or higher inorganic carbon conditions can impact coastal ecosystems negatively here we study the sensitivity of these cycles to changes that may occur in the coastal ocean focusing on a summer wind driven upwelling region off southern vancouver island shelf we use a quasi 2 d configuration of the regional ocean modeling system roms to perform six sensitivity experiments results indicate that carbon and oxygen cycles in this region may be significantly affected by an altered upwelling season a shallower offshore oxygen minimum zone and a carbon enriched environment combinations of these scenarios suggest a potentially increasing risk for the development of coastal hypoxia and corrosive conditions in the region

alleghenian age of the upper mississippi valley zinc lead deposit determined by rb sr dating of sphalerite mississippi valley type mvt ore deposits in north america are generally thought to have formed from warm brines which migrated from sedimentary basins to sites of deposition in sedimentary strata of the neighbouring craton long after unification of the sediments1 3 when and how these migrations occurred is not well understood but recent geological evidence suggests that continental scale brine migration can be triggered by tectonic collisions4 6 indirect evidence7 9has suggested an association of north american mvt mineralization with the late palaeozoic alleghenian ouachita orogeny recently however nakai et al 10obtained a rb sr age of 377 29myr for sphalerites from the east tennessee mvt district which they linked to the middle palaeozoic acadian orogeny here we report rb sr dates for sphalerites from the mvt type section the upper mississippi valley umv zinc lead district rb sr data from two distinct sphalerite bands from the west hayden ore body yield two independent but indistinguishable isochrons of permian age 269 6 myr and 270 4 myr consistent with a brine migration episode initiated by the alleghenian ouachita orogeny in conjunction with the previous data indicating a link to the acadian orogeny10 11 our results indicate that north american mvt deposits formed in at least two distinct tectonic episodes

geochronology and origin of the qi189 porphyry gold deposit in qiyugou orefield qinling orogen china abstract the qi189 gold deposit is a recently discovered porphyry system in the qiyugou orefield located in the northeastern qinling orogen along the southern margin of north china craton the orebodies are hosted in the porphyritic granite emplaced in the taihua supergroup three molybdenite and five pyrite samples from the ores yield re os isochron ages of 129 5 2 8 ma and 127 5 8 2 ma respectively which are coincident with the zircon u pb age of the porphyritic granite within analytical error 128 6 0 8 ma zircon grains from the post ore quartz monzonite yield weighted mean 206pb 238u age of 124 7 0 6 ma n 31 1 mswd 0 23 these ages constrain that the qi189 gold system was formed in the period of 130 127 ma the porphyritic granite and quartz monzonite show high k calc alkaline affinity enrichment of lree and lile depletion of hree and hfse and negligible eu anomaly zircon grains show negative ehf t values of 20 7 to 14 9 with tdm2 hf ages of 2 49 2 13 ga this indicates that the qi189 porphyry system originated from a source mixed by the materials from the north qinling accretion belt and the basement of north china craton with minor contribution from the mantle and developed under a post collisional tectonic setting

early cretaceous cryptoexplosive breccia related gold mineralization in the north china craton evidence from the puziwan gold deposit abstract the puziwan gold deposit located in north western shanxi province in north china is a typical cryptoexplosive breccia related gold deposit here we present new zircon u pb and pyrite rb sr geochronology and zircon lu hf and pyrite s pb isotopic data to constrain the timing of ore formation and to gain insights into the source of the metal and genesis of the deposit the clasts of the ore bodies of the deposit consist mainly of quartz porphyry and granulite pyrite and the oxidized limonite account for 70 of the total ore minerals associated with the entire ore forming process gold is dominated by electrum and native gold which mainly occur in the interstices and fissures of pyrite we identify six stages during the mineralization process 1 gold bearing quartz pyrite 2 quartz pyrite sericite 3 quartz sericite au ag polymetallic sulfides 4 quartz ag polymetallic sulfides 5 gold bearing sulfide quartz and 6 carbonate pyrite the pyrite from the main mineralization stage yields rb sr isochron age of 139 2 1 1 ma suggesting that the puziwan gold deposit formed during the early cretaceous much later than the triassic emplacement of the quartz porphyry 229 ma the s pb and sr isotopic data suggest that the source of the ore is closely related to deep seated magmatism derived through mixing of lower crust and mantle material the geochronological and isotopic data preclude the associated triassic quartz porphyry as the source and suggest probable hidden deep seated cretaceous magmatism forming an intrusion related auriferous system the brecciation resulted from the cryptoexplosion and fluidization synchronously or slightly after the brecciation the ore fluids were channeled along the breccias and fractures or faults within the fracture zone occurrence of other gold deposits in the north china craton which share similar geochronological and isotopic characteristics with puziwan gold deposit indicates that these cryptoexplosive breccia related gold deposits formed during lithospheric extension associated with craton destruction triggered by the subduction of paleo pacific plate during the late jurassic to early cretaceous

isotope geochemistry and geochronology of the qiubudong silver deposit central north china craton implications for ore genesis and lithospheric dynamics abstract the qiubudong silver deposit is a breccia type silver deposit in the fuping ore cluster region within the taihang mountain region of the central north china craton ncc the cylindrical breccia pipe occurs at the conjunction of a ne trending fracture and a nw trending fracture and along the latter a number of quartz porphyry and felsite dikes are emplaced the breccia clasts include quartz porphyry leptite and felsites cemented mainly by felsic magmatic and hydrothermal components the ore formation process can be divided into five stages magnetite quartz stage i biotite quartz stage ii quartz pyrite stage iii quartz polymetallic sulfide stage iv and quartz carbonate stage v hydrothermal alteration is characterized by pyritization sericitization silicification carbonatization potash feldspathization epidotization and chloritization with a systematic zoning from the ore body to the margin with transitional contact boundaries we present s pb he and ar isotope compositions of the ore minerals and evaluate the source of the ore forming materials and fluids the 34 s values of the pyrite range from 0 5 to 3 4 with an average of 1 6 consistent with a mantle input the pb isotope compositions from the sulfide minerals range from 15 799 to 16 049 for 206 pb 204 pb 15 143 to 15 241 for 207 pb 204 pb and 36 999 to 37 590 for 208 pb 204 pb suggesting a lower crustal origin helium isotopic compositions of the fluid inclusions trapped in pyrite vary from 0 45r a to 1 65r a with an average of 0 98r a r a is the 3 he 4 he ratio of air equal to 1 4 10 6 tending to crustal contribution with calculated mantle helium proportions ranging between 5 and 20 average at 12 six pyrite samples from the silver deposit yield a rb sr isochron age of 102 04 0 61 ma whereas crystallization of the quartz porphyry dike is dated by zircon u pb la icp ms chronology at 107 95 0 87 ma these ages suggest a close link between the silver mineralization and magmatism that generated the quartz porphyry combined with previous age data we infer that the magmatism and metallogenesis in the central ncc took place during 140 100 ma with a duration of 40 ma accompanied by mantle upwelling and lithospheric thinning

geochronology of the pengjiakuang and rushan gold deposits eastern jiaodong gold province northeastern china implications for regional mineralization and geodynamic setting the jiaodong gold province the largest gold producing district in china is located in the jiaodong peninsula at the eastern margin of the north china craton and bounded by the continental scale tan lu fault 40 kin to the west previous geochronological studies suggest that pervasive gold deposition took place in the western part of the province between 122 and 119 ma here we report high quality ar 40 ar 39 ages of the pengjiakuang and rushan deposits from the eastern part of the jiaodong gold province placing additional chronological constraints on the timing of regional mineralization seven sericite grains extracted from auriferous alteration assemblages at the pengiiakuang deposit yielded well defined plateau ages between 120 9 0 4 and 119 1 0 2 ma 2 sigma three separates of igneous biotite from a sample of the queshan gneissic granite adjacent to the pengjiakuang deposit gave reproducible plateau ages of 124 6 0 6 to 123 9 0 4 ma 2 sigma six sericite separates front two samples in the rushan deposit yielded ar 40 ar 39 plateau ages at 109 3 0 3 to 107 7 0 5 ma 2 sigma whereas biotite from the kunyushan monzogranite that hosts the rushan deposit had plateau ages ranging from 129 0 0 6 to 126 9 0 6 ma 3 separates front one sample the apparent age gap between hydrothermal sericite and magmtic biotite from both deposits together with the similar argon closure temperatures for these mica minerals suggest that gold mineralization had no direct relationship to the granitoid magmatism instead gold deposition coincided with the emplacement of mafic to intermediate dikes widespread in the jiaodong gold province which have been dated at ca 122 to 119 ma and less commonly at 110 to 102 ma the new ar 40 ar 39 ages from the eastern jiaodong peninsula when combined with published data from the western part suggest that gold mineralization was broadly contemporaneous throughout the district the early cretaceous gold mineralization also is widely developed in four other major gold districts along the tan lu fault the temporal and spatial correlation of these gold deposits with mafic to intermediate dikes commonly found in most mineralized areas the presence of well documented metamorphic core complexes and half graben basins along the tan lu fault and voluminous basalts therein suggest that the early cretaceous was an important period of lithospheric extension possibly caused by the late mesozoic lithospheric thinning beneath the eastern block of the north china craton lithospheric thinning and extension could have resulted in abnormally high heat and fluid fluxes necessary for large scaled gold mineralization

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

petrogenesis and tectonic setting of volcanic rocks in the xiaoshan and waifangshan areas along the southern margin of the north china craton constraints from bulk rock geochemistry and sr nd isotopic composition abstract as part of the xiong er volcanic belt along the southern margin of the north china craton volcanic rocks in the xiaoshan and waifangshan areas have a compositional range from the basaltic andesite andesite dacite to rhyolite which display consistent variation trends in terms of their major and trace elements and sr nd isotopic compositions the variable yb contents with nearly constant la yb and tb yb ratios of volcanic rocks in two areas suggest that the fractional crystallization may have played an important role in the differentiation from the basaltic andesite through andesite and dacite to rhyolite the volcanic rocks in these two areas are characterized by the lile and lree enrichments and negative hfse anomalies implying hydrous melting of a mantle wedge in a subduction zone variable sr nd ratios of the basaltic andesite and andesite are interpreted as a result of the fluid addition from a subducting slab non radiogenic nd isotopic compositions as well as high zr y and nb y ratios suggest that the volcanic rocks in these areas were derived from an enriched mantle source on the other hand the volcanic rocks of the basaltic andesite and andesite possess markedly higher fe ti and hfse concentrations than those of typical intra oceanic arcs implying that the mantle source from which the volcanic rocks were derived was metasomatised by siliceous melts during the archean to paleoproterozoic subduction collision in the trans north china orogen these data suggest that in the paleo mesoproterozoic the southern margin of the north china craton was most likely an andean type continental arc in which slab dehydration not only induced the melting of a pre existing metasomatised mantle source but also released lile enriched fluids into the mantle source masking the inherent hfse enriched characteristics of the volcanic rocks along the southern margin of the craton the results of this study indicate that the north china craton like many other continental components e g north america greenland baltica amazonia australia etc of the supercontinent columbia nuna also underwent a subduction related outgrowth along its southern margin during the paleo mesoproterozoic time

on the coupling of benthic and pelagic biogeochemical models abstract mutual interaction of water column and sediment processes is either neglected or only crudely approximated in many biogeochemical models we have reviewed the approaches to couple benthic and pelagic biogeochemical models it is concluded that they can be classified into a hierarchical set consisting of five levels differing in the amount of detail given to the sediment processes the most complex approach level 4 fully couples water column processes to a vertically resolved biogeochemical sediment model first simplification is achieved by using a vertically integrated dynamic sediment model level 3 next is a reflective type of boundary level 2 where particulate material arriving at the sediment surface is instantaneously transformed into dissolved components then comes a set of models in which either the bottom water concentration of dissolved substances or the sediment water exchange is imposed level 1 finally in some biogeochemical models the bottom is plainly ignored level 0 we have tested these various approaches in a coupled physical pelagic benthic biogeochemical model for oxygen nitrogen and carbon cycling in continental shelf areas we discuss the various model approaches with respect to their impact on the pelagic system and point out some of the inconsistencies hidden in certain formulations we conclude that lower boundary types in which sediment fluxes or concentrations are imposed level 1 are especially badly designed because they fail to assure conservation of mass finally we suggest as best choice a level 3 approach in which the evolution of sedimentary particulate matter is part of the solution and where the bottom fluxes of dissolved constituents are parameterised based on mass budget considerations these simplified formulations represent the best balance between computational demand and attained accuracy

giant mesozoic gold provinces related to the destruction of the north china craton abstract lode gold deposits in precambrian cratons represent the world s major gold source and were mostly generated during formation and stabilization of the cratons however there is an extraordinary exception in the north china craton ncc where lode gold deposits formed after prolonged stabilization of the craton molybdenite re os and hydrothermal sericite and biotite 40 ar 39 ar dating of major gold deposits from the xiaoqinling district southern ncc bracket their emplacement in the range of 154 1 1 1 to 118 9 1 2 ma n 23 postdating formation of the craton by more than 1 7 billion years fluid inclusions extracted from gold bearing pyrite have elevated 3 he 4 he ratios 1 52 0 22 ra and mantle like ne isotopes 20 ne 22 ne 10 02 9 22 and 21 ne 22 ne 0 033 0 027 indicating presence of mantle derived fluids in the ore system measured 34 s of pyrite and d and 18 o of hydrothermal micas and fluid inclusion waters in auriferous quartz further confirm a magmatic mantle source for sulfur and ore fluids gold deposits of similar ages also widely occur in the eastern and northern margins of the ncc which together with those in the xiaoqinling district have a total reserve of 2500 t gold forming the only known giant late mesozoic gold province in the world s precambrian cratons these deposits formed coevally with extensive felsic to mafic magmatism development of intracontinental rift basins and exhumation of metamorphic core complexes across the eastern ncc events interpreted as indicating thinning and destruction of the lithosphere beneath the craton rising of asthenosphere coupled with destruction of the lithosphere has generated voluminous mafic and felsic magmas that provided sufficient fluids sulfur and by inference other ore components to form the giant gold provinces

early mesozoic mo mineralization in the qinling orogen an overview abstract as one of the most important mo provinces in the world the qinling orogen is host to mainly late mesozoic late jurassic early cretaceous porphyry mo systems recently additional early mesozoic mainly triassic plus minor early jurassic mo deposits have been identified which occur as fault controlled quartz veins or as carbonatite veins and as such they are fundamentally different from the commonly observed porphyry systems furthermore early mesozoic porphyry systems are also present but they are different from those of late mesozoic age thus early mesozoic mo systems not only offer a new and comprehensive view of the mo metallogenesis but also provide unique insight into the tectonic evolution of the qinling orogen taking into consideration the role of mineral deposits as ideal probes of the geodynamic evolution the known early mesozoic mo deposits in qinling can be classified into three types based on their geological and geochemical features porphyry carbonatite and orogenic systems porphyry mo systems including porphyry porphyry skarn and intrusion related veins are spatially and genetically associated with granitic porphyries they display typical porphyry type alterations and are formed by magmatic water carbonatites are considered as mantle derived igneous rocks and mo mineralization is associated with magmatic fluids orogenic mo systems occur as fault controlled quartz lodes and the ore forming fluids are medium high temperature co2 rich metamorphic fluids spatially early mesozoic porphyry mo systems are concentrated in the western and middle part of the qinling orogen whereas carbonatite veins and orogenic mo systems are located in the northeastern part temporally orogenic mo deposits were the earliest mainly between 220 and 250 ma followed by carbonatite veins mainly between 205 and 225 ma and porphyry mo systems mainly between 190 and 205 ma with some exceptions there is generally a trend of decreasing deposit ages toward the western part of the orogen detailed comparison reveals that the early mesozoic porphyry mo systems in the qinling orogen are different from the late mesozoic ones in terms of their economic importance spatial distribution ore causative intrusions hydrothermal alteration and the ore forming fluids to explain the above geological and geochemical features the triassic qinling is considered as an active continental margin caused by the northward subduction of the mian lue oceanic plate a transition from continental arc to back arc basin is suggested for the formation of triassic orogenic and carbonatite vein mo deposits whereas continental arc is host to the early mesozoic porphyry mo systems

delineation of potential exploration targets based on 3d geological modeling a case study from the laoangou pb zn ag polymetallic ore deposit china abstract the laoangou pb zn ag polymetallic ore deposit lag is a hydrothermal vein type deposit in the east qinling polymetallic metallogenic belt which is controlled by nw ne and nearly sn trending faults and mainly hosted in the dolomite marble of meiyaogou and baishugou formations within the luanchuan ore district lod although district scale metallogenic prediction related to the pb zn ag deposits in the lod has been attempted there have been no studies to formulate a detailed deposit scale metallogenic prediction of the pb zn ag deposit in 3d space here we selected the lag to formulate a metallogenic prediction model for pb zn ag deposit based on data from 1 10 000 scale geological map and 66 boreholes and 39 sections of exploration lines on 1 1000 scale to extract the salient spatial features of the deposit we apply ordinary weights and weighted weights of evidence followed by boosted weights of evidence logistic regression and information entropy for integrating the features of the ore deposit for exploration targeting the c v fractal method is applied to classify the probabilities accordingly three levels of exploration targets are delineated the first level targets are mainly distributed in the periphery of known orebodies m2 m3 ii 3 and vi which are also located in the ore controlling strata and fault zones the second level targets are located in the region of known orebodies indirectly confirming that the prediction result is reliable and the third level targets which are mainly located at the contact between ore controlling strata and metagabbro bodies offer new targets for exploration in this ore district combining our results obtained in this study with those in previous studies we provide some guidelines for exploration targets in the pb zn ag deposits in the lod which might help in more effectively delineating the target zones

yttrium and rare earth elements in fluids from various deep sea hydrothermal systems rare earth element ree and yttrium y concentrations were measured in fluids collected from deep sea hydrothermal systems including the mid atlantic ridge mar i e menez gwen lucky strike tag and snakepit the east pacific rise epr i e 13 n and 17 19 s and the lau vai lili and manus vienna woods pacmanus desmos back arc basins bab in the south west pacific in most fluids y is trivalent and behaves like ho chondrite normalized y ree y reen concentrations of fluids from mar epr and two bab sites i e vai lili and vienna woods showed common patterns with lree enrichment and positive eu anomalies ree analysis of plagioclase collected at lucky strike strengthens the idea that fluid ree contents are controlled by plagioclase phenocrysts other processes however such as ree complexation by ligands cl f so42 secondary phase precipitation and phase separation modify ree distributions in deep sea hydrothermal fluids ree speciation calculations suggest that aqueous ree are mainly complexed by cl ions in hot acidic fluids from deep sea hydrothermal systems ree concentrations in the fluid phases are therefore influenced by temperature ph and duration of rock fluid interaction unusual y reen patterns found in the pacmanus fluids are characterized by depleted lree and a positive eu anomaly the demos fluid sample shows a flat y reen pattern which increases regularly from lree to hree with no eu anomaly these manus basin fluids also have an unusual major element chemistry with relatively high mg so4 h2s and f contents which may be due to the incorporation of magmatic fluids into heated seawater during hydrothermal circulation ree distribution in pacmanus fluids may stem from a subseafloor barite precipitation and the ree in demos fluids are likely influenced by the presence of sulfate ions

shrimp and la icp ms zircon geochronology of the xiong er volcanic rocks implications for the paleo mesoproterozoic evolution of the southern margin of the north china craton the paleo mesoproterozoic xiong er volcanic rocks along the southern margin of the north china craton are lithologically and geochemically similar to those formed in subduction related continental margin volcanic arcs the volcanic rocks are primarily composed of basaltic andesites and andesites with minor dacites and dacitic rhyolites traditionally the xiong er volcanic rocks have been divided from lower to upper into the xushan jidanping and majiahe formations but the ages of volcanic rocks in these formations have not been well constrained which has hindered further understanding the tectonic significance of the xiong er volcanic belt at the southern margin of the north china craton shrimp and la icp ms u pb zircon analyses combined with cathodeluminescence cl images have enabled resolution of xenocrystic and magmatic zircons that can be directed toward determination of the ages of the xiong er volcanic rocks shrimp and la icp ms u pb analyses on magmatic zircons from two basaltic andesite samples one dacite sample and one rhyolite sample of the xushan formation known as the lowest sequence of the xiong er volcanic rocks indicate that the volcanic eruption of this formation occurred at 1 78 ga but most xenocrystic inherited zircons in these samples yielded 207pb 206pb ages ranging from 2 55 ga to 1 91 ga of three samples collected from the jidanping formation two rhyolite samples 05xe015 and 05xe100 yielded weighted mean 207pb 206pb ages of 1778 5 5 ma and 1751 14 ma respectively similar to the ages of the volcanic rocks in the xushan formation whereas one dacite sample 05xe066 gave a weighted mean 207 pb

age and tectonic setting of late archean greenstone gneiss terrain in henan province china as revealed by single grain zircon dating the authors report precise u pb zircon ages for single grains of a metarhyodacite from the late archean dengfeng greenstone belt in henan province china near the southern margin of the north china craton most grains belong to an igneous population whose u pb isotopic systematics define a straight line intersecting concordia at 2512 12 ma and this is interpreted as the time of crystallization of the original greenstone volcanics several grains are distinctly older between 2576 9 and 2945 44 ma and the authors interpret the older grains as xenocrysts of pre greenstone continental crust that provide evidence for crustal derivation or crustal contamination of the original rhyodacitic lava the xenocrysts suggest evolution of the dengfeng greenstone belt in a continental environment that may be represented by the taihua high grade gneisses bordering the dengfeng greenstones and for which the authors obtained ages of 2806 7 and 2841 6 ma the data add evidence to the now widely held concept that most archean greenstones developed on or near older continental crust and were therefore prone to crustal contamination in such cases conventional zircon dating may not always record the precise age of rock formation

isotope systematics and fluid inclusion studies of the qiyugou breccia pipe hosted gold deposit qinling orogen henan province china implications for ore genesis abstract the qiyugou gold deposits henan province are hosted in breccia pipes within the xiong er terrane qinling orogen on the southern margin of the north china craton in these deposits three paragenetic assemblages have been recognized an early k feldspar epidote quartz pyrite a middle quartz polymetallic sulfide and a late quartz carbonate adularia in this paper we review and interpret fluid inclusion and stable and radiogenic isotopic data of host rocks and ores fluid inclusions in quartz and calcite include water rich co 2 rich and daughter crystal bearing the co 2 rich and daughter mineral bearing fluid inclusions are common in the early stage quartz and absent in the late stage quartz and calcite which only contain water rich fluid inclusions accordingly the early stage ore fluids are magmatic in origin and characterized by high temperature 350 c high salinity 30 wt nacl equiv and are co 2 rich fluid boiling in the middle ore stage resulted in co 2 release decreasing oxygen fugacity and rapid precipitation of ore materials the late stage fluids have low temperature low salinity are co 2 poor and lack daughter minerals these fluids are probably sourced from meteoric water h o c isotope systematics confirm that the ore fluid system evolved from magmatic to meteoric the carbon and lead isotope ratios indicate that the meso neoproterozoic sequence south of the xiong er terrane was the likely source of the ore forming materials the qiyugou breccia pipes and their associated gold ores were emplaced during an extensional regime following a transition from collision to rifting tectonics linked to collision and subduction of the yangtze plate beneath the north china craton geochronological studies show that mesozoic magmatism in the region occurred between the triassic and cretaceous the triassic to jurassic magmas were mostly derived from partial melting of ancient crust whereas the cretaceous magmas show juvenile signatures indicating mantle derived components processes of fragmentation of lithospheric roots crustal and lithospheric thinning extension and rifting were probably associated with the subducting pacific izanagi plate these crust mantle geodynamic processes were responsible for the development of anorogenic granitic melts that interacted with the meso neoproterozoic volatile rich sedimentary successions producing a flow of gas rich hydrothermal fluids that resulted in the emplacement of the qiyugou auriferous breccia pipes we conclude that the qiyugou gold deposits are intrusion related explosive breccia pipe type that evolved from hypothermal through mesothermal to epithermal

the sr and nd isotopic variations of the chinese loess plateau during the past 7 ma implications for the east asian winter monsoon and source areas of loess abstract 143 nd 144 nd and 87 sr 86 sr ratios of the acid insoluble residues of the red clay and overlying loess paleosols from the lingtai profile of the loess plateau china were investigated the results show that variations of the 87 sr 86 sr ratios of the lingtai profile can be divided into two stages from 7 ma b p to 2 5 ma b p the acid insoluble residues in the red clay rc formation are characterized by higher 87 sr 86 sr ratios with an average of 0 7230 from 2 5 ma b p to the present the acid insoluble residues in the wuchen loess wl4 ws1 lishi loess l15 s1 malan loess l1 and holocene loess s0 have relatively lower 87 sr 86 sr ratios and display an overall descending trend from 0 7223 at 2 5 ma b p to 0 7182 at the present among three possible interpretations for the variations of 87 sr 86 sr ratios of acid insoluble residues of the loess provenance change chemical weathering change or grain size distribution change only grain size distribution change provides a satisfactory interpretation this implies that the east asian winter monsoon strength was weak and relatively stable from 7 ma b p to 2 5 ma b p but became continuously enhanced from 2 5 ma b p to the present all the red clay and the overlying loess paleosols in the lingtai profile have generally identical e nd 0 implying that the source regions of these eolian deposits of the chinese loess plateau may be relatively stable and has not changed since 7 ma b p

europium redox equilibria in aqueous solution thermochemical data and recent advances in theoretical aqueous solution chemistry enable prediction of the relative stabilities of aqueous eu2 and eu3 over a wide range of temperatures and pressures at low temperatures near earth surface conditions the aqueous geochemistry of europium should be dominated by the trivalent state except possibly in the most reducing alkaline pore waters of anoxic marine sediments however at temperatures greater than about 250 c and elevated pressures divalent europium should predominate even with significant amounts of complexing trivalent europium is not stable at elevated temperatures and pressures consequently under most hydrothermal and metamorphic conditions europium in aqueous solution should be divalent at intermediate temperatures around 100 c significant activities of both eu2 and eu3 and related complexes can occur in aqueous solutions depending on the oxidation state and the ph of the solutions and the activities of potential ligands such as sulfate carbonate and chloride the predicted stability of divalent europium in aqueous solution at elevated temperatures is consistent with the large positive europium anomalies in rare earth element patterns of high temperature barites of hydrothermal and metamorphic origin reported by guichard et al 5 and with the observed depletion of europium as a result of high temperature sericitization of feldspar bearing assemblages discovered by alderton et al 1 it is suggested that significant fractionation of europium relative to the other rare earth elements may take place during high temperature hydrothermal alteration processes such as in the mid oceanic ridge systems because of the expected stability of divalent europium during these processes

the shanggong gold deposit eastern qinling orogen china isotope geochemistry and implications for ore genesis abstract the shanggong au deposit in the xiong er terrane east qinling china has resources of about 30 ton au making it one of the largest orogenic mesothermal au deposits hosted in volcanic rocks of the mesoproterozoic xiong er group three stages of hydrothermal activity are recognized early middle and late of which two early and middle were ore producing and characterized by quartz pyrite and polymetallic sulfides respectively the third and late stage is represented by a carbonate quartz assemblage hydrogen oxygen and carbon isotope systematics of the shanggong deposit from a previous work suggest that the early stage fluids were derived from magmatic and or metamorphic devolatilization of sedimentary rocks at depth this is supported by new c s and published sr and pb isotopic data presented in this paper these new data 13c values ranging from 1 5 for early stage ankerite to 2 2 for late stage ankerite negative 34s values for sulfides from the middle stage 19 2 to 6 3 suggest a contribution from organic matter and that the ore fluid evolved from deeply sourced to shallowly sourced with those of the middle stage representing a mixture of these two fluid systems the comparison of the hydrogen oxygen carbon sulfur lead strontium isotope systematics between the shanggong deposit and the main lithologies in the xiong er terrane shows that neither these nor the underlying lower crust and mantle or combinations thereof could be considered as the source of ore fluids for the shanggong au deposit a likely source was a carbonaceous carbonate sandstone shale chert sequence in the underthrusted guandaokou and luanchuan groups exposed south of the xiong er terrane ar ar and rb sr isochron ages for mineral phases of the early middle and late stages together with geological field data constrain the timing of the hydrothermal activity and au metallogenesis at 242 10 167 7 and 112 7 ma respectively this metallogenesis and associated granitic magmatism can be related to the continental collision between the yangtze and north china cratons that resulted in the formation of the qinling orogen led to the different hydrothermal systems that were responsible for the three stages that formed the shanggong au deposit over a period of about 130 myrs

diverse and multistage mo au ag pb zn and cu deposits in the xiong er terrane east qinling from triassic cu mineralization abstract the xiong er terrane is one of the representative regions in east qinling orogenic belt various polymetallic deposits have been discovered in the xiong er terrane such as porphyry mo carbonatite hosted type mo quartz vein type mo breccia pipes type au and orogenic type au ag pb zn deposits indicating that diverse significant mineralization occurred in the xiong er terrane recently numerous cu deposits have been observed in the xiong er terrane xianglugou is a quartz vein type copper mineralization which was discovered in xiayu district southern of the xiong er terrane four chalcopyrite samples from xianglugou yield re os isochron age of 230 31 ma 2 mswd 0 8 this is the first evidence for triassic cu mineralization in the xiong er terrane this not only shows the xiong er terrane contains considerable mo au and ag pb zn reserve but also indicates that there is a great potential of cu mineralization the discoverable cu mineralization can further emphasize the significance of the widespread triassic mineralization and widened exploration ideas and goals in the future in the xiong er terrane the xiong er terrane experienced three polymetallic mineralization events including paleoproterozoic triassic and late jurassic to early cretaceous deposits during the qinling orogen evolution these metallogenic events may be related to multiple tectonic events the paleoproterozoic mineralization was associated with the continental outgrowth occurred along the southern margin of the north china craton before 1760 ma the triassic cu mineralization may be associated with the northward subduction of the north qinling orogen beneath the huaxiong block during the collision between north china craton and yangtze craton late jurassic to early cretaceous mineralization perhaps caused by decompressional extension of the qinling orogenic belts and the north china craton intense destruction and lithospheric thinning which is now generally related to the westward subduction of paleo pacific plate

quantifying biological carbon export for the northwest north atlantic continental shelves 1 it has been suggested that continental shelf systems contribute disproportionately to the oceanic uptake of atmospheric co2 but the magnitude of this flux and the relative contributions of different underlying mechanisms are poorly quantified a biological continental shelf pump mechanism has been implied however the magnitude of this export depends on advective transport of carbon rich water off the shelf a process that is difficult to observe directly here we use a physical biogeochemical model for the northeastern north american continental margin to estimate the uptake of atmospheric co2 the fraction of this uptake that results from biological processes and the transport of organic carbon off the shelf our results suggest that there is no systematic difference in the area normalized co2 uptake between the shelf regions and the adjacent deep ocean the advective transport of carbon rich water off the shelf is insufficient to drive a continental shelf pump in this region

geology mineralization and geochronology of the qianhe gold deposit xiong ershan area southern north china craton the qianhe gold deposit in the xiong ershan area is located along the southern margin of the archean paleoproterozoic north china craton the deposit consists of six orebodies that are hosted in paleoproterozoic andesites to basaltic andesites and structurally controlled by roughly ew trending faults individual orebodies comprise auriferous quartz veins and disseminated au bearing pyrite within hydrothermally altered rocks on both sides of or close to the veins ore related hydrothermal alteration has produced various mixtures of k feldspar quartz sericite chlorite epidote carbonate and sulfides pyrite is the most important ore mineral associated with minor amounts of galena sphalerite and chalcopyrite other trace minerals include molybdenite arsenopyrite scheelite rutile xenotime and parisite gold occurs mostly as native gold and electrum enclosed in pyrite or along microfractures of sulfides and quartz microthermometric measurements of primary inclusions in auriferous quartz suggest that gold and associated minerals were precipitated in the range of 160 305 c from aqueous or carbonic aqueous fluids with salinities of 6 22 wt nacl equiv samples of molybdenite coexisting with au bearing pyrite have re os model ages of 134 135 ma whereas ore related hydrothermal sericite separates yield 40ar 39ar plateau ages between 127 and 124 ma the re os and 40ar 39ar ages are remarkably consistent with zircon u pb ages 134 5 1 5 and 127 2 1 4 ma 1 of the biotite monzogranite from the heyu intrusive complex and granitic dikes in and close to the qianhe gold mine indicating a close temporal and thus possibly genetic relationship between gold mineralization and granitic magmatism in the area fluid inclusion waters extracted from auriferous quartz have d values of 80 to 72 whereas the calculated 18oh2o values range from 3 1 to 3 8 the hydrogen and oxygen isotopes from this study and previous work indicate that ore fluids were likely derived from degassing of magmas with addition of minor amounts of meteoric water gold mineralization at qianhe is temporarily coincident with pervasive bimodal magmatism widespread fault basin formation and well development of metamorphic core complexes in the whole eastern north china craton that have been interpreted as reflecting reactivation of the craton in the late mesozoic after prolonged stabilization since its formation in the late paleoproterozoic it is therefore concluded that the qianhe gold deposit formed as a result of this craton reactivation event

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

single grain pyrite rb sr dating of the linglong gold deposit eastern china abstract this study employs the single grain pyrite rb sr technique to date mineralization using the example of the linglong lode gold deposit jiaodong peninsula eastern china the gold deposits in this area are interpreted to have a consistent spatial temporal relationship with widespread late jurassic early cretaceous magmatism in eastern china likely related to lithospheric thinning around 120 ma pyrite of the linglong gold mine contains different types of mineral inclusions such as sericite and feldspar that cause distinguishable variations in rb and sr contents and rb sr ratios four pyrite samples from veins of different mineralization stages give an average isochron age of 120 6 0 9 ma analyses of one quartz and two sericite samples yield isochron ages between 122 ma and 120 ma dating of mineralization is often hampered by disequilibrium of isotopic systems and or the lack of suitable minerals for dating purposes hence the successful attempt of the single grain rb sr technique of pyrite which occurs as a common mineral phase in orebodies and is genetically related to the mineralization has great potential for precise geochronology of hydrothermal mineral deposits

coefficients for sea surface wind stress heat flux and wind profiles as a function of wind speed and temperature surface layer coefficients for wind profiles wind stress and heat flux in typical open sea conditions are briefly reviewed businger dyer flux gradient relationships and a charnock wind stress formula fit the empirical data and are dimensionally consistent these have been solved by an iterative method and the results are presented in a tabular form suitable for climatological calculations from marine wind and temperature data

ore related breccias in volcanoplutonic arcs an overview of breccias related to a variety of base metal precious metal and lithophile element deposits in volcanoplutonic arcs permits definition of six possible mechanisms for subsurface brecciation 1 release of magmatic hydrothermal fluids from high level hydrous magma chambers during second boiling and subsequent decompression generates a spectrum of breccia types in which fragments may suffer collapse and or ascent single or multiple intrusion related breccia pipes and pre and intermineral breccias in porphyry copper deposits provide widespread examples 2 magmatic heating and expansion of meteoric pore fluids may lead to brecciation commonly of late or postmineral age and including pebble dikes in porphyry type and related deposits magmatic heating of rocks saturated with seawater may cause submarine hydrothermal eruptions late in the emplacement histories of kuroko type massive sulfide deposits many of the resultant breccias underwent limited sedimentary transport overpressuring of heated fluids beneath semipermeable partly self sealed cap rocks may lead to brecciation and subaerial hydrothermal eruptions in shallow epithermal precious metal settings magmatic heating or tectonic disturbance may have triggered brecciation 3 interaction of cool ground waters with subsurface magma can generate phreatomagmatic explosions postmineral phreatomagmatic diatremes associated with porphyry systems and premineral diatremes with epithermal precious or base metal deposits were generated in this manner these attained the palcosurface to produce pyroclastic base surge and fall deposits that accumulated as tuff rings around maar craters 4 magmatic hydrothermal brecciation may lead to disruption of rocks through to the paleosurface decompression and fragmentation and eruption of the top part of an underlying magma chamber pre and postmineral magmatic diatremes of this sort are inferred to accompany a few porphyry type and other base and precious metal systems they were manifested at the palcosurface by accumulations of pyroclastic fall and flow deposits 5 breccias may result from mechanical disruption of wall rocks during subsurface movement of magma any intrusion related deposit may include such intrusion breccias 6 tectonic breccias resulting from fault displacement may accompany any type of ore deposit a continuum exists between many of these breccia types and it is difficult to identify unique criteria for their unambiguous distinction

evaluation of the 87rb decay constant by age comparison against the u pb system abstract the rb sr decay system is one of the most widely used geochronometers for obtaining ages and cooling rates of terrestrial magmatic metamorphic and hydrothermal events it has also been extensively applied to date extraterrestrial early solar system events the accuracy of rb sr ages however strongly depends on the accuracy of the 87 rb decay constant 87 rb we determined 87 rb relative to the decay constants of 235 u and 238 u by comparing rb sr ages of minerals with u pb ages obtained from the same intrusion comparison of u pb emplacement ages with high precision rb sr mineral ages from three rapidly cooled igneous rocks covering an age range of ca 2 5 ga yields an unweighted mean 87 rb of 1 393 0 004 10 11 yr 1 i e 0 3 corresponding to a half life of 49 76 10 9 years because this decay constant is 2 lower than the presently recommended one many previously published ages are 2 too young and the resulting geologic interpretations may need revision

a review of the geodynamic setting of large scale late mesozoic gold mineralization in the north china craton an association with lithospheric thinning abstract abundant gold deposits are distributed along the margins of the north china craton ncc occurring throughout the precambrian basement and located in or proximal to mesozoic granitoids these deposits show a consistent spatial temporal association with late jurassic early cretaceous magmatism and are characterized by quartz lode or disseminated styles of mineralization with extensive alteration of wall rock their ages are mainly early cretaceous 130 110 ma and constrain a very short period of metallogenesis sr nd pb isotopic tracers of ores minerals and associated rocks indicate that gold and associated metals mainly were derived from multi sources i e the wall rocks precambrian basement and mesozoic granites and associated mafic rocks previous studies including high surface heat flow uplift and later basin development slow seismic wave speeds in the upper mantle and a change in the character of mantle xenoliths sampled by paleozoic to cenozoic magmas have been used to suggest that ancient cratonic mantle lithosphere was removed from the base of the ncc some time after the ordovician and replaced by younger less refractory lithospheric mantle the geochemistry and isotopic compositions of the mafic rocks associated with gold mineralization 130 110 ma indicate that they were derived from an ancient enriched lithospheric mantle source whereas the mafic dikes and volcanic rocks younger than 110 ma were derived from a relatively depleted mantle source i e asthenospheric mantle according to their age and sources relation to magmatism and geodynamic framework the gold deposits were formed during lithospheric thinning the removal of lithospheric mantle and the upwelling of new asthenospheric mantle induced partial melting and dehydration of the lithospheric mantle and lower crust due to an increase of temperature the fluids derived from the lower crust were mixed with magmatic and meteoric waters and resulted in the deposition of gold and associated metals

numerical simulations of a buoyancy driven coastal countercurrent off vancouver island abstract a three dimensional prognostic numerical model has been developed to study the ocean circulation around vancouver island british columbia in a series of simulations the model is applied to examine the role of buoyancy forcing in the dynamics of the summer coastal countercurrent found off the west coast of vancouver island the forcing is provided by the fraser river discharge into the strait of georgia an estuarine circulation establishes itself in juan de fuca strait from which a distinctive right bounded current is formed and advances along the coast sensitivity studies are conducted to determine the robustness of this current to initial conditions opposing wind enhanced vertical mixing and grid resolution finally various characteristics of the numerically modeled coastal flow are compared with observations

rb sr geochronology of chalcopyrite from the chehugou porphyry mo cu deposit northeast china and geochemical constraints on the origin of hosting granites the chehugou porphyry mo cu deposit is located ca 300 km north of beijing in the boundary zone between the archean north china craton and the neoproterozoic mesozoic central asian orogenic belt using hydrothermal chalcopyrite from this deposit we are able to show for the first time that the rb sr isotope system in massive nonfractured chalcopyrite grains can provide reliable age constraints for mo cu deposits we analyzed two chalcopyrite samples from slightly different petrogenetic environments showing contrasting texture and deformation history five 2 to 5 mg fragments of a single nonfractured chalcopyrite grain containing spatially isolated inclusions of k mica k feldspar and quartz yielded an rb sr isochron age of 256 7 ma 2 including uncertainty for this sample the dense chalcopyrite matrix apparently inhibited diffusion of rb and sr after chalcopyrite crystallization and the age should therefore reflect the time of crystallization of chalcopyrite from the mo cu mineralizing fluids the evidence for mo cu mineralization during the late permian requires a revision of the previous notion that the chehugou deposit was formed during the yanshanian orogeny lasting from 200 to 60 ma fragments of a second chalcopyrite sample that in contrast to the first had experienced deformation as indicated by intragranular fractures and alignment of k mica and k feldspar inclusions along these fractures this sample yielded a clearly younger rb sr isochron age of 207 15 ma 2 this age obviously reflects an isotopically open system due to fluid movement and or prolonged diffusion of rb and sr along the fractures single biotite crystals from an associated monzogranite yielded an rb sr isochron age of 250 ma which is interpreted as a lower age limit for the mo cu mineralization and the time when the granite cooled below 400 to 300 c considering the field evidence for a broadly contemporaneous origin of the mo cu mineralization and the hosting granitoids we suggest that the granitoids are not much older than ca 260 ma the mo cu hosting granitoids range in composition from monzogranite to highly evolved syenogranite with high la yb and sr y ratios initial end values of ca 21 to 23 nd crustal residence times of the sources 1 9 to 2 7 ga indicate melting of the predominantly archean north china craton and a subordinate juvenile mantlederived component much older u depleted lower crustal sources for the granitoids are supported by high initial 208pb 204pb ratios lithospheric delamination and underplating of hot mantle derived material may have facilitated crustal melting in a late orogenic to postcollision

persistently declining oxygen levels in the interior waters of the eastern subarctic pacific abstract fifty years of measurements at ocean station papa osp 50 n 145 w show trends in the interior waters of the subarctic pacific that are both impacted by short term few years to bi decadal atmospheric or ocean circulation oscillations and by persistent climate trends between 1956 and 2006 waters below the ocean mixed layer to a depth of at least 1000 m have been warming and losing oxygen on density surfaces found in the depth range 100 400 m 26 3 27 0 the ocean is warming at 0 005 0 012 c y 1 whereas oxygen is declining at 0 39 0 70 mol kg 1 y 1 or at an integrated rate of 123 mmol m 2 y 1 decrease of 22 over 50 years during this time the hypoxic boundary defined as 60 mol o 2 kg 1 has shoaled from 400 to 300 m in the alaska gyre the 26 2 isopycnal occasionally ventilates whereas at osp 26 0 has not been seen at the ocean surface since 1971 as the upper ocean continues to stratify to interpret the 50 year record at osp the isopycnal transport of oxygenated waters within the interior of the subarctic pacific is assessed by using a slightly modified no parameter broecker w 1974 no a conservative water mass tracer earth and planetary science letters 23 100 107 the highest nitrate oxygen signature in interior waters of the north pacific is found in the bering sea gyre western subarctic gyre and east kamchatka current region as a consequence of winter mixing to the 26 6 isopycnal by mixing with low no waters found in the subtropics and okhotsk sea this signature is diluted as waters flow eastward across the pacific evidence of low no waters flowing north from california is seen along the coasts of british columbia and se alaska oxygen in the subsurface waters of the alaskan gyre was supplied 60 by subarctic and 40 by subtropical waters during woce surveys whereas such estimates are shown to periodically vary by 20 at osp other features discernable in the osp data include periods of increased ventilation of deeper isopycnals on an 18 year cycle and strong short term few month variability caused by passing mesoscale eddies the potential impacts of declining oxygen on coastal ecosystems are discussed

rare earth elements and hydrothermal ore formation processes abstract the geochemical behaviour of ree is influenced by nearly all important hydrothermal ore formation processes including fluid rock interactions fluid precipitations adsorption and scavenging onto particles and changes in fluid temperature pressure ph eh alkalinity and ligand concentration destabilization of ree complexes in response to these physicochemical changes and possible chemical crystallographic controls determine the concentration and distribution of ree within hydrothermal minerals mineraloids and amorphous phases alteration assemblages of intrusive related mineralisations may exhibit a wide range of ree distributions and ree fractionation trends the ree distribution within these hydrothermally altered lithologies will depend on the ree concentration in the rock and the fluid the partitioning behaviour of the ree between the rock phases and the fluid and the types of alteration reactions which take place reactive rocks such as carbonate rich lithologies of skarn deposits may gain or loose significant amounts of ree during fluid rock interactions ree geochemical investigations combined with fluid inclusion and stable isotope studies may point to the origin of alteration products and the source s of ore fluids ancient massive sulphide ores commonly exhibit anomalous eu concentrations similar to many recent submarine hydrothermal precipitates the recognition of hydrothermal fluid seawater sedimentary or volcanically derived ree distributions within ores chemical sediments and hydrothermally altered lithologies may help to constrain genetic modelling of massive sulphide deposits care should be taken with the interpretation of ree distributions from metamorphosed hydrothermal ore deposits becase metamorphic and diagenetic alteration reactions may change the ree distributions mobility of ree may occur during diagenesis of carbonate rich rocks and during the development of shear zones and migmatites in contrast very large fluid rock ratios are necessary to cause significant changes in ree patterns of silicate rich rocks during diagenesis and regional metamorphism

gold deposits in the xiaoqinling xiong ershan region qinling mountains central china the gold rich xiaoqinling xiong ershan region in eastern shaanxi and western henan provinces central china lies about 30 50 km inland of the southern margin of the north china craton more than 100 gold deposits and occurrences are concentrated in the xiaoqinling west xiaoshan middle and xiong ershan east areas late archean gneiss of the taihua group and middle proterozoic metavolcanic rocks of the xiong er group are the main host rocks for the deposits mesozoic granitoids ca 178 104 ma are present in most gold districts but deposits are typically hosted in the precambrian basement rocks hundreds of meters to as far as 10 km from the intrusions and related hornfels zones deposits in the xiaoqinling and xiaoshan areas are best classified as orogenic gold deposits with ores occurring in a number of distinct belts both in quartz veins and disseminated in altered metamorphic rocks alteration assemblages are dominated by quartz sericite pyrite and carbonate minerals the ore forming fluids were low salinity co2 rich and characterized by isotopically heavy 18o four deposits dongchuang wenyu yangzhaiyu and dahu in the xiaoqinling area each contain resources of about 1 moz au some of the gold deposits in the xiong ershan area represent more shallowly emplaced tellurium enriched orogenic systems which include resources of approximately 1 1 5 moz au at shanggong and beiling or tantou others are epithermal deposits e g qiyugou and dianfang that are hosted in volcanic breccia pipes isotopic dates for all gold deposits although often contradictory generally cluster between 172 99 ma and are coeval with emplacement of the post kinematic granitoids the gold deposits formed during a period of relaxation of far field compressional stresses clearly subsequent to the extensive paleozoic early mesozoic accretion of arc terranes and the yangtze craton onto the southern margin of the north china craton hydrothermal and magmatic events occurred locally where extension related precambrian basement uplifting took place along the craton margin fluids for the orogenic gold deposits in the xiaoqinling xiaoshan and xiong ershan areas may have been released from evolving magmas or resulted from prograde metamorphic reactions within the uplift zones alternatively for the epithermal gold deposits at shallower levels in the xiong ershan area gold transporting fluids were mainly exsolved from coeval magmas although meteoric water was also involved in these hydrothermal systems

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