seismic evidence for overpressured subducted oceanic crust and megathrust fault sealing water and hydrous minerals play a key role in geodynamic processes at subduction zones however there are few seismological constraints on the presence of water within the subducting plate audet et al model converted teleseismic waves to constrain the seismological properties of subducted oceanic crust from the cascadia continental margin to its intersection with the forearc mantle their observations suggest that water is pervasively present in fluid form at high pore pressures indicating that the megathrust is a low permeability boundary these results may hold important implications for our understanding of seismogenesis subduction zone structure and the mechanism of episodic tremor and slip this study models converted teleseismic waves to constrain the seismological properties of subducted oceanic crust from the cascadia continental margin to its intersection with the forearc mantle the observations suggest that water is pervasively present in fluid form at high pore pressures indicating that the megathrust is a low permeability boundary these results may hold important implications for our understanding of seismogenesis subduction zone structure and the mechanism of episodic tremor and slip water and hydrous minerals play a key part in geodynamic processes at subduction zones1 2 3 by weakening the plate boundary aiding slip and permitting subduction and indeed plate tectonics to occur4 the seismological signature of water within the forearc mantle wedge is evident in anomalies with low seismic shear velocity marking serpentinization5 6 7 however seismological observations bearing on the presence of water within the subducting plate itself are less well documented here we use converted teleseismic waves to obtain observations of anomalously high poisson s ratios within the subducted oceanic crust from the cascadia continental margin to its intersection with forearc mantle on the basis of pressure temperature and compositional considerations the elevated poisson s ratios indicate that water is pervasively present in fluid form at pore pressures near lithostatic values combined with observations of a strong negative velocity contrast at the top of the oceanic crust our results imply that the megathrust is a low permeability boundary the transition from a low to high permeability plate interface downdip into the mantle wedge is explained by hydrofracturing of the seal by volume changes across the interface caused by the onset of crustal eclogitization and mantle serpentinization these results may have important implications for our understanding of seismogenesis subduction zone structure and the mechanism of episodic tremor and slip

fluid inclusions in the harney peak granite black hills south dakota usa implications for solubility and evolution of magmatic volatiles and crystallization of leucogranite magmas abstract experimental and theoretical studies have shown that magmatic fluids have strong influence on phase equilibria of granitic systems a microthermometric study of fluid inclusions in the proterozoic harney peak granite black hills south dakota usa was undertaken to obtain direct evidence for the composition and evolution of magmatic fluids in a leucogranitic system and to evaluate their effect on liquid lines of descent of leucogranite magmas a previous stable isotopic study has demonstrated that the granite has not interacted with nonmagmatic fluids since its crystallization therefore fluids found in the inclusions are of magmatic origin and present an opportunity to directly sample magmatic fluids trapped during crystallization of a granitic magma and during subsolidus conditions the harney peak granite was emplaced as multiple sills dikes and small intrusions many of which differentiated into coupled aplite pegmatite layers three types of fluid inclusions are found in the granite type 1 consist of variable saline h 2 o c0 2 mixtures with minor ch 4 or other gases inclusions of this type are found in tourmaline and quartz in aplite layers are generally isolated and have negative crystal shapes they are interpreted to be primary there is a general increase in salinity and decrease in isochore temperature with decreasing co 2 h 2 o ratio of the inclusions the trend is ascribed to progressive change in fluid composition with crystallization due to the differential solubility of co 2 and h 2 o in the high silica magma isochores coupled with independently determined crystallization temperatures suggest entrapment pressure 3 5 kbar consistent with geobarometry in the wallrocks type 2 inclusions are carbonic fluids dominated by co 2 whereas type 3 inclusions are saline aqueous fluids without a detected carbonic component both types are mostly found along healed fractures in quartz they are interpreted to be secondary inclusions that formed as a result of unmixing of type 1 inclusions at subsolidus conditions during uplift and cooling of the harney peak granite dome freezing point depressions birefringent daughter crystals phase equilibria considerations and track mapping of b and li distribution in thin sections all indicate that both type 1 and type 3 inclusions contain solutes such as k li and b in addition to nacl using published solubility models for h 2 o and co 2 in granitic melts and the composition of the most co 2 rich type 1 inclusions x co 2 0 55 the initial h 2 o and co 2 concentrations in the harney peak granite magma are deduced to have been 3 5 wt and 1500 ppm respectively the relatively low water concentration is consistent with temperatures of dehydration melting reactions that produced the magma it is suggested that the aplite pegmatite segregations found in parts of the harney peak granite are the result of initial rapid near liquidus crystallization of minerals with high na k ratios including plagioclase and tourmaline along a wide range of increasing h 2 o aplite crystallization was followed by crystallization of relatively potassic residual liquid enriched in fluxing elements under conditions of high h 2 o

grain boundary migration of water and carbon dioxide during uplift of garnet zone alpine schist new zealand deformed quartz veins in garnet zone schist adjacent to the active alpine fault new zealand have fluid inclusions trapped along quartz grain boundaries textures suggest that the inclusions formed in their present shapes during annealing of the deformed veins many of the inclusions are empty but some contain carbon dioxide with densities that range from 0 16 to 0 80 g cm 3 no water nitrogen or methane was detected the inclusions are considerably more co2 rich than either the primary metamorphic fluid 5 co2 or fluids trapped in fracture related situations in the same or related rocks 50 co2 enrichment of co2 is inferred to have resulted from selective migration wicking of saline water from the inclusions along water wet grain boundaries after cooling induced immiscibility of a water co2 mixture inclusion volumes changed after loss of water non wetting co2 remained trapped in the inclusions until further percolation progressively removed co2 in solution this mechanism of fluid migration dominated in ductile quartz rich rocks near but below the brittle ductile transition at deeper levels hydraulic fracturing is also an important mechanism for fluid migration whereas at shallower levels advection through open fractures dominates the fluid flow regime

tonnage cutoff model and average grade cutoff model for a single ore deposit abstract ore reserve estimation and resource prediction are important aspects of deposit exploration and mining the cutoff has great influence on the reserve and resource calculation despite this the study on the mathematical relationships of the tonnage average grade and cutoff is still scant according to the fractal distribution of element concentrations which are obtained from analysis of channel samples of constant length along exploration or mining works the tonnage cutoff and average grade cutoff models are constructed which are applicable in both exploration and operating mine environments via these models the relationships between ore tonnage metal tonnage and cutoff are obtained in terms of the fractal model of element concentrations moreover the thickness of the mineralized zone in each exploration or mining work follows a fractal model and assuming that the thickness is a continuous variable a model for calculating the mass of the mineralized zone in a single deposit is established given the mineralized zone mass the tonnage cutoff and average grade cutoff models can be utilized to calculate ore reserve and average grade especially when the cutoff changes a fault controlled disseminated and veinlet gold deposit in jiaodong gold province china is selected as a case study the estimates of the ore reserves obtained from these models are found to be consistent with the results obtained by the traditional geometric block method

timing duration and role of magmatism in wide rift systems insights from the jiaodong peninsula china east asia in east asia widespread extensional sedimentary basins together with the close association of metamorphic core complexes and magmatism are prominent features of the large scale wide rift system developed during late mesozoic times this region thus appears as a proper place to study continental extension as well as questions about the link between continental extension and magmatism this paper primarily provides pioneer exhumation time constraints on the linglong mcc jiaodong peninsula including cooling and deformation ages mcc cooling at mid crustal levels occurred at ca 143 ma besides last ductile deformation occurred at ca 134 ma while final exhumation stages under brittle 2 conditions occurred as late as ca 128 ma continuous crustal stretching were then recorded by the emplacement of a synkinematic pluton in the upper crust at ca 128 ma that cooled fast below an intracrustal shear zone crossing the ductile brittle transition at ca 123 ma the ca 120 118 ma age cluster is ascribed to the fast cooling of undeformed plutons marking the end of extension that lasted in the area over a minimum period of ca 30 my combining other mcc exhumation constraints and the onset of subsidence in the sedimentary basins total duration of late mesozoic extension in east asia could be estimated at ca 60 my related with a rather long process for extension from 160 to at least 100 ma east asian continental extension is heterogeneously distributed in space and time as revealed by fundamental differences between two end member classes of migmatite cored mcc already described in other wide rift systems extension seems to have first favoured partial melting which subsequently in turn maintained continental extension

rb sr sm nd and pb isotope systematics of pyrite implications for the age and genesis of lode gold deposits lode gold deposits commonly consist of pyrite and lesser amounts of lead and zinc sulfides accompanied by quartz and calcite their exact origin remains controversial mainly because of the scarcity of reliable geochronological data here we present direct rb sr dating of pyrite from a lode gold deposit and propose the method as a useful geochronological technique for gold mineralization for which age data are poor a positive correlation between present day 87 sr 86 sr and 87 rb 86 sr ratios of pyrite fes 2 subsamples from the linglong gold mine of china corresponds to an age of 122 123 ma which dates the age of gold mineralization the sr nd and pb isotopic compositions of pyrites and the associated rocks suggest that the hydrothermal fluids responsible for the pyrite and gold mineralization were probably derived from a mixed source i e degassing of mafic magmas and meteoric water that had leached the country rocks

nature age and tectonic setting of granitoid hosted orogenic gold deposits of the jiaodong peninsula eastern north china craton china the jiaodong gold province along the southeastern margin of the north china craton has combined production and resources of 900 tonnes of gold more than 95 of the gold in this province is hosted in mesozoic granitoids which intruded late archean metamorphic basement rocks episodically at ca 160 150 and 130 126 ma the deposits of the jiaodong peninsula form one of the largest provinces of granitoid hosted lode gold deposits in the world the jiaodong gold deposits occur as massive auriferous quartz veins hosted in subsidiary second or third order faults and as disseminated and stockwork style mineralization hosted in alteration zones along major regional scale faults mineralization took place during brittle reactivation d3 of pre existing d2 ductile shear zones wall rock alteration is dominated by k feldspar and sericite with also sulfide minerals and extensive silicification closest to the orebodies the alteration was accompanied by the introduction of volatiles fe mg k rb ag as au bi and sb enrichment of base metals in the gold lodes is generally low although locally significant gold deposition took place at temperatures of 250 to 350 c for most gold deposits and the ore fluids are co2 bearing and have calculated salinities of 6 13 wt nacl equiv deposits from the zhao ye xixia and muping rushan belts have similar if not identical structural controls alteration patterns ore mineral assemblages and stable isotope signatures lead isotope data indicate that the ore stage leads were buffered by their host rocks the granitoid hosted gold deposits in the zhao ye belt are most radiogenic the greenstone hosted deposits in the xixia belt is the least radiogenic and the granitoid hosted deposits in the muping rushan belt have intermediate compositions gold mineralization in the zhao ye xixia and muping rushan belts in the jiaodong gold province appears to be broadly contemporaneously at ca 130 120 ma as constrained by shrimp u pb zircon dating on host rocks and a post gold dike as well as by ar ar rb sr and k ar dating of hydrothermal alteration minerals and ores this early cretaceous age is about 100 million years younger than the peak of ultra high pressure metamorphism in the qinling dabie sulu orogen between the north china and yangtze cratons and about 500 km south of the gold province however it overlaps with the extension and exhumation stage of the collisional orogeny and the subduction of the pacific plate beneath the eurasian continental crust whereas the majority of the jiaodong gold deposits occur on the margin of the north china craton some also occur in the suture zone between the two cratons they are significantly landward relative to the subduction zone of the pacific plate compared with typical orogenic lode gold deposits globally lode gold deposits of ca 130 120 ma occurred on both sides of the tan lu fault zone available data favor a temporal link of gold mineralization with pacific plate subduction

contrasting origins of late mesozoic adakitic granitoids from the northwestern jiaodong peninsula east china implications for crustal thickening to delamination two suites of granitoids the late jurassic 158 3 ma linglong suite and the early cretaceous 130 126 ma guojialing suite crop out in the northwestern jiaodong peninsula eastern china the linglong suite is a monzogranite comprising alkali feldspar plagioclase quartz and fe rich biotite the guojialing suite includes at least five plutonic bodies of both granodiorite and monzo granite the rocks are composed of plagioclase alkali feldspar quartz mg rich amphibole and mg rich biotite both the linglong and guojialing suites have adakitic affinity they are enriched in lree with high la yb ratios and show positive eu anomalies the rocks are also enriched in lile and depleted in hfse with high sr y ratios the linglong granite shows very uniform sr nd isotopic compositions with initial 87 sr 86 sr ratios of 0 7119 0 7126 and e nd t values of 21 3 to 21 6 which are similar to those of the local neoarchaean basement the guojialing suite has variable initial 87 sr 86 sr ratios 0 7108 0 7120 and e nd t values 10 8 to 17 2 which are distinct both from those of the neoarchaean basement and from those of the local enriched lithospheric mantle inferred from the coeval mafic dykes in the studied area detailed petrological and geochemical data indicate that the linglong suite was derived by partial melting of neoarchaean metamorphic lower crustal rocks at depth of 50 km with a eclogite residue whereas the guojialing suite was formed by the reaction of delaminated eclogitic crust derived melt with the upwelling asthenospheric mantle the petrogenesis of these two contrasting adakitic granitoids suggests intensive lower crustal delamination during early cretaceous times following a crustal thickening process from the late stage of the early jurassic to early stage of the late jurassic with crustal thickness of 50 km respectively

analysis of sulfides in whole rock matrices by elemental analyzer continuous flow isotope ratio mass spectrometry abstract potential matrix effects in the sulfur isotopic analysis of whole rocks by elemental analyzer continuous flow isotope ratio mass spectrometry ea cfirms have been investigated by measuring mixtures of a well calibrated laboratory sulfide reference mineral and common rock forming minerals mixtures of sulfide and quartz orthoclase plagioclase kaolinite olivine magnetite ilmenite garnet halite fluorite calcite and graphite show consistent s yields and 34s values generally within 0 2 of the measured pure sulfide value however erratic results are obtained for mixtures of reference sulfide and pyroxene amphibole or biotite these minerals may suppress sample peaks cause extreme peak tailing and prohibit isotope ratio measurements pure sulfide minerals introduced after the mixtures also showed suppressed sample peaks suggesting so2 adsorption on mineral and residual ash surfaces removal of the residual ash resulted in normal measurements for reference sulfide minerals whole rocks with s concentrations in excess of 100 ppm can be successfully analyzed using ea cfirms provided that measurements are carefully monitored for evidence of so2 retention during and after combustion

docking carolina mid paleozoic accretion in the southern appalachians accretion of the extensive carolina zone to laurentia is one of the most critical unresolved problems in southern appalachian tectonics synthesis of southern appalachian tectonism reveals three lines of evidence from across the orogen that indicate a late ordovician to silurian time of accretion a tectonic unconformity in native laurentian rocks an extensive magmatic pulse in the piedmont zone of the orogen and active uplift in the carolina zone are all related to this accretionary event structural geometries in the carolina zone suggest that accretion involved sinistral transpression this new model for carolina accretion is consistent with models for the accretion of northern appalachian peri gondwanan terranes collectively their timing and mode of accretion to laurentia place tectonic constraints on paleozoic global reconstructions

metallogeny and craton destruction records from the north china craton abstract the link between metallogeny and craton destruction in the north china craton ncc remains poorly understood particularly the mechanisms within the interior of the craton in this overview we summarize the major stages in the history of formation and evolution of the ncc the spatio temporal distribution and types of major ore species as well as mantle contribution to the metallogeny in an attempt to evaluate the geodynamic settings of metallogeny and the mechanisms of formation of the ore deposits the early precambrian history of the ncc witnessed the amalgamation of micro blocks and construction of the fundamental tectonic architecture of the craton by 2 5 ga the boundaries of these micro blocks and the margins of the ncc remained as weak zones and were the principal locales along which inhomogeneous destruction of the craton occurred during later tectonothermal events these zones record the formation of orogeny related gold copper iron and titanium during the early to middle paleoproterozoic with ages ranging from 2 5 to 1 8 ma the early ordovician kimberlite and diamond mineralization at ca 480 ma the late carboniferous and early to middle permian calc alkaline i type granitoids and gold deposits of 324 300 ma and the triassic alkaline rocks and gold silver polymetallic deposits occurring along these zones and the margins of the blocks correlate with rising mantle plume southward subduction of the siberian plate and northward subduction of the yangtze plate respectively the voluminous jurassic granitoids and cretaceous intrusives carrying gold molybdenum copper lead and zinc deposits are also localized along the weak zones and block margins the concentration of most of these deposits in the eastern part of the ncc invokes correlation with lithosphere thinning associated with the westward subduction of the pacific plate although magmatism and mineralization have been recorded along the margins and few places within the interior of the ncc in the jurassic their peak occurred in the cretaceous in the eastern part of the ncc marking large scale destruction of the craton at this time the junctions of the boundaries between the micro continental blocks are characterized by extensive inhomogeneous thinning we propose that these junctions are probably for future mineral exploration targeting in the ncc

raman microspectrometry of fluid inclusions abstract for many kinds of fluid inclusions the coupling of microthermometry and raman microspectrometry is still the only viable option to obtain compositions of single fluid inclusions a review is given on the basis of 16 years of experience and helped with about 120 references of the instrumentation analytical conditions and methodology of the application of raman microspectrometry to gaseous aqueous and hydrocarbon inclusions and their daughter minerals

origin of the jiaodong type xinli gold deposit jiaodong peninsula china constraints from fluid inclusion and c d o s sr isotope compositions abstract the xinli gold deposit within the sanshandao cangshang gold belt in the jiaodong gold province is a typical jiaojia type ore deposit with high grade quartz sulfide vein veinlet stockworks that cut mesozoic granodiorite four ore stages are distinguished in the following sequences i quartz k feldspar sericite pyrite ii quartz pyrite iii quartz polymetallic sulfide and iv quartz calcite pyrite fluid inclusions in quartz and calcite in the ores contain c o h fluids dominantly of six types with varied liquid vapor ratio ore fluid in the main ore stage is characterized by medium low temperature low salinity reducing condition and nacl h 2 o co 2 ch 4 in composition the 18 o water smow of quartz in ore stages ii and iii range from 2 82 to 5 34 and the d smow are between 69 6 and 88 3 both suggest that the ore fluid was dominantly magmatic water the 13 c pdb of the calcite are from 6 4 to 2 4 indicating mantle contribution to the ore fluid the pyrite 34 s cdt from four ore stages are basically similar varying from 9 42 to 11 62 which implies significant involvement of crustal materials the initial 87 sr 86 sr ratios in the calcite ranging from 0 710657 to 0 711542 also denote a crustal contribution the fluid composition and systematic h o c s sr isotopic data are explained by a model of slab subduction induced gold mineralization in the model the ore fluid and metals were considered to associate with the dehydration and desulfidation of the subducting paleo pacific slab and the subsequent devolatilization of enriched mantle wedge the h 2 o in the fluid might have been released from the devolatilization of enriched mantle wedge the co 2 could be from mantle wedge or subcontinental lithospheric mantle and the sulfur and strontium would be initially released from the subducted seafloor sediments this process was further supported by the geochemical features of intermediate basic dykes contemporaneous to the gold ore deposits the deposit features and ore forming process of the xinli gold deposit hardly concur those of the orogenic gold deposit and the pluton related gold deposit the study supports the argument of that the gold deposits in the jiaodong belong to a unique gold type related to a complex slab subduction related process the geodynamic engine of the jiaodong type gold deposit is specific i e the slab subduction coupling with the consequent lithospheric thinning and structure adjustment

geology and timing of mineralization at the cangshang gold deposit north western jiaodong peninsula china the cangshang gold deposit of the north western jiaodong peninsula contains reserves of greater than 50 tonnes t and is developed by the largest open pit gold mine in china this deposit is a jiaojia style i e disseminated and veinlet deposit it is controlled by the san cang fault zone which trends 040 and dips 40 75 se at the mine site the main no 1 orebody lies between a hanging wall of precambrian metamorphic rocks mainly amphibolite of the fenzishan group and a footwall composed of the mesozoic linglong granitoid the ore zone is mainly composed of pyritized sericitized and silicified granitoid which has undergone variable degrees of cataclasis shrimp u pb dating of zircon indicates that the protolith of the hanging wall amphibolite was formed at 2530 17 ma and underwent metamorphism at 1852 37 ma the footwall granodiorite has been dated at 166 4 ma whereas zircons from the ore zone yield a younger age of 154 5 ma cathodoluminescence images of zircons from the granodiorite and ore zone show oscillatory zonation indicative of an igneous origin for both and the ages of these zircons therefore are all interpreted to be representative of magmatic crystallization dating of sericite by 40ar 39ar has been used to directly determine the timing of formation of the cangshang deposit providing the first time absolute age on formation of the jiaojia style gold deposits the well defined age of 121 3 0 2 ma provides the precise timing of gold mineralization at the cangshang deposit this age is consistent with those of linglong style vein type gold mineralization also from the north western jiaodong peninsula at between 126 and 120 ma therefore our work indicates that both styles of gold deposits in the jiaodong peninsula were formed during the same mineralization event

40ar 39ar geochronological constraints on the formation of the dayingezhuang gold deposit new implications for timing and duration of hydrothermal activity in the jiaodong gold province china abstract china s largest gold resource is located in the highly endowed northwestern part of the jiaodong gold province most gold deposits in this area are associated with the ne to nne trending shear zones on the margins of the 130 126 ma guojialing granite these deposits collectively formed at ca 120 5 ma during rapid uplift of the granite the dayingezhuang deposit is a large 120 t au orogenic gold deposit in the same area but located along the eastern margin of the late jurassic linglong metamorphic core complex new 40ar 39ar geochronology on hydrothermal sericite and muscovite from the dayingezhuang deposit indicate the gold event is related to evolution of the core complex at 130 4 ma and is the earliest important gold event that is well documented in the province the dayingezhuang deposit occurs along the linglong detachment fault which defines the eastern edge of the ca 160 150 ma linglong granite granodiorite massif the anatectic rocks of the massif were rapidly uplifted at rates of at least 1 km m y from depths of 25 30 km to form the metamorphic core complex the detachment fault with precambrian metamorphic basement rocks in the hangingwall and the linglong granitoids and migmatites in the footwall is characterized by early mylonitization and a local brittle overprinting in the footwall gold is associated with quartz sericite pyrite k feldspar altered footwall cataclasites at the southernmost area of the brittle deformation along the detachment fault our results indicate that there were two successive yet distinct gold forming tectonic episodes in northwestern jiaodong one event first reactivated the detachment fault along the edge of the linglong massif between 134 and 126 ma and then a second reactivated the shears along the margins of the guojialing granite both events may relate to a component of northwest compression after a middle early cretaceous shift from regional nw se extension to a ne sw extensional regime

sequence of late jurassic early cretaceous magmatic hydrothermal events in the xiong ershan region central china an overview with new zircon u pb geochronology data on quartz porphyries recent investigations have revealed several large au and mo deposits in the xiong ershan region central china most quartz porphyries associated with the mineralization occur as dikes and apophyses or as rubbles cemented in mineralized breccia pipes three types of quartz porphyries were sampled from the leimengou mo deposit the qiyugou au deposit and the niutougou au deposit la icp ms zircon u pb analysis was performed in zircons from two quartz porphyries the results yielded ages of 125 4 0 77 ma for leimengou mo deposit and 150 1 1 1 ma for qiyugou au deposit the magma source of leimengou quartz porphyry is similar to that of the mineralized cementing material in breccia pipes of the qiyugou au deposit whereas the magma source of qiyugou quartz porphyry is the same as that of quartz porphyries in niutougou au deposit based on the new u pb isotopic ages of granitic plutons reported in this study together with the age data in the literature we identify distinct magmatic pulses in the xiong ershan region at ca 160 150 143 133 125 and 115 ma during the late jurassic early cretaceous the ages of au and mo mineralization coincide with the thermal events at about 115 125 133 and 143 ma are considered to be co eval with granitic magmatism no mineralization ages of 150 and 160 ma thermal events have been previously reported our study demonstrates late jurassic early cretaceous multiple magmatic pulses and mineralization in the xiong ershan region

tectonics and distribution of gold deposits in china an overview gold exploration in china has expanded rapidly during the last two decades since a modern approach to economic development has become a national priority china currently produces 180 tonnes t of gold annually which is still significantly less than south africa usa and australia however china is now recognized as possessing significant gold resources in a wide range of mineral deposit types present estimates of gold resources in china exceed 4 500 t which comprise 60 in gold only deposits more than 25 in base metal rich skarn porphyry and vein deposits and more than 10 in placer accumulations the major gold provinces in china formed during the main episodes of phanerozoic tectonism such tectonism involved interaction of china s three major precambrian cratons north china tarim and yangtze or south china when combined with cathaysia block with the angara or siberian kazakhstan kyrgyzstan and indian cratons resulting collisions included deformation of accreted oceanic sequences between the cratonic blocks the most important ore forming orogenies were 1 the late paleozoic variscan 405 270 ma which led to amalgamation of the angara north china and yangtze cratons 2 the indosinian 270 208 ma which led to the collision of north china and south china cratons 3 the yanshanian 208 90 ma which was largely influenced by the subduction of the izanagi pacific plates beneath eastern china and 4 the himalayan 90 ma indentation of the indian continent into eurasia no important precambrian gold systems are recognized in china mainly because of reworking of exposed precambrian rocks by these younger orogenies but there are a few caledonian 600 405 ma gold bearing systems in northern xinjiang most of china s orogenic epithermal and carlin like gold deposits are in the reworked margins of major cratonic blocks and in metasedimentary rock dominated fold belts adjacent to these margins accordingly the major gold provinces are present along the northern southeastern and southern margins of the north china craton along the southwestern and northwestern margins of the yangtze craton in the tianshan and altayshan orogenic belts in northern xinjiang and throughout the southeastern china fold belt gold placer deposits derived from these primary deposits are concentrated in the northernmost part of northeastern china and along the northwestern margin of the yangtze craton the major provinces with significant gold in porphyry related copper systems and base metal skarns are present in the yangtze river area along the northeastern and southeastern margin of the yangtze craton in the fold belt in southwestern china and scattered through northern china three quarters of the chinese gold only deposits occur within the north china craton margins half are located in the uplifted precambrian metamorphic rocks and most of the remainder are hosted in the phanerozoic granitoids that intruded the reworked precambrian terranes the abundance of granite hosted gold contrasts the north china craton with other precambrian cratons such as those in western australia central canada and zimbabwe where gold is mainly hosted in the archean greenstone belts this difference may be explained by the multiple episodes of phanerozoic tectonism along the north china craton margins resulting from the collision of the angara north china and south china cratons and from subduction of the izanagi pacific oceanic plates underneath the eastern china continent

juvenile vs recycled crust in ne china zircon u pb geochronology hf isotope and an integrated model for mesozoic gold mineralization in the jiaodong peninsula abstract the continental crust of the north china craton ncc is a major reservoir of mineral resources with imprints of secular changes in tectonics and metallogeny the jiaodong peninsula located in the eastern margin of the north china craton ncc is currently one of the largest gold producers over the globe and preserves the records of multiple magmatic and metamorphic events here we characterize the timing and tectonics of the major mesozoic magmatism and the associated gold metallogeny in this region through a comprehensive u pb geochronological and hf isotope investigation of zircons in a suite of granitoids mafic magmatic enclaves melanocratic dikes and melted basement rocks the linglong granite hosting one of the major gold deposits in jiaodong shows emplacement ages between 150 and 160 ma and the dominantly negative e hf t values 34 0 to 23 8 of zircons from this intrusion suggest magma derivation from recycled components in the archean basement the guojialing granodiorite and its mafic magmatic enclaves show similar ages between 123 and 127 ma with negative e hf t values 19 3 to 16 8 corresponding to crustal magma source the melanocratic dikes belonging to pre and syn mineralization stages with u pb age range of 126 to 166 ma display large variation in their zircon e hf t values 25 7 and 2 3 suggesting the involvement of both recycled crustal and juvenile mantle components zircons in the melted basement rocks with ages in the range of ca 127 132 ma also display both positive and negative e hf t values 44 6 and 9 8 indicating a mixture of recycled ancient crust and juvenile magmas our study shows that although the peak of gold metallogeny coincided with the tectonics associated with pacific plate subduction which mobilized and concentrated the ores the source materials of gold mineralization and magmatism had multiple origins including from the precambrian basement rocks mesozoic granitoids and mantle derived mafic magmas with extensive mixing of crustal lithosphere mantle and asthenospheric components a combination of delamination mantle upwelling subduction related metasomatic enrichment and recycling of ancient components facilitated the gold metallogeny in this region our study provides a typical case of juvenile and recycled components in the formation and evolution of continental crust and associated mineral resources

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

geological and isotopic evidence for magmatic hydrothermal origin of the ag pb zn deposits in the lengshuikeng district east central china the lengshuikeng ore district in east central china has an ore reserve of 43 mt with an average grade of 204 53 g t ag and 4 63 pb zn based on contrasting geological characteristics the mineralization in the lengshuikeng ore district can be divided into porphyry hosted and stratabound types the porphyry hosted mineralization is distributed in and around the lengshuikeng granite porphyry and shows a distinct alteration zoning including minor chloritization and sericitization in the proximal zone sericitization silicification and carbonatization in the peripheral zone and sericitization and carbonatization in the distal zone the stratabound mineralization occurs in volcano sedimentary rocks at 100 400 m depth without obvious zoning of alterations and ore minerals porphyry hosted and stratabound mineralization are both characterized by early stage pyrite chalcopyrite sphalerite middle stage acanthite native silver galena sphalerite and late stage pyrite quartz calcite the 34s values of pyrite sphalerite and galena in the ores range from 3 8 to 6 9 with an average of 2 0 the c o isotope values of siderite calcite and dolomite range from 7 2 to 1 5 with an average of 4 4 v pdb and from 10 9 to 19 5 with an average of 14 8 v smow respectively hydrogen oxygen and carbon isotopes indicate that the hydrothermal fluids were derived mainly from meteoric water with addition of minor amounts of magmatic water geochronology employing la icp ms analyses of zircons from a quartz syenite porphyry yielded a weighted mean 206pb 238u age of 136 3 0 8 ma considered as the emplacement age of the porphyry rb sr dating of sphalerite from the main ore stage yielded an age of 126 9 7 1 ma marking the time of mineralization the lengshuikeng mineralization classifies as an epithermal ag pb zn deposit

metallogeny of the north china craton link with secular changes in the evolving earth abstract the north china craton ncc has experienced a complex geological evolution since the early precambrian and carries important records of secular changes in tectonics and metallogeny here we synthesize the salient geological and tectonic features of the evolution and destruction of the ncc vis a vis major metallogenic events and the formation of potential ore deposits we identify a close relationship between the major geological events in the ncc and those reported elsewhere on the globe we trace the records of a regular change in the pattern of metallogeny mineral deposit character spatial distribution and genetic mechanisms which closely match the timing and styles of the major geological and tectonic events in this craton the ncc went through five major tectonic cycles 1 neoarchean crustal growth and stabilization 2 paleoproterozoic rifting subduction accretion collision with imprints of the great oxidation event goe 3 late paleoproterozoic neoproterozoic multi stage rifting 4 paleozoic orogenesis at the margins of the craton and 5 mesozoic extensional tectonics associated with lithospheric thinning and decratonization coinciding with these major geological events are five major metallogenic systems identified as follows 1 an archean bif system 2 paleoproterozoic cu pb zn and mg b systems 3 a mesoproterozoic ree fe pb zn system 4 a paleozoic orogenic cu mo system and 5 mesozoic intracontinental au and ag pb zn and mo systems the ore deposit types in each of these metallogenic systems show distinct characteristics and tectonic affinities from early precambrian through late precambrian to paleozoic and mesozoic the ncc records a transition from primitive to modern style plate tectonics evidence for imbricated oceanic plate stratigraphy in a subduction accretion setting and collisional orogenesis along at least three major zones of ocean closure are documented major transitions in tectonic style and surface environmental changes recorded in other parts of the world are also reflected in the geological history and metallogenic events in the ncc large scale gold deposits formed through intraplate tectonics during the mesozoic provide important insights into mantle dynamics and crust mantle interaction associated with lithospheric thinning and craton destruction the ncc provides one of the best examples for documenting secular changes in the geological history and metallogenic epochs of an evolving earth

the novaya zemlya bora and its impact on barents sea air sea interaction 1 novaya zemlya is a mountainous archipelago in the eastern arctic weather station data indicates that southeasterly high speed winds are frequent especially during the winter although it has been proposed that a bora is responsible for these winds there has been no quantitative analysis of the flow in the region here we present the first high resolution climatology of the three dimensional wind field near novaya zemlya the high speed wind events are shown to share many characteristics with bora as well as models of downslope windstorms the highest wind speeds occur where barents sea dense water is observed to form and we show that there is a doubling in the turbulent heat transfer from the ocean to the atmosphere during bora it is argued that the bora plays an important role in the transformation of the atlantic water that passes by the archipelago en route to the central arctic ocean

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

the relationship of mantle derived fluids to gold metallogenesis in the jiaodong peninsula evidence from d o c s isotope systematics abstract the largest gold district in china is the jiaodong peninsula where three types of gold deposits are recognized quartz vein fracture altered and breccia types the first two developed along a group of ne trending faults and are hosted by granitic intrusions dated at 160 to 150 ma biotite granite and 130 to 126 ma granodiorite and by metamorphic rocks of the precambrian crystalline basement the breccia type gold system is mainly located around the northern margin of the jiaolai cretaceous basin where mineralisation is controlled by both detachment fractures and ne trending faults this study is based on stable isotope determinations from ten gold deposits including linglong jiaojia sanshandao cangshang wang ershan dayigezhuang denggezhuang pengjiakuang fayunkuang and dazhuangzi as well as the linglong jurassic biotite granite guojialing cretaceous granodiorite and archean gneiss the stable isotope systematics reflect the style of the three types of gold deposits but also show that they belong to the same metallogenic system in which the hydrothermal fluids were derived from a mantle fluid reservoir and mixed with crustal fluids the ore forming age is later than both the jurassic biotite granite and cretaceous granodiotite but overlaps with the 121 to 114 ma ages of lamprophyre and diabase dykes the hydrothermal fluids that were responsible for both gold mineralisation and the retrograde alteration of the diabase and lamprophyre dykes are similar and represent a co 2 and potassium rich system this fluid system is interpreted to be the consequence of cretaceous lithospheric thinning asthenospheric upwelling and mantle degassing in eastern china

a multifractal analysis of mineralization characteristics of the dayingezhuang disseminated veinlet gold deposit in the jiaodong gold province of china abstract the gold concentration distributions along drifts in the dayingezhuang fault controlled disseminated veinlet gold deposit in the jiaodong gold province eastern china has been analyzed using a multifractal technique with the aim of better understanding the ore forming processes some intensely mineralized areas show small gold singularities representing compact concentration distributions which is resulted from intense stress release and development of abundant microfractures with various sizes several intensely and moderately mineralized areas are characterized by isolated distributions of lower concentrations suggesting that only relatively large microfractures locally develop resulted from less intense stress release some barely and moderately mineralized areas show isolated distributions of higher concentrations due to occurrences of only a few fractures or large microfracture most barely mineralized areas are characterized by dense concentrations distributions because the widespread development of relatively small microfractures caused by weak stress release thus making the areas unsuitable for gold deposition these characteristics reflect that variable development of the structures is responsible for different gold mineralization within the deposit the ratios between the singularity a q and its fractal dimension f a q for the different drifts vary similarly as q 0 8 or q 0 8 thus from the multifractal viewpoint it is suggested that gold enrichment processes are consistent in both mineralized and barely mineralized areas despite their differing mineral intensities

ore forming fluids associated with granite hosted gold mineralization at the sanshandao deposit jiaodong gold province china the sanshandao gold deposit with total resources of more than 60 t of gold is located in the jiaodong gold province the most important gold province of china the deposit is a typical highly fractured and altered disseminated gold system with high grade quartz sulphide vein veinlet stockworks that cut mesozoic granodiorite there are four stages of veins that developed in the following sequence 1 quartz k feldspar sericite 2 quartz pyrite arsenopyrite 3 quartz base metal sulfide and 4 quartz carbonate fluid inclusions in quartz and calcite in vein veinlet stockworks contain c o h fluids of three main types the first type consists of dilute co2 h2o fluids coeval with the early vein stage molar volumes of these co2 h2o fluid inclusions ranging from 50 60 cm3 mol yield estimated minimum trapping pressures of 3 kbar homogenization temperatures obtained mainly from co2 h2o inclusions with lower co2 concentration range from 267 375 c the second inclusion type with a co2 h2o ch4 composition was trapped during the main mineralizing stages these fluids may reflect the co2 h2o fluids that were modified by fluid rock reactions with altered wallrocks isochores for co2 h2o ch4 inclusions with homogenization temperatures ranging from 204 325 c and molar volumes from 55 to 70 cm3 mol provide an estimated minimum trapping pressure of 1 2 kbar the third inclusion type aqueous inclusions trapped in cross cutting microfractures in quartz and randomly in calcite are post mineralization and have homogenization temperatures between 143 228 c and salinities from 0 71 7 86 wt nacl equiv stable isotope data show that the metamorphic fluid contribution is minimal and that ore fluids are of magmatic origin most likely sourced from 120 126 ma mafic to intermediate dikes this is consistent with the carbonic nature of the fluid and the cross cutting nature of those deposits relative to the host mesozoic granitoid