discriminating fluid source regions in orogenic gold deposits using b isotopes abstract the genesis of orogenic gold deposits is commonly linked to hydrothermal ore fluids derived from metamorphic devolatilization reactions however there is considerable debate as to the ultimate source of these fluids and the metals they transport tourmaline is a common gangue mineral in orogenic gold deposits it is stable over a very wide p t range demonstrates limited volume diffusion of major and trace elements and is the main host of b in most rock types we have used texturally resolved b isotope analysis by secondary ion mass spectrometry sims to identify multiple fluid sources within a single orogenic gold ore district the loulo mining district in mali west africa hosts several large orogenic gold ore bodies with complex fluid chemistry associated with widespread pre ore na and multi stage b metasomatism the gara deposit as well as several smaller satellites formed through partial mixing between a dilute aqueous carbonic fluid and a hypersaline brine hydrothermal tourmaline occurs as a pre ore phase in the matrix of tourmalinite units which host mineralization in several ore bodies clasts of these tourmalinites occur in mineralized breccias disseminated hydrothermal and vein hosted tourmaline occur in textural sites which suggest growth during and after ore formation tourmalines show a large range in 11 b values from 3 5 to 19 8 which record a change in fluid source between paragenetic stages of tourmaline growth pre mineralization tourmaline crystals show heavy 11 b values 8 19 8 and high x site occupancy na ca 0 69 1 apfu suggesting a marine evaporite source for hydrothermal fluids syn mineralization and replacement phases show lighter 11 b values 3 5 to 15 1 and lower x site occupancy 0 62 0 88 apfu suggesting a subsequent influx of more dilute fluids derived from devolatilization of marine carbonates and clastic metasediments the large overlapping range in isotopic compositions and a skew toward the opposing population in the 11 b data for both tourmaline groups reflects continual tourmaline growth throughout mineralization which records the process of fluid mixing a peak in 11 b values at 8 largely controlled by tourmalines of syn to post ore timing represents a mixture of the two isotopically distinct fluids this paper demonstrates that b isotopes in tourmaline can be instrumental in interpreting complex and dynamic hydrothermal systems the importance of b as an integral constituent of orogenic ore forming fluids and as a gangue phase in orogenic gold deposits makes b isotope analysis a powerful tool for testing the level of source region variability in these fluids and by extension that of metal sources

tectonic setting of synorogenic gold deposits of the pacific rim abstract more than 420 million oz of gold were concentrated in circum pacific synorogenic quartz lodes mainly during two periods of continental growth one along the gondwanan margin in the palaeozoic and the other in the northern pacific basin between 170 and 50 ma these ores have many features in common and can be grouped into a single type of lode gold deposit widespread throughout clastic sedimentary rock dominant terranes the auriferous veins contain only a few percent sulphide minerals have gold silver ratios typically greater than 1 1 show a distinct association with medium grade metamorphic rocks and may be associated with large scale fault zones ore fluids are consistently of low salinity and are co2 rich in the early and middle palaeozoic in the southern pacific basin a single immense turbidite sequence was added to the eastern margin of gondwanaland deformation of these rocks in southeastern australia was accompanied by deposition of at least 80 million oz of gold in the victorian sector of the lachlan fold belt mainly during the middle and late devonian lesser devonian gold accumulations characterized the more northerly parts of the gondwanan margin within the hodgkinson broken river and thomson fold belts additional lodes were emplaced in this flyschoid sequence in devonian or earlier palaeozoic times in what is now the buller terrane westland new zealand minor post devonian growth of gondwanaland included terrane collision and formation of gold bearing veins in the permian in australia s new england fold belt and in the jurassic early cretaceous in new zealand s otago schists collision and accretion of dozens of terranes for a 100 m y long period against the western margin of north america and eastern margin of eurasia led to widespread latest jurassic to eocene gold veining in the northern pacific basin in the former location late jurassic and early cretaceous veins and related placer deposits along the western margin of the sierra nevada batholith have yielded more than 100 million oz of gold additional significant ore forming events during the development of north america s cordilleran orogen included those in the klamath mountains region california in the late jurassic and early cretaceous the klondike district yukon by the early cretaceous the nome and fairbanks districts alaska and the bridge river district british columbia in the middle cretaceous and the juneau gold belt alaska in the eocene gold bearing veins deposited during the late jurassic and early cretaceous terrane collision that formed the present day russian far east have been the source for more than 130 million oz of placer gold the abundance of gold bearing quartz carbonate veins throughout the gondwanan north american and eurasian continental margins suggests the migration and concentration of large fluid volumes during continental growth such volumes could be released during orogenic heating of hydrous silicate mineral phases within accreted marine strata the common temporal association between gold veining and magmatism around the pacific rim reflects these thermal episodes melting of the lower thickened crust during arc formation slab rollback and extensional tectonism and subduction of a slab window beneath the seaward part of the forearc region can all provide the required heat for initiation of the ore forming processes

alteration of the damiao anorthosite complex in the northern north china craton implications for high grade iron mineralization abstract the damiao type iron deposit is hosted in a typical proterozoic anorthosite complex in the northern north china craton the types of ores in damiao mainly comprise massive fe ores massive fe p ores and disseminated fe and fe p ores the disseminated fe and fe p ores formed by fractional crystallization are generally hosted in oxide apatite gabbronorite and account for 70 of the proven reserve of the damiao type iron ore the massive fe and fe p ores account for 30 of the proven reserve of the damiao type deposit iron ore and generally occur as irregular dykes or veins filling vertical fractures of the previously consolidated anorthosite showing typical features of hydrothermal mineralization the contact between the massive orebodies and wall rocks is sharp and straight the anorthosite comprises white and dark varieties with the former resulted by the alteration of the latter that occurs as relicts petrographic observation and electron microprobe analyses show abundant fe ti oxide inclusions in plagioclase which impart the dark color to the rock the similar spider diagram patterns between fresh and altered plagioclase and between dark and white colored anorthosite imply a genetic relationship between the dark and white types during the alteration of anorthosite cao and mgo were slightly decreased the sio2 al2o3 and na2o were significantly increased and the tfe2o3 and tio2 were significantly decreased the tfe2o3 and tio2 in the dark colored anorthosite have a range of 4 86 12 18 wt and 0 37 1 65 wt respectively however the tfe2o3 and tio2 in the white colored anorthosite have a range of 1 67 3 1 wt and 0 14 0 31 wt respectively these features suggest that the alteration of the anorthosite led the fe element by leaching from the dark colored anorthosite at highly oxidized condition and then precipitated within the fractures of the anorthosite thus forming the massive fe and fe p orebodies because the estimated amount of transported fe is much more abundant than the proven ore reserve we infer that there should be huge potential for prospecting damiao type iron ores

formation and evolution of the tancheng lujiang wrench fault system a major shear system to the northwest of the pacific ocean abstract in the northwestern peri pacific tectonic belt on the continental margin of east asia there is a series of major faults trending ne nne i e the tancheng lujiang wrench fault system this fault system extends more than 5000 km with a width of 800 1000 km in the continent and a general strike of n30 e on the basis of the results of special research on the major faults and a lot of new information about the fault system the authors discuss early mesozoic triassic jurassic period sinistral transcurrent faulting in the different regions it is suggested that in the eastern continent of east asia the e w trending tectonic pattern of the paleozoic and beginning of the mesozoic appear in the nuclei of the sino korean continent massif and the yangtze continent massif these ancient continent massifs accreted both southwards and northwards which finally led to their collision and suturing to the angura continent massif later this tectonic framework was changed greatly by the tancheng lujiang wrench fault system along which left lateral horizontal displacement of 1000 1500 km took place since the mesozoic the dislocation and deformation of horizontal displacement of the tancheng lujiang fault system produced a series of structures trending ne nne in the continental margin which have greatly transformed the ancient structures of the preceding mesozoic this is an important diktyogenese in the continent of east asia during the horizontal displacement motion of these faults the folds nappes and decollement structures pull apart basins and subductions within the continent occurred in the continent at the same time some large sinistral ductile shear zones of horizontal displacement appeared the depth of the deformed horizon of ductile shear which belongs to simple shear was controlled by the tectonic element and distance away from the continental margin whilst the ductile shear deformation occurred the fault dynamo thermal metamorphism and the fault remelting took place and magma activity appeared within the continent in the mesozoic the fault zones used to be high energy zones and recently became the seismic belts within the continent formation of the tan lu fault system was due to the collision between the southern and northern blocks its large sinistral horizontal displacement in the mesozoic was closely related to the kula plate moving northwards therefore the continent disintegrated by shearing which produced some new terranes the shear edge belt was formed between the continent and ocean the change of relative motion between the continent and pacific ocean plate transformed the tan lu fault system into first extension and then compression clarifying the characteristics of the tan lu fault system is an important key in understanding the evolution of the east asia continent since the mesozoic

40ar 39ar constraints on a temporal link between gold mineralization magmatism and continental margin transtension in the jiaodong gold province eastern china abstract the jiaodong gold province is the largest gold repository in china both mineralization and granitoid hosts are spatially related to the crustal scale tan lu strike slip fault system which developed along the mesozoic continental margin in eastern china a series of 40ar 39ar laser incremental heating analyses of hydrothermal sericite muscovite from three major gold deposits jiaojia xincheng and wangershan and igneous biotite from the granodiorite hosts were performed to establish a possible temporal link between gold mineralization magmatism and movement along the tan lu fault zone magmatic biotite crystals yield well defined and concordant plateau ages between documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage pifont usepackage stmaryrd usepackage textcomp usepackage portland xspace usepackage amsmath amsxtra usepackage ot2 ot1 fontenc newcommand cyr renewcommand rmdefault wncyr renewco

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

origin and evolution of hydrothermal fluids in the taochong iron deposit middle lower yangtze valley eastern china evidence from microthermometric and stable isotope analyses of fluid inclusions abstract the middle lower yangtze river valley is one of the most important metallogenic belts in china hosting numerous cu fe au mo deposits the taochong deposit is located in the northern part of the fanchang iron ore district of the middle lower yangtze river metallogenic belt the fe orebody is hosted by middle carboniferous to lower permian limestones skarns and fe orebodies occur as tabular bodies along interlayer gliding faults at some distance from the inferred granitic intrusions field evidence and petrographic observations indicate that the three stages of hydrothermal activity the skarn iron oxide main mineralization stage and carbonate stages all contributed to the formation of the taochong iron deposit the skarn stage is characterized by the formation of garnet and pyroxene with high temperature hypersaline hydrothermal fluids with isotopic compositions similar to those of typical magmatic fluids these fluids were probably generated by the separation of brine from a silicate melt instead of the product of aqueous fluid immiscibility the iron oxide stage coincides with the replacement of garnet and pyroxene by actinolite chlorite quartz calcite and hematite the hydrothermal fluids at this stage are represented by saline fluid inclusions that coexist with vapor rich inclusions with anomalously low d values 66 to 94 the decrease in ore fluid 18 o water with time and decreasing depth is consistent with the decreases in fluid salinity and temperature the fluid d values also show a decreasing trend with decreasing depth both fluid inclusion and stable isotopic data suggest that the ore fluid during the main period of mineralization was evolved by the boiling of various mixtures of magmatic brine and meteoric water this process was probably induced by a drop in pressure from lithostatic to hydrostatic the carbonate stage is represented by calcite veins that cut across the skarn and orebody locally producing a dense stockwork this observation indicates the veins formed during the waning stages of hydrothermal activity the fluids from this stage are mainly represented by a variety of low salinity fluid inclusions as well as fewer high salinity inclusions these particular fluids have the lowest 18 o water values 2 2 to 0 4 and a wide of range of d values 40 to 81 which indicate that they were originated from a mixture of residual fluids from the oxide stage various amounts of meteoric water and possibly condensed vapor low temperature boiling probably occurred during this stage we also discuss the reasons behind the anomalously low d values in fluid inclusion water extracted by thermal decrepitation from quartz at high temperatures and suggest that calcite data provide a possible benchmark for adjusting low d values found in quartz intergrown with calcite

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

origin and evolution of ore forming fluids in the hemushan magnetite apatite deposit anhui province eastern china and their metallogenic significance abstract the middle lower yangtze river metallogenic belt in the northern yangtze block is one of the most important economic mineral districts in china the hemushan deposit is a medium class fe deposit located in the southern part of the ningwu iron ore district of the middle lower yangtze river metallogenic belt the fe orebodies are mainly hosted in the contact zone between diorite and triassic marble the actinolite phlogopite apatite magnetite ore shows metasomatic filling textures and disseminated mesh vein structures based on evidences and petrographic observations the ore forming process can be divided into three distinct periods the early metallogenic period albite diopside stage the middle metallogenic period magnetite stage and hematite stage and the late metallogenic period quartz pyrite stage and carbonate stage fluid inclusion studies show four types of inclusions type i daughter mineral bearing three phase inclusions l v s type ii vapor rich two phase inclusions l v type iii liquid rich two phase inclusions l v and minor type iv liquid phase inclusions l apatites from the magnetite stage contain type i type ii and type iii inclusions anhydrites from the hematite stage mainly contain abundant type ii inclusions and relatively less type i inclusions quartz and calcite from the late metallogenic stage are mainly characterized by type iii inclusions laser raman spectroscopy and microthermometry of fluid inclusions show that the ore forming fluids broadly correspond to unsaturated nacl h2o system from the magnetite stage to the carbonate stage the ore forming fluids evolved from moderate high temperature average 414 c moderate salinity average 25 01 wt nacl equiv conditions to low temperature average 168 c low salinity average 6 18 wt nacl equiv conditions hydrogen and oxygen isotopic studies indicate that the ore forming fluid during the early stage of middle metallogenic period was mainly of magmatic water and mixing of the ore fluids with meteoric water took place during the late phase during this evolution water rock interaction and boiling and mixing of the ore fluids with meteoric water occurred the boiling of fluids was a potential mechanism for the formation of magnetite

linking mesozoic lode gold deposits to metal fertilized lower continental crust in the north china craton evidence from pb isotope systematics abstract the source s of lode gold deposits formed in precambrian cratons related to accretion collision and cratonic reactivation formerly attributed to either supercrustal volcano sedimentary sequences or deep crustal sub crustal origin remain controversial largely because gold deposits are spatially related to metamorphosed rocks but geochemical data somewhat indicate a poorly understood deep source reconciling such conflicts is important to better understand the main factor controlling the formation of ore deposits and their genetic link with specific tectonic settings giant late mesozoic lode gold provinces in the north china craton ncc were formed ca 1 7 ga later than cratonization metamorphism and contemporaneous with intensively felsic to mafic magmatism related to cratonic reactivation in this study we conduct a comprehensive pb isotope study on major gold deposits from the eastern yanshan belt northern margin of the ncc in order to constrain the source s of gold we attempt to map regional pb isotope variations of lower continental crust lcc and develop a two stage quantitative model punctuated by three prominent geological events at 2 80 ga 1 85 ga and 0 16 ga to reproduce time integrated pb isotopic signatures of deep seated lithospheric reservoirs to make a comparison with pb isotopic signatures of the gold mineralization gold bearing pyrites within different types of host rocks have relatively uniform pb isotopic ratios which are significantly different to high grade metamorphosed host rocks but similar to those of spatially associated late mesozoic granitic rocks our data show that the pb isotopic signatures of gold deposits vary consistently with presumed regional pb isotopes of the lcc during the late mesozoic lead isotopic heterogeneity of the lcc was likely caused by underplating of mafic magmas derived from mantle sources during underplating highly chalcophile elements e g au ag and cu were concentrated at the base of the lcc due to sulfide saturation from mafic magmas integrating petrological geochemical geochronological and considering chalcophile element solubility we propose a new genetic model to describe the formation of late mesozoic gold deposits in the ncc 1 early formation of sulfide bearing cumulates with high au cu ratios during magma differentiation at the base of the lcc 2 subsequent fluid fluxed remelting of these cumulates at the onset of lithospheric extension and release and ascent of ore forming fluids to the site of precipitation considering the metallogenic characteristics of other au ore forming systems we suggest that metal fertilization in deep seated reservoirs and subsequent tectonic decompression are important factors controlling the development of au rich ore deposits worldwide this study demonstrates how pb isotope can be employed to trace source s of gold deposits

fluid inclusion and stable isotope o h c constraints on the genesis of the pedra branca gold deposit troia massif borborema province ne brazil an example of hypozonal orogenic gold mineralization abstract at the archean paleoproterozoic troia massif ne brazil two major paleoproterozoic greenstone belts are documented algodoes and serra das pipocas they share similar lithostratigraphic characteristics with other 2 2 2 1 ga greenstone belts of the surrounding cratonic domains e g guiana shield and west africa craton gold mineralization in the serra das pipocas greenstone belt is associated with a regional ne trending shear zone in the mineralized area the pedra branca gold deposit the main gold mineralization is found in association with quartz veins calc silicate alteration e g diopside k feldspar amphibole titanite biotite pyrite albite magnetite carbonates and albitization pyrrhotite is commonly found as inclusions in pyrite and late magnetite replaces pyrite suggesting progressive oxidation of the ore forming fluid free milling gold commonly precipitates at the late stages of alteration in close association with magnetite and tellurides the main tellurides found are hessite altaite sylvanite calaverite and tellurobismuthite two fluid inclusion assemblages were identified from mineralized quartz veins assemblage 1 is characterized by pseudo secondary trails that show the coexistence of co2 rich and low salinity 0 8 wt nacl equiv co2 h2o nacl and h2o nacl inclusions suggesting formation during phase separation fluid immiscibility assemblage 2 is represented by late secondary low temperature th

geochronology and isotopic character of ultrahigh pressure metamorphism with implications for collision of the sino korean and yangtze cratons central china the collision zone between the sino korean and yangtze cratons in central china is marked by subduction related metamorphic rocks composed of crustal protoliths these range in metamorphic grade from ultrahigh pressure eclogite to low greenschist facies the paragenesis of the ultrahigh pressure rocks coesite and diamond bearing indicates subduction to depths greater than 120 km as a result of continental collision despite extreme metamorphic conditions zircons have not undergone pb loss but rather illustrate two periods of growth crystallization between 700 and 800 ma and ultrahigh pressure metamorphism at 218 2 5 ma previous studies have predicted a time transgressive collision but age data presented in this study indicate that the collision was approximately coeval along the length of the suture u pb zircon ages of these ultrahigh pressure metamorphic rocks are 218 4 2 5 ma and 217 1 8 7 ma for the dabie mountains and shandong peninsula respectively the similar ages imply that the tan lu fault which offsets the ultrahigh pressure metamorphic rocks is a secondary feature not related to collision or subduction whole rock isotopic data show that both rb sr and u pb were open systems during metamorphism but that sm nd probably remained closed nd initial isotopes display crustal signatures indicating that the crust subducted as a coherent slab rather than becoming intercalated with mantle material at depth sm nd data in conjunction with u pb zircon dating indicate that the ultrahigh pressure rocks are not typical yangtze craton basement 2 9 ga but that they originally crystallized in a rift environment between 700 and 800 ma discrepancies between 40ar 39ar plateaus sm nd isochrons and u pb zircon ages render calculation of a p t t path unrealistic

high grade metamorphic processes which influence archaean gold deposits with particular reference to big bell australia mineralogical and geochemical evidence indicates that partial melting and desulphidation have occurred in the big bell gold deposit decarbonation may also have occurred to account for the lack of a carbonate alteration halo this is compatible with the present data but difficult to test the big bell deposit consists of auriferous sulphide bearing lode schists with muscovite and k feldspar and surrounding biotite schists all derived by intense premetamorphic alteration of rocks of mafic composition assemblages which include cordierite sillimanite k feldspar garnet biotite quartz suggest peak metamorphic conditions of 4 5 kbar and 650 700 c based on phase relations geobaro meters and garnet biotite fe mg exchange partitioning partial melting occurred at peak metamorphism particularly in the altered mafic rocks in and around the deposit and its occurrence may have been essential to the preservation of the deposit melting greatly limited the importance of devolatilization reactions resulting in negligible aqueous fluids and no means of removing appreciable gold minor gold loss may have accompanied desulphidation a diversity of complex metamorphic assemblages occurs around the mine compared to the assemblages developed regionally variable bulk rock composition influences this contrast but there is no evidence of higher metamorphic grades at the mine nor that this might have been the prime control on the different assemblages in this narrow belt it is suggested that the big bell and hemlo deposits are the higher metamorphic grade equivalents of the more abundant greenschist facies gold deposits within archaean greenstone belts this interpretation is favoured by the host rock setting and geochemical characteristics of big bell alternative models that suggest that this class of deposit is a new type must account for the absence of high grade equivalents of the greenschist facies deposits and also the lack of low grade equivalents of the big bell hemlo type archaean gold deposits in high grade metamorphic terrains have undergone a series of processes that are not recorded in the more typical gold deposits of the greenschist facies

geochronology and isotopic geochemistry of the a type granites from the huanggang sn fe deposit southern great hinggan range ne china implication for their origin and tectonic setting abstract the huanggang sn fe deposit inner mongolia is located in southern great hinggan range metallogenic belt la icp ms zircon u pb dating show that the k feldspar granite and granite porphyry in the huanggang mine were formed at 136 7 1 1 ma and 136 8 0 57 ma respectively sr nd pb isotope of the rocks and in situ zircon hf isotopic systematics show that 87 sr 86 sr i values range from 0 70211 to 0 70729 close to the 87 sr 86 sr i of oceanic basalts and lower than those of continental crust the e nd t values and nd model ages t dm vary from 0 8 to 0 9 and 855 to 993 ma respectively the pb isotopic compositions are also variable with 206 pb 204 pb 207 pb 204 pb and 208 pb 204 pb values of 18 974 26 107 15 554 15 914 and 38 894 39 890 respectively suggesting that the lead is derived from a mixed source the 176 hf 177 hf values range from 0 282744 to 0 282922 with corresponding e hf t values ranging from 1 9 to 18 3 and two stage hf model ages t dm2 of between 561 and 888 ma the isotope composition shows that huanggang granites were derived from partial melting of juvenile lower crust that originated from depleted mantle perhaps contaminated by small amounts of ancient continental crust younger nd hf isotope model ages imply that an important crustal growth event took place in this area during the neoproterozoic integrating our data with previously published results and the late mesozoic regional tectonic setting we conclude that the huanggang granites were generated in an intraplate tectonic magmatic setting asthenospheric mantle upwelling due to lithospheric delamination and magma underplating caused the partial melting of a mantle wedge metasomatized by the fluids released from subducted oceanic crust or by decompression of depleted mantle this resulted in remelting differentiation and a continued evolution of the mafic juvenile crust producing a large quantity of granitic magma the tectonic setting for these processes may be linked to the nnw subduction of the pacific plate izanagi in the mesozoic which affected most of eastern china

geology distribution and classification of gold deposits in the western qinling belt central china gold deposits of the western qinling belt occur within the western part of the qinling dabie sulu orogen which is located between the precambrian north china and yangtze cratons and east of the songpan ganzi basin the early paleozoic to early mesozoic orogen can be divided into northern central and southern zones separated by the shangdan and lixian shanyang thrust fault systems the northern zone consists of an early paleozoic arc accreted to the north china craton by ca 450 ma the central zone which contains numerous orogenic gold deposits is dominated by clastic rocks formed in a late paleozoic basin between the converging cratonic blocks the southern zone is characterized by the easternmost exposure of triassic sedimentary rocks of the songpan ganzi basin these early to late triassic turbidities in part calcareous of the immense songpan ganzi basin also border the western qinling belt to the west carlin like gold deposits are abundant 1 along a westward extension of the southern zone defined by a window of early paleozoic clastic rocks extending into the basin and 2 within the easternmost margin of the basinal rocks to the south of the extension and in adjacent cover rocks of the yangtze craton triassic and early jurassic synkinematic granitoids are widespread across the western qinling belt as well as in the songpan ganzi basin orogenic lode gold deposits along brittle ductile shear zones occur within greenschist facies highly deformed devonian and younger clastic rocks of the central zone mainly coarse grained gold along with pyrite pyrrhotite arsenopyrite and minor base metal sulfides occur in networks of quartz veinlets brecciated wall rock and are disseminated in altered wall rock isotopic dates suggest that the deposits formed during the late triassic to middle jurassic as the leading edge of the yangtze craton was thrust beneath rocks of the western qinling belt many gold bearing placers are distributed along the river systems that flow south from the lode bearing central zone carlin like gold deposits have only been identified during the last decade in the southern zone of the western qinling and in the northeastern corner of the songpan ganzi basin the deposits mainly contain micron diameter gold in arsenical pyrite are characterized by the common occurrence of cinnabar stibnite realgar and orpiment exhibit strong silicification carbonatization pyritization and decalcification dissolution textures and are structurally controlled the lack of reactive host lithologies may have prevented development of large 100 tonnes of gold stratigraphically controlled orebodies which are typical of the carlin deposits in the western usa these deposits are hosted by triassic turbidities and shallow water carbonates and an early paleozoic inlier in the songpan ganzi basin that extends in an east west belt for about 300 km rather than true carlin deposits these carlin like deposits may be some type of shallow crustal i e epithermal hybrid with features intermediate to nevada style carlin deposits and the orogenic gold deposits to the immediate north these carlin like deposits also overlap in age with the early mesozoic orogenic gold deposits and therefore also formed during the final stages of collision between the cratons and intermediate basin closure

meso cenozoic multiple exhumation in the shandong peninsula eastern north china craton implications for lithospheric destruction abstract the shandong peninsula in the eastern north china craton ncc forms part of the region that witnessed extensive tectonic reactivation with concomitant craton destruction and lithospheric thinning during the meso cenozoic previous studies concentrated mainly on the timing mechanism and tectonic setting of the meso cenozoic magmatism with inadequate evidence from low temperature thermochronology to constrain the thermo tectonic exhumation history of this region in this study we present new apatite u pb aupb and fission track aft data with corresponding thermal history models for igneous rocks from the two flanks of the tan lu fault zone tlfz that bisects the shandong peninsula with a view to gain insights into the meso cenozoic exhumation history of this region and to evaluate its implications on the lithospheric destruction of the ncc the newly obtained aupb ages of 2 5 1 5 ga for the precambrian intrusive rocks and of 162 112 ma for the mesozoic igneous suite are mainly used to constrain their thermal history models in addition the mesozoic aupb ages of 162 112 ma highly overlap with their corresponding zircon u pb ages 161 115 ma suggesting shallow granitoid emplacement and associated rapid post magmatic cooling in response to the westward subduction of the paleo pacific plate the aft dating results yield two groups of aft central ages at 122 113 ma and 98 59 ma and corresponding thermal history models also reveal two rapid cooling stages during the early cretaceous 130 105 ma and late cretaceous to paleogene 85 55 ma by integrating previous low temperature thermochronological studies with this study we interpret that the early cretaceous rapid exhumation corresponds to the peak timing of craton destruction resulting from the paleo pacific slab rollback within a back arc extensional setting the late cretaceous rapid exhumation is interpreted as a response to continuing craton destruction derived by the nnw directed pacific plate subduction the paleogene cooling might represent the termination of craton destruction of shandong peninsula associated with a dextral motion along the tlfz triggered by the change in direction of the pacific plate from nnw to wnw and or far field effect of the india eurasia collision

implications of pyrite geochemistry for gold mineralisation and remobilisation in the jiaodong gold district northeast china abstract the jiaodong gold district of eastern china the largest gold producing district in china is located on the eastern margin of the north china craton it consists of three mineralisation belts the western zhao ye belt the middle qixia belt and the eastern muping rushan muru belt over 85 of mineralisation is hosted in the zhao ye belt which is bordered by the mantle tapping tan lu fault zone pyrite crystals from three deposits in the zhao ye belt and three deposits in the muru belt were studied using a combination of optical petrography bulk pyrite geochemistry and in situ laser ablation icp ms results show that although mineralisation is broadly similar between the two belts there are significant differences in ore and gangue mineral textures pyrite geochemistry and style of gold mineralisation texturally pyrite grains from the zhao ye belt are generally cubic and do not exhibit zoning in contrast muru pyrite grains are more often pyritohedral commonly exhibit well defined concentric zoning and display textures in ore and gangue minerals indicative of open space growth bulk pyrite geochemistry suggests a distinct enrichment in pb bi au ag and te in the zhao ye belt whereas the muru belt pyrite is significantly enriched in as cu and co in situ pyrite geochemistry indicates that au and as are variably correlated in the zhao ye belt typically only exhibiting correlation at low au concentrations most gold occurs as visible electrum along pyrite fractures and grain boundaries with a minor generation of invisible gold formed through as facilitated uptake into pyrite in the muru belt au and as have a strong correlation and there is limited occurrence of gold particles indicating that most gold in the muru belt is invisible gold contained in the crystal structure of as rich pyrite the differences in style of gold mineralisation between the belts indicates an inherent difference in timing of gold introduction in the zhao ye belt the visible electrum accounting for most of the gold endowment is formed post pyrite whereas the invisible gold in the zhao ye and muru belts is formed syn pyrite the heterogeneity in gold distribution in the jiaodong district is attributed to melting of metallogenically fertile archean crust at the base of the well endowed zhao ye belt and the lack of a similarly fertile source region beneath the muru belt

electron microprobe analyses of ore minerals and h o s isotope geochemistry of the yuerya gold deposit eastern hebei china implications for ore genesis and mineralization abstract the yuerya gold deposit in eastern hebei province china is located on the eastern margin of the north china craton and is hosted by mesozoic yanshanian granitoid rocks and adjacent mesoproterozoic gaoyuzhuang formation carbonates the auriferous quartz veins in this deposit are dominated by pyrite with subordinate sphalerite chalcopyrite and galena in a quartz dominated gangue that also contains calcite dolomite barite apatite and fluorite gold is present as native gold and electrum which are generally present as micron size infillings in microfissures within pyrite and less commonly as tiny inclusions within pyrite quartz and tellurobismuthite the pyrite in this deposit has high co ni ratios and contains elevated concentrations of both of these elements suggesting that the yuerya gold deposit has a magmato hydrothermal origin and that the ore forming fluids that formed the deposit leached trace elements such as co ni as and au during passage through archean metamorphic rocks mesoproterozoic carbonates and the yanshanian yuerya granitoid pyrite in the study area has s se ratios and s isotopic compositions that suggest that the sulfur and by inference the gold within the deposit was sourced from magmato hydrothermal fluids that were probably originally derived from archean metamorphic rocks and yanshanian granitoids tellurobismuthite in the study area is closely intergrown with gold and was the single telluride phase identified during this study the fineness of gold associated with tellurobismuthite is greater than the fineness of gold associated with pyrite although the fine particle size of the gold surrounded by tellurobismuthite means that the recovery of this gold is difficult in turn meaning that the tellurobismuthite has little significance to the economics of the yuerya gold deposit only trace amounts of sulfides are associated with the tellurobismuthite within the yuerya gold deposit suggesting that this mineral was deposited under conditions of low fs2 and or high fte2 in addition the presence of tellurides within the yuerya gold deposit reflects a genetic relationship between the deposit and magmatism quartz from mineralized veins in the study area has 18o values of 11 2 12 9 and the fluids that formed these veins have d values of 78 3 to 72 1 the 34s values of pyrite within the deposit are rather restricted 2 3 3 5 these data combined with the trace element geochemistry of sulfides within the deposit suggest that the formation of the yuerya gold deposit was closely related to both archean metamorphic rocks and the yanshanian yuerya granitoid

molybdenite re os and albite 40ar 39ar dating of cu au mo and magnetite porphyry systems in the yangtze river valley and metallogenic implications abstract the area of the middle lower yangtze river valley eastern china extending from wuhan hubei province to western zhenjiang jiangsu province hosts an important belt of cu au mo and fe deposits there are two styles of mineralization i e skarn porphyry stratabound cu au mo fe deposits and magnetite porphyry deposits in several nne trending cretaceous fault bound volcanic basins the origin of both deposit systems is much debated we dated 11 molybdenite samples from five skarn porphyry cu au mo deposits and 5 molybdenite samples from the datuanshan stratabound cu au mo deposit by icp ms re os isotope analysis nine samples from the same set were additionally analyzed by ntims on re os results from the two methods are almost identical the re os model ages of 16 molybdenite samples range from 134 7 2 3 to 143 7 1 6 ma 2 the model ages of the five samples from the datuanshan stratabound deposit vary from 138 0 3 2 to 140 8 2 0 ma with a mean of 139 3 2 6 ma their isochron age is 139 1 2 7 ma with an initial os ratio of 0 7 8 1 mswd 0 29 these data indicate that the porphyry skarn systems and the stratabound deposits have the same age and suggest an origin within the same metallogenic system albite 40 ar 39 ar dating of the magnetite porphyry deposits indicates that they formed at 123 to 125 ma i e 10 20 ma later both mineralization styles characterize transitional geodynamic regimes i e the period around 140 ma when the main ns trending compressional regime changed to an ew trending lithospheric extensional regime and the period of 125 115 ma of dramatic ew trending lithospheric extension

gold deposit continuum a genetic model for lode au mineralization in the continental crust a model is presented dealing with the relations between convection in the continental crust and the formation of lode au deposits sufficient permeability exists in the brittle rheologic regime in large sections of the continental crust to permit convection of meteoric water on both local and regional scales the solubility of au in this fluid is high enough to permit the mobilization of quantities of au which are sufficient to form ore grade deposits this general process is shown to be responsible for a continuous series of deposit types ranging rom 1 2 km deep epithermal deposits to intermediate depth carlin type deposits to 10 12 km deep mesothermal deposits major geologic and geochemical differences among the deposit types are products of fluid convection at variable depths and the resulting effects on water rock ratios and gas solubilities

petrochemical evidence on the probable origin of ferriferous metasediments in western bushmanland the mineralized proterozoic metasediments of bushmanland are characterized by the presence of ferriferous rocks this includes banded and unbanded iron formations and various types of gossans these units are not laterally extensive and occur in different stratigraphic levels the prevalent minerals in the ferriferous rocks are hematite magnetite quartz garnet muscovite biotite and sillimanite but less common occurrences of graphite alunite plumbojarosite gahnite and dufrenite have been noted the chemical variation wt is extensive total fe2o3 1 3 93 5 sio2 4 93 al2o3 0 2 14 0 cao 0 02 20 7 mno 0 0 14 3 mgo 0 0 5 7 tio2 0 0 4 4 na2o 0 0 2 0 k2o 0 0 1 5 and p2o5 0 1 7 0 the preliminary nature of the data set precludes however firm conclusions regarding stratigraphic control of the chemical composition the trace element contents ppm extend over several orders of magnitude zn 0 7 000 ba 0 5 200 cu 0 1 400 pb 0 1 070 and ni 6 540 collectively the data indicate that most of the ferriferous rocks represent highly metamorphosed sediments

kinematics of exhumation of high and ultrahigh pressure rocks in the hong an and tongbai shan of the qinling dabie collisional orogen eastern china

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

processes of ore genesis at the world class yuchiling molybdenum deposit henan province china abstract the yuchiling molybdenum deposit is one of the most significant porphyry molybdenum systems in the eastern qinling of central china the mineralization is mainly hosted by a porphyritic granite and associated cryptoexplosive breccia hydrothermal alteration minerals include k feldspar sericite pyrite chlorite epidote carbonate kaolinite fluorite and gypsum ore minerals are dominated by molybdenite and pyrite with lesser amounts of chalcopyrite galena scheelite wolframite ilmenite leucoxene native gold sphalerite and hematite the 34 s compositions of sulfide minerals range from 6 0 to 4 0 the deposit is characterized by four hydrothermal stages quartz k feldspar stage i molybdenite quartz stage ii pyrite sericite quartz stage iii and quartz carbonate stage iv microthermometric studies of fluid inclusions show that the fluids evolved gradually during the ore forming process homogenization temperatures salinities and minimum pressure estimates for the inclusions from each mineralization stage evolved as follows 1 stage i homogenization temperatures 203 7 525 8 c salinities 2 96 10 49 and 29 66 wt nacl equiv and minimum pressures 101 9 196 2 mpa 2 stage ii homogenization temperatures 173 6 448 6 c salinities 1 81 9 74 wt nacl equiv and minimum pressures 93 1 172 0 mpa 3 stage iii homogenization temperatures 130 1 386 0 c salinities 1 40 9 73 and 34 07 wt nacl equiv and minimum pressures 95 5 142 5 mpa 4 stage iv homogenization temperatures 170 230 c and salinities 0 18 5 71 wt nacl equiv various fluid inclusions were observed to contain h 2 o co 2 ch 4 so 2 c 2 h 2 c 2 h 4 c 2 h 6 and or h 2 s as well as solids that include halite sylvite anhydrite chalcopyrite hematite molybdenite and jamesonite the 18 o and d of the hydrothermal fluids vary from 4 4 to 8 5 and 81 to 61 respectively microthermometric and stable isotope data indicate that the ore forming fluids for the yuchiling molybdenum deposit evolved from early magmatic to a mixture of meteoric and magmatic water and finally to a principally late stage meteoric water a molybdenite re os age of 131 2 1 4 ma coincides with the early part of the 131 112 ma period of magmatic and related ore forming events that are widely recognized in eastern qinling

correlation of rock mass classification parameters obtained from borecore and in situ observations abstract the paper describes an investigation carried out to establish correlation trends between rock mass classification parameters derived from borecore and in situ observations the purpose of this study was to determine the reliability of classifying rock masses for engineering purposes from borecore data alone rock mass classification parameters were obtained from three tunnels excavated in widely differing geological environments two in johannesburg and one in the cape province of south africa these parameters from the borecore and in situ measurements were used separately to classify the rock masses encountered both the geomechanics and q classification systems were employed in determining the quality of rock masses the paper describes the geological environments encountered the methods of observation used and the results obtained from the comparison of the in situ and borecore classification results conclusions are reached and discussed some comments are also offered regarding the applicability of the two classification systems under the conditions specified

zircon indicators of fluid sources and ore genesis in a multi stage hydrothermal system the dongping au deposit in north china abstract the syenite hosted dongping gold deposit represents the largest gold deposit on the northern margin of the north china craton here we present new u pb age trace element concentration and hf isotope data from magmatic and hydrothermal zircons to better constrain the timing and genesis of gold mineralization geochronological data combined with field and petrologic results document two mineralization events the earlier event in the mid devonian 380 ma was associated with the intrusion of the shuiquangou syenite whereas the later event in the early cretaceous 140 ma was related to the emplacement of the shangshuiquan granite devonian hydrothermal zircons extracted from gray auriferous quartz veins were formed via metasomatic alteration of magmatic zircons derived from the syenite by an oxidizing f rich fluid in contrast cretaceous hydrothermal zircons hosted in the altered shangshuiquan granite and milky gold rich quartz ores were precipitated directly from a high temperature zr saturated aqueous fluid that was contaminated by basement materials possessing a substantially different hf isotopic composition from the contemporaneous magmatic zircons we propose that the devonian au mineralization event at dongping involved a magmatic fluid and auto metasomatism during crystallization of the shuiquangou syenite complex whereas the cretaceous au mineralization event involved a fluid exsolved from the shangshuiquan alkaline pluton results from this study highlight the potential utility of zircons as indicators of fluid sources and ore genesis in a multi stage hydrothermal system

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

synmetamorphic lode gold deposits in high grade archean settings lode gold deposits that formed under conditions of the middle to upper amphibolite and granulite facies have been identified in the yilgarn block of western australia these deposits which form a continuum with lower metamorphic grade mesothermal gold depos its show that at least some of the fluids responsible for mesothermal gold deposits originated in or below the middle crust studies of 18 o suggest that fluid compositions were controlled by the wall rocks at least for some elements these more proximal gold deposits provide more information about deep fluid sources than do investigations of higher level mineralization deposited from fluids strongly modified by wall rock interaction during the early part of their ascent

archaean carbon reservoirs and their relevance to the fluid source for gold deposits it is commonly assumed1 2 that seawater derived carbon in altered volcanic rocks is the only major pre metamorphic carbon in carbonate reservoir in archaean greenstone belts thus carbonates from archaean gold deposits with stable isotope ratios too negative median 13c 3 to have been derived from such carbon 13c usually assumed to be near 0 have been interpreted as being derived from a local felsic magmatic source1 barley and groves3 however recognize two carbonate alteration styles that predate regional metamorphism and gold mineralization in the norseman wiluna greenstone belt of western australia evidence is summarized below these are seafloor alteration and fault controlled regional alteration which as shown below have completely different carbon isotope compositions the latter median 13c 4 8 implies a major juvenile carbon co2 flux from the mantle during greenstone belt evolution and is thus of fundamental importance in itself however here we show why the mere existence of two carbon in carbonate reservoirs and variation in carbon isotope ratios of carbonates between individual gold deposits in one area negate some of the fundamental assumptions used to support magmatic fluid models1

types characteristics and metallogenesis of gold deposits in the jiaodong peninsula eastern north china craton abstract the jiaojia type gold deposits in the jiaodong peninsula of the north china craton represent an emerging major gold reserve and constitute one of the two important types of gold deposits in china the other being the linglong type the gold mineralization in these deposits can be subdivided into seven categories namely altered rock type in the fracture zone gold bearing quartz vein type braided quartz vein type along fracture zones quartz sulfide vein type interlayer type along the detachment belt altered conglomerate type and breccia type along the basin margin faults the peak gold mineralization occurred during early cretaceous with the metallogeny controlled by extensive crust mantle interaction the deposits are hosted in the early precambrian basement and mesozoic intrusions which experienced phyllic sulfidic silicic and potassic alterations the structures of the ore bodies include pinchout repetition splay branches composite lateral tilting echelon and imbrications the upwelling of hot magma fluid activity and extensional detachment resulted in the formation of extensive gold deposits in the jiaodong peninsula the extensional detachment derived from magma upwelling provided favorable ore hosting structure for the gold deposition the ladder type ore hosting structures show variation from sharp to gentle dips with marked enrichment of the gold ores at the gentle angle of the fault segments and at the transition from steep to gentle dip angles displaying a step fault controlled ore deposition the formation of the gold deposits in the jiaodong peninsula coincided with the large scale early cretaceous thinning of the lithosphere in the north china craton mainly controlled by extensional tectonics

some trace element analyses of pliocene molasse and recent euphrates and tigris fluvial sediments abstract forty two samples of recent sediments were collected from the euphrates and tigris rivers and 92 samples from pliocene molasse sediments bakhtiari formation the claysize fraction was separated from the collected samples both the bulk and the clay size fraction were analysed for rb sr b ga cr ni v cu zr si al ti k and fe the data show that euphrates and tigris sediments originated from more basic igneous rocks than those of the pliocene molasse sediments as indicated by their enrichment in cr ni v and fe this may be partly due to weathering resistance of the rocks and of their constituent minerals which varies considerably or it may be due to differences in stability of the minerals subjected to weathering hence to differences in mobility of the chemical elements during the weathering processes

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

the jurassic danba hypozonal orogenic gold deposit western china indirect derivation from fertile mantle lithosphere metasomatized during neoproterozoic subduction the genesis of hypozonal orogenic gold deposits is highly controversial with both crustal metamorphic fluids and variously derived sub crustal fluids suggested as fluid and metal sources the lower jurassic danba gold deposit a rare phanerozoic hypozonal orogenic gold deposit on the western margin of the yangtze craton china provides an opportunity to resolve these controversies danba is characterized by biotite amphibole alteration and pyrrhotite dominant ore assemblages formed at 500 600 c the 34s values of ore related pyrrhotite range from 3 1 to 9 9 in sharp contrast to those of syn sedimentary pyrrhotite from devonian host rocks which are between 6 8 and 9 5 the pb isotope compositions of ore related pyrrhotite with 206pb 204pb 17 85 18 25 and 207pb 204pb 15 48 15 67 are less radiogenic and more variable than those of unaltered host rocks these differences combined with the hypozonal feature of the deposit indicate that ore metals and sulfur were derived from a sub crustal rather than a local crustal source the pge patterns of ore related pyrrhotites are similar to those of sulfides in baltic mantle lithosphere that was metasomatized by aqueous fluids in terms of marked enrichment of pd and ru but significantly differ from those of magmatic intrusions and related magmatic hydrothermal deposits this suggests that the metals that formed the danba deposit were transported via aqueous fluid from metasomatized mantle lithosphere rather than from a magmatic source the 18o of mantle fluid calculated from hydrothermal quartz and biotite ranges from 10 to 12 the anomalously high s and o isotope ratios and variable pb isotope ratios together with pge data support a model in which the inferred mantle lithosphere source was significantly hydrated metasomatized and fertilized by fluid derived from subducted oceanic sediments with elevated 34s and 18o values geological evidence suggests that this subduction event was neoproterozoic in age this study defines a model in which hydrated and metasomatized mantle lithosphere was formed during early subduction but it was over 500 million years later during later lower jurassic asthenosphere upwelling that metal and sulfur rich fluid was released into the crust to form the danba gold deposit

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

decratonic gold mineralization evidence from the shangzhuang gold deposit eastern north china craton abstract the jiaodong peninsula in the eastern north china craton ncc hosts some of the world class gold deposits among these the shangzhuang gold deposit represents a typical fault zone hosted disseminated and stockwork style gold mineralization the mineralization is characterized by intense hydrothermal alteration halos in the wallrocks with the mineralized veins intruding into altered wallrocks zircon u pb isotope dating constrains the timing of emplacement of the guojialing granodiorite as 130 1 ma five molybdenite samples from the main mineralization stage veins yielded a well fitted isochron age of 126 2 ma mswd 1 3 marking the timing of gold mineralization four types of fluid inclusions are identified at shangzhuang and their petrographic and microthermometric features suggest fluid immiscibility followed by fluid mixing this inference is also supported by oxygen and hydrogen isotopic data of quartz veins from stage iii the measured 18 o values of quartz are 12 3 to 13 7 for stage ii and 11 7 to 12 0 for stage iii with calculated 18 o fluid values for stage ii ranging from 5 9 to 7 3 and for stage iii from 3 4 to 3 7 d values for stage ii and iii quartz range from 65 3 to 75 2 and 70 6 to 74 7 respectively the data suggest that the ore forming fluids were initially derived from magmatic sources followed by mixing with meteoric water sims in situ sulfur isotope analyses of two types of pyrite py i and py ii from different mineralization stages show different sulfur isotope features the 34 s values for py i 10 2 to 11 3 mean 10 8 n 25 are higher than those of the later mostly gold related py ii 4 1 to 6 8 mean 5 4 n 27 the higher 34 s values of py i are correlated to degassing of mantle wedge metasomatized by the slab fluids the relatively lower 34 s values of py ii might suggest increasing of f o2 through fluid mixing between ore forming fluids and meteoric water the temporal spatial and tectonic relations between the giant gold mineralization and destruction of the ncc suggest a genetic linkage the gold mineralization between 126 and 117 ma at jiaodong was probably initiated at the peak of decratonization ca 125 ma of the eastern ncc phanerozoic craton margin orogeny also played a critical role in the generation of the early cretaceous giant gold deposits in the eastern ncc integrated geological characteristics mineralization features metallogenic age sources of ore forming fluids and sulfur and tectonic settings favor a decratonic gold mineralization model for the shangzhuang gold deposit the geodynamic scenario proposed for the early cretaceous giant gold mineralization event in the eastern ncc includes the paleo west pacific plate subduction asthenospheric upwelling multiple subduction collision processes along the margins

the geology and geochemistry of jinchangyu gold deposit north china craton implications for metallogenesis and geodynamic setting abstract the jinchangyu au deposits contained an original resource of 50 t of gold and is located close to the northeastern margin of the north china craton ncc the orebodies are controlled by structures in the amphibolite units of the archaean zunhua group mineralization is generally associated with albite and hematite which is indicative of na al si fe alteration the most common styles of mineralization are subdivided based on the cross cutting relationships of mineral assemblages as follows i quartz albite hematite ii quartz albite polymetallic sulfides with gold and molybdenite iii quartz pyrite and iv quartz carbonate quartz samples from the second stage ii and third stage iii assemblages contain two phase fluid inclusion types these are i co2 h2o fluid inclusions and ii daughter mineral bearing inclusions which have homogenization temperatures of 270 350 c for assemblage stage ii and 180 240 c for stage iii and salinities of 13 wt nacl equiv a few s type fluid inclusions suggesting salinities of 27 6 28 3 wt nacl equiv the s isotope composition of pyrite and molybdenite from stage ii 34s 4 4 to 1 9 indicates that the mineralizing fluid originated predominantly from a magmatic source the h o isotope signatures from stage ii indicate a magmatic dominated source for the mineralizing fluid with some addition of meteoric fluids previously published pb and c isotope data indicate that ore and magma in the eastern part of the hebei province of china interacted with precambrian country rocks and so the fluids moved from the lower crust to shallower level during mineralization the red quartz albite hematite veins from jinchangyu were generated under strongly oxidizing alkaline conditions that were favorable for the incorporation of gold into the fluid and the crystallization of albite during the early stage of gold deposition seven molybdenite samples from jinchangyu yield re os model ages of ca 233 to 219 ma with a weighted mean age of 225 4 ma and an isochron age of 223 5 ma this indicates that at least some of the gold associated with molybdenite is late triassic in age and could be associated with buried intrusions that are part of the late triassic dushan granites in the eastern portion of the ncc this mineralization was formed after the closure of the paleo asian ocean these results indicate that the intrusion related jinchangyu deposit is the far field structural product of the collision of the ncc with the siberian craton to the north along the northern margin of the ncc

the relationship between gold mineralization exhumation of metamorphic core complex and magma cooling formation of the anjiayingzi au deposit northern north china craton abstract the anjiayingzi gold deposit is hosted by the jiguanzi quartz monzonite in the footwall of the kalaqin metamorphic core complex mcc at chifeng in the northern part of the north china craton ncc an earlier ca 135 125 ma top to the ne ductile brittle shear and a later ca 121 ma top to the nw and se brittle detachment normal faulting are recognized around the kalaqin mcc the jiguanzi quartz monzonite intruded the footwall of the kalaqin mcc at ca 133 1 ma with crystallization temperatures of 640 691 c pressures of 167 271 mpa and an average depth of 8 6 km gold veins in the anjiayingzi gold deposit are hosted by the monzonite and controlled by the ne trending brittle ductile and brittle fault zones these ore bearing faults are products of a regional sinistral shearing event coinciding with the earlier top to the ne ductile brittle shear at the kalaqin mcc the ore of the anjiayingzi deposit is characterised by its low au ag ratio 2 o co 2 nacl fluid system with salinities of 1 3 15 6 wt nacl equiv trapping pressures of ore fluids were 50 110 mpa corresponding to an average depth of 2 5 km under a lithostatic load and 7 5 km under a hydrostatic load fluid mixing and immiscibility are potential causes for the rapid precipitation of sulphides carrying au the stable isotope d 80 3 to 96 5 and 18 o h 2 o 3 7 to 5 5 of the ore fluids the consistent pb isotope compositions between the ore bearing sulphides and k feldspar from the jiguanzi quartz monzonite and a 2 billion year time gap between the gold mineralization and metamorphism of the basement all indicate that the mineralizing fluids and metals are derived from a concealed intrusion near the major eastern louzidian fault in the kalaqin mcc this proposal is supported by the presence of mafic magmatic enclaves and rhyolite dykes in the jiguanzi quartz monzonite and higher average th total 322 c and 34 s 2 4 of eastern veins than those of western veins with a th total of 287 c and 34 s value of 0 3 the ca 133 126 ma gold mineralization at anjiayingzi was formed during rapid cooling of ca 133 126 ma jiguanzi quartz monzonite at a cooling rate of 42 71 c ma and fast exhumation and cooling of the kalaqin mcc between ca 135 and 121 ma at a cooling rate of 30 c ma this process was accompanied by fluid immiscibility and mixing within the structural transition from ductile brittle to brittle deformation with resultant fluid pressure fluctuations between the supra hydrostatic and hydrostatic regimes

shallow remineralization in the weddell gyre 1 the region influenced by the polar front in the southern ocean is characterized by relatively high productivity which is mirrored in strong depletions of 234th in the surface water a good tracer of export production and by high accumulation rates on the underlying seabed farther south the weddell sea is generally considered a low productivity region with very low export fluxes this finding is based on satellite observations sediment accumulation rates trap deployments and phytoplankton distribution if this would be true 234th should be close to equilibrium with its parent however in a series of high resolution transects of 234th 238u across the antarctic circumpolar current acc 234th was found to be depleted by 10 15 throughout the clear weddell gyre only to reach equilibrium in sea ice covered regions of the coastal zone vertical profiles showed that the depletion was limited to the upper mixed layer and was balanced by an enrichment of similar magnitude at 100 250m depth this implies that the export of particles below 250 m is negligible such shallow remineralization is in line with the discrepancies between biogenic silica production rates and sediment trap data observed in the weddell and ross seas these observations in the weddell sea are fully consistent with our inverse modeling results for both organic carbon and opal and they are not inconsistent with tco2 and oxygen sections that show a tco2 enriched oxygen reduced shallow subsurface layer this blue ocean characterized by upwelling of co2 enriched deep waters supports sufficient productivity to be a net sink for co2 to abyssal depths hoppema et al 1999 no record of this productivity and export is stored in the underlying sediment which has important palaeoceanographic consequences

a tectono genetic model for porphyry skarn stratabound cu au mo fe and magnetite apatite deposits along the middle lower yangtze river valley eastern china abstract the middle lower yangtze river valley metallogenic belt yrb situated along the northern margin of the yangtze craton is characterized by porphyry skarn stratabound cu au mo fe deposits in the areas of uplift and magnetite apatite deposits in cretaceous fault basins following detailed field investigations and a review of published data we recognize two episodes of magmatism and mineralization in the yrb 1 156 137 ma high k calc alkaline granitoids associated with 148 135 ma porphyry skarn stratabound cu au mo fe deposits and 2 135 123 ma shoshonitic series associated with 134 9 122 9 ma magnetite apatite deposits a type granitoids and associated alkaline volcanic have a small age range from 126 5 to 124 8 ma and are temporally spatially and genetically associated with the second episode the geodynamic history of the yrb did not experience the paleozoic to mesozoic lithospheric thickening that took place in the north china craton this process is inferred to be linked to partial melting of the delaminated lower crust at high pressures resulting in the development of c type adakitic rocks the petrochemical and sr nd isotopic data show that both the shoshonitic series and a type granitoids are quite different from adakites with only some of the k calc alkaline granitoids having adakitic signatures previous ore genesis models were established based on an assumed relationship with adakites and a continuous tectono thermal evolution from 150 to 100 ma all data obtained for the middle lower yangtze river region consistently show that the tan lu regional strike slip fault zone initiated at 233 6 to 225 6 ma from the collision between the north china and yangtze cratons and was reactivated at ca 160 ma the tan lu fault was caused by the oblique subduction of the izanagi plate which along the yrb the low angle subducted slab and the overlying crust was disrupted or broken due to the disharmonious movement of the two blocks the high k calc alkaline granitoids magmas were derived from melting of the subducted slab with some input of crustal material these magmas were emplaced at the intersections between ne and ew trending faults and formed porphyry skarn stratabound cu au mo fe deposits between 156 and 137 ma after 135 ma the subducted plate changed its direction of motion to northeast now running parallel to the eurasian continental margin and leading to large scale continental extension the shoshonitic series and subsequent a type granitoids magmatism and the development of magnetite apatite ores in the yrb took place in both fault basins and ne trending rifts between 135 and 124 ma

carbon isotope studies of auriferous quartz carbonate veins from two orogenic gold deposits from the neoarchean chitradurga schist belt dharwar craton india evidence for mantle magmatic source of auriferous fluid abstract carbon and oxygen isotopic compositions of carbonates from auriferous quartz carbonate veins qcvs of two orogenic gold deposits ajjanahalli and guddadarangavvana halli g r halli from the neoarchean chitradurga schist belt of the dharwar craton southern india are examined to understand the origin of the mineralizing fluids the average carbonate carbon 13cpdb and oxygen 18osmow isotope compositions of qcvs of ajjanahalli are 5 5 1 3 and 14 1 2 7 respectively the same ratios for the qcvs of g r halli are 6 2 1 9 and 14 1 0 5 the corresponding average fluid 13c and 18o compositions are 5 81 1 14 13 78 5 1 for ajjanahalli and 4 64 0 7 6 50 0 6 for g r halli the 13cpdb of syn sedimentary carbonates of bif of ajjanahalli 1 8 0 1 carbonated metabasalts of ajjanahalli 1 4 and g r halli 1 3 fall in the compositional range of marine carbonates 0 2 as dissolution decarbonation reactions during metamorphism of pre existing carbonate carbonated rocks produce co2 with 13c values similar to or more enriched than parent rock the carbonate or fluid 13c ratios of the qcvs which fall in the compositional range of mantle magmatic derived co2 or carbonates obtained in this work cannot be the result of metamorphism it is proposed that gold mineralizing fluids were derived from juvenile magmatic melts and were channeled through crustal scale shear zones to give rise to the gold deposits

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

zircon geochronology geochemistry and stable isotopes of the wang ershan gold deposit jiaodong peninsula china abstract the early cretaceous gold deposits of the jiaodong peninsula eastern china define china s largest gold province with an overall endowment estimated more than 3000 t au the wang ershan gold deposit at the northern margin of the jiaolai basin in jiaodong peninsula of eastern china is located in the central southern segment of the wang ershan fault zone the major mesozoic intrusions exposed in this region are the linglong granite and the guojialing granodiorite to the northeast of the deposit both these intrusions show high k and alkaline signature the linglong granite displays peraluminous feature whereas the guojialing granodiorite is metaluminous zircon u pb dating of the linglong granite yields 206 pb 238 u weighted mean age of 149 0 1 3 ma the muscovite from the alteration zones associated with mineralization in the linglong granite yields a plateau age of 130 35 0 96 ma representing the initial phase of the hydrothermal activity the 34 s values of pyrite from the gold mineralized veins range from 6 to 8 3 with the mean value of 7 66 the 3 he 4 he ratios of pyrite are in the range 1 58 2 71 ra with a mean value at 2 168 ra the 40 ar 36 ar ratios show variation from 1220 3 to 1625 7 with an average of 1483 8 the 18 o values of the mineralizing fluids show a range of 2 13 to 7 5 with an average of 2 4 the 18 d w values are in the range of 97 5 to 61 4 with a mean at 82 6 detailed elemental and isotopic data suggest that the hydrothermal fluids in early stage were mainly magmatic and derived from the guojialing granodiorite and the ore forming fluids in the main ore forming stages evolved into a mixture of magmatic and meteoric water the ore forming materials were primarily derived from crust with minor input of mantle components the ore forming fluids might be related to the subduction of the paleo pacific slab beneath the north china craton and the associated asthenosphere upwelling and consequent lithospheric thinning

mechanism of a long runout landslide triggered by the august 1998 heavy rainfall in fukushima prefecture japan abstract heavy rainfall from 26 to 31 august 1998 triggered many landslides in nishigo village of southern fukushima prefecture japan the hiegaesi landslide a long runout landslide with travel angle of 11 which occurred in loamy volcanic ash pumice layer and was deposited in a nearby rice paddy was investigated in an observation pit dug in the middle part of the landslide deposit the sliding zone just above the deflected rice plants was observed and it was confirmed that grain crushing occurred in the sliding zone the triggering and sliding mechanisms of this landslide then were investigated by ring shear tests in laboratory for the triggering mechanism one saturated naturally drained test test a torque controlled test and one saturated undrained test test b speed controlled test were conducted on the samples taken from the source area of the landslide even in the naturally drained test opening the upper drain valve of the shear box a temporary liquefaction occurred in the undrained test excess pore pressure was generated along with shearing and sliding surface liquefaction phenomenon was observed the effective stress and shear resistance finally decreased to near zero these results can explain the observed phenomenon of small friction resistance like a flow of liquid when the sliding mass slid out of the source area for the sliding mechanism of the landslide in the rice paddy saturated undrained test test c speed controlled test was performed on soil sample above the deflected rice plants the apparent friction angle obtained in this test was 8 in addition the residual friction angle measured after test b and test c was the same value of 41 combining with the observation on the shear zone in the ring shear box after test c it is concluded that during the sliding in rice paddy the undrained shear strength of the soil layer itself mainly influenced the high mobility of the landslide probably because the friction between rice plants and soils is greater than the undrained shear strength inside the soil mass

an integrated mineral system model for the gold deposits of the giant jiaodong province eastern china abstract the giant jiaodong gold province with more than 5000 t of proven gold resources is unique in that its mesozoic gold deposits are hosted in a precambrian basement block there has long been debate on the source of gold the mechanism for its extreme enrichment and a holistic genetic model for these spectacular deposits in order to improve understanding of these factors a mineral system model is proposed for the jiaodong gold deposits for the first time it is based on a detailed review of the architecture and composition of the underlying mantle lithosphere the geodynamic setting at the time of gold mineralization the geological and geochemical features of the deposits themselves and mechanisms of their preservation regional geodynamic reconstructions combined with the nature of mesozoic magmatic systems show that late mesozoic breakoff of the subduction slab and rollback of the paleo pacific plate caused asthenosphere upwelling and lithosphere extension and thinning robust geochronological studies demonstrate that the jiaodong gold deposits formed at ca 120 ma during a change of subduction direction of the paleo pacific plate and the synchronous transition of tectonic regime from regional compression to transpression or transtension prior to peak extension caused by thinning of the lithosphere geophysical exploration data and hf nd isotope mapping of the jiaodong peninsula reveal a relatively simple ancient crustal structure cut by near vertical shear or fault zones including the lithosphere scale tan lu and wulian yantai faults that provided the first order architecture for emplacement of mantle magmas and sub crustal fluids in terms of fertility the significant older pre mineralization crustal metamorphism combined with sulfur lead and strontium isotope ratios indicate a dominant sub crustal source for the ore components for the jiaodong gold deposits consistent with evidence for volatile and gold fertilized metasomatized mantle lithosphere beneath the north china block helium ar and c o isotope ratios implicate mantle sources of ore fluids with contamination by crustal components en route to crustal depositional sites in terms of crustal architecture combined geophysical structural mineralogical fluid inclusion and geochemical studies show that the deeply sourced ore fluids and metals advected upwards through lithosphere scale faults to deposit gold via sulfidation and phase separation in crustal scale nne ne trending fault systems at mid to upper crustal levels preservation of disseminated to stockwork style deposits and auriferous quartz pyrite vein deposits was enhanced by deep crustal formation combined with limited uplift and exhumation of the province the jiaodong gold deposits although commonly hosted in granite intrusions clearly post date them on the basis of robust and reliable geochronology the spatial but non temporal relationships of gold deposits with granites their strong structural control and their other characteristics clearly place them in the orogenic gold group it is suggested because of their uniqueness that they be termed jiaodong type orogenic gold deposits

geochronology fluid inclusions and isotopic characteristics of the chaganbulagen pb zn ag deposit inner mongolia china abstract the large chaganbulagen pb zn ag deposit is located in the derbugan metallogenic belt of the northern great xing an range the vein style orebodies of the deposit occur in the nww trending fault zones the ore forming process at the deposit can be divided into three stages an early quartz pyrite arsenopyrite pyrrhotite sphalerite galena chalcopyrite stage a middle quartz carbonate pyrite sphalerite galena silver bearing minerals stage and a late quartz carbonate pyrite stage the sericite sample yielded a 40 ar 39 ar plateau age of 138 1 ma and an isochron age of 137 3 ma and the zircon la icp ms u pb age of monzogranite porphyry was 143 2 ma indicating that the ages of mineralization and monzogranite porphyry in the chaganbulagen deposit should be the early cretaceous and that the mineralization should be slightly later than the intrusion of monzogranite porphyry there are only liquid inclusions in quartz veins of the chaganbulagen deposit homogenization temperatures densities and salinities of the fluid inclusions from the early stage are 261 340 c 0 65 0 81 g cm 3 and 0 7 6 3 wt nacl eqv respectively fluid inclusions of the middle stage have homogenization temperatures densities and salinities of 209 265 c 0 75 0 86 g cm 3 and 0 5 5 7 wt nacl eqv respectively for fluid inclusions of the late stage their homogenization temperatures densities and salinities are 173 219 c 0 85 0 91 g cm 3 and 0 4 2 7 wt nacl eqv respectively the ore forming fluids of the deposit are generally characterized by moderate temperature and low salinity and density and belong to an h 2 o nacl co 2 ch 4 system the 18 o water values calculated for ore bearing quartz vary from 17 9 to 10 8 and the d v smow values from bulk extraction of fluid inclusion waters vary from 166 to 127 suggesting that the ore forming fluids consist dominantly of meteoric water the 34 s v cdt values range from 1 4 to 4 1 the 206 pb 204 pb 207 pb 204 pb and 208 pb 204 pb values of the ore minerals are in the ranges of 18 302 19 037 15 473 15 593 and 38 110 38 945 respectively the data for the s and pb isotopic systems indicate that the ore forming metals and sulfur came from mesozoic magma the chaganbulagen deposit is a low sulfidation epithermal pb zn ag deposit and the temperature decrease is the dominant mechanism for the deposition of ore forming materials

a comparison of jiaojia and linglong type gold deposit ore forming fluids do they differ abstract the jiaodong peninsula contains the most important concentration of gold deposits in china which can be divided into jiaojia type and linglong type deposits based on mineralization style the former is characterized by disseminated and stockwork style mineralization hosted in first order regional faults with relatively larger tonnages and lower gold grades the latter is characterized by massive auriferous quartz veins commonly hosted in subsidiary second or third order faults with smaller tonnage but higher grade orebodies despite these differences both groups of deposits have the same alteration assemblages mineral paragenesis element concentrations and ore forming ages the mainly jiaojia type luoshan gold deposit and the mainly linglong type fushan gold deposit are characterized by h o s pb isotope data that indicate the ore forming fluids have a dominantly metamorphic source the fluids were derived during the yanshanian orogenic event and were most likely associated with dehydration and decarbonization processes near the top of the subducting paleo pacific plate the linglong type ores have relatively lighter calculated 18 o compositions 3 9 to 2 3 than the jiaojia type ores 0 3 8 0 possibly because of a greater degree of mixing with meteoric water petrographic cathodoluminescence microthermometric and laser raman spectroscopic analyses of fluid inclusion assemblages in quartz from the two types of ores indicate fluids were similar in both cases characterized by medium high homogenization temperatures 211 393 c significant co 2 15 mol minor ch 4 18 in the carbonic phase and low salinity 11 2 wt nacl eq the linglong type ores however have a wider range of co 2 and ch 4 concentration and salinity than the jiaojia type ores fluid immiscibility occurred in main ore stage of both ore types with the trapping conditions of 77 185 mpa and 284 328 c although the unmixing is more intense and widespread in the linglong type ores both fluid wallrock interaction and fluid immiscibility are important gold deposition processes in the two types but immiscibility is more important in the linglong type ores and that has led to the typical higher gold grade in general there is little geochemical differences between the ore forming fluids for jiaojia and linglong type gold deposits both jiaojia and linglong type ores can exist in a single deposit and form in the same metallogenic event the linglong type ores developed as more massive veins because of their location in zones of more extensive extension and they lack significant post ore cataclastic deformation

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

significance of crustal extension and magmatism to gold deposits beneath jiaodong peninsula eastern north china craton seismic evidence from receiver function imaging with a dense array abstract the jiaodong peninsula located in the eastern north china craton ncc is a key region to study the genetic linkage between large scale gold mineralization and craton destruction we construct a fine crustal structural image across the jiaodong peninsula using teleseismic p wave receiver function data recorded by a dense linear array of 340 short period seismic stations the results reveal significant similarities and differences between the eastern and the western jiaodong peninsula the presence of an intracrustal low velocity zone and the north dipping interfaces beneath the jiaolai basin imply widespread crustal extension in the whole region in the northwest jiaodong metallogenic belt the identified detachment faults small vertical velocity gradients in the upper part of the lower crust and the thick crust mantle transition zone provide evidences for intense crustal extension in this area probably coeval with the peak of lithospheric thinning and destruction of the eastern ncc in the late mesozoic in the muru metallogenic belt distinct differences are found on the opposite sides of the wulian yantai fault zone wyfz in the depth and structure of the moho intracrustal low velocity zone upper crustal vp vs ratios and bouguer gravity anomalies indicating that the wyfz may be a steep transcrustal fault we propose that the coupled effects of intense crustal extension voluminous magmatism and water released from the subducting paleo pacific slab may have been responsible for the concentrated gold deposits in the northwest jiaodong during the peak of the ncc destruction while limited gold deposits in the muru metallogenic belt may have been attributed to relatively weak crustal extension and steep faults

carbon dioxide as a proxy for orogenic gold source abstract despite many decades of study the genesis of orogenic gold deposits remains in debate one aspect of this debate concerns the origin of the mineralising fluids two important constraints are that the fluids are sulphur and co2 bearing and that high fluid fluxes are maintained in a spatially localised environment for a relatively short period of time whereas crustal metamorphism decarbonation operates over many millions of years the source is not localised and is of regional extent in this paper we explore the devolatilization of a subducting slab material using coupled petrological thermo mechanical numerical approach that takes into account dehydration and decarbonation processes recent phase equilibria calculations show that decarbonisation of the slab requires much higher temperatures that normally occurs within subduction zones and the devolatilization site in the slab is spatially and temporally localised during slab roll back or within a hot orogen when the slab material is incorporated into the overriding plate we also investigate the plausibility of large gold sources in the collisional and back arc environments

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

nanoparticles in groundwater of the qujia deposit eastern china prospecting significance for deep seated ore resources abstract the characterization of nanoparticles in groundwater is recognized as an important tool that can be applied to mineral exploration in this paper we investigate the concealed orebodies of the qujia gold deposit in the jiaojia orefield of eastern china by analyzing ore related nanoparticles in groundwater using transmission electron microscopy the nanoparticles contain variable amounts of ore related elements e g ag cu zn la ce pb pt and s some of these elements are rarely found in natural settings unrelated to orebodies or mineral extraction but are strongly linked to concealed orebodies in the study area these nanoparticles which are diverse in their shapes aggregated features and degrees of crystallinity can be grouped in terms of composition as i native metal nanoparticles ii metal based nanoparticles and iii carrier nanoparticles associated with trace elements we propose that these three main types of nanoparticles enable the efficient transport of ore forming elements in groundwater the results of this study provide insights into the migratory behaviour of ore related nanoparticles in groundwater and our methods could be applied for detecting deep seated mineral deposits

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

the crustal continuum model for late archaean lode gold deposits of the yilgarn block western australia most archaean gold ores belong to a coherent genetic group of structurally controlled lode deposits that are characteristically enriched in au with variable enrichments in ag as w sb bi te b and pb but rarely cu or zn and are surrounded by wallrock alteration haloes enriched in k lile and co2 with variable na and or ca addition evidence from the yilgarn block of western australia combined with similar evidence from canada and elsewhere indicates that such deposits represent a crustal continuum that formed under a variety of crustal regimes over at least a 15 km crustal profile at pt conditions ranging from 180 c at 1 kb to 700 c at 5 kb individual deposits separated by tens to hundreds of kilometres collectively show transitional variations in structural style of mineralisation vein textures and mineralogy of wallrock alteration that relate to the pt conditions of their formation at varying crustal depths specific transitions within the total spectrum may be shown also by deposits within gold camps although nowhere is the entire continuum of deposits recorded from a single gold camp or even greenstone belt

genesis of two different types of gold mineralization in the linglong gold field china constrains from geology fluid inclusions and stable isotope abstract the dongfeng and linglong gold deposits are located in the northwest jiaodong peninsula north china craton the deposits are mainly hosted in the mesozoic granitoids and structurally controlled by the zhaoyuan pingdu fault zone gold mineralization at dongfeng occurs as disseminated ores and sulfide stockworks typically enveloped by broad alteration selvages in contrast mineralization at linglong is characterized by massive auriferous quartz veins with narrow alteration halos three stages of mineralization were identified in both deposits with the early stage represented by quartz pyrite the middle stage by gold quartz pyrite or gold quartz base metal sulfides and the late stage by quartz carbonate pyrite respectively four types of fluid inclusions were distinguished based on petrography microthermometry and laser raman spectroscopy including 1 pure co2 fluid inclusions type i 2 h2o co2 nacl fluid inclusions type ii 3 h2o nacl fluid inclusions type iii and 4 daughter mineral bearing or multiphase fluid inclusions type iv in the dongfeng gold deposit the early and middle stage quartz mainly contains primary type ii fluid inclusions that completely homogenized at temperatures of 276 341 c with salinities of 2 8 11 7 wt nacl equivalent and temperatures of 248 310 c with salinities of 3 3 10 8 wt nacl equivalent respectively a few primary type i fluid inclusions could be observed in the early stage quartz in contrast the late stage quartz contains only the type iii fluid inclusions with homogenization temperatures of 117 219 c and salinities of 0 5 8 5 wt nacl equivalent the estimated pressures for the middle stage fluids are 226 338 mpa suggesting that gold mineralization mainly occurred at paleodepths of deeper than 8 4 12 5 km the mineralization resulted from extensive water rock interaction between the h2o co2 nacl fluids and wallrocks in the first order fault in the linglong gold deposit the early stage quartz mainly contains primary type ii fluid inclusions and a few type i fluid inclusions of which type ii fluid inclusions have salinities of 3 3 7 5 wt nacl equivalent and homogenization temperatures of 271 374 c the middle stage quartz mainly contains all four types of fluid inclusions among which the type ii fluid inclusions yield homogenization temperatures of 251 287 c and salinities of 5 5 10 3 wt nacl equivalent while the type iii fluid inclusions have homogenization temperatures of 244 291 c and salinities of 4 1 13 3 wt nacl equivalent fluid inclusions in the late stage quartz are type iii fluid inclusions with low salinities of 0 3 8 2 wt nacl equivalent and low homogenization temperatures of 103 215 c the trapping pressure estimated for the middle stage fluids is 228 326 mpa suggesting that the gold mineralization mainly occurred at paleodepths of about 8 4 12 1 km precipitation of gold is possibly a consequence of phase separation or boiling of the h2o co2 nacl fluids in response to pressure and temperature fluctuations in the open space of the secondary faults the 34s values of pyrite are similar for the dongfeng and linglong deposits and show a range of 5 8 to 7 0 and 5 9 to 7 4 respectively oxygen and hydrogen stable isotopic analyses for quartz yielded the following results 18o 3 8 to 6 4 and d 90 5 to 82 7 for the dongfeng deposit and 18o 0 0 to 8 9 and d 77 4 to 63 7 for the linglong deposit stable isotope data show that the ore forming fluids of the two gold deposits are of magmatic origin with gradual incorporation of shallower meteoric water during after mineralization