zircon u pb geochronology of the basement rocks and dioritic intrusion associated with the fushan skarn iron deposit southern taihang mountains china abstract the fushan iron ores located in the southern part of the taihang mountains tm within the trans north china orogen is among the medium sized skarn iron deposits in china in this paper we report u pb age data on zircon grains from the magmatic intrusion related with the skarn formation and from the neoarchean metamorphic basement in the area the results show that the dioritic intrusion which generated the skarn mineralization was emplaced at 128 8 1 9 ma zircon grains from the basement rocks and xenoliths as well as inherited zircon in the dioritic intrusion show neoarchean to paleoproterozoic ages corresponding to similar ages reported from elsewhere in the north china craton our results and those from previous studies suggest that the continental lower crust was the major source of mesozoic magmatism and associated ore mineralization the mesozoic magmatism and metallogeny in the fushan region correlate with the peak of lithospheric destruction of the north china craton

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

tectonics and magma dynamics coupling in a dyke swarm of iceland abstract to study the dynamics of dyke and fissure swarms in iceland we analyse the distribution of the dykes across the tertiary alftafjordur dyke swarm and that of open fissures and faults across the active krafla fissure swarm within these narrow 5 to 10 km wide and long length width ratio 10 swarms deformation is accommodated both by tectonics and magmatism the dyke swarm built during the westward regional tilting of the host rock lava pile the populations of dykes suggest that a characteristic thickness at about 3 m is involved during dyking dykes show a quasi periodic distribution across the swarm and form clusters spaced by about 2 5 km the analysis of the fissure distribution in the krafla volcanic system reveals a cluster spacing of about half of that of the dyke clusters we discuss the potential origins of these features as a result of magma dynamics host rock properties and tectonics clustering possibly reflects the intrinsic mechanical response to stretching of the upper levels of the brittle crust we propose a three dimensional model of dyke swarms in which magma likely migrates laterally within the upper crust from igneous centres where high magmatic supply rates locally perturb the regional stress field

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

paleoproterozoic accretionary orogenesis in the north china craton a shrimp zircon study abstract the inner mongolia suture zone imsz and the trans north china orogen tnco incorporate the major paleoproterozoic accretionary orogens in the north china craton ncc with the jiao liao ji belt jljb representing the third one here we investigate the paleoproterozoic tectonics of the imsz and tnco through zircon shrimp geochronology on a representative suite of rocks comprising metasediments and arc magmatic rocks shrimp analysis of zircons with textures indicating extreme recrystallization under ultrahigh temperature uht conditions from the metapelites at heling er in the southern domain of the imsz reveals a single population with a weighted mean 207 pb 206 pb age of 1913 17 ma the zircons in another uht granulite from this locality yield a weighted mean 207 pb 206 pb age of 1910 18 ma these data correlate with the ca 1 92 ga age reported from zircons in sapphirine bearing uht granulites further north and confirm the regional extent of the paleoproterozoic uht metamorphism within the imsz zircons in a charnockite from the southern margin of the khondalite belt fringing the uht granulites in the imsz show two distinct age groups an older population with a magmatic paragenesis and a weighted mean 207 pb 206 pb age of 1932 24 ma and a younger group of metamorphic zircons with an age of 1858 26 ma we also report zircon ages from charnockites in two localities around xing he in the huangtuyao belt belonging to the huai an complex within the westernmost domain of the tnco at the junction with the imsz the charnockite from first locality carries two distinct zircon populations with the older group yielding a weighted mean 207 pb 206 pb age of 2477 2 ma and the younger population showing an age of 1807 38 ma the internal structure as revealed from cl images and the overall high th u values up to 2 42 of the older zircons suggest their magmatic affinity whereas the younger group with extremely low th u 0 02 0 09 is of metamorphic origin zircons from the charnockite in the second locality also define two distinct age clusters with a dominant older magmatic group having a weighted mean 207 pb 206 pb age of 2147 11 ma and a minor younger group with an age of 1958 25 ma the range of ages from 2477 to 2147 ma from magmatic zircons in the charnockites from the eastern periphery of the imsz within the western margin of the tnco in combination with similar ages reported in recent studies from zircons in magmatic complexes within the imsz suggest a prolonged history of subduction related arc magmatism and accretionary tectonics analogous to those in some of the phanerozoic belts such as the central asian orogenic belt and the western pacific subsequent progressive collision and suturing of the continental blocks were accompanied by the exhumation of high pressure hp and uht metamorphic rocks the available data from the imsz and tnco suggest long lived convergent margins associated with the southward subduction of the yinshan block and westward subduction of the eastern block in a double sided subduction realm prior to the final amalgamation of the ncc and its incorporation within the columbia supercontinent in the late paleoproterozoic

finite fault parameters of the september 1976 m 5 aftershocks in friuli ne italy abstract on september 1976 four strong aftershocks with m 5 occurred in the friuli area ne italy causing more damage with respect to that caused by the m6 4 mainshock that occurred on may 6 1976 although many studies have been published on the 1976 friuli seismic sequence only recently have finite fault models based on geological considerations galadini et al 2005 burrato et al 2008 been proposed for these aftershocks the aim of our study is to model the september 1976 seismic sources as finite faults by computing finite fault synthetic seismograms for several possible proposed fault models and nucleation locations the seismicity distribution following each of the four events gives us some further information about the areal extent of the related fault and its rupture propagation about 9000 synthetic seismograms are computed for all the tested fault models adopting the reflectivity technique for an upper cutoff frequency of 1 hz a trial and error procedure is used to find the best fit between the recorded and computed peak ground acceleration derived from signals filtered at 1 hz that identifies the final models these are selected also on the basis of the existing knowledge of fault traces in the area the four best fit models seem to be well related to the main barcis staro selo fault system their spatial temporal sequence evidencing an overall progressive east to west migration of the seismic activity related to the 1976 sequence

can lamprophyres resolve the genetic controversy over mesothermal gold deposits associations between calc alkaline lamprophyres and mesothermal gold deposits archean to tertiary in which the lamprophyres are coeval as well as cospatial with mineralization are increasingly recognized worldwide our suggested hypothesis regards lamprophyres as transporting agents for au from au rich sources in the deep mantle which then undergo extensive crustal interactions generating felsic magmas or releasing their au into metamorphic hydrothermal systems such a model not only may reconcile the conflict between the extant magmatic and metamorphic models for mesothermal deposits but also may resolve the inconclusive relations between gold deposits and felsic porphyry granitoid intrusions because lamprophyres may act as parents to both the gold lamprophyre association implies that exceptionally deep seated magmatism repeatedly accompanied gold mineralization in postcollisional orogenic island arc oblique subduction or graben environments this has important implications for the late stage evolution of mineralized archean greenstone belts in particular and for gold deposit genesis in general

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

assembling north china craton within the columbia supercontinent the role of double sided subduction abstract an evaluation of recent s wave receiver functions s wave velocities and two versions of p wave tomographic images along various transects in the north china craton provides some clues on the subduction collision history of the different crustal blocks and their final amalgamation within the paleoproterozoic columbia supercontinent interpretation of a n s seismic section of the craton suggests thick slab debris sinking to various depths in the mantle the w e seismic corridors show the preservation of a thick 200 km lithospheric root tectosphere beneath the ordos block and its variable and extensive erosion towards the yanliao block eastern block this zone is characterized by layers with marked velocity contrast and suggests repeated stacking of the remnants of underplated and accreted paleoproterozoic oceanic lithosphere the present day lithosphere asthenosphere boundary beneath this region probably marks the erosional plane along which decratonization occurred through subduction erosion from the east and thermal and material erosion by upwelling asthenosphere from below resulting in the partial destruction of the tectosphere and its thinning towards the east within the asthenosphere below the yanliao block younger and thinner slabs predominate in the absence of any prominent thick high velocity layers these younger slabs define a westward polarity and constitute a mega scale duplex formed by underplating through phanerozoic subduction process particularly the pacific plate subduction from the east the lithologic associations within the inner mongolia suture zone dividing the yinshan block to the north and ordos block to the south correspond to an accreted ocean plate stratigraphic sequence with the tonalite trondhjemite granodiorite ttg gneisses charnockites and calc alkaline granites representing a continental arc built up through subduction from the north the seismic transects bring out a contrasting polarity in the subduction regime with an oblique east to southward subduction of the yinshan block and a westward subduction of the yanliao block here i propose a double sided subduction history for the ncc similar to the ongoing subduction process in the western pacific such double sided subduction is considered to promote rapid amalgamation of continental fragments within supercontinents and the subduction polarities and mantle dynamics of ncc are therefore considered to be critical in evaluating the final assembly of the paleoproterozoic supercontinent columbia

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

the beiminghe skarn iron deposit eastern china geochronology isotope geochemistry and implications for the destruction of the north china craton article i nfo the beiminghe bmh iron ore in the southern part of the taihang mountain tm hebei province is one of the largest skarn iron deposits in china here we report phlogopite 40 ar 39 ar and zircon u pb age data as well as sulfur lead and he ar isotope geochemistry of pyrite from the ores and skarnitized rocks in the deposit in an attempt to constrain the timing and mechanism of formation of the mineralization the phlogopite 40 ar 39 ar and la icp ms zircon u pb data show markedly consistent ages constraining the timing of ore formation as 136 137 ma the presence of several inherited zircons with late archean or paleoproterozoic ages indicates the participation of the basement rocks during the ore forming process the 34 sv alues of pyrite from the ores range from 12 2 to 16 5 with 206 he 0 036 0 421 the mesozoic magmatism and metallogeny in the bmh correlate well with the peak event of lithospheric thinning and destruction of the north china craton during this process the early precambrian lower crustal rocks in the region were re melted through underplating of mantle magmas leading to the forma tion of the beiminghe monzodioritic pluton minor mantle input occurred during the evolution of the monzodiorite magma which scavenged the ore forming materials from the lower crust interaction of the magmas and fluids with the surrounding rocks resulted in the formation of the beiminghe skarn iron deposits the magmatism and metallogeny in the taihang mountain are signatures of the extensive craton destruction and lithospheric thinning in the eastern part of the north china craton during mesozoic probably associated with pacific slab subduction

dyke swarms and their role in the genesis of world class gold deposits insights from the jiaodong peninsula china abstract jiaodong peninsula located at the southeastern margin of the north china craton is well known for its rich endowment of super large gold deposits this region is also characterized by hundreds of intermediate mafic dykes that cluster into several dyke swarms in this study we present zircon u pb ages which show that the timing of dyke emplacement as ca 120 ma which followed the crystallization of the quartz diorite porphyry at ca 130 ma these ages coincide with the peak ages reported for magmatism and metallogeny in the central north china craton the various ages 2450 2570 and 154 ma from the inherited zircon crystals in these rocks suggest that substantial lower to middle crustal basement rocks and jurassic granitoids were involved during dyke emplacement the dyke swarms varying between alkaline and subalkaline are compositionally low si low ti lamprophyre and low si high ti dolerite porphyry in the western of the jiaodong peninsula whereas those in the eastern part are composed of both high si low ti and low si high ti lamprophyres these features imply multiple sources for the dykes from convective asthenospheric mantle to ancient enriched lithospheric mantle with magma generation at different depths involving mixture of slab derived hydrous fluids the source magmas of the dykes were hydrous and enriched in volatiles as well as ore components and their evolution occurred under high oxygen fugacity conditions the relatively rapid emplacement and cooling of the dyke systems enabled the migration of fluids into ore controlling faults or fractures we envisage that the dyke swarms played an important role in generating the world class gold mineralization of jiaodong

fluid inclusions from the jinchang cu au deposit heilongjiang province ne china genetic style and magmatic hydrothermal evolution abstract the jinchang cu au deposit is located in the easternmost part of the central asian orogenic belt caob the mineralization here is associated with cretaceous porphyritic intrusions of ca 120 110 ma and is mainly hosted within intensely altered mesozoic granites breccia pipes ringed and radial faults the gold ores are disseminated in the wall rock and also occur as massive auriferous quartz sulfide veins in fractures and breccias fluid inclusion data from breccias chalcopyrite quartz vein and pyrite quartz vein display homogenization temperatures in the range of 200 to 550 c and the fluids show variable salinity in the range of 0 58 wt nacl equiv the halite absent fluid inclusions shows a slight increase in salinity with a sharp decrease in temperature we interpret that the high salinity brine and low salinity vapor or aqueous rich fluids from ores represent fluid unmixing from magma the fluid inclusion data from jinchang demonstrate that the main mineralization took place at temperatures from 480 c to 200 c and evolved from high to low salinities geology and fluid inclusion data suggest that the jinchang deposit is an oxidized intrusion related cu au deposit the voluminous hydrothermal magnetite formed during high temperature potassic alteration of wall rocks in this ore deposit can be used as a potential prospecting tool

geochronology and magmatic oxygen fugacity of the tongcun molybdenum deposit northwest zhejiang se china the tongcun mo porphyry deposit in northwest zhejiang is hosted in three porphyry units huangbaikeng songjiazhuang and tongcun from southwest to northeast u pb zircon ages of 162 3 0 ma for the huangbaikeng porphyry 159 9 3 0 ma for the songjiazhuang porphyry and 167 6 155 6 ma for the tongcun porphyry indicate that these intrusions formed during the jurassic and are most likely associated with the northwestward subduction of the izanagi plate trace element compositions of zircons from the tongcun deposit constrain the oxygen fugacity fo2 of the magma using zircon ce anomalies and ti in zircon temperatures the average magmatic fo2 for the porphyries in the tongcun deposit is fayalite magnetite quartz fmq 2 7 which is similar to the shapinggou fmq 3 2 and dabaoshan fmq 3 5 mo porphyry deposits but much higher than that of the reduced cretaceous ore barren shangjieshou porphyry fmq 1 1 around 8 km away from the tongcun deposit the distinct difference in magmatic oxygen fugacity between the jurassic and cretaceous porphyries may help to explain the absence of mo porphyry mineralization in northwest zhejiang during the cretaceous

the tectonic significance of ordovician magmatism in the eastern lachlan fold belt abstract the shoshonitic rock series is a suite of igneous rocks derived from the mantle and containing high potassium plus low abundances of high field strength elements it is commonly associated with calcalkaline igneous rocks but in most modern examples a contemporary active subduction zone is not present mantle derived shoshonitic magmatism in the lachlan fold belt commenced in the early ordovician and terminated at the end of the ordovician when it was replaced by tholeiitic magmatism and the onset of wholesale melting of the lower to middle crust associated calcalkaline igneous rocks are insignificant the shoshonites are widely distributed across the eastern part of the fold belt in a series of discontinuous belts and volcanic centres the largest of which is the orange wellington belt extending from east of cowra to dubbo the broad geographical distribution is not typical of the curvilinear belts of volcanics associated with subduction zones and would be even greater if the intervening basins or troughs were unfolded all rocks analyzed to date are either clearly shoshonitic or show chemical features that indicate shoshonitic affinities prior to alteration and metamorphism in some areas lavas rich in olivine and clinopyroxene potassic trachybasalts dominate in others the more evolved plagioclase rich shoshonites are most abundant it is suggested that the ordovician magmatism was not accompanied by coeval subduction as has been generally assumed more likely the lithospheric mantle beneath the lachlan fold belt was modified during an earlier subduction event associated with the assembling of the basement blocks recognized from granite studies the cause of melting in the ordovician may be related to lithospheric heating or overturning prior to the upwelling of unmodified asthenosphere the hot 1200 c asthenosphere was the source for the silurian tholeiites and provided conductive heat for the melting of the lower to middle crust

evolution of the lithospheric mantle beneath the southeastern north china craton constraints from mafic dikes in the jiaobei terrain abstract two stages of mafic dikes with ages of 117 116 ma and 95 87 ma respectively are identified in the jiaobei terrain based on zircon u pb ages the early cretaceous mafic intermediate dikes ecmds and late cretaceous mafic dikes lcmds show distinct geochemical and isotopic features the ecmds are enriched in large ion lithophile elements lile rb sr ba u and th and light rare earth elements lree la ce pr nd sm and eu with a strong depletion in high field strength elements hfse nb ta ti and p they show uniformly high 87sr 86sr i 0 70841 0 71387 low end t values 18 1 to 13 2 positive 206pb 204pb i 17 07 17 90 and negative ehf t 21 0 to 6 1 values these rocks were derived from partial melting of an enriched lithospheric mantle and the enrichment of the mantle source resulted from source metasomatism imparted by the melts generated from remelting of the subducted lower crust of the yangtze craton yc in contrast the lcmds show lower sio2 41 5 50 1 wt lack of hfse depletion and are depleted in whole rock nd and zircon hf isotope they are interpreted to have sourced from a newly accreted depleted lithospheric mantle generated through continuous erosion of older enriched lithospheric mantle by asthenospheric upwelling leaving out minor remnants of the older mantle in the newly accreted lithospheric mantle the geochemical and isotopic characteristics reported in our study demonstrate that the lithospheric mantle beneath the southeastern north china craton ncc was generally enriched during the early cretaceous 120 ma and the mechanism of the enrichment may be related to source metasomatism caused by the subducted lower crust of the yc however in late cretaceous the lithospheric mantle beneath southeastern ncc was highly heterogeneous which might be related to asthenospheric non uniform erosion the 116 87 ma marks the transition from enriched lithospheric mantle to depleted asthenospheric mantle

mineral chemistry of high mg diorites and skarn in the han xing iron deposits of south taihang mountains china constraints on mineralization process abstract the han xing region is located in the south taihang mountains tm in the central part of the north china craton and is an important iron producing area the iron deposits in this region are of skarn type related to an early cretaceous high mg diorite complex including gabbro diorite hornblende diorite diorite diorite porphyrite and monzonite in this study we report the detailed mineral chemistry of the high mg diorites and skarn rocks the olivine in the gabbro diorite shows chemical composition similar to that in mantle peridotite xenoliths clinopyroxene in the gabbro diorite is dominantly augite with only minor diopside whereas the clinopyroxenes in the diorite and monzonite are diopside amphiboles in the high mg diorites show compositional range from magnesiohornblende to magnesiohastingsite with minor pargasite and tschermakite most plagioclase in the high mg diorite is andesine and oligoclase the magnesio biotite in gabbro diorites shows chemical characteristics of re equilibrated primary biotites and those in calc alkaline rocks in the diorite and diorite porphyrite plagioclase shows complex chemical zoning clinopyroxene and garnet in skarn rocks show varying feo contents the former containing low feo 25 wt content we computed the pressure temperature oxygen fugacity and water contents based on the mineral chemistry of amphibole and biotite based on the results the magma crystallization can be divided into two stages one within the deep magma chamber forming clinopyroxene amphibole and plagioclase phenocrysts the other after emplacement forming the rim of phenocrysts and matrix minerals the magma during the early stage shows high temperature 900 c 950 c pressure 300 mpa 500 mpa relatively high logfo 2 nno nno 2 and h 2 o content in melt 4 8 during the late stage the magma temperature dropped to about 750 c and pressure came down to less than 100 mpa with the logfo 2 rising to nno 1 nno 2 the zoning of amphibole and plagioclase records the process of magma mixing and crystallization with injection of mafic magma into the felsic magma chamber the relatively high logfo 2 and h 2 o content inhibited partitioning of iron into mafic minerals and favored concentration of fe in the melt iron ore precipitation occurred when the magma was emplaced at shallow level and was principally controlled by the chemical composition of carbonate wall rocks the high logfo 2 fe 3 rich ore forming fluid generated andradite and clinopyroxene when it reacted with limestone and dolomitic limestone respectively

palaeoclimatic implications from micro facies data of a 5900 varve time series from the pianico interglacial sediment record southern alps abstract varve micro facies analyses have been carried out on a 405 cm thick annually laminated sediment sequence from the pianico palaeolake in the southern alps considered to correlate with the mis 11 interglacial this varve counted interval represents the uppermost 5900 yr of a ca 400 kyr old interglacial lacustrine deposit with a minimum length of 16 000 varve years intercalated in the varve succession are i detrital layers ii debris flows slump deposits and iii micritic calcite layers the annual couplets are composed of a dominant light summer layer of biochemically precipitated calcite and a thin dark winter layer consisting of organic and minerogenic detritus microscopic correlation of individual couplets in two outcrops 130 m apart demonstrated basin wide continuity of varve deposition summer layers have been found to be composed of up to four sub layers differing in grain size most likely reflecting discrete pulses of calcite precipitation two long periods of pronounced decreases in varve thickness occur within the interglacial 1100 varve years and during the decline of full interglacial conditions 480 varve years suggesting colder climatic conditions the decreases in varve thickness are further accompanied by changes in the pattern of summer sub layering the first cold interval reflects an exceptionally long intra interglacial climatic fluctuation indicating a mode of climatic variability different from the present interglacial wavelet analyses of seasonal layer thickness data revealed that periodic variations of solar activity 88 yr and 208 yr cycles and probably of thermohaline circulation 512 yr cycle impact on varve formation at certain intervals of the studied time window

the jiaodong type gold deposits characteristics origin and prospecting abstract the jiaodong type comprises a unique class of gold mineralisation which includes the linglong type quartz vein hosted and the jiaojia type fracture disseminated style deposits although the type area is in the jiaodong peninsula in ne china where some of the world s richest gold reserves occur we identify similar occurrences in other parts of china and elsewhere in the world under this category the ore fluids migrated upwards forming quartz vein type of gold ore linglong type wherever the ore controlling fractures are at high angles fluid infiltration into the surrounding wall rocks and generation of the jiaojia type disseminated style deposits resulted where the ore bearing fluids encountered low angle fractures on a regional scale the jiaodong type gold mineralisation occurs along the margins of reactivated cratons within the interior of cratons along paleosuture zones or along the junctions of micro blocks and is distinctly different from the classic orogenic gold in terms of their tectonic setting ore characteristics and genetic history unlike skarn and porphyry type of deposits the jiaodong type gold deposits do not always show close spatial relationship with magmatic intrusives and some of the deposits occur distal to plutons 10 km in this paper we evaluate the salient geological geochronological geochemical and isotopic features of the jiaodong type gold deposits and propose some general guidelines for gold prospecting based on case studies we predict that the gold lodes in the jiaodong type mineralised zones might extent vertically up to 3000 m with only minor mineralogical and geochemical variations

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

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

magmatism and metallogeny associated with mantle upwelling zircon u pb and lu hf constraints from the gold mineralized jinchang granite ne china abstract the jinchang gold deposit is located in the easternmost portion of the central asian orogenic belt caob and represents one of the major gold districts in eastern jilin heilongjiang provinces of china the gold ore bodies are hosted mainly in altered mesozoic granitoids breccia pipes and ring and radial faults gold mineralization consists of alteration stockwork in hydrothermally altered granites breccia and quartz sulfide vein types alteration assemblages around the alteration style ore body show a vertical sequence of potassic phyllic and propylitic zones in this study we present u pb and lu hf isotope data on zircons derived from mineralized granophyric granite biotite monzogranite granodiorite and granite porphyry and sericite rb sr ages from the jinchang gold deposit the results show 206pb 238u ages of 201 3 ma mswd 1 1 203 4 ma mswd 1 4 201 5 ma mswd 2 1 and 110 3 ma mswd 1 6 respectively sericite from the gold mineralized phyllic altered granodiorite and granite porphyry returns rb sr isochron ages of 110 4 ma mswd 1 04 and 107 5 ma mswd 0 91 respectively our new data indicate that the gold mineralization at jinchang took place at ca 110 ma and was temporally related to intrusion of the granite porphyry zircon e hf 200 ma values of the ca 200 ma granites vary from 4 8 to 8 1 with tcdm model ages of 727 1535 ma reflecting their derivation mainly by partial melting of juvenile proterozoic crust the gold bearing 110 ma granite porphyry returns e hf 110 ma values in the range of 1 6 to 9 8 with tcdm model ages of 542 1069 ma suggesting partial melts of juvenile proterozoic crust with notable input of mantle components as compared to the ca 200 ma granites compiled oxygen 18osmow 0 7 10 1 and hydrogen dsmow 99 to 70 stable isotopic values of quartz from ores indicate that the ore forming fluids were predominantly exsolved from magmas with minor amount of meteoric water in quartz sulfide veins at the late stage the hf isotope data from the granite porphyry integrated with the results from previous data on s and pb isotopic composition of ores constrain the source of ore forming components as lower crust with discernible mantle inputs and wall rock assimilation our results have implications bearing on the widespread magmatism and metallogenic event during the early cretaceous time in east china and link them to mantle upwelling that contributed both heat and volatiles for crustal melting and scavenging of metals which in turn were concentrated in upper crustal levels through exsolution for the magmas

timing and origin of mesozoic magmatism and metallogeny in the wutai hengshan region implications for destruction of the north china craton abstract the wutai hengshan region in the northwestern domain of taihang mountains tm occurs along the trans north china orogen tnco that amalgamates the western and eastern blocks of the north china craton ncc the metamorphic basement in the region is composed of ca 2 5 ga granite greenstone belts within which the mesozoic magmatic suites are widely emplaced associated with polymetallic mineralization the timing origin and evolution of the magmatic rocks in the wutai hengshan region provide important clues to evaluate the timing mechanism and process of the destruction of the ncc in this study we report new zircon u pb and in situ hf isotopic data on some of the mesozoic intrusions associated with au ag cu mo mineralization from this region the results show that magmatism and metallogeny in the yixingzhai and boqiang gengzhuang mining regions occurred during 142 130 ma starting with felsic granite porphyry with mo cu mineralization and intermediate magma associated with gold mineralization the emplacement of magma and mineralization in diaoquan mining region occurred about 132 130 ma with the intermediate magma emplaced earlier than felsic magma the in situ hf isotopic data indicate that most of the felsic magma was produced by partial melting of the lower crust and that the intermediate magma witnessed intrusion of mafic magma derived from mantle with magma mixing in different proportion the process of crystallization differentiation played an important role in the formation of diaoquan complex intrusion the magmatism and metallogeny in the wutai hengshan region were coeval with the craton destruction of the ncc the mesozoic magmatism and metallogeny in this region during 142 130 ma contributed to the destruction of the stable cratonic architecture of the ncc the mafic lower crust was modified by magma derived from mantle during this process the regional geodynamics associated with these processes are correlated to the subduction of the paleo pacific oceanic lithosphere

petrology geochemistry and zircon u pb and lu hf isotopes of the cretaceous dykes in the central north china craton implications for magma genesis and gold metallogeny abstract the trans north china orogen tnco a paleoproterozoic suture that amalgamates the western and eastern blocks of the north china craton ncc witnessed extensive magmatism and metallogeny during mesozoic associated with intraplate tectonics and differential destruction of the cratonic lithosphere here we investigate a suite of porphyry dykes surrounding the mapeng batholith in the fuping complex within the tnco in relation to the mesozoic gold and molybdenum mineralization the major element chemistry of these dykes show a range of sio 2 57 92 to 69 47 wt na 2 o 3 20 to 4 77 wt k 2 o 3 12 to 4 60 wt and mgo 0 51 to 3 67 wt together with high concentration of lree and lile and relatively low contents of hree and hfse the rocks display la yb n 13 53 48 11 negative nb ta th u and zr anomalies and distinctly positive ba k and sm anomalies the mineralogy and geochemistry of the porphyry dykes indicate the rocks to be high k calc alkaline and i type with adakitic features similar to those of the adjacent mapeng batholith the source magma for these rocks was derived from a mixture of reworked ancient continent crust and juvenile mantle materials the zircon u pb data from these rocks show ages in the range of 124 to 129 ma broadly coinciding with the emplacement age of the mapeng intrusion the inherited zircons of ca 2 5 2 0 and 1 8 ga in the dykes represent capture from the basement rocks during melting the zircon lu hf isotopic compositions show negative e hf t values varying from 27 8 to 11 3 with hf depleted model ages t dm ranging from 1228 ma to 1918 ma and hf crustal model ages t dm c of 1905 ma to 2938 ma suggesting that the mesozoic magmatism and associated metallogeny involved substantial recycling of ancient basement rocks of the ncc we present an integrated model to evaluate the genesis of the porphyry systems and their relation to mineralization we envisage that these dykes probably acted as stoppers impermeable barriers that prevented the leakage and run off of the ore bearing fluids and played a key role in concentrating the gold and molybdenum mineralization

paleoproterozoic ultrahigh temperature granulites in the north china craton implications for tectonic models on extreme crustal metamorphism abstract ultrahigh temperature uht metamorphic rocks associated with the khondalite belt within the inner mongolia suture zone imsz provide robust evidence for extreme thermal metamorphism in the north china craton ncc the imsz marks the collisional suture between the yinshan block to the north and the ordos block to the south as the ncc was incorporated within the columbia supercontinent amalgam during paleoproterozoic here we present a synthesis of the salient features of the uht rocks from the ncc including petrologic indicators fluid characteristics and monazite and zircon chronometry on the extreme crustal metamorphism the granulites carry diagnostic uht mineral assemblages including sapphirine quartz low zn fe3 spinel quartz high alumina orthopyroxene sillimanite quartz and high temperature mesoperthite the stability fields of the typical mineral assemblages conventional geothermobarometry and phase equilibria modeling using pseudosections as reported in a number of recent studies converge to indicate that these uht rocks experienced metamorphic temperatures up to or in excess of 1000 c at ca 10 kbar followed by an isobaric cooling segment the rocks were exhumed along a near isothermal decompression path microstructures mineral reactions and phase equilibria modeling suggest an anti clockwise p t path similar to those displayed by metamorphic orogens developed in subduction collision settings the dominant category of fossil fluids preserved within the major uht minerals is co2 consistent with the stability of the broadly anhydrous mineral assemblage in these rocks both chemical and radiogenic isotopic ages from monazite and zircon chronometry suggest the timing of the uht event as around 1 92 ga the paleoproterozoic high grade metamorphism younging from 1 95 ga in the western domain to 1 92 ga in the eastern domain of the khondalite belt might suggest a scissor like closure of oblique collision between the yinshan and the ordos blocks the salient features of the uht metamorphism in the ncc include 1 extreme metamorphic temperatures at moderate pressures 2 dominantly anhydrous nature of the mineral assemblages typically the stability of orthopyroxene 3 common presence of co2 rich fluid inclusions as the trace of the ambient fluid 4 regional extent of the uht granulites and 5 the association of the uht orogen with an accretionary belt in a continental collisional suture we evaluate the diverse models on the generation of uht orogens including their formation in thickened and inverted back arcs orogen self heating through heat producing elements heat and co2 input by plume impingement below a carbonated tectosphere and asthenospheric upwelling through ridge subduction and slab window process or during post collisional slab break off the ultra hot and dry uht rocks in the ncc provide one of the well preserved examples from the paleoproterozoic globe for investigating extreme metamorphism and related tectonic processes within the plate tectonic paradigm

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

archean lamprophyre dykes and gold mineralization matheson ontario the conjunction of lile enriched mafic magmas deep crustal structures and au concentration at the canadian arrow deposit matheson separate base and precious metal bearing fracture arrays are associated with a trondhjemitic stock transected by lamprophyre dykes peripheral to the stock high fe tholeiitic pillow basalts fe2o3 17 8 wt tio2 2 4 wt al2o3 tio2 13 7 with interbedded felsic units experienced amphibolite facies hydrothermal or regional metamorphism and intense ductile deformation focussed within mylonite zones at the interflow horizons the trondhjemite stock experienced pervasive reaction with marine water at temperatures that diminished to 150 c this was accompanied by conversion of plagioclase of igneous origin to albite concomitant enrichment of sodium na2o 8 32 1 16 wt 1 and shifts of albite up to 18o 14 with attendent variably negative quartz albite fractionations galena dominated veins were precipitated at 220 255 c from hypersaline cacl2 nacl hydrothermal fluids with 22 34 equivalent wt nacl 18o 0 6 to 2 5 these were of evolved mar