lead isotope constraints on the genetic relationships among different ore types in the dongshengmiao deposit northern china abstract the giant dongshengmiao cu zn pb s deposit is the most representative proterozoic sedimentary exhalative sedex deposit in china a detailed investigation of pb isotope compositions of sulfides from various types of ores and associated host rocks has been carried out to determine the genetic relationships among different ore types and to provide important insights on whether younger fluids have contributed mineralizing materials in the formation of the dongshengmiao cu zn pb ores the substantial similarity of the pb isotope composition between the studied stratiform cu zn pb and s orebodies suggests that the bulk of the dongshengmiao cu zn pb ores belong to the same polymetallic metallogenic system with the syngenetic s ores of the proterozoic age comparatively vein type ores show relative scattered pb isotope signatures that fall along a well correlated linear trend whereas their less radiogenic end member projects towards the pb isotope compositions of the overlying stratiform main orebody in addition the overall pb isotope compositions of these vein type ores have shown an apparent overlap and similar trend with the radiogenic disseminated pyrites in the mica schists indicating their radiogenic pb most likely originated from host rocks as well the scatter of pb isotope compositions of the dongshengmiao cu zn pb ores shows that lead was not homogenized regionally during subsequent metamorphism ruling out the possibility of a deposit scale remobilization furthermore the significant difference and lack of intermediate pb isotope values between the previously studied hercynian feldspars and the bulk of the dongshengmiao sulfide ores suggest that a significant introduction of metals from or overprinting by fluids derived from hercynian magmatism is unlikely to have played an important role in the metal endowment taken together all sulfide orebodies associated with various ore types in the dongshengmiao deposit belong to an integrated and progressive hydrothermal ore forming system of the proterozoic age and a portion of the vein type ores and associated disseminated pyrites experienced a minor addition of evolved rock lead during subsequent greenschist face metamorphisms

the enigmatic yinshan fold and thrust belt of northern china new views on its intraplate contractional styles the east to east northeast trending yinshan belt lies within north china extending westward at least 1100 km from china s eastern coast to inner mongolia this intraplate jurassic cretaceous belt underwent contractional and normal faulting folding and contemporaneous terrestrial sedimentation and magmatism current views on its contractional deformational style favor relatively limited thick skinned faulting of archean basement and cover units these views are challenged however by recent discoveries in the eastern part of the belt of south directed ductile nappe formation and large displacement 40 45 km thin skinned northward thrust faulting both involving archean and younger rock units collision of the siberian and north china plates upon closure of a jurassic and early cretaceous mongolo okhotsk ocean more than 800 1100 km to the north may have been responsible for yinshan north south contraction some patterns of contraction e g jurassic cretaceous ductile nappe formation appear to have been influenced by a superposed magmatic regime related to westward subduction of a pacific basin plate beneath the north china plate

formation epoch and genesis of intrusive rocks in huogeqi orefield of inner mongolia and their relationship with copper mineralization ingle zircon mc icp ms u pb dating and lithogeochemical studies of gabbro diorite intrusives in the huogeqi orefileld were conducted for the purpose of constraining their petrogenesis and their relationship with copper mineralization zircons collected from gabbro diorite display oscillatory zoning and high th u ratios 0 20 0 77 indicating their magmatic origin a weighted average u pb age of 273 9 1 2 ma for huogeqi intrusive rocks was obtained suggesting that the formation of gabbro diorite should be associated with the collisional event of the north china plate and siberia plate in late hercynian period their initial hf isotope ratios and hf two stage depleted mantle model ages range from 4 1 to 10 0 and from 1 56 to 1 92 ga respectively their peak model ages are consistent with the bulk rock nd two stage depleted mantle model age of 1 77ga implying that the rock forming materials were mostly derived from the paleo crust instead of from the depleted mantle geological and geochemical characteristics of the gabbro diorite intrusives reveal that they were derived from partial melting of archaean basement and interacted with mantle derive magmas by about 17 as estimated by simulated calculation a comparison of geochemical characteristics between gabbro diorite intrusives and the copper ore body suggests that hercynian diorite failed to provide significant metallogenic elements furthermore hercynian diorite intruded in the compressive orogenic environment 273 9 ma ago whereas copper mi neralization occurred in middle late proterozoic suggesting the absence of direct genetic relationship between the plutonic intrusion and the formation of the copper ore body based on field observation and decrepitation curves of quartz and chalcopyrite the authors have reached the conclusion that the huogeqi copper deposit was reformed by magmatic hydrothermal fluid along the contact zone between the gabbro diorite and the copper ore body

holocene climatic instability a prominent widespread event 8200 yr ago the most prominent holocene climatic event in greenland ice core proxies with approximately half the amplitude of the younger dryas occurred 8000 to 8400 yr ago this holocene event affected regions well beyond the north atlantic basin as shown by synchronous increases in windblown chemical indicators together with a significant decrease in methane widespread proxy records from the tropics to the north polar regions show a short lived cool dry or windy event of similar age the spatial pattern of terrestrial and marine changes is similar to that of the younger dryas event suggesting a role for north atlantic thermohaline circulation possible forcings identified thus far for this holocene event are small consistent with recent model results indicating high sensitivity and strong linkages in the climatic system

p t x conditions origin and evolution of cu bearing fluids of the shear zone hosted huogeqi cu pb zn fe deposit northern china abstract huogeqi is a shear zone hosted epigenetic deposit within the greenschist amphibolite facies of the mesoproterozoic langshan group in the langshan district on the northern margin of the north china craton ncc copper mineralization in the huogeqi deposit was formed in two stages a main stage controlled by the shear zone and characterized by brittle ductile ore forming structures and a lower greenschist facies mineral assemblage and a late stage characterized by open space filling textures and low temperature minerals based on microthermometric and raman microprobe analysis the main stage cu bearing fluid was mesothermal low salinity and h 2 o ch 4 dominant and was generated by an interaction between a deep crustal metamorphic fluid and graphite bearing host rocks this interaction resulted in a more ch 4 rich fluid which was more amenable to be immiscible we showed that immiscibility of the h 2 o ch 4 fluid occurred due to temperature decrease prior to the main stage cu mineralization cu was finally precipitated from the resultant h 2 o rich aqueous fluid main stage cu mineralization temperature was obtained using various methods 310 370 c by intersection of isochors of coexistent ch 4 and aqueous inclusions 364 41 c on average by pressure correction of the homogenization temperatures of aqueous inclusions and 362 26 c using the chlorite geothermometer pressure during cu deposition fluctuated between lithostatic and hydrostatic at depths of ca 10 12 km but it seemingly had no effect on the mineralization process the late stage cu bearing fluid was a low temperature low salinity h 2 o of meteoric origin

mesozoic granitic magmatism in extensional tectonics near the mongolian border in china and its implications for crustal growth abstract the yagan area of the southernmost sino mongolian border is characterized by an extensional structure where a large metamorphic core complex yagan onch hayrhan and voluminous granitoids are exposed new isotopic age data indicate that the granitoids which were previously regarded as paleozoic in age were emplaced in early and late mesozoic times the early mesozoic granitoids have 228 7 ma u pb zircon age and consist of linear mylonitic quartz monzonites and biotite monzogranites their chemical compositions are similar to those of potassic granites and shoshonitic series and show an intraplate and post collisional environment in tectonic discrimination diagrams their fabrics reveal that they experienced syn emplacement extensional deformation all these characteristics suggest that the adjustment thinning and extensional deformation at middle to lower crustal levels might have occurred in the early mesozoic the late mesozoic granitoids have a u pb zircon age of 135 2 ma and are made up of large elliptical granitic plutons they are high k calc alkaline and were forcefully emplaced in the dome extensional setting both the early and late mesozoic granitoids have end t values of 2 3 to 5 in strong contrast with the negative end t values 11 of the precambrian host rocks this suggests that juvenile mantle derived components were involved in the formation of the granitoids the similar situation is omnipresent in central asia this study demonstrates that tectonic extension magmatism and crustal growth are closely related and that post collisional and intraplate magmatism was probably a significant process for continental growth in the phanerozoic

oxygen isotope and palaeotemperature records from six greenland ice core stations camp century dye 3 grip gisp2 renland and northgrip oxygen isotope variations spanning the last glacial cycle and the holocene derived from ice core records for six sites in greenland camp century dye 3 grip gisp2 renland and northgrip show strong similarities this suggests that the dominant influence on oxygen isotope variations reflected in the ice sheet records was regional climatic change differences in detail between the records probably reflect the effects of basal deformation in the ice as well as geographical gradients in atmospheric isotope ratios palaeotemperature estimates have been obtained from the records using three approaches i inferences based on the measured relationship between mean annual 18o of snow and of mean annual surface temperature over greenland ii modelled inversion of the borehole temperature profile constrained either by the dated isotopic profile or iii by using monte carlo simulation techniques the third of these approaches was adopted to reconstruct holocene temperature variations for the dye 3 and grip temperature profiles which yields remarkably compatible results a new record of holocene isotope variations obtained from the northgrip ice core matches the grip short term isotope record and also shows similar long term trends to the dye 3 and grip inverted temperature data the northgrip isotope record reflects i a generally stronger isotopic signal than is found in the grip record ii several short lived temperature fluctuations during the first 1500 yr of the holocene iii a marked cold event at ca 8 2 ka the 8 2 ka event iv optimum temperatures for the holocene between ca 8 6 and 4 3 ka a signal that is 0 6 stronger than for the grip profile v a clear signal for the little ice age and vi a clear signal of climate warming during the last century these data suggest that the northgrip stable isotope record responded in a sensitive manner to temperature fluctuations during the holocene copyright 2001 john wiley sons ltd

evidence for proterozoic and late cretaceous early tertiary ore forming events in the coeur d alene district idaho and montana new 40 ar 39 ar age spectra on sericite and lead isotope data on tetrahedrite siderite galena bournonite and stibnite together with previously published isotopic geochemical and geologic studies provide evidence for two major vein forming events in the coeur d alene district and surrounding areas of the belt basin the data suggest that the zinc and lead rich veins e g bunker hill and star morning mines formed in the proterozoic 1 0 ga whereas the silver rich veins e g silver belt mines antimony veins e g u s antimony mine and gold bearing quartz veins murry subdistrict formed in late cretaceous to early tetitary time

architecture and mineral deposit settings of the altaid orogenic collage a revised model abstract the altaids are an orogenic collage of neoproterozoic paleozoic rocks located in the center of eurasia this collage consists of only three oroclinally bent neoproterozoic early paleozoic magmatic arcs kipchak tuva mongol and mugodzhar rudny altai separated by sutures of their former backarc basins which were stitched by new generations of overlapping magmatic arcs in addition the altaids host accreted fragments of the neoproterozoic to early paleozoic oceanic island chains and neoproterozoic to cenozoic plume related magmatic rocks superimposed on the accreted fragments all these assemblages host important many world class late proterozoic to early mesozoic gold copper molybdenum lead zinc nickel and other deposits of various types in the late proterozoic during breakup of the supercontinent rodinia the kipchak and tuva mongol magmatic arcs were rifted off eastern europe siberia and laurentia to produce oceanic backarc basins in the late ordovician the siberian craton began its clockwise rotation with respect to eastern europe and this coincides with the beginning of formation of the mugodzhar rudny altai arc behind the kipchak arc these earlier arcs produced mostly cu pb zn vms deposits although some important intrusion related orogenic au deposits formed during arc arc collision events in the middle cambrian and late ordovician the clockwise rotation of siberia continued through the paleozoic until the early permian producing several episodes of oroclinal bending strike slip duplication and reorganization of the magmatic arcs to produce the overlapping kazakh mongol and zharma saur valerianov beltau kurama arcs that welded the extinct kipchak and tuva mongol arcs this resulted in amalgamation of the western portion of the altaid orogenic collage in the late paleozoic its eastern portion amalgamated only in the early mesozoic and was overlapped by the transbaikal magmatic arc which developed in response to subduction of the oceanic crust of the paleo pacific ocean several world class cu mo porphyry cu pb zn vms and intrusion related au mineral camps which formed in the altaids at this stage coincided with the episodes of plate reorganization and oroclinal bending of magmatic arcs major pb zn and cu sedimentary rock hosted deposits of kazakhstan and central asia formed in backarc rifts which developed on the earlier amalgamated fragments major orogenic gold deposits are intrusion related deposits often occurring within black shale bearing sutured backarc basins with oceanic crust after amalgamation of the western altaids this part of the collage and adjacent cratons were affected by the siberian superplume which ascended at the permian triassic transition this plume related magmatism produced various deposits such as famous ni cu pge deposits of norilsk in the northwest of the siberian craton in the early mesozoic the eastern altaids were oroclinally bent together with the overlapping transbaikal magmatic arc in response to the northward migration and anti clockwise rotation of the north china craton the following collision of the eastern portion of the altaid collage with the siberian craton formed the mongol okhotsk suture zone which still links the accretionary wedges of central mongolia and circum pacific belts in the late mesozoic a system of continent scale conjugate northwest trending and northeast trending strike slip faults developed in response to the southward propagation of the siberian craton with subsequent post mineral offset of some metallogenic belts for as much as 70 400 km possibly in response to spreading in the canadian basin india asia collision rejuvenated some of these faults and generated a system of impact rifts

how accurately can we date the duration of magmatic hydrothermal events in porphyry systems an invited paper determining the absolute duration of magmatic hydrothermal events leading to the formation of porphyry systems i e including porphyry copper skarn and epithermal deposits is one of the key questions in ore geology this is so because the duration of magmatic hydrothermal events in porphyry systems is instrumental to the development of genetic models necessary to explore a category of mineral deposits that provide most of the copper and significant amounts of base and precious metals to our economy the problem of determining the absolute duration of magmatic hydrothermal events in porphyry systems has been addressed through thermal modeling of cooling intrusions and time needed to precipitate specified metal amounts from active hydrothermal systems with known metal concentrations and fluid fluxes both these methods have shown that the likely duration of hydrothermal systems is on the order of a few tens of kilo annum ka isotopic dating in contrast is the only possible way to determine the life span of magmatic hydrothermal events in fossil porphyry systems analytical and methodological developments during the last decade in the fields of the most robust isotopic systems commonly used for absolute dating u pb 40ar 39ar re os allow us to date minerals with internal precisions 0 2 2 for a 10 ma old mineral this corresponds to a 20 ka uncertainty which is marginally sufficient to discriminate the duration of hydrothermal systems at the tens of kilo annum scale however many geochronological studies on fossil porphyry systems have shown that these are most often formed through repeated cycles of several intrusion events which extend the overall life of the porphyry systems to a few 0 x and up to 2 ma in some cases internal precisions of the above mentioned dating methods allow us in theory to comfortably discriminate events at the 0 x scale and the combination of u pb 40ar 39ar and reos geochronology is a tool widely used by ore geologists to bracket the duration of cyclic magmatic hydrothermal events in porphyry systems in this review we discuss some fundamental problems that are systematically overlooked in most geochronological studies trying to bracket the life span of porphyry systems we show that if these problems are not adequately taken into account and tackled the result will be that fundamentally wrong life spans of porphyry systems will be estimated we also provide basic guidelines to follow when trying to resolve the duration of magmatic hydrothermal events in porphyry systems with the highest accuracy and precision currently achievable

post glacial vegetation reconstruction and a possible 8200 cal yr bp event from the low arctic of continental nunavut canada climate models suggest that the global warming during the early to mid holocene may have partly resulted from the northward advance of the northern treeline and subsequent reduction of the planetary albedo we investigated the holocene vegetation history of low arctic continental nunavut canada from a radiocarbon dated sediment core from tk 2 lake a small lake ca 200 km north of the limit of the forest tundra the pollen and loss on ignition data indicate the presence of dwarf shrub tundra in the region since the beginning of organic sedimentation at ca 9000 cal yr bp with dominance of betula especially since 8700 cal yr bp at 8100 7900 cal yr bp the dominance of the shrub tundra was punctuated by a transient decline of betula and coincident increases of ericaceae undiff vaccinium type and gramineae this suggests an abrupt disturbance of the betula glandulosa population approximately simultaneously with the sudden 8200 cal yr bp event in the north atlantic however in the absence of other sites studied in the area linkage to the 8200 cal yr bp event remains tentative the lack of any evidence of forest tundra in the region constrains the northern limit of the mid holocene advance of the forest tundra boundary in central northern canada consequently our results show that the climate models imposing a mid holocene advance of the limit of the forest tundra to the arctic coast of canada may have overestimated the positive climatic feedback effects that can result from the replacement of tundra by the boreal forest copyright 2003 john wiley sons ltd

ore forming conditions and genesis of the huogeqi cu pb zn fe deposit in the northern margin of the north china craton evidence from ore petrologic characteristics abstract the huogeqi cu pb zn fe deposit is located in the langshan district in the western segment of the northern margin of the north china craton the deposit is hosted by upper greenschist lower amphibolite facies 550 650 c rocks of the langshan group most orebodies are hosted in a shear zone that developed in parallel with the sedimentary bedding of the langshan group fe was precipitated coeval with the deposition of the host rocks i e a syngenetic origin whereas cu pb and zn were precipitated in hydrothermal systems postdating formation of the host rocks i e an epigenetic origin the hydrothermal mineralization process can be subdivided into two stages 1 a main stage with predominant cu pb zn mineralization stage where ore forming structures are characterized by brittle ductile and brittle shear deformation the main stage sulfide veins cut the mylonite fabrics of the host rocks mineral paragenesis and compositions indicate that main stage cu mineralization took place at 330 440 c and 3 4 3 9 kbar this pressure temperature p t condition is consistent with that of the brittle ductile transition zone but lower than that of the peak metamorphism of the host rocks compared with cu mineralization the main stage pb zn mineralization took place at relatively lower temperature and pressure the syngenetically formed fe orebodies and iron formations in the huogeqi deposit were favorable sites for epigenetic cu precipitation the h 2 s rich cu fluids would have reacted with fe in the host rocks when flowing through fe orebodies and iron formations such a reaction would have led to a reduction in h 2 s of the ore forming fluids and consequently cu precipitation 2 the late stage cu mineralization is of less economic importance characterized by open space filling textures and a low temperature mineral assemblage that constrains the ore forming temperature as lower than 330 c this late stage mineralization took place in an epithermal like hydrothermal system at a shallower crustal depth

development of the khao khwang fold and thrust belt implications for the geodynamic setting of thailand and cambodia during the indosinian orogeny abstract the indosinian orogeny in thailand is often viewed as having developed between strongly linear terranes which today trend approximately n s the terranes were subsequently disrupted by later tectonics particularly nw se trending cenozoic strike slip faults the ene wsw to ne sw striking thrusts and folds in the khao khwang platform area of the saraburi group on the sw margin of the indochina terrane are not easily explained in the context of this traditional view reversal of the clockwise rotation shown to have affected the block north of the mae ping fault zone only enhances the e w orientation of structures in the fold and thrust belt and moves the belt further east towards cambodia one solution for the trend that fits better with regional understanding from hydrocarbon exploration of the khorat plateau is that the indochina terrane was actually a series of continental blocks separated by permian rifting during the early triassic the early stages of collision south china cathaysian terrane collision with vietnam indochina resulted in the amalgamation of disparate blocks that now form the indochina terrane by closure along the rifts at the same time or following on from the collision there was closure of the back arc area between indochina and the sukhothai zone the rift basins were thrusted and inverted during the early stages of the indosinian orogeny and only underwent minor reactivated when later sibumasu collided with sukhothai zone indochina terrane margin during the late triassic the scenario described above requires the presence of a minor e w trending suture in nw cambodia evidence for this suture is suggested by the presence of permo triassic calc alkaline volcanism

contrasting late carboniferous and late permian middle triassic intrusive suites from the northern margin of the north china craton geochronology petrogenesis and tectonic implications two contrasting intrusive suites have been identified from the northern margin of the north china craton a late carboniferous dioritegranodiorite suite mainly made up of quartz diorite diorite granodiorite tonalite and hornblende gabbro and a late permian middle triassic suite of granitoid intrusions consisting of monzogranite syenogranite and quartz monzonite plutons from the late carboniferous suite exhibit variable sio2 contents and calc alkaline or high k calc alkaline metaluminous geochemical features most have low negative whole rock nd t values where t is the crystallization age of 17 1 to 11 5 and zircon hf t values of 38 3 to 11 2 indicating that they were derived mainly from anatectic melting of the ancient lower crust with some involvement of mantle materials however an older pluton in the suite exhibits higher nd t values of 11 5 to 9 9 nd model ages of 1 82 1 64 ga lower initial 87sr 86sr ratios of 0 7046 0 7048 and it contains some zircon grains that are characterized by high negative to positive zircon hf t values of 8 7 to 1 2 indicating strong involvement of juvenile materials derived from the lithospheric mantle the late carboniferous plutons are interpreted as subduction related and to have been emplaced in an andean style continental margin arc during the southward subduction of the paleo asian oceanic plate beneath the north china craton rocks from the late permian middle triassic intrusive suite display geochemical signatures ranging from highly fractionated i type to a type they exhibit higher zircon hf t values of 14 9 to 6 7 whole rock nd t values of 10 6 to 8 8 and younger hf and nd model ages than most of the late carboniferous plutons indicating that they could have been produced by extreme fractional crystallization of hybrid magmas resulted from mixing of coeval mantle and crust derived melts they are interpreted as postcollisional postorogenic granitoids linked to lithospheric extension and asthenosphere upwelling due to slab break off and subsequent sinking after final collision and suturing of the mongolian arc terranes with the north china craton these two contrasting intrusive suites suggest that the final closure of the paleo asian ocean and collision between the mongolian arc terranes and the north china craton occurred during the late permian and these events were followed by postcollisional postorogenic extension large volume magmatism and significant continental growth no significant syncollisional crustal thickening high pressure metamorphism or s type granitoid magmatism occurred during the collision process

spatial evolution of zn fe pb isotopes of sphalerite within a single ore body a case study from the dongshengmiao ore deposit inner mongolia china analyses of sphalerite minerals from the characteristic brecciated zn pb ores of the main ore body in the giant dongshengmiao deposit have revealed variations in 66zn from 0 17 to 0 40 and in 56fe from 1 78 to 0 35 further the investigated pyrrhotite samples have iron that is isotopically similar to that of associated sphalerite minerals the most distinctive pattern revealed by the zinc and iron isotope data is the lateral trend of increasing 66zn and 56fe values from southwest to northeast within the main ore body the lead isotopic homogeneity of ore sulfides from the main ore body suggests that there is only one significant source for metal thus precluding the mixing of multiple metal sources as the key factor controlling spatial variations of zinc and iron isotopes the most likely control on spatial variations is rayleigh fractionation during hydrothermal fluid flow with lighter zn and fe isotopes preferentially incorporated into the earliest sulfides to precipitate from fluids precipitations of sphalerite and pyrrhotite have played vital roles in the zn and fe isotopic variations respectively of the ore forming system accordingly the larger isotopic variability for fe than zn within the same hydrothermal system perhaps resulted from a larger proportion of precipitation for pyrrhotite than for sphalerite the lateral trend pattern revealed by the zinc and iron isotope data is consistent with the occurrence of a cystic shaped breccia zone which is characterized by marked elevation in cu the results further confirm that zn and fe isotopes can be used as a vectoring tool for mineral prospecting

timing of exhumation of the ereendavaa metamorphic core complex north eastern mongolia u pb and 40ar 39ar constraints abstract the occurrence of numerous ne sw trending rift basins that locally bound metamorphic core complexes in transbaikalia northern mongolia and north eastern china indicates that the eastern domain of the central asian orogenic belt was affected by a large scale nw se extensional tectonic event during late jurassic to early cretaceous times available geochronological information about the formation of metamorphic core complexes in the region define partly synchronous periods in transbaikalia 134 121 ma and north china 136 110 ma suggesting dome exhumation during the early cretaceous in north eastern mongolia the ereendavaa range lined by the onon shear zone was recently interpreted as one of these metamorphic core complexes of late jurassic to early cretaceous age on the basis of u pb zircons data from two synkinematic pegmatite dykes however this wide time range remains to be discussed the present work constrains the tectono thermal evolution of the range by providing new mc icp ms u pb zircons ages from pegmatite dykes and metamorphic igneous rocks and mica and amphibole 40 ar 39 ar laser step heating ages from metamorphic and magmatic rocks that crop out within the range the results show that 1 the ereendavaa range was the locus of a widespread magmatic activity prior to its exhumation from late jurassic times 2 cooling of the range began at least at 137 9 0 3 ma as revealed by a 40 ar 39 ar plateau ages obtained from an hornblende sampled within the range core and 3 exhumation along the onon shear zone occurred from 130 3 1 9 ma down to 124 8 0 3 ma as shown by ages of most of micas and amphiboles from the shear zone these more accurate ages are consistent with metamorphic core complex ages from adjacent areas furthermore they argue for an extensional dynamic paroxysm at the scale of eastern asia during a narrow time range in the early cretaceous between ca 130 ma and ca 120 ma

copper gold and silver enrichment in ore mylonites within massive sulphide orebodies at hongtoushan vhms deposit n e china abstract the hongtoushan archaean cu zn volcanic hosted massive sulphide vhms deposit occurs in the hunbei granite greenstone terrane liaoning province of ne china the ores were metamorphosed 3 0 2 8 ga to upper amphibolite facies at temperatures between 600 and 650 c and underwent three phases of deformation the deformation has transposed the stratiform orebodies into a y shaped configuration ore minerals in the deposit were originally composed of pyrite pyrrhotite chalcopyrite and sphalerite prograde metamorphism obliterated almost all the sedimentary textures in the ores and the present ore textures were formed substantially during peak and post peak metamorphism intensive remobilisations have occurred in the hongtoushan deposit at various scales there are more than 30 oreshoots inside the main massive sulphide orebodies the oreshoots range from 2 to 30 m in length 0 1 to 1 5 m in width and 2 to 30 m in depth extension most run parallel or sub parallel to the strike of the massive sulphide ore layers with only a few being developed in metamorphic rocks in the immediate vicinity of the sulphide orebodies almost all the sulphide and gangue minerals in the oreshoots have been affected by intense shearing pyrite is characterised by cataclastic flow pyrrhotite chalcopyrite and sphalerite exhibit strong plasticity hydrothermal alteration minerals in the oreshoots are dominated by deformation free hornblende actinolite epidote clinozoisite biotite muscovite albite carbonate and quartz cu au and ag in the ore mylonites average 11 wt 1 74 and 235 g t respectively compared to the massive sulphide ores these oreshoots show remarkable enrichment of these elements with enrichment coefficients of 5 3 5 0 and 4 6 respectively we draw the conclusion that these oreshoots are actually ore mylonites overprinted by late stage fluids the presence of annealing textures in pyrrhotite and the absence in pyrite suggest that formation and succeeding annealing of the ore mylonite took place over the temperature range from 550 to 450 c such a temperature range combined with the geology and mineralogy indicates that these ore mylonites and the derivative oreshoots were formed during upper greenschist facies retrograde metamorphism similarity of the ore mylonites to the massive ores in metal varieties and lead isotope ages suggest that cu au and ag of the overprinting fluids on the ore mylonites were derived mainly from the nearby massive sulphide ores however lead isotope compositions of the ore mylonites also suggest that an external source such as the metamorphic host rocks has also contributed to their metal budget

zircon u pb age hf isotope and geochemistry of carboniferous intrusions from the langshan area inner mongolia petrogenesis and tectonic implications abstract late paleozoic was a critical period for the tectonic evolution of the northern margin of the alxa north china craton but the evolutionary history is not well constrained the carboniferous intrusions in the langshan area in the western part of the northern margin of the alxa north china craton are mainly composed of tonalite quartz diorite olivine gabbro and pyroxene peridotite zircon la icp ms u pb dating indicates that the langshan carboniferous intrusions were emplaced at ca 338 324 ma the quartz diorites are characterized by high amounts of compatible trace elements cr ni and v and high mg values which may suggest a significant mantle source the positive pb and negative nb ta ti anomalies the variable ehf t 6 9 to 2 0 values and the old hf model ages 1218 1783 ma imply some involvement of ancient continental materials in its petrogenesis the tonalite has relatively high sr y ratios low mg yb and y contents features of adakite like rocks negative ehf t values 9 8 to 0 1 and older hf model ages 1344 1953 ma which suggest significant involvement of ancient crust materials and mantle derived basaltic component in its petrogenesis the high mg values high cr and ni contents and low zr and hf contents of the mafic ultramafic rocks show evidence of a mantle source and the relatively low zircon ehf t values 5 9 to 3 2 might point to an enriched mantle the trace element characteristics indicate the influence of subducted sediments and slab derived fluids in the tectonic discrimination diagrams all the rocks plot in subduction related environment such as volcanic arc and continental arc considering the regional geology we suggest that the carboniferous intrusions in the langshan area were likely emplaced during the late stage of the southward subduction of the paleo asian ocean plate which formed a continental arc along the northern margin of the alxa north china craton

constraints of lead isotopes on regional metallogeny of sediment hosted sulfide deposits in the langshan zhaertai ore belt northern china abstract the langshan zhaertai ore belt in northern china includes a dozen sediment hosted zn pb cu deposits which are traditionally considered to have been formed during sedimentary exhalative sedex activities in different subbasins in the same proterozoic marginal rift system however this assumption has never been systematically tested herein we re evaluate the regional metallogeny by the analysis and comparison of pb isotope data obtained in this study and published in literatures the pb isotope signatures of several representative deposits from this ore belt are heterogeneous and do not lie along similar secondary or anomalous lead evolution lines suggesting that these deposits belong to different metallogenic systems the pb isotope ratios of the bulk of the sulfide ores in south ore belt are characterized by unradiogenic isotope compositions and proterozoic pb pb model ages whereas the various types of sulfides from the huogeqi deposit in north ore belt show a very radiogenic lead signature 206pb 204pb 17 000 which is broadly consistent with common lead of associated indosinian magmatic rocks indicating an magmatic hydrothermal origin the dongshengmiao and tanyaokou massive type ore sulfides have similar and exceedingly unradiogenic isotope compositions grouped around 15 200 206pb 204pb their vein type sulfides show scattered pb isotope signatures that fall along a well correlated linear trend towards the right of the massive sulfide array indicating some modification during metamorphism the similarity of lead isotope compositions of the jiashengpan vein type sulfides to the common lead of hercynian igneous rocks indicates that the proximal source of the ore metals in its epigenetic hydrothermal system was hercynian igneous activity

sphalerite geobarometry in the cu fe zn s system phase relations have been determined among sphalerite pyrite pyrrhotite and intermediate solid solution iss from 439 degrees to 725 degrees c at 1 bar and 353 degrees to 760 degrees c at 5 kb the extents of solid solution in the four phase assemblage are described as functions of temperature in kelvins by the following equations log mole zns in iss 1 bar 2 795 1 632 t super 1 log mole zns in iss 5 kb 2 659 1 608 t super 1 log mole cus in pyrrhotite 1 bar 2 546 1 866 t super 1 log mole cus in sphalerite 1 bar 4 202 3 755 t super 1 and log mole cus in sphalerite 5 kb 4 084 3 791 t super 1 the pressure dependence in kb of the composition of sphalerite in equilibrium with pyrite and pyrrhotite with or without iss can be expressed for the temperature independent portion of the sphalerite geobarometer as p 42 30 32 10 log mole fes because of the low solubility of copper in sphalerite in the four phase assemblage below 650 degrees c the presence of chalcopyrite in natural ores should be of no consequence to sphalerite geobarometry over its temperature independent portion nevertheless sphalerites which are inhomogeneous in fes and which contain abundant blebs of chalcopyrite in excess of the amount that can be reasonably accounted for by an equilibrium process of solubility and subsequent exsolution are a common feature of many sulfide ores such sphalerite grains should be avoided in applying the geobarometer the chalcopyrite blebs may be a product of a premetamorphic sphalerite chalcopyrite intergrowth or represent true exsolution from sphalerite in any one of 1 a former sphalerite pyrrhotite iss equilibrium 2 a stable four phase assemblage at temperatures above the temperature independent portion of the geobarometer or 3 a metastable four phase assemblage in which pyrite was inert use of the sphalerite geobarometer requires a thorough understanding of the textural relationships and discrimination of equilibrium from disequilibrium or low temperature reequilibrated assemblages

significant zn pb cu remobilization of a syngenetic stratabound deposit during regional metamorphism a case study in the giant dongshengmiao deposit northern china abstract the giant dongshengmiao zn pb cu deposit is located in the langshan district northern china the ores are hosted within a proterozoic rift sequence which underwent lower greenschist facies metamorphism and shear deformation during development of early cretaceous intraplate orogenic belt northwest dipping thrust faults which share similar orientations and dip angles with the orebodies are well developed in the mining area syngenetic stratabound sulfides were formed during the proterozoic rifting event but syngenetic ore textures have seldom been preserved except for some pretectonic fine grained pyrite petrological observation 39 ar 40 ar geochronology combined with previous isotopic and fluid inclusion studies indicates that significant zn pb cu remobilization took place as a result of thrust faulting associated with metamorphic devolatilization of ore hosting rocks at ca 136 ma coeval with the intraplate orogeny and regional crustal shortening sulfides were redistributed in shear structures or along grain boundaries of ore hosting carbonates and fe rich carbonates were ideal sites for zn pb cu precipitation

world class base and precious metal deposits a quantitative analysis over 62 percent of the 193 000 metric tons of gold discovered to date is located in four countries and more than 68 percent occurs in four types of mineral deposits about 55 percent of the 1 740 000 metric tons of silver found is in four countries and 45 percent is in four types of deposits fifty six percent of the 1 52 billion metric tons of discovered copper is from four countries and four types of deposits contain 88 percent of the total over 50 percent of both the 713 000 000 metric tons of zinc and 349 000 000 metric tons of lead discovered to date come from four countries and 70 percent of both metals occur in four types of deposits all discovered gold would fit in a cube with a height of 22 m silver in a 55 m cube copper in a 550 m cube zinc in a 460 m cube and lead in a 310 m cube at least 74 percent of gold silver zinc and lead is in deposits having average grades above the respective median grades and 44 percent of copper is in deposits with average grades above the median grade of all deposits lower grade deposits contain less total metal than higher grade deposits tonnage of mineralized rock is an even better predictor of contained metal with over 96 percent of each metal s total residing in deposits having greater than median size and between 47 and 79 percent of metal contained in the largest 10 percent of deposits world class deposits defined as the upper 10 percent of deposits in terms of contained metal account for over 86 percent of all gold 79 percent of silver 84 percent of copper 71 percent of zinc and 73 percent of lead these giant deposits contain at least 100 metric tons 3 2 moz gold 2 400 metric tons 77 moz silver 2 million metric tons copper 1 7 million metric tons zinc or 1 million metric tons lead mineral deposits occur rarely in the earth s crust and large ones are especially uncommon this analysis shows that only the unusually large deposits can significantly affect supply

zircon ages and nd hf isotopic composition of the zhaertai group inner mongolia evidence for early proterozoic evolution of the northern north china craton the mesoproterozoic rifting and accompanying magmatism and sedimentation in the north china craton are interpreted to be related to the breakup of the paleoproterozoic supercontinent columbia this study presents zircon ages and nd hf isotopic data of the low grade mesoproterozoic zhaertai group exposed along the northern margin of the north china craton sandstones of the zhaertai group contain detrital zircon populations of about 2500 ma which originated from the late archean basement rocks underlying this group a close match between the u pb ages and the tdm hf ages with high initial ehf values at 2500 ma for the detrital zircon grains imply a juvenile origin for protoliths of the basement rocks sedimentation of the zhaertai group likely began around 1750 ma tentatively constrained by the formation time of an intercalated volcanic layer the volcanic rocks have low initial end values of 8 0 to 8 5 at 1750 ma similar to those of contemporaneous mafic dyke swarms within the north china craton which have been interpreted to be related either to the breakup of the supercontinent columbia or to the post collisional collapse of the trans north china orogen a progressive increase of end values of whole rock samples upwards in the stratigraphic sequence likely indicates an increase of juvenile material with time probably related to the contribution of mesoproterozoic mantle derived rocks 2007 elsevier ltd all rights reserved

trace elemental and sulfur lead isotopic variations in metamorphosed volcanogenic massive sulfide vms mineralization systems an example from the keketale pb zn ag deposit nw china abstract the effects of post vms volcanogenic massive sulfide deformation metamorphism on sulfide trace element and sulfur lead isotopic compositions remain unclear the greenschist to lower amphibolite facies metamorphosed keketale vms pb zn ag deposit located in the devonian maizi volcanic sedimentary basin in the chinese altay nw china provides an opportunity to resolve the abovementioned issue two mineralization stages are recognized at keketale including 1 primary banded massive and disseminated ores derived from sea floor hydrothermal mineralization and 2 ore remobilization as represented by intensively deformed ores and quartz polymetallic sulfide ore veins that crosscut the primary ores sulfide trace elements data suggest that stage ii pyrite and pyrrhotite have higher contents of cu zn ag sb and pb whereas contents of these elements are higher in stage i sphalerite and galena than their stage ii counterparts such elemental remobilization was probably caused by the rapid intragrain diffusion and subsequent fluid mediated liberation with trace elements re precipitated as particles within the same grain and nearby minerals respectively the 34scdt values in both stages show a trimodal distribution 25 9 to 22 7 17 0 to 10 6 and 0 6 to 2 1 sulfide mineral pairs formed during primary vms mineralization are not in sulfur isotopic equilibrium and only localized re equilibration occurs during deformation and metamorphism in addition the lead isotopic values of galena from remobilized sulfide veins overlap with those of the stage i galena and pyrite these data indicate that regional deformation and metamorphism of the keketale deposit can be approximated as a closed system in terms of sulfur lead isotopes whilst the presence of the anomalously low 34s values minimum 25 9 and the distinct lead isotopic ratios of sulfides from the calcite quartz veins argue for that in the late part of the metamorphic event some exotic lead and light sulfur were sourced from outside the ore field in situ 34s values of stage i sulfides vary widely 17 0 to 2 1 suggesting that the sulfur was originated from bacterial sulfate reduction bsr of marine sulfates with probably some magmatic input lead isotopes of the sulfides and mineralized meta sedimentary volcanic rocks display a linear distribution between the mantle and upper crust line in the 206pb 204pb vs 207pb 204pb diagram the lead source may be derived from both felsic volcanic rocks and mafic igneous rocks and or magmatic volatiles and the sulfur lead isotopes may result from a shallow level seawater circulating process an additional group of lead isotopic compositions of the meta volcanic rocks show elevated present day 206pb 204pb 207pb 204pb and 208pb 204pb values probably due to decay of th and u carried by deeply penetrative circulation 13 km of co2 f cl rich hydrothermal metamorphic fluids both syn vms shallow seawater and post vms deep metamorphic fluids circulation processes are critical for the metal concentration at keketale

zn and pb mobility during metamorphism of sedimentary rocks and potential implications for some base metal deposits comprehension of the genesis of pb zn ore systems is currently limited by a poor understanding of where these metals are sourced from our study of metal mobility during regional metamorphism in the mt lofty ranges south australia demonstrates that in staurolite absent siliciclastic metasedimentary rocks biotite contains 80 of the bulk rock zn as well as a considerable proportion of the total pb fluid flow through these metasedimentary rocks led to a continuous depletion of pb and zn on a mineral and bulk rock scale during prograde regional metamorphism we calculate that 80 of the bulk rock zn and 50 of the bulk rock pb were mobilised mainly through reactions involving biotite these reactions led to a calculated pb and zn loss of 2 7 and 27 mt respectively in the high grade metamorphic zone halogen contents of apatite and biotite and bulk rock zn isotope data provide evidence that cl rich metamorphic fluids were important for metal transport hence fluid flow accompanying prograde metamorphism of typical sedimentary rocks can mobilise base metals to the degree required to potentially supply significant pb zn ore systems

mesozoic contractional deformation in the middle of the asian tectonic collage the intraplate western ordos fold thrust belt china abstract intraplate deformation can occur at great distances from synchronous plate boundaries and is most likely the result of strain concentrations into weak zones these weak zones may be pre existing crustal heterogeneities such as faults thermally weakened zones due to magmatism and or the effects of a thick sedimentary cover or mechanical contrasts between adjacent crustal blocks intraplate deformation is not exclusively related to continent continent collision it can be the result of a change in subduction dynamics or the interaction of two convergent plate boundaries asia has many examples of active intraplate deformation that are thought to be related to the cenozoic indo asian collision although much attention is placed on active examples discerning controls on pre cenozoic asian intraplate deformation will lead to not only a better understanding of the processes involved in intraplate orogens but also the tectonic evolution of asia situated on either side of the yellow river along the western margin of the ordos plateau the intraplate western ordos fold thrust belt involves units as old as archean basement and as young as late jurassic the fold thrust belt is spectacularly exposed in two ranges the helan shan and the zhuozi shan cross sections drawn through the north trending fold thrust belt suggest 30 minimum shortening a paleocurrent reversal within the lower middle jurassic section is interpreted to mark the onset of contraction and mountain building a late jurassic synorogenic boulder conglomerate records the final deformation in the fold thrust belt synchronous with contraction and cutting across the fold thrust belt is an e w striking strike slip fault that displays right lateral drag and sub horizontal striae we interpret this fault as an accommodation structure in the thrust belt following e w contraction the thrust belt was dismembered by an n15 w trending left lateral strike slip fault the left lateral fault displaces the frontal portion of the thrust belt the zhuozi shan 62 km to the north relative to a more internal portion the helan shan we propose that the anomalous orientation and intraplate location of the western ordos fold thrust belt is a function of mechanical contrasts between a previously deformed area and a stable crustal block ordos to the east pre existing crustal weakness or anisotropy along the western margin of the ordos block is most likely related to either a late proterozoic early paleozoic aulacogen a triassic fault system or to both although its intraplate location and the complexities of mesozoic asian plate interactions make it difficult to relate deformation in the western ordos fold thrust belt to a specific contemporaneous plate boundary its n s trend may suggest a link with paleo pacific subduction along the eastern margin of asia