late carboniferous to permian sedimentation in inner mongolia china and tectonic relationships between north china and siberia a belt of deformed permo carboniferous sedimentary rocks in inner mongolia represents an orogenic zone between the north china and siberian blocks the belt apparently contains accretionary terranes thrust onto the margins of both blocks with scattered ophiolite blueschist suites indicating the consumption of oceanic crust at least slightly older than the age of deformation upper carboniferous to lower permian strata in central inner mongolia show both sedimentological and paleontological differences from middle and upper permian rocks in comparison with pre middle permian rocks younger permian strata 1 contain less laterally extensive limestone and more lensoidal carbonate in clastic sections 2 contain a higher percentage of coarse clastic material 3 grade upward from marine to terrestrial deposits 4 contain fauna indicating more restricted circulation particularly toward the western part of the belt and 5 contain fauna that are consistent with but do not require northward movement

diatreme breccias at the kelian gold mine kalimantan indonesia precursors to epithermal gold mineralization early miocene volcanism associated with a maar diatreme breccia complex preceded main stage epithermal gold mineralization at the kelian gold mine kalimantan indonesia prior to brecciation andesite intrusions 19 7 0 06 ma were emplaced into a package of felsic volcaniclastic rocks and overlying carbonaceous sand stones and mudstones and a weakly mineralized geothermal system was established intrusion of quartz phyric 19 8 0 1 ma and quartz feldspar phyric rhyolite 19 5 0 1 ma into the active geothermal system triggered widespread fragmentation and formation of the maar diatreme complex subsurface phreatomagmatic and phreatic explosions disrupted the preexisting hydrothermal system producing three composite diatreme breccia bodies the tepu runcing and burung breccias the diatremes consist of polymict breccias and sandstones that contain abundant carbonaceous matrix a distinctive facies association comprising coherent rhyohte jigsaw fit rhyolite breccia and matrix rich breccias that contain wispy to blocky juvenile rhyolite clasts define the root zones of the diatremes the surficial products of maar diatreme volcanic activity at kelian are preserved as large blocks of well stratified breccias they contain accretionary lapilli and were deposited by a combination of wet pyroclastic basesurge fallout and cosurge fallout processes evidence for syneruptive resedimentation of the pyroclastic deposits is preserved in poorly stratified breccia beds megablocks of phreatomagmatic base surge deposits were dropped down several hundred meters from the maar environment into the underlying diatremes volcanism in the kelian maar diatreme complex was dominated by a combination of phreatomagmatic and phreatic processes with subordinate hydraulic tectonic and dry magmatic fragmentation the carbonaceous matrix rich diatreme breccias acted as aquicludes during subsequent hydrothermal activity focusing fluid flow into the wall rocks adjacent to the diatremes where epithermal gold mineralization and hydrothermal brecciation occurred 2008 society of economic geologists inc

glacial northeast atlantic surface water pco2 productivity and deep water formation abstract the carbon isotopic composition of bound organic material within the crystal lattice of planktonic foraminiferal calcite is a valuable proxy for the isotopic composition of primary photosynthate in surface waters this proxy can be used to estimate pco2 in the surface waters of the northeast atlantic during the last glacial period if combined with data on the carbon isotopic composition of foraminiferal calcite our first estimates of surface water pco2 at the location of biogeochemical ocean flux studies core 5k 50 41 3 n 21 51 9 w indicate that this region was probably a more important sink for co2 during the glacial than during the holocene this increased sink could not have been caused by local high primary productivity because glacial primary productivity as estimated from benthic foraminiferal data was extremely low at 5k we thus conclude that the enhanced sink at these latitudes resulted from increased convection of surface water to intermediate or greater depths i e from the southward shift of an important centre of deep intermediate water formation as confirmed by computer simulation

gold mineralization in proterozoic black shales example from the haoyaoerhudong gold deposit northern margin of the north china craton abstract the haoyaoerhudong gold deposit in the northern margin of the north china craton ncc is a large tonnage lower grade deposit with a reserve of about 148 tons of gold gold mineralization is characterized by pyrite and pyrrhotite films and thin veins on the schistosity plane of the proterozoic black shales the orebodies strictly controlled by a near ew trending shear zone are stratabound within carbonaceous phyllite and andalusite garnet schist of the bilute formation hydrogen and oxygen isotopic data show that the ore forming fluid was derived from a magmatic source and mixed with meteoric water sulfur and carbon isotope data indicate that most of the sulfur and carbon came from the black shale strata well defined biotite ar ar plateau age and inverse isochron age show that the deposit formed at ca 270ma which suggests a probable link between hercynian magmatism and gold mineralization studies on regional geology ore geology isotope geochemistry and ore forming age substantiate a complex evolutionary history of the deposit the proterozoic black shales rich in gold sulfur and organic matter which were deposited in the proterozoic continental margin rifts comprised the source bed for gold mineralization ew ene structures products of palaeozoic orogenic process provided pathways and mineralization space for ore forming fluids hercynian tectono magmatism and subsequent hydrothermal events remobilized gold and drove the ore forming fluids to dilatational fracture zones related to postcollisional magmatic hydrothermal events the haoyaoerhudong gold deposit is considered as a special type of orogenic gold deposit formed in the compression extension transition stage

re os ages for the erdenet and tsagaan suvarga porphyry cu mo deposits mongolia and tectonic implications the erdenet and tsagaan suvarga deposits are the two largest known porphyry cu mo deposits in mongolia replicate re os analyses of molybdenite from these deposits yield ages of 240 7 0 8 and 240 4 0 8 ma for erdenet and 370 1 1 2 and 370 6 1 2 ma for tsagaan suvarga 2 errors the re os age of erdenet is significantly older and that of tsagaan suvarga is slightly older than published 40ar 39ar ages for sericite associated with mineralization in these deposits 207 4 5 0 and 364 9 7 0 ma respectively these re os results suggest that in the hydrothermal environment 40ar 39ar ages may be partly to significantly reset whereas re os ages record and maintain the age of primary mineralization events these re os ages indicate that porphyry mineralization at erdenet and tsagaan suvarga are related to porphyritic intrusions representing the youngest event during regional magmatism in northern and southern mongolia respectively the re os age of erdenet marks the final stage of arc magmatism in northern mongolia followed by late permian collision between the mongolian north china and siberian blocks the re os age of tsagaan suvarga indicates that devonian arc magmatism in southern mongolia was active at the present latitude of 44 n at least until 370 ma

textural control on gold distribution in as free pyrite from the dongping huangtuliang and hougou gold deposits north china craton hebei province china article i nfo pyrite from the dongping huangtuliang and hougou gold deposits hebei province china was investigated using a combination of ore microscopy including back scattered imaging and in situ laser ablation inductively coupled plasma mass spectroscopy la icp ms a range of elements including au te ag pb bi cu co ni and as was analyzed with the aim to constrain the textural controls and influence of superimposed deformation on the distribution of invisible gold in as free pyrite thedatasetshowsexcellentcorrespondence betweenmeasuredhighgoldvaluesandthreekeytexturalcriteria i areasofclusteredtellurideinclusions especiallyindongping ii microshearingandfracturing brecciation dongping and huangtuliang and iii pyrite recrystallization huangtuliang invisible gold is only at trace levels in the hougou and gold bearing telluride minerals are not observed this is considered to result from larger scale remobilization of gold during advanced brecciation and recrystallization of pyrite pyrite grains containing clustered inclusions have by far the highest gold concentrations up to 1 wt with consistent values of thousands of ppm au interpretation of textures and la icp ms data infers that in these areas the distribution of telluride inclusions extends pervasively from micron to nanoscale i e as fields of nanoparticles local employment of coupled dissolution reprecipitation reaction between pyrite and fluids driving the k metasomatic alteration dated at 150 ma is invoked to explain such patterns syn deformational grain scale mobilization of gold and other elements took place leading to a portion of the gold being recrystallized within fractures and microshears the deformational event leads to gold enrichment in the huangtuliang pyrite where brittle fracturing brecciation has been followed by a resorption and recrystallization in the latter case foam textured pyrites again without as can contain up to hundreds of ppm gold theinterpreted sequenceof pyritepost depositional eventsis inaccordancewith the protracted magmaticevolution of the area starting with variscan alkaline intrusions 390 ma and reactivated during the yanshanian orogeny 150 ma thestudyshows i thatas freepyritecanreadilycontainsignificantamountsofinvisiblegold bothasnanoparticles

great jurassic thrust sheets in beishan north mountains gobi areas of china and southern mongolia abstract jurassic thrust sheets with minimum displacements of 120 180 km have been discovered within the hercynian indosinian orogenic belt of the beishan of china and south gobi area the thrusts strike e w extend over 1200 km in length and carried meso proterozoic massive dolomitic limestones over strata ranging from neoproterozoic cryogenian and terminal proterozoic to lower middle jurassic slip linear plots based on kinematic indicators such as slickenlines and groove lineations fiber lineations and drag folds adjacent to the fault surface vergence of folds and imbricated thrusts in the upper plate indicate northward movement in the beishan area to the west and southward movement in the south gobi area to the east the two major thrust faults the beishan thrust and south gobi thrust are presumably separated by a major tear fault the ruo shui fault the major thrust faults were later deformed into a series of e w antiforms and synforms and the sheets are separated due to erosion into a number of klippen mainly located on synforms of the major faults the yagan metamorphic core complex which is a result of an extensional event that postdates the thrust event yields an 40 ar 39 ar plateau age of 155 1 10 ma and rb sr isochron age of 153 6 2 ma the thrust sheets formed during the late middle jurassic long after the closure of any oceans in the study area previously reported for this region and are ascribed to a phase of intracontinental deformation the closing of the jurassic tethys or retroarc deformation behind an active continental margin at the southern edge of asia prior to the tethyan collision or and the closing of mongolo okhotsk oceans might be responsible for this event

magmatic hydrothermal activity in the shuteen area south mongolia the shuteen area is located in the gurvansaikhan island arc terrane of south mongolia it contains a large domain of intensely developed silicic and advanced argillic alteration that has strongly affected the adakitic volcanoplutonic shuteen complex the local occurrence of low grade copper mineralization within porphyritic intrusive rocks is indicative of porphyry style mineralization hydrothermal quartz veins host gold mineralization locally the results of scanning electron microscope cathodoluminescence imaging and fluid inclusion microthermometry indicate that the veins and altered rocks at shuteen were produced by multiple hydrothermal events the occurrence of co2 inclusions in quartz from granitoids and the 34s values obtained for sulfide and sulfate within the hydrothermal breccias provide evidence of the involvement of magmatically derived fluids in the early stages of the shuteen magmatic hydrothermal system inferred to be sourced from a porphyry style intrusive center late stage fluids produced abundant barren quartz veins and clay alteration assemblages the weak mineralization and widespread alteration in the shuteen complex are typical of lithocaps found in high level porphyry copper gold molybdenum and high sulfidation epithermal districts the presentday erosion level at shuteen is relatively shallow implying that economic porphyry style mineralization may exist at depth within or beneath the shuteen lithocap

bulk particulate organic carbon in the east china sea tidal influence and bottom transport abstract five oceanographic surveys were carried out in the east china sea ecs and yellow sea from 1999 to 2003 in all seven different sections were surveyed but one section the pn section was observed on every cruise two time series stations were also surveyed one located at the changjiang river mouth the other over the continental shelf in the pn section we identified biogeochemical characteristics for waters close to the changjiang estuary and in the kuroshio waters kw respectively resuspension is a strong feature near bottom over the ecs continental shelf with suspended matter values 13 times higher than that for the surface a model of particulate organic carbon poc dynamics based on a rectangle equation reveals that poc concentration close to the changjiang estuary varies with a semidiurnal period of 13 h coinciding with the tidal period the upper limit for poc residence times in the seasons we covered over the shelf are estimated to be on the order of weeks and generally increase seaward from near the changjiang estuary to the kw short poc residence times suggest that poc in the ecs is rapidly exported from euphotic waters a nepheloid layer observed as elevated suspended matter in near the bottom of the water column is important in particle transfer over the shelf especially in winter when the residual current flows mainly eastward cross shelf transport of poc via the nepheloid layer is estimated to be 0 22 1012 g yr 1 comparison with other work indicates that poc transport is 2 of the changjiang poc input

synthetic fluid inclusions in natural quartz iii determination of phase equilibrium properties in the system h2o nacl to 1000 c and 1500 bars phase equilibria in the system h2o nacl have been determined to 1000 c and 1500 bars using synthetic fluid inclusions formed by healing fractures in inclusion free brazilian quartz in the presence of the two coexisting immiscible h2o nacl fluids at various temperatures and pressures petrographic and microthermometric analyses indicate that the inclusions trapped one or the other of the two fluids present or mixtures of the two salinities of the two coexisting phases were obtained from heating and freezing studies on those inclusions which trapped only a single homogeneous fluid phase results of the present study are consistent with previously published data on the h2o nacl system at lower temperatures and pressures and indicate that the two phase field extends well into the p t range of most shallow magmatic hydrothermal activity as a consequence chloride brines exsolved from many epizonal plutons during the process of second boiling should immediately separate into a high salinity liquid phase and a lower salinity vapor phase and produce coexisting halite bearing and vapor rich fluid inclusions this observation is consistent with results of numerous fluid inclusion studies of ore deposits associated with shallow intrusions particularly the porphyry copper deposits in which halite bearing and coexisting vapor rich inclusions are commonly associated with the earliest stages of magmatic hydrothermal activity

new 40 ar 39 ar age data and implications for porphyry copper deposits of mongolia porphyry copper deposits and related rocks of mongolia have not been generally well dated a few papers report radiometric ages but do not provide raw data or references and most papers that discuss ore deposits report the age at the period level only as part of a larger study examining several deposits and prospects in mongolia we present new 40 ar 39 ar data for three localities porphyry copper deposits and host rocks at erdenet and bayan uul 250 km northwest and 180 km southwest of ulaan baatar respectively yield early jurassic 207 4 or 2 5 ma and late triassic 220 223 ma ages samples from tsagaan suvarga in southern mongolia yield a devonian 364 9 or 3 5 ma age from the ore zone and a carboniferous 313 0 or 2 9 ma age from a porphyry dike that crosscuts the hydrothermal alteration these ages help constrain the timing of metallogenic and tectonic events the devonian and carboniferous ages record part of the development of magmatic arcs in southern mongolia and the late triassic ages may be evidence for the closing of the mongol okhotsk ocean

east asian gold deciphering the anomaly of phanerozoic gold in precambrian cratons early cretaceous orogenic gold deposits in eastern asia are globally unique in that large phanerozoic lode gold deposits occur in archean paleoproterozoic cratons in the northern pacific region ca 125 ma orogenic gold deposits in the north china yangzte and siberian craton margins as well as in young terranes in california may ultimately relate to the giant cretaceous mantle plume in the southern pacific basin and the relatively rapid tectonic consequences along both continental margins from resulting pacific plate reconfigurations in eastern asia such consequences include reactivation of and fluid flow along major fault systems with fluid focusing into simultaneously forming isolated core complexes of uncertain genesis deposition of gold ores in previously devolatilized high grade precambrian metamorphic rocks requires an exotic source of ore fluid most likely subducted mesozoic oceanic crust and or overlying sediment an implication is that phanerozoic metamorphic core complexes in other destabilized craton margins could host large gold resources

investigations on the time series partitioning of 210pb 207bi and 210po between marine particles and solution under different salinity and ph conditions abstract the long lived progeny of radon 222 lead 210 210pb polonium 210 210po and bismuth 210 210bi serve as a tool in the study of marine biogeochemical processes here we report our investigations on the partitioning of 210pb 210po and 210bi 207bi between seawater and solids twelve commonly occurring mineral particles under different values of ph salinity and contact time the kd values of 210pb and 207bi for mno2 varied widely between the synthetic and natural minerals and thus the suitability of using synthetic material for their partitioning studies in marine system needs to be re assessed the kd values of 210pb in clay minerals were found to be in the order smectite illite kaolinite the sorption efficiencies the particulate activity divided by the sum of particulate and dissolved activity of 210pb 207bi and 210po on illite were above 81 when the contact time was 2 h these radionuclides were more soluble when ph was 5 but show more particle reactive nature for ph of 6 to 8 the fractionation factor between 210po and 210pb fpo pb varied with salinity for different mineral components while the fbi pb was less affected by mineral components salinity and ph the in situ experimental results showed that the fbi pb increased with increase in chl a concentration considering the much shorter half life of 210bi 5 0 d and the high kd values established in this study we propose that 210bi 210pb activity ratio could potentially be used to estimate the particle export from phytoplankton bloom on time scale much shorter than 234th or 210po

progressive 18o depletion during co2 separation from a carbon dioxide rich hydrothermal fluid evidence from the grey river tungsten deposit newfoundland oxygen isotope data for the grey river tungsten prospect newfoundland canada indicate a progressive depletion in 18ofluid during mineralization early veins with pegmatitic affinities were deposited at 470 c and pressures greater than 1 kbar 100 mpa from a fluid with a 18o composition of 7 4 presumed to be of magmatic origin successive vein deposition at progressively lower temperatures and pressures culminated in the precipitation of wolframite bearing veins at a temperature of 300 c and pressures of 150 320 bar 15 32 mpa from a low salinity fluid with a 18o composition in the range 3 2 1 6 low values of 18o and dfluid are recorded in many vein tungsten deposits and are normally interpreted as reflecting mixing of isotopically light meteoric fluids or formation brines with magmatic fluids however fluid inclusion evidence for the grey river mineralization indicates that a 40 mol co2 loss occurred by immiscibility and retrograde boiling of the hydrothermal fluid between 420 and 3

geology age and fluid inclusions of the tanjianshan gold deposit western china two orogenies and two gold mineralizing events abstract the tanjianshan gold deposit located at the tectonic boundary between the oulongbuluk block ob and north qaidam orogenic belt nqo on the northern margin of the qaidam basin nmqb western china underwent early palaeozoic and late palaeozoic to early mesozoic multiple accretions and collisional orogenies it is a typical example of a deposit resulting from two gold mineralizing events related to two collisional orogenies two phases of ore controlling nw trending shear zones have been identified in the deposit dextral brittle ductile shear deformation during the late early palaeozoic collisional orogeny and sinistral strike slip shear deformation during the late palaeozoic early mesozoic orogeny n s trending folds developed in the nw trending shear zone and resulting from sinistral strike slip motion of the shear zone are nose shaped in plan view and control most gold orebodies in the deposit the major gold orebodies trend nne and are concentrated in the hinge zones of these n s trending folds occurring along the fault zones parallel to both limbs of these folds these gold orebodies composed of altered mylonite schist type ore and altered dyke type gold ore occur as saddle shaped bodies beds and lenses mainly within altered carbonaceous quartz sericite mylonite schist of a highly strained zone and locally in altered igneous dykes of the highly strained zone alteration related to gold mineralization includes silicification pyritization and sericitization a progressive increase of sio 2 s au ag as and sb from unaltered or weakly altered rocks through altered rocks to gold ore is consistent with progressively enhanced silicification and pyritization suggesting the flow of mineralizing fluids along the nw trending shear zone and n s trending folds native gold and electrum are present as very fine grains mainly enclosed in disseminated pyrite or occurring in fractures within the pyrite three generations of pyrite and associated hydrothermal quartz are observed the fabrics of gold ore generations of auriferous pyrite field relationship between multiple ore controlling structures and gold mineralization and the bimodal distribution of ore elements in the gold district suggest the occurrence of two main hydrothermal and mineralizing events the first event marked by a mineral assemblage of first generation quartz qz 1 and first generation pyrite py 1 was restricted to the carbonaceous mylonite schist within the nw trending shear zone sericite from the ore controlling nw trending shear zone gave a 40 ar 39 ar age of 409 4 ma which is consistent with the age of the regional late early palaeozoic collisional orogeny in the region the second event marked by a mineral assemblage of second generation quartz qz 2 and second generation pyrite py 2 occurred within the n s trending folds and was related to late palaeozoic orogeny in the region we have obtained a k ar age of 268 9 4 3 ma and an rb sr isochron age of 288 9 7 ma for hydrothermal minerals from gold ores the latter age is closer to the age of this event of gold mineralization mineralization of this event was superimposed onto gold mineralization of the early phase and formed most of the gold orebodies in the deposit the distribution and microthermometric data of fluid inclusions indicate that late early palaeozoic ore fluids belong to the h 2 o co 2 ch 4 nacl fluid system formed at 186 to 250 c whereas late palaeozoic fluids comprise two kinds of immiscible fluid a h 2 o nacl fluid with salinity of 1 6 to 10 8 wt nacl equiv which probably formed at temperatures of 381 to 449 c and and h 2 o co 2 nacl fluids with salinities of 1 8 to 7 9 wt nacl equiv which are genetically the product of evolution of former immiscible magmatic fluids and which formed at temperatures of 274 to 410 c

comparison of pelagic and nepheloid layer marine snow implications for carbon cycling abstract marine snow from upper and mid water i e pelagic depths on the california margin is texturally and compositionally different from that traveling in the nepheloid layer transmission electron microscopy shows that pelagic marine snow consists primarily of bioclasts e g diatom frustules foram tests organic matter and microbes these components are entrained as discrete particles or small aggregates 10 m in diameter in a loose network of exocellular muco polysaccharide material clays are infrequent but when present are constituents of comparatively compact organic rich microaggregates microbes are abundant and appear to decrease in number with increasing water depth in contrast marine snow aggregates collected from just above the sea floor in the nepheloid layer are assemblages of clay particles clay flocs and relatively dense clay organic rich microaggregates in an exocellular organic matrix bioclasts and microorganisms occur only rarely the prevalence of clay organic rich aggregates in the nepheloid layer suggests that prior to final deposition and burial marine snow from the pelagic zone is subject to disaggregation and recombination with terrigenous detrital material near or at the sea floor results have significant implications for the accumulation and burial rates of organic carbon on continental margins and the aging and bioavailability of sedimentary organic matter samples examined were collected offshore of northern and central california

genesis of giant early proterozoic magnesite and related talc deposits in the mafeng area liaoning province ne china abstract this study aims to understand the origin of giant magnesite and talc deposits in the liaohe group liaoning province ne china magnesite stromatolites and the composition of fluid inclusions suggest that magnesite or high mg calcite precipitated directly from strongly restricted seawater pools with meteoric influx a primary evaporitic origin is also indicated for parts of the investigated dolomites by comparably heavy 18o values later intense metasomatic activity led to the formation of a magnesite dolomite succession with irregular contacts and a lighter isotopic signature of oxygen a slight shift in 18o to more positive values was observed for talc hosting magnesite which can be explained by the incorporation of isotopically light oxygen into talc this highlights that the hydrothermal processes that led to talc formation influenced the hosting carbonates as well which is also documented by a tendency to smaller crystal sizes a higher whiteness and lower trace element concentrations in samples from locations nearby large talc bodies although 13c is suggested to be less sensitive to hydrothermal activity comparably light 13c values were determined for magnesite sinters as well as for remobilized magnesites in general the 13c signature of the investigated magnesites is lighter than expected for proterozoic carbonates a single stage generation of the giant talc deposit in the study area is suggested based on elemental and isotopic data later deformation led to a iso chemical re location of talc at least once during this process irregularly distributed cloudy massive talc bodies acted as weak zones and were incorporated into shear bands up to several meters in thickness which form the actually present structurally controlled deposit the original ore type is preserved only in areas with minor deformation lamprophyre dykes prove jurassic volcanism and are clearly younger than the main phase of talc generation a younger post jurassic intense tectonic event is indicated by strongly tectonized dyke material that is re worked into strike slip faults and shows siliceous contact zones to the surrounding magnesite these faults occasionally cross cut the older deposit forming talc shear bands indicating that the event that led to the deformation of lamprophyre dykes was younger than the main phase of talc re location however this younger event did not lead to a second phase of major talc generation or affect the quality of the initial deposit to a large extent

multiple isotope composition s pb h o he and ar and genetic implications for gold deposits in the jiapigou gold belt northeast china the jiapigou gold belt 150 t au one of the most important gold producing districts in china is located at the northeastern margin of the north china craton it is composed of 17 gold deposits with an average grade around 10 g t au the deposits are hosted in archean gneiss and ttg rocks and are all in shear zones or fractures of varying orientations and magnitudes the 34s values of sulfide from ores are mainly between 2 7 and 10 the pb isotope characteristics of ore sulfides are different from those of the archean metamorphic rocks and mesozoic granites and dikes and indicate that they have different lead sources the sulfur and lead isotope compositions imply that the ore forming materials might originate from multiple mainly deep sources fluid inclusions in pyrite have 3he 4he ratios of 0 6 to 2 5 ra whereas their 40ar 36ar ratios range from 1 444 to 9 805 indicating a dominantly mantle fluid with a negligible crustal component 18o values calculated from hydrothermal quartz are between 0 2 and 5 9 and d values of the fluids in the fluid inclusions in quartz are from 70 to 96 these ranges suggest dominantly magmatic water with a minor meteoric component the noble gas isotopic data along with the stable isotopic data suggest that the ore forming fluids have a dominantly mantle source with minor crustal addition

the source of ore fluids and solutes in archaean lode gold deposits of western australia abstract the ore fluids which produced archaean lode gold deposits in sub amphibolite facies rocks of the yilgarn block western australia are characteristically low to moderate salinity h 2 o co 2 ch 4 fluids wall rock alteration and ore deposition were from a generally reducing near neutral fluid at 200 350 c and 1 3 kbar although more oxidising fluids produced some assemblages in the giant golden mile deposit gold was transported as reduced sulphur complexes the ore fluid composition and stable and radiogenic isotope data indicate multiple sources for the fluid and solute deep plumbing systems are invoked with the fluids being either metamorphic fluids that derived solutes from the lower and upper crusts or fluids exsolved from deep seated granitoids formed by anatexis of such crust

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

granites of the southern mongolia carboniferous arc new geochronological and geochemical constraints the crust in southern mongolia is part of the central asian orogenic belt a vast accretionary orogen that records the opening and closure of the palaeo asian ocean in the late proterozoic to palaeozoic the crustal evolution of the region is revealed in basement inliers that also contain intrusion related porphyry ore bodies that are important mineral exploration targets the saykhandulaan inlier in southeast mongolia is a devonian carboniferous segment of island arc crust which is dominantly composed of extrusive and sedimentary lithologies but which also contains the oyut ulaan i type quartz monzonite intrusion a u pb zircon age for the oyut ulaan monzonite indicates emplacement at 330 0 0 5 ma to the east of the saykhandulaan inlier intrusive complexes dominate the neighbouring mandakh inlier new ages are presented for four of these plutons the bronze fox granodiorite 333 6 0 6 ma the narin hudag monzonite 333 2 0 6 ma the shuteen quartz monzonite 325 5 1 0 ma and the north mandakh granite 292 3 0 5 the intrusive bodies of the saykhandulaan and mandakh inliers have two distinct geochronological and geochemical associations 1 mid carboniferous i type monzonites that constitute the most easterly intrusive expression of the southern mongolia carboniferous arc and 2 early permian a type and peralkaline granites that represent a post orogenic phase of voluminous granite emplacement both groups are significantly younger than the nearby oyu tolgoi and tsagaan suvarga cu porphyry ore bodies which have previously been dated as early and late devonian respectively the new data presented here provide constraints on the timing of the transition from island arc magmatism to post collisional extension related magmatism in the region and possible controls on fertile and infertile granitoid intrusions with respect to cu au mineralisation

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

scanning electron microscope cathodoluminescence analysis of quartz reveals complex growth histories in veins from the butte porphyry copper deposit montana scanning electron microscope cathodoluminescence sem cl analysis of quartz reveals textures that cannot be observed using optical microscopy or backscattered electrons these cryptic textures yield insight into timing and physical conditions of quartz growth especially in environments with multiple quartz precipitation events hydrothermal quartz from quartz sulfide veins in the porphyry copper deposit in butte montana was analyzed by sem cl revealing the following textures euhedral growth zones wide nonluminescing bands that cut across multiple quartz grains rounded luminescent quartz grain cores with euhedral overgrowths nonluminescing splatters of quartz connected by networks of cobweb like nonluminescing quartz in otherwise luminescent quartz concentric growth zones and wide nonluminescent grain boundaries these textures indicate that many veins have undergone fracturing dilation growth of quartz into fluid filled space quartz dissolution and recrystallization of quartz precipitation and dissolution textures indicate that early quartz molybdenite veins formed as a result of pressure fluctuations between lithostatic and hydrostatic at high temperatures and later pyrite quartz veins formed near hydrostatic pressure in response to temperature decrease through and beyond the field of retrograde quartz solubility

the early cretaceous yangzhaiyu lode gold deposit north china craton a link between craton reactivation and gold veining the yangzhaiyu gold deposit is one of numerous lode gold deposits in the xiaoqinling district southern margin of the north china craton gold mineralization is hosted in neoarchean to early paleoproterozoic amphibolite facies metamorphic rocks and consists of auriferous quartz veins and subordinate disseminated ores in the vein proximal alteration zone ore related hydrothermal alteration is dominated by sericite quartz sulfide assemblages close to gold veins and biotite quartz pyrite chlorite epidote alteration generally distal from mineralization pyrite is the predominant sulfide mineral locally coexisting with minor amounts of chalcopyrite sphalerite and galena gold occurs mostly as free gold enclosed in or filling microfractures of pyrite and quartz and is also present in equilibrium with au bearing tellurides mainly petzite and calaverite coexisting with hessite tellurobismuthite and altaite fluid inclusion studies suggest that gold veins were deposited at intermediate temperatures 175 313 c from aqueous or aqueous carbonic fluids with moderate salinity 5 14 wt nacl equiv 34s values of sulfide minerals range mainly from 2 0 to 4 4 whereas auriferous quartz vein samples have 18o values of 12 4 to 9 6 with calculated 18oh2o values of 6 0 to 3 2 gold related pyrite grains yield elevated 3he 4he ratios 1 51 0 32 ra relative to crustal reservoirs and mantle like 20ne 22ne and 21ne 22ne ratios 9 90 9 68 and 0 029 respectively the stable and noble gas isotopes thus suggest deep seated most likely magmatic and mantle derived sources for the ore fluids sulfur and by inference other components in the ore system 40ar 39ar dating of ore related sericite and biotite separates indicates two episodes of gold genesis at 134 5 to 132 3 and 124 3 to 123 7 ma the mineralization ages overlap zircon u pb ages of 141 0 1 6 to 125 8 1 4 ma 2 for the wenyu and niangniangshan monzogranite plutons and a number of mafic to intermediate dikes intruding these plutons all being proximal to the yangzhaiyu gold deposit the synchronism of gold genesis and magmatism provides additional weights of evidence for a magmatic derivation of ore fluids and sulfur the geochronologic data also suggest that gold veining took place billions of years after the stabilization of the north china craton and associated metamorphism in the late archean to early paleoproterozoic this contrasts sharply to lode gold deposits in other precambrian cratons that formed predominantly in late archean to paleoproterozoic temporarily and genetically related to regional high grade metamorphism and compressional or transpressional tectonism available data have demonstrated that the north china craton was reactivated in the late mesozoic as marked by voluminous igneous rocks faulted basin formation high crustal heat flow and widespread metamorphic core complexes in the eastern part of the craton it is thus suggested that the yangzhaiyu gold deposit together with other deposits of similar ages in the xiaoqinling district were products of this craton reactivation event lithospheric extension and extensive magmatism related to the craton reactivation may have provided sufficient heat energy fluid and sulfur required for the formation of the gold deposits

intensity of quartz cathodoluminescence and trace element content in quartz from the porphyry copper deposit at butte montana textures of hydrothermal quartz revealed by cathodoluminescence using a scanning electron microscope sem cl refl ect the physical and chemical environment of quartz formation variations in intensity of sem cl can be used to distinguish among quartz from superimposed mineralization events in a single vein in this study we present a technique to quantify the cathodoluminescent intensity of quartz within individual and among multiple samples to relate luminescence intensity to specific mineralizing events this technique has been applied to plutonic quartz and three generations of hydrothermal veins at the porphyry copper deposit in butte montana analyzed veins include early quartz molybdenite veins with potassic alteration pyrite quartz veins with sericitic alteration and main stage veins with intense sericitic alteration cl intensity of quartz is diagnostic of each mineralizing event and can be used to fingerprint quartz and its fluid inclusions isotopes trace elements etc from specific mineralizing episodes furthermore cl intensity increases proportional to temperature of quartz formation such that plutonic quartz from the butte quartz monzonite bqm that crystallized at temperatures near 750 c luminesces with the highest intensity whereas quartz that precipitated at 250 c in main stage veins luminesces with the least intensity trace element analyses via electron microprobe and laser ablation icp ms indicate that plutonic quartz and each generation of hydrothermal quartz from butte is dominated by characteristic trace amounts of al p ti and fe thus in addition to cl intensity each generation of quartz can be distinguished based on its unique trace element content aluminum is generally the most abundant element in all generations of quartz typically between 50 and 200 ppm but low temperature main stage quartz containing 400 to 3600 ppm al is enriched by an order of magnitude relative to all other quartz generations phosphorous is present in abundances between 25 and 75 ppm and p concentrations in quartz show little variation among quartz generations iron is the least abundant of these elements in most quartz types and is slightly enriched in cl dark quartz in pyrite quartz veins with sericitic alteration titanium is directly correlated with both temperature of quartz precipitation and intensity of quartz luminescence such that bqm quartz contains hundreds of ppm ti whereas main stage quartz contains less than 10 ppm ti our results suggest that ti concentration in quartz is controlled by temperature of quartz precipitation and that increased ti concentrations in quartz may be responsible for increased cl intensities

timing of collision of the north and south china blocks controversy and reconciliation the qinling orogen was formed by the joining of the north and south china blocks but the timing of their integration has been debated for more than a decade the controversies obviously stem from different approaches to reconstruction of the integration history two contrasting lines of evidence yield two different ages for collision of the north and south china blocks middle paleozoic and late triassic the shangdan suture within the qinling was regarded in previous studies as the trace along which the north and south china blocks collided our studies however demonstrate that there are two sutures within the qinling the well documented shangdan suture and the newly discovered mianlue suture we show in this paper that the late proterozoic to early mesozoic evolution of the qinling involved interactions between the north china block the north and south qinling orogens and the south china block the middle paleozoic collision along the shangdan suture as constrained by some evidence accreted only the south qinling orogen to the southern part i e the north qinling of the north china block contemporaneous rifting of the south china block and subsequent drifting separated the south qinling from the south china block during the middle to late paleozoic the separation of the south from the north china blocks is supported by other evidence in particular geomagnetic data evidently it was the late triassic collision of the south china block with the south qinling orogen along the mianlue suture that led to final integration of the north and south china blocks

new constraints on the genesis and geodynamic setting of the wulong gold deposit liaodong peninsula northeast china evidence from geology geochemistry fluid inclusions and c h o s pb isotopes the wulong lode gold deposit is located in the liaoning province northeast part of north china craton gold ore bodies are mainly hosted in the late jurassic granite and structurally controlled by

characteristics of hydrothermal chlorite from the niujuan ag au pb zn deposit in the north margin of ncc and implications for exploration tools for ore deposits abstract the niujuan ag au pb zn deposit is located in the northern hebei province of north china which is hosted by permian coarse grained granite the orebodies are controlled by a ne striking fault chloritization is the most extensive alteration with increasing alteration intensity from the distal to proximal end of the orebody chlorite and biotite from twenty one altered samples from different depths of four drill holes were analyzed using electron microprobe empa and laser ablation inductively coupled plasma mass spectrometry la icpms empirical geothermometry shows that chlorite formed at 206 340 c through comparing with compositions of unaltered biotite two biotite converted to one chlorite 2bt 1chl is the main chloritization mechanism in weakly and moderately altered granites during the hydrothermal alteration in the niujuan deposit during the alteration hydrothermal fluid mainly brought in fe sr th pb and co2 and took out mg ti si f k li zn sc ga co from the biotite which was accompanied by the formation of quartz rutile calcite and fluorite during the chloritization chlorite in quartz chlorite veins was precipitated directly from the hydrothermal fluids veined chlorite in intensely altered granites formed by the dissolution transport precipitation mechanism under the high fluid rock conditions veined chlorite has nearly the same compositions as chlorite in quartz chlorite veins according to the compositions of chlorite from intensely altered granites and quartz chlorite veins we infer that the hydrothermal fluid had low hfses and transition elements such as ti ga sc and v and low fo2 from weak to intense chloritization granites feo sr th and pb contents of chlorite increase while mgo tio2 li zn sc ga v co and nb contents decrease the composition variations of chlorite are controlled by the composition of biotite the compositions of fluids and the intensity of fluid rock interaction during alteration this indicates that the chemical variations of chlorite could be as a tool for mineral exploration in the moderate low temperature ag au pb zn deposit comparison with chlorite of different genesis shows that compositions of chlorite mainly differ in mg fe and aliv which are mainly controlled by the composition of host rocks and the formation temperature

relationships between grain size and organic carbon 14c heterogeneity in continental margin sediments abstract the deposition and long term burial of sedimentary organic matter om on continental margins comprises a fundamental component of the global carbon cycle a key unknown in interpretation of carbon isotope records of sedimentary om is the extent to which om accumulating in continental shelf and slope sediments is influenced by dispersal and redistribution processes here we present results from an extensive survey of organic carbon oc characteristics of grain size fractions ranging from 14 c values defined here as h 14 to argue that the hydrodynamic processes amplify overall 14c heterogeneity within corresponding bulk sediment samples the magnitude and footprint of this heterogeneity carries implications for our understanding of carbon cycling in shallow marginal seas

space time patterns of magmatism along the tethysides a preliminary study five maps showing spatio temporal evolution of magmatism along the tethysides for the following time intervals late carboniferous and permian 320 248 ma triassic and early jurassic 247 188 ma

hydrothermal breccias and veins at the kelian gold mine kalimantan indonesia genesis of a large epithermal gold deposit mineralized hydrothermal breccias and veins formed during and after the waning stages of maar diatreme related volcanic activity at kelian kalimantan indonesia subsurface phreatic explosions occurred around the margins of the diatreme breccia complex focusing high temperature fluid flow and generating several large mineralized hydrothermal breccia bodies tectonic phreatomagmatic and hydraulic processes also contributed to hydrothermal brecciation explosive phreatic brecciation was followed by in situ hydraulic brecciation and then by minor veining as the system returned to steady state geothermal conditions brecciation and mineralization mostly occurred 400 to 700 m below the paleowater table the kelian deposit contained more than 240 t au prior to mining precious metals occur with sulfide minerals as disseminations in sheeted and conjugate veins and as breccia cement there is a progression from pyrite dominated stage 1 to base metal sulfide dominated stages 2 and 3 to sulfosalt dominated hydrothermal breccias and veins stage 4 in terms of gangue minerals the system evolved from illite quartz to adularia and or quartz and or illite dominated and then carbonate dominated boiling produced abundant bladed carbonate during stages 3 and 4 overall carbonate and base metal sulfide minerals are abundant whereas quartz is comparatively minor free gold is most abundant in stages 3 and 4 but also occurs in stages 1 and 2 native gold occurs principally as inclusions in pyrite sphalerite galena arsenopyrite quartz bladed carbonate and sulfosalts hydrothermal alteration assemblages are zoned about contacts faults breccias and veins and consist of secondary quartz illite pyrite chlorite and various carbonate minerals kelian preserves evidence of a magmatic component to the mineralizing fluids fluid inclusion analyses revealed the presence of saline fluid inclusions in particular from stage 3 isothermal mixing of low salinity 0 to 2 wt nacl equiv with moderate salinity fluids 10 to 25 wt nacl equiv rather than boiling resulted in the range of salinity and homogenization temperatures of fluid inclusions in sphalerite carbonate and quartz deposited during stage 3 salinities of 4 to 6 wt percent nacl equiv for inclusions in adularia and quartz from stages 2 and 4 and in rhodochrosite and proustite pyrargyrite from stage 4 may also reflect a component of mixing of low salinity water with a moderately saline fluid sulfur isotope values from kelian sulfides 34s 1 4 to 5 5 per mil are consistent with a magmatic sulfur source both boiling and fluid mixing contributed to high grade au mineralization at kelian rapid formation hundreds of years or less is inferred for the individual hydrothermal breccia bodies 2008 society of economic geologists inc

vertical distribution of isoprenoid gdgts in suspended particles from the east china sea shelf and implications for sedimentary tex86h records abstract the t e x 86 h or tex86 paleothermometer has been widely applied for reconstructing water temperature in marine settings particularly in marginal seas which often archive paleoclimate records with high temporal resolution yet debate remains regarding the water depth at which the t e x 86 h signal is imparted in these settings in this study east china sea ecs surface sediments and suspended particulate matter spm from different water depths 0 60 m were analyzed for lipid biomarkers to better constrain the depth to which the sedimentary t e x 86 h signal corresponds our data showed divergent vertical distributions between archaeal lipids and phytoplankton lipids the maximum concentration of core lipid isoprenoid glycerol dialkyl glycerol tetraethers core igdgts appeared in bottom waters 2 5 m above the sea floor at all sites whereas phytoplankton lipids showed highest abundance in surface waters 0 m consistent with the maximum core igdgts concentration in bottom waters the best correlation was observed between spm t e x 86 h values and 2 4 weeks averaged water temperatures from the bottom waters moreover the spm core igdgts content was higher in bottom waters than in surface sediments implying that in situ production rather than sediment resuspension leads to the maximum concentration of core igdgts in bottom waters by compiling published surface sediment data from water depths t e x 86 h with bottom water temperature bwt exceeds that with sea surface temperature sst therefore it is proposed that sedimentary t e x 86 h is a bwt proxy in the shallow ecs

gold deposits of the northern margin of the north china craton multiple late paleozoic mesozoic mineralizing events the northern margin of the north china craton is well endowed with lode gold deposits hosting a resource of approximately 900 tonnes t of gold the 1 500 km long region is characterized by east trending blocks of metamorphosed archean and proterozoic strata that were episodically uplifted during variscan indosinian and yanshanian deformational and magmatic events at least 12 gold deposits from the daqinshan yan liao includes the zhangjiakou yanshan and chifeng gold districts and changbaishan gold provinces contain resources of 20 100 t au each most deposits are hosted in uplifted blocks of precambrian metamorphic rocks although felsic paleozoic and mesozoic plutons are typically proximal and host 30 of the deposits the lodes are characterized by sulfide poor quartz veins in brittle structures with low base metal values and high au ag ratios although phyllic alteration is most common intensive alkali feldspar metasomatism characterizes the wulashan dongping and zhongshangou deposits but is apparently coeval with variscan alkalic magmatism only at wulashan stepwise 40ar 39ar geochronology on 16 samples from gangue and alteration phases combined with unpublished shrimp u pb dates on associated granitoids suggest that gold mineralizing events occurred during variscan indosinian and yanshanian orogenies at circa 350 250 200 180 150 and 129 ma however widespread permo triassic 250 ma and early jurassic 180 ma thermal events caused variable resetting of most of the white mica and k feldspar argon spectra as well as previously reported k ar determinations compiled and new stable isotope and fluid inclusion data show that most 18o values for ore stage veins range from 8 to 14 indicating a fluid in equilibrium with the precambrian metamorphic basement rocks d values from fluid inclusions range widely from 64 to 154 which is indicative of a local meteoric component in some veins and highly variable 34s data 7 to 17 even within individual deposits indicate various local country rock sources for sulfur fluid inclusions from all districts show variable homogenization temperatures between 240 and 400 c and are consistently characterized by low salinity h2o co2 ch4 n2 solutions although the data are largely consistent with that from orogenic gold veins intrusion related veins and epithermal veins are also recognized the multiple episodes of mineralization are coincident with episodic tectonic reactivations and associated magmatism along the northern margin of the north china craton electronic supplementary material to this paper can be obtained by using the springer link server located at http dx doi org 10 1007 s00126 001 0239 2

extrusion of the altyn tagh wedge a kinematic model for the altyn tagh fault and palinspastic reconstruction of northern china we propose that the altyn tagh uplift of northwest china is a southwest tapered structural wedge that has been extruded northeastward along the wedge bounding left slip ruoqiang xingxingxia fault and the net right slip altyn tagh fault currently active as a left slip fault this model posits that the leading edge of the altyn tagh wedge lies along the northern margin of a reactivated middle paleozoic orogenic belt the beishan which is the right laterally offset equivalent of the qilian shan orogen this internally consistent and testable model explains the partitioning of shortening in the tarim and qaidam blocks and adjacent areas the amount and sense of strike slip on the ruoqiang xingxingxia fault and altyn tagh fault and the location of the westward continuation of the truncated qilian shan orogen the wedge model also implies that the apparent present day continuity of precambrian basement from the tarim block through the altyn tagh wedge to the north china block actually reflects structural juxtaposition during wedge extrusion of two originally separate blocks

biological overprint of the geological carbon cycle the oxidation of earth s atmosphere is coupled to the net sequestration of organic matter which is related to the relative fractions of organic carbon forg and carbonate fcarb buried in marine sediments these fractions can be inferred from carbon isotope data we present bulk sediment d 13 c records of carbonate d 13 ccarb and organic carbon d 13 corg with a compilation of evolutionary trajectories of major eucaryotic phytoplankton for the past 205 million years our analysis indicates that changes in phytoplankton community structure coupled with the opening of the atlantic ocean basin and global sea level rise increased the efficiency of organic carbon burial beginning in the early jurassic in turn this organic carbon burial increased the oxidation state of earth s surface while drawing down atmospheric co2 levels assuming no substantial negative feedbacks the net oxidation and co2 drawdown appear to be related to the opening phase of the current wilson cycle where the newly formed passive plate margins store organic matter for hundreds of millions of years this process should reverse during the closing phase of the wilson cycle when the continents reassemble and the atlantic ocean basin closes the associated oxidation and storage of organic matter have contributed to the long term depletion of co2 which was a key factor that selected c4 photosynthetic pathways in marine and terrestrial ecosystems in the latter part of the cenozoic these pathways increasingly influenced d 13 corg and ultimately contributed to the reversal of the long term trend in d 13 ccarb

quantifying tidal signatures of the benthic nepheloid layer in gaoping submarine canyon in southern taiwan abstract the benthic nepheloid layer bnl has been observed in the head region of the gaoping kaoping submarine canyon kpsc throughout a year the top of the bnl could be as high as 100 m above the canyon floor in which the suspended sediment concentration ssc could be as high as 30 mg l in the bnl sand sized particles comprise the largest size class in the suspended sediment population based on three one month time series observations near the canyon floor of along canyon velocity water temperature and the volume concentration vc of clay very fine to medium silt coarse silt and sand size classes in 2000 2002 and 2004 the bnl is strongly modulated by the tides at semidiurnal diurnal quarter and sixth diurnal and spring neap frequencies in the course of a semidiurnal tidal cycle the flood up canyon current brings colder water from the seaward part of the canyon causing the ssc and the thickness of the bnl to increase the ssc immediately near the canyon floor also increases in response to the maximum flood and ebb currents of the m 2 tide the tidal to total energy ratio er of the along canyon flow is between 70 80 and between 50 80 among the suspended sediment of clay very fine to medium silt coarse silt and sand size classes the m 2 is the most important tidal constituent in the temporal variations of along canyon flow water temperature and the vc of the four size classes the local phase differences between the forcing velocity and the responses temperature and vc at the m 2 frequency show distinct phase lock that suggests patterns of standing and progressive internal tides suspended sediments in the bnl also respond to the m 2 forcing in a coherent fashion suspended sediment movements are strongly affected by nonlinear processes as indicated by the elevated values of the amplitude ratio of m 4 m 2 of the suspended sediment size classes comparing to that of the flow the cross canyon geometry and the slope of the submarine canyon floor affect the propagation of the barotropic and internal tides which in turn affect the nonlinearity generation in the bnl

glacial interglacial paleoenvironments of the eastern atlantic ocean the biogeochemical ocean flux study bofs paleoceanography program the papers in this special section discuss many aspects of paleoenvironmental analysis performed using various proxies on cores collected in the northeastern and tropical eastern atlantic during two cruises in the framework of the nerc biogeochemical ocean flux study program bofs coring of the northern bofs leg was carried out on leg 3 of the 1989 bofs program rrs discovery cruise 184 mccave 1989 forty one cores were taken on a north south transect at about 20 w from the flanks of the mid atlantic ridge 47 n to gardar drift 59 n at water depths between 1150 and 4050 m of these 15 cores were taken using a 3 m long large diameter kastenlot corer designed by zangger and mc cave 199o cruise and core data are given by manighetti et al this issue the southern leg coring was carried out on leg c of the 1990 bofs program rrs charles darwin cruise 53 shimmield 199o forty six cores including 14 using the kastenlot corer were taken along a transect at about 2o w between 18 and 42 n at depths between 3000 and 4900 m and focusing on an area off northwest africa

regional mineral mapping of island arc terranes in southeastern mongolia using multi spectral remote sensing data abstract over the last few decades many porphyry cu deposits have been discovered in southeastern se mongolia in particular the gurvansayhan and mandalovoo island arc terranes have high potential for ore deposits regional mineral mapping of these terranes using data from the landsat enhanced thematic mapper plus etm and the advanced spaceborne thermal emission and reflection radiometer aster have provided new geological information on the metallogenic province revealing potential mineral deposits for future explorations iron oxides hydroxides with high etm band 1 3 ratio values occur extensively in quaternary deposits located at the boundary between the gurvansayhan and mandalovoo island arcs terranes and basins the high average band ratios 1 35 registered for the porphyry cu and au deposits and their occurrences are associated with iron oxidation which originates from the erosion and weathering of ore zones regional mapping of the island arc terranes using the aster shortwave infrared swir logical operators showed circular or semicircular alteration patterns which usually cluster along faults the mineral assemblages mapped by the aster swir analysis in five major porphyry cu districts can be divided into two types the first type includes argillic phyllic and propylitic mineral assemblages as exemplified by the shuteen ikh shankhai and oyu tolgoi deposits the second type of assemblage includes phyllic and propylitic mineral assemblages as exemplified by the kharmagtai and tsagaan suvarga deposits within the deposits of the first type quartz was also mapped using the aster thermal infrared tir mineral index the difference between the two types may be related to the presence of a lithocap the results of a field survey including spectral reflectance measurements in the ikh shankhai porphyry cu district showed a good correlation with the image analysis results

observed fluxes of water salt and suspended sediment in a partly mixed estuary abstract observations of the residual fluxes of water salt and suspended sediment are presented for seven stations along the tamar estuary the data include measurements over single spring and neap tidal cycles and are generally applicable to medium or high run off conditions surface to bed differences in salinity are typically of the order of several parts per thousand gravitational circulation is an important component of residual flow in the deep lower reaches of the estuary here stokes drift is insignificant in the shallow upper reaches the major residual currents are generated by stokes drift and freshwater inputs data are compared with predictions from hansen and rattray s 1966 model of estuarine circulation salt fluxes due to tidal pumping and vertical shear are directed up estuary at spring tides tidal pumping being dominant tidal pumping of salt is also directed up estuary at neap tides although it is insignificant in the lower reaches where vertical shear dominates tidal pumping of suspended sediment is directed up estuary near the head at spring tides and probably contributes to the formation of the turbidity maximum the existence of the turbidity maximum is predicted using a simplified model of the transport of water and sediment the model shows that an additional mechanism for the existence of the turbidity maximum is an up estuary maximum in the tidal current speeds and thus resuspension in the lower reaches transport of suspended sediment is directed down estuary at both spring and neap tides and sediment is essentially flushed to sea with the fresh water

thermal evolution of two textural types of mafic granulites in the north china craton evidence for both mantle plume and collisional tectonics mafic granulites from the north china craton can be divided into two textural types referred to as a and b types a type mafic granulites display garnet quartz symplectic coronas and outcrop in the eastern and western zones of the craton whereas b type mafic granulites exhibit orthopyroxene plagioclase clinopyroxene symplectites or coronas and are mainly exposed in the central zone of the craton most a type mafic granulites preserve the prograde m 1 peak m 2 and post peak near isobaric cooling m 3 assemblages which are represented respectively by inclusions of hornblende plagioclase quartz a peak mineralogy of orthopyroxene clinopyroxene plagio clase quartz garnet and overprinted by garnet quartz symplectic coronas these mineral assem blages and their p t pressure temperature estimates define anticlockwise p t evolutionary paths the b type mafic granulites preserve the peak m 1 post peak near isothermal decompression m 2 and cooling m 3 assemblages which are represented by the peak assemblage of orthopyroxene clinopyroxene plagioclase quartz garnet hornblende post peak orthopyroxene plagioclase clinopyroxene symplectites or coronas and later hornblende plagioclase magnetite symplectites respectively these mineral assemblages and their p t estimates define clockwise p t paths the anticlockwise p t paths of the a type mafic granulites in the eastern and western zones of the north china craton are consistent with a model of underplating and intrusion of mantle derived magmas in combination with lithological structural and geochronological data the eastern and west ern zones of the north china craton are considered to represent two continental blocks that devel oped through the interaction of mantle plumes with the lithosphere from the palaeoarchaean to the neoarchaean era the b type mafic granulites and associated rocks in the central zone represent a magmatic arc that was metamorphosed and deformed during amalgamation of the eastern and west ern continental blocks in the late palaeoproterozoic era the mineral reaction relations and clockwise p t paths of the b type mafic granulites from the central zone record the tectonothermal history of the collision that resulted in the final assembly of the north china craton at c 1800 ma

geology geochronology and sulphur isotope geochemistry of the black schist hosted haoyaoerhudong gold deposit of inner mongolia china implications for ore genesis abstract the haoyaoerhudong gold deposit is located in the urad middle banner area of inner mongolia in china and is hosted by black schist of the bilute formation in the mesoproterozoic bayan obo group the gold mineralization is within a 4500 m long and 100 m wide zone associated with sulphide quartz veins following the schistosity and crosscutting fractures in the host rocks locally as disseminated sulphide in altered black schist the sulphide mineral assemblage is pyrrhotite pyrite arsenopyrite chalcopyrite sphalerite and is associated with a weak hydrothermal alteration characterized by a silica halo with variable amounts of biotite sericite and carbonate the bilute formation was intruded by multi stage dykes these include metamorphosed porphyritic diorite that pre dates mineralization unmetamorphosed amphibole olivine gabbro that pre dates mineralization and tourmaline bearing pegmatite that post dates mineralization in order to constrain the timing of the gold mineralization and host rocks zircons from the porphyritic diorite amphibole olivine gabbro and tourmaline bearing pegmatite were extracted for u pb dating gold bearing pyrite samples were analysed for 34 s to help determine the possible source of s in the mineral zones a weighted mean 206 pb 238 u age date of 288 3 ma mswd 2 4 was obtained for the porphyritic diorite a weighted mean 206 pb 238 u age date of 282 1 ma mswd 0 58 was obtained from the amphibole olivine gabbro and a weighted mean 206 pb 238 u age date of 182 1 ma mswd 1 04 was obtained from the tourmaline bearing pegmatite these dates constrain the timing of gold mineralization to between 282 1 and 182 1 ma and are consistent with the hydrothermal alteration ages of ca 267 246 ma reported from the literature these new zircon dates indicate that the regional metamorphism of the bayan obo group ceased by the time the haoyaoerhudong gold mineralization was deposited and the genesis of mineralization is not related to the regional metamorphic event the gold bearing pyrites gave positive 34 s v cdt values between 6 8 and 13 4 and are different from the 34 s widely distributed values for the typical black rocks indicating that the sulphur is not derived from the black bilute formation but sourced from some other relatively uniform reservoir widespread contemporaneous granitic magmatism is developed in the haoyaoerhudong area and we suggest that the sulphur forming the gold bearing sulphides is probably sourced from a carbonate contaminated granitic magma reservoir the new zircon dates for the dykes and the 34 s data for gold bearing sulphides indicate that the gold mineralization did not form from metamorphosed black schist in the bayan obo group but is associated with magmatic hydrothermal activity

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

flux of volatiles and ore forming metals from the magmatic hydrothermal system of satsuma iwojima volcano the satsuma iwojima volcano southwest japan degasses 5 x 10 6 t yr h 2 o 9 x 10 4 t yr s and 6 x 10 4 t yr cl from high temperature 880 c fumaroles atop a now altered rhyolite dome that erupted 1200 yr ago acidic hot springs ph 1 1 1 8 discharge 20 x 10 6 t yr h 2 o to the sea this water is composed of 1 part magmatic vapor absorbed by 6 parts meteoric ground water the cl and so 4 in solution originate from the vapor whereas cation components are derived largely by dissolution of the rhyolite the flux of pb zn cu and mo in the vapor and acidic springs ranges from 0 1 to 10 t yr each whereas the au flux is 10 5 and 10 3 t yr respectively the low concentrations of nacl and metals in the vapor are due to the condensation of a hypersaline liquid from the vapor during ascent and depressurization meaning that the atmospheric pressure vapor does not reflect the composition of the fluid exsolving from the magma neither this low pressure vapor nor the acidic waters can account for high sulfidation cu au ore deposits deduced to have formed in this environment such mineralization requires the subsequent ascent of a metal rich fluid

exploration tools for linked porphyry and epithermal deposits example from the mankayan intrusion centered cu au district luzon philippines the mankayan mineral district of northern luzon philippines hosts several significant ore deposits and prospects of various types within an area of similar to 25 km 2 including the far southeast porphyry cu au deposit the lepanto high sulfidation epithermal cu au deposit the victoria intermediate sulfidation epithermal au ag vein deposit the teresa epithermal au ag vein deposit the guinaoang porphyry cu au deposit and the buaki old palidan porphyry cu au prospects all having formed in a period of about 2 m y from similar to 3 ma the geologic units include 1 a basement composed of late cretaceous to middle miocene metavolcanic rocks volcaniclastic rocks 2 the miocene 12 to 13 ma tonalitic bagon intrusive complex 3 the pliocene similar to 2 2 to 1 8 ma imbanguila dacite porphyry and pyroclastic rocks and 4 postmineralization cover rocks including die similar to 1 2 to 1 0 ma bato dacite porphyry and pyroclastic rocks and the similar to 0 02 ma lapangan tuff extensive advanced argillic alteration crops out for similar to 7 kin along the inconformity between the basement rocks and the imbanguila dacite formation consists of quartz alunite pyrophyllite or diaspore with local zones of silicic alteration and a halo of dickite kaolinite the alteration and its subhorizontal geometry indicate that it is a lithocap or coalesced lithocaps the northwest striking portion is similar to 4 km long and hosts the lepanto enargite au ore deposit also controlled by the lepanto fault the lepanto epithermal deposit is related to the underlying far southeast porphyry the quartz alunite alteration halo of lepanto is contemporaneous with the similar to 1 4 ma potassic alteration of the porphyry there are also silicic advanced argillic alteration patches similar to 600 m above the far southeast orebody at the present surface these are interpreted to be perched alteration there is no systematic mineralogical or textural zoning in the lepanto lithocap that indicates direction to the intrusive source most surface samples of the lithocap contain less than 50 ppb au despite many being less than a few hundred meters from underground cu au ore this study found that several characteristics of the lepanto lithocap change systematically with distance from the causative intrusion the alunite absorption peak at similar to 1 480 nm in the short wavelength infrared swir spectrum shifts to higher wavelengths where the sample is closer to the intrusive center due to higher na and lower k content in the alunite published experimental studies indicate that high na na k is related to higher formation temperature high ca alunite including huangite also occurs at locations proximal to the intrusive center alunite mineral composition analyzed by laser ablation inductively coupled plasma mass spectrometry la icp ms indicates that the pb content decreases toward the intrusive center whereas sr la sr ph and la pb increase markedly whole rock compositions using only nonmineralized taken as cu similar to 350 m above the upper extent of the veins an airborne geophysics survey indicates that the far southeast orebody is associated with a wide zone of demagnetization due to extensive magnetite destructive phyllic alteration such low magnetic anomalies on the margin of a large lithocap elsewhere may deserve attention the directional indicators and mineralization signatures found in this study have the potential to indicate direction to the intrusive center during exploration of similar porphyry epithermal districts

cathodoluminescence and micro structural evidence for crystallisation and deformation processes of granites in the eastern lachlan fold belt se australia trace elements al k ti fe growth and deformation pattern in quartz of the multiple deformed carcoar barry and sunset hills granites were investi gated by electron micro probe and cathodolumines cence zoned quartz phenocrysts with high ti concentrations 70 ppm that show blue cathodolu minescence originated from the early stage of magma crystallisation multiple deformation of quartz causes the redistribution of al and k in the quartz lattice which results in the accumulation of these elements in submicroscopic inclusions 0 5 lm of muscovite like composition in contrast structural ti in quartz is mostly kept in the lattice common halos of defect poor secondary quartz around fluid inclusions result from re equilibration of fluid inclusions because of differences between fluid pressure and lithostatic pressure e g duringuplift isothermal decompression and or a b transition of quartz duringhealing defect poor sec ondary quartz grows at the cost of the host quartz and releases or replaces defect centres the results of micro structural investigations combined with al in horn blende thermobarometry allow the reconstruction of regional processes carcoar and barry granodiorites and sunset hills granite were intruded in the late ordovi cian early silurian at depths of 4 8 6 and 10 12 km respectively in contrast to the continuous crystallisation of the granodiorite magmas the magma of the sunset hills granite ascended in a stepwise fashion causing multiple quartz nucleation the two granodiorites were multiple post magmatically deformed first during early devonian under more brittle conditions at temperatures of 350 400 c whereas the sunset hills granite experienced more ductile deformation at tem peratures of around 550 c

terrestrial organic carbon contributions to sediments on the washington margin elemental and stable carbon isotopic compositions and biomarker concentrations were determined in sediments from the columbia river basin and the washington margin in order to evaluate geochemical approaches for quantifying terrestrial organic matter in marine sediments the biomarkers include an homologous series of long chain n alkanes derived from the surface waxes of higher plants phenolic and hydroxyalkanoic compounds produced by cuo oxidation of two major vascular plant biopolymers lignin and cutin all marine sediments including samples collected from the most remote sites in cascadia basin showed organic geochemical evidence for the presence of terrestrial organic carbon using endmember values for the various biomarkers determined empirically by two independent means we estimate that the terrestrial contribution to the washington margin is 60 for shelf sediments 30 for slope sediments and decreases further to 15 in basin sediments results from the same geochemical measurements made with depth in gravity core 6705 7 from cascadia seachannel suggest that our approach to assess terrestrial organic carbon contributions to contemporary deposits on the washington margin can be applied to the study of sediments depositing in this region since the last glacial period

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

fluid inclusion and noble gas studies of the dongping gold deposit hebei province china a mantle connection for mineralization the dongping gold deposit 100 t au occurs about 200 km inboard of the northern margin of the north china craton the deposit is mainly hosted by syenite of a middle paleozoic alkalic intrusive complex that was emplaced into late archean basement rocks both groups of rocks are intruded by late jurassic to early cretaceous crustal melt granite dikes and stocks some within a few kilometers of the deposit the gold ores were deposited during this latter magmatic period at about 150 ma a time that was characterized by widespread regional north south compression that formed the east west trending yanshan deformational belt the ores include both the telluride mineral bearing low sulfide quartz veins and the highly k feldspar altered syenite with most of the resource concentrated in two orebodies 1 and 70 fluid inclusion microthermometry indicates heterogeneous trapping of low salinity e g 5 7 wt nacl equiv fluids that varied from a few to 60 mole percent nonaqueous volatile species laser raman spectroscopy confirms that the vapor phase in these inclusions is dominated by co2 but may be comprised of as much as 9 mole percent h2s and 20 mole percent n2 methane concentrations in the vapor phase are consistently 1 mole percent the variable phase ratios are consistent with fluid immiscibility during ore formation fluid inclusion trapping conditions are estimated to be 250 to 375 c and 0 6 to 1 0 kbar helium isotope studies of fluid inclusions in ore stage pyrites indicate 3he 4he ratios of 2 1 to 5 2 ra ra 1 4 10 6 for air for orebody 1 and 0 3 to 0 8 ra for orebody 70 the former data suggest that at least 26 to 65 percent mantle helium occurs in the fluids that deposited the veins in orebody 1 the lower values for orebody 70 which is characterized by a more disseminated style of gold mineralization are interpreted to reflect an increased interaction of ore fluids with surrounding crustal rocks which may have contributed additional 4he to the fluids a mantle source for at least some of the components of the gold forming fluid is consistent with upwelling of hot asthenosphere and erosion of as much as 100 to 150 km of cool archean lithosphere beneath the craton during this time the dongping deposit is located along the 100 km wide north south gravity lineament which marks the western border of the thinned crust as both regional metamorphism of mesoproterozoic and younger cover rocks and widespread granite magmatism also occurred at ca 150 ma it is unclear as to whether one or both of these also contributed fluid and or metals to the hydrothermal system importantly these new data suggest that economically significant gold deposits of similar mineral style and fluid composition which are scattered along the margins of the craton may all be products of a fluid originally partly sourced within the mantle

a redesigned kasten core barrel and sampling technique abstract a modified kasten core barrel was developed to obtain cores with nearly 100 sediment retrieval while minimizing disturbance of the sediment water interface one side of the 15 15 cm square barrel is doubled by a second movable plate which can be moved upwards by a series of hand screws thus enabling complete sideways extrusion of the core this produces a set of subcores or slabs of equal quality with preserved stratigraphy which can be x rayed subsampled stored or frozen for geochemical studies the new kasten core barrel is effective in rough weather inexpensive to build easy to handle and enables fast core processing on board

trace element and fluid inclusion geochemistry constraint for genesis of gold polymetallic mineralization in the songhung deposit dpr korea abstract the songhung deposit is located in the southwestern part of the yangdok metamorphic core complex ymcc in the northern portion of the pyongnam basin the eastern part of the sino korean craton in this paper we present a detailed study on the magma sources of the granitoids yangdok and hoechang graintic intrusions genesis of pyrite and fluid inclusion characteristics for sufficient and additional understanding of tectonic events petrogenesis of the granitoids and mineralization in the study deposit the yangdok granite has lower al2o3 tio2 ratios mean value of 60 58 than the hoechang granite mean value of 994 46 indicating the higher temperature magma source of the former on the rb ba vs rb sr and cao tfeo mgo tio2 vs cao tfeo mgo tio2 discriminant diagrams the magma source of the yangdok granite belongs in the plagioclase rich and clay poor source rocks while those of the hoechang granite plots either in the plagioclase rich and clay poor source rocks for granite and fine grained granite or in the plagioclase poor and clay rich source rocks for granite porphyry and felsite on the nb vs y ta vs yb rb vs y nb and rb vs yb ta tectonomagmatic discrimination diagrams these two granites are connected with the volcanic arc related setting and plot in post collision setting moreover some data of the hoechang granite fall in wpg field suggesting that the volcanic arc setting may be changed to an intraplate setting from middle cretaceous the pyrite trace element geochemistry showing the high co ni ratio than one with an average of 8 2 and high co content and low ni content suggests that its formation was closely linked with i type granitic magma derived hydrothermal fluid mixed with meteoric water it could also be assumed by the co and as contents in pyrite indicating a certain degree of meteoric water in the ore forming fluid it is consonant to the pb s c and o isotope geochemistry in the previous study suggesting that ore forming fluids and metals could be derived from both the yangdok granite and the proterozoic and paleozoic meta sedimentary rocks exposed in the study area all of the pyrite grains have not compositional zoning and the similar distribution patterns of co and ni are appeared in single pyrite grain from core to rim suggesting the stable crystallization environment of pyrites and same ore forming fluid source in pyrite grains the positive correlation between gold and arsenic is appeared the au exists either as a micro and nano size inclusion in pyrite and other minerals or as a solid solution in pyrite lattice based on the petrological and microthermometric characteristics of the fluid inclusions in ore bearing quartz we suggest that the ore forming fluid is represented as nacl h2o or nacl kcl h2o systems with low salinity the absence of co2 enriched phase and vapor only or liquid only primary inclusions in quartz indicates the homogenous magma derived ore forming fluids and a lack of boiling during ore forming process the formation temperature and pressure of this deposit approximately vary from 317 to 326 c and from 105 46 to 111 69 105 pa respectively exhibiting the hydrothermal deposit origin in conclusion the songhung deposit is originated from i type granitic magma source derived hydrothermal fluid which was mixed with meteoric water

blueschists in major suture zones of china blueschist facies rocks and c type eclogites occur as allochthonous terranes or as small tectonic blocks in almost all the accretionary fold belts and major suture zones within the interior of china and along the circum pacific and tethys himalayan belts at least forty blueschist localities have been described blueschists around the pacific margins and the himalaya alpine belts are mostly mesozoic in age only those in taiwan and new caledonia are cenozoic intracratonal blueschists of china are older than late permian when the collision amalgamation presumably occurred several alleged precambrian blueschist localities ye 1987 are shown in the recently published metamorphic map of china a precambrian blueschist belt in anhui hubei central china extends for about 2300 km however except for the pre sinian blueschist terrane in aksu the age determination for precambrian blueschist metamorphism elsewhere has not been confirmed characteristic features of chinese blueschists include the following 1 blueschist facies metamorphism predates the continental collision amalgamation 2 most blueschists have undergone multistage metamorphism commonly with increasing temperature and or decreasing pressure for later events 3 assemblages include sodic amphibole epidote albite quartz phengite chlorite sphene lawsonite jadeitic pyroxene and aragonite are not common and 4 protoliths are mainly mafic pelagic and clastic rocks blueschist facies metamorphism in china may be divided into two types on the basis of the imposed geothermal gradient hence the progressive change in mineral assemblage the rare lawsonite bearing blueschists produced at lower temperatures and higher pressures are confined to the inner mongolia and yarlung zangbo suture zones where aragonite and possibly jadeitic pyroxene quartz occur and the blueschists are associated with subgreenschist facies rocks most other blueschists of china formed at higher temperatures along the transitional blueschist greenschist facies boundary where epidote sodic and calcic amphiboles are ubiquitous and the blueschists are interlayered with greenschist facies rocks the common occurrence of intracratonal blueschists in major suture zones of china and elsewhere in eurasia indicates pre mesozoic subduction accretion of oceanic crust and flysch sediments these zones of accretion represent growth around the periphery of major precambrian cratons this fact together with the distribution of ophiolite belts and available paleomagnetic data provides evidence for an extremely mobile history of plate movement in eurasia however the paleozoic intracontinental blueschists and ophiolites of china have formed before rather than during final closure between cratons they do not usually mark the location of terminal sutures but are the result of earlier accretion and continental growth by subduction underplating and imbrication of oceanic materials similar to the accretion history of westernmost north america

variation of turbidity and particle transport in the bottom layer of the east china sea abstract field surveys of the bottom turbid layer were undertaken from the changjiang estuary to the mid continental slope area in the east china sea to study the bottom turbid layer formation process and ascertain the role of material transport a dramatic development of bottom turbid layers in the continental shelf area of the east china sea was observed from summer to fall this seasonal variation is relatively consistent with seasonal changes in the discharge of suspended particles ss from the changjiang the ss forming the bottom turbid layer in the east china sea are often fine grained particles transported from the continental coastal area which undergo continuous settling and resuspension during transport through the convectively mixed seawater season the average current velocities at the bottom b 10 m layer at the edge of the continental shelf were approximately 5 2 cm s in an east northeast direction but 2 9 cm s almost true north during the stratified season with the 200 m depth contour as the benchmark the bottom current at the continental shelf edge flowed from inside the continental shelf outward during the mixing season and from outside the continental shelf inward during the stratified seawater season the average horizontal flux of the ss is 60 mg m 2 s during the mixing season and 24 mg m 2 s during the stratified season with almost the same direction as that of the bottom current the direction of the ss horizontal flux in the bottom layers is dominated by the bottom current which is driven by the strong south north monsoon in the east china sea

primary magmatic biotite in granitoid intrusions associated with late mesozoic jinchanggouliang erdaogou lode gold deposits north china craton linkage to gold mineralization abstract the late mesozoic jinchanggouliang and erdaogou lode gold deposits in the central segment of the northern north china craton are mainly hosted in late archaean metamorphic rocks of the jianping formation and jurassic volcanic sedimentary rocks these deposits are spatially and temporally associated with a series of i type granitoid intrusions i e the 128 136 ma duimiangou granodiorite complex with a massive margin and a porphyritic center at jinchanggouliang the 161 4 1 1 ma loushang quartz diorite intrusion and numerous syenite porphyry dykes 160 9 1 0 ma at erdaogou and the 227 217 ma xitaizi monzogranite batholith compositions of primary magmatic biotite in these granitoid intrusions have been used to investigate the nature of granitoid magmas and the evolution of magmatic processes and to identify possible linkages between gold mineralization and granitoid magmatism all primary magmatic biotite grains are mg rich in composition xmg mg mg fe 0 41 0 69 the cl contents of biotite 0 09 0 42 wt in the loushang quartz diorite and the duimiangou massive granodiorite correlate negatively with xmg and are consistent with the mg cl avoidance rule the cl contents of biotite 0 01 0 14 wt in the duimiangou porphyritic granodiorite syenite porphyry and xitaizi monzogranite on the other hand remain relatively constant and may be affected by multiple variables such as cl rich fluids and subtle changes in temperature halogen fugacity of the parental magma calculated from biotite shows that the duimiangou granodiorite complex at jinchanggouliang and syenite porphyry dykes at erdaogou have the log fhf fhcl ranges of 0 71 to 0 27 and 2 16 to 1 08 respectively and have similar log fh2o fhcl values from 3 53 to 4 23 oxygen fugacities logfo2 calculated from biotite equilibria for the duimiangou granodiorite complex and syenite porphyry dykes are 13 7 to 7 2 straddling on the nickel nickel oxide and hematite magnetite buffers the xitaizi monzogranite and the loushang quartz diorite have lower log fo2 values from 14 9 to 12 4 between the nickel nickel oxide and hematite magnetite buffers the duimiangou granodiorite complex and syenite porphyry dykes with high oxygen fugacities are similar to oxidized magmas associated with porphyry cu mo au deposits these results suggest that multiple episodes of i type granitoid magmas in the study area were rich in cl and high in oxygen fugacity especially those associated with the duimiangou granodiorite complex and syenite porphyry dykes the i type melts represented by the duimiangou granodiorite complex and syenite porphyry dykes as well as their related cl rich oxidizing fluids were likely efficient in dissolving transporting and precipitating gold for the formation of the jinchanggouliang and erdaogou lode gold deposits

genesis of the songhung gold polymetallic deposit in the hoechang district the democratic people s republic of korea constraints from geology petrochemistry and pb s c o isotope geochemistry abstract the songhung deposit is located in the southwestern part of the yangdok uplift zone yuz in the northern part of the pyongnam basin in the sino korean craton most of large and small scale gold deposits and occurrences were discovered and exploited in the western part of the yuz several tectonic events in this area are the key to understanding the gold and polymetallic mineralization in the sonhung deposit the yuz comprises the neoarchean rangnim metamorphic belt proterozoic and early paleozoic rocks in the central domain and granitoid intrusions of crustal and mantle derivation yangdok granitoid intrusions two extensive nne trending fault zones with mylonitized rocks are interpreted to represent detachment fault and two ne sw trending regional rift structures represent zones of subsidence e g the tokchon maengsan to the west the kowon to the east and the junghwa samdung subsidence to the south it is suggested that the yuz is a metamorphic core complex mcc similar to those in the north china craton ncc polymetallic mineralization in the songhung deposit is divided into early and late stages the early mineralization was formed during compressional deformation in the triassic accompanied by low grade metamorphism of the sedimentary host rocks variations in pb s c and o isotope ratios indicate that the ore forming fluids and metals were derived from the country rocks the au grade is insignificant in this style of mineralization the main gold polymetallic mineralization in the songhung deposit is related to tectonic extension of the region the pb s c and o isotope data indicate that these elements as well as ore forming fluids could be derived from both the granitic intrusion yangdok granitoid and the proterozoic and paleozoic country rocks

historical reconstruction of organic carbon decay and preservation in sediments on the east china sea shelf 1 sediment cores were collected from the east china sea inner shelf in 2010 to study the decay and preservation of organic carbon oc the highest sediment mass accumulation rate 0 61 0 20 g cm 2 yr 1 derived from 210pb was found near the river mouth and decreased alongshore to the south 0 17 0 004 g cm 2 yr 1 and in an offshore direction 0 31 0 08 g cm 2 yr 1 average total oc content was higher at inner shelf stations 0 52 than those offshore 0 38 the 13c was more depleted at nearshore 23 49 to 21 97 than offshore 22 49 to 21 60 stations principal component analysis indicated that terrestrial oc as indicated by lignin phenols 8 values was preserved in sediment closer to the coast 0 22 0 44 while offshore sediment was more composed of lignin poor 0 12 0 24 degraded oc that was likely hydrodynamically sorted marine derived oc as indicated by plant pigments was significantly more abundant in the sediment mixed layer than the underlying accumulation layer historical flooding events were detected in 8 profiles in two of the six cores located at midshelf stations despite the magnitude of the 2010 flood in east china we did not see any signature of this event with the chemical biomarker in these two cores this may suggest that reduced sediment loading due to recent dam construction may have greatly decoupled river inputs with sediment loading to shelf sediment the total oc standing stock since 1900 was approximately 1 62 1 15 kg c m 2 about one tenth of all the middle and lower lakes in the changjiang catchment basin this work further supports the need for more research to better understand how the reduced inputs of fluvial input of sediments from chinese rivers due to river diversions and dams affect carbon cycling in the east china sea

timing of multiple magma events and duration of the hydrothermal system at the yu erya gold deposit eastern hebei province china constraints from u pb and ar ar dating abstract the yu erya deposit is a large granite hosted gold deposit in the eastern hebei province classified as an intrusion related gold system the yu erya complex contains the causative intrusion which was the source of hydrothermal metal bearing fluids this composite granite complex contains miarolitic pegmatite like cavities and pegmatite veins a combination of detailed field observations and u pb dating by shrimp and la icp ms is used to document multiple magmatic events which occurred at 210 220 175 173 171 170 167 166 and 161 ma formed the yu erya granite complex the initiation of the hydrothermal system as determined via ar ar dating is closely related to the exsolution of a magmatic volatile phase from the g1 granite at ca 176 ma the hydrothermal system operated for 16 my 176 160 ma and produced multiple mineralising events 176 172 168 and 162 160 ma linked to emplacement of repeated magma pulses from 175 ma to 161 ma our results suggest that multiple magmatic hydrothermal events over a time period of several million years may be a fundamental factor responsible for the enrichment process during formation of intrusion related gold deposits and thus may be a requirement for forming economic orebodies

genesis of the wulong gold deposit northeastern north china craton constraints from fluid inclusions h o s pb isotopes and pyrite trace element concentrations abstract the wulong vein type gold deposit located along the northeastern margin of the north china craton ncc contains 80 tonnes of gold at an average grade of 5 35 g t a total of 380 auriferous quartz veins are hosted in late jurassic gneissic two mica granite and early cretaceous granodiorite a paragenetic sequence representing three hydrothermal stages has been identified 1 quartz pyrite 2 quartz polymetallic sulfide and 3 quartz calcite pyrite petrography fluid inclusion microthermometry and laser raman spectroscopy revealed three types of fluid inclusions co2 ch4 type i h2o co2 ch4 type ii and h2o nacl type iii fluid inclusion data indicate that during mineralization fluid temperatures evolved from 283 to 395 c to 219 328 c to 144 255 c and salinities varied from 0 70 to 8 95 wt to 0 18 7 86 wt to 0 18 4 96 wt nacl equivalent quartz yielded 18oh2o smow and dsmow values of 0 9 7 3 and 65 to 48 respectively indicating that the ore forming fluids were derived from magmatic water and mixed with meteoric water during the later stages of mineralization sulfides have 34scdt sulfur isotopic compositions ranging from 0 9 to 3 9 suggesting that the s was derived from a magmatic source pb isotopic compositions of sulfides 206pb 204pb 17 488 17 718 207pb 204pb 15 565 15 631 and 208pb 204pb 38 190 38 766 indicate that the pb was derived primarily from the upper crust with minor input from the mantle in situ laser ablation inductively coupled plasma mass spectrometry la icp ms trace element analyses of three generations of pyrite py1 py2 and py3 reveal that gold concentrations in py2 are higher than those in py1 and py3 which indicates that gold mineralization occurred primarily during the middle stage high co ni ratios of pyrite are consistent with a hydrothermal origin we suggest that the wulong gold deposit formed during lithospheric thinning associated with destruction of the ncc this process was triggered by subduction of the paleo pacific plate during the early cretaceous

illumination of vein quartz textures in a porphyry copper ore deposit using scanned cathodoluminescence grasberg igneous complex irian jaya indonesia vein quartz from the grasberg igneous complex in irian jaya indonesia displays a wide range of features when observed using scanned cathodoluminescence imaging on the electron microscope examination of seventeen samples revealed concentric growth zoning quartz filled microfractures dark luminescence near sulfides changes in crystal size and orientation from vein edges to vein centers turbid growth zoning and the truncation of concentric growth zoning individual features observed along two large photomosaic traverses from vein margins to vein centers coupled with trace element analyses from the electron microprobe allow determination of a detailed history of fracture infilling the two traverses indicate a simple two stage history of crystal growth into an open fracture followed by mechanical closing of the fracture with resulting microfractures electron microprobe trace element analyses show that the fe content of quartz reaches values of up to 4900 ppm in dark luminescent regions near sulfide crystals and decreases smoothly to 200 ppm along traverses away from the sulfides the solution to the diffusion equation coupled with existing experimental data about fe diffusion in sio2 indicate the duration of the diffusion was perhaps on the order of thousands of years

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

geometric and kinematic evolution of basement cored structures intraplate orogenesis within the yanshan orogen northern china abstract detailed surface mapping lithology facies analysis drillcore data and aeromagnetic interpretation reveal the geometries of the basement involved structures of laowopu nantan liudaohe xinglong and malanyu to have been generated by folding and thrusting the resulting basement cored anticlines are asymmetric with a shallowly dipping top and backlimb and a steep to overturned forelimb and or frontal fault linked with a gently dipping synclinal limb both the fold axes and frontal faults trend roughly east west suggesting north south shortening north to northeast trending faults behave as tear lateral or oblique ramp structures and formed coevally with their frontal faults their trends may have been inherited from proterozoic synsedimentary faults and archaean basement ductile shear zones foliations and mafic dikes thin skinned thrusts and their three dimensional geometry are locally controlled by detachment within mechanically incompetent layers four types of interrelationships between the thick and thin skinned structures occur including 1 lateral changes along the length of a fault 2 displacement transfer between thick and thin skinned structures 3 buttressing of thin skinned thrusts against the basement involved structures and 4 generation of an out of the syncline thrust under thick skinned shortening most of the deformation within the study area involved brittle behaviour but ductile shear zones developed where fluid access was possible both the basement involved structures and the thin skinned structures formed in the early mesozoic as constrained by cross cutting relationships isotopic ages of igneous rock and syntectonic basins the model of geometric and kinematic evolution of the basement involved structures and their relationship with the thin skinned structures defined in this paper provides an alternative to the current metamorphic core complex model used for the yanshan intraplate orogen

seasonality and composition of downward particulate fluxes at the continental shelf and okinawa trough in the east china sea abstract as part of the marginal sea flux experiment in the west pacific masflex program conventional sediment traps were deployed at three mooring sites on the east china sea shelf for 1 2 days during 4 seasonal cruises time series sediment traps also were deployed in the east china sea one at the northern part of the okinawa trough stn sst 1 and the other to the north west of the okinawa island sst 2 for 1 year from march 1993 to february 1994 the settling particles were analyzed for total mass flux and the abundance of major biogenic constituents organic carbon nitrogen inorganic carbon and opal on the inner shelf particulate fluxes were large and rapidly increased near the bottom throughout the year probably due to resuspended bottom sediment and suspended particles from the changjiang forming a bottom turbid layer btl on the central shelf particulate fluxes in the btl were extremely high in summer when changjiang discharge peaks possibly indicating a seasonal supply of the changjiang particles to the central shelf at the shelf edge the fluxes in the btl were significantly higher in autumn and winter than in spring and summer at the okinawa trough stations ca 1100 m particulate fluxes at 600 m depth were extremely low but increased noticeably with depth 800 and 50 m above the bottom the flux generally peaked from late autumn to early spring and was lowest during summer with an unusually large peak in september at sst1 considering that there is no strong seasonality of the primary productivity and phytoplankton biomass in the surface layers at the okinawa trough we hypothesize that the seasonality of particle fluxes at the deep waters of the trough is linked to seasonal events in shelf waters downwelling and seaward bottom flow induced by the northeast monsoon in winter favor the offshore transport of particles in the btl while in summer a transverse circulation pattern may inhibit it hu 1994 yanagi et al 1996 near bottom transport may be a key process for shelf to deep sea export of biogenic lithogenic particles as a result the continental slope and the okinawa trough may play an important role as a carbon sink for the east china sea

hydrothermal alteration and ore forming fluids associated with gold tellurium mineralization in the dongping gold deposit china abstract the dongping gold deposit hosted in syenites is one of the largest hydrothermal gold deposits in china and composed of ore veins in the upper parts and altered zones in the lower parts of the ore bodies pervasive potassic alteration and silicification overprint the wall rocks of the ore deposit the alteration minerals include orthoclase microcline perthite quartz sericite epidote calcite hematite and pyrite with the quartz pyrite and hematite assemblages closely associated with gold mineralization the phases of hydrothermal alteration include i potassic alteration ii potassic alteration silicification iii silicification epidotization hematitization iv silicification sericitization pyritization and v carbonation mass balance calculations in potassic altered and silicified rocks reveal the gain of k2o na2o sio2 hfses and transition elements tes and the loss of rees most major elements were affected by intense mineral reactions and the ree patterns of the ore are consistent with those of the syenites gold silver and tellurium show positive correlation and close association with silicification fluid inclusion homogenization temperatures in quartz veins range from 154 c to 382 c peak at 275 c 325 c with salinities of 4 9 wt nacl equiv at temperatures of 325 c the fluid is estimated to have ph 3 70 5 86 log fo2 32 4 to 28 1 with au and te transported as au hs 2 and te22 complexes the ore forming fluids evolved from high ph and fo2 at moderate temperatures into moderate low ph low fo2 and low temperature conditions the fineness of the precipitated native gold and the contents of the oxide minerals e g magnetite and hematite decreased followed by precipitation of au and ag bearing tellurides the hydrothermal system was derived from an alkaline magma and the deposit is defined as an alkaline rock hosted hydrothermal gold deposit

archean gold mineralization and oxidized hydrothermal fluids sulfate minerals hematite and isotopically fractionated sulfides are relatively rare in rocks of archean age several archean au deposits however contain one or more of these features indicative of oxidized hydrothermal fluids they include hemlo mcintyre hollinger macassa lake shore and ross which are all in ontario canada and kalgoorlie in australia examples of lesser deposits are in hislop township and in the matachewan area ontario canada with the exception of hemlo these are quartz carbonate vein deposits spatially and temporally associated with felsic plutonism because metamorphic fluids and archean surface waters were mostly reducing the most feasible general source for the fluids was felsic magmas parent magmas were relatively oxidized hydrous and co 2 rich the oxidized character may have favored the incorporation of au into the partial melt and its partitioning into magmatic aqueous fluids high contents of co 2 are conducive to the separation of an aqueous fluid from magma at greater depth than otherwise fluid inclusion data support the formation of major archean au vein deposits at deeper crustal levels than more recent magmatic hydrothermal mineralization such as porphyry cu deposits co 2 rich fluids can unmix into two phases at relatively high temperatures and pressures a saline aqueous liquid and a low salinity h 2 o co 2 liquid this can cause partitioning of cl complexed base metals from other metals including au sb and as the extensive carbonatization around most deposits has consistent delta 13 c values in the range of juvenile magmatic co 2

oyu tolgoi mongolia siluro devonian porphyry cu au mo and high sulfidation cu mineralization with a cretaceous chalcocite blanket the oyu tolgoi porphyry cu au mo deposit is located in the gobi desert of southern mongolia the deposit consists of three main mineralized zones north central and south oyu interpreted to constitute at least two separate porphyry copper centers oyu tolgoi is associated with a series of small structurally controlled stocks and dikes of monzonitic and dioritic composition which intrude a sequence of siluro devonian volcanic and sedimentary rocks country rocks consist of pillow basalt and basaltic andesite interbedded with fine grained clastic sedimentary horizons the sequence is interpreted to have formed in a subaqueous island arc volcanic environment which formed part of the extensive paleozoic tuva mongol arc these island arc rocks are covered by carboniferous terrigenous sequences and are intruded by carboniferous syenite and granite and permian alkaline granite much of the area is covered by poorly consolidated cretaceous sedimentary sequences central oyu consists of a multiple phase hydrothermal breccia crosscutting an altered fine grained feldspar porphyry containing porphyry type alteration and mineralization the breccia underwent texture destructive advanced argillic alteration characterized by several associations of quartz alunite dickite pyrophyllite sericite and zunyite plus lesser svanbergite and fluorite these associations overprint earlier formed k silicate and quartz sericite illite assemblages copper mineralization at central oyu is present in a supergene chalcocite blanket that formed at the expense of a pyrite rich hypogene chalcocite covellite tennantite arsenosul vanite sulvanite chalcopyrite bornite sulfide suite that accompanied the advanced argillic alteration event at south oyu a feldspar hornblende porphyry of monzonitic composition intrudes a sequence of fine grained andesite and basaltic andesite hypogene copper gold mineralization occurs as early magnetite rich pyrite poor quartz chalcopyrite bornite stockworks and sheeted veinlets hydrothermal alteration is composed of biotite and k feldspar with apatite and minor albite magnetite averages 7 to 10 vol percent and copper and gold grades vary sympathetically these early assemblages are overprinted by a sericite chlorite event with ore grade copper and erratic gold and molybdenum values and also by structurally controlled pyrite rich advanced argillic alteration k ar ages show that the hypogene copper gold mineralization at south oyu is latest silurian earliest devonian 411 3 ma and that the entire district was intruded by postmineralization syenite during the carboniferous 307 4 ma the supergene chalcocite blanket at central oyu formed in the early cretaceous earliest late cretaceous based on ages for supergene alunite of 117 1 and 93 1 ma which makes central oyu one of the oldest preserved chalcocite blankets in the world chalcocite blanket preservation was favored by climatic desiccation into the late cretaceous and the tertiary it is inferred that significant regional uplift took place at the silurian devonian boundary this synmineral ization uplift and erosion may have been in part responsible for the telescoping of the hydrothermal systems at oyu tolgoi including the superposition of epithermal style associations over higher temperature deeper seated assemblages typical of the porphyry environment