fluid inclusion and stable h o c isotope studies of the giant shuangjianzishan epithermal ag pb zn deposit inner mongolia ne china abstract the shuangjianzishan ag pb zn deposit with a reserve of 145 mt 128 5 g t ag c 18 600 t or 600 moz ag and 2 2 wt pb zn 3 2 mt in the great hinggan range ghr ore district in ne china is the largest known silver deposit in asia the ag pb zn mineralized veins are primarily hosted by a permian slate unit three primary paragenetic stages of early pyrite quartz k feldspar i main ore sulfide sulfosalt quartz calcite sericite chlorite epidote ii and post ore quartz iii have been identified the ore stage ii was the dominant period for silver mineralization with canfieldite ag8sns6 argentite ag2s and freibergite ag cu 12sb4s13 the prevailing silver bearing minerals fluid inclusion microthermometric studies revealed that the ag pb zn vein formation occurred within a temperature range of 250 to 210 c and at a salinity of

fluid inclusion h o s pb and noble gas isotope studies of the aerhada pb zn ag deposit inner mongolia ne china abstract the aerhada pb zn ag deposit is located in the western segment of the great hinggan range ag pb zn cu mo au fe metallogenic belt in ne china orebodies occur mainly as vein type and are hosted by sandstone and siliceous slate three stages of primary mineralization including an early arsenopyrite pyrite quartz a middle polymetallic and silver sulfides quartz and a late sphalerite pyrite calcite fluorite are recognized four types of fluid inclusions have been identified in the ore bearing quartz and fluorite veins i e liquid rich gas rich three phase co 2 aqueous inclusions and pure gas or liquid aqueous inclusions microthermometric studies on fluid inclusions reveal that homogenization temperatures from early to late stages range from 253 to 430 c 195 to 394 c and 133 to 207 c respectively fluid salinities range from 2 9 to 14 0 wt nacl equiv the vapor composition of the ore fluid is dominated by h 2 o co 2 and ch 4 with minor proportions of n 2 the fluid 18 o h2o and d h2o values vary from 1 6 to 9 3 and 122 to 56 respectively and reflect a magmatic fluid and a meteoric fluid dominant hydrothermal system for the early and late stages of mineralization respectively the calculated 34 s h2s values of hydrothermal fluids in equilibrium with sulfides range from 5 2 to 7 1 suggesting a mixed source for sulfur i e the local magmatic and sedimentary rocks the pb isotope compositions of sulfides are similar to those of the local magmatic and sedimentary rocks implying that lead and possibly silver relate to these sources the noble gas isotope compositions of fluid inclusions hosted in ore minerals suggest that the ore forming fluids were dominantly derived from a deep mantle source fluid mixing and dilution are inferred as the dominant mechanisms for ore deposition the aerhada pb zn ag deposit can be classified as a medium to low temperature hydrothermal vein type deposit

the effect of redox conditions and bioirrigation on nitrogen isotope fractionation in marine sediments abstract nitrogen isotopic signatures of sources and sinks of fixed nitrogen n can be used to constrain marine nitrogen budgets however the reported fractionation during benthic n 2 production varies substantially to assess the range and mechanisms responsible for such observations we conducted a model study to evaluate the extent to which nitrification denitrification and anaerobic ammonium oxidation contribute to the isotopic composition of in situ n 2 production different hydrodynamic regimes were taken into account ranging from bioirrigation to diffusion dominated transport the benthic redox conditions were found to control the n isotope effect which under reducing conditions is driven by fractionation during nitrification and anaerobic ammonium oxidation and under oxidizing conditions by fractionation during denitrification environmental parameters such as the mineralization rate the bioirrigation intensity and chemical composition of the overlying water affect the benthic redox zonation and therefore also the benthic n isotope effect the n isotope effect of benthic n 2 production was computed for a wide range of bioirrigation intensities and mineralization rates and found to be approximately 3 for commonly encountered conditions this value is similar to previous estimates of the global n isotope effect of benthic n 2 production and further constrains the relative importance of water column vs benthic n 2 production

source and possible leaching process of ore metals in the uragen sandstone hosted zn pb deposit xinjiang china constraints from lead isotopes and rare earth elements geochemistry abstract the uragen world class zn pb deposit is located in the ulugqat basin in xinjiang china the deposit is characterized by low grade zn pb 3 wt and large tonnage of 4 84 mt metals in the southern ore zone and potentially 10 mt metals for the whole deposit the deposit is mainly hosted in sandstone and conglomerate of the fifth member of the lower cretaceous kezilesu group to provide better constraints on the source of ore metals systematic analyses of the pb isotopes and ree were conducted on sulfides and possible source terranes the sulfides have homogeneous pb isotopic ratios for 206pb 204pb of 18 528 18 690 for 207pb 204pb of 15 545 15 743 and for 208pb 204pb of 38 429 39 082 these ratios are different from those of the upper silurian upper devonian tangaitaer and paleocene aertashi formations the fourth member of the lower cretaceous kezilesu group and the permian granite despite partly overlapping with the values of sulfides the ratios of the proterozoic aksu metamorphic rocks are different in extent and variability however the clastic rocks of the fifth member of the lower cretaceous kezilesu group have almost the same pb isotopic compositions as the sulfides if the preferential leaching of radiogenic pb is taken into account the sulfides in the disseminated ores show lree enriched patterns with high lree hree ratios 3 50 12 06 variable changes of ce anomalies 0 67 1 22 and eu anomalies 0 52 1 33 that are also similar to those of the clastic rocks of the fifth member of the lower cretaceous kezilesu group but are significantly different from those of the basement rocks of the proterozoic aksu group and the evaporite sequences of the paleocene aertashi formation in the ce and eu anomalies petrographic observations indicate that the clastic rocks of the fifth member of the lower cretaceous kezilesu group have undergone sedimentation diagenetic reddening and bleaching reddening is related to the in situ oxidation of mafic minerals such as biotite to produce ferric iron oxide and hydroxide ioh that accompanied the liberation of ore metals from the silicate phase during subsequent crystallization of ioh to hematite preferential adsorption onto hematite could have been the main mechanism for separating zn pb from cu bleaching resulted from the dissolution of ioh during the oil gas infilling stage and based on mass balance calculations substantial amounts of leachable fe zn pb were extracted from the red clastic rocks by the ore forming fluid therefore we propose that the red clastic rocks of the fifth member of the lower cretaceous kezilesu group may be the predominant source of ore metals in the uragen deposit and that the leaching may be possibly related to the bleaching process

the north chilean coast range an example for the development of an active continental margin analysis of extended plutons in the coast range of north chile between 25 30 and 26 35 led to the recognition of a complex magmatic and structural evolution from the upper paleozoic to the tertiary

isotopic analysis of the super large shuangjianzishan pb zn ag deposit in inner mongolia china constraints on magmatism metallogenesis and tectonic setting abstract the super large shuangjianzishan pb zn ag deposit is a newly discovered deposit located in the huanggang ganzhuermiao polymetallic metallogenic belt of inner mongolia ne china the deposit s resource includes 0 026 mt ag 1 1 mt pb and 3 3 mt zn the deposit is controlled by a nw trending ductile shear zone and ne and nw trending faults in black pelite assigned to the lower permian dashizhai formation lree enrichment hree depletion nb ta p and ti depletion and zr and hf enrichment characterize felsic magmatic rocks in the shuangjianzishan pb zn ag district the ages of porphyritic monzogranite rhyolitic crystal vitric ignimbrite and porphyritic granodiorite are 254 252 169 and 130 ma respectively pyrite sampled from the mineralization has re os isochron ages of 165 7 ma which suggest the mineralization is associated with the ca 169 ma magmatism in the shuangjianzishan district zircons extracted from the porphyritic granodiorite yield e hf t values of 11 34 to 1 41 with t dm2 dates of 1275 1901 ma the e hf t values of zircons in the rhyolitic crystal vitric ignimbrite and the ore bearing monzogranite porphyry are 7 57 16 23 and 10 18 15 96 respectively and their t dm2 ages are 177 733 and 257 632 ma respectively partial melting of depleted mantle resulted in the formation of the ca 254 252 ma ore bearing porphyritic monzogranite and the ca 169 ma rhyolitic crystal vitric ignimbrite dehydration partial melting of subducted oceanic crust resulted in the formation of the ca 130 ma porphyritic granodiorite the porphyritic monzogranite was emplaced during the late stages of closure of the paleo asian ocean during the transformation from a collisional to extensional tectonic setting the ca 170 and ca 130 ma magmatism and mineralization in the shuangjianzishan district are related to subduction of the mongolia okhotsk ocean and subduction of the paleo pacific ocean plate respectively

the diffusive tortuosity of fine grained unlithified sediments abstract use of fick s first law to estimate solute fluxes is arguably the most common and important calculation related to the geochemistry and environmental chemistry of fine grained unlithified sediments in such porous media the diffusion coefficient in this law must be reduced by the square of the tortuosity to account for the longer diffusive paths experimental methods to estimate tortuosity are specialized or time consuming and not routinely done an analysis of available data shows that tortuosity is accurately correlated to readily measured porosity values through the simple relation 2 1 l n 2

ethology of the trace fossil chondrites form function and environment abstract the behaviour of the iconic ichnogenus chondrites is re evaluated based on review of existing literature and analysis of novel data macroscopic thin section and esem edx observations ct scans and resin peels of modern analogues computer controlled serial grinding morphometric analysis and theoretical morphology the bedding plane expression of chondrites is well constrained by morphometry 1 the angle of dichotomy formed by a pair of adjacent branches is typically between 30 and 56 interquartile range mean 47 2 branching order is between 1 and 9 3 branches are on average nine times longer than wide in the third dimension downward branching is dominant but bundled shafts and upward branching may be present the size of chondrites increased markedly from the late jurassic to the late cretaceous suggesting that the tracemakers became larger and larger microfabric analysis of chondrites shows active fill or alternatively passive fill of empty tunnels by currents or clay percolation a new mechanism proposed herein the tracemakers built chondrites to obtain food 1 vermiform deposit feeders produced chondrites for searching for food in the sediment fodinichnion 2 asymbiotic bivalves built chondrites for cultivating and directly ingesting bacteria agrichnion 3 chemosymbiotic bivalves produced chondrites to provide symbionts with chemical agents chondrites was modified through the life of the tracemaker or it represented a part of the producer s lifespan chondrites and its modern tracemaker s is associated with a range of marine settings including well oxygenated dysoxic and space limited nucleocave environments as such chondrites is regarded as an extremotolerant ichnotaxon

numerical model on the flow dynamics around the sediment water interface in the tidal coastal area abstract investigating flow dynamics around the sediment water interface is one of difficult issues in marine environment it has important significance to study the physical chemical and biological activities between the overlying water and sedimentary layer with tidal forcing in this study we established a numerical model to investigate the flow dynamics around the sediment water interface in the tidal coastal area the model reflected the hydrodynamics of periodic reciprocating unsteady flow in the overlying water layer and the fully coupled simulation of flow movement between the overlying water layer and sedimentary layer a sedimentary layer an overlying water layer and an air layer were all treated as the fluid zone the unsteady reynolds averaged navier stokes equations and the reynolds stress model with porosity were solved by the finite volume method moreover the drag source term in the momentum equation was modified as the darcy forchheimer extended form the model showed a strong performance in simulating the hydrodynamics of coupled flow around the sediment water interface with tidal forcing in a coastal area with considering the sedimentary layer the benthic boundary layer velocity distributions were more accurate than those obtained by a wall function model around the sediment water interface there was inertial loss in the flow furthermore velocity increased with increasing porosity and velocity gradient became larger compared with models with darcy s law the numerical model in this study had better performance in the turbulent characteristics of sediment water interface layer the model can lead to better understanding of the exchange mechanisms of oxygen nitrogen and nutrient between overlying water and sediment

gold rich mesothermal vein deposits of the republic of korea geochemical studies of the jungwon gold area gold vein deposits of the jungwon area are among the first documented examples of mesothermal gold deposition in the republic of korea the deposits are composed of massive quartz veins up to 1 0 m wide which occupy fault planes in precambrian gneiss k ar dating of alteration sericite 146 156 m y indicates a late jurassic age for ore mineralization similar to that of a nearby granodiorite the veins are gold rich and sulfide poor with ore shoots up to 200 m in horizontal and vertical extent ore grades average 10 2 g ton gold with an average gold silver production ratio of 6 1 fluid inclusion data indicate that gold was deposited between 375 degrees and 290 degrees c from relatively dilute fluids asymp 4 equiv wt nacl containing asymp 15 to 25 mole percent co 2 evidence of fluid unmixing co 2 effervescence indicates pressures of 1 200 to 1 500 bars gold deposition was likely a result of decrease of sulfur activity caused by sulfide deposition and or h 2 s loss accompanying fluid unmixing measured and calculated compositions of ore fluids in the jungwon area delta 18 o 5 0 to 7 7ppm delta d 78 to 113ppm indicate that gold was deposited from a highly evolved meteoric water that underwent extreme 18 o enrichment and moderate d enrichment mineralogy and ore fluid chemistry of the jungwon area deposits are similar to those of mesothermal gold vein deposits of the canadian cordillera canadian archcan greenstone belts and the mother lode district of california the diversity of host rocks in these deposits indicates that host rock petrology is not a controlling factor in the formation of mesothermal gold vein deposits these observations together with our geochemical studies of korean deposits may validate a more general application of meteoric water models for the formation of mesothermal gold vein deposits

epithermal gold veins in a caldera setting banska hodrusa slovakia the central zone of the large miocene stiavnica stratovolcano in the western carpathians hosts epithermal au mineralization of intermediate sulfidation type located at deep levels of the historic rozalia base metal mine at banska hodrusa the au mineralization occurs as subhorizontal veins at the base of pre caldera andesites close to the roof of a subvolcanic granodiorite intrusion the veins are dismembered by a set of quartz diorite porphyry sills and displaced by the younger steeply dipping rozalia base metal vein and parallel structures the base metal vein structures are related to resurgent horst uplift in the caldera center the au mineralization formed during two stages based on fluid inclusion evidence both stages formed from fluids of low salinity 0 3 wt nacl eq which underwent extensive boiling at moderate temperatures 280 330 c variable pressure conditions 39 95 bars neglecting the effect of co2 indicate continual opening of the system and a transition from suprahydrostatic towards hydrodynamic conditions at shallow depths 550 m the fluid inclusions of the rozalia base metal vein show homogenization temperature peaks at 285 and 187 c and salinities between 1 and 4 wt nacl eq precipitation of au is considered to be the result of prolonged boiling of fluids and associated decrease in au solubility oxygen and hydrogen isotope data for quartz and carbonate from the au veins show a relatively homogeneous fluid composition 2 7 to 1 1 18o 78 to 62 d the combined 18ofluid and dfluid values suggest a mixed character of fluids falling between the fields of typical magmatic and meteoric water influenced by 18ofluid shift due to fluid rock isotopic exchange end stages of open system boiling and fractionation could have been reached at least locally significantly lower isotopic composition of meteoric fluids associated with au mineralization compared to those associated with the intrusion related mineralizations could have resulted from changing paleoclimate and or analytical problems of extraction of water from fluid inclusions the proposed genetic model for the au deposit at rozalia mine highlights the importance of hydrothermal activity during the early stage of caldera collapse caldera subsidence established new convective fluid flow paths along marginal caldera faults which acted as infiltration zones major metal precipitation occurred within subhorizontal structures that formed as the result of a collapse related stress field a shallow differentiated magma chamber at the base of the volcano was the likely source of heat and magmatic components for the mineralizing fluids

geochemistry and sr nd pb hf isotopes of early cretaceous basalts from the great xinggan range ne china implications for their origin and mantle source characteristics abstract late mesozoic volcanism is widespread throughout northeastern china mainly clustering in the great xinggan range where the major period of volcanic eruption was during the early cretaceous the spatial distribution of volcanic rocks shows a nne extending pattern the lithology of mesozoic basaltic rocks in the great xinggan range ranges from trachytic basalts basalts to basaltic andesites on the basis of lithological associations and spatial relationships we divide the basalts into four groups i e tahe genhe zalute and xiwu the early cretaceous volcanism in the great xinggan range is characterized by significant large ion lithophile elements lile and light rare earth elements lree enrichment and high field strength elements hfse depletion with a slightly enriched to depleted nd hf and weakly enriched sr isotopic compositions initial 87sr 86sr 0 7046 0 7079 end t 3 6 to 6 9 and ehf t 8 9 to 4 6 the pb isotopic compositions are also variable with 206pb 204pb 207pb 204pb and 208pb 204pb values of 17 791 18 530 15 477 15 597 and 37 761 38 497 respectively the sr nd pb hf isotopic data indicate that the magmatic sources are heterogeneous showing an enriched to depleted signature of continental lithospheric mantle the magmatic sources of the genhe and zalute groups are characterized by mixing among pm em ii and dm whereas the tahe and xiwu groups derive from enriched lithospheric mantle that had experienced metasomatism by fluids or melts from subducted paleo asian and mongol okhotsk ocean slabs and possible influence of precambrian blocks the late mesozoic volcanic rocks in the great xinggan range resemble those of the cenozoic calc alkaline magmatism in the basin and range province of the united states we therefore suggest that the widespread mesozoic volcanic rocks in the great xinggan range were generated in an extensional tectonic setting

a magmatic hydrothermal origin for ag pb zn vein formation at the bianjiadayuan deposit inner mongolia ne china evidences from fluid inclusion stable c h o and noble gas isotope studies abstract many new discoveries of base and precious metal veins in the great hinggan range district have made this region the most important ag pb zn metallogenic belt in northern china the bianjiadayuan ag pb zn deposit 4 81 mt 157 g t ag and 3 94 pb zn is one of the new discoveries located in the southern segment of this potentially important but poorly understood metallogenic belt vein type ag pb zn ore bodies are predominantly hosted by slate adjacent to a sn cu mo mineralized porphyry intrusion four primary ore stages of arsenopyrite pyrite quartz main sulfides quartz silver bearing sulfosalts quartz and boulangerite calcite are recognized and a subsequent supergene oxidation stage has also been identified an alteration assemblage of quartz sericite chlorite and epidote is spatially associated with this vein type mineralization the dh2o 139 to 106 and 18oh2o 16 4 to 12 1 isotope compositions obtained from different stage vein quartz and calcite reveal that the early stage ore fluids were dominated by magmatic fluids whereas the late stage ore fluids contained a significant proportion of meteoric waters which is consistent with the 13cpdb 7 7 to 2 7 and 18osmow 0 4 to 6 4 isotope signatures for waning stage calcites reflecting an addition of large volumes of meteoric waters in hydrothermal system noble gas isotopes i e 3he 4he ratios of 1 52 3 06 ra display evidences of a magmatic fluid responsible for ore formation in the deposit fluid inclusion studies suggest that vein formation occurred at progressively lower temperature 310 220 c and pressure 100 20 bars fluid cooling phase separation and mixing with meteoric waters are advocated as the important factors for ore deposition in combination available data for the bianjiadayuan deposit suggest that local ag pb zn veins and porphyry type sn cu mo mineralization are genetically related and formed in one porphyry ore system which is a useful concept for local and regional ag pb zn exploration

sulfur and lead isotopic compositions of bairendaba and weilasituo silver polymetallic deposits inner mongolia the bairendaba and weilasituo ore deposits are two silver polymetallic deposits discovered in eastern inner mongolia in recent years researches on the sulfur and lead isotopes of the sulfides from these two deposits are reported in this paper it is shown that the 34s values of the sulfides from the bairendaba and the weilasituo deposit vary from 4 0 to 1 6 and from 0 8 to 2 0 respectively close to the sulfur isotopic composition of the magmatic hydrothermal fluid suggesting that the sulfur in both the bairendaba and the wei lasituo deposit were mainly derived from the magma lead isotope studies of 43 sulfide separates from the bairendaba deposit and 20 sulfide separates from the weilasituo deposit demonstrate that the lead isotopic composition of sulfides from ores in these two deposits is characterized by low radiogenic values and narrow ranges of ratios with 206pb 204pb ranging from 18 333 to 18 515 and from 18 304 to 18 377 respectively 207pb 204pb from 15 532 to 15 656 and from 15 520 to 15 610 respectively and 208pb 204pb from 38 057 to 38 610 and from 38 112 to 38 435 respectively it is thus inferred that the lead in ores from these two deposits might have mainly come from the wall rocks of gneiss and deep magma

mineralogical textural sulfur and lead isotope constraints on the origin of ag pb zn mineralization at bianjiadayuan inner mongolia ne china degao zhai jiajun liu nigel j cook xilong wang yongqiang yang anli zhang yingchun jiao

oscillatory porewater bioadvection in marine sediments induced by hydraulic activities of arenicola marina we employed real time pressure recording and high temporal resolution two dimensional oxygen imaging to characterize the porewater bioadvection related to hydraulic activities of arenicola marina a widespread representative of benthic macrofauna behavior specific positive and negative pressure oscillations and hydraulic pulses resulted in bidirectional porewater flow and highly dynamic redox oscillations on the scale of minutes pumping of water by the worm into its blind ending burrow pressurized the sediment and caused sediment oxygenation at depth and the exit of anoxic porewater into the overlying water the sediment volume that was affected by bioadvective transport of oxygen and the porewater flow patterns varied strongly among sediment types in low permeability sediments localized plumes of anoxic porewater ascended from the sediment presumably through sedimentary cracks while porewater flowed evenly through highly permeable sediments hydraulic behaviors that moved water out through the open tail shaft caused a reduction of porewater pressures below the hydrostatic baseline which resulted in the collapse of plumes and enhanced oxygen penetration into the surficial sediments porewater bioadvection and the related perfusing and oscillatory phenomena will affect a variety of biogeochemical and ecological processes including organic matter mineralization benthic recruitment and prey localization we suggest that bidirectional porewater bioadvection and the associated transient geochemical conditions are prevalent features of biogenically active sediments

petrogenesis of the linxi granitoids northern inner mongolia of china constraints on basaltic underplating five representative granitoid plutons in the linxi area northern inner mongolia of china divided into two suites are mainly granodiorite and syenogranite and correspond to i and a type granites respectively zircon u pb dating yields an age of 230 ma but most ages range from 149 ma to 111 ma for intrusion of the five plutons suite 1 granitoids show lower sio2 66 1 72 51 and k2o higher al2o3 cao mgo feo and tio2 higher sr ba and eu and lower sm gd nb y and yb than suite 2 granitoids 71 73 78 14 sio2 modeling of major and trace elements shows that fractional crystallization of hornblende and lesser amounts of feldspars for suite 1 and plagioclase and alkali feldspar for suite 2 with overprint of magmatic hydrothermal fluids can explain the geochemical variations the linxi granitoids have initial end t values varying between 5 60 and 2 89 and initial 87 sr 86 sr t ratios ranging from 0 701764 to 0 707654 geochronology of inherited zircons coupled with the nd sr isotopic comparison between granitoids late jurassic basalts and proterozoic gneisses indicates that the linxi granitoids derive from a mixed source of dominantly underplated material or mafic magma with various amounts of the proterozoic gneiss basaltic underplating provides both material and heat to produce the late jurassic to early cretaceous granitoids variation of end t and 87 sr 86 sr t with age suggests involvement in the melting of increasingly greater amounts of the old lower crustal rock our refined equation yields less scattered nd isotope depleted mantle model ages the least fractionated granitoids from each suite have low ca sr rb sr rb ba and k ba ratios and hence represent parental magmas suite 1 parent magma is produced by dehydration melting or derives principally from the fluid metasomatized mantle melting of the underplated tholeiites and their differentiated products generates suite 2 parent magma d 2005 elsevier b v all rights reserved

simultaneous measurement of sulfur and lead isotopes in sulfides using nanosecond laser ablation coupled with two multi collector inductively coupled plasma mass spectrometers abstract we herein report the coupling of a nanosecond laser ablation system with a large scale multi collector inductively coupled plasma mass spectrometer nu1700 mc icpms np 1700 and a conventional nu plasma ii mc icpms np ii for the simultaneous laser ablation and determination of in situ s and pb isotopic compositions of sulfide minerals we found that the required aerosol distribution between the two spectrometers depended on the pb content of the sample for example for a sulfide containing 100 3000 ppm pb the aerosol was distributed between the np 1700 and the np ii spectrometers in a 1 1 ratio while for lead contents 3000 and

geochronology fluid inclusions and isotopic characteristics of the xiaoshan gold deposit henan province china abstract the xiaoshan gold deposit of western henan province is located in the southern margin of the north china craton ncc ore bodies of the deposit occur as veins in the fault zones the ore forming process can be divided into three stages an early quartz pyrite stage a middle quartz polymetallic sulfide stage and a late quartz carbonate stage the la icp ms zircon u pb age of the houhe granite which is related to au mineralization of the xiaoshan deposit was 139 137 ma the initial 176hf 177hf values of the houhe intrusion are 0 282126 0 282368 with the ehf t tdm1 hf and tdm2 hf values being 19 9 to 11 3 1242 1583 ma and 1912 2454 ma respectively indicating that the houhe granite is formed by partial melting of the lower crust and that the source is mainly the taihua group two types of fluid inclusions fis have been distinguished in various quartz veins including liquid rich wl type and h2o co2 c type inclusions the fis in the quartz of the quartz pyrite stage comprise wl and c type inclusions their homogenization temperatures salinities and densities vary from 300 c to 393 c 1 6 wt to 11 0 wt nacl eqv and 0 57 to 0 82 g cm3 respectively the fis in the quartz of the quartz polymetallic sulfide stage consist of wl and c type inclusions their homogenization temperatures salinities and densities range from 261 c to 298 c 1 1 wt to 11 8 wt nacl eqv and 0 74 to 0 89 g cm3 respectively only wl type inclusions are observed in the quartz of the quartz carbonate stage their homogenization temperatures salinities and densities vary from 193 c to 258 c 2 2 wt to 12 7 wt nacl eqv and 0 87 to 0 97 g cm3 respectively the ore forming fluids of the xiaoshan gold deposit are generally characterized by medium temperature moderate low salinity low density and belonging to an h2o nacl co2 system the 18oh2o values calculated for ore bearing quartz vary from 0 7 to 4 5 and the dv smow values from bulk extraction of fluid inclusion water vary from 69 5 to 47 8 suggesting that the ore forming fluid consists dominantly of magmatic water the 34sv cdt values range from 0 37 to 3 9 the 206pb 204pb 207pb 204pb and 208pb 204pb values of the ore minerals are in the ranges of 17 391 17 728 15 420 15 577 and 37 420 37 923 respectively the data from the s and pb isotopic systems indicate that the ore forming materials came from granitic magma the xiaoshan gold deposit is a mesothermal lode gold deposit of magmatic hydrothermal origin fluid phase separation and temperature decrease were the dominant mechanisms for the deposition of ore forming materials

mineragraphy of bairendaba and weilasituo silver polymetallic deposits in inner mongolia bairendaba and weilasituo are two silver polymetallic deposits discovered in recent years in eastern inner mongolia mineragraphic studies by using the semedx revealed the modes of occurrence of the silver bearing minerals such as allargentium dyscrasite argentobismutite freibergite and native silver metallic minerals in these two deposits are summarized systematically including their modes of occurrence and formation sequences the commonly existent jelly like pyrite is regarded as the product of the earliest ore forming stage suggesting a hot water sedimentary environment at low temperature during the later meso hypothermal ore forming process the assemblage of pyrite sphalerite galena pyrrhotite chalcopyrite arsenopyrite cassiterite was formed subsequently these minerals were crushed and mylonitized intensely and the ores were characte rized by plastic deformation brecciated and mylonitic structure after this structural deformation another meso hypothermal ore forming process took place forming the s rich metallic mineralization and bi ag sulfides of pyrite native bismuth argentobismutite galena pyrrhotite sphalerite chalcopyrite during the subsequent meso epithermal ore forming process a series of s poor sb and ag rich sulfides were formed such as pyrrhotite galena sphalerite robinsonite freibergite allargentium dyscrasite native silver in general three periods composed of 4 stages of mineralization occurred in the ore deposits whereas pb and zn mineralizations were related to the second and third periods and the silver mineralization was probably related to the late stage of the third period

pathways of organic carbon oxidation in three continental margin sediments we have combined several different methodologies to quantify rates of organic carbon mineralization by the various electron acceptors in sediments from the coast of denmark and norway rates of nh4 and sigma co2 liberation sediment incubations were used with o2 penetration depths to conclude that o2 respiration accounted for only between 3 6 17 4 of the total organic carbon oxidation dentrification was limited to a narrow zone just below the depth of o2 penetration and was not a major carbon oxidation pathway the processes of fe reduction mn reduction and sulfate reduction dominated organic carbon mineralization but their relative significance varied depending on the sediment where high concentrations of mn oxide were found 3 4 wt mn only mn reduction occurred with lower mn oxide concentrations more typical of coastal sediments fe reduction and sulfate reduction were most important and of a similar magnitude overall most of the measured o2 flux into the sediment was used to oxidized reduced inorganic species and not organic carbon we suspect that the importance of o2 respiration in many coastal sediments has been overestimated whereas metal oxide reduction both fe and mn reduction has probably been well underestimated

compositions of sandstones in circum pacific subduction complexes and fore arc basins arc trench systems of the circum pacific orogenic belt contain voluminous sandstones within fore arc terranes that include complexly deformed subduction complexes and relatively undeformed fore arc basins of several types turbidites incorporated within subduction complexes include not only axially transported trench fill but also abyssal plain sediments deposited on the sea floor beyond the trench and slope basin deposits perched on the accretionary trench slope mean framework modes of circum pacific sandstone suites can be expressed adequately by the use of qfl and qmflt plots supplementary qmpk and qplvls plots depict partial modes of mineral grains alone and polycrystalline lithic fragments respectively source rocks were mainly volcanic and plutonic terranes of he circum pacific magmatic arcs although some recycled sedimentary and metasedimentary debris is also present analysis of point counts for 2 587 rocks grouped into 104 suites from california the pacific northwest southern alaska southwest japan and new zealand indicates that the characteristic fore arc sandstones display similar compositional ranges everywhere and can be termed the circum pacific volcano plutonic graywacke suite knowledge of their petrology may aid the recognition of analogous tectonic settings in the geologic past frameworks vary across a compositional spectrum that ranges chiefly from feldspatholithic sands derived mainly from volcanic cover in undissected magmatic arcs to lithofeldspathic sands derived largely from plutonic batholiths in dissected magmatic arcs quartz contents are typically intermediate and the feldspar to quartz ratio is semiconstant plagioclas is the dominant feldspar and volcanic rock fragments are commonly the most abundant lithic fragments interpretations of compositional trends within subduction complexes and adjacent fore arc basins imply that simple transverse delivery of sediment from the arc orogene to the fore arc region is not the rule instead sand evidently is distributed along subduction zones by longitudinal turbidity currents initiated at widely spaced sediment delivery points where sediment derived from tectonic culminations along the arc trench system can bypass the sediment traps of fore arc basins moreover turbidites shed from dormant or transform segments of arc orogenes are locally spread far into the ocean basin as abyssal plains which are later rafted bodily into the subduction zone finally no sedimentologic explanations of compositional contrasts across fore arc graywacke terranes can be acce ted without considering the alternative of postdepositional tectonic transport by strike slip

genesis of the changlingzi zn pb deposit in the southern great xing an range northeastern china constraints from fluid inclusions and h o s pb isotope systematics the changlingzi pb zn deposit is located in the southern great xing an range metallogenic belt of northeast china this deposit experienced two types of mineralization including skarn ore block i

fluid immiscibility in natural processes use and misuse of fluid inclusion data ii interpretation of fluid inclusion data in terms of immiscibility abstract phase equilibrium analysis of the relevant systems together with the application of the principles of chemical equilibrium put severe constraints on the interpretation of fluid inclusion data in terms of immiscibility in part i following from that point the major limits on the accuracy and even the validity of fluid inclusion quantitative data and their interpretation in terms of fluid composition and density are briefly discussed the practical implications of the general constraints temperature pressure topology of the fluid systems are envisaged emphasis is laid on some important consequences such as the use of isochore intercepts and the possible resulting interpretation of fluid mixing rather than unmixing the case of highly saline inclusions the identification and interpretation of heterogeneous trapping the composition and density constraints on coexisting fluids are presented and illustrated by natural examples taking into account all the measurable parameters in fluid inclusions volume temperature and nature of phase transitions more or less complete individual spectroscopic analyses all the available experimental data and all the theoretical constraints may be long and difficult however it is most generally very informative and productive although part of these data is often sufficient to deny unmixing nevertheless a final example on metamorphic fluids demonstrates how such an approach can prove and also characterize a fluid unmixing during a geologic process

geochemical studies of the tongyoung gold silver deposits republic of korea evidence of meteoric water dominance in a te bearing epithermal system epithermal gold silver vein mineralization of the tongyoung mine was deposited in five stages i to v of quartz rhodochrosite calcite sulfide veins 0 3 7 0 m thick which fill fault planes in cretaceous volcanic rocks of the gyeongsang basin k ar dating of alteration sericite 72 9 or 1 2 ma indicates a late cretaceous age for ore mineralization stages i and ii are au ag bearing whereas stages iii iv and v are barren ore grades average 12 g metric ton gold with a gold silver ratio of 1 11 stage ii is composed of five rhythmically banded substages which show a progressive change in ore mineralogy with increasing paragenetic time electrum 68 wt au electrum 65 wt au argentitc electrum 50 wt au ag tellurides ag tellurides native silver the shift in mineralogy reflects decreases in temperature and fugacity of sulfur with a concomitant increase in fugacity of tellurium fluid inclusion data indicate a history of progressive cooling and dilution of ore forming fluids during stages i and ii higher temperature and salinity fluids 260 degrees c 6 equiv wt nacl mixed with cooler less saline waters resulting in most ore deposition from fluids of intermediate temperature and composition 190 degrees 230 degrees c 2 5 4 5 equiv wt nacl continued cooling and dilution coupled with decreasing fugacity of sulfur resulted in deposition of ag te mineralization and ultimately in barren stage iii and iv quartz and stage v calcite stable isotope compositions of mineralizing fluids from tongyoung delta d 44 to 61ppm delta 18 o 6 8 to 9 4ppm are similar to modern meteoric and thermal spring waters in the area and indicate meteoric water dominance during all stages of the au ag te mineralizing system comparison of tongyoung to other au ag te deposits indicates that its complex sequence of mineralization is a natural consequence of repeated inundation of a hydrothermal system by progressively cooler meteoric waters

the granite porphyry hidden in the shuangjianzishan deposit southern great xing an range ne china geochronology isotope geochemistry and tectonic implications

advection around ventilated u shaped burrows a model study 1 advective transport in the porous matrix of sediments surrounding burrows formed by fauna such as chironomus plumosus has been generally neglected a positron emission tomography study recently revealed that the pumping activity of the midge larvae can indeed induce fluid flow in the sediment we present a numerical model study which explores the conditions at which advective transport in the sediment becomes relevant a 0 15 m deep u shaped burrow with a diameter of 0 002 m within the sediment was represented in a 3 d domain fluid flow in the burrow was calculated using the navier stokes equation for incompressible laminar flow in the burrow and flow in the sediment was described by darcy s law nonreactive and reactive transport scenarios were simulated considering diffusion and advection the pumping activity of the model larva results in considerable advective flow in the sediment at reasonable high permeabilities with flow velocities of up to 7 0 10 6 m s 1 close to the larva for a permeability of 3 10 12 m2 at permeabilities below 7 10 13 m2 advection is negligible compared to diffusion reactive transport simulations using first order kinetics for oxygen revealed that advective flux into the sediment downstream of the pumping larva enhances sedimentary uptake while the advective flux into the burrow upstream of the larvae inhibits diffusive sedimentary uptake despite the fact that both effects cancel each other with respect to total solute uptake the advection induced asymmetry in concentration distribution can lead to a heterogeneous solute and redox distribution in the sediment relevant to complex reaction networks

conglomerate hosted copper mineralization in cretaceous andean molasse the coloso formation of northern chile alluvial fan sediments of the lower cretaceous coloso formation of northern chile were deposited during the evolution of a half graben arid intra arc basin the sediments were derived from an andesitic volcanic arc and show compositional variation which can be interpreted as an unroofing sequence copper mineralization is stratigraphically restricted to the upper 150 m of the sequence in conglomerates of predominantly granodioritic composition the presence of mineralized clasts at this level indicates the erosion of bedrock mineralization lead isotopic signatures of ore sulphide support the sedimentological evidence for derivation of the sediments and metals from an island arc volcano plutonic complex to the west of the basin a genetic model is proposed in which uneconomic metal concentrations were transported into the basin as detrital phases and released by diagenetic reactions the precipitation of copper minerals followed authigenic formation of quartz feldspar analcime and calcite and also some secondary parosity generation copper minerals include the oxychloride atacamite and the suphides bornite digenite djurleite and covellite sulphur isotope values for the sulphides are relatively heavy isotope enriched 34 s 3 6 to 12 8 although these results could be interpreted in terms of closed system bacterial sulphide reduction there is no known occurrence of organic material within the coloso basin an alternative explanation involving the mixing of diagenetically derived copper rich brines and sulphur rich hydrothermal fluids is proposed to account for the coloso mineralization

three step continental crust growth from subduction accretion and underplating through intermediary differentiation to granitoid production sensitive high resolution ion microprobe shrimp u pb dating laser ablation multi collector icpms hf isotope and electron microprobe element analyses of inherited antecrystal and magmatic zircons from five granitoid intrusions of linxi area in the southern segment of the great xing an range of china were integrated to solve continental crustal growth mechanisms these intrusions were divided into two suites suites 1 and 2 are mainly granodiorite and syenogranite and correspond to magnesian and ferroan granites respectively shrimp dating establishes an early cretaceous 135 125 ma age for most linxi granitoids and a time of 146 ma when their source rocks were generated or re melted however some granitoids were generated in early triassic 241 ma and late jurassic 146 ma after their source rock experienced precursory melting episodes at 263 ma and 165 ma respectively all zircon 206pb 238u ages 300 ma n 100 and high positive zircon ehf t values n 175 suggest juvenile source materials with an absence of precambrian basement hf nd isotopic decoupling of linxi granitoids suggests a source component of pelagic sediments i e paleozoic subduction accretion complexes zircon ehf t values t 263 165 ma form a trend sub parallel to the depleted mantle hf isotope evolution curve whilst those with t 146 125 ma fall markedly below the latter the first trend indicates a provenance from essentially subducted oceanic slabs however the abrupt ehf t decrease together with extensive early cretaceous magmatism is interpreted as reflecting mantle upwelling and resultant underplating and exhumation of subducted oceanic slabs suite 1 granitoids derive mainly from subducted oceanic slabs or paleozoic subduction accretion complex whereas suite 2 from underplated mafic rock and subordinately paleozoic subduction accretion complex compositions of suites 1 and 2 depend on the hydrous oxidized or relatively anhydrous reduced nature of source rocks among each of these five intrusions magmatic zircons have systematically lower 176hf 177hf than inherited antecrystal zircons hf isotopic and substituting element profiles through inherited antecrystal zircons t 263 to 146 ma indicate repeated low melt fraction melting in the source region in contrast profiles through inherited antecrystal and magmatic zircons t 146 125 ma reveal melting region expansion with a widening range of source compositions and increasing melt fractions these results lead to the conclusion that continental growth in this region involved a three step process this included subduction accretion and repeated underplating intermediary differentiation of juvenile rocks and granitoid production from these differentiated rocks

genesis of the hardat tolgoi ag pb zn deposit inner mongolia northeast china constraints from geology fluid inclusions and c o s pb isotope systematics abstract the hardat tolgoi ag pb zn deposit 4 3 mt at 3 15 pb zn and 26 4 g t ag is located in the erenhot east ujimqin polymetallic metallogenic belt on the western part of the great xing an range inner mongolia northeast china the ag pb zn mineralization mainly occurs as vein type ores hosted in argillaceous siltstone feldspar quartz sandstone with silty slate interlayers of the aobaotinghundi formation of lower devonian the hydrothermal ore forming process can be divided into three stages i e quartz pyrite arsenopyrite stage i quartz polymetallic sulfides stage ii and quartz calcite fluorite stage iii four types of fluid inclusions have been identified in the quartz bearing veins of each stage i e liquid rich two phase l type single liquid phase pw type vapor rich two phase v type and pure vapor phase pv type inclusions the fluid inclusions of stage i to iii yield homogenization temperatures of 285 407 c 202 317 c and 144 239 c with salinities of 1 2 9 2 wt nacl equiv 0 9 5 0 wt nacl equiv and 0 2 2 6 wt nacl equiv respectively the ore forming fluids at hardat tolgoi are characterized by moderate temperatures low salinities and low densities and dominated by the h2o nacl system carbon and oxygen isotope compositions of calcite demonstrate that the ore forming fluids come from a primary magmatic hydrothermal system with subsequent involvement of meteoric water at a later stage sulfur isotope analyses of sulfides yield 34sv cdt values of 1 8 to 8 7 with calculated 34sh2s values of 1 4 to 9 4 the 206pb 204pb 207pb 204pb and 208pb 204pb ratios of sulfides range from 18 141 to 18 468 15 521 to 15 617 and 38 040 to 38 377 respectively similar to those of granites from the hardat tolgoi deposit both sulfur and lead isotope data indicate that the ore forming metals were most likely derived from the magmatic reservoirs and sedimentary country rocks the available fluid inclusion results and isotope studies indicate that the pahse separation temperature decrease and fluid mixing resulted in large scale ag pb zn ore formation at hardat tolgoi

the crustal accretion history and tectonic evolution of the ne china segment of the central asian orogenic belt abstract the basement rocks in parts of ne china constitute a khondalitic sequence of sillimanite and garnet bearing gneisses hornblende plagioclase gneiss and various felsic paragneisses zircon u pb dating of garnet sillimanite gneiss samples from the erguna xing an jiamusi and khanka blocks indicates that high grade metamorphism occurred at 500 ma evidence from detrital zircons in paleozoic sediments from the songliao block also indicates the former presence of a 500 ma component this uniformity of u pb ages across all crustal blocks in ne china establishes a 1300 km long late pan african khondalite belt which we have named the ne china khondalite belt this indicates the blocks of ne china were amalgamated prior to 500 ma contrary to current belief one scenario is that this amalgamated terrane had a tectonic affinity to the siberia craton once forming part of the late pan african 500 ma sayang baikal orogenic belt extensively developed around the southern margin of the siberia craton this belt was the result of collision between currently unidentified terranes with the southeastern angara anabar province at about 500 ma where the rocks were deformed and metamorphosed to granulite facies it appears likely that at sometime after 450 ma the combined ne china blocks rifted away from siberia and moved southward to form what is now ne china the combined block collided with the north china craton along the solonker xar moron changchun suture zone at 230 ma rather than in the end permian as previously thought local rifting at the eastern extremity of the developing central asian orogenic belt caob resulted in the splitting away of the jiamusi khanka bureya blocks however this was only transient and sometime between 210 and 180 ma these were re united with the caob by the onset of pacific plate subduction which has dominated the tectonic evolution of the region since that time

petrogenesis and metallogenic potential of the wulanba granite southern great xing an range ne china constraints from whole rock and apatite geochemistry the wulanba granite consisting of biotite monzogranite and syenogranite is located in the southern part of the great xing an range ne china whole rock major and trace element geochemistry suggests the wulanba granite is a high k shoshonitic slightly peraluminous and highly differentiated i type granite the sr nd hf isotopes indicate that it originated from partial melting of juvenile crust derived from the depleted mantle with a minor input of old crust the relatively young t 2dm and t dm2 ages indicate it was most likely derived from a late neoproterozoic to early palaeozoic source we have demonstrated that the biotite monzogranite is the ore related intrusion of the haobugao zn fe mineralization based on the following geological geochronological and geochemical evidence 1 the chalcopyrite pyrite in the biotite monzogranite and the continuous mineralization of drill core zk2508 2 the consistence of the emplacement age of the biotite monzogranite 141 140 138 ma with the skarn mineralization age 142 ma and 3 the presence of rich ore forming elements fe zn cu in the biotite monzogranite and the similar pb compositions of the sulfides from the haobugao deposit and the biotite monzogranite compared to the barren syenogranite the fertile biotite monzogranite is more oxidized while the edges of the apatite grains in the biotite monzogranite are more oxidized than the centres the average f cl ratio of the fertile biotite monzogranite 123 45 is much higher than that of the barren syenogranite 73 98 we conclude that these differences reflect unique geochemical signatures and the geochemical composition of the apatite can be used to infer the economic potential of granites

fluid inclusions and isotopic characteristics of the jiawula pb zn ag deposit inner mongolia china abstract the large jiawula pb zn ag deposit is located in the derbugan metallogenic belt of the northern great xing an range the vein style orebodies of the deposit occur along nww to nnw trending fault zones the ore forming process at the deposit can be divided into three stages an early quartz pyrite pyrrhotite chalcopyrite stage a middle quartz carbonate pyrite galena sphalerite stage and a late quartz carbonate pyrite stage sulfide rb sr dating indicates that the jiawula deposit formed at ca 143 142 ma four types of fluid inclusions have been distinguished in quartz veins including liquid rich gas rich h2o co2 and daughter mineral bearing inclusions the fluid inclusions of the early stage are mainly liquid rich gas rich and h2o co2 types with a small number containing daughter minerals cumulatively the types have homogenization temperatures densities and salinities of 304 438 c 0 35 1 37 g cm3 and 0 8 44 6 wt nacl eqv respectively inclusions of the middle stage are mainly liquid rich and gas rich types with a small amount of h2o co2 and daughter mineral bearing types their homogenization temperatures densities and salinities vary from 242 c to 297 c 0 71 to 1 44 g cm3 and 0 4 wt to 36 8 wt nacl eqv respectively the late stage only comprises liquid rich inclusions with homogenization temperatures densities and salinities of 181 238 c 0 81 0 90 g cm3 and 0 2 1 9 wt nacl eqv respectively the ore forming fluids of the jiawula deposit are generally characterized by moderate temperature and low salinity and density and belong to an h2o nacl co2 ch4 system the 18owater values calculated for ore bearing quartz vary from 13 4 to 9 1 and the dv smow values from bulk extraction of fluid inclusion waters vary from 166 to 133 suggesting that the ore forming fluids mainly consist of meteoric water with a small amount of magmatic water the 34sv cdt values range from 1 2 to 8 4 the 206pb 204pb 207pb 204pb and 208pb 204pb values of the ore minerals are in the ranges of 18 319 18 377 15 499 15 596 and 38 094 38 314 respectively initial 87sr 86sr ratios of sulfides range from 0 712381 to 0 712770 the data for the s pb and sr isotopic systems indicate that the ore forming metals and sulfur came from mesozoic magma the jiawula deposit is a low sulfidation epithermal pb zn ag deposit and fluid boiling is the dominant mechanism for the deposition of ore forming materials

sedimentary and diagenetic controls on red bed ore genesis the middle tertiary san bartolo copper deposit antofagasta province chile the middle tertiary pacencia group of antofagasta province northern chile consists of over 2 km of continental sediments these include alluvial fan playa and lacustrine facies representing deposition in an arid closed basin copper mineralization is hosted by sheet and ribbon sandstone bodies which were deposited in a high energy playa marginal sandflat environment ore minerals occur dominantly as a matrix to these lithic arkoses replacing earlier carbonate and sulfate cements the main ore minerals are native copper cuprite and atacamite although there is an along strike passage into copper sulfide cements in a structurally complex zone copper iron and copper sulfides were deposited in crosscutting fractures commonly replacing evaporite veins primary chalcopyrite and bornite exhibit progressive oxidation to anilite digenite and djurleite chalcocite is not found much of this material has oxidized further to covellite of normal and blaubleibender varieties galena and native silver are present in uneconomic amounts atacamite has a complex paragenesis representing at least locally the earliest copper bearing phase provenance studies of the host sediments and lead isotope data for the sulfides indicate that both the sandstones and the metals were derived from a calc alkaline volcano plutonic complex to the east of the basin an area now obscured by the recent volcanic andes sulfur isotope results for copper sulfides show very light delta 34 s values 33ppm indicative of biogenic sulfate reduction under conditions of unrestricted sulfate supply

paleozoic multiple accretionary and collisional tectonics of the chinese tianshan orogenic collage abstract subduction related accretion in the junggar balkash and south tianshan oceans paleo asian ocean mainly in the paleozoic gave rise to the present 2400 km long tianshan orogenic collage that extends from the aral sea eastwards through uzbekistan tajikistan kyrgyzstan to xinjiang in china this paper provides an up to date along strike synthesis of this orogenic collage and a new tectonic model to explain its accretionary evolution the northern part of the orogenic collage developed by consumption of the junggar balkash ocean together with paleozoic island arcs northern ili issyk kul and chatkal located in the west which may have amalgamated into a composite arc in the paleozoic in the west and by addition of another two roughly parallel arcs dananhu and central tianshan in the east the western composite arc and the eastern dananhu and central tianshan arcs formed a late paleozoic archipelago with multiple subduction zones the southern part of the orogenic collage developed by the consumption of the south tianshan ocean which gave rise to a continuous accretionary complex kokshaal kumishi which separated the central tianshan in the east and other paleozoic arcs in the west from cratons tarim and karakum to the south cross border correlations of this accretionary complex indicate a general southward and oceanward accretion by northward subduction in the early paleozoic to permian as recorded by successive southward juxtaposition of ophiolites slices of ophiolitic melanges cherts island arcs olistostromes blueschists and turbidites which are mainly paleozoic in age with the youngest main phase being late carboniferous permian the initial docking of the southerly tarim and karakum cratons to this complicated late paleozoic archipelago and accretionary complexes occurred in the late carboniferous early permian in the eastern part of the tianshan and in the late permian in the western part which might have terminated collisional deformation on this suture zone the final stages of closure of the junggar balkash ocean resembled the small ocean basin scenario of the mediterranean sea in the cenozoic in summary the history of the altaids is characterized by complicated multiple accretionary and collisional tectonics

the control of basin evolution on patterns of sedimentation and diagenesis an example from the mississippian great orme north wales the mississippian north wales platform is located on the margins of the east irish sea basin and has been little studied over the last 30 years the exposed visean limestones provide new insights into the deposition porosity evolution distribution of dolomitization and pb zn and cu mineralization on the north wales carbonate platform this is of relevance to the characterization of fault related dolomite hydrocarbon reservoirs and age equivalent mississippi valley type mineral deposits in particular the study demonstrates the intimate relationship between sedimentation basin scale tectonism and post depositional fluid flux depositional cyclicity is marked with metre scale upward shallowing cycles in which pervasive marine and meteoric calcite cements occlude matrix porosity and syndepositional fractures consequently subsequent burial diagenetic replacive dolomitization is matrix selective and cements are primarily restricted to fractures seven phases of dolomite are defined based on texture and cathodoluminescence petrography with phases d1 d3 as the most volumetrically significant dolomite phases d0 d2 are matrix replacive cross cutting stratigraphy and locally fingering along beds for several metres dolomite phases d3 d7 are hosted by faults and fractures and also line vugs evidence of telogenesis is recorded where burial diagenetic products are post dated by calcite cements precipitated from meteoric fluids dolomitization probably occurred during the mississippian and continued into the pennsylvanian pb zn mineralization is also interpreted to have occurred during the pennsylvanian associated with variscan tectonism overall the north wales platform displays a more complex paragenesis than age equivalent platforms in the pennine basin owing to multiple phases of burial and exhumation the study demonstrates the importance of linking burial history to detailed field and petrographical data to understand and predict the spatial and temporal controls on diagenetic processes and products within syn and post rift sequences

tectonic and magmatic evolution of the andes of northern argentina and chile abstract two orogenic cycles both with different evolution are developed in the western margin of the south american continent in northern argentina and chile the paleozoic hercynic cycle and the meso cenozoic andean cycle the hercynic cycle a wide marine basin extending westward of the cordillera oriental which developed in cambrian ordovician times marks the beginning of this cycle in contrast to peru and bolivia where this basin developed between two precambrian blocks the western margin of this basin in northern argentina and chile is still unknown the ordovician sedimentation and accompanied volcanism ends with the ocloyic deformation phase and its synkinematic granitic plutonism two basins were developed in the silurian devonian separated by the puna arc uplifted during this ocloyic phase the shallow water marine terrigeneous sediments which were deposited in them were deformed by a new tectono magmatic associated phase chanic phase carboniferous to lower permian marine carbonates were deposited west of the puna arc and red beds east of it later on during the permian to triassic a magmatic belt was developed along the cordillera occidental the rhyolites ignimbrites and the granitic to granodioritic related intrusives are well represented in chile although the overall geologic history of this period is known many problems concerning its origin and relations to plate tectonics are still unsolved the andean cycle during this cycle a series of magmatic arc systems related to the subduction of the pacific crust was built up along the western margin of south america huge volumes of calc alkaline lavas and related plutons were emplaced since the jurassic along belts parallel to the present coastline showing a general eastward migration trend up to the lower cretaceous an ensialic back arc basin was formed east of this magmatic arc thousands of meters of marine and continental sediments were deposited in it this basin disappeared during the middle cretaceous probably as a result of the final opening of the atlantic and the active westward movement of the south american plate since middle cretaceous times the magmatic arc has been the fundamental paleogeographic element the arc progressively migrated stepwise eastward each step marked by a tectonic phase subduction related crustal erosion could explain the lack of fore arc petrotectonic assemblages the eastward magmatic polarity which characterizes this section of the andes could also be explained by such a mechanism

albian cenomanian a type granite related ag pb zn veins in the central yidun terrane sw china constraints from the xiasai deposit the xiasai lianlong metallogenic belt in the central yidun terrane china hosts several sn ag and sn ag pb zn deposits which are spatially associated with cretaceous granites the xiasai ag pb zn deposit about 0 27 mt pb zn 1028 t ag and 20 000 t sn is the largest deposit in the belt and is related to a monzogranite intrusion the deposit consists of sulfides in hydrothermal veins resulting from three successive mineralization stages i iii a rb sr isochron of sphalerite samples yielded an age of 99 3 ma and zircon u pb laser ablation inductively coupled plasma mass spectrometry la icp ms dating of the xiasai monzogranite gave ages between 102 1 and 101 1 ma the xiasai monzogranite has a weakly peraluminous a type granite composition with high sio2 alkali and feot contents and low cao mgo and tio2 contents it is marked by enrichments in rb th and u with depletions in ba nb sr p and ti relative to the primitive mantle the ree patterns show a negative slope due to lree enrichment with negative eu anomalies eu eu 0 1 0 3 the xiasai monzogranite with variable ehf t values 2 7 to 0 6 and meso to neoproterozoic two stages hf model ages tdm2 925 1095 ma was probably derived from mixing of melts derived from partial melting of the paleoproterozoic crustal basement and the early cretaceous mantle in an extensional tectonic setting hydrothermal fluids are characterized by high temperatures 423 481 c and salinities 14 9 19 0 wt nacl for sn mineralization stage i moderate temperatures 285 386 c and salinities 3 5 8 0 wt nacl for the cu zn mineralization substage ii 2 and low temperatures 158 242 c and salinities 3 4 5 7 wt nacl for the ag pb mineralization substage ii 3 the h o isotopes indicate that the hydrothermal fluid likely has a magmatic component that mixed over time with infiltrating meteoric water and organic matter during fluid rock interactions the 34s values of sphalerite range from 9 7 to 3 1 and those from galena from 10 5 to 4 9 the estimated 34s value of the hydrothermal fluid is 8 5 using the sulfur isotopic fractionation of sphalerite galena pairs that are interpreted to be in equilibrium sulfides from substages ii 2 and ii 3 have relatively homogeneous pb isotopic compositions which are similar with those of k feldspars from the xiasai monzogranite geochronological and isotope data support a magmatic hydrothermal origin for the xiasai ag pb zn deposit

data for s isotopic geochemistry zircon and cassiterite u pb geochronology of the haobugao sn polymetallic deposit southern great xing an range ne china abstract the southern great xing an range sgxr is the most important tin polymetallic metallogenic belt in north china the lack of previous research on the genesis of the tin mineralization especially its exact age prevents development of a deep understanding of tin deposits in this area haobugao sn polymetallic deposit is a large skarn type deposit in the huangang ganzhuermiao sn fe cu pb zn ag metallogenic belt in the sgxr the ore body occurs in the contact zone between a yanshanian intrusion and permian dashizhai formation marble 34 s v cdt values of sulfides from the haobugao sn polymetallic deposit range from 4 7 to 3 5 with an average of 0 65 and these values strongly indicate a deep magmatic source for the sulfur in the ore minerals of the deposit in this paper we also report the results of la icp ms u pb dating of tin mineralization in no i ore body and of the underlying granite cassiterite from no 1 ore body deposited at 139 0 6 ma and the closely associated granite has an age of 142 9 1 6 ma the similar ages indicate that the tin mineralization was produced by early cretaceous magmatic hydrothermal activity these results together with the ages of other tin deposits and related granites indicate extensive granitic magmatism and tin mineralization during the early cretaceous in the southern segment of the great xing an range

diagenetic processes and the mineralization in the triassic of central england continental red beds are the host rocks of a characteristic style of mineralization which suggests a genetic link between red bed formation and ore formation samples of unmineralized and mineralized triassic sediments from central england have been studied sedimentologically petrographically and geochemically with the aim of clarifying this link which may provide valuable guides for exploration on the basis of sedimentological and petrographic observations it is suggested that these red beds were formed as a result of diagenetic alteration whereby detrital silicates and oxides are progressively dissolved and the iron released is deposited as hematite a model for mineralization is proposed involving the release of trace metals from detrital minerals during diagenesis their retention in saline interstitial solutions migration to suitable sites of precipitation and deposition by reaction with trapped hydrocarbons or reduced sulphur

isotopic c o s geochemistry and re os geochronology of the haobugao zn fe deposit in inner mongolia ne china abstract the haobugao zn fe deposit is a typical skarn deposit located in the southern part of the great xing an range that hosts polymetallic mineralization over a large region the main ore minerals at the deposit include sphalerite magnetite galena chalcopyrite and pyrite and the main gangue minerals include andradite grossular garnet hedenbergite diopside ilvaite calcite and quartz there are broadly two mineralizing periods represented by the relatively older skarn and younger quartz sulfide veins in detail there are five metallogenic stages consisting of an early skarn late skarn oxide early quartz sulfide and late quartz sulfide calcite stages electron microprobe analyses show that the garnet at the deposit varies in composition from and97 95gro0 41pyr1 64 to and30 69gro66 69pyr2 63 and pyroxene is compositionally in the diopside hedenbergite range i e di90 63hd8 00jo1 37 hd88 98di4 53jo6 49 petrographic observations and electron microprobe analyses indicate that the sphalerite has three generations zn0 93fe0 08 s zn0 75fe0 24 s the zn associated with the first generation sphalerite replaced cu and fe of early xenomorphic granular chalcopyrite i e cu1 01fe1 03 s2 cu0 99fe0 99 s2 and part of the first generation sphalerite is coeval with late chalcopyrite i e cu0 96fe0 99zn0 03 s2 cu1 00fe1 03zn0 01 s2 magnetite has a noticeable negative ce anomaly ce 0 17 to 0 54 which might be a result of the oxidized ore fluid thirty 34sv pdb analyses of sulfides from the ore range from 2 3 to 0 1 in value which are indicative of a magmatic source the 13c and 18o values for calcite from the ore formed at quartz sulfide calcite stage vary from 9 9 to 5 5 and from 4 2 to 1 1 respectively contrasting with 13c 2 9 4 8 and 18o 9 8 13 9 values for calcite from marble it is suggested that the ore forming fluid associated with late stage of mineralization was predominantly magmatic in origin with some input of local meteoric water molybdenite from the haobugao deposit defines an isochron age of 142 1 ma which is interpreted as the mineralization age being synchronous within error with the zircon u pb ages of 140 1 141 2 and 141 1 ma for granite at the deposit these data and characteristics of lithology and mineralization further show that the zn fe mineralization is temporally and spatially related to the emplacement of granite in an extensional tectonic setting during the mesozoic

geochronology and geochemistry constraints of the early cretaceous taibudai porphyry cu deposit northeast china and its tectonic significance abstract the southern great xing an range sgxr located in the southeastern part of inner mongolia china shows intense mesozoic tectono magmatic activity and hosts economically important polymetallic cu pb zn sn fe ag au mo mineralization here we present new zircon u pb ages whole rock geochemical data nd sr hf isotopic data and re os ages for the taibudai deposit in the sgxr the taibudai granitoids show high sio2 70 62 72 13 wt and alkali na2o k2o 7 04 8 60 wt concentrations low mgo 0 89 1 37 wt and al2o3 14 wt asi ratios

what drove late mesozoic extension of the northern china mongolia tract the northern china mongolia tract exhibited a tectonic transition from contractional to extensional deformation in late mesozoic time late middle to early late jurassic crustal shortening is widely thought to have resulted from collision of an amalgamated north china mongolia block and the siberian plate but widespread late late jurassic early cretaceous extension has not been satisfactorily explained by existing models some prominent features of the extensional tectonics of the northern china mongolia tract are 1 late jurassic voluminous volcanism prior to early cretaceous large magnitude rapid extension 2 overlapping in time of contractional deformation in the yinshan yanshan belt with development of extensionrelated basins in the interior of the northern china mongolia tract and 3 widespread occurrence of alkali granitic plutonism extensional basins and metamorphic core complexes in the early cretaceous a new explanation is advanced in this study for this sequence of events the collision of amalgamated north china mongolia with siberia led to crustal overthickening of the northern china mongolia tract and formation of a high standing plateau subsequent breakoff at depth of the north dipping mongol okhotsk oceanic slab is suggested as the main trigger for late mesozoic lithospheric extension of that tract slab breakoff resulted in mantle lithospheric stretching of the adjacent northern china mongolia tract with subsequent ascent of hot asthenosphere and magmatic underplating at the base of the crust collectively these phenomena triggered gravitational collapse of the previously thickened crust leading to late late jurassic early cretaceous crustal extension and importantly coeval contraction along the southern margin of the plateau in the yinshan yanshan belt the proposed model provides a framework for interpreting the spatial and temporal relationships of distinct processes and reconciling some seemingly contradictory phenomena such as the synchronous extension of northerly terranes during major contraction in the neighboring yanshan yinshan belt d 2003 elsevier b v all rights reserved

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

extensive nitrogen loss from permeable sediments off north west africa the upwelling area off north west africa is characterized by high export production high nitrate and low oxygen concentration in bottom waters the underlying sediment consists of sands that cover most of the continental shelf due to their permeability sands allow for fast advective pore water transport and can exhibit high rates of nitrogen n loss via denitrification as reported for anthropogenically eutrophied regions however n loss from sands underlying naturally eutrophied waters is not well studied and in particular n loss from the north west african shelf is poorly constrained during two research cruises in april may 2010 2011 sediment was sampled along the north west african shelf and volumetric denitrification rates were measured in sediment layers down to 8 cm depth using slurry incubations with 15n labeled nitrate areal n loss was calculated by integrating volumetric rates down to the nitrate penetration depth derived from pore water profiles areal n loss was neither correlated with water depth nor with bottom water concentrations of nitrate and oxygen but was strongly dependent on sediment grain size and permeability the derived empirical relation between benthic n loss and grains size suggests that pore water advection is an important regulating parameter for benthic denitrification in sands and further allowed extrapolating rates to an area of 53 000 km2 using detailed sediment maps denitrification from this region amounts to 995 kt yr 1 average 3 6 mmol m 2 d 1 which is 4 times higher than previous estimates based on diffusive pore water transport sandy sediments cover 50 60 of the continental shelf and thus may contribute significantly to the global benthic n loss

the impact of biological bedforms on near bed and subsurface flow a laboratory evaluated numerical study of flow in the vicinity of pits and mounds the complex surface topography of river substrates controls near bed hydraulics and drives the exchange of subsurface and surface flow in rivers the topographic structures that are studied are usually formed by the flow but it is known that many animals also create biogenic bedforms such as pits and mounds here a large eddy simulation les model of flow over a pit and a mound is evaluated with flume experiments the model includes actual bedform topography and the topographic complexity of the surrounding bed surface subsurface grains are organized in a body centered cubic packing arrangement model evaluation showed strong agreement between experimental and modelling results for velocity r2 0 8 and good agreement for reynolds stresses r2 0 7 which is comparable to other similar studies simulation of the pit shows that the length of the downwelling region is smaller than the upwelling region and that the velocity magnitude is higher in the downwelling region simulation of the mound reveals that the flow is forced into the bed upstream of the mound and re emerges near the top of the mound the recirculation zone is limited at the leeside of the mound with increasing reynolds number the depth of the upwelling region at the leeside of the mound increases the analysis of shear stress indicates that sediments on the upstream edge of the pit and on the downstream face of the mound are relatively unstable these results demonstrate the effect of biogenic structures on the near bed flow field hyporheic exchange and sediment stability

hydrochemistry of the saline groundwaters of the lower mersey basin permo triassic sandstone aquifer uk saline groundwater occurs at depth in the triassic sandstones of the northern end of the cheshire basin in northwest england major and minor ion data suggest that the origin of the salinity is dissolution of evaporite deposits the salinity probably developed in an interval following the tertiary inversion of the basin which would have allowed faulted contact between the sandstones and the overlying evaporite sequence of the mercia mudstone group isotope evidence suggests the saline waters to have been considerably diluted by presumably dispersive mixing with a meteoric water recharged under cool and therefore quaternary climatic conditions comparison with other uk permo triassic basin brines suggests the merseyside waters are not unusual except in terms of the importance of exchange reactions and dilution by quaternary recharge waters these factors are due to the shallow maximum burial depth of the aquifer and the preservation of smectites and also to the geometry of the aquifer and its low permeability faults in the light of the water chemistry data it is suggested in a slight modification of the proposal of naylor et al q geol soc lond 146 685 699 1988 that the cheshire basin mineralization resulted from mixing of the relatively oxidized so4 rich evaporite brines with the reduced so4 poor metal rich barich coal measures brines which were expelled through faults from the coal measures during basin inversion some degree of oxyhydroxide stripping of the sandstones by the coal measures brines would have enhanced metal concentrations the water resulting from the mixing of brines would have been far from equilibrium and the barite and sulphide precipitation followed along the faults

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

melting behavior of fluid inclusions in laboratory grown halite crystals in the systems naclh2o naclkclh2o naclmgcl2h2o and naclcacl2h2o abstract the chemical composition of aqueous fluid inclusions in crystals of halite can be accurately determined from observed melting behaviors of ice hydrohalite and sylvite some fluid inclusion melting behaviors observed in laboratory grown halite crystals systems nacl h 2 o nacl kcl h 2 o nacl mgcl 2 h 2 o and nacl cacl 2 h 2 o differ from predicted stable equilibrium relations in the nacl h 2 o and nacl kcl h 2 o systems observed first melt temperatures are up to 15 c below the equilibrium eutectic temperatures of 21 2 and 22 9 c respectively the final melting temperature of ice in the presence of hydrohalite and the final melting temperature of hydrohalite are reproducible and match predicted melting temperatures the limit of detection of sylvite daughter crystals in the nacl kcl h 2 o system is approximately 5 wt 1 molal kcl final melting temperatures of sylvite match published equilibrium data to within 0 3 c in the nacl kcl h 2 o system at halite saturation m kcl can be determined from the final sylvite dissolution temperature or from the final melting temperature of hydrohalite fluid inclusions in the nacl mgcl 2 h 2 o and nacl cacl 2 h 2 o systems that form stable salt hydrates mgcl 2 12h 2 o and cacl 2 6h 2 o during freezing first melt within 3 c of predicted eutectic temperatures 37 and 52 c however fluid inclusions with mgcl 2 or cacl 2 may also start melting at temperatures as low as 80 c such low first melt temperatures indicate the presence of metastable salt hydrates presumably mgcl 2 8h 2 o mgcl 2 6h 2 o or cacl 2 4h 2 o the formation of metastable phases during freezing of fluid inclusions can lead to misinterpretation of the chemical composition of fluid inclusions in natural samples this is especially true for fluid inclusions with first melt temperatures below 37 c which may be erroneously interpreted as being rich in cacl 2 the final melting of ice in the presence of hydrohalite may vary by more than 15 c in fluid inclusions of different size but identical bulk composition and occurs at lower temperatures than predicted in fluid inclusions from the nacl mgcl 2 h 2 o and nacl cacl 2 h 2 o systems however the final melting temperature of ice in inclusions which fail to nucleate hydrohalite and the final melting temperature of hydrohalite are reproducible to within 0 1 c and can be used to determine mgcl 2 and cacl 2 molalities

characterization of metal bearing particles in groundwater from the weilasituo zn cu ag deposit inner mongolia china implications for mineral exploration abstract nanoparticles in groundwater have important implications for facilitating the transportation of metals in groundwater and to a certain extent can reveal the geochemical conditions of the groundwater therefore there is an increasing interest in analytical techniques that allow for in depth characterization of nanoparticles in the groundwater and utilize these characteristics for geochemical prospecting metal bearing particles in groundwater samples from deep lying orebodies referred to as deep groundwater of the weilasituo zn cu ag deposit inner mongolia china and the groundwater from motor pumped wells of a catchment basin around weilasituo were chosen to study using high angle annular dark field scanning transmission electron microscopy haadf stem and transmission electron microscopy tem coupled with energy dispersive x ray spectrometer eds individual particles were characterized based on the tem compositional and structural investigation ag pb cu zn sn as and mo bearing particles were observed in the groundwater samples collected in the deep ore and the catchment basin these metal bearing particles are compositionally and structurally similar to the ore mineral metal bearing particles observed in the ore bodies and can directly reflect the ore forming elemental characteristics e g metallogenic element assemblage and mineralization type of the weilasituo deposit the result indicates that the metal bearing particles originating from the concealed ore bodies migrate via the groundwater flow and discharge to the catchment basin this finding implies that the metal bearing particle phases have great significances in facilitating the transportation of ore related species and forming the geochemical anomalies in the groundwater this field scale study demonstrates that by applying the analytical transmission electron microscopy the nanocharacteristics of metal particles can be utilized to improve the accuracy and sensitivity for geochemical mineral exploration

ore genesis and hydrothermal evolution of the huanggang skarn iron tin polymetallic deposit southern great xing an range evidence from fluid inclusions and isotope analyses abstract the southern great xing an range is one of the most important metallogenic belts in northern china and contains numerous pb zn ag cu sn fe mo deposits the huanggang iron tin polymetallic skarn deposit is located in the sn polymetallic metallogenic sub belt skarns and iron orebodies occur as lenses along the contact between granite plutons and the lower permian huanggangliang formation marble or dashizhai formation andesite field evidence and petrographic observations indicate that the three stages of hydrothermal activity i e skarn oxide and sulfide stages all contributed to the formation of the huanggang deposit the skarn stage is characterized by the formation of garnet and pyroxene and high temperature hypersaline hydrothermal fluids with isotopic compositions that are similar to those of typical magmatic fluids these fluids most likely were generated by the separation of brine from a silicate melt instead of being a product of aqueous fluid immiscibility the iron oxide stage coincides with the replacement of garnet and pyroxene by amphibole chlorite quartz and magnetite the hydrothermal fluids of this stage are represented by l type fluid inclusions that coexist with v type inclusions with anomalously low d values approximately 100 to 116 the decrease in ore fluid 18oh2o values with time coincides with marked decreases in the fluid salinity and temperature based on the fluid inclusion and stable isotopic data the ore fluid evolved by boiling of the magmatic brine the sulfide stage is characterized by the development of sphalerite chalcopyrite fluorite and calcite veins and these veins cut across the skarns and orebodies the fluids during this stage are represented by inclusions with a variable but continuous sequence of salinities mainly low salinity inclusions these fluids yield the lowest 18oh2o values and moderate d values 1 6 to 2 8 and 101 to 104 respectively the data indicate that the sulfide stage fluids originated from the mixing of residual oxide stage fluids with various amounts of meteoric water boiling occurred during this stage at low temperatures the sulfur isotope 34s values of the sulfides are in a narrow range of 6 70 to 4 50 mean 1 01 and the oxygen isotope 18o values of the magnetite are in a narrow range of 0 1 to 3 4 both of these sets of values suggest that the ore forming fluid is of magmatic origin the lead isotope compositions of the ore 206pb 204pb 18 252 18 345 207pb 204pb 15 511 15 607 and 208pb 204pb 38 071 38 388 are consistent with those of k feldspar granites 206pb 204pb 18 183 18 495 207pb 204pb 15 448 15 602 208pb 204pb 37 877 38 325 but significantly differ from those of permian marble 206pb 204pb 18 367 18 449 207pb 204pb 15 676 15 695 208pb 204pb 38 469 38 465 which also suggests that the ore forming fluid is of magmatic origin

the early cretaceous weilasituo zn cu ag vein deposit in the southern great xing an range northeast china fluid inclusions h o s pb isotope geochemistry and genetic implications abstract the weilasituo vein type deposit hosted in hercynian middle to late paleozoic quartz diorite and palaeozoic gneiss occurs on the western slopes of the southern great xing an range in this paper we present results from fluid inclusion and isotope h o s pb investigations on the weilasituo deposit we identify three stages during the ore formation a barren pre ore stage stage 1 a main ore stage with economic grade cu zn ag mineralization stage 2 and a barren post ore stage stage 3 fluid inclusion and mineral thermometry constrain temperature intervals of approximately 243 to 333 c 192 to 425 c and 141 to 261 c for the three stages respectively fluids in the main ore stage are characterized by complex nacl h 2 o ch 4 co 2 low salinity 3 55 to 8 68 wt nacl equiv with isotopic signatures consistent with a magmatic source these fluids evolved by mixing with local meteoric water 18 o fluid 1 15 to 5 15 d fluid 139 4 to 88 2 measured and calculated sulfur isotope compositions of hydrothermal fluids 34 s fluid 3 0 to 3 4 indicate that the ore sulfur was derived mainly from a magmatic source the lead isotope ratios from the ores show mean values of 18 326 15 553 and 38 242 for 206 pb 204 pb 207 pb 204 pb and 208 pb 204 pb respectively indicating a mantle source our study shows that fluid mixing and or dilution played an important role in copper zinc and silver mineralization in the weilasituo deposit the weilasituo and bairendaba deposits represent a linked ore system genetically related to the late mesozoic magmatism the ore forming fluids associated with the early cretaceous mineralization in the southern great xing an range are of magmatic in origin and evolved by mixing with local meteoric water these deposits preserve the signature of a mantle source for lead however the deposits formed at ca 177 160 ma possess a dominantly magmatic signature with less radiogenic lead

a type granites in northeastern china age and geochemical constraints on their petrogenesis abstract a type granites are widely distributed in northeastern china ne china they were emplaced during three major episodes the permian late triassic to early jurassic and early cretaceous and evolved in different tectonic regimes according to their mineralogical and geochemical characteristics two subgroups of a type granites aluminous and peralkaline can be recognized the peralkaline subgroup contains alkali mafic minerals such as riebeckite arfvedsonite and sodic pyroxene while the aluminous subgroup contains annite and fe rich calcic or sodic calcic amphibole with respect to the aluminous subgroup the peralkaline granites contain higher rb ga and total rare earth elements ree but lower mgo cao al 2 o 3 ba and sr based on the discrimination criteria of eby geology 20 1992 641 the permian and late triassic to early jurassic a type granites belong to the a 2 post orogenic type whereas the early cretaceous granites are of the a 1 anorogenic type nd isotopic compositions of these a type granites indicate their derivation from a dominantly juvenile crustal source their origin is thought to have involved partial melting of an underplated lower crustal source because the generation of a type granites requires high melting temperature we propose models involving slab break off lithospheric delamination and extension the permian a type granites have the same age range as those in eastern junggar southern mongolia and central inner mongolia they occur along a major suture and form a narrow belt between the north china and siberian cratons we suggest that their formation was associated with post collisional slab break off the late triassic to early jurassic a type granites are likely to be the product of lithospheric delamination after the final collision of the major crustal blocks in the late paleozoic to early triassic the early cretaceous a type granites have an anorogenic affinity and were possibly associated with rifting in eastern china at this time associated with the onset of paleo pacific subduction consequently we conclude that the a type granites in ne china were generated at three different times involving multiple processes operative in different tectonic environments

u pb re os and 40ar 39ar geochronology of porphyry sn cu mo and polymetallic ag pb zn cu vein mineralization at bianjiadayuan inner mongolia northeast china implications for discrete mineralization events

late mesozoic metallogeny and intracontinental magmatism southern great xing an range northeastern china abstract mineral deposits are typically tied to plate margin processes such as accretion or rifting however some major deposits occur in plate interiors e g deposits in the southern great xing an range lacking a clear association with the supercontinent cycle intrusive activity in the southern great xing an range peaked in late mesozoic i e 155 120 ma simultaneously with large scale mineralization in this area in addition the late mesozoic granitoids show initial nd and hf isotopic signatures of depleted mantle possibly newly underplated basaltic materials with variable contamination from older crust and with model ages younger than 1 0 ga fluid inclusion waters extracted from ore minerals pyrite galena sphalerite and chalcopyrite associated with the late mesozoic mineralization have elevated 3he 4he ratios indicating a contribution of mantle derived helium stable isotopes of fluid inclusion waters hydrogen and oxygen and of sulfide minerals sulfur confirm a magmatic source for these components lead isotope data of ore minerals indicate a significant mantle lead contribution from the newly underplated material thus the southern great xing an range is best described as a typical late mesozoic intracontinental metallogenic belt related to magmatism with a significant mantle contribution the magmatism and mineralization took place in a setting of lithospheric extension and resulted because of the break off of the southerly dipping mongol okhotsk oceanic slab at depth during closure of the mongol okhotsk ocean which also restricted the westward movement of the paleo pacific oceanic plate this interplay between plate tectonic events and mantle dynamics provides a good example of the evolution of magmatism and hydrothermal activity in intracontinental settings

genesis of the ores of the zambian copperbelt abstract the theories for the origin of the ores of the copperbelt of zambia and zaire are reviewed following an account of the historical development of ideas from epigenetic through syngenetic to syngenetic diagenetic and ultimately to neohydrothermalist theories models for the genesis of these deposits are critically assessed in the light of the data currently available this examination is conducted with particular regard to the questions of the sources of copper and cobalt the timing of mineralizing events and the physicochemical conditions of metal sulphide precipitation although accepting that the origin of these ores remains controversial it is concluded that the most likely sources of both copper and cobalt are the rocks of the basement complex that metals were probably transported both in surface and ground waters and that the main mineralizing event took place during early diagenesis with sulphide precipitation occurring via bacterial reduction of seawater sulphate the precipitation of sulphides probably occurred at temperatures around 20 60 c and at near neutral ph with minor fluctuations in eh and variations in the solubilities of the metals involved causing mineral zonation the burial and compaction of these sediments probably resulted in the expulsion of metal rich fluids and formation of sulphides in the immediate footwall and hanging wall of the main ore horizon with continued burial resulting in the formation of sulphide bearing pods and veins of lateral secretion origin tectonic deformation and metamorphism in the lufilian orogeny although resulting in a set of cross cutting high temperature mineralized veins appears not to have resulted in significant remobilization of the sulphides

the genesis of metal zonation in the weilasituo and bairendaba ag zn pb cu sn w deposits in the shallow part of a porphyry sn w rb system inner mongolia china abstract the weilasituo and bairendaba zn pb ag cu sn w sulphide deposits are located in the southern part of great xing an range of inner mongolia in china the deposits are located at shallow depths in the newly discovered weilasituo porphyry hosting sn w rb mineralization the mineralization at weilasituo and bairendaba consist of zoned massive sulphide veins within fractures cutting the xilinhot metamorphic complex and quartz diorite the weilasituo deposit gradually zones from the cu rich zn cu sulphide mineralization in the west to zn rich zn cu sulphide mineralization in the east the bairendaba deposit has a cu bearing and zn rich core through a transitional zone devoid of copper to an outer zone of zn pb ag mineralization three main veins contain more than 50 wt of the contained metal in the two deposits with their metal ratios displaying a systematic and gradual increase in zn cu pb zn and ag zn ratios from the western part of weilasituo to the eastern part of bairendaba three stages of vein type mineralization are recognized early sub economic mineralization consists of a variable proportion of euhedral arsenopyrite pyrite quartz and rare wolframite scheelite cassiterite magnetite and cobaltite this was succeeded by main stage mineralization with economic concentration of zoned cu zn pb and ag sulphide minerals along strike within the veins the zones consist of the assemblages 1 pyrrhotite fe rich sphalerite chalcopyrite quartz fluorite at west weilasituo 2 pyrrhotite fe rich sphalerite chalcopyrite galena tetrahedrite quartz fluorite at east weilasituo 3 pyrrhotite fe rich sphalerite chalcopyrite galena tetrahedrite quartz fluorite in the centre of bairendaba 4 pyrrhotite fe rich sphalerite galena chalcopyrite tetrahedrite quartz fluorite in the transition zone of bairendaba and 5 pyrrhotite fe rich sphalerite galena tetrahedrite chalcopyrite falkmanite argentite pyrargyrite quartz fluorite in the outer zone at bairendaba post main ore stage is devoid of sulphides and characterized overprinting of fluorite sericite chlorite illite kaolinite and calcite zircon shrimp u pb dating zircon la icp ms u pb dating molybdenite re os isochron dating and muscovite ar ar dating indicate the beidashan granitic batholith was intruded at 140 3 ma mswd 3 3 the porphyritic monzogranite from marginal facies of the beidashan batholith was intruded at 139 2 ma mswd 0 75 the mineralized quartz porphyry was intruded at 135 2 ma mswd 0 91 the greisen mineralization occurred at 135 11 ma mswd 7 2 and the post main ore stage muscovite deposited at 129 5 0 9 ma the new geochronology data show the porphyry sn w rb and vein type sulphide mineralization are contemporaneous with granitic magmatism in the region the metal zonation at the weilasituo and bairendaba deposits is a result of progressive metal deposition this was during the evolution of a metal bearing fluid along the strike of the veins and during the main stage of ore formation at the upper part of the deep seated porphyry sn w rb system this progressive zonation indicates that the deposits represent end numbers formed from one ore forming fluid which moved from west to east from the porphyry the metal zonation patterns of the major veins are consistent with metal bearing fluid entering the system with the precipitation of chalcopyrite proximally and sphalerite galena and ag bearing minerals more distally we show that the mechanism of metal deposition is therefore controlled by thermodynamic conditions resulting in the progressive separation of sulphides from the metal bearing fluid the temperature gradient between the inflow zone and the outflow zone appears to be one of the key parameters controlling the formation of the metal zonation pattern the sulphide precipitation sequence is consistent with a low f s 2 and low f o 2 state of the acidic metal bearing fluid the metal zonation pattern provides helpful clues from which it is possible to establish the nature of fluid migration and metal deposition models to locate a possible porphyry mineralization at depth in the great xing an range which is consistent with the geology of the newly discovered porphyry sn w rb system

ore formation mechanism of the weilasituo tin polymetallic deposit ne china constraints from bulk rock and mica chemistry he ar isotopes and re os dating abstract china s w sn resources are dominant on a global scale a series of sn polymetallic deposits has been found in recent years at depth on the flanks of known volcanic subvolcanic cu pb zn ag deposits in the southern great xing an range ne china the large scale weilasituo tin polymetallic deposit formed at the depth of the weilasituo cu zn deposit is most typical of these types of deposit tin polymetallic orebodies are hosted in the early paleozoic xilingol complex and their mineralization is closely related to early cretaceous quartz porphyry in this contribution bulk rock and mica chemical compositions re os geochronology and he ar isotopic analyses are described in addressing the ore formation mechanism of the deposit geochemical characteristics indicate that the ore bearing quartz porphyry corresponds to the i type granite serie five types of mica have been identified in the study area based on detailed petrography and epma and la icp ms analyses i early magmatic fe li mica in albitized quartz porphyry ii late magmatic fe li mica in mineralized quartz porphyry iii hydrothermal fe li mica in a cryptoexplosive breccia pipe distributed around breccia fragments iv fe li mica in quartz veins and v fe li mica in plagioclase gneiss wall rock magmatic zinnwaldite from the upper mineralized part of the quartz porphyry is enriched in nb 100 160 ppm and ta 100 150 ppm hydrothermal zinnwaldite from the explosive breccia quartz veins and surrounding gneiss is unusually rich in mg up to 3 4 wt mgo and sn up to 200 ppm 3he 4he ratios of the weilasituo tin polymetallic and cu zn deposits are in the ranges 3 38 4 91 ra and 4 8 4 9 ra respectively indicating ore forming fluids sourced from mixed crustal and mantle materials molybdenite re os dating of w mineralization yielded an isochron age of 129 0 4 6 ma similar to the porphyry crystallization and mineralization ages of the weilasituo tin polymetallic deposit and also consistent with the mineralization age of the cu zn deposit we propose a new metallogenic model with all subtypes of w sn cu pb zn ag mineralization in the weilasituo area belonging to a single complex metallogenic system compared with other ore districts ore related granitoids in the southern great xing an range display relatively uniform emplacement ages and were derived from partial melting of juvenile lower crust rather than old basement their ore forming fluid source was greater influenced by mantle fluids than which found in south china