stability of i walls in new orleans during hurricane katrina failures of i walls during hurricane katrina were responsible for many breaches in the flood protection system in new orleans six breaches were examined in detail by task group 7 of the interagency performance evaluation taskforce four of these failures and breaches which occurred before the water levels reached the top of the wall were not caused by overtopping erosion the failure of the i wall at the 17th street canal resulted from shear through the weak foundation clay the south failure of the london avenue i wall was caused by subsurface erosion which carried massive amounts of sand inland and removed support for the wall leading to catastrophic instability at the north breach on london avenue the failure was caused by high pore pressures combined with a lower friction angle in the loose sand which resulted in gross instability of the i wall under the water pressure load from the storm surge looking back with the benefit of 20 20 hindsight these stability and erosion failures can be explained in terms of modern soil mechanics exploration techniques laboratory test procedures and analysis methods an important factor in all of the cases investigated was development of a gap behind the wall as the water rose against the wall and caused it to deflect formation of the gap increased the load on the wall because the water pressures in the gap were higher than the earth pressures that had acted on the wall before the gap formed where the foundation soil was clay formation of a gap eliminated the shearing resistance of the soil on the flood side of the wall because the slip surface stopped at the gap where the foundation soil was sand formation of the gap opened a direct hydraulic connection between the water in the canal and the sand beneath the levee this hydraulic short circuit made seepage conditions worse and erosion due to underseepage more likely it also increased the uplift pressures on the base of the levee and marsh layer landward of the levee reducing stability because gap formation has such important effects on i wall stability and because gaps behind i walls were found in many locations after the storm surge receded the presence of the gap should always be assumed in i wall design studies

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

geological fluid inclusion h o s pb isotope and ar ar geochronology constraints on the genesis of the nancha gold deposit southern jilin province northeast china abstract the nancha gold deposit located in the central part of southern jilin province in the northeastern portion of the north china craton contains orebodies hosted in a proterozoic metamorphosed volcanic sedimentary sequence the distribution of the orebodies is controlled by nne trending brittle ductile shear zones and faults the gold orebodies consist of auriferous quartz veins and auriferous altered rocks mineralization can be divided into three stages 1 quartz pyrite 2 quartz gold polymetallic sulfide and 3 quartz carbonate with gold being introduced mainly in the second stage three types of fluid inclusions were identified in the vein mineral assemblages based on petrography and laser raman spectroscopy nacl h 2 o w type co 2 h 2 o c type and pure co 2 pc type crystals in the early quartz pyrite stage veins mainly contain c type primary fluid inclusions and rare pc type inclusions the fluid inclusions in these veins completely homogenize at temperatures of 273 432 c and show low salinities of 0 63 7 78 wt nacl equiv in the middle quartz gold polymetallic sulfide stage all three types of fluid inclusions were observed these fluid inclusions homogenize at temperatures of 132 to 255 c and show salinities of 0 83 11 72 wt nacl equiv in contrast crystals in the late quartz carbonate stage contain only w type fluid inclusions that show homogenization temperatures of 132 255 c and salinities of 0 35 7 86 wt nacl equiv these data indicate that the metallogenic system evolved from a co 2 rich metamorphogenic fluid to a co 2 poor fluid due to inputs of meteoric waters fluid boiling and mixing caused the rapid precipitation of sulfides and gold trapping pressures estimated from boiling c type fluid inclusions were 152 367 mpa in the ore forming stage this suggests an alternating lithostatic hydrostatic fluid system controlled by a fault valve activity at a depth of 13 8 15 2 km one hydrothermal sericite sample from an auriferous quartz vein yielded an 40 ar 39 ar isotopic plateau age of 170 1 1 9 ma indicating that mineralization occurred in the middle jurassic and was unrelated to the volcanics and intrusions in the mineralized area the characteristics of h o s pb isotopes and fluid inclusions suggest that the ore forming fluids were of metamorphic origin with the s originating from proterozoic crustal components and the pb originating from a mixture of ore forming metamorphogenic fluids and host rocks the results combined with existing data on the regional geology ore geology fluid inclusions h o s pb isotope geochemistry age of mineralization and tectonic setting indicate that the nancha gold deposit was an orogenic type system that formed in a middle jurassic accretionary orogenic regime following subduction of the paleo pacific plate beneath the eurasian continent

the krasna hora milesov and přicovy sb au ore deposits bohemian massif mineralogy fluid inclusions and stable isotope constraints on the deposit formation the krasna hora milesov and p icovy districts czech republic are the unique examples of sb au subtype orogenic gold deposits in the bohemian massif they are represented by quartz stibnite veins and massive stibnite lenses grading into low grade disseminated ores in altered host rocks gold postdates the stibnite and is often replaced by aurostibite the ore zones are hosted by hydrothermally altered dikes of lamprophyres krasna hora milesov or are associated with local strike slip faults p icovy formation of sb au deposits probably occurred shortly after the main gold bearing event 348 338 ma au only deposits in the central part of the bohemian massif fluid inclusion analyses suggest that stibnite precipitated at 250 to 130 c and gold at 200 to 130 c from low salinity aqueous fluids the main quartz gangue hosting the ore precipitated from the same type of fluid at about 300 c early quartz arsenopyrite veins are not associated with the sb au deposition and formed from low salinity aqueous carbonic fluid at higher pressure and temperature 250 mpa 400 c the estimated oxygen isotope composition of the ore bearing fluid 4 1 smow based on post ore calcite suggests its metamorphic or mixed magmatic metamorphic origin and excludes the involvement of meteoric water rapid cooling of warm hydrothermal fluids reacting with cold host rock was probably the most important factor in the formation of both stibnite and gold

fluid inclusion geochemistry and 40ar 39ar geochronology constraints on the genesis of the jianchaling au deposit china abstract the giant jianchaling gold deposit is located in the shaanxi province china the mineralization is hosted by wnw trending faults in the mianxian lueyang yangpingguan mly area the mineralization can be divided into three stages based on mineralogical assemblages and crosscutting relationships of mineralized quartz veins these stages from early to late are characterized by the mineral assemblage of 1 quartz coarse grained pyrite pyrrhotite pentlandite dolomite 2 quartz pyrite gold sphalerite galena carbonate arsenopyrite fuchsite and 3 dolomite calcite quartz fine grained pyrite realgar orpiment three types of fluid inclusions have been recognized in this study based on petrographic and microthermometric measurements including pure co 2 and or ch 4 pc type nacl h 2 o w type and nacl co 2 h 2 o c type fluid inclusions these fluid inclusion types are present in quartz from the stage 1 and 2 assemblages whereas the stage 3 quartz only contains w type fluid inclusions the stage 2 assemblage is associated with the mineralization at the jianchaling deposit fluid inclusions of stage 1 quartz homogenize mainly between 250 and 360 c with salinities up to 15 6 wt nacl equiv whereas the stage 3 dolomite with homogenization temperatures of 160 220 c and salinities of 1 1 7 4 wt nacl equiv this indicates that the ore fluid system evolved from co 2 rich probably metamorphic hydrothermal to co 2 poor meteoric fluid all three types of fluid inclusions can be observed in the stage 2 quartz suggesting that this heterogeneous association was trapped from a boiling fluid system these inclusions homogenized at temperatures of 200 250 c and salinities of 1 2 12 4 wt nacl equiv the estimated trapping pressures of the fluid inclusions are between 117 and 354 mpa in stage 1 suggesting an alternating lithostatic hydrostatic fluid system which was controlled by a fault valve at the depth of 12 km two fuchsite samples collected from the stage 2 polymetallic quartz veins yielded well defined 40 ar 39 ar isotopic plateau ages of 197 2 and 194 2 ma and 39 ar 36 ar 40 ar 36 ar normal isochrones of 198 2 and 199 2 ma this indicates that the mineralization at jianchaling is early jurassic ca 198 ma in age we propose that jianchaling is an orogenic gold deposit and formed during continental collision related to the northward subduction of the mian lue oceanic plate during the early jurassic we also conclude that the beginning of the continental collision between the yangtze and the north china cratons took place around 200 ma

temporal evolution of mineralization events in the bohemian massif inferred from the re os geochronology of molybdenite molybdenite is a common mineral accompanying sn w au and base metal mineralizations located in different geotectonic units of the bohemian massif but it is also widespread in granitoids and or related quartz veins pegmatites forming disseminated mo mineralization thirty re os ages were obtained for molybdenite samples from the bohemian massif to provide constraints on the timing and duration of mineralization event s within the framework of previously published geochronological data for the host and or associated rocks the obtained data for sn w li deposits in the erzgebirge metallogenetic province indicate the predominance of one and or multiple short time mineralization events taking place between 319 and 323 ma with the exception of the krupka deposit associated with the altenberg teplice caldera where the data may suggest prolonged activity until 315 ma the ages of the pb zn au mo h rky u rakovnika and fe cu as ob i d l mineralizations from the exocontacts of the cista pluton and krkonose jizera plutonic complex respectively provide evidence for synchronous emplacement of the ore and the associated granitic rocks in contrast the padr fe as mo mineralization postdates the age of the associated padr granite disseminated mo mineralization in cadomian and variscan granitoids and or related to quartz veins pegmatites provides re os ages that overlap with the previously published geochronological data for the host rocks suggesting coeval evolution molybdenite samples from the sazava suite granites of the central bohemian plutonic complex cbpc have resolvable younger ages than their host granites but similar to the age of spatially related au mineralization which is associated with the latest evolution of the cbpc

sr nd isotopic constraints on the petrogenesis of the central bohemian pluton czech republic the sr nd isotopic data for selected granitoids of the central bohemian pluton show a broad negative correlation with the total range of 87sr 86sr 330 0 7051 0 7129 and nd330 0 2 to 8 9 the older intrusions have more depleted sr nd compositions and calc alkaline geochemistry sazava suite whereas the younger intrusions shift towards k rich calc alkaline blatna suite and shoshonitic rocks icany and certovo b emeno suites with more evolved isotopic signatures the distribution of the data is interpreted as reflecting a diversity of sources and processes rather than a single progressive crustal contamination trend the sazava suite could have originated by partial melting of metabasites or of a mantle source with an isotopic composition close to bulk earth or by hybridization of crustally derived tonalitic and mantle derived magmas variation within the blatna suite is modelled by mixing between a moderately enriched 87sr 86sr 330 0 708 nd330 3 mantle component with either an isotopically evolved metasedimentary component or with more evolved magmas of the suite the icany suite was most probably produced by partial melting of peraluminous lithologies possibly of the adjacent moldanubian unit the certovo b emeno suite evolved from strongly enriched mantle derived magmas 87sr 86sr 330 0 7128 end330 7 either through closed system fractional crystallization or interaction with magma corresponding to leucogranites of the central bohemian pluton

ore deposits of the french massif central insight into the metallogenesis of the variscan collision belt the french massif central fmc represents the whole west european variscan wev belt in terms of both the geodynamic evolution and the metallic content thus a study of the metallogenic evolution of the fmc may elucidate the conditions that allow the mineralisation of a collision belt since recent collision belts e g the himalayas or the alps show that mineralisation does not necessarily result from the collision process the palaeozoic history of the fmc is divided into three geodynamic stages unevenly involved from the metallogenic view point the eo variscan stage cambrian to silurian was not important the meso variscan stage devonian early carboniferous was of limited importance and most of the mineralisations formed during the neo variscan stage late carboniferous early permian in addition some more mineralisation was produced during the mesozoic because of the thermal reactivation linked with the alpine orogenies

40 ar 39 ar hornblende dating of a microgranodiorite dyke implications for early permian extension in the moldanubian zone of the bohemian massif laser fusion 40ar 39ar ages of titanian pargasite from a microgranodiorite dyke swarm in the southern bohemian massif effectively date the early permian late autunian emplacement of dykes into a cool moldanubian crust this intrusion represents the youngest magmatic phase recorded in this part of the moldanubian zone strontium and neodymium isotopic ratios of microgranodiorites point to magma derivation from re melting the lower crustal rocks with a possible component of upper mantle composition spatial and temporal association of the dykes with movements on a major n s nne ssw tectonic discontinuity blanice kaplice rodl fault zone suggests that their emplacement corresponds to the maximum age of fault movements associated with the e w oriented extension in this part of the bohemian massif

carbon oxygen isotopic covariation in hydrothermal calcite during degassing of co 2 the effect of the outgassing of co2 from a hydrothermal fluid on the c and o isotopic compositions of calcite which is precipitated from this fluid is quantitatively modelled in terms of batch and rayleigh distillation equations both co2 degassing and calcite precipitation are considered to be the removal mechanisms for dissolved carbon species from the fluid combined degassing precipitation models are then developed by taking h2co3 and hco 3 respectively as the dominant dissolved carbon species a positive correlation array between 13c and 13o values of calcite can be yielded by the precipitation of calcite from a h2co 3 dominant fluid accompanied by a progressive decrease in temperature during co2 degassing whereas calcite precipitated from a hco 3 dominant fluid under the same conditions tends to display much smaller variation in 13c values than in 18o values the combined processes of co2 degassing and calcite precipitation result in lowering the 13c value of calcites with respect to those precipitated in a closed system simply due to temperature effect carbon and oxygen isotopic data for calcite from the kushikino gold mining area in japan illustrate the application of quantitative modelling and degassing of co2 is suggested as a more likely cause for the precipitation of the calcite and quartz in this mining area

accretionary history and crustal evolution of the variscan belt in western europe abstract the variscan belt of western europe is part of a large intra paleozoic belt extending on both sides of the atlantic from the ouachitas in the us and the mauritanides in west africa to the bohemian massif in czechoslovakia and poland the belt was constructed between 500 and 250 ma as a result of convergence and collision between two main continents laurentia baltica and africa after the closure of various oceanic basins iapetus rheic and galicia massif central now recorded as discrete in part cryptic sutures which form the roots of large crystalline nappes in which are found dismembered remnants of oceanic crust and mantle the accretionary history of the variscan belt in western europe is related to the progressive closure of probably two oceanic basins the rheic in the north and another the galicia massif central in the south by respectively southward and northward intraoceanic subduction followed by obduction and intracontinental lithospheric subduction the result is a broad 700 800 km fan like divergent belt which must be considered as a classical obduction collision orogen with a long intracontinental history of about 100 150 ma its arcuate shape is probably due to the northwestward impingement of a promontory of the african continent into laurentia baltica

dike failure mechanisms and breaching parameters abstractdike risk management requires breaching parameters that can be estimated rapidly to support the prediction of inundation zones and decision making the objectives of this paper are to compile a database of dike breaching cases study common dike failure mechanisms and develop a set of empirical equations for estimating breaching length depth and peak discharge a database of over 1 000 dike failure cases was collected with information on pre breach dike geometry materials type of dike failure mechanisms breaching length depth and peak discharge a set of regression models are formulated using five control variables dike height width material type of dike and failure mechanism the standard error is set as a selection criterion and the akaike information criterion is used to optimize the proposed empirical models the new models are validated using independent cases and compared with available empirical equations for dikes and man made dams

evaluation and prediction of 17th street canal i wall stability using numerical limit analyses numericallimitanalyseshavebeenusedtoevaluatethestabilityofthe17thstreetcanali wallleveeduringhurricanekatrina the potential formation of a water filled gap along the canal side soil wall interface at failure is included in both the lower and upper bound for mulations the analyses replicate published two dimensional 2d cross sections and soil properties developed in forensic investigations car ried out by the interagency performance evaluation task force ipet and by the independent levee investigation team ilit the current results provide anindependent basis forunderstanding andevaluating the proposedfailure mechanisms anddemonstrate that awater filled gap is a necessary condition for the critical i wall failure mechanism further limit analysis calculations produce credible estimates of the surge elevation that caused failure of the 17th street canal i wall as well as predictions of a consistent failure mechanism the numerical limit anal yses show clearly how differences in the stability of the i wall are linked to different interpretations of the stratigraphy and undrained shear strengths by ipet and ilit the analyses also show that effects of a thin layer of weak organic clay as postulated by ilit are not necessary to explain the i wall failure doi 10 1061 asce gt 1943 5606 0000814 2013 american society of civil engineers ce database subject headings drainage walls clays lateral loads levees and dikes louisiana hurricanes structural stability author keywords upper and lower bound limits undrained stability walls clays limit equilibrium lateral loading

l or dans la metallogenie du massif de boheme les mineralisations auriferes du massif de boheme sont representees par plusieurs types morphologiques et paragenetiques dont l origine est expliquee par trois modeles genetiques i un modele volcanogenique pour les mineralisations sulfures stratiformes ii un modele hydrothermal metamorphique pour les mineralisations de quartz auriferes synmetamorphiques de morphologie tres variable et caracterisees par la presence de mineraux de bi te mo et w scheelite iii un modele hydrothermal de shear zones auriferes pour les mineralisations postmetamorphiques caracterisees par des teneurs en argent plus elevees electrum ou par une mineralisation complexe a stibine et or

geology geochemistry and ore genesis of the wenyu gold deposit xiaoqinling gold field qinling orogen southern margin of north china craton abstract the wenyu giant gold deposit is hosted in the precambrian taihua supergroup metamorphic rocks within the xiaoqinling terrane qinling orogen on the southern margin of the north china craton the mineralization can be divided into three stages quartz pyrite veins early quartz sulfide veins middle main and carbonate quartz veinlets late with gold being mainly introduced in main stage quartz formed in two earlier stages contains three compositional types of fluid inclusions i e pure co2 co2 h2o and nacl h2o but the late stage minerals only contain the nacl h2o inclusions the inclusions in quartz formed in the early main and late stages yield total homogenization temperatures of 262 417 c 236 407 c and 114 239 c respectively with salinities no higher than 13 wt nacl equiv trapping pressures estimated from co2 h2o inclusions are 139 399 mpa and 111 316 mpa in the early and main stages corresponding to mineralization depths of 14 km and 11 km respectively fluid boiling and mixing caused rapid precipitation of sulfides and native au through boiling and inflow of meteoric water the ore forming fluid system evolved from co2 rich to co2 poor in composition and from metamorphic to meteoric as indicated by decreasing 18owater values from early to late the carbon sulfur and lead isotope compositions suggest the hostrocks within the taihua supergroup to be a significant source of ore metals integrating the data obtained from the studies including regional geology ore geology fluid inclusion and c h o s pb isotope geochemistry we conclude that the wenyu gold deposit was an orogenic type system formed in the tectonic transition from compression to extension during the jurassic early cretaceous continental collision between the north china and yangtze cratons

new orleans and hurricane katrina iii the 17th street drainage canal the failure of the levee and floodwall section on the east bank of the 17th street drainage canal was one of the most catastrophic breaches that occurred during hurricane katrina it produced a breach that rapidly scoured a flow pathway below sea level so that after the storm surge had largely subsided floodwaters still continued to stream in through this breach for the next two and a half days this particular failure contributed massively to the overall flooding of the metropolitan orleans east bank protected basin slightly more than half of the loss of life and a similar fraction of the overall damages occurred in this heavily populated basin there are a number of important geotechnical and geoforensic lessons associated with this failure accordingly this paper is dedicated solely to investigating this single failure geological and geotechnical details such as a thin layer of sensitive clay that was laid down by a previous hurricane proper strength characterization of soils at and beyond the toe of the levee and recognition of a water filled gap on the inboard side of the sheet pile cutoff wall are judged to be among the most critical factors in understanding this failure the lessons learned from this study are of importance for similar flood protection systems throughout other regions of the united states and the world

variation in sericite compositions from fracture zones within the coso hot springs geothermal system two types of white micas are found in drillhole samples within the geothermal system at coso hot springs low permeability zones of the crystalline basement contain coarse grained relict muscovite whereas rock alteration near fracture zones at temperatures 150 c is characterized by abundant finegrained sericite in association with secondary calcite and quartz and unaltered relict microcline in this hydrothermal sericite there is an increase in interlayer k octahedral mg fetotal and tetrahedral al with increasing temperature between 215 to 250 c thermodynamic activity of the al2si4o10 oh 2 component of serielles calculated using site mixing approximations of helgeson and aagaard 1985 decreases with increasing temperature between 215 and 250 c as a consequence of the observed variations in the interlayer octahedral and tetrahedral site occupancies the activity of kal2 alsi3o10 oh 2 is essentially constant in the coso seriates over this temperature range the calculated equilibrium distribution of aqueous species in the hydrothermal solutions produced from well 16 8 together with cation activity phase diagrams that account for variations in sericite composition requires a ph of 6 7 6 8 at temperatures between 236 and 250 c comparison of predicted and observed phase relations with fluid compositions indicate that seriates are in local equilibrium with the geothermal reservoir fluid whereas relict metamorphic muscovites are metastable although the compositions of hydrothermal sericites are a complex function of temperature pressure and geothermal fluid composition compositional relations observed at coso together with published compositions of hydrothermal dioctahedral layer silicates from the salton sea geothermal system demonstrates that elemental compositions of interlayer k and tetrahedral al increase systematically with increasing temperature despite the dramatic differences in fluid compositions between these two geothermal systems this suggests that the observed variations in interlayer and tetrahedral site occupancy is largely dependent on the enthalpy of hydrolysis reactions representing equilibrium between sericite solid solutions and the geothermal reservoir fluids

new orleans levee system performance during hurricane katrina 17th street canal and orleans canal north centrifuge modeling of the 17th street canal and orleans canal north levees was performed in this study during hurricane katrina the levees on the 17th street canal failed leading to breaches in the outfall canal in the city two mechanisms were observed in the centrifuge modeling that could cause a breach first a water filled crack formed in front of the floodwall as the water in the canal rose above the top of the levee the levees on the 17th street canal which were supported on clay foundations failed when this cracking led to a translational sliding failure in the clay layer commencing at the toe of the floodwall the levees at orleans canal north where failure did not occur were also modeled to demonstrate that the model tests could successfully simulate failure and nonfailure conditions the centrifuge model tests identified the importance of the crack formation in relation to the stability of the floodwall these tests also confirmed that levee geometry floodwall depth of penetration and the underlying soil profile were all critical to the performance of the system under flood loading

ore geology fluid inclusion and 40ar 39ar geochronology constraints on the genesis of the yingchengzi gold deposit southern heilongjiang province ne china abstract the yingchengzi gold deposit located at the eastern margin of the zhangguangcai range southern heilongjiang province ne china is the only high grade gold deposit in the region the deposit is hosted in mylonitized paleozoic granite and metavolcanic rocks and is structurally dominated by brittle ductile shear zones and faults the orebodies consist of gold bearing quartz veins and gold bearing altered mylonites the hydrothermal ore forming process can be divided into early middle and late stages characterized by quartz pyrite veins quartz gold polymetallic sulfide veins and quartz carbonate veins or veinlets respectively ore minerals and gold mainly occurred in the middle stage four types of fluid inclusions were identified in the vein minerals based on petrography and laser raman spectroscopy nacl h 2 o w type co 2 h 2 o c type pure co 2 pc type and less common calcite bearing s type inclusions the early stage minerals contain c type and rare pc type fluid inclusions which have homogenization temperatures of 262 400 c and low salinities of 2 20 8 51 wt nacl equiv only the middle stage minerals contain all four types of fluid inclusions with homogenization temperatures of 173 316 c and salinities of 2 20 12 42 wt nacl equiv the late stage quartz and calcite crystals contain only w type fluid inclusions which have homogenization temperatures of 104 207 c and salinities of 1 05 6 58 wt nacl equiv fluid boiling and the mixing caused the rapid precipitation of sulfides and gold these indicate that the ore forming fluid system evolved from co 2 rich metamorphogenic to co 2 poor due to the boiling and input of meteoric water the trapping pressures estimated from c type fluid inclusions are 98 245 mpa in the main ore forming stage giving a reasonable estimate that an alternating lithostatic hydrostatic fluid system controlled a fault valve activity at a depth of 9 10 km 40 ar 39 ar dating of hydrothermal sericite from gold bearing altered rock shows that gold mineralization occurred at 248 ma we assume that the yingchengzi gold deposit was formed in a late permian early triassic continental collision regime following closure of the paleo asian ocean the regional geology ore geology fluid inclusions mineralization age and tectonic setting infer that the yingchengzi gold deposit is a mesozonal orogenic gold system making it the first orogenic gold deposit discovered in the zhangguangcai range ne china

insights into the genesis of orogenic gold deposits from the zhengchong gold field northeastern hunan province china abstract the zhengchong gold deposit is located in the central jiangnan orogen belt where gold ore occurs mainly as quartz veins altered slates and minor breccias hosted by shear zones in the lengjiaxi group based on its vein crosscutting relationships mineral assemblages and paragenetic sequences mineralization in this deposit is divided into four stages stage 1 quartz q1 pyrite stage stage 2 quartz q2 pyrite arsenopyrite stage stage 3 quartz q3 pyrite polymetallic sulfide mineral stage and stage 4 quartz q4 carbonate stage two types of fluid inclusions have been recognized in the quartz grains co2 bearing fluid inclusions c type and aqueous fluid inclusions w type fluid inclusions in hydrothermal quartz yield homogeneous temperatures and salinities of 312 406 c and 4 65 9 21 wt naclequiv stage 1 252 324 c and 2 20 8 10 wt naclequiv stage 2 193 296 c and 2 24 14 04 wt naclequiv stage 3 and 127 209 c and 2 57 6 59 wt naclequiv stage 4 the co occurrence of these inclusion types despite their variable fluid salinities can be explained by fluid boiling during stages 2 and 3 of mineralization possibly as a result of episodic pressure decreases linked to fault valve activity laser raman spectroscopic analysis results reveal that small quantities of ch4 and n2 are present in the stage 2 3 fluid inclusions fluid inclusion data and microthermometric results show that the ore fluids were low salinity and co2 rich yielding both co2 inclusions c type and aqueous inclusions w type the trapping pressures estimated from the c type inclusions are 80 180 mpa for stages 2 and 3 yielding gold mineralization depths of 7 8 km the mineralizing fluids had calculated 18oh2o values ranging from 3 7 to 8 2 and d values from 75 2 to 61 8 indicating derivation mainly from metamorphic fluids the sulfide minerals yield 34s values of 8 9 to 0 1 and 206pb 204pb 207pb 204pb and 208pb 204pb ratios of 17 83 18 12 15 67 15 76 and 38 03 38 62 respectively which differ significantly from the isotopic composition of the granodiorite 34s 2 4 to 1 0 206pb 204pb 18 57 19 28 207pb 204pb 15 69 15 76 208pb 204pb 38 97 40 34 however the s pb isotopic compositions of the sulfide minerals are similar to those of slates of the lengjiaxi group in the study area the zhengchong gold deposit probably originated from a metamorphic fluid system characterized by low salinity low density and co2 enrichment with limited admixture of magmatic fluids based on similarities to other orogenic gold deposits we infer that the zhengchong orebody represents an orogenic gold deposit formed during the late ordovician jiangnan orogeny caused by collision of the yangtze and cathaysia blocks

conjugate shear zones in the southern bohemian massif austria implications for variscan and alpine tectonothermal activity abstract mylonitic fabrics developed within conjugate wrench ductile shear and fault systems in the southern bohemian massif display both dextral nw se trending systems and sinistral ne sw trending systems shear senses contrasting temperature conditions of deformation can be observed in the different shear zones temperatures above 650 c were reached in the pfahl shear zone shearing under greenschist facies conditions took place in the rodl and danube shear zones brittle deformation dominated in the vitis and diendorf shear zones 40 ar 39 ar dating of various size fractions of muscovite formed and or deformed during mylonitization yield ages of ca 287 ma the nw se trending system and ca 288 281 ma the ne sw trending system the shear zones are interpreted as a late variscan conjugate system 40 ar 39 ar age spectra of fine grained newly grown sericite or rejuvenation of ages give evidence for post variscan reactivation of the shear zones brittle deformation within the shear zones was probably associated with maintenance of very high fluid pressure during variscan deformation foreland deformation during the alpine orogeny also played a significant role leading not only to the development of the ceske budejovice graben but also to local reactivation of the shear zones at higher crustal levels

isotope and fluid inclusion geochemistry and genesis of the qiangma gold deposit xiaoqinling gold field qinling orogen china abstract the qiangma gold deposit is hosted in the 1 9 ga taihua supergroup metamorphic rocks in the xiaoqinling terrane qinling orogen on the southern margin of the north china craton the mineralization can be divided as follows quartz pyrite veins early quartz polymetallic sulfide veinlets middle and carbonate quartz veinlets late stages with gold being mainly introduced in the middle stage three types of fluid inclusions were identified based on petrography and laser raman spectroscopy i e pure carbonic carbonic aqueous co 2 h 2 o and aqueous inclusions the early stage quartz contains pure carbonic and co 2 h 2 o inclusions with salinities up to 12 7 wt nacl equiv bulk densities of 0 67 to 0 86 g cm 3 and homogenization temperatures of 280 365 c the early stage is related to h 2 o co 2 n 2 ch 4 fluids with isotopic signatures consistent with a metamorphic origin 18 o water 3 1 to 5 2 d 37 to 73 the middle stage quartz contains all three types of fluid inclusions of which the co 2 h 2 o and aqueous inclusions yield homogenization temperatures of 249 346 c and 230 345 c respectively the co 2 h 2 o inclusions have salinities up to 10 9 wt nacl equiv and bulk densities of 0 70 to 0 98 g cm 3 with vapor bubbles composed of co 2 and n 2 the isotopic ratios 18 o water 2 2 to 3 6 d 47 to 79 suggest that the middle stage fluids were mixed by metamorphic and meteoric fluids in the late stage quartz only the aqueous inclusions are observed which have low salinities 0 9 9 9 wt nacl equiv and low homogenization temperatures 145 223 c the isotopic composition 18 o water 1 9 to 0 5 d 55 to 66 indicates the late stage fluids were mainly meteoric water trapping pressures estimated from co 2 h 2 o inclusions are 100 285 mpa for the middle stage suggesting that gold mineralization mainly occurred at depths of 10 km fluid boiling and mixing caused rapid precipitation of sulfides and native au through boiling and inflow of meteoric water the ore forming fluid system evolved from co 2 rich to co 2 poor in composition and from metamorphic to meteoric as indicated by decreasing 18 o water values from early to late the carbon sulfur and lead isotope compositions suggest the hostrocks within the taihua supergroup to be a significant source of ore metals integrating the data obtained from the studies including regional geology ore geology and fluid inclusion and c h o s pb isotope geochemistry we conclude that the qiangma gold deposit was an orogenic type system formed in the tectonic transition from compression to extension during the jurassic early cretaceous continental collision between the north china and yangtze cratons

formation of the baiyun gold deposit liaodong gold province ne china constraints from zircon u pb age fluid inclusion and c h o pb he isotopes abstract the baiyun gold deposit is located in the liaodong peninsula in ne china the gold orebodies are hosted in the paleoproterozoic liaohe group metamorphic rocks the alteration mineralization can be divided into three stages i quartz pyrite k feldspar veins ii quartz polymetallic sulfide veins iii quartz carbonate veins new la icp ms zircon u pb dating suggests all the ore related porphyries including monzonite porphyry 224 2 1 3 ma quartz porphyry 221 4 1 2 ma and diorite porphyry 221 8 1 2 ma were emplaced in the late triassic four types of fluid inclusions fis are identified in the ore related quartz i e liquid rich two phase vapor rich two phase co2 bearing and pure co2 fis the ore forming fluids were likely characterized by medium temperature low salinity low density co2 rich and belong to the h2o nacl co2 n2 c4h6 system we propose that fluid phase separation likely caused rapid precipitation of the ore minerals the c h o pb isotope data indicate that the ore forming fluids may have had multiple sources including magmatic metamorphic and meteoric fluids the ore forming materials may have mainly derived from metamorphic rocks of the proterozoic gaixian formation and minor from the triassic intermediate felsic rocks the he ar isotope data indicate that the ore forming fluids were mainly crust derived we conclude that the baiyun gold deposit is an orogenic type system formed during the late triassic north china yangtze continent continent collision

the collapse of diaphragm walls retaining clay five centrifugal model tests are reported which illustrate aspects of the collapse of stiff cantilever retaining walls embedded in overconsolidated clay the drainage of a heavy fluid in flight was used to simulate the effects of excavation following the establishment of a high initial groundwater level two modes of collapse were observed with unpropped walls the temporary stability of walls with small penetration was interrupted by the hydraulic action of a water filled crack opening on the retained side of the wall the long term rotational failure of walls of deeper penetration was also observed involving distributed strains in active and passive zones which could lead ultimately to sliding on shear rupture surfaces an analysis was developed based on admissible stress fields with active and passive zones switching about a pivot point so that the unpropped wall could satisfy the conditions of both moment and force equilibrium a back analysis of the two sudden failures using an undrained stre

the biards sb au bearing shear zone massif central france an indicator of crustal scale transcurrent tectonics guiding late variscan collapse structural textural mineralogic microthermometric and isotopic data obtained on the biards sb au district located in the south limousin area massif central france provide new evidence for the tectonic setting of stibnite and gold deposition during the late orogenic variscan collapse in western europe a variety of geologic and geophysical data define a major crustal scale left lateral strike slip shear zone that acted as a trap for sb au mineralization during these movements fault fill veins and then extensional veins of limited extent were created along rheologic heterogeneities that focused brittle deformation geometry and orientation of both vein sets indicate two main episodes of emplacement of ore related to a progressive wrench movement in response to an counterclockwise rotation of the regional stress axes both veins sets are filled by quartz and sulfides in three stages an early arsenopyrite pyrite stage with fine grained quartz a sphalerite pb sb sulfosalt native gold stage with comb quartz and a late stibnite berthierite stage with comb quartz combined fluid inclusion and stable isotope studies on quartz muscovite and sulfides reveal that the three stages result from the continuous evolution of a deep seated hydrothermal system in which the latest stages mixed with meteoric water these data argue for cooling and a pressure drop during ore deposition and indicate a shallow level of emplacement for sb au veins a comparison of the biards deposits with other upper paleozoic gold and antimony deposits in the massif central the western variscides and elsewhere in the world illustrates their common association with crustal scale strike slip shear zones the upper carboniferous age 305 300 ma of the sb au deposits indicates that they formed during the early stages of the postthickening extension of the variscan lithosphere sb au bearing strike slip shear zones resulted from the late variscan crustal collapse guided by the very large scale dextral shearing between central europe northern africa and the northern appalachians and associated with the opening of the paleo tethys and the closing of the theic ocean during the late paleozoic gondwana laurasia translation

ore genesis of the weibao lead zinc district eastern kunlun orogen china constrains from ore geology fluid inclusion and isotope geochemistry the weibao lead zinc district composed by two deposits named the east weibao deposit and the west weibao deposit respectively is located in the qimantagh area eastern kunlun orogen although both controlled by skarn alternation and experienced similar mineralization processes the east weibao deposit is dominated by massive ores while the west weibao deposit is characterized by banded ores the ore forming processes of both the deposits can be divided into four stages including prograde skarn stage retrograde skarn stage sulfide stage and carbonate stage three types of fluid inclusions i e pure co2 fluid inclusion pc type co2 bearing fluid inclusion c type and aqueous types w type have been identified in quartz calcite and sphalerite from different stages noteworthily only sulfide stage of the east weibao deposit contains carbonic fluid inclusions whereas only aqueous fluid inclusions were observed in sulfide stage of the west weibao deposit the co2 rich and aqueous type fluid inclusions in sulfide stage of the east weibao deposit were homogenized at temperatures between 263 and 424 c concentrating at 360 400 c with salinities ranging between 3 2 and 13 6 wt nacl eqv the w type fluid inclusions in sulfide stage of the west weibao deposit were homogenized at temperatures between 228 and 381 c concentrating at 280 340 c with salinities between 1 6 and 9 0 wt nacl eqv and the aqueous type fluid inclusions in carbonate stage in both deposits were homogenized at temperatures between 115 and 336 c concentrating at 200 240 c with salinities between 0 2 and 5 9 wt nacl eqv the ore forming fluid in sulfide stage at the east weibao deposit yielded calculated updelta 18 text o text h 2 text o and 18d values of 4 2 to 5 6 and 88 to 83 respectively the results are 8 8 to 10 8 99 to 92 for the sulfide stage at the west weibao deposit and 1 0 to 0 2 50 to 45 for carbonate stages in both deposits the lead isotopic ratios of sulfide samples from the weibao lead zinc district range between 18 259 and 18 336 for 206pb 204pb 15 580 and 15 659 for 207pb 204pb and 38 007 and 38 253 for 208pb 204pb respectively and the corresponding sulfur isotopic values range between 2 2 and 3 6 the fluid inclusion and isotope studies on the two deposits in the weibao lead zinc district suggest that they both have magmatic origin but mineralized by different mechanisms mineralization at the east weibao deposit may be caused by fluid immiscibility and mixing while at the west weibao deposit mineralization may result from water rock reactions between magmatic fluid and impure carbonate wall rocks combined with geological observation we conclude that the weibao lead zinc district as a united magmatic hydrothermal fluid system associated with the triassic magmatism that widely distributes in the qimantagh area

mineralogy fluid inclusion and stable isotope constraints on the genesis of the roudný au ag deposit bohemian massif orogenic gold deposits with gold of low fineness are relatively rare in the bohemian massif but occur locally within the late variscan blanice graben structure in the moldanubian zone among them the roudn deposit has been the most important with total production of about 6 t of gold between 1895 and 1930 the ore is related to an irregular quartz stockwork and is represented by sulfide and electrum impregnations within the quartz gangue and the altered host rocks ore grade varies from 4 to 25 g t au the gold is present as macro and microscopic electrum fineness 658 665 and also as invisible gold in the crystal structure of early sulfides as rich pyrite and sb rich arsenopyrite three mineralization stages have been distinguished 1 the largely barren pre ore stage 2 the main ore stage with economic au ag mineralization 3 the late stage with subeconomic ag pb zn mineralization fluid inclusion and mineral thermometry indicate that the three stages were formed at about 400 to 330 350 to 250 and 250 to 70 c respectively early mineralization stages are related to complex h2o co2 ch4 n2 low salinity 3 9 wt nacl equiv fluids with isotopic signatures consistent with a metamorphic origin 18ofluid 4 7 2 9 smow most of the main ore stage minerals including the electrum precipitated from aqueous fluids 2 4 wt nacl equiv during the late mineralization stage the salinity of aqueous fluid was higher 7 9 wt nacl equiv the isotopic composition of the late fluid however also records gradually increasing proportions of meteoric water 18ofluid 2 to 1 smow elevated arsenic contents 120 210 ppm as were found in aqueous carbonic fluids by the la icp ms technique models of fluid mixing at the transition of the main to late mineralization stages are used to estimate the temperature and paleogeothermal gradient possible ages of electrum mineralization 300 to 275 ma and ag pb zn vein type mineralization 275 to 265 ma are discussed overall the roudn deposit shows striking similarities with 300 ma gold deposits of the french massif central

geology and genesis of variscan porphyry style gold mineralization petrackova hora deposit bohemian massif czech republic a large number of variscan mesothermal gold deposits are located in the central part of the bohemian massif close to the central bohemian plutonic complex the petrackova hora deposit has many features that distinguish it from other deposits in the region and suggest its mineralization is closely related to the late magmatic processes associated with the petrackova hora granodiorite the gold ores occur as sheeted arrays of quartz veins and veinlets hosted by the small petrackova hora granodiorite stock gold is found mainly as free grains of 900 fineness and is accompanied by abundant pyrrhotite and chalcopyrite and accessory pyrite arsenopyrite loellingite and molybdenite molybdenite from the petrackova hora deposit has been dated by the re os method at 344 4 2 8 ma hydrothermal alteration in the petrackova hora deposit exhibits a distinct temporal paragenesis selectively pervasive early k alteration and silicification are the oldest hydrothermal phases these were followed by early quartz veins q1 to q4 that contain most of the gold mineralization late quartz veins q5 and fracture controlled silicification are gold poor or barren barren calcite veins are the youngest hydrothermal product extensive low temperature meteoric water dominated alteration as is typical of classic porphyry deposits is absent however the lower 18o whole rock values for petrackova hora granodiorite and aplite 2 4 to 5 1 smow compared to other intrusions in the region reflect either interaction with isotopically light external fluids or magma assimilation of small volumes of hydrothermally altered country rock the 18o isotopic compositions for quartz scheelite and hornblende 7 7 to 13 4 smow and the 34s compositions for sulfide minerals 1 to 3 5 cdt from early gold rich quartz veins indicate formation at high temperatures 590 to 400 c from fluids with a magmatic isotopic signature 18ofluid of 5 7 to 7 2 fluids related to late quartz veins q5 suggest the presence of a significant component of non magmatic water 18ofluid 2 5 to 4 0 the 34s values of post q5 sulfide minerals 4 5 to 3 5 reflect at least partial derivation of late stage sulfur from a source external to the intrusions aqueous aqueous carbonic and nitrogen bearing fluid inclusions were identified in hydrothermal and igneous quartz with the aqueous inclusions being the most common in hydrothermal vein quartz the salinity of primary aqueous inclusions falls into ranges 6 to 23 and 33 to 41 equiv wt nacl in igneous quartz populations in salinity were observed between 5 to 16 35 to 40 and 62 to 70 equiv wt nacl the salt component of these fluids is best and minimally approximated by the nacl kcl cacl2 system low and high salinity aqueous carbonic inclusions are accessory in many of the analyzed samples three large successive pulses of fluids are recognized each pulse begins with a high salinity 30 equiv wt nacl magmatic fluid and evolves toward a lower salinity 5 equiv wt nacl fluid data suggest that external meteoric water s were significant for only the third fluid pulse which formed the late q5 quartz veins and the calcite veins polyphase fluid inclusions hosted by igneous quartz of the petrackova hora granodiorite indicate minimum trapping conditions of about 3 kbar and 550 c the gold rich q1 to q4 veins may have formed along a quasi isobaric cooling path at 2 5 to 1 5 kbar and 590 to 400 c this was followed by uplift and formation of late q5 quartz veins 0 5 to 1 5 kbar 300 c and post ore calcite veins 0 5 kbar 100 to 140 c the characteristics of the petrackova hora deposit suggest that it may represent a position intermediate between intrusion related gold systems e g fort knox deposit alaska and gold rich copper poor porphyry deposits e g maricunga belt in chile as such the petrackova hora deposit might be an example of the reduced gold sub type of porphyry deposit

impact of intraseasonal oscillation on the tropical cyclone track in the south china sea this study investigates the impact of the intraseasonal oscillation iso on tropical cyclone tc tracks in the south china sea scs during 1970 2010 about one third of tcs in the scs move eastward while the other two thirds move westward in the tc genesis peak seasons of june october jjaso the westward moving tcs are controlled by the background tc steering flow of easterly and the eastward moving tcs by the tc steering flow induced by the iso the outgoing longwave radiation and wind fields show that the eastward moving tcs were mostly along the main axis of strong tc steering flow anomaly of westerly associated with the iso while the westward moving tcs were only weakly associated with the iso an experiment performed with a simple two level model further confirmed the result the interannual variation of tc tracks in the scs is also discussed it is found that the steering flow anomalies in the scs mostly favor eastward moving tcs in central pacific cp el nino and eastern pacific ep el nino years however the eastward flow anomalies are too weak to have strong influence on the majority of the tcs during la nina years tcs in the scs tend to move westward possibly related to the westward steering flow anomalies