major types and time space distribution of mesozoic ore deposits in south china and their geodynamic settings the ore deposits of the mesozoic age in south china can be divided into three groups each with different metal associations and spatial distributions and each related to major magmatic events the first event occurred in the late triassic 230 210 ma the second in the mid late jurassic 170 150 ma and the third in the early mid cretaceous 120 80 ma the late triassic magmatic event and associated mineralization is characterized by peraluminous granite related w sn nb ta mineral deposits the triassic ore deposits are considerably disturbed or overprinted by the later jurassic and cretaceous tectono thermal episodes the mid late jurassic magmatic and mineralization events consist of 170 160 ma porphyry skarn cu and pb zn ag vein deposits associated with i type granites and 160 150 ma metaluminous granite related polymetallic w sn deposits the late jurassic metaluminous granite related w sn deposits occur in a ne trending cluster in the interior of south china such as in the nanling area in the early mid cretaceous from about 120 to 80 ma but peaking at 100 90 ma subvolcanic related fe deposits developed and i type calc alkaline granitic intrusions formed porphyry cu mo and porphyry epithermal cu au ag mineral systems whereas s type peraluminous and or metaluminous granitic intrusions formed polymetallic sn deposits these cretaceous mineral deposits cluster in distinct areas and are controlled by pull apart basins along the south china continental margin based on mineral assemblage age and space time distribution of these mineral systems integrated with regional geological data and field observations we suggest that the three magmatic mineralization episodes are the result of distinct geodynamic regimes the triassic peraluminous granites and associated w sn nb ta mineralization formed during post collisional processes involving the south china block the north china craton and the indo china block mostly along the dabie sulu and songma sutures jurassic events were initially related to the shallow oblique subduction of the izanagi plate beneath the eurasian continent at about 175 ma but i type granitoids with porphyry cu and vein type pb zn ag deposits only began to form as a result of the breakup of the subducted plate at 170 160 ma along the nne trending qinzhou hangzhou belt also referred to as qin hang or shi hang belt which is the neoproterozoic suture that amalgamates the yangtze craton and cathaysia block a large subduction slab window is assumed to have formed in the nanling and adjacent areas in the interior of south china triggering the uprise of asthenospheric mantle into the upper crust and leading to the emplacement of metaluminous granitic magma and associated polymetallic w sn mineralization a relatively tectonically quiet period followed between 150 and 135 ma in south china from 135 ma onward the angle of convergence of the izanagi plate changed from oblique to parallel to the coastline resulting in continental extensional tectonics and reactivation of regional scale ne trending faults such as the tan lu fault this widespread extension also promoted the development of ne trending pull apart basins and metamorphic core complexes accompanied by volcanism and the formation of epithermal cu au deposits granite related polymetallic sn w deposits and hydrothermal u deposits between 120 and 80 ma with a peak activity at 100 90 ma

structural features and metallogenesis of the carlin type jinfeng lannigou gold deposit guizhou province china abstract jinfeng previously known as lannigou is the largest carlin type gold deposit in the yunnan guizhou guangxi region in southwestern china gold mineralization in the jinfeng deposit is almost entirely fault hosted and structurally controlled with very little disseminated ore occurring in the adjacent host rocks the structural elements in the jinfeng deposit can be subdivided into 3 groups comprising ns nw and ne striking faults and folds with nw striking structures controlling the overall framework of the deposit four tectonic stages have been recorded in the jinfeng area i e rifting orogenic compression lateral transpression and lithospheric extension a series of contemporaneous normal faults such as the n striking and east dipping f1 and f7 faults developed along the edges of a carbonate platform during basin rifting d 2 t 2 these structures provided an initial framework for subsequent basin evolution and also represent the principal hydrothermal conduits a gradual change of the compression direction during the orogenic stage t 3 from e w to ne sw gave rise to the nw striking structures including large tight to overturned folds such as the huangchanggou synclinorium and associated thrusts such as the f3 fault the development of these orogenic predominantly ne dipping structures as well as accompanying ne striking dextral shear and transform faults such as the f2 fault along the margin of the laizishan dome established the structural pattern of the deposit area the nw striking folds were refolded by ne striking superimposed folds during post collisional lateral transpression j 1 and nw se directed compression oblique stress distribution gave rise to ns trending compression and ew trending extension with dilational zones developing at the intersection of the f2 and the f3 faults east of the laizishan dome it is these dextral and sinistral normal dilational zones in which gold was precipitated during the main ore forming event at jinfeng following the main ore stage lithospheric extension occurred during the yanshan stage j 2 k resulting in minor reverse faults that in places cut pre existing structures the above four main structural deformation stages mirror the evolution of the youjiang basin from inception to basin inversion and post orogenic collapse and renewed extension significant gold metallogenesis at jinfeng occurred during the transition from collisional compression to extensional tectonics in the early jurassic and is focussed into intersections of f2 and f3 and fault splays adjacent to f3 this structurally controlled gold metallogenic model is likely to be applicable to analogous settings elsewhere in the yunnan guizhou guangxi triangle area and has implications for the targeting of carlin type gold mineralization in this region

multistage pyrites in the nibao disseminated gold deposit southwestern guizhou province china insights into the origin of au from textures in situ trace elements and sulfur isotope analyses abstract nibao is a unique thrust fault controlled and strata bound disseminated gold deposit in southwestern guizhou province china in nibao pyrite is the major sulfide mineral and au is structurally bound au within the pyrite lattice in this study we conducted detailed analyses of the pyrite chemistry and s isotope composition in nibao using laser ablation inductively coupled plasma mass spectrometry la icp ms and laser ablation multi collector inductively coupled plasma mass spectrometry la mc icp ms respectively through petrographic and pyrite chemical studies four pyrite generations py1 py4 were distinguished framboidal pyrite py1 pre ore sedimentary stage clean pyrite overgrowing framboidal pyrite py2 pre ore diagenetic stage spongy pyrite py3 early ore stage and overgrowth of narrow pyrite rims surrounding py2 py3 and disseminated pyrite associated with arsenopyrite py4 main ore stage among these py2 and py4 are the most abundant the trace element content in py2 is characterized by a wide range of as cu sb and pb concentrations 2480 58100 ppm 55 4 1610 ppm 29 1 232 ppm and 24 1 376 ppm respectively while py4 has the highest au as cu and se contents 70 ppm 4200 1630 ppm and 38 3 ppm respectively the 34s values of pre ore pyrites measured by la mc icp ms in this study and the available data in the literature range broadly from 53 3 to 114 8 indicating that they were most likely generated by bacterial reduction from marine sulfate during sedimentation diagenesis meanwhile the 34s values of ore pyrites have relative narrow 34s values mostly varying from 5 to 5 and indicating that the s was derived either from the average of sedimentary rocks or from a magmatic source since igneous rocks are scarce in the region and the exposed 77 99 ma are clearly younger than the mineralization age of the nibao gold deposit 141 ma a magmatic source is unlikely in nibao all pyrites in this study show a positive correlation r2 0 71 between co and ni and the co ni and zn ni ratios of main stage py4 are close to or within the range defined for a sedimentary diagenetic origin suggesting a sedimentary source is more likely in nibao

migration paths and precipitation mechanisms of ore forming fluids at the shuiyindong carlin type gold deposit guizhou china abstract shuiyindong is one of the largest and highest grade stratabound carlin type gold deposits in china this paper reports on the results of petrographic studies electron microprobe analyses empa of arsenian pyrite and the mass transfer during mineralization and alteration and it presents the deposit scale distributions of au as sb hg tl and trace elements in a representative cross section across the shuiyindong carlin type gold deposit guizhou province the main objectives were to identify the precipitation mechanisms of minerals or elements from fluids and the migration paths of ore forming fluids petrographic and empa studies indicate that gold in the primary ores is mainly hosted by arsenian pyrite mass transfer associated with alteration and mineralization shows that au as sb hg tl and s were significantly added to all mineralized rocks fe 2 o 3 and sio 2 were immobile in the main orebodies that are hosted in bioclastic limestone and cao na 2 o sr and li were removed from country rocks the relations between fe and s indicate that the sedimentary rocks at the shuiyindong deposit contain more iron than is needed to combine with all of their contained sulfur to form pyrite this suggests that sulfidation and decarbonation were the principal mechanism of gold precipitation at the shuiyindong deposit hg sb and as commonly formed sulfide minerals such as stibnite realgar and orpiment in late stage quartz calcite veins or absorbed by organic matter in argillite fluid cooling presumably led to depositions of stibnite realgar and orpiment in late stage quartz calcite veins organic matter likely served as a reductant in argillite for the ore fluids causing the precipitation of as sb hg and s as well as au deposit scale distributions of gold and other relevant elements reflect the passage of fluids through the rocks rock strata and structures allowed the ore forming fluids to migrate horizontally along the unconformity surface of the middle upper permian converge on the high position of an anticline and then ascend into the overlying strata along the anticlinal axis the distributions of the major and trace elements show that elements that accompanied the ore forming fluids include au as sb hg tl and s and that na 2 o and li were exhausted in the longtan formation at the anticlinal core during gold mineralization the enrichment of co cr and ni in the longtan formation at the anticlinal core might be associated with deformation that formed the anticline or with gold mineralization different host rocks were preferentially mineralized by different elements the bioclastic limestone is commonly enriched in au whereas the argillite is preferentially enriched in as hg sb and tl the zonation of ore forming elements in the deposit appears to be sb tl as hg au hg as from bottom to top enrichment of au as sb hg and tl provides useful guidance for the exploration for carlin type gold deposits in guizhou anomalies of as and hg in soil or stream sediment might be an important clue and these elements can be used as indicator elements ore forming fluids migrated along the unconformity surface of the middle upper permian and the anticlinal axis so these are favorable sites for exploration for carlin type gold deposits in guizhou

no genetic link between late cretaceous felsic dikes and carlin type au deposits in the youjiang basin southwest china abstract the youjiang basin in southwest china is distinguished by preserving a number of carlin type gold deposits tens of felsic dikes occur in this region and some are present within the ore fields a genetic link between these felsic dikes and ore formation has previously been proposed but detailed field investigation shows that the dikes crosscut the main ore body and clearly postdate gold mineralization three felsic dikes in the youjiang basin have been dated and sims zircon u pb dating results show that the liaotun and xiabaha dikes were emplaced at 97 2 1 1 ma mswd 2 9 and 95 4 2 4 ma mswd 0 56 respectively broadly consistent with a la icp ms zircon u pb age for the bama dike 99 4 0 37 ma mswd 1 4 combined with published dates of the other felsic dikes in this region it is suggested that the felsic magmatic event in the youjiang basin occurred between 100 and 95 ma although a wide range of ages for gold mineralization 275 46 ma has been reported by a variety of methods the best available ages suggest a timing between 235 and 193 direct re os dating on fe sulfides chen et al 2015 re os isochron ages for arsenopyrite from carlin like gold deposits in the yunnan guizhou guangxi golden triangle southwestern china significantly older than the emplacement age of the felsic dikes taken together we conclude that there is no genetic link between these late cretaceous felsic dikes and carlin type au mineralization in the youjiang basin

the mesoscale dynamics of thin tropical tropopause cirrus abstract thin cirrus clouds in the tropical tropopause layer ttl are warmed through the absorption of infrared radiation the response of the cloud and the surrounding atmosphere to this thermal forcing is investigated through linear theory and nonlinear numerical simulation linear solutions for the circulations forced by a fixed heat source representative of ttl cirrus clouds show ascent in the region of the heating accompanied by horizontal flow toward the heat source at the base of the heated layer and horizontal outflow at the top of the layer gravity waves propagate positive temperature perturbations well beyond the lateral edges of the heated region cool layers that also spread horizontally are produced immediately above and below the heated region numerical simulations with a cloud resolving model allow the radiative heating to change in response to the redistribution of the cloud by the evolving velocity field the basic atmospheric response in the numerical simulations is nevertheless simi

surface climate of the interior of the lambert glacier basin antarctica from automatic weather station data data from six automatic weather stations deployed around the interior of the lambert glacier basin antarctica at surface elevations of 1830 2741 m are used to compile a surface climatology of this part of interior antarctica for the period 1994 96 the stations measure air pressure near surface wind speed and air temperature at several levels wind direction and firn temperatures the topography of the basin which extends more than 800 km inland controls the katabatic wind regime and strongly influences the surface climate of the region windiest sites are on the steep coastal slopes and within the depression of the lambert and melior ice streams where the flow is topographic ally channelled surface winds here show greater seasonal variation in speed but less variation in direction than elsewhere the annual mean temperatures on the relatively steep slopes on the eastern side of the basin are 4 5 c warmer than at equivalent altitude on the western side during winter near synchronous synoptic temperature and pressure increases occur throughout the basin to at least 1000 km from the coast there is a consis tent pattern of diurnal wind variation in the summer at all stations with maximum wind speed at about 0900 lst local solar time and the most easterly direction at 1300 lst

snow density along the route traversed by the japanese swedish antarctic expedition 2007 08 during the japanese swedish antarctic traverse expedition of 2007 08 we measured the surface snow density at 46 locations along the 2800 km long route from syowa station to wasa station in east antarctica the mean snow density for the upper 1 or 0 5 m layer varied from 333 to 439 kg m 3 over a region spanning an elevation range of 365 3800 m a s l the density variations were associated with the elevation of the sampling sites the density decreased as the elevation increased moving from the coastal region inland however the density was relatively insensitive to the change in elevation along the ridge on the antarctic plateau between dome f and kohnen stations because surface wind is weak in this region irrespective of elevation the wind speed was suggested to play a key role in the near surface densification the results of multiple regression performed on the density using meteorological variables were significantly improved by the inclusion of wind speed as a predictor the regression analysis yielded a linear dependence between the density and the wind speed with a coefficient of 13 5 kg m 3 m s 1 1 this relationship is nearly three times stronger than a value previously computed from a dataset available in antarctica our data indicate that the wind speed is more important to estimates of the surface snow density in antarctica than has been previously assumed

lightning in the anvils of supercell thunderstorms abstractthis study uses data from the oklahoma lightning mapping array ok lma the national lightning detection network and the norman oklahoma koun prototype weather surveillance radar 1988 doppler wsr 88d radar to examine the evolution and structure of lightning in the anvils of supercell storms as they relate to storm dynamics and microphysics several supercell storms within the domain of the ok lma were examined to determine whether they had lightning in the anvil region and if so the time and location of the initiation of the anvil flashes were determined every warm season supercell storm had some flashes that were initiated in or near the stronger reflectivities of the parent storm and propagated 40 70 km downstream to penetrate well into the anvil some supercell storms also had flashes that were initiated within the anvil itself 40 100 km beyond the closest 30 dbz contour of the storm these flashes were typically initiated in one of three locations 1 coincident with a local reflec

densification of layered firn in the ice sheet at dome fuji antarctica in order to better understand the densification of polar firn firn cores from the three sites within 10 km of dome fuji antarctica were investigated using surrogates of density dielectric permittivities e v and e h at microwave frequencies with electrical fields in the vertical and horizontal planes respectively dielectric anisotropy e e v e h was then examined as a surrogate of the anisotropic geometry of firn we find that layered densification is explained as a result of complex effects of two phenomena that commonly occur at the three sites basically layers with initially smaller density and smaller geometrical anisotropy deform preferentially throughout the densification process due to textural effects second layers having a higher concentration of cl ions deform preferentially during a limited period from the near surface depths until smoothing out of layered cl ions by diffusion we hypothesize that cl ions dissociated from sea salts soften firn due to modulation of dislocation movement moreover firn differs markedly across the three sites in terms of strength of geometrical anisotropy mean rate of densification and density fluctuation we hypothesize that these differences are caused by textural effects resulting from differences in depositional conditions within various spatial scales

geochronology geochemistry and petrogenesis of late triassic dolerites associated with the nibao gold deposit youjiang basin southwestern china implications for post collisional magmatism and its relationships with carlin like gold mineralization abstract the relationship between gold mineralization and magmatism within the youjiang basin of sw china remains poorly constrained as a result of the lack of outcropping igneous units in this region this study presents new geological geochronological and geochemical data for recently discovered dolerite dykes associated with the nibao gold deposit which is located within the nw youjiang basin of sw china zircon laser ablation inductively coupled plasma mass spectrometry la icp ms u pb dating of these dykes yielded an age of 213 6 2 5 ma indicating that these dykes were emplaced during the late triassic and providing new evidence for late triassic magmatism within the study area these dykes also represent an opportunity to investigate the petrogenesis of mafic rocks and the tectonic setting of the late triassic magmatism in the youjiang basin these nibao dolerite dykes contain relatively low concentrations of sio 2 46 03 47 66 wt have moderate total alkali contents k 2 o na 2 o 2 71 3 15 wt and high total fe as fe 2 o 3 tfe 2 o 3 contents 13 49 14 96 wt their trace element compositions are indicative of an oib like geochemical affinity barring depletion in the high field strength elements hfse such as nb ta and th the nibao dolerites have homogeneous lu hf and sr nd isotopic compositions with 87 sr 86 sr i and 143 nd 144 nd i value of 0 70562 0 70677 and 0 51233 0 51239 respectively these dykes have associated e nd t and e hf t values that exhibit a narrow range from 0 70 to 0 51 and from 0 04 to 3 24 respectively these geochemical data indicate that the dolerites associated with the nibao gold deposit were derived from an enriched region of the asthenopheric mantle 90 km depth and the magmas that formed these dykes were generated by 5 10 partial melting of 75 garnet peridotite and 25 spinel peridotite material the ascending magmas underwent both crustal contamination and the fractional crystallization of olivine clinopyroxene and fe oxides e g magnetite or ilmenite prior to emplacement the nibao dolerites are geochemically distinct from mafic rocks related to the emeishan large igneous province suggesting that they are not linked to this mantle plume event instead they formed in an extensional setting generated by the subduction of the song ma oceanic plate beneath south china block and the subsequent collision between the indochina block and south china block the breakoff of the song ma oceanic slab was the process that caused the partial melting of the mantle source region for the nibao dolerite dykes these relationships suggest that the post collision extensional environment associated with this breakoff contributed to the deeply sourced mantle derived late triassic magmatism in this area and perhaps as well the gold mineralization in the youjiang basin most importantly the new geochronological data presented in this study the timing of extension in this region and the results of previous research together suggest that the carlin like gold deposits in the youjiang basin formed at around 213 ma i e the late triassic

source and evolution of ore fluids in the zhenyuan orogenic gold deposit se tibet constraints from the s c o isotopes abstract orogenic gold deposits commonly have large variation of stable isotopic values of ore minerals induced by complicated ore fluids evolution which was considered to provide equivocal evidence for ore sources in contrast this study has revealed relatively narrow range of s and c o isotopes of pyrites and carbonate minerals in the zhenyuan gold deposit 100 t at 3 5 g t on ailaoshan shear zone southeastern margin of tibet the zhenyuan deposit is a disseminated orogenic gold deposit with mineralization and alteration occurring in various types of wall rocks including carbonaceous slate meta quartz sandstone lamprophyre quartz porphyry and meta basalt the pre ore pyrites include the diagenetic pyrites in carbonaceous slate and meta quartz sandstone and the barren hydrothermal pyrites in quartz porphyry diagenetic pyrites have much varied 34s values from 54 58 38 31 and barren hydrothermal pyrites have elevated positive 34s values 8 76 43 24 the ore related pyrites disseminated in all types of host rocks and commonly with repetitive gold rich zones are the most important gold bearing minerals they contain high concentration of au along with other trace elements including cu as sb tl pb and bi little difference of 34s values is observed for the pyrites in different types of host rocks and for the low au and high au zones in single pyrite grain all ore related pyrites display a relatively narrow range of 34s values 5 22 4 16 with a peak at 0 this narrow range implies that the deposition of gold from ore fluids at zhenyuan deposit was mainly controlled by sulfidation of iron bearing minerals in the wall rocks the 34s values of ore related pyrites are consistent with the explanation that the ore fluids were from the subcrustal source instead of the crustal source with much varied sulfide 34s values carbonate minerals from different types of host rocks also have consistent and relatively narrow range of 13cpdb 3 77 0 68 and 18osmow 14 85 20 77 values indicating that the composition of ore fluids were little affected by water rock reaction at deposit scale the 13cpdb and 18osmow values of carbonates minerals are between those of the mantle peridotite and marine carbonates which can be explained by that the ore fluids have experienced crustal carbonate contamination in the subcrustal level or and along the migration conduit of the ore fluids

an empirical relation between overburden pressure and firn density two empirical equations for firn densification have been obtained considering firn porosity as a function of overburden pressure in the first equation thereduction ratio of porosity in firn is assumed to be proportional to the increasing ratioof overburden pressure and the mth power of the porosity the porosity exponent m should be close to 2 so as to have a best fit with 14 depth density profiles fromgreenland and antarctica in the second equation the reduction ratio of porosity wasassumed to increase proportionally to the increment of overburden pressure and thenth power of the porosity the most satisfactory values of the exponent range from 1 to 1 it has been suggested that firn density determined primarily by overburdenpressure and firn temperature contribute to a lesser degree

gold and sulfur sources of the taipingdong carlin type gold deposit constraints from simultaneous determination of sulfur isotopes and trace elements in pyrite using nanoscale secondary ion mass spectroscopy abstract the youjiang basin in southwestern china is known for the occurrence of abundant carlin type gold deposits similar to those of northern nevada in the u s among them taipingdong is a representative deposit nearby the super large shuiyindong mine in the huijiabao ore field though some data of in situ sulfur isotopes and trace element geochemistry of pyrite have been collected recently the ore forming fluid source and genesis model of the deposits remain under debate the mineral chemistry and isotopic compositions of au carrying pyrite in the taipingdong gold deposit were studied in detail using nanoscale secondary ion mass spectroscopy nanosims in this study to further understand the aforementioned issues petrographic observations identified two types of pyrite syn sedimentary framboidal pyrites and hydrothermal pyrites back scattered electron observations and electron microprobe analysis elemental mapping showed that the latter have three generations termed as as poor py1 the core as rich py2 the middle overgrowth and as weak py3 the outmost overgrowth zone respectively nanosims high resolution multiple elemental maps showed the following 1 py1 is poor in as and other trace elements py2 is rich in as and cu and relatively rich in se and py3 is rich in au and relatively rich in as cu and se 2 gold is heterogeneously distributed as solid solution and nanoparticle focusing on the outermost rim of the zoned pyrite py3 other metal nanoparticles of cu se and pb were identified in py2 or py3 3 arsenic elemental mapping showed dense mineral growth of pyrite in the subzones 4 line profile analyses of trace elements showed high cu contents in py2 and py3 and that as is positively correlated with cu but not with au in situ sulfur isotopic analyses showed that the 34s values range from 15 4 to 6 1 with a median of 2 0 for py1 from 1 8 to 7 1 with a median of 1 4 for py2 and from 3 0 to 6 2 with a median of 3 9 for py3 intensive spot analyses showed a slight fluctuation in s isotopic values within a short distance in pyrite subzones the 34s values of py2 and py3 dropped into a narrow range from 3 to 6 with a median of 3 3 considering the composition and isotopic characteristics py1 is classified as pre ore pyrite and py2 and py3 as ore pyrites with py3 representing the au climax event the au state and distribution in the pyrite of the taipingdong deposit imply that the ore forming fluid was unsaturated for au but occasionally hosted metal nanoparticles the au climax event occurred towards the end of the fluid evolution the decoupling of as and au in the ore pyrites indicate that the au carrying capacity of the pyrite was limited by the higher concentration of cu ions in the ore forming fluids the s isotopic data of the taipingdong deposit is similar to the available in situ s isotopic range of 5 to 5 of the representative au deposits in the basin except for the lannigou zhenfeng mine the s isotopic deviation of pyrite in the huijiabao ore field to the typical magmatic fluid 0 may be the result of a mixture of hydrothermal and basin fluid to a certain extent this feature combined with the intensive fluctuation of trace elements and isotopic compositions over a short duration accord with the characteristics of magmatic hydrothermal fluid combined with the strong silicification characteristic of the host rock and the previous geophysical works in the ore district a magmatic hydrothermal model might be suitable for the taipingdong gold deposit and even other carlin type gold deposits in the youjiang basin

gold and silver metallogeny of the south china fold belt a consequence of multiple mineralizing events abstract the south china fold belt is part of the south china block that is interpreted to be the result of multiple tectonic and magmatic events that formed a collage of accreted proterozoic and phanerozoic terranes the jurassic to early cretaceous yanshanian period 180 90 ma a time of major tectono thermal events that affected much of eastern and southeastern china is of great metallogenic importance in the fold belt this period is linked to subduction of the pacific plate beneath the eurasian continent and is manifested by voluminous volcano plutonic activity of predominantly calc alkaline affinity the distribution of gold and silver deposits in the south china fold belt indicates the presence of two distinct metallogenic provinces a region of basement uplifts which are controlled by shear zones and form neoproterozoic inliers of metamorphosed iron rich rock types defines the first province in this province orogenic lodes and volcanic related epithermal deposits represent the more significant precious metal mineralization the second province is essentially confined to a belt of yanshanian felsic intermediate volcanic and subvolcanic rocks that extends along most of the southeastern china coast in an area known as the coastal volcanic belt deposits in the coastal volcanic belt are silver and or copper rich volcanic hosted and epithermal in character the precious metal metallogeny of the south china fold belt is interpreted to have developed in at least three stages one as a result of collision events during the caledonian orogeny ca 400 ma the second during the indosinian orogeny ca 200 ma and the third during or soon after the formation of the yanshanian magmatic belt yanshanian orogeny 180 90 ma the latter was responsible for a hydrothermal event that affected large sections of the belt and its proterozoic substrate this may have resulted in the redistribution and enrichment of precious metals from preexisting orogenic gold lodes in neoproterozoic basement rocks which are now exposed as windows in zones of tectonic uplift the yanshanian hydrothermal activity was particularly widespread in the coastal volcanic belt and resulted in the formation of both low and high sulfidation epithermal gold and silver and locally copper and other base metal mineralization it is suggested that the coastal volcanic belt has greater potential for world class epithermal and porphyry deposits than previously realised

climate variables along a traverse line in dronning maud land east antarctica temperature density and accumulation data were obtained from shallow firn cores drilled during an overland traverse through a previously unknown part of dronning maud land east antarctica the traverse area is characterised by high mountains that obstruct the ice flow resulting in a sudden transition from the polar plateau to the coastal region the spatial variations of potential temperature near surface firn density and accumulation suggest that katabatic winds are active in this region proxy wind data derived from firn density profiles confirm that annual mean wind speed is strongly related to the magnitude of the surface slope the high elevation of the ice sheet south of the mountains makes for a dry cold climate in which mass loss owing to sublimation is small and erosion of snow by the wind has a potentially large impact on the surface mass balance a simple katabatic wind model is used to explain the variations of accumulation along the traverse line in terms of divergence convergence of the local transport of drifting snow the resulting wind and snowdrift patterns are closely connected to the topography of the ice sheet ridges are especially sensitive to erosion while ice streams and other depressions act as collectors of drifting snow

cloud classes and radiative heating profiles at the manus and nauru atmospheric radiation measurement arm sites 1 the tropical western pacific is a convective regime however the frequency and depth of convection is dependent on dynamical forcing which exhibits variability on a range of temporal scales and also on location within the region manus island papua new guinea lies in the heart of the western pacific warm pool region and exhibits frequent deep convection much of the time while nauru which lies approximately 20 degrees to the east of manus is in a transition zone where the frequency of convection is dependent on the phase of the el nino southern oscillation because of this difference in dynamical regime the distribution of clouds and the associated radiative heating is quite different at the two sites individual cloud types boundary layer cumulus thin cirrus stratiform convective outflow do occur at both sites but with different frequencies in this study we compare cloud profiles and heating profiles for specific cloud types at these two sites using data from the atmospheric radiation measurement arm climate research facility results of this comparison indicate that while the frequency of specific cloud types differ between the two sites as one would expect the characteristics of individual cloud classes are remarkably similar this information could prove to be very useful for applying tropical arm data to the broader region

association of tropical cirrus in the 10 15 km layer with deep convective sources an observational study combining millimeter radar data and satellite derived trajectories abstract in this paper millimeter cloud radar mmcr and geosynchronous meteorological satellite gms data are combined to study the properties of tropical cirrus that are common in the 10 15 km layer of the tropical troposphere in the western pacific millimeter cloud radar observations collected by the atmospheric radiation measurement program on the islands of manus and nauru in the western and central equatorial pacific during a 12 month period spanning 1999 and 2000 show differences in cirrus properties over manus where clouds above 7 km are observed 48 of the time the cirrus are thicker and warmer on average and the radar reflectivity and doppler velocity are larger over nauru clouds above 7 km are observed 23 of time to explain the differences in cloud properties the relationship between tropical cirrus and deep convection is examined by combining the radar observations with gms satellite derived back trajectories using a data record of 1 yr it is found that 47 of the cirrus observed o

structure of the annual mean equatorial planetary waves in the era 40 reanalyses abstract the three dimensional structure of the annual mean equatorial planetary waves in the 40 yr ecmwf re analysis era 40 is documented the features in the free atmosphere are predominantly equatorially symmetric driven by east west heating gradients the geopotential height and wind perturbations are strongest at or just below the 150 hpa level below the level of maximum amplitude the circulations in the waves are thermally direct with latent heat release in deep convective clouds and radiative cooling in the intervening cloud free regions within the overlying capping layer the wave related circulations are thermally indirect with rising of the coldest air and sinking of air that is less cold at the cold point just above the 100 hpa 17 km level the era 40 annual mean vertical velocity in the equatorial belt ranges up to 3 mm s 1 over the equatorial western pacific during the boreal winter implying diabatic heating rates of up to 3 c day 1 an order of magnitude larger than typical clear

an integrated view of the 1987 australian monsoon and its mesoscale convective systems i horizontal structure this observational study is organized around three issues the forcing of the monsoon flow by embedded deep convection the thermodynamic conditions that support the convection and the structures of the mesoscale convective systems mcss that constitute much of the deep convection the monsoon convective cloudiness occurred predominantly offshore over the earth s warmest waters week long periods of widespread deep convection caused cycles of monsoon spin up culminating in tropical cyclone formation momentum transports by the convection also created smaller scale vortex pairs in the upper troposphere sounding data suggest that the convection was modulated by low level processes not by large scale deep forced ascent triggering by mesoscale boundary layer cold pool boundaries and coastlines determined specifically where convection occurred while several positive feedbacks acted to keep regional thermodynamic conditions favourable hence monsoon convection once initiated persisted as self exciting superclusters composed at any instant of many distinct mcss the observed mcss all contained areas of deep convection and stratiform precipitation areas stratiform precipitation usually evolved in place from convective cells although precipitation also occasionally fell from overhanging anvils created by upper level shear the mcss within similar synoptic wind environments tended to have similar mesoscale structures this fact reflects the effects illustrated herein of environmental winds upon the relative motions of cold pools which trigger new convective cells and stratiform precipitation areas which evolve from old convective cells

the origin of the tongkeng changpo tin deposit dachang metal district guangxi china clues from fluid inclusions and he isotope systematics tongkeng changpo is the largest tin deposit within the giant dachang polymetallic tin ore field in guangxi southern china which is part of a large skarn system associated with cretaceous granitoids the tongkeng changpo mineralization consists of veins and stockworks in the upper levels and replacement stratiform orebodies mantos at lower levels based on textural relationships three major mineralizing stages can be recognized stage i with cassiterite sulphides stannite tourmaline and quartz stage ii with cassiterite sulphides sulphosalts quartz and calcite and stage iii with calcite as the main phase the study of fluid inclusions has shown that there are two main fluid types co2 and nacl h2o homogenization temperatures are 270 to 365 c 210 to 240 c and 140 to 190 c for stages i ii and iii respectively salinities range from 1 to 7 wt nacl equiv in the early ore stage and 3 to 10 wt nacl equiv in the late stages laser raman spectroscopy indicates that the inclusion fluids in stages i and ii were of carbono aqueous composition with minor amounts of ch4 and h2s whereas those in stage iii were aqueous helium isotopic analyses of inclusion fluids indicate that the 3he 4he ratios in the ore veins are in between 1 2 to 2 9 ra ra 1 4 10 6 modern atmospheric ratio and range from 1 6 to 2 5 ra in the stratiform orebodies this range of 3he 4he ratios is significantly higher than that of crustal fluids 0 01 0 05 ra the similar characteristics of fluid inclusions and their he isotopic composition as well as age constraints indicate that the ore veins and stratiform orebodies of the tongkeng changpo deposit formed from the same hydrothermal system likely related to granite intrusions of the mesozoic yanshanian tectono thermal event in addition the high r ra ratios indicate a mantle contribution in the ore fluids

effects of cirrus near the tropopause on anvil cirrus dynamics 1 recent space and airborne observations have noted tenuous cirrus near the tropopause and above deep convective anvil outflow we use a cloud resolving model initialized with aircraft observations taken during the crystal face experiment to explore the effects of such cirrus layers on anvil evolution numerical simulations demonstrate that anvil cirrus spreads because strong absorption of thermal radiation and emission at cloud base and top creates horizontal heating gradients between the cloud and its environment the presence of a second layer of cirrus near the tropopause forces the upper part of the anvil to equilibrate to warmer radiative temperatures than would normally be associated with a clear upper atmosphere compared to a case without thin cirrus the associated reduction to heating gradients at anvil cloud top corresponds to reduced anvil spreading and turbulent kinetic energy by as much as 19 and 40 respectively these results suggest that tropopause cirrus can affect climate indirectly by altering anvil cirrus dynamics

multiple element mapping and in situ s isotopes of au carrying pyrite of shuiyindong gold deposit southwestern china using nanosims constraints on au sources ore fluids and mineralization processes abstract this study employed high sensitivity and high resolution secondary ionizing mass spectrometry nanosims to determine the distribution of au as cu se and s isotopes of pyrite from the shuiyindong au deposit southwestern china nanosims maps show that au occurs as solid solution and heterogeneously distributes at micron scale in the ore pyrite which is the overgrowth of the preexisting synsedimentary or hydrothermal pyrite core commonly rimmed again by the as and au poor outermost zone there is no detectable au in the synsedimentary pyrite invisible au was observed to fill in the submicron scale cracks of the ore pyrite meanwhile element line profile analysis shows that au occurs in three discrete climaxes in the ore pyrite in situ s isotopic analyses identified two types of s sources the synsedimentary pyrites have large negative 34s values ranging from 38 3 to 18 8 which is a typical biogenetic s generated by bacterial reduction of sea water sulfate the hydrothermal pyrites with zoned texture have a narrow 34s range of 3 5 7 4 with a median of 2 3 similar to the recently published sulfur isotope data of the southwest china s carlin type gold deposits except for the lannigou mine combining the distribution of au and s isotopes in pyrite indicates that the au carrying zones have lower 34s values than that of the ore unrelated zones these nanosims observations indicate that the au mineralization was closely associated with strong deformation of the host rock the au forming the deposit was exotic instead of the reactivated au in the preexisting pyrite formed in the synsedimentary basin the mineralization progress was multistage the distribution of au and s isotopes is hard to interpret by the viewpoint of metamorphic fluid or fluid pressure fluctuation instead it is more consistent with magmatic fluid likely contaminated by sedimentary sulfur during its ascending to the surface in addition the multistage ore formation pattern discovered in this study poses new challenges to determine the mineralization age of the au deposits in southwestern china

accumulation variability and mass budgets of the lambert glacier amery ice shelf system east antarctica at high elevations the temporal and spatial variability of the annual accumulation rate and the mass budgets of five sub basins of the lambert glacier amery ice shelf system las east antarctica at high elevations are assessed using a variety of datasets derived from field measurements and modeling the annual temporal variations of the accumulation rate for four cores from the west and east sides of the las are around 34 decadal fluctuation of the accumulation from the dt001 firn core drops to 10 and the 30 year fluctuation to 5 which is assumed to contain the information about the regional and long term trend in accumulation the 15 point running mean of the annual accumulation rate derived from stake measurements can remove most of the high frequency spatial variation so as to better represent the local accumulation model simulations show that the spatial variability of erosion deposition of snow by the wind has a noticeable impact on the surface mass balance at the higher parts of the las mass budget estimates at high elevation sub basins of the las suggest drainage 9 has a negative imbalance of 0 7 0 4 gt a 1 lambert and mellor glaciers have a positive imbalance of 3 9 2 1 and 2 1 2 4 gt a 1 respectively and fisher glacier and drainage 11 are approximately in balance the higher elevation region as a whole has a positive mass imbalance of 4 4 6 3 gt a 1 which is consistent with the most recent radar altimetry assessment that shows an overall thickening over this region

an unusual reticular cloud formation abstract photographic documentation of a rare and enigmatic reticular cloud formation that occurred in conjunction with a thunderstorm outflow anvil on 4 june 1995 at 2230 utc at norman oklahoma is presented a national weather service vertical sounding taken within 1 h of the occurrence of the formation at norman is also presented possible formation mechanisms for these unusual cloud features are discussed

molybdenite re os and albite 40ar 39ar dating of cu au mo and magnetite porphyry systems in the yangtze river valley and metallogenic implications abstract the area of the middle lower yangtze river valley eastern china extending from wuhan hubei province to western zhenjiang jiangsu province hosts an important belt of cu au mo and fe deposits there are two styles of mineralization i e skarn porphyry stratabound cu au mo fe deposits and magnetite porphyry deposits in several nne trending cretaceous fault bound volcanic basins the origin of both deposit systems is much debated we dated 11 molybdenite samples from five skarn porphyry cu au mo deposits and 5 molybdenite samples from the datuanshan stratabound cu au mo deposit by icp ms re os isotope analysis nine samples from the same set were additionally analyzed by ntims on re os results from the two methods are almost identical the re os model ages of 16 molybdenite samples range from 134 7 2 3 to 143 7 1 6 ma 2 the model ages of the five samples from the datuanshan stratabound deposit vary from 138 0 3 2 to 140 8 2 0 ma with a mean of 139 3 2 6 ma their isochron age is 139 1 2 7 ma with an initial os ratio of 0 7 8 1 mswd 0 29 these data indicate that the porphyry skarn systems and the stratabound deposits have the same age and suggest an origin within the same metallogenic system albite 40 ar 39 ar dating of the magnetite porphyry deposits indicates that they formed at 123 to 125 ma i e 10 20 ma later both mineralization styles characterize transitional geodynamic regimes i e the period around 140 ma when the main ns trending compressional regime changed to an ew trending lithospheric extensional regime and the period of 125 115 ma of dramatic ew trending lithospheric extension

distinctive features of late palaeozoic massive sulphide deposits in south china abstract more than 20 sediment hosted massive sulphide deposits occur in late palaeozoic basins in south china these deposits are accompanied by a certain amount of volcanic rocks in the host sequence and are economically important for their cu pb zn au and ag reserves the deposits and their host strata were commonly intruded by mesozoic granitoids remobilisation of sedimentary ores and magmatic hydrothermal overprinting processes resulted in the coexistence of massive sulphides with vein skarn and porphyry type orebodies in the same region or within a single deposit the ore containing basins occur in different tectonic settings the lower yangtze basin occurs on a passive continental margin where the deposits are high in cu and au with minor pb and zn and recoverable ag co and mo the ores have a lower concentration of radiogenic lead and 34s values close to zero fluid inclusions are highly saline and na rich fluids and metals of the lower yangtze region are interpreted to have been derived essentially from deep sources including the precambrian basement by contrast basins of the nanling region formed in an intracontinental setting developed on a folded caledonian basement these deposits are higher in pb zn sn and w as well as cu with recoverable ag sb hg u bi tl and mo the ores are characterised by a higher concentration of radiogenic lead and a wide variation of 34s composition fluid inclusions have lower salinities and higher k na ratios fluids are considered to have been sourced substantially from seawater by convection metals for the nanling deposits were essentially derived from the caledonian basement by leaching the contrast in ore composition between these two regions appears to have been controlled by differences in basement composition of the ore forming basins

magmatic origin for sediment hosted au deposits guizhou province china in situ chemistry and sulfur isotope composition of pyrites shuiyindong and jinfeng deposits

evolution of a florida cirrus anvil abstract this paper presents a detailed study of a single thunderstorm anvil cirrus cloud measured on 21 july 2002 near southern florida during the cirrus regional study of tropical anvils and cirrus layers florida area cirrus experiment crystal face nasa wb 57f and university of north dakota citation aircraft tracked the microphysical and radiative development of the anvil for 3 h measurements showed that the cloud mass that was advected downwind from the thunderstorm was separated vertically into two layers a cirrus anvil with cloud top temperatures of 45 c lay below a second thin tropopause cirrus ttc layer with the same horizontal dimensions as the anvil and temperatures near 70 c in both cloud layers ice crystals smaller than 50 m across dominated the size distributions and cloud radiative properties in the anvil ice crystals larger than 50 m aggregated and precipitated while small ice crystals increasingly dominated the size distributions as a consequence measured ice water content

mammatus clouds as a response to cloud base radiative heating mammatus clouds are the pouchlike lobes seen hanging from mid to high level clouds they can look quite dramatic but they are also interesting because they provide clues to what controls anvil cirrus dynamic evolution thus far the most commonly accepted explanation for observed subsidence of mammatus lobes is that they are driven by evaporative cooling of precipitation accelerated by mixing with dry subcloud air here an alternative explanation is proposed radiative temperature contrasts between cloud base and the lower troposphere destabilize cloudy air to create a rapidly deepening mixed layer which creates positively buoyant intrusions of dry air into the cloud interior mammatus lobes are just the descending branch of the resulting circulations in this regard mammatus cloud fields might be considered an upside down analog to the radiatively driven formation of cloud holes seen at the tops of stratocumulus layers

multistage sedimentary and metamorphic origin of pyrite and gold in the giant sukhoi log deposit lena gold province russia gold mineralization at sukhoi log in eastern siberia is hosted in a deformed neoproterozoic organic bearing and pyritic black shale and siltstone sequence that is folded into a tight overturned anticline the deposit contains about 30 million ounces of gold at an average grade of 2 0 g t au and is one of the largest known undeveloped gold resources the high grade gold zone forms a gently dipping tabular body in the core of the anticline the best gold grades occur in narrow bedding parallel pyrite quartz veinlets that have been folded during the main deformation event lower grade gold is associated with disseminated pyrite developed in and around the high grade core of the deposit detailed paragenetic studies of the mineralization and host rocks have defined six stages of pyrite development in the carbonaceous sediments the two earliest forms of pyrite termed py1 and py2 are commonly developed in stratiform layers of micron sized crystals framboids and fine euhedra which are interpreted as synsedimentary to early diagenetic in origin coarser grained bedding parallel aggregates of inclusion rich pyrite termed py3 contain inclusions of arsenopyrite native gold and gold tellurides and are interpreted to form during late diagenesis and earliest deformation coarse euhedral pyrite py4 overgrows the earlier pyrite py1 py2 and py3 and the slaty cleavage developed in the host rocks indicating a syndeformation timing late stage inclusion free pyrite py5 overgrows and replaces earlier sulfides and is considered to be syn to late deformation laser ablation inductively coupled plasma mass spectrometry la icpms analyses of the various pyrite types indicate that the synsedimentary py1 contains the highest levels of invisible gold varying from 0 4 to 12 1 ppm with a mean of 3 22 ppm au and 1 900 ppm as py1 is also enriched in a suite of trace elements mo sb ni co se te ag cu pb zn mn ba cr u v which are similar to those concentrated by organic processes in euxinic sedimentary environments later generations of pyrite from py2 to py5 including pyrite in bedding parallel pyrite quartz veinlets contain progressively lower contents of invisible gold and most other trace elements however this metamorphic and postmetamorphic pyrite contains microinclusions of free gold arsenopyrite pyrrhotite sphalerite and chalcopyrite the paragenetic textural and chemical relationships at sukhoi log suggest that gold was clearly initially introduced prior to cleavage development accompanying sedimentation of the organic rich shales and fixed during diagenesis within the structure of diagenetic arsenian pyrite subsequently accompanying deformation gold was liberated from recrystallized diagenetic pyrite to become concentrated as free gold and gold tellurides within metamorphic pyrite and folded bedding parallel pyrite quartz veinlets two key processes are considered vital to the formation of the sukhoi log deposit original synsedimentary and early diagenetic concentration of gold dissolved within arsenian pyrite in organic rich black shales and metamorphic processes that liberated gold from the early forms of arsenian pyrite to be concentrated as free gold and gold tellurides within late diagenetic and metamorphic pyrite and associated pyrite quartz veinlets in the core of an overturned anticline these ore forming processes are unlikely to be unique to sukhoi log other black shale and turbidite hosted deposits that occur in rifted continental margin environments which have undergone collision and basin inversion may form by similar processes

geology and in situ sulfur and lead isotope analyses of the jinlongshan carlin type gold deposit in the southern qinling orogen china implications for metal sources and ore genesis abstract the jinlongshan gold deposit shaanxi province central china is a large deposit 150 t au in the southern qinling orogen gold mineralization is hosted in upper devonian to lower carboniferous carbonaceous clastic carbonate sequences four stages of pyrite and paragenetic sulfides have been identified based on morphology and paragenesis laser ablation inductively coupled plasma mass spectrometry la icp ms and laser ablation multi collector inductively coupled plasma mass spectrometry la mc icp ms analyses were conducted to determine the chemical and s pb isotopic composition of the sulfides pre ore stage pyrites py1 and py2 contain relatively high concentrations of mn co ni cu zn sb and pb exhibiting a wide range of 34s values ranging from 29 9 to 48 4 these two pyrites were formed by bacterial and thermochemical sulfate reduction of upper devonian marine sulfate respectively main ore stage pyrite py3 and arsenopyrite apy contain high concentrations of au as cu sb hg and tl with restricted ranges of 34s values from 9 6 to 15 3 which is interpreted as resulting from the underlying low grade metamorphic paleozoic sedimentary rocks by the decomposition of pyrite and or inorganic reduction of sulfate late or post ore stage pyrite py4 is characterized by low concentrations of au ag sn hg and bi and exhibited variable 34s values ranging from 4 4 to 27 7 that may reflect the mixing of metamorphic fluids with meteoric water similarly the pb isotope composition of ore stage sulfides resembles those of underlying low grade metamorphic paleozoic sedimentary rocks whereas differs from precambrian metamorphic basement rocks and granitoids around the basin indicating that the metals of the jinlongshan gold deposit were sourced from the underlying paleozoic sedimentary rocks detailed fieldwork revealed that the deposit has mainly undergone four deformation events the ore bodies developed in ne trending dextral oblique slip reverse faults of d3 that crosscut wnw trending shear zones of d2 the timing and corresponding stress regimes of the d3 event suggest that it formed in a local extensional environment of yanshanian intracontinental orogeny of qinling orogenic belt gold metallogenesis of the jinlongshan gold deposit occurred during the transition of tectonic setting from compression to extension which reactivated the shear zones and migrated deep ore bearing fluids to ne trending brittle faults the geological and geochemical features of the jinlongshan gold deposit are more analogous to the carlin type deposits than other orogenic gold deposits worldwide therefore we propose it is a typical carlin type gold deposit in south qinling orogen

geology geochemistry and age of the hukeng tungsten deposit southern china abstract the hukeng tungsten deposit located in the wugongshan area in central part of jiangxi province south china is a large scale quartz vein wolframite deposit it is hosted in the hukeng granitic intrusion based on the mineral assemblage and crosscutting relationship of the veins three mineralization stages are identified including 1 quartz wolframite stage 2 quartz fluorite wolframite stage and 3 quartz pyrite sphalerite wolframite stage the homogenization temperatures of fluid inclusions in vein quartz vary from 220 to 320 c and the salinities are from 0 to 10 wt nacl equiv corresponding densities range from 0 7 to 1 g cm 3 these features indicated that the ore forming fluids in the hukeng tungsten deposit have medium temperature low density and low salinity the 18 osmow values of quartz range from 10 8 to 14 4 with corresponding 18 o fluid values of 3 7 to 7 7 and d values of fluid inclusions of between 70 and 55 the combined isotopic data indicate that the ore forming fluids of the hukeng tungsten deposit were mainly derived from magmatic water with some minor input from meteoric water we have carried out molybdenite re os and muscovite 40 ar 39 ar dating to constrain the timing of mineralization re os dating of six molybdenite samples yielded model ages ranging from 149 1 2 0 to 150 7 3 7 ma with an average of 150 0 ma the re os analyses give a well defined 187 re 187 os isochron with an age of 150 2 2 2 ma mswd 0 60 hydrothermal muscovite yields a plateau 40 ar 39 ar age of 147 2 1 4 ma 40 ar 39 ar age is in good agreement with the re os age these ages show that the timing of tungsten mineralization occurred at about 150 ma our new data when combined with published geochronological results from the other major deposits in this region suggest that widespread w mineralization occurred in the late jurassic throughout south china

cirrus outflow dynamics abstract cirrus outflow from deep convection are analyzed as dynamically and thermodynamically active systems the initial outflow is considered as an analog to wake collapse in which a neutrally buoyant flow intrusion is flattened and stretched by its stratified environment and the initially isotropic turbulence within it is converted to other forms the early spread of the outflow is predicted on the basis of analytic and numerical calculations by dugan et al strong radiative heat flux curvature then leads to maintenance or regeneration of buoyant turbulence in the collapsed outflow plume mixed layer analysis allow predictions of entrainment rates in the case of strong net radiative heating the mixed layer model predicts an encroachment condition in which the upper boundary attains nearly the same temperature as the environment and grows into it rapidly this tendency is countered by bodily ascent of the warm mesoscale plumes the rate of which is predicted with the aid of a theory of drag on a f

syn collisional transform faulting of the tan lu fault zone east china origin of the continental scale tan lu fault zone tlfz east china remains controversial about 550 km sinistral offset of the dabie orogenic belt dob and sulu orogenic belt sob is shown along the ne nne striking tlfz syn collisional sinistral ductile shear belts in the tlfz have been identified thirteen phengite bulk separates from the mylonites were dated by the 40ar 39ar method they gave cooling ages of the 198 181 ma for the shear belts along the eastern margin of the dob and 221 210 ma from the western margin of the sob distribution of the foreland basin deposits suggests that sinistral offset of the dob and sob by the tlfz took place prior to deposition of the upper triassic strata the marginal structures around the dob and sob support syn collisional faulting and indicate anticlockwise rotation of the dob during the displacement the folding and thrust faulting related to crustal subduction coeval with the tan lu faulting is older than the foreland basin deposition related to the orogenic exhumation several lines of evidence demonstrate that the tlfz was developed as a syn collisional transform fault during latest middle to earliest late triassic time when the dob and sob experienced crustal subduction of the south china block scb eastward increase of the crustal subduction rates is believed to be responsible for the sinistral transform faulting

primary results of glaciological studies along an 1100 km transect from zhongshan station to dome a east antarctic ice sheet the chinese national antarctic research expedition ghinare carried out three traverses from zhongshan station to dome a princess elizabeth land and inaccessible area east antarctic ice sheet during the 1996 97 to 1998 99 antarctic field seasons the expeditions are part of the chinese international trans antarctic scientific expedition program in this project glaciological investigations of mass balance ice temperature ice flow stratigraphy in snow pits and snow firn ice cores as well as the glaciochemical study of surface snow and shallow ice cores have been carried out in the 1998 99 field season chinare extended the traverse route to 1128 km inland from zhongshan station the density profiles show that firnification over princess elizabeth land and inaccessible area 290 1100 km along the route is fairly slow and the accumulation rate recovered from snow pits along the initial 460 km of the route is 4 6 21 cm 46 210 kg m 2a 1 water equivalent the initial 460 km of the route can be divided into four sections based on the differences of accumulation rate this pattern approximately coincides with the study on the lambert glacier basin lgb by australian scientists during the past 50 years the trends of both air temperature and accumulation rate show a slight increase in this area in contrast to the west side of the lgb data on surface accumulation rates and their spatial and temporal variability over ice drainage areas such as the lgb are essential for precise mass balance calculation of the whole ice sheet and are important for driving ice sheet models and testing atmospheric models

sedimentary rock hosted au deposits of the dian qian gui area guizhou and yunnan provinces and guangxi district china abstract sedimentary rock hosted au deposits in the dian qian gui area in southwest china are hosted in paleozoic and early mesozoic sedimentary rocks along the southwest margin of the yangtze south china precambrian craton most deposits have characteristics similar to carlin type au deposits and are spatially associated on a regional scale with deposits of coal sb barite as tl and hg sedimentary rock hosted au deposits are disseminated stratabound and or structurally controlled the deposits have many similar characteristics particularly mineralogy geochemistry host rock and structural control most deposits are associated with structural domes stratabound breccia bodies unconformity surfaces or intense brittle ductile deformation zones such as the youjiang fault system typical characteristics include impure carbonate rock or calcareous and carbonaceous host rock that contains disseminated pyrite marcasite and arsenopyrite usually with m sized au commonly in as rich rims of pyrite and in disseminations late realgar orpiment stibnite and hg minerals are spatially associated with earlier forming sulfide minerals minor base metal sulfides such as galena sphalerite chalcopyrite and pb sb as sulphosalts also are present the rocks locally are silicified and altered to sericite clay illite rocks and or stream sediment geochemical signatures typically include elevated concentrations of as sb hg tl and ba a general lack of igneous rocks in the dian qian gui area implies non pluton related ore forming processes some deposits contain evidence that sources of the metal may have originated in carbonaceous parts of the sedimentary pile or other sedimentary or volcanic horizons this genetic process may be associated with formation and mobilization of petroleum and hg in the region and may also be related to as au and tl bearing coal horizons many deposits also contain textures and features indicative of strong structural control by tectonic domes or shear zones and also suggest syndeformational ore deposition possibly related to the youjiang fault system several sedimentary rock hosted au deposits in the dian qian gui area also are of the red earth type and au grades have been concentrated and enhanced during episodes of deep weathering

carlin style gold province linked to the extinct emeishan plume abstract carlin style gold deposits constitute one of the most important types of au resources in the world previous studies on these deposits correlated the source of au with metal enriched sedimentary formations or metasomatized subcontinental lithospheric mantle sclm associated with oceanic subduction the role of mantle plumes in generating carlin style deposits has remained enigmatic due to lack of adequate evidence here we investigate the second largest carlin style au province in the world after nevada in usa within the youjiang basin in the eastern part of the 260 ma emeishan large igneous province lip of southwestern china we present a novel model for the genesis of this ore province based on thermodynamic modeling which envisages that cumulates formed by high degree over 80 wt of crystal fractionation from the emeishan plume derived magmas under low oxygen fugacity conditions generated an enriched juvenile lower crust our new results from integrated in situ zircon geochronology and oxygen isotopes of mineralized tuffs from the au deposits hosted in the emeishan volcanic rocks reveal zircon growth at 129 136 ma and 239 ma with 18 o vsmow values of 5 9 to 6 9 suggesting that the gold mineralization events in the youjiang basin followed the emeishan plume activity and that the ore forming fluids were of magmatic origin in conjunction with evidence from the emeishan lip for native gold grains that precipitated in the early fractionation stage under low oxygen fugacity we propose a model involving juvenile lower crust beneath the eastern emeishan province as a potential au reservoir the reactivation of which by later magmatic hydrothermal activity associated with oceanic subduction events generated the large auriferous province in the youjiang basin we therefore conclude that the crustal magmatic underplate generated by mantle plume has the potential to contribute to the formation of carlin style au deposits thus offering new insights into the possible link between mantle plumes and various types of au deposits such as porphyry sediment hosted and orogenic au deposits associated with lips

the mysteries of mammatus clouds observations and formation mechanisms mammatus clouds are an intriguing enigma of atmospheric fluid dynamics and cloud physics most commonly observed on the underside of cumulonimbus anvils mammatus also occur on the underside of cirrus cirrocumulus altocumulus altostratus and stratocumulus as well as in contrails from jet aircraft and pyrocumulus ash clouds from volcanic eruptions despite their aesthetic appearance mammatus have been the subject of few quantitative research studies observations of mammatus have been obtained largely through serendipitous opportunities with a single observing system e g aircraft penetrations visual observations lidar radar or tangential observations from field programs with other objectives theories describing mammatus remain untested as adequate measurements for validation do not exist because of the small distance scales and short time scales of mammatus modeling studies of mammatus are virtually nonexistent as a result relatively little is known about the environment formation mechanisms properties microphysics and dynamics of mammatus this paper presents a review of mammatus clouds that addresses these mysteries previous observations of mammatus and proposed formation mechanisms are discussed these hypothesized mechanisms are anvil subsidence subcloud evaporation sublimation melting hydrometeor fallout cloud base detrainment instability radiative effects gravity waves kelvin helmholtz instability rayleigh taylor instability and rayleigh benard like convection other issues addressed in this paper include whether mammatus are composed of ice or liquid water hydrometeors why mammatus are smooth what controls the temporal and spatial scales and organization of individual mammatus lobes and what are the properties of volcanic ash clouds that produce mammatus the similarities and differences between mammatus virga stalactites and reticular clouds are also discussed finally because much still remains to be learned research opportunities are described for using mammatus as a window into the microphysical turbulent and dynamical processes occurring on the underside of clouds

metallogenic model of the jinchang au ni deposit in the ailaoshan belt sw china determined on the basis of pyrite trace element contents in situ sulfur isotope composition and pge geochemistry abstract the ailaoshan metallogenic belt in southwestern china contains numerous shear zone related au deposits with au reserves greater than 200 tonnes however the source of ore forming fluids and metals is controversial hampering the construction of genetic models in this study we selected the jinchang au ni deposit in the northern segment of the ailaoshan belt for detailed investigation of pyrite chemistry and in situ sulfur isotope compositions using laser ablation inductively coupled plasma mass spectrometry la icp ms the petrographic and pyrite chemistry analyses revealed four types of hydrothermal pyrite py1 pyrite is euhedral to subhedral and has in situ sulfur isotope 34s values of 5 30 to 6 26 median 2 93 and low concentrations of au ni as sb cu zn pb and ag py1 is interpreted to have formed during the early hydrothermal stage py2 pyrite is subhedral to anhedral and porous with variable size although py2 and py3 show different textural relationships we conclude that both of them formed during the intermediate hydrothermal stage as evidenced by similar sulfur isotope compositions and trace element contents and common intergrowth textures py2 and py3 pyrite have in situ 34s values ranging from 11 6 to 1 29 median 4 45 and relatively elevated concentrations of au ni as sb cu zn pb and ag in py2 and py3 pyrite ni concentrations correlate with co concentration whereas au exhibits moderate positive correlations with ni co and as indicating that au ni and other metals were predominantly sourced from the jinchang ultramafic rocks py4 pyrite is euhedral in shape and has relatively low in situ 34s values of 23 5 to 4 34 median 8 33 the metal concentrations in py4 pyrite are lower than those in py2 and py3 pyrite in general the metal concentrations in the different pyrite populations display systematic changes with low levels in py1 higher levels in py2 andpy3 and low levels again in py4 the average total platinum group element pge concentration of the jinchang ni bearing ultramafic rocks is 26 3 ppb similar to the average value of the primitive mantle of 22 0 ppb the au ni ores from the jinchang deposit have an average pd pt ratio of 5 98 similar to that of hydrothermal ni ores but higher than that of typical magmatic ni ores in contrast the jinchang ultramafic rocks have low pd pt ratios between 0 57 and 1 13 suggesting that the pges in the jinchang intrusion are of magmatic origin similarly the rh ir ratios of au ni ores are consistent with those of hydrothermal ni ores but differ from those of magmatic ni ores the pyrite chemistry in situ sulfur isotope compositions and pge geochemistry suggest that the ore forming fluids and metals associated with the jinchang au ni deposit were dominantly derived from the jinchang ultramafic intrusion mesozoic felsic magmatism or cenozoic regional strike slip activity may have triggered migration of the ore forming fluids leaching of metals from the jinchang intrusion and precipitation of these metals at the boundary between the intrusions and carbonaceous rocks

mineralogy of arsenian pyrites and arsenopyrites of carlin type gold deposits in yunnan guizhou guangxi golden triangle area southwestern china petrographic observations and electron probe micro analysis epma of sulfides from different subclasses of typical carlin type gold deposits in yunnan guizhou guangxi golden triangle area show that both arsenian pyrites and arsenopyrites are major gold bearing minerals gold bearing pyrites are dominated by zoned arsenic pyrites and fine grained euhedral arsenian pyrites zoned arsenian pyrites are characteristics by as poor and s fe rich cores mantled by later formed as rich and s fe poor rims and there is a positive correlation between au and as pyrites with as poor cores have complex origin with some being hydrothermal pyrites precipitated in the early metallogenic stage and the others being syngenetic pyrites altered by hydrothermal fluid core pyrite and rim pyrite were formed in different metallogenic stages the correlation between element contents indicates s was replaced by as in rims the characteristics of multi rims suggest that the hydrothermal fluid acted pulsatorily and the components of hydrothermal fluid varied constantly even if au of some analytical spots from the cores exceeds the detection limit rims can serve as the primary gold bearing location the fine grained euhedral arsenian pyrites with homogeneous texture are similar to the rims of zoned pyrite with characteristics of high as au and low s fe indicating that the as rich mantles of zoned pyrite were probably formed synchronously with the as rich tiny euhedral arsenian pyrite the pyrites from the aggregation of pyrite arsenopyrite are classified into two groups which are of zoned texture and homogeneous texture and have the characteristics of the above two types of pyrites respectively arsenopyrites are subdivided into three generations all having homogeneous texture and belonging to hydrothermal precipitation there are some analytical spots from every generation whose au exceeds the detection limit and whose contents of au as s fe are different insignificantly in different generations indicating they were deposited in the main metallogenic stage the arsenopyrites have higher au abundances than pyrites in the aggregation of pyrite arsenopyrite the precipitation order of gold bearing sulfides is as follows as poor sedimentary pyrites or early metallogenic stage pyrites as rich zoned arsenian pyrites and fine grained euhedral arsenian pyrites arsenopyrites the distribution of au in all types of pyrites and all generations of arsenopyrites is heterogeneous under the resolution of epma microbeam and the homogeneous texture of au map from zoned arsenic pyrites is likely to be a pseudomorph the major modes of occurrence for gold are invisible nanometer size sub microscopic inclusion gold grains with minor ones being invisible lattice gold and visible micrometer size microscopic native gold the gold bearing minerals and the gold modes of occurrence have no essential difference in different subclasses of carlin type gold deposits in yunnan guizhou guangxi golden triangle area suggesting that they had the same ore forming process and setting

uncloaking invisible gold use of nanosims to evaluate gold trace elements and sulfur isotopes in pyrite from carlin type gold deposits one hundred nm resolution secondary ionizing mass spectrometry nanosims was used to determine the distribution of au cu as sb and s and stable isotopes of s 34s 32s in gold bearing pyrite from two refractory carlin type gold deposits west banshee northern carlin trend and turquoise ridge getchell trend located in northern nevada nanosims maps reveal that gold occurs in two discrete episodes in each deposit elevated gold concentrations correlate with elevated concentrations of as sb cu te and lower 34s 32s ratios compared to periods when gold was not deposited precipitation of elevated gold and trace elements at west banshee was followed by precipitation of pyrite with lower gold concentrations whereas at turquoise ridge precipitation of trace element rich pyrite was followed by precipitation of late ore stage minerals these nanosims results are consistent with formation of the deposits by the episodic incursion of gold rich fluids into hydrothermal systems otherwise dominated by gold poor fluids such gold rich fluid pulses may be related to incursions of magmatic fluid which have been shown to have high concentrations of gold arsenic and copper in porphyry and high sulfidation epithermal systems

evaluation of the role of sulfidation in deposition of gold screamer section of the betze post carlin type deposit nevada this study was undertaken to evaluate the relation between sulfidation and gold deposition in the screamer section of the betze post carlin type deposit we also attempted to determine the source of sulfur in the deposit and the possibility that more than one gold depositing event contributed metal to the screamer system gold ore at screamer forms a generally stratiform body hosted largely by the wispy member of the devonian popovich formation and lacks obvious alteration of wall rock gangue minerals gold at screamer is hosted by arsenian pyrite that forms disseminated grains and overgrowths on diagenetic pyrite a strong correlation is observed between the gold content of rock samples and their proportion of ore related arsenian pyrite as determined by point counts isocon plots show that mineralization at screamer involved addition of both sulfur and iron along with gold arsenic antimony tungsten and local silica barium and phosphorus fe al vs s al plots show that most ore samples at screamer do not contain enough sulfur to account for all of their iron as pyrite petrographic examination shows that the iron occurs in pyrite ferroan dolomite and iron bearing micas in order of decreasing abundance the fe al vs s al plots also show that screamer samples with high gold contents contain more pyrite than samples with low gold contents and that samples inside the ore zone have more pyrite than those in the surrounding area these relations are interpreted to indicate that screamer has undergone at least two pyrite forming events the first event which probably took place during diagenesis involved incomplete sulfidation that left some iron in carbonate and silicate minerals the second event which probably took place during gold mineralization sulfidized most remaining iron and added pyrite in the screamer ore zone the 34 s values of chemically extracted sulfur from disseminated pyrite at screamer range from 13 8 to 16 5 per mil and 34 s values for hand picked separates of pyrite and other sulfides in veins cutting these rocks range from 21 2 to 11 7 per mil a significant fraction of samples with high gold contents and of samples in the ore zone regardless of gold content have 34 s values between 1 and 5 per mil these data suggest that early diagenetic sulfur with a wide range of 34 s values was overprinted by sulfur with isotopic compositions in the 1 to 5 per mil range that was associated with gold mineralization the 34 s values for gold related sulfur at screamer are lower than those reported for bulk mineral separates from most other carlin type deposits and from sims analyses of sulfides from the proximal post part of the betze post system and could be magmatic limited evidence can be found for multiple gold forming events in the screamer zone tungsten which might have been introduced by the jurassic age goldstrike stock is widespread in the deposit and correlates closely with gold a few samples with high tungsten gold ratios found along fault zones might be part of an earlier phase of mineralization related to the goldstrike stock a 34 s value for pyrite in one of these samples is similar to the high values reported for sulfides in auriferous polymetallic mineralization in the post section of the deposit but this mineralization is not reported to contain tungsten other veins containing sphalerite have lower 34 s values and lack consistent gold values whereas there is no correlation between gold values and the degree to which the host rocks have undergone sulfidation there is a strong and highly significant correlation between gold values and the abundance of ore related pyrite this shows that simple sulfidation of immediately adjacent wall rock cannot account alone for gold deposition at screamer and it might not be the only ore depositing process in some other carlin deposits a more general extended sulfidation process could be important however one likely process involves mixing of an invading mineralizing fluid containing sulfur and gold with a wall rock fluid containing iron derived from adjacent or distal wall rocks recognition of the source s for this iron and fluid flow pathways responsible for introducing it to the ore zone could provide useful guidance in exploration for the next carlin trend

firnification and the effects of wind packing on antarctic snow using firn core data from ten widely spread antarctic sites the depen dence of firnification on temperature wind and accumulation rate has been examined with two empirical models one model relates the square of the porosity to the logarithm of the overburden pressure and yields good fit to data through the first stage of firnifica tion up to around 0 70 0 75 mg m 3 beyond which it severely overestimates density all three meteorological factors enter into this model with higher temperatures and stronger winds increasing firnification rates whilst higher accumulation rates have the opposite effect at any given depth a temperature increase of looe has the equivalent effect to a wind speed increase of 5 m s i or an accumulation rate decrease of 0 10 m a w e a sec ond model equates the logarithm of the porosity to overburden pressure and gives a much better fit to field data at higher densities where values asymptote to the bubble free density of pure ice this model generally yields a poor match to field data in the upper layers with surface densities generally overestimated annual mean wind speed appears to be the least important of the local variables in this case consistent with the success of the model at greater depth in matching data profiles

tectonics of south china key to understanding west pacific geology abstract south china is not a post caledonian platform but a composite of orogenic belts this late proterozoic mesozoic orogen is a collage of three continental fragments the three blocks are yangzi huanan and dongnanya and they are separated by the banxi nanpanjiang formerly xianggangzhe and gunanhai suture zones yangzi was separated from gondwanaland during late precambrian when an open ocean called banxi was present between the two continents tectonic processes at an active margin during sinian and early paleozoic time led to the genesis of an accretionary wedge complex the banxi melange and the huanan flysch nappes on the northern margin of huanan which was then the northern margin of the gondwana continent reorganization of plates during the devonian suspended subduction at the huanan active margin huanan was uplifted and unconformably overlain by transgressive deposits of devonian and or carboniferous age a remnant ocean the nanpanjiang sea still existed between yangzi and huanan and deep water sedimentation continued both at the southern margin of yangzi and at the northwestern margin of huanan the latter again became an active margin during late paleozoic when permian and triassic flysch sediments were deposited in foredeeps ahead of advancing nappes huanan and yangzi collided during the triassic and resulted in the deformation of the passive margin of the latter to form the yangzi deformed belt huanan was separated from a more southerly continent dongnanya in the devonian by seafloor spreading which created a late paleozoic and early mesozoic ocean gunanhai ocean a continuously deposited sequence ranging in age from devonian to triassic was laid down on the southern passive margin of huanan on the other side of the ocean the dongnanya permian strata include glacial marine deposits of gondwanaland affinity dongnanya became separated from gondwanaland during the late permian when it marched northward to be reunited with huanan the huanan passive margin sequence was deformed by folding and overthrusting after the late mesozoic collision of huanan and dongnanya scattered outcrops of the suture melange resulting from this collision occur at a few localities in coastal fujian dongnanya in our model was the mesozoic continent of southeast asia peripheral to mainland asia this may or may not have been the eastern continuation of the microcontinent sibumasu siam thailand burma malaysia sumatra the collision of dongnanya and asia gave rise not only to the gunanhai melange of coastal fujian but also to the ophiolite melanges parts of which are present in taiwan tailuko the philippines and western malaysia

mesozoic molybdenum deposits in the east qinling dabie orogenic belt characteristics and tectonic settings abstract the east qinling dabie orogenic belt accommodates the largest mo ore district in the world it contains 8 43 mt of proven mo metal reserves which accounts for 66 of the total proven chinese mo reserves the mo ore district includes 24 deposits and 12 occurrences with four major types of mo mineral systems i e porphyry porphyry skarn skarn and hydrothermal veins the latter can be further subdivided into quartz vein and carbonatite vein types although mo mineralization in the belt began in the paleoproterozoic 1680 24 to 2044 14 ma all economically significant deposits were formed during the mesozoic re os dating of molybdenite has shown that there are three episodes of mo mineralization i e late triassic 233 221 ma late jurassic to early cretaceous 148 138 ma and early to middle cretaceous 131 112 ma late triassic mo deposits developed as molybdenite quartz veins and carbonatite vein types stable isotope systematics c o s and high contents of re and sr indicate that the carbonatite mo veins are mantle derived porphyry and porphyry skarn mo mineral deposits were formed in the late jurassic to early cretaceous and early to middle cretaceous the late jurassic to early cretaceous granite porphyries that are associated with the mo deposits usually occupy less than 1 5 km2 at the surface and are situated in the east qinling area far west of china s continental margin on the other hand the early to middle cretaceous batholiths and granite porphyries with associated mo deposits are located in the dabieshan area and eastern part of the east qinling area the late jurassic to early creataceous granitoids and related mo deposits possibly formed in a back arc extensional setting of the eurasian continental margin which was probably triggered by the oblique subduction of the izanagi plate the early to middle cretaceous batholiths and granite porphyries are linked to the tectonic regime of lithospheric thinning asthenospheric upwelling and partial melting of the crust induced by a change in izanagi plate motion parallel to the continent margin in the east qinling dabie belt there are vein type pb zn ag deposits surrounding porphyry and or porphyry skarn mo w deposits forming well defined ore clusters the same spatial arrangement i e porphyry mo stockworks and outlying pb zn ag ore veins is also observed at the deposit scale thus mo porphyry stockworks and distal polymetallic veins belong to the same ore system and may reflect an outward temperature decrease from the highly fractionated granite plutons both porphyry stockworks and polymetallic veins can be used as vectors for further prospecting

comparison of the native antimony bearing paiting gold deposit guizhou province china with carlin type gold deposits nevada usa the paiting gold deposit guizhou province china has been regarded as a carlin type gold deposit by several researchers alteration and ore related minerals from the paiting deposit were examined and results were compared with the cortez hills carlin type gold deposit nevada usa similarities include the structural and stratigraphic controls on the orebodies in both deposits and the occurrence of invisible gold ionically bound in arsenian pyrite significant differences include the following 1 the gold bearing mineral in nevada is arsenian pyrite however gold bearing minerals in the paiting deposit include arsenopyrite arsenian pyrite and trace pyrrhotite also euhedral or subhedral gold bearing arsenian pyrite at paiting contains significantly less as cu and hg than gold bearing pyrite from nevada 2 alteration in the paiting deposit displays significantly less decarbonatization instead dolomite precipitation which has not been described in nevada deposits is associated with deposition of gold bearing sulfide minerals 3 stibnite and minor native antimony typify paiting late ore stage minerals whereas in nevada realgar orpiment and calcite are common late ore stage minerals precipitation of native antimony in the paiting deposit reflects the evolution of a late ore fluid with unusually low sulfur and oxygen fugacities some characteristics of the paiting gold deposit including formation of ore stage dolomite and precipitation from co2 rich ore fluids at temperatures in excess of 250 c are more typical of orogenic deposits than nevada carlin deposits the presence of similarities in the paiting deposit to both carlin type and orogenic deposits is consistent with formation conditions intermediate to those typical of carlin type and orogenic systems

ground based measurements of spatial and temporal variability of snow accumulation in east antarctica the east antarctic ice sheet is the largest highest coldest driest and windiest ice sheet on earth understanding of the surface mass balance smb of antarctica is necessary to determine the present state of the ice sheet to make predictions of its potential contribution to sea level rise and to determine its past history for paleoclimatic reconstructions however smb values are poorly known because of logistic constraints in extreme polar environments and they represent one of the biggest challenges of antarctic science snow accumulation is the most important parameter for the smb of ice sheets smb varies on a number of scales from small scale features sastrugi to ice sheet scale smb patterns determined mainly by temperature elevation distance from the coast and wind driven processes in situ measurements of smb are performed at single points by stakes ultrasonic sounders snow pits and firn and ice cores and laterally by continuous measurements using ground penetrating radar smb for large regions can only be achieved practically by using remote sensing and or numerical climate modeling however these techniques rely on ground truthing to improve the resolution and accuracy the separation of spatial and temporal variations of smb in transient regimes is necessary for accurate interpretation of ice core records in this review we provide an overview of the various measurement techniques related difficulties and limitations of data interpretation describe spatial characteristics of east antarctic smb and issues related to the spatial and temporal representativity of measurements and provide recommendations on how to perform in situ measurements

high grade gold deposition and collapse breccia formation cortez hills carlin type gold deposit nevada usa the cortez hills breccia zone a nevada carlin type gold deposit located in the cortez district on the battle mountain eureka trend formed within a high grade polylithic breccia and grades at the center of the breccia zone are locally in excess of 1 oz ton au sample transects from low grade or below detection 5 ppb to high grade were collected and analyzed using petrography x ray diffraction xrd scanning electron microscopy sem electron probe microanalysis epma and laser ablation inductively coupled plasma mass spectrometry la icp ms analyses to correlate changes in ore pyrite geochemistry and alteration mineralogy with grade and to relate ore deposition to breccia formation ore related minerals textures and analyses are consistent with fluid rock reaction and replacement at relatively low hydrothermal temperatures 260 c during a single heating and cooling event and over a relatively short time frame coincident in time and space with regional magmatism prior to carlin mineralization roberts mountains wenban and horse canyon formations were affected by burial diagenesis and low grade contact metasomatism and metamorphism producing host rocks composed of calcite dolomite and quartz with generally minor dickite pyrite chalcopyrite sphalerite clinochlore tremolite and organic material and minor to trace k feldspar muscovite and biotite acidic ore fluids sulfidized fe in carbonate rock to form rims of au and trace element rich pyrite on earlier formed pyrite or produced small generally 10 m spheres of fuzzy ore pyrite with no apparent core trace elements in ore stage pyrite are dominated by as with strongly correlated hg tl and cu all greater than au lesser and variable sb and minor to undetected ag bi ti w and te ore fluids also variably dissolved calcite and dolomite and replaced carbonate minerals with jasperoid or produced minor pore space ore pyrite and jasperoid after calcite are enclosed in illite that replaced dickite clinochlore and tremolite and filled minor open space primarily between 227 and 277 c for most analyzed samples based on illite chemistry as hydrothermal collapse began ore pyrite chemistry transitioned to an evolved ore stage chemistry with abundant as low to undetected au lesser pb cu sb and diminished hg and tl compared to the ore stage evolved ore stage fluids coincidently precipitated sulfosalt minerals initially unusual cu and hg rich aktashite cu6hg3as4s12 and tl and hg rich christite tlhgass3 and later realgar as cu and zn in hydrothermal fluids and chalcopyrite and sphalerite in the host rocks respectively were consumed calcite only veins indicate termination of the hydrothermal system small fragmented clasts of realgar with chemically distinct au bearing evolved ore stage pyrite rims found in brecciated rock along a faulted dike wenban contact provide the first evidence in a carlin type gold deposit of precipitation of an au bearing pyrite rim on a late ore stage mineral these rare rims likely formed in response to fault movement along the dike wenban contact or by dike injection that allowed deep au bearing fluids to access a higher and cooler part of the system where late ore stage minerals had begun to form these rims further highlight the normal textures in carlin type gold deposits where ore stage pyrite was overgrown by late ore stage sulfosalt minerals demonstrating a single hydrothermal event followed by a single cooling event this paragenesis is consistent with previously modeled deposit formation time frames of 45 000 to 15 000 years two styles of breccia were identified within the deposit replacement matrix supported breccia in which an illite rich punky matrix encloses au bearing pyrite jasperoid and variable relict calcite formed during intense ore stage alteration and mineralization the fine grained ore and alteration replacement minerals did not require significant open space to form later evolved and late ore stage sulfosalt minerals and calcite that are visible at the hand sample scale provide the earliest evidence for the development of significant open space hydrothermal collapse allowed the incursion of cooler meteoric water into the system which along with the retrograde solubility of calcite provided coupled mechanisms driving significant calcite dissolution collapse brecciation and formation of the cortez hills breccia zone dissolution and collapse brecciation increasingly concentrated ore stage pyrite as the hydrothermal system transitioned to the late ore stage contributing to high au grades

u pb zircon geochemical and sr nd hf isotopic constraints on age and origin of jurassic i and a type granites from central guangdong se china a major igneous event in response to foundering of a subducted flat slab abstract the mesozoic geology of se china is characterized by widespread jurassic to cretaceous igneous rocks consisting predominantly of granites and rhyolites and subordinate mafic lithologies however the tectonic regime responsible for the inland jurassic granites remains controversial we report here u pb zircon ages geochemical and sr nd hf isotopic data for the nankunshan alkaline granite and the fogang granitic batholith in central guangdong mineralogical and geochemical features suggest that the fogang and nankunshan rocks are i and aluminous a type granites respectively shrimp u pb zircon analyses yield consistent ages ranging from 159 3 ma to 165 2 ma for four samples from the fogang batholith and an age of 158 5 ma for the nankunshan granite the fogang granites having i sr 0 7098 0 7136 e nd t 4 3 to 12 2 and e hf t 11 5 to 3 1 for the magmatic zircons were derived from paleoproterozoic mafic intermediate igneous protolith with minor addition of mantle derived magmas the nankunshan rocks have relatively lower i sr 0 706 0 708 higher e nd t 0 3 to 2 4 and e hf t 5 7 to 1 1 for the magmatic zircons and some oib like trace element ratios they were likely generated through extensive fractional crystallization of mantle derived alkaline parental magma associated with crustal assimilation these 160 ma i and a type granites in central guangdong were emplaced coeval with the widespread 165 155 ma i and a type granites and syenites following the initiation of intraplate basaltic and or bimodal igneous magmatism at 180 170 ma in the adjacent regions we interpret these jurassic igneous rocks as anorogenic magmatism formed during a major igneous event in response to foundering of an early mesozoic subducted flat slab beneath se china continent

anvil characteristics as seen by c pol during the tropical warm pool international cloud experiment twp ice abstract the tropical pacific warm pool international cloud experiment twp ice took place in darwin australia in early 2006 c band radar data were used to characterize tropical anvil i e thick nonprecipitating cloud associated with deep convection areal coverage height and thickness during the monthlong field campaign the morphology evolution and longevity of the anvil were analyzed as was the relationship of the anvil to the rest of the precipitating system the anvil was separated into mixed i e echo base below 6 km and ice only categories the average areal coverage for each anvil type was between 4 and 5 of the radar grid ice anvil thickness averaged 2 8 km and mixed anvil thickness averaged 6 7 km areal peaks show that mixed anvil typically formed out of the stratiform rain region peak production in ice anvil usually followed the mixed anvil peak by 1 3 h anvil typically lasted 4 10 h after the initial convective rain area peak twp ice experienced three distinct regimes an

simple relations for the close off depth and age in dry snow densification a physical model for the snow firn densification process salamatin and others 2006 and martinerie and others 1992 1994 correlation for the firn density at the pore closure are employed to perform a scale analysis and computational experiments in order to deduce simplified relations for the close off depth and ice age in quasi stationary ice formation conditions the critical snow density at which ice grain rearrangement stops is used to take into account variability of snow structures subjected to densification the results obtained are validated on a representative set of ice core data from 22 sites which covers wide ranges of present day temperatures and ice accumulation rates a simple analytical approximation for the density depth profile is proposed

sulfur isotope and trace element compositions of pyrite determined by nanosims and la icp ms new constraints on the genesis of the shuiyindong carlin like gold deposit in sw china the shuiyindong carlin like gold deposit the largest one of this type in china is located in the late paleozoic early mesozoic youjiang basin the pyrites in the studied ore bodies no i to v can be divided into four main types plus several sub types 1 as poor pyrites include py1 py1a and py1b py2 and py3 and 2 as rich pyrite py4 py4a and py4b in situ la icp ms analyses show that the as rich pyrite also contains higher au cu sb and tl than the other pyrite types in situ nanosims analyses show the 34s variation of py1 48 1 67 5 py2 2 4 7 6 py3 9 2 14 2 and py4 3 0 6 6 with the average values of 58 1 5 1 11 4 and 3 1 respectively the large 34s variations of as poor pyrites may reflect a sedimentary source however the narrow ranges of 34s values for the as rich pyrite py4 may not reflect a sedimentary but a magmatic or metamorphic origin a metamorphic sulfur source of py4 is favored due to paucity of coeval magmatism in the region and decreasing variations of 34s values from py1 to py4 integrated transmission electron microscope tem and nanosims element mapping show that the distribution and concentration of au are discordant with as and cu at the submicron scale also implied by the occurrence of some of au as nano submicron particles in py4 overall our new data indicate that the ore fluids were not only enriched in au but also in as cu and s taking an alternative of fluid oxidation probably resulting in the decreasing 34s values of py4 our result of i to v orebodies indicates the mixing between the underlying metamorphic fluid and meteoric water integrated variations in 34s and as au cu correlations across individual pyrite grains infer the physicochemical changes of aqueous and or aqueous carbonic fluids along migration paths