tectonic diffusion estimate of orogenic gold resources age frequency data are used to determine amounts of vertical tectonic displacement experienced by the global population of orogenic gold deposits following their emplacement at a crustal depth of 10 1 km knowledge of this tectonic dispersion allows for an estimate of the total crustal endowment of gold in orogenic gold deposits this estimate is based on a compilation of data on 365 orogenic gold deposits of which gold contents are available for 314 deposits and good age control is available for 126 deposits ages of well dated deposits form three clusters that range in age from 47 to 850 ma primarily phanerozoic 69 deposits 1730 to 2090 ma proterozoic 13 deposits and 2540 to 3107 ma archean 44 deposits gold endowments do not vary significantly among the three age groups and average 155 tonnes t per deposit for the entire population for which data on gold tonnages are available owing to the distinct tripartite nature of the age frequency distribution it is not possible that orogenic gold deposits represent largely invariant rates of ore formation and destruction uninterrupted tectonic dispersion would have resulted in the destruction of essentially all proterozoic and archean deposits separate tectonic diffusion calculations for each of the three deposit age populations were carried out while constraining biases to tectonic diffusion i e the most suitable ratios of uplift and erosion versus subsidence and burial with continental crustal thicknesses on the order of several tens of kilometers the results of these calculations indicated that a total of 25 236 orogenic gold deposits formed over the full span of geologic time that 23 664 of these 94 were destroyed during subsequent uplift and erosion and that 1 572 deposits remain at depth in earth s crust if all 365 known orogenic gold deposits have the same mean gold content as the deposits for which gold contents are available then 706 439 t of gold remain at depth in earth s crust gold in orogenic deposits constitutes about 0 0022 percent of the total gold content of the crust using estimates of gold released by prograde metamorphism of the otago schist gold in the deposits that remain in the crust could have been released from about 1 413 000 km3 of amphibolite facies rocks which constitute only about 12 percent of currently exposed metamorphic rocks if we assume a maximum depth of 3 km for future mining of these deposits the model results indicate that deposits containing almost 113 000 t of gold exist within crustal rocks above this depth discovered deposits make up about 8 percent of this endowment in the context of spatial density the areal concentration of orogenic gold deposits along phanerozoic metamorphic belts is about ten times that in proterozoic terranes and about three times higher than in archean belts this suggests that exploration for the next generation of orogenic gold deposits should be focused on phanerozoic terranes

filamentous microfossils in a 3 235 million year old volcanogenic massive sulphide deposit the record of archaean microfossils is sparse1 of the few bona fide fossil assemblages most are from shallow water settings and they are typically associated with laminated stromatolitic sedimentary rocks2 3 4 microfossils from deep sea hydrothermal systems have not been reported in precambrian rocks 544 million years old although thermophilic microbes are ubiquitous in modern sea floor hydrothermal settings5 6 and apparently have the most ancient lineages7 8 here i report the discovery of pyritic filaments the probable fossil remains of thread like microorganisms in a 3 235 million year old deep sea volcanogenic massive sulphide deposit from the pilbara craton of australia from their mode of occurrence the micro organisms were probably thermophilic chemotropic prokaryotes which inhabited sub sea floor hydrothermal environments they represent the first fossil evidence for microbial life in a precambrian submarine thermal spring system and extend the known range of submarine hydrothermal biota by more than 2 700 million years9 such environments may have hosted the first living systems on earth consistent with proposals for a thermophilic origin of life10 11 12 13

first whiffs of atmospheric oxygen triggered onset of crustal gold cycle lack of a suitable gold source has long been regarded as a major argument against a palaeoplacer model for the exceptionally well endowed witwatersrand gold province by comparing worldwide witwatersrand type deposits occurrences ranging in age from 3 1 to 1 8 ga we propose that the primary concentration of gold in the continental crust resulted from atmospheric and biological evolution in the mesoarchaean a high au flux off the archaean land surface orders of magnitude greater than today s was a consequence of the chemistry of the mesoarchaean atmosphere and hydrosphere when early life gradually changed from anaerobic anoxygenic to oxygenic photosynthesizers at around 3 0 ga the first whiffs of free oxygen produced by photosynthesis under an overall reducing atmosphere provided the ideal trap for au dissolved in the huge reservoir in meteoric and shallow sea water oxidative precipitation of gold on the surface of the o2 producing microbes probably cyanobacteria could fix huge amounts of gold over large areas some of this microbially mediated gold is still preserved in thin kerogen layers carbon seams that typically developed on erosional unconformities scour surfaces and bedding planes in near shore environments at around 2 9 ga this gold provided the principal source for the very rich placer deposits that formed by the subsequent sedimentary reworking of the delicate microbial mats on aeolian deflation surfaces into fluvial channels and delta deposits represented by meso to neoarchaean auriferous conglomerates tectonic reworking of these first gold rich sediments by orogenic processes explains the temporal peak of orogenic type gold formation at around 2 7 to 2 4 ga with time the strongly gold enriched archaean sediments became progressively eroded covered or tectonically reworked and their role as potential source of younger placer deposits diminished this explains why witwatersrand type deposits younger than 2 4 ga are rare and far less well endowed and effectively missing in the rock record after 1 8 ga

evidence from sulfur isotope and trace elements in pyrites for their multiple post depositional processes in uranium ores at the stanleigh mine elliot lake ontario canada

fission xenon dating of witwatersrand uraninites implications for geological activity in the central kaapvaal craton about 1 ga ago abstract four uraninite separates from different reefs from in and above the central rand group upper witwatersrand supergroup were obtained from gold mines in the east rand west rand and welkom goldfields of the witwatersrand basin in south africa these samples were dated by the xes xen spectrum technique all four age spectra have a typical stepup form with plateaux for high temperature xe release the plateau ages are 0 832 0 026 ga for the carbon leader reef sample from blyvooruitzicht gold mine 1 043 0 024 ga for the basal reef sample from free state geduld gold mine 1 115 0 036 ga for the main reef uraninite concentrate from sub nigel gold mine and 1 300 0 058 ga for the ventersdorp contact reef sample from kloof gold mine no apparent ages in excess of 1600 ma were observed it is obvious from the general witwatersrand chronological database that these fission xenon dating results do not correspond to primary crystallization ages for the uraninites instead they most likely represent resetting events that affected the u xe isotopic system in these samples comparison with other recent chronological results obtained on rocks from the region of and around the witwatersrand basin indicates that the region was affected by magmatotectonic activity at 1 3 to 1 ga ago which thus was not only localized along the southern margin of the kaapvaal craton the so called namaqua natal thrust front but also affected other parts of the craton

the spatial and temporal variability of convective storms over the northeast united states during the warm season abstract a spatial and temporal climatology of convective storms over the northeast united states during the warm season april september is presented using composite national operational weather radar nowrad data at 2 km grid spacing from 1996 to 2007 as well as cloud to ground lightning from the national lightning data network nldn on a 10 km grid from 2001 to 2007 there are preferred regions for convective storms within new york s hudson river valley western and southeastern pennsylvania central new jersey and across the delmarva peninsula a favored initiation area during the early afternoon is the immediate lee of the appalachians with a tendency for these convective systems to move eastward to the coast by late evening there is a sharp gradient in convective frequency within 20 km of the coast on average as a result of the relatively stable marine boundary layer but as the sea surface warms by midsummer this convective activity increases near the coast with a nocturnal 0600 1200 utc c

microstructural evolution and trace element mobility in witwatersrand pyrite microstructural analysis of pyrite from a single sample of witwatersrand conglomerate indicates a complex deformation history involving components of both plastic and brittle deformation internal deformation associated with dislocation creep is heterogeneously developed within grains shows no systematic relationship to bulk rock strain or the location of grain boundaries and is interpreted to represent an episode of pyrite deformation that predates the incorporation of detrital pyrite grains into the central rand conglomerates in contrast brittle deformation manifest by grain fragmentation that transects dislocation related microstructures is spatially related to grain contacts and is interpreted to represent post depositional deformation of the central rand conglomerates analysis of the low angle boundaries associated with the early dislocation creep phase of deformation indicates the operation of 100 slip systems however some orientation boundaries have geometrical characteristics that are not consistent with simple 100 deformation these boundaries may represent the combination of multiple slip systems or the operation of the previously unrecognized 120 slip system these boundaries are associated with order of magnitude enrichments in as ni and co that indicate a deformation control on the remobilization of trace elements within pyrite and a potential slip system control on the effectiveness of fast diffusion pathways the results confirm the importance of grain scale elemental remobilization within pyrite prior to their incorporation into the witwatersrand gold bearing conglomerates since the relationship between gold and pyrite is intimately related to the trace element geochemistry of pyrite the results have implications for the application of minor element geochemistry to ore deposit formation suggest a reason for heterogeneous conductivity and localized gold precipitation in natural pyrite and provide a framework for improving mineral processing

reconstruction of palaeohydrological conditions in a lagoon during the 2nd zechstein cycle through simultaneous use of δd values of individual n alkanes and δ 18 o and δ 13 c values of carbonates for the first time 18o and 13c values from carbonates and d values of individual n alkanes were used to reconstruct palaeohydrological conditions in a lagoon at the southern margin of the central european zechstein basin cezb a 12 m core covering the complete ca2 interval and adjacent anhydrites a1 and a2 was analyzed for 18o and 13c values of dolomitized carbonates and d values of individual n alkanes 18ocarb values 2 to 5 vs vpdb were strongly influenced by evaporation and temporal freshwater input into the lagoon the 13ccarb values 1 to 4 vs vpdb were controlled mainly by changes in primary production both isotopic ratios show an inverse relationship throughout most of the core contradicting diagenetic alteration since 13ccarb values are not altered significantly during dolomitization assuming a temperature range of 35 40 c in the lagoon 18ocarb values of 2 5 to 8 vs vsmow for the lagoonal water can be reconstructed the lagoon may have desiccated twice during the ca2 interval as indicated by very high 18ocarb and low 13ccarb values coinciding with increasing amount of anhydrite in the analyzed sample these events seem to reflect not just local but a regional intra ca2 cyclicity measured d values of the short chain n alkanes namely n c16 and n c18 which are widely used as indicators for photosynthetic bacterial and algal input reflect the isotopic composition of the lagoonal water assuming constant fractionation during incorporation of hydrogen into lipids of 160 an average d value of 70 vs vsmow can be reconstructed for the lagoonal water accounting for very arid conditions the long chain n alkanes n c27 n c28 n c29 and n c30 thought to be derived from the leaf waxes of terrestrial higher plants were shown to be depleted in d relative to the short chain alkanes therefore indicating a different hydrogen source terrestrial plants in arid areas mainly use water supplied by precipitation by using a smaller fractionation of 120 due to evaporation processes in the leaves reconstructed values vary between 74 and 9 vs vsmow these values are not indicating extremely arid conditions implying that the long chain n alkanes were transported trough wind and or rivers into the lagoon at the zechstein sea coast dwater values reconstructed using the n c16 alkane and 18o water values independently reconstructed on the same sample using the temperature dependant fractionation for dolomites are good agreement and suggest high amounts of evaporation affecting the coastal lagoon altogether our results indicate that hydrogen isotopic ratios of n alkanes give information on their origin and are a useful proxy for palaeoclimatic reconstruction

processes controlling the structure and longevity of two quasi linear convective systems crossing the southern new england coast abstractthis paper explores the structural evolution and physical processes that explain the modification of two quasi linear convective systems qlcss that encountered the densely populated new york city atlantic coastal region one qlcs on 31 may 2002 traversed the atlantic coastal boundary with little change in its intensity producing widespread severe wind damage across new york city and long island during this event warm air advection at 925 hpa helped destabilize the layer above this level over the coastal zone while the marine boundary layer deepened below this level the 0 3 km line perpendicular vertical wind shear was relatively strong which supported ascent along the leading edge of the diabatically generated cold pool the surface based convective system became slightly elevated as it moved over the marine waters in contrast the 23 july 2002 qlcs decayed upon encountering the atlantic coastline despite its coincidence with a surface cold front the most unstable cape values during thi

stable isotope study of the archaean rocks of the vredefort impact structure central kaapvaal craton south africa the vredefort dome in the kaapvaal craton was formed as a result of the impact of a large meteorite at 2 02 ga the central core of archaean granitic basement rocks is surrounded by a collar of uplifted and overturned strata of the witwatersrand supergroup exposing a substantial depth section of the archaean crust orthogneisses of the core show little variation in whole rock 18o value with the majority being between 8 and 10 with a mean of 9 2 n 35 quartz and feldspar have per mil differences that are consistent with o isotope equilibrium at high temperatures suggesting minimal interaction with fluids during subsequent cooling these data refute previous suggestions that the outer granite gneiss ogg and inlandsee leucogranofels ilg of the core represent middle and lower crust respectively granulite facies greenstone remnants from the ilg have 18o values that are on average 1 5 higher than the ilg host rocks and are unlikely therefore to represent the residuum from the partial melting event that formed the host rock witwatersrand supergroup sedimentary rocks of the collar which were metamorphosed at greenschist to amphibolite facies conditions generally have lower 18o values than the core rocks with a mean value for metapelites of 7 7 n 45 overall through an 20 km thick section of crust there is a general increase in whole rock 18o value with increasing depth this is the reverse of what is normal in the crust largely because the collar rocks have 18o values that are unusually low in comparison with metamorphosed sedimentary rocks worldwide the collar rocks have d values ranging from 35 to 115 average 62 n 29 which are consistent with interaction with water of meteoric origin having a d of about 25 to 45 we suggest that fluid movement through the collar rocks was enhanced by impact induced secondary permeability in the dome structure

a close ridge small scale atmospheric flow field and its influence on snow accumulation the rough steep and complex terrain in the alpine environment causes a variety of flow patterns such as blocking speed up or flow separation which influence precipitation snow deposition and ultimately snow distribution on the ground cloud terrain interactions flow particle interactions and snow transport affect snow accumulation patterns but the relative importance of these processes is not fully understood in particular in complex mountainous terrain a unique combination of measurements and model simulations is used in a local case study during a two day snowfall event to demonstrate the current understanding of snow accumulation in very steep alpine terrain doppler wind lidar measurements show an eddy like structure on the leeward side of the sattelhorn ridge in the dischma valley near davos switzerland which could partly be replicated by advanced regional prediction system arps flow simulations snow deposition measurements with a terrestrial laser scanner tls show a complex deposition pattern which is only partially captured by alpine3d deposition simulations driven by the arps flow fields this shows that additional processes such as avalanches may play a role or that a more refined simulation of flow or flow particle interactions is required to fully understand snow distribution in very steep mountainous terrain

ambient conditions associated with the maintenance and decay of quasi linear convective systems crossing the northeastern u s coast abstractquasi linear convective systems qlcss crossing the atlantic coastline over the northeastern united states were classified into three categories based on their evolution upon encountering the coast composite analyses show that convective lines that decay near the atlantic coast or slowly decay over the coastal waters are associated with 900 800 hpa frontogenesis with greater ambient 0 3 km vertical wind shear for the slowly decaying lines systems that maintain their intensity over the coastal ocean are associated with 900 hpa warm air advection but with little low level frontogenetical forcing neither sea surface temperature nor ambient instability was a clear delimiter between the three evolutions sustaining convective lines have the strongest environmental 0 3 km shear of the three types and this shear increases as these systems approach the coast in contrast the low level shear decreases as decaying and slowly decaying convective lines move toward the atlantic coastline there was als

interannual persistence of the seasonal snow cover in a glacierized catchment knowledge of the spatial snow distribution and its interannual persistence is of interest for a broad spectrum of issues in cryospheric sciences in this study snow depths derived from airborne laser scanning are analyzed for interannual persistence of the seasonal snow cover in a partly glacierized mountain area 36 km2 at the end of five accumulation periods the snow covered area varied by 16 of its temporal mean mean snow depth of the total area ranged by a factor of two 1 31 2 58 m with a standard deviation of 0 42 m interannual correlation coefficients of snow depth distribution were in the range 0 68 0 84 of the investigated area 75 was found to be interannually persistent the remaining area showed variable snow cover from year to year caused by occasional avalanches and changes in surface topography as a result of glacier retreat snow cover underwent a change from a homogeneous distribution on the former glacier surface to a more heterogeneous snow cover in the recently deglaciated terrain a geostatistical analysis shows interannual persistence in scaling behavior of snow depth in ice free terrain with scale break distances at 20 m scale invariant behavior of snow depth is indicated over 100 m on smooth glacier surfaces

gold mineralization within the witwatersrand basin south africa evidence for a modified placer origin and the role of the vredefort impact event the chemical composition of gold within the archaean metasedimentary rocks of the witwatersrand supergroup displays significant heterogeneity at the micro meso and regional scales a detailed electron microbeam analytical and petrological study of the main auriferous horizons in the central rand group throughout the witwatersrand basin indicates that gold has been remobilized late in the paragenetic sequence over distances of less than centimetres contemporaneous chlorite formation was strongly rock buffered gold mobilization occurred under fluid poor conditions at temperatures that did not exceed 350 c widespread circulation of mineralizing fluids within the central rand group is not supported by the gold and chlorite chemical data brittle deformation that affects most of the paragenetic sequence of the central rand group late in its post depositional history is followed by sequences of mineral growth and dissolution that appear throughout the central rand group and have consistent textural relationships with gold the consistent location within the paragenetic sequence the wide regional and stratigraphic extent of the brittle deformation together with mineral chemical and petrological data suggest that the vredefort impact event 2 02 ga was the cause of this late deformation and that post impact fluid poor metamorphism resulted in crystallization of a significant proportion of the gold on and within mineral grains that were deformed during this event

inhomogeneous precipitation distribution and snow transport in steep terrain 1 the inhomogeneous snow distribution found in alpine terrain is the result of wind and precipitation interacting with the snow surface over topography we introduce and explain preferential deposition of precipitation as the deposition process without erosion of previously deposited snow and thus in absence of saltation a numerical model is developed describing the relevant processes of saltation suspension and preferential deposition the model uses high resolution wind fields calculated with a meteorological model arps the model is used to simulate a 120 h snow storm period over a steep alpine ridge for which snow distribution measurements are available the comparison to measurements shows that the model captures the larger scale snow distribution patterns and predicts the total additional lee slope loading well however the spatial resolution of 25 m is still insufficient to capture the smaller scale deposition features observed the model suggests that the snow distribution on the ridge scale is primarily caused by preferential deposition and that this result is not sensitive to model parameters such as turbulent diffusivity drift threshold or concentration in the saltation layer

detrital origin of hydrothermal witwatersrand gold a review the witwatersrand basin is the largest known gold province in the world the gold deposits have been worked for moren than 100 years but there is still controversy about the ore forming process detailed petrographic studies often reveal that the gold is late in the paragenetic sequence which has led many researchers to propose a hydrothermal origin for the gold however observations such as the occurrence of rounded disc like gold particles next to irregularly shaped or idiomorphic secondary gold particles in the same sample suggest an initial detrital gold source within the witwatersrand strata mineral chemical and isotopic data together with sem cathodoluminescence imaging and fluid inclusion studies provide evidence for small scale variations in the fluid chemistry a requirement for the short range mobilization of the gold the existing data and observations on the witwatersrand rocks support a model of hydrothermally altered metamorphosed placer deposits with at least two subsequent gold mobilization events hydrothermal infiltration in early transvaal time 2 6 2 5 ga and during the 2 020 ga vredefort impact event

gold and uranium concentration by interaction of immiscible fluids hydrothermal and hydrocarbon in the carbon leader reef witwatersrand supergroup south africa highlights aggregates of uraninite nanocrystals host inclusions of native gold oil droplets triggered precipitation of gold precipitated from hydrothermal fluids hydrocarbon inclusions in native gold contain in situ grown uraninite nanocrystals water oil emulsions were responsible for the in situ growth of gold and uraninite lanarkite formed in local oxidation zones on galena uraninite interfaces high resolution scanning and transmission electron microscopy of pyrobitumen hosted uraninite reveal that uraninite grains are highly porous aggregates of uniformly sized nanocrystals and that many of their pores are filled by native gold these texturally late gold grains in turn contain small pores occupied by former oil droplets that were converted to pyrobitumen during burial and metamorphism the pyrobitumen in the pores of the gold grains contains in situ formed uraninite nanocrystals galena also occupies the pores of the uraninite aggregates in addition this study reveals the first occurrence of rare lanarkite that engulfs the galena in the pores of the uraninite on the basis of the nature of the uraninite and the filling of some of its pores with native gold we propose a mineralization model for the deposition of the uranium and gold in the carbon leader reef that calls upon the interaction of oil and aqueous hydrothermal fluids to form micro emulsions according to this model uraninite nanocrystals precipitated from uranium bearing hydrocarbon liquids and flocculated to form porous uraninite aggregates these liquids interacted with auriferous hydrothermal fluids in the carbon leader reef leading to the formation of a micro emulsion at the interface between the two fluids gold precipitated as native metal around droplets of the oil owing to a reduction in oxygen fugacity which destabilized the bisulfide species responsible for gold dissolution commonly this process went hand in hand with the flocculation of the uraninite nanocrystals causing entrapment of the native gold in the pores of the uraninite aggregates the hydrocarbon liquid which occurs as droplets in the gold and is the host to the uraninite aggregates was transformed to pyrobitumen as a result of this process a thin pyrobitumen seam containing uraninite nanocrystals formed along the inner walls of the pores in the native gold lead introduced by the hydrocarbon liquid precipitated as galena interaction of the uraninite with hydrothermal fluids or radiolysis of the pore water facilitated the development of local zones of oxidation between galena and uraninite which led to the crystallization of rare lanarkite

diurnal evolution and distribution of warm season convective storms in different prevailing wind regimes over contiguous north china the diurnal evolution and distribution of warm season convective storms in different prevailing wind regimes at the 925 hpa and 500 hpa levels over contiguous north china have been studied using a climatology based on radar reflectivity mosaics soundings and reanalysis data from 15 may to 15 september in 2008 2011 in the wind regimes at the 925 hpa level the frequency of occurrence of convection is highest for south southwesterly flows followed by that for south southeasterly flows the low level southerly warm and moist flow over the foothills and plains favors initiation and intensification of convection resulting from topographic forcing among the wind regimes at the 500 hpa level the frequency of occurrence of convection shows a pronounced maximum for west southwesterly flows and most of these storms initiate and develop over the foothills and plains convection in the wind regime shows the morphology and slowly east southeastward moving characteristics of well organized longer lived systems with environmental conditions conducive to vertical wind shear and instability at the 500 hpa level the high frequency of occurrence of convection for west southwesterly flows is followed by that for west northwesterly flows under west northwesterly flows convective storms initiated over mountains located to the northwest in the early afternoon move rapidly to the plains in the southeast of the study region these storms show the primary formation characteristics of shorter lived convection and intensify noticeably as they move from the mountains to the foothills and plains

the spatial and temporal distribution of organized convective structures over the northeast and their ambient conditions abstract organized convective structures over the northeastern united states were classified for two warm seasons may august using 2 km composite radar i e the national operational weather radar nowrad data nine structures were identified three types of cellular convection clusters of cells isolated cells and broken lines five types of linear convection lines with no stratiform precipitation lines with trailing stratiform precipitation lines with parallel stratiform precipitation lines with leading stratiform precipitation and bow echoes and one nonlinear system the occurrence of all structures decreases from the western appalachian slopes eastward to the atlantic coast isolated cellular convection forms primarily during the morning to late afternoon 1200 2100 utc mainly over the high terrain clusters of cells form primarily over the appalachians and the atlantic coastal plain during the daytime 1200 0000 utc linear convection is favored from midafternoon to early evening 18

end of winter snow depth variability on glaciers in alaska a quantitative understanding of snow thickness and snow water equivalent swe on glaciers is essential to a wide range of scientific and resource management topics however robust swe estimates are observationally challenging in part because swe can vary abruptly over short distances in complex terrain due to interactions between topography and meteorological processes in spring 2013 we measured snow accumulation on several glaciers around the gulf of alaska using both ground and helicopter based ground penetrating radar surveys complemented by extensive ground truth observations we found that swe can be highly variable 40 difference over short spatial scales tens to hundreds of meters especially in the ablation zone where the underlying ice surfaces are typically rough elevation provides the dominant basin scale influence on swe with gradients ranging from 115 to 400 mm 100 m regionally total accumulation and the accumulation gradient are strongly controlled by a glacier s distance from the coastal moisture source multiple linear regressions used to calculate distributed swe fields show that robust results require adequate sampling of the true distribution of multiple terrain parameters final swe estimates comparable to winter balances show reasonable agreement with both the parameter elevation relationships on independent slopes model climate data set 9 36 difference and the u s geological survey alaska benchmark glaciers 6 36 difference all the glaciers in our study exhibit substantial sensitivity to changing snow rain fractions regardless of their location in a coastal or continental climate while process based swe projections remain elusive the collection of ground penetrating radar gpr derived data sets provides a greatly enhanced perspective on the spatial distribution of swe and will pave the way for future work that may eventually allow such projections

convective episodes in the east central united states nine years of composited radar data are investigated to assess the presence of organized convective episodes in the east central united states in the eastern united states the afternoon maximum in thunderstorms is ubiquitous over land however after removing this principal diurnal peak from the radar data the presence and motion of organized convective systems becomes apparent in both temporally averaged fields and in the statistics of convective episodes identified by an objective algorithm convective echoes are diurnally maximized over the appalachian chain and are repeatedly observed to move toward the east partly as a result of this the daily maximum in storms is delayed over the piedmont and coastal plain relative to the appalachian mountains and the atlantic coast during the 9 yr studied the objective algorithm identified 2128 total convective episodes 236 yr 1 with several recurring behaviors many systems developed over the elevated terrain during the afternoon and moved eastward often to the coastline and even offshore in addition numerous systems formed to the west of the appalachian mountains and moved into and across the eastern u s study domain in particular many nocturnal convective systems from the central united states entered the western side of the study domain frequently arriving at the eastern mountains around the next day s afternoon maximum in storm frequency a fraction of such well timed systems succeeded in crossing the appalachians and continuing across the piedmont and coastal plain convective episodes were most frequent during the high instability low shear months of summer which dominate the year round statistics even so an important result is that the episodes still occurred almost exclusively in above average vertical wind shear despite the overall dominance of the diurnal cycle the data show that adequate shear in the region frequently leads to long lived convective episodes with mesoscale organization

numerical modeling of blowing and drifting snow in alpine terrain in mountainous regions snow transport due to wind significantly influences snow distribution and as a result avalanche danger a physically based numerical two layer model is developed to simulate blowing and drifting snow in alpine terrain one layer describes the driving wind field and the transport in suspension the description is based on the atmospheric boundary layer equations using an e model for the turbulent closure the second layer describes the transport due to saltation including erosion and deposition of snow here conservation equations for mass and momentum are formulated for the mixture of snow and air particle trajectory calculations are used to parameterize quantities characterizing the saltation layer both layers are mutually coupled by boundary conditions a two way coupling between particles and airflow is taken into account comparisons between simulation results and field measurements around an alpine crest show encouraging results

snow avalanche formation 1 snow avalanches are a major natural hazard endangering human life and infrastructure in mountainous areas throughout the world in many countries with seasonally snow covered mountains avalanche forecasting services reliably warn the public by issuing occurrence probabilities for a certain region however at present a single avalanche event cannot be predicted in time and space much about the release process remains unknown mainly because of the highly variable layered character of the snowpack a highly porous material that exists close to its melting point the complex interaction between terrain snowpack and meteorological conditions leading to avalanche release is commonly described as avalanche formation it is relevant to hazard mapping and essential to short term forecasting which involves weighting many contributory factors alternatively the release process can be studied and modeled this approach relies heavily on snow mechanics and snow properties including texture while the effect of meteorological conditions or changes on the deformational behavior of snow is known in qualitative or semiquantitative manner the knowledge of the quantitative relation between snow texture and mechanical properties is limited but promising developments are under way fracture mechanical models have been applied to explain the fracture propagation and micromechanical models including the two competing processes damage and sintering have been applied to explain snow failure there are knowledge gaps between the sequence of processes that lead to the release of the snow slab snow deformation and failure damage accumulation fracture initiation and fracture propagation simultaneously the spatial variability that affects damage fracture initiation and fracture propagation has to be considered this review focuses on dry snow slab avalanches and shows that dealing with a highly porous media close to its melting point and processes covering several orders of scale from the size of a bond between snow grains to the size of a mountain slope will continue to be very challenging

evolution of cretaceous cenozoic quartz pebble conglomerate gold placers during basin formation and inversion southern new zealand abstract numerous auriferous fluvial quartz pebble conglomerates qpcs are present within the late cretaceous recent sedimentary sequence in southern new zealand the qpcs formed in low relief settings before during and after regional marine transgression in alluvial fan and a variety of fluvial and near shore depositional settings in particular during slow thermal subsidence associated with late cretaceous early cenozoic rifting and during the early stages of orogenic uplift following mid cenozoic marine regression qpc maturity characteristics are complex and vary with sediment transport and recycling history stratigraphic proximity to the transgressive waipounamu erosion surface and the amount of first cycle detritus incorporated during recycling for pre marine qpcs the amount of first cycle detritus varies with tectonic intensity and proximity of the depositional setting to remnant cretaceous topography for post marine qpcs it varies with tectonic intensity and proximity to late cenozoic uplift of basement ranges qpcs do not form during a single bedrock erosion sediment deposition cycle non oxidised and or oxidized groundwater alteration kaolinisation of labile minerals in immature sediment and the upper part of underlying basement and repeated sedimentary recycling are fundamental processes of qpc formation regardless of the tectonic or sedimentary settings altered immature rock disaggregates easily upon erosion and alteration clays are winnowed to leave quartz rich residues containing resistant heavy minerals such as zircon and gold detrital sulfide survives recycling if deposition and burial in saturated sediments are rapid qpcs result only if sediment recycling is not accompanied by excessive erosion of fresh basement rock uplift of many parts of the otago schist belt since late miocene has raised rocks above the water table increased erosion rates and inhibited groundwater alteration and qpc formation qpc formation is still occurring in southland where the water table is high sediments are saturated and undergoing alteration and uplift and erosion rates topography and fluvial gradients are all low the qpcs accumulate as residual gravel on the valley floors of low competence streams that are slowly incising pervasively altered dominantly late miocene pliocene immature conglomerates qpcs formation essentially represents physical and chemical lagging of precursor strata accumulation of detrital gold and other heavy minerals is an inevitable consequence and most qpcs contain some gold three types of significant gold placer have developed in the qpcs type 1 placers are essentially eluvial and or colluvial in origin and form without significant fluvial transport by residual accumulation in low competence valleys during low rate uplift fluvial incision and qpc formation type 2 placers have formed during significant fluvial transport and subsequent fluvial incision mainly in higher energy proximal and medial reaches of larger pre marine eocene and post marine fluvial systems type 3 placers formed by wave base and marine current winnowing in the shallow shelf setting during low rate regional marine transgression especially in the eocene

original size of the vredefort structure implications for the geological evolution of the witwatersrand basin abstract historically there have been a range of diameter estimates for the large deeply eroded vredefort impact structure within the witwatersrand basin south africa here we estimate the diameter of the transient cavity at the present level of erosion as 124 140 km based on the spatial distribution of shock metamorphic features in the floor of the structure and downfaulted transvaal outliers taking erosion into account 6 km and scaling to original final rim diameter an estimate of close to 300 km for the rim diameter is obtained independent estimates of the final rim diameter based on an empirical relation of central uplift diameter to rim diameter spatial distribution of pseudotachylites and concentric large scale structural patterns give a similar estimate of close to 300 km for the original final rim diameter an impact structure of this size is expected to have had an original multi ring form at this size the vredefort impact structure encompasses the bulk of the witwatersrand basin which appears to owe its preservation to the vredefort impact in addition the vredefort impact event may have been the thermal driver for some of the widespread hydrothermal activity in the area which in recent interpretations is believed to be a component in the creation of the world class gold deposits of the witwatersrand basin

instruments and methods simulating complex snow distributions in windy environments using snowtran 3d we present a generalized version of snowtran 3d version 2 0 that simulates wind related snow distributions over the range of topographic and climatic environments found globally this version includes three primary enhancements to the original liston and sturm 1998 model 1 an improved wind sub model 2 a two layer sub model describing the spatial and temporal evolution of friction velocity that must be exceeded to transport snow the threshold friction velocity and 3 implementation of a three dimensional equilibrium drift profile sub model that forces snowtran 3d snow accumulations to duplicate observed drift profiles these three sub models allow snowtran 3d to simulate snow transport processes in variable topography and different snow climates in addition snowtran 3d has been coupled to a high resolution spatially distributed meteorological model micromet to provide more realistic atmospheric forcing data micromet distributes data precipi tation wind speed and direction air temperature and relative humidity obtained from meteorological stations and or atmospheric models located within or near the simulation domain snowtran 3d has also been coupled to a spatially distributed energy and mass balance snow evolution modeling system snowmodel designed for application in any landscape and climate where snow is found snowtran 3d is typically run using temporal increments ranging from 1 hour to 1 day horizontal grid increments ranging from 1 to 100 m and time spans ranging from individual storms to entire snow seasons

organic geochemistry and mineralogy i characterisation of organic matter associated with metal deposits abstract as geochemical appraisals of mineral regions of commercial prospectivity evolve the organic matter associated with metal rich ores has attracted greater attention petroleum basin and modern seafloor hydrothermal vent studies have suggested that organic matter can have a significant influence on the behaviour of mineralising fluids there have been many isolated reports of certain organic compositional or morphological e g pyrobitumen features showing an apparent relationships with hydrothermal fluids or minerals raising expectations that organic based parameters might be useful to mineral exploration however the understanding of organic inorganic relationships in earth systems is far from complete for example the detailed mechanics of the interaction of organics with hydrothermal fluids over geological time remain largely undefined organic geochemistry studies have traditionally involved the measurement and interpretation of the hydrocarbon composition of sedimentary rocks here we review the types of aliphatic hydrocarbons aromatic hydrocarbons and metalloporphyrins often detected from organic geochemical investigations in mineral rich regions such molecular data can be particularly diagnostic of biochemical sources and the palaeo environments at the time mineral associated organic matter was deposited sub surface trends of hydrocarbon alteration may also reflect major biogeochemical processes such as thermal maturity and biodegradation organic geochemistry data can also occasionally provide information about the nature e g origin composition temperatures and migration pathways of hydrothermal fluids and can make a contribution to holistic ore genesis models the well preserved organic matter associated with the economic here s your chance pb zn ag mine paleoproterozoic barney creek formation mcarthur basin australia and the transition metal rich early permian kupferschiefer formation germany poland have attracted significant attention a more detailed summary of the organic character of these deposits is provided to highlight the contribution organic geochemistry can make to understanding mineralisation processes most organic geochemical studies of highly mineralised regions however have not adequately addressed the significance of organic matter to mineralisation a slightly different analytical focus than traditionally used for exploration appraisal of petroleum hydrocarbons may be required to properly evaluate the significance of organic species to the mobilisation transport and deposition of ore metals the characterisation and subsequent thermodynamic modeling of organic substances and complexes within metalliferous hydrothermal systems will contribute to a better understanding of the nature and role of organic inorganic fluids or other affiliated organics in ore systems

changes in palaeoenvironmental conditions during deposition of the permian kupferschiefer lower rhine basin northwest germany inferred from molecular and isotopic compositions of biomarker components abstract biomarker distributions based on gc and gc ms data supplemented by stable carbon isotopic compositions based on irm isotope ratio monitoring gc ms data have been used to investigate changes in depositional conditions in a number of samples from a 2 m core rheinberger heide covering the entire deposition of the permian kupferschiefer lower rhine basin northwest germany compound classes investigated are aliphatic and aromatic hydrocarbons and maleimides 1h pyrrole 2 5 diones the core has been previously divided into four sections ti tiia tiib and tiii based on lithology the biomarker distributions and the 13c values of components indicate contributions from cyanobacteria algae green sulphur bacteria and higher plants minor throughout kupferschiefer deposition all of the phytoplanktonic components show 13c enrichment in the lowest section suggesting a greater productivity the occurrence of components derived from green sulphur bacteria chlorobiaceae indicates that the entire deposition was characterised by periods of photic zone anoxia such conditions were rapidly established after the initial transgression of the zechstein sea and may have been productivity driven but were less prevalent during deposition of the upper core sections

mountain snow distribution governed by an altitudinal gradient and terrain roughness 1 the heterogeneous mountain snow cover is challenging the eye and the analytical mind of the observer the snow distribution affects water resources natural hazards such as avalanches and ecology while a lot of recent research has helped to better understand this snow distribution and the processes that cause the heterogeneity it has not yet been possible to predict snow distribution satisfactorily on the basis of terrain parameters alone we present a model of the mean snow depth in topographic control units as a function of two terrain parameters the conventional elevation plus a fractal roughness parameter for this we used a unique data set of high resolution measurements of snow depth from an airborne laser scanner the model captures the heterogeneous snow distribution by merely analysing the terrain and the mean precipitation this unusually simple relationship holds for clusters of the snow depths of small topographical units by applying fractal analysis we describe the roughness of the terrain and use this parameter for the prediction of snow deposition rougher terrain holds less snow than smoother terrain this finding is important not only for avalanche warning or eco hydrological applications but also for reliably predicting how snow water storage may change in the light of the pronounced climate change already ongoing in mountain regions

are flat field snow depth measurements representative a comparison of selected index sites with areal snow depth measurements at the small catchment scale single or a limited number of point observations such as from index stations are commonly assumed to be representative for the snow cover of larger areas in many applications this study presents a systematic investigation of the relationship between point observations and areal mean snow depths ranging from the scale of tens of metres to entire catchments we analyse aerial snow depth information from four mountain regions in the european alps one in the spanish pyrenees and one in the canadian rocky mountains obtained from airborne laser scanning surveys this rich data set allowed to compare point values with snow cover statistics reflecting the real snow depth distribution of the investigation areas we present two contrasting approaches in order to assess the representativeness of typical flat field snow depth measurements in the first approach we define potential index stations based on topographic characteristics as commonly applied for snow cover monitoring stations the point observations of these index stations are then compared with the mean values in their vicinities we show that most of the index stations strongly overestimate the snow depth of the catchment and of their surrounding area at distances of several hundreds of metres results confirm the expectation that the larger the support area the smaller the difference to the mean of the complete catchment the second approach was to analyse topographic characteristics of all cells with snow depths that deviated less than 10 from the catchment mean it appears that these representative cells are rather randomly distributed and cannot be identified a priori in summary our results show large potential biases of index stations with respect to snow distribution and therefore also snow water equivalent copyright c 2014 john wiley sons ltd

evidence for an intrabasinal source and multiple concentration processes in the formation of the carbon leader reef witwatersrand supergroup south africa laser ablation inductively coupled plasma mass spectrometer la icp ms trace element maps of pyrite and gold from the carbon leader reef in the witwatersrand basin provide new evidence that a significant proportion of the pyrite and gold was intrabasinal derived from the west rand group or equivalent shales stratigraphically below this reef rounded detrital pyrite grains in the carbon leader reef vary from compact to porous to sooty with similar textures and composition to diagenetic pyrites reported from sedimentary rocks in the west rand group detrital porous and sooty pyrites contain 0 4 to 11 3 ppm solid solution gold sulfur isotope 34s values from 17 to 16 and high levels of as and te plus a wide range of other trace elements in decreasing order ni co sb cr cu u pb bi mo zn and ag the sooty pyrite is the most au te and mo rich and is intergrown with alumino silicates and organic matter the detrital pyrite textures s isotopes and geochemistry resemble diagenetic pyrite developed under suboxic to anoxic bottom water conditions the laicp ms maps also show that the detrital pyrite grains have euhedral hydrothermal pyrite overgrowths containing micro inclusions of gold brannerite and ni as sulfides the pyrite overgrowths are also enriched in solid solution gold tellurium and other trace elements including in decreasing order as co ni cr cu mn pb bi and ag fractured and brecciated pyrite associated with brittle bedding parallel fracture zones in the carbon leader reef are also enriched in these elements due to alteration of pyrite surrounding the fractures laser icp ms pb isotope determinations on the cores of detrital pyrite indicate an age between 2750 and 2950 ma with hydrothermal overgrowths originating between 2100 and 2020 ma incorporating highly radiogenic pb this study demonstrates that both of the two competing theories for the origin of the witwatersrand gold reefs are likely to be correct we suggest that the hydrothermal event was widespread kilometer scale and involved basinal fluids that scavenged gold tellurium arsenic and trace elements co ni cr cu mn pb bi ag from gold bearing sedimentary units in the central rand group 2013 society of economic geologists inc

petrographic evidence for emplacement of carbon into witwatersrand conglomerates under high fluid pressure abstract much gold in the witwatersrand conglomerates is directly associated with seams of carbon that are generally parallel with bedding some seams locally crosscut bedding and form anastomosing fracture patterns showing that emplacement of liquid hydrocarbons in those seams was postdepositional and infilled fractures that are generally parallel to bedding seams that are not observed to crosscut bedding are nonetheless petrographically identical and are believed to have a common postdepositional origin carbon also occurs along sets of bedding parallel microfractures through individual quartz pebbles in mineralized conglomerates planes of fluid inclusions parallel to the microfractures in pebbles show further evidence for the importance of bedding parallel fluid flow the occurrence of carbon seams on sedimentary discontinuity surfaces may reflect preferential emplacement of carbon along planes of weakness brittle extensional fracturing in pebbles indicates high fluid pressures which may relate to hydrocarbon generation bedding parallel minealization by quartz clays metamorphic chlorite pyrophyllite and gold which reflect a complex multistage paragenesis indicate repeated reactivation of bedding plane permeability previous arguments against a hydrocarbon origin for the carbon seams have been based upon the low intergranular permeability of the rocks however the present study shows that this condition actually caused focusing of hydrocarbon fluid flow along discontinuity surfaces and facies boundaries interaction with uranium could have caused fixation of fluid hydrocarbon by radiolytic polymerization the columnar nature of carbon in many of the seams interpreted by others as a biogenic structure could instead reflect polymer swelling normal to bedding in the direction of least confining stress

a radar based climatology of mesoscale convective systems in the united states abstractthis research applies an automated mesoscale convective system mcs segmentation classification and tracking approach to composite radar reflectivity mosaic images that cover the contigu