genetic implications of regional vs fracture controlled fluid flow in carlin type gold deposits nevada abstract the ability to identify differences in the chemistry of hydrothermal solutions that formed carlin type gold deposits in areas that experienced regional fluid flow in proximity to eocene igneous rocks e g the carlin trend vs fracture controlled fluid flow distal to eocene igneous rocks e g the getchell trend was evaluated using fluid inclusion microthermometry quadrupole mass spectrometer qms gas analyses and h isotopes primary fluid inclusions were measured in eleven samples of main stage quartz late stage quartz realgar and barite and post ore calcite interlayered with chalcedonic quartz from the getchell and twin creeks mines fluid inclusions in main stage jasperoid from the ne trending turquoise ridge fault are cogenetic one phase co2 and liquid rich that homogenize at 178 237 c with salinities of 4 3 6 2 wt nacl equiv inclusions in late stage quartz containing disseminated stibnite have th of 122 253 c and salinities of 4 2 6 7 wt nacl equiv barren realgar hosts inclusions with th of 65 119 c and salinities of 0 18 wt nacl equiv finally inclusions in hydrothermal barite and post ore calcite have salinities of 5 7 8 1 wt nacl equiv and 0 9 1 1 wt nacl equiv respectively but th overlap between 65 134 c gas data include 22 samples of late stage realgar stibnite orpiment mineralization from the getchell twin creeks and betze mines fluid inclusions in samples of auriferous stibnite from the getchell trend have total gas contents 7 7 mol plot near the n2 apex magmatic gas source in a n2 ar he ternary diagram and trend from the shallow meteoric to magmatic field of a co2 ch4 vs n2 ar diagram barren stibnite and realgar contain gas poor inclusions 0 01 2 2 mol total gas with fluid mixing for realgar indicated by the positive correlation of he ch4 and data trending from the shallow meteoric to evolved crustal field in a co2 ch4 vs n2 ar diagram hydrogen isotopes were measured for nine samples of main and late stage minerals from the getchell twin creeks and betze mines main stage siliceous ore from the getchell trend have d of 128 to 98 realgar samples from all three mines have d of 152 to 142 and two orpiment samples from the getchell mine have d of 57 and 44 distinct differences are evident in the fluid inclusion and h isotope data for hydrothermal systems that formed carlin type deposits distal vs proximal to eocene igneous rocks magmatic and crustal fluids dominated in the fracture controlled turquoise ridge deposit getchell trend and meteoric water did not become prominent until the formation of post ore chalcedonic quartz calcite veins in contrast regional flow along the carlin trend incorporated large amounts of meteoric water by interpreting h isotopes with respect to fluid inclusion data for the carlin and getchell trends gold did have a magmatic source in both areas however meteoric water also leached gold from country rocks during regional flow to contribute to the large endowment of gold in the carlin trend genetic models used in the exploration for carlin type deposits must therefore account for mineralization that is fracture controlled or related to regional fluid flow

geochemistry of the alginite and amorphous organic matter from type ii s kerogens abstract maceral fractions of the type ii s kerogens from the monterey formation miocene california u s a and duwi formation campanian maastrichtian egypt were separated by density gradient centrifugation the monterey fm kerogen sample was comprised chiefly of light red fluorescing amorphous organic matter aom the flash pyrolyzate of which was characterized by a predominance of alkylbenzenes alkylthiophenes and alkylpyrroles in contrast the pyrolyzates of its alginite concentrate showed a highly aliphatic character typical of this maceral with the series of n alkenes and n alkanes c6 c26 predominating the pyrolyzate of the dominant light brown fluorescing aom of the duwi fm kerogen had a relatively high concentration of alkylbenzenes and alkylthiophenes while its alginite concentrate showed a more aliphatic character upon pyrolysis there was a marked enrichment of thiophenic sulfur in the light colored aom of both samples and also pyrrolic nitrogen in the case of the monterey relative to the alginite the results support a bacterially mediated degradative origin for type ii s amorphous organic matter with algal remains as the primary source of the kerogen

a global climatology of atmospheric fronts 1 atmospheric fronts in the lower troposphere often mark regions of significant weather and serve as an important conceptual tool that is frequently used and well understood by the public this study uses an objective method to identify fronts in the era 40 reanalysis and to compile a quantitative global climatology of their occurrence the climatology confirms the mid latitude storm tracks as the regions of highest front frequency and identifies slow moving frontal boundaries in the subtropics corresponding to major climate features such as the mei yu front the climatology also shows fronts to be common features of the south pacific convergence zone in the northern hemisphere fronts shift poleward in summer in the southern hemisphere this and other aspects of seasonal behavior are rather different

wave cloud lines over northwest australia the frequency of occurrence and formation mechanisms of wave cloud lines off the northwest coast of australia are investigated prior to the present study little was known about these wave cloud lines apart from being spectacular atmospheric phenomenon in their own right these wave clouds can have a role in the secondary initiation of convection and can be a hazard to low flying aircraft a climatology of wave clouds produced from visible satellite imagery suggests two main types of cloud lines form over northwest australia the first are bore like waves similar in structure to the morning glory of northeast australia and occur at least 2 to 3 times per month throughout the entire year the second type are convectively generated cloud lines which are more circular in shape appear to originate from convective storms and occur at least 0 5 to 1 5 times per month during the wet season high resolution nested simulations are performed with the met office unified model for case studies of each type of wave the bore like waves occurred in the presence of synoptic scale low level southeasterly flow and a heat low along the northwest coast of australia at night the offshore southeasterlies accelerate into the heat low and collide with the onshore sea breeze the southeasterlies override the sea breeze and the wave cloud lines form at the leading edge of this front the convectively generated waves radiate outwards from the convective storms producing compensating subsidence and adiabatic warming these waves take the form of n 2 mode wave fronts which span the entire depth of the troposphere and are similar in structure to waves produced by deep convection which are described in previous studies

organic matter in senonian phosphorites from israel origin and diagenesis abstract the organic matter associated with senonian phosphorites from israel was studied and compared with that in tertiary phosphorites from morocco and modern phosphate rich sediments from south west africa namibia humic acids were found to be the main constituents of the organic matter in all samples the n alkane distribution pattern in the c15 c26 range and the lack of odd over even predominancy in the higher hydrocarbons indicate microbial degradation of marine derived organic matter significant phytane over pristane predominance indicates accumulation under euxinic conditions the high humic acid content and its relatively light 13c composition apparently reflect the two evolution stages suggested for the formation of phosphorites by g n baturin high decomposition rates of marine organic matter under limited oxygen supply led to the differential accumulation of more resistant fractions such as cellulose and lignin these compounds are known to be enriched in 12c relative to other marine organic compounds when exposed to oxidizing conditions during the second stage of non phosphate mud winnowing these compounds were easily converted into humic substances further conversion into kerogen was prevented due to shallow overburden and low maturation

diurnally forced convergence lines in the australian tropics observations and analyses of low level convergence lines over the gulf of carpentaria region of northeastern australia made during the second and third gulf lines experiments glex ii and glex iii are reported during glex ii the initiation of the north australian cloud line nacl was documented using a small autonomous aircraft and two doppler sodars nacls are long convergence lines that form on the western side of northern cape york peninsula and are typically marked by a line of contiguous cumulus or cumulus congestus cloud the observations show that the degree of asymmetry between west coast and east coast sea breezes as characterized by the wind field depends on the strength of the background easterlies and that nacls develop only when the background easterlies are sufficiently large 5 m s 1 glex iii focused on morning glories which are mostly southwestward moving bore like convergence lines that originate over the southern part of the gulf region the field experiment involved doppler sodar measurements as well as high temporal resolution data from operational automatic weather stations the sodar measurements showed that undular bore like morning glory cloud lines develop only when the background easterlies are sufficiently weak 10 m s 1 and that strong bore like morning glories develop when the background winds exceed about 10 m s 1 if the background easterlies are too strong no morning glories develop numerical simulations show that the structure of convergence line produced depends on the strength of the collision between the sea breezes from each side of the cape york peninsula which in turn depends on the strength of the background easterlies when the easterlies are weak 10 m s 1 the sea breezes have similar depths and strengths and their collision is relatively violent whereas when the background easterlies are strong 10 m s 1 the sea breezes have very different depths and strengths and their collision is comparatively benign

alteration associated with gold deposition at the getchell carlin type gold deposit north central nevada wall rock alteration at the getchell underground deposit was examined to determine the effects of au bear ing fluids on host lithologies and the relationship between k bearing alteration minerals and au deposition the major minor and trace element geochemistry of highly altered and mineralized to unmineralized rocks from the getchell deposit was quantified for more than 50 samples collected along 13 transects through calcareous siltstone and carbonaceous limestone and along one transect through a rhyodacite dike each transect in sedimentary rocks was collected along a single homogeneous bed that could be followed from high grade ore to moderately altered rock or waste rock analyses were obtained for 39 elements 10 oxides and loss on ignition using multiple techniques petrographic studies were integrated with geochemistry and x ray diffraction and electron microbeam analyses to identify ore and alteration minerals and to correlate mineralogy with geochemical fluxes geochemical analyses indicate that ti al zr and th behave as immobile elements immobility isocon diagrams show that significant hg sb se te tl and cs are typically added to the wall rocks with au fe is im mobile in some transects added to wall rocks in others and removed from rhyodacite host rocks minor s and w are usually added to the rock whereas minor cu and mo are variably added or removed sio 2 appears to be either added during alteration or remain constant elements that are consistently removed during alteration include ca mn sr and sc and minor mg ba and k na was significantly removed from the rhyodacite au correlates positively with ag hg sb se si te and tl and negatively with ca mn and sc element fluxes correspond with observations of mineral abundances and show that sulfidation and decar bonitization are spatially associated with gold mineralization au hg sb tl cu and possibly te and w were incorporated in trace element rich pyrite as host rock fe was sulfidized fe was added to mineralized rocks in some transects indicating that pyritization occurred in addition to sulfidation cs is a component of galkhaite a trace mineral that is relatively common in some parts of the getchell system decarbonitization removed as much as 95 wt percent calcite from mineralized rocks in some transects and is responsible for loss of ca mn sr and sc although sio 2 as and s are significantly added to carlin type systems they do not appear as major added components in the isocon diagrams this is because the halos for these components are much larger than the areas examined by the sample transects x ray diffraction analyses identified minerals in ore and waste samples and quantified clay minerals including illite and montmorillonite kaolinite was not identified or is present in low abundances in both mineralized and unmineralized rocks montmorillonite does not correlate with gold and textures are consistent with pore filling deposition of montmorillonite following au deposition illite abundance exhibits a positive correlation with au r 2 0 80 intergrowths of illite with ore stage pyrite support a genetic relationship between the two minerals and indicate that illite formed as part of the au related hydrothermal event mineral abundances and textures suggest that illite formed by alteration of k feldspar during au deposition results show that dating of k bearing phases in sedimentary rocks other than illite would provide ages unrelated to gold deposition

early formation of k feldspar in shallow marine sediments at near surface temperatures southern israel evidence from k ar dating authigenic k feldspar was investigated in two albian to turonian sections in israel using k ar and ar ar dating x ray diffraction scanning electron microscopy and chemical analysis both sections comprise a similar succession of shallow marine limestones dolomites and marls with some sandstone and shale beds of continental origin the hcl insoluble residue fraction of the studied samples consists of clays quartz feldspars goethite and trace amounts of heavy minerals most of the insoluble residues have a relatively high k feldspar content that has an adularia habit and is concentrated in the 4 7 m size fraction the authigenic origin of the k feldspar in the fine silt fraction is indicated by its high content relative to quartz the uniform and idiomorphic shape of the crystals and its limited size range of the fine silt 4 7 or 4 10 m separates 40 have ages that are similar to stratigraphic ages within the analytical and biostratigraphic errors ar ar dating of a fine silt fraction with 94 k feldspar 4 10 m sample gyp 7 yields a plateau age identical to the total gas age and similar to the stratigraphic age these results indicate that the k ar age is not a mixture between detrital and late diagenetic k feldspar ages but is rather an age of formation within a few million years after deposition it is suggested that the early formation of the k feldspar was associated with dolomitization and was induced by residual brines as part of a reflux process

timing constraints of orogeny to cratonization thermochronology of the paleoproterozoic trans hudson orogen manitoba and saskatchewan canada abstract a comprehensive thermochronometric investigation across a 600 km transect of the paleoproterozoic trans hudson orogen tho in canada has resolved two first order thermal events 1 widespread peak metamorphism at 1 82 1 79 ga associated with terrane amalgamation and 2 a late collisional metamorphic episode at ca 1 77 ga that is characterized by significant strike slip deformation and rapid cooling geophysical observations of the lithosphere beneath the tho reveal crust that is markedly different on either side of the crustal scale tabbernor sturgeon weir tsw strike slip fault system which offsets lower crustal reflectors the tho east of the fault system records u pb titanite and total pb monazite domain ages that are relatively indistinguishable from 40ar 39ar hornblende and mica cooling ages indicating rapid cooling and perhaps exhumation following 1 77 ga metamorphism seismic imaging indicates the eastern orogen is an irregular package of stacked crustal blocks and our thermochronometric data demonstrate it behaved as a single coherent element shortly 20 30 m y following cessation of convergence in contrast rocks located west of the tsw fault system cooled distinctly later preserving 40ar 39ar muscovite and biotite ages between 1 74 and 1 72 ga this crustal architecture delineated from seismic surveys illustrates a more homogeneous slightly 5 km thinner crust in the case of this orogen apparent stabilization and cratonization occurred ca 100 m y after peak terrane amalgamation and notably the orogen was likely cratonized as two blocks east and west of the tsw fault system

petrographic and geochemical study of organic matter in surficial laminated sediments from an upwelling system mejillones del sur bay northern chile a study of recent laminated sediments accumulated in the oxygen minimum zone of mejillones bay northern chile shows that the organic matter is autochthonous and deposited under varying oceanographic conditions sedimentary units dominated by light laminations have low values of total organic carbon total nitrogen and sulphur and chaotoceros content coupled with high values of yellow amorphous organic matter these were deposited under conditions of low primary productivity favoring the recycling of the major part of metabolizable organic matter in the water column and the accumulation only of non metabolizable organic matter in the bottom sediments in contrast a unit rich in dark laminations with high values of total organic carbon total nitrogen and sulphur shows high values of brown and black aom and chaetoceros content this sedimentary unit reflects increased flocculation of organic particles during a period of high productivity and fast transit of organic material through the column water thus diminishing the recycling of metabolizable organic matter and its accumulation with non metabolizable organic matter in the sediments finally a unit characterized by presence of both light and dark laminations was formed by abrupt alternations of the two oceanographic states described previously

turbulent mixing processes in atmospheric bores and solitary waves deduced from profiling systems and numerical simulation abstract families of solitary waves solitons associated with two atmospheric bores on the same day were observed by an unprecedented number of ground based and airborne profiling systems during the international h2o project ihop in addition a very high resolution numerical weather prediction model initialized with real data was used with success to simulate one of the bores and the evolving soliton the predicted wave amplitude phase speed wavelength and structure compared well to these extraordinarily detailed observations the observations suggest that during the active phase when turbulent mixing was active which was prior to bore collapse the bores and waves vigorously mixed dry air from above a nocturnal boundary layer down to the surface refractivity computed from near surface radar observations showed pronounced decreases due to sudden drying during the passage of the bores in this phase but refractivity increases appeared during the period of bore collapse during both phases the

dynamics of solitary waves observed over the north indian ocean during the indian ocean experiment indoex 1999 during the indian ocean experiment indoex experiment january march 1999 mesoscale solitary waves have been observed and tracked over the north indian ocean on a series of meteosat 5 satellite images these solitary waves have a horizontal wavelength of 10 15 km and propagate westward at low level at a speed of 10 18 m s unlike similar wave phenomena observed mainly over land they have a long lifetime which can exceed 48 h a key element explaining the existence and longevity of the solitary waves is the presence of an inversion layer acting as a waveguide and separating the boundary layer into two sublayers a lower layer over the ocean marine boundary layer and an upper layer originating from the indian subcontinent land plume layer profiles from radiosondes launched from the ron brown and from dropsondes from the hercules c 130 airplane helped to determine this waveguide structure a suggested mechanism leading to the generation of solitary waves is a collision between the sea breeze in the vicinity of the west indian coast and the easterly northeasterly winter monsoon winds with a possible contribution of convection reinforced by topography western ghats range during the local afternoon another phenomenon related to sea breeze and local convection in this coastal area the injection of bubbles of moisture into the drier upper boundary layer has also been identified on european centre for medium range weather forecasts analyses these bubbles form daily during the afternoon and drift westward over the north indian ocean at latitudes around 12n and progressively subside and dissipate or become integrated into larger air masses copyright 2011 by the american geophysical union

lead in the getchell turquoise ridge carlin type gold deposits from the perspective of potential igneous and sedimentary rock sources in northern nevada implications for fluid and metal sources lead isotope compositions of bulk mineral samples fluorite orpiment and realgar determined using conventional techniques and of ore stage arsenian pyrite using the sensitive high resolution ion microprobe shrimp in the getchell and turquoise ridge carlin type gold deposits osgood mountains require contribution from two different pb sources one pb source dominates the ore stage it has a limited pb isotope range characterized by 208pb 206pb values of 2 000 to 2 005 and 207pb 206pb valuesof 0 8031 to 0 8075 as recorded by 10 mm diameter spot shrimp analyses of ore stage arsenian pyrite these values approximately correspond to 206pb 204pb of 19 3 to 19 6 207pb 204pb of 15 65 to 15 75 and 208pb 204pb of 39 2 to 39 5 this pb source is isotopically similar to that in average neoproterozoic and cambrian clastic rocks but not to any potential magmatic sources whether those clastic rocks provided pb to the ore fluid cannot be unequivocally proven because their pb isotope compositions over the same range as in ore stage arsenian pyrite are similar to those of ordovician to devonian siliciclastic and calcareous rocks the pb source in the calcareous rocks most likely is largely detrital minerals since that detritus was derived from the same sources as the detritus in the neoproterozoic and cambrian clastic rocks the second pb source is characterized by a large range of 206pb 204pb values 18 34 with a limited range of 208pb 204pb values 38 1 39 5 indicating low but variable th u and high and variable u pb values the second pb source dominates late and postore stage minerals but is also found in preore sulfide minerals these pb isotope characteristics typify ordovician to devonian siliciclastic and calcareous rocks around the carlin trend in northeast nevada petrologically similar rocks host the getchell and turquoise ridge deposits lead from the second source was either contributed from the host sedimentary rock sequences or brought into the hydrothermal system by oxidized ground water as the system collapsed late ore and postore stage sulfide minerals pyrite orpiment and stibnite from the betze post and meikle deposits in the carlin trend and from the jerritt canyon mining district have pb isotope characteristics similar to those determined in getchell and turquoise ridge this observation suggests that the pb isotope compositions of their ore fluids may be similar to those at getchell and turquoise ridge two models can explain the pb isotope compositions of the ore stage arsenian pyrite versus the late ore or postore sulfide minerals in either model pb from the ordovician to devonian siliciclastic and calcareous rock source enters the hydrothermal system late in the ore stage but not to any extent during the main stage of ore deposition in one model ore stage pb was derived from a source with pb isotope compositions similar to those of the neoproterozoic and cambrian clastic sequence transported as part of the ore fluid and then deposited in the ore stage arsenian pyrite and fluorite the second model is based on the observation that the pb isotope characteristics of the ore stage minerals also are found in some ordovician to devonian calcareous and siliciclastic rocks hence ore stage pb could have been derived locally and simply concentrated during the ore stage critical to the second model is the removal of all high 206pb 204pb 20 material during alteration it also requires the retention of only the low 206pb 204pb component of the ordovician to devonian sedimentary rocks this critical step is possible only if the high 206pb 204pb values are contained in readily dissolvable mineral phases whereas the low 206pb 204pb values are found only in refractory minerals that released pb during a final alteration stage just prior deposition of auriferous arsenian pyrite distinguishing between pb transported with the ore fluid or inherited from the site of mineral deposition is not straightforward however it is simpler to explain the pb isotope compositions of ore stage arsenian pyrite and fluorite in two different but spatially related carlin type deposits getchell and turquoise ridge with different host rocks by input of pb with the ore fluid once the limited pb in the hydrothermal fluid was exhausted by incorporation in ore stage arsenian pyrite or other ore stage minerals pb from the second source the ordovician to devonian sedimentary rock sequences became available for incorporation in some but not all of the late stage sulfide minerals

overlapping cretaceous and eocene alteration twin creeks carlin type deposit nevada we report here new ar ar dates for adularia illite and muscovite from the twin creeks carlin type deposit all illite samples were obtained from altered intrusive and volcanic rocks that are interlayered with mineralized sedimentary rocks thus largely avoiding complications caused by detrital illite and muscovite in sedimentary rocks interpretation of the illite age spectra was based in part on newly developed models for the behavior of argon in fine grained illite the results indicate that all adularia in the megapit area formed at about 42 ma eocene whereas most illite in the megapit area and muscovite in alteration zones beneath chimney creek formed at about 109 to 103 ma cretaceous additional events involving formation of illite at 200 ma and muscovite at about 310 ma were also observed but were not widespread enough to be considered significant our eocene date for adularia is in complete agreement with previous measurements on adularia from twin creeks but our cretaceous dates are considerably older than dates determined in previous studies of the nearby getchell district particularly the osgood stock which has a date of 98 to 92 ma our results suggest that the osgood stock is part of a more protracted cretaceous igneous hydrothermal event that took place between about 109 and 83 ma the relationship of adularia and illite to gold mineralization is not completely clear making it impossible to use our data to assign a unique age to the twin creeks deposit we favor an eocene age for some gold mineralization because the adularia that we dated is intimately intergrown with auriferous arsenian pyrite typical of carlin type mineralization however adularia has a very restricted distribution in the deposit and temperatures at which it formed were probably not great enough to reset cretaceous and older ages of illite illite is much more widespread and its association with gold is supported by correlation between gold content and k al ratios of mineralized material thus cretaceous illitization was at least an important ground preparing event at twin creeks and it is not possible to show from our data that gold ore or protore were not deposited during this event

a new boundary layer mixing scheme part i scheme description and single column model tests a new boundary layer turbulent mixing scheme has been developed for use in the ukmo weather forecasting and climate prediction models this includes a representation of nonlocal mixing driven by both surface fluxes and cloud top processes in unstable layers either coupled to or decoupled from the surface and an explicit entrainment parameterization the scheme is formulated in moist conserved variables so that it can treat both dry and cloudy layers details of the scheme and examples of its performance in single column model tests are presented

a study of the organic matter in tunisian phosphates series relevance to phosphorite genesis in the gafsa basin tunisia abstract in the gafsa basin tunisia peloidal fracolite is interbedded with shales limestones and rocks of intermediate lithology the rocks were deposited in an epicontinental sea and have been buried no more than 500 m the organic matter they contain is therefore thermally immature and in all units derived mainly from marine plankton particularly dinoflagellates the organic matter in the phosphorite units is composed predominantly of humic acids ha which are essentially located within the pellets these pellets are surrounded by an outer matrix in which the organic matter is similar to the kerogen comprised in the shally strata alternating with the phosphorite and limestone beds during weathering the content of the organic matter assocciated with the matrix decreases more rapidly than that of the organic matter entrapped within the pellets geochemical and palynological study of the organic matter in interbedded rocks of different lithology shale limestone phosphorite suggest that the shales were deposited in a reducing environment the limestones in one that was oxic whilst the phosphorites were formed in a redox environment inermediate between the two the interpretation of the data presented in this paper is that the genesis of shales phosphate and some carbonate beds excluding coquinas did not result from the deposition of initially sharply differentiated sediments but resulted from differences in diagenesis of sediments initially containing planktonic organic matter associated with clay and carbonate minerals

speciation and weathering of selenium in upper cretaceous chalk and shale from south dakota and wyoming usa abstract in geologic materials petroleum and the environment selenium occurs in various oxidation states vi iv 0 ii mineralized forms and organo se complexes each of these forms is characterized by specific chemical and biochemical properties that control the element s solubility toxicity and environmental behavior the organic rich chalks and shales of the upper cretaceous niobrara formation and the pierre shale in south dakota and wyoming are bentoniferous stratigraphic intervals characterized by anomalously high concentrations of naturally occurring se numerous environmental problems have been associated with se derived from these geological units including the development of seleniferous soils and vegetation that are toxic to livestock and the contamination of drinking water supplies by se mobilized in groundwater this study describes a sequential extraction protocol followed by speciation treatments and quantitative analysis by hydride generation atomic absorption spectroscopy this protocol was utilized to investigate the geochemical forms and the oxidation states in which se occurs in these geologic units organic se and di selenide minerals are the predominant forms of se present in the chalks shales and bentonites but distinctive variations in these forms were observed between different sample types chalks contain significantly greater proportions of se in the form of di selenide minerals including se associated with pyrite than the shales where base soluble humic organo se complexes are more prevalent a comparison between unweathered samples collected from lithologic drill cores and weathered samples collected from outcrop suggest that the humic organic se compounds in shale are formed during oxidative weathering and that se oxidized by weathering is more likely to be retained by shale than by chalk selenium enrichment in bentonites is inferred to result from secondary processes including the adsorption of se mobilized by groundwater from surrounding organic rich sediments to clay mineral and iron hydroxide surfaces as well as microbial reduction of se within the bentonitic intervals distinct differences are inferred for the biogeochemical pathways that affected sedimentary se sequestration during periods of chalk accumulation compared to shale deposition in the cretaceous seaway mineralogy of sediment and the nature of the organic matter associated with each of these rock types have important implications for the environmental chemistry and release of se to the environment during weathering

numerical simulations of a gravity wave event over ccope part ii waves generated by an orographic density current a mesoscale numerical model and detailed observations are used to investigate the generation and maintenance of a mesoscale gravity wave event observed in eastern montana on 11 july 1981 during the cooperative convective precipitation experiment ccope it is shown that the interaction between an orographic density current and a mountain barrier leads to the generation of the gravity waves the simulation results suggest the following four stage conceptual model during stage i shortly after sunset the remnant up branch of a thermally driven upslope flow east of the rockies was driven back toward the mountain by the pressure gradient force associated with a cool pool over north dakota the nocturnal stable layer over eastern montana was strengthened during passage of this density current during the 1 2 h transition period of stage ii the advancing density current became blocked as it encountered the higher terrain an isentropic ridge developed above the original warm lee trough due to strong adiabatic cooling caused by the sustained upward motion in the presence of orographic blocking during stage iii an even stronger upward motion center formed to the east of the density current head updraft in response to an eastward horizontal pressure gradient force produced by the isentropic ridge in stage iv as the density current head collapsed and downward motion developed to the west of the original updraft in quadrature phase with the isentropic perturbation a gravity wave was generated this wave propagated eastward with the mean wind opposite to the motion of the earlier density current and was maintained by the strong wave duct established earlier by the density current thus the mountain plains circulation may at times generate mesoscale gravity waves and deep convection hours after diurnal heating has ended

the nexus between groundwater modeling pit lake chemogenesis and ecological risk from arsenic in the getchell main pit nevada u s a abstract the proliferation of mine pits that intersect the groundwater table has engendered interest in the environmental consequences of the lakes that form after cessation of dewatering the getchell main pit gmp in nevada hosts arsenic sulfide asxsy mineralization e g orpiment and realgar and ambient groundwater as up to 1 8 mg l 1 making groundwater inflow a potentially significant as source to the future pit lake predictive simulations using modflow surfact show that the gmp lake water level will recover to within 99 of the pseudo equilibrium stage within 100 years after the end of dewatering resulting in a 75 m deep terminal pit lake the juvenile gmp lake after 5 years will be a calcium sulfate ph 7 8 water body containing 920 mg l 1 tds and 0 6 mg l 1 as evolving towards a ph 7 9 1580 mg l 1 tds and 0 9 mg l 1 as water body after 100 years the predicted pit lake chemistry is consistent with earlier pit lake water quality after 16 years when the south and center pits precursors to the main pit were allowed to fill during a mining hiatus 1968 1984 the gmp mature pit lake chemistry was used to assess ecological risk to potential local receptors i e mallard duck cliff swallow golden eagle little brown bat spotted sandpiper deer mouse mule deer and cattle arsenic does not strongly bioaccumulate through the food chain at getchell hence pit lake as will not pose an unacceptable risk

microtextures of authigenic or rich feldspar in the upper jurassic humber group uk north sea detrital alkali feldspars currently at burial depths of 3 2 3 5 km in the upper jurassic humber group of the fulmar oilfield uk north sea are overgrown and have been partially replaced by authigenic or rich feldspar intracrystal microtextures suggest several different provenances for the detrital grains the overgrowths are uniformly non cathodoluminescent and have occasional celsian rich zones transmission electron microscopy shows that they are composed of a microporous mosaic of sub m to m sized sub grains associated with barite illite and pyrite the subgrains are somewhat rounded but have an approximate 110 adularia habit and display a faint modulated microtexture on the nanometre scale they have triclinic symmetry but the lattice angles depart only slightly from monoclinic symmetry these features are characteristic of k feldspar precipitated relatively rapidly and at low temperature authigenic or rich feldspar has also partially replaced microcline and perthitic albite within the detrital grains often at a suboptical scale although like diagenetic albitization replacement by k feldspar is probably a very common diagenetic reaction it has rarely been reported owing to difficulties in imaging the diagnostic textures with the scanning electron microscopy techniques used by most workers the permeability of the subgrain microtexture may significantly hinder the use of feldspar overgrowths for k ar and 4 0 ar 3 9 ar dating of diagenesis and the existence of suboptical replacive authigenic k feldspar within detrital grains may significantly modify the apparent ar ages of detrital grains similar subgrain microtextures in optically featureless quartz overgrowths are also illustrated

evidence of boiling and epithermal vein mineralization in carlin type deposits on the getchell trend nevada abstract boiling in northeast ne trending faults during eocene gold mineralization at the getchell and twin creeks deposits is indicated by cogenetic liquid rich and vapor rich fluid inclusions both primary and secondary fluid inclusions in orpiment record similar evidence of boiling however banding in paragenetically younger calcite indicates that boiling was episodic in addition to being localized to ne trending faults the presence of co2 rich secondary fluid inclusions in fluorite from the getchell mine is an artifact of boiling and a depth of 980 m is representative of the late stage in these carlin type deposits an 0 5 m wide crystalline white quartz vein in the dz fault twin creeks mine contains cogenetic liquid rich and vapor rich fluid inclusions intergrown with the quartz is 42 ma adularia and native gold that occurs both as disseminations within and along boundaries between quartz grains this vein extends beyond the dz fault and cuts massive brown jasperoid of the hgo ore zone the contrasting styles of mineralization e g low sulfidation epithermal versus carlin type crosscutting relationship and precise adularia age provides an important constraint on the age of carlin type gold mineralization at the twin creeks mine

numerical simulation of the large amplitude mesoscale gravity wave event of 15 december 1987 in the central united states abstract an observational study employing spectral methods is first made to establish a background for a modeling effort of the mesoscale gravity wave event of 15 december 1987 the waves are found to have wavelengths of 100 160 km phase speeds of approximately 30 m s 1 and lifetimes of over 6 h conditions for their maintenance are evaluated indicating the presence of a wave duct and a supportive role for wave cisk convection shearing instability and geostrophic adjustment are all implicated as possible source mechanisms for the observed waves the case is then simulated with the pennsylvania state university national center for atmospheric research mm4 mesoscale forecast model with the following primary objectives i to test the model s ability to simulate a mesoscale gravity wave event ii to examine in detail the environments of mesoscale gravity wave development and iii to investigate the mechanisms of mesoscale gravity wave generation and maintenance the full physics control experim

dating gold deposition in a carlin type gold deposit using rb sr methods on the mineral galkhaite significant effort has been expended in an attempt to date hydrothermal activity that generated carlin type gold deposits ctds in the great basin of nevada thus far these efforts have been only partially successful because the relationship s between the dated mineral and hydrothermal activity are equivocal in many cases galkhaite a trace component of at least four ctds in nevada contains significant amounts of rb and virtually no sr making it an ideal candidate for radiometric dating at the getchell deposit galkhaite is paragenetically late but clearly associated with gold mineralization our data place gold mineralization at getchell at 39 0 2 1 ma this is the first unequivocally gold related date produced for any of the carlin type systems galkhaite also has been reported at the carlin rodeo and betze deposits and is likely present in other ctds in nevada this mineral may provide a solution to the conundrum of dating of ctds

a solitary wave packet in the atmosphere observed from space a group of parallel cloud lines was identified in seven successive space shuttle photographs taken over the pakistani offshore zone in the northern arabian sea on april 29 1993 there are a total of 19 lines aligned with the length of the leading line longer than 250 km and an average separation distance wavelength of 1 km we suggest that the lines are generated by an atmospheric solitary wave packet characterized by decreases in amplitudes and wavelengths from the front to the rear these features are comparable with the dnoidal soliton solution to the korteweg de vries kdv equation the land breeze and katabatic flow are proposed as a possible generation mechanism

geochemistry of trace elements and their relations with organic matter in kuh e sefid phosphorite mineralization zagros mountain iran abstract the kuh e sefid phosphorite is located in zagros fold thrust belt in the ramhormoz area northeast of khuzestan province phosphorite mineralization occurred as phosphorite lenses of eocene age hosted by the pabdeh formation the aim of this study is to investigate the role of organic matter in trace metal portioning during phosphorite mineralization in the kuh e sefid deposit field observations and petrographic studies indicate that the host rock of mineralization is mainly consists of shale marl and limestone with textures varying from wackestone to packestone phosphoritic components such as authigenic apatite pellets intraclasts fish skeletal fragments and micro fossils are present moreover non phosphorite minerals including calcite glauconite pyrite iron oxide and to a lesser extend montmorillonite with microcrystalline quartz occurred in phosphorite lenses nasc normalized patterns of rees showed the enrichment of heavy rare earth elements hree and negative ce anomaly with co existence of slightly negative and positive eu anomalies represent a transitional change from oxic to anoxic sedimentation conditions during mineralization importantly ni co versus v cr ratios and v v ni diagrams confirmed dysoxic to anoxic conditions for the hydrocarbon bearing phosphorite and hosted shales while non hydrocarbon bearing phosphorites exhibit oxic conditions the ftir studies revealed qualitative information about the component bonds and nature of the organic matter and mineral organic bonds like oh carboxylic oh carboxylic acid c o c c alkaline group ch2 c c aromatic ch aliphatic and aromatic stretching associated with phosphate mineralization it seems that there is a link between a relatively high concentration of trace metals i e rees u co zn ni v sr and mo and phosphorites enriched in organic matter especially those of aromatic hydrocarbon groups

mesoscale structure in the megalopolitan snowstorm of 11 12 february 1983 part iii a large amplitude gravity wave abstract a large amplitude singular gravity wave is studied through the analysis of hourly observations radar and satellite data and observations of cloud to ground lightning flashes the wave activity was initiated just ahead of and to the left of the track of the major atlantic coast cyclone of 11 12 february 1983 the initial wave of depression was followed by a wave of elevation and finally a wake depression pressure amplitudes were several millibars the system propagated northeastward at 15 m s 1 accelerating to more than 25 m s 1 against increasing northeasterly flow in the lower troposphere surface northeasterlies increased and became gusty with the approach of the first pressure falls reaching a maximum at the pressure trough then abruptly weakening and backing as strong pressure increases were observed strong fluctuations in column total condensation rate and radar reflectivity occurred with the passage of the wave clustered lightning activity accompanied wave passage principally near

dike hosted ores of the beast deposit and the importance of eocene magmatism in gold mineralization of the carlin trend nevada a reply we appreciate the comments of g d langstaff and the opportunity to elaborate on the origin of carlin type gold deposits langstaff focuses on two of the critical issues regarding these deposits their age and spatial association with igneous rocks although his comment mentions almost every known carlin type deposit our reply focuses on deposits in major districts direct dating of hydrothermal minerals and indirect dating based on crosscutting relations with pre syn or postmineral rocks in nevada have demonstrated that major deposits in all trends are eocene emsbo et al 1996 leonardson and rahn 1996 phinisey et al 1996 groff et al 1997 hall et al 1997 2000 hofstra et al 1999 hofstra and cline 2000 johnston 2000 ressel et al 2000a b tretbar et al 2000 although many carlin type deposits are not dated we emphasize that no deposit has been demonstrated to be any other age preliminary 40ar 39ar dating of white micas from mineralized eocene dikes at meikle and griffin in the carlin trend gives eocene ages ressel et al 2000b any discussion of the origin especially spatial association of carlin type deposits with igneous rocks must emphasize the northern and central carlin trend fig 1 deposits there constitute 60 percent of the total estimated contained gold in carlin type deposits of nevada and utah hofstra and cline 2000 we interpreted the 700 km2 aeromagnetic anomaly fig 1 there to reflect an underlying composite eocene intrusion emplaced between about 40

the tuscarora au ag district eocene volcanic hosted epithermal deposits in the carlin gold region nevada the tuscarora mining district contains the oldest and the only productive eocene epithermal deposits in nevada the district is a particularly clear example of association of low sulfidation deposits with igneous activity and structure and it is unusual in that it consists of two adjoining but physically and chemically distinct types of low sulfidation deposits moreover tuscarora deposits are of interest because they formed contemporaneously with nearby giant carlin type gold deposits the tuscarora deposits formed within the 39 9 to 39 3 ma tuscarora volcanic field along and just outside the southeastern margin of the caldera like mount blitzen volcanic center both deposit types formed at 39 3 ma contemporaneous with the only major intrusive activity in the volcanic field no deposits are known to have formed during any of the intense volcanic phases of the field intrusions were the apparent heat source and structures related to the mount blitzen center were conduits for hydrothermal circulation the ore forming fluids interacted dominantly with eocene igneous rocks the two deposit types occur in a northern silver rich zone that is characterized by relatively high ag au ratios 110 150 narrow alteration zones and quartz and carbonate veins developed mostly in intrusive dacite and in a southern gold rich zone that is typified by relatively low ag au ratios 4 14 more widespread alteration and quartz fissure and stockwork veins commonly developed in tuffaceous sedimentary rocks the deposit types have similar fluid inclusion and pb and s isotope characteristics but different geochemical signatures quartz veins from both zones have similar thermal and paragenetic histories and contain fluid inclusions that indicate that fluids cooled from between 260 and 230 c to less than 200 c fluid boiling may have contributed to precious metal deposition veins in both zones have relatively high as and sb and low bi te and w the silver zone has high ca pb mn zn cd tl and se the gold zone has high hg and mo a few samples from an area of overlap between the two zones share chemical characteristics of both deposit types the deposit types could represent a single zoned or evolving system in which hydrothermal fluids rose along structures within the silver zone preferentially deposited ag and base metals and then spread into the gold zone alternatively the deposit types could represent two distinct but temporally indistinguishable hydrothermal cells that only narrowly overlapped spatially as noted in previous studies the hydrothermal fluids that generated the tuscarora and other epithermal deposits could have evolved from carlin type fluids by boiling and mixing with meteoric water if so the tuscarora deposit may represent epithermal conditions above carlin type deposits and carlin type deposits may lie beneath the district

wave cloud lines over the arabian sea meteosat visible satellite images between 2006 and 2011 show wave cloud lines over the arabian sea in all months outside the summer monsoon june september these lines are most frequent between january and may 2 3 per month in a given year all wave cloud lines in the region propagate offshore as these wave cloud lines are associated with coherent convergence lines the objective technique described by berry and reeder is applied to the era interim reanalysis and a climatology of convergence lines at 850 hpa developed despite the coarse resolution of the era interim reanalysis the statistical properties of these lines are broadly constant with those deduced from the meteosat visible satellite images the generation mechanism is investigated in a simulation with the met office unified model of a particular wave cloud line 12 march 2011 the process appears to be similar to that over northwestern australia which has been documented previously during the day a synoptic scale northeasterly flow opposes the inland advection of the sea breeze on the west coast of india however as the daytime turbulence decays and the boundary layer stabilizes the northeasterly flow accelerates pushing offshore the leading edge of the sea breeze during the late evening and early hours of the morning a wave is generated as the northeasterlies penetrate the marine boundary layer and this wave propagates westward producing cloud at its leading edge where there is strong ascent

a mesoscale gravity wave event observed during ccope i multiscale statistical analysis of wave characteristics abstract this paper is the first in a series of three papers concerning a gravity wave event that occurred over the north central united states on 11 12 july 1981 the event is analyzed with superb detail resulting from the availability of digitized radar surface mesonetwork and other special data from the cooperative convective precipitation experiment ccope in montana the subject matter of this paper consists of 1 a statistical determination of the wave characteristics 2 a demonstration that the observed phenomena display a nature consistent with that of gravity waves and 3 a discussion of the principles and limitations of statistical methods for detecting and tracking mesoscale gravity waves two distinct wave episodes of 8 h duration within a longer 33 h period of wave activity are studied in detail both episodes contain strongly coherent bimodal wave activity the primary secondary wave mode isolated from autospectral and perturbation map analyses displays mean periods of 2 5 0 9 h

source of iron for sulfidation and gold deposition twin creeks carlin type deposit nevada this study was undertaken to determine the source of iron in comus formation sedimentary rocks that were sulfidized during deposition of gold in the megapit area of the twin creeks carlin type deposit sedimentary rocks in and near the megapit contain ferroan dolomite largely as overgrowths on iron poor dolomite iron to form these overgrowths appears to have been released from mafic volcanic rocks that are interlayered with the sedimentary rocks these igneous rocks have undergone two stages of hydrothermal alteration the first stage involved formation of albite and iron rich chlorite possibly caused by interaction with seawater the second stage involved destruction of the iron rich chlorite by illite or sericite which released iron to form ferroan dolomite in the sedimentary rocks comparisons show that transfer of iron from the igneous rocks to the sedimentary rocks can account for the present distributions of iron in these rocks relative to basalts comus formation igneous rocks are enriched in iron and potassium these results suggest that ferroan dolomite in sedimentary rocks is not solely a product of diagenetic processes and can form when iron is released from adjacent iron bearing igneous rocks recognition of this additional mechanism for formation of ferroan dolomite expands the range of geologic settings that can be favorable for formation of gold deposits formed by sulfidation

data for distinguishing generations of quartz and a distinct gas signature of deep high grade carlin type gold mineralization using quadrupole mass spectrometry abstract carlin type gold deposits in north central nevada occur in a region that was the locus of igneous and or hydrothermal activity over time and the overprinting of silicification associated with metamorphism base metal mineralization barren jasperoid and post ore alteration hinders exploration efforts therefore the potential to distinguish unrelated generations of quartz using the results of quadrupole mass spectrometer qms gas analyses was evaluated for the getchell trend and compared to results from the goldstrike property in the carlin trend and a carlin type gold occurrence in the huijiabao trend china the results of fluid inclusion petrography qms analyses and interpretation of gas data using n 2 ar he ternary diagrams and co 2 ch 4 vs n 2 ar plots indicate that different generations of quartz in the getchell trend were deposited by hydrothermal fluids having distinct characteristics metamorphic quartz containing one phase ch 4 and halite bearing liquid water dominant vapor poor inclusions has the highest gas content 37 6 mol and highest n 2 ar values 3250 which are suggestive of an evolved magmatic fluid pre ore and quartz base metal veins contain co 2 bearing inclusions base metal veins have n 2 ar values 675 and a positive correlation between h 2 s ar vs n 2 ar that is suggestive of a magmatic fluid carlin type quartz contains liquid dominant vapor poor inclusions and is characterized by total gas contents 10 mol and n 2 ar values 300 that are suggestive of mixed crustal meteoric magmatic fluid sources post ore quartz and barren jasperoid formed from mixtures of gas poor meteoric water and crustal fluids samples of deep high grade mineralization from the goldstrike property have total gas contents up to 10 5 mol and n 2 ar values 300 fluid sources include crustal meteoric and magmatic gas data from the goldstrike property turquoise ridge deposit and metamorphic quartz of the getchell trend plot near the n 2 apex of n 2 ar he diagrams which is indicative of a magmatic fluid end member carlin type mineralization in the huijiabao trend is unique because fluids were ch 4 rich and there is a correlation between ch 4 and hydrocarbons gas analyses commonly record 2 is the dominant gas specie together the results show that fluid inclusion gases can be used to distinguish different generations of quartz in mining districts with complex origins

a study of cyclone mesoscale structure with emphasis on a large amplitude inertia gravity wave abstract an analysis is presented of prominent mesoscale structure in a moderately intense cyclone with emphasis on a long lived large amplitude inertia gravity wave igw that moved through the northeastern united states on 4 january 1994 available national weather service wsr 88d doppler radar and wind profiler observations are employed to illustrate the rich time dependent three dimensional structure of the igw as the igw amplified peak crest to trough pressure falls exceeded 13 hpa 30 min 1 it also accelerated away from the cyclone reaching a peak forward speed of 35 40 m s 1 across eastern new england the igw was one of three prominent mesoscale features associated with the cyclone the others being a weak offshore precursor warm frontal wave and an onshore band of heavy snow snow bomb in which peak hourly snowfalls of 10 15 cm were observed none of these three prominent mesoscale features were well forecast by existing operational prediction models particularly with regard to preci

comparative study by infrared spectroscopy of the organic matter of phosphate rich oulad abdoun basin and black shale timahdit basin series morocco abstract fourier transform infrared spectroscopy has been used to get quantitative information on the oxidation state of the organic matter of stable residues extracted from strata of the phosphate rich basin of oulad abdoun and from oil shales of the timahdit basin morocco throughout the respective filling of both basins the redox conditions have been more oxidizing in the top part of the sediments in oulad abdoun basin than in the timahdit basin this is interpreted as the result of the sedictural evolution of the basin oulad abdoun basin having evolved in stable platform conditions while the timahdit basin evolved in subsiding ones the phosphate rich beds contain the more oxidized organic stable residues sedimentological evidence shows that the oxidation was associated reworking processes these processes are responsible for the progressive concentration of the phosphatic grains and prove to be necessary for the p 2 o 5 content to become higher than 10 this value being the highest encountered in the sediment within which the phosphatic grains form

timing of gold and arsenic sulfide mineral deposition at the getchell carlin type gold deposit north central nevada pregold mineralization at the getchell carlin type gold deposit includes quartz and base metal vein mineralization associated with intrusion of a cretaceous granodiorite stock the veins contain minor pyrite and trace chalcopyrite arsenopyrite galena and sphalerite the pyrite is moderately coarse and in thin section has high relief is well polished and is fractured and locally cemented by the gold ore assemblage white micas are associated with veins near the granodiorite intrusion gold was not observed or detected by fire assay analyses of samples or electron microprobe analyses of pyrites microprobe analyses show that pregold pyrites have near stoichiometric compositions variable low arsenic is present in pyrite in samples overprinted by gold mineralization secondary ion mass spectrometry sims analyses detected trace gold in the coarse near stoichiometric pyrite in overprinted samples the pregold vein assemblage was fractured and cemented by gold ore stage mineralization the gold ore stage assemblage consists of gold and arsenic enriched pyrite and marcasite encompassed by jasperoid and drusy quartz and local late fluorite orpiment and galkhaite the consistent spatial association of jasperoid and ore pyrite reflects their near contemporaneous formation the ore pyrite occurs as either fine irregularly shaped grains or rims on earlier gold free pyrite in thin section the pyrite is visibly distinct and has a low polishing relief and a poor polish sims and electron microprobe analyses show that ore pyrites commonly contain 8 to 11 wt percent arsenic and as much as 2 400 ppm gold near the end of the ore stage fluorite orpiment and galkhaite precipitated locally in open space created by faulting or limestone dissolution late ore stage mineralization consists dominantly of open space filling realgar and calcite with minor quartz stibnite and framboidal pyrite realgar conforms to euhedral crystal faces of ore stage quartz fluorite and galkhaite calcite filled most remaining open space and conforms to euhedral crystal faces of quartz fluorite and realgar significant textural observations argue against an earlier interpretation that the gold mineralization and arsenic minerals formed as two discrete events separated by 40 m y in a few areas where calcite and realgar are in contact with ore stage quartz containing gold bearing pyrite realgar and calcite enclose gold bearing pyrite grains massive realgar and calcite distal from these contacts do not contain the gold bearing pyrite the presence of ore pyrite in realgar calcite and jasperoid requires close timing of these minerals and shows that there is no major time break separating ore stage and late ore stage mineral deposition textures indicate instead that the ore stage and late ore stage formed as part of a single evolving hydrothermal system the consistent successive overgrowth of younger minerals on perfectly preserved euhedral faces of older minerals supports the continuous evolution of the gold ore stage into the late ore stage these results are consistent with fluid inclusions that indicate that paragenetically successive minerals precipitated from an aqueous ore fluid with consistent salinity and gas contents but at declining temperatures results show that within error the 34 39 and 42 ma ages determined for fluorite and galkhaite at getchell and adularia at the nearby twin creeks mine respectively most closely approximate the timing of gold deposition at getchell

abrupt cloud clearing of marine stratocumulus in the subtropical southeast atlantic we document rapid and abrupt clearings of large portions of the subtropical marine low cloud deck that have implications for the global radiation balance and climate sensitivity over the southeast atlantic large areas of stratocumulus are quickly eroded yielding partial or complete clearing along sharp transitions hundreds to thousands of kilometers in length that move westward at 8 to 12 meters per second and travel as far as 1000 kilometers from the african coast the westward moving cloudiness reductions have an annual peak in occurrence in the period from april through june the cloud erosion boundaries reduce cloud at 10 kilometer scale in less than 15 minutes move approximately perpendicular to the mean flow and are often accompanied by small scale wave features observations suggest that the cloud erosion is caused by atmospheric gravity waves

precipitation associated with convergence lines precipitation is often organized along coherent lines of low level convergence which at longer time and space scales form well known convergence zones over the world s oceans here an automated objective method is used to identify instantaneous low level convergence lines in reanalysis data and calculate their frequency for the period 1979 2013 identified convergence lines are combined with precipitation observations to assess the extent to which precipitation around the globe is associated with convergence lines in the lower troposphere it is shown that a large percentage of precipitation between 65 and 90 over the tropical oceans is associated with such convergence lines with large regional variations of up to 30 throughout the year especially in the eastern pacific and atlantic oceans over land the annual mean proportion of precipitation associated with convergence lines ranges between 30 and 60 and the lowest proportions less than 15 associated with convergence lines occur on the eastern flank of the subtropical highs overall much greater precipitation is associated with long coherent lines greater than 300 km in length than with shorter fragmented lines less than 300 km and the majority of precipitation associated with shorter lines occurs over land the proportion of precipitation not associated with any convergence line primarily occurs where both precipitation and frequency of convergence lines are low the high temporal and spatial resolution of the climatology constructed also enables an examination of the diurnal cycle in the relationship between convergence lines and precipitation here an example is provided over the tropical maritime continent region

stable isotopic characterisation of francolite formation stable isotopic data are presented for 112 samples of francolite from 18 separate phosphate deposits values of 13c and 34s in most offshore deposits suggest formation within oxic or suboxic environments either by carbonate replacement or direct precipitation of francolite from water of normal marine compositions the exceptions are concretionary francolite from namibia which has an isotopic composition in keeping with its formation within organic rich sediments and that from offshore morocco which has an isotopic signature of the anoxic suboxic interface onshore deposits from jordan mexico south africa and possibly the permian phosphoria formation in the western u s a are substantially depleted in18o they appear to be too altered for deductions to be made about their environments of formation in other onshore deposits which are unaltered or minimally altered the isotopic composition suggests that some formed within sulphate reducing sediments sedhura morocco whilst francolite from the georgina basin of australia formed at the oxic anoxic boundary where oxidation of biogenic h2s decreases the 34s of pore water in general pelletal samples show non oxic isotopic signatures whilst non pelletal samples show oxic isotopic signatures but samples from namibia peru ica plateau and the californian and moroccan margins are exceptions to this rule morphology may therefore be a misleading indicator of francolite genesis as no definitive relation exists between phosphorite type and isotopic signature

organic matter accumulation and preservation controls in a deep sea modern environment an example from namibian slope sediments the luderitz upwelling cell is presently the most productive area of the benguela current system and abundant organic matter om accumulates on the adjacent slope sediments even at great water depth om from two cores taken on the slope and covering the last 280 kyear was analysed in terms of petroleum quality rock eval chemical features ftir eds and petrographic composition light microscopy and tem these data indicate that the om is more oxidized at 3606 m water depth than on the upper slope sediments 1029 m although the petroleum quality of the om throughout the deep water core remains surprisingly high for hemipelagic deep sea sediments hi 200 400 mg g the petroleum quality of om accumulated on the upper slope is consistently high hi averages 450 mg g two petrographic types of om are distinguishable from microscopic observation each ascribed to distinctive preservation mechanisms 1 granular amorphous om which dominates in the deep water core is formed by organo mineral aggregates aggregation appears to be the primary preservation mode at this depth although is quantitatively limited maximum toc value of 4 wt of bulk sediment obtained through this process the ultrastructure of the aggregates highlights an intimate association pattern between sedimentary om and clays 2 gel like nannoscopically amorphous om naom largely dominates at 1000 m water depth and contains sulfur thus early diagenetic sulfurization was probably involved in the preservation of this om but a contribution from the classical degradation recondensation pathway cannot be ruled out moreover selective preservation occurred at both sites but represents an insignificant part of the om organic fluxes mainly control the occurrence and extent of sulfurisation at both water depths by determining the redox conditions at the sea floor aggregate formation is limited by both organic and mineral fluxes at the lower slope whereas om supply is never limiting on the upper slope although consistently operating through time at both depths preservation by organo mineral association is limited by mineral availability and thus accounts for a relatively minor portion of the om accumulated on this organic rich slope in the case of large organic fluxes sulfurisation and or degradation recondensation is required to obtain toc contents above 4 wt of bulk sediment in the area

the morning glory of the gulf of carpentaria an atmospheric undular bore abstract this paper presents the results of a field expedition mounted in late september early october 1979 to investigate the structure and origin of the morning glory of the gulf of carpentaria in northern australia the morning glory is a line wind squall accompanied by a pressure jump and often by a long roll cloud or series of such clouds it frequently occurs in the early morning especially in october in the gulf area a light aircraft fitted with a temperature and humidity probe was flown in two glories to determine their thermodynamic structure and wind fields wore obtained principally by tracking pilot balloons using the double theodolite method data also were obtained from a network of surface stations recording wind velocity and pressure installed at locations across cape york peninsula which is believed to be the area of genesis the morning glory is identified as an internal undular bore propagating on the nocturnal and or maritime inversion its origin appears to lie frequently

depositional environments of the senonian chert phosphorite and oil shale sequence in israel as deduced from their organic matter composition in the upper cretaceous sequence of the negev southern israel the organic matter in phosphorites and cherts differs from that associated with oil shales in its higher content of humic substances and lower kerogen content and in its more intensive microbial alteration the n alkane distribution pattern of the oil shales phosphorites and cherts indicates that marine biota probably algae are the main organic precursors of their organic matter in some of the oil shales however some contribution of terrestrial organic matter is also evident similar high phytane pristane ratios indicate that the organic matter in the oil shales as well as in the phosphorites and cherts accumulated under reducing conditions the main differences in the organic matter composition are attributed to early diagenetic processes rather than to different biotic precursors or to late modifications due to temperature induced maturation the depositional model suggested for the sequence involves upwelling conditions at the boundary between the deep tethys and the shallow shelf which induced high organic productivity deep into the inner shelf bottom water circulation enabled intensive microbial alteration of the organic matter followed by a winnowing process leading to phosphorite formation since humification is considered an oxygen consuming reaction these processes favoured the formation of oxygen enriched humic substances and the oxidation of humic substances already present these humic substances are relatively resistant to further alteration and their conversion into kerogen is thus retarded subsequently syndepositional tectonic activity resulted in the introduction of less saline water restriction of bottom water circulation and the establishment of a density stratification in the water body consequently aeration of the bottom layer and the sediments was inhibited microbial alteration was reduced and later winnowing processes were prevented such conditions favoured the formation of kerogen directly rather than through humic substances and also favoured the preservation of most of the organic matter in the form of oil shale deposits instead of phosphorites

geochemical study of organic matter rich cycles from the kimmeridge clay formation of yorkshire uk productivity versus anoxia abstract in this contribution we study two meter scale cycles from the kimmeridge clay formation cored near marton yorkshire which shows cyclic organic matter om distribution our aim is to try to understand the factors responsile for om accumulation the first cycle called lower cycle shows a total organic carbon toc content between 1 and 10 whereas the second called upper cycle shows a toc content varying between 5 and 35 the geochemical composition major elements and trace elements the organic geochemistry toc hi palynofacies and mineralogy of the sediments have been determined in both cycles the cyclicity is expressed through variations in the nature and in the relative abundance of the various types of organic matter constituents furthermore dilution effects by inorganic components of the sediment cannot account for the toc cyclicity for lower cycle the mo v and u content is low and little variable as is the intensity of the oxidation which om suffered from this indicates that variations in phytoplanktonic productivity may be held responsible for the cyclicity in steady and mildly reducing redox conditions in the upper cycle cyclicity also appears to depend on productivity but variations in the concentration of mo v and u and in the oxidation state of the om suggest the environment was temporarily more reducing it is proposed that larger amounts of h 2 s were released into marine bottom waters as a result of initial om decomposition forced the oxic anoxic boundary to rise in the water column and thus favoured om storage the main driving force for variations in the om concentration was the productivity of organic matter walled phytoplankton redox conditions of the depositional environment could have had a positive action but only by acting as a positive feedback effect

evaluation of radioisotope dating of carlin type deposits in the great basin western north america and implications for deposit genesis a variety of techniques have been used in attempts to date the mineralization in carlin type deposits in the great basin with highly variable results these techniques and results are reviewed in this paper along with presentation of two new dates for the rodeo deposit on the carlin trend and for the barneys canyon deposit in utah complete resetting of sericite by hydrothermal fluids of the temperature and duration of hydrothermal activity that form carlin type deposits is considered highly unlikely therefore dates from sericite are generally of questionable value unless that sericite can be shown to have formed during the same hydrothermal event during which au was deposited for the deposits that have been investigated to date sericite dates rarely if ever record the age of au mineralization however sericite ages do appear to record pre au events in some districts such events may have contributed to ground preparation and to a much lesser extent to the tenor of the ore fission track and u th he techniques provide important age constraints on mineralization in some districts but also suffer from a less than clear association with au rb sr dating of galkhaite an hg sulfosalt provides the only direct age of mineralization but galkhaite has been recognized in only a few locations and dated in only two deposits in a similar manner adularia is contemporaneous with au at twin creeks but twin creeks is the only carlin type deposit where adularia has been reported several other techniques u pb reos sm nd have been used in attempts to date the deposits but with limited success the best available ages are those from preore and postore igneous events and those from galkhaite galkhaite from getchell indicates a mineralization age of 39 ma and that from rodeo carlin trend indicates a mineralization age of 40 ma a new u th he age 34 ma for apatite at barneys canyon suggests contemporaneity with the nearby bingham porphyry cu system the most reliable data from several deposits and districts in the great basin indicate that carlin type mineralization occurred in a relatively narrow time interval between 33 and 42 ma this interval coincides with the transition from a compressional to an extensional tectonic environment in the region although similar tectonic environments have existed at different times and places in western north america no other carlin type mineralization is known to exist in the region therefore although the age and tectonic environment of these deposits is now reasonably well constrained it is clear that tectonic environment alone is insufficient to explain the genesis of carlin type deposits additional perhaps unique factors such as host rock geochemistry must have contributed to the development of these exceptional deposits

40 ar 39 ar and k ar geochronology of magmatic and hydrothermal events in a classic low suphidation epithermal bonanza deposit el penon northern chile the epithermal el penon gold silver deposit consists of quartz adularia veins emplaced within a late upper paleocene rhyolitic dome complex located in the paleocene lower eocene au ag belt of northern chile detailed k ar and 40ar 39ar geochronology on volcano plutonic rocks and hydrothermal minerals were carried out to constrain magmatic and hydrothermal events the paleocene to lower eocene magmatism in the el penon area is confined to a rhomb shaped basin which was controlled by n s trending normal faults and both ne and nw trending transtensional fault systems the earliest products of the basin filling sequences comprise of middle to upper paleocene 59 55 ma welded rhyolitic ignimbrites and andesitic to dacitic lavas with occasional dacitic dome complexes later rhyolitic and dacitic dome complexes 55 52 ma represent the waning stages of volcanism during the latest upper paleocene and the earliest eocene lower eocene porphyry intrusives 48 43 ma mark the end of the magmatism in the basin and a change to a compressive tectonomagmatic regime 40ar 39ar geochronology of hydrothermal adularia from the el penon deposit yields ages between 51 0 0 6 and 53 1 0 5 ma these results suggest that mineralization occurred slightly after the emplacement of the el penon rhyolitic dome at 54 5 0 6 ma 40ar 39ar age and was closely tied to later dacitic rhyodacitic bodies of 52 to 53 ma k ar ages probably as short lived pulses related to single volcanic events

gregarious tropical convection abstract a beat source with a vertical profile like that of observed tropical mesoscale convective systems mcss is shown to cause through inviscid gravity wave dynamics upward displacement at low levels in a mesoscale region surrounding the heating typical values are 10 30 area contraction at the surface everywhere within 270 km of the heating 6 h after it starts as a result conditions near an existing mcs but beyond the area of mcs outflow become more favorable for the development of additional convection this theory predicts that cloud clusters should be gregarious infrared satellite imagery confirms that almost half of the cold cloudiness observed in a month over the oceanic warm pool region was contributed by just 14 objectively defined multiday supercluters

the generation of the morning glory abstract a high resolution cloud model is used to explore in detail the generation of the morning glory a low level nonlinear atmospheric internal wave observed on the southwestern side of cape york peninsula australia the model is two dimensional and nonhydrostatic and simulates an east west cross section of the southern part of cape york peninsula at a horizontal resolution of 200 m most of the numerical experiments are initialized at sunrise with a 5 m s 1 easterly flow and a sounding taken upstream from the peninsula the sea breezes that develop over cape york peninsula are highly asymmetric with the east coast sea breeze being both deeper and warmer than its western counterpart when the sea breezes meet the east coast sea breeze rides over that from the west coast and in the process produces a series of waves that propagate on the west coast sea breeze the model calculations show that when the phase speed of these waves matches the westward propagation speed of the east coast sea breeze the

re os isochron ages for arsenopyrite from carlin like gold deposits in the yunnan guizhou guangxi golden triangle southwestern china abstract the yunnan guizhou guangxi golden triangle is considered to be one of the regions hosting carlin like gold deposits in china gold deposits in this region can be grouped into lode type that are controlled by faults and layer like type controlled by stratigraphy arsenopyrite is one of the major gold bearing minerals in these deposits rhenium os isotopic dating of arsenopyrite from the lode type lannigou and jinya and the layer like type shuiyindong gold deposits yields isochron ages of 204 19 ma 206 22 ma and 235 33 ma respectively the data suggest that the carlin like gold deposits formed in late triassic to early jurassic which is clearly earlier than the ca 100 80 ma acid to ultra basic magmatism in this part of southwestern china the ages are consistent with ore formation during a period of post collisional lateral transpression which is similar to that of the carlin like gold deposits in western qinling of china but quite different from carlin type gold deposits in nevada u s a

calcite sm nd isochron age of 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 it is hosted in permian bioclastic limestone near the axis of an anticline hydrothermal calcite is common on the periphery of central zones of ferroan carbonate dissolution that provided the main source of iron that was sulfidized during gold deposition these calcite veins contain relatively high concentrations of rare earth elements with mree enriched patterns and yield sm nd isochron ages of 134 3 ma to 136 3 ma with significant different initial end values of 12 9 and 2 0 respectively these ages are interpreted to record age of decarbonation and gold deposition during the late stages of yanshanian orogeny the initial nd isotopic compositions of the calcites suggest that nd was primarily derived from the permian longtang formation that hosts all ore bodies at the deposit this study shows that sm nd isotopic compositions of hydrothermal calcites can be used to constrain the age and source of nd in carlin type gold deposits

40 ar 39 ar dating and mineral paragenesis for carlin type gold deposits along the getchell trend nevada evidence for cretaceous and tertiary gold mineralization the orebodies at the getchell and twin creeks mines were studied through mineral paragenesis geologic relationships and 40 ar 39 ar dating mineral paragenetic relationships are based on observations made during the logging of 18 000 m of drill cuttings and core and crosscutting relationships recognized in the field and main pit at the getchell mine ages for igneous and mineralizing events were determined through 40 ar 39 ar incremental heating analyses of 15 samples of biotite k feldspar sericite and vein adularia a thermal history for the area was also developed using k feldspar multiple diffusion domain results and age determinations on cogenetic minerals which have different argon closure temperatures mineral paragenetic relationships and 40 ar 39 ar dating at the getchell and twin creeks deposits document that gold mineralization occurred in five stages between 95 and 42 ma stage 1 pyrrhotite quartz arsenopyrite chalcopyrite biotite gold mineralization in skarn is associated with 95 ma dacite dikes and granodiorite plugs stage 2 chalcopyrite sphalerite galena pyrite arsenopyrite or gold and silver mineralization in skarn is related to the 92 ma osgood mountains stock secondary k feldspar and sericite in stage 3 quartz pyrite kaolinite gold mineralization formed at 83 ma and are not related to 95 or 92 ma igneous activity stage 4 low grade quartz pyrite gold mineralization formed at about 75 ma in the matrix of a breccia pipe that cuts 83 ma silicic and argillic ores adularia intergrown with stibnite orpiment pyrite quartz gold or realgar mineralization yields precise 40 ar 39 ar plateau ages of 42 11 or 0 43 and 41 90 or 0 25 ma for stage 5 this study documents the temporal complexity of mineralization and igneous activity at the getchell and twin creeks deposits minor gold in skarn type mineralization stages 1 and 2 associated with 95 and 92 ma igneous intrusions preceded and was not genetically related to carlin type gold mineralization stages 3 and 5 the carlin type deposits at getchell and twin creeks therefore represent a composite orebody formed by the overprinting of 83 ma stage 3 quartz pyrite gold by 42 ma stage 5 orpiment stibnite pyrite gold mineralization

fluid mixing during late stage carlin type mineralization in the getchell and twin creeks deposits nevada abstract a stable isotope study of orpiment realgar calcite stibnite mineralization in the getchell and twin creeks deposits nevada was undertaken to determine the origin s of late stage fluids samples of orpiment have d values of 48 4 to 90 5 and 34s values of 0 3 2 2 which are indicative of a magmatic source whereas samples of realgar have d values of 129 1 to 139 7 that are indicative of meteoric water and 34s values of 4 2 4 9 similar to pre ore diagenetic pyrite the d and 13c data of calcite plot to form a mixing trend between fluids with magmatic and meteoric sources fluid mixing and wall rock interaction is supported by the distribution of data in a d and 18oh2o plot for calcite additional evidence of fluid mixing is provided by d values of 55 4 to 137 9 for stibnite these data document how a magmatic fluid produced orpiment au mineralization fluid mixing occurred during calcite deposition and barren realgar formed from a meteoric water