statistical probability distribution of snow depth at the model sub grid cell spatial scale comprehensive snow depth data collected using georadar and hand probing were used for statistical analyses of snow depths inside 1 km grid cells the sub grid cell spatial scale was 100 m statistical distribution functions were found to have varying parameters and an attempt was made to connect these statistical parameters to different terrain variables the results showed that the two parameters mean and standard deviation of snow depth were significantly related to the sub grid terrain characteristics linear regression models could explain up to 50 of the variation for both of the snowcover parameters mentioned copyright 2004 john wiley sons ltd

winds of neptune voyager observations of cloud motions high temporal and spatial resolution images acquired from voyager cameras have been used to measure cloud motions to improve the meridional profile of the zonal mean circulation on neptune a wide range of atmospheric periods between 12 and 21 hours is revealed by the average cloud motions consistent with the previous observations new observations have expanded latitudinal coverage improved the determination of streak motions especially near 30 n and added statistical weight to latitudes already covered by previous measurements both new and earlier observations have been subjected to quality control procedures to reduce dispersion caused by erroneous observations the resulting data set emphasizes short time intervals to maximize target recognition most reliable cloud targets last less than one neptune rotation many only a fraction of it a broad equatorial retrograde jet extends from approximately 50 s to at least 45 n the northernmost latitude at which discrete cloud features have been seen a relatively narrow prograde jet of at least 300 m s 1 is found near 70 s the wind observations have a high degree of variability some of which is due to variability of motions but at many latitudes it reflects observation errors arising from rapid evolution of neptune s clouds a bias observed in the measured meridional component is most likely due to a small discrepancy between the true rotation pole of neptune and the pole position used in the data reduction zonal motions and morphology suggest the global circulation to be symmetric about the equator

persistence in intra annual snow depth distribution 1 measurements and topographic control 1 terrestrial and airborne laser scanning tls and als techniques have only recently developed to the point where they allow wide area measurements of snow distribution in varying terrain in this paper we present multiple tls measurements showing the snow depth development for a series of precipitation events we observe that the pattern of maximum accumulation is similar for the two years presented here correlation up to r 0 97 storms arriving from the northwest show persistent snow depth distributions and contribute most to the final accumulation pattern snow depth patterns of maximum accumulation for the two years are more similar than the distribution created by any two pairs of individual storms based on the strong link between accumulation patterns and terrain we investigated the ability of a model based on terrain and wind direction to predict accumulation patterns this approach of winstral et al 2002 which describes wind exposure and shelter was able to predict the general accumulation pattern over scales of slopes but failed to match observed variance furthermore a high sensitivity to the local wind direction was demonstrated we suggest that winstral et al s model could form a useful tool for application from hydrology and avalanche risk assessment to glaciology

dynamics of neptune s major cloud features abstract we used voyager 2 images of neptune to investigate the dynamics of the great dark spot gds the scooter the second dark spot ds2 and the south polar features spf relative to previous studies we covered a longer time base achieved more complete sampling of the available data and improved accuracy by using stars to correct navigation errors we tracked the gds 8 day shape oscillation for more than 2000 hr measuring amplitudes of 7 4 in longitude and 1 5 in latitude we found a surprisingly large increase in the mean latitudinal size of the gds from 8 in january 1989 to 17 in august during the same period we measured steady gds northward motion from 26 s to 17 s and found no evidence of the latitudinal limits we confirmed that the varying longitudinal drift rates of the gds and ds2 were simple functions of latitude that approximately match the zonal wind profile measurements of at least three cycles of the periodic motions of the ds2 defined a 36 day period and amplitudes of 2 4 in latitude and 47 5 in longitude relative to its mean drift longitude we found that the bright core of the ds2 varied in step with the ds2 latitudinal oscillation reaching a maximum area when the ds2 was furthest north a large increase in relative core brightness at high phase angles is consistent with forward scattering cloud particles we measured one cycle of a scooter longitudinal oscillation of 20 about its mean drift position with a period of 120 days but the scooter s latitudinal motions are too small and of the wrong frequency to be consistent with an advective model of the zonal motions we found that the highly variable spf formation region has the same mean longitudinal drift rate as the ds2 but an offset of 180 in longitude and a 20 difference in latitude the apparent synchronization of these widely separated and dramatically different features is unexplained coupling to the deep interior is ruled out by the significant difference between the radio and cloud periods observed motions of all features are described by empirical models valid over the voyager time period comparisons of voyager results with groundbased observations did not lead to conclusive constraints on the long term dynamics although much of the data seem to be consistent with a 5 8 year oscillation in gds latitude

gold mineralization in the diadema shear belt northern brazil in the southern part of the state of part the mo notony of the amazon forest is broken by a series of roughly parallel east west to n 70 o w ridges these ridges often mark linear domains of strongly foliated silicified rocks which contrast with the fiat lying deeply weathered regions of low deformation gra nitic tonalitic terranes the diadema shear belt is one such lineament formed by the serra de diadema a ridge lying between the serra de carajts to the north and the serra das andorinhas to the south fig 1 both these ridges are also the topographical expres sion of major shear zones where intense brittle ductile shearing processes have taken place often accom panied by gold mineralization the diadema shear belt though roughly coincident with the sapucaia greenstone belt of hirata et al 1982 is formed by a complex array of conjugated shear zones which crosscut both the greenstone sequence and the ad joining granitic tonalitic terranes the marked area in the central part of the diadema shear belt fig 1 corresponds to the geologic outline of figure 2 comparison of both figures shows that the belt forms a structure showing a general n 50 o w trend in its central part conjugated with the re gional east west to n 70 o w fault zones the shear zones in the central part being branched into n 30 o w sets and transversed by late n 20 o to 45 o w fault

clouds and circulation on neptune implications of 1991 hst observations abstract images of neptune recorded by the hubble space telescope hst wide fields planetary camera in late 1991 provide a basis for the first significant comparison with the circulation results obtained from voyager 2 observations 2 years earlier the hst images using red f675w and methane band f889n filters contain isolated bright cloud features suitable for tracking atmospheric motions near planetocentric latitudes of 67 s 57 5 s 50 s 5 n and 27 n wind speeds inferred from the feature rotational periods are consistent with the latitudinal wind profile established by the 1989 voyager observations the latitudinal distribution of clouds also matches the voyager distribution reasonably well except for a notable lack of clouds between the equator and 40 s a region where the great dark spot gds and its companion cloud were observed in 1989 the 1991 hst images contain no cloud feature at any latitude with an integrated brightness comparable to the gds companion suggesting that the gds itself may not have survived its projected november 1990 arrival at neptune s equator

an analysis of snow cover patterns in a small alpine catchment snow cover patterns in a 9 4 km2 basin in the austrian alps are examined during spring and summer 1989 digital mono plotting from oblique aerophotographs is used for mapping on the basis of a square grid with 25 m spacing snow cover as mapped during nine surveys is analysed as a function of elevation and slope during winter conditions the snow cover is found to be much better related to these terrain features than during the late ablation period

the unusual dynamics of northern dark spots on neptune abstract hubble space telescope hst and ground based observations of neptune from 1991 to 2000 show that neptune s northern great dark spots ngds remained remarkably stable in latitude and longitudinal drift rate in marked contrast to the 1989 southern great dark spot gds which moved continuously equatorward during 1989 and dissipated unseen during 1990 ngds 32 discovered in october 1994 hst images h b hammel et al 1995 science268 1740 1742 stayed at 32 n from 1994 through at least 1996 and possibly through 2000 the second northern gds ngds 15 discovered in august 1996 hst images l a sromovsky et al 2001 icarus146 459 488 appears to have existed as early as 8 march 1996 and remained near 15 n for the 16 months over which it was observed ngds 32 had a very uniform longitudinal drift rate averaging 36 28 0 04 day from 10 october 1994 to 2 november 1995 and 35 84 0 02 day from 1 september 1995 through 24 november 1995 a single circulation feature certainly exists during each of the first two periods though it is not certain that it is the same feature it is probable but less certain that only a single circulation feature was tracked during the 1996 1998 period during which positions are consistent with a modulated drift rate averaging 35 401 0 001 day but with a peak to peak modulation of 1 5 day with an 760 day period if nds 32 varied its drift rate in accord with the local latitudinal shear in the zonal wind then all its drift rate changes might be due to only 0 4 of latitudinal motion the movement of ngds 15 is also not consistent with a uniform longitudinal drift rate but the nature of its variation cannot be estimated from the limited set of observations the relatively stable latitudinal positions of both northern dark spots are not consistent with current numerical model calculations treating them as anticyclonic vortices in a region of uniform potential vorticity gradient r p lebeau and t e dowling 1998 icarus132 239 265 possible explanations include unresolved latitudinal structure in the zonal wind background or unaccounted for variations in vertical stability structure

uranus at equinox cloud morphology and dynamics abstract as the 7 december 2007 equinox of uranus approached collaboration between ring and atmosphere observers in the summer and fall of 2007 produced a substantial collection of ground based observations using the 10 m keck telescope with adaptive optics and space based observations with the hubble space telescope both near infrared and visible wavelength imaging and spatially resolved near infrared spectroscopic observations were obtained we used observations spanning the period from 7 june 2007 through 9 september 2007 to identify and track cloud features determine atmospheric motions characterize cloud morphology and dynamics and define changes in atmospheric band structure atmospheric motions were obtained over a wider range of latitudes than previously was possible extending to 73 n and for 28 cloud features we obtained extremely high wind speed accuracy through extended tracking times we confirmed the existence of the suspected northern hemisphere prograde jet locating its peak near 58 n the new results confirm a small n s asymmetry in the zonal wind profile and the lack of any change in the southern hemisphere between 1986 near solstice and 2007 near equinox suggests that the asymmetry may be permanent rather than seasonally reversing in the 2007 images we found two prominent groups of discrete cloud features with very long lifetimes the one near 30 s has departed from its previous oscillatory motion and started a significant northward drift accompanied by substantial morphological changes the complex of features near 30 n remained at a nearly fixed latitude while exhibiting some characteristics of a dark spot accompanied by bright companion features smaller and less stable features were used to track cloud motions at other latitudes some of which lasted over many planet rotations though many could not be tracked beyond a single transit a bright band has developed near 45 n while the bright band near 45 s has begun to decline both events in agreement with the idea that the asymmetric band structure of uranus is a delayed response to solar forcing but with a surprisingly short delay of only a few years

high s n keck and gemini ao imaging of uranus during 2012 2014 new cloud patterns increasing activity and improved wind measurements abstract we imaged uranus in the near infrared from 2012 into 2014 using the keck nirc2 camera and gemini niri camera both with adaptive optics we obtained exceptional signal to noise ratios by averaging 8 16 individual exposures in a planet fixed coordinate system these noise reduced images revealed many low contrast discrete features and large scale cloud patterns not seen before including scalloped waveforms just south of the equator and an associated transverse ribbon wave near 6 s in all three years numerous small 600 700 km wide and mainly bright discrete features were seen within the north polar region north of about 55 n two small dark spots with bright companions were seen at middle latitudes over 850 wind measurements were made the vast majority of which were in the northern hemisphere winds at high latitudes were measured with great precision revealing an extended region of solid body rotation between 62 n and at least 83 n at a rate of 4 08 0 015 h westward relative to the planet s interior radio rotation of 20 88 h westward near equatorial speeds measured with high accuracy give different results for waves and small discrete features with eastward drift rates of 0 4 h and 0 1 h respectively the region of polar solid body rotation is a close match to the region of small scale polar cloud features suggesting a dynamical relationship the winds from prior years and those from 2012 2014 are consistent with a mainly symmetric wind profile up to middle latitudes with a small asymmetric component of 0 09 h peaking near 30 and about 60 greater amplitude if only prior years are included suggesting a declining mid latitude asymmetry while winds at high southern latitudes 50 90 s are unconstrained by groundbased observations a recent reanalysis of 1986 voyager 2 observations by karkoschka karkoschka 2015 icarus 250 294 307 has revealed an extremely large north south asymmetry in this region which might be seasonal greatly increased activity was seen in 2014 including the brightest ever feature seen in k images de pater et al 2015 icarus 252 121 128 as well as other significant features some of which had long lives over the 2012 2014 period we identified six persistent discrete features three were tracked for more than 2 years two more for more than 1 year and one for at least 5 months and continuing several drifted in latitude towards the equator and others appeared to exhibit latitudinal oscillations with long periods we found two pairs of long lived features that survived multiple passages within their own diameters of each other zonally averaged cloud patterns were found to persist over 2012 2014 when averaged over longitude there is a brightness variation with latitude from 55 n to the pole that is similar to effective methane mixing ratio variations with latitude derived from 2012 stis observations sromovsky et al 2014 icarus 238 137 155

fine scale modeling of the boundary layer wind field over steep topography 1 this paper describes the adaptation of wind fields to steep and complex terrain using fine scale numerical modeling the work is motivated by the need of high resolution flow fields to predict snow transport and snow cover development for avalanche warning purposes applying the nonhydrostatic and compressible atmospheric prediction model advanced regional prediction system arps to steep alpine topography the boundary layer flow was simulated and evaluated against measurements the adaptation of the wind field to steep terrain for specific initial and boundary conditions was simulated the topography used in our study has a length scale of 500 m a typical height of 150 m and maximum slopes of 45 numerical experiments with idealized triangular ridges were conducted to find an adequate model configuration this analysis indicates that a high resolution grid with horizontal spacing of at least 25 m and vertical spacing of 3 m near the surface is necessary to reproduce small scale flow features such as speed up separation and recirculation the onset of flow separation is highly sensitive to initial and boundary conditions slope angle and surface roughness the results of the comparison between the model simulations and measurements on our experimental site show that typical wind field characteristics are well reproduced the simulated wind fields have been used to drive a numerical three dimensional snow drift model which is presented in a companion paper by lehning et al 2008

topographic meteorologic and canopy controls on the scaling characteristics of the spatial distribution of snow depth fields 1 in this study lidar snow depths bare ground elevations topography and elevations filtered to the top of vegetation topography vegetation in five 1 km 2 areas are used to determine whether the spatial distribution of snow depth exhibits scale invariance and the control that vegetation topography and winds exert on such behavior the one dimensional and mean two dimensional power spectra of snow depth exhibit power law behavior in two frequency intervals separated by a scale break located between 7 m and 45 m the spectral exponents for the low frequency range vary between 0 1 and 1 2 for the one dimensional spectra and between 1 3 and 2 2 for the mean twodimensional power spectra the spectral exponents for the high frequency range vary between 3 3 and 3 6 for the one dimensional spectra and between 4 0 and 4 5 for the mean two dimensional spectra such spectral exponents indicate the existence of two distinct scaling regimes with significantly larger variations occurring in the larger scale regime similar bilinear power law spectra were obtained for the fields of vegetation height with crossover wavelengths between 7 m and 14 m further analysis of the snow depth and vegetation fields together with wind data support the conclusion that the break in the scaling behavior of snow depth is controlled by the scaling characteristics of the spatial distribution of vegetation height when snow redistribution by wind is minimal and canopy interception is dominant and by the interaction of winds with features such as surface concavities and vegetation when snow redistribution by wind is dominant

scaling properties and spatial organization of snow depth fields in sub alpine forest and alpine tundra this paper reports on a study analysing the spatial distribution functions the correlation structures and the power spectral densities of high resolution lidar snow depths 1 m in two adjacent 500 m 500 m areas in the colorado rocky mountains one a sub alpine forest the other an alpine tundra it is shown how and why differences in the controlling physical processes induced by variations in vegetation cover and wind patterns lead to the observed differences in spatial organization between the snow depth fields of these environments in the sub alpine forest area the mean of snow depth increases with elevation while its standard deviation remains uniform in the tundra subarea the mean of snow depth decreases with elevation while its standard deviation varies over a wide range the two dimensional correlations of snow depth in the forested area indicate little spatial memory and isotropic conditions while in the tundra they indicate a marked directional bias that is consistent with the predominant wind directions and the location of topographic ridges and depressions the power spectral densities exhibit a power law behaviour in two frequency intervals separated by a break located at a scale of around 12 m in the forested subarea and 65 m in the tundra subarea the spectral exponents obtained indicate that the snow depth fields are highly variable over scales larger than the scale break while highly correlated below based on the observations and on synthetic snow depth fields generated with one and two dimensional spectral techniques it is shown that the scale at which the break occurs increases with the separation distance between snow depth maxima in addition the breaks in the forested area coincide with those of the corresponding vegetation height field while in the tundra subarea they are displaced towards larger scales than those observed in the corresponding vegetation height field

a comparison of measurement methods terrestrial laser scanning tachymetry and snow probing for the determination of the spatial snow depth distribution on slopes determination of the spatial snow depth distribution is important in potential avalanche starting zones both for avalanche prediction and for the dimensioning of permanent protection measures knowledge of the spatial distribution of snow is needed in order to validate snow depths computed from snowpack and snowdrift models the inaccessibility of alpine terrain and the acute danger of avalanches complicate snow depth measurements e g when probes are used so the possibility of measuring the snowpack using terrestrial laser scanning tls was tested the results obtained were compared to those of tachymetry and manual snow probing laser measurements were taken using the long range laser profile measuring system riegl lpm i800ha the wavelength used by the laser was 0 9 mm near infrared the accuracy was typically within 30 mm the highest point resolution was 30 mm when measured from a distance of 100 m tachymetry measurements were carried out using leica tcrp1201 systems snowpack depths measured by the tachymeter were also used the datasets captured by tachymetry were used as reference models to compare the three different methods tls tachymetry and snow probing this is the first time that the accuracy of tls systems in snowy and alpine weather conditions has been quantified the relative accuracy between the three measurement methods is bounded by a maximum offset of 8 cm between tls and the tachymeter the standard deviation is 1 2 cm and between manual probing and tls it is up to 1 10 cm for maximum distances for the tls and tachymeter of 300 m

coordinated 1996 hst and irtf imaging of neptune and triton iii neptune s atmospheric circulation and cloud structure the first coordinated multispectral imaging of neptune and triton using both the hubble space telescope and the nasa infrared telescope facility in august 1996 l a sromovsky et al 149 416 434 435 458 provides new insights into neptune s atmospheric circulation and cloud structure from our 1996 data we derived cloud tracked winds for 18 features spanning latitudes from 61 s to 38 n finding generally close agreement with the smoothed 1989 voyager wind profile sromovsky et al 1993 icarus105 110 141 except for features associated with a northern great dark spot gds which moved with the spot rather than with the local mass flow providing another example of gds traveling companions in addition to finding a gds at 32 n thought to be the same one first seen in 1994 near the same latitude hammel et al 1995 science268 1740 1742 we also found a new kind of gds at 15 n which is unusual because of its low latitude and lack of a bright companion from blue images we determined that the dark cloud band near 60 s latitude is significantly nonaxisymmetric as was a similar band in 1989 voyager images both with a wavenumber one zonal structure and a 5 latitudinal variation we also identified a persistent pattern of clouds at 45 s which exhibit strong variations in brightness on yearly time scales using hst archived observations we determined cloud tracked winds for june and november 1994 and september 1995 confirming and extending the 1995 result of hammel and lockwood 1997 icarus129 466 481 that most winds agreed with the voyager profile a significant exception we found in november 1994 is the 100 m s meridional motion within the transient structure identified as the bright complex by h b hammel and g w lockwood 1997 icarus129 466 481 the integrated brightness of this group of gds traveling companions is sufficient to produce a hemispheric brightness asymmetry of 0 36 mag sromovsky et al 149 435 458 comparable to the 0 44 mag associated with the 1987 outburst maximum hammel et al 1992 icarus99 363 367 we determined spectral differences in cloud bands using complete global mosaics of 1996 imagery colocation of features in hst and groundbased near ir images enabled us to characterize spectral variations in discrete features from the visible to 2 4 m from which we estimated cloud heights for discrete bright features ranging from 60 to 230 mbars we found the equatorial atmosphere that is free of bright clouds to be very dark beyond 0 7 m from which we derived new upper bounds of 0 2 and 0 1 at 1 27 and 1 6 m respectively on the single scattering albedo of the putative 3 8 bar h2s cloud

uranus in 2003 zonal winds banded structure and discrete features abstract imaging of uranus in 2003 with the keck 10 m telescope reveals banded zonal structure and dozens of discrete cloud features at j and h bands several features in the northern hemisphere are also detectable at k by tracking features over four days we extend the zonal wind profile well into the northern hemisphere we report the first measurements of wind velocities at latitudes 13 19 and northward of 43 the first direct wind measurements near the equator and the highest wind velocity seen yet on uranus 218 m s at northern mid latitudes 20 to 40 the winds appear to have accelerated when compared to earlier hst and keck observations southern wind speeds 20 to 43 have not changed since voyager measurements in 1986 the equator of uranus exhibits a subtle wave structure indicated by diffuse patches roughly every 30 in longitude the largest discrete cloud features on uranus show complex structure extending over tens of degrees reminiscent of activity seen around neptune s great dark spot during the voyager encounter with that planet there is no sign of a northern polar collar as is seen in the south but a number of discrete features seen at the expected latitudes may signal the early stages of development of a northern collar

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

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

lidar measurement of snow depth a review laser altimetry lidar is a remote sensing technology that holds tremendous promise for mapping snow depth in snow hydrology and avalanche applications recently lidar has seen a dramatic widening of applications in the natural sciences resulting in technological improvements and an increase in the availability of both airborne and ground based sensors modern sensors allow mapping of vegetation heights and snow or ground surface elevations below forest canopies typical vertical accuracies for airborne datasets are decimeter scale with order 1 m point spacings ground based systems typically provide millimeter scale range accuracy and sub meter point spacing over 1 m to several kilometers many system parameters such as scan angle pulse rate and shot geometry relative to terrain gradients require specification to achieve specific point coverage densities in forested and or complex terrain additionally snow has a significant volumetric scattering component requiring different considerations for error estimation than for other earth surface materials we use published estimates of light penetration depth by wavelength to estimate radiative transfer error contributions this paper presents a review of lidar mapping procedures and error sources potential errors unique to snow surface remote sensing in the near infrared and visible wavelengths and recommendations for projects using lidar for snow depth mapping

interannual variability in the spatial distribution of winter accumulation at a high arctic glacier finsterwalderbreen svalbard and its relationship with topography glacier mass balance and hydrology are strongly influenced by the distribution of snow accumulation at the start of the melt season two successive end of winter snow cover surveys at finsterwalderbreen svalbard are here used to investigate the interannual variability in the spatial distribution of accumulation and its relationship with topography 40 62 of the variance in snow depth was not determined by elevation assessed by linear regression of snow depth on surface elevation which could not therefore necessarily be used as a sole predictor of the spatial distribution of accumulation here principal components pc analysis of the topographic variables elevation slope north south and east west aspects shows that only two of six pcs determined for 2 years sampling locations had maximum loadings on altitude aspect was more important with maximum loadings on four pcs hierarchical cluster analysis was then applied to these pcs significant correlations with accumulation in each of two terrain clusters were given by 1 elevation and slope 2 east west aspect only 1999 1 elevation only 2 no significant correlations 2000 there is strong interannual variability not only in the magnitude of winter accumulation 0 41 m w e in 1999 0 58 m w e in 2000 but also in its spatial distribution and its relationship with topography

scaling properties of wind and snow depth distribution in an alpine catchment 1 the spatial variability of the snow cover is driven by wind induced snow transport processes the main aim of this study is to investigate the link between the scaling behavior of snow depths and the wind induced processes driving the spatial structure of snow depths we used very high resolution atmospheric and snow transport simulations to compare their spatial characteristics with snow depths obtained from airborne and terrestrial laser scans the directions of the strongest autocorrelations of snow depths and wind velocities were predominantly perpendicular to the modeled local flow direction independent of whether more homogeneous lee slope loading in one area was considered or the formation of drifts in another area in the case of homogeneous lee slope loading the same direction of anisotropy was only found in the modeled preferential deposition of precipitation as for both wind and snow distribution this deposition process appears to dominate homogeneous lee slope loading in contrast saltation driven processes seem to dominate the formation of drifts and snow dunes furthermore the fractal analysis suggests similar scale breaks for the modeled wind velocity field and measured snow depths defining the upper scale of landscape smoothing through snow

persistence in intra annual snow depth distribution 2 fractal analysis of snow depth development 1 we present an analysis of high resolution laser scanning data of snow depths of three different slopes in the wannengrat catchment introduced in part 1 using omnidirectional and directional variograms for three specific terrain features cross loaded slopes lee slopes and windward slopes a break in scaling behavior was observed in all subareas which can be seen as the roughness scale of bare earth terrain which is modified by the snow cover in the wind protected lee slope a different scaling behavior was observed compared to the two wind exposed areas the wind exposed areas have a smaller ordinal intercept a smaller short range fractal dimension d and a larger scale break distance l than the wind protected lee slope snow depth structure inherits characteristics of dominant nw storms which results e g in a trend toward larger break distances in the course of the accumulation season this can be interpreted as a result of surface smoothing at increasing scales similar scaling characteristics were obtained for two different years at the end of the accumulation season since snow depth structure is altered strongly by nw storms this inter annual consistency may strongly depend on their frequency in an accumulation period with the analysis of directional variograms anisotropies of fractal parameters were detected which were related to dominant wind directions

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

characterization of sulfide deposits by airborne magnetic and gamma ray responses in eastern finland abstract integrated interpretation of aerogeophysical data permits geophysical characterization of sulfide deposits in eastern finland the structural control and the hydrothermal alteration of the rocks can be discerned from airborne magnetic and radiometric data the cu co zn deposits associated with serpentinite dolomite calc silicate rock siliceous rock black shale settings of the outokumpu type are locally characterized by reduced intensity of magnetization and electrical conductivity and reduced eth and k radiation enhanced eu eth anomalies are commonly spatially related to major structural lineaments such as the boundaries of structurally more coherent bedrock blocks or intersections of faults and shear zones electromagnetic surveys can be used to distinguish black shales and serpentinites in the region the sulfide deposits in eastern finland can be divided into two groups on the basis of airborne geophysical characteristics 1 intense magnetization and high electrical conductivity and 2 moderate magnetization and electrical conductivity in the sulfide deposits of group 1 ore forming constituents mainly precipitated during primary sedimentation for example the black shale hosted ni cu zn ore at talvivaara group 2 is related to sulfide deposits where major ore forming processes have affected the associated black shale formation after the sedimentation phase outokumpu type cu co zn deposits in cases where the magnetization and electrical conductivity of black shales are especially weak ore formation processes probably continued during late metamorphic or post metamorphic deformation the theoretical basis for the observed differences in magnetic response between different deposits has to do with the mineralogy of the black shales pyrite changes into ferrimagnetic monoclinic pyrrhotite during metamorphism above greenschist facies especially along tectonic structures if no further alteration occurs pyrrhotite bearing black shale formations appear as highly magnetic and electrically conductive zones on geophysical maps wherever intense tectonic deformation emplacement of quartz sulfide veins hydrothermal alteration or contact metamorphism has affected the black shale formation after sedimentation both magnetic and electromagnetic responses may be weakened because of diminished amounts of the pyrrhotite bearing and graphite rich material in addition the presence of antiferromagnetic pyrrhotite of hexagonal crystal structure may decrease the magnetic response the classification presented here applies specifically to eastern finland but may be widely applicable to terranes with abundant black shale formations that have undergone regional metamorphism of upper greenschist facies or higher association of sulfide ores with black shales is a common feature in the geological record our integrated geophysical method offers a quick way of examining large areas and it should prove useful in the search for sulfide deposits in other parts of the world

epic simulations of bright companions to neptune s great dark spots abstract we present a three dimensional model of the bright companion clouds associated with neptune s great dark spots gdss our results support the hypothesis that the bright companions of the southern hemisphere gds discovered in 1989 and of the northern hemisphere gds discovered in 1994 are methane clouds that form at or just below the tropopause and that they are caused by lifting in a manner analogous to the formation of orographic clouds we vary the vertical position of the gds and find that the companion cloud is a robust feature except when the anticyclone itself does not survive when a gds is started with its top in the stratosphere it drifts much too rapidly toward the equator and quickly disperses on the other hand if its top is well below the tropopause there is a tendency for the companion clouds to be too large hence the top of a gds is probably at the tropopause along an open streamline that threads a bright companion the typical pressure and temperature drops are about 3 mb and 1k respectively corresponding to a lift of about half a kilometer or 4 of the pressure scale height and the relative horizontal wind speed is about 45 m s 1 eastward through the cloud

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

the altitude of neptune cloud features from high spatial resolution near infrared spectra we report on observations of neptune from the 10 meter w m keck ii telescope on june 17 18 ut 2000 and august 2 3 ut 2002 using the adaptive optics ao system to obtain a spatial resolution of 0 06 arcseconds with this spatial resolution we can obtain spectra of individual bright features on the disk of neptune in a filter centered near 2 microns the use of a gas only simple reflecting layer radiative transfer model allows us to estimate the best fit altitudes of 18 bright features seen on these 4 nights and to set a constraint on the fraction of hydrogen in ortho para equilibrium on these nights there were three main types of features observed northern hemisphere features in the range from 30 to 45 degrees southern hemisphere features in the range from 30 to 50 degrees and small southern features at 70 degrees we find that the altitudes of the northern features are in the range from 0 023 0 064 bar which places them in neptune s stratosphere southern features at 30 to 50 degrees are mainly at altitudes from 0 10 to 0 14 bars the small features at 70 degrees are somewhat deeper in the upper troposphere at 0 17 and 0 27 bars this pattern of features located at higher altitudes in the northern hemisphere and lower altitudes in the south has also been noted by previous observers the best fits for all the observed spectra give a value of 1 0 for the fraction of hydrogen in ortho para equilibrium the value of the helium fraction is less well constrained by the data at 0 24 we suggest that the southern mid latitude features are methane haze circulated up from below while the 70 features may be isolated areas of upwelling in a general area of subsidence northern bright features may be due to subsidence of stratospheric haze material rather than upwelling and condensation of methane gas we suggest that convection efficiently transports methane ice clouds to the tropopause in the southern mid latitudes and thus plays a key role in the stratospheric haze production cycle published by elsevier inc

self similarity in glacier surface characteristics catchment wide information on glacier snow cover depth surface albedo and surface roughness is important input data for distributed models of glacier energy balance in this study we investigate the small scale mm to 100 m spatial variability in these properties with a view to better simulating this variability in such models data were collected on midre lovenbreen a 6 km 2 valley glacier in northwest svalbard the spatial variability of all three properties was found to be self similar over the range of scales under investigation snow depth and albedo exhibit a correlation length within which measurements were spatially autocorrelated late winter and summer properties of snow depth differed with smaller depths in summer due to melt and shorter correlation lengths similar correlation lengths for snow depth and surface albedo may suggest that snow depth variation is an important control on the small scale spatial variability of glacier surface albedo for surface roughness the data highlight a possible problem in energy balance studies which use microtopographic surveys to calculate aerodynamic roughness in that the scale of the measurements made affects the calculated roughness value this suggests that further investigations of the relationships between surface form and aerodynamic roughness of glacier surfaces are needed

the structure of shear related vein type gold deposits a review abstract the structure of vein type gold deposits is defined by the shapes and geometrical relationships of mineralized bodies the form of the mineralization making up these bodies and the sequence of vein forming events most mineralized zones occur within or are spatially associated with shear zones especially shear zones in larger systems of intersecting shear zone sets they range in shape from tabular to linear and in form from disseminated to breccia to stockwork or sheeted veinlet zones to single veins there typically is a complex history of mineral deposition which overlaps and is genetically related to the deformation that generated the host structural zone the purpose of this paper is to consider the structural features of vein type deposits in relation to the geometrical properties and evolution of veinhosting fractures particularly shear zones the evidence indicates that veins are localized by tectonically generated dilatancy in an environment of low mean stress caused by high fluid pressure it is proposed that a major cause of tectonic dilation of shear zones is the interference between intersecting shears during bulk inhomogeneous flattening by movement on systems of intersecting shear zone sets

analysis of neptune s 2017 bright equatorial storm abstract we report the discovery of a large 8500 km diameter infrared bright storm at neptune s equator in june 2017 we tracked the storm over a period of 7 months with high cadence infrared snapshot imaging carried out on 14 nights at the 10 m keck ii telescope and 17 nights at the shane 120 inch reflector at lick observatory the cloud feature was larger and more persistent than any equatorial clouds seen before on neptune remaining intermittently active from at least 10 june to 31 december 2017 our keck and lick observations were augmented by very high cadence images from the amateur community which permitted the determination of accurate drift rates for the cloud feature its zonal drift speed was variable from 10 june to at least 25 july but remained a constant 237 4 0 2 m s 1 from 30 september until at least 15 november the pressure of the cloud top was determined from radiative transfer calculations to be 0 3 0 6 bar this value remained constant over the course of the observations multiple cloud break up events in which a bright cloud band wrapped around neptune s equator were observed over the course of our observations no dark spot vortices were seen near the equator in hst imaging on 6 and 7 october the size and pressure of the storm are consistent with moist convection or a planetary scale wave as the energy source of convective upwelling but more modeling is required to determine the driver of this equatorial disturbance as well as the triggers for and dynamics of the observed cloud break up events

small scale spatial structure of shallow snowcovers the results of a field study of the small scale spatial structure of the depth of shallow seasonal snowcovers in prairie and arctic environments are presented it is shown that the spatial distribution of snow depth is fractal at small scales becoming random at scales beyond some limiting length this is due to the autocorrelation of depth at small sampling distances the transition of fractal to random behaviour is indexed by a cutoff length which is defined by the intersection of the fractal slope and horizontal tangent of a logarithmic plot of the standard deviation of depth versus sampling distance the magnitude of the cutoff length is related to the degree of macroscopic variability of the underlying topography an increase in length due to the effects of macroscopic topographic variability on snowcover accumulation is confirmed by de trending field measurements the de trended data shown a cutoff length for wheat stubble and fallow surfaces of approximately 30 m which is consistent with the distance determined from measurements on flat fields the implications of the transition of snow depth from fractal to random structure on the scales of snow sampling and modelling are presented the cutoff length may provide a statistic for stratifying shallow snowcovers by linking snowcover properties to the underlying topography

field experiments and numerical modeling of mass entrainment in snow avalanches 1 snow entrainment alters the speed and hence the run out distance of avalanches yet little is known about this significant process we studied entrainment in snow avalanches using observations from 1 the swiss vallee de la sionne test site 2 the italian pizzac site 3 catastrophic avalanches that occurred during the winter 1998 1999 in switzerland and 4 a medium sized spontaneous avalanche that occurred in 2000 in davos switzerland we determined mass and energy balances for 18 avalanche events on average the mass increased by a factor of 4 the primary mode of entrainment appeared to be frontal ploughing although entrainment behind the avalanche front was also observed step entrainment where a snow cover layer fractures and is entirely consumed by the avalanche also occurred basal erosion was negligible mass availability and snow cover structure were the limiting factors governing entrainment other factors such as track topography and avalanche dimension played a secondary role using the experimental results we introduced an entrainment model into a saint venant type flow model where the internal shear deformation of the avalanche is governed by a bagnold law and the shear stress at the basal layer is treated as a voellmy fluid the model with entrainment not only improves the prediction of the velocities and flow heights in comparison to measurements but also reproduces the variations in run out distances which characterize avalanches with similar terminal velocities but different masses

snow depth structure fractal behavior and interannual consistency over haut glacier d arolla switzerland snow depth patterns over glaciers are controlled by precipitation snow redistribution due to wind and avalanches and the exchange of energy with the atmosphere that determines snow ablation while many studies have advanced the understanding of ablation processes less is known about winter snow patterns and their variability over glaciers we analyze snow depth on haut glacier d arolla switzerland in the two winter seasons 2006 2007 and 2010 2011 to 1 understand whether snow depth over an alpine glacier at the end of the accumulation season exhibits a behavior similar to the one observed on single slopes and vegetated areas and 2 investigate the snow pattern consistency over the two accumulation seasons we perform this analysis on a data set of high resolution lidar derived snow depth using variograms and fractal parameters our first main result is that snow depth patterns on the glacier exhibit a multiscale behavior with a scale break around 20 m after which the fractal dimension increases indicating more autocorrelated structure before the scale break than after second this behavior is consistent over the two years with fractal parameters and their spatial variability almost constant in the two seasons we also show that snow depth patterns exhibit a distinct behavior in the glacier tongue and the upper catchment with longer correlation distances on the tongue in the direction of the main winds suggesting spatial distinctions that are likely induced by different processes and that should be taken into account when extrapolating snow depth from limited samples

dynamics of cloud features on uranus abstract near infrared adaptive optics imaging of uranus by the keck 2 telescope during 2003 and 2004 has revealed numerous discrete cloud features 70 of which were used to extend the zonal wind profile of uranus up to 60 n we confirmed the presence of a north south asymmetry in the circulation karkoschka e 1998 science 280 570 572 and improved its characterization we found no clear indication of long term change in wind speed between 1986 and 2004 although results of hammel et al hammel h b rages k lockwood g w karkoschka e de pater i 2001 icarus 153 229 235 based on 2001 hst and keck observations average 10 m s less westward than earlier and later results and 2003 observations by hammel et al hammel h b de pater i gibbard s lockwood g w rages k 2005 icarus 175 534 545 show increased wind speeds near 45 n which we do not see in our 2003 2004 observations we observed a wide range of lifetimes for discrete cloud features some features evolve within 1 h many have persisted at least one month and one feature near 34 s termed s34 seems to have persisted for nearly two decades a conclusion derived with the help of voyager 2 and hst observations s34 oscillates in latitude between 32 s and 36 5 s with a period of 1000 days which may be a result of a non barotropic rossby wave it also varied its longitudinal drift rate between 20 day and 31 day in approximate accord with the latitudinal gradient in the zonal wind profile exhibiting behavior similar to that of the ds2 feature observed on neptune sromovsky l a limaye s s fry p m 1993 icarus 105 110 141 s34 also exhibits a superimposed rapid oscillation with an amplitude of 0 57 in latitude and period of 0 7 days which is approximately consistent with an inertial oscillation

spatial and temporal zoning of hydrothermal alteration and mineralization in the sossego iron oxide copper gold deposit carajas mineral province brazil paragenesis and stable isotope constraints the sossego iron oxide copper gold deposit 245 mt 1 1 cu 0 28 g t au in the carajas mineral province of brazil consists of two major groups of orebodies pista sequeirinho baiano and sossego curral with distinct alteration assemblages that are separated from each other by a major high angle fault the deposit is located along a regional wnw ese striking shear zone that defines the contact between metavolcano sedimentary units of the 2 76 ga itacaiunas supergroup and tonalitic to trondhjemitic gneisses and migmatites of the 2 8 ga xingu complex the deposit is hosted by granite granophyric granite gabbro and felsic metavolcanic rocks the pista sequeirinho baiano orebodies have undergone regional sodic albite hematite alteration and later sodic calcic actinolite rich alteration associated with the formation of massive magnetite apatite bodies both these alteration assemblages display ductile to ductile brittle fabrics they are cut by spatially restricted zones of potassic biotite and potassium feldspar alteration that grades outward to chlorite rich assemblages the sossego curral orebodies contain weakly developed early albitic alteration and very poorly developed subsequent calcic sodic alteration these orebodies contain well developed potassic alteration assemblages that were formed during brittle deformation that resulted in the formation of breccia bodies breccia matrix commonly displays coarse mineral infill suggestive of growth into open space sulfides in both groups of deposits were precipitated first with potassic alteration and more importantly with a later assemblage of calcite quartz epidote chlorite in the sequeirinho orebodies sulfides range from undeformed to deformed sulfides in the sossego curral orebodies are undeformed very late weakly mineralized hydrolytic alteration is present in the sossego currral orebodies the sulfide assemblage is dominated by chalcopyrite with subsidiary siegenite and millerite pyrrhotite and pyrite are minor constituents of ore in the sequerinho orebodies while pyrite is relatively abundant in the sossego curral bodies oxygen isotope partitioning between mineral pairs constrains temperatures in the deposit spatially and through time in the sequeirinho orebody the early sodic calcic alteration stage was characterized by temperatures exceeding 500 c and delta text 18 text o text h text 2 text o values for the alteration fluid of 6 9 0 9 temperature declines outward and upward from the zone of most intense alteration paragenetically later copper gold mineralization displays markedly lower temperatures 300 c and was characterized by the introduction of 18o depleted hydrothermal fluids 1 8 3 4 the calculated dh2o and delta text 18 text o text h text 2 text o values suggest that the fluids that formed the early calcic sodic alteration assemblage were of formational metamorphic or magmatic origin the decrease of delta text 18 text o text h text 2 text o values through time may reflect influx of surficially derived waters during later alteration and mineralization events influx of such fluids could be related to episodic fluid overpressure resulting in dilution and cooling of the metalliferous fluid causing deposition of metals transported as metal chloride complexes

wind influence on snow depth distribution and accumulation over glaciers 1 in mountain regions wind is known to cause snow redistribution while physically based models of snow redistribution have been developed for flat to gently rolling terrain extension of these findings to steep terrain has been limited by the complexity of wind fields in such areas in this study we applied a nonhydrostatic and compressible atmospheric prediction model to steep alpine topography and compared the results to a fully distributed data set of snow depth estimations the results show reduced horizontal wind velocity as well as an increasing downward vertical wind velocity over areas with the largest winter accumulation which are mostly glacierized we show that the wind velocity normal to the local surface which should be zero in a nondivergent flow field and is a direct measure of increased or decreased local deposition is a function of small scale features of local topography the correlation between wind fields snow accumulation and glacierization suggests that accurate modeling of wind fields over glacierized areas in complex terrain is a key factor for understanding the mass balance distribution of glaciers

radiosity approach for the shortwave surface radiation balance in complex terrain the influence of topography on the radiation balance in complex terrain has so far been investigated either with very simple or very sophisticated approaches that are limited respectively by an uncontrolled spatial representation of radiative fluxes or heavy computational efforts to bridge this gap in complexity this paper proposes the radiosity approach well known in computer graphics to study anisotropic reflections of radiation in complex terrain to this end the radiosity equation is rederived in the context of three dimensional radiative transfer the discretized equation is solved by means of an adapted version of progressive refinement iteration to systematically study terrain effects the geometrical disorder provided by the topography is considered in its simplest approximation by gaussian random fields these model topographies capture the most important length scales of complex terrain namely a typical elevation and a typical valley width via the variance and the correlation length of the field respectively the mean reflected radiation is computed as a function of these length scales and sun elevation thereby explicitly addressing finite system sizes and grid resolutions a comparison with an isotropic parameterization of terrain reflections reveals that mean values are similar whereas spatial distributions vary remarkably it is also shown that the mean reflected radiation in real topography is reasonably well characterized by the gaussian approximation as a final application of the method the effective albedo of a topography is shown to vary with sun elevation and domain averaged albedo leading to albedo differences up to 0 025

strong spatial variability of snow accumulation observed with helicopter borne gpr on two adjacent alpine glaciers the spatial distribution of snow accumulation plays an essential role for the mass balancedistribution on alpine glaciers traditional point measurements snow pits and probes are labour intensive and interpolation in between the points causes uncertainties airborne radar measurements have already been used for snow mapping innon glacierized terrain but not on alpine glaciers to enhance our understanding ofthe spatial distribution of accumulation and pin down reasons for observed variations we have conducted high resolution helicopter borne radar measurements on the temperatedglacier findel and neighbouring adler glacier in southwestern switzerland the radar sensor was mounted underneath a helicopter and operated at a centre frequencyof 500 mhz with a bandwidth of 400 mhz the results were validated withextensive ground based profiling of the snow cover the radar data allows a clearrecognition of the snow cover 6 of the total profile length of 10 km did not allowinterpretation due to missing or disturbed layering and agreed well with the groundbased measurements r2 0 85 reduced accumulation has been observed in allcrevassed zones statistical analysis of the correlation between observed accumulationand terrain characteristics have been performed in a gis environment revealing differingaccumulation patterns on the lower part of findel glacier accumulation showsa clear altitudinal trend while the upper part is dominated by strongly varying snowdepth without an altitudinal trend the accumulation characteristic on adler glacieris similar to the upper part of findel glacier but despite of their close vicinity accumulationis reduced by 40 compared to the same elevation on findel glacier thisstudy reveals a large potential of helicopter borne snow profiling for measurements ofaccumulation distribution on alpine glaciers

the gold carbonate association source of co2 and co2 fixation reactions in archaean lode deposits abstract abundant carbonate is a ubiquitous feature of archaean lode gold deposits both in domains of alteration enveloping veins and in rocks enclosing auriferous sediments detailed studies of chemical mass balance in metabasalts progressively altered towards gold bearing quartz carbonate veins disposed within shear zones at yellowknife reveal massive additions of co2 k si and fe accompanying mineralisation with concomitant depletions of na coherent behaviour of al sc zr also v and nb provides a reference for constraining the volume relations during hydrothermal alteration in the peripheral regions of alteration depletions of ca and mg result in overall volume reduction but these elements are added to veins and their immediate alteration envelopes where there is a large positive volume change precious metals together with cr ni cu zn pb rb cd and ba have been added to the veins and altered wall rocks whereas quartz noble metals and other trace elements have been precipitated from hydrothermal fluids solution of ca mg and some fe indigenous to peripheral alteration regions combining with co2 from the mineralising reservoir appears to be the process for forming the abundant ferri dolomite gangue observations of many archaean au deposits reveals that carbonate chemistry reflects the nature of wall rocks with wall rocks donating the bivalent metal cations and hydrothermal fluids the co2 alteration reactions at yellowknife involved hydrolysis of albite accompanied by fixation of kaqueous to produce muscovite with na loss and hydrolysis of chlorite epidote with co2 fixation to form ferri dolomite studies of oxygen isotopes fe 2 fe 2 fe 3 and structure reveal that au quartz and carbonate were precipitated in the presence of fluids of probable metamorphic origin 18 o 8 9 at low redox potential and at ambient temperatures of 400 450 c during episodes of hydrofracturing the abundant co2 and k required for extensive carbonate muscovite replacement alteration could be supplied by fluids released during prograde metamorphism under greenschist or greenschist amphibolite facies conditions where the relative proportion of co 2 h 2 o is in the order of 0 2 to 0 5 and k na 1 given high co2 co in the hydrothermal reservoir these molecules may act as complexing agents for transport of au and other rare elements e g w pd ni cr