determinants of peak discharge in steep mountain catchments case of the rift valley escarpment of northern ethiopia peak discharge is an important hydrological parameter of mountain torrents however due to the flashy and destructive nature of their stream flows it is usually difficult to understand the hydrological behavior of steep mountain catchments through direct measurements of discharges in this study 332 daily peak discharge events from 11 steep 0 27 0 65 m m 1 catchments 0 4 25 km2 were measured in three rainy seasons 2012 2014 with the objective of analyzing runoff response of steep mountain catchments in the western rift valley escarpment of northern ethiopia seven rain gauges were installed at different altitudes 1623 2851 m a s l in and nearby the catchments event peak discharges were calculated using the manning s equation from daily measurements of maximum discharge height at 11 crest stage gauges percentages of land cover classes were detected from high resolution 0 6 m google earth imagery february 1 2014 morphometric characteristics of the catchments were computed both from aster digital elevation model dem and topographic maps correlation analysis between average daily precipitation pd and peak discharge qp showed strong positive relation r2 0 32 0 94 p 0 05 in all the catchments catchment specific peak discharge coefficient cp showed a strong decreasing relation with vegetation cover r2 0 85 p 0 01 relative distance of vegetation cover from the thalweg r2 0 55 p 0 01 combined index of vegetation cover and its relative distance from the thalweg r2 0 76 p 0 01 catchment length r2 0 37 p 0 05 and time of concentration r2 0 43 p 0 05 it was correlated positively with catchment slope gradient r2 0 37 p 0 05 and index of vegetation distribution r2 0 45 p 0 05 a stepwise multiple regression analysis revealed that 99 p 0 01 of the variability of catchment specific peak discharge coefficient in the catchments can be predicted by vegetation cover and infiltration number overall this study demonstrates that in reforesting steep mountain catchments where direct measurement of discharges using the conventional methods is difficult due to the flashy and destructive nature of the stream flows hydrological variability can easily be understood using simple measurements of daily precipitation and peak discharges further runoff response is determined by precipitation event and strongly by percentage of vegetation cover and its strategic location farther from the thalweg in the sloping sides of the catchments

sulfur isotopes and the origin of stibnite mineralisation in new england australia stibnite mineralisation in the antimony province of new england can be divided into central type ores veins of stibnite quartz berthierite and peripheral type ores of stibnite quartz native antimony berthierite the central stibnites have 34scdt values of 5 2 1 which may represent equilibrium precipitation from mantle sulfur at about 200 c peripheral stibnites have 34s values between 0 and 25 with a large group at 0 2 they represent precipitation from a limited supply of mantle sulfur and the acquisition of sedimentary sulfur we consider that the different ore types were produced from distinct ore solutions derived from two immiscible melts these originated in the deep mantle were mobilised by tectonic activity and supplied the antimony and most of the sulfur to the ores

iron and other transition metals in patagonian riverborne and windborne materials geochemical control and transport to the southern south atlantic ocean abstract the bulk of particulate transition metals transported by patagonian rivers shows an upper crustal composition riverine particulate 0 5 n hcl leachable trace metal concentrations are mainly controlled by fe oxides complexation of fe by dissolved organic carbon doc appears to be an important determinant of the phases transporting trace metals in patagonian rivers in contrast aeolian trace elements have a combined crustal and anthropogenic origin aeolian materials have fe mn and al contents similar to that found in regional topsoils however seasonal concentrations of some metals e g co pb cu and zn are much higher than expected from normal crustal weathering and are likely pollutant derived we estimate that patagonian sediments are supplied to the south atlantic shelf in approximately equivalent amounts from the atmosphere 30 10 6 t yr 1 and coastal erosion 40 10 6 t yr 1 with much less coming from the rivers 2 0 10 6 t yr 1 low trace metal riverine fluxes are linked to the low suspended particulate load of patagonian rivers inasmuch most of it is retained in pro glacial lakes as well as in downstream reservoirs based on our estimation of aeolian dust fluxes at the patagonian coastline the high nutrient low chlorophyll sub antarctic south atlantic could receive 1 0 to 4 0 mg m 2 yr 1 of leachable 0 5 n hcl fe past and present volcanic activity in the southern andes through the ejection of tephra must be highlighted as another important source of fe to the south atlantic ocean based on the 1991 hudson volcano eruption it appears that volcanic events can contribute several thousand fold the mass of leachable fe to the ocean as is introduced by annual patagonian dust fallout

aeolian processes and the biosphere ravi s d odorico p breshears d d field j p goudie a s huxman t e li j okin g s swap r j thomas a d pelt s v whicker j j zobeck t m 2011 aeolian processes and the biosphere reviews of geophysics 49 3

shrub mound formation and stability on semi arid slopes in the northern negev desert of israel a field and simulation study in semi arid areas vegetation is scarce and often dominated by individual shrubs on raised mounds the processes of formation of these mounds are diverse and still debated often shrub mound formation is directly related to the formation of vegetation patterns thereby assuming that shrub mound formation is driven by biological interactions we hypothesize that water related erosion and sedimentation are also important drivers of shrub mound formation in the northern negev desert of israel we test this hypothesis by combining field observations with model simulations we studied shrub mounds in the semi arid catchment of sayeret shaked in the northern negev desert 200 mm annual precipitation height and diameter of shrub canopy and shrub mounds were measured and micro morphological techniques were used to reconstruct the formation of the shrub mounds we used landscape evolution model lapsus to simulate shrub mound formation at short single precipitation event and longer 100 years timescales at different slope angles both field and model results indicate that shrub mounds in sayeret shaked are at least partly formed by redeposition of eroded material below the shrubs and by erosion and lowering of the surrounding crust additional model simulations suggest that mounds are formed most under low shrub density and large shrub canopy diameter shrub mound formation increases with slope in dryer and wetter climates than the studied 200 mm rainfall semi arid climate zone shrub mound formation is less likely

interactions of plant growth and sediment movement on slopes in a semi arid environment abstract the morphology and architecture of the tussocks of alpha grass stipa tenacissima as well as its associated micro topography have been described in several sites on the south versant of the filabres range in southern spain the annual rainfall of this area is between 225 and 275 mm and plant cover ranges from 20 to 45 the results show the formation of micro topographic mounds upslope of the tussocks which are interpreted as deposition bodies originating from the interception of downslope sediment movement by the vegetated patches the tussock architecture shows an outer growing zone a middle mature zone and a central senescent zone the outward expansion of the tussock is performed by tillers in the growing zone which bend at the nodes and root when they come into contact with the soil surface the mat of dead leaves inside the tussock may prevent the stems from bending and this factor plays a significant role in controlling tussock growth a similar effect on slopes is produced by the mound of sediments which accumulate upslope of the tussock and press upon the growing stems a simple simulation model has been built from the above field observations the model is able to reproduce the tussock shapes found in nature and predicts that at low plant rates the tussocks become unstable and collapse while at higher levels of plant vigour and sediment movement rates sedimentation occurs upslope of the tussock and erosion downslope these foci of sedimentation and erosion are crescent shaped and their relative importance depends on the splash factor

modified topsoil islands within patchy mediterranean vegetation in se spain the spatial distribution of some chemical and physical soil properties was determined in the microenvironment of individual plants of three matorral species rosmarinus officinalis l stipa tenacissima l anthyllis cytisoides l in an area of patchy vegetation in south east spain the influence of isolated plants on the chemical and physical status of the topsoil decreased significantly from the plant axis to the bare inter plant area giving rise to islands of improved topsoil properties beneath each plant i e increased organic matter content and aggregate stability and decreased bulk density penetration resistance shear strength and rock fragment content and cover the degree and lateral extent of topsoil modification was significantly more pronounced under rosmarinus and stipa plants than under anthyllis shrubs mainly because of the differential influences of species morphology i e above ground structure and components i e canopy and litter covers on soil properties and erosion sedimentation processes

geologic and fluid controls on as sb au mineralization in the moretons harbour area newfoundland 50 veins classified into three types arsenopyrite dominated stibnite dominated and base metals arsenopyrite dominated type i veins are enriched in au type iii are enriched in au ag and type ii are poor in au but slightly enriched in ni and pd fluid inclusion data indicate deposition of type i veins from co 2 rich low salinity fluids at temperatures above 300 degrees c type ii au poor veins were deposited from relatively saline low co 2 fluids at temperatures below 220 degrees c pressures of 900 to 1 500 bars gold mineralization is considered to have resulted from a temperature drop through 300 degrees c modified journal abstract

are mima like mounds the consequence of long term stability of vegetation spatial patterning abstract the origins of large 5 m diameter 1 m height and regularly spaced i e over dispersed non anthropogenic earth mounds e g mima mounds heuweltjies nabhkas that occur across all biomes remain unresolved an extensive literature documenting diverse explanations for mound genesis has accumulated that primarily ascribes mound formation to faunal agents recent modeling efforts suggest that both abiotic and biotic processes commonly interact to produce striking vegetation patterning e g spots labyrinths the hypothesis that many earth mounds apart from those with a clear faunal genesis e g termitaria may result from vegetation trapping of sediment or aeolian dust and or protection of soil from erosion is reviewed here the literature on the occurrence and properties of some of these mima like mounds is reviewed and the evidence for their origins evaluated some mounds such as coppice dunes otherwise known as nabkhas clearly form as a consequence of aeolian deposition of sediment around vegetation patches however the clay stone and rock content of some mima like mounds is not consistent with purely aeolian origins instead it is suggested that non aeolian mound over dispersion elongation volumes soil properties and stratigraphy are consistent with vegetation patches protecting soil from erosion resulting in preferential erosional deflation of the inter mound area leaving regularly spaced mounds although mima like mounds around the world are formed in diverse vegetation types climates and edaphic conditions many may be long term products of vegetation spatial patterning in which plant canopies and root systems increase sediment capture and reduce erosional losses

fluid inclusion study of the bournac polymetallic sb as pb zn fe cu vein deposit montagne noire france mineralogical studies demonstrate that the hercynian polymetallic antimony rich deposit of bournac can be described by four stages of ore deposition and one of partial ore remobilization fluid inclusion data permit calculation of the composition and temperature of the fluids associated with each stage of hydrothermal mineralization and concomitant wall rock alteration stages i and ii fe as and zn are represented by moderate salinity h2o co2 nacl inclusions which correlate closely with early carbonate deposition stage iii fluids which are responsible for the deposition of pb sb ores are characterized by low salinity h2o nacl inclusions during the final stage of mineralization iv corresponding to the main phase of stibnite deposition abundant aqueous inclusions confirm the continued involvement of low salinity fluids and the intense development of potassic clays and secondary silica in the wall rocks homogenization temperatures suggest that the whole cycle of mineralization took place during a gradual decrease in fluid temperature of 380 140 c stibnite deposition is restricted to the interval of 230 140 c thus confirming an essentially epithermal environment stage v partial remobilization is distinguished by the presence of high salinity cacl2 rich inclusions which are tentatively related to triassic barite mineralization in the region and therefore postdate the bournac antimony ores homogenization temperatures for this stage range 140 60 c

origin of the fluids associated with granodiorite hosted sb as au w mineralisation at dubrava nizke tatry mts western carpathians mineral parageneses of the polymetallic sbrich deposit at dubrava has been formed during five separated stages a fluid inclusion study demonstrates that the earliest stages with scheelite molybdenite and arsenopyrite have been associated with immiscible co2 ch4 rich low saline fluids at temperatures between 300 and 400 c and pressures as much as 2 kbar deposition of the main superimposed ores stibnite and zinckenite has been intimately connected with circulation of aqeuous moderately saline fluids 15 5 23 5 wt nacl equiv upon epithermal conditions salinity of the aqueous fluids associated with tetrahedrite is clustered around 10 wt nacl equiv quartz from the latest barite stage has precipitated from aqueous fluids enriched in divalent cations these fluids are believed to be genetically linked with triassic evaporite formations preserved in the region temperature salinity diagrams constructed from microthermometry data indicate influx of diluted meteorite water in the stibnite tetrahedrite and barite stages isotopic data are in accordance with model the 18o values between 9 3 and 1 5 have been derived for water in equilibrium with quartz coexisting with sphalerite tetrahedrite and barite thus confirming the participation of isotopically lighter meteoric waters in the mineral forming solutions the 18o values between 3 3 and 8 5 estimated for the water associated with the scheelite and arsenopyrite stages are suggestive for the majority of metamorphic and or magmatic water in the mineral forming co2 rich solutions

gravel dispersion on a granite pediment east mojave desert california a short term look at erosional processes hypotheses about the influence of surface shape landscape unit and vegetation cover on gravel dispersion were tested on a shallowly dissected portion of a low sloping granite pediment in the east mojave desert of california painted gravels 2 to 20 mm diameter were placed at 117 nodes on a 6m 3m grid gravel movements were recorded after 9 7 cm of precipitation over a four month period vectors indicating the magnitude and direction of gravel movement were longest for summits 24 cm 34 nodes observed and shortest for backslopes 14 cm 27 nodes observed gravels beneath shrub canopies were protected significantly from rainsplash transport to describe dispersion symmetry eccentricity values were calculated using a ratio of variances of major and minor axes of an ellipse mean eccentricity values ranged from about 3 to 250 with dispersion on summits being the most symmetrical and dispersion in washes being the most elongated erosion is the most important soil and pediment modifying process at upper elevations of the granite cove pediment which is cut off from sediment additions because of washes incised at the base of the mountain front copyright 1999 john wiley sons ltd

fracture controlled antimony quartz mineralization lake george deposit new brunswick mineralogy geochemistry alteration and hydrothermal regimes veins are of two orientations 000 degrees 35 degrees e lawrence vein and 090 degrees 33 degrees n hibbard and prout veins to date approximately 1 million short tons of ore grading 3 0 to 3 5 percent sb have been mined from hibbard the dominant vein two way chemical mass balance reveals that wall rock alteration accompanying stibnite quartz vein emplacement involved major additions of sb as s and volatiles with minor introduction of k 2 o rb and si fe 2 o 3 mgo cao and na 2 o along with co ni ba and zn were stripped whereas sc ti and al behaved essentially isochemically the argillic alteration developed at 360 degrees to 490 degrees c from fluids with a delta 18 o 10 per mil the hibbard vein was precipitated at 325 degrees to 350 degrees c from a saline hydrothermal fluid with a delta 18 o value of 11 to 12 per mil and a delta d value of 20 to 30 per mil undergoing transient boiling at a pressure of 270 to 420 bars salinity is estimated at 38 to 40 weight percent nacl hematitic alteration was formed at 200 degrees to 350 degrees c in the presence of a fluid with a delta 18 o value of 2 to 8 per mil the ore forming solutions may have been a late stage magmatic fluid evolved off a high 18 o granitic intrusion modified journal abstract

surface microtopography and soil penetration resistance associated with shrub patches in a semiarid rangeland the surfaces of hillsides in semiarid regions are characterized by vegetative patchiness and an associated pattern of soil characteristics in a semiarid patchy rangeland in the northern negev region of israel the pattern of ground surface microtopography and soil penetration resistance were investigated along transects centred on randomly selected shrubs of sarcopoterium spinosum each transect comprised five segments on the hillslope axis upslope us and downslope ds of the central stem cluster of the shrub patch immediately upslope of the shrub tr an upper intershrub ui segment above tr and a lower intershrub li segment below ds significant differences were found among the different segments with regard to both slope and soil penetration resistance segment us had a relatively shallow slope 9 0 in average and the deepest penetration depth 20 5 mm segment ds had the steepest slope 21 0 and a relatively deep penetration depth 16 4 mm segments ui and li had intermediate values for both slope 15 1 and 13 4 respectively and penetration depth 10 5 and 9 8 mm a spatial relationship between the shrub patches and grazing was found segment tr immediately above the shrub tended to be a flock trampling route and had the lowest values of both slope 5 1 and penetration depth 6 1 mm a conceptual model was proposed to explain these results it suggests that under the prevailing conditions of the study site these relationships regulate the redistribution of soil resources on the hillside

the evolution of holocene reg gravelly soils in deserts abstract reg soil is an aridisol developed upon a stable alluvial surface composed of sand to coarse gravel the objectives of the present study were 1 to examine the initial evolution of reg soil properties with time 2 to assess and explain the rates of development of different properties 3 to establish the suitability of different soil properties for relative age dating the time dependent soil properties examined were 1 mechanical weathering of surficial rocks and desert pavement evolution 2 chemical and biological weathering of surficial rocks 3 the thickness of soil profiles and soil horizons 4 soil texture in the different horizons 5 salts and gypsum distribution and concentration in different soil horizons 6 degree of mechanical weathering of gravel in c horizons fifteen successive surfaces of the nahal wadi ze elim sequence of alluvial fans were selected for study dead sea region israel under an extremely arid climate the sequence is of holocene age 14 000 years b p to recent the main conclusions are 1 reg soils develop rather fast in several 10 3 years since their initiation however the various soil properties developed at different rates 2 the rates of change of three soil properties decrease with time these are the texture in different horizons change in added airborne and rain washed dust salinity within the soil profile change in added salts and gypsum and the amount of mechanically shattered rocks 3 soil thickness is established rather rapidly young and older holocene soil have practically the same depth surficial weathering rates appear to remain fairly constant with time 4 in coarse gravel the evolution of reg soils is dependent on added fines and salts of airborne origin and the resultant changing hydrologic regime in the soil profile the run off infiltration ratio changes as more fines and salts are added to the soil profile and as desert pavement develops 5 surficial features and fine clay in the soil profile may be used for approximate dating of otherwise undatable holocene alluvial surfaces salts and gypsum content should be cautiously used in a rather general way

some new lead isotope determinations from the proterozoic sulfide ores of central sweden lead isotope determinations were made on galenas from three strata bound sulfide ores in the early proterozoic svecokarelian bergslagen district of central sweden and four epigenetic deposits in the alvdalen and vansbro districts in the early to middle proterozoic post svecokarelian belt the leads from the strata bound bergslagen deposits show exceptional isotopic homogeneity over large areas their isotopic composition suggests the existence of a pre svecokarelian crust in the district and is consistent with exhalative sedimentary ore formation in an active continental margin environment the vansbro and alvdalen leads display constant compositions within each district but marked divergence between the districts their compositions preclude derivation exclusively from recycled svecokarelian lead and suggest a substantial lead contribution from a mantle like source the difference between model ages and geologic ages for many of the deposits with a small but significant excess of radiogenic lead suggests a significant deviation of the fennoscandian shield from conventional global lead evolution models

quartz veins with associated sb pb ag au mineralization in the schwarzwald sw germany a record of metamorphic cooling tectonic rifting and element remobilization processes in the variscan belt a combination of textural observations from 38 permian sb pb ag au bearing quartz veins in the schwarzwald sw germany with isotopic fluid inclusion and geochemical data allows to refine genetic models for this common type of mineralization to understand the origin of mineralogical diversity and the correlation with large scale tectonic events textures record four main mineralization stages i fe as sb au ii pb zn cu iii pb sb and iv ag sb stage i sulfides dominated by pyrite and arsenopyrite formed due to cooling of low salinity metamorphic fluids during the permian with maximum homogenization temperatures of 400 c invisible gold in arsenopyrite pyrite marcasite and stibnite was remobilized and locally precipitated as electrum at the end of stage i minerals of stages ii and iii comprise a rich diversity of sb bearing sulfosalts including e g bournonite zinkenite and jamesonite this assemblage formed during jurassic times due to mixing of high salinity mid and upper crustal fluids up to 27 wt nacl cacl2 with homogenization temperatures between 50 and 250 c stage iii is marked by a rich variety of pb sb sulfosalts its local abundance is directly related to the presence of stage i mineralization and its extent of remobilization during a significant influx of pb in the jurassic cretaceous the formation of the upper rhine graben during the tertiary reactivated especially ne sw oriented veins percolating ag rich fluids reacted with earlier stage iii pb sb sulfosalts forming ag rich minerals stage iv such as miargyrite pyrargyrite and stephanite the transition from metamorphic fluids to basinal saline e g pb bearing brines over hundreds of millions of years as is shown in this study and present in other variscan occurrences indicates a possibly typical poly stage characteristic of sb deposits worldwide which has however not been investigated in detail so far

mounds associated with shrubs in aridic soils of northeastern patagonia characteristics and probable genesis abstract studies of mounds associated with shrub clumps in northeastern patagonia indicate that these forms have an average major diameter of 355 cm and an average height of 41 cm mound cover and density are 40 and 450 mounds ha respectively mound and intermound soils present a similar textural composition as well as a similar coarse fragment content 10 20 root and organic matter contents are significantly higher whereas calcium carbonate is significantly lower in the mound than in the intermound soils mounds may represent a relict land surface level lowered in the intermound area mainly by wash erosion mound development is related to discrete shrub clumps that shelter the underlying soil once established the shrub clump and the underlying mound remain as a stable and self maintained system

fluid inclusion study of stibnite using infrared microscopy an example from the brouzils antimony deposit vendee armorican massif france a microthermometric study using infrared microscopy was performed on fluid inclusions hosted in stibnite crystals of the brouzils antimony deposit in order to characterize the fluids responsible for the deposition of the antimony at the end of the variscan metallogenic sequence primary fluid inclusions in stibnite were moderately saline 3 5 4 75 wt nacl equiv with homogenization temperatures varying between 140 and 160 c two generations of later fluids are also contained in the stibnite samples the first generation of secondary fluid inclusions is found exclusively in stibnite and is characterized by low salinities 1 35 2 2 wt nacl equiv homogenization temperatures of approximately 215 c and the presence of one or more solid mineral phases the second generation of fluid inclusions is younger and is found in stibnite along secondary planes as well as in quartz gangue it corresponds to h2o co2 fluid with homogenization temperatures of about 180 c this infrared microscopy study thus shows that the quartz and stibnite of the brouzils veins are not cogenetic and reveals the polyphase character of the vein infill in which three successive episodes of hydrothermal circulation are identified

evolution of reg soils in southern israel and sinai abstract reg soils mostly camborthids and gypsiorthids cover some 15 of the negev and sinai deserts analytical data of seven profiles on depositional surfaces of increasing age in the negev show clear relationships between ages of surfaces and soil profile features exemplified in the development of the cambic salic and gypsic horizons the youngest soil a coarse desert alluvium soil typic torriorthent of dry wadi beds up to a few thousand years old has little profile differentiation and is generally non saline or slightly saline on the higher terraces connected with the lisan formation about 70 000 12 000 years b p clear profile differentiation and the beginning of development of cambic horizons can be discerned evident in their colour textural p differences the soils are already saline and somewhat gypsiferous both soils are not yet defined as regs because of their negligible or restricted profile differentiation reg soils on the older and higher geomorphic surfaces in the arava rift valley several hundred thousand years old have well differentiated profiles with cambic salic and gypsic horizons below their stony desert pavements typical reg soils have light coloured vesicular horizons over mellow very pale brown loam frequently with laminar structure almost completely stone free layers the reddish brown loamy to clay loam b horizons are very saline and show intensive salt weathering of gravels gypsic and petrogypsic horizons occur at depth such reg soils represent the stable surfaces and soils of deserts and were developed over a long period of desert weathering

fluid inclusions and ore precipitation mechanism in the giant xikuangshan mesothermal antimony deposit south china conventional and infrared microthermometric constraints abstract the giant xikuangshan antimony deposit located in the xiangzhong central hunan basin south china is the largest antimony deposit in the world stibnite is the predominant ore mineral and gangue minerals consist of quartz calcite fluorite and barite the ore mineral assemblages include early stage quartz stibnite fluorite quartz stibnite and barite quartz stibnite and late stage calcite stibnite in spite of numerous research works on the xikuangshan deposit during the past several decades the signatures of the ore forming fluids and the ore precipitation mechanisms are poorly constrained in order to characterize the fluids responsible for antimony mineralization and ascertain the genetic processes in the xikuangshan ore district conventional and infrared microthermometric measurements have been performed in this study on fluid inclusions hosted in transparent minerals quartz fluorite and barite and opaque stibnite respectively four types of fluid inclusions were identified for the early stage mineralization based on their phase assemblages including type i pure liquid inclusions type ii two phase liquid rich aqueous inclusions type iii two phase vapor rich aqueous inclusions and type iv pure vapor inclusions stibnite only contains type i and type ii inclusions while all types of fluid inclusions are common in the gangue minerals the homogenization temperatures and salinities of fluid inclusions in stibnite and associated gangue minerals in this ore district display significant differences fluid inclusions in stibnite exhibit relatively low homogenization temperatures 112 323 c and higher salinities 0 2 15 4 wt nacl equiv than inclusions in coexisting gangue minerals 119 366 c 0 2 4 2 wt nacl equiv usually about 50 c less than the intergrown gangue minerals according to the petrography of fluid inclusions and the relationship between their homogenization temperature and salinity it was concluded that stibnite and gangue minerals in the xikuangshan ore district are not co genetic instead they were deposited from two distinctly different hydrothermal solutions fluid mixing was responsible for stibnite precipitation but the precipitation of gangue minerals resulted from fluid boiling due to an abrupt drop in pressure the xikuangshan deposit is a typical example of mesothermal deposits rather than an epithermal deposit as previously considered

antimony quartz and antimony gold quartz veins from northern portugal abstract antimony and pb sb quartz veins from the braganca district portugal are mainly hosted by silurian phyllites antimony au quartz veins from the durico beira region are mainly hosted by a cambrian schist metagraywacke complex as well as ordovician phyllites and quartzites the deposits were mostly exploited in the late 19th century mineralogical characteristics and chemical compositions of individual ore minerals are similar in the two areas first and second generations of arsenopyrite precipitated at 390 and 300 c respectively berthierite and stibnite are the most abundant sb bearing minerals and precipitated between 225 and 128 c native antimony at

multi stage fluid incursion in the palaeozoic basement hosted saint salvy ore deposit nw montagne noire southern france abstract the saint salvy vein hosted zn ge deposit occurs in an e w fault system which flanks the southern margin of the late variscan sidobre granite and cross cuts cambrian black shales of the palaeozoic basement comprehensive mineralogical and geochemical studies of vein samples have revealed four mineralizing events m1 m4 related to late and post variscan tectonic events a further late stage event may be related to weathering m1 skarn deposits and m2 patchily mineralized quartz veinlets are associated with granite emplacement quartz contains low salinity h2o co2 nacl dominated fluids 6wt nacl equiv of relatively high temperature 300 580 c trapped under moderate to high pressure estimated m1 fluid d and calculated fluid 18o plot within the metamorphic water field there appears to be no involvement of magmatic fluids by contrast m3 barren quartz and m4 zinciferous economic mineralization stages have h2o co2 nacl cacl2 fluid inclusions with high salinities 23 25 wt nacl equiv and low temperatures 80 140 c which were trapped under low pressure conditions the high salinity and nacl cacl2 content of both m3 and m4 indicates that their parent fluids leached evaporitic salts m3 fluids are meteoric water dominated falling close to the meteoric water line d and 18o averaging 64 and 8 respectively m4 fluids have highly distinctive d averaging 101 and calculated fluid 18o varying from 1 2to 7 1 the unusually low d composition of m4 suggests the involvement of organic fluids in which h is derived directly or indirectly from organic matter the relatively high 18o of m4 fluids indicates that considerable isotopic exchange with sedimentary material took place displacing the 18o from the meteoric water line the data imply interaction of meteoric waters with evaporite and hydrocarbon bearing sedimentary sequences most probably the adjacent aquitain basin the main economic mineralization m4 stage took place during a tensional event probably coincident with the lias dogger transition calculated 34sh2s of m4 sulphide 5 4to 8 2 is almost identical to 34s of local cambrian sulphides 4 7to 9 4 suggesting a genetic link abundant siderite associated with m4 sphalerite has 13c ranging from 2 6to 4 4 indicating that carbon was sourced from sedimentary carbonate mobilized by or equilibrated with the hydrothermal fluid late stage sulphides exhibit extraordinary and highly distinctive 34s sphalerite has extremely low 34s 42 5to 50 5 whereas pyrite has an extraordinary large range from 33 2 to 74 3 closed system sulphate reduction is held to be responsible for the extremely high 34s whereas more open system reduction produces the very low values the coincidence of isotopically low 13c 7 6to 11 9 for co genetic calcite suggests the involvement of organic matter in the reduction process

the massive stibnite veins of the french palaeozoic basement a metallogenic marker of late variscan brittle extension the stibnite ore deposits of the french palaeozoic basement are spatially related to major late variscan strike slip faults they occur as small discontinuous veins mostly hosted in epizonal or catazonal siliciclastics stibnite crystallizes in the final stage of a polymetallic paragenesis from an antimony bearing solution which deposits a first discrete fe as assemblage at 300 400 c and 0 5 0 8 kbar experimental data have shown that antimony solubility drastically decreases on cooling characterization of the late variscan antimony bearing fluids enables us to predict the temperature range 270 150 c under which stibnite was precipitated since the latter coincides with the fluid inclusion homogenization temperature range the pressure at which stibnite crystallized can be estimated from vapour pressure data to have been around 0 1 kbar extensional brittle shear zones developed at the end of the late variscan orogeny probably at the westphalian stephanian boundary drained the hydrothermal fluids near to the surface c 1000 m reaching the critical p t conditions for stibnite crystallization

desert pavements as indicators of soil erosion on aridic soils in north east patagonia argentina abstract desert pavements are prominent features of many geomorphic surfaces in arid and semiarid lands in the semiarid soils of north eastern patagonia gravel cover in the shrub interspace areas of shrub dominated communities is generally high and contrast with that of grass dominated patches where gravel cover is either absent or negligible in the present study we analyze the relationship between soil erosion and desert pavement formation in three sites the upper middle and lower slope positions of a flank pediment where well conserved soils served as reference areas we used the gravel cover and mass as well as the thickness of the remnant a horizon as determined by the depth of the bt horizon of a xeric calciargid as measures of soil erosion surface gravel at four cardinal points in respect to mounds associated with shrub clumps was collected and the depth to the bt horizon was determined the mean thickness of the a horizon in the well conserved soils were 11 3 10 0 and 13 5 cm for the upper middle and lower slope positions respectively for the same positions the mean coarse fragment contents 2 0 mm in the 0 10 cm depth of the a horizon in the well conserved soils were 144 92 and 119 g kg 1 and the mean surface gravel mass in the eroded patches were 5 3 3 1 and 4 7 kg m 2 surface gravel mass and depth of the remnant a horizon gave different estimates of the magnitude of soil erosion in the flank pediment thus the mean maximum soil loss as determined by the mean gravel mass on the soil surface for the upper middle and lower slope positions were 28 3 68 2 27 0 63 8 and 31 5 56 4 mm respectively these figures increased to a mean of 50 0 52 5 and 82 0 mm for the same positions when soil loss was determined as the difference between the thickness of the a horizon of the well conserved soil and that of the remaining a horizon in eroded patches the loss of the a horizon by wind and water erosion seems to initiate the change from grass steppe to a stable shrub steppe characterized in the shrub interspaces by well developed desert pavements the strong correlation between surface gravel mass and the thickness of the remaining a horizon indicates that accelerated soil erosion has played an important role in the formation of desert pavements and that desert pavements are good indicators of the extent and intensity of the erosion process in the punta ninfas area

phytogenic mounds of four typical shoot architecture species at different slope gradients on the loess plateau of china abstract in semi arid regions the spatial pattern of vegetation usually appears as a mosaic of plants surrounded by bare soil phytogenic mounds often develop under these plants and create microenvironments that promote plant establishment this study examined the effects of ground slope and plant shoot architecture on mound formation four species representing different shoot architectures artemisia gmelinii with dense shoot architecture artemisia giraldii with expanding shoot architecture tussock forming bothriochloa ischaemum and sophora viciifolia with a main stem shoot architecture and four classes of slope were selected a two dimensional microprofilemeter was used to measure mound shape and height and mound area was measured using the image pro plus software with a planer mound picture phytogenic mound shapes changed from symmetrical mound type to asymmetrical terrace type as slope increased with increasing slope mound height increased for all species the mound area of s viciifolia decreased and that of a giraldii increased a gmelinii and b ischaemum had a relatively constant mound area irrespective of slope among the plant shoot architecture parameters the basal diameter along the slope d ba significantly correlated with mound height while the plant basal diameter perpendicular to the slope d bp and the total cross sectional area of the stem at the base s n were related to mound area the results indicate that phytogenic mounds on gentler slopes are formed due to the difference in rain splash erosion beneath the plant canopy and surrounding bare surfaces on steeper slopes mounds are formed due to water erosion on bare soil and the prevention of erosion and sediment accumulation under plants plant shoot architecture also influences mound formation species with expanding shoot architecture such as a giraldii that spread laterally to create high density stems and occupy a large area can create relatively large mounds species with main stem shoot architecture such as s viciifolia have a mound area that shrinks rapidly with increasing slope

influence of alpine plants growing on steep slopes on sediment trapping and transport by runoff abstract understanding the interactions between soil and the organisms that are conducive to decreasing sediment runoff is a great concern on high elevation ski trails intense rainfalls on steep slopes combined with soil formed on gypsum result in recurrent erosion this study was conducted in the northern french alps to determine the abilities of species 1 to make mounds and 2 to trap sediment and thereby to control erosion at the slope scale we also investigated relevant above ground plant characteristics related to those abilities sediment runoff or deposition was investigated at small and large spatial scales we assessed whether hoof prints in soil reflect sediment runoff at the slope scale by trapping sediment populations of plants growing on two slope angles 25 and 35 and three vegetation cover densities 15 35 60 were surveyed an experiment was also conducted to measure the sediment deposit upslope of target species and over three months during the autumn small mounds were found upslope of the plant and sediment deposit measurements showed that they resulted from a sedimentation process nevertheless the species differed in their capacity to make mounds sesleria caerulea and festuca alpina had the highest amount of sediment deposition over the experimental period among the plant characteristics plant length was positively correlated with mound area while the roundness index of the canopy was negatively correlated with mound height mound formation was also positively related to the number of tillers or shoots sediment accumulation in cow hoof prints was linked to runoff that occurred at the slope scale low deposition in hoof prints means low sediment runoff or a large deposition on mounds due to the increase in vegetation cover all the findings stressed that understanding the processes in action at larger scales requires studying processes at smaller scales