scratching technique for the study and analysis of soil surface abrasion mechanism aeolian abrasion is the most fundamental and active surface process that takes place in arid and semi arid environments its nature is a wear process for wind blown grains impinging on a soil or sediment surface which causes particles and aggregates to fracture from the soil surface through a series of plastic and brittle cracking deformation such as cutting ploughing and brittle fracturing using a universal micro tribometer umt a scratching test was carried out on six soil surfaces sandy soil sand loam silt loam loam silt clay loam and silt clay the results indicate that traces of normal and tangential force vs time show a jagged curve which can reflect the plastic deformation and brittle fracturing of aggregates and particles of various sizes fractured from the soil surfaces the jagged curve peaks and the area enclosed underneath may represent the bonding forces and bonding energies of some aggregates and grains on the soil surface respectively connecting the scratching test with an impact abrasion experiment furthermore demonstrates that soil surface abrasion rates are proportional to the square of speeds of impacting particles and to the 2 6 power of mean soil grain size and inversely proportional to the 1 5 power of specific surface abrasive energy or to the 1 7 power of specific surface hardness

ventifacts at the pathfinder landing site about half of the rocks at the mars pathfinder ares vallis landing site appear to be ventifacts rocks abraded by windborne particles comparable resolution images taken by the imager for mars pathfinder imp camera and the viking landers show that ventifacts are more abundant at the pathfinder site the ventifacts occur in several forms including rocks with faceted edges finger like projections elongated pits flutes grooves and possible rills the trends of elongated pits flutes grooves and rills cluster at 280 330 clockwise from north and generally dip 10 30 away from their trend direction these orientations are indicative of southeast to northwest winds and differ from the trend of wind tails at the landing site the direction of local wind streaks and predictions of the global circulation model all of which indicate northeast to southwest winds the disparity between these data sets strongly suggests that local circulation patterns have changed since the abrasion of the ventifacted rocks the greater number of ventifacts at the pathfinder site compared to either of the viking sites is most easily explained as being due to a larger supply of abrading particles composed of either sand sized grains or indurated dust aggregates and higher surface roughness which should increase the momentum of saltating grains the pathfinder ventifacts may have formed shortly after the deposition of outflow channel sediments nearly 2 gry ago when a large local supply of abrading particles should have been abundant and atmospheric conditions may have been more conducive to rock abrasion from saltating grains based on how ventifacts form on earth the several ventifact forms seen at the pathfinder site and their presence on some rocks but not on others are probably due to local airflow conditions original rock shape exposure duration rock movement and to a lesser extent rock lithology the abundance of ventifacts at the pathfinder site together with other evidence of weathering indicates that unaltered rock surfaces are rare on mars

the factors influencing the abrasion efficiency of saltating grains on a clay crusted playa the entrainment and subsequent transport of pm10 particulate matter 10 m has become an important and challenging focus of research for both scientific and practical applications arid and semi arid environments are important sources for the atmospheric loading of pm10 although the emission of this material is often limited by surface crusts it has been suggested that the primary mechanisms through which pm10 is released from a crusted surface are abrasion by saltating grains or disturbance by agricultural and recreational activities to examine the importance of saltation abrasion in the emission of pm10 a series of field wind tunnel tests were conducted on a clay crusted surface near desert wells arizona in a previous part of this study it was found that the emission rate varies linearly with the saltation transport rate although there can be considerable variation in this relationship this paper more closely examines the source of the variability in the abrasion efficiency the amount of pm10 emitted by a given quantity of saltating grains the abrasion efficiency was found to vary with the susceptibility of the surface to abrasion the ability of the sand to abrade that surface and the availability of material with a caliper size 10 m within the crust specifically the results of the study show that the abrasion efficiency is related to the crust strength the amount of surface disturbance and the velocity of the saltating grains it is concluded that the spatial and temporal variability of these controls on the abrasion efficiency imposes severe contextual limitations on experimentally derived models and can make theoretical models too complex and impractical to be of use copyright 2001 john wiley sons ltd

controls on the siting and style of volcanogenic massive sulphide deposits abstract volcanogenic massive sulphide vms deposits form in subaqueous environments from circulating hydrothermal fluids heated by volcanic activity these deposits form as sulphide mounds stratiform exhalative and or replacive bodies and commonly have stockwork vein mineralization in their immediate footwall these various styles are essentially facies of mineralization each one being the product of a particular set of conditions that control the ore forming processes and the consequent geometry and architecture style of the deposits these controls include the physical and or chemical nature of the host rocks the temperature and composition of the hydrothermal fluids and the redox state of the depositional environment the style of exhalative deposits is controlled by the salinity of the vented fluids and the redox state at the seafloor hydrothermal fluids with salinities less than twice that of seawater that vented into open oxic oceanic environments typically formed small mound and chimney complexes unless they were rapidly covered by sediments or volcanic rocks the massive sulphides were rapidly oxidized and partly dissolved by seawater in contrast stratiform sheet like deposits are typically formed in anoxic bottom waters anoxic marine conditions were periodically of global extent particularly prior to 2 4 ga or of a regional nature local anoxic conditions can also be self induced by the exhalation of saline and reducing hydrothermal fluids that ponded in bathymetric depressions such as second or third order basins to form a brine pool these exhalative systems may have been initiated as chimney vent complexes and subsequently overlain by stratiform sulphides formed under the self induced anoxic conditions deposits formed in anoxic environments can be significantly larger than those in oxic settings and this is attributed to several factors that include longer lived hydrothermal circulation more efficient sulphide precipitation and reduced or inhibited oxidation thereof replacement of volcanic and sedimentary strata by sulphide typically occurs within the feeder zones beneath the exhalative mineralization however successions with abundant porous permeable and or reactive rocks such as glassy and or pumiceous volcaniclastic rocks and in some cases limestone favoured the development of large replacive deposits that may have had little surficial expression on the sea floor vms deposits at spreading centres within oceanic crust formed almost exclusively as mounds most of them have not been preserved likely due to oxidation of the sulphides in the prevailing oxic environment and or destruction of oceanic crust during subsequent subduction intra continental rifts arc rifts and back arc rifts commonly have more complexity in their structure and facies architecture and environments and can host all styles of vms mineralization in these settings early extension favoured the formation of restricted basins with ideal conditions for the onset of hydrothermal activity and development of anoxic bottom waters whereas in mature rifts the conditions were less conducive for the formation of regionally extensive anoxic environments formation of replacive deposits was permissible in all settings with porous or reactive subsea floor strata replacive mineralization is the most likely to be preserved in the geological record due to the sulphides being physically shielded from oxidative weathering and mechanical erosion at the seafloor the various styles of vms mineralization can rarely be distinguished using a single criterion in most cases multiple criteria are required mound style mineralization is distinguished by a mound or lens shaped morphology b presence of chimney fragments c presence of abundant sedimented sulphide breccias d location on a stratigraphic boundary ore horizon and e association with a thin horizon or thicker stratigraphic interval of fine grained clastic rocks e g shale mudstone that accumulated at slow sedimentation rates stratiform exhalative mineralization is distinguished by a sheet like morphology prior to deformation b presence of fine grained clastic host rocks that accumulated at relatively slow rates e g mudstone c presence of local or extensive planar stratification replacive mineralization is characterized by a irregular geometry and distribution of sulphide bodies b gradation from massive sulphides to semi massive sulphides and disseminated mineralization with relict textures of the host rock and c originally pumiceous glassy or reactive host rocks emplaced at high depositional rates mass flow deposits lavas carbonate altered mass flow deposits or limestone one deposit or district may comprise two or more of these main styles of mineralization in many cases the main styles of vms mineralization present in a particular region can be predicted from examination of the facies architecture and depositional environments of the host succession recognition of the style s of mineralization that occur in a particular basin or mineral belt enables exploration models to be improved and should influence the strategy of exploration for vms deposits

recent ventifact development on the central oregon coast western usa the unusual location of ventifacts on a boulder built jetty at the mouth of the siuslaw river oregon coast western usa allows ventifact age and wind abrasion rates to be estimated with some precision the jetty was built mainly between 1892 1901 and extended throughout the twentieth century consideration of historical shoreline position and the history of jetty construction and repair suggests the ventifacts have formed since about 1930 morphologically the ventifacts are aligned south to north reflecting winter winds and sediment transport from the adjacent beach wind parallel grooves and ridges with sharp sinuous crests are developed on inclined boulder surfaces on top of the jetty and reflect suspended sand transport in wind vortices deeply pitted surfaces on steep boulder surfaces nearest the beach reflect impact by saltating sand grains based on present wind regimes 1992 2000 from three regional weather stations southerly winds above the sand transport threshold occur for 21 9 29 6 per cent of the time based on estimated depth of loss from boulder surfaces wind abrasion rates are calculated to be on the order of 0 24 1 63 mm a 1 this is the first well constrained field estimate of ventifact age and ventifaction rate from a modern coastal environment copyright c 2003 john wiley sons ltd

velocity profile of a sand cloud blowing over a gravel surface particle dynamic analyzer pda measurement technology was used to study the turbulent characteristics and the variation with height of the mean horizontal in the downwind direction and vertical in the upward direction particle velocity of a sand cloud blowing over a gravel surface the results show that the mean horizontal particle velocity of the cloud increases with height while the mean vertical velocity decreases with height the variation of the mean horizontal velocity with height is to some extent similar to the wind profile that increases logarithmically with height in the turbulent boundary layer the variation of the mean vertical velocity with height is much more complex than that of the mean horizontal velocity the increase of the resultant mean velocity with height can be expressed by a modified power function particle turbulence in the downwind direction decreases with height while that in the vertical direction is complex for fine sands 0 2 0 3 mm and 0 3 0 4 mm there is a tendency for the particle turbulence to increase with height in the very near surface layer 4 mm the movement of blown sand particles is very complex due to the rebound of particles on the bed and the interparticle collisions in the air wind starts to accelerate particle movement about 4 mm from the surface the initial rebound on the bed and the interparticle collisions in the air have a profound effect on particle movement below that height where particle concentration is very high and wind velocity is very low

controls on the formation of coastal ventifacts abstract ventifacted boulders are present within the intertidal zone of a mixed sand and boulder beach in gweebarra bay northwest ireland the boulders show features typical of wind abrasion by sand including polished surfaces pits and grooves orientation of ventifact keels was measured and direction of prevailing winds responsible for ventifaction was inferred from a sample of 50 boulders in each of two adjoining locations on the beach 30 m apart the keel orientations and inferred wind direction are both strongly clustered but results from each location differ by 90 from one another and neither corresponds closely to the present day regional wind regime since wind flow patterns were not significantly different during the little ice age when the ventifacts were likely formed the orientation of ventifact keels cannot be used uncritically as in many studies as a proxy record of prevailing wind direction it is likely that ventifact development in gweebarra bay was controlled by sediment availability rather than by wind direction

rate of wind abrasion on mars estimation of the rate of aeolian abrasion of rocks on mars requires knowledge of 1 particle flux 2 susceptibilities to abrasion of various rocks and 3 wind frequencies on mars fluxes and susceptibilities for a wide range of conditions were obtained in the laboratory and combined with wind data from the viking meteorology experiment assuming an abundant supply of sand sized particles estimated rates range up to 2 1 10 2 cm of abrasion per year in the vicinity of viking lander 1 this rate is orders of magnitude too great to be in agreement with the inferred age of the surface based on models of impact crater flux the discrepancy in the estimated rate of abrasion and the presumed old age of the surface cannot be explained easily by changes in climate or exhumation of ancient surfaces we consider the primary reason to be related to the agents of abrasion either windblown grains are in very short supply or the grains are ineffective as agents of abrasion at least some sand sized 100 m grains appear to be present as inferred from both lander and orbiter observations high rates of abrasion occur for all experimental cases involving sands of quartz basalt or ash however previous studies have shown that sand is quickly comminuted to silt and clay sized grains in the martian aeolian regime experiments also show that these fine grains are electrostatically charged and bond together as sand sized aggregates laboratory simulations of wind abrasion involving aggregates show that at impact velocities capable of destroying sand aggregates form a protective veneer on the target surface and can give rise to extremely low abrasion rates

thermomechanical milling of accessory lithics in volcanic conduits accessory lithic clasts recovered from pyroclastic deposits commonly result from the failure of conduit wall rocks and represent an underutilized resource for constraining conduit processes during explosive volcanic eruptions the morphological features of lithic clasts provide distinctive textural fingerprints of processes that have reshaped them during transport in the conduit here we present the first study focused on accessory lithic clast morphology and show how the shapes and surfaces of these accessory pyroclasts can inform on conduit processes we use two main types of accessory lithic clasts from pyroclastic fallout deposits of the 2360 b p subplinian eruption of mount meager british columbia as a case study i rough and subangular dacite clasts and ii variably rounded and smoothed monzogranite clasts the quantitative morphological data collected on these lithics include mass volume density 2 d image analysis of convexity c and 3 d laser scans for sphericity and smoothness s shaping and comminution i e milling of clasts within the conduit are ascribed to three processes 1 disruptive fragmentation due to high energy impacts between clasts or between clasts and conduit walls 2 ash blasting of clasts suspended within the volcanic flux and 3 thermal effects we use a simplified conduit eruption model to predict ash blasting velocities and lithic residence times as a function of clast size and source depth thereby constraining the lithic milling processes the extent of shape and surface modification i e rounding and honing is directly proportional to clast residence times within the conduit prior to evacuation we postulate that the shallow seated dacite clasts remain subangular and rough due to short 2 min residence times whereas monzogranite clasts are much more rounded and smoothed due to deeper source depths and consequently longer residence times up to 1 h larger monzogranite clasts are smoother than smaller clasts due to longer residence times and to greater differential velocities within the ash laden jet lastly our model residence times and mass loss estimates for rounded clasts are used to estimate minimum attrition rates due to volcanic ash blasting within the conduit e g 12 cm3 s 1 for 25 cm clasts sourced at 2500 m depth

the precious metal rich south hercules mineralization western tasmania a possible subsea floor replacement volcanic hosted massive sulfide deposit south hercules is a newly delineated disseminated to semimassive base metal sulfide deposit with significant gold and silver grades the deposit lies a kilometer along strike south from the hercules mine a 2 0 mt polymetallic massive sulfide deposit in the mount read volcanics belt western tasmania the mineralization and alteration at the south hercules deposit has been divided into two major facies the mineralized sulfide facies and the carbonate facies the carbonate facies interfingers with and surrounds the upper part of the sulfide facies the mineralized sulfide facies includes three zones a massive pyrite or barite zone a siliceous or stringer sulfide zone and a sphalerite galena or pyrite zone the carbonate facies also consists of three zones a blebby carbonate chlorite zone a massive carbonate zone and a cherty carbonate zone the massive pyrite or barite zone contains significant gold grades and occurs mostly at the top of the sulfide facies this zone is characterized by colloform aggregates of pyrite and compact massive pyrite in chert the siliceous or stringer sulfide zone is a silicified and sericitized tuffaceous shale with disseminated to stringer pb zn mineralization the massive sphalerite galena or pyrite zone contains subordinate gold and silver and occurs as thin lenses toward the base of the sulfide facies significant zinc and lead values occur throughout the mineralized sulfide facies with the highest values occurring along stratigraphically controlled layers copper values are conspicuously low throughout the south hercules deposit rarely exceeding 0 5 percent the carbonate facies is conspicuous by its lack of significant precious metal and base metal grades mineragraphic investigations indicate that electrum occurs in two general associations with pyrite and with other sulfides such as sphalerite galena and tetrahedrite the electrum locked in the pyrite euhedra is generally fine grained 5 40 mu m whereas the electrum associated with other sulfides displays a range between 5 and 200 mu m microprobe analysis indicates that the fineness 1 000 au au ag wt for gold in the deposit ranges from 427 to 965 the delta 18 o isotope composition of the carbonate varies from 9 8 to 16 7 per mil and the delta 13 c values range from 3 5 to 0 6 per mil the calculated isotopic composition of the ore fluid at 150 degrees and 250 degrees c is consistent with derivation from evolved seawater sulfur isotope analyses of selected samples from the mineralized facies give delta 34 s values of 8 2 to 14 1 per mil which is in the same range as values from the rosebery deposit and consistent with values of sulfur derived from cambrian seawater the form texture mineralogy stable isotopes and fluid inclusion data for the south hercules deposit suggest that it was formed largely by a subsea floor replacement process from relatively low temperature 150 degrees 250 degrees c near neutral fluids the very low copper content and relatively high au ag pb zn ratio of the ores support a low temperature environment in which gold was transported as the au hs 2 super complex and pb and zn were transported as chloride complexes

chemical remobilization of volcanic hosted sulphide deposits at rosebery and mt lyell tasmania abstract devonian hydrothermal activity has resulted in localised chemical remobilization of the cambrian massive sulphide deposits at rosebery and mt lyell in the mt read mineral province of western tasmania at rosebery part of the massive pyrite sphalerite galena chalcopyrite quartz phyllosilicate lens has been replaced volume for volume by a pyrite pyrrhotite chalcopyrite magnetite phlogopite tourmaline quartz assemblage with complete removal of cambrian sphalerite and galena the replacement is later than folding of probable devonian age the likely temperature the presence of tourmaline and the relatively reduced nature of the secondary assemblage suggest that the related fluids were derived from devonian granitoids which on independent evidence tourmaline veins pyrrhotite deposits metamorphic biotite and shallow granites nearby appear to extend beneath the rosebery mice lead and zinc dissolved from the cambrian sulphide lens may have been redeposited as veins and replacements in younger rocks the resulting lead is likely to yield anomalous isotopic ages and be associated with sulphur having the isotopic characteristics of cambrian massive sulphide deposits at mt lyell altered felsic volcanics host large disseminated pyrite chalcopyrite quartz phyllosilicate lenses and minor stratabound exhalative massive sulphide bodies all of probable cambrian age in the north lyell fault zone late cambrian early ordovician siliciclastic sediments have been replaced by cherty quartz bornite chalcopyrite chalcocite sericite pyrophyllite ores of likely devonian age this assemblage probably formed from acid pyrophyllite oxidized barite solutions that may have derived high a cu a fe by dissolution of cambrian chalcopyrite disseminated pyrite chalcopyrite ores of cambrian age have a well developed devonian cleavage in which hematite has crystallized thereby indicating circulation of oxidized fluids during or after cleavage development precipitation mechanisms for the bornite ores may have involved fluid sulphide and or fluid sediment reactions the fluids are unlikely to have been derived directly from devonian granitoids but they may have been modified groundwaters circulating either during cleavage growth or as a result of heating by post kinematic devonian granitoid plutons

an introduction to the geology and metallic ore deposits of tasmania the major operating metallic ore deposits of tasmania are a volcanic hosted massive sulfide deposits at que river rosebery and hercules fe zn pb cu type mt lyell fe cu type and savage river fe oxide type b tin tungsten deposits in veins at aberfoyle lutwych storys creek and mt oakleigh c tin deposits of carbonate replacement type at renison and cleveland and d scheelite skarn deposits at king island and kara the massive sulfide deposits are cambrian and occur in calc alkaline volcanics the magnetite deposits at savage river are proterozoic and occur in basaltic volcanics and the tin and tungsten deposits are related to devonian granitoids of various types tasmania has in the past been also a producer of osmiridium nickel sulfide ore in cambrian mafic ultramafic rocks and gold in early paleozoic mudstone graywacke successions

an experimental study of wind abrasion rocks were abraded by a sand laden air jet in the laboratory to examine the quantitative relationships between wind abrasion and wind velocity quantity and grain size of windblown sand particles and physical properties of the target rocks the results of 101 runs are expressed by an experimental equation with dimensionless constant which indicates that the rate of abrasion is directly related to the kinetic energy of the sand projectiles and inversely proportional to the compressive strength of the target rocks a tentative extension of the experimental equation to field condition leads to an equation for the wind abrasion in fields an application of the latter equation to the natural settings is preliminarily examined by comparing it with sharp s 1964 field experiments and a plausible result is obtained

formation of massive sulfide lenses by replacement of folds the hercules pb zn mine tasmania the hercules pb zn deposit consists of a number of isolated ellipsoidal massive sulfide pods hosted in a tuffaceous slate unit of middle cambrian age these pods are aligned roughly parallel to the main cleavage and have completely discordant to moderately folded bedding mineralization is localized in the short limb zones of parasitic f 2 folds from the micro to the macroscopic scale antithetic shearing induced along the bedding during d 3 caused localized dilation and fracturing of some of the short limb zones this resulted in alteration and replacement late in d 3 such that sa was overprinted by the mineralization the following paragenetic replacement sequence exists pyrite i quartz chlorite pyrite ii sphalerite galena chalcopyrite pb isotope age data are consistent with the derivation of the deposit from dispersed primary sulfides in the mount read volcanics by synmetamorphic mobilization into structural traps at higher levels in the crust

foliation boudinage control on the formation of the rosebery pbzn orebody tasmania abstract the rosebery pb zn ag au massive sulphide deposit occurs within the middle cambrian mount read volcanics of western tasmania it is hosted by a tuffaceous slate lens that is surrounded by felsic volcanics the volcanic belt and its ordovician cover were deformed and metamorphosed during an early to middle devonian orogeny tabberabberan orogeny during this orogeny d 3 e w shortening was partially accommodated by reverse bedding parallel shearing within the slate unit and immediately underlying volcanic rocks this caused reactivation and intensification of an early foliation s 2 and the development of asymmetric chocolate tablet foliation boudinage structures with boudin necks parallel to the x and y directions the mineralization occurs along extensional shear planes that are associated with foliation boudinage mineralogical zoning in the orebody can be directly related to dilational bends in shears associated with foliation boudin necks it is proposed that these structures gaped during the d 3 deformation allowing infiltration of metalliferous hydrothermal fluids along shear plane and cleavage directions into the fractured wall rock progressive metasomatic replacement of the wall rock resulted in the formation of a sulphide sulphate silicate orebody the orebody is completely discordant to folds in the host rock this observation confirms a structurally controlled origin and refutes earlier interpretations of the deposit as a tightly folded chemical sediment isotope data indicate that the orebody was probaby derived from volcanogenic sulphides within the mount read volcanics the rosebery orebody is best regarded as a metamorphogenic deposit that formed by dissolution upward transport concentration and re precipitation of primary sulphides the proposed macroscopic model complements separate microstructural evidence by the author indicating a syn d 3 timing of mineralization

dissolution solution transfer diffusion versus fluid flow and volume loss during deformation metamorphism dissolution and solution transfer during deformation metamorphism are controlled by the partitioning of deformation into progressive shearing and shortening components progressive shearing is readily accommodated by slip on the planar crystal structure of phyllosilicates and graphite without accumulating dislocation density gradients across grain boundaries progressive shortening is accommodated by the cores of most other minerals including sulphides these minerals develop strain and hence dislocation density gradients on their rims due to progressive shearing along grain boundaries these gradients are particularly large when the mineral abuts phyllosilicate or graphite the resulting chemical potential gradients between the core and rim drive dissolution causing removal of the highly strained grain margins removal of dissolved material by solution transfer is aided by the geometry of shearing of phyllosilicates and graphite around other grains in an active anastomosing foliation interlayers and interfaces on boundaries lying at a low angle to the direction of shearing and oriented relative to the sense of shear such that they can open gape by small amounts water present in these interlayer spaces becomes destructured considerably enhancing diffusion rates along the foliation penetrative volume loss especially in deforming metamorphosing pelitic rocks is large at all metamorphic grades increasing and becoming more penetrative with depth to at least the transition into granulite and eclogite facies transference of material by fluid flow from deep to high levels in the earth s crust is precluded because thousands to tens of thousands of rock volumes of fluid are required necessitating continual recirculation of fluid from shallow to deep crustal levels in one large or several small sets of cells unless some extremely large scale form of fluid channelling is possible reassessment of diffusion mechanisms and hence rates during deformation and pervasive foliation generation in large volumes of rock where fluid channeling cannot provide enough fluid indicates that diffusion can proceed with sufficient rapidity that massive recirculation of fluid is no longer required the amount of fluid can be reduced sufficiently to allow large volume losses by a one way flow of fluid to the earth s surface in deforming metamorphosing environments where the fluid pressure equals or exceeds the hydrostatic pressure deformation partitioning controlled dissolution progressively changes the bulk chemistry of a rock containing phyllosilicates or graphite during deformation metamorphism because matrix minerals other than phyllosilicates and graphite are preferentially removed the large size of porphyroblasts if present tends to preserve them from dissolution hence the bulk chemistry operative during subsequent porphyroblast growth can have changed considerably from that operative when the first porphyroblasts grew in rocks in which bedding is still well preserved

height profile of the mean velocity of an aeolian saltating cloud wind tunnel measurements by particle image velocimetry abstract the velocity of saltating particles is an important parameter in studying the aeolian sand movement we used particle image velocimetry to measure the variation with height of the mean particle velocity of a saltating cloud over a loose sand surface in a wind tunnel the results suggest that both the horizontal and vertical particle velocities fit the gaussian distribution well and that the mean particle velocity of a saltating cloud varies with wind velocity particle size and the height above bed the mean horizontal velocity is mainly the result of acceleration by the wind and increases with an increase in friction wind velocity but decreases with an increase in grain size because greater wind velocity causes more acceleration and finer particles are more easily accelerated at a given wind velocity it also increases with an increase in height by a power function in agreement with previous results obtained by other methods such as the high speed multi flash photographic method and particle dynamics analyzer pda reflecting first the increase in wind velocity with height through the boundary layer and second the longer trajectory particle path length increases with height and affords a longer time for acceleration by the wind an empirical model relating the mean horizontal particle velocity and height friction wind velocity as well as particle size is developed the ratio of the mean horizontal particle velocity to the clean wind velocity at the same height increases with height but decreases with grain size the magnitude of mean vertical velocity is much less one or two orders less compared with the mean horizontal velocity the average movement in the vertical direction of a saltating cloud is upward the mean vertical velocity is positive although the upward velocity of a saltating particle should decrease with height due to gravity the mean vertical upward velocity the average of both ascending and descending particles generally shows a tendency to increase with height it seems that at higher elevations the data are more and more dominated by the high flyers the underlying mechanism for the mean vertical velocity distribution patterns needs to be clarified by further study

river incision into bedrock mechanics and relative efficacy of plucking abrasion and cavitation improved formulation of bedrock erosion laws requires knowledge of the actual processes operative at the bed we present qualitative field evidence from a wide range of settings that the relative efficacy of the various processes of fluvial erosion e g plucking abrasion cavitation solution is a strong function of substrate lithology and that joint spacing fractures and bedding planes exert the most direct control the relative importance of the various processes and the nature of the interplay between them are inferred from detailed observations of the morphology of erosional forms on channel bed and banks and their spatial distributions we find that plucking dominates wherever rocks are well jointed on a submeter scale hydraulic wedging of small clasts into cracks bashing and abrasion by bedload and chemical and physical weathering all contribute to the loosening and removal of joint blocks in more massive rocks abrasion by suspended sand appears to be rate limiting in the systems studied here concentration of erosion on downstream sides of obstacles and tight coupling between fluid flow patterns and fine scale morphology of erosion forms testify to the importance of abrasion by suspended load rather than bedload particles mechanical analyses indicate that erosion by suspended load abrasion is considerably more nonlinear in shear stress than erosion by plucking in addition a new analysis indicates that cavitation is more likely to occur in natural systems than previously argued cavitation must be considered a viable process in many actively incising bedrock channels and may contribute to the fluting and potholing of massive unjointed rocks that is otherwise attributed to suspended load abrasion direct field evidence of cavitation erosion is however lacking in terms of the well known shear stress or stream power erosion law erosion by plucking is consistent with a slope exponent n of 2 3 to 1 whereas erosion by suspended load abrasion is more consistent with a slope exponent of 5 3 given that substrate lithology appears to dictate the dominant erosion process this finding has important implications for long term landscape evolution and the models used to study it

the emission and vertical flux of particulate matter 10 mum from a disturbed clay crusted surface arid and semi arid environments are important sources for the atmospheric loading of pm10 particulate matter 10 lm although the emission of this material is often limited by surface crusts this study investigates the emission and vertical flux of pm10 from a clay crusted playa with and without saltating grains to abrade the surface using a portable field wind tunnel it was found that despite disturbance to the surface the emission of pm10 decays rapidly without abrasion only in the presence of saltating grains was pm10 continuously liberated from the surface such that the emission rate the total amount of pm10 emitted from the surface expressed as a horizontal flux varied linearly with the saltation transport rate although the emission of pm10 was found to depend on saltation abrasion past studies have tended to focus on the relationship between the vertical flux of pm10 the amount of pm10 being transported vertically through the boundary layer and the shear velocity in this study the vertical flux of pm10 was found to vary with the shear velocity to the power of 2ae14 although the vertical pm10 flux is a proportion of the emission rate the horizontal flux no statistically significant relationship was observed between the emission rate and the shear velocity the disparity of these results is explained by the lack of a consistent relationship between the shear velocity and the saltation transport rate in this supply limited environment this suggests that the observed relationship between the vertical pm10 flux and the shear velocity is a spurious correlation resulting from the use of shear velocity to calculate the vertical dust flux it is thus concluded that shear velocity is not an appropriate variable for emission modelling in supply limited environments and that improvements in dust emission modelling will only be realized if the abrasion process is the focus of a concerted research effort

the xinqiao cu s fe au deposit in the tongling mineral district china synorogenic remobilization of a stratiform sulfide deposit abstract the cu s fe au deposit at xinqiao is located in the tongling mineral district anhui province people s republic of china it is a large scale polymetallic deposit with drilling indicated reserves of 0 5 million tonnes of cu averaging 0 71 75 5 million tonnes of s averaging 29 3 and 24 9 million tonnes of fe averaging 46 as well as 11 2 tonnes of au averaging at 4 7 g tonne plus 248 4 tonnes of ag averaging at 248 4 g tonne there are two major mineralization types in the xinqiao deposit one is the economically significant stratiform orebody hosted in the lower carboniferous gaolishan siltstone c1g and overlying middle carboniferous huanglong limestone c2h while the other is the less important skarn type mineralization restricted to the contact between the yanshanian diorite 110 168 ma and the lower permian qixia marble p1q the ore in the xinqiao deposit is dominated by massive pyrite with minor amount of chalcopyrite magnetite pyrrhotite galena sphalerite quartz and dolomite four stages of deformation have been recognized to affect the sedimentary rocks in the xinqiao area the first two d1 and d2 produced mainly ne sw and nne ssw trending open folds whereas d3 is characterized by normal faults striking nne ssw and d4 is dominated by post mineralization strike slip faults segmenting the orebody the structural information obtained by this study not only revealed the transgressive nature of the stratiform orebody but also identified a strong structural control on the formation of the deposit it is concluded that the xinqiao polymetallic deposit was formed through remobilization of a carboniferous sulfide source bed by hydrothermal solutions related to late yanshanian plutonism 110 ma during which d3 normal faulting played an important role in localization of the mineralization such a two stage ore forming model is consistent with the most recent genetic interpretations of the deposit

foliation development and refraction in metamorphic rocks reactivation of earlier foliations and decrenulation due to shifting patterns of deformation partitioning reactivation of early foliations accounts for much of the progressive strain at more advanced stages of deformation its role has generally been insufficiently emphasized because evidence is best preserved where por phyroblasts which contain inclusion trails are present reactivation occurs when progressive shearing operating in a synthetic anastomosing fashion parallel to the axial planes of folds changes to a combination of coarse and fine scale zones of progressive shearing some of which operate antithetically relative to the bulk shear on a fold limb reactivation of earlier foliations occurs in these latter zones reactivation decrenulates pre existing or just formed crenulations generating shearing along the decrenulated or rotated pre existing foliation planes partitioning of deformation within these foliation planes such that phyl losilicates and or graphite take up progressive shearing strain and other minerals accom modate progressive shortening strain causes dissolution of these other minerals this results in concentration of the phyllosilicates in a simi lar but more penetrative manner to the for mation of a differentiated crenulation cleavage except that the foliation can form or intensify on a fold limb at a considerable angle to the axial plane of synchronous macroscopic folds reactivation can generate bedding parallel schistosity in multideformed and meta morphosed terrains without associated folds heterogeneous reactivation of bedding gen erates rootless intrafolial folds with sigmoidal axial planes from formerly through going struc tures reactivation causes rotation or refrac tion of axial plane foliations forming in the same deformation event causing reactivation in those beds or zones in which an earlier foli ation has been reactivated and results in destruction of the originally axial plane foli ation at high strains reactivation also provides a simple explanation for the apparently wrong sense but normally observed rotation of gar net porphyroblasts whereby the external foli ation has undergone rotation due to antithetic shear on the reactivated foliation alter natively the rotation of the external foliation can be due to its reactivation in a subsequent deformation event porphyroblasts with inclusion trails com monly preserve evidence of reactivation of earl ier foliations and therefore can be used to ident ify the presence of a deformation that has not been recognized by normal geometric methods because of penetrative reactivation reac tivation often reverses the asymmetry between pre existing foliations and bedding on one limb of a later fold leading to problems in the geo metric analysis of an area when the location of early fold hinges is essential the stretching lineation in a reactivated foliation can be rad ically reoriented potentially causing major errors in determining movement directions in mylonitic schistosities in folded thrusts geometric relationships which result from reactivation of foliations around porphyroblasts can be used to aid determination of the timing of the growth of porphyroblasts relative to deformation events other aspects of reac tivation however can lead to complications in timing of porphyroblast growth if the presence of this phenomenon is not recognized for example d grown porphyroblasts may be dis solved against reactivated s and hence appear to have grown syn d

microstructural evidence for an epigenetic origin of a proterozoic zinc lead silver deposit dugald river mount isa inlier australia the zn pb ag deposit contained in the metasediments of middle proterozoic age at dugald river forms one of a number of significant zones of sulphide mineralization within the eastern fold belt of the mount isa inlier it is characterized by its high zn pb grade high zn zn pb ratio and strong structural controls with the present resource standing at 38 million tons averaging 13 zn 2 1 pb and 42 g t ag microstructural timing relationships and a variety of microscopic ore textures indicate that the deposit resulted from replacement and partial infill of carbonaceous and pyritic host rocks by hydrothermal ore forming fluids during the d4 deformation event this genesis is contrary to earlier syngenetic based interpretations but accords with the discordant nature and structural controls on emplacement of the mineralization key timing criteria include 1 truncation of s2 and or s3 by the late ore minerals 2 replacement textures in undeformed mineral paragenesis 3 slightly preferred dimensional orientation and undulating extinction of quartz and muscovite that are intergrown but which crystallized earlier than sulphide minerals in veins the presence of these microstructural relationships throughout the deposit and the complete absence of any syngenetic stratiform precursor to zinc lead silver mineralization indicates that the zinc lead and silver at dugald river were epigenetically introduced rather than just having undergone syngenetic deposition during sedimentation and remobilization during deformation the regional distribution of the mineralization in a specific stratigraphic zone is most likely due to the partitioning of deformation between different rock types this caused the weaker lithology to accommodate significantly higher strain than adjacent more competent units resulting in fracturing and localization of the syntectonic mineralization

kinematic and metamorphic aspects of cleavage formation in very low grade metamorphic slates abstract fabric studies on first cleavages in very low grade metamorphic slates from the rheinisches schiefergebirge and other very low grade metamorphic fold belts reveal two types of slaty cleavage 1 1 cleavage without syntectonic phyllosilicate recrystallization these are generally crenulation cleavages 2 2 cleavage with syntectonic phyllosilicate recrystallization with increasing syntectonic metamorphism the crenulation fabric is modified by solution of grains along cleavage planes and precipitation of material within the cleavage lamellae with further increase of metamorphism the crenulation fabric is gradually obliterated the finite fabric results from progressive solution crystallization and recrystallization superimposed with bending kinking and internal rotation achieved by slip parallel to the basal planes of phyllosilicates

syndeformational carbonate replacement model for the copper mineralization at mount isa northwest queensland a microstructural study the mount isa base metal deposits show a definite spatial separation between stratiform ag pb zn lenses generally regarded as syngenetic and cu ores within a recrystallized and brecciated host lithology the silica dolomite microstructural evidence indicates that the cu orebodies and the silica dolomite formed during early syndeformational syn d 3 replacement processes in a dolomitic shale sequence three stages of alteration are distinguished 1 dolomite recrystallization silicification 2 dolomitization and 3 chalcopyrite or fe sulfide or quartz or chlorite deposition structural timing constraints suggest a post d 2 to pre s 3 interval for the first stage whereas the last two stages occurred during early d 3 the formation of the silica dolomite with the cu orebodies is separated in time from the adjacent syngenetic stratiform ag pb zn ores by a period including at least two regional deformation events

false pyroclastic textures in altered silicic lavas with implications for volcanic associated mineralization there is strong emphasis in recent literature that zn cu pb massive sulfide deposits associated with felsic volcanism the kuroko type deposits are directly related to submarine calderas formed by large submarine pyroclastic eruptions altered silicic volcanic rocks with the appearance of welded and nonwelded pyroclastic flow deposits volcaniclastic debris flows and massive to thin bedded tuffaceous rocks form a major component of a silurian succession that hosts zn cu pb massive sulfide deposits at benambra southeastern australia however critical evaluation of rock textures indicates that these silicic volcanic rocks are mainly lavas and associated autoclastic facies with remarkably deceptive false pyroclastic and volcaniclastic textures including apparent pumice fiamme and glass shards intercalated sediments indicate that most of the silicic volcanics were emplaced in subaqueous settings ranging from relatively shallow water to deep marine the false textures were produced mainly in originally glassy lava by the combined effects of devitrification perlitic fracture and pervasive hydrothermal alteration these processes are related to the emplacement and cooling history of individual lavas and to a regional essentially synvolcanic hydrothermal system tectonic foliation of the more altered and mechanically weakened rocks has led to partial dismembering of phenocrysts and groundmass fabrics thereby further enhancing clastic appearance subsequent to recognition of widespread false pyroclastic textures at benambra similar features have been identified in three other australian massive sulfide districts these results suggest that a reinvestigation of host rocks is warranted at other deposits where submarine pyroclastics are documented noncaldera settings combining subsidence in an extensional volcano tectonic basin passive submarine lava effusion within the basin and ambient sedimentation derived from basin margins including resedimented pyroclastic debris may be more relevant models in a number of massive sulfide districts

rock coatings and aeolian abrasion on mars application to the pathfinder landing site rock coatings can be used to constrain the rate of abrasion by wind on mars the susceptibility to abrasion for potential rock coatings on mars salt salt cemented coatings rock varnish and amorphous silica were determined experimentally rock coatings generally abrade more easily than the host rock although amorphous silica is an exception if coatings exist on rocks at the mars pathfinder landing site then the rate of abrasion is extremely low consistent with previous studies of erosion rates alternatively rock varnish or silica coatings could protect the rocks from sandblasting although this may require coating formation under current to recent conditions the pathfinder area may lack efficient abrasive particles and the observed duneforms may be composed of sand size dust aggregates rather than crystalline particles

microstructural timing of the rosebery massive sulphides tasmania evidence for a metamorphic origin through mobilization of disseminated base metals microstructural timing relationships indicate that the rosebery massive sulphide ore western tasmania australia formed by metasomatic replacement of sericite schist during a devonian deformation event d3 this interpretation is contrary to earlier volcanogenic based interpretations but accords with the discordant position and inferred structurally controlled emplacement of the orebody the main timing criteria are overprinting of s3 by the late ore minerals replacement textures in undeformed mineral parageneses and a d3 structural control from the microscopic to the macroscopic scales the consistent observation of these criteria in the orebody and the complete lack of pre d3 ore argue against in situ dissolution of a primary orebody and local redeposition of sulphides by replacement d3 deformation at rosebery is inferred to have been characterized by heterogeneous cleavage parallel extension which resulted in localized microfracturing and selective replacement of zones of maximum strain rate continuous shifts in the strain rate distribution pattern during progressive mineralization led to the compositional ore banding published pb isotope data point towards a cambrian source rock for the orebody this suggests a metamorphogenic origin by regional scale dissolution of dispersed volcanogenic metals focused solution transfer and concentrated redeposition in a structural trap

textural evidence for remobilization in metamorphic environments remobilization of stratabound massive sulphide deposits involves both dislocation flow mechanical remobilization and fluid state processes chemical remobilization textural support for such remobilization is presented at micro meso and macroscales microscale evidence establishes the degree the amount of a deposit affected of remobilization likewise mesoscale textures establish the degree and may provide mesoscale models of macroscale remobilization processes but still do not establish the extent the distance over which translocation may have occurred of remobilization where macrotexture indicates a departure from an original conformable relationship gross remobilization is suggested and may be the consequence of mechanical and or chemical processes the case for gross mechanical and or chemical remobilization is often difficult to sustain because alternative hypotheses e g hydrothermal replacement may be compatible with the observed relationships remobilization of a conformable ore layer may involve internal redistribution during which sulphides have been modified by dislocation flow and or fluid state processes within the layer constraints or external where the layer constraints have been substantially transgressed during dislocation flow and or fluid phase remobilization if mesoscale textures indicate remobilization of the external type then macroscale gross remobilization remains a possibility subject to substantiation

district scale alteration associated with massive sulfide deposits in the mount read volcanics western tasmania the distribution of secondary mineral assemblages in six mineralized areas of the mount read volcanics defines a district wide zonation which is subconformable with massive sulfide host horizons and the contacts of sill like granitoids where present the relationships between alteration patterns and elements of cambrian geology strongly suggest that the alteration is related to cambrian hydrothermal circulation responsible for massive sulfide mineralization there is a later greenschist facies metamorphic overprint the major components of the principal assemblages are quartz albite chlorite epidote quartz albite chlorite calcite quartz sericite chlorite and quartz k feldspar chlorite several complex assemblages involving the above minerals biotite magnetite pyrite and tourmaline are characteristic of granite contacts secondary biotite is also present sporadically in the rosebery area probably related to devonian granitoids at depth there is a districtwide zonation of sodic or calcic versus nonsodic noncalcic assemblages in felsic volcanic rocks in preore volcanics nonsodic noncalcic assemblages occur immediately beneath the host horizon and may persist several hundred meters before passing into a zone including granite contacts where calcium minerals and albite occur sporadically the nonsodic noncalcic assemblages are predominantly sericitic but assemblages with prominent k feldspar occur locally in postore volcanics sericitic non sodic noncalcic assemblages may persist up to 200 m above the ore horizon before passing into relatively fresh volcanics with common albite and calcic greenschist minerals preore assemblages probably largely reflect downward circulation upwelling zones are characterized by intense sericite chlorite or chlorite development with or without k feldspar lateral spreading of solutions immediately beneath the ore horizon is common chlorite compositions preserve local patterns due to cambrian hydrothermal processes but they do not vary systematically with alteration assemblages throughout the province chlorite mg to fe ratios appear to have been preserved through metamorphism a combination of structural and alteration data is useful to mapping in the mount read volcanics this approach indicates that most syngenetic deposits and sedimentary lenses in the rosebery hercules area may lie on a single host horizon and suggests a continuity of geology from mount farrell through red hills to mount sedgwick

two phase syntectonic gold mineralization and barite remobilization within the main ore body of the golden giant mine hemlo ontario canada abstract structural analysis of the central part of the hemlo gold deposit in the hemlo heron bay greenstone belt has revealed four generations of deformation structures d1 d4 the second d2 and fourth d4 deformations significantly influenced the orebody and controlled the localization of gold mineralization development of d3 dextral shearing during retrogressive conditions resulted in strain partitioning around the feldspathic orebody such that this deposit appears to be controlled by the hemlo shear zone however the orebody dominantly preserves vertical d2 parasitic folds rather than d3 structures the earliest occurrence of gold is with molybdenite as s1 inclusion trails in vanadium muscovite grains that grew during d2 this suggests that the gold deposit was emplaced by at least early d2 syngenetic banded barite was partially dissolved transported and redeposited during each deformation event and in particular in association with brittle deformation that occurred during d4 microstructural relationships indicate two distinct generations of gold the first generation is associated with molybdenite and potassic alteration and was deposited before or early in d2 during progressive amphibolite facies metamorphism the second generation formed by redistribution and concentration of gold together with stibnite in ductile brittle d4 structures after peak metamorphic conditions

imaging of the moho depth in madagascar through the inversion of gravity data geodynamic implications several e w profiles of bouguer anomalies across the precambrian basement were inverted by applying a linearized inversion procedure in the spectral domain and using a simplified two layer model with a crust upper mantle interface of constant density contrast from these inverted profiles a contour map of moho topography has been constructed which covers the area of exposed precambrian basement in the eastern and central parts of the island such imaging of the moho depth in particular exhibits a n20 e trending zone of substantially thinned crust along the axis of the island this parallels the east coast margin which resulted from the northward motion of india relative to madagascar in the upper cretaceous from combined analysis of geological tectonic and metamorphic observations this prominent crustal feature in the precambrian basement of madagascar is interpreted as the relic of continental lithospheric extension and thinning possibly related to panafrican collapse tectonics on the eastern edge of the mozambique belt this extensional feature would have been reactivated only in part during the rifting and dislocation stages of the madagascar and india continental blocks as evidenced by an axis of cretaceous volcanism emphasized by the ankaratra and itasy massifs final separation nevertheless occurred further east at the site of the east coast margin

replacement textures in cai and implications regarding planetary metamorphism textural and chemical features of five coarse grained calcium aluminum rich inclusions from the allende meteorite indicate that some of the melilite in these inclusions was formed by a secondary metamorphic event and not by primary crystallization from a melt or by a sequential nebular condensation process these inclusions contain embayed pyroxene surrounded by melilite physically separated pyroxene crystals are often in optical continuity indicating that they were once part of larger single crystals that have been partly replaced by melilite other evidences of metamorphism include reaction textures between melilite and spinel and metamorphic textures such as kink band like features lobate sutured grain boundaries and 120 triple points this type of metamorphic process requires the addition of ca which we propose came from calcite or by introduction of a fluid phase we believe that the most likely environment for this metamorphic process is on a small planetary body and not in the solar nebula the results of this study are compatible with oxygen isotopic heterogeneities within cai and provide a mechanism for producing lower temperature alteration phases and the rim phases found in these inclusions we conclude that planetary processes must thus be considered in the formation history of cai and that it is necessary to reconsider the classification system of these objects in light of the replacement process proposed here

base metal exploration of the mount read volcanics western tasmania pt iii application of lead isotopes at elliott bay lead isotope studies were carried out in the southern part of the mount read volcanics on rock chip drill core and bed rock geochemical samples in order to improve the genetic model of mineralization and to assign exploration priorities samples analyzed from 20 separate mineralized occurrences fall into three major isotopic groups which correspond to three different styles and episodes of mineralization samples of the cambrian stratiform massive sulfide pb zn ag mineralization at the stratigraphic top of the rhyolite volcanic pile constitute the least radiogenic group 206 pb 204 pb 18 06 to 18 14 and samples from the devonian vein style pb zn as mineralization emplaced along major faults in the western epiclastic and sedimentary rocks form the most radiogenic group 206 pb 204 pb 18 44 to 18 53 a third group consists of samples with isotopic ratios mostly intermediate between the other two the majority of the 206 pb 204 pb ratios range from 18 18 to 18 30 the samples come from disseminated and vein type pb zn mineralization associated with bodies of quartz porphyry which intrude the pyroclastic sequence and are considered to be later than the episode of massive sulfide formation the samples also contain strata bound gold mineralization which is typically associated with carbonate alteration in the host volcanics a plot of lead contents versus isotopic ratios of these samples gives an inverse correlation and indicates that the spread in ratios results from radioactive decay since mineralization the samples as a whole indicate one source of lead emplaced in the cambrian rather than a mixing of two sources one cambrian and the other devonian lead isotope data for all samples of mineralization and volcanics studies can be interpreted in a multistage model to imply an ultimate source for the lead from the precambrian basement the ratios of massive sulfide mineralization at elliott bay are distinctly less radiogenic than for massive sulfide mineralization farther north in the mount read volcanics at rosebery and que river and this implies the possibility of different ages for the separate mineralizing systems or a variation in the u th pb characteristics of source regions along the volcanic belt

the stratigraphic and structural setting of the mt lyell volcanic hosted sulfide deposits volcanic hosted sulfide deposits at mt lyell are confined to a complex silicic volcanic unit mine sequence which is up to 800 m thick and includes laterally impersistent lavas ash flow and ash fall deposits as well as abundant open framework volcanic mass flow breccias pervasive hydrothermal alteration involving na depletion is associated with the sulfide mineralization and persists with minor disseminated pyrite mineralization over a strike length of 8 km within the mine sequence stratigraphic relations together with lithofacies and thickness variations in volcanic units suggest that the sulfide mineralization and hydrothermal alteration occurred at a major eruptive center and that ore deposition occurred over an extended time interval during the accumulation of the mine sequence two orientation groups of middle devonian folds are present in the area first generation d 1 folds are closed to tight and upright north northwest trending structures which largely control the distribution and orientation of rock units in the volcanic sequence but have not been associated with significant microstructural modification of the ores or host rocks open west to west northwest trending upright second generation d 2 folds are well developed in sedimentary sequences overlying the volcanic sequence but are poorly developed in the volcanic sequence itself d 2 strain has been accommodated in the volcanic sequence largely by the development of a mesoscopically penetrative west to west northwest trending upright foliation s 2 and associated downdip lineation l 2 shortenings of up to 60 percent perpendicular to s 2 and elongations of up to 150 percent parallel to l 2 have modified primary sulfide microstructures and are responsible for many of the sulfide deposits in the area being elongate in the l 2 direction

the environmental significance of ventifacts a critical review abstract ventifacts wind abraded clasts or rock surfaces are common features of many terrestrial hot and cold deserts coastal periglacial and mountain environments as well as on mars and have a long history of investigation this review paper discusses some of the main themes in terrestrial ventifact research including their formation and geomorphic controls the varied morphological forms of ventifacts in terrestrial environments and their environmental significance as indicators of past and present wind direction and sediment mobility are critically evaluated future research directions are identified

mount isa silica dolomite and copper orebodies the result of a syntectonic hydrothermal alteration system complex hydrothermal alteration system postdates deposition of the mount isa group and the lead zinc silver orebodies silica dolomite results from differential progressive metasomatic alteration of the entire range of microfacies constituting the lead zinc sequence the main components of this alteration are phyllosilicate development dolomitization and silicification this study concentrates on the latter two components and their role in breccia host formation all stages from incipient bedding and vein controlled alteration to total pervasive brecciation can be related to a deformational history of folding cleavage development and faulting a regional folding event d 2 formed the fold limb which constitutes the ore setting dolomite replacement veins and pseudobreccia complexes developed with varying intensity in favorable zones combinations of bedding and fracture controlled replacement continued until total dolomitization of the former shales occurred all forms and stages of dolomitic pseudobreccias are preserved by pseudomorphic quartz replacement in silicification zones which form the core of the orebody systems the separation in timing and mode of formation of lead zinc and copper orebodies is significant for exploration in the mount isa inlier the lead zinc mineralization appears to accumulate either syngenetically or at a very early stage in diagenesis but the copper has a structural control and a basic igneous association and is estimated to have been introduced at least 150 m y later modified journal abstract

stratigraphy and mineralization in the mt read volcanics western tasmania most of the known sulfide mineralization in the mt read volcanics occurs within a central belt of rhyolitic dacitic andesitic volcanics 9 to 12 km wide and roughly 90 km long in which felsophyric lavas and ash flows are common but sediments are rare the volcanics resemble rhyolitic caldera complexes in part and large sections appear to be subaerial sediments and tuffs which probably represent marine embayments are also present and the exhalative massive sulfides tend to coincide with local marine units preliminary radiometric dating indicates a middle cambrian age for the belt at queenstown the central belt is flanked on the western side by folded volcano sedimentary marine sequences partly of middle cambrian age in which volcanic lithic turbidites and quartz phyric tuffs are common contacts with the central belt range from abrupt and faulted to conformable and possibly interfingering and interpretation of the relationship is difficult some evidence suggests that the mineralized belt may represent a volcano tectonic rift structure superimposed on a larger marine basin overlying the central belt in the queenstown mt darwin area is an unmineralized sequence of volcaniclastic conglomerates and quartz phyric volcanics of late middle cambrian to late cambrian age deposition of this sequence occurred largely in local graben structures and was accompanied by considerable erosion of the earlier volcanics some mineralization in the darwin mt lyell area was probably removed at this stage

flow mechanisms in sulphide minerals abstract the sulphide minerals as a group display a diverse range in strength and mechanical behaviour in crustal environments deforming by a range of different flow mechanisms which can lead to the development of characteristic microfabrics the dependence of creep rate on imposed parameters such as stress difference temperature grainsize effective confining pressure and the activities of various components varies for each type of flow mechanism for particular phases changes in the dominant operative flow mechanism may occur in response to changes in the imposed environmental variables at high applied stress differences low effective confining pressures and low temperatures brittle failure and cataclastic flow are significant deformation mechanisms in some sulphide minerals at elevated confining pressures brittle failure can be suppressed and low temperature plasticity processes involving dislocation glide and or deformation twinning may operate with decreasing applied stress difference and at elevated temperatures even though strain may be accommodated largely by dislocation glide deformation may be rate controlled by recovery processes and dynamic recrystallization may be significant in influencing microfabric development the operation of dislocation glide processes leads to the development of crystallographic preferred orientations at very low applied stress difference various grainsize dependent atomic transfer deformation mechanisms may be important in many fluid present low to medium grade metamorphic environments solution precipitation creep processes are active in the deformation of some sulphide phases in fluid absent situations grain boundary diffusion creep may be significant at higher temperatures where intragranular diffusion is relatively rapid lattice diffusion creep processes are expected to be a major deformation mechanism in fine grained sulphide assemblages at elevated temperatures grain boundary sliding may be an important deformation mechanism

distribution mineralogy and geochemistry of gold and silver in the north end orebody rosebery tasmania study of the spatial and mineralogical distribution of gold and silver in the rosebery north end orebody indicates that both silver and gold are concentrated in massive sphalerite galena pyrite ore and barite mineralization six styles of gold mineralization have been recognized 1 in massive sphalerite galena pyrite ore the dominant occurrence 2 in massive barite mineralization 3 in the upper parts of pyrite chalcopyrite pods in general pyrite chalcopyrite pods are gold poor 4 in distal pyrite mineralization at the edges of sphalerite galena pyrite mineralization and in the overlying host rocks 5 in footwall mineralization poorly sampled and understood and 6 in remobilized quartz carbonate veins mineralogically gold occurs as electrum which is commonly associated with pyrite in sphalerite galena pyrite ore and distal pyrite mineralization a lesser association of gold with tetrahedrite has been noted by brathwaite 1969 the grain size of electrum has a lognormal distribution with most grains having dimensions of less than 25 mu m silver occurs dominantly in tetrahedrite and to a lesser extent in galena henley and steveson 1978 remobilized tetrahedrite is silver and antimony rich whereas in tetrahedrite from both sphalerite galena pyrite ore and massive barite mineralization the silver contents increase with the antimony contents

the nature and controls on downstream fining within sedimentary links abstract at scales of 100 to 102 km grain size change in gravelly alluvial systems is characterized by punctuated downstream fining significant lateral sediment inputs define a sequence of sedimentary links within which fluvial processes produce fining trends using a new set of surface grain size data eighteen such links along two canadian gravel bed rivers are examined negative exponential functions are found to be most appropriate for describing within link grain size changes development of a pragmatic means of predicting grain size is then pursued by searching for a means to relate model diminution coefficients to link attributes consideration of lithologically differentiated fining trends indicates that lithology plays an insignificant role in controlling fining rate examination of within link longitudinal profiles indicates a reasonable relation between fining rate and the rate of change of channel slope the predictive value of this relation is limited by the regional nature of the data upon which it is based and the relative difficulty of obtaining accurate gradient information however as previously noted for alluvial fans although for different reasons channel gradient is correlated with link length and a reasonable predictive tool is apparent in a relation between link length and diminution rate the validity of the derived relation cannot be tested for want of a suitable data set several lines of evidence indicate that abrasion is unimportant as a fining mechanism on these rivers and it is argued that this may be typical of sedimentary links fining rate must then be a function of the efficiency with which sorting processes operate and it is suggested that this efficiency is dependent on aggradation rates associated with the lateral sediment influxes at the head and terminus of individual links

formation of surface features on ventifacts modeling the role of sand grains rebounding within cavities surface textural features pits grooves flutes and scallops of sand blasted ventifacts have been attributed to various erosional mechanisms and to variations in material hardness this study develops a numerical model of abrasion to examine feature formation by direct grain impacts we demonstrate that abrasion by a continuous supply of impactors arriving from a single direction each hitting the surface once transforms existing cavities into transient features similar to scallops flutes and pits which shrink and eventually vanish however by incorporating additional impacts within the features from rebounding particles persistent continuously growing features emerge we conclude that 1 rebounding particles concentrate their effect within features and therefore increase their size 2 the development of features is sensitive to material type and 3 the ultimate maximum feature scale is related to the size of the rock and the size and velocity of impactors our model helps organize diverse ventifact field observations into an initial framework of pattern formation and confirms field and laboratory observations that the most common features are linear in wind parallel directions

crust strength a wind tunnel study of the effect of impact by saltating particles on cohesive soil surfaces a wind tunnel study examined the effect of distributions of saltating particles on sediment surfaces which were characterized by distributions of their tensile strength the sediments consisted of varying proportions of large sand sized particles with a fine particle cement the energies of the impacting particles and the surface strengths were compared with the mass of material lost from the surface it is important to consider distributions of parameters rather than mean values only since abrasion and erosion may occur from surfaces not predicted from average strength and saltation velocities at the impact velocities used in this study mean velocity 4 4 m s 1 with standard deviation of 0 51 surfaces containing less than 12 per cent fine material were easily eroded but insignificant erosion occurred when the fine particle content exceeded 60 per cent small amounts of cementing material were easily ruptured allowing the large sand grains to be moved largely in creep by the bombarding particles a significant amount of energy was lost to the bed as the percentage of fine material increased the surface became more difficult to break up and less energy was lost to the bed the probability that erosion will occur for known energy distributions of impacting particles and surface strength can be calculated and the mass loss increases exponentially with a decrease in the percentage of fine cementing particles copyright 2001 john wiley sons ltd

metallogeny and tectonic development of the tasman fold belt system in tasmania abstract in western tasmania precambrian sedimentary sequences form the basement for narrow trough accumulations of eocambrian and younger sequences the main trough the meridional dundas trough is flanked to the west by the rocky cape region of precambrian rocks within which major apparently stratiform exhalative magnetite pyrite deposits are intercalated with metabasaltic volcanics and ultramafic bodies the eocambrian cambrian troughs apparently developed during extension of precambrian continental crust early shallow water deposition includes thick dolomite units in some troughs deepening of the troughs was accompanied by turbidite sedimentation with minor limestone and submarine basaltic volcanism with associated minor disseminated native copper ultramafic and related igneous rocks were tectonically emplaced in some troughs during a mild compressional phase they contain only minor platinoids copper nickel sulphides and asbestos but are source rocks for tertiary secondary deposits of platinoids chromite and lateritic nickel in the dundas trough eocambrian early cambrian rocks are separated by an inferred erosional surface from structurally conformable overlying middle to late cambrian fossiliferous turbidite sequences the structural conformity continues through overlying ordovician to early devonian terrestrial and shallow marine stable shelf deposits a considerable pile of probable middle cambrian felsic volcanics accumulated between the sedimentary deposits of the dundas trough and the tyennan region of precambrian rocks to the east a lava dominated belt within the volcanics hosts major volcanogenic massive sulphide deposits including those of the exhalative type which in the south are enriched in copper gold and silver whereas in the north they are rich in zine lead copper gold and silver cambrian movements along faults near the margin of the tyennan region resulted in erosion of the mineralized volcanics locally exposing sub volcanic granitoids above the local unconformities occur unmineralized volcaniclastic sequences that pass conformably into ordovician to early devonian shelf deposits ordovician limestone locally hosts stratabound disseminated and veined base metal sulphide deposits pre middle devonian rocks of western tasmania differ for most part from those in the northeast where deeper marine turbidite quartz wacke sequences were deposited during the ordovician and early devonian the eocambrian to early devonian rocks of tasmania were extensively deformed in the mid devonian the precambrian regions of western tasmania behaved as relatively competent blocks controlling early fold patterns in northeastern tasmania folding is of similar age but resulted from movements inconsistent with those affecting rocks of equivalent age in western tasmania the final metallogenic event is associated with high level granitoid masses emplaced throughout tasmania during the middle to late devonian in northeastern tasmania extensive i type granodiorite and s type granite with alkali feldspar granites are associated with mainly endogranitic stanniferous grelsens and wolframite cassiterite vein deposits in contrast scheelite bearing skarns and cassiterite stannite pyrrhotite carbonate replacement deposits are dominant in western tasmania associated mainly with s type granites several argentiferous lead zinc vein deposits occur in haloes around tin tungsten deposits a number of gold deposits are apparently associated with i type granodiorite but some have uncertain genesis the contrasting regions of western and northeastern tasmania have probably been brought together by lateral movement along an inferred fracture flat lying late carboniferous and younger deposits rest on the older rocks and the only known post devonian primary mineralization is gold associated with creta ceous syenite

the murchison gorge tasmania a possible cross section through a cambrian massive sulfide system the murchison gorge northeast of rosebery in tasmania is believed to expose a section through the main elements of an inferred volcanogenic massive sulfide forming system the top of the steeply dipping section is dominated by shallow marine siltstones of the farrell slates which host several sulfide bodies the farrell slates conformably overlie an altered succession of rhyodacitic and dacitic tuffs and lavas the murchison volcanics a sill like monzonitic quartz monzonitic body the murchison granite is emplaced in the murchison volcanics about 2 to 3 km stratigraphically below the farrell slates the sulfide deposits in the farrell slates are of devonian age but sulfur isotope studies and comparisons with the cambrian massive sulfide horizons at red hills and rosebery suggest that the slates are a local cambrian mineralized horizon the murchison granite and the murchison volcanics appear to be comagmatic and coeval and are similar to calc alkaline intrusions and volcanics of orogenic continental margins both the volcanics and the granite are extensively altered the granite has been subject to potassic alteration chloritization and late calcite epidote alteration minor greisenization was also noted there is a vertical zonation of alteration mineralogy in the volcanics between the farrell slates and the top of the granite as follows top sericite zone a sericite quartz b sericite quartz calcite k feldspar chlorite hematite chalcopyrite pyrite c sericite quartz chlorite calcite hematite k feldspar albite chlorite zone chlorite sericite albite calcite hematite magnetite epidote zone epidote chlorite calcite magnetite allanite potassic zone chlorite epidote calcite k feldspar pyrite magnetite the increasing predominance of hematite over magnetite toward the top of the section is consistent with an increase in fluid f sub o 2 away from the granite chlorites from the four zones lie in fairly clear fields on an mgo vs feo plot trends of decreasing mgo and increasing feo up the section are consistent with decreasing temperature sulfide delta 34 s values increase from about 9 per mil within the granite through 10 to 14 per mil in the overlying volcanics to 17 per mil in the farrell slates the high values suggest cambrian seawater sulfate 30 35ppm as the dominant sulfur source in the system the up section variation is ascribed to varying degrees of mixing between cambrian seawater derived sulfur and lighter magmatic sulfur

experimental replacement of chalcopyrite by bornite textural and chemical changes during a solid state process chalcopyrite was reacted with covellite and with chalcocite respectively between 200 c and 500 c the ensuing solid state replacement of chalcopyrite by bornite was studied both texturally and chemically the relatively oxidizing conditions of the reaction chalcopyrite covellite result in massive replacement lacking structural control where bornite and pyrite form complex intergrowth textures in chalcopyrite bornite nucleates around growing pyrite aggregates because of the release of copper and a decrease in volume diffusion of sulphur along grain boundaries and fractures largely controls the textural development reaction under the relatively reducing conditions involving chalcopyrite chalcocite results in replacement of chalcopyrite in the sequence where chalcopyrite is replaced by bornite below about 355 c and by intermediate solid solution iss and later bornite above 355 c the textural development changing from replacement apparently uninfluenced by directional properties in the host to semioriented replacement is structurally controlled this suggests that the process is governed by diffusion of copper and iron through a sulphur framework it is suggested that the observed formation of oriented bornite lamellae in chalcopyrite and in iss during the chalcopyrite chalcocite reaction may be explained by replacement exsolution at constant temperature

structure hydrothermal alteration and composition of the rubiales pb zn orebody lugo spain genetic model the rubiales pb zn ore deposit northwestern spain is situated in the westasturian leonese zone according to the division of the hercynian chain in the iberian peninsula julivert et al 1972 the orebody is placed in a subvertical shear zone developed at the eastern limb of the baralla syncline within the middle and upper members of the lower cambrian transition series the deposit is a vertical lenticular mass with a n30 w direction its length is about 1200 m in a n s direction by 600 m wide and has an average thickness of 30 m

wind tunnel experimental investigation of sand velocity in aeolian sand transport sand velocity in aeolian sand transport was measured using the laser doppler technique of pdpa phase doppler particle analyzer in a wind tunnel the sand velocity profile probability distribution of particle velocity particle velocity fluctuation and particle turbulence were analyzed in detail the experimental results verified that the sand horizontal velocity profile can be expressed by a logarithmic function above 0 01 in while a deviation occurs below 0 01 m the mean vertical velocity of grains generally ranges from 0 2 m s to 0 2 m s and is downward at the lower height upward at the higher height the probability distributions of the horizontal velocity of ascending and descending particles have a typical peak and are right skewed at a height of 4 turn in the lower part of saltation layer the vertical profile of the horizontal rms velocity fluctuation of particles shows a single peak the horizontal rms velocity fluctuation of sand particles is generally larger than the vertical rms velocity fluctuation the rms velocity fluctuations of grains in both horizontal and vertical directions increase with wind velocity the particle turbulence intensity decreases with height the present investigation is helpful in understanding the sand movement mechanism in windblown sand transport and also provides a reference for the study of blowing sand velocity c 2007 elsevier b v all rights reserved