controls on sand ramp formation in southern namibia sand ramps have the potential to provide rich palaeoenvironmental information in dryland regions wherein proxy records are typically scarce however current knowledge of the geomorphic controls and processes of sand ramp formation is limited this study provides a data rich examination of the key factors controlling sand ramp formation the location and morphology of 75 sand ramps in southern namibia are examined the sediments and chronologies of 10 sand ramps are studied in detail using 51 osl dates and 83 grain size and loi samples heavy mineral assemblages are used to determine the provenance of 10 samples and osl sensitivity is used to explore geomorphic processes of 8 samples sand ramp morphology can be grouped into one of four classes of increasing size and complexity and is closely linked to the available accommodation space heavy mineral assemblages indicate local sediment sources and all 75 studied sand ramps are within 4 km of a large ephemeral river channel or within 5 5 km of a dune field therefore accommodation space and sediment supply are identified as the primary controls of sand ramp formation sedimentology and osl sensitivity suggest a complex interplay of aeolian fluvial and colluvial processes contribute to sand ramp formation with large variability observed between ramps three of the ten dated sand ramps have been present in the namibian landscape for 100 ka eight sand ramps show episodic deposition between 75 12 ka and five show evidence of surface reworking over the past 2 ka environmental sensitivity is likely to be linked to the size and availability of the accommodation space therefore individual sand ramps are expected to reflect local environmental conditions recording when an abundant sediment supply coincided with available accommodation space whilst a regional analysis of multiple sand ramps with chronometric data offers the potential to identify larger scale palaeoenvironmental controls of sediment supply

diffusion of ar in k feldspar present and absent the mechanisms of ar release from k feldspar samples in laboratory experiments and during their geological history are assessed here modern petrology clearly established that the chemical and isotopic record of minerals is normally dominated by aqueous recrystallization the laboratory critique is trickier which explains why so many conflicting approaches have been able to survive long past their expiration date current models are evaluated for self consistency especially arrhenian non linearity leads to paradoxes the models testable geological predictions suggest that temperature based downslope extrapolations often overestimate observed geological ar mobility substantially an updated interpretation is based on the unrelatedness of geological behaviour to laboratory experiments the isotopic record of k feldspar in geological samples is not a unique function of temperature as recrystallisation promoted by aqueous fluids is the predominant mechanism controlling isotope transport k feldspar should therefore be viewed as a hygrochronometer laboratory degassing proceeds from structural rearrangements and phase transitions such as are observed in situ at high temperature in na and pb feldspars these effects violate the mathematics of an inert fick s law matrix and preclude downslope extrapolation the similar upward concave non linear shapes of arrhenius trajectories of many silicates hydrous and anhydrous are likely common manifestations of structural rearrangements in silicate structures

climbing and falling dunes in valles marineris mars 1 multiple occurrences of wall dunes are found several kilometers above the valles marineris canyon floor dune slip face orientation and bed form morphologies indicate transport direction and whether the wall dunes are climbing dunes or falling dunes on earth these types of dunes form in a unidirectional wind regime and are strongly controlled by the local topography newly acquired mars reconnaissance orbiter mro images and topography of the walls of valles marineris show similar sand dune morphologies as wind blown sediment has interacted with local and regional topography primarily found in melas and coprates chasmata these climbing and falling dunes are relevant for understanding aeolian sediment flux sediment sources and wind directions falling dunes show photogeologic and thermophysical evidence of their sand being provided by adjacent outcrops

simulation and measurement of surface shear stress over isolated and closely spaced transverse dunes in a wind tunnel topographic interactions generate multidirectional and unsteady air ow that limits the application of velocity pro le approaches for estimating sediment transport over dunes results are presented from a series of wind tunnel simulations using irwin type surface mounted pressure sensors to measure shear stress variability directly at the surface over both isolated and closely spaced sharp crested model dunes findings complement existing theories on secondary air ow effects on stoss transport dynamics and provide new information on the in uence of lee side air ow patterns on dune morphodynamics for all speeds investigated turbulent unsteadiness at the dune toe indicates a greater more variable surface shear despite a signi cant drop in time averaged measurements of streamwise shear stress at this location this effect is believed suf cient to inhibit sediment deposition at the toe and may be responsible for documented intermittency in sand transport in the toe region on the stoss slope streamline compression and ow acceleration cause an increase in ow steadiness and shear stress to a maximum at the crest that is double that at the toe of the isolated dune and 60 70 per cent greater than at ow reattachment on the lower stoss of closely spaced dunes streamwise ow accelerations rather than turbulence have greater in uence on stress generation on the stoss and this effect increases with stoss slope distance and with incident wind speed reversed ow within the separation cell generates signi cant surface shear 30 40 per cent of maximum values for both spacings this supports eld studies that suggest reversed ow is competent enough to return sediment to the dune directly or in a de ected direction high variability in shear at reattachment indicates impact of a turbulent shear layer that despite low values of time averaged streamwise stress in this region would inhibit sediment accumulation downwind of reattachment shear stress and ow steadiness increase within 6 h h dune height of reattachment and approach upwind values by 25 h a distance of at least 30 h is suggested for full boundary layer recovery which is comparable to uvial estimates the irwin sensor used in this study provides a reliable means to measure skin friction force responsible for sand transport and its robust simple and cost effective design shows promise for validating these ndings in natural dune settings copyright 2003 john wiley sons ltd

grain size trends associated with net sediment transport patterns an example from the belgian continental shelf grain size trends in relation to net sediment transport pathways are examined using some commonly used grain size parameters the results of the trend analysis for 15 types of the trends are compared with a known net sediment transport pathways established on the basis of the sandbank hydro and sediment dynamics i e general water and sediment movement patterns and bedform asymmetry it is shown that 1 the results for grain size trends associated with a worsening in sorting along the transport pathways have little similarity to transport pathways 2 the results for grain size trends associated with an improvement in sorting along the transport pathways have relatively high degree of similarity to the identified pathways and 3 the residual pattern derived on the basis of a combined grain size trend used elsewhere gao and collins 1992 appears to be most similar and suitable for defining transport pathways

net sediment transport patterns over the bohai strait based on grain size trend analysis grain size trend analysis indicates two distinct characteristics of sediment transport in bohai strait eastward transport dominates the western area and along the coast of the shangdong peninsula this result supports the previous work which indicated that the yellow river sediments are transported from the bohai sea to the yellow sea through the south channel of bohai strait and dispersed into the southern yellow sea along the coast of shangdong peninsula in the central eastern bohai strait net deposition is taking place as indicated by the convergence of the grain size trends this result is consistent with current circulation pattern on bohai strait and the interpretation of strata disclosed by seismic reflection profile this study supports the use of grain size trend analysis for large scale areas on the continental shelf

high cu grades in porphyry cu deposits and their relationship to emplacement depth of magmatic sources observations at several porphyry cu deposits indicate that in those formed above source magma chambers emplaced to relatively shallow levels roofs 3 4 km deep zones of higher cu grade are associated with the oldest intrusions of a central porphyry cluster abundant early a type quartz veins secondary feldspar alteration and usually high fe fe cu low s fe cu sulfide oxide mineral assemblages in deposits for which source magma chambers were deeper roofs 5 km porphyries closest in age to ore are spatially less directly related to mineralization in these higher cu grades in early mineralization comprise swarms of veinlets with alteration halos that include sericite as well as secondary feldspar and biotite sulfide oxide assemblages are usually of lower fe fe cu and higher s fe cu these differences in deposit characteristics appear to correspond with a change from two phase chloride bearing aqueous fluids that would exsolve from magma at shallow depths to one phase fluids deeper

residual sediment transport paths on a tidal sand bank a comparison between the modified mclaren model and bedform analysis abstract in order to evaluate the validity of the modified mclaren model for sand transport on a tidal sand bank 42 grab samples taken from the northern part of the kwintebank were decalcified sieved and analyzed for statistical parameters the areal distribution of mean grain size standard deviation and skewness were defined and used to determine the residual transport directions the grain size trends taken into consideration were that the sediment becomes finer better sorted and more negatively skewed along the transport pathways f b and the sediment becomes coarser better sorted and more positively skewed along the transport pathways c b these were compared with the transport paths inferred from bedform asymmetries obtained by side scan sonar records there were major differences between the sediment transport paths resulting from the two techniques when the f b trend and small dune asymmetries are compared only 5 out of 24 cases showed agreement 30 whereas in 9 cases the trends were 180 30 different there was even less agreement between the c b trend and the asymmetry of the small dunes only 1 out of 24 cases agreed 30 and almost half of the cases were 90 30 different the sediment transport directions deduced from the morphological analysis of the large dunes all point in the direction of the peak flood current the large dunes seem to be more suitable indicators of the sediment transport paths than the small ones however they conflict with the vectors resulting from the f b trend only one out of 20 cases agrees 30 while in 13 cases the vectors are 180 30 different and in three cases 90 30 neither do the transport directions from the c b trend agree with those deduced from the large dunes only one case agrees 30 while in four out of 20 cases the vectors point in opposite directions in four cases the vectors are 90 30 different the asymmetric cross section of the sand bank suggests sediment transport in a northwest direction it does not seem probable however that sediment transport occurs by migration of the whole sand bank the transport directions inferred from the bank morphology are quite different from the f b trend in 12 out of 42 cases the vectors agree 30 in four cases the vectors point in opposite directions and in 15 cases they are 90 30 different there is slightly more agreement between the c b trend and the transport directions deduced from the sand bank 16 out of 42 cases agree 30 in nine cases the vectors point in opposite directions and three cases are 90 30 different from this study it seems that the residual sediment transport directions can best be deduced from the morphological characteristics of the large dunes the departures between the results of the sediment trend analysis according to the modified mclaren model and the morphology of the subaqueous bedforms are partly explained by the location of the study area near the edge of the sand bank probably better results of the sediment trend analysis would be obtained if samples over the whole length of the sand bank were analyzed and compared perhaps a smaller spacing between the samples would improve the results as well and maybe the samples should not have been decalcified possibly the different transport patterns are attributed to different sediment transport processes which makes a comparison virtually impossible

application of grain size trend analysis for the determination of sediment transport pathways in intertidal areas abstract in this paper we apply the gao and collins procedure of grain size trend analysis for the first time in an intertidal sedimentary system our purpose is to evaluate a reliable method to determine residual transport directions in intertidal environments where sediment movement is not well understood residual transport patterns can be determined by grain size trend analysis if the following criteria are applied 1 a single sediment transport unit must be precisely defined and investigated 2 the thickness of sampling has to be chosen in order to investigate the most recent sedimentary event and 3 a regular mesh grid is sampled to avoid bias in the calculation of grain size trends the gao and collins method was undertaken simultaneously with a topographic survey and a tracer experiment during consecutive meteorological conditions of fair weather and a storm event the topographic changes observed between these two situations and the directions of sediment movement deduced from tracer tracking are coherent with the residual transport pattern calculated from the grain size trend analysis the method was tested on a ridge and runnel system which corresponds to the intertidal part of a macrotidal beach called la salie beach located along the southwest french coast in a high wave energy environment this study permits us to recognize two different residual transport patterns for this intertidal ridge and runnel system one for fair weather and a second for storm conditions during fair weather specific sites are subject to sand accretion while during storm conditions these sand stocks are subsequently spread out over the whole area and remain partly on the beach

cross shore grain size and sorting patterns for the bed profile variation at a dissipative beach hasaki coast japan abstract three field observations were conducted in three consecutive years on a sandy beach on the east coast of japan sediment cores were collected from the shoreline to the end of the offshore bar region each core was subdivided into layers and the sorting and skewness were analyzed using predefined trask coefficients the correlations between sediment properties that is median diameter sorting and skewness with respect to the change in the bed profile are discussed in this paper the weekly bed profiles offshore wave conditions and wave energy along the bed profile during the observation periods are discussed two significant sediment types were observed finer well sorted sediment and coarser poorly sorted sediment both coarser skewed the latter sediment properties were observed near the shoreline and at deeper elevations of the cross shore bed profile finer well sorted sand was transported away from and toward the coast depending on the wave intensity which causes in depth materials of coarser poorly sorted sediments to reappear with time the offshore bar and trough region has a limited erosional depth due to the existence of poorly sorted coarser materials which has been confirmed using weekly bed profile measurements the sediment properties have a direct influence on the change of the bed profile

scanning electron microscope cathodoluminescence analysis of quartz reveals complex growth histories in veins from the butte porphyry copper deposit montana scanning electron microscope cathodoluminescence sem cl analysis of quartz reveals textures that cannot be observed using optical microscopy or backscattered electrons these cryptic textures yield insight into timing and physical conditions of quartz growth especially in environments with multiple quartz precipitation events hydrothermal quartz from quartz sulfide veins in the porphyry copper deposit in butte montana was analyzed by sem cl revealing the following textures euhedral growth zones wide nonluminescing bands that cut across multiple quartz grains rounded luminescent quartz grain cores with euhedral overgrowths nonluminescing splatters of quartz connected by networks of cobweb like nonluminescing quartz in otherwise luminescent quartz concentric growth zones and wide nonluminescent grain boundaries these textures indicate that many veins have undergone fracturing dilation growth of quartz into fluid filled space quartz dissolution and recrystallization of quartz precipitation and dissolution textures indicate that early quartz molybdenite veins formed as a result of pressure fluctuations between lithostatic and hydrostatic at high temperatures and later pyrite quartz veins formed near hydrostatic pressure in response to temperature decrease through and beyond the field of retrograde quartz solubility

porphyry related polymetallic au ag vein deposit in the central city district colorado mineral paragenesis and pyrite trace element chemistry abstract the colorado mineral belt is a 500 km long segment of calc alkaline to alkaline laramide age intrusions and related porphyry and polymetallic vein deposits the central city historic au ag mining district in the front range of colorado usa has been one of the most productive au deposits in the colorado mineral belt with a total of 119 1 t of au produced between 1859 and 1959 development of ne trending laramide strike slip faults and re activation of pre existing proterozoic brittle structures in proterozoic gneiss provided the structural controls for the mineralization of au and ag in re opened pyrite quartz and base metal veins previous studies have related ore formation in the district to the emplacement of late cretaceous paleogene laramide porphyritic alkaline intrusions it remains however unclear how to reconcile the au ag enrichment of this deposit with the historic vein descriptions and the evolution of a deep magmatic hydrothermal porphyry system here we document the crosscutting relationships and the mineral paragenesis of the different vein types and use the trace element chemistry in pyrite to fingerprint au mineralization and the succession of different veining styles in the central city district based on comparisons to porphyry and polymetallic style veins worldwide a revised vein classification is proposed which distinguishes porphyry transitional pyrite quartz and polymetallic veining styles these veining styles led to the development of an almost concentric district wide metal zoning comprising a central and an intermediate zone both enriched in cu au ag grading into a peripheral zone enriched in zn pb ag rare porphyry style veins include k feldspar veins and quartz veins with molybdenite ribbons the transitional style veins include abundant pyrite quartz veins that crosscut the earlier formed porphyry style veins and disseminated pyrite accompanied by phyllic alteration formation of the au ag bearing polymetallic style veins was associated with the brecciation and re opening of pyrite quartz veins based on mineral paragenetic relationships the polymetallic style base metal veins can be subdivided into four subtypes comprising sphalerite chalcopyrite veins tetrahedrite veins enargite pyrite quartz veins and galena sphalerite carbonate veins the textures mineral inclusions and trace element concentrations in pyrite are distinct for the different vein types and associated alteration halos pyrite in pyrite quartz veins is enriched in co and ni and contains quartz inclusions in contrast pyrite in polymetallic base metal veins is characterized by elevated au 20 ppm cu as pb ag and sb concentrations and contains inclusions of electrum and galena the observed veining styles paragenetic relationships and associated pyrite chemistry in the central city district confirm that ore formation is porphyry related the central city district also shares several similarities with cordilleran polymetallic style cu zn pb ag vein deposits associated with cu mo porphyries however the high au and low cu mo grades make central city an example of a newly recognized porphyry related polymetallic au ag vein deposit type

intensity of quartz cathodoluminescence and trace element content in quartz from the porphyry copper deposit at butte montana textures of hydrothermal quartz revealed by cathodoluminescence using a scanning electron microscope sem cl refl ect the physical and chemical environment of quartz formation variations in intensity of sem cl can be used to distinguish among quartz from superimposed mineralization events in a single vein in this study we present a technique to quantify the cathodoluminescent intensity of quartz within individual and among multiple samples to relate luminescence intensity to specific mineralizing events this technique has been applied to plutonic quartz and three generations of hydrothermal veins at the porphyry copper deposit in butte montana analyzed veins include early quartz molybdenite veins with potassic alteration pyrite quartz veins with sericitic alteration and main stage veins with intense sericitic alteration cl intensity of quartz is diagnostic of each mineralizing event and can be used to fingerprint quartz and its fluid inclusions isotopes trace elements etc from specific mineralizing episodes furthermore cl intensity increases proportional to temperature of quartz formation such that plutonic quartz from the butte quartz monzonite bqm that crystallized at temperatures near 750 c luminesces with the highest intensity whereas quartz that precipitated at 250 c in main stage veins luminesces with the least intensity trace element analyses via electron microprobe and laser ablation icp ms indicate that plutonic quartz and each generation of hydrothermal quartz from butte is dominated by characteristic trace amounts of al p ti and fe thus in addition to cl intensity each generation of quartz can be distinguished based on its unique trace element content aluminum is generally the most abundant element in all generations of quartz typically between 50 and 200 ppm but low temperature main stage quartz containing 400 to 3600 ppm al is enriched by an order of magnitude relative to all other quartz generations phosphorous is present in abundances between 25 and 75 ppm and p concentrations in quartz show little variation among quartz generations iron is the least abundant of these elements in most quartz types and is slightly enriched in cl dark quartz in pyrite quartz veins with sericitic alteration titanium is directly correlated with both temperature of quartz precipitation and intensity of quartz luminescence such that bqm quartz contains hundreds of ppm ti whereas main stage quartz contains less than 10 ppm ti our results suggest that ti concentration in quartz is controlled by temperature of quartz precipitation and that increased ti concentrations in quartz may be responsible for increased cl intensities

porphyry epithermal transition maricunga belt northern chile the refugio aldebaran and la pepa districts in the maricunga belt of northern chile contain advanced argillic alteration zones that locally host high sulfidation epithermal gold deposits in proximity to porphyry gold copper deposits the spatial association suggests a genetic link mineralized zones are characterized by four main vein types that formed at different times and have specific zonal relationships a veinlets are the earliest and deepest vein type they are restricted to potassic alteration zones in intrusive rocks a veinlets contain variable amounts of quartz magnetite biotite and chalcopyrite and locally have k feldspar halos they have nonmatching irregular vein walls and lack internal symmetry hypersaline liquid rich inclusions coexisting with vapor rich inclusions in a veinlets indicate temperatures as high as nearly 700 c and pressures between 200 and 400 bars assuming a lithostatic load depths of 0 8 to 1 6 km are inferred zones of abundant a veinlets contain mostly 1 ppm gold and 0 1 to 0 4 percent hypogene copper banded quartz veinlets occur mostly above a veinlets and cut a veinlets where they overlap dark gray bands the color resulting from a high density of vapor rich fluid inclusions and micron sized grains of magnetite commonly occur as symmetric pairs near the vein walls vein walls are parallel and slightly wavy vuggy vein centers are common and alteration envelopes are absent data from rare liquid rich inclusions in banded quartz veinlets indicate temperatures 350 c at pressures between 20 and 150 bars assuming a hydrostatic load depths of 0 2 to 1 5 km are inferred zones of abundant banded quartz veinlets generally contain 0 5 to 2 ppm gold and 0 1 percent hypogene copper d veins are pyrite veins with quartz sericite pyrite halos they are widespread and crosscut a veinlets and banded quartz veinlets the brittle nature of d veins and limited fluid inclusion data suggest temperatures 400 c d veins serve as important time lines they are nowhere truncated or crosscut by intrusions a veinlets or banded quartz veinlets quartz alunite replacement veins referred to as ledges in this paper are typical of the high sulfidation epithermal environment they are mostly limited to overlying volcanic rocks they contain local core zones of vuggy residual quartz that can contain enargite or at higher elevations barite of the three districts studied only la pepa has mineable quartz alunite ledges which contain an average gold grade of about 20 ppm a spectrum of porphyry style deposits exists cerro casale at aldebaran shares many characteristics of porphyry copper deposits worldwide whereas verde at refugio is a true porphyry gold deposit potassic alteration zones and a veinlets are strongly developed at cerro casale whereas they are absent at verde banded quartz veinlets predominate at verde whereas they occur only at the upper levels of cerro casale the pancho deposit at refugio and the cavancha deposit at la pepa are telescoped systems in which banded quartz veinlets overprint potassic alteration zones and a veinlets a veinlets and banded quartz veinlets cut and are cut by intrusions indicating multiple cycles of intrusion potassic alteration a veinlets banded quartz veinlets during formation of porphyry style mineralization banded quartz veinlets are thought to have formed by flashing of magmatic fluids during episodic transitions from lithostatic to hydrostatic pressure loss of sulfur to the vapor phase during flashing inhibited formation of copper sulfides in banded quartz veinlets and therefore resulted in high gold copper ratios where rising magmatic vapors condensed into overlying meteoric water along faults barren quartz alunite ledges formed this conclusion is supported by equivalent 40ar 39ar dates on hydrothermal biotite associated with porphyry style ore and alunite from barren ledges at aldebaran 40ar 39ar dates at la pepa indicate alunite formed at least 140 000 years to as long as 900 000 years after hydrothermal biotite within the high sulfidation epithermal environment the development of ore depends on the ability of late moderate salinity magmatic fluids to reach the surface without condensing a brine upon ascent cooling and boiling of the moderate salinity fluid below its critical temperature results in the formation of sericite at depth and alunite near the surface that is essentially synchronous with high sulfidation ore formation the timing of the switch from lithostatic pressures to brittle hydrostatic conditions relative to the life of the hydrothermal system might determine how much porphyry style ore forms relative to high sulfidation epithermal ore

paleomagnetism and geochronology of sills of the doherty mountain area southwestern montana implications for the timing of fold and thrust belt deformation and vertical axis rotations along the southern margin of the helena salient paleomagnetic and 40ar 39ar data from intermediate composition sills exposed along the southern margin of the helena salient in southwestern montana help refine the age of late cretaceous contraction in this part of the north american cordillera the structures in the doherty mountain fold complex deform cambrian through mississippian strata in the hanging wall of the jefferson canyon lombard fault system sills exposed within these strata which are complexly deformed into northeast to northwest plunging anticlines and a northwest plunging syncline give well defined remanent magnetizations and after correction for fold plunge followed by bedding tilt paleomagnetic data from 20 of 21 sites from four folds yield positive fold tests at 100 percent unfolding the magnetizations from these sites are interpreted to be primary remanent magnetizations acquired during sill emplacement prior to fold and thrust deformation although pre folding remagnetization due to widespread latest cretaceous magmatism in the area cannot be ruled out one site yields a magnetization that appears to postdate folding this site has either been remagnetized or is in a distinct intrusive phase emplaced subsequent to folding biotite mineral separates from sills from two folds yield identical 40ar 39ar plateau dates of 77 ma although the group mean directions from sills in each of the folds may represent incomplete samplings of the geomagnetic field and the number of independent readings is low their grand mean direction declination dec 347 inclination inc 66 k 71 9 95 9 n 5 independent observations based on results from 21 sites is similar to the expected late cretaceous reference direction for the study area based on results from the essentially coeval adel mountain volcanics therefore these data suggest that deformation began after 77 ma campanian maestrichtian and that upper plate strata in the lombard thrust sheet of the helena salient in this area have not experienced significant local vertical axis rotation due to thrust movement and impingement with foreland structures along the southwest montana transverse zone the absence of appreciable vertical axis rotations is consistent with data obtained from other paleomagnetic studies in the region

effects of atmospheric conditions on wind profiles and aeolian sand transport with an example from white sands national monument quantifying aeolian sand transport rates relies upon the computation of the near surface shear velocity u determined from velocity profiles of the wind while it has been recognized that various conditions such as saltation surface roughness surface slope and atmospheric conditions have an effect on the velocity profile it is commonly assumed that measurements made above the surface will be representative of the near surface shear velocity airflow and temperature data collected over a flat substrate at white sands national monument in new mexico however show the significant effects that atmospheric conditions have on velocity profiles during the day when solar insolation is heating the surface atmospheric conditions in the lowest several metres become unstable resulting in enhanced convection and vertical mixing so that the velocity gradient changes little with height as a result the shear stress in this region of vertical mixing lessens while the near surface shear stress is increased because the higher wind speeds are now nearer the surface at night the near surface atmospheric conditions are stable thereby reducing convection and vertical mixing resulting in stratified airflow and increased shear velocity away from the surface unless this atmospheric effect is accounted for estimates of sediment transport rates may be in error by as much as a factor of 15 times when wind speeds are near threshold velocity at wind speeds approaching 10 ms1 at 5m above the surface this error in computing sediment transport is reduced to a factor of only two to three times and may be within the range of measurement error

an alternative approach to the identification of net sediment transport paths based on grain size trends abstract progressive changes in grain size parameters have long been linked to net sediment transport paths however the methods employed to date suffer from limitations potentially leading to serious interpretational errors which necessitate the formulation of an integrated quantitative technique the approach advocated here is a step in this direction as it eliminates some of the problems inherent in the older methods previously trend vectors were obtained by comparing the grain size parameters of only two sampling stations at a time which gives a low probability of identifying the actual transport direction in the proposed method groups of five stations comprising a central station and four satellite stations are used for each trend vector grain size parameters are first combined in such a way that bias towards any one of them is climated the resultant dimensionless numbers are then substituted for the proportional frequencies of recorded directions in conventional vector analysis the satellite stations must be located equally far from the central station on radials 90 from each other which is seldom the case an iterative trigometric technique is therefore employed to determine the combined grain size parameters at these localities conventional vector analysis adapted to the situation of using four raials instead of 10 sectors allows the calculation of a vector mean azimuth and vector magnitude

shrimp u pb and 40ar 39ar age constraints for relating plutonism and mineralization in the boulder batholith region montana the composite boulder batholith montana hosts a variety of mineral deposit types including important silver rich polymetallic quartz vein districts in the northern part of the batholith and the giant butte porphyry copper molybdenum pre main stage system and crosscutting copper rich main stage vein system in the southern part of the batholith previous dating studies have identified ambiguous relationships among igneous and mineralizing events mineralizing hydrothermal fluids for these types of deposits and magma for quartz porphyry dikes at butte have all been considered to be late stage differentiates of the boulder batholith however previous dating studies indicated that the boulder batholith plutons cooled from about 78 to 72 ma whereas copper rich main stage veins at butte were dated at about 61 ma recent efforts to date the porphyry copper molybdenum pre main stage deposits at butte resulted in conflicting estimates of both 64 and 76 ma for the mineralizing events silver rich polymetallic quartz vein deposits elsewhere in the batholith have not been dated previously to resolve this controversy we used the u s geological survey stanford shrimp rg ion microprobe to date single age domains within zircons from plutonic rock samples and 40 ar 39 ar geochronology to date white mica biotite and k feldspar from mineral deposits u pb zircon ages are rader creek granodiorite 80 4 1 2 ma unionville granodiorite 78 2 0 8 ma pulpit rock granite 76 5 0 8 ma butte granite 74 5 0 9 ma altered steward type quartz porphyry dike i 15 roadcut 66 5 1 0 ma altered steward type quartz porphyry dike continental pit 65 7 0 9 ma and quartz monzodiorite of boulder baldy big belt mountains 66 2 0 9 ma zircons from rader creek granodiorite and quartz porphyry dike samples contain archean inheritance the 40 ar 39 ar ages are muscovite silver rich polymetallic quartz vein basin district 74 4 0 3 ma muscovite silver rich polymetallic quartz vein boulder district 74 4 1 2 ma muscovite early dark micaceous vein continental pit 63 6 0 2 ma biotite early dark micaceous vein continental pit 63 6 0 2 ma potassium feldspar early dark micaceous vein continental pit 63 to 59 ma and biotite biotite breccia dike continental pit 63 6 0 2 ma outlying silver rich polymetallic quartz veins of the basin and boulder mining districts probably are directly related to the 74 5 ma butte granite whereas steward type east west quartz porphyry dikes and butte pre main stage deposits are parts of a 66 to 64 ma magmatic mineralization system unrelated to emplacement of the boulder batholith the age of the crosscutting main stage veins may be about 61 ma as originally reported but can only be bracketed as younger than the 64 ma pre main stage mineralization and older than the about 50 ma eocene lowland creek intrusions the 66 ma age for the quartz monzodiorite of boulder baldy and consideration of previous dating studies in the region indicate that small ca 66 ma plutonic systems may be common in the boulder batholith region and especially to the east the approximately 64 ma porphyry copper systems at butte and gold mineralization at miller mountain are indicative of regionally important mineralizing systems of this age in the boulder batholith region resolution of the age and probable magmatic source of the butte pre main stage porphyry copper molybdenum system and of the silver rich polymetallic quartz vein systems in the northern part of the boulder batholith documents that these deposits formed from two discrete periods of hydrothermal mineralization related to two discrete magmatic events

coarse muscovite veins and alteration deep in the yerington batholith nevada insights into fluid exsolution in the roots of porphyry copper systems veins and pervasive wall rock alteration composed of coarse muscovite quartz pyrite are documented for the first time in a porphyritic granite at luhr hill in the yerington district nevada coarse muscovite at luhr hill occurs at paleodepths of 6 7 km in the roots of a porphyry copper system and crops out on the scale of tens to hundreds of meters surrounded by rock that is unaltered or variably altered to sodic calcic assemblages coarse muscovite veins exhibit a consistent orientation subvertical and n s striking which structurally restores to subhorizontal at the time of formation along strike coarse muscovite veins swell from distal millimeter thick muscovite only veinlets to proximal centimeter thick quartz sulfide bearing muscovite veins crosscutting relationships between coarse muscovite veins pegmatite dikes and sodic calcic veins indicate that muscovite veins are late stage magmatic hydrothermal features predating final solidification of the luhr hill porphyritic granite fluid inclusions in the muscovite quartz veins are high density aqueous inclusions of 3 9 wt nacl eq and 1 mol co2 that homogenize between 150 and 200 c similar to fluid inclusions from greisen veins in sn w mo vein systems our results indicate that muscovite forming fluids at luhr hill were mildly acidic of low to moderate salinity and sulfur content and low co2 content and that muscovite in deep veins and alteration differs in texture composition and process of formation from sericite at shallower levels of the hydrothermal system although the definition of greisen is controversial we suggest that coarse muscovite alteration is more similar to alteration in greisen type sn w mo districts worldwide than to sericitic alteration at higher levels of porphyry copper systems the fluids that form coarse muscovite veins and alteration in the roots of porphyry copper systems are distinct from fluids that formed copper ore or widespread shallower acidic alteration we propose that this style of veins and alteration at luhr hill represents degassing of moderate volumes of overpressured hydrothermal fluid during late crystallization of deep levels of the yerington batholith

relative age of cordilleran base metal lode and replacement deposits and high sulfidation au ag epithermal mineralization in the colquijirca mining district central peru at colquijirca central peru a predominantly dacitic miocene diatreme dome complex of 12 4 to 12 7 ma 40ar 39ar biotite ages is spatially related to two distinct mineralization types disseminated au ag associated with advanced argillic alteration and local vuggy silica typical of high sulfidation epithermal ores are hosted exclusively within the volcanic center at marcapunta a second economically more important mineralization type is characterized as cordilleran base metal lode and replacement deposits these ores are hosted in mesozoic and cenozoic carbonate rocks surrounding the diatreme dome complex and are zoned outward from pyrite enargite quartz alunite to pyrite chalcopyrite dickite kaolinite to pyrite sphalerite galena kaolinite siderite alunite samples related to the au ag epithermal ores have been dated by the 40ar 39ar method at 11 3 11 6 ma and those from the cordilleran base metal ores in the northern part of the district smelter and colquijirca at 10 6 10 8 ma the significant time gap 0 5 my between the ages of the two mineralization types in the colquijirca district indicates they were formed by different hydrothermal events within the same magmatic cycle the estimated time interval between the younger mineralization event base metal mineralization at 10 6 ma and the ages of 12 5 ma obtained on biotites from unmineralized dacitic domes flanking the vicinity of the diatreme vent suggest a minimum duration of the magmatic hydrothermal cycle of around 2 ma this study on the colquijirca district offers for the first time precise absolute ages indicating that the cordilleran base metal lode and replacement deposits were formed by a late hydrothermal event in an intrusive related district in this case post au ag high sulfidation epithermal mineralization

foredune accretion under offshore winds experiments carried out at magilligan strand on the north coast of ireland suggest that topographic steering of offshore winds is an important facet of the aeolian sediment transport system at this location a five day study 18 22 june 2005 investigated the pattern of airflow over the foredune while simultaneously collecting data on sediment flux a simple instrument setup was used to characterise the airflow a sonic anemometer was placed at the dune crest with another on the mid beach horizontal traps electronic and integrating measured sediment flux on the supra tidal beach results show that offshore wind flow deviated from its original direction in the lee of the dune seaward of foredune the change in direction was not a simple steering of flow to a singular new direction but rather flow separation resulting in turbulent multidirectional flow including reversal traps located at the foot of the dune scarp recorded sediment transport during events forced by offshore winds data from sediment traps wind and observational evidence have been used to argue that sedimentation was occurring in this zone when budgeting for sediment movement within beach dune systems it is important to take into account the effect of secondary airflow patterns during offshore winds and their role in constructive processes of foredune formation particularly in post storm recovery c 2008 elsevier b v all rights reserved

reconstructing extensional basin architecture and provenance in the marrakech high atlas of morocco implications for rift basins and inversion tectonics

beach systems of the central netherlands coast processes morphology and structural impacts in a storm driven multi bar system abstract the 124 km long central netherlands coast consists of a sand barrier system fronted by beach and surf zone containing 2 to 3 bars the beach and surf zone are the product of wind waves generated in the north sea interacting with the medium to fine shoreface sands in a micro tidal environment the inner bar is usually attached to the beach as a ridge and runnel cut by drains and rips the second and third bars are highly rhythmic and are characterised respectively by transverse bars and rips and rhythmic to longshore bar and trough bar types structural impacts influence 48 km of shore with harbour moles inducing lower wave energy and shoreline progradation a 4 5 km long dyke replaces part of the beach but apparently has had little impact on mesoscale bar dynamics while 158 groynes in three fields have produced more intermediate rip driven surf zones natural beach processes however dominate the entire coast with the hierarchical bar morphology related to cross shore wave breaking the equilibrium beach concept of wright et al 1987 was used to empirically predict beach bar type the results explain both the hierarchy of bar type and the temporal variation in beach bar type finally a multi bar beach model for the coast is presented which builds upon the single bar model of wright and short 1984

zircon petrochronological evidence for a plutonic volcanic connection in porphyry copper deposits bridging the gap between the plutonic and volcanic realms is essential for understanding a variety of magmatic processes from caldera forming eruptions to the formation of magmatic hydrothermal ore deposits porphyry copper deposits are commonly associated with large and long lived volcanic centers but the temporal and dynamic link between mineralized intrusions and volcanic eruptions has remained controversial based on the combination of 1 high precision zircon u pb geochronology and trace element geochemistry with 2 plagioclase textures we discovered an intimate connection between an ignimbrite eruption and a nearby world class porphyry deposit bajo de la alumbrera in the late miocene farallon negro volcanic complex of argentina our results indicate that the magmatic hydrothermal deposit and explosive volcanism were derived from a common magma reservoir that evolved over a minimum duration of 217 25 k y before the final eruption we show that the volcanic pile represents the inverted magma reservoir recording systematic differences in plagioclase textures and juvenile clast content from bottom to top this tight temporal and geochemical link suggests that deposit formation and volcanic eruption were both triggered by the same injection of a volatile saturated primitive magma into the base of the magma chamber a time gap of 19 12 k y between porphyry mineralization and the onset of explosive volcanism indicates a minimum duration of magma reservoir rejuvenation that led to the explosive eruptive event catastrophic loss of volatiles by explosive volcanism terminated the ore forming capacity of the upper crustal magma chamber as evidenced by the intrusion of a syn eruptive barren quartz feldspar porphyry our results demonstrate that porphyry copper deposits provide critical information to understand how volatiles control the fate of hydrous magmas between pluton formation and explosive volcanism

pattern of sediment transport in a microtidal river mouth using geostatistical sediment trend analysis abstract we perform a grain size trend analysis gsta to investigate sediment transport mechanisms in the grand rhone microtidal mouth during various hydroclimatic conditions the objective is to determine the efficiency of this method to explain the directions of residual transport pattern and mode of distribution of the fluvial sediment input in an environment that is very difficult to equip with instrumentation during extreme events the known biases of this sedimentological approach are reduced by using enriched geostatistical processing and choosing periods of sampling subject to unequivocal hydrodynamic forcings the modeling results and grain size distributions of surface sediments clearly show three vector fields during periods of low river discharge the first vector field corresponds to an upstream zone under fluvial influence the second field is characteristic of a mixing zone confined inside the river mouth and marked by heterogeneous sedimentation this sector is interpreted as the confrontation zone between alluvial and marine dynamics farther offshore the vectors are oriented towards the river and at counter slope in deeper zones the vectors reflect the sediment transport generated by wave refraction at the top of the mouth bar at the delta front bathymetry from 5 m to 20 m the vectors are interpreted as representing a lag deposit the periods of medium and extreme floods are associated with storms the marine dynamic regime generates a longshore drift current which brings sediments onto the mouth bar during medium flood events only the inner part of the mouth bar is highly influenced by the river during extreme flood events the river influences both the eastern part of the mouth and the wave regime in the central part consequently the gsta method shows that even during flood events the river solid discharge is not transferred towards the adjoining upper shoreface in the context of a wave dominated delta the distribution of surface sedimentation in a microtidal mouth remains controlled mainly by the swell even in periods of flood when the intensity of river dynamics is exacerbated finally all these results are similar to the known hydro sedimentological behaviours of the rhone river mouth nevertheless gsta results seem not self sufficient to explain all the processes but this method proposes an alternative approach to traditional methods used to measure bed load sediment transfer during extreme events

toward a model for airflow on the lee side of aeolian dunes the interaction between dunes and the primary wind results in a complex pattern of secondary airflow on the lee side of dunes from 15 dunes studied during transverse flow conditions at padre island in texas white sands in new mexico and the algodones in california distinct flow regions can generally be recognized with the overall flow structure comparing favourably to that proposed for subaqueous bedforms downwind of dunes with flow separation is a back flow eddy that extends about four dune brink heights downwind from the brink of the dune beyond the separation cell the velocity profiles can be divided into regions based upon segments separated by kinks in the velocity profiles the interior is an area above the dunes of relative high wind speed but low velocity gradient beneath the interior is the wake which consists of two layers the upper wake exhibits an uppermost portion where the flow decelerates while the remainder exhibits accelerating flow so that the overall velocity gradient decreases downwind the lower wake exhibits low velocity gradients and wind speeds that accelerate downwind at all heights but primarily near the top of the layer thereby causing the velocity gradient to increase downwind at about eight dune heights downwind the upper and lower wakes equilibrate to a single profile with the kink between them no longer apparent the lowest recognizable region is the internal boundary layer it is recognized by a relatively steep velocity gradient below the wake and never exceeds a few tens of centimetres in height for our data set because of acceleration and increasing shear stress within this layer interdune flats are at least potentially erosional overall the wake and internal boundary layer show a downward transfer of momentum from upper regions so that the flow recovers where flow separation does not occur simple flow expansion down the lee face causes flow deceleration

two event lode ore deposition at butte usa 40ar 39ar and u pb documentation of ag au polymetallic lodes overprinted by younger stockwork cu mo ores and penecontemporaneous cu lodes abstract the ore genesis model for world class deposits of the butte mining district montana usa is deep pre main stage porphyry cu mo and overlying main stage ag zn cu zoned lode deposits both of which formed from hydrothermal fluids driven by minor volumes of rhyolitic magma the lode specific model is that hydrothermal processes diminished in intensity outward from district center along lode veins synchronously forming metal zones the accepted models are controverted by new geologic and multi method geochronologic studies the new data reveal the following sequence of events 1 thermal study of country rock indicates that the 76 9 ma butte granite cooled to 350 400 c by 4 m y after emplacement 2 five quartz porphyry rhyolite dikes were emplaced at 67 65 ma and another at 60 ma shrimp u pb into the cooled butte granite without resetting 40ar 39ar ages in country rock 3 fifty eight white mica and k feldspar samples from alteration envelopes adjacent to ag au polymetallic lodes in outer parts of the district zn rich lodes in intermediate parts and cu rich lodes in the district center yield 40ar 39ar ages of 73 70 ma for ag rich lodes 65 64 ma for cu rich lodes and complex age spectra of 69 65 ma for zn rich lodes the data show that ag au polymetallic lodes occupied cross district fractures by about 73 ma forming the greater butte mining district at 67 65 ma minor quartz porphyry dikes were emplaced into central and eastern parts of the rejuvenated fracture system but without evidence of related cupola or volcanic rocks or of thermal disturbance in the country rock at 64 5 ma overlapping hydrothermal cells formed two stockwork cu mo domes in deep parts of the fracture system at 65 64 ma and closely related to late stage stockwork cu mo activity a penecontemporaneous hydrothermal pulse formed a high sulfidation hydrothermal plume that 1 utilized the large re opened fractures to cannibalize and remobilize cu from autologous stockwork and older ag au polymetallic lodes 2 deposited the rich high sulfidation cu lodes and 3 mobilized metals from early ag au polymetallic veins in middle parts of the district transported the metals outward and redeposited them enriching early veins especially in the intermediate zn plus cu areas metals zones in lodes of the butte district are the result of an intensely focused cu rich hydrothermal plume that variably reworked the center of significantly larger 10 m y older ag au polymetallic lodes

a diatreme hosted gold deposit at montana tunnels montana a bulk minable gold silver deposit at montana tunnels southwestern montana is located in the central part of a diatreme this diatreme was emplaced along the faulted contact between andesitic volcaniclastic rocks assigned to the late cretaceous elkhorn mountains volcanics and a sequence of quartz latitic ignimbrites which are part of the lowland creek volcanics of middle eocene age a north northeast striking swarm of quartz latite porphyry dikes was emplaced during the waning stages of lowland creek volcanism the two largest dikes dated at 45 to 50 m y middle eocene were intruded into the diatreme prior to the cessation of brecciation and mineralization the diatreme underlies a 1 km 2 area and is known from drilling to extend steeply downward for at least 310 m the principal rock type in the diatreme is a matrix rich breccia it is characterized by a sand size tuffaceous matrix of quartz latitic composition containing fragments of contiguous volcanic wall rocks and intrusive rocks derived from the late cretaceous boulder batholith the batholith is inferred to underlie the montana tunnels area foundered blocks of volcanic wall rocks lie at various attitudes against the walls of the diatreme and within it those composed of elkhorn mountains volcanics underwent hydraulic brecciation after they sank into the diatreme blocks interpreted to be composed of pyroclastic base surge deposits from a subaerial tuff ring and a piece of carbonized wood subsided into the diatreme from the palcosurface the diatreme is separated into two unequal parts by a west northwest striking oblique slip fault sulfide minerals in the diatreme occur as disseminations in the breccia matrix and in sub ordinate amounts as widely spaced multidirectional veinlets and as the matrix to brecciated blocks of elkhorn mountains volcanics all forms of mineralization consist of pyrite sphalerite galena minor chalcopyrite and rare electrum accompanied by a gangue of manganocalcite siderite and minor quartz clastic grains and fragments of the sulfides and gangue minerals are common and attest to multiple alternating episodes of brecciation and mineralization in the ore zone the introduction of abundant manganocalcite and siderite was accompanied by pervasive sericitic alteration but only weak kaolinization and silicification sericitization grades outward beyond the ore zone to chlorite montmorillonite carbonate alteration an assemblage that also characterizes the interiors of the late mineral dikes in the diatreme gold occurs in electrum with a fineness of about 550 as inclusions of less than 200 mu m in pyrite and sphalerite inclusions of electrum and galena were precipitated together silver is present mainly in solid solution in galena the montana tunnels gold silver deposit is characterized geochemically by anomalously high concentrations of zinc lead and manganese and in comparison to many volcanic hosted precious metal deposits is low in arsenic antimony and mercury this metal association and the low fineness of the gold are features shared by the wau gold deposit in papua new guinea it is suggested that the mineralized diatreme observable at montana tunnels was emplaced several hundred meters beneath the palcosurface upon which a gold bearing maar volcano like that partly preserved at wau was constructed

investigation of three dimensional wind flow behaviour over coastal dune morphology under offshore winds using computational fluid dynamics cfd and ultrasonic anemometry the behaviour of offshore directed winds over coastal dune and beach morphology was examined using a combination of modelling 3 d computational fluid dynamics cfd and field measurement both model simulations and field measurements showed reversal of offshore flows at the back beach and creation of an onshore sediment transport potential the influence of flow reversals on the beach dune transport system and foredune growth patterns has previously received little attention detailed wind flow measurements were made using an extensive array of mast mounted 3 d ultrasonic anemometers 50 hz arranged parallel to the dominant incident wind direction large eddy simulation les of the offshore wind flow over the dune was conducted using the open source cfd tool openfoam the computational domain included a terrain model obtained by airborne lidar and detailed ground dgps measurements the computational grid 22 million cells included localized mesh refinement near the complex foredune terrain to capture finer details of the dune morphology that might affect wind flows on the adjacent beach measured and simulated wind flow are presented and discussed the cfd simulations offer new insights into the flow mechanics associated with offshore winds and how the terrain steering of wind flow impacts on the geomorphological behaviour of the dune system simulation of 3 d wind flows over complex terrain such as dune systems presents a valuable new tool for geomorphological research as it enables new insights into the relationship between the wind field and the underlying topography the results show that offshore and obliquely offshore winds result in flow reversal and onshore directed winds at distances of up to 20m from the embryo dune toe the potential geomorphological significance of the findings are discussed and simple calculations show that incoming offshore and obliquely offshore winds with mean velocities over 13m s 1 and 7m s 1 respectively have the potential to create onshore directed winds at the back beach with mean velocities above 3 3m s 1 these are above the threshold of movement for dry sand and support previous conclusions about the significance of offshore winds in dune and beach budget calculations

secondary airflow and sediment transport in the lee of a reversing dune lee side windspeed and sediment transport were measured over a small 1 2 m transverse ridge in the silver peak dunefield west central nevada usa using an intensive array of 25 cup anemometers and seven total flux traps during crest transverse and transporting flow conditions u0 3crest 8 4 m s 1 windspeed near the surface of the lee slope averaged half 48 per cent that of crest speeds dimensionless speeds in the separation zone ranged from 0 2 to 0 8 that of the outer flow u12 along the boundary of the separation cell windspeed increased by 10 per cent of the crest speed before separation equilibrium of upper and lower wake regions was not observed by the documented eight dune heights suggesting that wake recovery may not occur over closely spaced dunes sediment transport measured directly on both the lee slope and interdune surfaces averaged approximately 15 per cent of crest inputs this suggests that a significant amount c 70 95 per cent of sediment transported over the crest moved as fallout for this data set flux was approximately proportional to the cube of the near surface windspeed u0 3 and in general there was an order of magnitude difference between flux measured at the crest and that measured within the separation zone transport direction in the separation zone was acutely oblique to the incident direction owing to secondary flow deflection beyond the interdune transport direction progressed from oblique to crest transverse this indicates that an appreciable amount of sediment may move laterally along the lee slope and interdune corridor under crest transverse flows regarding the grain size and sorting properties of transported sediment there was no significant difference in mean grain size over the dune although in general particles were finer and more poorly sorted in the lee copyright 1999 john wiley sons ltd

a wind tunnel simulation of the effects of stoss slope on the lee airflow pattern over a two dimensional transverse dune 1 secondary airflow plays an important role in dune formation and development the lee airflow pattern over transverse dunes is important in determining the shape alignment and spacing of dunes and is influenced significantly by the lee slope angle in this paper we present the results of scaled wind tunnel simulations of the effects of stoss slope on the mean lee airflow patterns of transverse dunes the leeward velocity field was measured nonintrusively using particle image velocimetry to assess the airflow pattern we found that the flow separated over the dunes with a leeward angle close to the slip face angle of natural transverse dunes and was insensitive to stoss angle separation cells were characterized by a back eddy reattachment distance height area and aspect ratio were used to characterize the separation cell the first three parameters increased with increasing stoss angle for angles less than 15 but remained constant or decreased slightly with angles greater than 15 on the basis of the leeward velocity profiles six flow regions corresponding to those in previous models were recognized these regions are initially bounded by kinks but gradually transition downwind and merge to recover a uniform velocity profile after a significant distance we suggest that the separation cell is most developed when the angle of stoss slope reaches 15 but the significance of this angle in the evolution of transverse dunes needs further exploration

an interpretation of trends in grain size measures abstract the mean grain size sorting and skewness of a sedimentary deposit are dependent on the sediment grain size distribution of its source and the sedimentary processes of i winnowing erosion ii selective deposition of the grain size distribution in transport and iii total deposition of the sediment in transport if a source sediment undergoes erosion and the resultant sediment in transport is deposited completely the deposit must be finer better sorted and more negatively skewed than the source this trend is referred to as case i the lag remaining after erosion on the other hand must be coarser better sorted and more positively skewed case ii if sediment in transport undergoes selective deposition the resultant deposit can either be finer case iiia or coarser cas iiib than the source but the sorting will be better and the skew more positive although exceptions to these trends may occur they suggest that comparison of one sediment must be made with another for the proper identification of the sedimentary process and therefore it is not possible for a single grain size distribution to identify the depositional environment the trends also suggest that the skewness of a grain size distribution has been widely misinterpreted and implies neither the truncation of one of the tails nor the mixing of more than one mode rather a skewed sediment is the natural result of the sedimentary process in a system of related environments these trends can be used to identify both the probable source and the probable deposit and by inference the net sediment transport paths among sedimentary deposits such an analysis provides a rapid understanding of the sedimentary processes identifies patterns of erosion and accretion and may suggest transport processes

sediment flux and airflow on the stoss slope of a barchan dune abstract measurements of sediment flux on the windward slope of an isolated barchan using an array of 30 sand traps provide new data that can constrain models of dune dynamics the data show that at low wind incident speeds flux increases up the dune exponentially whereas at higher wind speeds the increase with distance approaches linearity wind profile measurements conducted at the same time as the flux measurements indicate that although wind speed at a given height increases by 1 2 times from dune toe to brinkline wind shear velocity derived from the profile data decreases up the dune and is in many cases below transport threshold values this demonstrates that conventional wind profiles derived from anemometry on dunes do not measure the part of the boundary layer that is significant for sediment transport

giant porphyry deposits characteristics distribution and tectonic controls more than half of the 25 largest known porphyry copper deposits defined in terms of contained copper metal formed during three time periods the paleocene to eocene eocene to oligocene and middle miocene to pliocene these giant deposits are clustered within three provinces central chile northern chile and southwest arizona northern mexico other giant deposits occur in montana utah panama peru argentina irian jaya mongolia and iran compressive tectonic environments thickened continental crust and active uplift and erosion were associated with the formation of many of these deposits calc alkalic magmas are most favorable for the formation of giant porphyry copper deposits although several of the largest systems are associated with high k calc alkalic intrusions the 25 largest gold rich porphyry deposits are concentrated in the southwest pacific and south america with other occurrences in eurasia british columbia alaska and new south wales many of the deposits formed in the last 13 m y the largest of the deposits are associated with high k calc alkalic intrusions many calc alkalic porphyritic intrusions have also produced giant gold rich porphyries in the last 20 m y the formation of giant porphyry copper molybdenum and copper gold deposits in the circum pacific region has been closely associated with subduction of aseismic ridges seamount chains and oceanic plateaus beneath oceanic island and continental arcs in several examples these tectonic perturbations have promoted flat slab subduction crustal thickening uplift and erosion and adakitic magmatism coeval with the formation of well endowed porphyry and or epithermal mineral provinces similar tectonic features are inferred to be associated with the giant porphyry copper molybdenum provinces of northern chile eocene oligocene and southwest united states cretaceous paleocene topographic and thermal anomalies on the downgoing slab appear to act as tectonic triggers for porphyry ore formation other factors such as sutures in the overriding plate permeability architecture of the upper crust efficient processes of ore transport and deposition and in some cases formation and preservation of supergene enrichment blankets are also vital for the development of high grade giant ore deposits a low grade geochemical anomaly may be the final product of mineralization if ore forming processes do not operate efficiently even in the most favorable geodynamic settings

a review of shallow ore related granites textures volatiles and ore metals shallow texturally complex granites can be associated spatially introduction and temporally with hydrothermal alteration and mineralization granite related ore deposits include porphyry and skarn the formation of a granite related ore deposit represents the confluence type ores and other hydrothermal deposits that are of many chemical and physical geological factors including magma spatially and temporally associated with granitic sensu composition e g concentrations of ore metals chlorine and water lato rocks in this paper i emphasize characteristics magma oxidation state the relative timing of crystallization magma found in porphyry style cu mo au deposits and some ascent magmatic volatile phase exsolution and the depth of em related systems however my treatment here is not meant placement early magmatic crystallization of ore metal rich minerals to cover the full range of granitic rocks and mineralization coupled with late exsolution of the magmatic volatile phase is that make up the granite related ore systems the forpromoted by deeper emplacement levels and lower magmatic water mation of granite related ore deposits by orthomagmatic concentrations and leads to low eyciencies of removal of compatible hydrothermal processes is dependent upon many physical elements from melts into the magmatic volatile phase s water and chemical magmatic factors including but not limited concentrations in the melt and pressures of crystallization can be to the composition and evolution of the associated estimated from phase equilibria and textural relationships of horn magmas the rate of magma ascent the depth and blende in some felsic systems physical factors avect the dynamics geometry of magma emplacement and the local temof fluid magma melt and volatile phase movement which in turn perature and stress fields at the site of magma emavect the size of zones of alteration and mineralization granite placement detailed studies of the igneous rocks textures can record the partial history of some dynamic processes associated with ore deposits can therefore yield critical miarolitic cavities are good evidence for magmatic volatile phase information regarding the source of metals and ligands exsolution both miarolitic cavities and pegmatitic texture exhibit in the ore generative hydrothermal solutions that are evidence for external nucleation of crystals nucleation controlled operative in the formation of granite related ores in this phenomena expressed as variations in granite textures can result review i will present a series of narratives consistent in from a multiplicity of causes including undercooling of the melt my view with prevailing field and experimental data on textural elements such as pegmatite aplite skeletal crystals and the orthomagmatic hydrothermal theory for the genesis graphic textures can form as a result of undercooling interconnected of some granite related deposits volumes of the magmatic volatile phase allow for advection of some high level granites i e those that are emplaced hydrothermal ore fluids through the magma in shallow granitic at depths of 8 km or less represent the crystallized systems miarolitic cavities can be interconnected consistent with remains of magmas that were associated with subvolcanic this hypothesis ore generative hydrothermal systems therefore studies of shallow granites aimed at understanding magmatic evolution and volatile phase exsolution at shallow levels are necessary if we are to understand ore genesis and the deep inputs to present day geothermal systems as well as evaluate hazards associated with the volcanic

velocity profiles measured on the windward slope of a transverse dune velocity gradients measured on the windward slope of a transverse dune show that flow acceleration strongly affects the turbulence structure of wind wind profiles measured below a height of 1 6m are nonlogarithmic and the altered nature of velocity profiles varies over the windward slope of a dune these findings suggest that calculated values of shear velocity are largely dependent upon the height and location of wind speed measurements as well as the strength of the prevailing wind moreover if bagnold type transport equations are used to calculate rates of sand transport on a dune wind speeds must be measured within 0 2 m of the dune surface if wind speeds are measured above this height the resulting errors in calculated shear velocity will manifest themselves as errors in calculated rates of sand transport if rates of sand transport are derived from wind speeds measured above 0 2 m the calculated rates may underestimate sand transport on the windward face of a dune as a result of flow acceleration in contrast if a dune has a separate crest upwind of the brink the expansion and subsequent deceleration of flow downwind from the crest may result in an overestimation of sand transport

geomorphology of desert sand dunes a review of recent progress through the 1980s and 1990s studies of the geomorphology of desert sand dunes were dominated by field studies of wind flow and sand flow over individual dunes alongside these there were some attempts numerically to model dune development as well as some wind tunnel studies that investigated wind flow over dunes as developments with equipment allowed field measurements became more sophisticated however by the mid 1990s it was clear that even these more complex measurements were still unable to explain the mechanisms by which sand is entrained and transported most importantly the attempt to measure the stresses imposed by the wind on the sand surface proved impossible and the use of shear or friction velocity as a surrogate for shear stress also failed to deliver at the same time it has become apparent that turbulent structures in the flow may be as or more important in explaining sand flux in a development paralleled in fluvial geomorphology aeolian geomorphologists have attempted to measure and model turbulent structures over dunes progress has recently been made through the use of more complex numerical models based on computational fluid dynamics cfd some of the modelling work has also suggested that notions of dune equilibrium form may not be particularly helpful this range of recent developments has not meant that field studies are now redundant for linear dunes careful observations of individual dunes have provided important data about how the dunes develop but in this particular field some progress has been made through ground penetrating radar images of the internal structure of the dunes the paradigm for studies of desert dune geomorphology for several decades has been that good quality empirical data about wind flow and sand flux will enable us to understand how dunes are created and maintain their form at least some of the difficulty in the past arose from the plethora of undirected data generated by largely inductive field studies more recently attention has shifted although not completely to modelling approaches and very considerable progress has been made in developing models of dune development it is clear however that the models will continue to require accurate field observations in order for us to be able to develop a clear understanding of desert sand dune geomorphology

the use of grain size trend analysis in macrotidal areas with breakwaters implications of settling velocity and spatial sampling density abstract in a macrotidal environment with offshore breakwaters elmer west sussex a new approach for the identification of the sediment transport pathways with grain size trend analysis gsta was undertaken using statistical parameters mean sorting and skewness directly derived from settling velocities distributions the same samples were analysed with sieving quarter and half phi resolution and gsta was performed again in order to directly compare the resultant sediment transport directions derived with the two analytical techniques furthermore both regular and irregular sampling distributions were used to recalculate gsta hydrodynamic data were collected in different locations around the breakwaters and net sediment transport directions were calculated in order to assess the accuracy of the sediment transport pathway directions derived with the different analytical techniques the accuracy of settling velocity in determining the statistical parameters of the grain size distribution is identified especially for the fine medium sand sediments settling velocities produced better results than the sieving the quarter phi resolution producing the poorer results in comparison with the coarser half phi resolution the results for the different spatial sampling strategies are found to depend upon the number of samples utilised that shows that the accuracy of the gsta is based upon the ability of representing adequately the spatial distribution of the sediment parameters

qaidam basin as an analog for linear dune formation in chasma boreale mars a comparative analysis abstract this paper identifies a terrestrial analog for linear dune fields in the chasma boreale located in the north polar region of mars and analyzes it to explain linear dune formation the straight indurated linear dunes are elongated downwind of dome dunes and barchans under a unimodal wind regime providing a novel research opportunity for geomorphologists to investigate the coexistence of transverse and longitudinal dunes and the effect of sediment induration on dune morphology the linear dunes around the chaerhan salt lake in the qaidam basin are good analogs for the chasma boreale linear dunes because of the similarities in dune morphology and evolution process further the effects of the indurating agents salt and ice on the formation of the linear dunes are similar in both locations in this paper we have contrasted and analyzed their dune patterns the influence of cohesive sediment and wind regimes in the two areas the formation process and underlying mechanisms that create the linear dunes are analyzed through geomorphological evidence and dune flow simulation experiments the results show that there is a remarkable morphological resemblance between the two areas cohesive sediments especially the interbedded frozen laminae on mars increase dune stability and thus allow the formation of linear dunes under a small divergence angle in a bidirectional wind regime the proto linear dune facilitates the deposition of sediment along the major axis of the dune and the lateral wind maintains and promotes the development of linear dunes we also discuss how cohesive sediment influences dune morphology and leads to a transition from barchans to linear dunes and we examine the feedback between dune form and airflow the different effects of sediment induration on dune morphology make the determination of aeolian patterns less certain which has implications for the development of climate models of mars and titan

radio frequency identification rfid technology applied to the definition of underwater and subaerial coarse sediment movement abstract in this paper radio frequency identification technology has been applied to track both underwater and subaerial displacement of pebbles along an artificial coarse beach at marina di pisa italy several preliminary laboratory tests have been performed to adapt the rfid technique for underwater use which has been the primary impediment to this promising approach to the study of coarse sediment transport and movement tests showed the reliability of low frequencies for this kind of work since they enable good signal transmission and reception through water passive abs plastic transponders were inserted into about 100 pebbles and released onto the beach in march 2009 a core 125 reader was chosen as the operating antenna to continuously transmit low frequency 125 khz signals an acoustic signal toned whenever a pebble was detected while the unambiguous identification code of the pebble is shown immediately on the screen of a laptop connected to the reader the positions of the pebbles were recorded with a total station after two months may 2009 74 marked pebbles were retrieved 77 of the total the positions of the retrieved pebbles were also recorded with the total station thus allowing calculation of the coarse sediment transport tendency about 60 of the recovered pebbles 44 out of 74 were found on the upper shoreface the analysis of the marked pebble trajectories revealed a divergent transport movement in the northernmost sector of the beach this movement was probably triggered by an irregularity of the submerged breakwater fronting the shoreline the southern sector is characterised by chaotic pathways related to the formation and evolution of beach cusps this outcome highlights and confirms the importance of a complete definition of the beach system with no separation between the underwater and the subaerial portion of the shore when it comes to sediment transport and movement this successful application of rfid technology to the underwater environment provides a chance to broaden understanding of a topic in need of further study

origin and ore forming consequences of the advanced argillic alteration process in hypogene environments by magmatic gas contamination of meteoric fluids metasomatic effects have been thermodynamically computed for magma derived sulfur gases which may contaminate convecting meteoric fluids in the monzonite k silicate protore and are compared with natural assemblages in the butte district of montana the advanced argillic assemblage with covellite is produced in hypogene environments at 300 degrees c by sulfur metasomatism of protore only for a limited range of net sulfur valences essentially 1 to 2 placing limiting constraints on the possible ratios of so 2 and h 2 s gases a second important factor is the relative reaction rates of protore and contaminating sulfur gases contamination by sulfur gases is a third factor of importance a final factor is that a minimum negative net volume of reaction causes by wall rock dissolution and fracture enlargement the high permeability necessary for circulation of enormous quantities of hydrothermal fluids and vein growth characteristic of this extreme alteration facies modified journal abstract

net sediment transport patterns inferred from grain size trends based upon definition of transport vectors reply abstract a new approach to the analysis of the grain size trends associated with net sediment transport directions in shallow marine environments is developed here two specific trends modified from mclaren and bowles 1985 on the basis of a literature review are used to define a grid of trend vectors such vectors are filtered and transformed into transport vectors it is suggested that an ordered pattern of the transport vectors represents net transport paths the orderliness of the derived pattern is examined on the basis of a significance test using the average length of the transport vectors as a criterion both the filtering operation and the significance test procedure are based upon the assumption that the trend vectors which are not associated with net transport have the same probability of being in any direction the technique is applied to data from yangpu harbour southern china the technique can be applied to inner continental shelf and coastal environments for such an analysis the area under investigation should be sampled at an interval large enough to reflect the real grain size trends resulting from net sediment transport but small compared with the dimensions of the sedimentary environment the time scale of the results depends upon the sampling depth applicability of the technique is likely to be somewhat limited where the environment is highly variable over short distances furthermore due to its statistical character the analysis may fail to identify net transport patterns

deriving transport pathways in a sediment trend analysis sta abstract sediment trend analysis sta is a technique that enables patterns of net sediment transport to be determined by relative changes in grain size distributions of all naturally occurring sediments in addition sta can determine the dynamic behaviour of bottom sediments with respect to erosion accretion or dynamic equilibrium the data requirements for sta are the full grain size distributions taken from sediment grab samples collected at a regular spacing over a particular area of interest two types of methods are presently used in the derivation of the transport pathways a line by line approach in which transport pathways are determined by searching for sample sequences in which the distributions change in a statistically acceptable manner and various vector approaches in which each sample is compared to neighbouring sites from which a vector sum is calculated the basic assumption for sta is that the processes that cause sediment transport will affect the statistics of sediment distributions in a predictable way in reality this type of analysis is complicated through the inclusion of a number of uncertainties or noise the goal of sta is to extract the information the transport pathways from the noisy signal the grain size distributions an approach that is made difficult because neither the nature of the information nor the noise is known because of this obtaining results by simply applying its theory in a black box approach may provide poor solutions the line by line approach to sta draws from communications theory to achieve a solution in some communications systems the information from many sources is combined into one signal the resulting signal is from a statistical viewpoint nothing but noise the extraction of specific information assumes that information is indeed present and determines if that assumption is consistent with the received signal for sta the procedure is to assume a transport direction over an area comprising many sample sites from this assumption the predicted sediment trends are compared with the pathways determined by the actual samples the assumed transport direction is repeatedly modified until the best fit is achieved vector techniques may be very helpful to provide insights and guidance to the line by line approach however the approach is ultimately necessary to finalize a credible solution as well as providing important further information on the dynamic behaviour of the sediments and to delineate specific sediment transport environments

the role of streamline curvature in sand dune dynamics evidence from field and wind tunnel measurements abstract field measurements on an unvegetated 10 m high barchan dune in oman are compared with measurements over a 1 200 scale fixed model in a wind tunnel both the field and wind tunnel data demonstrate similar patterns of wind and shear velocity over the dune confirming significant flow deceleration upwind of and at the toe of the dune acceleration of flow up the windward slope and deceleration between the crest and brink this pattern including the widely reported upwind reduction in shear velocity reflects observations of previous studies such a reduction in shear velocity upwind of the dune should result in a reduction in sand transport and subsequent sand deposition this is not observed in the field wind tunnel modelling using a near surface pulse wire probe suggests that the field method of shear velocity derivation is inadequate the wind tunnel results exhibit no reduction in shear velocity upwind of or at the toe of the dune evidence provided by reynolds stress profiles and turbulence intensities measured in the wind tunnel suggest that this maintenance of upwind shear stress may be a result of concave unstable streamline curvature these additional surface stresses are not recorded by the techniques used in the field measurements using the occurrence of streamline curvature as a starting point a new 2 d model of dune dynamics is deduced this model relies on the establishment of an equilibrium between windward slope morphology surface stresses induced by streamline curvature and streamwise acceleration adopting the criteria that concave streamline curvature and streamwise acceleration both increase surface shear stress whereas convex streamline curvature and deceleration have the opposite effect the relationships between form and process are investigated in each of three morphologically distinct zones the upwind interdune and concave toe region of the dune the convex portion of the windward slope and the crest brink region the applicability of the model is supported by measurements of the rate of sand transport and the change of the dune surface in the field

residual transport model in correlation with sedimentary dynamics over an elongate tidal sandbar in the gironde estuary southwestern france abstract this study qualitatively describes by a multidisciplinary approach hydrodynamic and residual sediment transport over a sandbar in a macrotidal environment the sandbar is elongated and attached to a headland that is located in the gironde estuary southwestern france bathymetric surveys side scan sonar sonograms grain size trends of surficial sediment and 2dh numerical simulations of current patterns were used to define a conceptual model for the dynamics of this sandbar the sandbar is oriented anticlockwise with respect to the main flow the channel oriented bar face is ebb dominated whereas the opposite face is flood dominated resulting in a clockwise residual transport the line of sediment flux convergence corresponds to the crest of the bar the residual flow over the bar appears to originate from the regional estuarine flow the dominant process responsible for the maintenance of the sandbar seems to be the depth averaged main tidal flow rather than secondary circulation due to headlands or the interaction between the tidal flow and the seabed to generalize this regional conceptual model a qualitative comparison is made with the theories of sandbar dynamics due to tidal currents pingree and maddock 1979 zimmerman 1981 huthnance 1982 and others the seabed stability approach developed by huthnance 1982 seems to be the most reliable theory to explain the saint georges bank dynamics even though many natural factors are not taken into account

influence of the gap ratio on variations in the surface shear stress and on sand accumulation in the lee of two side by side obstacles changes in the surface shear stress in the lee of two side by side obstacles result in sand deposition and the development of aeolian sand drifts through direct wind tunnel measurements using irwin type sensors surface shear stress behind two side by side obstacles separated by gaps with different gap ratios the ratio of the gap spacing between the obstacles to the center to center distance for the obstacles was measured particular attention to the effects of the spacing between the two obstacles on the initiation of sand drifts has been paid the results showed that the gap ratio was the key factor that determined the shear stress patterns wind speed increased through the gap but decreased a short distance downwind causing higher peak skin friction velocities and higher shear stress immediately behind the obstacles producing a range of sand deposition patterns in the sheltered lee side of the obstacles comparison of plots of surface shear stress and isoline plots of for the fraction of the total time in which a given threshold skin friction velocity was exceeded with the sand deposition patterns confirmed that sand drift may form in the lee of a gap between two adjacent obstacles when the gap ratio g 0 44 and it may disappeared when the gap ratio larger than this value

ore related breccias in volcanoplutonic arcs an overview of breccias related to a variety of base metal precious metal and lithophile element deposits in volcanoplutonic arcs permits definition of six possible mechanisms for subsurface brecciation 1 release of magmatic hydrothermal fluids from high level hydrous magma chambers during second boiling and subsequent decompression generates a spectrum of breccia types in which fragments may suffer collapse and or ascent single or multiple intrusion related breccia pipes and pre and intermineral breccias in porphyry copper deposits provide widespread examples 2 magmatic heating and expansion of meteoric pore fluids may lead to brecciation commonly of late or postmineral age and including pebble dikes in porphyry type and related deposits magmatic heating of rocks saturated with seawater may cause submarine hydrothermal eruptions late in the emplacement histories of kuroko type massive sulfide deposits many of the resultant breccias underwent limited sedimentary transport overpressuring of heated fluids beneath semipermeable partly self sealed cap rocks may lead to brecciation and subaerial hydrothermal eruptions in shallow epithermal precious metal settings magmatic heating or tectonic disturbance may have triggered brecciation 3 interaction of cool ground waters with subsurface magma can generate phreatomagmatic explosions postmineral phreatomagmatic diatremes associated with porphyry systems and premineral diatremes with epithermal precious or base metal deposits were generated in this manner these attained the palcosurface to produce pyroclastic base surge and fall deposits that accumulated as tuff rings around maar craters 4 magmatic hydrothermal brecciation may lead to disruption of rocks through to the paleosurface decompression and fragmentation and eruption of the top part of an underlying magma chamber pre and postmineral magmatic diatremes of this sort are inferred to accompany a few porphyry type and other base and precious metal systems they were manifested at the palcosurface by accumulations of pyroclastic fall and flow deposits 5 breccias may result from mechanical disruption of wall rocks during subsurface movement of magma any intrusion related deposit may include such intrusion breccias 6 tectonic breccias resulting from fault displacement may accompany any type of ore deposit a continuum exists between many of these breccia types and it is difficult to identify unique criteria for their unambiguous distinction

sediment transport patterns inferred from grain size trends and trace metal dispersion near the santa rosalia mining district gulf of california abstract the transport of continental materials of natural and or anthropic origin as well as their dispersion and final deposition in marine environments can be inferred from the analysis of the textural tendencies of sediments the exploitation of copper ore since the 19th century in the santa rosalia mining district has caused the accumulation of potentially toxic elements ptes in sediments off the western coast of the gulf of california however after several decades of mining little is known about the mobilization and final destination of these ptes in the present work the net sedimentary transport and dispersion of cu and zn is inferred in front of the mining district of santa rosalia at the western margin of the gulf of california net sedimentary transport is dominantly towards the southeast with a change towards the east of the port of santa rosalia the spatial distribution of cu and zn showed the same pattern as the net sediment transport which suggests that the dispersion of ptes is controlled by the textural tendencies of the sediments and their transport corroborated by hydrodynamic models of the marine currents at the western margin of the gulf of california

porphyry cu mo stockwork formation by dynamic transient hydrothermal pulses mineralogic insights from the deposit at butte montana the systematic distribution of vein and alteration mineral assemblages in porphyry cu deposits largely arises from changes in the temperature and pressure of fluids that traversed fractures throughout the hydrothermal system magmatic and hydrothermal minerals record the complex history of the fluctuating temperature and pressure regime as hydrothermal fluids transfer heat from their magmatic source to cold wall rock in response to lithostatic to hydrostatic pressure variations we examine the thermal profile of the porphyry cu mo deposit in butte montana by determining formation temperatures for magmatic and hydrothermal samples representing different time frames and depths within the deposit in context with sample pressure estimates we use three independent mineral thermobarometers ti in quartz zr in rutile and x mg ti in biotite from which we estimate that final dike injection temperature and hence the initial magmatic hydrothermal fluid temperature was 700 c while the ambient host rock temperature was 450 to 500 c we find a magmatic hydrothermal continuum represented in hydrothermal veins ranging from 710 to

mean airflow patterns upwind of topographic obstacles and their implications for the formation of echo dunes a wind tunnel simulation of the effects of windward slope 1 secondary airflow plays an important role in dune formation and development in the case of the echo dunes that form upwind of an obstacle it introduces considerable complexity because both the initiation and development processes are influenced by airflow patterns in this study we measured the variations of airflow in front of obstacles with different windward stoss slope angles by means of particle image velocimetry in a series of wind tunnel tests the windward slope angle was the key factor in determining the secondary airflow patterns the horizontal velocities decreased and the vertical velocities increased as the airflow approached perpendicular to the obstacle and a vortex of reversed flow formed in front of obstacles with a stoss slope of 60 or steeper the positions of airflow separation and of the core of the reversed vortex were a function of the windward slope angle depending on the position of the reverse vortex and its significance for the formation of echo dunes the windward slope could be divided into three groups 65 or less 70 75 and 80 or more the horizontal velocity profiles deviated from a log linear distribution resulting in five airflow regions with different rates of change of horizontal velocity we discuss the significance of these velocity variations for sand accumulation and the effects of each airflow region on echo dune formation

short term morphological change and sediment dynamics in the intertidal zone of a macrotidal beach abstract this paper describes the morphological and sedimentological evolution of amacrotidal beach over a 20 day period under varying hydrodynamicconditions signi cant breaker heights of 0ae3 2 m and tidal ranges of 2 5 m during the eld campaign an intertidal bar developed around the mid tidelevel migrated onshore welded to the upper beach and was then attenedunder energetic wave conditions the bar had a wave breakpoint origin and itsformation was triggered by a reduction in tidal range causing more stationarywater level conditions rather than an increase in wave height most of theonshore bar migration took place while the bar was positioned in the inner tomid surf zone position such that the bar moved away from the breakpoint andexhibited divergent behaviour the depth of disturbance over individual tidalcycles was 10 20 of the breaker height such values are more typical of steepre ective beaches than gently sloping dissipative beaches and are consideredto re ect the maximum height of wave generated ripples the grain sizedistribution of sur cial sediments did not vary consistently across the beachpro le and temporal changes in the sedimentology were mostly unrelated tothe morphological response the lack of clear links between beach morphologyand sedimentology may be in part due to shortcomings in the samplingmethodology which ignored the vertical variability in the sediment sizecharacteristics across the active layer keywords beach sediment depth of disturbance intertidal bar macrotidalbeach morphology introductionbeaches respond rapidly to changing wave andtide conditions through the redistribution of theirsediments by oscillatory and quasi steady cur rents resulting in spatial patterns of erosion sediment divergence and accretion sedimentconvergence given suf cient time these bed level changes modify the beach shape by theformation modi cation destruction and ormigration of secondary morphological features such as berms beach cusps swash bars ripchannels and nearshore bars the dynamics ofthese secondary morphological features and theirrole in affecting beach stability has been a majorfocus of beach research over the last few decades e g komar 1998 short 1999 most short term days to weeks eld investi gations addressing the morphological response ofsandy beaches to wave and tide forcing have beenconducted in microtidal or mesotidal settings beaches in macrotidal settings have on the otherhand only received limited attention despitetheir common occurrence short 1991 a mainreason for this imbalance is that macrotidalbeaches are often planar and lack pronouncedsecondary morphological features indeed theonly type of macrotidal beach that does featureprominently in the coastal literature is the ridgeand runnel beach which is characterized bysedimentology 2007 54 39 53

structural geologic evolution of the butte district montana the butte district contains two porphyry cu mo deposits and the younger zoned main stage base metal lode deposits that formed in the period from 66 to 62 ma synchronous with laramide compressional thrust faulting and folding in southwest montana new geologic mapping of the butte district reveals three distinct episodes of deformation 1 gentle 20 10 ne tilting produced during laramide compressional deformation uplift and exhumation during and after ore formation in the late cretaceous to paleocene 66 53 ma 2 moderate 10 50 nw tilting of eocene age produced by ne striking normal faults that are limited to the northwest part of the district and synchronous with the eruption of the lowland creek volcanics and 3 miocene to present gentle 15 ese tilting in the hanging walls of the continental east ridge and rocker normal faults stratigraphic relationships isotopic ages hornblende barometry and fluid inclusion data indicate that exposures of the butte granite which hosts mineralization crystallized at 6 to 9 km depth and that early porphyry cu mo deposits formed at similar depths of 5 to 9 km a period of rapid uplift and erosion removed about 7 km of rock from above the ore deposit between 66 to 64 ma and 53 ma but was mostly completed by 59 ma estimated exhumation rates range from 0 5 to 2 mm yr and uplift was likely most rapid between 63 5 and 62 ma during main stage mineralization which occurred at depths of 2 to 6 km the butte granite and boulder batholith were emplaced at 79 to 76 ma into thrust fault ramps which later became inactive near butte as laramide crustal shortening moved eastward in the helena salient the accelerated period of uplift and unroofing is attributed to renewed deformation along the montana disturbed belt south of butte that uplifted the south end of the boulder batholith and produced 20 of gentle ne tilting episode i in the district the exhumation history of the deposit is therefore broadly contemporaneous with ore formation and is consistent with the general transition from lithostatic to hydrostatic conditions that is evident from the telescoping of early porphyry cu mo ores cut by the main stage lode veins within a 5 m y period the laramide compressional regime near butte evolved into an extensional environment characterized by normal faulting the normal faults were synchronous with eruption of the 53 to 48 ma lowland creek volcanics which directly overlie the main stage veins in the northwest part of the district structural reconstruction of the district at the time of mineralization produces orientations of quartz porphyry dikes porphyry cu mo veinlets main stage veins and alteration zonal patterns that are steeply dipping and symmetrical similar to observations from other upright or restored porphyry copper deposits early porphyry cu mo veins and dikes are oriented e w and likely originated as tensile hydrofractures above a ductile magma carapace during laramide shortening additionally during the laramide compressional phase two conjugate fault systems occupied by main stage veins are normal oblique slip faults that record minor e w and vertical shortening and n s extension these normal faults with minor offset likely resulted from brittle failure caused by doming above a volatile rich and buoyant granitic magma chamber and cupola at depth the structural evolution of the butte district therefore reflects the interaction of a far field compressive stress regime with local buoyant magmatic forces

geomorphology and sediments of sand ramps in the mojave desert abstract sand ramps are amalgamated accumulations of aeolian fluvial and talus deposits they have developed as a result of the interactions of wind blown sand and desert piedmont processes adjacent to mountain ranges in the mojave desert and occur next to regional and local sand transport corridors sand ramps are dominated by aeolian sand that was deposited as sand sheets against the mountain front but also include significant fluvial units periods of geomorphic stability are represented by paleosols and talus accumulations the sand ramps provide a record of the response of aeolian processes to climatic change in the mojave desert most are now relict features and accumulated in periods of higher sediment supply from fluctuating and or desiccating paleolakes during the late pleistocene and early holocene

stable isotope and fluid inclusion investigations of epithermal vein and porphyry molybdenum mineralization in the rico mining district colorado the rico mining district western san juan mountains colorado contains epithermal vein deposits carbonate replacement deposits and a large zone of porphyry style molybdenum mineralization historically the vein and replacement deposits have produced significant amounts of silver lead and zinc with minor gold and copper all the mineralization formed nearly contemporaneously about 5 m y ago the veins and replacement deposits occur in paleozoic and mesozoic sedimentary rocks that have been uplifted into the rico dome which is cored by a horst of precambrian greenstone and quartzite the porphyry molybdenum mineralization 40 million tons of 0 31 mo is 1 500 m beneath the surface in the east end of the district and consists of stockwork veining in precambrian quartzite and greenstone and in pennsylvanian sedimentary rocks the epithermal veins occur above and peripheral to the porphyry mineralization widespread high silica alaskite porphyry dikes were also emplaced at the same time as the porphyry mineralization and are probably related to the source intrusion for the molybdenum mineralization and the heat source for the hydrothermal system that produced the epithermal and replacement deposits fluid inclusions in quartz from the veins homogenize at temperatures in the range 200 degrees to 300 degrees c and yield salinities less than 5 equiv wt percent nacl the delta d values of quartz inclusion fluids 112 to 121ppm and calculated delta 18 o values of fluids in equilibrium with the quartz 3 to 17ppm show that the epithermal vein fluids were 18 o shifted meteoric waters vein samples with large 18 o shifts also exhibit very saline fluid inclusions indicating that the fluids which experienced the greatest degree of water rock interaction contain the highest concentration of dissolved components the porphyry fluid delta d 90 to 104ppm delta 18 o 2ppm was derived from mixed magmatic and meteoric sources primary inclusions in the porphyry veinlets homogenize to both liquid and vapor in the temperature range 350 degrees to 420 degrees c suggesting that boiling occurred during their formation trains of secondary inclusions are abundant in the veinlets and show that a later lower temperature fluid encroached upon the porphyry system no evidence for mixing of magmatic and meteoric fluids was found in any of the epithermal veins the porphyry mineralization formed early in the history of the rico hydrothermal system epithermal vein formation occurred later than the porphyry mineralization and the meteoric hydrothermal fluid collapsed into the porphyry core of the system during the retrograde stages of the hydrothermal system