the geochemistry of gold bearing chemical sediments dickenson mine red lake ontario a reconnaissance study auriferous sedimentary rocks at the dickenson mine red lake are characterized by large enrichments of rare elements au ag pd as sb b and metals conventionally considered to be relatively immobile ni w with negligible concentrations of the abundant and mobile base metals based on a reconnaissance survey involving 12 rocks analysed for 42 elements these sediments can be represented in terms of a mixture of two components mafic volcaniclastic material and hydrothermal precipitates the volcaniclastic component has a composition closely comparable to mafic volcanic rocks that conformably envelope the sediments and contributes all of the al ti v sc zr and f the hydrothermal component donates si fe mn mg ca k si and c together with au ag pd as sb b w and ni chromium and nickel are contributed from both sources alteration of the mafic volcanic rocks that envelope the auriferous sediments involved fixation of si k and co2 in contrast to the typical patterns of metasomatis

early carbonate veining and gold mineralization in the timmins camp depositional context of the dome mine ankerite veins abstract the earliest auriferous veining event in the development of the over 16 moz gold endowment at the dome mine was an extensive set of ankerite veins over 5400 m strike length the depositional context of the dome mine ankerite veins has been historically contentious and their role in the mineralization history of the deposit not well understood we present a deposit wide geochemical study of the ankerite veins and their host rocks with observations from new underground mapping ankerite veining across the mine is almost exclusively restricted to the vipond formation which is fe rich and tholeiitic in nature metamorphic fluids and ankerite vein formation generally focused along flow boundaries in the volcanic sequence however carbonatization is ubiquitous the flows of the vipond formation maintain their protolith geochemical signatures as ree zr al2o3 tio2 and y are largely immobile during mineralization and alteration which mobilized na2o k2o and locally fe2o3 the ankerite vein structures are reactivated and overprinted by quartz and quartz tourmaline veining and gold grade is variable ranging from

alteration mineralization and metamorphism in the area of the east south c ore zone 24th level of the dickenson mine red lake northwestern ontario the area of the east south c esc orebody of the dickenson mine red lake consists of variably altered and mineralized basalt basaltic volcaniclastic rocks minor sulphidic iron formation and

indirect and direct effects of soil properties on soil splash erosion rate in calcareous soils of the central zagross iran a laboratory study abstract detachment of soil particles by means of raindrop impact is mainly affected by soil properties especially in the absence of vegetation cover this study was conducted to investigate the direct and indirect effects of soil properties on splash erosion rate in calcareous soils of low vegetation cover in lordegan region iran for this purpose total soil splash tse downslope dse and upslope use splash erosion rate are measured under the following four conditions that comprised different values of slope s and rainfall intensity ri mm h 1 5 50 5 80 15 50 15 80 respectively using multiple splash sets mss as potential estimating parameters surface shear strength sss mean weight diameter mwd organic matter om calcium carbonate clay content silt and sand fractions were estimated the effects of soil estimators on soil splash erosion rate were quantified using a path analysis and multi linear regression mlr approaches applied to data collected from 105 points of soil profiles a horizon the results showed that the particle size distribution sss and mwd are sensitive to some of the parameters for estimating tse dse and use rate mwd carried the highest direct effects while sss the highest indirect ones via mwd on splash erosion particle size effects on soil splash weren t in general observed in higher slopes and rainfall intensities the particle size has in general a more direct rather than an indirect effect on splash erosion fine silt exerted an ambivalent role on splash erosion a high detachability of fine silt directly increases splash erosion while its capability to form a surface crust reduces splash erosion indirect effect of om through its association with mwd and sss is more than it s direct effects positive direct effect of calcium carbonate is more than its indirect negative effect via its association with mwd probably due to the presence of calcium carbonate within the size of silt and fine sand in the studied soils causing an increase in soil detachability

fluorapatite fenitization and gold enrichment in sheeted trondhjemites within the destor porcupine fault zone taylor township ontario pronounced fluorapatite mineralization is present in sheeted trondhjemites near timmins the trondhjemites intrude a deformed ultramafic to fe tholeiite volcanic sequence disposed in the structural hanging wall of the destor porcupine fault and they bound a domain of high grade gold ore spinifex textured ultramafic flows record variable intensities of secondary alteration to a carbonate cr muscovite assemblage they are characterized by chondritic al2o3 tio2 ratios 19 1 7 enhanced cr 1570 2090 ppm and ni 470 1070 ppm together with low levels of the incompatible elements ta nb and th fresh quartz oligoclase trondhjemitic intrusions are compositionally coherent with respect to sio2 average 63 wt al2o3 16 3 wt and na2o 6 7 wt as well as to the alteration insensitive elements v sc zr and hf whole rock 18o values of 10 0 10 6 combined with magmatic quartz feldspar 0 8 0 9 signify that these are primary high 18o magmas likely derived by partial melting of 18o enriche

effects of erosion degree rainfall intensity and slope gradient on runoff and sediment yield for the bare soils from the weathered granite slopes of se china abstract soil erosion caused by rainfall is a dominant driving force of ecosystem degradation and has become a worldwide environmental issue however few studies have been conducted to investigate the effect of erosion degree on the characteristics of soil erosion this study aims to investigate the effects of erosion degree rainfall intensity and slope gradient on erosion processes on bare weathered granite slopes of southeast china the method of simulated rainfalls was applied with two soil tanks under three slope gradients 8 15 25 four rainfall intensities 60 90 120 150 mm h and three erosion degrees slight e1 moderate e2 severe e3 the rainfall time lasted 90 min and the paddy samples were collected at every 3 min to determine the runoff rate for surface flow rr s and interflow rr i sediment rate sr sediment concentration sc and particle size distribution psd the enrichment ratio er and mean weigh diameter mwd of different particles were finally calculated and evaluated the occurring time of surface flow tr s and interflow tr i presented a negative relationship with rainfall intensity and slope gradient while tr s presented an order of e2 e1 e3 and tr i was negatively related to erosion degree rr s increased with runoff duration and was positively correlated to rainfall intensity and slope gradient but negatively correlated to erosion degree but rr i displayed single peak curves with runoff duration and was positively related to erosion degree sr showed an increasing deceasing trend with runoff duration and was positively correlated to rainfall intensity and slope gradient sr on different slopes displayed an order of e1 e2 e3 at the 60 and 90 mm h rainfalls while it reversed at heavier rainfalls sc decreased with runoff duration with light fluctuations it was found that sediment psd was corresponding to original soils to a definite extent while mwd and er were positively correlated to erosion degree these results facilitate the understandings of runoff and soil erosion processes in the weathered granite regions and erosion degree should be considered in future erosion prediction and modeling

mixing layer distortion at the confluence of channels of different depth channel confluences have received considerable recent attention in the fields of geomorphology1 3 sedimentology4 9 and hydraulic engineering10 13 where channels join rapid changes in fluid velocity turbulence intensity channel hydraulic geometry and bed geometry may occur14 17 previous models of junction dynamics have tended to assume that the confluent channels are of equal depth10 18 a condition that may be found only rarely in natural junctions more often the depths of confluent channels are different19 this discordance is commonly the result of the forma tion at the mouth of each confluent channel of bars that possess steep avalanche faces which dip into a central junction scour1 2 5 20 here we suggest that when channels of different depth join the mixing layer that forms at their confluence is distorted by interacting with a separation zone which forms in the lee of the mouth of the shallower channel this mixing layer distortion imparts a complex three dimensional flow to the junction promoting vertical fluid upwelling and significantly enhancing rapid mixing within the flow of the shallow tributary while retarding the rate of mixing across the flow of the deeper channel suspended sediments or contaminants within the deeper channel may be transferred rapidly across the flow of the shallower tributary upwelling downstream of the junction

soil formation on calcium carbonate rich parent material in the outer carpathian mountains a case study abstract in this study ten stratified calcium carbonate rich soil profiles from the polish outer carpathians were investigated in order to identity the influence of parent material variability and slope processes on soil diversity and their evolution moreover we evaluated the morphological and physico chemical soil properties to recognize the diagnostic horizons and classification of such soils while it is usually thought that carbonate rich soils are considered as formed in situ these study soils clearly presented layering and contribution of materials as they were developed from mixed substrates of different origin e g as the result of mass movements and possible aeolian silt contribution irrespective of the type of parent material every investigated soil showed traces of slope processes resulting in heterogeneous soil profiles further a few different patterns of primary calcium carbonate arrangement were found in general the studied soils were characterized by enrichment with calcium carbonate not only due to inheritance from calcium carbonate rich parent material but also translocation of calcium carbonate within soil profiles the latter depending on soil stratification based on the obtained results four pathways of soil evolution were formulated leptosols which represent initial calcium carbonate rich soils may evolve in different directions first formation of the thick layer suitable for cambic horizon development under deciduous forests which enables the classification of such soils as cambisols depends on slope processes and allochthonous material deposition in turn the decrease of mineralization rates for organic matter delivery of soil material from the upper parts of the slope as well as mixing of organic matter by mesofauna result in the formation of mollic horizons and transformation of leptosols into phaeozems further erosion and redeposition of fine soil material provide two types of slope sediments i those with silt loam texture dominance and ii clay loams interstratified with silty substrates the first type of sediments are more suitable for water percolation and after carbonate leaching clay dispersion and translocation occur in such materials luvisols may develop sediments with a prevalence of clay loam aided stagnosol formation in which pools of carbonates were stabilized due to the reduction of water percolation leading to stagnation

regional variation of mechanical and chemical denudation upper colorado river basin u s a the variation of mechanical and chemical denudation is investigated using discharge and sediment yield data from the upper colorado river system annual precipitation ranges from approximately 150 mm to 1500 mm mean specific yield ranges from 0 2 1 s km2 6 mm p a to 151 s km2 475 mm p a the hydrological geomorphological system adjusts itself to these varying climatic conditions in some areas however the effects of lithology or land use seem to override the climatic controls it is demonstrated that the increase in the absolute and particularly the relative amount of suspended sediment is closely related to a decrease in annual runoff and to an increase in the importance of high magnitude low frequency events this indicates that in areas of low annual runoff and high runoff variability soluble rocks are more resistant than in more humid areas during high magnitude low frequency events suspended sediment concentrations and loads are very high in semiarid areas due to sparse vegetation cover and dominance of direct runoff events of moderate magnitude and frequency which in more humid areas transport most of the dissolved load seldom occur the trend towards increasing mechanical denudation is even observed in areas of very low runoff 0 221 s km2 7 mm p a the peak of sediment yield in dry areas seems to approximate the point of no runoff very closely mechanical and chemical denudation are of equal importance at a runoff of about 300 mm per year

aggregate stability of soils in central spain and the role of land management the paper examines the relationships between soil aggregate stability selected soil properties and land use in central spain aggregate stability indices derived from three procedures were found to be significantly p 0 01 correlated with each other as well as with clay content organic carbon and a range of water soluble salts soils with a higher clay content have a lower aggregate stability it appears that the presence of expandable clays has a major negative influence although this impact is strongly modified by recent land use history and contemporary land management practices agricultural land abandoned in the 1940s was subsequently invaded by cistus matorral or planted with pinus the most stable aggregates occur under matorral and may represent a lag of more resistant aggregates surviving past land use related erosional processes comparisons with aggregates under pinus however suggest that hydrophobic substances from the cistus may have increased aggregate stability aggregates from areas remaining in cultivation are the least resistant although the stability envelope overlaps with areas under pinus these differences may be related to cultivation practices whereby clay rich subsurface horizons characterized by higher proportions of expandable clays are drawn to the surface and to enhancement of aggregate stability under forest by fungal hyphae

geochronological constraints on the timing of magmatism deformation and gold mineralization in the red lake greenstone belt northwestern ontario the paper presents u pb ages on zircon baddeleyite titanite rutile and monazite from volcanic and plutonic rocks of the red lake greenstone belt in the northern superior province the purpose of the study was to refine a previously outlined time frame for the volcanic evolution of the belt define the time of major plutonism and deformation and constrain the age of formation of gold deposits volcanism spanned at least 270 ma between 3000 and 2730 ma new ages of 2989 3 and 2894 2 ma for units of a lower volcanic sequence and and 2744 1 ma for units of an upper volcanic sequence corroborate and refine the previously established relationships local gabbroic and felsic intrusions cutting through the lower sequence yield ages of 2870 15 and respectively volcanism was succeeded by major plutonism deformation alteration and metamorphism between about 2730 and 2700 ma these processes were interrelated and progressed as a relatively continuous sequence of events accentuated by major activity d

protracted fluid rock interaction in the mesoarchaean and implication for gold mineralization example from the warrawoona syncline pilbara western australia abstract oxygen isotopic and geochemical analyses on whole rock and quartz veins are combined with structural observations in order to constrain the fluid circulation history within the mesoarchaean warrawoona syncline of the north pilbara craton western australia the plumbing system which is the focus of this study is localized in the so called fielding s find shear zone ffsz a km scale shear zone formed during the burial of greenstones and coeval exhumation of granitic complexes this shear zone runs parallel or close to the axial plane of the syncline it involves a prominent quartz vein network and is lined with strongly hydrothermally altered mafic felsic and sedimentary rocks towards the ffsz felsic and mafic volcanic rocks become intensely silicified with an increase in bulk rock 18 o values from 10 8 to 25 1 for altered felsic volcanics and from 7 1 to 18 3 for altered mafic volcanics geochemical modelling ascribes the silicification to a dissolution precipitation process ree and most other trace elements are strongly depleted in the silicified units with the exceptions of elements such as v cr ni and co which are enriched throughout the warrawoona syncline vein quartz 18 o data are within a small range of 13 2 2 significantly lower than their silicified host rocks these data are interpreted as the result of two main paleo fluid circulation stages intense silicification and 18 o enrichment represent alteration driven by low temperature hydrothermal convection probably involving archaean seawater in contrast the quartz veins network is related to the infiltration of metamorphic and or magmatic fluids during a later deformation episode these quartz veins represent the event responsible for the bulk of economic lode gold formation in the area the protracted fluid rock interaction history in the warrawoona syncline may have played a major role in setting the stage for the late mineralizing event the early hydrothermal circulation could have formed an efficient plumbing system characterized by high permeability low reactivity and possibly au enrichment upgrading the au endowment to the late hydrothermal fluids

effective sediment transporting discharge from magnitude frequency analysis the long term effectiveness of a geomorphic event of a particular magnitude is the product of the effect of a single event of that magnitude times the frequency with which it recurs magnitude frequency analysis if discharge frequency of a stream is assumed to be log normally distributed and if sediment transport rate is assumed to be a power function of discharge then transport effectiveness attains a maximum value at some discharge termed here the effective discharge that moves the most sediment over the long term the effective discharge and its recurrence interval may be predicted if both assumptions are correct analysis of 55 u s streams demonstrates that the observed and the predicted recurrence intervals of the effective discharge are in poor agreement this lack of agreement results from the failure of the power function of discharge to predict adequately the sediment transport rate above some high discharge threshold or thresholds the observed recurrence interval of the effective discha

timing of gold mineralization at red lake northwestern ontario canada new constraints from u pb geochronology at the goldcorp high grade zone red lake mine and the madsen mine the goldcorp high grade zone at the red lake mine has reserves proven and probable established at 1 775 million tons mt at an average grade of 80 6 g t au new u pb geochronologic data combined with detailed mapping and crosscutting relationships provide timing constraints and new insights into the formation of the exceptionally rich goldcorp high grade zone the results show that the main stage of the high grade mineralization in the high grade zone formed before 2712 ma and that a second stage of gold mineralization much smaller in terms of total gold content but spectacular in terms of grade formed after 2702 ma this second stage is attributed to gold remobilization caused by the enhanced thermal gradient and deformation associated with the emplacement of the cat island pluton 2699 ma approximately 7 km east of the deposit or by the ca 2 63 to 2 66 ga postorogenic regional thermal event indicated by hornblende muscovite and biotite ar ar cooling ages from the uchi subprovince it is proposed that the main stage of high grade mineralization formed between ca 2723 to 2712 ma possibly synchronous with emplacement of the dome and mckenzie island stocks the abino granodiorite and hammell lake batholith as well as with penetrative d2 main stage regional deformation lamprophyre dikes spatially associated with the deposit postdate main stage mineralization by at least 10 m y a postore granodiorite dike from the madsen mine the second largest deposit in the district was dated at 2698 1 ma this age is similar to a postalteration and late deformation diorite dike at the creek zone showing near the former starratt olsen mine which was dated at 2696 2 ma the crosscutting relationships confirm that the main stage of mineralization at the madsen mine is pre 2698 ma a folded and metamorphosed polymictic conglomerate located stratigraphically above the campbell red lake deposit and deposited after ca 2747 but before 2712 ma is correlated with the newly recognized huston assemblage crosscutting and overprinting relationships between the conglomerate and the alteration indicate protracted multistage aluminous and iron carbonate quartz veining and or alteration event s before and after deposition of the conglomerate the age of the conglomerate confirms that the campbell red lake deposit is proximal to a folded regional unconformity consistent with the empirical relationship between large gold deposits and unconformities elsewhere in archean greenstone belts this paleosurface represents a key first order exploration target and it is proposed that areas of high potential for gold exploration in red lake occur in the balmer assemblage rocks within 500 m to 1 km of the unconformity

splash erosion under natural rainfall on three soil types in ne spain article i nfo article history splash detachment and transport of soil particles by raindrops impacting a soil surface are the initiating mechanisms of water erosion the amount of splash depends on rainfall characteristics mainly kinetic ener gy and intensity and soil properties experimental results of rainfall and splash monitoring in three soil types under natural rainfall in ne spain are presented some 27 rainfall events were evaluated during which high rates of soil splash were measured 6 06 g per splash cup stressing its importance as an erosion process on bare soils sources of variation of soil splash were analyzed by a linear mixed effects lme model significant relationships were found between the splash erosion rates and the rainfall erosivity index ei30 no significant differences in erosion were found among the soil types analyzed the lme model explained 55 of variance in the erosion rates and most of the residual variability 74 was due to differences between splash cups within a single soil type and event i e random effects

splash detachment runoff depth and soil cohesion summary a set of laboratory experiments has been carried out in order to investigate the importance of soil cohesion and the interference due to the depth of the surface runoff on the detachment rate of soil particles and aggregates experimental data show that the soil detachment rate decreases as the runoff depth increases this indicates that the detachment power of the raindrops is partially dispersed by the water layer an inverse relationship between soil detachment and soil cohesion has been confirmed nevertheless the grain size distribution must also be used in order to define soil detachability

the effect of slope on interrill erosion at short slopes abstract slope gradient is an important factor that affects soil erosion this study was conducted to investigate the effect of slope gradient on soil erosion and determine the splash contribution to interrill erosion at short steep slopes an experimental device was used to make simultaneous measurements of interrill splash and wash at 9 18 27 36 47 58 70 84 and 100 slopes under a constant rainfall intensity of 67 mm h 1 in a laboratory setting the specially designed runoff and sediment collection system provided a means of partitioning total splash into four directional components and interrill sediment transport into wash and splash components the results revealed that the total splash loss net downslope splash loss and wash loss all increased with slope and then decreased after a maximum value was reached the slope factor equation of short slopes in rusle matched the wash loss from this study very well when the slope gradient was less than or equal to 58 the ratio of net downslope splash loss to wash loss increased from 0 21 to 1 33 as the slope gradient increased from 9 to 100 taken together these results indicate that upslope splash loss was a very important component of the total splash loss on gentle slopes and may be neglected on slopes greater than 36 splash transport was a significant part of interrill sediment delivery at short steep slopes

archean gravity driven tectonics on hot and flooded continents controls on long lived mineralised hydrothermal systems away from continental margins abstract we present the results of two dimensional numerical modelling experiments on the thermal evolution of archean greenstones as they sink into a less dense hot and weak felsic crust we compare this thermal evolution to that obtained via the analysis of isotopic data and fluid inclusion microthermometry data obtained in the paleoarchean to mesoarchean warrawoona synform eastern pilbara craton western australia our numerical experiments reveal a two stage evolution in the first stage cooling affects zones of downwelling as greenstone belts are advected downward whereas adjacent domes become warmer as deep and hot material is advected upward we show that this is consistent with stable isotopes data from the warrawoona synform which reveal an early episode of seafloor like alteration 90 160 c strongly focused along steeply dipping shear zones in a second long lived stage lateral heat exchanges between domes and basins dominate the system as domes cool down while downwelling zones become increasingly warmer in the warrawoona greenstone belt stable isotopes in gold bearing quartz veins post dating the sagduction related vertical fabrics reveal that rock fluid interaction occurred at much higher temperatures 234 372 c than seafloor like alteration we propose that emplacement of thick and dense continental flood basalts on flooded hot and weak continental plates led to conditions particularly favourable to hydrothermal processes and the formation of mineral deposits we further argue that sagduction was able to drive crustal scale deformation in the interior of continents away from plate margins on largely flooded continents sagduction related shear zones acted as fluid pathways promoting gold mineralisation far away from active plate boundaries continental rift zones or collisional mountain belts

soil loss by splash and wash during rainfall from two loess soils abstract physical processes occurring during surface seal formation through a rainstorm are well understood but limited information is available regarding the quantity and particle size distribution of splash and runoff at certain time intervals in this study we evaluated the quantity and particle size distribution of suspensions of both splash and interrill runoff in two loess soils with different mineralogy and aggregate stability and somewhat different particle size distribution but similar organic matter content the soils were subjected to simulated rainstorms of 40 turn h 1 and 100 mm h 1 intensities the amount of splash was about four times higher for the saskatchewan soil typic haploboroll with high smectite than for the grenada soil typic fragiudalf which is rich in fe oxyhydroxides the amount of splashed material and sediment load increased with increased rainfall intensity for both soils splash was decreased after wetting of the soil surface the decrease in splash rate was more rapid with high rainfall intensity the amount of clay size particles of the splash was similar to the original soil material micromorphological observations confirmed the fluctuations in clay content with time at the very surface soil materials splashed were much higher 10 to 20 times than the interrill runoff losses the latter was controlled by the rainfall intensity the soil material from saskatchewan produced more than 11 mg ha 1 of interrill runoff with low rainfall intensity high rainfall intensity produced 10 times more soil loss than low rainfall intensity high amount of soil loss clearly shows that the saskatchewan soil would benefit from erosion control measures both rainfall intensities removed preferentially more clay from the saskatchewan b horizon material this has important agronomic and environmental implications for this soil interrill soil losses from the granada a horizon material were much less with no clear evidence of preferential removal of clay size particles

measured rates of sedimentation what exactly are we estimating and why abstract data on rates of sedimentation are essential in studies of sedimentation systems these data are obtained in three main study contexts 1 the study of sedimentation systems that are active today 2 the source to sink study of sedimentation systems that no longer are active and 3 the study of the relationship between accumulation rate and measurement timespan the aim of this paper is to question the meaning of measured rates of sedimentation and their interpretability particularly in these three contexts individual measurements of rate of sedimentation must always be interpreted with care firstly there are different definitions for instance with different statistical support or measurement dimension values that are defined differently cannot be compared directly secondly appropriate sampling schemes must have been used for the measurement this minimises sampling bias thirdly the inherent limitations of the data sources must be taken into account rates of sedimentation can usually be measured successfully in active sedimentation systems the same is not true for systems that are no longer active these can only be studied using the stratigraphic successions left behind rates of erosion can never be measured successfully in stratigraphic successions rate of sedimentation is essentially a ratio an amount of sedimentation per length of time therefore the obvious strategy to use in determining it is first to measure the amount and the time independently then to combine the values the amount can be measured in terms of thickness or volume or mass per unit area the duration of the time interval can be preset using quasi continuous measurement techniques or site reoccupation or it can be identified from interval specific sedimentary structures or it can be measured using dated horizons an alternative strategy is to use a surrogate measurement variable rates of erosion in ancient systems are usually measured in this way using cosmogenic radionuclide concentrations these two strategies are reviewed in this paper sets of measurements made in systems that are active today can certainly be used to estimate the rate of sedimentation for the system as a whole this estimation is best carried out using geostatistical estimation techniques the alternative is simply to average the measured rate values this latter approach should not be used however because the mean sedimentation rate in a system gives information only about the net sediment movement at the system boundaries it says nothing at all about how the system is operating or about its spatial and temporal variability measurements of rates of sedimentation made for source to sink studies are necessarily made in stratigraphic successions the measurements are used to estimate quantities in the sediment mass budget equation the amount of decumulation is inherently incapable of being measured in stratigraphic successions therefore there are always unknowns in the mass budget equation whenever the lithic surface at the start of the time interval considered cannot be recognised everywhere this means that the mass budget equation is applicable in practice only when all the systems involved in the study are entirely non erosional for that entire time interval a highly unrealistic situation the consistently inverse relationship documented between accumulation rates and measurement timespan is taken usually to indicate that this relationship is substantially scale invariant this in turn is often taken as indicating that the stratigraphic record is fractal in nature there are nevertheless grounds for doubt all of which relate to the ways that the data are collected and used for estimation the relationship is in fact the natural mathematical result of last in first out lifo operation and is produced in any type of system in which addition and removal processes both operate it says nothing particular about sedimentation processes the future analysis of accumulation rate data collected from stratigraphic successions will sensibly be framed in the context of estimating the parameters of a lifo model

extreme 18o enriched volcanics and 18o evolved marine water aljustrel iberian pyrite belt transition from high to low rayleigh number convective regimes abstract quartz eye keratophyric tuffs at aljustrel s portugal iberian pyrite belt possess unusually high uniform whole rock values up to 18 1 with a mean of 16 7 0 7 because the quartz eye cores have 18o 12 0 to 13 5 the felsic tuffs may have had an original whole rock oxygen isotope composition of 10 to 11 the deduced enrichments of up to 8 in keratophyric derivatives is attributed to isotope exchange with abundant marine water under temperatures which diminished to 100 c during thermally driven convective cooling the isotopic uniformity requires elevated permeability of 10 8 cm2 such that the second critical rayleigh number was exceeded and drifting non steady state convection cells dominated with relatively smooth thermal structures in mineralised counterparts of the tuffs beneath the feitais estacao zn pb cu massive sulphide orebodies whole rock values are 12 and quartz 13 3 15 4 chlorite 3 2 6 3 fractionations correspond to temperatures of 220 270 c and a calculated fluid 18o of 1 4 to 5 7 this local isotopic overprinting in vent domains of the regionally high 18o was induced by a stable second stage convective regime imposed by drastic reduction of permeability accompanying capping of the geothermal discharge by hydrothermal cherts and or progressive spilitisation of the tuffs at lower water rock coupled with higher temperatures the recirculating marine water underwent variable 18o enrichment up to 5 7 by exchange with the high 18o tuffs an upwards increase in 18o quartz and quartz reflects progressive cooling of the geothermal discharge from 15 4 270 c in the stockwork through 18 3 220 240 c in the orebody to 20 1 110 130 c in overlying hydrothermal cherts probably induced by entrainment of ambient marine bottom water in sub seafloor aquifers

fine grained splay deposition in the avulsion belt of the lower saskatchewan river canada abstract in or about 1883 a northward avulsion of the meandering lower saskatchewan river at the cumberland marshes initiated a broad belt of alluvial sedimentation that has continued to evolve to the present and now covers some 500 km2 the avulsion belt comprises a complex alluvial terrain dominated by individual and coalesced splays and associated wetlands connected by networks of active and abandoned channels of various sizes the windy lake splay a predominantly fine grained feature typical of large parts of the avulsion belt was examined to investigate the relationships between splay evolution and facies development the splay now largely inactive mostly formed over a 35 year period depositing nearly 2 m of sediment over a 7 2 km2 area the splay surface is ch racterized by stable well defined anastomosed distributary channels that separate interchannel wetland basins heights of channel levees diminish downstream and the levees merge with channel mouth bars whose progradation forms the locus of lakeward channel extension and the base for subsequent subaerial levee deposition the anastomosed channel pattern was created when the mouth bars of separate distributary channels merged during progradation vibracore and soil probe profiles show the splay to be dominated by upward coarsening lacustrine prodeltaic mouth bar facies sequences capped by levees and organic rich interchannel wetland deposits channels now containing sand only sporadically in narrowed or slightly migrated reaches will eventually fill with fine sediment when abandonment s complete the windy lake splay is typical of stage iii splays smith et al 1989 whose deposits and associated lacustrine fills form at least half of the avulsion belt thin widespread predominantly upward coarsening sequences capped by either nondepositional horizons or true overbank fines may be characteristic of many avulsive suites in the ancient alluvial record

frequency analysis of annual maximum suspended sediment concentrations in abiod wadi biskra algeria sediment transport processes in the mediterranean semi arid areas have interested a great number of hydrologists and statisticians frequency analysis fa procedures are commonly applied for several hydrological events such as floods and droughts however in general fa is not widely applied to treat suspended sediment concentration ssc especially in semi arid regions in the present study an fa was performed on ssc data from 1979 to 1991 observed upstream from the foum el gherza dam which is located at biskra in the south east of algeria this dam is problematic in terms of silting therefore this study is mainly motivated by providing an fa model and risk evaluation in order to assist dam managers to better evaluate the potential of silting resulting from ssc transport to the reservoir probability distributions commonly used in hydrology were tested to ssc data recorded at the m chounech station on abiod wadi located upstream the dam all the fa steps were considered including classical techniques e g goodness of fit tests statistical criteria as well as recently developed tools tail distribution classification their application led to the selection of the lognormal distribution ln2 to fit the considered data and hence an accurate risk assessment could be obtained because of the presence of a slight trend non stationary models are also considered in the present study copyright 2013 john wiley sons ltd

effects of vegetation type on soil resistance to erosion relationship between aggregate stability and shear strength article i nfo soil water erosion and shallow landslides depend on aggregate stability and soil shear strength we investigated the effect of vegetation on both soil aggregate stability and shear strength through direct shear tests in former croplands converted to vegetated erosion protection areas within the context of china s sloping land conversion programme four treatments were analysed in plots comprised of i 4 year old crop trees vernicia fordii where understory vegetation was removed ii v fordii and the dominant understory species artemisia codonocephala iii only a codonocephala and iv no vegetation soil samples were taken at depths of 0 5 cm and 45 50 cm root length density rld in five diameter classes was measured soil organic carbon soc hot water extractable carbon hwec texture and fe and al oxides were also measured we found that mean weight diameter after slow wetting mwdsw in the a horizon was significantly greater 0 94 1 01 mm when a codonocephala was present compared to plots without a codonocephala 0 57 0 59 mm soc and rld in the smallest diameter class b0 5 mm were the variables which best explained variability in mwdsw a significant positive linear relationship existed between mwdsw and soil cohesion but not with internal angle of friction as herbaceous vegetation was more efficient than trees in improving aggregate stability this result suggests that the mechanisms involved include modifications of the cohesive forces between soil particles adjacent to plant roots and located in the enriched in soc rhizosphere thus also affecting shear strength of the corresponding soil volume thus vegetation stabilised soil under different hierarchical levels of aggregate organisation i e intra and inter aggregate our results have implications for the efficacy of techniques used in land conversion programs dedicated to control of soil erosion and shallow landslides we suggest that mixtures of different plant functional types would improve soil conservation on slopes by reducing both surface water erosion and shallow substrate mass movement planting trees for cropping or logging and removing understory vegetation is most likely detrimental to soil conservation

the role of fluids during formation and evolution of the southern superior province lithosphere an overview models for fluid flow and hydrothermal alteration for the abitibi greenstone belt are reviewed in the light of lithoprobe results in the region in the abitibi greenstone belt eruption of volcanic sequences over 2750 2700 ma was accompanied by pervasive low temperature hydrothermal alteration at high water rock ratios giving systematic 18o enrichment archean ambient ocean water bottom temperatures were likely ca 30 c and 18o 0 1 chert iron formations precipitated from low temperature hydrothermal discharge base metal massive sulphide deposits formed at or near the seafloor from focussed discharge of high temperature 300 400 c fluids in convective cells sited above subvolcanic intrusions the ore fluids were evolved seawater that had undergone compositional and isotopic evolution by high temperature low water rock exchange with the volcanic pile to nacl 3 7 wt or cacl2 nacl up to 30 wt brines of 18o 0 8 these volcanic associated hydrothermal deposits are associated with greenst

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