major types and time space distribution of mesozoic ore deposits in south china and their geodynamic settings the ore deposits of the mesozoic age in south china can be divided into three groups each with different metal associations and spatial distributions and each related to major magmatic events the first event occurred in the late triassic 230 210 ma the second in the mid late jurassic 170 150 ma and the third in the early mid cretaceous 120 80 ma the late triassic magmatic event and associated mineralization is characterized by peraluminous granite related w sn nb ta mineral deposits the triassic ore deposits are considerably disturbed or overprinted by the later jurassic and cretaceous tectono thermal episodes the mid late jurassic magmatic and mineralization events consist of 170 160 ma porphyry skarn cu and pb zn ag vein deposits associated with i type granites and 160 150 ma metaluminous granite related polymetallic w sn deposits the late jurassic metaluminous granite related w sn deposits occur in a ne trending cluster in the interior of south china such as in the nanling area in the early mid cretaceous from about 120 to 80 ma but peaking at 100 90 ma subvolcanic related fe deposits developed and i type calc alkaline granitic intrusions formed porphyry cu mo and porphyry epithermal cu au ag mineral systems whereas s type peraluminous and or metaluminous granitic intrusions formed polymetallic sn deposits these cretaceous mineral deposits cluster in distinct areas and are controlled by pull apart basins along the south china continental margin based on mineral assemblage age and space time distribution of these mineral systems integrated with regional geological data and field observations we suggest that the three magmatic mineralization episodes are the result of distinct geodynamic regimes the triassic peraluminous granites and associated w sn nb ta mineralization formed during post collisional processes involving the south china block the north china craton and the indo china block mostly along the dabie sulu and songma sutures jurassic events were initially related to the shallow oblique subduction of the izanagi plate beneath the eurasian continent at about 175 ma but i type granitoids with porphyry cu and vein type pb zn ag deposits only began to form as a result of the breakup of the subducted plate at 170 160 ma along the nne trending qinzhou hangzhou belt also referred to as qin hang or shi hang belt which is the neoproterozoic suture that amalgamates the yangtze craton and cathaysia block a large subduction slab window is assumed to have formed in the nanling and adjacent areas in the interior of south china triggering the uprise of asthenospheric mantle into the upper crust and leading to the emplacement of metaluminous granitic magma and associated polymetallic w sn mineralization a relatively tectonically quiet period followed between 150 and 135 ma in south china from 135 ma onward the angle of convergence of the izanagi plate changed from oblique to parallel to the coastline resulting in continental extensional tectonics and reactivation of regional scale ne trending faults such as the tan lu fault this widespread extension also promoted the development of ne trending pull apart basins and metamorphic core complexes accompanied by volcanism and the formation of epithermal cu au deposits granite related polymetallic sn w deposits and hydrothermal u deposits between 120 and 80 ma with a peak activity at 100 90 ma

indicator element selection and geochemical anomaly mapping using recursive feature elimination and random forest methods in the jingdezhen region of jiangxi province south china abstract determining indicator element association for mineralization can not only improve mineral exploration efficiency but also reduce the cost of unnecessary element analysis during geochemical exploration this study provides a case study of zhuxi tungsten copper deposits and presents a workflow using recursive feature elimination and random forest methods to select the indicator element association for copper and tungsten mineralization in regional geochemical mapping first a training dataset containing positive and negative samples was built based on the known mineral deposits and mineral deposit model second a 100 time simulation of recursive feature elimination with cross validation based on random forest rfecv rf was run to get a robust result of indicator elements by the ranking of variable importance third the random forest rf method was used to integrate six indicator elements for mapping geochemical anomaly the youden index and prediction area p a plot were used to determine the threshold value for geochemical anomaly identification the results demonstrated the hybrid workflow was useful to determine key indicator element for geochemical anomaly identification associated with copper and tungsten mineralization bi mo cu cd w and as were selected as the key indicator elements for geochemical exploration of cu w mineralization bi mo w and cu elements correspond to skarn and altered granite mineralization at depth while cd and as elements correspond to the hydrothermal vein mineralization at shallow levels the result of receiver operating characteristic roc curve showed that geochemical anomaly identified using the hybrid method proposed in this study had the best performance in producing comprehensive geochemical signatures the six indicator elements also exhibited an excellent performance of identifying geochemical anomaly associated to cu w mineralization this study provides a cost benefit solution to reduce the cost of unnecessary elements concentration detection by determining a small number of key indicator elements using machine learning methods in the regional geochemical mapping for discovering mineral deposits

tectonothermal evolution of the mayuan assemblage in the cathaysia block implications for neoproterozoic collision related assembly of the south china craton the mayuan assemblage in the cathaysia block southeast china consists of felsic paragneiss pelitic schist greenschist amphibolite marble calcsilicate and quartzite that underwent three episodes of deformation d1 d3 and four episodes of metamorphism m1 m4 in the early neoproterozoic the m1 assemblage consists of mineral inclusions defining an early foliation s1 within porphyroblasts represented by chlorite muscovite biotite plagioclase quartz in pelitic schist and actinolite chlorite epidote albite quartz enclosed in amphibolite m2 coincides with the development of the regional schistosity s2 and represents the formation of the porphyroblasts and growth of matrix minerals resulting in development of prograde metamorphic zones chlorite biotite garnet staurolite and kyanite zones m3 is simultaneous with the third phase of deformation d3 and produced sillimanite bearing mineral assemblages in pelitic schist and hornblende bearing assemblages in amphibo lite the last metamorphic episode m4 gave rise to the retrogressive assemblage chlorite muscovite in pelitic rock and actinolite chlorite epidote in amphibolite the sequence of mineral assemblages and history of metamorphic reactions built from the petrogenetic grid of pelites suggest a near isothermal decompression clockwise p t path for the mayuan pelitic schists using the tweequ software program the garnet biotite thermometer and garnet muscovite biotite plagioclase barometer yield p t conditions for m1 of 5 5 to 6 0 kb and 450 to 500 c and conditions for the garnet staurolite and kyanite zones of m2 of 6 0 to 7 0 kb and 550 to 600 c 6 0 to 7 5 kb and 600 c and 11 0 to 11 5 kb and 600 c the p t conditions of m3 were estimated at 570 to 625 c and 4 0 to 4 5 kb using the muscovite biotite thermometer and hornblende plagioclase geothermo barometer the garnet chlorite thermometer yields temperatures of 300 to 400 c for m4 but the pressures of m4 cannot be quantitatively estimated because of the lack of a suitable geobarometer these p t estimates also define an near isothermal decompression clockwise p t path which is involved in initial crustal thickening followed by rapid exhumation and final cooling and is related to amalgamation of the cathaysia and yangtze blocks to form the south china craton

a froude scaled model of a bedrock alluvial channel reach 2 sediment cover previous research into sediment cover in bedrock alluvial channels has focussed on total sediment cover rather than the spatial distribution of cover within the channel the latter is important because it determines the bedrock areas that are protected from erosion and the start and end of sediment transport pathways we use a 1 10 froude scaled model of an 18 by 9 m reach of a bedrock alluvial channel to study the production and erosion of sediment patches and hence the spatial relationships between flow bed topography and sediment dynamics the hydraulic data from this bed are presented in the companion paper in these experiments specified volumes of sediment were supplied at the upstream edge of the model reach as single inputs at each of a range of discharges this sediment formed patches and once these stabilized flow was steadily increased to erode the patches in summary 1 patches tend to initiate in the lowest areas of the bed but areas of topographically induced high flow velocity can inhibit patch development 2 at low sediment inputs the extent of sediment patches is determined by the bed topography and can be insensitive to the exact volume of sediment supplied and 3 at higher sediment inputs more extensive patches are produced stabilized by grain grain and grain flow interactions and less influenced by the bed topography bedrock topography can therefore be an important constraint on sediment patch dynamics and topographic metrics are required that incorporate its within reach variability the magnitude and timing of sediment input events controls reach scale sediment cover

physically based modeling of bedrock incision by abrasion plucking and macroabrasion 1 many important insights into the dynamic coupling among climate erosion and tectonics in mountain areas have derived from several numerical models of the past few decades which include descriptions of bedrock incision however many questions regarding incision processes and morphology of bedrock streams still remain unanswered a more mechanistically based incision model is needed as a component to study landscape evolution major bedrock incision processes include among other mechanisms abrasion by bed load plucking and macroabrasion a process of fracturing of the bedrock into pluckable sizes mediated by particle impacts the purpose of this paper is to develop a physically based model of bedrock incision that includes all three processes mentioned above to build the model we start by developing a theory of abrasion plucking and macroabrasion mechanisms we then incorporate hydrology the evaluation of boundary shear stress capacity transport an entrainment relation for pluckable particles a routing model linking in stream sediment and hillslopes a formulation for alluvial channel coverage a channel width relation hack s law and exner equation into the model so that we can simulate the evolution of bedrock channels the model successfully simulates various features of bed elevation profiles of natural bedrock rivers under a variety of input or boundary conditions the results also illustrate that knickpoints found in bedrock rivers may be autogenic in addition to being driven by base level fall and lithologic changes this supports the concept that bedrock incision by knickpoint migration may be an integral part of normal incision processes the model is expected to improve the current understanding of the linkage among physically meaningful input parameters the physics of incision process and morphological changes in bedrock streams

geology and molybdenite re os age of the dahutang granite related veinlets disseminated tungsten ore field in the jiangxin province china this is a brief research report about the recently discovered and currently being explored dahutang tungsten deposit or ore field in northwestern jiangxi south central china the deposit is located south of the middle lower yangtze river valley cu au mo fe porphyry skarn belt yrb the mineralization is genetically associated with cretaceous porphyritic biotite granite and fine grained biotite granite and is mainly hosted within a neoproterozoic biotite granodiorite batholith the dahutang ore field comprises veinlets disseminated 95 of the total reserve breccia 4 and wolframite scheelite quartz vein 1 ore styles the mineralization and alteration are close to the pegmatite shell between the cretaceous porphyritic biotite granite and neoproterozoic biotite granodiorite and the three styles of ore bodies mentioned above are related to zoned hydrothermal alteration that includes greisenization k feldspar alteration silicification carbonatization chloritization and fluoritization arranged in time early to late and space bottom to top five samples of molybdenite from the three types of ores have been collected for re os dating the results show re os model ages ranging from 138 4 ma to 143 8 ma with an isochron age of 139 18 0 97 ma mswd 2 9 the quite low re content in molybdenite falls between 0 5 ppm and 7 8 ppm that is indicative of the upper crustal source this is quite different from molybdenites in the yrb cu au mo fe porphyry skarn deposits that contain between 53 ppm and 1169 ppm re indicating a mantle source the dahutang tungsten system is sub parallel with the yrb porphyry skarn cu au mo fe system both are situated in the north margin of the yangtze craton and have a close spatial temporal relationship this possibly indicates a comparable tectonic setting but different metal sources both systems are related to subduction of the paleo pacific plate beneath the eurasian continent in early cretaceous the cu au mo fe porphyry skarn ores are believed genetically related to granitoids derived from the subducting slab whereas the porphyry w deposits are associated with s type granitoids produced by remelting of the upper crust by heat from upwelling asthenoshere

weights of evidence and logistic regression modeling of magmatic nickel sulfide prospectivity in the yilgarn craton western australia abstract bayesian weight of evidence and logistic regression models are implemented in a gis environment for regional scale prospectivity modeling of greenstone belts in the yilgarn craton western australia for magmatic nickel sulfide deposits the input variables for the models consisted of derivative gis layers that were used as proxies for mappable exploration criteria for magmatic nickel sulfide deposits in the yilgarn about 70 of the 165 known deposits of the craton were used to train the models the remaining 30 was used to validate the models and therefore had to be treated as if they had not been discovered the weights of evidence and logistic regression models respectively classify 71 4 and 81 6 validation deposits in prospective zones that occupy about 9 of the total area occupied by the greenstone belts in the craton the superior performance of the logistic regression model is attributed to its capability to accommodate conditional dependencies amongst the input predictor maps and provide less biased estimates of prospectivity

distribution of erosion across bedrock channels lateral erosion in bedrock rivers is an important control on the shape of channel crosssections and the coupling of channels and hillslopes recent observations link lateral erosionto the variability of flow we propose two mechanisms to explain this one is based on changing shear stress distributions within the channel with varying flood level the other on the competition between cover and tool effects in fluvial bedrock erosion we assess these processes for the liwu river taiwan and conclude that cover and tool effects dominate the partitioning of lateral and vertical erosion in this case

struggles with stream power connecting theory across scales abstract two empirically consistent explanations exist for the morphology and dynamics of bedrock rivers the stream power law appears to explain rates of rock incision at large scale large drainage basins or landscape scale but appears to be of limited value in predicting reach scale morphology and dynamics the underlying reason why stream power is such an effective tool for understanding landscape evolution is because it is an explicit representation of the inverse power relation between slope and area in rivers incising bedrock this morphometric relation is nearly universal subject to exogenous contingencies independent testing and validation of the stream power incision model is challenging because of the contingencies that exist in almost all landscapes mechanistic models of erosion have been tested and validated at small scales generally below the reach scale and opportunities exist for independent testing and validation by using them to predict reach scale morphologies predicting larger scale bedrock river morphology requires the assumption that flow sediment fluxes and bedrock erosion processes that occur at smaller scale are adequately averaged at larger scales which is not well supported reconciling these two scales of explanation is one of the grand challenges of fluvial geomorphology unless we accept that theory and explanations will be scale delimited

metallogenic characteristics and quantitative prediction of hydrothermal pb zn ag polymetallic ore deposits in northwest zhejiang multivariate spatial geo database of pb zn ag polymetallic ore deposits of hydrothermal type in northwestern zhejiang province was established with morpas platform based on gis spatial analysis technology based on the study of metallogenic rules for pbzn ag polymetallic the use of the multivariate data related with the mineralization in the area such as strata structures magmatic rocks geochemistry geophysics and so on the authors analyzed and established the mineral deposit prospecting model and made quantitative predication using weights of evidence it was concluded that pb zn ag polymetallic ore deposits had a close relationship with local formation magmatic folds faults gravity geochemistry and their derived variables according to the ore forming beneficial degree and contour map the study area was divided into 18 metallogenic targets and two advantageous mineral prospects

a mechanistic model for river incision into bedrock by saltating bed load 1 abrasion by bed load is a ubiquitous and sometimes dominant erosional mechanism for fluvial incision into bedrock here we develop a model for bedrock abrasion by saltating bed load wherein the wear rate depends linearly on the flux of impact kinetic energy normal to the bed and on the fraction of the bed that is not armored by transient deposits of alluvium we assume that the extent of alluvial bed cover depends on the ratio of coarse sediment supply to bed load transport capacity particle impact velocity and impact frequency depend on saltation trajectories which can be predicted using empirical functions of excess shear stress the model predicts a nonlinear dependence of bedrock abrasion rate on both sediment supply and transport capacity maximum wear rates occur at moderate relative supply rates due to the tradeoff between the availability of abrasive tools and the partial alluviation of the bedrock bed maximum wear rates also occur at intermediate levels of excess shear stress due to the reduction in impact frequency as grain motion approaches the threshold of suspension measurements of bedrock wear in a laboratory abrasion mill agree well with model predictions and allow calibration of the one free model parameter which relates rock strength to rock resistance to abrasive wear the model results suggest that grain size and sediment supply are fundamental controls on bedrock incision rates not only by bed load abrasion but also by all other mechanisms that require bedrock to be exposed in the channel bed

characteristics of rees and trace elements in scheelite from the zhuxi w deposit south china implications for the ore forming conditions and processes abstract the zhuxi w deposit in jiangxi south china with a resource of 2 86 mt w and an average grade of 0 54 wo3 is the largest w deposit in the world the deposit occurs at the contact between a late mesozoic granitic intrusion and carboniferous permian carbonate rocks and neoproterozoic metamorphic rocks the ores are divided into three types skarn ore dominant sulfide ore and greisen ore based on occurrences and petrographic relationships scheelite the dominant ore mineral is classified into three types i e type i greisen type ii skarn specifically in the retrograde stage and type iii hydrothermal sulfides type i and type ii are time equivalent but spatially separated whereas type iii is later the different types of scheelite have distinctly different ree and trace element compositions type i scheelite is characterized by an average ree of 67 9 ppm lree hree ratio of 24 4 eu of 8 5 mo of 0 1 ppm and sr of 1058 ppm whereas type ii scheelite features an average ree of 48 1 ppm lree hree ratio of 10 6 eu of 0 67 mo of 1892 ppm and sr of 90 1 ppm type iii scheelite has an average ree of 53 9 ppm lree hree ratio of 4 8 eu of 17 5 mo of 92 9 ppm and sr of 37 1 ppm the extremely high concentrations of sr and highly positive eu anomalies in type i scheelite are likely related to release of these elements from plagioclase in the granite during greisenization whereas the extremely low concentrations of mo may be related to the reducing and high temperature nature of the magmatic fluid mo probably was mainly in the mo4 state and could not replace w6 in the scheelite lattice in contrast the negative eu anomalies and high mo concentrations in type ii scheelite suggest that the mineralizing environment in the retrograde alteration stage was relatively oxidizing causing eu to exist mainly as eu3 which is difficult to replace ca2 in scheelite and mo mainly as mo6 which is easy to replace w6 in scheelite in the sulfide mineralization stage the fluid became relatively reducing again and eu2 could easily replace ca2 in scheelite causing positive eu anomalies whereas mo mainly exists as mo4 and precipitated as molybdenite and so has limited substitution for w6 in scheelite the ree and trace element compositions of the dominant w mineral type ii scheelite characterized by high concentrations of mo high lree hree ratios and negative eu anomalies indicate that the ore forming materials were mainly derived from the granitic intrusions the variation of ree and trace elements in scheelite in time and space reflects a complex magmatic hydrothermal mineralization process involving various fluid rock reactions within the intrusion and in the country rocks the formation of the zhuxi w deposit is linked with a large fertile granitic intrusion which delivered a large amount of w to the site of mineralization through convection within the magma chamber and w precipitation in the skarn was largely caused by an abrupt drop in temperature and increase in ph of the ore forming fluid

a numerical investigation of excess pore pressures and continental slope stability in response to ice sheet dynamics submarine landslides are common at glaciated continental margins the onset of large scale landslides coincides with the initiation of northern hemisphere glaciations in the quaternary this implies that processes related to glacial cycling provide favourable conditions for submarine landslides at high latitude margins potential processes include glacial deposition patterns and enhanced seismicity it is also possible that advances and retreats of ice sheets a highly dynamic process in geologic terms makes slopes discernible to failure by modifying the stress regime here we quantify this effect using 2d finite element modelling of a glaciated continental margin different model runs investigate the pore pressure development in homogeneous as well as layered slopes during glaciation when loaded by an ice stream with one or multiple ice advances ice streams cause significant variations in excess pore pressure in the very shallow sediment sequences at the continental shelf however lateral fluid flow is not efficient enough to increase pore pressures significantly at the slope where large scale submarine slides are observed hence while ice sheet dynamics appear to favour the occurrence of shallow slides close to the shelf edge ice sheets seem to be irrelevant for the generation of large scale submarine landslides at the continental slope

feedbacks between erosion and sediment transport in experimental bedrock channels natural bedrock rivers flow in self formed channels and form diverse erosional morphologies the parameters that collectively define channel morphology e g width slope bed roughness bedrock exposure sediment size distribution all influence river incision rates and dynamically adjust in poorly understood ways to imposed fluid and sediment fluxes to explore the mechanics of river incision we conducted laboratory experiments in which the complexities of natural bedrock channels were reduced to a homogenous brittle substrate sand and cement a single sediment size primarily transported as bedload a single erosion mechanism abrasion and sediment starved transport conditions we find that patterns of erosion both create and are sensitive functions of the evolving bed topography because of feedbacks between the turbulent flow field sediment transport and bottom roughness abrasion only occurs where sediment impacts the bed and so positive feedback occurs between the sediment preferentially drawn to topographic lows by gravity and the further erosion of these lows however the spatial focusing of erosion results in tortuous flow paths and erosional forms inner channels scoops potholes which dissipate flow energy this energy dissipation is a negative feedback that reduces sediment transport capacity inhibiting further incision and ultimately leading to channel morphologies adjusted to just transport the imposed sediment load copyright 2007 john wiley sons ltd

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

bedrock channel incision along piccaninny creek australia piccaninny creek in northwestern australia drains approximately 60 km 2 of high relief sandstone and conglomerate terrain the drainage basin lies within the seasonal tropics and is characterized by ephemeral high magnitude flows flood flows of 50 to 100 m 3 s 1 are probably primarily responsible for the spectacular erosional features along the bedrock channel segments of the creek these erosional features occur in two basic forms as parallel longitudinal grooves and as a downstream sequence that begins with shallow linear depressions parallel to flow and ends in a deep narrow inner channel the longitudinal grooves are assumed to result from longitudinal vortices while the erosional sequences which closely resemble von karman vortex streets are interpreted to result from turbulent vortices shed off irregularities of the channel bed the longitudinal grooves and the inner channel sequence alternate with each other and with gravel floored depositional reaches downstream along the channe

data driven predictive mapping of gold prospectivity baguio district philippines application of random forests algorithm the random forests rf algorithm has recently become a fledgling method for data driven predictive mapping of mineral prospectivity and so it is instructive to further study its efficacy in this particular field this study carried out using baguio gold district philippines examines a the sensitivity of the rf algorithm to different sets of deposit and non deposit locations as training data and b the performance of rf modeling compared to established methods for data driven predictive mapping of mineral prospectivity we found that rf modeling with different training sets of deposit non deposit locations is stable and reproducible and it accurately captures the spatial relationships between the predictor variables and the training deposit non deposit locations for data driven predictive mapping of epithermal au prospectivity in the baguio district we found that a the success rates of rf modeling are superior to those of weights of evidence evidential belief and logistic regression modeling and b the prediction rate of rf modeling is superior to that of weights of evidence modeling but approximately equal to those of evidential belief and logistic regression modeling therefore the rf algorithm is potentially much more useful than existing methods that are currently used for data driven predictive mapping of mineral prospectivity however further testing of the method in other areas is needed to fully explore its usefulness in data driven predictive mapping of mineral prospectivity

jiangnan orogen in south china developing from divergent double subduction abstract the jiangnan orogen is considered as a continent continent collisional belt resulting from the closure of a meso neoproterozoic ocean separating the southeastern margin of the yangtze block from the northwestern margin of the cathaysia block recent data indicate the existence of early neoproterozoic 1000 825 ma volcanic arc assemblages on both sides of the orogen suggesting that the ocean lithosphere between the yangtze and cathaysia blocks must have undergone divergent double sided subduction during the period of 1000 825 ma the divergent double subduction eventually resulted in the closure of the ocean basin at 825 ma leading to the soft collision of the yangtze and cathaysia blocks to form the jiangnan orogen without involvement of continental deep subduction high grade metamorphism of continental crust and uplift exhumation of high grade metamorphic rocks shortly after the collision the initial detachment of the ocean lithosphere from the overlying crust and sedimentary sections induced underplating of mantle magmas triggering partial melting of accretionary wedge strata to form some peraluminous s type granites in the period 825 815 ma finally the sinking of the oceanic slab pulled down the overlying strata to form some basins in which the banxi group and its equivalent strata including bimodal volcanic rocks were formed in the period 815 750 ma

prospectivity mapping for zhuxi type copper tungsten polymetallic deposits in the jingdezhen region of jiangxi province south china abstract the zhuxi deposit is the largest copper tungsten polymetallic deposit in the world and is in jiangxi province in south china the ore body is characterized by hydrothermal vein deposits of copper lead and zinc minerals at shallow levels skarn deposits of tungsten and copper minerals at middle levels and altered granite hosted copper and tungsten minerals at depth such metallogenic systems are typically intrusion related the intrusive granites related to the zhuxi polymetallic deposit have been dated at 152 9 ma to 146 9 ma the intrusions provided the thermal energy and the source material for the ore mineralization skarns mineralization the main type of ore mineralization developed in the contact zone of carboniferous permian formations with the granites nappe structures changed the dip of the ore bodies from steep in the top part to gentle in the bottom ne trending faults provided the fluid pathways and controlled the geological framework and distribution of ore deposits on a regional scale in this study recognition exploration criteria were analyzed based on a mineral deposit model and the geological setting extraction of favorable geological information and gis based data integration methods were used for mineral prospectivity mapping of zhuxi type polymetallic deposits buffering analysis was employed to extract structural information e g faults and lithologic or stratigraphic information e g granites or geologic units the singularity method and spatially weighted principal component analysis were used to enhance and delineate geochemical anomalies the derivative norm was utilized to extract magnetic gradient anomalies associated with intrusive granites student t test of weights of evidence wofe proved to be an effective way to optimize threshold values for binarization of variables as evidence layers by evaluating the spatial correlation between known deposits and geological variables the posterior probabilities of wofe gave a relative estimation of mineralization potential areas delineated by high posterior probability had much higher potentiality for the discovery of new deposits where had none had been found yet

upstream facing convex surfaces bedrock bedforms produced by fluvial bedload abrasion bedrock bedforms are a common sight in many bedrock river channels but few process form linkages have been established for the myriad of forms recognised in the literature direct observations from bedrock channels on rates and distributions of erosion involved in bedrock bedform development are rare because of difficulties in making observations in these high energy environments upstream facing convex surfaces ufcs are common in bedrock rivers and are partnered with downstream facing surfaces we have made observations of bedrock morphology aspect and surface texture of ufcss in bedrock river channels exposed at low river stage in taiwan a distinct contrast in morphology and surface texture exists between upstream and downstream facing surfaces on a millimetre scale of observation ufcss have a three dimensional brittle fracture dominated granular surface texture but on a decimetre to metre scale have an overall convex form downstream facing surfaces in contrast have millimetre to micrometre scale rugosity characterised by smooth polished surfaces that on a centimetre to metre scale are concave or undulating with intricately sculpted features a curvilinear topographic feature or crest line marks the change in slope aspect and surface textures between upstream and downstream facing surfaces and is orientated approximately perpendicular to the reach azimuth and therefore mean flow direction we used a system of removable datums and terrestrial laser scanning to monitor the three dimensional erosion of nine bedforms at sites in the liwu river taiwan over a period of one year 2007 2008 all sites had an asymmetric distribution of erosion with higher rates of erosion on upstream facing surfaces and minor to undetectable erosion on downstream facing surfaces with local complexity the crest line mapped the boundary between relatively high and low erosion rates between the upstream facing and downstream facing surfaces respectively observations from unscaled flume experiments show that bedload particles transit a flow obstacle by travelling up the upstream facing surface where erosion is focused and hop over the top of the obstacle our field and flume observations indicate that ufcss observed in natural rivers are produced by bedload abrasion which by being decoupled from the flow can only impact the stoss surface to any significant extent micropitting found on polished downstream facing surfaces indicate that they are dominantly formed by suspended load abrasion the aspect of a surface its position in a channel cross section the topography of the channel upstream and the local topography of the bedrock bedform are significant controls on the location and magnitude of abrasion by bedload and resultant surface textures because of their effect on steering a bedload particle stream the high erosion rates observed indicate that abrasion by bedload is the controlling process in the formation of this variety of bedrock bedform and possibly the channel at large in this setting

substrate controls on the longitudinal profile of bedrock channels implications for reach scale roughness 1 in this paper we examine the relationships among bedrock properties and hydraulics in shaping bedrock channel morphology at the reach scale the ocoee river and four other bedrock streams in the blue ridge province of the southeastern united states which have reach scale differences in bedrock erodibility controlled by lithologic and structural variation are the focus of this study we describe a simple conceptual model for concentrated erosion in bedrock channels and test three hypotheses in order to investigate the interactions among rock erodibility characteristics of undulating rib like bed forms reach scale gradient and hydraulic roughness and energy dissipation substrate differences correlate with variation in reach morphology i e gradient bed form orientation and amplitude such that less erodible substrates are associated with steeper reach gradient and with transversely oriented ribs of greater amplitude one dimensional modeling in hec ras indicated that in the reach with the least erodible substrate and greatest bed slope and rib amplitude the reach averaged hydraulic roughness was the greatest increased hydraulic roughness in steeper reaches points to the importance of positive and negative feedbacks in these systems greater substrate erosional resistance limits profile lowering which likely creates steeper bed slopes and greater stream power creating a self enhancing feedback this local increase in stream power is balanced by increased roughness resulting from the erosional processes that produce bedrock ribs which represents a self regulating feedback the overall result reflects quantifiable adjustments between substrate resistance and hydraulic driving forces in bedrock channels

modeling the effects of bed topography on fluvial bedrock erosion by saltating bed load abrasion by saltation is an important mechanism of fluvial incision into bedrock sklar and dietrich 2004 introduced an abrasion model in which the erosion rate of an approximately planar bed is linearly dependent on the kinetic energy transferred by the vertical velocity of saltating grains however most bedrock floored channels exhibit topographic variations that yield deviations from a planar surface referred to as bed topography observations show that bed topography affects erosion here the saltation abrasion model is extended for a nonplanar bed a several centimeter high bump transverse to the flow is repeated every 50 cm the kinetic energy of grain impacts is calculated in two ways 1 impact velocity normal to bed topography and 2 vertical impact velocity by comparing the latter case with the planar model it is possible to isolate the effects of topography on the interception of saltation trajectories incorporating bed topography changes erosion in three ways first erosion is 10 to 1000 times faster depending upon transport stage and grain size enhanced erosion results from both the interception of grains by topography and the increased kinetic energy transfer associated with high angle impacts on the stoss side of bumps second erosion increases monotonically with transport stage whereas maximum erosion occurs at low to intermediate transport stage with a planar bed third erosion decreases monotonically with grain size whereas maximum erosion occurs with intermediate sized grains with a planar bed although the model is highly simplified results show that bed topography should be considered when simulating erosion of bedrock

prospectivity analysis of the plutonic marymia greenstone belt western australia abstract the plutonic marymia greenstone belt is the sixth largest gold camp in western australia quantitative estimates of the residual endowment of this greenstone belt based on zipf s law indicate that the belt contains between 5 5 and 5 9 moz of gold in undiscovered deposits larger than 0 1 moz including six undiscovered deposits ranging in size between 0 7 moz and 0 4 moz and another six undiscovered deposits ranging between 0 3 moz and 0 2 moz in addition to several smaller deposits gis based prospectivity analyses using weights of evidence and logistic regression models were undertaken to delineate prospective areas where these yet to be discovered deposits could be spatially located this knowledge will be critical in guiding future exploration programs in the plutonic marymia greenstone belt

modeling the effects of weathering on bedrock floored channel geometry 1 field and modeling studies suggest that bedrock channels equilibrate to base level change through geometry and slope adjustment to imposed discharge sediment supply and substrate erodibility conditions in this study we model the influence of bedrock weathering on channel geometry and slope as mean peak discharge qm and uplift rate u vary we find that channels in which weathering is allowed to increase erodibility are wider deeper and less steep than nonweathering channels with the same initial conditions while fixed erodibility channels maintain similar width depth ratios regardless of qm or u the width depth ratio of weathering channels is sensitive to uplift rate at low uplift rates weathering outpaces erosion and channels obtain similar width depth ratios but are wider and less steep than fixed erodibility channels with equal initial conditions at high uplift rates erosion outpaces weathering and erodibility remains near the unweathered value with channel shape and slope nearly identical to a fixed erodibility channel with equal initial conditions weathering channels differ most from fixed erodibility channels at intermediate uplift rates with greater width depth ratios and lower slopes than fixed erodibility channels with the same initial conditions our results support the hypothesis that cross channel variations in erodibility created by weathering may be an important control on channel geometry and provide guidance for further testing of this hypothesis in natural systems

channel reach morphology in mountain drainage basins a classification of channel reach morphology in mountain drainage basins synthesizes stream morphologies into seven distinct reach types colluvial bedrock and five alluvial channel types cascade step pool plane bed pool rime and dune ripple coupling reach level channel processes with the spatial arrangement of reach morphologies their links to hillslope processes and external forcing by confinement ripar ian vegetation and woody debris defines a process based framework within which to assess channel condition and response potential in mountain drainage basins field investigations demonstrate character istic slope grain size shear stress and roughness ranges for different reach types observations consistent with our hypothesis that alluvial channel morphologies reflect specific roughness configurations ad justed to the relative magnitudes of sediment supply and transport ca pacity steep alluvial channels cascade and step pool have high ratios of transport capacity to sediment supply and are resilient to changes in discharge and sediment supply whereas low gradient alluvial channels pool rime and dune ripple have lower transport capacity to supply ra tios and thus exhibit significant and prolonged response to changes in sediment supply and discharge general differences in the ratio of transport capacity to supply between channel types allow aggregation of reaches into source transport and response segments the spatial distribution of which provides a watershed level conceptual model linking reach morphology and channel processes these two scales of channel network classification define a framework within which to in vestigate spatial and temporal patterns of channel response in moun tain drainage basins

evaluating the controls of shear stress sediment supply alluvial cover and channel morphology on experimental bedrock incision rate 1 we explored the dependence of experimental bedrock erosion rate on shear stress bed load sediment flux alluvial bed cover and evolving channel morphology we isolated these variables experimentally by systematically varying gravel sediment flux qs and water discharge qw in a laboratory flume gradually abrading weak concrete bedrock all else held constant we found that 1 erosion rate was insensitive to flume averaged shear stress 2 erosion rate increased linearly with sediment flux 3 erosion rate decreased linearly with the extent of alluvial bed cover and 4 the spatial distribution of bed cover was sensitive to local bed topography but the extent of cover increased with qs qt where qt is flume averaged transport capacity once critical values of bed roughness and sediment flux were exceeded starting from a planar geometry erosion increased bed roughness due to feedbacks between preferential sediment transport through interconnected topographic lows focused erosion along these zones of preferential bed load transport and local shear stresses that depended on the evolving bed morphology finally continued growth of bed roughness was inhibited by imposed variability in discharge and sediment flux due to changes in spatial patterns of alluvial deposition and impact wear erosion was preferentially focused at lower bed elevations when the bed was cover free but was focused at higher bed elevations when static alluvial cover filled topographic lows natural variations in discharge and sediment flux may thus stabilize and limit the growth of roughness in bedrock channels due to the effects of partial bed cover

mapping singularities with stream sediment geochemical data for prediction of undiscovered mineral deposits in gejiu yunnan province china abstract this paper proposes the concept of singularity for characterizing hydrothermal mineralization processes a singular physical process may result in anomalous amounts of energy release or material accumulation within a narrow spatial temporal interval mineralization can be considered as a type of singular process due to large amounts of material accumulation and element enrichment a spatial singularity mapping technique is developed based on the local singularity involved in the context of multifractal theory it assembles geochemical map at different scales and calculates an index indicating the scaling characteristics of enrichment and depletion of geochemical concentration at multiple scales this index was used for quantifying spatial singularity of mineralization associated geochemical anomalies a case study for the gejiu tin polymetallic mineral district yunnan province china demonstrates that the concepts of singularity and the singularity mapping technique are applicable and useful for delineating anomalies caused by mineralization and for predicting the locations of undiscovered mineral deposits

post orogenic extension in the eastern part of the jiangnan orogen evidence from ca 800 760ma volcanic rocks we present a systematic geochronological and geochemical study on ca 800 760 ma volcanic rocks in the eastern part of the jiangnan orogen the xucun composite dykes are dated at ca 805 ma the mafic components have oib like trace element patterns and positive anomalies in zr and hf the least contaminated sample has relatively depleted nd isotopic features suggesting the xucun mafic dykes may have been generated from the partial melting of oib like asthenosphere with later crustal contamination the xucun felsic dykes have decoupled nd hf isotopes and the hf isotope compositions of zircons indicate that the dykes may be derived from the partial melting of the early neoproterozoic juvenile crustal materials with minor incorporation of paleoproterozoic crustal components the ca 800 790 ma shangshu volcanics include two compositional series calc alkaline and tholeiitic the shangshu calc alkaline volcanics in the minjiawu area have low abundances of lile hfse and high na2o contents and sr y ratios similar to adakitic rocks the evident arc like geochemical features and radiogenic nd isotopes nd t values of 3 7 to 4 8 suggest that these rocks may have been generated from the partial melting of juvenile lithospheric mantle metasomatized by na rich melts released from the subducted slab the tholeiitic mafic rocks from the shangshu bimodal volcanics represent two different magma sources the partial melting of metasomatized lithospheric mantle led to the formation of arc like basalts with low tio2 contents negative anomalies in zr and hf and high values of mg and nd t 6 2 whereas the partial melting of asthenospheric mantle generated volcanic rocks with high tio2 contents and low positive nd t 1 4 to 2 7 without negative anomalies of nb ta zr and hf the shangshu felsic rocks were formed by the reworking of early neoproterozoic juvenile arc crustal materials the ca 760 ma mafic rocks from the puling bimodal volcanics generally have low tio2 contents 0 9 wt nearly flat ree distributions and arc like trace element patterns they may have been generated from the high degree partial melting of metasomatized lithospheric mantle one sample has a high tio2 content 2 41 wt and high nd t 6 2 with overall oib like trace element patterns implying the local partial melting of asthenospheric mantle the occurrence of significant volumes of bimodal volcanics in the eastern part of the jiangnan orogen suggests an extensional setting in the period ca 800 760 ma the evident partial melting of newly metasomatized lithospheric mantle and subordinate partial melting of asthenosphere suggest that post orogenic extension shortly after the neoproterozoic orogenesis may be a better explanation for the genesis of the mid neoproterozoic magmatic rocks in the eastern part of the jiangnan orogen post orogenic extension may be diachronous along the whole orogenic belt and probably has no direct relationship with the rodinia rifting event a more detailed model is presented to illustrate the evolution of the eastern part of the jiangnan orogen

machine learning predictive models for mineral prospectivity an evaluation of neural networks random forest regression trees and support vector machines abstract machine learning algorithms mlas such us artificial neural networks anns regression trees rts random forest rf and support vector machines svms are powerful data driven methods that are relatively less widely used in the mapping of mineral prospectivity and thus have not been comparatively evaluated together thoroughly in this field the performances of a series of mlas namely artificial neural networks anns regression trees rts random forest rf and support vector machines svms in mineral prospectivity modelling are compared based on the following criteria i the accuracy in the delineation of prospective areas ii the sensitivity to the estimation of hyper parameters iii the sensitivity to the size of training data and iv the interpretability of model parameters the results of applying the above algorithms to epithermal au prospectivity mapping of the rodalquilar district spain indicate that the rf outperformed the other mla algorithms anns rts and svms the rf algorithm showed higher stability and robustness with varying training parameters and better success rates and roc analysis results on the other hand all mla algorithms can be used when ore deposit evidences are scarce moreover the model parameters of rf and rt can be interpreted to gain insights into the geological controls of mineralization

erosional dynamics flexural isostasy and long lived escarpments a numerical modeling study erosional escarpments are common features of high elevation rifted continents fission track data suggest that these escarpments form by base level lowering and or marginal uplift during rifting followed by lateral retreat of an erosion front across tens to hundreds of kilometers previous modeling studies have shown that this characteristic pattern of denudation can have a profound impact upon marginal isostatic uplift and the evolution of offshore sedimentary basins yet at present there is only a rudimentary understanding of the geomorphic mechanisms capable of driving such prolonged escarpment retreat in this study we present a nonlinear two dimensional landscape evolution model that is used to assess the necessary and sufficient conditions for long term retreat of a rift generated escarpment the model represents topography as a grid of cells with drainage networks evolving as water flows across the grid in the direction of steepest descent the model accounts for sediment production by weathering fluvial sediment transport bedrock channel erosion and hillslope sediment transport by diffusive mechanisms and by mass failure numerical experiments presented explore the effects of different combinations of erosion processes and of dynamic coupling between denudation and flexural isostatic uplift model results suggest that the necessary and sufficient conditions for long term escarpment retreat are 1 incising bedrock channels in which the erosion rate increases with increasing drainage area so that the channels steepen and propagate headward 2 a low rate of sediment production relative to sediment transport efficiency which promotes relief generating processes over diffusive ones 3 high continental elevation which allows greater freedom for fluvial dissection and 4 any process including flexural isostatic uplift that helps to maintain a drainage divide near an escarpment crest flexural isostatic uplift also facilitates escarpment retreat by elevating topography in the vicinity of an eroding escarpment thereby increasing channel gradients and accelerating erosion which in turn generates additional isostatic uplift of all the above conditions high continental elevation is common to most rift margin escarpments and may ultimately be the most important factor

evolution of the santa cruz mountains california through tectonic growth and geomorphic decay i describe a strategy for modeling a specific large scale topographic feature that recognizes the discrepancy between tectonic and geomorphic scales and allows for important feedbacks between these processes in the geomorphic model the largest channel in each 4 4 km cell is explicitly treated the channel incision being driven by a stream power rule hillslopes internal to each cell respond rapidly to incision of the local channel prompting their treatment in the model as steady state forms i present analytic expressions for the local relief which is controlled by the local channel incision rate and rate constants associated with the dominant hillslope process either diffusive or landsliding initial conditions include any preexisting topography and a lightly etched a channel network the model is illustrated using the santa cruz mountains california i show that an earlier hypothesis that the santa cruz mountains are due to advection of topography past an uplift source related to a restraining bend in the san andreas fault remains viable when more specific geomorphic processes are considered the local tectonics are represented by crustal thickening necessitated by conservation of mass in the bend right lateral translation of crust with respect to the bend and flexural response to the distributed load the model produces reasonable geographic and statistical distributions of topography using rates of tectonic and geomorphic processes that are within the range of those measured locally this argues that this restraining bend is a long lived feature of the san andreas fault the slightly higher crest and shorter length of the southern santa cruz mountains may potentially be explained by slightly faster slip of the crust west of the fault with respect to the bend than of that to the east deflection is minimal beneath these relatively small mountains disallowing the interesting feedback of erosionally driven uplift the predicted pattern of exhumation could be used to guide the search for fission track sites that could aid in the testing of the model

erosion profiles due to particles entrained by wind application of an eolian sediment transport model erosion by impacts of particles entrained in the wind scales with the kinetic energy of impacting grains a recent model of eolian sediment transport permits calculation of expected erosion patterns in objects of simple geometry the modeling of vertical erosion profiles in turn provides an exacting test of the transport model realistic distributions of liftoff velocities for saltating grains give rise to kinetic energy flux profiles characterized by a strong maximum as much as 1 4 m above the bed during strong winds kinetic energy flux due to suspended grains also peaks above the bed the height and strength of the maxima depend very strongly on the grain size distribution as grain size diminishes increased particle deflection by the air flow around an obstacle reduces delivery of kinetic energy to the surface for both saltating and suspended grains kinetic energy flux scales with the fifth power of the wind shear velocity erosion profiles in man made obstacles are well modeled with only slight modification of the saltation model to account for the relatively high elasticity of actual deflationary surfaces lending considerable support for the model the modeling also elucidates several aspects of ventifaction as small ventifacts 1 2 m in diameter and the lower portions of larger ones are predominantly eroded by saltating grains upwind surface irregularities are quickly damped leading to facets that dip upwind and sharply truncate lee surfaces sandblasting by suspended grains dominates along the upper portions of large ventifacts where grain paths are partially deflected by the obstacle and may lead to radially symmetrical flutes and grooves

numerical modeling of fluvial strath terrace formation in response to oscillating climate many river systems in western north america retain a fluvial strath terrace rec ord of discontinuous downcutting into bedrock through the quaternary their importance lies in their use to interpret climatic events in the headwaters and to determine long term incision rates terrace formation has been ascribed to changes in sediment supply and or water discharge produced by late quaternary climatic fluctuations we use a one dimensional channel evolution model to explore whether temporal variations in sediment and water discharge can generate terrace sequences the model includes sediment transport vertical bedrock erosion limited by alluvial cover and lateral valley wall erosion we set limits on our modeling by using data collected from the terraced wind river basin two types of experiments were performed constant period sinusoidal input histories and variable period inputs scaled by the marine 18 o rec ord our simulations indicate that strath terrace formation requires input variability that produces a changing ratio of vertical to lateral erosion rates straths are cut when the channel floor is protected from erosion by sediment and are abandoned and terraces formed when incision can resume following sediment cover thinning high sediment supply promotes wide valley floors that are abandoned as sediment supply decreases in contrast wide valleys are promoted by low effective water discharge and are abandoned as discharge increases widening of the valley floors that become terraces occurs over many thousands of years the transition from valley widening to downcutting and terrace creation occurs in response to subtle input changes affecting local divergence of sediment transport capacity formation of terraces lags by several thousand years the input changes that cause their formation our results suggest that use of terrace ages to set limits on the timing of a specific event must be done with the knowledge that the system can take thousands of years to respond to a perturbation the incision rate calculated in the field from the lowest terrace in these systems will likely be higher than the rate calculated by using older terraces because the most recent fluvial response in the field is commonly downcutting associated with declining sediment input since the last glacial maximum this apparent increase in incision rates is observed in many river systems and should not necessarily be interpreted as a response to an increase in rock uplift rate

field evidence for the influence of weathering on rock erodibility and channel form in bedrock rivers erosion processes in bedrock floored rivers shape channel cross sectional geometry and the broader landscape however the influence of weathering on channel slope and geometry is not well understood weathering can produce variation in rock erodibility within channel cross sections recent numerical modeling results suggest that weathering may preferentially weaken rock on channel banks relative to the thalweg strongly influencing channel form here we present the first quantitative field study of differential weathering across channel cross sections we hypothesize that average cross section erosion rate controls the magnitude of this contrast in weathering between the banks and the thalweg erosion rate in turn is moderated by the extent to which weathering processes increase bedrock erodibility we test these hypotheses on tributaries to the potomac river virginia with inferred erosion rates from 0 1 m kyr to 0 8 m kyr with higher rates in knickpoints spawned by the migratory great falls knickzone we selected nine channel cross sections on three tributaries spanning the full range of erosion rates and at multiple flow heights we measured 1 rock compressive strength using a schmidt hammer 2 rock surface roughness using a contour gage combined with automated photograph analysis and 3 crack density crack length area at three cross sections on one channel all cross sections showed significant p 0 01 for strength p 0 05 for roughness increases in weathering by at least one metric with height above the thalweg these results assuming that the weathered state of rock is a proxy for erodibility indicate that rock erodibility varies inversely with bedrock inundation frequency differences in weathering between the thalweg and the channel margins tend to decrease as inferred erosion rates increase leading to variations in channel form related to the interplay of weathering and erosion rate this observation is consistent with numerical modeling that predicts a strong influence of weathering related erodibility on channel morphology copyright 2017 john wiley sons ltd

controls on and prospectivity mapping of volcanic type uranium mineralization in the pucheng district nw fujian china abstract a number of volcanic type uranium deposits occur in pucheng district fujian province china structural controls and volcanic rocks clearly explain the uranium mineralization in this area to explore the subtle spatial associations of uranium occurrences with certain geological features these uranium deposits were subjected to l function fry and fractal analyses the results reveal that 1 these deposits are clustered have a bifractal distribution and are spatially parallel to the ne striking faults 2 the regional scale ne striking and prospect scale ne and nw striking faults exhibit significant spatial associations with uranium deposits as illustrated by the fry models 3 intersections of the faults with larger permeability and connectivity promote the mineralization process and 4 the spatial complexities of structures and lithological contacts quantified by the fractal dimension form strong and positive correlations with uranium occurrences and sizes finally by integrating nine spatial evidential layers representing the controlling factors for the occurrence of mineralization the artificial neural network model was applied to map mineral prospectivity for the uranium mineralization the receiver operating characteristics roc curve and the under the roc curve auc were utilized to measure the performance of the prospectivity models the model is highly capable of mapping uranium prospectivity because the auc is greater than 0 5 and close to 1 the prospectivity mapping confirmed that there is significant potential for uranium mineralization in the study area which opens up new avenues for further explorations on uranium deposits in pucheng district

experimental simulation of channel incision into a cohesive substrate at varying gradients six flume runs using a substrate of 30 bentonite and 70 fine sand were used to examine channel incision into a cohesive homogeneous substrate gradients for the various runs were 1 2 5 10 and 20 other variables remained constant discharge 2 l s sediment discharge averages 3 g s run time 15 with increasing flume gradient bed forms change from parallel longitudinal grooves to a broad shallow channel with weakly undulating bed and walls and then to a progressively deeper and more undulating inner channel downstream changes in reach scale several channel widths gradient may thus be responsible for downstream variability of erosional bed forms in the absence of changes in other controlling variables for bedrock channels it is not necessary to invoke substrate variability to explain the presence of erosional bed forms and associated variations in cross sectional area erosional bed forms may approximate an equilibrium state in which negligible change occurs in bed form dimensions or shape with time downstream alternations between solely erosion and deposition of an alluvial veneer over incisional features occur along channel reaches of constant gradient the downstream length of these alternations is inversely proportional to gradient

exploration feature selection applied to hybrid data integration modeling targeting copper gold potential in central iran abstract a sugeno type fuzzy inference system is implemented in the framework of an adaptive neural network to map cu au prospectivity of the urumieh dokhtar magmatic arc udma in central iran we use the hybrid adaptive neuro fuzzy inference system anfis jang 1993 algorithm to optimize the fuzzy membership values of input predictor maps and the parameters of the output consequent functions using the spatial distribution of known mineral deposits generic genetic models of porphyry copper gold and iron oxide copper gold iocg deposits are used in conjunction with deposit models of the dalli porphyry copper gold deposit aftabru iocg prospect and other less important cu au deposits within the study area to identify recognition criteria for exploration targeting of cu au deposits the recognition criteria are represented in the form of gis predictor layers spatial proxies by processing available exploration data sets which include geology stream sediment geochemistry airborne magnetics and multi spectral remote sensing data an anfis is trained using 30 of the 61 known cu au deposits prospects and occurrences in the area in a parallel analysis an exclusively expert knowledge driven fuzzy model was implemented using the same input predictor maps although the neuro fuzzy analysis maps the high potential areas slightly better than the fuzzy model the well known mineralized areas and several unknown potential areas are mapped by both models in the fuzzy analysis the moderate and high favorable areas cover about 16 of the study area which predict 77 of the known copper gold occurrences by comparison in the neuro fuzzy approach the moderate and high favorable areas cover about 17 of the study area which predict 82 of the copper gold occurrences

cover effect in bedrock abrasion a new derivation and its implications for the modeling of bedrock channel morphology the sediment load of a bedrock river plays an important role in the fluvial incision process by providing tools for abrasion the tools effect and by covering and thereby protecting the bed the cover effect we derive a new formulation for the cover effect in which the fraction of exposed bed area falls exponentially with increasing sediment flux or decreasing transport capacity and explore its consequences for the model of bedrock abrasion by saltating bed load erosion rates predicted by the model are higher than those predicted by earlier models in a closed system the maximum erosion rate is predicted to occur when sediment supply is equal to transport capacity for a flat bed by optimizing the channel geometry to minimize the potential energy of the stream and using representative values for both discharge and grain size we derive equations for the geometry of a bedrock river and explore how predictions for width slope and bed cover vary as functions of drainage area rock uplift rate and rock strength the equations predict a dependence of channel width on drainage area similar to the relations using a simple shear stress incision law the slope area relationship is predicted to be concave up in a log log regime with a curvature dependent on uplift rate however this curvature does not deviate sufficiently from a straight line to allow discrimination between models using empirical data dependence of channel width and slope on rock uplift rate can be separated into two domains for low uplift rates channel geometry is largely insensitive to uplift rate due to a threshold effect at high uplift rates there is a power law dependence bed cover is predicted to increase progressively downstream and to increase with increasing uplift rate in our model the width to depth ratio is a function of both tectonic and climatic forcing this indicates that the scaling between channel width and bed slope is neither a unique indicator of tectonic forcing at steady state nor a signature of transience or steady state we conclude that sediment effects need to be taken into account when modeling bedrock channel morphology

experimental study on coarse grain saltation dynamics in bedrock channels saltation of bed load particles on bedrock surfaces is important for landscape evolution and bedrock incision in steep landscapes however few studies have investigated saltation in bedrock channels where unlike alluvial channels the bed roughness height and the sediment size may be independent to address this data gap we measured the saltation hop height hop length and velocity of gravel saltating over a planar bed using 80 160 readings from high speed photography and direct measurements two separate dimensional analyses are used one leading to a bed shear stress scaling and another leading to a froude number fr scaling our new saltation data coupled with numerous data from previous studies suggest that both shear stress and fr scaling analyses are valid in characterizing bed load saltation dynamics with bed roughness ranging from smooth to alluvial beds however the fr approach has the advantages that 1 there is no need to estimate a critical shields stress c which alone can vary up to 2 orders of magnitude e g 0 001 0 1 due to changes in relative bed roughness and slope and 2 the fr based scaling fits the saltation data set better in a least squares sense results show that the saltation velocity of bed load is independent of grain density and grain size and is linearly proportional to flow velocity saltation height has a nonlinear dependence on grain size saltation length increases primarily with flow velocity and it is inversely proportional to submerged specific density our results suggest that either c or bed roughness coefficient must be properly estimated to yield accurate results in saltation abrasion models

data fusion and porphyry copper prospectivity models southeastern arizona abstract mineral exploration programs commonly use a combination of geological geophysical and remotely sensed data to detect sets of optimal conditions for potential ore deposits prospectivity mapping techniques can integrate and analyse these digital geological data sets to produce maps that identify where optimal conditions converge three prospectivity mapping techniques weights of evidence fuzzy logic and a combination of these two methods were applied to a 32 000 km 2 study area within the southeastern arizona porphyry cu district and then assessed based on their ability to identify new and existing areas of high mineral prospectivity validity testing revealed that the fuzzy logic method using membership values based on an exploration model identified known cu deposits considerably better than those that relied solely on weights of evidence and slightly better than those that used a combination of weights of evidence and fuzzy logic this led to the selection of the prospectivity map created using the fuzzy logic method with membership values based on an exploration model three case study areas were identified that comprise many critical geological and geophysical characteristics favourable to hosting porphyry cu mineralisation but not associated with known mining or exploration activity detailed analysis of each case study has been performed to promote these areas as potential targets and to demonstrate the ability of prospectivity modelling techniques as useful tools in mineral exploration programs

precise molybdenite re os and mica ar ar dating of the mesozoic yaogangxian tungsten deposit central nanling district south china the yaogangxian deposit in the central nanling region south china consists of vein type ore bodies hosted in cambrian to jurassic strata and mesozoic granitic intrusions wolframite and molybdenite are the dominant ore minerals intergrown with gangue minerals of quartz feldspar phlogopite and muscovite we have carried out molybdenite re os and phlogopite and muscovite 40ar 39ar dating to better understand the timing and genesis of mineralization re os dating of eight molybdenite samples yielded model ages ranging from 152 0 3 5 to 161 1 4 5 ma with an average of 156 0 ma the re os analyses give a well defined 187re 187os isochron with an age of 154 9 2 6 ma mswd 2 4 hydrothermal phlogopite and muscovite display extremely flat 40ar 39ar age spectra phlogopite yields a 40ar 39ar plateau age of 153 0 1 1 ma whereas muscovite yields a plateau age of 155 1 1 1 ma both 40ar 39ar ages are in good agreement with the re os ages placing the timing of tungsten mineralization at about 154 ma this age is consistent with the field relationships our new data when combined with published geochronological results from other major deposits in this region suggest that large scale w sn mineralization occurred throughout the central nanling region in the late jurassic

partial melting of thickened or delaminated lower crust in the middle of eastern china implications for cu au mineralization abstract field relations isotope systematics and plate tectonic reconstructions require that felsic adakites in the yangtze block and the dabie orogen eastern china were not derived from a subducting slab despite the signature of a mantle component in the contemporaneous mafic adakite hosts of cu au deposits in the same areas the apparently contradictory requirements are accounted for by a a deep crustal melting origin for barren adakites and b a crustal delamination origin followed by ascent through lithospheric mantle for adakites associated with mineralization the crustal delamination process associated with the prospective porphyries duplicates the metallogenically essential aspects of the subduction environment the importance of adakitic magmas in the genesis of porphyry style cu au deposits is affirmed by these findings but the range of prospective tectonic environments is extended to include an important intraplate postsubduction setting the porphyries of eastern china demonstrate

petrogenesis of ore forming granites with implications for w mineralization in the super large shimensi tungsten dominated polymetallic deposit in northern jiangxi province south china abstract the shimensi deposit is a newly discovered super large tungsten w polymetallic deposit in northwestern jiangxi province south china in this paper we reported new zircon u pb ages for the ore bearing porphyritic biotite granite 151 3 2 8 ma and fine grained granite 150 1 1 2 ma and 150 7 2 4 ma which represent the oldest mesozoic granitic magmatism reported at shimensi our ore bearing granite porphyry ages 142 7 2 3 ma and 143 3 1 5 ma have better constrained the timing of the jurassic early cretaceous ore forming magmatism geochemically the shimensi granitoids are strongly peraluminous with high contents of sio2 70 7 78 7 wt and k2o 4 0 wt p2o5 rb ta and u and low contents of ti sr ba and hrees the rocks also show positive p2o5 vs sio2 correlation suggesting a highly fractionated s type affinity different from most w bearing granites in the jiangxi region the calculated zircon ehf t 10 0 to 2 4 two stage model ages 1350 1824 ma and 18ozircon values 6 40 to 8 87 of the shimensi granites suggest that the latter were mainly derived from the partial melting of heterogeneous source rocks probably with combined contributions from the neoproterozoic shuangqiaoshan group metamorphic rocks and jiuling granodiorite the calculated zircon eu eu 0 05 0 58 mean 0 20 and ce4 ce3 3 83 96 49 mean 20 99 ratios of the granites indicate very low oxygen fugacity fo2 for the ore forming magmas a highly favorable factor for w mineralization potentially w and cu rich source rocks and highly fractionated and reducing granitic magmas were important factors that triggered super large w mineralization at shimensi

prospectivity for epithermal gold silver deposits in the deseado massif argentina previous prospectivity modelling for epithermal au ag deposits in the deseado massif southern argentina provided regional scale prospectivity maps that were of limited help in guiding exploration activities within districts or smaller areas because of their low level of detail because several districts in the deseado massif still need to be explored prospectivity maps produced with higher detail would be more helpful for exploration in this region we mapped prospectivity for low and intermediate sulfidation epithermal deposits liseds in the deseado massif at both regional and district scales producing two different prospectivity models one at regional scale and the other at district scale the models were obtained from two datasets of geological evidence layers by the weights of evidence wofe method we used more deposits than in previous studies and we applied the leave one out cross validation loocv method which allowed using all deposits for training and validating the models to ensure statistical robustness the regional and district scale models were selected amongst six combinations of geological evidence layers based on results from conditional independence tests the regional scale model 1000 m spatial resolution was generated with readily available data including a lithological layer with limited detail and accuracy a clay alteration layer derived from a landsat 5 7 band ratio and a map of proximity to regional scale structures the district scale model 100 m spatial resolution was generated from evidence layers that were more detailed accurate and diverse than the regional scale layers they were also more cumbersome to process and combine to cover large areas the evidence layers included clay alteration and silica abundance derived from aster data and a map of lineament densities the use of these evidence layers was restricted to areas of favourable lithologies which were derived from a geological map of higher detail and accuracy than the one used for the regional scale prospectivity mapping the two prospectivity models were compared and their suitability for prediction of the prospectivity in the district scale area was determined during the modelling process the spatial association of the different types of evidence and the mineral deposits were calculated based on these results the relative importance of the different evidence layers could be determined it could be inferred which type of geological evidence could potentially improve the modelling results by additional investigation and better representation we conclude that prospectivity mapping for liseds at regional and district scales were successfully carried out by using wofe and loocv methods our regional scale prospectivity model was better than previous prospectivity models of the deseado massif our district scale prospectivity model showed to be more effective reliable and useful than the regional scale model for mapping at district level this resulted from the use of higher resolution evidential layers higher detail and accuracy of the geological maps and the application of aster data instead of landsat etm data district scale prospectivity mapping could be further improved by a a more accurate determination of the age of mineralization relative to that of lithological units in the districts b more accurate and detailed mapping of the favourable units than what is currently available c a better understanding of the relationships between liseds and the geological evidence used in this research in particular the relationship with hydrothermal clay alteration and the method of detection of the clay minerals and d inclusion of other data layers such as geochemistry and geophysics that have not been used in this study

geologic constraints on bedrock river incision using the stream power law denudation rate in unextended terranes is limited by the rate of bedrock channel incision often modeled as work rate on the channel bed by water and sediment or stream power the latter can be generalized as ka m s n where k represents the channel bed s resistance to lowenng whose variation with lithology is unknown a is drainage area a surrogate for discharge s is local slope and m and n are exponents whose values are debated we address these uncertainties by simulating the lowering of ancient river profiles using the finite difference method we vary m n and k to match the evolved profile as closely as possible to the corresponding modern river profile over a time period constrained by the age of the mapped paleoprofiles we find at least two end member incision laws ka 0 3 0 5 s for australian rivers with stable base levels and k f a 0 1 0 2 s n for rivers in kauai subject to abrupt base level change the long term lowering rate on the latter expression is a function of the frequency and magnitude of knickpoint erosion characterized by k f incision patterns from japan and california could follow either expression if they follow the first expression with m 0 4 k varies from 10 7 10 6 m 0 2 yr for granite and metamorphic rocks to 10 5 10 4 m 0 2 yr for volcaniclastic rocks and 10 4 10 2 m 0 2 yr for mudstones this potentially large variation in k with lithology could drive strong variability in the rate of long term landscape change including denudation rate and sediment yield

sediment and rock strength controls on river incision into bedrock recent theoretical investigations suggest that the rate of river incision into bedrock depends nonlinearly on sediment supply challenging the common assumption that incision rate is simply proportional to stream power our measurements from laboratory abrasion mills support the hypothesis that sediment promotes erosion at low supply rates by providing tools for abrasion but inhibits erosion at high supply rates by burying underlying bedrock beneath transient deposits maximum erosion rates occur at a critical level of coarse grained sediment supply where the bedrock is only partially exposed fine grained sediments provide poor abrasive tools for lowering bedrock river beds because they tend to travel in suspension experiments also reveal that rock resistance to fluvial erosion scales with the square of rock tensile strength our results suggest that spatial and temporal variations in the extent of bedrock exposure provide incising rivers with a previously unrecognized degree of freedom in adjusting to changes in rock uplift rate and climate furthermore we conclude that the grain size distribution of sediment supplied by hillslopes to the channel network is a fundamental control on bedrock channel gradients and topographic relief

topographic hydraulic and vegetative controls on bar and island development in mixed bedrock alluvial multi channeled dryland rivers we investigate processes of bedrock core bar and island development in a bedrock influenced anastomosed reach of the sabie river kruger national park knp eastern south africa for sites subject to alluvial stripping during an extreme flood event 4470 5630 m3 s 1 in 2012 pre and post flood aerial photographs and lidar data 2d morphodynamic simulations and field observations reveal that the thickest surviving alluvial deposits tend to be located over bedrock topographic lows at a simulated peak discharge 4500 m3 s 1 most sediment sand fine gravel is mobile but localized deposition on bedrock topographic highs is possible at lower simulated discharges 1 000 m3 s 1 topographic highs are not submerged and deposition occurs in lower elevation areas particularly in areas disconnected from the main channels during falling stage field observations suggest that in addition to discharge rainwash between floods may redistribute sediments from bedrock topographic highs to lower elevation areas and also highlight the critical role of vegetation colonization in bar stability and in trapping of additional sediment and organics these findings challenge the assumptions of preferential deposition on topographic highs that underpin previous analyses of kruger national park river dynamics and are synthesized in a new conceptual model that demonstrates how initial bedrock topographic lows become topographic highs bedrock core bars and islands in the latter stages of sediment accumulation the model provides particular insight into the development of mixed bedrock alluvial anastomosing along the kruger national park rivers but similar processes of bar island development likely occur along numerous other bedrock influenced rivers across dryland southern africa and farther afield

bed load transport i mechanical characteristics this paper deals with the mechanical characteristics of saltation of bed load transport in flowing water experiments have been carried out by means of high speed photography and advanced data processing techniques taking saltation as the mode of bed load transport systematic analysis has been made with regard to the forces acting on grains and the variation of their magnitudes along the saltation trajectories to obtain the kinematic and dynamic properties of these grains moveover the relations between magnitudes of saltation parameters and flow intensity are attained from the measured data some parameters in bagnold s theory of bed load transport are also discussed

implications of sediment flux dependent river incision models for landscape evolution 1 developing a quantitative understanding of the factors that control the rate of river incision into bedrock is critical to studies of landscape evolution and the linkages between climate erosion and tectonics current models of long term river network incision differ significantly in their treatment of the role of sediment flux we analyze the implications of various sediment flux dependent incision models for large scale topography in an attempt 1 to identify quantifiable and diagnostic differences between models that could be detected from topographic data or from the transient responses of perturbed systems and 2 to explain the apparent ubiquity of mixed bedrock alluvial channels in active orogens although certain forms of the various models can be discarded as inconsistent with morphological data we find that the relative intrinsic concavity indices of detachment and transport limited systems defined herein largely dictate whether the various models can be tied to distinctive steady state morphologies preliminary data suggest that no such diagnostic differences may exist and other methods must be developed to test models accordingly we develop and explore differences in the scaling behavior of topographic relief and the extent of detachment versus transport limited channels as a function of rock uplift rate that may allow discrimination among various models further we explore potentially diagnostic differences in the rates and patterns of transient channel response to changes in rock uplift rate in addition to general differences between detachment and transport limited systems our analysis identifies an interesting hysteresis in landscape evolution hybrid channels at the threshold between detachment and transport limited conditions are expected to act as detachment limited systems in response to an increase in rock uplift rate or base level fall and as transport limited systems in response to a decrease in rock uplift rate especially during postorogenic topographic decline the analyses presented set the stage for field studies designed to test quantitatively the various river incision models that have been proposed

patterns of bedrock channel erosion on the boso peninsula japan three channels on the boso peninsula japan were examined to assess how cross sectional to reach scale channel morphology relates to substrate variables and how cross sectional to reach scale erosional patterns relate to basin scale longitudinal profile two of the channels shichiri gawa and torii zawa are deeply incised into interbedded sandstone and mudstone whereas the third channel futama gawa is incised into mudstone reach scale channel morphologies include knickpoints chutes and pools plane beds and both transverse and longitudinal bed erosional features step backwater modeling of a september 1996 typhoon related flood flow along each channel indicated that unit stream power is highly variable downstream stream power minima are associated with bends and with coarse clast deposition magnitude of erosional bed features correlates with hydraulics and flow energy expenditure along futama gawa and with variability in substrate resistance along shichiri gawa and torii zawa thickness and ori