continental rifting as a function of lithosphere mantle strength abstract the role of the uppermost mantle strength in the pattern of lithosphere rifting is investigated using a thermo mechanical finite element code in the lithosphere the mantle crust strength ratio s m s c that decreases with increasing moho temperature t m allows two strength regimes to be defined mantle dominated s m s c and crust dominated s m s c the transition between the two regimes corresponds to the disappearance of a high strength uppermost mantle for t m 700 c 2d numerical simulations for different values of s m s c show how the uppermost mantle strength controls the style of continental rifting a high strength mantle leads to strain localisation at lithosphere scale with two main patterns of narrow rifting coupled crust mantle at the lowest t m values and deep crustal decollement for increasing t m values typical of some continental rifts and non volcanic passive margins the absence of a high strength mantle leads to distributed deformations and wide rifting in the upper crust these numerical results are compared and discussed in relation with series of classical rift examples

shear wave splitting and subcontinental mantle deformation splitting observations are interpreted in terms of the strain induced lattice preferred orientation of mantle minerals especially olivine we consider three hypotheses concerning the origin of the continental anlsotropy 1 strain associated with absolute plate motion as in the oceanic upper mantle 2 crustal stress and 3 the past and present internal deformation of the subcontinental upper mantle by tectonic episodes it is found that the last hypothesis is the most successful namely that the most recent significant episode of internal deformation appears to be the best predictor of q for stable continental regions this is interpreted as fossil anisotropy whereas for presently active regions such as alaska the anisotropy reflects present day tectonic activity in the stable portion of north america there is a good correlation between delay time and lithospheric thickness this is consistent with the anisotropy being localized in the subcontinental lithosphere and suggests that intrinsic anisotropy is approximately constant the acceptance of this hypothesis has several implications for subcontinental mantle deformation first it argues for coherent deformation of the continental lithosphere crust and mantle during orogenies this implies that the anisotropic portion of the lithosphere was present since the deformational episode and rules out the addition of undeformed material to this layer by subsequent underplating or conductive growth of the thermal boundary layer one of the most important issues in the study of orogenies is the need to reconcile the formation of thickened lithosphere with the paradoxically high mantle temperatures often associated with orogenic episodes most efforts to date have focussed on modes of deformation whereby the cold lithospheric mantle is removed by convective instability or delamination and replaced by warm asthenosphere these models however are incompatible with the evidence for preserved coherent lithospheric deformation rather the deformed mantle appears to have been heated in place we suggest that the elevated mantle temperatures may be due to the strain heating accompanying the deformation

fluid inclusion characteristics and geological significance of the xi ao copper tin polymetallic deposit in gejiu yunnan province abstract the newly discovered xi ao cu sn polymetallic deposit is located in the inner alteration zone of the laochang kafang granite edge in gejiu yunnan province the mineralization process of this deposit can be divided into four stages cassiterite and chalcopyrite mainly formed at stages ii and iii respectively fluid inclusions at different stages were studied by petrography microthermometry and laser raman spectrometry five fluid inclusion types are observed microthermometry results revealed that the ore forming fluid evolved from high temperature with low to intermediate salinity to low temperature with low salinity at stage i the fluid was under near critical conditions and then separated into coexisting liquid and vapor phases at stage ii finally the fluid was boiling and immiscible at stage iii a meteoric fluid mixing process was also observed at this stage laser raman spectra identified ch4 at the skarn and mineralization stages combined with other geological features the deposit was concluded to have formed under a relatively reduced environment the co2 component abruptly increased at stage iii and probably originated from the exterior fluorine may play an important role in mineralization cassiterite and chalcopyrite were mainly deposited at 340 440 and 300 400 c under pressures of 18 50 and 12 36 mpa respectively boiling and immiscibility are probably the main reason for mineral deposition the deposit of cassiterite and chalcopyrite showed similar salinities but higher temperatures than other mineralization types of deposits in the gejiu area this finding indicated that the study deposit probably represents the high temperature part of the gejiu mineralization system thereby benefiting mineral explorations in the gejiu area

tin metallogenesis associated with granitoids in the southwestern sanjiang tethyan domain nature deposit types and tectonic setting article i nfo tin mineralization in the southwestern sanjiang tethys sn metallogenic domain extends from the southeast asia tin belt in the south the eastern part of the domain does not contain significant sn deposits whereas the central part of the domain composed of the changning menglian sn belt and related to ca 239 178 ma s type granitoids generated by the collision between tengchong baoshan and simao blocks carries wide spread the hydrothermal vein type mineralization the western part of the domain composed of the tengchong baoshan sn metallogenic belt is related to both 136 113 ma and 89 52 ma s type granitoids the former granitoids resulted from the collision between western burma and tengchong baoshan blocks and generated skarn type tin deposits the younger groups correspond to the india asia continental collision and are associated with the xiaolonghe and lailishan greisen type sn deposits

an s receiver function analysis of the lithospheric structure in south america 1 we make use of s receiver function to investigate the structure and thickness of the crust and mantle lithosphere in the south american continent and adjacent areas the moho discontinuity has been detected at all stations and goes from 18 km beneath the coast of the continent to 80 km in the andean region the depth of the lithosphere asthenosphere boundary can be clearly detected below those stations that are located on stable areas from 50 km to 160 km the identification of this phase becomes more difficult when the stations are located near subduction zones we also observed the base of the subducted oceanic lithosphere down to depths of 220 km

stream sediment geochemical data analysis for district scale mineral exploration targeting measuring the performance of the spatial u statistic and c a fractal modeling abstract recognition of mineralization related geochemical footprints and modeling their multi element dispersion patterns are important aspects to consider when vectoring toward undiscovered ore deposits the collection analysis and interpretation of stream sediment geochemical data together make an exploration method that has proven to be successful at the district scale mineral exploration targeting identifying the possible sources of stream sediment geochemical anomalies and mapping evidence i e footprints of the underlying ore forming processes however are not trivial tasks this is because stream sediment samples represent transported material reflecting the entire geology upstream from the sample locations furthermore indicator element distribution patterns are commonly strongly affected by local factors such as regolith topographic gradient vegetation density and or climate therefore there is a need for finding a better geochemical anomaly separation method regarding the nature of geochemical data obtained from the area sampled the main objectives of this study were 1 evaluating and comparing the spatial u statistic and concentration area fractal modeling methods of anomaly identification both amenable to spatial analysis for recognizing geochemical footprints of porphyry copper mineralization and 2 measuring their performance in the context of district scale exploration targeting in an area located in southeast iran subsequently the methods were first evaluated on a dataset of element contents to decompose anomalous populations finally the geochemical model that proved more efficient with respect to predicting the known mineral deposits was integrated with additional evidence maps to delineate exploration targets our evaluation of the resulting geochemical targeting model demonstrated that the targets derived from this method are robust and worthy of follow up exploration

predictive mapping of prospectivity and quantitative estimation of undiscovered vms deposits in skellefte district sweden mapping of mineral prospectivity and assessment of undiscovered mineral deposits both aim to delineate prospective ground for mineral exploration but the latter is usually carried out exclusive of the former we propose that the spatial distribution of known mineral deposits of the type sought is the key to link mapping of mineral prospectivity and assessment of undiscovered deposits we demonstrate this proposition in regional scale mapping of prospectivity for volcanogenic massive sulphides vms deposits and estimation of undiscovered vms endowment in the skellefte district sweden the results of analyses of the spatial distribution of known vms deposits and their spatial associations with geological features are consistent with existing knowledge of geological controls on vms mineralization in the district and we used them to define spatial recognition criteria of regional scale vms prospectivity integration of layers of evidence representing spatial recognition criteria of vms prospectivity via application of data driven evidential belief functions results in a regional scale map of prospective areas occupying 15 of the district and having fitting and prediction rates of 100 we used the map of prospective areas and proxy measures for degrees of exploration based on the spatial distribution of known vms deposits in one level prediction of undiscovered mineral endowment we obtained estimates of 709 kt undiscovered cu endowment 3190 kt undiscovered zn endowment 95 mt undiscovered ore tonnage and 48 undiscovered vms deposits these estimates are slightly ca 5 on average lower than and thus corroborated by estimates obtained via radial density fractal analysis of the spatial distribution of known vms deposits therefore mineral prospectivity mapping can be a part of mineral resource assessment if the spatial distribution of discovered deposits of the type sought is considered in both predictive modeling processes

models of seismic anisotropy in the deep continental lithosphere seismological observations sks wave polarizations systematic p residual variations azimuthal dependence of pn and surface wave velocities or a dispersion of surface waves are not consistent with isotropic if laterally heterogeneous upper mantle structure therefore an anisotropy should be considered as an a priori aspect of future large scale studies of mantle structure most studies of anisotropy however have assumed horizontal or vertical axes of symmetry but such orientations cannot explain bipolar patterns of spatial variations of p residuals which we have observed at many seismological stations on the basis of the petrophysical properties of real upper mantle rocks we consider anisotropy formed either by hexagonal or by orthorhombic aggregates composed of olivine orthopyroxene and clinopyroxene rotations of the aggregates about vertical and horizontal axes allow us to find the three dimensional orientations of symmetry axes that fit combinations of both p and s seismological observations in central europe and in western north america the orientations with plunging symmetry axes velocity extremes seem to be consistent across large spatially uniform tectonic units and change abruptly at important suture zones

seismic anisotropy and mantle creep in young orogens summary seismic anisotropy provides evidence for the physical state and tectonic evolution of the lithosphere we discuss the origin of anisotropy at various depths and relate it to tectonic stress geotherms and rheology the anisotropy of the uppermost mantle is controlled by the orthorhombic mineral olivine and may result from ductile deformation dynamic recrystallization or annealing anisotropy beneath young orogens has been measured for the seismic phase pn that propagates in the uppermost mantle this anisotropy is interpreted as being caused by deformation during the most recent thermotectonic event and thus provides information on the process of mountain building whereas tectonic stress and many structural features in the upper crust are usually orientated perpendicular to the structural axis of mountain belts pn anisotropy is aligned parallel to the structural axis we interpret this to indicate mountainparallel ductile i e creeping deformation in the uppermost mantle that is a consequence of mountain perpendicular compressive stresses the preferred orientation of the fast axes of some anisotropic minerals such as olivine is known to be in the creep direction a consequence of the anisotropy of strength and viscosity of orientated minerals in order to explain the anisotropy of the mantle beneath young orogens we extend the concept of crustal escape or extrusion tectonics to the uppermost mantle we present rheological model calculations to support this hypothesis mountain perpendicular horizontal stress determined in the upper crust and mountain parallel seismic anisotropy in the uppermost mantle require a zone of ductile decoupling in the middle or lower crust of young mountain belts examples for stress and mountain parallel pn anisotropy are given for tibet the alpine chains and young mountain ranges in the americas finally we suggest a simple model for initiating mountain parallel creep

application of geographically weighted regression to identify spatially non stationary relationships between fe mineralization and its controlling factors in eastern tianshan china abstract marine volcanic sedimentary fe mineral deposit is one of the most productive mineralization types in eastern tianshan mineral district uyghur autonomous region china previous researches have revealed that fe deposits in this area are mainly hosted by the lower carboniferous yamansu bimodal volcanic rocks and characterized by extensive skarn alteration due to variable effects of controlling factors across the study area fe mineralization occurs at limited locations with favorable geological environment in order to understand ore genesis of different fe deposits and to assist in fe mineral exploration in this area it is essential to investigate the spatial relationships between fe mineralization and its controlling factors across the study area in this paper fe mineralization and its controlling factors are characterized and delineated on the basis of spatial distributions of geochemical signatures obtained by principal component analysis the spatially non stationary relationships between these spatial distributions of geochemical signatures are further analyzed by a geographically weighted regression gwr method the comparison of applications of the ordinary regression and gwr shows that gwr is superior in depicting localized spatial relationships between fe mineralization and its controlling factors the gwr results demonstrate that influences of controlling factors on fe mineralization are spatially varied and imply that geological environments favorable to fe mineralization are diverse at different locations based on currently achieved results suggestions to support future fe mineral exploration at different subareas are proposed at the end of this paper

crustal fabric in the tibetan plateau based on waveform inversions for seismic anisotropy parameters 1 the tibetan plateau has the thickest continental crust on earth and fabrics within the crust that are anisotropic to seismic waves may provide clues to how it reached such extreme proportions and how it is currently deforming waveform modeling using a global minimization inversion technique applied to receiver functions computed from 11 stations spanning the north south length of the eastern plateau has yielded a suite of crustal models that include anisotropy these models suggest that the tibetan crust contains 4 14 anisotropy at different depths that is likely a result of both fossil fabrics and more recent deformation all models contain anisotropy in the surface layer and for most stations the alignment of the slow symmetry axis suggests a relationship with crustal fabrics associated with e w trending thrust faults or sutures middle to lower crustal anisotropy is present at most stations with a fast axis trending n s to nw se in the south nearly e w in the central plateau and n s to ne sw in the northern plateau this pattern appears consistent with recent ductile deformation due to both topographically induced flow and to boundary forces from subducting lithosphere at the northern and southern margins of the plateau the orientations of crustal anisotropy determined for most stations in this study are significantly different from shear wave splitting fast polarization directions implying distinct deformation in the crust and mantle

subduction zone anisotropy beneath corvallis oregon a serpentinite skid mark of trench parallel terrane migration 1 we studied the back azimuth dependence of ps converted phases at gsn station cor corvallis oregon using broadband p receiver functions computed from 602 teleseismic earthquakes the amplitudes and polarities of the transverse ps phases are largely two lobed which indicates anisotropy with a tilted symmetry axis a double peaked ps conversion at 4 5 6 5 s delay has the moveout of a dipping slab but is not consistent with simple deflection of the ps converted phase by the dipping interface a polarity flip on the transverse receiver function near north south back azimuth indicates an anisotropic symmetry axis aligned north south far from the convergence direction n68 e the ps phase is modeled using reflectivity synthetics with a highly anisotropic layer of depressed wave speed vp 6 0 6 5 km s near 40 km depth at the slab interface with the overriding north american plate one dimensional modeling suggests 10 anisotropy in the supraslab layer with a slow symmetry axis oriented n5 w at a 60 tilt from the vertical adjustments for the effect of slab interface dip on ps amplitude suggest a somewhat lower 7 anisotropy we infer a thin 7 km anisotropic detachment zone for the northward slippage of the siletz forearc terrane along the top of the descending slab a motion consistent with gps measurements and models of regional lithospheric dynamics serpentinite is a likely constituent for the deep anisotropic layer owing to its reduced vp and high poisson ratio the ductile rheology and hydrated composition of serpentinite make it a plausible lithology for a mechanical detachment zone

evidence for upper crustal anisotropy in the songpan ganze northeastern tibet terrane 1 the radial and transverse receiver functions obtained at several stations located on the songpan ganze terrane tibetan plateau are characterized by strong p to s conversions in the first 4 s after the direct p wave we show that the amplitude variations of these phases with back azimuth can be well explained by a simple model with one or two anisotropic layers the anisotropy we obtained is quite strong about 15 and might be related to the presence of highly deformed flyschs and schists in the first 25 km of the crust this study shows that anisotropy in the crust could be locally high and has to be taken into account when analyzing teleseismic data

gis based mineral potential modeling by advanced spatial analytical methods in the southeastern yunnan mineral district china this paper demonstrates a modeling procedure of mineral potential mapping based on singularity theory and further presents an idea to look into metallogeny of sn cu polymetallic deposits in southeastern yunnan mineral district china by applying a localized regression method mineralization is a typical cascade process generally accompanied by irregular geological geochemical and geophysical signatures singularity index as an efficient anomaly analytical tool helps to identify anomalies as well as characterize formation processes of these anomalies in this study the singularity based mineral potential mapping method was utilized to characterize hydrothermal mineralization associated with magmatic tectonic and sedimentary processes in this district based on the results a mineral prospectivity model was constructed to delineate target areas in addition to mineral prospectivity controlling effects of geo processes on mineralization are spatially non stationary geographically weighted regression analysis was thus employed to investigate these spatially varied controlling effects and it has contributed to improve understanding to local metallogeny in the study area results of the spatial analysis presented can be used to guide following stages of mineral exploration in the district

depth variant azimuthal anisotropy in tibet revealed by surface wave tomography azimuthal anisotropy derived from multimode rayleigh wave tomography in china exhibits depth dependent variations in tibet which can be explained as induced by the cenozoic india eurasian collision in west tibet the e w fast polarization direction at depths 100 km is consistent with the accumulated shear strain in the tibetan lithosphere whereas the n s fast direction at greater depths is aligned with indian plate motion in northeast tibet depth consistent nw se directions imply coupled deformation throughout the whole lithosphere possibly also involving the underlying asthenosphere significant anisotropy at depths of 225 km in southeast tibet reflects sublithospheric deformation induced by northward and eastward lithospheric subduction beneath the himalaya and burma respectively the multilayer anisotropic surface wave model can explain some features of sks splitting measurements in tibet with differences probably attributable to the limited back azimuthal coverage of most sks studies in tibet and the limited horizontal resolution of the surface wave results

translating the mineral systems approach into an effective exploration targeting system abstract holistic mineral systems approaches are being increasingly adopted in the study of ore deposits but application in industry has been suboptimal because of the lack of a conceptual framework to help translate the mineral system understanding to practical application a four step process is proposed for linking the conceptual mineral system with data available to support exploration targeting these steps include translation from 1 critical processes of the mineral system to 2 constituent processes of the mineral system to 3 targeting elements reflected in geology and 4 targeting criteria used to detect the targeting elements directly or by proxy this translation process is illustrated using examples from komatiite hosted ni cu pge and orogenic au mineral systems ranking of targets must be at the critical process level rather than the current practice of mixing processes elements and proxies the significance of targeting elements and their mappable criteria changes as a function of the scale at which the critical processes operate and the availability of relevant geoscience datasets this scale dependence is rarely recognised in current practice sources of uncertainty when translating the mineral system understanding into an effective exploration targeting system include 1 resolution of a mappable criterion in a dataset 2 how well the targeting criterion reflects the targeting element 3 how well the targeting element reflects the critical process and 4 whether the process being mapped is critical for the genesis of a mineral deposit the first three sources of uncertainty collectively are termed the representativeness of the targeting criteria i e how representative is a mappable criterion of the constituent process for which it is a proxy the last source of uncertainty reflects our lack of understanding of the processes that control mineralisation and highlights areas for further research

the origin of the world class tin polymetallic deposits in the gejiu district sw china constraints from metal zoning characteristics and 40ar 39ar geochronology the gejiu tin polymetallic deposits in the western cathaysia block of south china comprise the world s largest primary tin district with a total resource of approximately 300 million metric ton ores at an average grade of 1 wt percent sn tin polymetallic mineralization occurs in five deposits and has four ore types i e greisen skarn stratabound cassiterite sulfide mostly oxidized and vein type ore in each deposit the orebodies typically occur in an extensive hydrothermal system centered on a shallow late cretaceous granitoid cupola metal zoning is well developed both vertically and horizontally over the entire district from w be bi mo sn ores inside granite intrusions to sn cu dominated ores at intrusion margins and farther out to pb zn deposits in the surrounding host carbonate this zoning pattern is similar to that of other hydrothermal deposits in other parts of the world indicating a close genetic relationship between magmatism and mineralization in this paper we dated thirteen mica samples from all types of mineralization and from the five deposits in the gejiu district the ages range from 77 4 0 6 ma to 95 3 0 7 ma and are similar to the existing zircon u pb age of the granitic intrusions 77 4 2 5 85 8 0 6 indicating a genetic relationship between the mineralization and the intrusions geological characteristics metal zoning patterns and new geochronological data all indicate that the tin polymetallic ores in the gejiu district are hydrothermal in origin and are genetically related to the nearby granitic intrusions it is unlikely that the deposits are syngenetic as has been proposed in recent years

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

three dimensional seismic velocity structure of the northwestern united states 1 we present a high resolution three dimensional p wave tomography model for the northwestern united states major features of the model include clear well resolved images of the juan de fuca gorda slab to depths of at least 500 km reduced velocities beneath newberry volcano and north central oregon increased velocities beneath the idaho batholith and a deep slab like eastward dipping feature of increased velocities beneath nevada we find no evidence for a mantle plume in this region and demonstrate that suggested disruption of the juan de fuca slab beneath oregon in the vicinity of newberry volcano is an inversion artifact we interpret the primary features of this new model within the framework of post laramide tectonomagmatism and the continuing tectonic evolution of the cascadia subduction zone a model explaining the regional tectonomagmatic history consistent with the imaged seismic velocity structure is one driven by mantle flow responding to the evolving subduction system

integrated gis based modelling for the quantitative prediction of magmatic ti v fe deposits a case study in the panzhihua xichang area of southwest china abstract the estimation of undiscovered mineral resources is an important part in the potential value of a mineral field and its long term use this manuscript documents six procedures for estimating the volume of potential mineral resources in an area that is based on integrated geological information forming part of a metallogenic model the technique for this methodology includes 1 the development a metallogenic model or models for mineral deposits in the study area 2 the integration of the characteristics of known mineral anomalies with geology geochemistry and geophysics to establish a predictive model for mineralization 3 the definition of possible mineral resources incorporating predictive models with characteristic analyses the knowledge driven delphi method and magnetic anomalies 4 calculate the parameters for the quantitative prediction areas of known mineral deposits and their estimated dip extension ore bearing coefficients and their similarity coefficients based on explored ore deposits in the area studied 5 complete quantitative predictions using an synthetic volumetric equation and 6 assess zones that are considered prospective for mineral resources the procedure is tested for magmatic ti v fe resources in a known mineralized zone in the sichuan province of china

joint interpretation of upper mantle anisotropy based on teleseismic p travel time delays and inversion of shear wave splitting parameters abstract we inverted shear wave splitting parameters and simultaneously analysed delays of teleseismic longitudinal waves to obtain a self consistent three dimensional 3 d image of the anisotropic upper mantle beneath the continents efficiency of the simultaneous 3 d analyses of p residual spheres and shear wave polarizations is demonstrated on data from two regions southern sweden and the western usa the anisotropic inferences of the subcrustal lithosphere are to a first approximation represented by homogeneous hexagonal or orthorhombic media with plunging symmetry axes

neighbourhood inversion of teleseismic ps conversions for anisotropy and layer dip summary the inversion of teleseismic receiver functions for lithospheric structure is difficult due to the non linearity of the problem which is greatly increased in the presence of dipping interfaces and layer anisotropy given an efficient ray theoretical tool for forward modelling teleseismic seismograms we perform a directed monte carlo search technique using the neighbourhood algorithm of sambridge enabling us to search 20 30 parameters in a reasonable amount of computer time tests on synthetic data reveal inherent velocity depth trade offs in typical data sets due to the limited moveout present in teleseismic ps the azimuth of the anisotropic symmetry axis and the strike of a dipping interface prove to be well resolved given adequate backazimuthal coverage we apply this technique to two single station data sets the first from permanent station pgc vancouver island british columbia displays dipping low velocity sediment layers in the mid crust the second from a station at the northern end of the tibetan plateau operating in 1991 and 1992 requires a sequence of thick crustal anisotropic layers to explain the observed pattern of receiver function arrivals

on the interpretation of sks splitting measurements in the presence of several layers of anisotropy summary concerns over the validity of expressions derived by montagner et al that link sks splitting measurements to the variation with depth of anisotropic parameters in the upper mantle have been recently expressed pointing out that the long period approximations applied by these authors may not be valid for the frequency range commonly used in sks studies and in particular that the anisotropy splitting parameters should depend on the order in which different anisotropy layers are arranged with depth we show here that indeed measurements of splitting time and fast axis direction performed at individual azimuths do depend on the order of layering however the expressions of montagner et al concern station averaged quantities that do not depend on the order of layers it is therefore correct to use these expressions in joint inversions of surface waveforms and sks station averaged splitting measurements on the other hand the depth dependent sensitivity of surface waveforms naturally provides constraints on the order of layering having clarified this confusion we extend the expressions of montagner et al to the case of a tilted axis of symmetry and non vertical incident waves and show that station averaged estimates of effective splitting parameters splitting time fast axis direction and tilt of the fast axis can be related to the integral with depth of quantities which now depend not only on the local splitting time and fast axis direction but also on the local tilt of the fast axis thus providing constraints also on the variation of the tilt with depth we show that the effective parameters used as constraints in the inversion can be obtained either from the measurement of splitting intensity or through a parameter search and cross convolution method in particular in the case when the effective tilt is significant the splitting intensity no longer presents 180 periodicity with azimuth providing a diagnostic tool for the presence of such tilts in the upper mantle thus combining body wave and surface wave observations also has the potential of constraining the variation with depth of the tilt of the fast axis of anisotropy a geodynamically important parameter

introduction to the special issue gis based mineral potential modelling and geological data analyses for mineral exploration this introduction provides an overview of the procedures involved in mineral potential modelling the papers included in this special issue are also summarized

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

mantle flow geometry from ridge to trench beneath the gorda juan de fuca plate system shallow mantle flow could be induced by the motions of overriding tectonic plates or by deeper mantle convection analysis of mantle flow patterns in the pacific northwest shows that flow aligns with the motions of the largest oceanic plates

shear wave birefringence in wedge shaped anisotropic regions summary a popular method for studies of seismic wave speed anisotropy within the earth is based on observations of birefringence in subvertically propagating shear waves a well recognized shortcoming of the method is that individual birefringence measurements commonly interpreted as a path average of anisotropy do not reveal the potential complexity of anisotropic structure consequently there is a necessary ambiguity in the interpretation of observed birefringence parameters fast polarization directions and delays between components in this paper we explore the influence of observational geometry and the configuration of an anisotropic region on the birefringence parameters we use full wavefield simulations in 3 d models to access these influences in a subduction zone setting our primary findings are that a modest wavefield complications associated with the non planar geometry of a subduction zone can significantly bias the determination of the fast polarization and time delay associated with shear wave birefringence b shear wave splitting associated with flow in the mantle wedge near the trench e g the forearc is likely to be weak owing to short path lengths through an anisotropic region and c popular splitting estimators are vulnerable to waveform distortions caused by s wave interaction with the dipping slab interface we show that simultaneous interpretation of numerous birefringence observations from a variety of propagation directions is a more reliable way to constrain parameters of anisotropy at depth

identification and mapping of geochemical patterns and their significance for regional metallogeny in the southern sanjiang china abstract the southern sanjiang region southwestern china comprises various continental blocks tectonic sutures and arcs this complex structural area is a proper place for the recognition of geochemical patterns and understanding of regional metallogenesis considering each individual tectonic unit i e western south china block ailaoshan suture simao block changning menglian suture baoshan block and tengchong block as a statistical unit this study identifies the distribution patterns of geochemical elements distinguishes elemental associations for different geological backgrounds controlled by the regional lithology and diverse mineralizations and thereby delineates the mineralized anomalies to achieve the goals the kriging interpolation staged factor analysis and local singularity technology were utilized after the centered logratio clr transformation of stream sediment geochemical data the spatial distributions of metallogenic elements au ag cu pb zn and sn show that not all the areas with high concentrations of elements contain ore deposits it means that the formation of ore deposits is an independent anomalous geological event not necessarily related to the original regional abundance of geochemical elements the different element associations obtained by staged factor analysis of 28 elements are able to reveal the geological backgrounds and metallogenic signatures for different tectonic units for example the element associations for the first second and third factors fs in the western south china block are groups of ti co v sb ag as and th u be see text for the detailed element associations which represent the emeishan flood basalts ag pb mineralization and felsic rocks respectively similarly the element associations co v cu be u th and sb ag au for f1 f2 and f3 in the ailaoshan suture respectively represent the ophiolite complex and mafic rocks felsic rocks and au mineralization the associations from f1 to f4 in the simao block are th u sn v co cr cd ag pb and au sb which represent the linchang batholith mafic rocks ag pb zn mineralization and au mineralization respectively the distribution patterns of their factor scores can roughly distinguish the anomalies caused by regional backgrounds and mineralizations the local singularity of factor scores for mineralization can further identify mineralized areas in most of the tectonic units nevertheless an exception occurs in the western south china block where the background element association ti co v cu ni cr p mn nb zn f1 obscures the au signature therefore we substituted the single element au for mineralized element association f1 to perform singularity mapping and obtained better result it was concluded that the combination of staged factor analysis local singularity and tectonic setting is effective in regional metallogenic potential analysis

gis based prospectivity mapping based on geochemical multivariate analysis technology a case study of mvt pb zn deposits in the huanyuan fenghuang district northwestern hunan province china abstract this paper demonstrates a partial least squares regression pls method for geochemical modelling and then uses the models and geological favourable features to obtain mineral potential maps the pls is one of multivariate analysis technologies which can identify variations in associations and correlations among geochemical elements and mineralisation the method is here used to calculate principal components as well as to identify correlations between pb zn mineralization and 25 stream sediment elements for constructing geochemical models in the huayuan fenghuang district of northwestern hunan province china the models showing the distribution of geochemical anomaly are useful in interpreting the distribution of faults and the cambrian qingxudong formation ore bearing formation and to better define the architecture on mineralisation in the study area in addition the models and other favourable features proxies are easily integrated into single possibility map by boost weights of evidence boost wofe approach for targets

gis based mineral prospectivity mapping using machine learning methods a case study from tongling ore district eastern china abstract predictive modelling of mineral prospectivity using gis is a valid and progressively more accepted tool for delineating reproducible mineral exploration targets in this study machine learning methods including support vector machine svm artificial neural networks ann and random forest rf were employed to conduct gis based mineral prospectivity mapping of the tongling ore district eastern china the mineral systems approach was used to translate our understanding of the skarn cu mineral system into mappable exploration criteria resulting in 12 predictor maps that represent source transport physical trap and chemical deposition processes critical for ore formation predictive svm ann and rf models were trained by way of predictor maps and corroborated using a 10 fold cross validation the overall performance of the resulting predictive models was assessed in both training and test datasets using a confusion matrix set of statistical measurements receiver operating characteristic curve and success rate curve the assessment results indicate that the three machine learning models presented in this study achieved satisfactory performance levels characterized by high predictive accuracy in addition all models exhibited well interpretability that provided consistent ranking information about the relative importance of the evidential features contributing to the final predictions in comparison the rf model outperformed the svm and ann models having achieved greater consistency with respect to variations in the model parameters and better predictive accuracy importantly the rf model exhibited the highest predictive efficiency capturing most of the known deposits within the smallest prospective tracts the above results suggest that the rf model is the most appropriate model for cu potential mapping in the tongling ore district and therefore was used to generate a prospectivity map containing very high high moderate and low potential areas in support of follow up exploration the prospective areas delineated in this map occupy 13 97 of the study area and capture 80 95 of the known deposits the fact that two newly discovered deposits occur within the prospective areas predicted by the prospectivity model indicates that the model is robust and effective regarding exploration target generation

shear wave anisotropy beneath the tibetan plateau eleven broadband digital seismic stations were deployed across the central tibetan plateau in the first extensive passive source experiment attempted within the tibetan plateau one year of recording resulted in 186 event station pairs which we analyze to determine the characteristics of shear wave splitting in the upper mantle beneath the array measurements of the fast polarization direction and delay time t for sks and direct s arrivals reveal systematic variations along the north south oriented array in the north central region of the plateau very large delay times are observed at three stations the largest of which is budo with of t 2 4 s however at tunl which is off the northern edge of the plateau and 110 km from budo and at sites in the south central plateau t decreases by nearly a factor of 3 we also observe systematic rotation of from about 45 ne to 90 e w from south to north along the array a previously identified zone of inefficient sn propagation correlates well with our region of large t observations the large delay times suggest that a relateively high number of anisotropic crystals are preferentially alligned within the mantle lid beneath the north central portion of the tibetan plateau in most cases fast polarization directions appear to be parallel to surface geologic features suggesting as much as 200 km of the upper mantle has been involved in the collisional deformation that has produced the tibetan plateau

a case study on geochemical anomaly identification through principal components analysis supplementary projection abstract based on a case study in which a single geochemical anomaly was located in the vicinity of an abandoned mine in central portugal a recursive methodology for anomaly background separation was developed this methodology relies on the supplementary projection of each of the samples taken from a subset of anomaly candidates onto the axes provided by principal components analysis of the background subset the concept of anomaly intensity defined by the average of the distances from the original to the supplementary projections is the basis for final anomaly identification

shear wave splitting measurements problems and solutions abstract we compare sensitivity and reliability of three basic techniques of shear wave splitting analysis cross correlation of wave components minimization of covariance matrix eigenvalues and minimizing energy on the transverse component of both synthetic and real data point out some problems and propose solutions we discuss major difficulties of evaluating shear wave splitting parameters which are not always obvious in routine processing and can sometimes lead to false results and wrong interpretations we describe effects of pre processing of digital records of shear waves e g filtering and setting lengths of analyzed signals and discuss reliability of results to minimize outliers in evaluated splitting parameters for reliable evaluation of splitting of medium quality sks wave forms which are valuable mainly in temporary deployments of stations we recommend a careful band pass filtering of the signal using a window length not shorter than the dominant period inspecting the signal noise ratio on t component and the particle motion the transverse minimization method provides usually more robust and stable solutions than the other two methods in the conclusion we suggest how to proceed in evaluation of splitting parameters to ensure reliable solutions even for medium or low quality shear waveforms recorded frequently during temporary field measurements

precambrian plate tectonics seismic evidence from northern hudson bay canada the canadian shield is one of the largest exposures of precambrian rocks on earth it is a mosaic of several archean terranes that were brought together during a series of paleoproterozoic orogens culminating in the so called trans hudson orogen which is thought to have been similar to the himalayan orogen in scale and nature the tectonic evolution and lithospheric subdivisions of this region are poorly understood but new seismic networks in northern hudson bay provide fresh opportunity to place constraints on the precambrian processes that formed and shaped it we show via a study of seismic anisotropy that the lithosphere of the northern hudson bay region retains a strong signature of archean paleoproterozoic tectonics we map the boundary between the upper churchill and lower superior plates that collided ca 1 8 ga and identify back azimuth dependent splitting parameters t on baffin island that indicate complex anisotropy e g dipping fabric beneath the region our results support the view that significant lithospheric deformation occurred during the paleoproterozoic and that modern day plate tectonic processes were thus in operation by at least ca 1 8 ga

seismic anisotropy in the eastern united states deep structure of a complex continental plate we have analyzed shear wave splitting recorded by portable and permanent broadband and long period stations located in the eastern united states teleseismic shear waves sks skks and pks were used to retrieve the splitting parameters the orientation of the fast wave polarization plane and the delay time t in total 120 seismic events were processed allowing for more than 600 splitting measurements within the appalachians stations located in the western external part are characterized by t 1s and trending n50 70 e in the south and central regions and n30 40 e in the north closely following the trend of the orogenic belt in these areas the transition region between north and central is characterized by t 1 1 3 s and by e w trending that are at a high angle to the regional geologic trend measurements at two stations located in the eastern internal part of the belt indicate very weak anisotropy the large scale pattern of anisotropy is not consistent with that predicted for simple asthenospheric flow beneath the plate splitting along the southern and eastern margins of the continent is consistent with that expected for grenvillian deformation an alternative model of asthenospheric flow around the cratonic keel cannot be ruled out within the cratonic core the correlation between t and lithospheric thickness suggests a lithospheric anisotropy smaller length scale variations also argue for a significant contribution of lithospheric structures the fabric responsible for shear wave splitting may have formed during tectonic episodes that affected the eastern united states i e the grenville and appalachian orogenies and the subsequent rifting of the north atlantic ocean our observations in the western appalachians suggest that the anisotropy may be preserved since the grenvillian orogeny the absence of detectable splitting in the two stations in the eastern appalachians is attributed to the igneous intrusions related to the atlantic rifting the measurements in the transition between the northern and central southern appalachians constitute an intriguing anomaly whose e w have little obvious relation to the regional surface geology we suggest two possible causes 1 the local dominance of asthenospheric flow motivated by the proximity of a pervasive low velocity anomaly and 2 lithospheric deformation in a transcontinental strike slip fault zone active during the appalachian collision

mapping of prospectivity and estimation of number of undiscovered prospects for lode gold southwestern ashanti belt ghana in the southwestern part of the ashanti belt the results of fractal and fry analyses of the spatial pattern of 51 known mines prospects of mostly lode gold deposits and the results of analysis of their spatial associations with faults and fault intersections suggest different predominant structural controls on lode gold mineralisation at local and district scales intersections of nne and nw trending faults were likely predominantly involved in local scale structural controls on lode gold mineralisation whilst nne trending faults were likely predominantly involved in district scale structural controls on lode gold mineralisation the results of the spatial analyses facilitate the conceptualisation and selection of spatial evidence layers for lode gold prospectivity mapping in the study area the applications of the derived map of lode gold prospectivity and a map of radial density of spatially coherent lode gold mines prospects results in a one level prediction of 37 undiscovered lode gold prospects the applications of quantified radial density fractal dimensions of the spatial pattern of spatially coherent lode gold mines prospects result in an estimate of 40 undiscovered lode gold prospects the study concludes finally that analysis of the spatial pattern of discovered mineral deposits is the key to a strong link between mineral prospectivity mapping and assessment of undiscovered mineral deposits

controls on mineral deposit occurrence inferred from analysis of their spatial pattern and spatial association with geological features in this paper point pattern analysis fractal analysis and fry analysis were employed to study the spatial pattern of known occurrences of mineral deposits of the type sought whereas distance distribution method was applied to study the spatial associations between various geological features and known occurrences of mineral deposits of the type sought in the aroroy district philippines the results of the applications of these spatial analytical techniques support a conceptual model of district scale mechanism of geologic controls on low sulphidation epithermal au mineralization which involves a more or less regular mesh of interlinked zones of extension faults fractures at and or around intersections of nnw and nw trending strike slip faults fractures integration of spatial evidential data layers representing these structural controls and surficial geochemical anomalies via knowledge guided application of data driven evidential belief functions results in delineation of prospective areas occupying about 25 of the district in which there is about 70 likelihood of undiscovered occurrences of low sulphidation epithermal au deposits

upper mantle anisotropy and transition zone thickness beneath southeastern north america and implications for mantle dynamics a variety of models for mantle flow beneath southeastern north america have been proposed including those that invoke westward driven return flow from the sinking farallon slab small scale convective downwelling at the edge of the continental root or the upward advective transport of volatiles from the deep slab through the upper mantle we use shear wave splitting observations and receiver function analysis at broadband seismic stations in the southeastern united states to test several of these proposed mantle flow geometries near the coast stations exhibit well resolved null no splitting behavior for sks phases over a range of back azimuths consistent with either isotropic upper mantle or with a vertical axis of anisotropic symmetry farther inland we identify splitting with mainly ne sw fast directions consistent with asthenospheric shear due to absolute plate motion apm lithospheric anisotropy aligned with appalachian tectonic structure or a combination of these phase weighted stacking of individual receiver functions allows us to place constraints on the timing of arrivals from the 410 and 660 km discontinuities and on average transition zone thickness beneath individual stations at most stations we find transition zone thicknesses that are consistent with the global average 240 km with two stations showing evidence for a slightly thickened transition zone 250 km our results are relevant for testing different models for mantle dynamics beneath the southeastern united states but due to the sparse station coverage we are unable to uniquely constrain the pattern of mantle flow beneath the region our sks splitting observations support a model in which mantle flow is primarily vertical either upwelling or downwelling beneath the southeastern edge of the north american continent in contrast to the likely horizontal apm driven flow beneath the continental interior however our receiver function analysis does not provide unequivocal support either for widespread hydration of the transition zone or for widespread thickening due to the downwelling of relatively cold mantle material we expect that the necessary data to constrain such models more tightly can be obtained from the operation of denser seismic networks including the transportable array and flexible array components of usarray

a tectono genetic model for porphyry skarn stratabound cu au mo fe and magnetite apatite deposits along the middle lower yangtze river valley eastern china abstract the middle lower yangtze river valley metallogenic belt yrb situated along the northern margin of the yangtze craton is characterized by porphyry skarn stratabound cu au mo fe deposits in the areas of uplift and magnetite apatite deposits in cretaceous fault basins following detailed field investigations and a review of published data we recognize two episodes of magmatism and mineralization in the yrb 1 156 137 ma high k calc alkaline granitoids associated with 148 135 ma porphyry skarn stratabound cu au mo fe deposits and 2 135 123 ma shoshonitic series associated with 134 9 122 9 ma magnetite apatite deposits a type granitoids and associated alkaline volcanic have a small age range from 126 5 to 124 8 ma and are temporally spatially and genetically associated with the second episode the geodynamic history of the yrb did not experience the paleozoic to mesozoic lithospheric thickening that took place in the north china craton this process is inferred to be linked to partial melting of the delaminated lower crust at high pressures resulting in the development of c type adakitic rocks the petrochemical and sr nd isotopic data show that both the shoshonitic series and a type granitoids are quite different from adakites with only some of the k calc alkaline granitoids having adakitic signatures previous ore genesis models were established based on an assumed relationship with adakites and a continuous tectono thermal evolution from 150 to 100 ma all data obtained for the middle lower yangtze river region consistently show that the tan lu regional strike slip fault zone initiated at 233 6 to 225 6 ma from the collision between the north china and yangtze cratons and was reactivated at ca 160 ma the tan lu fault was caused by the oblique subduction of the izanagi plate which along the yrb the low angle subducted slab and the overlying crust was disrupted or broken due to the disharmonious movement of the two blocks the high k calc alkaline granitoids magmas were derived from melting of the subducted slab with some input of crustal material these magmas were emplaced at the intersections between ne and ew trending faults and formed porphyry skarn stratabound cu au mo fe deposits between 156 and 137 ma after 135 ma the subducted plate changed its direction of motion to northeast now running parallel to the eurasian continental margin and leading to large scale continental extension the shoshonitic series and subsequent a type granitoids magmatism and the development of magnetite apatite ores in the yrb took place in both fault basins and ne trending rifts between 135 and 124 ma

the fate of the downgoing oceanic plate insight from the northern cascadia subduction zone abstract in this study we use teleseismic receiver function analysis to image the seismic structure of the juan de fuca oceanic plate during its subduction beneath the north american plate seismic data have been recorded at 58 seismic stations deployed along the northern cascadia subduction zone harmonic decomposition of the receiver function data set along a trench normal profile allows us to image both the isotropic and the anisotropic structure of the plate slab our images highlight the presence of a highly anisotropic region at 40 70 km depths across the cascadia subduction zone the detected seismic anisotropy is interpreted to be related to both metamorphic facies e g blueschists and fluid released during the dehydration of the subducting mantle the processes of dehydration and metamorphism produce the variations of the seismic properties within each lithologic unit that constitutes the subducted slab i e basalts gabbro layer and upper mantle as the oceanic plate sinks in the upper mantle such variations make it almost impossible to recognize the plate boundary as a characteristic velocity jump at depth neither positive nor negative along the cascadia subduction zone based on the comparative interpretation of both the isotropic and the anisotropic structures retrieved we propose a 4 stage model of the evolution of the juan de fuca oceanic plate during its subduction beneath the north american plate

geodynamic settings and tectonic model of skarn gold deposits in china an overview seventy skarn type gold deposits including 1 super large 19 large and 24 medium sized are known from different geotectonic units of china they contain a total resource of approximately 1000 t of gold 625 t in south china and account for 20 of china s gold reserves these skarn deposits are sited in collisional orogenic belts fault controlled magmatic belts and reactivated cratonic margins all of the chinese skarn gold provinces were affected by phanerozoic collisional orogenesis the timing of the metallogenic events and the spatial temporal distribution of the chinese skarn gold deposits indicates that they were formed during ore forming processes linked to the transition from shortening to extension in the geodynamic evolution of a collision orogen and not to subduction systems as is commonly advocated for porphyry copper systems around the pacific rim

a prediction model for important mineral resources in china abstract prediction models for mineral resources provide an analytical foundation and method to express the results of resource evaluations the project china national mineral resources assessment initiative was conducted during 2006 2013 with the aim to determine the location quantity and quality of 25 important mineral resources occurring at depths of

spatially quantitative characterization of geological processes associated with polymetallic sn w mineralization in the malipo mineral district southeastern yunnan china abstract the current geographic information system gis based mineral prospecting models focus on delineating high probability locations for mineral deposits these models do not attempt to characterize the geological evolution of the area under study either spatially or quantitatively the study described in this paper demonstrates an innovative approach that quantitatively describes the mineralization processes in a spatial way this improves predictions by adding information concerning the areas geologic evolution this study quantitatively characterizes the mineralization in the malipo mineral district china in relation to tectono magmatic activity from caledonian to yanshanian time these findings extend the existing geological knowledge of the study area a critical step for further investigating and interpreting the geochemical signatures the malipo mineral district is a well studied area and thus appropriate for evaluating a new modeling technique our preliminary results show that the quantitative spatial characterizations retrieved from our model offer highly correlated predictive information regarding geologic evolution when compared with the information obtained from traditional ground truthing investigations therefore employing our model in a new and under studied area would potentially provide significant benefits and advance the level of knowledge in the new area

na sws 1 1 a uniform database of teleseismic shear wave splitting measurements for north america 1 this version of shear wave splitting sws database db for north america na contains 6224 pairs of splitting parameters fast polarization directions and splitting times measured using all the available data recorded by digital broadband seismic stations over the period of 1980 2007 and archived at the incorporated research institutions for seismology data management center the measurements were produced using a set of robust procedures that involve automated batch processing and manual screening and were ranked quantitatively on the basis of a uniform criterion the result is a homogeneous database of individual rather than station averaged splitting parameters that can be used by a variety of geoscientists for the understanding of the structure and dynamics of the earth s deep interior beneath na this data brief describes the seismic data and techniques used to generate the sws results the spatial and azimuthal coverage and the limitations of the db the db will be periodically updated and enhanced by adding newly recorded data and by measuring splitting parameters using the pks and skks phases in addition to sks the database can be accessed at http www mst edu liukh sws

geology and genesis of kafang cu sn deposit gejiu district sw china kafang is one of the main ore deposits in the world class gejiu polymetallic tin district sw china there are three main mineralization types in the kafang deposit i e skarn cu sn ores stratiform cu ores hosted by basalt and stratiform cu sn ores hosted by carbonate the skarn mainly consists of garnet and pyroxene and retrograde altered rocks these retrograde altered rocks are superimposed on the skarn and are composed of actinolite chlorite epidote and phlogopite major ore minerals are chalcopyrite pyrrhotite cassiterite pyrite and scheelite sulfur and pb isotopic components hint that the sources of different types of mineralization are distinctive and indicate that the skarn ore mainly originated from granitic magma whereas the basalt hosted cu ores mainly derived from basalt microthermometry results of fluid inclusions display a gradual change during the ore forming process the homogenization temperature of different types of inclusions continuously decreases from early to late mineralization stages the salinities and freezing temperatures exhibit similar evolutionary tendencies with the t homogenizaion while the densities of the different types keep constant the majority being less than 1 oxygen and hydrogen isotopic values o and d of the hydrothermal fluids fall within ranges of 3 1 to 7 7 with an average of 6 15 calculated at the corresponding homogenization temperature and 73 and 98 with an average of 86 5 respectively microthermometry data and h o isotopes indicate that the ore forming fluid of the kafang deposit is mainly derived from magma in the early stage and a mixture of meteoric and magmatic water in late stage molybdenite re os age of the skarn type mineralization is 83 4 2 1 ma and the stratiform ores hosted by basalt is 84 2 7 3 ma which are consistent with the la icp ms zircon age of the xinshan granite intrusion 83 1 0 4 ma the evidence listed above reflects the fact that different ore styles in the kafang deposit belong to the same mineralization system

effective use and interpretation of lithogeochemical data in regional mineral exploration programs application of geographic information systems gis technology abstract a geographic information system gis in concert with statistical and geostatistical software has been used to compile manipulate analyze and visualize a large lithogeochemical dataset collected from the archean age swayze greenstone belt sgb located in northern ontario canada altered samples from this database have been identified using a variety of univariate and multivariate statistical and visualization techniques alteration maps are produced for each method and compared to known gold mineralization using the weights of evidence wofe technique major oxide data are interpolated using different sample groups all altered unaltered normalized samples and anomalous concentrations are separated from background using breakpoints on probability plots of the data as well as statistics generated from wofe analysis these maps are also evaluated using wofe analysis with respect to locations of known gold prospects the atypical normative mineral method is more sensitive for identifying alteration in felsic rocks felsic volcanic rocks granitoids whereas the volatile method is more sensitive for detecting alteration in mafic volcanic rocks and sedimentary rocks altered samples are characterized by higher sio2 k2o and mno concentrations and lower mgo and tio2 concentrations areas within the greenstone belt characterized by high concentrations of cao fe k2o and al2o3 were found to the best predictors of the known gold prospects anomalously high concentrations of these oxides reflect carbonatization fe carbonate alteration and potassic alteration trends and indicate that these alteration styles are spatially related to gold mineralization the wofe method is a useful technique with which to evaluate the geochemical maps produced in this paper the wofe technique is useful not only for comparing geochemical anomalies to the location of known gold prospects but also for providing a quantitative measure of association between anomalies and gold prospects furthermore the gold potential maps generated using wofe not only highlight or predict known areas of gold mineralization but also identify high potential areas where no known mineralization occurs a number of areas within the sgb have been identified as having high gold potential on many of the geochemical maps produced in this paper many of these areas coincide with areas of known gold mineralization however others are enigmatic and await follow up exploration

selection of coherent deposit type locations and their application in data driven mineral prospectivity mapping data driven prospectivity mapping can be undermined by dissimilarity in multivariate spatial data signatures of deposit type locations most cases of data driven prospectivity mapping however make use of training sets of randomly selected deposit type locations with the implicit assumption that they are coherent i e with similar multivariate spatial data signatures this study shows that the quality of data driven prospectivity mapping can be improved by using a training set of coherent deposit type locations analysis and selection of coherent deposit type locations was performed via logistic regression by using multiple sets of deposit occurrence favourability scores of univariate geoscience spatial data as independent variables and binary deposit occurrence scores as dependent variable the set of coherent deposit type locations and three sets of randomly selected deposit type locations were each used in data driven prospectivity mapping via application of evidential belief functions the prospectivity map based on the training set of coherent deposit type locations resulted in lower uncertainty better goodness of fit to the training set and better predictive capacity against a cross validation set of economic deposits of the type sought this study shows that explicit selection of training set of coherent deposit type locations should be applied in data driven prospectivity mapping