mapping geochemical anomalies related to fe polymetallic mineralization using the maximum margin metric learning method abstract geochemical anomaly identification is an important task in mineral exploration targeting this task can be regarded as a binary classification problem whereby the aim is to discriminate between anomalous and not anomalous i e background we can analyze geochemical data from the aspects of frequency distributions correlations and variances geometrical properties of geochemical anomalies and scale independence of geochemical patterns in this study we recognize geochemical anomalies based on the intrinsic relationship between geochemical elements which can be addressed by measuring their separation distance as a machine learning method metric learning aims at exploiting the statistical information between the geochemical features in limited training samples and developing a more suitable distance to evaluate the similarity of samples without priori distribution assumptions accordingly a metric learning method based on the maximum margin frame was applied to identify multivariate geochemical anomalies related to fe polymetallic mineralization in the southwestern fujian province of china the geochemical exploration data were firstly translated into a dimensional reduced subspace with the help of maximum margin metric learning mmml the adaptive coherence estimator ace detector from the field of target detection was then employed to identify geochemical anomalies the anomaly results obtained by this integrated procedure using a combination of mmml and ace were compared to those obtained by ace without metric learning using a receiver operating characteristic roc curve the area under the curve value implied superior performance using the combination of mmml and ace suggesting that this hybrid method can be effectively applied to recognize geochemical anomalies linked to mineralization

decomposing of mixed pattern of arsenic using fractal model in gangdese belt tibet china abstract decomposing mixed geochemical patterns is a challenge in geochemical exploration and environmental assessment in this paper the spectrum area technique s a is used to decompose a mixed pattern of arsenic in gangdese belt based on stream sediment data s a is a multifractal model based on power law relationships between area of the set consisting of wave numbers with spectral energy density above s a s on the 2d frequency domain the original spatial distribution map of arsenic obtained by inverse distance weighted idw shows a mixed pattern due to superposition of different geological processes or events and is converted into the frequency domain by means of fourier transformation two components including power spectrum density and phases are obtained the spectrum energy density s and the area a enclosed by the above threshold spectrum energy density is plotted on a log log scale two cutoff values determined by three straight lines define three filters which decompose the original map of arsenic into background anomalous and high frequency noise components the areas with high anomaly of arsenic mainly are located surrounding known cu deposits indicating that arsenic anomalies may be related to cu mineralization

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

lithospheric thinning during the evolution of continental large igneous provinces a case study from the north atlantic tertiary province lithospheric thickness can act as an important physical control on the composition of asthenosphere derived melts by restricting the minimum depth at which decompression melting can occur a case study of plume related tertiary lavas from the isle of mull scotland has revealed the presence of three successive magma types which become progressively more depleted in the incompatible trace elements geochemical modeling suggests that melting initially took place within the garnet iherzolite stability field but subsequently involved more extensive melting 10 of spinel iherzolite at shallower mantle depths these results can be explained in terms of a progressively thinning lithosphere beneath the region during the evolution of the volcanic center the observed degree of lithospheric thinning cannot be explained by extension alone and it appears that some relatively rapid lower lithospheric erosion by the plume head is also required theoretical modeling suggests that lithospheric erosion can be a comparatively rapid process and this has important implications for the various starting plume models

three dimensional modelling of alteration zones based on geochemical exploration data an interpretable machine learning approach via generalized additive models abstract the inference of deep alterations plays an important role in the analysis of deep geological processes and the targeting of buried mineral resources however the construction of three dimensional 3d models of alteration zones based on geochemical data is challenging due to the diverse geological processes and scarcity of information related to deep alterations in this paper we propose an interpretable machine learning method to infer 3d geological models of alteration zones based on geochemical data from the dayingezhuang area china to expose the information hidden in geochemical data that is indirectly and weakly related to alteration zones a generalized additive model gam is used it learns a nonlinear intelligible model associating geochemical anomalies extracted by pca with alteration features the model learned via gam and is then combined with a bayesian framework to infer the thickness of alterations in a no drilling area thus enabling 3d modelling of deep alteration zones with such an intelligible model geologists are capable of inspecting the reliability of the model and better understanding the association between the distribution of geochemical elements and deep alterations the inference results show that the relationship between geochemical anomalies and alteration depth is significant while the relationship with alteration thickness is complex the results of this study provide the underlying insights needed to guide the analysis of deep geological mineralization processes

vertical lithogeochemical halos and zoning vectors at goushfil zn pb deposit irankuh district southwestern isfahan iran implications for concealed ore exploration and genetic models abstract the vertical lithogeochemical halos of indicator elements in host rocks over a blind zn pb deposit are developed by upward migration of geochemical halos this may prove to be a useful exploration guide for targeting undiscovered zn pb mineral systems the main objective of this investigation is to assess the vertical distribution patterns of the composite lithogeochemical halos for detecting possible exploration guides as well as a possible genetic model of zn pb sulfide mineralization the goushfil zn pb deposit is one of the most important lower cretaceous carbonate and shale hosted deposit in the irankuh district west central iran the deposit contains about 4 3 million tonnes of sphalerite galena barite ore with an average grade of 8 zn and 2 4 pb in order to examine the exploration significance of the vertical lithogeochemical halos about 274 rock samples from 26 boreholes were sampled and analyzed by icp ms for a multi element package the results demonstrate that the highly anomalous values for ag 0 1 120 ppm as 3 1165 ppm ba 9 2820 ppm ca 0 07 25 cd 0 005 210 ppm hg 0 9 24 ppm mg 0 03 11 75 pb 15 15 000 ppm zn 65 15 000 ppm and sb 1 305 ppm are developed in faulted or fracture controlled hydrothermally dolomitized and jasperoid carbonates and shales the newly proposed multiphase composite geochemical halos defined by ratios of ag cd pb zn ag as pb zn ca mg pb zn sb as pb zn hg sb pb zn sb ba pb zn and ba ca pb zn correlate with three exploration zones at the average depth of 10 200 and 310 m above and below the main ore zone all the composite lithogeochemical halos in particular ag cd pb zn in both rock and soil samples tend to increase toward the shallow depths but decrease as they approach the main zn pb ore toward the deeper parts of the ore zone this geochemical response of the composite halos could be used for targeting undiscovered zn pb sulfide mineralization the low contents of cu and fe in the mineralized rocks indicate a low modal content of chalcopyrite and pyrite in the precursor sulfide ore which correlate with those of the mississippi valley type mvt zn pb deposits this is also highlighted on the log pb zn pb pb zn cu pb zn cu and homogenization temperature salinity variodiagrams on which the goushfil data plot close to the mvt type zn pb mineralization

a comparative study of two modes for mapping felsic intrusions using geoinformatics abstract identifying felsic intrusions is an essential task in support of mineral exploration because the intrusions can be a source of energy and metals for magmatic hydrothermal mineralization in this paper two models for mapping felsic intrusions are compared based on regional geochemical and geophysical data geochemical data as a type of compositional data which carry relative information should be preprocessed using log ratio transformation the first model a factor ratio f2 f1 model was developed based on the chemical characteristics of the felsic intrusions which are rich in k2o and high field strength elements f2 but poor in fe2o3 and compatible elements f1 the second model a hybrid model that combines principal component analysis and local singularity analysis was based on the chemical and physical properties of the felsic intrusions the results showed that 1 raw geochemical data should be processed using log ratio transformation prior to multivariate data analysis to avoid spurious correlations between variables and 2 the hybrid model performed better than the ratio of factors model for inferring felsic intrusions in the study area the felsic intrusions mapped in this study provide information that can support further mineral exploration in the dong ujimqin fe cu polymetallic district inner mongolia northern china

sensitivity analysis of prospectivity modeling to evidence maps enhancing success of targeting for epithermal gold takab district nw iran abstract the takab metallogenic province in the northwestern iran hosts a number of gold resources including carline like and epithermal type mineralization these occurrences are hosted by tectonized country rocks of precambrian basement metamorphic rocks and tertiary volcanic and sedimentary units which are intruded by the intrusion of probable age of eocene and the sub volcanic domes of miocene age plausible mineralized zones in this high potential area can be delimited based on mineral prospectivity maps during the regional exploration surveys however the success of mineral prospectivity mapping mpm is always plagued by different types of uncertainties stochastic and systemic the main aim of this study is to reduce those uncertainties resulting from a the imprecise incorrect selection of targeting criteria b adverse effects of using inefficient or least efficient evidence maps and c employing an integration methodology which suffers from user interference in this regard the first case was modulated through the precise identification and selection of controls on mineralization as well as ore forming processes the second case was declined by the sensitivity analysis of input geochemical geological and structural parameters to mpm using the area under the receiver operating characteristics roc curve and the third case was controlled by incorporation of genetic algorithm ga and artificial neural networks here mlp ann as a suitable data driven mpm method through sensitivity analysis and using mlp ga ann and mlp ann algorithms various prospectivity models were generated and compared the results of prediction rate curves demonstrated that the exclusion of poor evidence maps and that employing a self adapted data driven approach e g mlp ga ann can significantly reduce the systematic uncertainty in mapping of mineral prospectivity accordingly the superior model was then selected for delineating efficient exploration targets

gap winds and wakes sar observations and numerical simulations the nature of terrain induced gap winds and wakes in the atmosphere is examined using surface wind data from synthetic aperture radar sar and the shallow water equations the shallow water model is used to predict the types of wake jet wind patterns that might occur behind an idealized pair of bell shaped hills with a gap between them a regime diagram is constructed based on the width of the gap and the upstream froude number specific predictions of the model are found to compare moderately well with sar data from four examples of airflow near unimak island in the aleutian chain the model predicts the observed wakes and jets including jets that exceed the upstream speed theoretical analysis considers the relative importance of rising terrain and narrowing valley walls in the acceleration of gap winds wind speeds in the wake region are controlled by the bernoulli function and regional pressure gap winds therefore are streams of air that have avoided bernoulli loss over the terrain by passing through gaps the speed of gap winds can exceed the upstream speed only in ridgelike situations when the regional leeside pressure is lower than the upstream pressure

causes and consequences of protracted melting of the mid crust exposed in the north himalayan antiform gneiss domes exposed by the north himalayan antiform in southern tibet provide evidence for protracted melting of the mid crust during convergent tectonics anatexis was initiated during underthrusting and recurred during the southwards extrusion of a low viscosity crustal sheet sr nd isotope systematics establish that the cores of the domes dominated by cambrian gneiss form a window of the high himalayan crystalline series hhcs indian plate combined trace element and isotopic analyses from 4 two mica granites that intrude both core and the metasedimentary mantle of the domes indicate an origin from melting of the high himalayan crystalline series by the incongruent breakdown of muscovite and to a lesser extent biotite at temperatures from 680 to 760 c u pb dating of accessory phases extends the known period of granite magmatism from the late oligocene to mid miocene a ca rich garnet bearing leucogranite of oligocene age 27 5 ma provides a rare insight into the pre miocene history of the underthrust indian plate reflecting prograde melting at greater depths during a period of crustal thickening the origin of the miocene granites 15 10 ma can be modeled from the exhumation of an extruding channel at a rate of ca 1 mm year constrained by ar isotope data melting over a protracted time scale along the leading edge of the indian plate less than 50 km from the suture accelerated horizontal shortening within the collision zone and provided a positive feedback mechanism between magmagenesis and deformation

exploring uni element geochemical data under a compositional perspective abstract different features of geochemical information were studied by comparing spatial distribution of concentration values and compositional data values geochemical data are compositional and should be treated as such to avoid spurious correlations and misleading interpretations however geochemists are also interested to discuss in terms of elemental concentrations in this work the spatial distribution of fe mn ti co cr ni and v based on 3535 topsoil samples collected in campania region southern italy and analysed by icp ms after aqua regia digestion is studied unielement maps and coda based maps namely of ilr transformed data and of two subcompositions of 3 components have been produced and interpreted results show that the ilr maps often show different geochemical patterns from those provided by the maps based on raw concentrations namely for v fe and co this is not surprising as each studied ilr is a log ratio of an element against the others and account for the compositional variability nevertheless the geochemical patterns of both raw and ilr based maps relate mostly with the geolithological features of the region 1 ti ni cr log ratio variables are the best pathfinder in differentiating between volcanic relative enrichment in ti and non volcanic relative enrichment in ni and cr areas 2 soil alteration phenomena could locally enhance log ratios of ti due its high geochemical stability 3 the spatial analysis of ilr fe and ilr mn variables amplifies their relative degree of enrichment in correspondence of silici clastic formations suggesting that mn fe oxides of clay minerals mainly dominate the geochemical composition of the soils of the survey area 4 local enrichments of cr and ni at the main rivers mouths and in the metropolitan areas of naples and salerno possibly of anthropogenic origin are highlighted in the 3 part subcomposition analysis the developed exploration methodology of uni element geochemical data under a compositional perspective leads to deeper insight and the gain is a more accurate interpretation of processes controlling soils geochemical variability

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

application of the tectono geochemistry method to mineral prospectivity mapping a case study of the gaosong tin polymetallic deposit gejiu district sw china abstract the tectono geochemistry method as a lithogeochemical exploration tool is a process centric approach based on the premise that element migration and concentration within and adjacent to geological structures are controlled by large scale dynamic earth processes that operate on a variety of scales to focus mass and energy flux here we present a case study of the gaosong tin polymetallic deposit gejiu district sw china illustrating how the tectono geochemistry method can be applied to mineral prospectivity mapping as a first step 2216 fault rock samples collected within the geiju district were assayed followed by a detailed examination of the assay results by means of factor analysis and multifractal singularity mapping the main aims of these analyses were to 1 statistically explore the data with respect to specific element concentrations associations and geochemical patterns by which the fault rock samples can be grouped 2 better characterize the samples in terms of whether or not the rocks recorded any evidence for hydrothermal mineralization processes and 3 identify any geochemical anomalies that may present vectors to buried ore the results illustrate that element distribution patterns are greatly influenced by fault permeability and that ne sw striking faults are the most favorable in terms of concentration of ore elements factor analysis greatly assisted the identification and interpretation of for example element associations and geochemical zonation patterns genetically related to intrusions recognition of singularities was of particular importance with respect to identifying and delineating primary fault tectono geochemical anomalies that may be caused by buried ore of particular interest are low singularity values as these correspond with positive geochemical anomalies over known ore deposits in the gejiu district anomalies delineated by local singularity exponents may represent undiscovered ore and thus warrant further exploration

geochemical metallogenic potential based on cluster analysis a new method to extract valuable information for mineral exploration from geochemical data abstract geochemical data are widely regarded as valuable for mineral exploration because they can be used to recognize ore related geochemical anomalies many techniques have been used to identify geochemical anomalies within geochemical datasets but most of these techniques focus on the concentration or fractal characteristics of one or a combination of indicator element s indicator elements for a particular type of deposit are selected based on expert knowledge but this approach is subjective and valuable information associated with the elements that are not selected is lost this study describes a new method that maximize the extraction of valuable information from all elements available in a geochemical dataset the technique involves geochemical metallogenic potential mapping based on cluster analysis gmpm ca which enables the identification of prospective areas suitable for further mineral exploration the results show that gmpm ca can produce a map of mineralization potential with excellent predictive capacity furthermore gmpm ca is a practical method that does not require expert geological or geochemical knowledge and can be integrated with existing geochemical anomaly identification methods

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

an application of exploratory data analysis eda as a robust non parametric technique for geochemical mapping in a semi arid climate abstract exploratory data analysis eda techniques based on the boxplot and robust class selection were applied to the analysis of single element stream sediment data in the collo area n e algeria the area is characterised by many factors that affect data variability variation of lithology combined existence of permanent and ephemeral streams flash floods rugged terrain and climate the boxplot proved to be very useful in capturing the empirical data distribution the skewness and in defining outliers no data transformation was needed prior to the analysis of single element distributions cr pb zn cu as and fe as is the case in classical statistics geochemical mapping of these elements was based on resistant class selection as defined by the boxplot results showed the close spatial correlation of outlier data for cr with a plagioclase lherzolite intrusion and known chromite pods the geochemical maps of pb zn cu and as concentrations showed an association of these elements coincident with known base metal sulphides and arsenopyrite mineralisation delineating a northeastern anomaly spreading well over known mineralisation the choice of the robust classes based on the boxplot also showed the close spatial distribution of fe with known hematite and magnetite mineralization eda techniques proved to be very useful in delineating known mineralisation in the collo area where stream sediment data is subject to variability owing to many factors geologic physiographic and climatic eda proved to be a simple and very useful tool in analysing single element geochemical data eda could be used in similar terrains as an alternative to the classical methods where a normality precondition is needed prior to analysis and where class selection may be affected by the presence of wild data

anomaly threshold estimation and data normalization using eda statistics application to lithogeochemical exploration in lower cretaceous zn pb carbonate hosted deposits northern spain abstract a lithogeochemical survey of lower cretaceous sediments 1293 samples in the basque cantabrian basin northern spain was carried out in order to estimate the mean contents of major oxides and ba co cu ni pb rb s sr v zn and zr in different lithological subsets and to identify anomalies related with zn pb carbonate hosted mineralization after a detailed evaluation of different anomaly recognition methods using both real and synthetic data the cut off values used in the exploratory data analysis eda were selected as thresholds a prior classification of the rocks based on chemical mineralogical and petrographical data guarantees appropriate homogeneous with respect to major oxides rock groups during the evaluation of the data a data standardization method was developed and applied to the samples collected from the carranza sector n 330 zinc and pb values for each sample were normalized to the particular threshold and interquartile range of their corresponding rock type these normalized values were plotted in geochemical maps the results reveal the presence of zn up to 0 6 and pb max 1380 ppm anomalies concentrated in carbonate facies mainly in limestones dolostones and dolomitic limestones magnesium rich carbonates host the most significant anomalies in the carranza area the great majority of outliers occur around known zn pb mineral occurrences and are concentrated at the edge of the carbonate platform in some cases fault control of the anomalies is indicated

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

compositional data analysis in the study of integrated geochemical anomalies associated with mineralization abstract geochemical data are typical compositional data which should be opened prior to univariate and multivariate data analysis in this study a frequency based method robust principal component analysis rpca and a frequency space based method spectrum area fractal model s a are applied to explore the effects of the data closure problem and to study the integrated geochemical anomalies associated with polymetallic cu mineralization using a stream sediment geochemical dataset collected from the zhongteng district fujian province china the results show that 1 geochemical data should be opened prior to rpca to avoid spurious correlation between variables 2 geochemical pattern is a superimposition of multi processes and should be decomposed and 3 the s a fractal model is a powerful tool for decomposing the mixed geochemical pattern

detecting subtle alteration information from aster data using a multifractal based method a case study from wuliang mountain sw china abstract remote sensing has been widely used to interpret hydrothermal alteration zones and it can support the geological field mapping which is very useful for mineral exploration in inaccessible regions however the alteration information in covered terrains is usually not strong enough to be detected using traditional remote sensing methods so how to efficiently detect subtle alteration information remains a challenging task in this study the multifractal theory based spectrum area s a method is used for the processing of remote sensing data and the new method of principal component analysis pca s a is proposed as a tool to interpret hydrothermal alteration beneath covered areas in order to test the efficiency of this method the pca s a method was compared with the traditionally used pca method based on advanced spaceborne thermal emission and reflection radiometer aster data the wuliang mountain in the yunnan province of sw china a rugged terrain with high altitudes and dense vegetation coverage was selected as a case study to detect information on chlorite epidote biotite and muscovite alteration respectively the following field survey and petrographic studies reveal that 1 the average detection accuracy of the pca s a method is 90 80 9 34 higher than that of the pca method 2 in the covered areas where the traditional pca method cannot detect any subtle hydrothermal alteration the pca s a method can be successfully applied and 3 in those areas where the fractional vegetation cover fvc is greater than 0 8 the detection of subtle hydrothermal alteration using the proposed method is inefficient which requires further studies

early cretaceous 140 ma aluminous a type granites in the tethyan himalaya tibet products of crust mantle interaction during lithospheric extension a type granites have been the focus of considerable research due to their distinctive major and trace element signatures and tectonic significance however their petrogenesis magmatic source and tectonic setting remain controversial particularly for aluminous a type granites the earliest cretaceous ca 140 ma comei granite in the eastern tethyan himalaya is associated with coeval oceanic island basalt oib type mafic lava and has a type granite geochemical characteristics including high 10 000 ga al up to 6 feototal mgo 4 6 6 1 and na2o k2o al2o3 0 50 0 61 ratios but low cao 0 6 1 6 wt and na2o 1 8 2 6 wt contents the comei granite also has variable peraluminous compositions a cnk 1 00 1 36 along with zircon 18o end t and initial 87sr 86sr values of 8 2 to 9 3 13 0 to 12 4 and 0 7238 to 0 7295 respectively this range of compositions can be interpreted as the interaction between high temperature upwelling oib type basaltic magmas and a shallow crustal 5 kbar metapelitic source the comei granite and coeval oib type basaltic rock could represent the earliest stage 145 140 ma of a large igneous event in eastern tethyan himalaya which may well have been triggered by pre breakup lithospheric extension prior to the arrival of the kerguelen plume head

paleocene eocene record of ophiolite obduction and initial india asia collision south central tibet 1 uppermost cretaceous to eocene marine sedimentary sequences occur both to the south and north of the yarlung zangbo suture in south central tibet they consist of indian margin strata of the northern tethyan himalaya and asian margin strata of the gangdese forearc both assemblages are characterized by major changes in depositional environment and sedimentary provenance at 65 ma and an appearance of detrital chromium rich spinel of ophiolite affinity tio2 generally 0 1 wt during the paleocene ophiolitic melange exposed along the suture could have provided a source for detrital spinel the melange occurs in the hanging wall of a north dipping south directed mylonitic shear zone which includes a tectonic sliver of mafic schist amphibole from the schist yields 40ar 39ar ages of 63 ma which we attribute to cooling during slip along the shear zone and southward obduction of the melange melange obduction was coeval with the development of an angular unconformity within the gangdese forearc basin to the north between late maastrichtian time and 62 ma upper paleocene to middle eocene sandstones in the northern tethyan himalaya yield 200 120 ma u pb detrital zircon ages and 190 170 ma 40ar 39ar detrital mica ages these detrital grains were most likely sourced from regions north of the yarlung zangbo suture suggesting that onset of india asia collision in south central tibet is middle eocene or older in age collectively our results support previous suggestions that oceanic rocks were obducted onto the northern margin of india during latest cretaceous earliest tertiary time coeval changes in gangdese forearc sedimentation raise the possibility that this obduction event marks onset of tectonic interaction between india and asia at 65 ma alternatively in concert with the conventional view of eocene collision initiation the obducted oceanic rocks may be of intraoceanic origin while coeval changes in gangdese forearc sedimentation may be a consequence of an increase in the rate of ocean continent convergence following the demise of the intraoceanic subduction zone

multifractal idw interpolation and fractal filtering method in environmental studies an application on regional stream sediments of italy campania region in recent years environmental geochemical mapping has assumed an increasing relevance and separation of background values to evaluate pollution is probably even more critical than the separation between background and anomalies in mineral prospecting studies the recognition of background values assumes particular relevance as a function of national environmental legislation which fixes intervention limits for some elements such as the harmful ones e g as cd hg pb in this paper a recently developed multifractal idw interpolation method and a fractal filtering technique are applied to separate natural background and anthropogenic values for the compilation of environmental geochemical mapping from stream sediment samples of campania region italy where no mineralization occurs to discuss the application of these recently developed techniques the elements pb and u were selected because they show two completely different situations the high pb values being mostly of anthropogenic origin and high u values being mostly of geogenic origin the new fractal filtering method works well in both extreme situations

a comparison study of the c a and s a models with singularity analysis to identify geochemical anomalies in covered areas abstract fractal multifractal modeling of geochemical data is an interesting topic in the field of applied geochemistry identification of weak anomalies for mineral exploration in covered areas is one of the most challenging tasks for utilization of geochemical data in this study three fractal models consisting of the concentration area c a spectrum area s a and singularity index models were applied to identify geochemical anomalies in the covered area located in the chaobuleng fe polymetallic district inner mongolia china the results show that 1 the grassland cover weakens the concentrations of geochemical elements 2 the c a model has a limitation to identify weak anomalies in covered areas 3 the s a model is a powerful tool to decompose mixed geochemical patterns into a geochemical anomaly map and a varied geochemical background map but suffers edge effects in an irregular shaped study area and 4 the singularity index is a useful tool to identify weak geochemical anomalies

evaluation of uncertainty in mineral prospectivity mapping due to missing evidence a case study with skarn type fe deposits in southwestern fujian province china in this paper the southwestern fujian metallogenic belt one of the important fe polymetallic belts in southern china was chosen as a case study area to evaluate the uncertainty due to missing evidence in mineral prospectivity mapping four geological features were considered important for mineral prospectivity mapping based on the geological model for skarn deposits in the belt 1 the yanshanian granitic intrusions because they provided energy fluids and part of the metal budget 2 faults because they served as pathways for hydrothermal fluids 3 the carboniferous permian carbonate sequences because they supplied part of the metal budget and served as host rocks for ore deposition and 4 geochemical anomalies because they indicate presence of skarn type alteration and mineralization four separate predictive evidence layers depicting each the above geological features were extracted from relevant geoscience data and were integrated using a modified fuzzy weights of evidence model which retains the advantages of both fuzzy weights of evidence and logistic regression modeling the results show that most of the known fe deposits occur in or near and thus have strong correlation with areas of high posterior probabilities as indicated by the delineated prospective areas that occupy only 4 6 of the studied region but contain 88 5 of the total number of known fe deposits different combinations of predictive evidence layers were used to examine prediction uncertainty related to missing evidence plots of accumulative number of fe deposits versus accumulative prospective areas show that the order of the most to the least important evidence of mineral prospectivity in the studied region is favorable rock types geochemical anomalies intrusive rocks faults results of blind testing the prospectivity models indicate that the geological model of fe mineralization in the belt is suitable for predicting exploration target areas for skarn type fe deposits and suggest that the highest risk in follow up exploration is related to sequences of carbonates in the carboniferous permian formations that were likely either not mapped or not represented at the present regional scale of mapping

exploratory and spatial data analysis eda sda for determining regional background levels and anomalies of potentially toxic elements in soils from catorce matehuala mexico abstract the threshold between geochemical background and anomalies can be influenced by the methodology selected for its estimation environmental evaluations particularly those conducted in mineralized areas must consider this when trying to determinate the natural geochemical status of a study area quantifying human impacts or establishing soil restoration values for contaminated sites some methods in environmental geochemistry incorporate the premise that anomalies natural or anthropogenic and background data are characterized by their own probabilistic distributions one of these methods uses exploratory data analysis eda on regional geochemical data sets coupled with a geographic information system gis to spatially understand the processes that influence the geochemical landscape in a technique that can be called a spatial data analysis sda this eda sda methodology was used to establish the regional background range from the area of catorce matehuala in north central mexico probability plots of the data particularly for those areas affected by human activities show that the regional geochemical background population is composed of smaller subpopulations associated with factors such as soil type and parent material this paper demonstrates that the eda sda method offers more certainty in defining thresholds between geochemical background and anomaly than a numeric technique making it a useful tool for regional geochemical landscape analysis and environmental geochemistry studies

a type granites in northeastern china age and geochemical constraints on their petrogenesis abstract a type granites are widely distributed in northeastern china ne china they were emplaced during three major episodes the permian late triassic to early jurassic and early cretaceous and evolved in different tectonic regimes according to their mineralogical and geochemical characteristics two subgroups of a type granites aluminous and peralkaline can be recognized the peralkaline subgroup contains alkali mafic minerals such as riebeckite arfvedsonite and sodic pyroxene while the aluminous subgroup contains annite and fe rich calcic or sodic calcic amphibole with respect to the aluminous subgroup the peralkaline granites contain higher rb ga and total rare earth elements ree but lower mgo cao al 2 o 3 ba and sr based on the discrimination criteria of eby geology 20 1992 641 the permian and late triassic to early jurassic a type granites belong to the a 2 post orogenic type whereas the early cretaceous granites are of the a 1 anorogenic type nd isotopic compositions of these a type granites indicate their derivation from a dominantly juvenile crustal source their origin is thought to have involved partial melting of an underplated lower crustal source because the generation of a type granites requires high melting temperature we propose models involving slab break off lithospheric delamination and extension the permian a type granites have the same age range as those in eastern junggar southern mongolia and central inner mongolia they occur along a major suture and form a narrow belt between the north china and siberian cratons we suggest that their formation was associated with post collisional slab break off the late triassic to early jurassic a type granites are likely to be the product of lithospheric delamination after the final collision of the major crustal blocks in the late paleozoic to early triassic the early cretaceous a type granites have an anorogenic affinity and were possibly associated with rifting in eastern china at this time associated with the onset of paleo pacific subduction consequently we conclude that the a type granites in ne china were generated at three different times involving multiple processes operative in different tectonic environments

outlining of high quality coking coal by concentration volume fractal model and turning bands simulation in east parvadeh coal deposit central iran abstract this study aims at identifying the proper parts of c 1 and b 2 coking coal seams in the north block of east parvadeh coal deposit central iran using the concentration volume c v fractal modeling according to sulfur and ash values which were calculated by turning bands conditional simulation the c v log log plots were generated based on results of 100 realizations derived via turning bands simulation which show seven different geochemical populations for both sulfur and ash data in b 2 seam which has a relatively good quality for coking coal with sulfur and ash values lower than 1 548 and 6 39 respectively additionally c v log log plots indicate that there are seven and six for sulfur and ash geochemical populations in c 1 seam containing a proper coal quality with respect to sulfur and ash values less than 1 41 and 6 92 respectively high quality populations are located in the northern and western parts of the studied area which correlated with usgs standard the logratio matrix was used for the correlation between results obtained by the c v fractal modeling and geological particulars consisting of pyritic veins and ash coals based on the logratio matrix for sulfur values higher than 3 55 and 3 39 for c 1 and b 2 respectively low quality parts of the seams have good correlation with pyritic veins in the eastern and central parts of the area moreover there are high values of overall accuracy oa for correlation between parts of the seams with high values of ash which are 47 86 and 39 81 for c 1 and b 2 respectively and ash coals obtained by geological data