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Current Science 2011 Mar; 100(5)
High fluoride incidence in groundwater and its potential health effects in parts of Raigarh District, Chhattisgarh, India.
High concentrations of fluoride (F–) in drinking water are harmful to human health. Knowledge of spatiotemporal distribution of F– content in groundwater is thus a prerequisite for taking preventive measures. This communication reports F– incidence i... expand abstractn groundwater and its relation with the prevalence of fluorosis in Tamnar area, Raigarh District, Chhattisgarh, India. Nearly 18% of the sampled wells had F– concentrations above the desirable limit (>1.0 mg/l), the highest value being 8.8 mg/l. High F– concentrations primarily occurred in coal-bearing Barakar Formation of the Gondwana Supergroup. Prevalence of dental fluorosis was observed in five villages, viz. Dholnara, Kunjhemura, Muragaon, Pata and Saraitola; whereas skeletal fluorosis was found to occur only in Muragaon. The spatial distribution of F– in groundwater, as indicated by hydrogeochemical analyses, corroborated well with the prevalence of dental and skeletal fluorosis. It is envisaged that, in addition to the people already affected, a large fraction of the population in the area is at potential risk, especially considering that the region falls in the coal mining and industrial belt. The health-risk map prepared using a Geographic Information System provides baseline information in taking mitigation measures. collapse abstract
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Resource Geology 2011 Jan; 61(1)
From Predictive Mapping of Mineral Prospectivity to Quantitative Estimation of Number of Undiscovered Prospects
This paper proposes that the spatial pattern of known prospects of the deposit-type sought is the key to link predictive mapping of mineral prospectivity (PMMP) and quantitative mineral resource assessment (QMRA). This proposition is demonstrated by ... expand abstractPMMP for hydrothermal Au-Cu deposits (HACD) and by estimating the number of undiscovered prospects for HACD in Catanduanes Island (Philippines). The results of analyses of the spatial pattern of known prospects of HACD and their spatial associations with geological features are consistent with existing knowledge of geological controls on hydrothermal Au-Cu mineralization in the island and elsewhere, and are used to define spatial recognition criteria of regional-scale prospectivity for HACD. Integration of layers of evidence representing the spatial recognition criteria of prospectivity via application of data-driven evidential belief functions results in a map of prospective areas occupying 20% of the island with fitting- and prediction-rates of 76% and 70%, respectively. The predictive map of prospective areas and a proxy measure for degrees of exploration based on the spatial pattern of known prospects of HACD were used in one-level prediction of undiscovered mineral endowment, which yielded estimates of 79 to 112 undiscovered prospects of HACD. Application of radial-density fractal analysis of the spatial pattern of known prospects of HACD results in an estimate of 113 undiscovered prospects of HACD. Thus, the results of the study support the proposition that PMMP can be a part of QMRA if the spatial pattern of discovered prospects of the deposit-type sought is considered in both PMMP and QMRA. collapse abstract
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Earth Surface Processes and Landforms 2010 Dec; 35(15)
Rock slope instability assessment using spatially distributed structural orientation data in Darjeeling Himalaya (India)
We discuss a geographic information system (GIS)-based methodology for rock slope instability assessment based on geometrical relationships between topographic slopes and structural discontinuities in rocks. The methodology involves (a) regionalizati... expand abstracton of point observations of orientations (azimuth and dip) of structural discontinuities in rocks in order to generate a digital structural model (DStM), (b) testing the kinematical possibility of specific modes of rock slope failures by integrating DStMs and digital elevation model (DEM)-derived slope and aspect data and (c) computation of stability scenarios with respect to identified rock slope failure modes. We tested the methodology in an area of 90 km2 in Darjeeling Himalaya (India) and in a small portion (9 km2) within this area with higher density of field structural orientation data. The results of the study show better classification of rock slope instability in the smaller area with respect to known occurrences of deep-seated rockslides than with respect to shallow translational rockslides, implying that structural control is more important for deep-seated rockslides than for shallow translational rockslides. Results of scenario-based analysis show that, in rock slopes classified to be unstable, stress-induced rock slope instability tends to increase with increasing level of water saturation. The study demonstrates the usefulness of spatially distributed data of orientations of structural discontinuities in rocks for medium- to small-scale classification of rock slope instability in mountainous terrains. collapse abstract
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Computers & Geosciences 2010 Dec; 36(12)
Development of a controlled vocabulary for semantic interoperability of mineral exploration geodata for mining projects
Semantic interoperability of mineral exploration geodata is a long-term concern in mining projects. Inconsistent conceptual schemas and heterogeneous professional terms among various geodata sources in a mining project often hinder their efficient us... expand abstracte and/or reuse. Our study of a controlled vocabulary focuses on interoperability of mineral exploration geodata of different mining projects of a mining group in China. In order to achieve this purpose, a proper representation of concepts and their inter-relationships in the knowledge domain of mineral exploration for mining projects is proposed. In addition, we propose that for wider interoperability of mining project geodata the controlled vocabulary underpinning them should be interoperable with concepts in related applications in the mineral exploration domain. In developing our controlled vocabulary, we adopted/adapted national standards of geosciences taxonomies and terminologies. The organization structure of terms, coding method, metadata schema for database applications and an extensible structure of our controlled vocabulary are discussed. The controlled vocabulary we developed was then used to reconcile heterogeneous geodata and to set up integrated databases for various mining projects of the mining group. Our study shows that a properly organized controlled vocabulary not only allows for efficient reconciliation of heterogeneous geodata sources in similar or related projects, but also makes related geodata to be interoperable with extramural applications in the same knowledge domain. collapse abstract
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Ore Geology Reviews 2010 Nov; 38(3)
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... expand abstract 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. collapse abstract
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Geochemistry: Exploration, Environment, Analysis 2010 Nov; 10(4)
Catchment basin modelling of stream sediment anomalies revisited: Incorporation of EDA and fractal analysis
This paper revisits catchment basin modelling of stream sediment geochemical anomalies with regard to two aspects: (1) standardization of uni-element residuals derived from analysis of a number of subsets of stream sediment geochemical data in order ... expand abstractto obtain a single set of uni-element residuals for classification of anomalies; and (2) objective classification of anomalies in dilution-corrected uni-element residuals and in derivative scores representing multi-element associations. These two aspects of catchment basin modelling of stream sediment geochemical anomalies were examined in the Aroroy epithermal-Au district (Philippines). For the first aspect, the results of the case study show that, for the standardization of dilution-corrected uni-element residuals per data subset in order to derive a single set of dilution-corrected uni-element residuals for classification of anomalies, the application of robust statistics in exploratory data analysis is preferable to the application of classical statistics in confirmatory data analysis. For the second aspect, the results of the case study show that anomalies in standardized dilution-corrected uni-element residuals and in derivative scores representing multi-element associations can be identified objectively by application of the concentration-area fractal analysis. The results of the case study further show that the area of individual sample catchment basins is useful in GIS-based screening of significant anomalies by integrating derivative geochemical variables with fault/ fracture density, which was estimated as the ratio of number of pixels representing faults/fractures in a sample catchment basin to number of pixels in the same sample catchment basin. collapse abstract
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Geomorphology 2010 Oct; 122(1-2)
Spatial analysis of mutual fault/fracture and slope controls on rocksliding in Darjeeling Himalaya, India
In this paper, the Fry analysis was applied to study the spatial patterns (in terms of trends) of rockslides; proportion analysis was applied to study the spatial associations between rockslides and slope aspects; and distance distribution analysis w... expand abstractas applied to study the spatial associations of rockslides with different sets of faults/fractures based on trends. In a study area in the Darjeeling district (India), the results of applications of these spatial analytical techniques support a proposition of mutual fault/fracture and slope controls on rocksliding. In different parts of the study area, deep-seated rockslides are associated with (a) NE-trending faults/fractures and SSE-facing slopes, (b) NW-trending faults/fractures and ENE-facing slopes, and (c) NNE-trending faults/fractures and SE- or ENE-facing slopes; whereas shallow translational rockslides are associated with (a) NNE-trending faults/fractures and SE-, NW-, WNW- or WSW-facing slopes, (b) WNW-trending faults/fractures and SW-facing slopes, (c) NNW-trending faults/fractures and ESE- or SW-facing slopes, and (d) NW-trending faults/fractures with SW-facing slopes. Creating and integrating spatial evidence layers representing mutual fault/fracture and slope controls on rocksliding can be achieved satisfactorily via application of evidential belief functions. A predictive map of rockslide susceptibility derived by using slope aspects, slope inclinations and proximity to the faults/fractures that are spatially associated with rockslides is superior to that derives by using slope aspects, slope inclinations and proximity to all faults/fractures. The proposed analytical methods are suitable for first-pass regional-scale assessment of rockslide susceptibility. collapse abstract
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Computers & Geosciences 2010 Jul; 36(7)
Algorithms for multi-parameter constrained compositing of borehole assay intervals from economic aspects
Compositing of borehole assay intervals based on economic aspects is a primary step when the cross-sectional method is applied in orebody modelling and mineral resources estimation. The compositing is important because the resulting ore composites ev... expand abstractentually determine the outlines of orebody models. However, numerous boreholes and borehole intervals make ore compositing tedious and time-consuming for manual work. A computer program for compositing is desirable to facilitate the task and to obtain accurate results. In the design of computer algorithms for such a computer program, dilution is the most difficult part because dilution means adding waste intervals into an ore composite in order to transfer it from unminable to minable and this causes some special situations in a compositing procedure. In order to obtain economically optimized compositing results, we paid special attention to dilution in the designed algorithms. A demo program has been developed to test and implement these algorithms using borehole assay datasets from a mine site in China. Results show the accuracy of designed computer algorithms and the feasibility of applying a computer program in compositing of borehole assay intervals. collapse abstract
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Resource Geology 2010 May; 60(2)
Improved Wildcat Modelling of Mineral Prospectivity
Wildcat modelling of mineral prospectivity has been proposed for greenfields geologically-permissive terranes where mineral targets have not yet been discovered but a geological map is available as a source of spatial data of predictors of mineral pr... expand abstractospectivity. This paper (i) revisits the initial way of assigning wildcat scores (Sc) to predictors of mineral prospectivity and (ii) proposes an improvement by transforming Sc into improved wildcat scores (ISc) by using a logistic function. This was shown in wildcat modelling of prospectivity for low-sulphidation epithermal-Au (LSEG) deposits in Aroroy district (Philippines). Based on knowledge of characteristics of and controls on LSEG mineralization in the Philippines, the spatial predictors of LSEG prospectivity used in the study are proximity to porphyry plutonic stocks, faults/fractures and fault/fracture intersections. The Sc and ISc of spatial predictors are input separately to principal components analysis to extract a favourability function that can be interpreted as a wildcat model of LSEG prospectivity. The predictive capacity of the wildcat model of LSEG prospectivity based on the ISc of geological predictors is roughly 70% higher than that of the wildcat model of LSEG prospectivity based on the Sc of geological predictors. A slight increase of predictive capacity of wildcat modelling of LSEG prospectivity is also achieved when the ISc of geological predictors are integrated with the ISc of geochemical anomalies, but not with the Sc of geochemical anomalies. The proposed improvement is significant because if the study district were a greenfields exploration area, then a wildcat model of LSEG prospectivity based on the old wildcat methodology would have caused several LSEG targets to be missed. collapse abstract
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Geochemistry: Exploration, Environment, Analysis 2010 May; 10(2)
Mapping of anomalies in continuous and discrete fields of stream sediment geochemical landscapes
In this study, continuous field models of geochemical landscapes were obtained by interpolating stream sediment geochemical data while discrete field models of geochemical landscapes were obtained by attributing stream sediment geochemical data to th... expand abstracteir sample catchment basins. This study aimed to: (1) compare and contrast anomaly maps derived from continuous and discrete field models of stream sediment geochemical landscapes; and (2) determine which empirical frequency distributions - those of original point data or those of pixels values in models of stream sediment geochemical landscapes - are more useful in mapping of anomalies in such geochemical landscapes. Anomalies were mapped by using the mean+2SDEV (standard deviation), median+2MAD (median absolute deviation) and concentration-area (C-A) fractal methods of identifying threshold values in a geochemical data set. The results of the study in the Aroroy gold district (Philippines) highlight the following findings. In mapping of anomalies in either continuous or discrete field models of stream sediment geochemical landscapes, the C-A fractal method performs best, followed by the median+2MAD method and then by the mean+2SDEV method. Anomalies mapped in discrete field models, compared to anomalies mapped in continuous field models, of stream sediment geochemical landscapes mostly have stronger positive spatial associations with the known epithermal Au deposit occurrences in the study area. Empirical frequency distributions of either the original point data or the pixels values in the models of stream sediment geochemical landscapes are similarly useful in applying the C-A fractal method, but not in applying either the median+2MAD or mean+2SDEV method, to map anomalies in either continuous or discrete field models of such geochemical landscapes. collapse abstract
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Journal of the Geological Society of India 2009 Nov; 74(5)
A quantitative approach for improving the BIS (Indian) method of medium-scale landslide susceptibility
In India, the Bureau of Indian Standards (BIS) recommends a heuristic method for medium-scale (1:25,000/1:50,000) landslide susceptibility mapping. This is based on fixed ratings of geofactors, without the inclusion of landslide inventory information... expand abstract. In BIS method, the pre-defined ratings of geofactors are applied over diverse areas, irrespective of the terrain-specific spatial inter-dependence of geofactors and landslide types, which leads to rather moderate prediction. In this paper, we evaluate the effectiveness of the existing BIS method in Darjeeling Himalaya through a quantitative method adapting weights of evidence (WofE) modeling. The quantified spatial associations between specific geofactors for different landslide types and failure mechanisms that were generated, using this method showed improved prediction rates as compared to the BIS method of fixed ratings of geofactors. We therefore recommend adjusting the existing BIS guidelines by inclusions of weights, derived locally through quantitative spatial analysis of landslide inventories and geofactor maps. collapse abstract
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Mineralium Deposita 2009 Nov; 44(8)
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 in... expand abstracttersections 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. collapse abstract
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Computers & Geosciences 2009 Oct; 35(10)
Objective selection of suitable unit cell size in data-driven modeling of mineral prospectivity
In GIS-based data-driven modeling of mineral prospectivity, a suitably fine unit cell size is used for spatial representation of known occurrences of mineral deposits of the type sought (D) in a study area (T). However, until now, the unit cell size ... expand abstractis chosen subjectively. In this paper, a methodology is proposed for objective selection of the most suitable unit cell size for data-driven modeling of mineral prospectivity using a raster-based GIS. A set of choices of suitable unit cell sizes is first derived via point pattern analysis of a set of known occurrences of mineral deposits of the type sought. Then, (a) the lower limit of a set of choices of suitable unit cell sizes is considered and defined according to the map scales from which spatial data for mineral prospectivity mapping were derived, and (b) the upper limit of the same set of choices of suitable unit cell sizes is considered (and revised as necessary) based on knowledge of spatial extents of mineral deposits of the type sought or via analysis of reflexive nearest neighbour points. Finally, it is shown that fractal analysis of spatial contrast between unit cells containing D and unit cells not containing D in T provides for objective selection of the most suitable unit cell size. In a case study application of the weight-of-evidence method to mineral prospectivity mapping, using the most suitable unit cell size, found via the proposed methodology, results in spatial evidence weights and weight uncertainties that are nearly identical to those derived by using the finest (i.e., lower limit) unit cell size. In contrast to using the most suitable unit cell size, using coarser unit cell sizes result in higher positive weights, lower negative weights and higher weight uncertainties of spatial evidence of mineral prospectivity. The proposed methodology for objective selection of the most suitable unit cell size in data-driven modeling of mineral prospectivity using a raster-based GIS is robust and can easily be implemented. collapse abstract
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Ore Geology Reviews 2009 Jun; 35(3-4)
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 ass... expand abstractociations 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. collapse abstract
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Transactions in GIS 2009 Jun; 13(3)
Representation of Uncertainty and Integration of PGIS-based Grazing Intensity Maps Using Evidential Belief Functions
In a project to classify livestock grazing intensity using participatory geographic information systems (PGIS), we encountered the problem of how to synthesize PGIS-based maps of livestock grazing intensity that were prepared separately by local expe... expand abstractrts. We investigated the utility of evidential belief functions (EBFs) and Dempster's rule of combination to represent classification uncertainty and integrate the PGIS-based grazing intensity maps. These maps were used as individual sets of evidence in the application of EBFs to evaluate the proposition that “This area or pixel belongs to the high, medium, or low grazing intensity class because the local expert(s) says (say) so”. The class-area-weighted averages of EBFs based on each of the PGIS-based maps show that the lowest degree of classification uncertainty is associated with maps in which “vegetation species” was used as the mapping criterion. This criterion, together with local landscape attributes of livestock use may be considered as an appropriate standard measure for grazing intensity. The maps of integrated EBFs of grazing intensity show that classification uncertainty is high when the local experts apply at least two mapping criteria together. This study demonstrates the usefulness of EBFs to represent classification uncertainty and the possibility to use the EBF values in identifying and using criteria for PGIS-based mapping of livestock grazing intensity. collapse abstract
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Ore Geology Reviews 2008 Dec; 34(4)
Karst bauxite deposits in the Zagros Mountain Belt, Iran
More than 190 occurrences of bauxitic-lateritic deposits were investigated in seven areas within the Zagros Simply Folded Mountain Belt in southwestern of Iran. The bauxitic horizons are situated in eroded major NW-SE trending anticlines and occur in... expand abstract karst cavities near or at the boundary between the Sarvak and Ilam Formations. Uplift in the Cenomanian-Turanian period had exposed the Sarvak limestone to karst weathering and, during a period of unconformity, layers of ferruginous-argillaceous limestone debris developed and accumulated on its surface. The ferruginous-argillaceous debris was partly converted to bauxite. Folding and faulting in Oligocene-Miocene time, with ensuing erosion, exposed the bauxitic horizons on the limbs and cores of anticlines. The karst bauxite deposits are probably of authigenic origin, as evidenced by their lithologic associations, textural and mineralogy. collapse abstract
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International Journal of Applied Earth Observation and Geoinformation 2008 Sep; 10(3)
Knowledge-guided data-driven evidential belief modeling of mineral prospectivity in Cabo de Gata, SE Spain
Spurious evidence and spurious spatial associations between target mineral deposits and certain classes of spatial data undermine GIS-based data-driven modeling of mineral prospectivity. In a case study application of data-driven evidential belief fu... expand abstractnctions, such problems were recognized and then, based on sound geological judgment, were addressed accordingly. By invoking knowledge of genetic associations between mineral deposits of the type sought and spatial geological attributes (lithology, fault/fracture density, hydrothermal alteration intensity), spurious spatial associations depicted in 'original' evidence maps were addressed by treatment of input spatial data via applications of certain basic GIS functionalities in order to derive 'treated' evidence maps. By invoking knowledge of geological processes involved in the formation of mineral deposits of the type sought and knowledge of how operations to combine evidence maps function, the integration of evidence maps was guided such that the inter-play of geological processes involved in the formation of mineral deposits of the type sought is represented in the modeling procedure and such that spurious evidence is filtered and not transmitted into the output map representing likelihood of mineral deposit occurrence in every location within a study area. The results show that: (a) using 'treated' evidence maps, instead of 'original' evidence maps, results in better mineral prospectivity maps and, thus, (b) knowledge-guided data-driven modeling of mineral prospectivity is better than a 'purely' data-driven modeling of mineral prospectivity. collapse abstract
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Ore Geology Reviews 2008 Jun; 33(3-4)
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-t... expand abstractype 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. collapse abstract
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Geothermics 2008 Jun; 37(3)
Spatial data analysis and integration for regional-scale geothermal potential mapping, West Java, Indonesia
Conceptual modeling and predictive mapping of potential for geothermal resources at the regional-scale in West Java are supported by analysis of the spatial distribution of geothermal prospects and thermal springs, and their spatial associations with... expand abstract geologic features derived from publicly available regional-scale spatial data sets. Fry analysis shows that geothermal occurrences have regional-scale spatial distributions that are related to Quaternary volcanic centers and shallow earthquake epicenters. Spatial frequency distribution analysis shows that geothermal occurrences have strong positive spatial associations with Quaternary volcanic centers, Quaternary volcanic rocks, quasi-gravity lows, and NE-, NNW-, WNW-trending faults. These geological features, with their strong positive spatial associations with geothermal occurrences, constitute spatial recognition criteria of regional-scale geothermal potential in a study area. Application of data-driven evidential belief functions in GIS-based predictive mapping of regional-scale geothermal potential resulted in delineation of high potential zones occupying 25% of West Java, which is a substantial reduction of the search area for further exploration of geothermal resources. The predicted high potential zones delineate about 53-58% of the training geothermal areas and 94% of the validated geothermal occurrences. The results of this study demonstrate the value of regional-scale geothermal potential mapping in: (a) data-poor situations, such as West Java, and (b) regions with geotectonic environments similar to the study area. collapse abstract
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International Journal of Remote Sensing 2007 Dec; 28(23)
Similarity measures for spectral discrimination of salt-affected soils
This paper illustrates a pilot study designed to examine the spectral response of soils due to salt variations. The aim of the study includes determining whether salt-affected soils can be discriminated based on their spectral characteristics, by est... expand abstractablishing a relationship between soil properties and soil spectra and by testing if variations in the spectra of salt-affected soil samples are statistically significant. To answer the research questions, a laboratory experiment was designed to simulate salt transport to a column of soil in order to provide direct measurements of soil spectra and soil properties when salt concentration in a soil sample changes. The measured spectra were examined by the application of spectral matching techniques to quantify the variations and ascertain a relationship that supports the spectral identification of saline soils. The Ward's grouping method was conducted as an exploratory tool to statistically create homogeneous classes among data, which were obtained from the application of the spectral matching techniques to salt affected soil spectra. A nonparametric statistical test (Mann-Whitney U-test) was used to determine whether the differences between the classes are statistically significant. The results of spectral matching techniques showed differences in absorption strength, absolute reflectance and spectral angle in the near and shortwave infrared regions. The results also showed significant correlations between soil electrical conductivity (EC) and spectral similarity measures, indicating that similarity between the samples' spectra decreases as the salt concentration in the soil increases. The generated clusters indicate two classes at the highest level, which were subdivided at the next level and further subdivided into multiple subclasses as the dissimilarity decreased. The spectral data were grouped into classes and were used to test the null hypothesis by applying the Mann-Whitney U-test. The results indicate a significance level of α<0.02 between salinity classes and α<0.05 per waveband, meaning variations between the classes are higher than within each class. collapse abstract
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Remote Sensing of Environment 2007 Sep; 110(1)
Quantitative analysis of salt-affected soil reflectance spectra: A comparison of two adaptive methods (PLSR and ANN)
In this paper the possibility of predicting salt concentrations in soils from measured reflectance spectra is studied using partial least squares regression (PLSR) and artificial neural network (ANN). Performance of these two adaptive methods has bee... expand abstractn compared in order to examine linear and non-linear relationship between soil reflectance and salt concentration. Experiment-, field- and image-scale data sets were prepared consisting of soil EC measurements (dependent variable) and their corresponding reflectance spectra (independent variables). For each data set, PLSR and ANN predictive models of soil salinity were developed based on soil reflectance data. The predictive accuracies of PLSR and ANN models were assessed against independent validation data sets not included in the calibration or training phase. The results of PLSR analyses suggest that an accurate to good prediction of EC can be made based on models developed from experiment-scale data (R2 > 0.81 and RPD (ratio of prediction to deviation) > 2.1) for soil samples salinized by bischofite and epsomite minerals. For field-scale data sets, the PLSR predictive models provided approximate quantitative EC estimations (R2 = 0.8 and RPD = 2.2) for grids 1 and 6 and poor estimations for grids 2, 3, 4 and 5. The salinity predictions from image-scale data sets by PLSR models were very reliable to good (R2 between 0.86 and 0.94 and RPD values between 2.6 and 4.1) except for sub-image 2 (R2 = 0.61 and RPD = 1.2). The ANN models from experiment-scale data set revealed similar network performances for training, validation and test data sets indicating a good network generalization for samples salinized by bischofite and epsomite minerals. The RPD and the R2 between reference measurements and ANN outputs of theses models suggest an accurate to good prediction of soil salinity (R2 > 0.92 and RPD > 2.3). For the field-scale data set, prediction accuracy is relatively poor (0.69 > R2 > 0.42). The ANN predictive models estimating soil salinity from image-scale data sets indicate a good prediction (R2 > 0.86 and RPD > 2.5) except for sub-image 2 (R2 = 0.6 and RPD = 1.2). The results of this study show that both methods have a great potential for estimating and mapping soil salinity. Performance indexes from both methods suggest large similarity between the two approaches with PLSR advantages. This indicates that the relation between soil salinity and soil reflectance can be approximated by a linear function. collapse abstract
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IEEE Transactions on Geoscience and Remote Sensing 2006 Dec; 44(12)
Abundance estimation of spectrally similar minerals by using derivative spectra in simulated annealing
This paper presents a method for estimating the partial abundance of spectrally similar minerals in complex mixtures. The method requires formulation of a linear function of individual spectra of individual minerals. The first and second derivatives ... expand abstractof each of the different sets of mixed spectra and the individual spectra are determined. The error is minimized by means of simulated annealing. Experiments were made on several different mixtures of selected endmembers, which could plausibly occur in real situations. The variance of the differences between the first derivatives of the observed spectrum and the first derivatives of the endmember spectra gives the most precise estimates for the partial abundance of each endmember. We conclude that the use of first-order derivatives provides a valuable contribution to unmixing procedures provided that the signal-to-noise ratio is at least 50:1. collapse abstract
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Ore Geology Reviews 2006 Nov; 29(3-4)
Tectonostratigraphy and base-metal mineralization controls, Aravalli province (western India): New interpretations from geophysical data analysis
Analysis and synthesis of multi-disciplinary geoscience information from geological literature/maps and from digitally-processed aeromagnetic and gravity data pertinent to the Aravalli province were carried out to address some hitherto unresolved que... expand abstractstions about the tectonostratigraphy of this Archaean-Proterozoic metallogenic province. Based on the magnetic anomalies, several tectonic domains were identified. These domains, bounded by regional-scale geophysical lineaments, have distinct crustal, lithological, metamorphic, and metallogenic characteristics and correlate broadly with lithostratigraphic belts identified by several earlier workers. New interpretations on the tectonostratigraphy and the base-metal mineralization controls in the Aravalli province are as follows. The Hindoli sequences, in the eastern parts of the province, constitute an independent Palaeo-Proterozoic tectonic domain and do not form part of the Archaean basement complex. The base-metal-bearing metasedimentary enclaves in the central parts of the province also constitute an independent Palaeo-Proterozoic tectonic domain, which is quite distinct from the surrounding (basement complex?) rocks. The base-metal-bearing metavolcano-sedimentary sequences in the western parts of the province constitute an independent Neo-Proterozoic tectonic domain. The base-metal deposits in the province are spatially associated with the regional-scale lineaments and with the mafic metavolcanic rocks deduced from the aeromagnetic data. The regional-scale lineaments, which possibly represent Proterozoic crustal-scale faults, are plausible structural controls on the base-metal mineralization in the province. The mafic metavolcanic rocks are plausible heat-source controls on the SEDEX- and/or VMS-type base-metal mineralizations and are possible metal-source controls on the VMS-type base-metal mineralization in the province. collapse abstract
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Natural Hazards 2006 Mar; 37(3)
Predicting lahar-inundation zones: Case study in West Mount Pinatubo, Philippines
This paper demonstrates techniques for pre-eruption prediction of lahar-inundation zones in areas where a volcano has not erupted within living memory and/or where baseline geological information about past lahars could be scarce or investigations to... expand abstract delimit past lahars might be incomplete. A lahar source (or proximal lahar-inundation) zone is predicted based on ratio of vertical descent to horizontal run-out of eruptive deposits that spawn lahars. Immediate post-eruption distal lahar-inundation zones are predicted based on "pre-eruption" distal lahar-inundation zones and on spatial factors derived from a digital elevation model. Susceptibility to distal lahar-inundation is estimated by weights-of-evidence, by logistic regression and by evidential belief functions. Predictive techniques are applied using a geographic information system and are tested in western part of Pinatubo volcano (Philippines). Predictive maps are compared with a forecast volcanic-hazard map through validation against a field-based volcanic-hazard map. The predictive model of proximal lahar-inundation zone has "true positive" prediction accuracy, "true negative" prediction accuracy, "false positive" prediction error and "false negative" prediction error that are similar to those of the forecast volcanic-hazard map. The predictive models of distal lahar inundation zones have higher "true positive" prediction accuracy and lower "false negative" prediction error than the forecast volcanic-hazard map, although the latter has higher "true negative" prediction accuracy and lower "false positive" prediction error than the former. The results illustrate utility of proposed predictive techniques in providing geo-information could be used, howbeit with caution, for planning to mitigate potential lahar hazards well ahead of an eruption that could generate substantial source materials for lahar formation. collapse abstract
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Natural Resources Research 2006 Mar; 15(1)
A hybrid fuzzy weights-of-evidence model for mineral potential mapping
This paper describes a hybrid fuzzy weights-of-evidence (WofE) model for mineral potential mapping that generates fuzzy predictor patterns based on (a) knowledge-based fuzzy membership values and (b) data-based conditional probabilities. The fuzzy me... expand abstractmbership values are calculated using a knowledge-driven logistic membership function, which provides a framework for treating systemic uncertainty and also facilitates the use of multiclass predictor maps in the modeling procedure. The fuzzy predictor patterns are combined using Bayes' rule in a log-linear form (under an assumption of conditional independence) to update the prior probability of target deposit-type occurrence in every unique combination of predictor patterns. The hybrid fuzzy WofE model is applied to a regional-scale mapping of base-metal deposit potential in the south-central part of the Aravalli metallogenic province (western India). The output map of fuzzy posterior probabilities of base-metal deposit occurrence is classified subsequently to delineate zones with high-favorability, moderate favorability, and low-favorability for occurrence of base-metal deposits. An analysis of the favorability map indicates (a) significant improvement of probability of base-metal deposit occurrence in the high-favorability and moderate-favorability zones and (b) significant deterioration of probability of base-metal deposit occurrence in the low-favorability zones. The results demonstrate usefulness of the hybrid fuzzy WofE model in representation and in integration of evidential features to map relative potential for mineral deposit occurrence. collapse abstract
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