Occurrence Of Mineral Deposits Research Articles

Brittle tectonic evolution of Gondwana: implications for shale-gas and groundwater exploration

Abstract Brittle structures are crucial for enabling several key natural processes in the Earth's upper crust. In addition, understanding the 3D characteristics and geological evolution of these features is equally important to support various developmental objectives, such as those, inter alia , linked to natural gas, groundwater, hydrothermal minerals and seismicity. In this study, we map various fractures of Gondwana based on the available geological information, satellite imagery and digital elevation data. The lengths and orientations of more than 10 000 fractures in their present-day position reveal four clearly defined patterns, with those striking NW being predominant. Archean–Paleoproterozoic domains are defined by fractures oriented north and NE, whereas the Mesoproterozoic has dominant NNW-striking fractures. In contrast, the Neoproterozoic has mostly NE-striking fractures and the Phanerozoic sequences are defined by a predominant NW and a subordinate west fracture pattern. The style and geometry of these structures can be linked to major geodynamic events that led to the formation of Gondwana building blocks during the Eburnean ( c. 2.2–1.8 Ga), Kibaran ( c. 1.4–1.0 Ga) and Pan African–Brasiliano ( c. 800–550 Ma) orogens, and amalgamation of Pangaea ( c. 350–250 Ma). Many structures were reactivated and new faults formed during opening of the Atlantic and Indian oceans ( c. 180–120 Ma), the India–Asia collision and rifting across East Africa since about 40 Ma. Although the changes in palaeogeography remain difficult to model with accuracy, major structural orientations are corroborated by the occurrence of major mineral deposits and seismicity. The spatial distribution of mapped patterns across the different continents also correlates well with large shale gas prospects and increased groundwater yields. Thus, Gondwana fractures need to be considered in more detail for informing future development related to water and energy use, especially across regions of Africa.

Mining and women’s agency: Evidence on acceptance of domestic violence and shared decision-making in India

We study the impact of proximity to mineral deposits and active mines on women’s agency in India. Identification leverages the plausibly exogenous spatial variation in the occurrence of mineral deposits and mineral types across districts. Results indicate that women’s outcomes improve near mines: women have less tolerance of physical violence and they report fewer barriers to accessing healthcare. Concomitantly, men’s likelihood of making decisions jointly with spouses increases, and men are less likely to justify domestic violence. These benefits are larger near mines that employ relatively high shares of women. The key mechanism is the sharing of mining royalties with local groups to support investments in vulnerable populations, which contributes to better economic conditions for women. Findings imply that mineral mining can bring measurable benefits to women’s agency, especially when profits are invested in improving the welfare of local populations.

The role of mineral resources knowledge in the economic planning and development in Poland

Geological reconnaissance of the country and gathering knowledge on the occurrences of mineral deposits is a permanent task of geological survey carried out in cooperation with academia and mineral industry. In Poland, a fundamental role in this process is played by the Polish Geological Institute-National Research Institute (PGI-NRI) operating as the geological survey under the supervision of the Ministry of Climate and Environment. PGI-NRI creates concepts of geological structures of the country, conducts independent prospecting studies, archives geological documentations made by mineral companies and verifies geological forecasts. The results of these works carried out for over 50 years are periodically published in the form of scientific monographs entitled The balance of prospective mineral resources in Poland. Presented in The balance of prospective mineral resources in Poland data on prognostic and perspective areas, as well as on the documented deposits are indispensable for country planning of economic development through, among others, protection of mineral deposits in the process of spatial management of the country. Polish prospective mineral resource studies include archival geological data reprocessing, mineral deposit modelling and new geological exploration projects. The synthesis of this research is The balance of prospective mineral resources in Poland which is a unique publication in terms of scope and content, because such data are not published in similar form and with the same scope of geological information in other countries. Therefore, authors would like to familiar international geological opinion with Polish experience and to widespread knowledge about mineral resources in Poland. The last edition (2020) of The balance of prospective mineral resources in Poland was prepared, edited and written among others by the authors of this article. In agreement with the conclusions presented in The balance of prospective mineral resources in Poland, our country is still of high geological potential, especially as regards the deposits of Cu, Ag, Pb, Zn ores, chemical and rock minerals. Thanks to this information mineral companies can plan and realize projects to document deposits and then finally develop the deposits. It is necessary to underline that proved and prospective deposits should be protected against such land development which would limit or eliminate mining activity in the future. Unfortunately, the current legal protection of undeveloped deposits in Poland is insufficient and requires new legislative solutions.

Morphometric and Structural Evaluations of Satellite Data from the Bosumtwi Impact Structure and Adjacent Areas in Ashanti, Ghana

The Bosumtwi impact crater in Ashanti, Ghana is one of the most thoroughly investigated impact structures in Africa. Nevertheless, by the evaluations of Sentinel 1 and 2, and Landsat data as well as by ALOS PALSAR, ASTER and SRTM digital elevation model (DEM) data further geomorphological and structural knowledge can be derived. Morphometric maps were used to visualize the concentric and radial drainage and valley pattern surrounding the impact crater. The larger valleys are arranged in a nearly concentric and radial pattern like the river Pra and its tributaries, the Ofin, Anum and Brim river, tracing the outer, southern border of the impact affected area. From the ASTER and SRTM DEM data the morphological drainage basin was calculated. The drainage basin-outline is nearly circular, discharging into the Pra river in the southern part. Structural evaluations of satellite radar and optical data reveal that linear and circum-linear features can be detected more than 80 km around the Bosumtwi impact crater. Small-scale/artisanal mining activities in this area are visible on satellite images and, thus, indirectly tracing ore deposits. As detailed mineral maps are not publicly available, the position and distributions of mining areas was used as indicator for the occurrence of mineral deposits, especially placer deposits. Their occurrence and the distribution of the mining areas follows the larger rivers. Weathering processes along the deformation pattern and erosion and sedimentation probably had an influence on placer deposit development.

Spatio-Geologically Informed Fuzzy Classification: An Innovative Method for Recognition of Mineralization-Related Patterns by Integration of Elemental, 3D Spatial, and Geological Information

Recognition and mapping of mineralization-related patterns in geochemical data is a key computational analysis to achieve a predictive model of prospectivity for mineral deposit occurrence. This contribution describes a spatio-geologically informed fuzzy classification (SGIFC) for portraying the spatial-frequency distribution of mineralization through integration of geochemical concentrations, 3D spatial properties, and geological knowledge contained in surface samples. A spatio-geological interaction model (SGIM) was defined to constitute an SGIFC by modulating fuzzy memberships in each iteration of standard fuzzy c-means (FCM) according to the incorporation of both spatial and geological inter-sample similarities. This strategy was adapted to the compositional nature of multi-elemental data and implemented by programming over packages supplied within the R language environment. A comparative experiment on soil samples collected in a porphyry Cu–Au system was subjected to understand how the SGIM affects standard memberships spatially, statistically, and geostatistically. Spatial autocorrelation analysis of fuzzy memberships through Moran’s I calculation and Monte Carlo simulation indicated that SGIFC leads to more robust spatially connected patterns compared to FCM models. Moreover, variogram analysis illustrated that SGIM orients the spatial continuity of mineralization-related memberships along the diffusion bearing of hydrothermal fluids across geological structures of the study area. Rock samples collected along trenches, as well as Cu volumetric productivities, were used as benchmarks to evaluate the integrity of the derived predictive models. The results reveal that the distribution pattern of mineralization-related memberships for SGIFC, compared to that of FCM, is more consistent with sub-outcropping and deep metallogenic realities and describes a more significant quantitative association with subsurface mineral content within the study region. The incorporation of SGIM into fuzzy classification has demonstrated the sufficiency to synthesize the comprehensive information of samples to predict effectively potential targets for follow-up exploration.

A View on Integrated and Sustainable Minerals Value Chains

Geology defines the occurrence of mineral deposits, and, therefore, mining is geographically constrained. However, the use of the mineral products in down-stream industries often takes place in countries different from the location of the mine. Therefore, mining communities do not necessarily appreciate the importance of mineral production for the benefit of people living in other countries, particularly if there is no tangible sharing of those benefits. Mining cannot choose locations that are logistically, socially, environmentally, or politically appropriate or ‘friendly’. This means that mining companies may have to deal with circumstances that could pose challenges such as the relationship with local communities, position in the landscape/environment, relationship with local and national governments, weak governance and associated increased risk of corruption and bribery. In order to deal with these challenges in a responsible way it means that geoscientists and engineers will need to build their capacity and skills on how to deal with local communities and related social issues. The outcome should be the equitable distribution of the benefits of development, including also mineral land-use planning issues, and minimization of the negative impacts on people and the environment. Thus, a sustainable and integrated view on minerals value chains requires looking even further upstream into the pre-exploration that includes planning process for mineral land use and development at the earliest stage.

Modeling of Cu-Au prospectivity in the Carajás mineral province (Brazil) through machine learning: Dealing with imbalanced training data

Machine learning (ML) is becoming an appealing tool in various fields of Earth Sciences, especially in mineral prospectivity mapping (MPM) to support mineral exploration. ML algorithms are designed to assume a relatively balanced amount of training data for the estimation of the decision boundaries between the classes of interest (i.e., in MPM: mineralized- and non-mineralized locations). However, in MPM the numbers of mineralized and non-mineralized locations are naturally imbalanced, as the number of known mineral deposit occurrences (as a proxy of mineralized or positive class) are naturally much smaller than the number of non-mineralized locations (the negative class). The use of imbalanced data leads to difficulties in the training of ML models for MPM, due to the learning bias towards the features of the predominant (i.e., negative) class. In the present study, using support vector machine for Cu-Au prospectivity modeling in the Carajás mineral province (Brazil), we evaluated the effects of Synthetic Minority Over-sampling Technique (SMOTE), which addresses the issue of imbalanced training data on the performance of MPM. The original training data for the positive (i.e., minority) class was modified by over-sampling the mineralized locations using SMOTE and by randomly under-sampling the non-mineralized locations at different proportions, producing 400 training datasets with proportions of mineralized-to-non-mineralized samples ranging from 600:30 to 30:600. Each of these individual training datasets was used to evaluate the performance of MPM under different proportions of mineralized-to-non-mineralized samples. The performance of each prospectivity model was objectively evaluated using the F1 score and the success-rate curve. The results show that SMOTE can significantly increase the performance and the spatial efficiency of MPM. The main differences between the performances of the derived prospectivity models illustrate the sensitivity of MPM to the number of samples and distribution of classes in the training data. According to the results, better performance is achieved using SMOTE when the prospectivity models are trained with an equal number of mineralized and non-mineralized samples. The best prospectivity model trained with a modified dataset with 600:600 proportion of mineralized to non-mineralized samples resulted in 100% classification of the training mineralized locations and almost 80% of the testing mineralized locations, and outlined only 7% of the study area as prospective.

Mining and Gender Gaps in India

This study on the economics of gender differences examines whether the mining industry acts as a blessing or curse for women's well-being and economic status. The analysis focuses on the impact of proximity to mineral deposits and active mines on various measures of women's agency and health in India. Identification leverages the plausibly exogenous spatial variation in the occurrence of mineral deposits across districts. Results indicate that women's outcomes improve in the vicinity of mines with improvements in shared decision-making, reductions in barriers to accessing medical care, and reduced tolerance of physical violence. These benefits are pronounced among younger women, and in the proximity of mines that employ relatively high shares of women. The underlying mechanisms include employment gains for women and improvements in women's health near mines. Their children also experience gains in nutritional status. Men's likelihood of making decisions jointly with partners increases, and men are less likely to justify domestic violence. A key explanation for these results is the sharing of mining royalties with local groups that support investments in women and children. Findings imply that mineral mining can bring substantial benefits to women's well-being, which is critical for sustainable development.

Analyses of high resolution aeromagnetic data for structural and porphyry mineral deposit mapping of the nigerian younger granite ring complexes, North - Central Nigeria

This study report the results of the different geophysical analyses carried out on the aeromagnetic data of north-central Nigeria with the object of delineating the occurrence and evaluate the structural influence on the emplacement of the porphyry mineral deposits of the Ring Complexes. The residual magnetic intensity extracted using Low Cut Guassian filter, from the high resolution aeromagnetic data of north-central Nigeria were filtered to remove high frequency near surface cultural noise and subsequently Reduced to Pole at Low Latitude (RTPLL) to focus anomaly peaks on the corresponding geological sources in order to resolve anomaly complexity associated with mid-latitude potential data. The data were further enhanced using upward continuation filter to extract desired magnetic responses at various continuation distances. Analytic Signal (AS), Centre for Exploration Techniques (CET) Grid and Porphyry Analyses were then carried out on the filtered, transformed and enhanced magnetic data to generate diagnostic magnetic attributes employed to map the boundaries of geologic magnetic sources, extract linear features and delineate the occurrence of porphyry mineral deposits across the study area.The AS responses defined twenty-four (24) arcuate/circular shaped AS anomalies which correspond to Younger Granites Ring Complexes in the northeast, northwest, southeast and central part of the study area from the low AS response Basement Complex rocks that host them. The CET grid analysis delineates several linear structures which generally trend NE – SW, NNE – SSW and ENE – WSW directions and their average length (500 m–17,500 m) and population (212–32) directly and inversely, respectively, correlate with the upward continuation distances. The CET porphyry analysis also delineates fifty (50) porphyry mineral deposits which vary in radial size from 300 m–4300 m. The occurrence of the porphyry mineral deposits within or in close proximity with the Younger Granite Ring Complexes which are either crosscut or flanked by the linear structures, suggests hydrothermal non-orogenic origin of the structurally controlled ring complexes and the associated porphyry mineralisation that result from phase mineralisation that accompanied Jurassic hydrothermal activities.

A Modified Weights-of-Evidence Method for Mineral Potential Prediction Based on Structural Equation Modeling

Structural equation modeling (SEM) was applied here to modify the ordinary weights-of-evidence (WofE) method for calculating posterior probability to improve conditional independence (CI) in the application of this method mineral potential prediction. The new method attempts to reduce the effect of CI by defining new binary patterns with an optimum combination of cutoff values of patterns. The solution is calculated through SEM, and the goodness of fit between evidence and mineral deposit occurrences is evaluated by a specified target function. The main difference between the new WofE and ordinary WofE is that evidence in the new method maintains a balance between the significance for mineral potential prediction and CI, rather than the significance for mineral prediction only as in ordinary WofE. A case study of prediction of potential for hydrothermal Au mineral deposits in Nova Scotia, Canada, is discussed here. The results indicate that the new method performs better than the ordinary WofE.

Compositional balance analysis for geochemical pattern recognition and anomaly mapping in the western Junggar region, China

The western Junggar region of China is endowed with considerable resources of gold, copper and chromite. Complex geological conditions and diversity deposit types could lead to various geochemical patterns and geochemical anomalies. In this study, compositional balance analysis (CoBA) is demonstrated for recognition of geochemical patterns and mapping geochemical anomalies that are closely associated with gold/copper/chromite mineralization and particular geological units in the western Junggar region. Here, CoBA was based on hierarchical cluster analysis and sequential binary partition technique, which provides a new path for intuitively distinguishing particular relationships between groups of parts that are of interest. To recognize anomalous patterns in stream sediment geochemical data that are closely associated with mineralization, 18 geochemical elements were used to construct 17 balances by means of the CoBA method, of which four key balances were selected for further investigation. Relevant geological information (e.g. mineral deposit occurrences) provides important references for interpreting and validating the results. By comparison of geochemical patterns of the square roots of Au and Cu concentrations with that of factor scores, the results indicate that the CoBA method provides straightforward and robust interpretation of stream sediment geochemical data by suppressing background patterns and enhancing anomalous patterns in the western Junggar, China.

Precursor and ambient rock paleothermometry to assess the thermicity of burial dolomitization in the southern Cantabrian Zone (northern Spain)

Paleozoic rocks in the Cantabrian Zone, and the Variscan foreland fold-and-thrust belt on the Iberian Peninsula have been affected by a sequence of diagenetic to epizonal thermal events. Late- to Post-Variscan hot fluid circulation caused a large-scale burial dolomitization and ore mineralization, mostly in Cambrian and a Lower to Middle Carboniferous carbonate sucessions. The goal of this study is to analyze and compare the temperatures experienced by the carbonate precursor rocks, as well as the under- and over-lying siliciclastic ambient rocks to gain a better understanding of the thermicity of dolomitization. These temperatures are evaluated based on published paleothermal datasets combined with new data obtained from Rock–Eval pyrolysis and vitrinite reflectance analysis of Carboniferous rocks rich in organic matter. The overall results indicate that reworking of detrital sediments in synorogenic ambient siliciclastics results in an anomalously high thermal maturity recorded by bulk rock techniques such as illite crystallinity and Rock–Eval pyrolysis. In situ VR-derived paleotemperatures recorded by ambient siliciclastic rocks appear to be higher compared to CAI-derived temperatures for carbonate precursor rocks. This variation in thermal maturity is likely related to the analytical techniques used to obtain CAI and VR data, and the empirical equations applied to calculate corresponding paleotemperatures. Conodont fragments were not as sensitive compared to vitrinite, and the color alteration process could have suffered from hydrothermal alteration. A secondary cause might be a different response to mechanical deformation between siliciclastic and carbonate units during the Variscan and post-Variscan geodynamic evolution of the study area. Rigid precursor carbonate units experienced fluid circulation mainly along distinct and spaced fracture zones, creating fracture-related dolomite geobodies and ore mineralization. Soft ambient siliciclastic rocks experienced more diffuse fluid circulation and heat dissipation. The different paleothermometry datasets compiled for the study area indicate that the fluids circulating during Late- to Post-Variscan times, with associated fracture-related dolomitization and ore mineralization in carbonate precursors, are hydrothermal. The highest paleotemperatures were recorded in ambient and precursor rocks in the highly tectonized northern part of the study area, where several thrusts and faults allowed intense fluid circulation. Positive temperature anomalies within the precursor carbonates correlate well with the occurrence of dolomite geobodies and ore mineral deposits. Such anomalies could thus be used as an exploration tool for hydrothermal dolomite bodies in analog sub-surface settings.

Scanning and transmission analytical electron microscopy (STEM-EDX) can identify structural forms of lead by mapping of clay crystals

To increase the analytical precision in identifying structural forms of heavy metals, it is necessary to refine the methodology for analysis of mineral crystals. The aim of this study was to characterize clay crystals in soils, and relate their mineralogy to the structural occurrence of Pb using scanning transmission electron microscopy (STEM) together with energy dispersive X-ray (EDX) spectrometry. We sampled soils from two areas naturally rich in heavy metals, with known occurrences of mineral deposits (PbS) in carbonate and phyllite/mica schist rocks. There was an association of P with Pb, and the main mineral phase containing Pb in the soil clay fractions was plumbogummite. No associations between Pb and Fe oxides were observed. Secondary phyllosilicate minerals, such as kaolinite and smectite, did not contain structural Pb. There was isomorphous substitution of Ti by Pb in an anatase crystal, despite the differences in ionic radii. The chemical analysis of individual crystals by STEM-EDX was hampered by the high occurrence of microaggregates of clay minerals.

Criteria for Geo-Environmental Evaluation of Prospective Areas of Mineral Deposit Occurrence

Abstract In this work, we present the problem of geo-environmental assessment of prospective areas of mineral deposits occurrence in Poland. T he issue is discussed mainly based on data from the database of Geo-environmental map of Poland, scale 1:50 000 (MGśP II). While for proven deposits a classification based on environmental conditions has been used for many years, for prospective areas of mineral occurrence such an assessment is not conducted. Taking into consideration not only protection of the natural environment, but also protection of mineral resources in Poland, it is necessary to review the approach to areas with prospective mineral resources from the point of view of their role in land use planning. Such prospective areas have - depending on the type of mineral in question, how large an area has been prospected, its geological structure - highly diverse surface area, from just a few to thousands of hectares. T his means the approach to environmental assessments of prospective areas of mineral occurrence must be different from that for already proven locations of mineral resources. The article presents quantitative characteristics of prospective areas of mineral occurrence presented on the aforementioned MGśP II map for Poland. We propose herein criteria for environmental evaluation of such prospective areas, differentiating them mainly depending on the type of mineral, manner of exploitation, surface area and land use legal forms, as well as possibility of future reclamation.

More aggressive sequential extraction procedure to access stable forms of Pb and As in clay minerals of soils

Lead (Pb) and arsenic (As) are potentially toxic in their most reactive forms, but can also occur as structural and specifically adsorbed (more stable forms) ions on clay minerals. Due to their lower mobility in soils, structural and specific adsorbed forms are usually neglected in environmental studies, but can be important, for example, in geochemistry researches. The aim of this study was to evaluate the occurrence of stable forms of Pb and As in the clay fraction of soils in a region rich in Pb ore (galena) in south Brazil using more aggressive sequential extractions (boiling 5molL−1 NaOH, successive citrate-bicarbonate-dithionite steps, and sodium bisulfate fusion). X-ray diffraction was used to follow possible mineralogical variations after each sequential extraction. We sampled soils from two areas rich in trace elements, with high occurrence of mineral deposits (PbS) in carbonate and phyllite/mica schist rocks. A reference soil formed on mineralized granite/gneiss was also sampled. In different mineral phases of the sequential extraction, preferential association of Pb with minerals extracted by 5molL−1 NaOH (kaolinite, low crystalline smectite and precipitated of Pb-S and Pb-P) was observed. In soils formed from parent materials at the phyllite/mica schist metamorphic stage, Pb contents solubilized by NaOH were extremely high (maximum >28,000mgkg−1). Lead exists in the mineral structure, such as Fe oxides, as result of the isomorphic substitution of Fe for Pb. Manganese oxides were also important host of Pb in the clay fraction. The largest As contents occurred at greater depth in the soil. The more aggressive sequential extraction procedure is more suitable to estimate the structural and specific adsorbed forms of Pb and As in clay minerals.

Metallogenic efficiency from deposit to region–A case study in western Zhejiang Province, southeastern China

Metallogenic (ore) efficiency can be defined as the ratio of metal reserves to its total supply, and we expanded a typical efficiency-calculation model available at the single mineral scale to the regional scale. A new cell-based model was developed by analogy and by taking some other influences into account: i) a thicker sedimentary cover; ii) regional ore- and rock-controlling structures and their intersections; iii) the crustal heterogeneity unrelated and related to ores; and iv) metallic geochemical anomalies. Finally, a regional contour map of weighted efficiency, which is essential to metallogenic prediction, was obtained. It shows that the efficiency anomalies can provide a much better target area for ore-positioning than do metallic content anomalies, and greater ore efficiency may indicate the likelihood of occurrence of mineral deposits that are larger in size (reserves). Taking northwestern Zhejiang province as a case study, in which the geochemistry of Mesozoic porphyries plausibly show considerable mineralized potential, we found that due to the lower magmatic temperature, delayed exsolution of the hydrothermal solution, and very thick sedimentary cover, the Cu-polymetal ore efficiency associated with granitic plutons in this area is generally low; the relatively higher ore-productivity (efficiency) appears mainly in and around small rock bodies, rock margins, and the contacting zone between different lithologies. Most ore spots, no matter their size, fall into areas with nonzero efficiency values. There seems to be no interdependence between most ore spots of smaller size and ore efficiency, whereas efficiency is essential to regional small- and medium-scaled metallogensis.

General features relating to the occurrence of mineral deposits in the Urals: What, where, when and why

This study of metallogeny of the Urals is strongly tied up with a stage-by-stage geodynamic analysis of the orogen. The analysis includes a revised understanding of geodynamic development of the Timanides (development of a deep sedimentary basin since the Mesoproterozoic, ocean formation and subduction in the Neoproterozoic and collision in the Late Ediacaran). For the Uralides, a new interpretation includes relationships between Tagil and Magnitogorsk arcs, arc–continent collision in the Late Devonian, subduction jump in the Early Carboniferous, and thrust stacking in the Late Carboniferous to Permian. Attention is paid to metallogeny of the platform (Middle Jurassic to Paleogene) and neo-orogenic (late Cenozoic) stages. For the first time an effort is made to consider the role of mantle plumes and superplumes in the geodynamic development and metallogeny of this fold belt. Many deposits are polygenetic, and different stages of their formation belong to different geodynamic stages and substages, therefore the deposits becoming additional geodynamic indicators themselves.

Data-Driven Predictive Modeling of Mineral Prospectivity Using Random Forests: A Case Study in Catanduanes Island (Philippines)

The Random Forests (RF) algorithm is a machine learning method that has recently been demonstrated as a viable technique for data-driven predictive modeling of mineral prospectivity, and thus, it is instructive to further examine its usefulness in this particular field. A case study was carried out using data from Catanduanes Island (Philippines) to investigate further (a) if RF modeling can be used for data-driven modeling of mineral prospectivity in areas with few (i.e., <20) mineral occurrences and (b) if RF modeling can handle predictor variables with missing values. We found that RF modeling outperforms evidential belief (EB) modeling of prospectivity for hydrothermal Au–Cu deposits in Catanduanes Island, where 17 hydrothermal Au–Cu prospects are known to exist. Moreover, just like EB modeling, RF modeling allows analysis of the spatial relationships between known prospects and individual layers of predictor data. Furthermore, RF modeling can handle missing values in predictor data through an RF-based imputation technique whereas in EB modeling, missing values are simply represented by maximum uncertainty. Therefore, the RF algorithm is a potentially useful method for data-driven predictive modeling of mineral prospectivity in regions with few (i.e., <20) occurrences of mineral deposits of the type sought. However, further testing of the method in other regions with few mineral occurrences is warranted to fully determine its usefulness in data-driven predictive modeling of mineral prospectivity.

A novel filtering technique for enhancing mineralization associated geochemical and geophysical anomalies

A novel method named optimal filtering is introduced in this paper. This method is aimed at producing maps resulting from the filtering of geochemical or geophysical data in order to indicate occurrences of mineral deposits most effectively. Two measures are proposed to enhance the capability of indicating deposits: (1) area under operating characteristic curve (AUC); and (2) Fisher's measure for discriminant analysis. Six Fourier filter functions introduced for different situations are ideal high-pass filter (IHPF), ideal low-pass filter (ILPF), Butterworth high-pass filter (BHPF), Butterworth low-pass filter (BLPF), Gauss high-pass filter (GHPF) and Gauss low-pass filter (GLPF). The effectiveness of this approach is demonstrated in a case study using a geochemical and aeromagnetic dataset from southwestern Nova Scotia, Canada. The anomalies resulting from ILPF and IHPF show strong association with the occurrences of gold deposits in this area. The high-pass cutoff wavelength correctly predicts regular spacing between mineralization zones. Pros and cons of the parameters for optimal filtering are discussed, and preliminary guidelines are proposed for how to choose these parameters. Additionally, a test of the case study results shows the method is robust to lack of deposits.

Predictive modelling of gold potential with the integration of multisource information based on random forest: a case study on the Rodalquilar area, Southern Spain

Mineral exploration activities require robust predictive models that result in accurate mapping of the probability that mineral deposits can be found at a certain location. Random forest (RF) is a powerful machine data-driven predictive method that is unknown in mineral potential mapping. In this paper, performance of RF regression for the likelihood of gold deposits in the Rodalquilar mining district is explored. The RF model was developed using a comprehensive exploration GIS database composed of: gravimetric and magnetic survey, a lithogeochemical survey of 59 elements, lithology and fracture maps, a Landsat 5 Thematic Mapper image and gold occurrence locations. The results of this study indicate that the use of RF for the integration of large multisource data sets used in mineral exploration and for prediction of mineral deposit occurrences offers several advantages over existing methods. Key advantages of RF include: (1) the simplicity of parameter setting; (2) an internal unbiased estimate of the prediction error; (3) the ability to handle complex data of different statistical distributions, responding to nonlinear relationships between variables; (4) the capability to use categorical predictors; and (5) the capability to determine variable importance. Additionally, variables that RF identified as most important coincide with well-known geologic expectations. To validate and assess the effectiveness of the RF method, gold prospectivity maps are also prepared using the logistic regression (LR) method. Statistical measures of map quality indicate that the RF method performs better than LR, with mean square errors equal to 0.12 and 0.19, respectively. The efficiency of RF is also better, achieving an optimum success rate when half of the area predicted by LR is considered.