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 PMMP 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.     

Mineralogy and geochemical behaviour during weathering of greenstone belt under tropical dry conditions in the extreme North Cameroon (Central Africa)

Mineralogy, major, trace and rare earth elements of a weathering profile developed on tertiary greenstone belt in the extreme North Cameroon are reported. The aim of which was to investigate mineralogical evolution and element mobilization and redistribution during weathering under dry tropical climate. The weathering profile consists of four main horizons: (1) a spheroidal weathering zone constituted by a corestone–shell complex, (2) a C horizon, (3) a Bw horizon and an Ah horizon. The results indicate that nontronite, a Fe-rich smectite, is the exclusive clay mineral formed in the exfoliated shells and the C horizon. It is associated with kaolinite in the upper horizons. The coexistence of these two clay minerals induced a decrease of CEC and pH which becomes neutral. The weathering index (WI) values reveal that weathering becomes more and more intensive from the corestone up to Bw horizon, which is the most weathered horizon in the weathering profile. Mass balance calculations, using Th as immobile element, indicate that Ti is quite mobile and that Al and Fe are relatively enriched at the bottom and strongly leached at the top of the profile. Alkalis and alkaline earth elements are strong leached through out the profile, except Ca which displays similar trend as Al and Fe. The same goes for LILE (Cs, Sr), TTE (Cr, Co, Ni) and HSFE (Y, Nb, Hf). In opposite, REE are depleted at the bottom and enriched in the upper horizons, with more enrichment for LREE than for HREE. It appears that weathering of greenstone belt causes a fractionation of HREE and induces a concentration of LREEs. Ce and Eu anomalies display opposite behaviour.     

Application of Mineral Exploration Models and GIS to Generate Mineral Potential Maps as Input for Optimum Land-Use Planning in the Philippines

The inherent problems of classifying or inventorying potential mineral resources (as opposed to known mineral resources) pose specific challenges. In this paper, the application of a conceptual mineral exploration model and GIS to generate mineral potential maps as input to land-use policy decision-making is illustrated. We implement the criteria provided by a conceptual exploration model for nickeliferous-laterites by using a GIS to classify the nickeliferous-laterite potential of an area in the northeastern part of the Philippines. The spatial data inputs to the GIS are geological map data, topographic map data, and stream sediment point data. Processing of these data yields derivative maps, which are used as indicators of nickeliferous-laterite potential. The indicator maps then are integrated to furnish a nickeliferous-laterite potential map. This map is compared with present land-use classification and policy in the area. The results indicate high potential for nickeliferous-laterite occurrence in the area, but the zones of potential are in places where mineral resources development is prohibited. The prohibition was imposed before the nickeliferous-laterite potential was assessed by this study. Mineral potential classification therefore is a critical input to land-use policy-making so that prospective land is not alienated from future mineral resource development.     

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.     

Distribution and transfer of trace elements in the Western Mediterranean

Results concerning the concentration of cadmium and lead in Mediterranean waters collected during the 2nd PHYCEMED cruise (Oct. 1983) are discussed. Sampling has been performed at seven stations in the Western Mediterranean Basin, two in the Strait of Gibraltar and the near Atlantic, two in the Sicily Strait and the Eastern Basin.In the Western Basin the observations are in fair agreement with those of PHYCEMED 1. Cadmium has a fairly homogeneous distribution vertically as well as from one station to another, with an average concentration of 8 ng l⁻¹; while lead shows a slight but continuous decrease in concentrations with depth (from at least 50 ng l⁻¹ in surface waters to 20 or 25 ng l⁻¹ at depth). On the other hand, at the basin boundaries, where waters from different origins are present, vertical distributions appear very different. On the basis of calculated water budgets it can be estimated that the Mediterranean Sea discharges about 200 t y⁻¹ of cadmium and about 250 t y⁻¹ of lead into the Atlantic Ocean while 1000 t y⁻¹ of lead are transferred from the Western to the Eastern Basin.     

Water balance components estimation under scenarios of land cover change in the Vea catchment,West Africa

ABSTRACT

The need for a detailed investigation of the Vea catchment water balance components cannot be overemphasized due to its accelerated land-cover dynamics and the associated impacts on the hydrological processes. This study assessed the possible consequences of land-use change scenarios (i.e. business as usual, BAU, and afforestation for the year 2025) compared to the 2016 baseline on the Vea catchment’s water balance components using the Soil and Water Assessment Tool (SWAT) model. The data used include daily climate and discharge, soil and land use/land cover maps. The results indicate that the mean annual water yield may increase by 9.1% under the BAU scenario but decrease by 2.7% under the afforestation scenario; actual evapotranspiration would decrease under BAU but increase under afforestation; and groundwater recharge may increase under both scenarios but would be more pronounced under the afforestation scenario. These outcomes highlight the significance of land-cover dynamics in water resource management and planning at the catchment.     

Human choices and environmental constraints: deciphering the variability of large game procurement from Mousterian to Aurignacian times (MIS 5-3) in southwestern France

The evolution in the selection of prey made by past humans, especially the Neandertals and the first anatomically modern humans, has been widely debated. Between Marine Isotope Stages (MIS) 5 and 3, the accuracy of absolute dating is still insufficient to precisely correlate paleoclimatic and archaeological data. It is often difficult, therefore, to estimate to what extent changes in species procurement are correlated with either climate fluctuations or deliberate cultural choices in terms of subsistence behavior. Here, the full development of archeostratigraphy and Bayesian statistical analysis of absolute dates allows the archeological and paleoclimatic chronologies to be compared. The variability in hunted fauna is investigated using multivariate statistical analysis of quantitative faunal lists of 148 assemblages from 39 archeological sequences from MIS 5 through MIS 3. Despite significant intra-technocomplex variability, it is possible to identify major shifts in the human diet during these stages. The integration of archeological data, paleoclimatic proxies and the ecological characteristics of the different species of prey shows that the shifts in large game hunting can be explained by an adaptation of the human groups to climatic fluctuations. However, even if Middle and Early Upper Paleolithic men adapted to changes in their environment and to contrasting landscapes, they ultimately belonged to the ecosystems of the past and were limited by environmental constraints.     

Analysis of groundwater quality using water quality index and conventional graphical methods: the Volta region,Ghana

Conventional graphical and statistical methods were used with water quality indices to characterize the hydrochemistry of groundwater from the northern part of the Volta region of Ghana. The objective was to determine the processes that affect the hydrochemistry and the variation of these processes in space among the three main geological terrains: the Buem formation, Voltaian System and the Togo series that underlie the area, and to determine the suitability of groundwater from the area for drinking purposes. The Q-mode cluster analysis reveals three main water groups. The groups established from the Q-mode HCA appear to indicate different degrees of weathering which could further indicate varying levels of fracturing aquifer hydraulic properties. R-mode HCA and factor analysis (using varimax rotation and Kaiser Criterion) were then applied to determine the significant sources of variation in the hydrochemistry. This study finds that groundwater hydrochemistry in the area is controlled by the weathering of silicate and carbonate minerals, as well as the chemistry of infiltrating precipitation. Mineral activity diagrams for the CaO–Na₂O–Al₂O₃–SiO₂–H₂O and CaO–MgO–Al₂O₃–SiO₂–H₂O systems plotted for the area indicate stability in the smectite field and attribute hydrochemistry to the weathering of silicate minerals. Silicate mineral weathering and the effects of precipitation appear to be pervasive among all the three main geological terrains, whereas carbonate weathering is localized among the Voltaian aquifers. Cation exchange does not appear to play a significant role in the hydrochemistry but mild Water quality indices (WQI) were calculated for the samples using the concentrations of Na⁺, Ca²⁺, Mg²⁺, Cl⁻, NO₃ ⁻, F⁻, and EC at the various sample locations. The WQI values indicate that groundwater from the study area is of excellent quality for drinking purposes. WQI values from groundwater samples are averagely higher than samples taken from surface water sources in the area. This implies that geology has had an impact on the WQI of groundwater in the area.     

Paleoproterozoic volcanic rocks in the southern margin of the North China Craton,central China:Implications for the Columbia supercontinent

The volcanic rocks of the Xiong'er Group are situated in the southern margin of the North China Craton(NCC).Research on the Xiong er Group is important to understand the tectonic evolution of the NCC and the Columbia supercontinent during the Paleoproterozoic.In this study,to constrain the age of the Xiong'er volcanic rocks and identify its tectonic environment,we report zircon LA-ICP-MS data with Hf isotope,whole-rock major and trace element compositions and Sr-Nd-Pb-Hf isotopes of the volcanic rocks of the Xiong'er Group.The Xiong'er volcanic rocks mainly consist of basaltic andesite,andesite.dacite and rhyolite,with minor basalt.Our new sets of data combined with those from previous studies indicate that Xiong'er volcanism should have lasted from 1827 Ma to 1746 Ma as the major phase of the volcanism.These volcanics have extremely low MgO.Cr and Ni contents,are enriched in LREEs and LILEs but depleted in HFSEs(Nb,Ta,and Ti),similar to arc-related volcanic rocks.They are characterized by negative zircon ε_(Hf)_(t) values of-17.4 to 8.8,whole-rock initial ~(87)Sr/~(86)Sr values of 0.7023 to 0.7177 andε_(Nd)(t) values of-10.9 to 6.4.and Pb isotopes(~(206)Pb/~(204)Pb =14.366-16.431,~(207)Pb/~(204)Pb =15.106-15.371,~(208)Pb/~(204)Pb= 32.455-37.422).The available elemental and Sr-Nd-Pb-Hf isotope data suggest that the Xiong'er volcanic rocks were sourced from a mantle contaminated by continental crust.The volcanic rocks of the Xiong'er Group might have been generated by high-degree partial melting of a lithospheric mantle that was originally modified by oceanic subduction in the Archean.Thus,we suggest that the subduction-modified lithospheric mantle occurred in an extensional setting during the breakup of the Columbia supercontinent in the Late Paleoproterozoic,rather than in an arc setting.     

Integrated compression of vehicle spatio‐temporal trajectories under the road stroke network constraint

With fast growth of all kinds of trajectory datasets, how to effectively manage the trajectory data of moving objects has received a lot of attention. This study proposes a spatio‐temporal data integrated compression method of vehicle trajectories based on stroke paths coding compression under the road stroke network constraint. The road stroke network is first constructed according to the principle of continuous coherence in Gestalt psychology, and then two types of Huffman tree—a road strokes Huffman tree and a stroke paths Huffman tree—are built, based respectively on the importance function of road strokes and vehicle visiting frequency of stroke paths. After the vehicle trajectories are map matched to the spatial paths in the road network, the Huffman codes of the road strokes and stroke paths are used to compress the trajectory spatial paths. An opening window algorithm is used to simplify the trajectory temporal data depicted on a time–distance polyline by setting the maximum allowable speed difference as the threshold. Through analysis of the relative spatio‐temporal relationship between the preceding and latter feature tracking points, the spatio‐temporal data of the feature tracking points are all converted to binary codes together, accordingly achieving integrated compression of trajectory spatio‐temporal data. A series of comparative experiments between the proposed method and representative state‐of‐the‐art methods are carried out on a real massive taxi trajectory dataset from five aspects, and the experimental results indicate that our method has the highest compression ratio. Meanwhile, this method also has favorable performance in other aspects: compression and decompression time overhead, storage space overhead, and historical dataset training time overhead.