Deriving Optimal Exploration Target Zones on Mineral Prospectivity Maps     

Pravesh Debba  Emmanuel J. M. Carranza  Alfred Stein  Freek D. van der Meer 《Mathematical Geosciences》2009,41(4):421-446

This paper describes a quantitative methodology for deriving optimal exploration target zones based on a probabilistic mineral prospectivity map. The methodology is demonstrated in the Rodalquilar mineral district in Spain. A subset of known occurrences of mineral deposits of the type sought was considered discovered and then used as training data, and a map of distances to faults/fractures and three band ratio images of hyperspectral data were used as layers of spatial evidence in weights-of-evidence (WofE) modeling of mineral prospectivity in the study area. A derived posterior probability map of mineral deposit occurrence showing non-violation of the conditional independence assumption and having the highest prediction rate was then put into an objective function in simulated annealing in order to derive a set of optimal exploration focal points. Each optimal exploration focal point represents a pixel or location within a circular neighborhood of pixels with high posterior probability of mineral deposit occurrence. Buffering of each optimal exploration focal point, based on proximity analysis, resulted in optimal exploration target zones. Many of these target zones coincided spatially with at least one occurrence of mineral deposit of the type sought in the subset of cross-validation (i.e., presumed undiscovered) mineral deposits of the type sought. The results of the study showed the usefulness of the proposed methodology for objective delineation of optimal exploration target zones based on a probabilistic mineral prospectivity map.  相似文献   

Quantitative reconstruction of climatic variations during the Bronze and early Iron ages based on pollen and lake-level data in the NW Alps, France     

M. Magny  O. Peyron  E. Gauthier  Y. Rouche  A. Bordon  Y. Billaud  E. Chapron  A. Marguet  P. Ptrequin  B. Vannire 《Quaternary International》2009,200(1-2):102

Vegetation and lake-level data from the archaeological site of Tresserve, on the eastern shore of Lake Le Bourget (Savoie, France), are used to provide quantitative estimates of climatic variables over the period 4000–2300 cal BP in the northern French Pre-Alps, and to examine the possible impact of climatic changes on societies of the Bronze and early Iron Ages. The results obtained indicate that phases of higher lake level at 3500–3100 and 2750–2350 cal BP coincided with major climate reversals in the North Atlantic area. In west-central Europe, they were marked by cooler and wetter conditions. These two successive events may have affected ancient agricultural communities in west-central Europe by provoking harvest failures, more particularly due to increasing precipitation during the growing season. However, archaeological data in the region of Franche-Comté (Jura Mountains, eastern France) show a general expansion of population density from the middle Bronze Age to the early Iron Age. This suggests a relative emancipation of proto-historic societies from climatic conditions, probably in relation to the spread of new modes of social and economic organisation.  相似文献   

Water‐bottom multiple attenuation by Kirchhoff extrapolation     

Emmanuel Spadavecchia  Vincenzo Lipari  Nicola Bienati  Giuseppe Drufuca 《Geophysical Prospecting》2013,61(4):725-734

Despite being less general than 3D surface‐related multiple elimination (3D‐SRME), multiple prediction based on wavefield extrapolation can still be of interest, because it is less CPU and I/O demanding than 3D‐SRME and moreover it does not require any prior data regularization. Here we propose a fast implementation of water‐bottom multiple prediction that uses the Kirchhoff formulation of wavefield extrapolation. With wavefield extrapolation multiple prediction is usually obtained through the cascade of two extrapolation steps. Actually by applying the Fermat’s principle (i.e., minimum reflection traveltime) we show that the cascade of two operators can be replaced by a single approximated extrapolation step. The approximation holds as long as the water bottom is not too complex. Indeed the proposed approach has proved to work well on synthetic and field data when the water bottom is such that wavefront triplications are negligible, as happens in many practical situations.  相似文献   

Magnetic Characterization of Amphibolites from the Fomopéa Pluton (West Cameroon): Their Implication in the Pan-African Deformation of the Central African Fold Belt     

NJANKO Théophile  FOZING Eric Martial  KWéKAM Maurice  YAKEU SANDJO Angéline Flore  NJONFANG Emmanuel 《《地质学报》英文版》2012,86(1):73-84

The Fomopea granitic pluton is emplaced in gnessic and amphibolitic basement.These gneissic and amphibolitic basement rocks are represented in the pluton's body as sub-rounded,elongated or stretched xe...  相似文献   

An approach for estimating sustainable yield of karst water in data sparse regions     

Dan Yin  Longcang Shu  Chundong Xu  Zhenlong Wang  Emmanuel Kwame Appiah-Adjei 《Environmental Earth Sciences》2012,66(2):399-407

This study presents an approach for transferring the qualitative analysis of groundwater sustainability for development to quantitative evaluation by an analogy of two similar regions. A concept of groundwater exploitation sustainability (GES), which is an evaluation index based on water supply capability, eco-geo-environment maintaining capability and the harmony between water and society, is put forward. The fuzzy analytic hierarchy process method is applied to calculate the GES for the Xiangshan and Dianchang karst groundwater sources in the Huaibei city, Anhui Province, China. The GES of the Xiangshan karst system was calculated to be 0.53 and represents medium exploitation sustainability, while that for the Dianchang is relatively high with a value of 0.70. These two karst systems are separate units but have similar hydrogeological conditions. The Dianchang area had limited groundwater observation data, while the Xiangshan area had long series of observation data, which enabled the computation of the sustainable yield. The sustainable yield of the Xiangshan karst area was used to calibrate the GES, and develop a linear equation between the GES and sustainable yield, which was used to calculate the sustainable yield of the Diangchang karst area as 40.4 million m³.  相似文献   

Grain boundary and volume diffusion experiments in yttrium aluminium garnet bicrystals at 1,723 K: a miniaturized study     

Katharina?Marquardt  Elena?Petrishcheva  Emmanuel?Gardés  Richard?Wirth  Rainer?Abart  Wilhelm?Heinrich 《Contributions to Mineralogy and Petrology》2011,162(4):739-749

Yb-Y inter-diffusion along a single grain boundary of a synthetic yttrium aluminium garnet (YAG) bicrystal has been studied using analytical transmission electron microscopy (ATEM). To investigate the diffusion, a thin-film containing Yb as the diffusant was deposited perpendicular to the bicrystal grain boundary by pulsed laser deposition (PLD). Structural properties and their change with time in both the diffusant source and the grain boundary are reported. The diffusion profiles are incorporated in a numerical diffusion model, which is applied to determine the grain boundary diffusion coefficient, D _gb , at 1.723 K it is equal to 3 × 10⁻¹⁵ m²/s. We find that grain boundary diffusion is 4.85 orders of magnitude faster than volume diffusion, which was determined from the same diffusion experiment. This result is discussed in the context of special versus general grain boundaries. Finally, we successfully tested the capability of synchrotron-based nano-X-ray fluorescence analysis to map micro-chemical patterns in two dimensions with sub-micrometre resolution.  相似文献   

Experimental growth of åkermanite reaction rims between wollastonite and monticellite: evidence for volume diffusion control     

Bastian Joachim  Emmanuel Gardés  Rainer Abart  Wilhelm Heinrich 《Contributions to Mineralogy and Petrology》2011,161(3):389-399

Growth rates of monomineralic, polycrystalline åkermanite (Ca₂MgSi₂O₇) rims produced by solid-state reactions between monticellite (CaMgSiO₄) and wollastonite (CaSiO₃) single crystals were determined at 0.5 GPa dry argon pressure, 1,000–1,200°C and 5 min to 60 h, using an internally heated pressure vessel. Inert Pt-markers, initially placed at the monticellite–wollastonite interface, indicate symmetrical growth into both directions. This and mass balance considerations demonstrate that rim growth is controlled by transport of MgO. At 1,200°C and run durations between 5 min and 60 h, rim growth follows a parabolic rate law with rim widths ranging from 0.4 to 16.3 μm indicating diffusion-controlled rim growth. The effective bulk diffusion coefficient \( D_{\text{eff,MgO}}^{\text{Ak}} \) is calculated to 10^?15.8±0.1 m² s^?1. Between 1,000°C and 1,200°C, the effective bulk diffusion coefficient follows an Arrhenius law with E _a = 204 ± 18 kJ/mol and D ₀ = 10^?8.6±1.6 m² s^?1. Åkermanite grains display a palisade texture with elongation perpendicular to the reaction interface. At 1,200°C, average grain widths measured normal to elongation, increase with the square root of time and range from 0.4 to 5.4 μm leading to a successive decrease in the grain boundary area fraction, which, however, does not affect \( D_{\text{eff,MgO}}^{\text{Ak}} \) to a detectible extent. This implies that grain boundary diffusion only accounts for a minor fraction of the overall chemical mass transfer, and rim growth is essentially controlled by volume diffusion. This is corroborated by the agreement between our estimates of the effective MgO bulk diffusion coefficient and experimentally determined volume diffusion data for Mg and O in åkermanite from the literature. There is sharp contrast to the MgO–SiO₂ binary system, where grain boundary diffusion controls rim growth.  相似文献   

From Predictive Mapping of Mineral Prospectivity to Quantitative Estimation of Number of Undiscovered Prospects     

Emmanuel J. M. Carranza 《Resource Geology》2011,61(1):30-51

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.  相似文献   

Formation of the Dongmozhazhua Pb–Zn Deposit in the Thrust‐Fold Setting of the Tibetan Plateau,China: Evidence from Fluid Inclusion and Stable Isotope Data     

YingChao LIU  ZengQian HOU  ZhuSen YANG  ShiHong TIAN  TianNan YANG  YuCai SONG  HongRui ZHANG  Emmanuel John M. CARRANZA 《Resource Geology》2011,61(4):384-406

The Dongmozhazhua deposit, the largest Pb–Zn deposit in south Qinghai, China, is stratabound, carbonate‐hosted and associated with epigenetic dolomitization and silicification of Lower–Middle Permian—Upper Triassic limestones in the hanging walls of a Cenozoic thrust fault system. The mineralization is localized in a Cenozoic thrust‐folded belt along the northeastern edge of the Tibetan plateau, which was formed due to the India–Asia plate collision during the early Tertiary. The deposit comprises 16 orebodies with variable thicknesses (1.5–26.3 m) and lengths (160–1820 m). The ores occur as dissemination, vein, and breccia cement. The main sulfide assemblage is sphalerite + galena + pyrite + marcasite ± chalcopyrite ± tetrahedrite, and gangue minerals consist mainly of calcite, dolomite, barite, and quartz. Samples of pre‐ to post‐ore stages calcite yielded δ¹³C and δ¹⁸O values that are, respectively, similar to and lower than those yielded by the host limestones, suggesting that the calcite formed from fluids derived from carbonate dissolution. Fluid inclusions in calcite and sphalerite in the polymetallic sulfidization stage mostly comprise liquid and gas phases at room temperature, with moderate homogenization temperatures (100–140°C) and high salinities (21–28 wt% NaCl eq.). Micro‐thermometric fluid inclusion data point to polysaline brines as ore‐forming fluids. The δD and δ¹⁸O values of ore fluids, cation compositions of fluid inclusions, and geological information suggest two main possible fluid sources, namely basinal brines and evaporated seawater. The fluid inclusion data and regional geology suggest that basinal brines derived from Tertiary basins located southeast of the Dongmozhazhua deposit migrated along deep detachment zones of the regional thrust system, leached substantial base metals from country rocks, and finally ascended along thrust faults at Dongmozhazhua. There, the base‐metal‐rich basinal brines mixed with bacterially‐reduced H₂S‐bearing fluids derived from evaporated seawater preserved in the Permo–Triassic carbonate strata. The mixing of the two fluids resulted in Pb–Zn mineralization. The Dongmozhazhua Pb–Zn deposit has many characteristics that are similar to MVT Pb–Zn deposits worldwide.  相似文献   

http://www.sciencedirect.com/science/article/pii/S1674987111000405   总被引：1，自引：0，他引：1  

Jean de la Paix Mupenzi  Lanhai Li  Jiwen Ge  Achal Varenyam  Gabriel Habiyaremye  Nzayisenga Theoneste  Kamanzi Emmanuel 《地学前缘(英文版)》2011,2(4):599-607

This study has focused on the processes of soil degradation and chemical element concentration in tea-growing regions of Rwanda, Africa. Soil degradation accelerated by erosion is caused not only by topography but also by human activities. This soil degradation involves both the physical loss and reduction in the amount of topsoil associated with nutrient decline. Soil samples were collected from eleven tropical zones in Rwanda and from variable depth within each collecting site. Of these, Samples from three locations in each zone were analyzed in the laboratory, with the result that the pH of all soil samples is shown to be less than 5 (pH < 5) with a general average of 4.4. The elements such as iron (Fe), copper (Cu), manganese (Mn), and zinc (Zn) are present in high concentration levels. In contrast calcium (Ca) and sodium (Na) are present at low-level concentrations and carbon (C) was found in minimal concentrations. In addition, elements derived from fertilizers, such as nitrogen (N), phosphorous (P), and potassium (K) which is also from minerals such as feldspar, are also present in low-level concentrations. The results indicate that the soil in certain Rwandan tea plantations is acidic and that this level of pH may help explain, in addition to natural factors, the deficiency of some elements such as Ca, Mg, P and N. The use of chemical fertilizers, land use system and the location of fields relative to household plots are also considered to help explain why tea plantation soils are typically degraded.  相似文献