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11.
Weights of Evidence Modeling of Mineral Potential: A Case Study Using Small Number of Prospects,Abra, Philippines 总被引:9,自引:1,他引:9
Weights of evidence (WofE) modeling usually is applied to map mineral potential in areas with large number of deposits/prospects. In this paper, WofE modeling is applied to a case study area measuring about 920 km2 with 12 known porphyry copper prospects. A pixel size of 100 m × 100 m was used in the spatial data analyses to represent in a raster-based GIS lateral extents of prospects and of geological features considered as spatial evidence. Predictor maps were created based on (a) estimates of studentized values of positive spatial association between prospects and spatial evidence; (b) proportion of number of prospects in zones where spatial evidence is present; and (c) geological interpretations of positive spatial association between prospects and spatial evidence. Uncertainty because of missing geochemical evidence is shown to have an influence on tests of assumption of conditional independence (CI) among predictor maps with respect to prospects. For the final predictive model, assumption of CI is rejected based on omnibus test but is accepted based on a new omnibus test. The final predictive model, which delineates 30% of study area as zones with potential for porphyry copper, has 83% success rate and 73% prediction rate. The results demonstrate plausibility of WofE modeling of mineral potential in large areas with small number of mineral prospects. 相似文献
12.
Rainfall thresholds for landsliding in the Himalayas of Nepal 总被引:5,自引:0,他引:5
Emmanuel J. Gabet Douglas W. Burbank Jaakko K. Putkonen Beth A. Pratt-Sitaula Tank Ojha 《Geomorphology》2004,63(3-4):131-143
Landsliding of the hillslope regolith is an important source of sediment to the fluvial network in the unglaciated portions of the Himalayas of Nepal. These landslides can produce abrupt increases of up to three orders of magnitude in the fluvial sediment load in less than a day. An analysis of 3 years of daily sediment load and daily rainfall data defines a relationship between monsoonal rainfall and the triggering of landslides in the Annapurna region of Nepal. Two distinct rainfall thresholds, a seasonal accumulation and a daily total, must be overcome before landslides are initiated. To explore the geomorphological controls on these thresholds, we develop a slope stability model, driven by daily rainfall data, which accounts for changes in regolith moisture. The pattern of rainfall thresholds predicted by the model is similar to the field data, including the decrease in the daily rainfall threshold as the seasonal rainfall accumulation increases. Results from the model suggest that, for a given hillslope, regolith thickness determines the seasonal rainfall necessary for failure, whereas slope angle controls the daily rainfall required for failure. 相似文献
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Khadijeh Alinezhad Elias Ramezani Morteza Djamali Arash Sharifi Alireza Naqinezhad Cyril Aubert Emmanuel Gandouin Ali Pourmand 《第四纪科学杂志》2021,36(4):598-610
Palynological and geochemical analyses provide valuable information about modern and past climatic regimes and vegetation. The impact of climate and humans on past vegetation in the semi-arid areas of northwestern Iran has received increased interest in the wake of warming temperatures in the Middle East. Palynological and down-core XRF elemental abundances from a peat core from Lake Neor enabled a reconstruction of vegetational changes of the past 7000 years over the highlands of northwestern Iran. Periods of increased arboreal pollen (AP) types and high (Artemisia + Poaceae)/Chenopodiaceae ratios along with low titanium abundances, high percentages of total organic carbon, more negative δD values, and higher carbon accumulation rates suggest a relatively wet climate. These conditions have persisted during the periods 6700–6200, 5200–4450 and 3200–2200 cal a bp. The overall low AP values, substantial rise of Chenopodiaceae, high Ti abundances and low values of palaeo-redox proxies, are all evidences of a drier climate, as has been reconstructed for the periods 6200–5200 and 4030–3150 cal a bp and the last 2200 years. An important feature of the last centuries is the increase of anthropogenic and pastoral indicator pollen types. Our results may provide basic data to predict future trends in vegetation dynamics under future climate change in western Asia. 相似文献
16.
This paper presents a novel dynamical model to analyze the long‐term response of a percussive drilling system. This departs from existing approaches that usually consider a single activation and bit/rock interaction cycle for the analysis of the process performance. The proposed model integrates the axial dynamics of an elastic piston and an elastic drill bit, a motion‐dependent pressure law to drive the piston, and a generalized bit/rock interaction law representative of the dynamic indentation taking place at the bit/rock interface. It applies to down‐the‐hole percussive drilling as well as top‐hole, with minor modifications. The model does not account for the angular motion or the hole cleaning, however. The model is first formulated mathematically; then, a finite‐dimensional approximation is proposed for computations. Numerical analyses of the model response, for a low‐size down‐the‐hole percussive system, follow. The period‐1 stationary response for the reference configuration is studied in detail, and parametric analyses assessing the influence on the rate of penetration of the bit/rock interaction parameters, the feed force, and the percussive activation parameters are conducted. These analyses reveal that the multiscale nature of the process is well captured by the model and recover expected trends for the influence of the parameters. They also suggest that a significant increase of the penetration rate can be achieved by increasing the percussive frequency. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
17.
Ahzegbobor P. Aizebeokhai Kehinde D. Oyeyemi Emmanuel S. Joel 《Arabian Journal of Geosciences》2016,9(7):496
Geoelectrical resistivity techniques are increasingly being applied in addressing a wide range of hydrological, environmental, and geotechnical problems. This is due to their effectiveness in near-surface characterization. In the present study, a suite of vertical electrical soundings (VESs) was integrated with 2D geoelectrical resistivity and time-domain induced polarization (IP) imaging to characterize the near-surface and delineate the underlying aquifer in a sedimentary terrain. The geophysical survey was conducted as part of preliminary studies to evaluate the potential of groundwater resource in Iyana-Iyesi and Canaan Land area of Ota, southwestern Nigeria. A high-yield confined sandy aquifer overlain by a low-yield aquitard was delineated; overlying the aquitard is a very resistive and thick layer that is predominantly composed of kaolinitic swelling clay intercalated with phosphate mineral. 相似文献
18.
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. 相似文献
19.
Hamid Geranian Seyed Hassan Tabatabaei Hooshang H. Asadi Emmanuel John M. Carranza 《Natural Resources Research》2016,25(2):145-159
In this contribution, we used discriminant analysis (DA) and support vector machine (SVM) to model subsurface gold mineralization by using a combination of the surface soil geochemical anomalies and earlier bore data for further drilling at the Sari-Gunay gold deposit, NW Iran. Seventy percent of the data were used as the training data and the remaining 30 % were used as the testing data. Sum of the block grades, obtained by kriging, above the cutoff grade (0.5 g/t) was multiplied by the thickness of the blocks and used as productivity index (PI). Then, the PI variable was classified into three classes of background, medium, and high by using fractal method. Four classification functions of SVM and DA methods were calculated by the training soil geochemical data. Also, by using all the geochemical data and classification functions, the general extension of the gold mineralized zones was predicted. The mineral prediction models at the Sari-Gunay hill were used to locate high and moderate potential areas for further infill systematic and reconnaissance drilling, respectively. These models at Agh-Dagh hill and the area between Sari-Gunay and Agh-Dagh hills were used to define the moderate and high potential areas for further reconnaissance drilling. The results showed that the nu-SVM method with 73.8 % accuracy and c-SVM with 72.3 % accuracy worked better than DA methods. 相似文献
20.
Integrated compression of vehicle spatio‐temporal trajectories under the road stroke network constraint 下载免费PDF全文
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. 相似文献