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351.
Vanessa Cerqueira Koppe João Felipe Coimbra Leite Costa Rodrigo de Lemos Peroni Jair Carlos Koppe 《Natural Resources Research》2011,20(2):131-142
Data from a mineral deposit are commonly obtained by core drilling. This kind of sampling involves high costs, limiting the
number of drill holes. Additional holes should be located to bring the maximum benefit. The benefit can be evaluated by various
ways and must take into account the goals of sampling. This article presents a case study where the deposit has been sampled
and the new drillings must be added to reduce the uncertainty about a transfer function, Net Present Value (NPV) of the mining
project. There are basically two ways to choose locations where new drillings should be placed for cases where the aim of
sampling is to reduce uncertainty about a global function: the addition of new drillings outlining a quasi regular grid with
previously collected drillings or the addition of new drillings on the locations of high uncertainty about the attribute of
interest (or the attribute that is considered most influential in the transfer function). The performances of these patterns
on reducing the uncertainty measured by the function selected are compared. The results point out that the most efficient
pattern relates to the distribution (histogram) of the uncertainty about the attribute of interest. Thus, the choice of which
sampling pattern should be adopted varies depending on data distribution and its influence on the transfer function. 相似文献
352.
Heidi Wehrmann Kaj Hoernle Guillaume Jacques Dieter Garbe-Schönberg Kai Schumann Julia Mahlke Luis E. Lara 《International Journal of Earth Sciences》2014,103(7):1945-1962
Here we present the first systematic investigation of volatile geochemistry along the Southern Volcanic Zone (SVZ) of Chile. Holocene olivine-hosted melt inclusions in the most mafic tephras sampled from 16 volcanoes along the volcanic front of the SVZ between 33°S and 43°S were analysed for pre-eruptive sulphur, chlorine, and major element contents. These results are combined with trace element compositions of the host whole rocks. The highest fractionation-corrected gas contents occur in the least-degassed melt inclusions from small monogenetic cones of Los Hornitos, Cabeza de Vaca, and Apagado from both the transitional and the southern-central SVZ, reaching ~3,000 μg/g S and 1,400 μg/g Cl, while the lowest abundances of ~1,100 μg/g S and ~600 μg/g Cl were found in the central SVZ at Volcán Lonquimay, Volcán Llaima, and Volcán Villarrica. Chlorine co-varies with trace element indicators for the degree of melting and/or source enrichment, such that the lowest Cl contents are found in high-degree melts from the most depleted mantle sources. The size of the volcanic edifices correlates inversely with Cl abundances in the melt. This could reflect more extensive degassing during ascent through the complex magma plumbing systems beneath the stratovolcanoes or greater dilution during larger degrees of melting of more depleted sources, or a combination of these factors. Compared to other subduction zones, the SVZ melt inclusions exhibit Cl and S abundances in the same range as most of those from the Central American and those from the Marianas arcs. 相似文献
353.
Gerson P. Almeida Stephan Borrmann João B. V. Leal Junior 《Meteorology and Atmospheric Physics》2014,125(3-4):159-176
Ground-based aerosol instrumentation covering particle size diameters from 25 nm to 32 µm was deployed to determine aerosol concentration and cloud condensation nuclei (CCN)-activation properties at water vapor supersaturations in the range of S = 0.20–1.50 % in the remote Brazilian northeast semi-arid region (NEB) in coastal (maritime) and continental (inland) regimes. The instruments measured aerosol number concentration and activation spectra for CCN and revealed that aerosol properties are sensitive with respect to the sources as a function of the local wind circulation system. The observations show that coastal aerosol total number concentrations are above 3,000 cm?3 on average, exhibiting concentration peaks depending on the time of the day in a consistent daily pattern. The variation on aerosol concentration has also influences on the fraction of particles active as CCN. At 1.0 % water vapor supersaturation, the fraction can reach as high as 80 %. Inland aerosol total concentrations were about 1,800–1,900 cm?3 and did not show much diurnal variation. The fraction of particles active as CCN observed inland depend on the history of the air masses, and was much higher when air masses were originated over the sea. It was found that (NH4)2SO4 and NaCl are the major soluble inorganic fraction of the aerosols at the coast. The major fraction of NaCl was present in the coarse mode, while ammonium sulfate dominates the inorganic fraction at the submicron range, with about 10 % of the total aerosol mass at 0.32 µm. Inorganic compounds are almost absent in particles with sizes around 0.1 μm. The study suggests that the air masses with high concentration of CCN originate at the sea. The feasible explanation lies in the fact that the NEB’s beaches have a particular morphology that produces a wide surf zone and creates a large load of aerosols when combined with strong and permanent winds of the region. 相似文献
354.
The volcano Hekla in south Iceland had its latest eruption in January–March 1991. The eruption was accompanied and followed by considerable seismic activity. This study examines the seismicity in the Hekla region (63°42′–64°18′N, 18°30′–20°12′W) during a period when the high activity related to the eruption had ceased, from July 1991 to October 1995. The aim is to define the level of the normal background seismicity of the area that can be compared to the eruption-related activity. The Hekla Volcano proper was generally aseismic during the study period. The most prominent earthquake cluster is in the neighbouring Torfajökull Volcano. The epicentres are concentrated in the western part of the caldera and west of it. The hypocentres are located at all depths from the surface down to 14?km, with highest activity at 5–12?km. Inside this cluster, in the northwest part of the caldera, is a spherical volume void of earthquakes, approximately 4?km in diameter and centred at 8?km depth. This is interpreted as a cooling magma body. Small, low-frequency events of volcanic origin were occasionally recorded at Torfajökull. This activity has mainly occurred in swarms and was most abundant during the first year of the study period, presumably reflecting some kind of connection to the 1991 Hekla eruption. Our study area also includes the easternmost section of the South Iceland seismic zone, a transform zone characterized by bookshelf faulting on transverse faults. Two lineaments of epicentres were identified, roughly corresponding to mapped faults of the South Iceland seismic zone. The hypocentres are relatively deep, mainly at 6–12?km, matching the general trend of hypocentral depth increasing toward the east. The seismicity is highest in the area of the mapped faults. However, the epicentres extend beyond them and indicate greater width of the South Iceland seismic zone, or 20–30?km rather than approximately 10?km as indicated by the length of the surface faults. The seismicity in the volcanic systems of Hekla and Vatnafjöll shows some characteristics of the South Iceland seismic zone. Epicentres are concentrated into two N–S lineaments, one of which coincides with the location of the 1987 Vatnafjöll earthquake (Mw=5.9), a strike-slip event on a N- to S-trending fault. The hypocentres of the Hekla–Vatnafjöll events are mainly at 8–13?km depth, which indicates a continuation of the depth trend of the earthquakes of the South Iceland seismic zone. The events located at Hekla proper and immediately north of it are all of low-frequency character, which can be held as an indication of volcanic origin. On the other hand, they show clear S arrivals at observing stations like normal high-frequency tectonic earthquakes. 相似文献
355.
ABSTRACT It is important to understand the exact process whereby very large amounts of sediment are transported. This paper reports peculiar conglomerate beds reflecting the transition of submarine debris flows into hyperconcentrated flows, something that has been well documented only in subaerial debris-flow events until now. Voluminous debris flows generated along a Cretaceous submarine channel, southern Chile, transformed immediately into multiphase flows. Their deposits overlie fluted or grooved surfaces and comprise a lower division of clast-supported and imbricated pebble–cobble conglomerate with basal inverse grading and an upper division of clast- to matrix-supported, disorganized conglomerate with abundant intraformational clasts. The conglomerate beds suggest temporal succession of turbidity current, gravelly hyperconcentrated flow, and mud-rich debris flow phases. The multiphase flows resulted from progressive dilution of gravelly but cohesive debris flows that could hydroplane, in contrast to the flow transitions in subaerial environments, which involve mostly non-cohesive debris flows. This finding has significant implications for the definition, classification, and hazard assessment of submarine mass-movement processes and characterization of submarine reservoir rocks. 相似文献
356.
Results of observations of the Galilean satellites during the week of the impact of comet Shoemaker-Levy 9 on Jupiter are reported. These observations have been carried out at the Pico dos Dias observatory, at Brasópolis, Brazil. The satellites's light flux was monitored with a photometer during the time of the predicted impact of fragments B, F, J and L. No conclusive flash was observed in any of the data adquired. This non-detection imposes an upper limit to the energy released during the impact of these fragments.Observations carried out at the Observatório do Pico dos Dias, operated by the Laboratório Nacional de Astrofísica/CNPq/MCT, Brazil 相似文献
357.
358.
The aim of this paper is to test the ability of neural network approaches to hindcast the spring standardized precipitation index on a 6‐month time scale (SPI6) in Portugal, based on winter large‐scale climatic indices. For this purpose, the linkage of the spring SPI time series with the winter North Atlantic Oscillation (NAO) and the sea surface temperature (SST) was investigated by means of maps of the correlation coefficient for the period from October 1910 to September 2004. The results indicate that the winter NAO is a good predictor for the SPI6 of the spring (SPI6 finishing in April, May and June, SPI6April, SPI6May and SPI6June, respectively) for the northern, central and southern regions of Portugal. The winter SST1 (area of the Mediterranean Sea) must only be considered for the northern region, and the winter SST3 (area of the North Atlantic between Iberia and North America) only for the southern region. Spatial maps of predictive SPI6 for April, May and June were created and validated. The neural models explained more than 81% of the total variance for the SPI6April and SPI6May and more than 64% of the total variance for the SPI6June. Probability maps were also developed considering the values predicted by the neural methods for the spring months and all drought categories (moderate, severe and extreme). These maps indicating the probability of droughts can provide valuable support for the integrated planning and management of water resources throughout Portugal. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
359.
360.
Britta Planer-Friedrich Cornelia Härtig Heidi Lissner Jörg Steinborn Elke Süß M. Qumrul Hassan Anwar Zahid Mahmood Alam Broder Merkel 《Applied Geochemistry》2012
Currently, the most widely accepted hypothesis to explain high As concentrations in Bangladesh groundwaters is that dissolved organic C (DOC) reduces solid Fe (hydr)oxides and mobilizes sorbed arsenate. The nature of the DOC and its release mechanism are still controversial. Based on weekly to biweekly sampling over the course of one monsoon cycle at six monitoring wells of different depths, it is proposed that storativity changes drive natural DOC release from clay–peat layers to the adjacent aquifers. With a decrease in hydraulic heads during the dry season, total mineralization and DOC concentrations increased. With the onset of the rainy season and an increase in hydraulic heads, release of clay–peat derived components stopped and vertical water displacement due to groundwater recharge from rainwater occurred, causing aquifer flushing and a decrease in total mineralization and DOC concentrations. Total As and DOC concentrations correlated over depth. However, at the depth of maximum concentrations, the As peak was observed during the rainy season. At present, the reason for this inverse seasonal trend between As and DOC is unclear. Higher mineralization or DOC concentrations could lead to increased As sorption or the increased arsenite release is a time-lag abiotic or microbial response to the DOC peak. The vulnerability of the Pleistocene aquifer towards increased As concentrations was found to be much higher than previously assumed. Though sorption capacities were determined to be higher than in the Holocene aquifer, probably due to intact Fe (hydr)oxides, long-term continuous As input from overlying clay and peat layers by the proposed seasonal storativity changes has led to increased aqueous As concentrations of 85 μg/L, considerably higher than drinking water standards. Until now, aquifer and especially aquitard and aquiclude hydraulics have not been considered sufficiently when attempting to explain As mobilization in Bangladesh. 相似文献