The July 1974 solar events: A possible lower limit for microwave activity

The active region McMath 10433 was the source of several flares and radio outbursts during the early part of July 1974. This region was tracked continuously, for several periods during the month at 22.2 GHz using a telescope with a 4 beam. Comparison with the results obtained simultaneously with a normal 7 GHz solar patrol instrument indicate that there is important burst activity occurring at levels below the detection limit of normal solar patrol instruments. The time-development morphology of these bursts is similar to those normally observed and has enabled the simple events to be re-interpreted. A completely new type of event - the fast absorption - has also been recognized. The correlation of the microwave events with SPA events observed on VLF propagation is also discussed.Spending a sabbatical year at CRAAM, São Paulo, Brazil.     

Additional Samples: Where They Should Be Located

Information for mine planning requires to be close spaced, if compared to the grid used for exploration and resource assessment. The additional samples collected during quasimining usually are located in the same pattern of the original diamond drillholes net but closer spaced. This procedure is not the best in mathematical sense for selecting a location. The impact of an additional information to reduce the uncertainty about the parameter been modeled is not the same everywhere within the deposit. Some locations are more sensitive in reducing the local and global uncertainty than others. This study introduces a methodology to select additional sample locations based on stochastic simulation. The procedure takes into account data variability and their spatial location. Multiple equally probable models representing a geological attribute are generated via geostatistical simulation. These models share basically the same histogram and the same variogram obtained from the original data set. At each block belonging to the model a value is obtained from the n simulations and their combination allows one to access local variability. Variability is measured using an uncertainty index proposed. This index was used to map zones of high variability. A value extracted from a given simulation is added to the original data set from a zone identified as erratic in the previous maps. The process of adding samples and simulation is repeated and the benefit of the additional sample is evaluated. The benefit in terms of uncertainty reduction is measure locally and globally. The procedure showed to be robust and theoretically sound, mapping zones where the additional information is most beneficial. A case study in a coal mine using coal seam thickness illustrates the method.     

Uncertainty Estimate in Resources Assessment: A Geostatistical Contribution

For many decades the mining industry regarded resources/reserves estimation and classification as a mere calculation requiring basic mathematical and geological knowledge. Most methods were based on geometrical procedures and spatial data distribution. Therefore, uncertainty associated with tonnages and grades either were ignored or mishandled, although various mining codes require a measure of confidence in the values reported. Traditional methods fail in reporting the level of confidence in the quantities and grades. Conversely, kriging is known to provide the best estimate and its associated variance. Among kriging methods, Ordinary Kriging (OK) probably is the most widely used one for mineral resource/reserve estimation, mainly because of its robustness and its facility in uncertainty assessment by using the kriging variance. It also is known that OK variance is unable to recognize local data variability, an important issue when heterogeneous mineral deposits with higher and poorer grade zones are being evaluated. Altenatively, stochastic simulation are used to build local or global uncertainty about a geological attribute respecting its statistical moments. This study investigates methods capable of incorporating uncertainty to the estimates of resources and reserves via OK and sequential gaussian and sequential indicator simulation The results showed that for the type of mineralization studied all methods classified the tonnages similarly. The methods are illustrated using an exploration drill hole data sets from a large Brazilian coal deposit.     

Geostatistical Simulation of Acoustic Log Data for Seismic Depth Conversion

Seismic reflection methods measure the time a seismic wave takes to travel through the ground, from the user defined source to a series of signal monitoring sensors known as geophones. The measured times need to be depth converted to allow for integration with other geological data. In order to convert from time to depth, an estimate of the rock volume velocity field must be made. The velocity field estimate can be made by assignment of velocity estimates to a geological model independent of the seismic processing. This article presents the results of using the acoustic geophysical log data extrapolated via sequential Gaussian simulation to derive the velocity field. The uncertainties associated with the velocity estimates were significant and provided the means to assess confidence limits for the actual depth determination. The technique is assessed by application to a major coal deposit, approximately 2.1 m thick and 210 m deep. Considering only the uncertainty associated with estimating the velocity field, half of the confidence interval values showed approximately 1 m of uncertainty in depth. The application of sequential Gaussian simulation to model the 3D distribution of acoustic velocity can be extended to other geophysical log parameters or derived estimates.     

Assessing Uncertainty Associated with the Delineation of Geochemical Anomalies

A pedogeochemical exploratory survey of gold deposits was carried out in the region of São Sepé (southernmost Brazil). The region comprises a predominantly metamorphosed belt of volcanoclastics, sediments, serpentinites, basalts, gabbros, chert, tuffs, and banded iron formation of the Proterozoic age. The anomalies were identified first by stream sediment heavy mineral survey at the regional scale of exploration. Once spatial continuity was modeled, ordinary block kriging was performed to generate geochemical maps. Indicator block kriging also was used as an alternative in analyzing and interpreting geochemical data. A novel approach is proposed, which combines both ordinary and indicator kriging for delineating geochemical anomalies. Probability maps proved to be appropriate for selecting new sites for further exploration. Gold anomalies in soils trending NE were well defined by geostatistical analysis and subsequently confirmed by drilling.     

Geology and geochemistry of the Caxias gold deposit, and geochronology of the gold-hosting Caxias Microtonalite, São Luís Craton, northern Brazil

The Caxias gold deposit, located in the São Luís Craton, is hosted by a steeply dipping strike-slip shear zone crosscutting schists and a fine-grained, hydrothermally altered tonalite (Caxias Microtonalite). Petrography and whole-rock geochemistry have characterized both pelitic and mafic protoliths for the hosting schists. The Caxias Microtonalite shows major and trace element behavior compatible with modern calc-alkaline, metaluminous, subduction-related granitoids. Geochronological studies on the Caxias Microtonalite have defined a minimum crystallization age of 1985±4 Ma, obtained by single-zircon Pb evaporation, and Sm–Nd crustal residence age (T_DM) of 2.17 Ga, with Nd(T) +0.74, suggesting a juvenile protolith. The exact origin and role of the Caxias Microtonalite remain uncertain. It may be interpreted as representing either a late manifestation of the regionally dominant Tromaí magmatism, or a juvenile episode unrelated to this major magmatism. Rock, quartz veins, and saprolite geochemistry have shown that As, Sb, Ba, Rb, V, Cr, Co, and Ni, as well as Au, are useful elements that can be used in exploration for similar deposits in the region.     

Accounting for Extensive Secondary Information to Improve Watertable Mapping

Generally, multiple variables are sampled in addition to the one used to quantify the main phenomenon under study. In some situations, this secondary information is sampled exhaustively for the study area and can be incorporated for helping in estimating the variable of interest. There are several methodologies available for incorporating densely sampled secondary information. Collocated cokriging is one of these methodologies and has the advantage to other methodologies, of accounting for spatial correlation. However, one drawback in its application comes from the difficulty in modeling the coregionalization. Simplified models of coregionalization were developed specifically for the collocated cokriging case. This paper presents, through a case study, the incorporation of dense secondary information using collocated cokriging. The watertable above a coal underground mine is mapped using water-level readings at monitoring piezometers complemented by highly correlated topographic data. The incorporation of dense secondary information through the utilization of a linear model of coregionalization and Markov models is comparatively evaluated in various aspects such as mathematical quality, coherence with the natural phenomena and the ease of utilization and modeling. Simple kriging with local varying means also is evaluated as it accounts for nonstationarity and is easily implemented. All these methods that incorporate topography as secondary information for mapping the watertable provided maps more in accordance with the natural phenomena than ordinary kriging using the principal attribute solely. Among these methods, strictly collocated cokriging using a linear model of coregionalization showed overall superior performance.     

Coastal protection of the isle of usedom — conceptional design of an offshore breakwater system at the streckelsberg, Baltic Sea

The Isle of Usedom is located in the South of the Baltic Sea on the border between Poland and Germany. The Streckelsberg is midway along the coastline of the island. The cliff coast area is extremely exposed to waves.Coastal protection works have been carried out here for the last 100 years, starting in 1895 with the construction of a revetment. All efforts could not solve the erosion problems in the long-term. Therefore, it was decided to install a new system of coastal protection measures in 1994. The conceptional design includes a system of three offshore breakwaters in combination with a beach nourishment system. To minimize downdrift erosion a groyne scheme will be additionally installed.The aim of the offshore breakwaters is to reduce the wave energy transformed into the sheltered area and to consequently reduce the longshore sediment transport. It is expected to support the natural development of a salient which will form the main part of the complete coastal protection system.     

Choosing Between Two Kind of Sampling Patterns Using Geostatistical Simulation: Regularly Spaced or at High Uncertainty Locations?

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.     

Gamma-Ray Data Processing and Integration for Lode-Au Deposits Exploration

A large number of mineral deposits are associated with hydrothermal processes, especially auriferous deposits. In such processes, studies on percolating fluids may indicate the presence of potash (K), among other elements. In this study, aerogammaspectrometric data-processing methodologies are evaluated, especially those methods based on the suppression of the primary contribution of potassium, the result of lithological and soil variations, and to environmental conditions. Resulting maps point out the contribution of hydrothermal K. This processing procedure was used because of the association of hydrothermal K and auriferous mineralizations according to the deposit model defined for the studied region. Intensity maps locate the areas with great influence of hydrothermal K. Data integration required to improve a change in the gammaspectrometric data processing in order to positively correlate hydrothermalised areas. Data integration could distinguish high and medium favorable targets for mineral exploration of lode-Au deposits in the studied region.