Adelir José Strieder

Cr-Spinels from Brazilian Mafic-Ultramafic Complexes: Metamorphic Modifications

Chemical compositional data on the Cr-spinels from selected Brazilian mafic-ultramafic complexes are presented and compared. The massive stratiform chromitites from the Pium-Hi and Serro complexes and massive podiform chromitites from the Abadiânia and Morro Feio bodies were strongly deformed and metamorphosed from greenschist to epidote-amphibolite facies. The massive stratiform chromitites from Campo Formoso, Medrado-Ipueiras, and Luanga were metamorphosed to the upper amphibolite facies and variably deformed. The large Barro Alto, Niquelândia, and Canabrava (and the small Americano do Brasil, Mangabal-I and -II, and Caraiba) stratiform complexes were polydeformed and metamorphosed to granulite and amphibolite facies. Regardless of their metamorphic and deformational changes, the chromitites still retained some primary features, such as: (1) texture, (2) structures, and (3) original chemical composition. It was observed that the chemical changes imparted to the Cr-spinels during metamorphicdeformational...

Neoproterozoic geotectonic evolution of Tocantins structural province central Brazil.

Abstract Tocantins Structural Province (TSP) is the main tectonic feature in Central Brazil. It separates two main cratonic areas ( former continental plates): the Amazonian Craton to the West and the Sao Francisco Craton to the East. Recent geochronological data (U–Pb and Sm–Nd) and structural studies show that the actual structural framework of the province was developed during the Neoproterozoic. It is herein proposed that Brasiliano Orogenic Cycle in the TSP was developed in four broad tectonic stages: 1) an ocean opening stage began possibly 1270 Ma; 2) an island-arc system development stage started 1000 Ma and its amal- gamation lasted until ca. 800 Ma; 3) a continental collision stage began ca. 800 Ma with the accretion of the island-arcs to the upper Amazonian plate, the closure of the Goias Ocean and the development of a foreland basin upon the lower Sao Francisco plate; and 4) a post-collisional stage (650–500 Ma) with the development of transcurrent faults (Transbrasiliano lineaments), back-thrust reverse faults, and intrusion of alkalic granitic plutons.

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.

The Palma Volcano-Sedimentary Supersuite, Precambrian Sul-Riograndense Shield, Brazil

Komatiites are generally found in Archean greenstone belts, but have been reported in some Mesozoic volcano-sedimentary sequences. The Palma Volcano-Sedimentary Supersuite (PVSS) is a Neoproterozoic sequence composed of meta-ultramafic volcanic rocks, mafic-to-felsic metavolcanic rocks, and metasedimentary rocks ranging from quartzites to chlorite-mica-quartz schists, marbles, and marls. Original PVSS structures were overprinted by two penetrative deformational surfaces (So//Sn and Sn+1); associated metamorphic assemblages are assigned to the upper greenschist facies. Basalts predominate over andesites and rhyodacites, and their major, minor, trace, and rare-earth elements display compatible geochemical trends characteristic of calc-alkaline magmas. Meta-ultramafic rocks are variable-thickness flows in the metasedimentary sequence. Metamorphism caused the development of a metasomatic tremolite zone around the serpentinite bodies, as well as chlorite and talc schist metasomatic zones. Evaluation of the geochemical mobility of the elements showed that the ratios between major and minor elements have not changed in the serpentinites. It was then possible to investigate the lithogeochemical nature of the serpentinites by studying the minor, trace, and rare-earth elements. The lithogeochemical investigation and the structures of the serpentinite bodies enable them to be regarded as komatiitic flows extruded under shallow water. These komatiite flows and calc-alkaline basalt to rhyodacite flows associated with shallow-water sediments suggest that this volcano-sedimentary sequence was developed in a Neoproterozoic arc-related tectonic setting.

A heuristic algorithm for pattern identification in large multivariate analysis of geophysical data sets

This paper aims to present a heuristic algorithm with factor analysis and a local search optimization system for pattern identification problems as applied to large and multivariate aero-geophysical data. The algorithm was developed in MATLAB code using both multivariate and univariate methodologies. Two main analysis steps are detailed in the MATLAB code: the first deals with multivariate factor analysis to reduce the problem of dimension, and to orient the variables in an independent and orthogonal structure; and the second with the application of a novel local research optimization system based on univariate structure. The process of local search is simple and consistent because it solves a multivariate problem by summing up univariate and independent problems. Thus, it can reduce computational time and render the efficiency of estimates independent of the data bank. The aero-geophysical data include the results of the magnetometric and gammaspectrometric (TC, K, Th, and U channels) surveys for the Santa Maria region (RS, Brazil). After the classification, when the observations are superimposed on the regional map, one can see that data belonging to the same subspace appear closer to each other revealing some physical law governing area pattern distribution. The analysis of variance for the original variables as functions of the subspaces obtained results in different mean behaviors for all the variables. This result shows that the use of factor transformation captures the discriminative capacity of the original variables. The proposed algorithm for multivariate factor analysis and the local search system open up new challenges in aero-geophysical data handling and processing techniques.

Geostatistical Framework for Modelling Clay Deposits: Nova Veneza Case Study in Southern Brazil

The region of Criciuma, Southern Brazil, is known as one of the main ceramic industrial districts in the world. Clay minerals are one of the key ingredients in the ceramic industry. Clay characteristics including several physical and chemical parameters need to be known throughout the entire deposit to help in defining the mining plan, scheduling and blending strategies.

Predicting Debris Flow Susceptible AreasThrough GIS Modelling In AparadosDa Serra (Brazil)

This paper aims to present the results of a GIS modelling to predict debris flow susceptible areas in the Aparados da Serra region (Brazil). The region shows a 1000 m high scarp located close to Atlantic Ocean in southern Brazil. The scarp is developed upon sandstones (Botucatu Fm.) and basalts and dacites (Serra Geral Fm.) of the Parana Basin, after the break-up of the Gondwana Supercontinent and the opening of the South Atlantic Ocean. It is a topographic barrier to convective clouds migrating from ocean to the continent, mainly in spring and summer seasons. Geologic, geomorphologic, geotechnical mapping were conducted in order to enable GIS data modelling for debris flow in the region. The prediction of areas susceptible to debris flow along the scarp was based upon USPED algorithms. However, some changes were introduced into USPED algorithms in order to model debris flows in this region. The GIS modelling results distinguished susceptible areas for erosion and deposition of the debris, according the modified USPED procedures. These results were compared with a large debris flow event occurred in December 1995, and also recent small scale and localized debris flow events. All these observed debris flows show good correlation with predicted area of occurrence. Thus, it can be concluded that such GIS modelling can be applied to predict areas susceptible for erosion and deposition of debris related to concentrated convective storms.

Predicting favourable areas for landsliding through GIS modelling in Aparados da Serra (Brazil)

This paper presents the results of GIS modelling for predicting areas where natural landslides can occur in the Aparados da Serra region (Southern Brazil). The scarp is mainly developed upon basalts and dacites (Serra Geral Fm.) and sandstones (Botucatu Fm.) of the Parana Basin. The 1000 m high scarp has been geomorphologically evolving since the break-up of the Gondwana Supercontinent and the opening of the South Atlantic Ocean. Geologic, geomorphologic and geotechnical mapping were conducted in order to acquire field data and to define a conceptual geomorphologic-geotechnical model for GIS data modelling. These mappings were aided with ASTER image processing and aerial photograph analysis. ASTER images do permit a high resolution and accurate DEM. The prediction of areas able to develop natural landslides along the scarp was based upon Factor of Safety (FS) algorithms. The GIS modelling results for Aparados da Serra region were grouped into four categories. The areas with the lowermost FS number were defined as highly susceptible to developing natural landslides. Field investigations upon some existing landslide structures in the region do confirm such predictions. However, large scale FS determination through GIS modelling in order to predict susceptible areas for landslides must be interpreted in a relative manner. FS modelling can, then, be applied to landslide susceptibility mapping in areas of poor historical records, since supported by adequate geological and geotechnical investigations.

Arcabouço Estrutural da Ilha cristalina de Rivera (Uruguai) e sua implicação na potencialidade mineral

A Ilha Cristalina de Rivera, situada no extremo norte do Uruguai, constitui uma janela do embasamento pre-cambriano, circundada por sedimentos da bacia do Parana. Essa regiao, apesar de ter pequena dimensao, possui fundamental importância geoeconomica na Republica Oriental do Uruguai, por possuir diversas ocorrencias minerais de ouro, especialmente em veios de quartzo e uma mina de ouro em atividade (Mina San Gregorio). Esse trabalho apresenta uma analise a respeito do arcabouco estrutural dessa regiao, com base em levantamentos estruturais, aerogeofisicos e imagens de satelite. A partir desses elementos geologicos, o controle estrutural das ocorrencias auriferas e do deposito de ouro e avaliado em escala local e regional. Com base na organizacao estrutural regional, e avaliado o potencial mineral comparativo entre os setores oeste e leste da Ilha Cristalina de Rivera.