Botryoidal platinum, palladium and potarite from the Bom Sucesso stream, Minas Gerais, Brazil: Compositional zoning and origin

Platinum-Pd nuggets from the Born Sucesso stream alluvium Minas Gerais, Brazil. have been investigated by electron-probe microanalysis. The nuggets attain 1 mm in maximum dimension and have a botryoidal habit, with pronounced compositional core-to-margin zoning of internal structures, Although there is a wide variation in internal morphology and individual zones vary markedly in thickness (<1-100 mum), a typical composite arborescent nugget comprises a broad irregular core region of massive auriferous Pd-Hg alloy (potarite delta-PdHg) or cavity space + relict potarite enclosed by a narrow zone of platiniferous, palladium or alloy of near Pt50Pd50 composition, and is progressively oscillatory zoned by palladian platinum, with growth eventually enveloping the whole botryoidal colony, to a narrow rim of palladian platinum or pure platinum. Other nuggets comprise an arborescent to dendritic core of auriferous potarite, a broad internal zone of either pure platinum or palladian platinum, and a narrow rim of platinum, the mineral palladium contains up to about 65 at.% Pd; this is the first detailed modern confirmation of palladium in its type locality. Auriferous potarite ranges in composition from similar toPd(3)Hg(2) to near Pd(Hg,Au). The origin of these nuggets remains unclear, but their mineralogy is broadly equivalent to that of palladian gold. potarite and platinum in alluvial sediments and overburden from Devon, England, which are considered to be detrital, and their platinum-group-clement geochemistry is consistent with precipitation from hydrothermal fluids. We suggest that the Bom Sucesso nuggets resulted from high-level episodic hydrothermal alteration of mafic and ultramafic rocks within the drainage basin, with the remobilized Pt and Pd precipitated in open spaces in the enclosing metaquartzites.

Análise geoambiental da região de marília, SP: Suscetibilidade a processos erosivos frente ao histórico de ocupação da área

The study area comprises the western portion of the Marília Plateau, State of São Paulo, southeastern Brazil. The geological substrate encompasses Cretaceous sedimentary rocks of the Bauru Group and local Neocenozoic units like colluvium aprons, fluvial terrace deposits, in situ regoliths, and modern alluvial deposits. In a geomorphologic sense, the study area might be characterized as showing two main pediplanes, viz. P1 Surface (upper) and P2 Surface (lower), both surfaces are presently under dissecation processes. After the 1920's the expansion of the railroad system fostered the removal of the natural vegetation, which in turn was followed by the introduction of coffee, peanut, corn and cotton crops. This intense exploitation was conducted without respect to the soil carrying capacity and its natural susceptibility to erosional processes, including an aggressive form known as voçoroca. As a result, the study shows that the most susceptible material includes colluvium aprons, in situ regoliths, and colluvium-alluvium or alluvium deposits. The most critical situation is in the P2 Surface context, near the bottom of the Marília Plateau scarpment, where surface runoff can be very strong. Another point of active erosion is represented by the exposed walls of gullies and voçorocas, mainly in fluvial reaches subjected to talweg lowering. In a general sense, this study shows current evidence of erosional stability due to the ìntroduction of pastures as a predominant type of land occupation and to a series of erosion control procedures. Among these actions are terrace implantation, construction of small pits for runoff control, natural or induced reforestation by land owners. Despite these efforts, some erosion points remain chiefly in steeper country roads and trail stretches, in areas of concentration of cattle tracks (e.g., near cattle ponds), gullies or voçorocas exposed walls, and badly planned urbanization. The permanence of these erosion points demonstrates the necessity of a continuous monitoring of surface dynamics as well as a rapid and effective intervining measures of erosion and/or silting control.

Estudo da permeabilidade dos solos de fundação do aterro de resíduos sólidos urbanos de Bauru

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Zoneamento geoambiental do planalto de Poços de Caldas, MG/SP a partir de análise fisiográfica e pedoestratigráfica

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Caracterização geológica do município de Assis: a importância do estudo das coberturas cenozóicas

Pós-graduação em Geologia Regional - IGCE

Investigação da condutividade hidráulica dos solos de uma área de aterro de resíduos sólidos urbanos por meio de ensaios de campo e laboratório

A contaminant plume due to leachate infiltration was found in the solid waste landfill from Bauru, SP. The soil hydraulic conductivity (K) is an important parameter to understand the moving of this plume. This paper intends to show representative K values for the soils that occur in the vicinity of this landfill determined by field and laboratory tests. There are four soil types in the area: colluvium, alluvium, sandstone residual soil and the sandstone. Laboratory tests were performed using constant and variable head in rigid and flexible wall permeameters. Slug tests and hydraulic conductivity tests with the Guelph permeameter were also carried out in situ in the area. Representative K values of 3.7x10-7 m/s for the saturated zone and 2.4x10-8 m/s for the unsaturated zone were determined for the residual soil. A K value of 5.3x10-5 m/s was obtained for the colluvium soil. A great variation of K with depth was observed for the alluvium and the assumed average values for the saturated zone were 7.9x10-7 m/s and 1.1x10-4 m/s for the unsaturated surficial layer. An average K value of 3.3x10-8 m/s was determined in laboratory for the sandstone and it was assumed representative for this material.