Navegando por Autor "Bacellar, Luis de Almeida Prado"

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Artigo
3D geoelectric modeling to characterize ferruginous caves in Brazil, using numerical and physical simulation
(2024-03) Cardoso, Luiz Henrique; Bacellar, Luis de Almeida Prado; Oliveira, Nilciléia Cristina de Magalhães; Maciel, Álvaro Simões
In Brazil, the discovery of ferruginous pseudokarst caves in laterite profiles on iron mining areas has been significant. As a result, speleological legislation has restricted mining activity to protect caves considered to be most relevant, however, with subjective criteria. This requires the collection of precise data to better guide them. The application of techniques for the identification and characterization of caves is still limited, due to the irregular topography, vegetation and the obstruction of conduits and saloons by material that fell from the ceiling and walls, and it was also mobilized by miners. A relatively cheap and quick alternative to mapping the caves, compared to classical methods such as boreholes, is Electrical Resistivity (ER). Literature data are apparently controversial, as caves filled with air sometimes have high resistivity (tens to hundreds of thousands of ohms. meter), and sometimes low (up to a few thousand ohms. meter). Thus, the objectives were to investigate the electrical resistivity duality that can be observed in these caves, and present a non-invasive cave mapping methodology and a 3D geoelectric model (inverted), to be used as a reference in future field research. To this end, direct and inverse 3D geoelectrical numerical modeling was carried out to predict the electrical resistivity of typical elements in the ferruginous pseudokarst system of the Quadrilátero Ferrífero (QF), southeast region, where hundreds of caves were cataloged. Field surveys, laboratory analysis of collected material and simulations in a reduced physical model validated the predictions. The results showed that moisture around ferruginous caves can attenuate the electrical signal or even mask the high resistivity of conduits and saloons filled with air. Therefore, it was the main factor considered in the geoelectric model.
Texto publicado em jornal
A hydrogeological conceptual model for the groundwater dynamics in the ferricretes of Capão Xavier, Iron Quadrangle, Southeastern Brazil
(2021-12) Dias, Jordania Cristina dos Santos; Bacellar, Luis de Almeida Prado
In the Iron Quadrangle (IQ), southeastern Brazil, ferricretes usually overlie the banded iron formations (BIFs) of the Cauê Formation, rocks that not only host the most important iron ore deposits of this region but are also its major groundwater source. Little is known about the water dynamics in ferricretes and therefore how they influence the recharge of the subjacent aquifer (Cauê aquifer). The objective of this research was to identify ferricrete typologies and investigate their water dynamics in the Capão Xavier region, northwest of IQ. Field work consisted of macroscopic description of ferricretes, infiltration tests and multitemporal electrical resistivity surveys. Two ferricrete typologies were distinguished: structured ferricretes, which are older and occur on top of plateaus, and detrital ferricretes of colluvial-alluvial origin, which were deposited downslope and in topographic lows. The structured ferricretes preserve the medium- to high-angle foliation inherited from the underlying BIFs, whereas the detrital ferricretes constitute thick packs subparallel to the topographic surface and are intercalated with argillaceous layers in areas of karstic depressions. The structured ferricretes are more porous (20.8% to 24.4%) than the detrital ferricretes (14.4% to 17.6%), hence they have higher mean basic infiltration rates (8.3x10-6 m/s) than detrital ferricretes (2.8x10-6 m/s). Despite these low mean basic infiltration rates, infiltration advances thanks to the karstic-fissural porosity (fractures and joints widened by karstification), and superficial cavities that are connected to caves in the interface between the ferricrete and the subjacent, less resistant, transition horizon. Karstification is controlled by the subvertical foliation in the structured ferricretes and subparallel layering in the detrital ferricretes. Some factors that favor infiltration and deep percolation of water are superficial rugosity in structured ferricretes, and karstic depressions in both typologies. The recharge of the Cauê aquifer is diachronic, firstly taking place via the karstic-fissural system and later via the ferricrete matrix.