This paper reports the application of weights-of-evidence, artificial neural networks, and fuzzy logic spatial modeling techniques to generate prospectivity maps for gold mineralization in the neighborhood of the Amapari Au mine, Brazil. The study area comprises one of the last Brazilian mineral exploration frontiers. The Amapari mine is located in the Maroni-Itaicaiúnas Province, which regionally hosts important gold, iron, manganese, chromite, diamond, bauxite, kaolinite, and cassiterite deposits. The Amapari Au mine is characterized as of the orogenic gold deposit type. The highest gold grades are associated with highly deformed rocks and are concentrated in sulfide-rich veins mainly composed of pyrrhotite. The data used for the generation of gold prospectivity models include aerogeophysical and geological maps as well as the gold content of stream sediment samples. The prospectivity maps provided by these three methods showed that the Amapari mine stands out as an area of high potential for gold mineralization. The prospectivity maps also highlight new targets for gold exploration. These new targets were validated by means of detailed maps of gold geochemical anomalies in soil and by fieldwork. The identified target areas exhibit good spatial coincidence with the main soil geochemical anomalies and prospects, thus demonstrating that the delineation of exploration targets by analysis and integration of indirect datasets in a geographic information system (GIS) is consistent with direct prospecting. Considering that work of this nature has never been developed in the Amazonian region, this is an important example of the applicability and functionality of geophysical data and prospectivity analysis in regions where geologic and metallogenetic information is scarce.
Resumo Este artigo aborda o processamento e a interpretação de dados aerogeofísicos (magnetometria e gamaespectrometria) de alta resolução espacial e densidade de amostragem (Projeto Rio Araguari-CPRM), visando à geração de produtos para o mapeamento geológico e exploração mineral da porção centro-sul do estado do Amapá. Essa região se reveste de especial importância visto que se trata de uma das últimas fronteiras exploratórias do país, onde são reconhecidos terrenos do embasamento Arqueano, seqüências do tipo greenstone-belts (Província Vila Nova) e suítes intrusivas, coletivamente de evolução geológica complexa e com amplo potencial metalogenético. Com base no processamento dos dados aerogeofísicos, foram gerados mapas de domínios e lineamentos magnéticos e domínios gamaespectrométricos, a partir dos quais novas unidades litogeofísicas foram reconhecidas, assim como redefinida, com grande precisão, a extensão de unidades previamente mapeadas (e.g., corpos enderbíticos, complexos máficos ultramáficos e intrusivas graníticas). As estruturas magnéticas são multi-orientadas. O extenso lineamento denominado Cupixi Alto Jarí aparece com destaque nos mapas aerogeofísicos, separando o Terreno Cinturão Jari e o Terreno Antigo CupixiTartarugal Grande. As estruturas de direção NNW são predominantes e se associam, com maior freqüência, às mineralizações auríferas da região.Palavras-chave: aerogeofísica, greenstone belts, mapeamento geológico, mineralizações auríferas, Amapá. Abstract Geologic-geophysical mapping of the central portion of the Amapa state throughprocessing and interpretation of airborne potential field data. This article approaches the processing and interpretation of high spatial resolution airborne geophysical data (magnetometry and gama-spectrometry) (Projeto Rio Araguari-CPRM), aiming to produce products for geologic mapping and mineral exploration of the central portion of the Amapa State, Brazil. This region is of special interest since it comprises one of the last exploration frontiers in Brazil, where Archaean basements units, greenstone belts (Vila Nova Province) and intrusive rocks collectively show a complex geologic evolution and an ample metallogenic potential. The processing of the geophysical data yielded maps of magnetic lineaments and magnetic and gammaspectrometric domains, from which new litho-geophysical units were recognized and previously mapped units were redefined (e.g., enderbitic bodies, mafic-ultramafic complexes and granitic intrusives). The magnetic structures are multi-oriented. The extensive Alto Cupixi Jari lineament shows prominently in the magnetic maps, separating the Cinturao Jari and the Atingo-Cupixi-Tartarugal Grande terranes. The NNW-trending structures appear ubiquitously in these maps and are often associated to gold mineralizations in the region.Keywords: airborne geophysics, greenstone belts, geologic mapping, gold mineralizations, Amapa-Brazil 1 -Universidade Estadual de Campinas, Campinas, São Paulo, Brasil. E-mail:luciola@ige.unicamp.br; beto@ige.unicamp.br 2 ...
Leaks from accidents or damage to pipelines that transport liquid petroleum hydrocarbons (PHC) such as gasoline and diesel are harmful to the environment as well as to human health, and may be hard to detect by inspection mechanisms alone when they occur in small volumes or persistently. In the present study, we aim to identify spectral anomalies in two plant species (Brachiaria brizantha and Neonotonia wightii) linked to contamination effects at different developmental phases of these plants. To do so, we used spectroscopy and remote sensing approaches to detect small gasoline and diesel leaks by observing the damage caused to the vegetation that covers simulated pipelines. We performed a contamination test before and after planting using gasoline and diesel volumes that varied between 2 and 16 L/m3 soil, in two experimental designs: (i) single contamination before planting, and (ii) periodic contaminations after planting and during plant growth. We collected the reflectance spectra from 35 to approximately 100 days after planting. We then compared the absorption features positioned from the visible spectral range to the shortwave infrared and the spectral parameters in the red edge range of the contaminated plants to the healthy plants, thus confirming the visual and biochemical changes verified in the contaminated plants. Despite the complexity in the indirect identification of soil contamination by PHCs, since it involves different stages of plant development, the results were promising and can be used as a reference for methods of indirect detection from UAVs (Unmanned Aerial Vehicles), airplanes, and satellites equipped with hyperspectral sensors.
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