Identification of mafic-ultramafic rocks using fuzzy logic classification of airborne geophysical data in the Anapu-Tuere region, Brazilian Amazon

摘要

The Anapu-Tuere region, in the Brazilian Amazon, is known for the occurrence of mineral deposits associated with mafic-ultramafic rocks. The spatial distribution of these rocks was investigated by integrating airborne magnetic and gamma ray spectrometry data using Geographic Information System (GIS) and fuzzy logic classification. Highest values of relevance fuzzy were associated with mafic-ultramafic rocks mapped regionally by the Brazilian Geological Survey (CPRM). Furthermore, mineral occurrences mapped by the CPRM showed good spatial correlation with the higher values of relevance fuzzy presented in this paper.rnThe region of Anapu-Tuere is located in the southeastern region of Para state, in the Amazon region, north of Brazil. In the region, occurrences of gold, chromium, nickel, copper, titanium, vanadium and platinum are associated with mafic-ultramafic rocks. In 2004, the CPRM collected high-resolution magnetic and gamma ray spectrometry data. These data enabled the generation of maps relevant to geological mapping and mineral exploration.rnMagnetics and gamma ray spectrometry attributes, such as magnetic gradient and levels of radioelements, were used to map mafic-ultramafic rocks. Values of pertinence were processed in order to highlight the relative importance of each variable. Thus, greater relevance was attributed to low values of gamma ray spectrometry channels (K, U and Th) and to high values of the analytical signal of the magnetic field (AS).rnHighest values of relevance fuzzy are associated with features elongated and fragmented, evenly distributed in the form of extensive lineaments, or in the form of preferential sigmoids with NW-SE direction, sometimes inflected for the EW direction. These features are related to mafic-ultramafic rocks mapped regionally by CPRM, such as Rio Preto piroclasite and Itata amphibolite. Units of mafic rocks were present in the shear zones not yet mapped. The mineral deposits and occurrences mapped by the CPRM showed good spatial correlation with the higher values of relevance fuzzy here highlighted.