Mineralogia e geoquímica de sedimentos e solos no perímetro urbano de Manacapuru, Amazonas

Abstract

In the northern region of Brazil, 57% of the cities rely on aquifers for water supply, while 13% combine aquifers and surface water sources. Aquifers are preferred due to the good quality and accessibility of their water resources, especially during drought periods. However, their use without proper evaluation may expose populations to natural groundwater contamination. This study characterized the surface and subsurface sediments of geological units in the urban area of Manacapuru, State of Amazonas, to identify elements that could impact groundwater quality. Sixteen sampling points near tubular wells were selected, with auger drilling reaching depths of 2 to 5 meters. Samples were collected every meter or when significant lithological changes were observed. At point P11-União, sediments were also collected down to 174 meters during the drilling of a deep tubular well. A total of 138 samples were selected for granulometric analysis, and 16 samples underwent X-ray fluorescence and diffraction analyses. The results revealed stratigraphic profiles with interbedded layers of sand, silt, and clay. Chemical analysis identified ten oxides, predominantly SiO2, Al2O3, and Fe2O3. Mineralogical analysis showed the presence of quartz, kaolinite, goethite, gibbsite, hematite, rutile, microcline, and nontronite. Although previous studies indicated the presence of fluoride in groundwater, this study found traces of smectite and vermiculite minerals potentially associated with fluoride only at point Poço União at a depth of 160 meters. No fluoride-containing minerals were detected in the shallow samples analyzed. The identification of smectite and vermiculite in the region highlights the need for further investigation of these minerals due to their potential fluoride content.