Regional patterns of soil magnetic susceptibility and color in the Itacaiúnas River Watershed: Geological influences and practical applications

Magnetic susceptibility (MS) is directly related to magnetic minerals in soils, primarily magnetite and maghemite. Determining MS and soil color is easy and cost-effective using sensors. They have great potential in agriculture, mining, and pedometrics, as they provide numerical characterization of these properties and can be correlated with other soil attributes. This study aimed to determine MS and color of surface (SS) and subsurface (SP) soil samples from a regional geochemical survey of the Itacaiúnas River Watershed, Carajás Mineral Province, and deduce relationships between these properties and soil chemical element contents and geological features. A total of 1204 composite samples from 602 locations at depths of 0–20 cm (SS) and 30–50 cm (SP) were selected for study. For MS determination, samples were analyzed at low frequency (0.47 kHz) and color numerical determination was quantified using a portable colorimeter sensor. The MS variations were strongly associated with local geology. Higher MS values were found along two east–west-oriented zones corresponding to northern and southern hydrothermal copper belts. These belts host iron oxide–copper–gold (IOCG) mineralization, where magnetite is systematically present among hydrothermal minerals. Reddish soils exhibit a spatial distribution similar to samples with higher MS values, indicating soil color indirectly reflects magnetic mineral content. MS and soil redness (a* International Commission on Illumination parameter) were positively correlated with Cu, Fe, Ni, and other elements, highlighting their potential for soil monitoring, although correlation strength varied among geological domains. These findings contribute to a soil MS database for the Amazon and may refine existing geological maps, while also indicating MS as an indicator of IOCG mineralization potential to guide new prospecting efforts.