Integrating multispectral satellite data and geomorphology for secondary iron mineral mapping in the Sierra Minera de Cartagena-La Unión (SE Spain)

Abstract

The Sierra Minera de Cartagena-La Unión (SE Spain) is a historical mining district where acid mine drainage (AMD) continues to impact soils and water resources. This study, on the one hand, maps three of the secondary iron minerals linked to AMD processes—hematite, goethite, and jarosite—using Sentinel-2 multispectral imagery and, on the other, evaluates how their spatial distribution relates to geomorphological processes and landform configuration. Three spectral techniques were applied: band ratio, minimum wavelength mapper, and a parabola fitting technique. Seventy-four field samples were analysed using X-ray diffraction (XRD) to validate mineral identification. Results indicate that the parabola fitting technique provided the most reliable classification. Sentinel-2 successfully distinguished the three minerals despite its multispectral resolution, due to its red-edge bands capturing diagnostic VNIR features associated with iron-bearing mineral spectral features. Integration of mineral maps with landform units mapped through aerial photointerpretation revealed a strong geomorphological control on AMD mineral deposition: hematite dominates well-drained depositional environments such as alluvial fans, while jarosite and goethite concentrate in colluvial slopes, drainage channels, marshes, and substratum units affected by sulphide oxidation and intermittent moisture conditions