The source rocks are mainly containing quartz, pyrite and chlorite (tabell) where the river originates and springs up in the Aracena Ranges region. In that region are the Iberian Pyrite Belt (IPB) is present, which was formed during the Paleozoic era. (Fernández-Remolar et al., 2004) The sulfide-rich minerals (e.g. pyrite) are thought, as mentioned in History section, to originate from the IPB in form of acid rock drainage and as acid leachate as a product of extensive mining. The sulfides are then transported and deposited downstream in the river. The quartz is mainly from eroded Neogene and Quaternary sediments further down from the origin of Río Tinto. (Cáceras et al., 2013)