Comment on “Identification of the subsurface sulfide bodies responsible for acidity in Río Tinto source water, Spain” by Gómez-Ortiz et al. (Earth Planet. Sci. Lett. 391 (2014) 36–41)

Reply to the Comment on “Identification of the subsurface sulfide bodies responsible for acidity in Río Tinto source water, Spain” (Earth Planet. Sci. Lett. 391 (2014) 36–41)

“…Regarding the estimation of the groundwater age using the tritium content of water samples, we strongly disagree with the interpretation of Olías and Nieto (2014) that all the water samples can be explained by the infiltration of precipitations after 1982. Olías and Nieto (2014) compiled monthly values of tritium from the station located in Madrid belonging to the Global Network of Isotopes in Precipitation (GNNIP).…”

“…150 m at ∼400-600 m in depth without the presence of water. Olías and Nieto (2014) do not provide any alternative explanation for these low resistivity values. In spite of the fact that productive water wells in crystalline rocks usually reach the maximum yield at shallower depths (up to ∼50 m), this does not mean that there is no groundwater at deeper depths, and many examples of the occurrence of groundwater in fractured aquifers at depths ranging from 50 to more than 100 m exist (e.g.…”

“…Such a distribution of subsurface solutions agrees with an acidification of the waters once the rainwater has replenished the aquifer at the catching area of Peña de Hierro (boreholes BH4, BH8 and BH10), and interacts with the subsurface ore bodies after flowing downstream (boreholes BH1 and BH11) through the faulting system (Gómez-Ortiz et al, 2014). Indeed, the perforation of the basement detected large fractures affecting the host rock and conducting subsurface waters at different depths (unpublished data) that goes against the idea of decreasing hydraulic conductivity in depth (Olías and Nieto, 2014).…”

“…The comment of Olías and Nieto (2014) to the article "Identification of the subsurface sulfide bodies responsible for the acidity in Río Tinto source water, Spain" addresses the interpretation of the data presented in the manuscript, using hydrological, sedimentological, archaeological and historical arguments and concludes by stating that the extreme conditions of the river are due exclusively to mining contamination, an opinion with which we strongly disagree.…”

“…Following the arguments used in the comment, we will direct our response mainly to the hydrological and stratigraphic evidence, offering some final remarks on the archaeological and historical arguments also used in the comment. Olías and Nieto (2014) state that 'the existence of a low resistivity zone at depth does not imply the presence of an aquifer', and they claim that the circulation of groundwater in metamorphic and igneous rocks is usually restricted to the surface (∼10 m). However, given that typical resistivity values for unweathered metamorphic rocks range from 1500 to 4 ·10 7 m (Telford et al, 1990;Reynolds, 1997), it is very difficult to explain resistivity values as low as http://dx.doi.org/10.1016/j.epsl.2014.07.023 0012-821X/© 2014 Elsevier B.V. All rights reserved.…”