Identification of the subsurface sulfide bodies responsible for acidity in Río Tinto source water, Spain

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)

“…As documented below, these conclusions are not supported at all by the data provided by Gómez-Ortiz et al (2014) and contradict much other reported evidence (hydrogeological, sedimentological, archaeological and historical). Gómez-Ortiz et al (2014) performed a hydrogeological interpretation of the geophysical data obtained by TDEM and deduced the existence of a zone of lower resistivity (150-1000 m), between approximately 100 and 400 m deep, which they explained as a high water content zone that would constitute the recharge area of Peña de Hierro. Also inferred was the existence of unexploded sulfide deposits at a depth of approximately 500 m. assumed the groundwater flow from this zone would discharge into the acidic springs of the headwaters of the Río Tinto through strike-slip normal faults.…”

“…Based on the isotopic composition of the acidic discharges Gómez-Ortiz et al (2014) concluded that some sampling points have a major proportion of water coming from rainfall earlier than 1950. For the pit lake, they provided a value of 50% (sample 9b), but they did not explain how this percentage was obtained.…”

“…From a study using geophysical methods (mainly time-domain electromagnetic sounding -TDEM-) and water isotopes in the area of Peña de Hierro, Gómez-Ortiz et al (2014) concluded that the source of acidity of the Río Tinto is a deep aquifer and that mining has little or no influence on the generation of the acidic waters carried by the river. As documented below, these conclusions are not supported at all by the data provided by Gómez-Ortiz et al (2014) and contradict much other reported evidence (hydrogeological, sedimentological, archaeological and historical).…”

Fungal Iron Biomineralization in Río Tinto

“…The physico-chemical characteristics of the water are shown in Table 1. Iron concentration was around 1188 mg/L, and the sulfate reached up to 1700 mg/L, both interpreted as the products of the oxidation of pyrite by chemolithotrophic microorganisms [1]. The pH was, on average, 2.7˘0.3.…”

“…Río Tinto is a natural rock drainage system generated as the result of subsurface biooxidation of the sub-outcropping volcanogenic massive sulfide ores of the Iberian Pyrite Belt by the activity of chemolithotrophic prokaryotes [1]. As a consequence, water has elevated concentrations of ferric iron, responsible for the oxidation of existing sulfides and the river buffering, and sulfuric acid, responsible for maintaining in solution the high concentration of heavy metals generated by bioleaching (Fe, Cu, Zn, As, Mn, and Cr) [2,3].…”