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Chemical characteristics of groundwater around two massive sulphide deposits in an area of previous mining contamination, Iberian Pyrite Belt, Spain
Authors:Hlne Pauwels  Marie-Lou Tercier-Waeber  Miguel Arenas  Ricardo Castroviejo  Yves Deschamps  Arnault Lassin  Flavio Graziottin  Francisco-Javier Elorza
Institution:Hélène Pauwels, Marie-Lou Tercier-Waeber, Miguel Arenas, Ricardo Castroviejo, Yves Deschamps, Arnault Lassin, Flavio Graziottin,Francisco-Javier Elorza
Abstract:A detailed chemical study of groundwater was carried out to elucidate the processes controlling the oxidation and dissolution of sulphide minerals at two massive sulphide deposits in the Iberian Pyrite Belt (IPB), i.e. the mined La Zarza deposit and the unmined Masa Valverde deposit. It was found that major-element compositions varied according to the hydrological regime, La Zarza being in a relatively high area with groundwater recharge (and disturbance due to the human factor) and Masa Valverde being in a relatively low area with groundwater discharge. The variations mainly concern pH, Eh, SO4 and Na concentrations. Metal concentrations were determined (a) by ICP-MS after filtration, and (b) in some cases by voltammetric measurement of Cu, Pb, Zn, Cd and Mn using the Voltammetric In situ Profiling (VIP) System, which allows detection of only the mobile fractions of trace elements (i.e., free metal ions and small labile complexes a few nanometers in size). If one compares the results obtained by each of the two methods, it would appear that the groundwater shows significant enhancement of metal solubility through complexing with organic matter and/or adsorption onto colloids and/or small particles. In areas of sulphide oxidation, however, this solubility enhancement decreases according to Cu>Zn>Cd>Pb. Under very low redox conditions, the attained metal concentrations can be several orders of magnitude (up to 108–109 for Cu and 102–103 for Pb) larger than those expected from equilibrium with respect to sulphide minerals as calculated with the EQ3NR geochemical code; Zn concentrations, however, are close to equilibrium with respect to sphalerite. The implication of these results is discussed with respect both to mineral exploration and to environmental issues.
Keywords:Groundwater  Metal  Speciation  Mineral exploration  Buried ore deposit  Iberian Pyrite Belt  Environment  Natural pollution  Remediation
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