Zinc Melanterite Formation from Acid Mine Drainage in Pan de Azúcar Mine (Zn-Pb-Ag), Northwest Argentina.

MURRAY JESICA; KIRSCHBAUM ALICIA; DOLD BERNHARD

Florencia

Congreso; Goldschmidt2013 Conference; 2013

Melanterite formation in Pan de Azucar Mine: Evaporation of acid mine waters formed by oxidation of sulfide rich tailings in Pan de Azúcar Mine (Zn-Pb-Ag) favors the formation of soluble sulfates as Melanterite (Fe2+SO4?7H2O), which is one of the most common ferrous sulfates in nature and one of the first phases to precipitate from evaporation of acid mine drainage. One of the most important characteristic of these phases is their ability to store metals as Ni(II), Cu (II), Zn (II) [1] Zn-Melanterite: Acid mine drainage (139 g/L SO42-; 8960 mg/L Zn; 99,7 mg/L Cd; 47 mg/L Fe (total); 44 mg/L As; 10 mg/L Cu; 1,4 mg/L Pb) seeps from one of the tailings impoundments during dry season. High evaporation rates and high concentration of sulfate and iron favors the precipitation of melanterite at pH=2.1. Some preliminary SEM-EDS studies show high Zn concentrations in melanterite crystals, which indicates its ability to capture this metal in their structure instead of Cu or Ni, probably due to the Zn excess in the acid water. XRD and field observation suggests that during the dry season, melanterite dehydrates and changes to rozenite (Fe2+SO4?4H2O) as has been described by Nordstrom [1, 2]. In the following rainy season that phases dissolves and metals are again available to the hydrological cycle. This process has an important influence on temporal variation of metals in surface waters. [1] Sulfate Minerals, Cristallography, Geochemistry and Environmental Significance (2000). Reviews in Mineralogy and Geochemistry, V 40. [2] Nordstrom (1982). Acid Sulfate Weathering: Soil Science Society of America Spec. 10, 37-56