A mineralogical and geochemical assessment of the As-, Cu-, In-, Pb-, Sb-, and Zn-rich mine wastes at the Pefka epithermal deposit, Greece

Abstract

Mining waste residues from the abandoned Pefka polymetallic epithermal deposit (northeastern Greece) were studied to document the products of sulfide oxidation and to evaluate the mobility of the wide range of trace metals and metalloids in these environments. Acidic to circumneutral waste rock and sediment samples (pH 3.3 to 6.7) are characterized by elevated As (up to 640 mg/kg), Cu (up to 1900 mg/kg), In (up to 11 mg/kg), Pb (up to 2300 mg/kg), Sb (up to 480 mg/kg) and Zn (up to 1500 mg/kg). The primary sulfide and sulfosalt minerals are almost completely transformed to gypsum as well as into different (hydr)oxide and (hydroxy)sulfate phases. Mineralogical investigation (powder X-ray diffraction, electron microprobe, Raman spectrometry) and sequential extraction revealed that As and Sb are principally stored in Fe(III) (hydr)oxides (especially goethite) and Pb hydroxysulfates (especially beudantite and hidalgoite). Fe (hydr)oxides also appear to be the main reservoirs of Cu and In. Lead is primarily bound to minerals of the beudantite group (especially beudantite, hidalgoite, and hinsdalite); while Zn is preferentially associated with Mn (hydr)oxides and minerals of the woodwardite group. The leaching test indicates that the Fe(III) (hydr)oxides and Fe(III)/Al(III) hydroxysulfate minerals retain the trace metal(loid)s efficiently but not completely (especially Cu and Zn). However, the mobility of most elements (especially As, In, Pb, and Sb) is very low because of the low solubility of hydroxysulfate minerals and the effective sorption of anionic metalloids under acidic to near-neutral conditions of the waste rocks and sediment.