Supergene alteration, environmental impact and laboratory scale acid water treatment of Cyprus-type ore deposits: case study of Mathiatis and Sha abandoned mines

Waste-rock dumps and the water quality of pit-lakes formed at abandoned mines of pyrite-rich ore deposits are of considerable environmental concern around the world. The Mathiatis and Sha mines provide typical examples of abandoned mines where Cyprus-type Cu-pyrite ore was exploited. Supergene alteration of the sulphide ore and the mine waste leads to the formation of efflorescence and generation of acid mine drainage filling the pit-lakes. Sulphate concentrations range from 4600 to 4850 mg/l and from 35 900 to 38 500 mg/l for the Mathiatis and Sha mines, respectively. Concentrations of heavy metals exceed the established regulatory limits in water. A preliminary assessment of the mine waste at the Mathiatis mine indicated that it cannot be characterized as inert material according to current European legislation, posing an environmental threat as a source of acid mine drainage (AMD). The identified Mg, Ca and Fe(II)- Fe(III) efflorescence mineral phases retain temporarily trace metals near the mine waste and the open pit-lake shore. Neutralization experiments on the acidic waters of the epilimnion indicated local limestone is not sufficient for full remediation. However, it could be used as a low-cost pretreatment method for AMD. The study expands the international database of AMD affected areas and provides the basis for future remediation efforts.