Secondary Sulphate Minerals in a Cyprus-Type Ore Deposit,Apliki, Cyprus: Mineralogy and Its Implications Regarding the Chemistry of Pit Lake Waters

The Apliki mine, a Cyprus-type massive sulphide deposit in Cyprus, was exploited for copper until the mid-1970s. Abandonment of the mine left a deep pit that now hosts a lake fed by surface runoff from the surrounding mineralized zone and hydrothermally altered basalt. Oxidation of the sulphide minerals and factors such as climate and terrain relief control the water–rock interactions that generate acid mine drainage (AMD), which ultimately affects and defines the quality of the lake waters. Pyrite and chalcopyrite constitute an almost inexhaustible sulphide source that leads to the formation of a variety of secondary iron and copper mineral phases. The secondary mineral assemblages in the ore zone are mainly iron, copper, and magnesium sulphates, whereas the lakeshore assemblage is dominated by magnesium-, calcium-, sodium-, and aluminum-bearing sulphate minerals. Near the lakeshore, the highly soluble iron sulphate salts dissolve in the lake water, increasing its iron content. Other less soluble salts are more stable and persist in the lakeshore environment. The precipitation and dissolution of efflorescent salts, and, to a lesser extent, the oxidative weathering of the remaining ore minerals, produce additional AMD. Due to the perpetual cycle of mineral dissolution and precipitation, the lake has a low pH (≈3) and contains high concentrations of some contaminants. The processes that contribute to the formation of the efflorescent mineral assemblages and their environmental impact on pit lake waters, and indeed the complete geochemical system, is a typical example of secondary mineral formation in Cyprus-type Cu-pyrite massive sulphide ore deposits.