PHREEQC modeling of an abandoned high sulfidation open pit and SEM-EDS analyses of the mineralogy and geochemistry of the secondary phases developed

Open pit exploitation of the Kirki high sulfidation epithermal deposit (Thrace, NE Greece) resulted in the formation of an acidic pit lake by infilling of the open cast by rain and draining waters after mine closure. Three case specific PHREEQC geochemical models were developed including "Direct Precipitation", "Evaporation", and "Mixing with Rain water" in order to simulate the environmental conditions through the year, and to investigate the behavior of the acidic and rich in heavy metals waters of the pit-lake. Scanning Electron Microscopy examination revealed the predominance of jarosite species and goethite in the mineral precipitate, followed by lower amounts of hematite, schwertmannite and anglesite. According to PHREEQC modeling, jarosite species formation is favored during both dry and wet periods, while the presence of schwertmannite, goethite, hematite and anglesite depicts the fluctuation of the physicochemical conditions through the year. These phases play a key role in controlling the As and Pb dissolved concentrations, mainly through adsorption and co-precipitation, whereas the soluble metals Zn, Cd and Mn remain dissolved. The current status of the Kirki open pit system is the most stable for the environment, therefore a case-specific remediation plan focused on both the protection of the environment and the preservation of the Kirki open pit is proposed. The socio-economic benefits of such an approach could include increased tourist numbers due to case-oriented tourism, enhancement of local economy, education, whereas this approach is also cost effective relative to other proposed remediation measures.