One of the lessons learnt by the legacy of mining is that involvement of environmental scientists in the initial planning stages, in geochemistry baseline studies is significant for setting up realistic goals for monitoring and remediation programs.
A recent PhD project in the Department of Economic Geology and Geochemistry at the University of Athens, Greece investigated the geochemical characteristics of surface water and stream sediments of Asprolakkas drainage basin, an area of sulphide mineralization within metamorphic rocks, located in Chalkidiki peninsula, north Greece. One of the research objectives was to establish the geochemical baseline conditions prior to any type of new mining activity. The area represents the only example of active mining and processing of base metal sulphide ore in Greece and also includes an unmined porphyry Cu-Au ore deposit that will be exploited in the near future. In a wider context, this research represents a pre-mining baseline geochemical study that can be used as an analogue for similar metallogenetic provinces in areas with a Mediterranean type climate. The deposits of the area have a long exploitation history that started in 600 BC and continues until today, mainly because of their Au potential. It is believed that the mining activity in Chalkidiki during ancient times was the major source of gold during the era of Fillip II and Alexander the Great.
Concentrations of dissolved major ions and trace metals displayed wide variability within the study area. Kokkinolakkas, the stream draining the exploited Pb-Zn (±Ag) ore bodies, is strongly influenced by chemical weathering of sulphide minerals and presents elevated levels of SO4, Pb, Zn, Mn, Ni, Cd, As and Sb. Stream water of the unmined areas demonstrated a different chemical composition with elevated values mainly for Pb and As. It was found that hydrological conditions are important in modeling the element concentrations in water under present conditions. Major ion content decreases in the wet period as a result of dilution owing to the heavy winter rainfall. A contrasting behavior was observed for heavy metal composition in Kokkinolakkas water samples, due to the enhanced base metal dissolution under high run off conditions. It appears that downstream dispersion of metals is favoured by transport via adsorption processes onto very fine particles (< 0.45 μm). The study also revealed that weathering of the mineral deposits supports the occurrence of a prevalent Fe-Mn oxyhydroxide surface, which is considered to be capable of scavenging toxic metals. However, these precipitates could be a secondary source of trace metals for the water column upon dissolution of the oxides under reduced conditions. Cadmium is the only labile metal indicating the different chemical binding, and higher solubility of this element, compared to the other heavy metals. High actual concentrations were also measured in the carbonate fraction of Kokkinolakkas stream sediment samples, highlighting that pH is the principal variable governing the potential release of these elements to the dissolved phase.
Bearing in mind the ongoing mining developments in the area, results of this study are very significant, providing scientific data about the present environmental-geochemical baseline conditions of the drainage basin and are available for any future comparison. These data can enable mine planners to better anticipate and plan for potential environmental impacts and are useful for setting up realistic goals in monitoring and remediation programs.
Dr Ariadne Argyraki, Assistant Professor in Geochemistry, National and Kapodistrian University of Athens. E-mail: email@example.com
Stream water sampling in Chalkidiki, Greece.
Kelepertzis, E., Argyraki, A., Daftsis, E (2012). Geochemical signature of surface water and stream sediments of a mineralized drainage basin at NE Chalkidiki, Greece: A pre-mining survey, Journal of Geochemical Exploration, 114, 70-81. (doi:10.1016/j.gexplo.2011.12.006)