An epithermal, high-sulfidation, gold deposit, hosted in Tertiary volcanic rocks, was exploited from 1997 to 2003 at Furtei in Sardinia (Italy). Gold and silver were recovered from oxidized ores by cyanidation, and copper concentrates from sulfide ores by flotation. After exploitation, pit lakes were filled by rainfall, and by interception of the groupdwater table. The pit lakes at Santu Miali Cima and Sa Perrima have been completely recovered in 2004 and 2007, respectively. Cyanide solutions were disposed in a tailings impoundment, which is constructed on a rock embankment with a minimum of 5 m wide compacted clay inner surface with very low permeability. Seeps downstream of the impoundment were observed since 1998, probably due to fractures, especially in the part hosting the dam. Seeps have been contihuously collected in a well, and pumped back to the impoundment. Following bankrupt in 2008, sulfide-rich materials derived from exploitation, and processing residues were left on site. Open pit exploitation at Furtei was preceded and accompanied by studies on the environmental impact, particularly on the aquatic system. Pre-gold mining baseline studies were carried out in 1994. Hydrogeochemical surveys were carried out since 1997, i.e. when gold exploitation started. Surveys were more frequent under exploitation (1998 to 2003), especially for cyanide monitoring that was carried out 2-3 times per month. Water sampling at sites downstream of the tailings impoundment, the plant and pit lakes, were repeated under different seasonal conditions. Waters in the Furtei area show a large variability in pH and dissolved chemical components. Hydrochemical features prior to gold mining can be summarized as follows. Waters interacting with the mineralized rocks were acid, had a dominant sulfate-chloride composition, and high levels of contaminants. The extreme acidic water (lowest pH: 2.3) showed up to 2000 mg/L Al, 29 mg/L Cu, 11 mg/L Zn, 4 mg/L Ni, 3 mg/L Co, and 0.4 mg/L As. With respect to pre-mining conditions, the water chemistry generally showed small variations, either under gold exploitation or after mine closure, but dilution effects were observed when sampling was carried out in the rainy season. Since the beginning of gold exploitation, cyanide has been the main concern for the local population. The highly toxic cyanide species underwent natural degradation within 3 years since cyanidation stopped. However, waters draining the mining area still have high acidity and elevate concentrations of contaminants. The waste materials disposed on dumps, flotation tailings confined in an impoundment, and mineralized rocks exposed in open pits have a high capacity of acid drainage generation and release of toxic elements. During the rainy season, sulfide-rich materials in the waste rock dumps produce extreme acidic, and high contaminated drainage that flows downstream of the mine, and poses a hazard to a cultivated plain. Results of this study can help the Sardinia Regional Government in the implementation of reclamation programs.
Impact of the Furtei gold mine (Italy) on aquatic systems
CIDU, ROSA;DA PELO, STEFANIA;FRAU, FRANCO
2012-01-01
Abstract
An epithermal, high-sulfidation, gold deposit, hosted in Tertiary volcanic rocks, was exploited from 1997 to 2003 at Furtei in Sardinia (Italy). Gold and silver were recovered from oxidized ores by cyanidation, and copper concentrates from sulfide ores by flotation. After exploitation, pit lakes were filled by rainfall, and by interception of the groupdwater table. The pit lakes at Santu Miali Cima and Sa Perrima have been completely recovered in 2004 and 2007, respectively. Cyanide solutions were disposed in a tailings impoundment, which is constructed on a rock embankment with a minimum of 5 m wide compacted clay inner surface with very low permeability. Seeps downstream of the impoundment were observed since 1998, probably due to fractures, especially in the part hosting the dam. Seeps have been contihuously collected in a well, and pumped back to the impoundment. Following bankrupt in 2008, sulfide-rich materials derived from exploitation, and processing residues were left on site. Open pit exploitation at Furtei was preceded and accompanied by studies on the environmental impact, particularly on the aquatic system. Pre-gold mining baseline studies were carried out in 1994. Hydrogeochemical surveys were carried out since 1997, i.e. when gold exploitation started. Surveys were more frequent under exploitation (1998 to 2003), especially for cyanide monitoring that was carried out 2-3 times per month. Water sampling at sites downstream of the tailings impoundment, the plant and pit lakes, were repeated under different seasonal conditions. Waters in the Furtei area show a large variability in pH and dissolved chemical components. Hydrochemical features prior to gold mining can be summarized as follows. Waters interacting with the mineralized rocks were acid, had a dominant sulfate-chloride composition, and high levels of contaminants. The extreme acidic water (lowest pH: 2.3) showed up to 2000 mg/L Al, 29 mg/L Cu, 11 mg/L Zn, 4 mg/L Ni, 3 mg/L Co, and 0.4 mg/L As. With respect to pre-mining conditions, the water chemistry generally showed small variations, either under gold exploitation or after mine closure, but dilution effects were observed when sampling was carried out in the rainy season. Since the beginning of gold exploitation, cyanide has been the main concern for the local population. The highly toxic cyanide species underwent natural degradation within 3 years since cyanidation stopped. However, waters draining the mining area still have high acidity and elevate concentrations of contaminants. The waste materials disposed on dumps, flotation tailings confined in an impoundment, and mineralized rocks exposed in open pits have a high capacity of acid drainage generation and release of toxic elements. During the rainy season, sulfide-rich materials in the waste rock dumps produce extreme acidic, and high contaminated drainage that flows downstream of the mine, and poses a hazard to a cultivated plain. Results of this study can help the Sardinia Regional Government in the implementation of reclamation programs.
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