Riverine Cu-distribution in sediments of the Jaba-Kawerong river system 30 years after cease of mining at Panguna/Bougainville

Abstract The investigation of surface and river sediments over 30 years after the cease of large scale Cu and Au mining operation at Panguna (Bougainville) shows the impact of mining and tailings disposal on the associated riverine environment. While Zn, Pb and Cd have elevated concentrations in the former mining area and are low (< 100, < 28, < 1 mg/kg, respectively) in sediment of the Jaba-Kawerong river system, Cu represents the dominant environmental metal emission. Sediments of active streams and overbank deposits range between 1000 and 3000 mg/kg Cu. Most samples exceed freshwater sediment or soil quality guideline values, indicating the probability of toxic effects on sediment dwelling or aquatic organisms and ecological or health risks associated to agricultural use of the former mining area and floodplains. Copper in surface and river sediments is associated to bornite, chalcopyrite and chloritized biotite of the primary Panguna ore mineral assemblage. This attests to ongoing remobilization of sediment and/or reflects mobilization of additional Cu bearing material from the waste rock dump of the Panguna mine. Copper in surface and river sediments is also contained in secondary Cu-phases such as covellite as well as hydrated basic Cu-sulfates, which formed under locally variable redox conditions. Fe-oxihydroxides, occurring in variable abundance as reflected by Fe concentrations between 18,200 and 379,000 mg/kg (Mn 145–3086 mg/kg), can be identified as further Cu-carriers, taking up the metal from the aqueous phase in the sedimentary pore space. Mine derived input of Cu bearing minerals is confined to the sedimentary body of the Jaba-Kawerong river system. The diversity of Cu bearing phases with different environmental and processing properties sets constraints on re-processing sediments as secondary Cu-ores or re-using of sediments as building material.