Abandoned copper mine tailings deposits. Problems and possible solutions Henrik K. Hansen Universidad Técnica Federico Santa Maria, Chile

Copper production in Chile 6 Mton/year > 40 % of GNP is due to copper production 35 % of world copper Several important mines and smelters El Teniente Chuquicamata Escondida Collahuasi

Copper mine tailings Main residue from copper mining (separated during concentration of copper minerals)‏ Daily production: > ton (Domestic waste: ton)‏ 95 % of the mineral treated ends as tailings Cu concentration: 0.1 – 0.3 % Other elements of concern: As, Zn, Pb Accumulated in tailing deposits/ponds

Problems with tailing ponds Mechanical Stability Damn failures Chemical Stability Leaching of contaminants Can cause severe environmental impact, collapse of Tailing pond “El Cobre” in 1965 caused the death of more than 200.

Examples of pond wall collapse 1928: Barahona Pond (El Teniente)‏ 1965: El cobre Pond (200 deaths)‏ 1981: Minera Las Cenizas (collapse affected severely the nearby agricultural activity)‏ 2002: Cobrex ( t tailings spilled)‏ 2003: Minera Cerro Negro ( t tailings)‏

Chilean legislation for new mining projects

Decreto Supremo Nº 248 “Reglamento para la aprobación de proyectos de diseño, construción, operación y cierre de los depósitos de relaves” Suggested December 2006 Published April 2007 Fiscalization unit: Servicio Nacional de Geología y Minería, SERNAGEOMIN

Mechanical stability Damn construction inadequate Specially in small and medium scale tailing ponds Hydrodynamic effect, e.g. rainwater accumulation Seismic activity Wind erosion/escape of wind borne material

Mechanical stability Tranque Ovejería, CODELCO Small scale tailings deposit

Chemical stability Chemical reactions in the tailing ponds: Pyrite oxidation (Air + humidity)‏ Chemical reactions in the tailing ponds: 2 FeS 2 (s) + 7 O H 2 O → 2 Fe SO H + Dissolution of Cu-sulphides Precipitation/settling of new solids Leaching/filtration

8 km Caren tailing pond Wall CuSO4 accumulation Tailing inlet Cu infiltration

Tailing pond monitoring by SERNAGEOMIN Studies done 1992 and 2004 Quantify tailing ponds Analyse risks

Abandoned and paralysed mining sites (FMA/P) with tailing ponds representing environmental risk : 20 %

Abandoned and paralysed mining sites (FMA/P) with tailing ponds representing mechanical risk : 33 %

Possible solutions (in Chile)‏ Stabilization Control of wind borne material Protection from rainwater Reforestation Esthetical and natural solution Mine tailings only inorganic material No “natural eco-system” exisitng Pyrite oxidation --> pH ?

Tailing pond: Planta M. A. Matta, III Región: Application of Bischoffite (MgCl 2 6H 2 O), to avoid wind erosion

Tailing pond: San José de Pucobre

Tailing pond: Ojancos, III Región : Reforestation

Tailing Pond: Las Cenizas V Región: Reforestation

Tailing pond Las cenizas: Before (1995)‏ After (2007)‏

Tailing pond Planta M. A. Matta, III Región: Reforestation

Some species used for reforestation Espino Acacia caven Aromo azul Acacia saligna Álamo Populus alba Pimiento Shinus molle Granado de flor Punica granatus Albizia Albizia lophanta Tamarindo Tamarix sp. Aromo australiano Acacia melanoxylon

Conclusions Awareness of problem Legislacion OK for new and present project Problems with abandoned ponds still not generally solved

Abandoned copper mine tailings deposits. Problems and possible solutions Henrik K. Hansen and Alejandra Muñoz Universidad Técnica Federico Santa Maria, Chile