Life Cycle impacts assessment of two gold extraction systems in Colombia: Open-pit and alluvial mining

Abstract

Purpose Gold mining has historically and significantly contributed to the Colombian economy. Gold extraction in Colombia is mainly done through two techniques: open-pit and alluvial mining. In this study, the environmental impacts of both these mining systems were analyzed using the Life Cycle Assessment (LCA) framework, including identification of the system components that contribute most to impacts. Methods Inventory data were obtained for two medium-scale mines1 in Colombia, one representing the open pit method and the other the alluvial method. Environmental impacts were classified and characterized by mid-point impact categories and further aggregated into end-point indicators through the ReCiPe (v. 1.11) methodology, which uses a hierarchist perspective. Results Results for end-point indicators show that the open-pit mining presents higher values in the Human Health damage category, influenced primarily by tailings and by the excavation process. For the alluvial mining, the overall impacts were an order of magnitude lower, with Ecosystem Quality as the most significant contributor due to the stripping of soil and vegetation. In the case of mid-point indicators, freshwater and marine ecotoxicity contribute the most to open-pit mining, while for alluvial mining, metal depletion and natural land transformation contribute the most. Climate change is also a significant impact category for alluvial and open-pit mining. Conclusions The is a substantial difference in environmental impacts between the two mining systems: the quantified total environmental impact was 1.0 x 1004 points for the open-pit mine and 2.4 x 1003 points for the alluvial mine. Since these mines represent specific Colombian operational conditions, this conclusion cannot be confidently extended to other operational contexts while. For example, results in other cases may depend on the local geological features and natural environment conditions. Knowing the critical mining supply chain stages for environmental performance will allow the decision-makers to provide the tools for more sustainable extraction and production. 1 The Colombian mining classification lies on small, medium, and big scale based on the number of hectares granted in the mining concession: small (≤150 ha), medium (≥150 ha, ≤5000 ha), big (≥ 5000 ha, ≤10000) or according with the volume of the maximum annual mining production small (≤250000 m3/year), medium (≥250000 m3/year, ≤1300000 m3/year), big (1300000≥m3/year), and not on the number of workers (Código de Minas, Ley 685 DE 2001, 2001)