The role of geomorphic connectivity on the mobilisation of artisan mine tailings

Artisan small-scale mining (ASM) plays an important role in the global mineral supply but is also a considerable contributor of contamination, due to the unregulated nature of the ASM sector. Artisan mine tailings, often contaminated with trace metals and chemicals used at the extraction process, are typically disposed in the local environment where they enter rivers and spread through sediment transport processes. This unsustainable practice has been largely ignored because ASM mines and processing facilities are tiny compared to their industrial equivalents, despite the fact that ASM collectively accounts for a substantial proportion of global mining output (20% gold, 26% tantalum, 25% tin). Here we examine a small Philippine catchment with extensive ASM activity and use the Caesar-Lisflood numerical model to show that 73% of solid mine tailings (SMT) disposed by pushing them into nearby watercourses during a decade of ASM operation are mobilised becoming a diffuse source of pollution that is difficult to manage. Conversely, when SMT are not disposed into watercourses and instead deposited at the location of ore processing only 26% is mobilised, primarily from areas of high geomorphic connectivity near rivers. 90 years after mine cessation, the amount of diffuse pollution increases further to 80% when SMT have been disposed into rives and only to 30% when SMT have been deposited locally. These results show that the legacy of mine waste dispersal long after ASM has stopped is heavily influenced by the initial decision to dispose or deposit SMT. Our findings underscore that diffuse pollution from the ASM sector must not be overlooked and approaches must be taken to sustainably manage ASM tailings now and in the future.