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This article reviews hydrogeological studies carried out between 2016 and 2018 in the Silala River basin, a catchment shared by Chile and Bolivia. These were conducted in the context of the Case Concerning the Status and Use of the Waters of the Silala River, submitted to the International Court of Justice in 2016, and contributed to multidisciplinary science to demonstrate that this system is an international watercourse. In 2016, the hydrogeological understanding of the Silala River basin was poor. The studies reviewed here filled many knowledge gaps, providing a solid hydrogeological baseline, and establishing new monitoring infrastructure to collect relevant aquifer data. The most important hydrogeological units were identified as the fluvial deposits, alluvial deposits, and the Cabana ignimbrite. The latter is highly heterogeneous, weathered and fractured, and exhibits a high permeability. It is the most important unit in terms of productivity, and is the major regional aquifer providing spring flows to Bolivian wetlands and groundwater flow across the international border. The studies provided a preliminary understanding of the main aquifers in Chile and their properties, which underpinned the development of a robust hydrogeological conceptual model of the system, reviewed elsewhere in this special issue. Subsequent refinements are also summarized. This work confirmed that both surface water and groundwater flows from Bolivia to Chile, and thus confirms the status of the Silala River as an international watercourse and provided the basis for a basin‐scale groundwater numerical model, used to investigate the impact of wetland channelization on surface water/groundwater partitioning. This article is categorized under:Science of Water > Hydrological Processes [ABSTRACT FROM AUTHOR]

The existence of enormous volumes of mine tailings (MTs) deposits around the World, and specially in Chile, has generated a growing interest about the potential economic and socio-environmental benefits of reprocessing them. The present study assesses this possibility in the world class example of Mineral Valle Central (MVC), one of the few MTs reprocessing plants that has been under operation since 1992. To do so, 20 sampling points along the mineral processing plant were selected and monitored every two months from April 2018 to January 2019, generating a total of 120 samples. The multivariate statistical analysis of detailed chemical and mineralogical information confirmed the existence of two main groups, a first one corresponding to the elements (As, Ag, Fe, Cd, Co, Ni, Pb, Sb and Zn) linked to sulphides and a second one including elements mainly hosted by silicates. As expected, the first group of elements showed a general increasing tendency in their concentration along the processing plant while the second group tended to decrease their concentrations. It was observed that during the generation of the current Cu-concentrate in MVC, Co concentrations are increased as high as ten times (~0.25 g/kg) from the original concentration in the MTs entering the reprocessing plant (~0.025 g/kg). Therefore, the design and theoretical addition of new operational units to generate pyrite concentrates was evaluated. Such a de-pyritization process unit could link economic and environmental potential benefits thanks to the recovery of the Co hosted in pyrite and to the reduction of the acid generation potential of the final MTs sent to Caren MTs deposit. This exploratory study shows important environmental benefits as well as some economic potential thanks to the recovery of Co hosted in pyrite. Notwithstanding, future comprehensive Co deportment studies and a detailed technical – economical evaluation are needed to determine the economic feasibility for the construction of the proposed de-pyritization process unit. [Display omitted] • Plant geochemistry can determine opportunities for by-product recovery. • Reprocessed tailings improve plant profitability and avoid environmental problems. • By-product recovery can increase production, increasing revenue • Elements with low concentrations increase their value by almost 2 orders of magnitude. [ABSTRACT FROM AUTHOR]