Hydrogeological Risks of Mining in Mountainous Karstic Terrain: Lessons Learned in the Peruvian Andes

Abstract

Managing mine waste is one of the greatest challenges facing mining companies globally. Over the next 20 years, more than 10 billion of tons of waste will be generated in Peru based on the projected mining rates from existing mines and new projects. Most of Peru’s metal ore deposits are located at high elevations within a narrow, tectonized carbonate-rock belt extending over 2,000 km in length. Many of the limestone formations are karstified and characterized by high recharge and percolation rates, well-developed subsurface drainage and complex flow patterns. Mine tailings and waste rock facilities are preferably located close to the mine and processing operations and are often underlain, at least partially, by karstic limestone. Mining companies prefer to place mine waste in unlined basins when it can be shown that “natural hydraulic containment” will limit seepage to environmentally acceptable levels. Such a demonstration relies on detailed geological and hydrogeological investigations and the development of sound conceptual groundwater flow models. The depth of epigenetic karstification is greatly influenced by carbonate purity, bedding dip, faulting intensity, and oxidation of sulfide minerals (ARD). In addition, hypogenic karstification is common, particularly in areas with recent volcanism and hydrothermal activity. Detailed three-dimensional geological and numerical seepage models are used to predict seepage and environmental risk although simulating the effect of the channel network is often challenging.