BEDROCK GEOCHEMISTRY AND ITS CONTROL ON WATER QUALITY DURING RAPID GLACIAL RETREAT IN THE CORDILLERA BLANCA, PERU

The Cordillera Blanca is the highest elevation and the most heavily glaciated mountain range in the Peru. Glacial melt in Huascaran National Park, in the Cordillera Blanca, supplies freshwater for over one million of people living in the Ancash region of central Peru and millions more in coastal Peru making water quantity and quality in the Cordillera Blanca a large concern both locally and globally. Many of these glaciers are retreating rapidly, due to climate change, changing the hydrologic character and chemical composition of the local streams and rivers, causing lower pH water and high concentrations of trace metals. The changes in water chemistry seem to be driven by bedrock composition: the basement rocks exposed in the Cordillera Blanca are dominantly granodiorite, which is heavily altered along the mylonitic fault surface and the contact zone with the overlying Jurassic and Cretaceous marine sedimentary units. The contact zone is located along the high-spine of much of the Cordillera Blanca which was, until recently, covered by glaciers. As the glaciers retreat the sulfide minerals are exposed to the oxygenated atmosphere which causes them to alter to sulfite which is then dissolved into the water and transported along with trace metals to populated areas to the east of the range. This study presents detailed maps and geochemistry of the mineralized zone along the contact between the granodiorite and the overlying Jurassic units that were previously covered by glaciers to predict where there will likely be contaminated streams in the future.