GEOLOGIC MAPPING OF SULFIDE-BEARING BEDROCK EXPOSED BY DEGLACIATION IN THE CORDILLERA BLANCA, PERU

The Cordillera Blanca, a mountain range of the northern Andes in Ancash, Peru, is known for its extreme topography, tropical glaciers, and its setting at the boundary between the Andean foreland and hinterland. The Cordillera Blanca consists of the Neogene Cordillera Blanca Batholith (CBB) that was emplaced into Mesozoic marine sedimentary rocks represented locally by the Jurassic Chicama Formation.The most recent geologic maps were published in the 1990s, using a 1:100,000 scale and a base map with the 1967 glacial extent. However, the tropical glaciers that cover the bedrock are extremely sensitive to climate change and have begun to recede at an increasing rate since the 1960s. Ongoing deglaciation uncovers a larger volume of bedrock. Additionally, this deglaciation exposes a zone of heavily mineralized, sulfide-bearing Chicama bedrock. Oxidation of the mineralized zone causes contamination of groundwater and surface water that serves as a source for human consumption and agriculture for a large portion of the population west of the Cordillera Blanca. By mapping newly exposed sulfide-bearing zones, we can interpret locations of current water contamination and predict where water contamination may get worse in the future. Within the past several years, we have mapped multiple valleys in the Cordillera Blanca to identify the extent of the mineralized zones. We present a new geologic map for part of Llanganuco valley at the 1:25,000 scale and additions to our research group’s mapping of Ulta valley at the 1:50,000 scale. Remoteness and high relief limit the area covered, so we chose sites where our collaborators have collected surface water chemistry data. In addition to mapping bedrock, we mapped Quaternary glacial, fluvial, and mass wasting deposits, as well as minor faults, all of which are glacial runoff pathways. This research project has provided a way for the local government to make more informed decisions about their water sources. Many institutes have funded this research to help understand climate change in real time. Continued research will provide models for areas experiencing deglaciation in the future.