Client: Compañía Pangea Minera /McEwen Mining
Location: Mina El Gallo, Sierra Madre Occidental, Sinaloa, Mexico

Challenge: To store tailings produced by reprocessing gold leaching piles in a cost-effective manner that is protective of the environment. 

Solution: We determined that the safest and most economical solution for storing the tailings was to place them in one of the inactive mine pits. To accomplish this, INTERA characterized the hydrogeology of the pit and the geochemistry of the tailings and potentially reactive surfaces of the pit. These efforts supported the preparation and submittal of a successful permit application to the SEMARNAT for the in-pit disposal of tailings from reprocessed ore . A hydraulic testing program was conducted to characterize the andesite aquifer adjacent to the candidate pit. The program consisted of drilling five deep core holes (approximately 200 meters each) to identify fractures that could conduct groundwater, performing packer tests, and installing vibrating wire piezometers. To achieve a better understanding of groundwater flow, we also collected hydraulic field data, performed a water balance for the pit, and oversaw the development of a hydrogeological conceptual model of regional and local groundwater flow systems. The geochemistry program included static geochemical analyses of tailings and pit surfaces, and a hydrochemical assessment of seeps in the pit. 

Results: Our hydrogeological and geochemical evaluations showed that most of the groundwater flow is through fractures under the pit, the tailings have no potential for acid generation, and that the contrast between the hydrogeological characteristics of the tailings and the fractured rock will minimize the inflow of groundwater and the outflow of tailings solutions during their consolidation. The permit for in-pit tailings storage obtained from the SERMANAT was the first of its kind issued in Mexico.