Challenge. Evaluate metal leaching and acid rock drainage (ML/ARD) potential of waste rock dumps from recent and historic
mining operations at a low sulfidation epithermal vein deposit that has been mined intermittently since 1757. As required by the SEMARNAT permit for the new facility, develop a management plan for potentially hazardous waste rock that will be deposited in a new waste dump.

Solution. To manage potential risks associated with mine waste, INTERA personnel developed and implemented a phased geochemical characterization program over a 12-year period to evaluate legacy waste dumps as well as to support the permitting of a new waste dump in the Piaxtla River valley. Initial phases of work were focused on identifying, measuring and characterizing over 40 waste rock dumps to determine their ML/ARD potential. Based on the results of characterization, detailed static tests were completed for the waste rock destined for a new dump in an incised river bend. Results of the tests were used to develop a preliminary waste rock management plan and kinetic characterization program, which was submitted to the SEMARNAT as an element of the waste rock dump permit.