A Case Study for Final Closure of a Mine Site, Santa Fe Calvada Mine, Nevada

 

 

This paper presents a case study for the final closure of heap leach pads and dumps for an inactive open-pit gold mine in Nevada with the focus on management of draindown solution from the leach pads. Design and lessons learned in the permitting and construction phases will be discussed. Several options were considered for long-term fluid management including soil covers for the leach pads, evapotranspiration cells, infiltration galleries and evaporation cells (E-cells).  Evapotranspiration cells and galleries were subsequently eliminated as viable options.   The E-cell was HDPE doubled-lined and included a leak collection and recovery system. The primary liner was covered with soil for protection and a medium for solution storage. The Design criteria included zero discharge, passive fluid management, minimal maintenance, limited surface water expression, and provide for safe access for monitoring. As the site receives low annual average precipitation of around 6.8 inches and a high potential evaporation of around 55 inches with low flow rates, the criteria could be met with passive E-Cells and soil-covered leach pads. The E-cell design included elements that reduce long term monitoring and maintenance requirements. The E-cells were constructed in the summer of 2016 so it is too early to gage the success; however, inspection of the E-cells in the spring of 2017 revealed no open water was present in the E-cells.