Minera Penmont purchases Sodium Cyanide exclusively from ICMI certified manufacturers (Cyanco and Dupont). Sodium cyanide is transported and delivered to our facilities by ICMI certified transporters, following adequate protocols to safely manage cyanide. Sodium Cyanide is supplied to our operations either as a liquid or as solid briquettes. Liquid Sodium Cyanide (~30% aqueous solution) is transported in tanker trucks and off-loaded onsite into our storage tank. Solid briquettes (~98% purity) are transported in ISO-containers designed so that the cyanide can be safely dissolved in a high-pH solution. The pH value of cyanide solutions is maintained high during dissolution to prevent the volatilization of hazardous hydrogen cyanide (HCN) gas. The resulting solution is then pumped to our storage tank. Throughout the unloading of Sodium Cyanide we apply strict Health and Safety measures to prevent spills and exposure of our employees and contractors to cyanide. Likewise, we mobilize our response teams to be ready to contain releases or respond to incidents causing exposure of our employees and contractors to cyanide.

The process used by Minera Penmont to extract gold from ore is known as “heap leach”.  In this process, the ore is staked in layers on an impermeable membrane known as “leach pad”. The cyanide solution is dripped onto to the heap by a drip irrigation system. The solution percolates through the heap leaching the gold from the ore. The cyanide solution applied is indeed water containing a very low concentration of sodium cyanide (~.05% solution). The leach pad is made of an impermeable liner cover made of high-density polyethylene (HDPE) to recover the pregnant solution and protecting groundwater from seepage.  The pH is controlled throughout the process (pH > 10.5 - strongly alkaline) using lime to ensure that when the cyanide solution is added, hydrogen cyanide (HCN) gas is not generated and cyanide remains in solution, ready to dissolve the gold. The resultant gold bearing solution is collected on the leach pad and channeled to the Merrill-Crowe plant for further processing.

The Merrill-Crowe plant separates gold and silver using a process to filter the pregnant solution, removing oxygen and precipitating the desired metals (using zinc). The gold/silver precipitate is smelted to form crude and impure bars which are sent to a refinery. The residual solution is returned to the heap leach process allowing our operations to reduce the use of new water in our processes. Furthermore, our processing plants have contingency ponds to store the solution when the inflow rate exceeds the processing capacity, for instance when rain increases the percolation volumes in the heap.