Geochemical Risk Assessment Process for Rio Tinto’s Pilbara Iron Ore Mines

Abstract

Acid Rock Drainage (ARD) and geochemical mobility of contaminants are now more than ever a major consideration for evaluation of new deposits. They can have a significant impact on the environmental and economic sustainability of a mining operation. Rio Tinto Iron Ore (RTIO) have developed a unique hazard assessment score sheet which allows the relative risk at each operation to be compared and flags the major risks upfront. Assessment is based on four key areas: � A preliminary assessment � including assessment of the geology, incipient risk, scale of disturbance, transport pathways and sensitivity of the receiving environment; � Geochemistry � including assessment of sulfur content in waste and ore and the spatial distribution; � Mine planning� including assessment of the tonnes of Potentially Acid Forming (PAF) and neutralising material and the likely dump locations; � Water management� including assessment of water discharge volumes, likely water quality and final void management. This hazard assessment is accompanied by a detailed risk assessment document that interrogates all drill hole data for the deposit, mine planning tonnages and considers final pit wall exposures. Finally an inherent risk for all possible scenarios, causes and potential impacts is assigned based on likelihood and consequences. This risk is refined based on the implementation of controls and management measures. The hazard assessment is completed for RTIO�s Pilbara operations and has been a useful tool to identify significant risks upfront. This tool allows RTIO to manage PAF material appropriately and through thorough identification of the risks ensure appropriate management techniques are selected and implemented to proactively reduce the risk of ARD or mobility of metals soluble at neutral pH.