The Grasberg Mine is the world’s largest gold mine, and is also one of the largest copper producers in the world. The mine poses a real challenge for hydrogeologists due to its size and complex hydrogeological setting, including structurally controlled groundwater flow. The mine sits in a mountainous area with rainfall of up to 5 m per year. The site geology features highly undulated sedimentary rocks and vertical intrusions hosting the mineralization. Karstification exists in the area and influences structural control of the groundwater flow path in the vicinity of the open pit and underground mines.
The applied mining method for the Grasberg intrusive complex (GIC) also complicates water management. The existing open pit is approximately 1.5 km deep and a block cave operation is under development approximately 400 m below the pit bottom. Block caving will propagate to the pit bottom eventually and will create a highly transmissive cave zone, which will connect drawpoints to the bottom of the open pit.
Near the GIC, the East-Ertsberg skarn system (EESS) has been mined since 1982 by systems of five vertical block caves (GBT1, GBT2, IOZ, DOZ, and DMLZ). The implemented dewatering systems for both the GIC and EESS areas, with a total flow of approximately 41,000 gallons per minute (gpm) or 2.6 m3/s, allows lowered water levels in the vicinity of the open pit and underground mines by discharging groundwater via gravity by a system of upward drainholes drilled from the underground drifts.
To assist in the development of dewatering and mine water management strategies for the remaining life of mine, a comprehensive groundwater flow model was developed by using the finite-element MINEDW code and calibrated to the available flow and water level data collected over a 20-year period of active mining.
Fonte: SRK Consulting
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