Description

The Grasberg minerals district includes open-pit and underground mines.

Did you know?

PT Freeport Indonesia (PT-FI) commenced mining operations in 1972 and in 1988 discovered the Grasberg mine. Today, after significant production, the Grasberg mining district contains one of the world’s largest recoverable copper reserve and the largest gold reserve.

Location

The remote highlands of the Sudirman Mountain Range in the province of Papua, Indonesia, which is on the western half of the island of New Guinea.

Processes and facilities

The Grasberg minerals district has three operating mines, the Grasberg open pit, the Deep Ore Zone (DOZ) underground mine and the Big Gossan underground mine. In September 2015, PT-FI initiated pre-commercial production, which represents ore extracted during the development phase for the purpose of obtaining access to the ore body, at the Deep Mill Level Zone (DMLZ) underground mine. PT-FI also has several projects in progress in the Grasberg minerals district related to the development of the large-scale, long-lived, high-grade underground ore bodies located beneath and nearby the Grasberg open pit. In aggregate, these underground ore bodies are expected to produce large-scale quantities of copper and gold following the transition from the Grasberg open pit.

Grasberg open pit. PT-FI began open-pit mining of the Grasberg ore body in 1990 and is currently mining the final phase of the Grasberg open pit, which contains high copper and gold ore grades. PT-FI expects to mine high-grade ore over the next several quarters prior to transitioning to the Grasberg Block Cave underground mine in the first half of 2019. Production from the ore stockpiles, which are located outside of the pit limits, is expected to continue through the end of 2019.

Crushing and conveying systems are integral to the Grasberg mine and provide the capacity to transport more than 250,000 metric tons of ore per day.

DOZ underground mine.The DOZ ore body lies vertically below the now depleted Intermediate Ore Zone. PT-FI began production from the DOZ ore body in 1989 using open-stope mining methods, but suspended production in 1991 in favor of production from the Grasberg open pit. Production resumed in September 2000 using the block-cave method and is at the 3,110-meter elevation level.

The DOZ is a mature block-cave mine that previously operated at 80,000 metric tons of ore per day. Current operating rates from the DOZ underground mine are driven by the value of the incremental DOZ ore grade compared to the ore from the Grasberg open pit and ore grade material from the development of the DMLZ and Grasberg Block Cave underground mines. Ore milled from the DOZ underground mine averaged 31,200 metric tons of ore per day in 2017, 38,000 metric tons of ore per day in 2016 and 43,700 metric tons of ore per day in 2015. Production at the DOZ underground mine is expected to continue through 2021.

Using ore passes and chutes, the LHD units transfer ore into 55-metric ton capacity haul trucks. The trucks dump into two gyratory crushers, and the ore is then conveyed to the surface stockpiles for processing.

The success of the development of the DOZ mine, one of the world’s largest underground mines, provides confidence in the future development of PT-FI’s large-scale, underground ore bodies.

DMLZ underground mine.The DMLZ ore body lies below the DOZ underground mine at the 2,590-meter elevation and represents the downward continuation of mineralization in the Ertsberg East Skarn system and neighboring Ertsberg porphyry. During 2017 and late January 2018, the DMLZ underground mine was impacted by mining-induced seismic activity, which is not uncommon in block cave mining.