Batu Hijau mine

In 1990 mineral exploration on the island of Sumbawa resulted in the discovery of copper mineralization that would be developed into the Batu Hijau mine.[1] The deposit was named for the discovery outcrop, a bright-green oxide-copper occurrence; in Indonesian, "Batu Hijau" means "green rock." [2] Over the next ten years PT Newmont Nusa Tenggara delineate the resource and began developing the mine and building the required infrastructure. In 1999 construction was complete and by the next year Batu Hijau was producing ore.[3]

In 2016, Newmont Mining Corporation successfully completed the sale of its ownership stake in PT Newmont Nusa Tenggara, which operates the Batu Hijau copper and gold mine in Indonesia, to PT Amman Mineral Nusa Tenggara.

The orebody at Batu Hijau is a porphyry copper type and includes a high gold component, which is common for such copper deposits in southeast Asia. The host rock for porphyry copper deposits in southeast Asia is typically diorite and quartz diorite. Copper sulphides such as chalcopyrite and bornite are frequently associated with the gold component of these deposits.

As of the end of 2008, Batu Hijau had an ore reserve of 968mt of ore at 0.41% Cu and 0.29g/t Au. [3]

Haul trucks at the Batu Hijau mine

Batu Hijau is an open-pit mine. Ore is removed from the mining face using P&H 4100 electric shovels (pictured) and loaded into Caterpillar 793C haul trucks. Each haul truck can move a payload 220 t (240 short tons) of ore. The trucks haul ore from the shovel to primary crushers. Crushed ore is sent by a conveyor 1.8 m (6 ft) wide and 6.8 km (4.2 mi) long to the mill. Daily production from the mine is an average of 600,000 t (660,000 short tons) ore and waste combined. Ore from the mine has an average copper grade of 0.49% and an average gold grade of 0.39g/t.[3]

Crushed ore is further reduced in size by Semi-Autogenous Grinding and ball mills. Once milled it is sent through a flotation circuit which produces a concentrate with a grade of 32% copper and 19.9g/t gold.[3] The mill realizes a copper recovery of 89%.[4] The concentrate is thickened into slurry and piped 17.6 km (10.9 mi) to the port at Benete where water is removed from the slurry. The concentrate storage at the port can hold 80,000 t (88,000 short tons) of copper-gold concentrate.[3]

Disposal of tailings from the processing operation of the Batu Hijau mine takes place in the ocean, using a process called Submarine Tailings Disposal (STD). Indonesia is currently the only location that PT. Amman Mineral Nusa Tenggara uses this process, claiming that it is more an environmentally sound practice despite being more costly to the company. The process involves piping the tailings 2.1 miles (3.4 km) off the coast to a drop-off of 400 feet (120 m), which carries the waste down another 10,000 feet (3,000 m). Waste rock from the Batu Hijau mine is disposed of in the rainforest, with space for newly produced waste rock running out. Environmentalists are raising concern with the declining population of the yellow-crested cockatoo.

• PT. Amman Mineral Nusa Tenggara, official website