Batu Hijau Gold Mine
|Batu Hijau Gold Mine|
Location: Sumbawa, West Nusa Tenggara, Indonesia.
Products: Copper & Gold.
Owner: P.T. Newmont Nusa Tenggara.
Ore Type: Porphory Copper deposits.
Reserves: the Batu Hijau included 2.77 million tonnes of copper with an average grade of 0.69g/t gold, which would allow mining to continue until 2025.
Ore geology and Mineralization: The Batu Hijau porphyry Cu‐Au deposit is a world‐class island arc type porphyry deposit, located on the southwestern portion of Sumbawa Island, Nusa Tenggara Barat Province, Indonesia. This 12 km by 6 km district contains an estimated 914 million tonnes of ore at an average grade of 0.53% Cu and 0.40 g/t Au (Garwin, 2002; Arif and Baker, 2004), and is one of the largest and richest porphyry Cu‐Au deposits in Asia.
Ore fluids produced distinct quartz ± sulfide veins and veinlets that cross cut the tonalite intrusions and their surrounding host rocks. Within these veins, fluid inclusions trapped in quartz contain ore fluids, which represent fluids moving through the deposit during the time of its formation. The ore fluids in the fluid inclusions are key to defining the temperature and pressure conditions under which the deposit formed, and defining the geochemistry of the hydrothermal system, which was responsible for the distribution Cu and Au within the deposit.
Preliminary fluid inclusion studies have suggested that deposit formation temperatures ranged from 280 to over 700 °C. Based on the coexistence of magnetite‐bornite ,chalcocite, Garwin (2000) suggested that the earliest veins at Batu Hijau likely formed at > 500–700 °C (cf. Simon et al., 2000). A preliminary fluid inclusion study by Garwin (2000) on inclusions in halite‐bearing transitional veins produced homogenization temperatures that ranged from about 450 to 500 °C. These temperatures are consistent with phase equilibria temperature estimates based on a chalcopyrite , bornite vein mineralogy (Simon et al., 2000).
Homogenization temperatures of < 400 °C were obtained by Garwin (2000) for late pyrite‐bearing veins. A fluid inclusion study conducted by Imai and Ohno (2005) documented homogenization temperatures ranging from 280 to 454 °C, significantly lower than temperatures obtained by Garwin (2000). This temperature is similar to Au saturation temperatures for bornite (~300 °C) and chalcopyrite (250 °C) (Kesler et al., 2002; Arif & Baker, 2004).
A detailed fluid inclusion microthermometry study to clarify processes of ore formation is warranted. Microthermometric data on well‐characterized fluid inclusions with appropriate pressure corrections can provide the temperatures and pressures at which the deposit formed. Additional qualitative and quantitative data from synchrotron x‐ray fluorescence (SXRF) and laser ablation inductively coupled plasma mass spectrometry (LA‐ICP‐MS), respectively, can document and quantify major and trace element concentrations. Such data will contribute to a model describing the transport of metals by hydrothermal fluids, and the precipitation of Cu‐ and Au‐bearing minerals.
Mining & Milling: 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.
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. The mill realizes a copper recovery of 89%. 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.