Bougainville Copper Company - Panguna, Bougainville - Papua New Guinea

The Bougainville ore body was discovered in 1964 by a partnership of Conzinc Rio Tinto of Australia and New Broken Hill Consolidated Limited. The ore body is a porphyry copper in a fine-grained quartz diorite, which intrudes andesite volcanics and is located at an elevation of about 2, 000 ft in the Crown Prince Range of Bougainville in the Solomon Islands. Mineralization is predominantly chalcopyrite with some bornite and some gold and silver present. Rainfall in the area amounts to 200 in. (5. 08 m) per year. An active volcano is situated only 24 miles (38.4 km) from the mine, and all structures were designed to resist seismic shocks. An interesting and unique feature of the Bougainville operation was that the overburden was stripped with hydraulic monitors. Bougainville Copper, at 90,000 tpd, is the largest copper concentrator to be designed and constructed at one time; and besides the twin 54 in. by 74 in. Allis-Chalmers gyratories, it features seven 7 ft (2. 13 m) standard and fourteen 7 ft shorthead crushers, in addition to nine 18 ft diameter by 21 ft long (5. 5 m by 6. 4 m), 4250 hp, single -stage ball mills. During the design stage of the Bougainville primary crushing plant, several alternates were studied because the ore was expected to break with the production of large amounts of small-sized particles but with a minimum of fines. These alternates included two 54 in. by 74 in. gyratories with grizzlies, two 60 in. by 89 in. gyratories, and one 72 in. by 96 in. gyratory, the latter two installations without grizzlies. The two 54 in. units with grizzlies were finally selected as giving good reliability and the ability to handle the large amounts of small material in the feed. As originally installed, grizzly bars were set at 8 in. (203 mm); but, in an effort to perform more interparticle crushing in the primary and less rock-on-steel crushing in the secondaries and tertiaries, a test is underway (1976) to determine the effect of using 6 in. (152 mm) grizzly spacings (see write -up on Anaconda's crusher at Butte). The Bougainville ore is mined with 17 cu yd (13 cu m) shovels and hauled in 105, 170, and 210 st trucks to the crushers, which are equipped for two-side dumping. Up to 40% of the ore passes the grizzlies, which are equipped with splitters; and additional horizontal splitter bars are located directly above the spider caps. Because of the grizzlies, the crushers are supported by unique U-shaped enclosures, which are in turn supported by the end and center walls of the installation.