Grinding facilities are arranged either as single-stage circuits, or in a two-stage configuration with ball mills. Another major concentrator, designed with an autogenous mill, ball mill, crusher (ABC circuit), is presently under construction and scheduled for start-up late this year.
The host rock of the Island Copper deposit is a highly fractured fine-grained andesite. A prominent alteration product of this porphyry intrusion is a siliceous breccia. Sulfide minerals in order of abundance are pyrite, chalcopyrite and molybdenite with very minor amounts of chalcocite, bornite and sphalerite.
Feed to the grinding section is the product of a 1372 x 1880 mm (54 x 74 in) primary gyratory crusher set at 210 mm. Crusher discharge is conveyed to a screening plant where a separation is made at 100 mm.
Island Copper concentrator throughput is 34 000 tonnes/day. The six semi-autogenous mills are 9.75 m diameter by 4.27 m cylinder length and are driven by two 2 618 kw wound rotor motors through two gear reducers to twin pinions. Each primary mill is in partially closed circuit with a bank of eight 510 mm hydroclones. Primary cyclone underflow is split into two approximately equal fractions with one fraction closing with SA Mill No. 1 and the other joining a similar split from SA Mill No. 2 as feed to the ball mill.
The Los Ranchos Formation of Lower Cretaceous age hosts the Pueblo Viejo ore body. This formation is composed mainly of volcanic flows and tuffs and volcanically derived sediments. Mineralization appears as both bedded and vein-type sulfides. Identified sulfide minerals include pyrite, marcasite, sphalerite, covellite, chalcocite, chalcopyrite and enargite. Gangue minerals are quartz, hematite, limonite and various clay minerals including pyrophyllite.
Run-of-mine ore is screened at 458 mm and fed direct to the primary semi-autogenous mills or stockpiled for weekend and other periods of mine outages. The ore is carried to stockpile by a 1220 mm belt 150 meters in length.
The two semi-autogenous mills are 5.64 m diameter by 1.83 m shell length and are diven by one 515 kw induction motor through a single reduction gear reducer and mill pinion. The ball mills are 2.59 m diameter by 3.66 m shell length with 343 kw induction motor drive. Each ball mill is in closed circuit with a bank of four 508 mm hydroclones. Percent circulating load ranges from 125 to 200, and averages 150.
The host rock of the Bagdad ore body is a mineralized stock of quartz monzonite that has been hydrothermally altered and somewhat enriched in quartz and potassic minerals. It is usually a fine to medium grain rock with equigranular-texture. Porphyritic texture is not uncommon in some zones.
Cyprus Bagdad concentrator is designed for a throughput of 36 000 tonnes/day. Each grinding line consists of an autogenous mill 9.75 m diameter by 3.96 m cyclinder length with twin 2 984 kw drives, a ball mill 4.77 m diameter by 6.77 m shell length with 2 238 kw drive and a 2134 mm (7 ft) short head cone crusher with 361 kw drive.
