Antamina is a polymetallic (copper, zinc and molybdenum predominate) skarn deposit resulting from complex multiple intrusive events. Copper mineralization occurs mainly as chalcopyrite except for some areas of bornite, representing approximately 5% of the deposit. Zinc mineralization generally occurs as sphalerite. Other significant sulphide minerals include molybdenite and pyrite, while trace amounts of numerous silver and bismuth bearing minerals and local areas of galena (lead sulphide) are also found within the deposit.

The Antamina and Usu Pallares deposits comprise a very large copper skarn with zinc, silver, molybdenum, lead, bismuth and arsenic formed by the intrusion of quartz monzonite body into limestones. Characteristics of the skarn zone depend upon the nature of both the intruded rock and the emanations from the intrusive body. Two types of alteration are recognized; recrystallization, or rearrangement of the constituents already in the rocks, and addition of chemical elements. Most skarn deposits show both features. The most striking skarn deposits are developed when the host rock is a sedimentary rock of carbonate composition. Mineral deposition in skarn deposits typically displays structural and stratigraphic controls. Skarn lithology is usually zoned from the fluid source both inward and outward. A typical sequence is; intrusive altered to garnet rich endoskarn, garnet rich exoskarn, diopside exoskarn, wollastonite exoskarn, hornfels, marble, and unaltered limestone.

The Antamina and Usu Pallares orebodies have proven to be consistently well mineralized and predictable, both in terms of grade and metal zoning over large areas, however short distance variability is quite high as is typical in most skarn deposits. Very little of the skarn lithology comprising the deposits is unmineralized.

As with the skarn silicate mineralogy, Antamina and Usu Pallares are horizontally and vertically zoned with respect to major metal components. This lateral zoning is clearly related to the orientation of the intrusive and limestone contacts and continues throughout the nearly one kilometer of vertical range of the deposit explored to date.

Metal zonation is quite distinctive within the deposit. Copper occurs relatively evenly distributed from endoskarn to the limestone contact. Zinc and bismuth tend to occur within 70 meters of the contact of green garnet exoskarn with limestone/marble/hornfels. Molybdenite is generally located within the intrusive core and surrounding endoskarn. Silver is present in any of the exoskarn lithologies. Lead is generally located in green garnet and diopside exoskarn and hornfels. Cobalt is generally associated with sphalerite mineralization. However veins and blebs of tennantite and other minerals can be found as rare occurrences in any rock type at Antamina. Arsenic occurs in solid solution within the copper minerals and in a variety of arsenic bearing minerals, contained within a valley parallel structural corridor and within a zone at the intersection of this structural trend with the Oscarina Dike structural trend.

Chalcopyrite is the predominant copper sulfide mineral. Approximately five percent of the copper mineralization is in the form of the copper sulfide mineral bornite. Zinc occurs primarily as the sulfide mineral sphalerite. Silver is normally associated in solid solution with chalcopyrite. However, it is also associated with galena, bismuth sulphosalts and tennantite. Molybdenum exists as the sulfide mineral molybdenite.

The most common bismuth minerals are bismuthinite, cosalite, whittichenite, cuprobismutite, aikinite, and kobellite, although various other Bi minerals as well.

There was little exposure of the deposit to oxidation and the evidence is in the way of a very limited oxidation cap and minimum supergene enrichment. This is due to the recent glaciation of the deposit, and the cold climate. However, there were zones of acetate soluble copper mineralization in Phase 2, resulting in material unsuitable for the production of salable quality concentrate. This oxidized portion has been almost completely mined to date.

Antamina is a large open pit mining operation using standard mining equipment and methods. Drilling is done with large rotary drills and blasting uses bulk explosives. Electric cable shovels and haul trucks do the principal material movement mining in 15 meters benchs.

4 Bucyrus shovels, 2 P&H shovels,
77 CAT 793 C/D/F, 15 Komatsu 930E
9 Drills (5 49R, 2 49HR & 2 DMM2)
3 Letorneau 2350.

The Antamina Concentrator processes multiple ore types on a campaign basis.

Antamina Operations - Concentrator:
* Batch processing of Cu and Cu/Zn ores.
* 2 SAG & 4 ball mills - sequential flotation of bulk Cu and Zn concs.
* Bulk Cu concentrate is further treated to produce a Moly or Pb/Bi conc.

Currently run-of-mine (ROM) ore is delivered to the 1.524 meter x 2.261 meter primary gyratory crusher via 240 tonnes haulage trucks. The ore is reduced in size from 1.5 meters to a nominal -178 millimeter product. The primary crusher product is transported via a 3.0 kilometer conveyor through a 2.7 kilometer tunnel which runs southeast of the crusher location and into the Yanacancha valley where the Concentrator process facilities are located. The coarse ore conveyor passes the material onto a radial-arm stacker that deposits the crushed ore onto one of two 50,000 tonne live-capacity coarse ore stockpiles. Coarse ore is reclaimed by apron feeders located underneath the coarse ore stockpiles in a reclaim tunnel that runs longitudinally to the stockpiles. Pulp discharged from the SAG Mill (11.6 meter x 6.4 meter EGL) is distributed to the Ball Mills (7.3 meter x 10.8 meter). The Ball Mills are operated in closed circuit with hydrocyclones and serve as the secondary stage of size reduction prior to the flotation circuits.

The initial flotation step following grinding is the Bulk Copper Rougher Circuit. The flotation product from the Bulk Copper Roughers is fed to the Bulk Copper Cleaner/Regrind Circuit. The cleaned flotation product from the Bulk Copper Cleaner/Regrind is then fed to the Bulk Copper Thickener.

From the Bulk Copper Thickener, the Bulk Copper concentrate is fed to the Bi/Mo Circuit. This flotation circuit operates in a bimodal fashion, depending on the ore type being campaigned. The circuit is used to either clean the Bulk Copper Concentrate of bismuth (a penalty element) by producing a Pb-Bi-Ag concentrate, or to separate a saleable Molybdenum Concentrate from the Bulk Copper feed material. The flotation product (either Pb-Bi-Ag concentrate or Mo concentrate) is fed to a small dewatering and product bagging plant. The ‘tailings’ product from the Bi/Mo Circuit is a final Copper Concentrate, which is fed to the Copper Concentrate Thickener.

The tailings from the Bulk Copper Rougher and Cleaner Circuits are fed to the Zinc Rougher Circuit. Zinc Rougher flotation product is processed through the Zinc Cleaner/Regrind Circuit whose product is the final Zinc concentrate, which is fed to the Zinc Concentrate Thickener. Tailings from the Zinc Circuits constitute the final tailings material, which is disposed of in the tailings impoundment.