Radomiro Tomic Copper Mine

Radomiro Tomic Copper Mine

Location: 3,000m above sea level in the Atacama Desert of northern Chile

Products: Copper

Owner: CODELCO Production future.

Ore Type: Porphyry copper deposit.

Overview: Radomiro Tomic is the first mine to have been entirely developed by the Chilean state copper-mining company, Codelco. Located at 3,000m above sea level in the Atacama Desert of northern Chile, this new mining and hydrometallurgical operation is 4km from the Chuquicamata mine and smelter. Development was approved in 1995, started in 1996 and was essentially completed in 1997. The initial target capacity was 150,000t/y of copper cathodes but optimisation during construction raised the rating to 180,000t/y by the commissioning date. Prime contractor LX Ltda (Bechtel and ARA in joint venture) completed work early, below the budgeted $641 million. Recovering copper by heap leaching and electrowinning, Radimiro Tomic was inaugurated in 1998. In 1999 Codelco contracted Kvaerner Metals to increase the plant capacity to 250,000t/y of cathode at a cost of $220 million. This expansion was completed in 2001. Codelco initially created a new Radomiro Tomic Division with a streamlined organisation to manage the facility. During 2002, the corporation decided to amalgamate Chuquicamata and RT as one division - Codelco Norte - and developed a consolidated resource exploitation plan for the deposits in this area. About 460 people work at Radimiro Tomic.

Geology of the Deposit: The Radomiro Tomic porphyry copper deposit is located along the West Fissure structural domain, one of the main strands of the Domeyko fault zone (Cuadra and Camus, 1998). The orebody is 1 km wide, elongated north-south, and is completely buried by 30 to 150 m of Tertiary to Quaternary alluvial gravels, below which a thick oxidation zone was developed on granitic bedrock during a semiarid regime.

The host rock of copper mineralization at RadomiroTomic is the Chuqui Porphyry, the youngest intrusion emplaced on the eastern side of a Tertiary intrusive sequence. To the east the Chuqui Porphyry is in contact with a coarse-grained granodioritic intrusion, the Elena Granodiorite, and to the west with the Fortuna Granodiorite Complex (Fig. 2). The latter is a north-northeast–elongated intrusion 22 km long by 5 km wide that comprises five intrusive bodies of fine- to mediumgrained hornblende-biotite granodiorite. This complex, dated 39 to 37 Ma (Dilles et al., 1997) intruded Triassic to early Tertiary andesitic volcanics. Contact relationships between the Chuqui Porphyry and its host rocks are not well defined because information is based only on a few existing drill holes along the margins of the deposit.

The hypogene alteration and mineralization processes are restricted almost entirely to the Chuqui Porphyry, a granodioritic to monzonitic intrusion with medium- to coarse-grained phenocrysts set in a fine groundmass, and they were originated within the West Fissure fault zone. Recent 40Ar/39Ar dating on the Chuqui Porphyry at Radomiro Tomic gives an average age of 32.7 Ma for the K silicate late-magmatic phase and an age of 31.8 ± 0.3 Ma for the sericitic alteration (Cuadra et al., 1997). These ages define a slightly different hydrothermal timing compared to Chuquicamata (33.4 and 31.1 Ma, respectively; Zentilli et al., 1995). At Radomiro Tomic, potassic alteration is younger and the quartz-sericitic event is older than at Chuquicamata, so the time duration of alteration is shorter at Radomiro Tomic than at Chuquicamata.

The mineralized intrusion is buried beneath Tertiary to Quaternary alluvial gravels, with a thickness ranging from 30 m on the east side to 150 m on the west side. As a result the bedrock surface has a relatively gentle slope to the west, with some abrupt changes indicating possible faults, but this is not well-defined yet. The gravels are composed of angular andesitic fragments, 1 to 10 cm in diameter, in a sandy and poorly to moderately cemented matrix. This unit is in direct contact with the underlying leached or oxide zones of the deposit. Locally, the gravel is mineralized with exotic copper reaching thicknesses of tens of meters, mainly along northwest-trending paleochannels according to the paleotopography. A tuff intercalated in the gravels, 2 m below the current surface, was dated in biotite by the K-Ar method at 9.7 ± 0.7 Ma (Cuadra et al., 1997).

Alteration

K silicate alteration is developed pervasively throughout the entire Radomiro Tomic deposit, with the highest intensity found in the area between coordinates 10,000 N and 11,000 N (Fig. 2). It is represented typically by quartz-K feldspar veinlets and biotitization of hornblende phenocrysts. Quartz-sericitic alteration is less abundant and is clearly controlled by northeast- and north-south–striking subvertical structures. These structures are marked by quartz-pyritechalcopyrite D-type veins, with quartz-sericite halos. In the upper part of the oxidation zone supergene argillic alteration is defined by montmorillonite and kaolinite in fractures and as replacement of feldspars.

Hypogene mineralization

Hypogene mineralization follows a concentric distribution of inner bornite-chalcopyrite, intermediate chalcopyrite > pyrite, and outer pyrite > chalcopyrite zones centered around the coordinates 9,700 N and 11,000 N (Fig. 2) and averaging 0.5 wt percent total copper. Minor molybdenite mineralization is present alone or associated with chalcopyrite and pyrite in quartz veins and veinlets striking north and dipping subvertically. Arsenic minerals such as enargite are absent in significant contrast to the Chuquicamata orebody. This difference may indicate a greater degree of erosion for the Radomiro Tomic orebody. Hypogene mineralization continues to at least 400 m below the top of sulfides.

Supergene mineralization

Supergene oxidation and leaching processes affected the hypogene mineralization to an average depth of about 200 m beneath the gravel-bedrock contact (Fig. 3). Supergene mineralization is present immediately below the gravels with a typical vertical distribution of leached oxide zones, a mixed (oxide sulfide) zone, and a secondary sulfide zone. Locally, along quartz-sericite-faulted veins enrichment has reached depths of up to 800 m. The description of the different zones follows.

Fig. 2. Surface geology of the Radomiro Tomic area. The shaded area represents the subsurface geologic projection of the orebody at level 2,825 m.

Copper Mining

The conventional open pit strips at a 1.5:1 waste-to-ore ratio using rotary drills, P&H 4100 shovels, a LeTourneau loader, Caterpillar 793B and Komatsu 330st-capacity trucks. An FFE Minerals gyratory primary crusher near the pit rim supplies coarse ore, which travels to the main processing area via a 9,615t/h Krupp conveyor. The expansion added tertiary cone crushing (SRP Hydrocones) to the secondary Symons cone. Conveyors take stockpiled ore to pre-treatment and stacking on the racetrack-style heap-leach pads. Leached material is reclaimed by a bucket wheel and is conveyed to the dump area. Rahco and MAN-Takraf supplied the crawler-mounted materials-handling equipment. To handle the expanded production, the conveyor drives were fitted with programmable soft braking systems.

Copper Processing

Following acid leaching, the copper is separated from the heap-leach solution by four-stage solvent extraction with Acorga reagents and is fed in solution to the electrowinning tankhouse for recovery as cathodes using sophisticated technology. Four solvent-extraction trains designed and supplied by Outokumpu Engineering (including VSF mixer-settlers, Proscon 2100 NT process control system and OTI 99 titrators) remove the copper. The electrowinning feed and reagent streams are cleaned using molecular sieve coagulators and electrolyte filters designed by Codelco, and by CPT flotation columns. The large and highly automated electrowinning tankhouse was fitted with unique cathode cranes and stripping machines as well as a system of blowers and aerosol chimneys to ventilate the cells. The expansion added 272 cells, two travelling cranes and a cathode washing-stripping machine. Secondary leaching of waste will add 24,000t/y to 28,000t/y of copper to the cathode output.

Copper Production

After start-up, Radomiro Tomic recorded total operating costs of $0.44/lb, producing 162,000t copper in 1998 and 190,100t in 1999. The expansion boosted output to 256,000t/y in 2001 and Codelco hoped to maintain production at around 300,000t/y thereafter. Actual output in 2002 was 297,119t at a cash cost of $0.33/lb.

References

- Economic Geology 96, 401-420 (2001).
- Cameron, E.M., Leybourne, M.I., and Palacios, C. (2007): Atacamite in the oxide zone of copper deposits in northern Chile: involvement of deep formation waters? Mineralium Deposita 42, 205-218.