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Bajo de la Alumbrera is Argentina's first major mining project. MIM has a 50% interest in the development and operating company, Minera Alumbrera Limited (MAA). Wheaton River Minerals Limited and BHPBilliton have equal joint ownership of the remaining 50%. MAA has the right to mine the deposit by agreement with Yacimientos Mineros de Agua de Dionisio (YMAD), an Argentine statutory entity which has title to the deposit and which will earn 20% of the net before tax proceeds after project capital plus interest has been recovered. Bajo de la Alumbrera is located in the north-west of Argentina, in the province of Catamarca, in the Eastern foothills of the Andes mountain range, at an altitude of 2,600 metres. The project was developed at a cost of US$1.2 billion and began commercial production in February 1998.
The project consists of five facilities in three provinces, namely:
The project also has support offices in Tucuman, Catamarca and Buenos Aires. Following a review of operations a low capital cost expansion, to be funded from cashflows is planned. Processing capacity will be expanded by 30%. Annual average mine production will be increased to 190 000 tonnes of copper in concentrate and 600 000 oz of gold in concentrate over eight years before declining as low grade stockpiled ore is processed. While total future copper and gold output will be unchanged, the remaining total project life will be shortened by 2 ½ years to 10 ½ years, giving total project life of 14 ½ years. The Alumbrera area has been known since the 1800's for its veins of copper and gold ore as well as alum which appeared by pyrite oxidation. The presence of this mineralisation gave rise to small-scale mining activity at the end of the 1800's and at the beginning of this century, and these works were situated at the southern sector of the edges of the present "Bajo" area. The Alumbrera deposit was discovered in 1949. From 1968 onwards, several drilling programmes were completed in the area. In 1990, the concession was put up for international tender. The concession was awarded to International Musto Explorations. In 1993, Minera Alumbrera Limited (MAA) was formed to develop and operate the Alumbrera mine. In 1994, MIM acquired 50% of MAA with the project's development announced in May 1995. In 1995, North Limited of Australia and Rio Algom of Canada obtained equal joint ownership of the remaining 50%. The project was commissioned in August 1997 with commercial production commencing in February 1998. During 2000, North Limited of Australia was acquired by Rio Tinto, and Rio Algom was acquired by BHPBilliton, with the corresponding changes in the MAA shareholdings occurring. The Alumbrera alkalic porphyries were intruded some 8 million years ago into the roots of the Farallon Negro volcano. The intrusion generated large-scale hydrothermal circulation which resulted in alteration and mineralisation of the porphyry itself and its volcanic host rocks. Subsequent erosion has exposed the upper part of the volcano and its porphyry system at a level that is favourable to mining. Topographically, the Alumbrera deposit is a bowl-shaped, north-east to south-west oriented ellipsoidal depression surrounded by ridges formed mostly by andesitic breccia of the Farallon Negro volcano. The floor of the bowl covers an area of 2.5 square kilometres. The primary mineralised rocks of Bajo de la Alumbrera consist of a series of porphyritic intrusions into the andesites of the Farallon Negro complex. A total of seven distinctive porphyritic intrusions have been recognised, which form stocks (earliest units) and dyke-like bodies (youngest units) that extend to the outer edge of the deposit with some of the dykes forming a radial pattern around the central stocks. The ore grades correlate with alteration with the highest copper-gold grades associated with intense Potassic (quartz-magnetite) alteration of two of the earliest mineralised porphyritic intrusions, and in adjacent biotised or potassium feldspar altered andesites. Younger porphyries are less mineralised or barren. The majority of the copper is primary and occurs as chalcopyrite in disseminated grains, and in veinlets. Copper and gold are positively correlated with gold occurring in association with early pyrite - chalcopyrite - magnetite as free gold grains in the 10 to 50 micron range and as inclusions within chalcopyrite crystals. State of the art mining techniques are employed in the open pit, with 41 cubic metre bucket shovels and 218 tonne haul trucks used to move both ore and waste. The mining bench height is 17 metres. The Alumbrera mine produces a copper-gold concentrate and a gold-silver rich dore on-site. The concentrator uses contemporary equipment and is designed to treat 80,000 tonnes of primary ore per day, through two identical grinding and flotation lines. MAA is currently undertaking an expansion of its plant facilities which will expand the throughput capacity to an average of 100 000 tonnes per day. The expansion facilities will comprise an additional grinding circuit and a "pebble" crushing circuit, which are scheduled for commissioning in the final quarter of 2001/2002. Tailings are pumped to an engineered tailings storage facility for long term containment. The copper and gold concentrates are pumped with added water through a 316 km, 175 mm diameter pipeline over the Nevados del Aconquija mountains to the province of Tucuman, where concentrates are dewatered to obtain an almost dry product (less than 8% moisture content). From Tucuman, concentrates are railed through the Nuevo Central Argentino railway, with Minera Alumbrera Limited's (MAA's) privately owned trains, to MAA's port facility in Puerto General San Martin, located near Rosario in the province of Santa Fe, where vessels are loaded and shipped to international markets. Some of the gold in the Alumbrera deposit is 'free gold', not chemically dissolved in the other minerals, but freely liberated as discrete gold particles. The particles are very small, averaging about 10 microns, but a significant fraction of the gold can be separated from the other material by gravity processes. The high density of gold allows a centrifuge-type device (called a Knelson concentrator) to separate the gold from other particles of lower density. The Knelson concentrate, which contains about 500 grams per tonne of gold, is transferred to the gold room for further upgrading to dore bullion.
MIM Holdings is committed to conducting business responsibly and in a manner designed to protect employees, the community's health and the environment. MIM Holdings developed an Environmental Policy and Standards in 1997 for all sites to follow to ensure minimal impact of our operations on the surrounding environment.
Environmental initiatives
Since commissioning our Alumbrera operation, several environmental initiatives have been implemented to mitigate environmental risk.
From the early stages of Alumbrera's development, local communities were kept informed regarding the progress of the operation. Since commissioning, Alumbrera has had considerable impact as a direct and indirect employer and provider of infrastructure. The project has helped fund roads, including heavy vehicle by-passes around the towns of Aimogasta, Santa Maria, Londres and Belen, so that the movement of trucks transporting supplies to the mine does not compromise people's safety and quality of life. Minera Alumbrera Limited (MAA) works closely with Government at the national, provincial and municipal levels to resolve the inevitable problems arising as a consequence of the development of a large scale mining industry in its infancy in Argentina. MAA recognises its responsibility to the communities in which it operates and provides a range of support, including sponsorship. We concentrate community assistance in the Alumbrera neighbourhood on training, education and health, and buying supplies locally where available, to encourage regional business development.
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