Located near Belen, Argentina, in Catamarca province, Alumbrera is 1,100 kilometres northwest of Buenos Aires, and six hours by paved and dirt roads from the airport at San Miguel de Tucumán. The mine is on a 600-hectare mining lease in a valley west of the easternmost range of the Andes at an elevation of 2,600 metres above sea level and is served by air and all-weather roads.
The deposit is a bowl-shaped, northeast- to southwest-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 mineralized rocks consist of a series of porphyritic intrusions into the andesites of the Farallon Negro complex. These alkalic porphyries were intruded some eight million years ago into the roots of the Farallon Negro volcano. The intrusion generated large-scale hydrothermal circulation, which resulted in alteration and mineralization 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.
The Farallon Negro host rocks are about 90% autobrecciated flows in a thick bedded sequence of fragment-poor to fragment-crowded, weak to strong porphyritic potassic andesite. The remaining 10% comprises lithic and non-porphyritic flow units.