Por: William Martínez Valladares, Alonso Marchena Campos y Jorge Chira Fernández, Instituto Geológico, Minero y Metalúrgico. 

Abstrac

World-class copper-molybdenum (Cu-Mo) porphyry systems were emplaced in southern Peru during the Cretaceous-Paleogene transition. This was associated with crustal thickening resulting from a large volume of previously generated magma, in an event known as a magmatic flare-up. Subsequent crustal thinning led to the collapse of the continental crust and triggered intense felsic magmatism, which deposited a succession of rhyolitic pyroclastic materials more than 1,000 m thick, known as the Toquepala Group.

Following this magmatic event, significant world-class Cu-Mo porphyry systems developed during the Paleogene, including the deposits currently mined at Cerro Verde, Cuajone, Quellaveco, and Toquepala, as well as projects such as Los Calatos, Suyawi, Chaska, Pampa Esperanza, and Elisa Sur (Moquegua), and Curibaya-Sambalay, Cinto, Pampa M or Chipispaya (Tacna). 

Exploration for these important systems relies on traditional tools and, more recently, modern technologies such as artificial intelligence and fractal theory. The latter is supported by a coherent structural interpretation applied to a convergent margin currently undergoing extension. 

This study draws on several proposals by the late British geologist Jeremy Richards, whose conceptual research is applicable to the Central Andes, particularly Peru. Tectonic, stratigraphic, geochemical, kinematic, emplacement, and preservation controls are all critical to the formation of world-class porphyry deposits. 

The Toquepala Group played a significant role in the evolution of porphyry systems, with its regionally extensive magmatism and volcanism associated with this type of mineralization. This geological unit consists of a thick sequence of predominantly pyroclastic volcanic rocks of calc-alkaline and rhyolitic composition, exceeding 1,000 m in thickness. One way to explain the sequence of steps involved in the generation of these major deposits is to consider how these processes played a role in and contributed to the origin, formation, and deposition of this type of deposit. 

This intrusive and extrusive magmatism originated at the base of the continental crust, possibly as a result of a thermal flare-up, which generated high heat flow and caused thinning of the upper crust. This led to the formation of calderas that subsequently collapsed, depositing thick pyroclastic sequences during the Cretaceous-Paleogene transition. 

The Toquepala Group is underlain by the Huaracane Formation, dated at 80 Ma (Martínez et al., 2025), and overlain by the Paralaque Formation, dated at 65 Ma (Martínez and Cervantes, 2003), marking the transition from the Cretaceous to the Paleogene (the K-Pg boundary). It is important to note that this enormous volume of pyroclastic material was deposited over a period of just 15 million years and is exposed from Quebrada  Guaneros at the base of the sequence to the area near the town of Torata at the top, in the Moquegua region. This magmatism, possibly resulting from a flare-up, was channeled and emplaced along the Incapuquio Fault System, the region’s main structural control on mineralization. The magmatism and subsequent pyroclastic eruptions preceded mineralization in the region and, in particular, the formation and emplacement of the subvolcanic bodies that preceded the southern Peruvian copper-molybdenum porphyry deposits (DPC, by its Spanish initials).