This site is located in the Andes Mountains of Central Chile, at the boundary between Region VI and the Metropolitan Region, between coordinates 6 212 000 and 6 223 000 m UTM North, and 393 000 and 401 000 m UTM East. It is located 60 km east of the city of Rancagua and 25 km southeast of the El Teniente copper deposit. Its elevation varies between 2500 and 4765 meters above sea level, with a high point at the peak of Cerro Catedral (4765 m). The area is only accessible during the summer.
The prospect comprises 970 mining rights units that cover 10 100 hectares located at the boundary between Region VI and the Metropolitan Region.
The prospect is located on the western edge of the Andes, where the land rises to the east of the central Salar El Huasco depression. This area of volcanic underlying geology features a large proportion of andesitic and dacitic tuff in which morpho-structural features have been observed in bands running N-S, where epithermal processes have occurred. This hydrothermal action took place in the upper Tertiary to Quaternary periods (Neogene), as a result of alteration complexes from fossil geothermal systems, domes, stratovolcanoes, and craters.
The prospect area is dominated by a thick sequence of mudstones and limestone that have been assigned to the Lo Valdés and Colimapu formations. The area’s sedimentary, volcanic, and volcanic-sedimentary rocks feature intrusions mainly of diorite, monzodiorite, granodiorite, and monzonite, comprising mainly veins, stocks, and dikes.
Breccias found in the prospect are differentiated into two types, based mainly on the mineralogy of the matrix: one type, found in the principal sector, features a siderite matrix, while other breccias rich in iron oxides (particularly specularite) are found in peripheral areas. The siderite matrix breccias also contain calcite, quartz, limonite, chalcopyrite, and albite at some sites. The most significant is the principal breccia, which measures 300 x 150 meters and is located in the eastern sector of the prospect. Breccias found in an iron oxide rich matrix contain specularite, hematite, magnetite, goethite, limonite, quartz, baritine, carbonate, and low levels of sulfide (mainly pyrite). The largest (300 x 400 metros) reaches the surface in the southeastern sector of the prospect.
This district’s mineralization is directly or indirectly associated with the locations of intrusive bodies. Surface sampling of porphyry copper mineralization types in the Laura sector, and tourmaline-associated mineralization, in potassium-rich rock, has shown the presence of copper at levels ranging from 59 ppm to a maximum of 1.37% Cu. Meanwhile, Skarn deposits have been identified with copper levels between 0.12% and 0.9% Cu. The area’s carbonate veins have also been sampled for copper, with some showing a content of more than 0.6% Cu. Finally, chalcopyrite has been detected in hydrothermal breccia, with a copper content of up to 800 ppm in limestone.
The large areas covered by zones of amphibole-plagioclase alteration, and the presence of diopside-scapolite alteration, together with the geographic dispersion of these alteration areas, including high levels of potassium and low levels of copper content, are factors that suggest that this district’s Cajón del Diablo – Escaladores sector represents a deeper and lower-sulfide hydrothermal system, and may therefore form the base of a porphyry copper deposit.
The types of mineralization present are: copper porphyry, copper porphyry (in which mineralization is associated with tourmaline – sericite – chlorite), Skarn, carbonate veins, and hydrothermal breccia.
The zone’s alteration and mineralization are essentially linked to the formation and cooling of intrusive bodies and the creation of magmatic fluids, which could have involved the circulation of local fluids as a consequence of the intrusion. The formation of hydrothermal fluids is observed, creating mainly sodium-rich to potassium-rich metasomatism, with further deposition of some plagioclase.
In the areas surrounding porphyry copper alteration-mineralization, carbonate breccia and veins have been found. These breccia formations have a low copper content, even lower than in the limestone sectors, so there is no need to theorize copper influx from magmatic fluids.
The following exploration work has been conducted at this prospect: geological, geochemical, geophysical, and drilling studies.
The company with adjacent mineral rights holdings is CODELCO, with the prospect lying 25 km SE of the El Teniente Mine.
This area’s geology has not been studied in as much depth as that of the nearby El Teniente zone, which has better access and economic interest. Its structures are defined at a different scale, and a narrow strip immediately to the west of the Cajón del Diablo has not been mapped in detail.