GEO 381R Field Excursion to the Chilean Andes

In May, 1999, a combined group from the University of Texas at Austin, New Mexico Tech, and the University of Utah spent three weeks in northern Chile, experiencing the spectacular tectonic and volcanic geology of the central Andes, the stark terrain and climate of the Atacama Desert, and the worldclass mineral deposits.  The trip was a fabulous educational opportunity for students with interests in tectonics and subduction-related magmatism ((Karah Wertz, Tip Meckel), ore deposits (Asif Muzaffar, Jim Corboy), and climate-related weathering phenomena (Joy Griffin, Tony Troutman), as well as Pre-Columbian history and Andean culture.  The trip followed a Spring Semester seminar in which the graduate students studied various aspects of the geology of the region in GEO 381R Regional Studies in Mineral Resources Geology.  Each student prepared a section of a guidebook for the trip. 

The trip included 10 geologic professionals who shared invaluable experiences from the real world of mining and mineral exploration.  They and their companies also provided field vehicles and per diem support that helped make the trip affordable for the students.  The Geology Foundation provided scholarships to cover most of the international airfare for the students, thus making the trip an incredible value for the students.

Chile is the world's leading copper-producing country, so predictably the trip was dominated by tours of various types of copper deposits.  These deposits are hosted by Mesozoic and younger igneous rocks of a variety of types.  The deposits are complex mineralogically, as the result of the variability of the original copper concentrations and the overprint of weathering phenomena associated with the hyperarid climate of the Atacama Desert.

The trip started in Copiapo, following an overnight bus ride from Santiago.  The first visit was to the Candelaria copper deposit in Mesozoic metavolcanic strata, arguably the most controversial deposit of the entire trip.  Next was a tour of El Salvador, the subject of many classic studies of the relationship between hydrothermal alteration and "porphyry" copper mineralization.  El Salvador also provided the only underground mine experience for the group.  We toured the new Manto Verde copper deposit, an interesting variety of structurally controlled copper mineralization without a genetically associated pluton.  A day was devoted to regional geology, including tracking the Atacama fault and coastal batholith complex cut by spectacular dike swarms.  We ended up at the coastal town of Taltal from which we ventured out to examine three manto-type copper deposits in Mesozoic andesitic volcanics.   Traveling further inland, we toured El Guanaco, an interesting study in metal zonation from a high-level gold-rich deposit that becomes increasingly copper-rich with depth.  Lomas Bayas provided an example of the climatically induced complexity to near-surface copper deposits in the Atacama region, where the high nitrate and chlorine content of the secondary ores complicates copper recovery via the solvent extraction process.  The nearby Fortuna deposit illustrated a well-evaluated copper resource that awaits better metal prices before production can commence.  El Abra, at 4200m elevation, provided the high point of the trip, with one of the world's largest copper producers against a backdrop of snow-covered Andean volcanic peaks.  Mina Sur (Exotica), the last copper deposit visited on the trip, was also one of the most spectacular.  Mina Sur formed where groundwater, carrying copper derived during weathering of the nearby supergiant Chuquicamata porphyry deposit, precipitated secondary copper minerals within the matrix of Tertiary gravels forming a high-grade "exotic" deposit.

The Tejanos stayed after the conclusion of the mine trip to see some of the other geologic features of northern Chile in the San Pedro de Atacama area, one of the few habitable sites within the heart of the Atacama region.  This trip provided many additional experiences, including an earthquake in Calama and a surreal sunrise at 4,000m elevation at the steaming El Tatio geyser field after arriving in the freezing dark.  We visited the Salar de Atacama, which contains the world's largest lithium producer from the interstitial brines beneath a rugged evaporitic crust; the limited water in the salar hosts a thriving biological community including a flamingo colony.  The visit was punctuated by an impromptu concert from a Chilean folk group on the return bus to Calama.  The students made their way back to Santiago with an intermediate stop on the beach at La Serena. 

As was advertised for the course, the trip should not be confused with a vacation.  Although everyone returned bone-tired, an unforgettable experience was had by all participants.

Modified from story by Rich Kyle in the 1999 DGS Newsletter

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