NMT SEG Student Chapter Field Trip Report

SEG Student Chapters Field Course
Ore Districts of Northern Chile
18-25 February, 2012
The New Mexico Institute of Mining and Technology SEG Student Chapter organized
a six-day, multi-student chapter collaborative field course highlighting various ore districts and
mineralization styles of northern Chile. The field course was led by Dr. William X. Chávez, Jr.
of New Mexico Tech and Dr. Erich U. Petersen of University of Utah. Participants consisted of
two industry professionals from Perú, ten graduate students, and five undergraduate students.
Our field course began at the La Coipa high sulfidation epithermal system in the
Maricunga District near Copiapó. Jack Pritting and Claudio Ahumada of Kinross provided
discussions dealing with the mineralogy of the La Coipa epithermal system as we examined core
from several prospects in the La Coipa area. We also visited several field areas in which
solfatara-style alteration, including surface exposures abundant native sulfur, gave rise to
discussions of the importance of recognizing shallow-level alteration associated with welldeveloped
epithermal systems.
The Punta del Cobre breccia-manto system, characterizes Cu-(Au) mineralization
styles in this venerable district. Chief Geologist Radu Almasán discussed alteration assemblages
as we reviewed and identified ore and alteration minerals from several properties in the district.
While reviewing core we used activity diagrams to help explain copper mineralogy, and the main
alteration mineral assemblages.
The Altamira Cu-Ag mine is part of an historic district comprising both underground
and open pit mines; mine geologists Leonardo Retamál F. and Gerardo Garrido S. discussed
the geology of the Cretaceous hostrocks and the high-grade copper-silver sulfides. During the
visit we discussed copper systems hosted by volcanic rocks and how low-temperature redox
conditions and structural components control ore mineralization.
The high sulfidation Au-(Cu-As) epithermal system at El Guanaco was introduced to
our group by Geology and Exploration Manager Christián Cubelli B., and we were able to
compare El Guanaco to the La Coipa epithermal system and their geochemical variations.
Our visit to the world largest copper mine at the La Escondida property allowed us to
explore their Baker prospect, with discussions and a detailed presentation by Senior Exploration
Geologist Chilong Wong and Exploration Manager Javier Urrutia F. We discussed porphyry
systems and exploration considerations for large hydrothermal systems, supergene processes, and
ore system structural controls. Review of core samples provided the opportunity to discuss ore
assemblages and their relationships to specific alteration minerals, and the relationships between
vein types, and ore mineral paragenesis.