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

GEO 381R Field Excursion to the Peruvian Andes

In May 2000, three University of Texas at Austin students, Marcy Davis, Amy Gilmer, and Jenny Head, joined students and faculty from New Mexico Tech and the University of Utah for a two-week field trip to study the geology of Per.  This was an excellent opportunity for students to see the unique mineral deposits of Per, to experience Andean culture, and to meet geologic professionals representing several mining and exploration companies.  The Geology Foundation provided scholarships to cover the international airfare for the University of Texas at Austin students, and the Society of Economic Geologists supported the trip through its field trip fund. The professional geologists and their companies helped to support the per diem expenses.

The trip began in Lima with the first of two transects across the Andes.  The first transect began in the coastal batholith at Lima at sea level and continued through the fold and thrust belt at Yauli Yacu (4816 m), then descended to San Ramon (900 m) on the edge of the Amazon basin.  Crossing the entire Cordillera was a dramatic transition to experience not only geologically, but also in terms of the vegetation and culture.

The first mine visit was to the San Vicente zinc mine in the eastern Amazon owned and run by SIMSA.  San Vicente is the 12^th largest mine in Per with 1999 production of 940,000 tonnes of ore averaging 8.5% Zn.  The San Vicente ore is distinctly banded within Jurassic carbonates and is similar to Mississippi Valley-type lead-zinc ores that are believed to result from metal-bearing basinal brines.  The group toured both the underground mine and the mill.  The La Oroya custom smelter operated by Doe Run Per provided an opportunity to see how metals were extracted from their ore.  The La Oroya smelter produces 20 products from the polymetallic ores mined in central Per. 

The Yauli Yacu mine was the highest mine toured on the trip at an elevation of 3700 m (12,135 ft).  This area, formerly known as the Casapalca district, contains complex Zn-Cu-Pb-Ag ores in veins and in replacement zones in Cretaceous limestones and conglomerates.  The Yauli Yacu mine extends laterally about 4 km and covers a vertical extent of 2 km.  The tour group was transported underground by train and then via an interior shaft to a depth of approximately 1 km below the surface.

The group also visited several volcanic-hosted orebodies that occur as roof pendants in the Coastal batholith about 50 km east of Lima.  Initially these deposits were mined for barite, but today Perbar is mining zinc-bearing ore. The underground workings of the Cecilia Norte had a projected production of 540,000 tonnes for 2000.  The enigmatic orebodies of the Raul-Condestable district occur about 100 km south of Lima.  The district is primarily known for its copper ore, but also produces some gold and silver ore as well. On the return trip, the group visited the pre-Incan ruins at Pachacamac about 40 km southeast of Lima. This area was inhabited before the time of the Incas along one of the few irrigable valleys of the coastal desert.

To save some travel time, the group flew to the city of Arequipa in southern Per.  Arequipa, the second largest city in Per, served as the base for the second Andean transect.  Arequipa is surrounded by mountains, including the spectacular volcano, El Misti, whose summit at 5822 m towers over the suburbs, offering an impromptu tutorial in volcanic hazards.  El Misti has been active many times since historic records began, including a lava dome in the 1950s and current fumarolic activity.  The group traveled from Arequipa to Moquegua, crossing over the Incapuquio fault zone, a major structure that is thought to be the extension of the Falla de Domeyko along which the major copper deposits are localized in northern Chile. Moquegua and surrounding region are known for the production of wines and pisco (the typical and national drink of Per).

The focus of the southern Per portion of the trip was the Tertiary intrusion-hosted porphyry copper deposits, the continuation of the worlds largest copper belt in northern Chile.  All are huge open pits producing copper to satisfy the global appetite for this important industrial metal, particularly for electrical transmission.  Weathering-related processes have produced large volumes of low-grade copper concentrations that are suitable for bulk mining and processing.  Reserves of the Southern Per Copper Co. at the Cuajone porphyry copper deposit are estimated to be 1.24 billion tonnes at 0.64 % Cu.  The Cuajone deposit has experienced limited leaching and enrichment, perhaps because of interruption of weathering by the eruption of the Huaylias tuffs that blanket the area. 

The Toquepala porphyry copper deposit about 50 km south of Cuajone has a much more extensive enrichment zone, perhaps because the Huaylias tuffs are absent in this area.  Tourmaline breccias and anhydrite veins are common at Toquepala.  Reserves are estimated to be 700 Mt of 0.74 % Cu with an additional 1.1 Gt of leachable ore at 0.20% Cu.  The Cerro Verde deposit owned by Phelps Dodge is located 30 km south of Arequipa, where the highest copper concentrations occur in the potassic-altered core of the intrusion.

The trip to Per was an amazing adventure and an experience not to be forgotten.   Everyone learned a great deal about the mineral deposits and culture of Per. 

Modified from story by Amy Gilmer in the 2001 DGS Newsletter

 

GEO 381R Field Excursion to the Iberian Peninsula

In May 2001, graduate students Christine Fox, Karah Wertz, and James McGuire participated in a tour of Portugal and Spain, a region with an ancient mining history.  The focus of the trip was the Iberian Pyrite Belt (IPB) that contains numerous large volcanic-hosted massive sulfide (VMS) deposits, the ancient equivalents of modern sea-floor hydrothermal vent systems. The students spent Spring Semester studying the geology and mineral deposits of the Iberian Peninsula, including preparing a contribution for a guidebook on a topic of interest.  Over two weeks, the students toured many of the larger ore deposits in southern Spain and Portugal, as well as experiencing Iberian culture and history.  Thanks to generous funding from the Geology Foundation, the students were able to gain direct experience on the regional geologic framework and mineralization in Iberia that they had studied in class.

The group, sponsored in part by the Society of Economic Geologists, met in Lisbon, Portugal, and consisted of 22 students and professionals from the University of Utah, New Mexico Tech, and the University of Texas at Austin (for additional coverage, see http://www.mines.utah.edu/pyrite/spain2001/index.html ).  Fees collected from participating institutions and companies helped defray transportation and housing costs during the IPB tour.  Group leaders were Dr. Bill Chavez of New Mexico Tech and Dr. Erich Petersen of the University of Utah; local geologists provided a great deal of detailed information at each major site.

The first stop on the tour was the relatively new Neves-Corvo mine, outside of the small Portuguese hamlet of Castro Verde where the group enjoyed terrific seafood.  The Neves-Corvo deposit is a blind orebody that was discovered almost entirely with geophysics and is a very large VMS deposit characterized by high copper grades and high tin zones.  At Neves-Corvo, the group learned the frighteningly simple, but effective, approach used when logging core in the IPB: a basal metamorphic phyllite-quartzite (PQ), overlain by a volcano-sedimentary sequence (VS), capped by the flysch group.  Typically, VMS orebodies like those at Neves-Corvo are found at the top of the VS.

The next stop was the inactive Aljustrel VMS deposits that currently are undergoing a feasibility study for zinc production.  Students examined cores for orebodies at Aljustrel that averaged 1% Cu and 5% Zn, and learned an important lesson about how easily sphalerite can be overlooked when logging core.  The group moved on to Lousal, a site of Roman tunnels precariously perched on steep hillsides, where children were forced to labor in the gossan to provide gold for the Empire.  The Sao Domingo deposits, next on the itinerary, are VMSs initially operated as an open pit by the Romans, but more recently were used to provide pyrite for the production of sulfuric acid.  Acid mine drainage from the workings had a pH of 2 (!), and both Sao Domingo and Lousal have received attention recently as the Portuguese have begun to recognize the environmental legacy of abandoned VMS mines.

Nowhere was these effects more apparent than at the groups next stop, Spains historic Rio Tinto open pit mine.  At the mines museum, mining implements from the area believed to be 9,000 years old were displayed.  There has been almost continuous activity for the past 2,000 years, as the Romans and Phoenicians initially exploited its riches.  In excess of 500 million tons of massive sulfide ore have been removed from the main orebody.  Rio Tinto is so named because of the blood-red color of the river the captures all of the runoff from the area.  The Rio Tinto has a pH of 2, and biologists who specialize in extreme environments study its oxygen-generating bacteria, the only creatures hardy enough to live in it.

At Spains Aguas Teidas, Spanish for dyed waters, the group saw more small VMSs with acid mine drainage problems.  Due to these historic environmental problems, the Las Cruces mine, another Spanish VMS deposit visited by the group, has been developed with very strict environmental standards.  The Las Cruces orebody has no surface expression and was discovered by drilling a gravity anomaly.  Production will begin soon and Las Cruces will be one of Europes largest mines, meeting 6% of its copper demands.  After visiting the Las Cruces offices in Seville, students were given a day to experience the wonders of the city.

Los Frailes, the last VMS system visited, was perhaps the most infamous.  A tailings dam broke in 1998, spilling its contents down a river to a sanctuary that is the breeding grounds for many European waterfowl.  Poor evaluation of the properties of the underlying marl led to the dam failure.   The resulting environmental disaster is a primary reason that the mine is set to shut down in the next year, though significant reserves and resources remain.  Witnessing disasters like this made everyone acutely aware of the need for interaction between geologists and engineers in all phases of a project.

After Los Frailes, the group spent a day in Cordoba.  The days festivities included the Cordoba fair, visiting La Mezquita, a Moorish mosque built 1200 years ago, and viewing Roman ruins.  The remaining destinations would be out of the IPB, examining some of the other ore deposit types in central Spain and Portugal.

Almaden, a mercury deposit that is the worlds oldest continually active mine, has accounted for at least one-third of global mercury production. Regardless of the economic aspects, Almaden is a remarkable geochemical anomaly essentially without equal for any element on the planet.  These stratabound cinnabar deposits are monometallic and thought to be related to seafloor mafic volcanism.  Grades are as high as 20% mercury, but the cutoff grade is 3.5%.  Students descended to an active stope and broke open pieces of ore to find droplets of native mercury and shiny red crystals of cinnabar in the shale host.

The group explored the scenic mountain-top villa of Marvo, Portugal, on the way to Panasqueira, the last tour on the itinerary.  Panasqueira is a tin-tungsten mine located in north-central Portugal, and is known worldwide by mineral collectors for its assortment of large crystals of quartz, apatite, arsenopyrite, and wolframite.  The two- to five-ft wide quartz veins that host the tin-tungsten minerals formed during the Hercynian orogeny (~300 Ma).  After the mine tour, each member of the group was given a prize mineral specimen. 

Each member of the group returned to Lisbon having greatly increased their respective knowledge of Iberian geology and ore deposits.  Equally impressive were the increases in luggage weight, as despite my best efforts at being selective, my bag contained nearly 40 lbs of rocks!  The success of this trip, and previous GEO 381R trips to Chile in 1999 and Per in 2000, bodes well for opportunities for future international field courses.

Modified from story by Mac McGuire in the 2002 DGS Newsletter

The 2003 offering of GEO 381R was taught by Rich Kyle and Sharon Mosher and focused on the Geologic Evolution and Mineral Resource Development of Western Australia.  The course culminated in a three-week trip to Western Australia in May 2003 that provided an exceptional educational opportunity for 12 UT graduate students with diverse interests to study many classic geologic sites.   Western Australia offers an excellent 381R destination, as it has varied geologic environments and is one of the worlds major mineral producers.  The Geology Foundation provided scholarships to help cover the international airfare for the students.  Other costs were kept low by camping for most of the trip.   

This trip represented a return visit for a trip that Sharon organized for a group of University of Western Australia graduate students and faculty three years ago.  Annette George, Senior Lecturer in Sedimentology & Basin Analysis at UWA, organized and led most of the trip, along with other UWA colleagues and local authorities.  The trip began and ended in Perth and consisted of a 6,800-km clockwise traverse through a large part of Western Australia.

Following a day for travel recovery and trip organization, the caravan headed north along the Western Australia coast to Kalbarri with the first stop to look at the Ordovician Tumblagooda sandstone and its trace fossils at Red Bluff.  The next day started with similar exposures along the Z-bend of the Murchison River in Kalbarri National Park, followed by a long drive to arrive near dusk at low tide at the world famous modern stromatolites at Hamelin Pool at Shark Bay.  The next morning provided an even more intimate experience with stromatolites and related sediments at the Carbla Point.

After night in Carnavon and a dust storm along the coast, the group turned toward the interior to begin a several day tour of the Hamersley Basin, known for its extensive banded iron formations that supply much of the worlds iron for the steel industry.  The origin of these unusual sedimentary rocks remains controversial, but commonly is tied to the evolution of the early Earth atmosphere, hydrosphere, and biosphere.  Extensive exposures of the Hamersley Group were provided by traverses near Woongarra Pool, the gorges in Karinjini National Park, and on Mt. Nameless (Jarndunmunha).  The group later toured the commercial iron concentrations developed from the BIFs at BHPs Mt. Whaleback mine near Newman that produces about 80 million tonnes of iron ore per year.

The next major site was the Marble Bar and North Pole regions of the Archean Pilbara Craton.  The region represents one of the worlds oldest greenstone-granite terranes with classic structural styles, but of particular current interest are the silica- and barite-rich chemical sediments on which much research continues in the search for early life on Earth.  These include the controversial stromatolites in dolostones at the North Pole dome that are arguably the Earths oldest biogenic structures.  Martin Van Kranendonk of the Geological Survey of Western Australia and Malcolm Walter, Director of the Australian Centre for Astrobiology, and graduate students from Macquarie University shared their extensive knowledge of the geology of the region and on the early life issues.  Travels through the outback on the primitive tracks to view these features provided considerable challenges for the rental minivan and the skills of the driver!

The group headed south to Newman, where Rich departed for the Geological Association of Canada meeting in Vancouver and Annette returned to Perth for teaching obligations. Warrick Crowe of the University of Western Australia guided the group for the remainder of the tour.  The caravan continued with a long drive south to Kalgoorlie, one of the worlds most famous gold mining regions within the Archean Yilgarn Craton, for a several day visit. Kevin Cassidy of Geoscience Australia gave us an excellent overview of the Yilgarn Craton and took us on a field excursion to see the Mt. Hunt komatiite-felsic volcanic sequence; we were fortunate to have several other geologists join us including Bruce Groenewald from the Western Australia Survey and Chris Swager from a local mining company.   In contrast to the well-exposed Pilbara Craton, the Yilgarn is best exposed in the mines or drill core.  We visited the gold mine superpit in Kalgoorlie and had a fascinating underground mine tour of a komatiite-hosted nickel-sulfide deposit in Kambalda, plus viewed core at the mine and at the Geological Survey of Western Australia core library.  A visit to the Mining Hall of Fame was gave us a good historical perspective on mining in Western Australia.

The group next drove to the southern coast to see some superb exposures of the Grenville-age Albany-Fraser belt.  Warwick Crowe led us along white sand beaches and rocky coves to spectacular structures in multiply folded pelites at Hopetown and high-grade gneisses at Bremer Bay.  As we headed towards Perth along the southern coast, we visited the Greenbushes pegmatite mine, a major tantalum producer and high-grade lithium resource. On our last day we drove to Perth with a brief tourist stop at Margaret River.

The trip to Western Australia was a great geoadventure and learning experience, and we are grateful for the support of the School of Earth & Geographical Sciences at the University of Western Australia, particularly Annette George who converted our diverse interests into a working travel plan.  Discussions are already underway about destinations for the next international field excursion. 

                        Modified from story by Rich Kyle and Sharon Mosher in the 2003 DGS Newsletter

Photo 1.  Domal stromatolites in the Shark Bay intertidal zone at Carbla Point, Western Australia.