It has been my experience that in the world of graduate studies, it is very common for graduate students to spend too much time in the office without any opportunity to get out and see the very things we study. Being a graduate student in economic geology, I believe it is important for students like me to get out on as many field excursions as possible so that we can see ore deposits and mining operations first hand.
From January 5 to January 13, 2007, my supervisor, Dr. David Lentz, and I were fortunate enough to have been accepted in the Society of Economic Geologists (SEG) student-dedicated field course on the ore deposits of northern Chile. Not only did the industry sponsors and SEG provide me with a travel grant to pay for my airfare, they also provided me with an unparalleled opportunity to observe and study some of the richest coppermolybdenum porphyry deposits on the planet. Amazing opportunities like this provide an enormous incentive for students to do their graduate studies in the field of geology, as well as give students like myself the chance to see ore deposits and mining operations in faroff parts of the world.
The reason that this field excursion was such an amazing experience is that I had the good fortune to be allowed to visit a different open pit mine every day of the course, as well as the opportunity to experience a different culture and network with other students and industry professionals from across the globe. After arriving in Antofagasta on January 5, I prepared to meet and discuss our itinerary with the rest of the group involved in the field course, comprised of 16 students from across the globe, three industry representatives, and our course leaders, Dr. William X. Chavez of New Mexico Tech, and Dr. Erich U. Petersen of the University of Utah.
The following days involved a lot of getting up at 5:00 a.m. in order to arrive promptly at the various mines on our itinerary, largely due to the fact that there was much preparation that had to take place on behalf of the mines in order to ensure the safety of all those involved. The early mornings were a small price to pay in order to be able to safely gain access and study these deposits, be able to take as many samples and photographs as I desired, get a really good free lunch at every mine I visited, and have the opportunity to meet other students from Canada, the United States, Europe, Argentina, and Chile. With the help of the bilingual students, it took a surprisingly short period of time for all of us to learn a little Spanish and become fast friends as we set out to visit our first stop on January 6, the Lomas Bayas porphyry Cu-Mo deposit.
My visit to Loma Bayas consisted of a discussion of porphyry systems in general, and the importance of regional structures in the control of porphyry emplacement and timing. On January 7, I visited the Quetena copper breccia system where we had a discussion on the “Toki Cluster” porphyry Cu-Mo deposits located adjacent to the Domeyko Fault Zone, and had a chance to collect some very beautiful Cu sulphate minerals. I went to 4,400 m.a.s.l. to visit the El Abra copper oxide/porphyry Cu-Mo deposit on January 8, where we reviewed copper oxide zone genesis and supergene enrichment. The following day involved a visit to Radomiro Tomic Cu oxide/porphyry Cu-Mo system where we discussed the Chuquicamata porphyry system as well as Oligocene Belt porphyry systems in general. I visited the El Tesoro exotic copper deposit and Sierra Gorda tourmaline breccia Cu-Mo systems on January 10, where we examined the exotic mineralized fanglomerates at the mine, and discussed the mobility of metals within porphyry systems. January 11 and 12 involved visits to the Spence Cu-Mo porphyry deposit and the Zaldivar porphyry Cu-Mo system, respectively. The visit to Spence included a review of Paleocene/Oligocene age porphyry “belts,” whereas the visit to Zaldivar involved an evaluation of leached capping, the geochemistry of supergene oxidation processes, as well as copper oxide genesis and preservation (and a view of the Escondida open pit from a distance).
These deposits provided me with the opportunity to collect samples of supergene minerals like atacamite [Cu2Cl(OH)3], chrysocola [Cu(Fe, Mn)Ox-SiO2-H2O], pseudomalachite [Cu5(PO4)2(OH)4], chalcanthite (CuSO4.5H2O), and turquoise [CuAl6 (PO4) 4(OH)8.4H2O], but the most incredible samples were the sulphates from the Quetena copper breccia system, such as antlerite [Cu3SO4(OH)4], bonattite (CuSO4.3H2O), brochantite [Cu4SO4 (OH)6], chalcanthite (CuSO4.5H2O), copiapite [Fe5(SO4)6(OH)2. 20H2O], coquimbite [Fe2(SO4).9H2O], and voltaite [K2Fe8Al (SO4)12.18H2O], to name a few. Furthermore, I obtained iron and copper hydroxide samples from the leached cap zone, as well as some hypogene samples containing sulphide minerals like bornite (Cu5FeS4), chalcopyrite (CuFeS2), chalcocite (Cu2S), and covellite (CuS). To gain access to an abundance of these extremely colourful minerals is the dream of any person with a mineral collection, although the majority of the sulphate samples rapidly lose their colour from hydrating after collection.
I found one of the most interesting deposits I visited was the El Tesoro exotic copper system in that the mineralized fanglomerates bore a striking similarity to “continental red bed-type” copper mineralizations in Carboniferous sandstones of southern New Brunswick. The Cu ± Pb ± Zn ± Ag base-metal sulphide mineralizations seen in southern New Brunswick’s Carboniferous rocks is represented by over 30 major and minor occurrences, and is associated with carbonized plant material or diagenetic pyrite within grey, fluvial sandstone bodies above thick red bed and/or evaporate sequences. However, El Tesoro contained a more diverse mineralogy in that the ore minerals are comprised of malachite [Cu(CO3)(OH)2], azurite [Cu3(CO3)2(OH)2], atacamite, chrysocola, copper wad, and copper pitch as opposed to the New Brunswick mineralizations, which are comprised predominantly of malachite and azurite.
By the time I had to leave I had been completely overwhelmed, not only by the shear abundance of potential there is in northern Chile for porphyry Cu-Mo exploration, but also by the amazing technology they use to find and mine these largescale deposits. For example, at the Spence mine, they performed grid drilling through piedmont gravels of Miocene age and identified a 1,000 ppb Cu anomaly above the deposit by sampling the groundwater from 25 drill holes. After further drilling and sampling, it took the Spence mine approximately six months to construct an open pit and begin economical mining operations via the use of modern mining technology.
After this experience I can’t help but feel that my intrinsic interest in geology has been magnified significantly, and that every graduate student should have the opportunity to get out in the world and see first hand how large-scale mining operations function in foreign countries. The experience has also shown how it is important for graduate students in geology to get out and explore deposits in far-off parts of the world so that they can broaden their scope of where they might base themselves in the future, and learn about how mining regulations vary from country to country. This opportunity was without a doubt one of the most positive experiences of my entire life, and has left me with a love for Chilean culture, a broadened mind in terms of international employment, and a great feeling of gratitude towards the industry and professional sponsors who provided the funding to make it all possible.