SEG-UNLP Field Trip Report September 2015

Transcription

1 Porphyry and Epithermal deposits of the Farallón Negro Volcanic Complex, Catamarca, Argentina September 18-27, 2015 Field Trip Report Bajo la Alumbrera access. Left to Right: Palma Diego, Arramon Cornejo Esteban, Cañon Parisi Tabaré Tupac, Gonzales Alex, Omar Jesica, Escalona Maximiliano, Burgos Florencia, Quinteros Cintia. 1

2 Participants: 1-Quinteros, Cintia 2-Arramon Cornejo, Esteban 3-Escalona, Maximiliano Rodrigo 4-Gonzales, Alex 5-Omar, Jesica Romina 6-Cañon Parisi, Tabaré Tupac 7-Burgos, Florencia Elizabeth 8-Palma, Diego Sebastián Field Trip Schedule First and Second day (September 18-19): We took the train ride from Buenos Aires to Tucuman, which lasted about 30 hours. That same Saturday we went to visit the Historical House of Independence, which is a historic building located in downtown San Miguel de Tucuman, where a body of delegates from most of the United Provinces of the Río de la Plata, known as the Congress of Tucuman, proclaimed the declaration of independence of Argentina, July 9, Third day (September 20): We took the bus from Tucuman to Santa Maria (a city in east central Catamarca). There, we visited an archeological museum called Eric Boman. This museum had suffered a fire, and Alumbrera mine gave him money to be rebuilt. We consider this fact important because it shows the interaction between large mining companies and communities. Fourth day (September 21): We took two taxis from Santa Maria to Farallón Negro. At morning we arrive and had an introductory talk of mining induction and security measures. Then we took a walk to see the surface geology and main veins, and we have a general explanation of the deposit geological model. After having lunch, we were guided by an engineer and a geologist to the underground mine where they showed us the major work done, and we look the vein at depth. Fifth day (September 22): At morning we were guided by a mining engineer through the mineral processing plant, and explain us the process of milling, crushing and concentration. Then, after having lunch, we visited the laboratory where the final product (gold and silver concentrate) is obtained. Apart from this, a technician showed us all the equipment they have and what is each function. Sixth day (September 23): At morning we depart to Bajo la Alumbrera Mine. After this, we had a geological explanation of the Bajo de la Alumbrera porphyry geological and mineralization model. 2

3 Then we visited the mineral processing and flotation plant, the machine shop where machinery is arranged (shovels and trucks) and the Open pit. Seventh and Eigth day (September 24-25): We went to Cafayate, Salta, to saw the Regional Geology of the NOA (Argentine Norwest), and we visited the natural reserve La Quebrada de las Conchas. This area have very striking rock formations with reddish colors. It is also an important paleontological site belonging to the Cretaceous period. The gorge is a geologically modern accident, caused by tectonic movements that took place in the last two million years. In this place emerges the Salta group, which is a sedimentary deposit of continental rift, formed during the Cretacic period. This Group is also important because it has a formation (Yacoraite) that was formed during a marine transgression, which is mother rock of oil, reservoir and seal. Apart from this, appears some sinorogenic deposits that belong to the Tertiary. Farallón Negro Volcanic Complex The Farallón Negro mining district is located about 1300 km from the capital city of Argentina, and about 300km from Tucumán Province. Being part of Santa María, Belén and Andalgalá department, in Catamarca province, Argentina. At the same time, it is part of northwestern Sierras Pampeanas Orientales geological province (Figure 1). Figure 1: Location of the Farallón Negro district 3

4 Farallón Negro volcanic group lays over the basement and Miocene Red sandstones. It is part of a NW volcanic belt wich includes Capillitas, Agua Rica, Atajo, Culampaja districts and Carachipampa volcano (Figure 2). Figure 2: Regional geological setting of the Farallón Negro Volcanic Complex The Farallón Negro volcanic complex is interpreted as a stratovolcano, crowned by an elliptic caldera NW-SE of 16 x 13 km. It s age is about 8 to 6 Ma and the actual level of erosion is beneath the floor of the caldera, reason why it can be see various outcrops of intrusive rocks can be seen. 4

5 Different subvolcanic domes can be discriminated; a little one situated in the center of the caldera, constituted by the Alto de la Blenda Monzonite, several porphyritic rocks like the one from Bajo de la Alumbrera and dikes systems mainly at the Farallón Negro mine. The external limits of the volcano are covered by modern deposits or have been affected by faults. Most of the intrusive rocks are intruded in the oldest volcanic unit called Brecha Morada, wich is composed by: 1) BRECHAS POLIMICTICAS, preserved mainly at the external limits of the volcano and 2) BRECHAS IGNEAS ANDESITICAS ESTRATIFICADAS with basaltic and andesitic flows at the internal part of the volcano. The composition of the Rocks changes through time from andesitas to basalts and from andesitas to riolites. The areas that shows hidrothermal alteration started to develop after the intrusion of Alto de La Blenda Monzonite, probably contemporaneously with the intrusion of Macho Muerto domes, wich means that the alteration appeared when the magmatic differenciation processes, reaching a high level of silica. The oldest dike system has basaltic composition and a NW direction wich is similar to the main orientation of the caldera. A second dike system, younger than the other one, has NNW orientation. Moreover, it has been recognized a radial dike system around the bigger intrusive. Alto de La Blenda intrusive Monzonite is the only one in Farallón Negro with granular textures and plutonic features. Despite of this, the presence of other components crowned by Sanidine indicates a subvolcanic ambience. This intrusive is subsequent to the dike system NW and prior to Macho Muerto dacite. El Durazno intrusive is external to the caldera and probably belongs to the same volcanic complex. It is a granite-diorite porphyry associated with annular and radial dikes, and it is connected with Bajo de la Alumbrera by a system of dikes NNE. Farallón Negro Mine Farallón Negro is an epithermal deposit, located in Catamarca Province. Is owned by the state company Yacimentos Mineros Aguas de Dionisio (YMAD). This company is formed 60% by the government of Catamarca and 40% by the National University of Tucuman. It is responsible for operating the site, and it has about 800 employees. The geology of this mineral deposit it is characterized by a set of dikes and veins with NNW-SSE orientation mainly intruded on middle Miocene andesites and in a Monzonite stock (Figure 3). It is a group of quartz and carbonate veins, interpreted as low to intermediate sulphidation epithermal type. 5

6 The veins are mineralized with Au and Ag, with anomalous Mn contents. This precious metals are hosted in sulfides, oxides (like the quartz), or even free. Gangue minerals are carbonates (Calcite, Rhodochrosite, and Mn-rich calcite) and quartz, with several Mn-bearing minerals. The more important sectors are Alto de La Blenda and Farallón Negro, with large and thick veins in each one. The alterations halos produced by the hydrothermal system are not much penetrative, reaching up to 20 meters, and the propyllitic alteration type dominates. 6

7 It has reserves of about 0.4 Moz Au and 7.3 Moz Ag, and the mining method applied for the mineral extraction is by cut and fill underground type, and the mineral processing is done in the mine using cianuration method. 7

8 Bajo de la Alumbrera Mine Bajo de la Alumbrera is a site of Cu, Au and Mo being mined area since It is located northwest of the province of Catamarca, Argentina, at an altitude 2600 meters above sea level. Is a porphyry that is exploited by opencast (Open Pit), and is one of the largest mining operations in the world. It has 2385 employees (direct and indirect). Yacimientos Mineros Aguas de Dionisio (YMAD) is the state company that owns the site. It is formed by the government of Catamarca (60%) and the National University of Tucuman (40%). YMAD formed a joint venture with Minera Alumbrera to mine the deposit. Other investors in this mine are: -Glencore Plc, which holds a 50% stake and is the current operator of the deposit. -Goldcorp: 37.5%. -Yamana: 12.5% More locally, it is located in a topographic low in which by differential erosion let the upper part of the system available for its mining. The intrusion of a set of dacitic porphyries to this complex caused the circulation of hydrothermal fluids at great scale which altered and mineralize the intrusions and the host rock. This deposit has been affected by an important post-mineral faulting which displaced hydrothermal alterations and mineralization. The predominant sulfides are pyrite and chalcopyrite, with a low percent of chalcocite belonging to a narrow zone of supergene enrichment which has been mostly eroded. The Chalcopyrite is the 8

9 mineral of cooper, and it is disseminated in veinlets. Molybdenite is a common mineral, but not economic, whilw the sphalerite and galena are restricted to faulted areas. The Cu and Au grade are approximately around 0.50 % and 0.5 % g/t respectively, and it is supposed, with the actual reserves, that the mine will still go on production up to The rocks are extracted from the quarry with four electric shovels and are transported to the concentrator via by a fleet of 53 large-sized heavy equipment, each with a capacity of 220 tons. A Au, Cu, concentrate, with also Ag and Mo, is obtained using crushing, griding and flotation processes. The concentrate obtained (containing copper, gold and silver), is pumped with added water through a pipeline 317 km long and 175 mm diameter, that cross the Nevados de Aconquija to the filter plant, located in Tucuman. In the filter plant it will be dewatered to obtain a drier concentrated, with 7% humidity. Then it transports by the Nuevo Central Argentino railway to the port facilities in Puerto General San Martin, Santa Fe. The crude product is loaded onto ships bound for international markets. Molybdenum is exported to Chile by land. Au is recovered in the concentrate and also in the form of Dore by a gravitational physical process. The final product is obtained in international refineries. The concentrate did not contain cyanide, mercury, lead and arsenic, and are not involved in any stage of the process. Molybdenum is exported to Chile by land. 9

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