SEG UFRGS FIELD TRIP 2017

Transcription

1 SEG UFRGS FIELD TRIP 2017 EXPEDITION TO THE QUADRILÁTERO FERRÍFERO September, th Report prepared by: Betina Friedrich Cristiano Rocha Born Pedro Sulzbach de Andrade Renan Guilherme de Souza Porto Alegre, October of 2017

2 1. INTRODUCTION The Quadrilátero Ferrífero (Iron Quadrangle, in a free translation) region is internationally recognized as one of the biggest mineral provinces on the planet. The region extends for approximately 7,160 km² in the south-central part of the state of Minas Gerais, Brazil. It consists of rocks that register an important part of Earth's history, with a significant Archaean and Paleoproterozoic contribution. The iron ore produced in the region corresponds to 60% of Brazil s iron production. Current iron ore reserves are estimated at approximately 29 billion tons. Gold, bauxite, limestone and manganese are also important ores in the region, as the extraction of clays. Despite the important iron deposits, the origin of the region's development in the 17th century was caused by the famous gold cycle, which brought the first impulse of advancement and settlement to the region. The Quadrilátero Ferrífero mineral goods explored in its more than 300 years of mining play an undeniable role in the history and occupation of Brazil s countryside. The news of the enormous treasures found in America by the Spaniards, especially by the discovery of the rich silver mines of Cerro de Potosí (Bolivia) in 1545, lead to frequent and attentive entries of gold searchers in Brazil s interior. These primitive pathfinders, then called bandeirantes, used to pan gold from the gravel and sands of the rivers, as they were experienced in the coastal fields placers. The news of the earliest discoveries, at around 1690, increased the number of exploration expeditions, and the finds proliferated rapidly causing the first great mining rush of world history (Ruchkys & Machado, 2013). This happened initially in the cities of Ouro Preto and Mariana, and by the end of the first decades of the 18th century almost the entire territory of Minas Gerais was occupied, with a profusion of cities and towns due to the spread of the gold fields (Machado, 2009). Throughout the 19th century the region was the scene of what was most recent in terms of science in Europe, receiving on its grounds, renowned foreign researchers. Some of these foreigners, with more specific education in Geology, such as the Baron von Eschwege, Peter Claussen, Virgil von Helmreichen, realized studies of the rock formations and produced geological maps that became the first representations of the geology in Brazil. In the first decade of the 20 th century, the discovery of the huge reserves of manganese and iron in the region boosted mining activities. The region was, once again, in evidence on the international stage. Interest in the area remains to the present day, not only because of the great reserves of iron ore and other mineral riches, but also because of its fascinating geology, mineralogy and geodynamics. The region significant geological heritage have exceptional scientific and pedagogical interest that allow the understanding of the evolution processes of Earth's history. In this context, we conceived the project SEG UFRGS Field Trip 2017 Expedition to Quadrilátero Ferrífero as a unique opportunity to deepen our knowledge in Economic Geology by studying geological contexts, structural controls, geochemical barriers, and the mineralization itself in the region. Once we do not have such a mining tradition in our state, the chance to perform technical visits to Quadrilátero Ferrífero mining district in the company of professors and professionals who work in the area is a great opportunity to provide academic and professional growth to all students involved.

3 Our itinerary ( Fig.2, Table 1) included visits to active and deactivated iron mines, gold mines, historical gold garimpos, dolomite and komatiites quarries. Besides, we walked along geological profiles to better understand the stratigraphy and the evolution of the sedimentary environments that allowed mineralization. Table 1: Itineray of the SEG UFRGS Field Trip 2017 Expedition to the Quadrilátero Ferrífero. DATE September, 12 th Tuesday September, 13 th Wednesday September, 14 th Thursday ACTIVITIES Arrival in Minas Gerais, Confins Airport. Visit to Vale S/A iron mines. Lecture with Rosaline Silva (Exploration Professor at UFMG) about Au mineralizations in the Q.F.* Visit to Lamego gold mine (AngloGold Ashanti). Lecture with Carlos Alberto Rosière (Structural Geology Professor at UFMG) about iron mineralizations in Q.F.* September, 15 th Friday September, 16 th Saturday September, 17 th Sunday September, 18 th Monday September, 19 th Tuesday Profile along the Moeda Syncline, guided by Mariana Madeira (MSc student at UFOP).** Visit to Capanema iron mine and old Au garimpos. Guide by professors Maximiliano Martins and Marco Antônio Fonseca (UFOP).** Geology of eastern Q.F.: visit to dolomite and komatiite mines, observation of thrust structures and the dam of Fundão. Visit to the gold complex Córrego do Sítio (AngloGold Ashanti) Return to Porto Alegre. Notes: *Activity developed with the support of UFMG SEG Student Chapter. **Activity developed with the support of the Maximiliano Martins (Professor at UFOP).

4 Figure 1: (A) Simplified geological map of the Q.F. (extracted from Alkmin & Marshak, 1998); (B) Itinerary of the SEG UFRGS Field Trip 2017 Expedition to the Quadrilátero Ferrífero.

5 2. PARTICIPANTS Table 2: List of participants José Carlos Frantz Economic Geology Professor Academic Advisor SEG Fellow Betina Maria Friedrich MSc Student Vice President ID: Bruno Petracco de Miranda Undergraduate Student Member ID: Cristiano Rocha Born Undergraduate Student Member ID: Gabriel Barbosa Drago Undergraduate Student Member ID: Luiz Henrique Cadaxa Silveira Undergraduate Student Member ID: Nadine Goulart da Silva Undergraduate Student Member ID: Natanael de Matos Cezario Undergraduate Student Member ID: Pedro H. Sulzbach de Andrade MSc Student Treasurer ID: Renan Guilherme de Souza Undergraduate Student President ID: Thaiane Niederauer dos Santos Undergraduate Student Member ID:910018

6 3. GEOLOGICAL SETTING The Quadrilátero Ferrífero is a geographic denomination of the historical mining district to the south of the city of Belo Horizonte, State of Minas Gerais. Its name was given because of the metasedimentary rock ridges, keels and domes that roughly outline the shape of a quadrilateral. Five main lithostratigraphic units occur in the area: the Archean crystalline basement, the Rio das Velhas Supergroup, the Minas Supergroup, post-minas igneous bodies, and Itacolomi Group (Fig. 2). The Archean crystalline basement rocks are mostly gneisses and migmatites with ages of Ga (Teixeira, 1993; Carneiro et al., 1995). Yet, there are two massive generations of late-archean plutons: one of them is calc-alcaline bodies of Ga, and the other anorogenic granites of Ga (Carneiro et al., 1994; Machado et al., 1992; Noce, 1995). The Archean Rio das Velhas Supergroup consists of a greenstone belt (basalts and komatiites) intercalated by rhyolites and metasedimentary rocks. The metasediments include Algoma type banded iron formations (BIF), besides carbonate and siliciclastic rocks. Most of the iron and gold mining sites are located in the BIF and in its contacts with the overlapping units (Alkmin & Marshall, 1998). The Paleoproterozoic Minas Supergroup is a metasedimentary unit which is discordant to the Rio das Velhas Supergroup. Minas' quartzites are more resistant to weathering than the basement and form the tetragonal shape ridges that name the region. Basal units of the Minas Supergroup are conglomerates and sandstones that grade to shallow sea pelites (Tamandua and Caraça Groups). Over them, there are some Lake Superior type BIF (Cauê Formation) and carbonate sequences (Gandarela Formation). A thick sequence of deltaic and shallow sea sediments (Piracicaba Group) overlay Gandarela Formation. Then, there are turbidites, tuffs, conglomerates and volcanoclastic rocks overlaying the Piracicaba Group. Some of these rocks are metamorphosed up to amphibolite facies by a granitic intrusion (Alkmin & Marshak, 1998). Thin pegmatite veins crosscut the Rio das Velhas and Minas Supergoups. Granitic intrusive bodies are Ga old. Mafic dykes also occur and have ages of Ga (Noce, 1995). The Itacolomi Group is the younger unit and consists of coarse sandstones and conglomerates that contain clasts of BIF (Alkmin & Marshak, 1998). The tectonic model for the area proposed by Alkmin & Marshak (1998) begins with the emplacement by thrust or the deposition of the Rio das Velhas Supergroup over a continental basement in a convergent-margin setting. The authors believe that after 2.6 Ga and prior to 2.4 Ga, the region evolved into an ensialic or passive-margin basin During the Transamazonian Event (2.1 Ga), the Quadrilátero Ferrífero region evolved into northwest-verging foreland fold-thrust belt, developing shear zones and regional-scale folds. At about 1.75Ga, the opening of the Espinhaço rift basin to the north of the Quadrilátero Ferrífero allows the intrusion of mafic dykes in the region. After that, at about 0.7 Ga, the Brasiliano Orogeny creates west-verging thrust belt that reactivated and overprinted older structures in the Quadrilátero Ferrífero.

7 Figure 2: Stratigraphic column of the Quadrilátero Ferrífero. Column on the right provides radiometric dating constraints. The right-hand portion of the column represents relationships in the eastern part of the Quadrilátero Ferrífero, while the left-hand side of the chart represents relationships in the western part of the Quadrilátero Ferrífero (Alkmin & Marshak, 1998).

8 4. DAILY SUMMARY September 12 th : Arrival in Minas Gerais, Confins Airport. The first day of our field was dedicated to travel to Minas Gerais. We went by plane from Porto Alegre to Belo Horizonte (Confins Airport), where our driver was waiting for us. September 13 th : Visit to Vale S/A iron mines and lecture with Prof Rosaline The second day of our field trip was destined to visit Vale iron operations at the locality of Nova Lima, just south of Belo Horizonte. There we were greeted by the geologist Natércia Drumont, who introduced us the geology of Mutuca and Capão Xavier mines. Natércia explained that at Mutuca mine the old waste dump is now being exploited, reinforcing the idea that the concept economic refers to a specific context of ore prices and technology available. With an open pit of m and 350m deep, the Capão Xavier mine is now at the end of its useful life, with estimatives of around 3 more years. It is located exactly at the junction of two important geomorphological features, Serra da Moeda and Serra do Curral, that delimit the Quadrilátero Ferrífero to the west and northwestern, respectively. The main ore types in Capão Xavier are soft hematite, manganesiferous hematite and goethitic hematite, resulted from hydrothermal enrichment from a dolomitic itabirite (metamorphosed banded iron formation). The final products (lumpy ore, coarse sinter feed, sinter feed and pellet feed) contain 61 % of Fe and are transported by train to the harbor of Rio de Janeiro to be exported. The BIF belongs to the Cauê Formation of the Paleoprotherozoic Minas Supergroup. Figure 3: (A) View of Capão Xavier Mine, with the soft hematite in grey, goethitic hematite in yellow and a dome of itabirite in the center; (B) sample of canga, a typic product of supergenic enrichment over BIF; (C) sample of itabirite (right) and hematitite (left); (D) the group visiting the Capão Xavier Mine.

9 In the early evening, the group went to the facilities of the Federal University of Minas Gerais, where professor Rosaline Silva gave a lecture titled Examples of Orogenic Au Deposits hosted in the Rio das Velhas Greenstone Belt, Quadrilátero Ferrífero, organized by the UFMG SEG Student Chapter. Rosaline talked about general aspects of Au mineralization in the QF, as the transcrustal structures controlling mineralization, common depth of mineralization, characterization and origin of the fluids carrying metals, etc. She also talked about specific features, as Au reserves, historic of the mine, characterization of the ore, vein and wall rock of some of the main gold deposits in the QF: Cuiabá, Lamego, Córrego do Sítio and Sao Bento (currently Córrego do Sítio II). Figure 4: Professor Rosaline Silva giving a talk about the Au mineralizations in the Q.F. September 14 th : Visit to Lamego gold mine and lecture with Prof Rosière During the third field trip day we visited the facilities of AngloGold Ashanti at the Lamego mine, in the locality of Sabará, circa 30 km NE of Belo Horizonte. We were greeted by the geologists André Vitorino and Rafael Costa Chaves, who explained to us the geological context of the Lamego gold mine. Lamego, as the giant Cuiabá deposit, is hosted in the Rio das Velhas Supergroup exposed along structural windows. The Lamego deposit is composed by four mineralized bodies, whose plunge vary from 90 at the N and 120 to the S. Lamego is a small deposit, with an average content of 4 g/t and cutoff of 2 g/t. After going through the primary jaw crusher, the ore is taken by truck to the Cuiabá Complex, about 15 km far, to be processed there. We visited a deactivated open pit that used to be mined by Jaguar Mining, where we could see the structurally controlled mineralization of gold in situ, hosted in the veins of smoky quartz along the contact of ferrous metacherts with impermeable phylite. Most of the Au mineralization in the Q.F. occurs in the contact with BIFs, or, as in the case of Lamego, with ferrous metachert. In this specific case the phylite acted as a physical barrier, preventing fluids to spread and focusing it to flow along the contact. The ferrous metachert acted as a chemical barrier, making iron to interact with fluid and allowing the precipitation of sulphides with gold. It is possible to recognize some vertical quartz veins, interpreted as the feeders of the mineralization. The veins of smoky quartz vary from few centimeters to some meters in thickness. They commonly show boudings and pinch-and-swells. The ore is mainly pyrite with minor arsenopyrite.

10 Figure 5: (A) Boudins (in yellow and white) of smoky quartz containing pyrite and arsenopyrite with Au in the contact with phylite (above) and ferrous metachert (bellow); (B) feeder conduits (massive quartz vein) of mineralizing fluids, spreading laterally and precipitating ore (pale yellow are weathered Py+Apy releasing S; (C-E) ore and structures seen on the drill cores during the visit to the core shed. During the evening we had the opportunity to watch a lecture titled Iron formations and Fe mineralizations: implication for the geotectonic of the Sao Francisco Craton, given by professor Carlos Alberto Rosière, once again organized by the UFMG SEG Student Chapter. Rosière talked about the position of the BIFs in relation to the craton and the different ways of iron enrichment in the BIFs of the Q.F. Figure 6: SEG UFRGS SC field trip members and UFMG SEG SC members with Prof Rosière.

11 September 15 th : Profile along the Moeda Syncline During the fourth field trip day we performed a profile along the western limb of the Moeda Syncline (Fig. 1A). We were accompanied by the MSc student Mariana Madeira (Federal University of Ouro Preto - UFOP), who is developing a detailed stratigraphic study in the area. The Moeda Syncline is one of the folds generated during the Transamazonian Orogeny and is geomorphologically represented by the Serra da Moeda, western limit of the Quadrilátero Ferrífero. Mariana guided us through outcrops that mark the opening and evolution of the Paleoproterozoic basin that hosts the sediments of the Minas Supergroup. One of the outcrops was an old garimpo with the basal conglomerates of the Minas Supergroup mineralized with Au and with occurrences of U; these conglomerates are interpreted to represent the alluvial fans deposits associated to the fault scarps generated at the first phases of opening of the hemi-graben; we also saw metasandstones interlayered with phylite and lenses of metaconglomerates of the Moeda Fm, that represent the fluvial deposits of the basin; going upstratigraphy, we saw the phylites of the Batatal Fm, representing the beginning of the marine phase.these were covered by the BIF of the Cauê Fm, which represents the deep marine sediments of the basin. At the end of the day we headed to the locality of Rio Acima MG, where a group from UFOP was taking a geological mapping course under the guidance of professors Maximiliano Souza Martins and Marco Antônio Fonseca. Figure 7: (A) View of the old garimpo, where detrital Au was mined from the basal conglomerates of the Minas Supergroup; (B) fluvial metasandstones from the Moeda Fm, in which lenses of metaconglomerates (C) occur; (D) evolution to a marine basin is marked by the phylites from the Batatal Fm (light gray) overlaid by BIFs from the Cauê Fm (redish). September 16th: Visit to Capanema iron mine and old Au garimpos In our fifth day we were greeted by the professors Maximiliano and Marco Antônio with their mapping course students, as well as the PhD student Ana Alkmin. Early in the morning Professor Max gave us a lecture to contextualize the stratigraphy and the

12 geotectonic models of the Quadrilátero Ferrífero, and Ana talked about the Au mineralization and U occurrences hosted in the basal metaconglomerates of the Moeda Fm. After that we visited the facilities of the deactivated Capanema iron mine where Professor Marco Antônio presented the mine geology and its mineralization model. This deposit is located on the Ouro Fino Syncline and there, the iron enrichment is essencialy supergenic over itabirite. In the Capanema Mine the ore used to be mined with 61-63% Fe, while the itabirite has about 46% Fe. The mine is currently in view to be reopened to exploit the waste dump with 56% Fe in average. After Marco Antônio s explanations the group drove up to the Pico do Monge, a belvedere located in the center of the Quadrilátero Ferrífero. With its 1753 m high, the Pico do Monge offers a spectacular view of the area, where we could accompany on the morphology some of the important tectonic features of the QF, as, for example, the basement domes. Lastly we had the opportunity to know one of the underground galleries from the Brazilian colonial era. These galleries are located close to the deactivated Ouro Fino Mine (Jaguar Mining), but Prof Max pointed to the substantial differences between the gold extracted by garimpeiros since the colonial era and the gold extracted currently by mining companies: the first refer to detrital gold hosted in conglomerates of basal part of the Moeda Fm, Minas Supergroup, and the last refers to hydrothermal gold, always associated to structures, hosted in the Archean Nova Lima Group, Rio das Velhas Supergroup. The gallery in which we entered strikes along a shear zone, as we could observe by the occurrence of highly stretched clasts at the gallery s walls. At the end of the day we headed to the city of Ouro Preto, where we met our advisor, Professor José Carlos Frantz, to continuous the field trip. Figure 8: (A) View of the Capanema iron mine, from Pico do Monge: the reforested area in center-left of the picture refers to the waste dump that should be exploited in the future; (B) Prof Max showing our location on the geological map and comparing the structures with the geomorphological features; (C) the group entering a Au gallery from the colonial era; (D) stretched clasts in the Au gallery.

13 September 17 th : Geology of eastern Q.F. During the sixth day we had once again the opportunity to know the geology of the QF. First we visited an old marble quarry (metamorphosed dolomite) of the Gandarela Fm, which is stratigraphically above the BIFs of the Cauê Fm that we have seen in the Capão Xavier Mine and along the profile we have done with Mariana (Minas Supergroup). In our way to the city of Santa Bárbara we could see along the road some of the thrust structures that mark the diverse orogenic episodes that shaped the Q.F. and were fundamental for the occurrence of the diverse mineralization of the region. We also made a stop to see the tailing dam of Fundão, which collapsed in November The episode had great repercussion on media, since it provoked a huge human, environmental and social disaster. The last stop was at an old komatiite quarry, where we could see the rocks of the Quebra Ossos Fm, which represent the Archean greenstone belt of the base of the Rio das Velhas Supergoup. Figure 9: (A) Visit to a marble quarry Gandarela Fm; (B) one of the various thrust structures, responsible for inverting stratigraphy in the Q.F.; (C) view of the dam of Fundão, which collapsed in 2015; (D) view of the komatiite quarry from the Quebra Ossos Fm, base of the Rio das Velhas Supergroup. September 18th: Visit to the Au complex of Córrego do Sítio (AngloGold Ashanti) In the seventh day of our field trip day we were once again greeted by AngloGold Ashanti, this time by geologists Juliano Maciel and Bruno Afonseca at Córrego do Sítio (CDS), Santa Bárbara-MG. Córrego do Sítio is actually a complex including three bodies (CDS I, II and III) following a trend 15 km long, in a context of reworked marine sediments. The mineralization occurs as quartz veins with free Au hosted in BIF (CDS II) as well as Au inclusions in arsenopyrite in schist with sericite, chlorite and quartz (CDS I and III). Although the Au content of the ore is higher when the host rock is BIF, the presence of the structure is fundamental, independent of the lithology. Including CDS II (former São Bento Mine), bought in 2008 from Eldorado Gold, CDS Complex has already produced

14 2 million ounces of Au. After being introduced to the local geology we were taken to see the open pit of Rosalino, at CDS I. At there we could observe the structures and the mine in operation, besides the beautiful view of the Serra do Caraça mountains. We were also taken to visit a drilling plant in operation within a conservation area. Figure 10: (A) SEG UFRGS SC members visiting the Rosalino open pit and (B) a drilling plant in the CDS complex. September 19 th : Return to Porto Alegre The last day of the field trip was dedicated to quickly visit Belo Horizonte's public market and to travel back to Porto Alegre.

15 5. FINANCIAL REPORT This fieldtrip was mostly supported by the Stewart Wallace Fund Grant. We also received support from Core Case. Besides, the Student Chapter members contributed with BRL each. The rest of the expenditures were covered by the SEG UFRGS SC funds, obtained through several money raising activities along the year. Expenditure $ (BRL) $ (USD)* 10 Airplane tickets (Porto Alegre-Belo Horizonte) Vehicle hire for transportation Accommodation (for 10 people) Belo Horizonte (4 overnight stays) Rio Acima Ouro Preto Santa Bárbara TOTAL EXPENDITURE SEG/Stewart R. Wallace Fund Grant ** Core Case Contribution from SEG UFRGS members SEG UFRGS SC Contribution *- Exchange rate at October 14 th, 2017: 1 USD = 3.14 BRL **- At February 4 th, the exchange rate was 1 USD = 3.12 BRL AKNOWLEDGMENTS The field trip was supported by the Society of Economic Geologists through the Stewart Wallace Funding Program and by Core Case Company. The field trip was great because we had the engagement and technical support of many people, to whom the SEG UFRGS Student Chapter would like to thank: to Vale, especially to the name of the geologist Natércia Drumond, and Guilherme Pimenta from the communication sector; to AngloGold Ashanti Brasil, in special to the geologists André Vitorino, Rafael Costa Chaves, Marco Antônio Castoldi, Juliano Maciel and Bruno Afonseca; to the UFMG SEG Student Chapter and to the professors from UFMG Rosaline Silva and Carlos Alberto Rosière; to the professors Maximiliano Souza Martins and Marco Antônio Fonseca, and to the PhD student Ana Alkmin and MsC student Mariana Madeira from UFOP; and to our academic advisor Prof José Carlos Frantz.

16 REFERENCES Alkmin, F. F., & Marshak, S., Transamazonian Orogeny in the Southern São Francisco Craton Region, Minas Gerais, Brazil: evidence for Paleoproterozoic collision and collapse in the Quadrilátero Ferrífero. Precambrian Research 90, pp Carneiro, M.A., Teixeira, W., Machado, N., Geological evolution of a sialic Archean crustal fragment from the Quadrilátero Ferrífero in eastern-central Brazil, based on U Pb, Sm Nd, Rb Sr and K Ar isotopic constrains. Terra Nostra 2, pp Carneiro, M.A., Noce, C.M., Teixeira, W., Evolucção tectônica do Quadrilátero Ferrífero sob o ponto de vista da Geocronologia. Revista da Escola de Minas, Universidade Federal de Ouro Preto, Ouro Preto (Brazil) 48, pp Machado M. M. M Construindo a imagem geológica do Quadrilátero Ferrífero: conceitos e representações. Tese de Doutorado. Pós- Graduaçãoem Geologia, Departamento de Geologia, Universidade Federal de Minas Gerais, 256p. Machado, N., Noce, C.M., Ladeira, E.A., Belo de Oliveira, O., U Pb Geochronology of Archean magmatism and Proterozoic metamorphism in the Quadrilátero Ferrífero, southern São Francisco craton, Brazil. Geological Society of America Bulletin 104, pp Noce, C.M., Geocronologia dos eventos magmáticos, sedimentares e metamórficos na região do Quadrilátero Ferrífero, Minas Gerais. Ph.D. Thesis, Instituto de Geociências, Universidade de São Paulo, São Paulo, Brazil. Ruchkys, U. A. & Machado, M. M. M., Geological and mining heritage of iron quadrangle, Minas Gerais - Characterization and strategies for education and geotourism. Boletim Paranaense das Geociências, volume 70(2013) ( ), 136p. Teixeira, W., Avaliação do acervo de dados geocronológicos e isotópicos do Cráton do São Francisco Implicações tectônicas. In: Dominguez, J.M.L., Misi, A. (Eds.), O Cráton do São Francisco. Sociedade Brasileira de Geologia, Núcleo Bahia/Sergipe, Salvador, pp

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