University of Campinas Society of Economic Geologists Student Chapter Field trip report Quadrilatero Ferrífero

Transcription

1 University of Campinas Society of Economic Geologists Student Chapter Field trip report Quadrilatero Ferrífero

2 UNICAMP - SEG student chapter 2017 committee: President: José Henrique da Silva Nogueira de Matos Vice-President: Poliana Iara de Freitas Toledo Treasure: Beatriz Matos Spalletta Secretary: Thais Magaldi

3 The Quadrilátero Ferrífero field trip was organized by the UNICAMP SEG chapter, according to SEG committee instructions and partially funded by the SEG Stewart R. Wallace Fund (Student Chapter Grants for Field-Based Education october 2015 round). It was performed in six days, from March 7 th to March 12 th, including transfers to Nova União and Ouro Preto regions, visits to gold mines, and two regional traverses. Ten students from the Institute of Geosciences, University of Campinas (Brazil), composed the group, including seven postgraduate and three undergraduate students, as follows: José Henrique Matos Ph.D. candidate UNICAMP-SEG chapter president. Poliana Toledo M.Sc. candidate UNICAMP-SEG chapter vice-president. Beatriz Spaletta M.Sc. candidate UNICAMP-SEG chapter treasurer. Raphael Hunger M.Sc. candidate UNICAMP-SEG member. Gustavo Melo Ph.D. candidate UNICAMP-SEG member. Ananda Lopes M.Sc candidate UNICAMP-SEG member. Igor Moreira M.Sc candidate UNICAMP-SEG member. Henrique Fedel Undergraduate student UNICAMP-SEG member. Thais Murer- Undergraduate student UNICAMP-SEG member. Paulo Lima- Undergraduate student UNICAMP-SEG member. The main goal of the field trip was to provide an overview of the stratigraphic sequence of the Quadrilatero Ferrífero region and the orogenic gold deposits located in the region.. In this sense, the field trip was concentrated around the city of Ouro Preto, and in the Córrego do Sítio and Lamego gold mines, both under Anglo Gold Ashanti operation. In fact, Ouro Preto is a historical city that was settled around old mines from Brazil s colonial time and its surroundings offer a magnificent geological scenario in terms of structural geology and stratigraphy of the Archean Quadrilátero Ferrífero district. Quadrilatero Ferrífero represents the second most important mine district of Brazil and hosts important gold, iron and manganese world-class deposits mainly operated by Anglo Gold Ashanti and Vale companies. The geology of Quadrilátero Ferrífero encompass the Archean greenstone belts of the Rio das Velhas Supergroup with TTG domes and a Palaeoproterozoic metasedimentary sequence of the Minas Supergroup, which hosts the giant, high-grade iron-ore deposits hosted by Banded Iron Formation.

4 The field trip started on March 7 th, with the transfer from Campinas, São Paulo state, to Nova União, Minas Gerais state, in the half way to Córrego do Sítio mine in Santa Bárbara city, and Lamego mine in Sabará city. The visits to the mines occurred during March 8 th and 9 th. We were receptioned by the Anglo Gold Ashanti team. At Córrego do Sítio Mine (Fig. 1), Bruno Figuinha and Thiago Rolla (mine geologists) were responsible for showing the mine site and presenting institutional features, projects around the world, the mine s geologic model, open pit operation, and drill core logging. Figure 1: Field trip s attendees with Bruno Figuinha, mine geologist at Córrego do Sítio Mine. At Lamego mine, the visit was guided by the mine geologist Rafael Chaves, besides Julia Ferreira and Frederico Figueiredo, brownfield exploration geologists. At Lamego facilities, Anglo Gold team showed an overview of gold occurrences at Rio das Velhas greenstone belt and tectonic implications in ore deposits structural controls at Quadrilatero Ferrífero. They also presented the geologic model of Lamego region and their challenges in exploration to improve Anglo Gold reserves. The visit proceeded to an old open pit where host rocks and main ore controlling structures are preserved (Fig. 2 a), and afterwards the group examined some drill cores (Fig. 2 b).

5 A B Figure 2: a) Quartz-sulfide veins in ore shoot zone at Lamego mine; b) Rounded pyrite with shadow pressure in a drill core. In Ouro Preto, Prof. PhD. Maximiliano Martins from the Federal University of Ouro Preto (UFOP), guided the field trip. He lead the group through two geological transects, between Ouro Preto and Mariana, and Ouro Preto and Lavras Novas districts. They provided a complete view of Quadrilatero Ferrífero stratigraphy and the main structural controls of gold occurrences around Ouro Preto. Additionally, Professor Maximiliano pointed out some historical facts about the gold rush in Quadrilatero Ferrífero associated with the development of the city (Fig. 3). A B

6 C D Figure 3: A) Professor PhD. Maximiliano presenting some relevant points of Quadrilátero geology; B) Geologic transects between Ouro Preto and Lavras Novas; C) An old gold-digging in Ouro Preto; D) Prospecting practices for heavy minerals concentration