Caracterização estrutural da região do depósito aurífero Sertão, greenstone belt de Faina - GO
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Data
2019-04-26
Autores
Medeiros, Isabella Da Gama de [UNESP]
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Universidade Estadual Paulista (Unesp)
Resumo
O Terreno Arqueano Paleoproterozoico de Goiás é um fragmento de crosta que contém complexos TTG arqueanos e sequências greenstone belt. A área de estudo está inserida na região sul desse terreno e abrange a porção sudeste do Greenstone belt de Faina (GBF), onde ocorre o depósito aurífero Sertão, a porção norte do Greenstone belt Serra de Santa Rita (GBSSR), e parte dos complexos TTG Uvá e Caiçara. Esses dois greenstone belts são separados pela Falha direcional de Faina com direção N50E e movimentação destral. No GBF, foram identificadas rochas de duas sequências metassedimentares, uma denominada de Inferior e outra de Superior, que apresentam contato tectônico. A Sequência Inferior é constituída de camadas de quartzito, xisto, formação ferrífera bandada e mármore. A Sequência Superior apresenta espesso pacote de clorita-muscovita-quartzo xisto com algumas intercalações de formação ferrífera e quartzito que para o topo grada para uma sequência química com mármore e mármore impuro sobreposta por quartzito. No GBSSR, identificou-se uma Sequência Metavulcânica Ultramáfica sotoposta a uma Sequência Metassedimentar, esta última constituída por xistos muscovíticos e carbonosos, quartzitos, formação ferrífera e metachert. O mapeamento geológico permitiu avanços na definição da estratigrafia da área, como a identificação de rochas da Sequência Metassedimentar Inferior nas porções sudeste e sudoeste do GBF, caracterizando-se que é esta a unidade que hospeda o depósito aurífero Sertão, também se reconheceu o truncamento dessa Sequência pela Sequência Superior a NE. Além disso, foi identificado que as rochas do GBSSR, a NW da Falha de Faina, cavalgam sobre o GBF, diferentemente do que foi descrito em trabalhos anteriores da região. A superposição de estruturas permitiu a identificação de cinco fases deformacionais nos greenstone belts. Utilizando-se a foliação principal (Sn) como marcador: a fase Dn-2 se caracteriza por uma foliação metamórfica frequentemente paralela ao acamamento, em geral transposta por dobras da fase Dn; a fase Dn-1 se caracteriza por uma sinforma quilométrica, reconhecida no GBF, marcada pelos contatos litológicos e que em ambos os flancos é cortada pela foliação Sn, guardando a mesma assimetria; a fase Dn definida pela foliação principal que se trata frequentemente de uma clivagem de crenulação; além disso, a foliação Sn é afetada por dobras e crenulações, com duas orientações preferenciais de eixos, que foram denominadas de Dn+1 e Dn+2. Essas fases de deformação são correlacionadas com processos tectônicos de escala mais ampla representados por estruturas de primeira ordem: A fase Dn-2 está associada com o cavalgamento da Sequência Superior sobre a Inferior do GBF e da Sequência Metassedimentar sobre a Sequência Metavulcânica Ultramáfica do GBSSR; As fases Dn-1 e Dn são responsáveispelo cavalgamento do GBSSR sobre as rochas do GBF e Complexo Caiçara, e também pela colisão do Complexo Uvá com esse conjunto de compartimentos.
The Archean-Paleoproterozoic Terrane of Goiás is a crust block consisting of Archean TTG Complexes and greenstone belt sequences. The study area is in the southern region of this terrane comprising the southeastern portion of the Faina Greenstone Belt (FGB), where Sertão gold deposit is located, the northern portion of the Serra de Santa Rita Greenstone Belt (SSRGB), and small portions of Caiçara and Uvá TTG complexes. These two greenstone belts are separated by a strike-slip fault, known as Faina Fault, that strikes N50E showing dextral movement. Rocks of two distinct sedimentary cycles separated by a tectonic contact were identified in the FGB, denominated Lower and Upper Metasedimentary Sequences. The Lower Sequence shows quartzite, schist, banded iron formation and marble. The Upper Sequence shows, at the base, a thick package of chlorite-muscovite-quartz schist, with quartzite and BIF intercalations that grades to a sequence of marble and impure marble overlaid by quartzite. In the SSRGB, a Meta-ultramafic Volcanic sequence and a Metasedimentary Sequence were mapped. The last one comprises muscovitic and carbonaceous schists, quartzite, banded iron formation and metachert. The geological mapping provided advances in the definition of the stratigraphy of the area, such as the identification of rocks belonging to the Lower Metasedimentary Sequence in the southeastern and southwestern portion of the FGB, revealing that the Sertão gold deposit is hosted by this unit, and the truncation of this sequence by the Upper Sequence in the northeastern region of the study area. Besides SSRGB rocks were identified to the NW of the Faina Fault, overthrusting the FGB rocks. These findings are in contrast with previous works and demonstrate the need to review the stratigraphic correlations between the two greenstone belts. The superimposition of structures permitted the identification of five deformation phases in the greenstone belts. Using the main foliation (Sn) as marker: Dn- 2 is characterized by a tectonic foliation frequently parallel to bedding, it is generally transposed by Dn folds; Dn-1 is characterized, mainly, by a kilometric synform in the FGB marked by the lithological contacts in which both flanks are cut by Sn, with the same asymmetry; Dn is defined by the main foliation that usually occurs as a differentiated crenulation cleavage; the Sn foliation is affected by folds and crenulations with two distinct orientations that were called Dn+1 and Dn+2. These deformation phases are related to large scale tectonic events: Dn-2 is associated to the thrusting of FGB’s Upper Sequence onto the Lower Sequence and the thrusting of the SSRGB’s Metasedimentary Sequence onto the Meta-ultramafic Volcanic Sequence; the Dn-1 and Dn phases are responsible for the thrusting of SSRGB rocks onto theFGB and Caiçara Complex, and also, for the collision between Uvá Complex and the former domains.
The Archean-Paleoproterozoic Terrane of Goiás is a crust block consisting of Archean TTG Complexes and greenstone belt sequences. The study area is in the southern region of this terrane comprising the southeastern portion of the Faina Greenstone Belt (FGB), where Sertão gold deposit is located, the northern portion of the Serra de Santa Rita Greenstone Belt (SSRGB), and small portions of Caiçara and Uvá TTG complexes. These two greenstone belts are separated by a strike-slip fault, known as Faina Fault, that strikes N50E showing dextral movement. Rocks of two distinct sedimentary cycles separated by a tectonic contact were identified in the FGB, denominated Lower and Upper Metasedimentary Sequences. The Lower Sequence shows quartzite, schist, banded iron formation and marble. The Upper Sequence shows, at the base, a thick package of chlorite-muscovite-quartz schist, with quartzite and BIF intercalations that grades to a sequence of marble and impure marble overlaid by quartzite. In the SSRGB, a Meta-ultramafic Volcanic sequence and a Metasedimentary Sequence were mapped. The last one comprises muscovitic and carbonaceous schists, quartzite, banded iron formation and metachert. The geological mapping provided advances in the definition of the stratigraphy of the area, such as the identification of rocks belonging to the Lower Metasedimentary Sequence in the southeastern and southwestern portion of the FGB, revealing that the Sertão gold deposit is hosted by this unit, and the truncation of this sequence by the Upper Sequence in the northeastern region of the study area. Besides SSRGB rocks were identified to the NW of the Faina Fault, overthrusting the FGB rocks. These findings are in contrast with previous works and demonstrate the need to review the stratigraphic correlations between the two greenstone belts. The superimposition of structures permitted the identification of five deformation phases in the greenstone belts. Using the main foliation (Sn) as marker: Dn- 2 is characterized by a tectonic foliation frequently parallel to bedding, it is generally transposed by Dn folds; Dn-1 is characterized, mainly, by a kilometric synform in the FGB marked by the lithological contacts in which both flanks are cut by Sn, with the same asymmetry; Dn is defined by the main foliation that usually occurs as a differentiated crenulation cleavage; the Sn foliation is affected by folds and crenulations with two distinct orientations that were called Dn+1 and Dn+2. These deformation phases are related to large scale tectonic events: Dn-2 is associated to the thrusting of FGB’s Upper Sequence onto the Lower Sequence and the thrusting of the SSRGB’s Metasedimentary Sequence onto the Meta-ultramafic Volcanic Sequence; the Dn-1 and Dn phases are responsible for the thrusting of SSRGB rocks onto theFGB and Caiçara Complex, and also, for the collision between Uvá Complex and the former domains.
Descrição
Palavras-chave
Geologia estrutural, Greenstone belt, Ouro, Greenstone belt de Faina, Greenstone belt Serra de Santa Rita, Complexo Caiçara, Complexo Uvá, Caracterização estrutural, Depósito Sertão, Falha de Faina, Faina greenstone belt, Serra de Santa Rita greenstone belt, Caiçara complex, Uvá complex, Structural geology, Sertão gold deposit, Faina fault