Características petrográficas e químicas das rochas encaixantes das mineralizações auríferas do depósito Lavra Velha (Região de Ibitiara, borda oeste da Chapada Diamantina, Bahia)
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Data
2016-10-10
Autores
Carlin, Aline de Cassia [UNESP]
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Universidade Estadual Paulista (Unesp)
Resumo
O depósito de ouro Lavra Velha, que pertence ao Alvo de Prospecção Lavra Velha, da empresa Yamana Gold, localiza-se na cidade de Ibitiara, centro-oeste do Estado da Bahia e borda oeste do domínio fisiográfico da Chapada Diamantina, situado no Aulacógeno do Paramirim, na região norte do Cráton São Francisco. O depósito foi recentemente inserido na classe de modelo IOCG (Iron Oxide Cooper Gold), onde a mineralização de ouro se hospeda em brechas hematíticas sericitizadas. O principal objetivo do trabalho foi caracterizar química e petrograficamente as rochas encaixantes do depósito Lavra Velha, cujas litologias predominantes são metatonalitos e meta-quartzo diorito. Estas rochas encontram-se completamente alteradas, com atuação dos processos hidrotermais predominando sobre a deformação de baixo strain, resultando em intensa sericitização e formação de óxidos de ferro, além de cloritização, epidotização, carbonatação e, localmente, albitização. A análise petrográfica, suportada pela análise química, sugere que as rochas encaixantes são correspondentes alteradas do Granitoide Ibitiara, metamorfizadas, deformadas e alteradas hidrotermalmente. O Granitoide Ibitiara e o Granito Matinos apresentam comportamento de magmatismo misto e afinidade para ambiente de arco magmático (sin-colisional) ou orogênico, com idades correlatas ao ciclo orogênico Transamazônico. A intrusão do Granitoide Ibitiara ocorre, provavelmente, em ambiente mais raso da crosta, sugerindo que fluidos hidrotermais e mineralizantes sejam mais tardios. Apesar de integrado até o momento à classe de depósitos IOCG, a análise tectono-estrutural e hidrotermal do depósito Lavra Velha sugere que a mineralização de ouro tenha origem relacionada à fase mais tardia de evolução da bacia do Espinhaço, relacionada à inversão do aulacógeno do Paramirim.
The Lavra Velha gold deposit, which belongs to the prospecting target “Lavra Velha” of the Yamana Gold Company, is located in Ibitiara, Bahia’s central west and the western edge of the physiographic domain of the Chapada Diamantina, situated in Paramirim aulaconge, in northern of São Francisco Craton. The deposit was recently insert into the IOCG model class (Iron Oxide Cooper Gold), where the gold mineralization is hosted at hematite sericitic breccias. The main objective of the study was the chemical and petrographic characterization of the host rocks of the Lavra Velha deposit, whose predominant lithologies are meta-tonalites and metaquartz diorite. These rocks are completely altered due to hydrothermal process, that predominates under the deformation at low-strain rate, resulting in intense sericitization and iron oxide formation, also chloritization, epidotization, carbonatation and, locally, albitization. The petrographic analysis, supported by chemical analysis, suggests that the host rocks correspond to metamorphosed, deformed and hydrothermalized portion of Ibitiara Granitoid. The Ibitiara Granitoid and Matinos Granite show behaviors of mixed magmatism and also affinity for arc magmatic (syn-collisional) or orogenic ambient with correlative age to the Transamazônico Cycle. The Ibitiara Granitoid intrusion probably occurs at a shallower crust environment, suggesting that the hydrothermal and mineralizer fluids are later. In spite of the Lavra Velha deposit has being classified as IOCG’s class, the tectonic, structural and hydrothermal analysis suggests that the gold mineralization has originated during Espinhaço basin later deformation stage, related to inversion of the Paramirim aulacogen.
The Lavra Velha gold deposit, which belongs to the prospecting target “Lavra Velha” of the Yamana Gold Company, is located in Ibitiara, Bahia’s central west and the western edge of the physiographic domain of the Chapada Diamantina, situated in Paramirim aulaconge, in northern of São Francisco Craton. The deposit was recently insert into the IOCG model class (Iron Oxide Cooper Gold), where the gold mineralization is hosted at hematite sericitic breccias. The main objective of the study was the chemical and petrographic characterization of the host rocks of the Lavra Velha deposit, whose predominant lithologies are meta-tonalites and metaquartz diorite. These rocks are completely altered due to hydrothermal process, that predominates under the deformation at low-strain rate, resulting in intense sericitization and iron oxide formation, also chloritization, epidotization, carbonatation and, locally, albitization. The petrographic analysis, supported by chemical analysis, suggests that the host rocks correspond to metamorphosed, deformed and hydrothermalized portion of Ibitiara Granitoid. The Ibitiara Granitoid and Matinos Granite show behaviors of mixed magmatism and also affinity for arc magmatic (syn-collisional) or orogenic ambient with correlative age to the Transamazônico Cycle. The Ibitiara Granitoid intrusion probably occurs at a shallower crust environment, suggesting that the hydrothermal and mineralizer fluids are later. In spite of the Lavra Velha deposit has being classified as IOCG’s class, the tectonic, structural and hydrothermal analysis suggests that the gold mineralization has originated during Espinhaço basin later deformation stage, related to inversion of the Paramirim aulacogen.
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Depósito Lavra Velha, Cráton São Francisco, Aulacógeno do Paramirim, Depósito IOCG, Supergrupo Espinhaço, Lavra Velha deposit, São Francisco Craton, Paramirim Aulacong, IOCG deposits, Espinhaço Supergroup