Abstract The Bonsucesso zinc-lead (Zn-Pb) sulfide deposit is hosted in carbonate rocks from the Vazante Group (transition of the Mesoproterozoic to the Neoproterozoic time), northwest of Minas Gerais State, Brazil. Regional deformation is associated with the thin-skinned tectonics that led to the formation of the foreland zone of the Brasília Orogen during the Neoproterozoic. These orogenic processes are the trigger of Zn-Pb mineralization in many base-metal deposits in the Vazante Group. Here, we describe the ore textures and the structures of the deposit to define its structural controls in deposit scale and formulate hypotheses about its forming process in the context of other Vazante Zn-Pb deposits. Mineralization distribution is controlled by a high-angle fault zone striking NNW and dipping 60° to WSW. Fault-related fractures functioned as pathways for Zn-Pb-rich fluids to be redistributed and crystallize where chemical conditions were adequate. Mineralization was likely formed in an extensional setting in breccia zones controlled by flexurally induced normal faults related to development of the foreland basin of Brasília Orogen. Later, the entire Vazante sequence underwent an inversion process and extensional structures were reactivated or obliterated. Finally, an understanding of local controls may be of good use to target exploration for new orebodies in the district scale.

Abstract Fracturing analysis of low-permeability rocks as reservoir analogs have increased in recent years. The main mechanism involved in the development of secondary porosity in low-permeability, fine-grained limestones of the Irati Formation is fracturing. In these rocks, oil accumulates along fracture planes, vuggy porosity, microfractures, breccias, as well as bedding discontinuities. Joints represent the central element for oil migration and the connection between accumulation sites. Joints are unevenly distributed across the succession of rock types, where carbonate rocks have a much denser array of joints than shales and siltstones. From a mechanical stratigraphy point of view, limestones have a brittle behavior and constitute mechanical units. Ductile shale and siltstone are mechanical interfaces capable of blocking joint propagation. Joints running NW-SE are more effective in trespassing the mechanical interface and are, therefore, more persistent. Joints running NE-SW are less persistent because the ductile behavior of the first two shale beds above the limestone blocks their propagation. The spatial arrangement of regional NW-SE and NE-SW joints promoted reservoir connection, allowing oil migration and accumulation. The joints and oil migration (at least three phases) developed as a consequence of the Gondwana Breakup and are also associated with local pressure gradients.

As rochas carbonáticas do Grupo Macaé (Albiano) representam a sedimentação carbonática relacionada ao início da fase drifte na Bacia de Campos. Discutem-se aqui aspectos deposicionais, diagenéticos e estratigráficos das rochas carbonáticas do Grupo Macaé, englobando a porção superior da Formação Quissamã e a porção basal da Formação Outeiro. Análises macroscópicas em testemunhos e microscópicas utilizando-se lâminas delgadas permitiram o reconhecimento de onze fácies sedimentares - nove delas correspondentes à Formação Quissamã e duas à Formação Outeiro. Estas foram agrupadas em cinco associações de fácies, relacionadas às diferentes posições fisiográficas de uma plataforma carbonática. Os bancos carbonáticos estão relacionados à deposição de grainstonesoolíticos e grainstonesoncolíticos em profundidades rasas, acima do nível de base de ondas de tempo bom (NBTOB). Os baixios oncolíticos ou interbancos foram formados em águas menos agitadas e são caracterizadas pela deposição de packstonespeloidais bioclásticos e wackestones,representativos da sedimentação em águas calmas Packstonesbioclásticos e wackestone/packstonesoolíticos representam depósitos alóctones relacionados ao início do afogamento regional da plataforma que ocorre na porção superior da Formação Quissamã. Wackestonescom pitonelídeos e wackestonesbioclásticos com glauconita são aqui relacionados a depósitos de água profunda, característicos da Formação Outeiro. As feições pós-deposicionais revelaram a atuação de processos diagenéticos de micritização, cimentação, dissolução, compactação, dolomitização e recristalização, ocorridos nas fases eo- e mesodiagenética. A análise da sucessão vertical das fácies indica a presença de diversos ciclos de raseamento ascendente, empilhados com uma tendência retrogradacional da sequência em direção ao topo (passagem da Fm. Quissamã para Fm. Outeiro).

Carbonate rocks from the Macaé Group (Albian) represent an example of carbonate sedimentation related to the drift phase in Campos Basin. This study presents depositional features, integrating them with diagenetic and stratigraphic aspects of the Macaé Group carbonates including the upper part of the Quissamã Formation and the lower part of the Outeiro Formation. Macroscopic analyses in cores and microscopic ones in thin sections allowed the recognition of eleven sedimentary facies - nine of them corresponding to the Quissamã Formation and two of them representing the Outeiro Formation. These facies were grouped into five facies associations. Oolitic grainstones and oncolitic grainstones are interpreted to be deposited in shallow depth probably in shoals above the fair weather wave base. The interbanks between shoals were formed in less agitated waters and characterized by deposition of peloidal bioclastic packstones and wackestones representative of sedimentation in calm waters. Bioclastic packstones and oolitic packstones/wackestones represent allochthonous deposits related to the beginning of the regional drowning that occur in upper Quissamã Formation. Pithonellids wackestones and bioclastic wackestones with glauconite are related to deep water deposits, characteristics of the Outeiro Formation. Post-depositional features revealed the action of diagenetic processes as, micritization, cimentation, dissolution, compaction, dolomitization and recrystallization occurred during the eo- and mesodiagenesis phases. Vertical facies analysis suggests shallowing upward cycles stacked in a sequence progressively deeper towards the top (from the Quissamã Formation to the Outeiro Formation).