Estudo de cloritas e carbonatos em rochas reservatório da Bacia de Santos

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Caracterização dos veios de quartzo da mina Aurora - Lavras do Sul/RS

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Isótopos de Carbono em Filitos Carbonosos da Seqüência Metavulcano- Sedimentar Marmeleiro, Sul de Ibaré, Rio Grande do Sul

Carbon isotope ratios for carbonaceous material in the graphite prospect of Marmeleiro Sequence, southwestern of the Sul-rio-grandense Shield, have been determined. The results are approximately constant with δ13C-values between -27 and -24 per mil. These values suggest that the studied carbonaceous rocks were formed from syngenetic organic detritus, which were converted to graphite during metamorphism. The degree of cristallinity of carbonaceous material has also been investigated. The results of X-ray diffraction [d(002): 3.35 - 3.37 Å] indicate this material cristallinity is intermediate between amorphous carbon and fully ordered graphite

Isótopos de Carbono em Filitos Carbonosos da Seqüência Metavulcano- Sedimentar Marmeleiro, Sul de Ibaré, Rio Grande do Sul

Carbon isotope ratios for carbonaceous material in the graphite prospect of Marmeleiro Sequence, southwestern of the Sul-rio-grandense Shield, have been determined. The results are approximately constant with δ13C-values between -27 and -24 per mil. These values suggest that the studied carbonaceous rocks were formed from syngenetic organic detritus, which were converted to graphite during metamorphism. The degree of cristallinity of carbonaceous material has also been investigated. The results of X-ray diffraction [d(002): 3.35 - 3.37 Å] indicate this material cristallinity is intermediate between amorphous carbon and fully ordered graphite

Caracterização preliminar da alteração hidrotermal na área da mina Valdo Teixeira - Lavras do Sul/RS

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Caracterização petrográfica da alteração hidrotermal da área da mina Valdo Teixeira - Lavras do Sul/RS

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Geochemical modeling of gold precipitation conditions in the Bloco do Butiá Mine, Lavras do Sul/Brazil

Com auxílio dos pacotes de programas EQ3/EQ6 foi realizado um modelamento geoquímico deposicional para ouro e comparado com dados geológicos, petrográficos, geoquímicos e de inclusões fluidas da mina de ouro do Bloco do Butiá, Lavras do Sul/RS. O ouro ocorre na estrutura da pirita (ouro invisível) associado a mica branca (fengita) na alteração fílica. Foi demonstrado que os processos que levamà deposição do ouro são aqueles relacionados ao decréscimo da temperatura e ao abaixamento do pH. O pH também mostrou ser fundamental para a deposição do ouro com as espécies de enxofre [Au(HS)−2 , HAu(HS)02 e Au(HS)0], em razão de potencializar sua desestabilização, sendo Au(HS)0 a principal espécie complexante. A entrada de KCl é de difícil aceitação como causa da precipitação do ouro visto que não foi identificado Cl− na fengita, apesar de que em todos os cálculos de balanço geoquímico de massa sempre foi necessário admitir a entrada de um pouco de potássio na alteração fílica. A precipitação da pirita (± aurífera) deve ter sido fortemente influenciada pela disponibilidade de ferro de clorita ferrosa, quando da sua dissolução pelos fluidos que depositaram fengita. As baixas salinidades verificadas nas inclusões fluidas dos grãos de quartzo da encaixante propilitizada também advogam para a pouca importância do cloro como agente transportador de ouro. Compostos de enxofre e não de cloro devemter dominado como complexos transportadores de ouro na área do Bloco do Butiá.A geochemical modeling of gold deposition was performed using the EQ3/EQ6 software package using conditions inferred from geological, petrographic, geochemical and fluid inclusion data from the Bloco do Butiá gold mine, Lavras do Sul, RS. Gold in the mine occurs only in the pyrite structure (invisible gold). The pyrite occurs associated with white mica (phengite) in the zone of phyllic alteration. The process of gold deposition showed to be related to temperature and pH decrease. The pH decrease was fundamental to gold deposition by destabilization of sulfur species [Au(HS)−2 , HAu(HS)02 and Au(HS)0] dissolved in the aqueous solution, being Au(HS)0 the main gold transporting complex. The addition of KCl is hard to accept as cause of gold precipitation because no Cl– was detected in phengite. However, the geochemical mass balance calculation resulted in the gain of some potassium in the zone of phyllic alteration. The precipitation of pyrite (± auriferous) may have been strongly influenced by iron availability resulting from dissolution of ferrous chlorites by the fluids responsible for phengite deposition. The low salinity in quartz grain fluid inclusions from the propylitized wall rock also indicates the little importance of chlorine as gold transporting agent. Sulfur, and not chlorine, compounds must have dominated the gold transporting complexes in the Bloco do Butiá gold area

Estratigrafia do Batólito Florianópolis, Cinturão Dom Feliciano, na Região de Garopaba-Paulo Lopes, SC

In southern Brazil, the Florianopolis Batholith results from prolonged, mainly granitic magmatism, as part of the Neoproterozoic Dom Feliciano Belt. Plutonic associations in this belt are related to transpressive tectonism (650-580 Ma) in post-collisional setting, where the translithospheric discontinuities of the Southern Brazilian Shear Belt have triggered magmatism, acting as channels for melts originated in deep crustal or mantle sources. In the region of Garopaba-Paulo Lopes, a fraction of this magmatism was studied, resulting in a formal proposition for its stratigraphic organization in igneous suites. A small volume of gneissic host rocks is found as roof pendants. The Paulo Lopes Suite comprises the foliated Paulo Lopes Granite, Garopaba Granitoids and Silveira Gabbro. It is characterized as porphyritic granitoids of high-K tholeiitic affinity, coeval with mafic, tholeiitic magmatism. It is followed by metaluminous, alkaline series granitoids of the Pedras Grandes Suite, namely the Vila da Penha Granite, comprising heterogranular and porphyritic facies, and the Serra do Tabuleiro Granite, comprising heterogranular, equigranular and porphyritic facies. The Cambirela Suite, last magmatic episode in the study area, encompasses alkaline plutonic, volcanic and subvolcanic rock types, as the Ilha Granite, the Cambirela Rhyolite and the Itacorumbi Granite. Hypabissal rocks are also part of this suite, and result from recurrent acid and basic magma pulses emplaced either as idividual dykes or composite ones. The magmatic associations described in this region attest to magma emplacement under a moderate to low stress field, possibly extinguished by the time the Cambirela Suite crystallized. Their age values indicate that they are mostly contemporaneous to the post-collisional, syntectonic magmatism of the Southern Brazilian Shear Belt, and the preservation of magmatic structures such as modal layering, relatively uncomon in granitoids, may also be attributed to their emplacement far from the main deformation sites. Features indicative of coeval mafic and felsic magmas are described in all three magmatic associations, and are especially significant in the Paulo Lopes and Cambirela suites. They attest to continuous mantle participation in the batholith construction.In southern Brazil, the Florianopolis Batholith results from prolonged, mainly granitic magmatism, as part of the Neoproterozoic Dom Feliciano Belt. Plutonic associations in this belt are related to transpressive tectonism (650-580 Ma) in post-collisional setting, where the translithospheric discontinuities of the Southern Brazilian Shear Belt have triggered magmatism, acting as channels for melts originated in deep crustal or mantle sources. In the region of Garopaba-Paulo Lopes, a fraction of this magmatism was studied, resulting in a formal proposition for its stratigraphic organization in igneous suites. A small volume of gneissic host rocks is found as roof pendants. The Paulo Lopes Suite comprises the foliated Paulo Lopes Granite, Garopaba Granitoids and Silveira Gabbro. It is characterized as porphyritic granitoids of high-K tholeiitic affinity, coeval with mafic, tholeiitic magmatism. It is followed by metaluminous, alkaline series granitoids of the Pedras Grandes Suite, namely the Vila da Penha Granite, comprising heterogranular and porphyritic facies, and the Serra do Tabuleiro Granite, comprising heterogranular, equigranular and porphyritic facies. The Cambirela Suite, last magmatic episode in the study area, encompasses alkaline plutonic, volcanic and subvolcanic rock types, as the Ilha Granite, the Cambirela Rhyolite and the Itacorumbi Granite. Hypabissal rocks are also part of this suite, and result from recurrent acid and basic magma pulses emplaced either as idividual dykes or composite ones. The magmatic associations described in this region attest to magma emplacement under a moderate to low stress field, possibly extinguished by the time the Cambirela Suite crystallized. Their age values indicate that they are mostly contemporaneous to the post-collisional, syntectonic magmatism of the Southern Brazilian Shear Belt, and the preservation of magmatic structures such as modal layering, relatively uncomon in granitoids, may also be attributed to their emplacement far from the main deformation sites. Features indicative of coeval mafic and felsic magmas are described in all three magmatic associations, and are especially significant in the Paulo Lopes and Cambirela suites. They attest to continuous mantle participation in the batholith construction