Orientador: Roberto Perez Xavier / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Geociências / Made available in DSpace on 2018-08-28T02:16:57Z (GMT). No. of bitstreams: 1 Trevisan_VeronicaGodinho_M.pdf: 12082378 bytes, checksum: 8a62864dd0b76538367589ff9f11e172 (MD5) Previous issue date: 2015 / Resumo: O setor leste da Província Aurífera de Alta Floresta, Cráton Amazônico, Brasil, hospeda um grande número de depósitos de ouro na forma de veios, sistemas de veios em stockwork e disseminados associados à sequências plutôno-vulcânicas paleoproterozóicas, incluindo os depósitos filonares de Au + metais base Luiz e Au ± Cu Paraíba e Pezão. Descrição de testemunhos de sondagem, petrografia e geocronologia U-Pb SHRIMP IIe em zircão permitiram a caracterização dos diferentes atributos geológicos desses depósitos. A rocha hospedeira do depósito Paraíba é representada por biotita tonalito, enquanto que nos depósitos Luiz e Pezão corresponde a um biotita granodiorito intrudido por feldspato-pórfiro e sienogranito cortado por quartzo-pórfiro, respectivamente. As zonas de metassomatismo incluem as alterações clorítica, potássica com biotita e sericítica e, em direção aos setores distais, alterações potássica com K-feldspato e propilítica, preenchimento por carbonato, silicificação + preenchimento por quartzo e, vênulas pós-mineralização compostas por quartzo, carbonato, epidoto, sericita e/ou clorita. O veio de quartzo aurífero dos três depósitos apresenta textura maciça, enquanto que nos depósitos Luiz e Pezão é comum a ocorrência de texturas de preenchimento de espaços vazios em veios de quartzo e/ou quartzo + carbonato não mineralizados. As zonas mineralizadas do depósito Paraíba e Pezão são representadas por pirita + calcopirita, enquanto que no depósito Luiz a paragênese do minério é caracterizada por pirita + esfalerita + galena ± calcopirita. O regime de fluidos nas zonas de minério do depósito Paraíba é representado essencialmente por fluidos aquo-carbônicos, enquanto que nos depósitos Luiz e Pezão por fluidos aquosos bifásicos de baixa salinidade. Análises U-Pb SHRIMP IIe em zircão das rochas hospedeiras e feldspato-pórfiro Luiz forneceram idades de cristalização entre 2,01 e 1,97 Ga. A evolução do sistema hidrotermal dos depósitos indica redução da temperatura e incremento da ¿O2 e pH dos fluidos mineralizantes. A precipitação do minério no depósito Paraíba deve estar relacionada com o processo de imiscibilidade e interações fluido-rocha, enquanto que nos depósitos Luiz e Pezão pode ser atribuída a expansão adiabática seguida por boiling. A integração dos dados sugere que o depósito Paraíba se formou em um nível crustal mais profundo, enquanto que os depósitos Luiz e Pezão em níveis crustais mais rasos. A estreita relação espacial com plútons graníticos sugere que os depósitos Paraíba, Luiz e Pezão possam representar sistemas magmático-hidrotermais que se desenvolveram a partir da cristalização de corpos sub-vulcânicos (e.g. pórfiros), considerados com a possível fonte de fluidos, calor e metais para estes sistemas. Neste contexto, o depósito Paraíba pode ser considerado como um sistema filonar rico em ouro-quartzo hospedado por intrusões, enquanto que os depósitos Luiz e Pezão podem representar sistemas mineralizados similares a depósitos epitermais polimetálicos de sulfuração intermediária e rico em ouro-cobre de baixa sulfuração, respectivamente. Embora a idade da mineralização seja ainda desconhecida nos três depósitos, as relações geológicas entre as hospedeiras, os corpos sub-vulcânicos e zonas de minério, combinadas com os dados geocronológicos obtidos neste estudo e disponíveis na literatura, abrem a possibilidade de que a metalogênese do ouro no setor leste da província não esteja restrita a um único evento intrusivo (1.787 ± 3.2 a 1.786 ± 1 Ma), mas apontam para a possível existência de pelo menos dois eventos mineralizantes (~1.78 e ~1.97 Ga). Os dados geocronológicos U-Pb SHRIMP em zircão obtidos neste estudo sugerem a correlação das rochas graníticas hospedeiras com o primeiro evento magmático (1.98 a 1.97 Ga) do setor leste da província, ou mesmo a expansão desse intervalo de idades / Abstract: The easternmost sector of the Alta Floresta Gold Province, Amazon Craton, Brazil, hosts a significant number of disseminated, stockwork and vein-type gold deposits associated with paleoproterozoic plutonic-volcanic sequences, including the Luiz Au + base metals and the Paraíba and Pezão Au ± Cu vein-type deposits. Description of drill cores, petrography and U-Pb sensitive high-resolution ion microprobe (SHRIMP) IIe zircon geochronology allowed the characterization of the different geological attributes of these three deposits. At the Paraíba deposit the host lithotype is represented by biotite tonalite, whereas at the Luiz and Pezão deposits the host rocks encompass a biotite granodiorite intruded by a feldspar-porphyry and a syenogranite truncated by a quartz-porphyry, respectively. Metasomatic zones include chloritic, sericitic and potassic (biotite) alteration, and, outwards from the ore zones, carbonate infill, silicification plus quartz infill, potassic (K-feldspar) and propylitic alteration, besides post-mineralization quartz, carbonate, epidote, sericite and/or chlorite veinlets. The auriferous quartz veins in all deposits display massive texture, whereas barren quartz and/or quartz + carbonate veins at the Luiz and Pezão deposits commonly display open-space filling textures. Ore zones at Paraíba and Pezão deposits are represented by pyrite + chalcopyrite, whereas at Luiz deposit is characterized by pyrite + sphalerite + galena ± chalcopyrite. Fluid regime at the Paraíba ore zones encompasses aqueous-carbonic fluids, whereas at the Luiz and Pezão deposits are essentially characterized by low salinity two-phase aqueous fluids. U-Pb SHRIMP IIe zircon analysis of host rocks and Luiz feldspar-porphyry provided crystallization ages between 2,01 and 1,97 Ga. The evolution of the hydrothermal systems of these three deposits indicates a decrease in temperature and an increase in ¿O2 and pH of the fluid. Ore precipitation at the Paraíba deposit would be related to a combination of immiscibility process and fluid-rock interactions, while at the Luiz and Pezão deposits can be attributed to adiabatic expansion followed by boiling process. Data integration suggest that the Paraiba deposit may have originated at deeper crustal levels, whereas the Luiz and Pezão deposits would be positioned at shallower crustal levels. The close spatial relationship with granitic plutons suggests that the Paraíba, Pezão and Luiz deposits may be genetically linked to magmatic-hydrothermal systems, which developed as a result of the crystallization of sub-volcanic rocks (e.g. porphyries), considered as the possible source of fluids, heat and metals for these systems. In this context, the Paraíba deposit can be classified as an intrusion-hosted gold-quartz vein system, whereas the Luiz and Pezão deposits may represent mineralized systems similar to intermediate sulfidation polymettalic and low sulfidation gold-copper-bearing epithermal deposits, respectively. Although the mineralization ages are still unknown for these three deposits, the geological relationships between host and sub-volcanic rocks and ore zones, combined with geochronological data from this study and from literature, open the possibility that gold metallogeny within the province is not restricted to a single paleoproterozoic intrusive event (1.787 ± 3.2 to ± 1.786 1 Ma), but point to the possible existence of at least two mineralizing events (~ 1.78 and ~ 1.97 Ga). The U-Pb zircon geochronological data from this study suggest the correlation of the granitic rocks to the first magmatic event (1.98 to 1.97 Ga) in the easternmost portion of the province, or even an expansion of this age interval / Mestrado / Geologia e Recursos Naturais / Mestra em Geociências

[Truncated abstract] The Tintina Gold Province (TGP) comprises numerous (<15) gold belts and districts throughout interior Alaska and Yukon that are associated with Cretaceous plutonic rocks. With a gold endowment of ∼70Moz, most districts are defined by their placer gold contributions, which comprise greater than 30 Moz, but four districts have experience significant increases in gold exploration with notable discoveries at Fort Knox (5.4 Moz), Donlin Creek (12.3 Moz), Pogo (5.8 Moz), True North (0.79 Moz), and Brewery Creek (0.85 Moz). All significant TGP gold deposits are spatially and temporally related to reduced (ilmenite-series) and radiogenic Cretaceous intrusive rocks that intrude (meta-) sedimentary strata. The similar characteristics that these deposits share are the foundation for the development of a reduced intrusion-related gold deposit model. Associated gold deposits have a wide variety of geological and geochemical features and are categorized as intrusion-centered (includes intrusion-hosted, skarns and replacements), shear-related, and epizonal. The TGP is characterized by vast, remote under-explored areas, unglaciated regions with variable oxidation depths and discontinuous permafrost, which, in combination with a still-evolving geological model, create significant exploration challenges. Twenty-five Early and mid-Cretaceous (145-90 Ma) plutonic suites and belts are defined across Alaska and Yukon on the basis of lithological, geochemical, isotopic, and geochronometric similarities. These features, when combined with aeromagnetic characteristics, magnetic susceptibility measurements, and whole-rock ferric:ferrous ratios define the distribution of magnetite- and ilmenite-series plutonic belts. Magnetite-series plutonic belts are dominantly associated with the older parts of the plutonic episode and comprise subduction-generated metaluminous plutons that are distributed preferentially in the more seaward localities dominated by primitive tectonic elements. Ilmenite-series plutonic belts comprise slightly-younger, slightly-peraluminous plutons in more landward localities in pericratonic to continental margin settings. They were likely initiated in response to crustal thickening following terrane collision. The youngest plutonic belt forms a small, but significant, magnetite-series belt in the farthest inboard position, associated with alkalic plutons that were emplaced during weak extension. Intrusion-related metallogenic provinces with distinctive metal associations are distributed, largely in accord with classical redox-sensitive granite-series. Copper, Au and Fe mineralisation are associated with magnetite-series plutons and tungsten mineralisation associated with ilmenite-series plutons. However, there are some notable deviations from expected associations, as intrusion-related Ag-Pb-Zn deposits are few, and significant tin mineralisation is rare. Most significantly, many gold deposits and occurrences are associated with ilmenite-series plutons which form the basis for the reduced intrusion-related gold deposit model

L’objectif principal de cette thèse est de décrire et interpréter la mise en place des différents types de minéralisations présents dans le district minier de Nefza (NO de la Tunisie), qui constitue une région complexe et particulière du point de vue géologique dans ce pays.<p>En effet, outre la présence de diapirs triasiques (commune à tout le Nord de la Tunisie), le district minier de Nefza est caractérisé par :(1) la mise en place d’épaisses nappes au Néogène qui forment le substratum sédimentaire régional, et (2) la présence d’une grande variété de roches magmatiques tant plutoniques que volcaniques, d’âge miocène (12,9 à 6,4 Ma),<p>-\ / Doctorat en Sciences / info:eu-repo/semantics/nonPublished

Use of Re-Os systematics in sulfides from the Bagdad porphyry Cu-Mo deposit provide information on the timing of mineralization and the source of the ore -forming elements. Analyzed samples of pyrite, chalcopyrite and molybdenite mainly from the quartz monzonite and porphyritic quartz monzonite units are characterized by a moderate to strong potassic alteration (secondary biotite and K- feldspar). Rhenium concentrations in molybdenite are between 330 and 730 ppm. Two molybdenite samples from the quartz monzonite and porphyritic quartz monzonite provide a Re-Os isotope age of 71.7 ± 0.3 Ma. A third sample from a molybdenite vein in Precambrian rocks yields an age of 75.8 ± 0.4 Ma. These molybdenite ages support previous suggestions of two mineralization episodes in the Bagdad deposit. An early event at 76 Ma and a later episode at 72 Ma. Pyrite Os and Re concentrations range between 0.008-0.016 and 3.9-6.8 ppb, respectively. Chalcopyrite contains a wide range of Os (6 to 91 ppt) and Re (1.7 to 69 ppb) concentrations and variable ¹⁸⁷Os/¹⁸⁸Os ratios that range between 0.13 to 22.27. This variability in the chalcopyrite data may be attributed to different copper sources, one of them the Proterozoic volcanic massive sulfides in the district, or to alteration and remobilization of Re and Os. Analyses from two pyrite samples yield an eight point isochron with an age of 77 ± 15 Ma and an initial ¹⁸⁷Os/¹⁸⁸Os ratio of 2.12. This pyrite Re-Os isochron age is in good agreement with the molybdenite ages. We interpret the highly radiogenic initial 1870s/188Os as an indication that the source of Os and, by inference, the ore-forming elements for the Bagdad deposit, was mainly the crust. This conclusion agrees with previous Pb and Nd isotope studies and supports the notion that a significant part of the metals and magmas have a crustal source.