Orientador: Roberto Perez Xavier / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Geociencias / Made available in DSpace on 2018-07-25T00:05:32Z (GMT). No. of bitstreams: 1 Silva_GilbertodeLimaPereira_M.pdf: 4720997 bytes, checksum: 8740815167ddd2826e2cd76a34789793 (MD5) Previous issue date: 1998 / Resumo: Litotipos carbonosos comumente hospedam ou ocorrem associados a mineralizações auríferas filoneanas nos depósitos mesotermais da Fazenda Canto (FC) e Fazenda Maria Preta (FMP), na seqüência Paleoproterozóica do Greenstone Belt do Rio Itapicuru, NE Brasil. Nestes depósitos, a matéria carbonácea (MC) ocorre principalmente como: (i) bandas retas a anastomosadas (Tipo I); (ii) grãos individuais compostos por agregados de sub-grãos altamente anisotrópicos (Tipo II); ou (iii) grãos individuais com textura interna homogênea (Tipo III). Estudos de espectroscopia Raman indicaram que estes tipos de MC correspondem a alguma forma de material grafítico microcristalino desordenado e definem um trend de grafitização do depósito FMP para o depósito FC, que é interpretado como sendo o resultado de diferentes graus de maturação da MC, que foi alcançado durante o metamorfismo regional no fácies xisto-verde e o alojamento de corpos graníticos no Greenstone Belt do Rio Itapicuru. Estudos de inclusões fluidas revelaram que os veios de quartzo mineralizados são dominados por populações de inclusões ricas em CO2 (Tipo 1), contudo grupos de inclusões H2OCO2 (Tipo 2) primárias, de baixa salinidade (<5% eq. NaCl), compreendem o tipo de inclusões dominantes em apenas alguns veios. Ambos os tipos de fluidos mineralizantes podem ser interpretados como parte de um sistema hidrotermal magmático-metamórfico profundo. No depósito FC, o geotermômetro da clorita (variedade ripidolita - limite inferior) e a paragnese sulfetada (arsenopirita-pirita-pirrotita - limite superior) indicaram limites de temperatura para a deposição do ouro entre 390ºC e 491ºC, com pressões estimadas entre 2.4 a 4.6 kbars, respectivamente. A MC do depósito FMP é isotopicamente mais leve (g13C= -23.3 0/00 a -30.8 0/00) do que a MC do depósito FC (g13C= -18.5 0/00 a -21.0 0/00) Estes valores de g 13C, juntos com as evidências geológicas apontam uma origem biogênica orgânica para a MC. Os composição de g13C calculada do CO2 derivado da oxidação ou hidrólise da MC, aplicando o equilíbrio isotópico calcita-grafita, produziu valores de g13C no intervalo de -9.3 °/00 a -12.8 °/00 entre 390°C e 491°C. Estes valores de 813C calculados são menores do que aqueles obtidos Rara carbonatos do depósito FC (-4.8 °/00 a -8.9 °/00). Por outro lado, os valores da composição de g13C calculada de CO2 de paleo-fluidos responsáveis pela formação de carbonatos (calcita-ankerita), aplicando o equilíbrio calcita-CO2, produziu valores no intervalo de -2.3 °/00 a -6.6 °/00 para temperaturas entre 390°C e 491°C. Estes valores de g13C calculados são compatíveis com o intervalo obtido para inclusões fluidas do depósito FC (-2.8 °/00 a 4.9 °/00) e confirmam que os minerais de alteração de carbonato foram formados pela ação de fluidos oriundos de fonte magmática ou metamórfica profunda. O processo de maturação termal da MC contribuiu pouco para mudanças na composição química e isotópica do fluido mineralizante. Com relação à deposição do ouro, a MC provavelmente atuou como: (1) uma barreira química, reduzindo a 102 do fluido mineralizante ou promovendo a imiscibilidade do fluido pela adição de pequenas quantidades de CH4 e N2 à fase fluida; elou (2) uma barreira física, adsorvendo ouro sobre sua superfície como carvão ativado. Adicionalmente, a MC pode ser usada como um guia indireto na prospeção de mineralizações auríferas / Abstract: Carbonaceous units commonly host or occur closely related to the lode-gold mineralization in the mesothermal Fazenda Canto (FC) and Fazenda Maria Preta (FMP) deposits of the Paleoproterozoic Rio Itapicuru Greenstone Belt, northeast Brazil. In these deposits, the carbonaceous matter (CM) occurs mainly as: (i) straight to anastomosing seams (Type I); (ii) single grains composed of an agglomerate of highly anisotropic subgrains (Type 11); or (iii) single grains with an homogeneous internar texture (Type III). Raman spectral characteristics indicated that these types of CM correspond to some form of microcrystalline disordered graphitic material and define a graphitization trend from the FMP to the FC deposit, which is interpreted as being the result of different degrees of thermal maturation of the CM that was attained during the regional greenschist metarnorphisrn and granite intrusions of the Rio Itapicuru Greenstone Belt. Fluid inclusion studies revealed that the mineralized quartz veins are dominated by populations of CO2-rich inclusions (Type 1), whereas primary groups of low salinity (< 5 wt% eq. NaCl) H2O-CO2 (±CH4 ± N2) inclusions (type 2) comprise the dominant inclusion type in only a few veins. Both types of mineralizing fluids may be interpreted as part of a deep metamorphic - magmatic hydrothermal system. In the FC deposit, chlorite (ripidolite variety - lower limit) geothermometer and sulfide assemblage (arsenopyrite-pyrite-pyrrhotite - upper limit) indicated a temperature of gold deposition between 390 °C to 491°C with estimated pressures of 2.4 to 4.6 kbars, respectively. The CM of the FMP deposit is isotopically lighter (g13C= -23.3 0/00 to -30.8 0/00) than the CM of the FC (g13C= -18.5 0/00 to -21.0 0/00) These g13C values, together with the geologie evidence, point towards a primarily biogenic organic origin for the CM. The calculated g13C compositions of CO2 derived by the oxidation or hydrolysis of the CM, applying the equilibrium calcite - graphite fractionation, yield g13C values in the range -9.3 0/00 to -12.8 0/00 at 390°C 491ºC. These calculated g13C values are lower than those obtained from carbonates of the FC deposit (-4.8 0/00 to -8.9 0/00). On the other hand, the calculated g13C compositions of CO2 from paleo fluids responsable bicarbonate (calcite-ankerite) formation, applying the equilibrium calcite - CO2 fractionation, yield g13 C values in the range -2.3 0/00 to -6.6 0/00 at 390°C ¿ 491ºC. These calculated g13C values are compatible with the range obtained from fluid inclusions of the FC deposit (-2.8 0/00 to -4.9 0/00) and insure that carbonate alteration minerals were formed by action of fluids from a magmatic or deep metamorphic source. The thermal maturation process of the CM contributed little to changes in the chemistry and isotopic composition of the mineralizing fluid. Regarding gold deposition, the CM is likely to have acted as: (1) a chemical trap, reducing the fO2 of the mineralizing paleo-fluids or enhancing fluid immiscibility by adding small quantities of CH4 and N2 to the fluid phase; and/or (2) a physical barrier, adsorbing gold on its surface as activated carbon. Addictionally the CM may be used as a indirect guide in surveys for gold mineralization / Mestrado / Metalogenese / Mestre em Geociências

Various organic compounds, including graphitic carbon, can be formed abiotically in hydrothermal systems, such that evidence for early life must necessarily combine geological, morphological and geochemical data to be compelling. Carbonaceous materials (CM) have been isolated from three rock packages of mid to early Archaean age from the Pilbara Craton of Western Australia. This CM has been subjected to a multidisciplinary approach utilising a variety of analytical and observational techniques, in an attempt to establish the occurrence, associations, mineral affinities, historical environments of growth, and the metamorphic/thermal history experienced by what may be some of the earliest, relatively pristine record of 3500 million year old life on this planet. CM isolated from drillcore obtained from the first of these localities, the 3.24 Ga Sulphur Springs volcanic hosted massive sulphide (VHMS) deposit, occurs as isotopically light (δ13C values of −34.0 ‰ to −26.8 δ13C) finely striated, lenticular to banded material emplaced parallel to original sedimentary bedding planes within the fine-grained silicified epiclastic hanging wall sediments. Petrological and transmission electron microscopy (TEM) observations have revealed well-preserved bundles of filamentous and tubular structured microbial remains closely resembling both modern-day and more ancient microbial forms documented from sea floor hydrothermal environments. Total organic carbon (TOC) has a range of <1.0 to 2.3 %, while the thermal maturity (%Ro) of the filamentous bundles points to maximum temperatures since deposition of around 90–100 °C, a factor that has enabled the preservation of their morphology. These results are suggestive of a well-developed Archaean sediment-hosted microbial community, situated within a basinal environment associated with an active centre of seafloor hydrothermal activity. The majority of the CM isolated from drillcore samples of the second locality, the 3.46 Ga Salgash Subgroup, a lower member of the Apex Basalt, also appears as in situ, bedding parallel bands intercalated with foliated altered argillaceous sandstone beds. TOC of the samples ranges from 1.25 to 11.48 %, while carbon content varies from 2.05 to 32.17 %. δ13C results are relatively heavy, varying from -30.4 to -22.5 ‰. Thermal maturity indicators of 10-13 %Ro suggest the CM having been subjected to temperatures greater than normally obtained from processes associated with burial. Electron paramagnetic resonance (EPR) results showed this CM in a highly ordered graphitic state. Optically, the graphite lacks the typical pronounced anisotropy characterising graphites in metamorphic terranes. Graphitisation therefore, is likely the result of rapid heating at very high temperature. HRTEM of this material revealed an extremely high level of molecular ordering contemporaneous with the presence of the C60 fullerene molecules within carbon nanotubes. These forms are a key to the distinction between biologically and abiotically synthesized CM, both by their small size and their resistance to thermal degradation. The occurrence of these carbon forms in terrestrial deposits is rare, and usually associated with wildfires, lighting strike or meteoritic impact. In the case of the Salgash CM, the formation of these molecules and the isotropic graphitised state of the CM is interpreted as a result of emplacement under pressure of very high temperature (komatiitic/ peridotite) lavas. The thermal overprint of the CM by such a high temperature process resulted in the volatilisation of the organic material, destruction of any primary biological morphology and the subsequent reorganisation of the residual CM, resulting in increased molecular ordering. In the third part of the study, CM isolated from drillcore samples of the ca. 3.5 Ga Dresser Formation bedded black chert-barite units, occurs in both dispersed and layered forms, interlayered with fine-grained silica. The intimate association of the CM and silica strongly resembles silicified microbial colonies from active hydrothermal systems, which have been previously proposed as analogues of Archaean hydrothermal sites. Isotopically light δ13C values from -38.2 to -32.1 ‰, and the association of C, H, and N, are highly indicative of a biological origin for the material. Palaeotemperatures calculated from δ18O isotope analysis of quartz chips indicate a depositional temperature for the hydrothermal veins ranging from ~120 °C to ~200 °C. 207Pb-206Pb isotope analyses conducted on pyrites extracted from the interbedded barite units reveal a dual MORB and Erosion mix source for the Pb, which gives an average 207Pb/206Pb age of 3531±42 Ma for the deposit. Ro measurements reveal four distinct CM populations, defined as ACM, A1CM, BCM, and CCM, which represent temperatures ranging from 170 °C to potentially >400 °C. TEM and HRTEM observations of the lower temperature CM population show morphological entities strongly suggestive of microbial remains, including possible cell wall remnants. Higher Ro rank CM commonly fills or coats mineral grains and lacks distinguishable structures, which is consistent with an increased thermal degradation /hydrothermal overprint. The geological setting and mineralogy of the Dresser Formation endorse its formational history as a silica-barite dominated seafloor hydrothermal deposit, most likely analogous to modern “white smokers”. The occurrence of the predominant CM (type ACM) in more or less continuous bands and laminae within the sedimentary rocks suggest an in situ, syndepositional source for the majority of this material, whereas the dispersed nature of type BCM particles indicates a recycled nature. The occurrence of type CCM within fluid inclusions gives an insight into the primary morphology of the non-degraded original microbial cells that may have existed at that time. These observations, combined with the carbon isotopic heterogeneity and fractionations are suggestive of chemosynthetic microbes occupying a seafloor hydrothermal system where rapid silicification at relatively low temperature preserved the CM. Finally, in an effort to further understand the CM structures observed in the rocks of the Dresser Formation in the context of present day microbial colonies in similar environments, a comparative morphological study was conducted using a potential modern analogue derived from an active seafloor hydrothermal environment. Such methodology utilises the standard classification used in biological species identification, which is initially based on visual identification of specific features, whether by the naked eye, light microscopy or electron microscopy. The extant hyperthermophilic microbe Methanocaldococcus jannaschii was cultured under conditions similar to the Archaean seafloor, simulating an increased thermal maturity by artificially induced autoclaving at 100 °C (1 atm) and 132 °C (2 atm). A striking resemblance to the early Archaean forms observed in the Dresser CM was evident in both wall structure and thermal degradation mode of the cultured microbe. Cell disintegration of the cultures occurred at 100 °C marking the limits of life, whereas complete disintegration, deformation and shrinkage of the cells occurred at 132 °C. These comparative observations present as a feasible way of understanding the structural features in CM identified in Archaean sedimentary packages.

Metamorphic processes can transform the organic matter in sedimentary rocks into structurally organized carbonaceous matter, in ideal conditions to graphite. In the centre of West Alpine arch, the metasedimentary rocks are rich in dispersed carbonaceous matter and were used in this thesis to specify the thermal range of metamorphism based on the structural state. Previous studies have used mainly the Raman spectrometers to determine the structural state of carbonaceous matter. Unfortunately this method doesn't allow in-situ analyses which, in addition to Earth studies, can be essential for studying other planetary bodies and moons of our solar system. As only the smallest and lightest instruments are required for analyses during potential planetary missions to Mars, it is important to verify that the small instruments are able to detect even the small concentrations of carbonaceous matter. Currently available miniature and portable Raman spectrometers have started to become more precise but are still not as precise as laboratory Raman microspectrometers. This thesis is divided into two parts. First part aims to duplicate the results from previous studies by Raman microspectrometers in the West Alpine arch. Furthermore, the excitation laser wave length dependence of spectral signs in carbonaceous...

No / The first Raman spectrometers to be used for in situ analysis of planetary material will be launched as part of powerful, rover-based analytical laboratories within the next 6 years. There are a number of significant challenges associated with building spectrometers for space applications, including limited volume, power and mass budgets, the need to operate in harsh environments and the need to operate independently and intelligently for long periods of time (due to communication limitations). Here, we give an overview of the technical capabilities of the Raman instruments planned for future planetary missions and give a review of the preparatory work being pursued to ensure that such instruments are operated successfully and optimally. This includes analysis of extremophile samples containing pigments associated with biological processes, synthetic materials which incorporate biological material within a mineral matrix, planetary analogues containing low levels of reduced carbon and samples coated with desert varnish that incorporate both geo-markers and biomarkers. We discuss the scientific importance of each sample type and the challenges using portable/flight-prototype instrumentation. We also report on technical development work undertaken to enable the next generation of Raman instruments to reach higher levels of sensitivity and operational efficiency.