<p> Sulfide-poor platinum-group element (PGE) mineralization occurs within the Archean Boston Creek Flow ferropicrite, Abitibi greenstone belt, Canada. The PGE mineralization (∑PGE+Au = up to 1000 ppb) is manifest as metre-scale platinum-group mineral-bearing pods of disseminated chalcopyrite and pyrite (< 1 modal%) within titaniferous magnetite-rich gabbroic rock at the base of its central gabbroic layer. This mineralization is distinct in character from well known PGE mineralization associated with massive Fe-Ni-Cu sulfides at the base of komatiite flows at Kambalda, Western Australia and elsewhere. Exploration strategies presently used to search for PGE in mafic and ultramafic volcanic rock terrains are based on the geological and geophysical characteristics of sulfide-rich PGE mineralization. Consequently, refinements in exploration strategies are required if economic concentrations of sulfide-poor PGE mineralization are to be discovered in volcanic terrains.</p> <p> To begin development of such exploration criteria, ground-based magnetic and VLF surveys were conducted over the PGE mineralization along a single cross-section through the BCF. Drill core samples were collected along this transect to characterize the volume magnetic susceptibility and natural remanent magnetization (NRM) of the mineralization. Magnetic highs ranging in intensity from 64000 to 65000 nT were recorded for the base of the gabbroic layer, including mineralized outcrops. Susceptibilities of up to 9700 cgs and high remanence values with variable directions were determined. VLF, as expected, was not useful in identifying the mineralized horizons. The peridotite at the base of the flow appears to be the only conductive rock in the BCF.</p> <p> The magnetic highs associated with the base of the gabbroic layer define a positive anomaly that appears to be podiform in outline and up to ten metres in maximum dimension. This result suggests that the titaniferous magnetite-rich rock is itself podiform, like the enclosed PGE mineralization. This magnetic anomaly is not extensive enough to be evident on a regional scale aeromagnetic map as a separate anomaly within the BCF, and is not evident through VLF techniques. The rocks hosting the PGE mineralization is defined by the paleomagnetic results but this is not a practical field method.</p> <p> The geophysical characterization of the PGE mineralization host rocks, and of the BCF in general, demonstrates the potential of detailed magnetic and susceptibility mapping, together with petrographic and petrologic studies, in the search for economic PGE concentrations of sulfide-poor PGE mineralization in other volcanic and possibly plutonic rocks as well. Specifically, the results suggest that podiform magnetic anomalies within titaniferous magnetite-rich pyroxenites and gabbroic rocks may have potential use in the exploration for economic sulfide-poor PGE mineralization. Although the paleomagnetic methods used in this study are probably not of direct use in exploration, they were able to distinguish the different lithologies in the BCF. This substantiates the results of the susceptibility measurements in characterizing PGE mineralized, titaniferous magnetite-bearing rocks. The results of the paleomagnetic study also show that the NRM of the Ghost Range intrusive complex is not primary and therefore the Archean apparent polar wander path as it is currently defined is incorrect.</p> / Thesis / Bachelor of Science (BSc)

Submitted by Igor Matos (igoryure.rm@gmail.com) on 2017-01-31T14:38:14Z No. of bitstreams: 1 DISS_2015_Jennifer Cardoso Farias Almada.pdf: 5724861 bytes, checksum: 75d76d597050375391c29d0a04f80995 (MD5) / Approved for entry into archive by Jordan (jordanbiblio@gmail.com) on 2017-01-31T15:18:18Z (GMT) No. of bitstreams: 1 DISS_2015_Jennifer Cardoso Farias Almada.pdf: 5724861 bytes, checksum: 75d76d597050375391c29d0a04f80995 (MD5) / Made available in DSpace on 2017-01-31T15:18:18Z (GMT). No. of bitstreams: 1 DISS_2015_Jennifer Cardoso Farias Almada.pdf: 5724861 bytes, checksum: 75d76d597050375391c29d0a04f80995 (MD5) Previous issue date: 2015-08-28 / CAPES / Os estágios do período pós-cosilisional do Ciclo Brasialiano/Panafricano na região de Cocalinho, porção leste do estado de Mato Grosso, divisa com o estado de Goiás, é marcado por corpos graníticos intrusivos associados a rochas máficas e ultramáficas. O Plutão Itacaiu é um corpo extenso e alongado segundo um trend regional, na direção NE/SW. É caracterizado por um magmatismo expressivo de natureza alcalina e composição que varia de monzo a álcali-feldspato-granitos. Este extenso corpo é definido por três fácies petrográficas denominadas de Fácies Biotita-Granito, Fácies RiebeckitaBiotita-Granito e Fácies Biotita-Granito Porfirítico. Os granitóides imprimem evidências de processos deformacionais decorrentes de duas fases de deformação, representada principalmente pelo desenvolvimento da foliação penetrativa marcada pela orientação preferencial dos minerais placóides, com direção NE e mergulho para SE, variando de baixo a alto ângulo, e foliação milonítica decorrente do cisalhamento de característica transcorrente. A composição química permitiu classificar essas rochas como granitos do tipo-A, gerados em ambiente de arco magmático e intra-placa pós-colisional. Dados geocronológicos U/Pb extraídas de cristais de zircão indicaram idade de cristalização variando de 806.6±4.0 a 582.9±6.3 Ma, consistentes com aquelas registradas para o Arco Magmático de Goiás. Idades modelo TDM= 0.97 a 1.08 Ga, mostram valores positivo εNd(T) = +4.39, +4.31,+3.69. Os valores positivos de εNd sugerem um empobrecimento do magma que deu origem aos granitóides em ETR leves. O valor negativo de εNd indica origem a partir de fusão parcial de crosta continental Paleoproterozóica. As rochas máficas-ultramáficas ocorrem alinhadas aproximadamente a leste-oeste, com variáveis níveis de alteração. Definem um magmatismo toleítico a cálcio-alcalino, metaluminoso, de caráter intermediário a ultrabásico. Os estudos isotópicos sugerem caráter juvenil do magma parental, devido aos valores positivos de εNd(T). As idades modelo variam de TDM = 0,71 a 1,44Ga e estão relacionadas a outras unidades de rochas juvenis do Arco Magmático de Goiás / Post-collisional stages of the Brasiliano/Pan-African Cycle in the region of Cocalinho on eastern Mato Grosso, bordering the State of Goiás, are represented by granitic intrusive bodies associated with mafic and ultramafic rocks. The Itacaiu Pluto is an NE-SWelongated body conform to the regional trend. It is characterized by a expressive magmatism of alkaline nature and composition ranging from monzo the alkali-feldspargranites. This extensive body is defined by three petrographic facies termed biotitegranite Facies, riebeckite-biotite-granite Facies and biotite-granite porphyry Facies. The granitoids show evidence of deformational processes resulting two-phase of deformation, represented mainly by development of penetrative foliation marked by the preferred orientation of minerals placoid, with direction NE and dip to SE, ranging from low to high angle, and mylonitic foliation resultant by strike-slip shear. The chemical composition allowed to classify the rocks as granite type-A, generated in magmatic arc environment and intra-plate post-collisional. Geochronological data U / Pb extracted in zircon crystals indicated crystallization age ranging from 806.6 ± 4.0 to 582.9 ± 6.3 Ma, consistent with those recorded for the Goiás Magmatic Arc. model ages TDM= 0.97 to 1.8 Ga, show positive values of εNd(T) = +4.39, +4.31,+3.69. Positive values of εNd suggest impoverishment of the magma that gave rise to the granitoids in LREE. The negative value of εNd indicates origin from partial melting of continental crust Paleoproterozoic. The rocks mafic-ultramafic occur aligned approximately east-west, with varying degrees of alteration. Define a tholeiitic to calcium-alkaline magmatism, metaluminous, of character intermediate to ultrabasic. The Isotopic studies suggest juvenile character of the parental, magma due to positive values εNd(T). The model ages ranging from TDM = 0.71 to 1,44 Ga and are related to other units of juvenile rocks of the Goiás Magmatic Arc.

Submitted by Simone Souza (simonecgsouza@hotmail.com) on 2017-11-06T16:06:43Z No. of bitstreams: 1 DISS_2014_ Regiane Ferreira de Oliveira.pdf: 6027017 bytes, checksum: f165c49fb24857b10d67f0c0b49ba85f (MD5) / Approved for entry into archive by Jordan (jordanbiblio@gmail.com) on 2018-02-02T15:10:33Z (GMT) No. of bitstreams: 1 DISS_2014_ Regiane Ferreira de Oliveira.pdf: 6027017 bytes, checksum: f165c49fb24857b10d67f0c0b49ba85f (MD5) / Made available in DSpace on 2018-02-02T15:10:33Z (GMT). No. of bitstreams: 1 DISS_2014_ Regiane Ferreira de Oliveira.pdf: 6027017 bytes, checksum: f165c49fb24857b10d67f0c0b49ba85f (MD5) Previous issue date: 2014-03-21 / Este trabalho apresenta os resultados de estudos geológicos e petrográficos realizados na região do Distrito de Noroagro – município de Comodoro no Estado de Mato Grosso com enfoque na geoquímica e geocronologia Sm e Nd de diques e “plugs máficos”, intrudidos nas rochas do Granito Rio Piolho e do Complexo Rio Galera. Os diques estudados situam-se no sudoeste do Cráton Amazônico na província Rondoniana San – Ignacio, especificamente nos domínios da Faixa Alto Guaporé. Petrograficamente, as rochas apresentam como aspectos macroscópicos feições estruturais características de rochas maciças de granulação fina a media variando de máficas a ultramáficas e cor cinza- esverdeada a preta. Apresentam texturas inequigranulares e composição gabroica ou peridotítica, constituídas, essencialmente, por minerais máficas (piroxênios e anfibólios) e plagioclásio por vezes alterados por processos de saussuritização. Opticamente, são rochas holocristalinas, textura ofítica a cumulática (peridotitos) onde os piroxênios representam à fase cumulus e os plagioclásios a fase inter-cumulus. Dados geoquímicos enfatizam que o magmatismo é do tipo toleítico, de natureza subalcalina, estando a totalidade das rochas no campo dos Basaltos de Fundo Oceânico – OFB (Ocean Floor Basalts), sendo que duas amostras apresentam assinatura de arco de ilhas. Datações de Sm- Nd indicaram idades de 1,24 , 1,27 e 1,57 (Ga) e apresentam ɛ Nd (t)a entre +6,27e + 6,50 para os gabros +5,80 para metapiroxênito. Os valores positivos de ɛ Nd (t)a juntamente com a razão 87Sr/86Sr de 0,704 para litotipo metagabro confirma que as rochas máficas –ultramáficas da região da Fazendas Maringá e Imaculada são derivadas de manto empobrecido / This works presents the results of Geological studies and petrographics realized in the Noroagro District, Comodoro municipality of Mato Grosso State focused on Geochemistry and Sm/Nd geochronology of dykes and maphic plugs emplaced in Rio Piolho Granite and Rio Galera Complex. The studied dykes is located in southwest of Amazonian Craton, Rondonian-San Ignácio Province, specifically in the Alto Guaporé Belt. Petrographically the rocks exhibit macroscopic strutural feature characteristics of massiveslightelly oriented rocks, fine to médium grain ranging of mafic to utramafic composition and greenhish – gray to black color. They presets inequigranular textures and gabbroic or peridotite composition, consisting essentially of mafic minerals (pyroxene and amphibole) and sometimes altered plagioclase and its partial saussuritization process. Optically Show holocrystalline granular rocks, with cumulate and ophitic texture ( peridotites) where pyroxene representes the cumulus crystal phase and the plagioclase inter-cumulus phase. Geochemical data emphasize that the magmatism is tholeiitic with sub-alkaline nature, being all of the rocks in the field of Ocean Floor Basalts (OFB) and two samples representes signatures island arc. Geochoronological Sm-Nd data indicated ages of 1,24 ,1,27 and 1,57 (Ga) and Show ɛ Nd (t)a between + 6,27 and +6,50 for gabbro and +5,80 for pyroxenite. The positive ɛ Nd (t)a values together with razão 87Sr/86Sr ratio of 0,704 for metagabbro suggests for the mafic- ultramafic rocks of region of Maringa and Imaculada Farm are derived of depleted mantle.