Caracterização das emanações gasosas de hidrocarbonetos na região do Remanso do Fogo (MG), através do uso integrado de sensoriamento remoto, geoquímica, geofísica, geologia estrutural e espectrometria de reflectância

Mapas de íso-concentração de hidrocarbonetos gasosos, juntamente com dados de levantamento espectral aéreo e terrestre foram integrados à imagens do LANDSAT TM com o objetivo de estudar as emanações naturais de gás existente numa região conhecida como Remanso do Fogo, localizada no interior da Bacia Proterozóica do São Francisco, no norte do Estado de Minas Gerais. Técnicas de realce aplicadas em imagens digitais mostraram a existência de anomalias espectrais relacionadas à diferenças de coloração dos solos e diferenças na densidade da cobertura vegetal, dentro de uma área de plantio de eucaliptos. A análise geoquímica de amostras de solo, mostram, em alguns casos, a correlação espacial entre a elevada concentração de hidrocarbonetos gasosos e as anomalias do TM. Informações de campo comprovam que as anomalias espectrais identificadas encontram-se relacionadas à existência de áreas onde os eucaliptos encontram-se pouco desenvolvidos mostrando claros sinais de deficiência nutricíonal. Além disto, solos localizados dentro das áreas de anomalias geoquímicas de hidrocarbonetos apresentam uma coloração cinza, diferente da coloração marrom avermelhado dos solos posicionados fora das áreas de anomalias. Curvas espectrais de amostras de solo, coletadas dentro e fora das anomalias geoquímicas de hidrocarbonetos comprovam estas diferenças. Da mesma forma obteve-se dados espectrais utilizando-se um sistema aerotransportado (SADA) operante no intervalo entre 400 e 1100 rim. A integração destes dados de natureza distinta revelaram a presença de anomalias combinadas significantes de solo e vegetação, causadas provavelmente pela ocorrência dos hìdrocarbonetos gasosos. A interpretação dos elementos estruturais de campo e do perfil sísmica de reflexão demonstraram que o sistema de falhas inversas com trend N30-40E e o sistema de juntas (N30E e N40-60W) controlam as emanações de hidrocarbonetos gasosos. A fim de melhor investigar este fenômeno e objetivando-se obter o melhor entendimento dos efeitos causados pelos hidrocarbonetos gasosos no solo e na vegetação, foi desenvolvido um experimento que ocorreu dentro de um ambiente  controlado (greenhouse). Três conjuntos de vasos contendo solos coletados na área de estudo e duas espécies de vegetação (eucalipto e gr~ea) foram utilizados. Hidrocarbonetos gasosos foram injetados continuamente durante o experimento em um período de oito semanas em dois conjuntos de vasos. O terceiro conjunto de vasos, não afetado pela injeção do gas, foi utilizado para comparação no decorrer do experimento. As características físicas, químicas e radiométricas dos solos e vegetação foram quantificadas e avaliadas para todos os conjuntos de vasos. Medidas radìométricas da vegetação foram realizadas periodicamente através do espectroradiométro portátil Spectron SE-590, operante na faixa entre 400 e 1100 rim do espectro eletromagnético. A presença dos hidrocarbonetos gasosos no sistema causou mudança nos padrões espectrais e químicos da vegetação devido à deficiências nutricionais comprovadas. As curvas espectrais das folhas de eucaliptos e das gramínea demonstraram um aumento do albedo nas faixas do visível e infravermelho próximo. Observou-se uma migração do gradiente abrupto da curva espectral da vegetação (red edge) em direção a comprimentos de onda inferiores (blue shift). Mudanças no conteúdo relativo dos nutrientes, tais quais nitrogênio, fósforo, potássio, cálcio, zinco e ferro também detectados, resultaram na clorose das folhas. O hidrocarboneto gasoso também modificou as características espectrais dos solos, que demonstraram um decréscimo do albedo acima dos 550 rim. Tal fato é corroborado pela coloração do solo observada variando de tons de marrom amarelado do solo original para tons de marrom nos solos injetados com hidrocarbonetos gasosos. Interpretou-se estas mudanças cromáticas como uma indicação da mudança química evidenciada pela redução dos íons férricos ^{Fé, 3} para os íons ferrosos Fe".

Abstract:  Hydrocarbon soil geochemistry and airborne spectrometry survey were integrated with Landsat Thematic Mapper - LANDSAT TM - imagery for an arca known asRemanso do Fogo, located in a portion of the São Francisco basin in Central Brazil, where hydrocarbon seeps were previously known. Digital image enhancement allowed the identification of spectrally anomalous arcas related to different soil color and geobotanical anomalias within an extensiva eucalyptus plantation. Soil geochemistry showed, in some placas, spatial correlation between high leveis of gaseous hydrocarbons and TM anomalias. Field checking of these anomalias revealed that eucalyptus specimens in the anomalous arcas were poorly developed, showing olear signs of nutritional deficiency. Furthermore, soils froco sitas corresponding to geochemical anomalias had a distintiva gray color differing froco the usual brownish-red color of surrounding superficial soils. Reflectance spectra were measured for soil samples froco the anomalous and non-anomalous arca and showed differences. Spectral data werecollected ovar anomalous and non-anomalous eucalyptus stands, using an airborne system operating between 400 and 1100 nm. The integration of these different data seis reveals the presente of a significant combined soil-vegetation anomaly, caused probably by long-terra hydrocarbon gasêeepage. The interpretation of field structural data and reflection seismic profiles shows that N30-40- ending thrust faults and two joint systems (N30E and N40-60W) control hydrocarbon gas seepage. To further investigate the phenomena and to understand the effects of hydrocarbon gas in soils and vegetation, we devised an environment-controlled (greenhouse) experiment. Three seis of vessels containing soilcollected in the study ares and two different vegetation assemblages (eucalyptus and grass) were used. Hydrocarbon gas was injected continuously throughout the experiment (8 weeks) finto two seis of vessels. The third set of vessels, in which no gas was injected, was used for comparison throughout the experiment. Physical, chemical and radiometric characteristics of soils and vegetation (leaves) were measured and evaluated for both sete. Radiometric measurements on vegetation were made periodically using a Spectron SE-590 handheld radiometer, operating in the 400 to 1,100nm range. The presente of hydrocarbon gas caused changes on the spectral and chemical pattems of the vegetation due to nutritional deficiencies. Spectral curves of eucalyptus and grass leaves showed an overall increase in albedo within the visible and near infrared range. A shift of the vegetation red edge towards smaller wavelengths lias been observed (the "blue shift"). Changes on the relativa content of nutriente such as nitrogen, phosphorus, potassium, calcium, zinc and irou was also detected, which resulted in chlorosis of the leaves. Hydrocarbon gas also modified the spectral characteristics of the soils, which showed a decrease in albedo above the 550-nm region. The fact is supported by the observed soil color changes, ranging froco yellowish-brown tones in the original soils to brown tones in the gas-injected soils. We interpret this as an indication of chemical modification of the ferric ions, which have been reduced to ferrous ions.

A região de Castro é constituída por uma bacia extensional, Eo-Cambriana e Eo-Ordoviciana tardia a pós-Brasilianok. Diques e plugs andesíticos cortam sedimentos pelíticos e rudáceos bem laminados, com tufos e ignimbritos subordinados. Um complexo de domos riolíticos maciços a extremamente bandados por fluxo, originado em vários pulsos magmáticos, tufos e epiclásticas completam a sequência, próximo à cidade de mesmo nome no centro -leste do estado do Paraná. As rochas da bacia hospedam mineralização aurífera epitermal de baixa sulfetação, a primeira de seu tipo e idade a ser descrita no Brasil. O ouro é encontrado tanto nas rochas intermediárias e félsicas. Sedimentos são estéreis mas os  contatos entre as rochas vulcânicas e estes são locais de silicificação e mineralização. A textura comun aos veios mineralizados é a substituição de carbonato, e cinábrio e arsenopirita ocorrem em pequena quantidade. Calcedônia, calcita, ilita e barita são típicos como minerais e ganga. Também ocorrem hematita, limonita e goetita, em geral em fraturas e/ou cavidades, fluorita, sericita e epidoto. Estibnita, zeolita, e granada ocorrem localmente e em pequena quantidade. A geoquímica multielementar de 750 amostras de sedimento de corrente nas frações acima e abaixo de 80#, além de contagem de pintas em concentrado de batéia, foram importados de arquivos de resultados enviados pelo laboratório e associados através do número da amostra às coordenadas das estações de amostragem, obtidas por GPS. Cartas topográficas 1:50.000 foram digitalizadas em CAD e editadas em SIG para obtenção de uma base, e as bacias hidrográficas foram delimitadas. Cada bacia foi associada à amostra correspondente. Mapas geológicos de diversas origens e fotointerpretação 1:60.000 das estruturas foram igualmente digitalizadas, georreferenciadas, editadas e integradas em SIG. O modelamento em SIG de associações de elementos farejadores da geoquímica multielementar,  selecionados tanto pela técnica knowledge driven quanto data driven, leva à seleção de quatro grupos de onze bacias, por sua vez também relacionadas à estruturas ou contatos litológicos, a serem investigados para mineralizações aflorantes ou não. O ponderamento dos valores de ouro pela sinuosidade das drenagens amostradas permite a filtragem dos efeitos de dispersão física e de acumulação do ouro, resultando em um mapa de anomalias modificado, que melhor representa a distribuição química original  do ouro nas rochas, e portanto, de anomalias correlacionáveis à mineralizações.                          

Abstract: Castro is an extensional, Eocambrian to Eordovician late to post-Brasiliano foreland basin. Plug and dyke bodies of andesite cut pelitic and rudaceous sequences of well-bedded red to green siltstone and sandstone, with subordinate ignimbrite. A dome complex of massive to highly flow-banded rhyolite from several pulses, tuff and epiclastics, fill the basin nearby the town of the same name, in central-eastern state of Paraná. The basin is host to lowsulphidation epithermal gold mineralization, the first of its type and age to be reported in Brazil. Gold is found in both intermediate and felsic volcanic rocks. Sediments are virtually barren, but rhyolite / sediment contacts are known sites of silicification and mineralization. Carbon replacement is a common vein texture and cinnabar and arsenopyrite occur in small quantities. Chalcedony, calcite, illite and barite are typical gangue minerals. Also present are hematite, limonite and goethite, usually in fractures and/or cavities, fluorite, sericite and epidote. Stibnite, zeolite, and garnet occur locally and in small quantities. The integration, validation and analysis at different scales of the great diversity of data suitable for the exploration of commodities associated with epithermal systems, are met by the implementation of a Geographic Information Systems (GIS). Data used in deposit modeling includes multielementary geochemistry in various media and regional and detail geological mapping. Multielementary geochemistry of 750 stream sediment samples in two sieve fractions (above and below 80#), plus color count for gold in pan concentrates collected nearby the stream sediment stations, were captured from lab result spreadsheets and associated by their corresponding sample number to sample site location obtained from GPS. Topo sheets in 1:50.000 scale were digitized in CAD to provide a base map and edited in the GIS to become seamless; catchment basins were delimited and each basin was assigned its corresponding sample. Geology maps and photointerpretation of structures were also digitized, georeferenced and edited for consistency in the GIS. Modeling by GIS, using both knowledge driven and data driven pathfinder associations for multielementary geochemestry, lead to selection of four clusters of eleven catchment basins, which are related to structures or lithological boundaries, to be investigated for surfacing and non-surfacing orebodies. Weighting gold values based on sinuosity of the streams, to filter out the effects of physical dispersion and accumulation of gold, results in a modified anomaly map which more closely represents the original chemical  distribution of gold in rocks, and thus anomalies related to mineralization.

Abstract: The scientific and technical activies of gological survey, or geologic mapping, provides the necessary information to exploitation of mineral, energetic and water resources, to prevention of natural hazards and to protection of the environment. These activities are not a simple data collection task but a highly specialized and interpretative work. All over the world , its execution has been done by public agencies normally called “geologic survey”. This work discussed and comparatively analyzes the evaluation mechanisms of the geologic mapping activities currently adopted by the nacional geological surveys (GSs) of England, United States, Canada, France, Finland, South Africa, Australia and Brazil, and also the evaluation programs which these organizations have been submitted. In the same way as other scientific and technological activities, the geological surveys activities are complex and very hard to be evaluated. While European research institutions began to be evaluated in late 70’s, the GSs started to be evaluated in 80’s, however most of the evaluation programs were established in the 90-decade. The initiative for the evaluation/review of the GSs has been arisen from government or agencies of publics policies at high level hierachy, i.e.,from top to bottom, and from outside to inside the corporation. On the trail of the evaluation programs the GSs organizations have been restructured to be adapted to new reality and social demands. One common recomendation of these evaluation programs has been to establish or to strenght a Board,Advisory Councils or Advisory Committees with representatives from the privete sector, universities and other governmental agencies.
The specificevaluation of the geologic mapping activities is also a recent practice that the GSs of developed countries startedin the late 80’s na which steel is under way. The mechanisms and processes utilized, such as peer review process, and the establishment of advisory councils or advisory committees, are essentially qualitative.
The establishement of advisory council and/or advisory committees including representatives from the clients, users and stakeholders, in the planning, monitoring and evaluation of the geologic surveys projects and programs, constitutes a current and future trend in the management of the GSs organizations that approaches to the first primary tenet of the Total Quality Management – the customer is the ultimate determiner of quality. The presence of regional GSs, advisory councils/committees, universities, as well as associations of mineral and oil producers, or entities, as the American Association of States Geologists, in interaction with nacional GSs, characterize the existence of a heavy net of social relationship. This “social network” is clear in GSs of developed countries, while in GSs of developing countries like Council for Geoscience (South Africa) and Geological Survey of Brazil (CPRM) this social network may be considered incipient.

Abstract: The platinum-group elements metallogeny of the Paraná Continental Igneous Province is evaluated from new geochemical (major, trace, rare-earth and platinum-group element) and geochronological eoAr--39Ár) data. The Paraná rocks vary widely in chemical composition but can be categorised into five basic units (Gramado, Esmeralda, Paranapanema, Pitanga and Urubici) and three acid units (Ca)ias do Sul, Santa Maria and Chapecó). The low-Ti and low-P basic units (Gramado and Esmeralda) and the associated low­Ti acid units (Caxias do Sul and Santa Maria) are located at the south - southeast of the province. The basic units of Ti and P intermediate (Paranapanema) and high (Pitanga) and the associated high-Ti acid unit (Chapec6) dominate in the north-northwest. The Urubici unit (high-Ti and -P) occurs interbedded with Gramado unit at the eastern border of the province in Santa Catarina state. This observed preferable distribution of the magmatic units does not confirm the geochemical subdivision of the province in three main zones: North, Central and South. Also, the Rio Uruguai and Rio Piquiri lineaments have no obvious control on the nature and distribution of the magmatic units. The distinct geochemical signatures of the basic units can be related to different grades of partial melt of the continental lithospheric mantle, with the crustal contamination playing an important role in the evolution of the Gramado unit (Th/Ta - 8,2). The genesis and evolution of acidic units were related to the evolution of the basaltic units, to which they occur associated. The geochronological data indicated that the magmatism of the Paraná province lasted about 3,5 My (between 133,90 and 130,36 My) with a mean eruption rate of 0,23 km3.yrl and was linked to northward opening of South Atlantic ocean. From the PGE geochemistry, the Paraná basalts were characterised as highly fractionated (Pd/Ir = 75), and that were generated from S-undersaturated magmas. This favourable condition together with the geological controls of Ni-Cu-PGE ore deposits in CFB provinces allows to indicate the Gramado unit (low-Ti and -P) at the eastern border of the province, as the principal target for this kind of deposit. However the potentiality of the other basic units of the province cannot be ignored, because the low PGE abundance of some flows of the Pitanga unit might be related to the segregation of sulphides during the ascension of those magmas.

Abstract: The Bahia State, Brazil, hosts a number of tholeiitic and alkaline dyke swarms that evolved within several geologic periods spanning from the Archaean-Paleoproterozoic to the Phanerozoic. The alkaline provinces are restricted to the Meso-Neoproterozoic interval and are usually associated with brittle shear zones such as the Itabuna-Itajú do Colônia Shear Zone (IICSZ), the focus of this thesis. The IICSZ is a N45°-trending, 30km wide, intracratonic shear zone, extending for some 150km through the SSE portion of the Bahia State. The IICSZ is closely related to dykes and syenites of the Southern Bahia Alkaline Suite and its southwestern extension is cut by the N140°­trending, ductile-brittle Potiraguá Shear Zone (PSZ). The PSZ is located in the tectonic limits between the Neoproterozoic Araçuaí Mobile Belt and the Archaean-Paleoproterozoic Sao Francisco Craton. The study of kinematic indicators in faults, fractures and dykes planes of both the IICSZ and PSZ indicated that two tectonic phases were responsible for their present structure. The first phase was connected to a N-S compression that triggered reverse faulting in the PSZ e sinistral transpressional shearing in the IICSZ. The second phase was akin to a E-W compression that resulted in sinistral and dextral transtension strains in the PSZ and IICSZ, respectively. The alkaline dykes were emplaced later in the first phase and throughout the second phase. Palaeostress fields in both the IICSZ and PSZ were controlled by the orientation of the far-field stress, disturbances in field stress around re-actived shear zones, 3D-geometry of shear zones, tension canalization along shear zones, position of secondary faults and fractures and orientation of shear zones in relation both to the limit of the Araçuaí Mobile Belt and the Sao Francisco Craton and to the site of intersection between the IICSZ and the PSZ (where tension vectors converged to). Magmatic flow patterns associated with the shear zones were yielded from 524 dykes in the IICSZ. These were divided into two distinct groups: (i) a radial pattern, related to magmatic fracturing and displaying centre-divergent flow sense and (ii) a linear pattern, arranged in parallel to sub-parallel position to the shear zone. Alkaline dykes comprised in linear patterns were emplaced during active shearing. They were modelled in this study in order to simulate all possible orientation of magma flow indicators that might be produced within a vertical dyke emplaced under coeval internal and external stresses. The effect of magmatic driving pressures were portrayed in terms of magma flow velocities (MFV) and the external stresses in terms of wall motion velocities (WMV) divided by two (WMV/2). Using these assumptions, five cases were proposed: MFV>>WMV/2, MFV>WMV/2, MFV=WMV/2, MFV<WMV/2 e MFV<<WMV/2. The model was tested in the field using dykes hosted in the central portion of the IICSZ. Comparisons of features predicted in the model with those observed in the field showed a remarkable equivalence, improving on aspects of paleostress analysis of dykes emplaced under similar tectonic environments. The IICSZ and PSZ dynamic evolution along the Paleoproterozoic and Neoproterozoic was accessed from new Sm/Nd, Ar/Ar e Pb/Pb isotopic data stemming from a number of plutonic bodies in the region. Among the results, the following Pb/Pb ages are highlighted: (i) the 2089±4 Ma Pau Brasil anorthosite; (ii) the 2087±1 Ma to 2079±4 Ma Potiraguá granite; (iii) the 688±10 Ma Ibicaraí and the 732±3 Ma Potiraguá syenites and (iv) the 676±15 Ma Potiragud and the 551±36 Ma Itabuna felsic dykes.

Abstract. This thesis proposes an interpretation of the tectonic evolution of the AlgodoesChoro Metamorphic Suite (ACMS) - a paragneiss-amphibolite association intruded by granite-tonalite orthogneisses that crops out in the central region of the Ceara State, NE Brazil. The geological data support the division of this suite in the following units: 1) Algodões amphibolite - garnet-bearing and garnet-free amphibolite found in the homonymous village of the Quixeramobim district; 2) Choro meta-sedimentary unit - biotita-gneisses with quartzites and metaconglomerate horizons croping out around the Choro Limão dam; and 3) granite-tonalite orthogneisses - intrusive bodies into the older units as stocks, dikes and sheets.
The fine grained garnet-free amphibolite of ACMS was interpreted as tholeiite lavas having flat chondrite-normalized rare earth element patterns (REE), and negative Nb-Ta anomalies and positive Sr anomaly on primitive mantle normalized multi-elements diagrams. These rocks yielded a whole-rock Sm-Nd age of 2,240±50 Ma with Nd model
ages (TDM) varying between 2,403-2,257 Ma with positive ENd values. Petrogenetic modelling suggests the derivation of these rocks from a Depleted Morb Mantle source. The Choró meta-sedimentary unit was characterized as dominantly feldspar-rich metagraywackes made up of fragments of mafic and felsic-intermediate igneous rocks. The enrichment in Sc and Co relative to La and Th supports this assumption. The REE-patterns are fractionated without prominent Eu-anomalies. Isotopic data indicate Nd model ages (TDM) in the interval 2,449-2,216 Ma and positive ENd values. In general the granitetonalite orthogneisses of ACMS have a calc-alkaline geochemical signature, strong fractionation between the large ions lithophile and high field strenght elements, positive ENd values and low 87Sr/ Sr initial ratios (0,7013-0,7018). A small stock of high-alumina tonalite orthogneiss located in the Algodoes village yielded a precise single grain zircon UPb age of 2,131±12 Ma and single grain zircon Pb-Pb evaporation age of 2.123±20 Ma. Similarly, a meta-andesite dike and a granitic sheet respectively yielded a poor single grain zircon U-Pb ages of 2.137±34,8 Ma and 2.056±164 Ma, as well as a single grain zircon Pb-Pb evaporation ages of 2.153±5 Ma and 2107±16Ma. Petrogenetic modelling admits the generation of the tonalite orthogneiss through partial melting of garnet-amphibolite. Structural data demonstrate that the tectonic units of the studied area, i.e., ACMS, Quixeramobim metapelitic unit and Quixadá-Quixeramobim Granitic Complex have their tectonic evolution significantly controlled by movements of the Sen. Pompeu, Quixeramobim, and Custodia ductile shear zones. The clockwise kinematics characterized in the shear zones coupled with progressive change from mylonitic to regional scale foliation suggest that the structural evolution was largely achieved under transpressive conditions. However, the late stage of tectonic evolution was characterized by inversion of the transpressive regime to a transtensional one. Finally, it is suggested that the supracrustal sequence of ACMS was generated in a back-arc basin around 2,24 Ga, followed by emplacement of tonalite-granite bodies between 2,17-2,05 Ga. As such, the AlgodoesChoro Metamorphic Suite constitutes a juvenile segment of the Transamazonian/Eburnean orogeny (ca. 2,1±0,1 Ga). However taking into account the 40Ar/39Ar ages of the literature it is admitted that the above referred to units have been reworked between 580 Ma and 530 Ma, during the formation of Western Gondwana.

Abstract. The Itapicuru River greenstone belt of the (IRGB) is outstanding as one of the most important Paleoproterozoic belts in the northeastern portion of the Sao Francisco Craton. Various small and medium-sized deposits of mesothermal gold occur in this belt, located in the central-northern (Maria Preta district) and southern (Fazenda Brasileiro district) sectors of the greenstone belt. U-Pb SHRi P dating on zircons, monazite and xenotime derived from felsic intrusive rocks from both districts, indicate that the granite-greenstone terrain of the River Itapicuru developed in two stages between 2152 - 2080 Ma. The first was characterized by the generation of magmas derived from the mantle (2152 - 2130 Ma), and the second by the production of syntectonic granitoids (2130 - 2080 Ma) as a result of reworking of archean basement rocks. The older intrusions are indicated by ages of 2152 ± 6 Ma in monazite, and 2155 ± 9 Ma in zircons derived from the Trilhado granodiorite in the northern region of the belt, and by the ages of 2130 ± 7 Ma and 2128 ± 8 Ma in zircons derived from tonalite, and by Teofilândia quartz-feldspar porphyry in the southern region of the belt. The ENd(t) and 87Sr/86 Sri signatures provided by these granitoids are compatible with a depleted mantle, the less radiogenic 87Sr/%6Sr; (0.70167) and more positive sNd(t) (+ 2.65) values being provided by the Trilhado granodiorite. The evolution trajectories of these rocks and the andesites show that they are cogenetic. A common source is indicated by their TDM ages of around 2.2 Ga. This data is consistent with the development of a magmatic arc, whose progressive tectonic accretion must have occurred during the subsequent closure of the back-arc basin. The predominance of inherited zircons and the abundance of gneiss inclusions in the granodiorites of the Ambrósio dome suggest that the basement of the supracrustal rocks was composed of continental crust rocks with components of 2937 ± 16 Ma, 3111 ± 13 Ma and 3162 ± 13 Ma. This legacy suggest an important crustal reworking phase succeeding the formation of the magmatic arc and mark the period of highest thermal and tectonic activity in the orogenic belt. The emplacement age of the Ambrósio dome is indicated by few zircons in the granodiorites dated at 2077 ± 22 Ma and 2063 ± 55 Ma, and by xenotime grains derived from a granite dyke, which provided an age of 2080 ± 2 Ma. The latter is the best estimate of the crystallization age and probably marks the end of the felsic magmatism. This age shows good agreement with the Ar-Ar plateau age of 2080 ± 5 Ma obtained in homblendes from an amphibolite occurring close to the edge of the Ambr6sio dome, and with a U-Pb SHRIMP age of 2076 ± 10 Ma obtained in overgrowths of detrital zircons from a quartzite occurring close to Vila de Monte Santo, interpreted as the age of the metamorphism. This data suggests that the metamorphism must have reached maximum intensity around 2080 Ma. The Ar-Ar plateau ages of 2050 ± 4 Ma and 2054 ± 2 Ma provided by the hydrothermal muscovite samples were interpreted as the minimum ages for gold mineralization in the Fazenda Brasileiro district and must be close to the true age of gold deposition. The Ar-Ar data indicate that the mineralization must have occurred until 30 Ma after the peak of the metamorphism. The isotopic composition of the mineralizing fluids in the Fazenda Brasileiro mine is compatible with deep sources, either the depleted mantle or lower crust reservoirs, as indicated by the Sr-Sri ratios (0.70238 and 0.70260) and sNd(t) values (1.68 to 6.61) in scheelite and calcite, and by the S 34S values in pyrite and pyrrhotite (-1.11 %o and +1.23 %o). However, these fluids must have interacted with more evolved reservoirs, as indicated by: (1) isotopic Pb data, which suggest a mixed (orogenetic) or upper crust reservoir; (2) the higher values of de b 34S (+0.90 and +5.47 %.o) at Fazenda Maria Preta, and (3) the Sr-Sr ratio in calcite from Fazenda Maria Preta (0.70328), more radiogenic than the calcite and scheelite from Fazenda Brasileiro. The mineralizing fluids do not demonstrate a temporal relationship with the juvenile magmatism of the orogenic belt (2152 - 2130). Possibly, they were produced at depth by the metamorphism of the ocean crust subducted between 2130 and 2090 Ma. They ascended during the uplifting and exhumation of the orogenic belt, between 2080 and 2050 Ma, through conduits with a high inclination angle and along old shear surfaces reactivated by the extensional tectonics.

Abstract.The Ambrosio Dome is a 40 km long, up to 8 km thick eliptic body emplaced into volcanic-sedimentary rocks of the Palaeoproterozoic Rio Itapicuru greenstone belt. Geologic mapping of the dome allowed us to distinguish three main igneous suite, namely (i) granodioritic to tonalitic orthogneisses, (ii) monzogranite and porphyritic to equigranular granodiorites, and (iii) granitic-, pegmatitic and aplitic dykes, and quartz veins. In addition to these rock units, the dome comprises large domains of migmatic gneisses, migmatites and undifferentiated granites to granodiorites, with complex field relationships. The region underwent two events of deformation of NW-SE direction. The first (En) is a low-angle thrust which is marked by down-dip strechting lineations on the western border of the dome and its country-rocks. The second one (En+l) is a left-sense transcurrent tectonics that wipe out most of the early structure. This event comprises three progressive deformation phases with the following characteristics: (i) the first was responsible for the development of N-S oriented, high- to moderate dipping, solid-state and magmatic planar structures, as well as subhorizontal mineral lineations; (ii) the second is marked by the intrusion of granitic and pegmatitic dykes, (iii) whereas the third is illustrated by folds with subhorizontal axis paralleling the strechting and (or) mineral lineations. The Ambrosio dome was emplaced syn-tectonically during the second deformation event (En+l) as evidenced by (i) widespread mylonitic foliation and strechting mineral lineations at the dome edges parallel both magmatic layering and mineral lineations on the dome centre, (ii) s-c relationships of biotite and quartz ribbons observed on the dome margin are identical to those in magmatic biotite of the dome central portion, (iii) oblique fabric of schlieren layering are concordant with solid-state fabrics of pegmatititc dykes, (iv) the emplacement age (2,080 Ma, U-Pb on xenotime) of granitic rocks of the dome is consistent with the metamorphic age (2,080 Ma, ArAr on hornblende) of host-rock amphibolite, (v) changes of magmatic textures into subsolidus ones ate hightemperature, (vi) magmatic segregation (leucossome or schlieren layering) parallel to solid-state foliations, (vii) foliation refraction from host-gneiss into granite dyke, and (viii) and dyke off shoots with magmatic fabric paralleling solid-state structures of the host gneiss. Furthermore, petrofabric studies of quartz c-axis on several rocks of the Ambrosio dome yielded a temperature range of 650-750 °C for planar structures nucleation. The crystalization age of rocks from the Ambrosio dome (2,080 Ma) coupled with inherited zircons (up to 3,160 Ma), Nd model ages between 3,059-2,586 Ma and negative epsilon Nd values (-10.67-4.35) indicate a significant contribution of older, basement rocks in the genesis of the dome. Whole-rock major and trace element geochemistry reflects a syn-collisional to volcanic arc signature, which is interpreted as inherited mostly from the basement protoliths. The presence of dykes, migmatite leucossomes and schlieren layering paralleling the major N-S axis of the dome, as well as the existence of left-lateral shear zones on both eastern and western margins of it, and the lack of high-angle lineations usually associated with diapyric ascent of magmas, strongly support a model of dome formation during the escape tectonics that followed a regional shortening from NW to SE.

A mineralização aurífera da Mina Córrego Paiol é associada às rochas da Seqüência Vulcano-Sedimentar de Almas (SVSA), terreno granito greenstone de Almas-Dianópolis, TO. A Formação Córrego Paiol, unidade metavulcãnica da SVSA, é composta por metandesito, metadacito e por rochas metabásicas como metadiabásio e anfibolito. A unidade de topo desta seqüência é representada por metassedimentos da Formação Morro do Carneiro, tais como filitos sericíticos, quartzitos, formação ferrífera bandada e turmalinitos. Granitóides intrusivos do Batólito Serra das Areias e da associação TTG, são as rochas encaixantes da SVSA. A característica química dos metandesitos e metadacitos são compatíveis com rochas cálcio-alcalinas a tholeíiticas, enquanto as metabásicas seguem a tendência toleíitica. As rochas citadas são enriquecidas em LILE, ETRL e HFSE e originam-se em ambiente extensional ou de ri1 eamento de possível arco magmático à proximidade de uma margem continental ativa. As rochas graníticas intrusivas, quimicamente, descrevem uma tendência cálcio-alcalina e peraluminosa, estas possuem padrão altamente fracionado dos ETRL e anomalia negativa de Yb, formaram-se em possível ambiente de arco-vulcânico no campo dos granitos sin-colisionais. Dois eventos tectono-metamórficos foram identificados nas rochas supra citadas. 0 evento mais antigo D„ atingiu as rochas da associação TTG e da SVSA, em condições de fácies anfibolito médio. As estruturas de D_n são pertencentes à tectônica transtensional, formadas em regime de deformação dúctil, obliqua à direcional. Posterior e progressivamente instalou-se dentro de um regime compressional, transpressional, zonas de cisalhamento direcionais, de caráter dúctil-rúptil D„+1, responsável pelo retrometamorfismo das rochas em condições de fácies anfibolito baixo a xisto-verde, e pela colocação dos granitóides intrusivos em zonas transtensionais. No fechamento de D"1, houve aporte de fluidos hidrotermais canalizados em zonas de cisalhamento direcionais. Ao final da evolução tectono-estrutural, tanto as rochas das SVSA, quanto os granitóides intrusivos, foram afetados por zonas de cisalhamento rúptil D_n+2. São zonas rúpteis representadas por famílias de fraturas e falhas, de extensão T, sintéticas R, e antitéticas R' e sintéticas P. A mineralização na Mina Córrego Paiol, hospeda-se em rochas metabásicas controladas por cisalhamentos D,,+1, enquanto as mineralizações nas rochas graníticas são controladas por cisalhamentos D„+2. No entanto, ocorrem remobilizações das mineralizações de D_n+l para D„₊2, pela interseção destes sistemas de cisaihamento, formando sítios favoráveis a umneralizações auríferas de médio a grande porte, conhecidas como ore shoots, observadas na mina. Os fluidos responsáveis pela mineralização aurífera na mina, são aquosos com sais de Na, Ca, Mg e Fe, e nas rochas graníticas, aquosos com sais de Mg, Na. Estes fluidos possuem salinidade moderada à alta, atingindo até 40% NaCI para as rochas da mina e Thtotai da ordem de 450^°C. São responsáveis pela mineralização hospedada ao longo do strike das rochas do cisalhamento Dn+1. A mistura de fluidos causou o rebaixamento da temperatura até cerca de 100^°C, propiciando a instabilidade das condições fisico-químicas, propiciando para a deposição do ouro em estruturas rúpteis, contribuindo para um segundo pulso mineralizante do tipo ore shoots. Em resumo, o conjunto de fatores que controlaram a mineralização aurífera na Mina Córrego Paiol da SVSA, são a interseção da foliação S-C de S_n+₁ com planos extensionais Sn+2, que abriram espaços em zonas transtensionais pelas quais grande volume de fluidos passaram facilmente, resultando os ore shoots. Estudos de inclusões fluidas mostram uma gradual diluição dos fluidos de alta salinidade acompanhado pela decréscimo de temperatura que foram responsáveis pela mineralização aurífera.

Abstract: Gold mineralization at the Córrego Paiol mine is hosted by rocks of the Almas volcano­sedimentary sequence (SVSA) in the Almas-Dianópolis greenstone belt, Tocantins State, Brazil. The SVSA is a metavolcanic unit, the CórregoPaiol Formation, with meta-andesite, metadacite and metabasic rocks such as metadiabase and amphibolite. On top is the metasedimentary Mono do Carneiro Formation that consists of sericite phyllites, quartzites, banded iron formation and tourmalinites. Intrusive granitic rocks of the Serra das Areias Batholith and a TTG association are the country rocks of the SVSA. Chemical compositions show that meta-andesite and metadacite belong to a calc-alkaline t group; the metabasics follow a tholeiitic trend. Besides, the fresh, unaltered metabasics cluster in the field of continental basalts. These rocks are enriched in LILE, LREE and HFSE, and it is c therefore possible that they originated in an extensional setting, or rifted magmatic arc, close to  an active continental margin. The granitic rocks are peraluminous and follow a calc-alkaline trend. Their strongly fractionated LREE and a Yb anomaly suggest that they may have formed as syncollisional bodies in a volcanic arc. Two deformation events have been identified at the Córrego Paiol mine. The older D„ affected the TTG and the volcanic rocks, and reached middle amphibolite facies conditions. The structures related to D„ are transtensional, having formed in an oblique to directional ductile regime. The later ductile-brittle D,+1 deformation took place progressively in a compressional regime, giving rise to directional shear zones. This event resulted in retrogression of the rocks from amphibolite to greenschist facies, and also the emplacement of the intrusive granites in transtensional zones. The D_n+1 deformation enabled the passage of fluids in directional shear zones. The deformation events culminated in brittle D_n+2 shear zones that affected both the SVSA and the granitic rocks. The main structural elements of D_n+2 are faults and fractures of the type T­extensional, synthetic and antithetic R and R', and synthetic P. Gold mineralization at the Córrego Paiol mine is hosted by metabasic rocks and controlled by D.+1 shears, whereas the mineralization in the granitic rocks is controlled by D_n+2 shears. Nevertheless, there appears to have been a remobilization of gold from D_n+1 to D_n+2, as can be inferred from the intersection of the two shear zone systems that were favourable sites for gold deposition. This process led to the higher gold grades in ore shoots at the mine site. Fluid inclusion analysis revealed that the fluids associated with the ore at the mine are aqueous and saline with Na, Ca, Mg and Fe. Those in the granitic rocks are aqueous with K, Mg and Na salts. These fluids have moderate to high salinity, up to 40% NaCI for the rocks at the mine, and Th_totn, on the order of 450^° C. These are related to mineralization along the D_n+1 shear strike of the rocks. Lower temperatures around 100° C were recorded for brittle structures that contributed to the second pulse of mineralization and the formation of ore shoots. In summary, Gold mineralization is most probably related to the intersection of S-C foliations in dextral shear zones D_n+1 with D_n+2 brittle fault planes, opening transtensional zones through which large volumes of fluids could easily pass, resulting in ore shoot zones. Fluid inclusion studies show that gradual dilution of high salinity fluids accompanied by decreasing temperature may have been responsible for the mineralization.

A caracterização cristaloquímica da incorporação de íons Cu(II) em goethita (a-FeOOH) sintética foi estudada para definir, estruturalmente, o ambiente local do cobre na goethita. As amostras, preparadas em meio fortemente alcalino, foram caracterizadas química e mineralogicamente com ênfase à difração de raios X (DRX) e aplicação do método de Rietveld e espectroscopia de absorção de raios X (XAS) com fonte de luz síncrotron. A análise térmica diferencial (ATD) mostrou uma desestabilização na estrutura do mineral, através da diminuição da temperatura da segunda endoterma (296,3 - 290,3 oC), no decorrer da substituição. A análise de microscopia eletrônica de transmissão (MET) das amostras de goethita contendo cobre, mostrou que os cristalitos aciculares (0,7<Cu<1,6 mol%), no decorrer da incorporação, tornavam-se geminados em forma de estrelas (2<Cu<3,9 mol%). A aplicação do método de Rietveld mostrou que esta variação morfológica dos cristalitos afeta, diretamente, a orientação preferencial nos planos cristalográficos (100), (010) e (001), produzindo uma instabilidade estrutural ao longo dos eixos a e c. As variações locais no sítio do cobre, observadas com XAS, mostraram distorções nos octaedros de cobre, porém os encadeamentos poliméricos Fe(III) e Cu(II), conservam o mesmo ambiente estrutural do ferro. Os diagramas de densidade eletrônica (Fourier diferença) mostraram a existência de substituição isomórfica entre ferro e cobre. O desequilíbrio eletrônico gerado é compensado estequiometricamente com o aumento do teor de água, via inserção de hidroxilas, confirmando a fórmula estrutural [a-(Fe1-xCux)1-y/3O1-y(OH)1+y] proposta. A análise química e mineralógica mostrou, no entanto, que esta substituição isomórfica é limitada  a  3,9 mol%,  aproximadamente.   Para   teores   superiores,  a  hematita (a-Fe2O3) foi identificada como segunda fase mineralógica juntamente com goethita. Estes resultados, aplicados à formação de depósitos lateríticos, sugerem que estes seriam enriquecidos em cobre, por limitada substituição isomórfica Fe-Cu na estrutura da goethita, imobilizando o metal no meio superficial.                 

Abstract: The crystallochemical characterization of Cu(II) ions incorporated in synthetic goethite (a-FeOOH) was studied to define the structural local environment of copper in this mineral The samples were prepared under highly alkaline conditions and characterized chemistry and mineralogically with emphasis in Rietveld refinement using X-ray diffraction (XRD) data and X-ray absorption spectroscopy (XAS) with synchrotron light source. Results from differential thermal analysis (DTA) showed a decrease of the temperature of the second endoterma (296,3 - 290,3 ^°C) with substitution, interpreted as a structural instability. Transmission electron microscopy (TEM) of the Cu-goethite samples showed acicular crystallites (0,7<Cu<1,6 mol%) and star shaped particles (2<Cu<3,9 mol%) in the elapsing of incorporation. The application of the Rietveld method showed that this morphological modification of the crystallites affects, directly, the preferential orientation of the crystallographic plans (100), (010) and (001), producing a structural instability along the axes a and c. The local variation in Cu(II) sites, observed by XAS, showed distortions in the copper octahedra, but the polymeric linkages Fe(Ill) and Cu(II), preserve the structural environment of iron. The electron density diagrams (Fourier difference) confirmed the copper-iron isomorphous substitution in goethite. The generated electronic unbalance was, stoichiometrically, compensated by an increase in water content, through hydroxyl insertion, confirming the structural proposed formula (a-(Fel__XCu.)I__y/30,__y(OH)i.t_y]. The chemical and mineralogical analysis showed, however, that this isomorphic substitution is limited to 3,9 mol%, G approximately. With higher Cu values, hematite (a-Fe203) was identified as a second mineralogical phase beside goethite. These results, applied to the formation of I Iateritic deposits, suggest that these would be enriched in copper, by limited isomorphic substitution Fe-Cu in goethite structure, immobilizing the metal in the superficial environment.  

Abstract: The Quadrilátero Ferrifero is the most intensively studied area in Brazil due to its metallogenic potential and its comple? geological evolution. One of the most important investigations of this region was the aerogeophysical survey of the Rio da: Velhas Project (gamma-ray, magnetic and electromagnetic data). The high-resolution characteristics of this project have provides several studies in this region. However, some of the outlined goals haven't been reached, because it is possible to recognize nevi relationships between geophysical features and mineralization environments. Analysis of gamma-ray data from a selected are: where a series of gold deposits are associated with a NW/SE-trending shear zone has identified an association with mineralizatior processes and intense hydrothermal alteration. Electromagnetic anomalies are shown as a line bodies with significant electric conductivity. In addition, magnetic anomalies are associated with higher amplitudes, despite the interferences caused b) anomalies from deeper sources in the region. The present research was aimed at investigating the geophysical response of the gold deposits in suitable environments with the use of aerogeophysical data supported by studies of background geology. A review of the geological and geophysical knowledge of the area and an evaluation of the possibilities of the processing of the aerogeophysical data where made. During the processing of the magnetic data, the truncated anomalies prevented the characterization of the deep sources, masking the interpretation of the shallow sources due to overlapping of anomalies. The effec of the truncation restricts the use of the reduction-to-pole, which generates features that do not correspond to reality. From this two questions could be answered. First is related to the origin and characterization of the truncated anomalies that was solves through processing and interpreting magnetic regional data from the Brazil-Germany Geophysical Covenant. The second is related to the forecast of the response of magnetic data to general processing that was based on simulation studies using magnetic models. Once the magnetic response in this area was understood, anomalies interference problems could be resolved using information derived from the application of techniques, such as vertical gradient maps and amplitude of the analytical signal. The vertical gradient was particularly useful in the delimitation and characterization of a portion of the Sao Vicente Shear Zone tha presents compatible anomalies to sources with total magnetization of strong remanence and, in this case, associated witt concentrations of gold. The analytical signal has reinforced the interpretation of the vertical gradient map that shows a greater magnetization degree to the mineralization. The gamma-ray responses obtained have demonstrated the existence of a relationship between structural control, host rock, mineralization, metamorphic grade and hydrothermal alteration. Out of these, hydrothermá alteration, associated to relative enrichment of Potassium, was of great help to map areas of favorable gold concentration Thorium was depleted under these this conditions and Uranium presented a varied behavior. Responses of the electromagnetic system (frequencies of 935, 4175 and 33000 Hz) were influenced by the effect of weathering cover (up to 100 m thick) in almos all units of the region studied. The amplitudes of the electromagnetic field (20 ppm for higher frequencies) were much lower thar the expected and the apparent calculated conductivity maps permitted only a superficial mapping of the area. The horizonta: coplanar array (4175 Hz) permitted a higher grade of penetration and was most sensitive to the presence of the horizonta conductors, compensating the lower penetration grade and the noise interferences in high frequencies. Medium to high values o: apparent conductivity have been observed, corresponding to mafic-ultramafic and metapelitic rocks from Nova Lima Group Similar values are found along the Sao Vicente Shear Zone, represented by a "conductivity corridor" with high values in it^, nmthem sector and medium to high in its southern sector. Finally, considering the significant number of gold occurrences along the southern São Vicente lineament, it can be considered that mineralization processes are associated with the specific geologica event, which aligned the magnetic material with reminiscence features along the fault zone. This possibility, as suggested by the magnetic anomaly signature, is re-enforced by its close correspondence with the electromagnetic and gamma-ray anomalies Therefore, it must be considered in prospective and tectonic studies about the genesis of the mineralization.

Abstract: The Quadrilátero Ferrifero, located in the state of Minas Gerais, is the most famous Brazilian gold district, and has educed 1.3 million tonnes of gold during the last three centuries. Given the As/Au ratios of the ores, it is estimated that at ad 390000 tonnes of As were liberated in the environment, mainly due to the dumping of wastes in the drainages. This Ph.D. thesis focussed on: (i) the distribution of As in water and sediments from fluvial basins under influence of the major ng districts of the Quadrilátero Femfero, and test the biological availability of As in sediments; (ii) the development of a method of As - •n in water; (iii) the description of processes and products related to the supergene alteration of arsenopyrite from gold ores; and the hydrogeochemicai modeling of groundwater in mines. The results indicated that the gold districts sited in the basins of the das Velhas, Carmo and Conceição rivers, contain high . •ns of As in the sediments, with values up to 4.000 mglkg As. Tests of bioavailability of As in sediments indicate = -'ins below 4% of the total grades, thus representing a potential risk in certain areas. Concentrations of up to 350 µg/L As were obtained in samples of filtered surface water, whereas ground water collected in gold in the Ouro Preto and Marian region, indicate values as high as 2.800 µg/L of total arsenic. The development of a method able tD the different species of inorganic As (Asp e Ask), via the combination of hydride generator and atomic absorption - , allowed the identification of different inorganic species of As in surface and groundwater, with [As³*]4As⁵] ratios ranging 1.10-¹ to 4.10-². The original distribution of the inorganic arsenic species in water samples remained unaltered until 10 days after regardless the method of sample preservation. Although, after 30 days, the conservation of samples containing HCI or HNO3 recoveries above 80% of the original Asp concentration.  The geochemical processes that guide the supergene alteration of gold deposits were studied in detail via X-ray diffraction, ng electron microscopy, chemical analyses of groundwater from mines, and via hydrogeochemical modelling. It was noted that the oxidation of arsenopyrite from quartz veins (without carbonate minerals) originated scorodite, while the oxidation of quartz­ nopyrite veins generated low-crystallinity Fe-Ca-arsenates, and minor scorodite, kolfanite, yukonite and farmacossiderite. iteration of As into surface and ground water occurs according to the following stages: (i) during the oxidation of arsenopyrite part of As is  soluble and part is incorporated in Fe-arsenate or scorodite; (ii) during the total or incongruent dissolution of secondary As­ part of the As is soluble, and part is adsorbed and retained in Fe-oxides. The presence of carbonate minerals in sulfide ores acidic waters derived from the oxidation of sulfide minerals. Although, neutral to alkaline pH induces the liberation of As via of Fe-arsenates and scorodite. Collectively the geochemical studies performed in the Quadrilátero Ferrifero indicate that concerns regarding the ulation health must be present. It is recommended a periodical monitoring of surface waters, particularly in areas to gold mines or waste dumps, and the adoption of methods that prevent waters contaminated by As to be d. The highest possibility of contamination of wells, springs and groundwater, relate to groundwater hosted by that bear sulfide-rich gold mineralizations or to sites impacted by solutions contaminated by As, derived from waste or water from contaminated sediments.

Abstract: Volcanic-associated massive sulfide deposits represent important sources of lead, zinc, copper and precious metals worldwide. The present study is a contribution to a better understanding of the origin of the Zn-Pb sulfide deposits of the Serra do Expedito, State of Mato Grosso, Brazil. These deposits are located in the SW portion of the Amazonian Craton, associated with Paleoproterozoic felsic volcanic and plutonic rocks, correlate to Magmatismo Teles Pires. Studies undertaken included geological mapping, drill-core examination, lithogeochemical and geochronological  studies, petrographic and eletron-microprobe analyses of minerals in the ore, wall rocks and hydrothermal alteration zones, as well as applications of Sr and Pb isotope geochemistry to ore-deposit modeling. Geochemical data place  the acid rocks in A-type, indicating an anorogenic or post-orogenic origin, possibly due to mantle activation during a long lasting extensional event, in an ensialic environment. SHRIMP U-Pb zircon ages at 1762 ± 6 Ma and 1755 ± 5 Ma were obtained for volcanic and plutonic rocks, respectively. The predominant volcanic host rocks include crystal and lapilli tuffs that are interpreted as a sub-aqueous record of a distal volcanic center of unknown localization. Field evidence suggests that the orebodies form one single belt, representing the actual trace of a system of synvolcanic fault that channeled the hydrothermal fluids and sulfide deposition. The orebodies present normal sulfide mineralogy for volcanogenic deposits with pyrite, pyrrhotite, sphalerite, galena, chalcopyrite and with locally accessory arsenopyrite. On the other hand, the alteration is atypical since it presents chloritic zones locally associated with actinolite and magnetite. Mineral chemical studies indicate that the main mineralization event  occurred in the interval 300-350°C at elevated O₂ and S₂ partial pressures whereas some portions of orebodies underwent heating and fluid interaction that yielded the calc-silicate and  magnetite assemblage overprint. A Pb-Pb model age in galena was obtained at 1.75 Ga which indicates that the deposit was formed during the last stages of a magmatic-tectonic-hydrothermal event that occurred in the interval 1.76-1.75 Ga. The lead isotopic data for K-feldspar and a Rb-Sr isochron for sphalerites leachates indicate a later post-depositional event at 1.1 Ga. The Sr-isotope compositions of carbonate are clearly suggestive of its hydrothermal origin and, in conjunction with elevated lead-isotope ratios in galena, point to hydrothermal sources located in the Upper Crust. These results lead to consider a sub-aqueous deposition of wall-rocks and sulfide deposition in epizonal crustal levels, along synvolcanic fault zones thet channeled mineralizing fluids of plutonic and supracrustal origin. Theses processes are consistent with the VHMS – Volcanic Hosted Massive Sulfide model presently attributed to the Expedito Zn-Pb deposit.

Abstract.The Itapetim gold-bearing district, within the Transversal Zone of the Província Borborema, NE Brazil, comprises a series of low tonnage lode gold deposits, such as of hosted by mylonitic gneisses confined to a regional scale shear zone named Itapetim shear zone. The gold mineralization at Sertãozinho, Piedade, Pimenteiras e Gurgueia, the main deposits investigated in this work, are closely associated with vein shear systems. An integrated study involving the 3D analysis of quartz c-axis in veins and host rocks, distribution and pattern of microfractures, fluid inclusions and stable isotopes (18O/16O and d/H) was carried out with the purpose of evaluating the deformation mechanisms responsible for the porosity generation and, as consequent, permeability for fluid circulation within the Itapetim Shear Zone. Additionally, the nature and evolution of the fluids involved in the formation of the gold mineralization in this shear zone were also constrained. The plot of quartz c-axis in veins and host rocks showed a distribution pattern averaging 10º/310 Az, in high angle (mean of 75º) with the direction of the Itapetim Shear Zone. Intra and intercrystalline microfractures, empty or delineated by planes of fluid inclusions (PIFs), form an arrangement of steeply – dipping (between 75 and 85º) and shallowly - dipping (between 20° and 25º) planes, along strikes varying from NNW-SSE to NNE-SSW. The 3D arrangement of the quartz c-axis, together with that of the microfractures, demonstrate that quartz underwent deformation at temperatures close to 400ºC, possibly as result of crystal-plastic and pure elastic deformation mechanisms, accompanied by sliding in <a>. These data also confirmed that the principal stress (1) associated with the regional transpressional deformation was sub-parallel to the direction of the great majority of the microfractures, perpendicular to the plane (σ2-σ3). Textural relationships, microthermometry and Raman microspectroscopy analysis of fluid inclusion in gold-bearing vein quartz defined three types of fluids: (i) type I, low salinity (0.8 to 10.0 wt % NaCl eq.) aqueous-carbonic (H2O + CO2  CH4); (ii) type II, CO2-rich carbonic, with subordinate amounts of CH4 (up to 8 mol%); and (iii) type III, aqueous with salinities ranging from 0.8 to 5.0 % wt % NaCl eq.). The fluid inclusions which represent fluid types I, II and III coexist either in isolated groups or along intra- and intercrystalline microfractures, suggesting heterogeneous trapping of a H2O-CO2 fluid undergoing immiscibility. Such a process may have taken place episodically, under pressure and temperature in the range of 215° - 413°C and 1.3 kb - 4.4 kb, respectively, equivalent to crustal depths of 3 to 11 km. 18O and d/H values calculated for the gold mineralizing fluids varied from -1.6 ‰ to 6.5 ‰ and from -63.8 ‰ to -80.8 ‰, respectively, indicating a fluid regime characterized by the contribution of magmatic (18OH2O = 6.5 ‰; DH2O = -75.9 ‰) and metamorphic - derived (18OH2O = 2.4 ‰;DH2O = -63.8 ‰) fluids, with cooler fluids of meteoric origin

Abstract. The Rio Itapicuru Greenstone Belt (RIGB) is a Paleoproteozoic sequence situated in the northern portion of the São Francisco Craton, Bahia state, Brazil. Overlying a basement consisting of gnaisse and migmatites, this volcanic-sedimentary belt is intruded by several granitoid intrusions of different chemical compositions. Two of the most important intrusive bodies, the Barrocas (BGr) and the Teofilandia granitoids (TGr), which are early Proterozoic in ages (2130 and 2127 Ma, respectively), are located in the southern portion of the RIGB, and display E-W and NE-SW trending orientation, in contrast with the N-S trend of most of the remaining intrusions related to the supracrustal pile. Even being considered time- and spatial-related granitoids, the field relationships reveal the TGr as the earlier intrusion. It has a granodioritic to quartz-monzodioritic modal composition, and associated with a quartz-porfiritic sub-volcanic rock. The BGr has a granodioritic modal composition and rare transitions to tonalite. Both belong to the calc-alkaline and I-type suites and have metaluminous signatures, characteristic of felsic igneous rocks of orogenic environments. The TGr displays SiO2 (64%-71%), Na2O (4,02% -5,92%), CaO (2,32% - 4,44%) and TiO2 (0,28% - 0,48%), with low to moderate Rb/Sr, Rb/K and Sr/Y ratios. The BGr has higher SiO2 values (up to 73,57%), and lower Rb/Sr, Rb/K and Sr/Y ratios and Na2O, CaO, TiO2, Sr, Ba and Y. Although both granitoids have juvenile arc signatures, characterized by low 87Sr/86Sr isotopic ratios (0,69964-0,70177) and positive Nd2130Ma (>+2.03), their initial isotopic ratios indicate different sources, revealing a likely intra-oceanic tectonic setting for them. Geochemical modellings point to their being the result of partial melting of a basaltic protoliths of the RIGB sequence (oceanic crust) under amphibolite-eclogite facies conditions. All these features, in addition to the whole-rock O isotope data (> 7.5‰), preclude the accretion of recycled materials, suggesting a pervasive alteration of their basaltic protoliths before melting. Fine to medium-grained microdioritic enclaves having metaluminous and calc-alkaline compositions are scattered in the TGr, as well as more restricted coarse-grained varieties, formed by mafic mineral accumulation from the host granitoid. Another coarse-grained enclave type resulted from the mixture with more primitive magmas. Neither the TGr nor the BGr has xenoliths of the surrounding regional rocks. Small and irregular granodioritic bodies cut the TGr;, which are characterized by high Rb and K values and narrow negative isotopic variation (Nd2130Ma = -8.49 to - 9.38), indicating partial melting of an ancient crustal material. Of the two deformational events documented in RIGB, the D1 tectonic event directly affected the granitoids. This event, characterised by a NW-SE dextral transpression movement, was responsible for an expressive curved fault along the contact of the BGr with the basalt units of the supracrustal RIGB in the north, and for another one along the contact plane of the TGr with the basement in the south, representing a possible suture zone. The ongoing transpression developed E-W planes, E-NE mineral and stretchting lineation trends, as well as kinematic indicators in the TGr, whereas imprinted a high (medium) angle dipping S-C foliation structures in the BGr granitoid. Open upright folds with low NW-trending angle axes nucleated in a northeastern sector within the area determined by these two main faults, which gradually became closed-like folds in the central sectors, with their axes uprighting westward according to an apparent clockwise rotation. The dextral movement culminates in the two expressive upright mylonitic segments which form the wedge of a delta-like megastructure. Notwithstanding, as expected in syn-tectonics granitoids bodies emplaced in transpressional domains, the movement not inferred sigmoidal patterns to the geometric elements of the TGr and BGr intrusions. All these features indicate the folding as the dominant movement instead of rotation. These relationships support the suggestion that both igneous bodies are sheet-like intrusions, and provide evidence for the interplay between the TGr and BGr and the D1 tectonic event. The young D2 event locally affected the TGr and BGr through dominantly brittle features with many parallel N-S trending faults.

Abstract: This study is designed to investigate the relationship between Zn/Ag mineral deposits emplacement and the host rock, dolostones of the Sete Lagoas Formation, (Bambuí Group) in the Januária region, MG. The definition of the timing and possible origin of the massíve dolomitization and dissolution/collapse brecciation is of primary importance to understand the evolution of carbonate rocks and define the relationslup between carbonate sedimentation, diagenetic processes and the emplacement of mineral deposits. The recognition of unconformities and their relationship with regional, large-scale brecciation is also envisaged. In order to afain these objectives, a regional and detailled mapping was done. In this research, the Sete Lagoas Formation is informally divided into seven members, grouped into three main shallowingupwards successions, named basal intermediate and upper. The basal succession consists of the argillaceous lime mudstone member 1(basal), and calcirudite member 2, and are interpreted as recording a prograding interval deposited on a lowenergy platform or shallow shelf cutted by tidal channels and sporadically affected by storms. The intermediate succession comprises the dolomitec calcarenite member 3, dolostone member 4, stromatolite dolostone member 5, ooid-intraclast dolostone member 6, and the lowermost unit (7A) of the dolomudstone member 7. Its overall interpretation is that it represents a shallowing-upwards succession from muddy to sandier sediments deposited in offshore through a sandier shoreface with stromatohte reefal barner, lagoonal and beach to tidal flat environments; subaerial exposure of the carbonate platform ended the intermediate shallowing-upwards succession. An unconformity assumed by some authors as developed above the ooid-mtraclast dolostone member 6 (the pink dolostone) is not recogruzed in this research The uppermost succession, made up of small peritidal cycles, is interpreted as representing a series of prograding tidal flat successions that record low energy environments. The three mam succession are interpreted as a parasequence set of a progradational stacking pattera The increase in pelitic sediments upwards in the overlying Serra de Santa Helena shut down the carbonate platform. Regarding diagenesis, the carbonate rocks of the Sete Lagoas Formation has undergone diagenetic alteration in subaerial, submarne and subsurface environments. Diagenetic features of subaenal diagenesis iriclude desiccation cracks, tepees, vadose cements and small-scale dissolution vugs; submarine envirorunent is represented by isopachous fibrous cernem around allochems suggesting beachrock cementation. Subsurface diagenesis resulted in the most important modifications in the carbonate rocks and mcludes, among others, compaction, blocky sparry calcite, hydrothermal dlssolut'On, do1omitization, sulfide and silicate ore minerals, late-stage coarse-crystalline calcite, fluorite and bitumen. The dolostones hosting mineral deposits are made up of replacement dolomites and cements and are strongly af'-ted bY dissolution/collapse brecciation. The main dolomite types recognized in the Januária region related to mineral deposits, are in paragenetic sequence: microcrystalline (McCD), medium-crystalline (MCD), coarse-crystalline (CCD), very-coasecrystalline (VcCD), saddle (SD) and very finelly crystalline. McCD represent early, penecontemporaneous replacement dolomites and MCD/CCD, late replacement dolomites. Very coarse-crystallme dolomite (VcCD), saddle dolomite (SD) and very fmely crystalline dolomite (VfCD) are dolomite cements. MccD occurs mostly in sediments of the dolomudstone member 7 and stromatolites/fure sediments of the member 5. MCD/CCD are widespread and affect mostly the dolostone and ooid-intraclast dolostone member (4 and 6). VcCD and SD are closely associated with each other and occur in cavities and fractures in MCD/CCD, crosscut the limits between the members 6 and 7 what indicate they are formed later Um the presumed unconformity developed above member 6, as already mentioned. SD occurs in rhombohedral (pink or pale gray saddle dolomite) and saddle fornis (Mãe saddle dolomite); white SD is later than rhomboliedrai ones. VfCD is restricted to dissolution/collapse breccia layer and affects the ali above described dolomites, except possibly the white SD. The dolomites and late-stage coarse-crystalline calcite (LCC) were analysed for CIO isotopes, as well as to Sr isotopes. Samples of the basal limestones were analysed in order to have bench markers representing the estimated isotopic signature of the Neoproterozoic seawater of the Sete Lagoas Fonnation and these values will be used as a reference to determine post-depositional diagenetic changes. The Sr isotopic composition suggests sedimentation of the Bambuí Group staried at around 590 to 600Ma. The obtained 8'80 values (PDB) inferred to represent the composition of seawater or slighly modified seawater during deposition of the Sete Lagoas Formation.range from -6.11 to -6.56%o (mean = -6.39) and 8'3C range from 0.26 to 0.58%o (mean = 0,42%o). The "SrP'Sr ratio of seawater during deposition of the Sete Lagoas Formation is estimated to be between 0.7076 and 0.7079 based on micritic limestones at the base of the section. McCD: 8'80 values is within lhe range of values for dolomites that would precipitated from Sete Lagoas Formation seawater, or slighly modified seawater. The 8'SrP'Sr ratios range are slighly higher fim the estimated original isotopic signature of the Neoproterozoic Sete Lagoas Fonnation seawater, suggesting that their original isotopic signature were pardy modified by later diagenetic fluids. MCD/CCD: 8'80 values are shghly depleted compared to the Neoproterozoic seawater. The "Sr/B6Sr ratios are more radiogemc tlian the estimated seawater of the Sete Lagoas Formation. The present data do not provide an unegwvocal conclusion conceniing the origin of MCD/CCD; these dolomites could result from previous dolomites late affected by . neomorphism and diagenetic fluids Sr-nch or formed imder burial conditions by Sr-rich fli ids. MCD/CCD postdate stylolites suggesting that dolomitizahon occured during bunal.,VcCD/SD show similar 8'80 values, the most depleted ones. "SrP" Sr ration are similar to MCD/CCD, thus more radiogenic than the estimated seawater. Fiuid inclusion measurements in SD suggest entrapment temperature above 231°C. Thus VcCD/SD are interpreted as being formed in subsurface during burial by warm diagenetic fluids of similar chemical composition. VfCD cements ali kind of breccia fragments but also act as internal sediment displaying lamination and/or normal grading. Locally is closely related to mineralization. The 8180 values is within the range of Sete Lagoas Formation seawater, hovever the "SrP'Sr values are not compatible with the estimated Neoproterozoic seawater. There is no diagenetic feature or field relationship couid suggest formation of VfCD directly from seawater. Thus, ViCD is interpreted as resulting from chemical or chemically induced meclianical disaggregation by warm brines. VfCD is similar to the named "sanded dolomites" deposited in internai cavities and related to hydrothermal activity. Ali described dolomites occur in the brecciated dolostone levei making a stratigraphic levei in the Januária region, as well as in the middle São Francisco valley, and resulting from dissolution/collapse brecciation. This study indicate that dissolution occured mostly in subsurface; dissolution related to subaerial exposure are minor and differ from subsurfaoe in at least three main aspects: dissolution vugs related to meteoric waters are small, areally restricted and the infilling material are only fine dolomitized sediment. Dissolution features considered as resulting from subsurface warm fluids, are widespmad, tile filling material inciudes VICD, SD, VfCD, sulfide, LCC, fluorite and bitumen, and dissolution/brceciation crosscut the hypothetical unconformity of previous suthors developed above the member 6. Thus, most of the dissolution and breccias resulted from action of hydrothermal flmds dwing burial, and ore-bearing dissolutin/collapse breccias are interpreted to be the result from selective sulfide replacement of pre-ore collapse breccia. Mmeralization is thus epigenetic, resulting from the action of subsurface warm fluids, interpreted as hydrothermal. The tìming of minerahzation is one of the unsolved problems. As dolomitization and the emplacement of ore nimerals took place during burial of the sediments, considering the compressional model, the Januária mineral deposit could be related to the evolution of the Brasiliano Cycle and thus restricted to the Neoproterozoic. However, if emplacement of mineral deposits is related to extensional tectonics, the timing of mineralization need not be restricted to the Neoproterozoic and could be Phanerozoic in age. The main metallogenic control is tectonics, that provide the driving forces responsible for fluid flow over large arcas. Faults and fractures are the main conduits for the ascending flow in a basin. Withm the basin, fluid flow is controlled also by Porosity and permeability of sedimentary units. Thus, the interaction of fauts with permeable sedimentary units and urxonforrnitiia of the basin define the regional pattem of related dolomitization and dissolution/collapse breccia development. This same association, depending on the availability of lhe sulphur, also controls ore emplacement. Thus, the first ".lm confiol in the study arca related to the carbonate sediments is the distribution of strata with contrasting Permeabilities. The porcus units are lithofacies of the dolostone and ooid-intraclast dolostone members (4 and 6), fmited by'P us, impermeable ones (aquitards); the lowermost unit to act as aquitards was the basal fine carbonate of the do~ calcarenite member 3 and the uppermost unit was lithologies of the dolomudstone member 7. These aquitards controlled dolomitization, dissolution/collapse brecciation and ore mineral deposits. During burial, the permeable units acted as ~ts for wann, hydrothemial dolomitizing and mineralizing fluids..

Abstract The large Carajás iron ores belongs to the Carajás formation, which is a 100-400m thick banded and laminated iron formation (jaspilite), located at Pará state in North Brazil. This almost continuous formation outcrops for at least 260km, in 60 ore deposits, distributed in three main ridges, São Felix, Leste and Carajás. The last one is a sinformal structure sub-divided in South and North ridges. This work was carried out on detailed mapping, stratigraphic raising and petrographic, geochemical, isotopic and geochronological sampling of the North ridge, where the mining activity is currently running and bench and drill-core are available. Levels (4 m to 3 cm) composed by chert or jasper alternated with magnetite-maghemite-hematite was deposed between 2,754 and 2,744 Ma (22m/Ma) at depths of 100-200m, locally affected by bottom currents. This hydroplastic chemical sediments precipitated by supersaturation (Si) and oxidation (Fe) from upwelling waters where the base was richer in hydrothermal source waters (REE=6,66; Eu*=3,54; (La/Yb)N=1,52 ) than the top (REE= 3,89; Eu*=3,18; (La/Yb)N=0,66). Besides, the major elements content have more variability at base than top. The Carajás jaspilite have twice Ga (21ppm), Bi (6ppm), Pb (18ppm) and seven times Sb (7ppm) than the world average for similar rocks. The Fe oxidation may have be promoted by organic activity, attested by delicate double wall spherulites and kerogen preservation in siltstones of a light younger unit. Local hydrothermal carbonatization has affected the jaspilite producing 13C mean of –4.3‰PDB and two groups of 18O (+24,9 to +15,4 and +12,8 to +6,6‰SMOW). Otherwise, metamorphic imprints on this rocks are minimal. Regional work, bibliographic compilation and correlations of the Carajás formation with overlying units of Bahia and Azul mines leaves to propose a evolutionary model for the Grão Pará Basin, initiated as a intracontinental rifting stage, marked by crustal contaminated tholeiitic basalt volcanism (2.76 Ga - U-Pb zircon ages). The second stage was the deposition of the Carajás formation over a wide, quiet marine continental shelf, influenced by upwelling of Fe-Si rich waters. In a third stage, the last was recovered by volcanics associated with clastic sedimentation (2.74 Ga - Pb-Pb zircon ages). The fourth stage comprises the installation of another continental shelf environment, where clastics and carbonate rocks has deposed (2.68 Ga - U-Pb zircon ages). Basin inversion and fluvial deposition closes the evolution..

Abstract.This research addresses the geology, ore assemblages and SHRIMP U-Pb geochronology of the Igarapé Bahia, Breves and Cento e Dezoito copper-gold deposits, and the geology and metallogenesis of the Serra Pelada Au-Pd-Pt deposit. The data indicate that two temporally distinct metallogenetic events occurred in the Carajás Copper-Gold Belt, one Neoarchean (~2.57 Ga) represented by the Igarapé Bahia Fe-oxide Cu-Au-(U-REE) deposit, and other Paleoproterozoic (~1.88 Ga) represented by the Breves Cu-Au-(W-Bi-Sn) deposit. The results suggest that Cento e Dezoito is possibly a hybrid deposit resulting from the interplay of Neoachean and Paleoproterozic ore forming processes. The metallogenesis of the belt initiates in the Archean with the development of a continental rift where syngenetic iron, and possibly copper, were accumulated. This environment also favored the formation of Pt-Pd deposits associated with layered mafic-ultramafic intrusions. The early cratonization and the complex tectonic history of the Carajás Copper-Gold Belt, that includes multiple transtensional events, allowed the formation of Fe-oxide Cu-Au-(U-REE) during the Neoarchean. During the Paleoproterozoic the belt underwent other transtensional episode that favored the ascent of several A-type granites to which Cu-Au-(W-Bi-Sn) deposits are associated. The juxtaposition of these distinct metallogenetic events resulted in a complex scenario that includes a variety of ore deposits some of which exotic, as for example the Serra Pelada Au-Pd-Pt deposit, a unique case of Au-Pd-Pt deposit hosted by meta-sedimentary rocks.

Abstract. Auriferous tourmalinites of the Anticlinal de Mariana region, southeastern Quadrilátero Ferrífero, have long raised debates regarding their origin. Genetic models have considered the tourmalinites as syngenetic, invoking the importance of exhalative focus, as well as epigenetic formed as a result of hydrothermal alteration and/or granitic magmatism. This study was centred on the Passagem, Mata Cavalo, Chico Rei, Scliar and Duas Bocas gold deposits, where three distinct modes of tourmaline occurrences were identified: (T1) tourmaline as the essential component of stratiform tourmalinites; (T2) tourmalines concentrated as hydrothermal alteration envelopes around gold –bearing quartz-carbonate-sulphide veins; (T3) aggregates of tourmalines as part of gold –bearing quartz-carbonate-sulphide veins. In spite of their compositional differences, all belong to the group of alkaline tourmalines and are classified as dravite. Combining field relationships, together with petrography, mineral chemistry and Nd and Sr isotope data, the following conclusions regarding the origin of the gold-related tourmalinites may be pointed out: i) boron-rich submarine exhalative fluids caused the syngenetic precipitation of the stratiform bodies of tourmalinites; ii) remobilization of boron, possibly by metamorphic fluids sensuo stricto derived from the metamorphic devolatilization of the enclosing rocks and deep-seated synmetamorphic fluids, may have caused the precipitation of vein-related tourmaline, as part of an epigenetic gold-bearing hydrothermal system..