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Item Acesso aberto (Open Access) Condutividade elétrica complexa de rochas(Universidade Federal do Pará, 1979-08-14) ROCHA, Brígida Ramati Pereira da; SAUCK, William August; http://lattes.cnpq.br/6655455534234531Laboratory measurements of complex conductivity were made on 28 drill-core samples from area MM1-Prospect 1 of the Carajás Mining District. The objective of this research was to help interpret field geophysical survey of the area using Induced Polarization and AFMAG methods. The laboratory measurements of amplitude and phase of conductance were taken in the frequency interval of 10-3Hz to 104Hz. The method used was the direct measurement of impedance using a memory osciloscope, a signal generator, and two high input impedance differential preamplifiers. The electrode system chosen for the measurements was the 2 electrode platinized-platinum because its frequency response is flat in the frequency range used. AlI the measurements were made at a constant temperature of 24°C±1°C. A petrographic study of the samples was done, using thin sections, polished sections and X-ray diffraction. Copper content, in the form of sulfides, was determined using atomic absorption. As a result of the petrographic study, the samples were classified in five distinct groups: granite, biotite schist, amphibolite and magnetite quartzite-iron formation. The grade of Cu was variable in the five groups, ranging from 50 ppm to 6000 ppm. In the conductivity measurements it was observed that, among the five groups, the samples of iron formation gave the largest variations with frequency. The granite samples had spectra flatter than those of schist or amphibole. In conclusion, these measurements show that the field Induced Polarization and AFMAG anomalies near these three drill holes (F1, F2 and F3) are due primarily to the magnetic iron formation, and secondarily due to associated low-grade chalcopyrite mineralization.Item Acesso aberto (Open Access) Contribuição à petrologia do granito central da serra dos Carajás(Universidade Federal do Pará, 1980-09-02) ALMEIDA, Regina Célia Cunha; RONCAL, Juan Rolando ZuletaThis study was carried out in the central region of the Serra dos Carajás in the South of the State of Pará. The area referred to is underlain by a granite batholith, surrounded by basic volcanic rocks in the north-east and slightly metamorphised sedimentary clastic rocks. In order to characterize the petrogenetic nature of the granitic body, a study was realized of the petrography and petrochemistry of the various facies of the granite and of the country rocks. Petrographic and geochemical evidence suggests a magmatic origin for the granite of Carajás. During its consolidation the granitic magma underwent a slight differentiation in the formation of various facies. The intrusive character of the body is e4denced by the presence of contact metamorphism of the hornblende hornfels in the country rocks in the proximity of the contacts. The observed mineralogical association (orthoclase and plagioclase) indicates that the granitic body may be included in the SUBSOLVUS group in the classification of the Tuttle and Bowen (1958). The magma was probably originated by partial melting of older crustal rocks.Item Acesso aberto (Open Access) Distribuição dos elementos Si, Al, Fe, Ca, Mg, Mn, Ti, Cu, K e Na em solos desenvolvidos na região do granito central da Serra dos Carajás - sul do estado do Pará(Universidade Federal do Pará, 1981-03-13) DAMOUS, Nina Rosa Leal; RONCAL, Juan Rolando ZuletaThe distribution of elements in the weathered pro rocks is effected mainly by climate, geomorphology and parent material. The present study deals with the distribution of Si, Al., Fe, Ca, Mg, Mn, Ti, Cu, K and Na in the weathered products of the Central Gravite at Serra dos Carajas - Para, Brazil, which occurs in an area which is characterized by ondulated relief and humid tropical climate. Samples representing two selected weathering profiles were collected to depths that did not exceed 6 m. The analytical treatment consisted of poten/biometric determinations of pH values, the determination of the chemical and mineralogical compositions of the sand, silt and clay fractions, and the determination of the chemical composition of the oxide fraction. The two profiles reveal an intensa process of feldspar removal from the parent granite and the formation of a sand-clayey lato-soil. In this process quartz has been preserved and clay minerals and aluminium and iron hidroxides have been formed constituting the dominant assemblage of the soil. Ca, Mg, Mn, Na and K from the parental rock were nearly completely leached away to the extent that these elements are only found in small amounts in the remaining feldspars or adsorbed on clay minerals. On the other hand, Ti present principally in resistant minerals, practically maintains its' original concentration. Cu is sligthly enriched in the profiles due to adsorption in the clay minerals. The presence of only very small amounts of feldspar along the profiles shows the great intensity of the weathering process acti.ng on the granitic rocks. The direct transformation of feldspar to clay minerals or aluminium oxides is related to the climatic conditions frainy and dry seasons) prevalent in the area.Item Acesso aberto (Open Access) Estimativas da condutividade térmica dos minerais e rochas e influência de parâmetros térmicos e petrofísicos na resistividade aparente da formação(Universidade Federal do Pará, 1995-08-09) COZZOLINO, Klaus; HOWARD JUNIOR, Allen Quentin; http://lattes.cnpq.br/6447166738854045The present study carries out estimates of thermal conductivity in the principal rock-forming minerals, as well as estimates of the average conductivity of the solid phase of five common lithologies (sandstones, dolomites, limestones, anhydrites, clay lithologies). Several thermal models were compared, permitting the verification of one as the most appropriate to represent the aggregate of minerals and fluids of which rocks are composed. The results of this study can be applied to a wide variety of thermal models. The chosen methodology is based on a non-linear regression algorithm denominated Random Search. The algorithm's behaviour is evaluated with sinthetic data before being applied to real data. The geometric mean model is used in the regression to obtain the values of thermal conductivity in these rock-forming minerals. The regression method used in each lithological sub-group gave the following values for average thermal conductivity in the solid phase: sandstones 5.9 ± 1.33 W/mK, limestones 3.1 ± 0.12 W/mK, dolomites 4.7 ± 0.56 W/mK anhydrites 6.3 ± 0.27 W/mK and for argillceous lithologies 3.4 ± 0.48 W/mK. In the sequence the fundaments for the study of heat diffusion are presented in cylindrical coordinates. The effects of invasion of mud filtrate into the formation are considered using an adaption of simulation of well injection techniques originating in theories developed in reservoir engineering. Assuming the original temperature of the formation as a reference, the relative errors in apparent resistivity can be estimated. In this phase of the work the finite differences method is used to measure distribution of the well-formation temperature. Simulation of the invasion is carried out in cylindrical coordenates via an adaptation of the Buckley-Leverett equation into carthesian coordenates. Effects such as the appearance of mudcakes in the borehole, gravity and capilliary pressure are not taken into consideration. The radial distribution of resistivity is obtained via the distribution of saturation and temperature, and is convolved with the radial geometrical factor of the induction tool (transmissor-receiver), resulting in the apparent resistivity of the formation. Admitting as reference the original temperature of the formation, the relative errors in apparent resistivity are obtained at each time. Through variation of certain parameters, it becomes clear that the porosity and original saturation of the formation can be responsible for serious errors in the measurement of resistivity, especially if such readings are taken immediately after drilling (MWD). The difference in temperature between well and formation is the principal cause of such errors. In situations where this difference is large, therefore, profiles with- induction tools should only be carried out between 24 and 48 hours after the well has been drilled.Item Acesso aberto (Open Access) Estudo da estrutura geo-elétrica da Região do Juruá, AM, pelo método magnetotelúrico(Universidade Federal do Pará, 1991-11-25) PORSANI, Jorge Luís; TRAVASSOS, Jandyr de Menezes; http://lattes.cnpq.br/9611024254232348A clear geoelectric picture from the Juruá region in the Solimões Basin was obtained using magnetotelluric (MT) data. Field data were recorded along three profiles of 15 km long, spaced 3.5 km, covering 100 km2. The spacing between each of the 35 stations was irregular, ranging from 400 m to 3500 m. The frequency range was 0.001 Hz to 300 Hz. This allows investigation depths of 100 m down to 60 km. The data were affected by the so called static effect. To correct that effect the median of the resistivity of the first conductor which corresponds to the Solimões Formation was used. The invariant of the MT tensor was used to interpret the Juruá geoelectric structure. The results are presented in the form of geoelectric sections. The geoelectric sections were obtained using both the Bostick transformation and the 1D Occam inversion at each station. It was possible to identify a sequence of conductive and resistive layers corresponding to the sedimentary sequence, a fault zone and the geoelectric basement characterizing the Solimões Basin. Below the geoelectric basement a conductive zone was also identified, followed by a Low Conductive Layer at depths of 20 km or more. This layer is interpreted as being composed of gabbro, which is associated to processes of vertical accretion, which in turn are linked to both crustal stabilization and lithosphere thickening. The results show a good agreement with resistivity well logs and surface seismic data.Item Acesso aberto (Open Access) Estudo em laboratório de anomalias de potencial espontâneo(Universidade Federal do Pará, 1978-11) FERREIRA, Lindalva do Carmo; ALVAREZ BEJAR, RománThis work is an application in the laboratory of the Spontaneous or Self Potential method of field geophysics. Pairs of differente rocks and residual soils were placed in contact in the laboratory to determine whether they could produce a difference in potential, as had been occasionally observed during field investigations. The samples of rock used are limestones, basalts, and rhyolite from the area of "Caldera de Los Humeros" in Mexico. The residual soils are from the area MM1 of "Serra dos Carajás", Pará, Brasil. The measurements were carried out using dry systems (room humidity) and humid systems (water added). The changes of measured potential for rocks and soils in the laboratory show differences in average values ranging from 5mv to 50 mv from one side of a contact to the other. Thus, the result of this investigation in positive and indicates that changes in Self Potential values can originate from changes in superficial soil type or by contacts between different types of rocks.Item Acesso aberto (Open Access) Evolução geológica da região de Colméia(Universidade Federal do Pará, 1980-09-03) COSTA, João Batista Sena; HASUI, Yociteru; http://lattes.cnpq.br/3392176511494801A geological mapping of the Colmeia region, in northern Goiás, has been carried out on a 1:100.000 scale. Semi-detailed geological observations coupled with stratigraphic, structural and petrological data are integrated aiming at the geological evolution of that region. The oldest recognized unit, the Archean Colmeia Complex, is represented by gneisses, granites and migmatites with associated schists, quartzites and amphibolites, and forms the central core of the Colmeia brachyanticline. Two main deformation periods have affected these rocks at the end of the Archean: the earliest period, F1deformed the rock banding surfaces into folds with E-W orlented axes and originated a well-defined axial-plane schistosity; the other one, F2, caused the refolding of the banding surfaces and folded the schistosity planes as to produce folds also with E-W oriented axes. Furthermbre, two migmatization phases were recognized: the first phase was contemporaneous with F1 and formed quartz-feldspar-rich neossomes in which minerais show a preferred orientation; the second phase predates F2 but post-dates F1, and is characterized by neossomes consisting essentially of non-oriented quartz and feldspar minerals. In the Middle Proterozoic, the Amazon Craton was regenerated leading to the accumulation of a thick volcano-sedimentary pile known as the Baixo Araguaia Super Group (Abreu, 1978). The lower unit of this pile is represented by the Estrondo Group which consists, from bottom to top of the Morro do Campo Formation (quartzites with schist intercalations), the Xambioá Formation (schists of various lithologies) and the Canto da Vazante Formation (feldspathic schists with biotite schist intercalations). The upper unit constitutes the Tocantins Group which is represented in the Colmeia region by the chlorite-quartz schists of the Pequizeiro Formation. Metamorphosed mafic and ultramafic rocks are associated with both the Estrondo and the Tocantins Group. In the Colmeia region, the Baixo Araguaia Super Group had a poliphasic evolution throughout the Middle Proterozoic. Its rocles recorded three major deformation periods: the first one is represented by intrafolial folding of the So surfaces and by the formation of an axial-plane schistosity; the second deformation event disturbed the schistosity surfaces generatinÉ folds with inclined axial planes and N-S oriented axes; the third deformation period is characterized by crenulation of the schistosity. The resulting folds have milimetric to kilometric dimensione and their axes parallel. NW-SE directions. Where the schistosity was completely transposed, crenulation cleavage was developed and biotite and chlorite recrystallizations took place on the transposition planes. The planar structures of the Baixo Araguaia basement were bent in response to shearing. Regional metamorphism of greenschist and amphibolite facies is concomitant with the first deformation episode while the second event affected the underlying Colmeia Complex superirnposing a similar folding style; at the same time contemporaneous migmatization originated N-S oriented quartz-feldspathic neossomes. Subsequent remobilization of the Colmeia Complex and the emplacement of intrusive granitic bodies gave rise to the Colmeia brachyanticline with which minor N-S oriented folds are associated. Radial faults were developed cutting both the basement and the metasedimentary cover. Other major discontinuities are also related to this event. The sedimentation of the Rio das Barreiras Formation marks the final act of the evolutionary history of the Colmeia region. Such an evolution included lithogenetic processes of the Archean and Middle Proterozoic as well as thermo-tectonic phenomena related to the Jequié and Uruaçuano cycles. K-Ar and Rb-Sr radiometric dating indicates reheating associated with the Transamazonic and Brazilian cycles.Item Acesso aberto (Open Access) Evolução geológica da região de Tucuruí - Pará(Universidade Federal do Pará, 1982-05-27) MATTA, Milton Antonio da Silva; HASUI, Yociteru; http://lattes.cnpq.br/3392176511494801The northern part of the Araguaia Belt is exposed in the Tucuruí region and their stratigraphic, structural, metamorphic and magmatic features had been studied aiming at contributing for the understanding of the geological evolution of the area. The oldest stratigraphic unit of the area is represented by the Xingu Complex, composed by gneisses and granitos and subordinated schists and anphibolites. These rocks show evidence of a polycyclic metamorphic and structural history. Over this unit, during the niddle Proterozoic, the Tucuruí Group was developed. The bottom of this unit is composed by a sequence of tholeiitic basal-tic flows which were hera enclosed in the Caripé Formation. The Morrote Formation, is made up of graywackes, and constitutes the upper part of the Tucurui Group. The geossinclinal evolution of the Araguaia Belt took place during the Uruaçuano Cycle. This geotectonic unit is represented in the studied area by the Couto Magalhães Formation (Tocantins Group) which comprises pelitic and psamitic metasediments. These rocks show a greenshist facies metamorphism and structures generated by two phases of deformation in conditions of lower structures level. After the metamorphism of the Araguaia Belt, the Couto Magalhães Formation acted as the place of mafic and ultramafic intrusion and, lately, the Tucuruí Fault thrusted the metamorphic rocks of the Tocantins Group over the Tucuruí Group lithotypes. This faulting, besides generating a. series of structural features in the both groups as well as in the later migmatites, has also induced a dynamic metamorphic event into the rocks under green-schist facies conditions. Through the statistic treatment of structural data from the denso fault population which cuts the area, it was possible to deduce the shertening and the eterlding directiors related to the progressivo deformation induced by the thrust faulting had acted from E to W. Post-faulting mafic dykes represent the last magmatic event related to the Mesozoic Era. During the Cenozoic the area was a place of Tertiary sedimentation (Barreiras Formation), with sand, clays and conglomeratic levels. A final reactivation was responsible for the fracturing and faulting showed by the Barreiras Formation lithotypes Quatérnaty deposits mostly alluvial sediments, are the final units of the area.Item Acesso aberto (Open Access) Evolução petroquímico-metalogenética das rochas e mineralizações associadas à suite Vila Nova na Serra do Ipitinga (NW do Pará)(Universidade Federal do Pará, 1997-05-08) FARACO, Maria Telma Lins; MCREATH, Ian; http://lattes.cnpq.br/5299851252167587The Vila Nova Metamorphic Suite in the 'pitinga Hills (NW Pará) consists of a supracrustal sequence of mafic and ultramafic metavolcanics, cordierite-antophyllite - and quartz-chlorite-bearing rocks underlying chemical (oxide and silicate-type BIFs) and clastic metasediments. Part of the basic lavas was hydrothermally altered under greenschist facies conditions, similar to mid-ocean-ridge axis hydrothermal systems, creating quartz-chiorite-bearing rocks (which occur as large clots within the metavolcanic sequence) and hydrothermal syndepositional exhalative volcanogenic sulphide deposits, formed by pyrrhotite, pyrite, chalcopyrite and sphalerite with associated Au and Ag and traces of galena, molybdenite and silver telluride. The temperature range of generation of these host rocks, dalculated from AI-saturated chlorite, is 273°C to 320°C, with an average value of 308°C. Afterwards, metamorphism under amphibolite facies transformed the basic volcanics to amphibolites, and part of the quartz-chlorite to cordierite-antophyllite rocks. Geothermometric calculations using the cordierite-antophyllite pair, point to 547°C for the generation of these rocks. Present-day mineralogical associations of BIFs and clastic metasediments were formed during that metamorphism. All the metavolcano-sedimentary sequence was deformed by brittle-ductile shearing and transformed in present-day NW-SE trending shear belts with subvertical-NE dip. The deformational shearing episode yielded mylonites, polymetamorphic and hidrothermalized rocks, showing retrogressive metamorphic paragenesis. There was also hydrothermal alteration produced by granitic fluids. Gold is present in three typologies: associated to volcanogenic sulphides, sheared Iodes, and supergene altered rocks. Platinum anomalies were registered in many hydrothermalized rocks, but not in association with sulphide mineralization. Four hydrothermal events were identified. Fluid inclusion studies indicated tweive types of inclusions which pointed to finco fluid systems, one consisting of a CH4-rich aqueous-carbonic phase and the other of an aqueous phase with sahnites ranging from 40% CaCl2 equivalent to near pure water. The first is related to sulphide-bearing rocks and the second to the shearing episode. The homogenization temperatures of the fluid inclusions in the sulphide mineralization's host-rocks, point to 250°C-450°C to the origin of these rocks. The CH4-isochores and the temperature range of generation of the host-rocks, provide a pressure range of 0,7 kb to 2,3 kb for the mineralization. The protoliths of mafic metavolcanics are subaikaline tholeiitic basalts. Komatiitic basalts were also characterized, suggesting the presence of a komatiitic affinity to the magmatism. The lithochemical study revealed a volcanic environment similar to back-arc basins to the Vila Nova Suite. The Nd isotopic study yielded model ages between 2.26 Ga and 2.19 Ga for Vila Nova metavolcanics, while the BIF's REE patterns are equivalent to many Paleoproterozoic banded iron-formation of the world. This is in agreement with the 2.11 Ga (Sm/Nd) and 2.25 Ga (U/Pb) ages from French Guyana and Guyana's rocks, correlatives to Vila Nova Suite. The petrological, lithochemical, metallogenetic and isotopic data from the Vila Nova metamorphic suite account also for its correlation with the paleoproterozoic birimian metavolcano-sedimentary belts of the West African craton.Item Acesso aberto (Open Access) Geologia e gênese do veio de cristal de rocha do Garimpo da Lagoa, Xambioá – TO.(Universidade Federal do Pará, 2000-08-31) FERREIRA, Iêda de Oliveira; KOTSCHOUBEY, Basile; http://lattes.cnpq.br/0096549701457340The crystal rock occurrences from Xambioá region, situated in the northem part of the Araguaia Belt, are associated with quartzites of the base of the Morro do Campo Formation and schists of the Xambioá Formation, both of the Upper Proterozoic Estrondo Group. The crystal rock occurs mainly as irregular pockets within milky to grayish translucent quartz veins. The “Garimpo da Lagoa” crystal rock vein is hosted by biotite - schists of the Xambioá Formation, displays a general sub-meridian direction and is up to 5 m thick. Petrography and microthermometry of vein samples revealed the presence of two distinct fluids types: 1) oversaturated aqua - carbonic fluids in pseudo - secondary inclusions, containing up to 4 solid phases and 2) aqueous fluids of low to high salinity in secondary inclusions. The aqua — carbonic fluid inclusions contain almost pure CO», with traces of N; due probably due to the presence of carbonatic rocks and graphite in the area. Most fluid inclusions underwent crepitation before they reached Th. Even so, the minimum trapping temperature for these fluids was estimated in 550 to 600º C. It is believed that fluids are basically of deep metamorphic origin, though they also show significant contribution of magma derived solutions. The aqueous fluids were found in three-phase oversaturated, two-phase and monophase inclusions. The solutions contained in the three-phase inclusions revealed a salinity from 30 to 40% in weight of NaCl and a minimum trapping temperature between + 182 and + 321ºC. K is believed that these fluids were injected after the aqua — carbonic ones and were essentially of magmatic origin. Concemning the fluids contained in the two-phase inclusions, were distinguished solutions of low salinity (1,23 to 11,81% in weight of NaCl) and a minimum trapping temperature from + 123,8 to + 150,9ºC, and solutions of high salinity, sub-divided in two categories (a) and (b), mainly based on their morphology. The (a) type revealed a salinity of about 23% in weight of NaCl and a minimum trapping temperature between +130 and 210%, more frequently at + 160ºC, while the (b) type indicated a salinity ffom 20 to 25% in weight of NaCl and a minimum trapping temperature from + 65 to + 114,Sth C, more frequently at + 70ºC. The fluids contained in the monophase inclusions displayed a salinity of 1.91% to 18.22% in weight of NaCl. The solutions trapped in two-phase and monophase inclusions would represent late injections of hydrothermal fluids of magmatic origin, which underwent progressive cooling and composition modifications in agreement with the importance of the contribution of more superficial (meteoric, conate, etc.) waters. During the final phase of the Araguaia Belt evolution, in predominantly distensive conditions, at first aqua — carbonic fluids were injected, that resulted, in formation of a hyaline quartz vein, poor in fluid inclusions. Later on, the vein suffered multiple fracturing phases and aqueous solutions were injected showing a progressive lowering of the temperature and, in a less systematic and less regular way, of the salinity. These late injections were responsible in variable degree for the transformation of the original hyaline quartz into translucent or milky quartz. Pockets which were not affected by these late hydrothermal displays remained as crystal rock. Crystal rock, mainly as third quality chips is used as raw material for production of synthetic crystal. Prismatic, well developped quartz crystals and first quality chips are used in mineral craft for production of adornment pieces, balls, key rings and cut stones. Crystal rock is mainly exported to Belo Horizonte, Sete Lagoas, Governador Valadares, where already cut stones are commercialized , and to São Paulo and Rio de Janeiro, where raw crystals are mainly appreciated.Item Acesso aberto (Open Access) A geoquímica da camada laterítica da Serra do Quatipuru(Universidade Federal do Pará, 1980-09-03) SÁ, Osvaldo Batista; SCHWAB, Roland GottliebA study was carried out on the modes of distribution of the trace elements Cu, Zn, Ni, Co, Mn and Cr in a layer of laterite soil overlying a parent rock composed of serpentinised ultrabasics and partly of talc-chlotite (schists). The layer of soil is influenced by weathered coming from the upper levels of the Serras leading to a possible upsetting of the equilibrium of the profile. The investigation of various profiles indicates that it can be proved that the type of mode of distribution is constant and only depends on the parent rock. The lateral contribution from the upper level of the Serras only increases or decreases the maximum and minimum values along the profile. It is proven that there exists a strong relationship between Co-Mn and Cr-Fe independent of the horizon and the parent rock. The enrichment factors of weathering are presented, as well as the conclusions which may be drawn on the basis of analyses of these trace elements on soil near the surface with the respect to possible enrichment in underlying horizons and values in the parent rock, enabling identification of the parent rock by preliminary simple geochemistry.Item Acesso aberto (Open Access) Implantação da metodologia Pb-Pb em rocha total: exemplos de aplicação na província mineral de Carajás (PA)(Universidade Federal do Pará, 1992-12-12) RODRIGUES, Elizabeth Maria Soares; LAFON, Jean Michel; http://lattes.cnpq.br/4507815620234645Item Acesso aberto (Open Access) Intemperismo químico de rochas graníticas na zona bragantina nordeste do Pará(Universidade Federal do Pará, 1980-05-13) GOULART, Antonio Taranto; RONCAL, Juan Rolando ZuletaProfiles of residual soils derived from granitic rocks which occur in the Bragantina Region, Northeastern Pará, were studied chemically and mineralogically. These soils were developed in an ares of gentle topography and good drainage under tropical conditions with well defined "dry" and rainy seasons. The mineral composition of these soils consists essentially of quartz and with decreasing abundantes also appear kaolinite, muscovite, secondary oxides, feldspar and heavy minerals. This mineral assemblage resulted from the chemical weathering of the parent granitic rocks wh.ose original minerals were decomposed in the following sequence: biotite, feldspars, muscovite, quartz and heavy minerals. The soils are dominantly sandy from which significant amounts of kaolinite, produced during the earlier stages of weathering, were lost in consequente of the intense leaching that is favored by the high pluvial precipitation oves the region. The great stability of quartz under tropical conditions together with the intense leaching of the regolith has led to the development of texturally homogeneous soils in the Bragantina Region.Item Acesso aberto (Open Access) Metamorfismo das rochas pelíticas do segmento setentrional da faixa Paraguai-Araguaia(Universidade Federal do Pará, 1980-03-20) SILVA, José Maurício Rangel da; HASUI, Yociteru; http://lattes.cnpq.br/3392176511494801Petrographic, petrochemical and microstructural data were used in the study of the metamorphism. In keeping with the work's scalé, the data .are regionally consistent. The metamorphism acted on sedimentary parent rocks, chemically similar to shales and greywacke admixtures. Relict sedimentary structures point to a sedimentary origin. The mineral assembrages distribution in Baixo Araguaia Group shows, from west to east, a regional metamorphic zoning with sericite, chlorite and biotite. Around megastructures (with supposed basement nucleus) a garnet zone has been recognized. The baric type is medium-pressure and corraspodds to Northern Appalachians and Scottish Highlands. Metamorphism and tectonic events are correlativa. The intensity of metamorphism, correspondingly to staurolite and kyanite crystallization, outlasts the deformation F2. The cooling of the meta sedimentary sequence brought out the biotite and muscovite crystallization. The metamorphism is referable to a polyphase cycle. The final manifestations .of the metamorphism belong to the Brasiliano Cycle.Item Acesso aberto (Open Access) Mineralização aurífera de Montes Áureos (Maranhão): rochas hospedeiras, controles deposicionais e fluidos mineralizantes.(Universidade Federal do Pará, 2000-04-03) YAMAGUTI, Humberto Sabro; VILLAS, Raimundo Netuno Nobre; http://lattes.cnpq.br/1406458719432983The Montes Áureos gold mineralization occurred within the Tentugal Shear Zone (ZCT) which is a + 100km long, 15km wide NW-SE trending structure that marks the south-southwest boundary of the São Luís craton and may represent a collisional suture between the Belém block and this craton. This zone is characterized by tectonites produced by compressive/transpressive and strike-slip movements, and corresponds to the most deformed rocks of the Gurupi mobile belt. The ore bodies are hosted by Proterozoic Gurupi Group metavolcanic and metasedimentary rocks which have been metamorphosed under conditions of low (chlorite + sericite), medium to high greenschist (chlorite + biotite + muscovite + epidote + actinolite + Mg- hornblende + Fe-hornblende) and low amphibolite facies (biotite + plagioclase + edenite + pargasite + ferrotchermakite). They have been also deformed under a brittle-ductile regime, leading to the formation of structures with different shapes, styles and degree of strain. A superimposed hydrothermal event generated assemblages composed of chlorite, carbonates and epidote that partially replaced metamorphic amphiboles, plagioclase and biotite. It also produced a system of vein and veinlets both concordant and discordant with respect to the rock foliation. Gold occurs in up to 2 cm thick, late-tectonic quartz + carbonates veins or veinlets associated with arsenopyrite, pyrite and minor chalcopyrite. The spatial distribution of the mineralized zones forms lenticular to tabular bodies with gold contents less than 2 ppm. Texture features and the time relationship between hydrothermal and metamorphic assemblages indicate that mineralization followed the metamorphic peak and that gold occurs in at least two different forms: 1) granular gold deposited simultaneously with sulfides; and 2) in microfractures in arsenopyrite. Gold had been most likely transported by the sulphur thio- complex [Au(HS)"] in an aqueous-carbonic, low salinity fluid (2 to 10 wt% equiv. NaCl) at temperature < 450ºC. Deposition occurred in a temperature range of 260 to 350C. For the prevalent value of 300ºC, obtained by the chlorite geothermometer, pressure estimates fall between 1,3 and 2,8 kb, corresponding to depths of 5-10 km. Desestabilization of that complex as temperature dropped and as the fluids interacted with the host rocks brought about gold precipitation. Fluids related to the systems CO; + CH,, H,0-C0O,-NaCl + CH, + MgCl e/ou FeCl, and H;0-NaCl + MgCl e/ou FeCl, circulated through Montes Áureos rocks. The aqueous-carbonic fluids are considered to be products of dehydration and decarbonization of carbon- fluids are considered to be products of dehydration and decarbonization of carbon-bearing sedimentary rocks at temperature probably above 500ºC. At first homogeneous, these fluids have undergone imiscibility and were then trapped in fluid inclusions with different H,)0/CO; ratios, some almost pure H,O or CO>. As the metamorphic thermal regime decreased and carbonates precipitated, the aqueous-carbonic fluids became progressively impoverished in CO, and less saline. Mixture with cooler and low salinity superficial waters may have occurred by the end of the evolution of the Montes Áureos hydrothermal system. The geotectonic setting, the structural control of the mineralization by shear zone, the hydrothermal alteration features, the time relations between the metamorphic peak and hydrothermal alteration, the gold ore mineral association and the physical-chemical characteristics of the mineralizing fluids allow the Montes Áureos gold deposit to be classified in the lode category, as many others that are formed at convergent plate margins.Item Acesso aberto (Open Access) Modelamento da permissividade dielétrica de rochas saturadas de óleo e água e suas aplicações em perfilagem de poço(Universidade Federal do Pará, 1990-10-12) GOMES, Arnaldo Lopez Pereira; VERMA, Om Prakash; http://lattes.cnpq.br/2723609019309173The electromagnetic propagation tool (EPT) provides the propagation time (Tpl) and the attenuation (A) of an electromagnetic wave propagating in a lossy medium. These EPT responses depend on the dielectric permittivity of the medium. There are several models and mixing equations concerning the dielectric permittivity of reservoir rocks that can be used in the interpretation of the high frequency tool. However, the mixing equations do not take into account the distribution and the geometry of the pore space, and these parameters are essential to obtaining dielectric responses approximating a true rock. A model based on the parameters described above was selected and this was applied to dielectric data available in the literature. A good agreement was reached between the theoretical curves and experimental data, confirming that the distribution and geometry of the pore space must be considered in the development of a realistic model. Aspect ratio distribution functions of the pores were also obtained, which were used for generating several curves relating the EPT responses to various oil/gas saturations. These curves were applied to the log analysis. The selected model fit the dielectric data available in the literature reasonably well, thus, making it suitable for application to experimental data of rock from Brazilian producing fields for the interpretation of the EPT in these fields.Item Acesso aberto (Open Access) Modelo fractal para resistividade complexa de rochas: interpretação petrofísica e aplicação à exploração geoelétrica(Universidade Federal do Pará, 1995-12-21) ROCHA, Brígida Ramati Pereira da; HABASHY, Tarek MohamedRocks containing disseminated metallics or clay particles in natural environment where electrolytic solutions fill the pore spaces, show a certain type of polarization at low frequencies known as induced electrical polarization. In this thesis, a new model to describe the electrical polarization on rocks was developed, not only for low frequencies, but spanning the entire electromagnetic spectrum used in geolectric prospection. This new model encompasses most of the other commonly used models as special cases, and overcomes some of the known limitations. The proposed circuit analog includes a non-linear impedance r(iwtf)-1 which simulates the effects of the rough surface of the interfaces between the blocking grains (metallic or clay particles) and the electrolyte. This generalized Warburg impedance is in series with the resistance of the blocking grains and both are shunted by the double layer capacitance. This combination is in series with the resistance of the electrolyte in the blocked pore passages. The unblocked pore paths are represented by a. resistance which corresponds to the normal DC resistivity of the rock. The parallel combination of this resistance with the "bulk" sample capacitance is finally connected in parallel to the rest of the above-mentioned circuit. The parameters of this model include the DC resistivity (p0), the chargeability (m), three relaxation times (T, Tf and T0), a grain resistivity factor (δr) and the frequency exponent (η). The fractal relaxation time (Tf) and the frequency exponent (η) are related to the fractal geometry of the rough pore interfaces between the conductive grains (metallic or clay minerals which are blocking the pore paths) and the electrolyte. The relaxation time T is a result of the low-frequency relaxation of the electrical double layers formed between the electrolyte and the crystals, whereas T0 is a macroscopic relaxation time of the "bulk" sample. The grain resistivity factor (δr) relates the resistivity of the conductive grains with the DC resistivity value of the rock. The DC resistivity of the rock and δr are related to the porosity, the electrolyte conductivity and the volumetric ratios between the matrix and the conductive grains. The model was tested over a wide range of frequencies against experimental data obtained for amplitude and phase of resistivity or conductivity as well as for the complex dielectric constant. The data used in this work were obtained from digitizing published experimental data, obtained by several authors from sedimentary, metamorphic and igneous rocks. The results show that the parameters of this model are related to textural and mineralogical aspects of the rocks. This model was introduced firstly as the intrinsic electric property of a homogeneous and polarizable half-space, and it was demonstrated, in this thesis, that the response observed at the surface is equivalent to the intrinsic property of the polarizable medium, been the electromagnetic coupling irrelevant to frequencies lower than 104 Hz. Next, the polarizable medium was embedded as an intermediate layer between two non-polarizable layers with the same De resistivity. The response obtained shows that the frequency exponent of the fractal medium could be determined even when the polarizable medium is at a considerable depth in relation to the dipole-dipole length. This justifies the use of simple models developed to explain the response of laboratory samples to fit field data, and that is being used without a right justification. These results shows the importance of the proposed model to the geoelectric prospection.Item Acesso aberto (Open Access) Partição da deformação no limite entre o terreno granito-greenstone de Rio Maria e o Cinturão Itacaiúnas, Carajás (PA)(Universidade Federal do Pará, 2009-05-22) VIEGAS, Luís Gustavo Ferreira; PINHEIRO, Roberto Vizeu Lima; http://lattes.cnpq.br/3251836412904734This research is primarily concerned with the tectonic evolution of an Archaean crustal segment of the Amazonian Craton which is thought to encompass two distinct Archaean terranes: the Rio Maria Granite-Greenstone Terrain, to the south, and the Itacaiúnas Belt, to the north. These two terranes show similar lithologies and a short range variation in geochronological ages, but their structural pattern differs significantly. The rocks exposed in the domains of the Rio Maria Granite-Greenstone Terrain comprise mainly TTG series (2.9 – 2.86 Ga), alkaline plutons (2.86 Ga) and greenstone belts (2.9 Ga), which display ages older than those found on the Itacaiúnas Belt. A compositional layering can be seen in the tonalites, trondhjemites and granodiorites, and a magmatic foliation is locally observed in the monzogranites and syenogranites. These fabrics strike NW-SE to E-W with medium to shallow dips to NE and SW. The linear fabrics associated with these structures are only locally developed, and generally show shallow plunges to SE. In the Itacaiúnas Belt the main structural feature is a coarse mylonitic foliation present in the tonalites, granodiorites and migmatites associated with the Xingu Complex (2.7 Ga), and also in the syenogranites and alkali-feldspar granites of the Plaquê Suite (2.7 Ga). This foliation is steeply dipping to N and S, trending E-W to NW-SE. The stretching lineation present in the mylonitc foliation planes shows shallow dips to NE, SE, NW and SW. Five structural domains were defined based on strain facies analysis method. From north to south, these facies show partition of displacement into compressional and strike-slip components and also distinct fabric generation patterns. Facies V and IV, located in the southern portion of the studied area, are characterized by a dominant compressional component of frontal to oblique nature associated with structures generated by magmatic to submagmatic flow. The central portion of the study area is marked by facies III, which represents a junction between different structural patterns and fabric generation processes. This facies shows interplay between compressional and strike-slip displacements, as well as fabrics developed either by magmatic flow and solid-state flow. The northern portion of the studied area comprises facies II and I, which contain fabrics derived mainly from plastic strain associated with a high degree of planar transposition. The overall kinematic pattern is mainly sinistral, with dextral displacements observed where the compressional component of partitioned transpression is stronger. The two northern facies display sinistral displacement, while facies III and facies IV show a combination of compressional and transcurrent motion. Local shear sense indicators suggest sinistral displacement for facies V. The geological evolution of the studied area involved two main stages: i) a first stage of emplacement of TTG granitoids in an Archaean protocrust mainly located at the region of Rio Maria Granite Greenstone Terrain, and ii) a second stage marked by shear zone nucleation, magma generation and pluton emplacement in a partitioned transpressional setting. The partitioned transpression was responsible for nucleation of a regional scale set of shear zones which partitioned the deformation across the area. In the northern facies, the deformation pattern is mainly characterized by strike-slip transposition of planar fabrics formed under solid state conditions. To the south, magmatic flow is dominant and compressional components of transpression are evident. The regional shear zones also worked as conduits for magma ascension and emplacement at higher levels of the crust. These magmas were derived from partial melting of the TTG series and are mainly alkaline and/or migmatitic in composition. The structural pattern observed in the area between the Rio Maria Granite-Greenstone Terrain and the Itacaiúnas Belt is interpreted as a result of progressive deformation in a sinistral partitioned transpressional setting. This strain pattern comprised geometric and kinematic partitioning in zones of strike-slip displacement and compressional components, and also distinct fabric generation patterns ranging from magmatic to solidstate flow. These characteristics suggest that these two terranes are involved in the same transpressional event and, as such, the Itacaiúnas Belt can be interpreted as a crustal fragment associated with the Rio Maria Granite-Greenstone Terrain, which evolution is marked by progressive events of tectonic reworking and granite emplacement.Item Acesso aberto (Open Access) Petrologia e evolução crustal das rochas de alto grau de Porto Nacional - TO(Universidade Federal do Pará, 1996-03-03) GORAYEB, Paulo Sérgio de Sousa; OLIVEIRA, Marcos Aurélio Farias de; http://lattes.cnpq.br/6704755061378988The Porto Nacional region, located at central-southern portion of the Tocantins State, is part of Structural Tocantins Province. That region forms a crustal segment mainly composed by granulitic and gneissic terraines, with a wide variety of lithotypes due to the effects of successive magmatic, sedimentary, tectonic and metamorphic processes during the Precambrian Eon. In the oldest units, from the Lower Proterozoic, have been recognized orthoderived rocks, as tholeiitic basalts type TH-1, calc-alkaline basalts and tonalites as well as paraderived rocks as graywackes, pelites, graphitic and silicic-iron-manganesiferous, submited to high grade metamorphism (Porto Nacional Complex, Morro do Aquiles Formation). Another set of rocks includes tonalites associated with minor granodiorites and granites, occurring along with a supracrustal sequence made up of calc-silicate gnaisses, pelites, psamites and gondites, metamorphosed in the amphibolite facies (Rio dos Mangues Complex). Meta-igneous bodies of anorthositic (Carreira Comprida Anorthosite), nepheline-sienitic (Estrela Suite) and K-rich granitic rock compositions (Matança and Serrote Suite), metamorphosed in the amphibolite facies, constitutes batholites and stocks enclosed by the former units. They represent magmatic events of different origins and ages. Other units from the end of Lower Proterozoic are represented by the Monte do Carmo Formation, composed by conglomerates, arkoses, graywackes and acid to intermediary volcanic rocks, and the Lajeado Suite, which encloses a set of granites. These unites represent intra-continental volcanic and plutonic magmatic processes related to extensional tectonic environment. The Upper Proterozoic and the Phanerozoic are represented, respectivelly, by psamo-pelites low grade metassediments (Natividade Group) and by sedimentary rocks of the Parnaiba Basin (Serra Grande and Pimenteiras Formations). The tectono-structural framework is here designed by the Tocantins Shear Belt, which trends NE-SW between the Amazônico and Paramiririm Archean cratons. This belt defines a regional imbricated system wide about 300 km, where mixed segments of different crustal level. The evolution of the belt is related to the oblique colision of Porangatu and Araguacema crustal blocks during the Lower Proterozoic, and to late transcurrent shears. The metamorphic studies developed in the Tocantins Shear Belt allowed characterize rocks of high grade metamorphism (Domine 1), with maximum temperature of 850°C and pressure of 8 kbar, which indicate that the rocks reached the granulite facies in a depth of about 30-35 km. The second terrain (Domine 2) includes rocks of high amphibolite facies with temperatures of 680°C and pressures of 6-5 kbar, indicating depths of about 20 km. The Domine 3 includes a migmatized gnaissic terrain, that underwent a middle to high amphibolite facies metamorphism, above the hornblende isograde and the curve of granite melt in high H2O activity. The petrogenetic records suggest a anticlockwise P-T-t path for the high grade metamorphism. This path is initially progressive with an increase of temperature, and crosses muscovite, biotite, andaluzite, garnet and sillimanite isogrades in the aluminous sequences, and hornblende, clivo and orthopyroxene in mafic compositions. The metamorphic path cross cuts the curve of granite melt in low H2O activity and generates S-type granites, and charnockites. The thermal peak is reached near 880°C and is followed by a significative increasing in pressure, with the stabilization of kyanite and garnet. Later, there was stablished retrograde pattern whose records suggest an overprinting in amphibolite and greenschist facies conditions at temperatures lower than 600°C and pressures about 5 kbar. The geochronologic data obtained by whole-rock Rb-Sr and single zircon Pb evaporation analysis suggests a minimum ages 2,1 - 2,2 Ga for the high grade metamorphism, indicating effects of the Transamazonian thermo-tectonic event. The petrogenetic interpretations based on lithochemical and tectonic data, suggest that the evolution of the high grade rocks may be related to the rupture of the pre-existent Archean crust. In this crust affected by extensional tectonism, and strongly controled by magmatic underplating, restricted oceans were installed. The crustal evolution was followed by A subduction, delamination and crustal-stacking wedge, which end up with the transportation of infracrustal segments to upper leveis of the crust.Item Acesso aberto (Open Access) Rochas encaixantes, alteração hidrotermal e caracterização dos fluídos relacionados à formação do corpo sequeirinho do depósito Cu-Au do Sossego, Região de Carajás(Universidade Federal do Pará, 2006-09-06) ROSA, Ana Glória Noronha; VILLAS, Raimundo Netuno Nobre; http://lattes.cnpq.br/1406458719432983The Sossego Cu-Au deposit is located at about 25 km NW of Canaã dos Carajás city (PA), southern of the Carajás transcurrent system, at the contact zone between the Archean granitic-gneisses of the basement and the Grão Pará Group rocks. This deposit is made up of five ore bodies, being Sequeirinho and Sossego the most important. The present work focused primarily on the Sequeirinho ore body, but observations have been occasionally extended of the Sossego ore body. Its main purpose was to study the hydrothermal fluids responsible for the alteration and mineralization of the Sossego deposit. Several rock types have been recognized in the deposit area: granitoids, both granular (GRA) and porphyritic (MVA), mafic volcanic (Grão Pará Group) and intrusive (GBA) rocks, biotite-rich rocks (BIX), magnetitites (MAG), ore (BSE) and dikes. These rocks are variably deformed and altered, some being essentially products of the hydrothermal alteration, namely the magnetitites and ores. The petrographic study allowed to infer that the granitic (albite + quartz +actinolite + chlorite + epidote) and mafic intrusive (scapolite + Cl-K-Fe- hastingsite ±actinolite + albite + chlorite + epidote + magnetite) had as protoliths mainly quartzdiorites and gabbros/ diorites, respectively. The BIX are mylonitized granitoids that interact with high saline fluids and are characterized by a fine banding in which light bands, composed basically of quartz and/or marialitic scapolite), alternate with black bands composed dominantly of Clbiotite, Cl-K-Fe- hastingsite and tourmaline. The MAG have magnetite contents higher than 50% and variable amounts of apatite, epidote, albite, titanite and chalcopyrite, whereas the BSE consist of chalcopyrite±siegenite + magnetite + apatite + scapolite. Felsic (quartzdiorite and riolitic/riodacitic in composition) and diabase/gabbro dikes cut the above mentioned rocks Albitization, sericitization, silicification, chloritization, epidotization, actinolitization and scapolitization, are the most important types of hydrothermal alteration, although biotitization and Fe-metasomatism also occur. The carbonation represents the final stage of the alteration. Microthermometric studies of fluid inclusions (FI) trapped in quartz, scapolite, apatite and calcite crystals from different rocks of the Sequeirinho ore body reveal aqueous fluids that may be represented, in a simplifying way, by the H2O–NaCl–CaCl2, H2O–NaCl–CaCl2–FeCl2 e H2O–NaCl–FeCl2 chemical systems. The FI show variable salinity (0.2 to 57% wt. % eq. NaCl) and homogenization temperatures that range from 100 to 480ºC. Saturated FI, corresponding to the H2O–NaCl–CaCl2, have their salinity estimated in terms of the main solutes at 15-26% NaCl and 15-23% CaCl2. FI trapped In calcite crystals show salinity between 2 and 15 wt. % eq. NaCl and the 100 to < 275ºC range as the most frequent homogenization temperature interval. The evolution of the Sossego hydrothermal system involved two primary fluids (a) H2O–NaCl–CaCl2 and (b) H2O–NaCl– FeCl2. As these fluids gradually mixed, they generated a third fluid (c) H2O–NaCl–CaCl2–FeCl2 which is interpreted to be responsible for the mineralization and associated alteration. All fluids show evidences of dilution most likely by superficial water. Fluid a is related to albitization, amphibolitization and scapolitization, whereas fluid b was the one that should have carried large amounts Fe to be later deposited as magnetitites. Fluid c is interpreted to be responsible for actinolitization, epidotization and chloritization as well as by the main stage of the mineralization. High saline fluids (>30 wt. % equiv. NaCl) are assigned to interaction with preexisting evaporite and/or exahalite layers that have been dissolved out by metamorphic processes. Magmatic aqueous fluids have also contributed to the Sossego hydrothermal system as well as meteoric waters whose influx caused strong dilution and cooling of the fluids. Comparatively to other Carajás Cu-Au deposits, the aqueous fluids related to the Sossego hydrothermal system show more similarities with those of the Archean Igarapé Salobo and Igarapé Bahia deposits, despite having a distinct typology. Most likely, these similarities arise from the fact that all three deposits are associated with metavolcanosedimentary sequences of the Itacaiunas Supergroup which resulted in part from exhalative activity and might have locally included evaporite beds. As halite was dissolved out, the resulting high saline fluids infiltrated into and were stored in the rock pores from which they might have subsequently migrated in response to thermal and/or tectonic disturbances.