BDTD - Biblioteca Digital de Teses e Dissertações

URI Permanente desta comunidadehttps://repositorio.ufpa.br/handle/2011/2289

Biblioteca Digital de Teses e Dissertações da UFPA (BDTD). Sistema Eletrônico de Teses e Dissertações (TEDE). Projeto BDTD/UFPA e Instituto Brasileiro de Informação em Ciência e Tecnologia (IBICT).

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Acesso aberto (Open Access)
Desenvolvimento de técnicas de filtragem e sua aplicação a dados aeromagnéticos da Bacia Amazônica
(Universidade Federal do Pará, 1976-08) SILVA, João Batista Corrêa da; LOURENÇO, José Seixas
In this thesis two filtering methods were combined in order to enhance some features in an aeromagnetic map such as lineaments and anomalies caused by sources of large proportions. The visual filtering consisted of stereoscopic examination of pairs of maps. The numeric filtering involved the elimination of the undesirable spectral components (noise) and the enhancement of the desired spectral components (signal). Both methods were tested on aeromagnetic maps of the Middle Amazon Basin. All the numeric filtering operations were done in the space domain by convolving the aeromagnetic data with a 13x13 filter matrix. Special attention was paid to the preliminary analysis of the spectrum, as a guide in filter design. The results of the application of each filter was discussed in detail. A further topic also dealt with was basement fault models. The model analysis established a complementary interpretation method to the filtering methods. A structural interpretation of the Middle Amazon Basin's basement was provided. The dominant aeromagnetic trends were E-W, N60°W, N-S, N45°E and N60°E. Two grabens were quite evident. The younger one trends N-S, while the older one strikes N45°E. Two anomalies caused by sources of intermediate and large proportions (15-60km) exhibit remanent magnetization and high values of negative inclination, which shows that the Amazon Basin would be southernmost in the Paleozoic. In performing the integration of aeromagnetic data with other geophysical data avaiIable, the interpretation from other data proved consistent with the aeromagnetic interpretation, illustrating the reliability of the techniques employed in this thesis.
Acesso aberto (Open Access)
Interpretação de anomalias magnéticas usando integrais finitas dos momentos das componentes
(Universidade Federal do Pará, 1976-08) LEÃO, Jorge Wilson Delgado; LOURENÇO, José Seixas
The objective of this work is to develop a methodology to determine the parameters of a body causing a magnetic anomaly. This methodology is based on the use of analytic expressions, derived for the finite integrals of the moments of the anomaly of total intensity and of the Hx, Hy and Hz components, according to the cartesian coordinate system. By fitting these analytic expressions and the numerical integrals of the moments of the magnetic components obtained from a geophysical survey, the parameters of magnetization, position, depth and dimensions of the anomalous body can be obtained through an iterative process. When only one magnetic component is known, the method is still applicable, since the other components may be obtained by means of a mathematical filtering scheme. This methodology was succesfully tested for point dipole and line of dipoles models, which are widely used in Geophysics to interpret magnetic anomalies caused by geologic bodies which have one or two horizontal dimensions much less than the depth.
Acesso aberto (Open Access)
Tratamento quantitativo de anomalia de potencial espontâneo
(Universidade Federal do Pará, 1976-10) GUERREIRO, Sonia Dias Cavalcanti; LOURENÇO, José Seixas
Acesso aberto (Open Access)
Fosfatos da região de Santa Luzia (nordeste do estado do Pará)
(Universidade Federal do Pará, 1977) OLIVEIRA, Nilson Pinto de; SCHWAB, Roland Gottlieb
Four occurrences of aluminum phosphates in Santa Luzia, Pará State. Brazil were studied in terms of their field relations, mineralogy and trace element contents. Crandallite is the dominant phosphate and less frequently wavellite can be found. The phosphates occur in metamorphic pre-Cambrian rocks of the Gurupi Group and are essentially structurally controled. A disseminated level of crandallite at the basis of the metamorphic sequence, problably originated from the alteration of sedimentary apatite, is considered to be the source of phosphate which was dissolved by solutions flowing through it. These phosphorous-rich solution moved upward and precipitated phosphate-bearing minerals in the upper units of that metamorphic sequence. The occurrences have no economical value in the mapped area but the presence of a crandallite level with about 16 wt. % P2O5 leads to consider prospecting for phosphate in the neighboring areas to be attractive.
Acesso aberto (Open Access)
Pesquisas mineralógicas e geoquímicas para a distinção de basaltos intrusivos e extrusivos no Vogelsberg Alemanha Federal
(Universidade Federal do Pará, 1977-07) OLIVEIRA, Elson Paiva de; SCHWAB, Roland Gottlieb
In a drill hole of 450m made in the central part of the volcanic complex Vogelsberg, West Germany many authors found an alternating sequence of alkali olivinbasalts and tholeiites, consisting of 7 series with a total of 293m. Radiometric age dating suggests that two of the alkali olivinbasalts are intrusive. One of them, serie 3, however shows traces of weathering on its surface. The present study includes chemical analyses of major and trace elements (Ni, Co, Cu, Zn, Li and Be) as well as mineralogical investigation by means of X-ray diffraction and optial methods. The objective of these analyses was the chemical and mineralogical characterization of the weathering horizons and of the possible effects of differentiation in the units considered intrusive. The commom association of haematite, montmorillonite and quartz fragments in the weathered horizons, as well as the increase of Ni, Co, Cu, H2O and Fe2O3 and the decrease of Li, Be, FeO, MgO and CaO from the bottom to the top of one of the "intrusive units" in serie 3, shows that this unit was exposed to the earth's surface and therefore cannot be considered intrusive. The other alkali olivinbasalt in serie 5 shows incipient gravitative differentiation effects but witho ut significant textural variations. On the other hand there is amigdaloidal texture on its top suggesting also an extrusive nature.
Acesso aberto (Open Access)
Elementos traços no caulim do Rio Capim, estado do Pará
(Universidade Federal do Pará, 1977-10) MONTEIRO, Reginaldo Wanghon; SCHWAB, Roland Gottlieb
The parent rock material controls the trace element content of a kaolin. The trace element association of Rio Capim kaolin is examined and utilized to verify the provenance of the deposit. The method of emission spectrographye is used for the analysis and is described in its essential parte, in particular the construction of the work curve and the detection limite of the elements The trace element association of the deposit is compared with the trace element association of other kaolin deposits of known provenance. On the basis of this comparison, it is concluded that the deposit was formed by weatering of a granitic parent rock. These conclusions confirm geologic observations about the deposit and the assemblage of heavy minerals, indicating a paraautochtonic origin.
Acesso aberto (Open Access)
Mineralogia e petrologia do complexo ultramáfico e alcalino de Santa Fé - GO
(Universidade Federal do Pará, 1978) SOUSA, Ana Maria Soares de; GIRARDI, Vicente Antonio Vitório; http://lattes.cnpq.br/6876269679513816
Acesso aberto (Open Access)
Relaxações dielétricas do sistema carvão-pirita
(Universidade Federal do Pará, 1978-07) PAIVA, José Airton Cavalcante de; ALVAREZ BEJAR, Román
Acesso aberto (Open Access)
Estudo em laboratório de anomalias de potencial espontâneo
(Universidade Federal do Pará, 1978-11) FERREIRA, Lindalva do Carmo; ALVAREZ BEJAR, Román
This 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.
Acesso aberto (Open Access)
Métodos geofísicos aplicados a prospecção de água subterrânea no município de Ponta de Pedras - Ilha de Marajó - Pará
(Universidade Federal do Pará, 1979-02-22) KOBAYASHI, Carmelina Nobuko; SAUCK, William August; http://lattes.cnpq.br/6655455534234531
This work was perfomed in an area of 25 km2 in Ponta de Pedras, Marajó Island. The purpose of this work was to study the geometry of the aquifers and to select favorable zones for development of ground water. Two geophysical methods were used: seismic refraction and electroresistivity. The first one was used experimentally intending to find out the possibility of its application in the area. The seismic results obtained confirm the original expectance of the existence of shallow geologic horizon at the subsurface, not able to be distinguished by the seismic method. Vertical electrical soundings and horizontal perfil resistivity were done with the electrical resistivity method. The results of the interpretation point out favorable areas in the central part of the study area and in a zone extending to the north of the prospected area. The thickness of the shallow aquifer varies between 0 and 50 m.
Acesso aberto (Open Access)
Estratigrafia e evolução estrutural do segmento setentrional da faixa de desdobramentos Paraguai - Araguaia
(Universidade Federal do Pará, 1979-06-13) ABREU, Francisco de Assis Matos de; HASUI, Yociteru; http://lattes.cnpq.br/3392176511494801
The northern part of the Paraguai-Araguaia orogenic belt comprises a significant portion of the South American Platform. Here, the Brazilian geotectonic cycle (550-900 m.y), produced a mountain chain through a complex sequence of sedimentary metamorphic, magmatic, and structural events along the eastern margin of the Amazon craton. The lithologic sequence is designated stratigraphically as the Baixo Araguaia Supergroup which comprises the Estrondo Group and the overlying Tocantins Group. The basal formation in the Estrondo Group is the Morro do Campo Formation which consists of quartzites and subordinate schists and gneisses. The Xambioá overlies the Morro do Campo and includes several kinds of schists. The Tocantins Group is formed by Couto Magalhães Formation, represented by phyllites and intercalated quartzites and the overlying Pequizeiro Formation consiwts of pelitic sediments and Mg-rich igneous derivatives. The Estrondo and the Tocantins groups are intruded by ultramafic, mafic, and granitic rocks that are associated with late and post-tectonic igneous events. The Rio das Barreiras Formation, a sedimentary sequence represented by a polymictic conglomerate with carbonate matrix and sandy and silty interlayers, unconformably overlies the Pequizeiro Formation and may represent erosional remnants of a final phase of the Brazilian cycle. Primary lithologic structures in Baixo Araguaia Su pergroup are preserved as relict compositional stratification, inclined, parallel, and graded bedding in metasediments, and flow structures in the igneous rocks. Superposed penetrative planar and linear deformation structures are present in several generations. The regional N-S striking schistosity is of axial-plane type and is related to the intrafolial folds, with an easterly dip getting vergence to Amazon craton. The regional dip is 309 and decreases to abaut 159 adjacent to the Amazon craton. Gneissic banding parallels schistosity of overlying schists in the larger folds and they share a common mineral lineation. Polyphase deformation is recorded by a fold sequence which varies in scale from 1 cm to 30 km and is related to the differents structural levels within the crust. The lower structural level includes: a) similar-type intrafolial isoclinal folds which are contemporaneous with regional metamorphism; b) similar tight folds which involve the s.chistosity and transposed bedding; c) shear folds of crenulation developed near to the top of the level in the more plastic horizons. The intermediate level comprises; d) isolated regional flexures near the localities of Colméia, Xambioà-, Lontra, Muricizal; e) two generations of open and cross folds associated with the Iriri-Martírios lineament zone. N-S and NW-SE fracture and fault systems cut ali stratigraphi.c units of the Baixo Araguaia Supergroup. The faults consist of: 1) NW treding transcurrent fault with strike iengths of severa]. Kilometers; 2) thrust faults with N-S- strike such as those near Andorinhas and Muricizal mountains; 3) N-S striking normal faults developed at the edge of the Parnaíba basin and elsewhere. The mapped facies sequence ranges from incipient greenschist facies in the west to amphibolite facies in the east implying an Bastward increase in metamorphic grade. Sericite to garnet isograds are discernibles. Three magmatic events are distinguished. They comprises: a) pre-tectonic basic and ultrabasic plutonic-volcanic magmatism; b) late-tectonic granitic intrusion; c) post- tectonic unfoliated granitic intrusions. Eleven K-Ar mica dates from gneisses and schists of the orogenic belt yield values in the range of 516 ± 10 m.y to 358 ± 19 m.y. (Brazilian Cycle). Five Rb/Sr determinations from the gneissic core of the Colméia fold gives values around 2,000 m.y (Amazonic cycle). The geologic evolution of the northern Paraguai-Araguaia orogenic belt consists of three sequential stages: I) deposition of psammitic and pelitic sediments comprising the Estrondo and lower Tocantins Groups. Basic and ultrabasic igneous activity in late Tocantins time result in the deposition of mixture of pelitic sediments and Mg-rich igneous material which comprise the Pequizeiro Formation. II) polyphase deformation, metamorphism, magmatism, and orogenic uplift followed. These events are subdivided as follows: 1) F1 - deformation and regional metamorphism (Ma) in which So (original bedding) was transposed by isoclinal folding to S1 (regional schistosity) and progressive metamorphism produced sericite and garnet map zunes; 2) F2 - deformation produced tight folds in the schistosity (S1) resulting an axial plane surface (S2); well-marked mineral lineation (L2); 3) F3 deformation developed crenulation folds and a second phase of transposition (S3); e) F4 - deformation produced large folds accopanied by migmatization and late-tectonic granitic intrusions; 5) F5 - deformation formed small-scale plastic folds in cataclastic zones along the Iriri-Martírios lineament. III) The post-metamorphic Rio das Barreiras Formation was then deposited unconformably over this structural sequente and the final deformation event produced fault movements (transcurrent, thrust and normal), established joints, and permitted the rise of post-tectonic granitic plutons. This stage marks a transition from an environment of compressional stress to one of tensional stress on the regional scale. Subsequent to stageIII, consolidation of the South American platform occurred. Related erosional, sedimentary, magmatic, and'tectonic processes affedted this ares at numerous times throughout post-Brazilian cycle time.
Acesso aberto (Open Access)
Eletroresistividade aplicada ao estudo de água subterrânea no município de Salvaterra-Marajó-Pará
(Universidade Federal do Pará, 1979-08-14) BEZERRA, Cesar Augusto Campos de Alencar; SAUCK, William August; http://lattes.cnpq.br/6655455534234531
A pilot area of 200 Km2 in Salvaterra county along the east edge of Marajo island was selected to make a study of groundwater using electrical resistivity methods. Sixty-five Schlumberger vertical electric soundings and six horizontal Wenner resistivity profiles were made. The sounding data were first interpreted individually with the auxiliary point method, and later reinterpreted in groups using an iterative curve-calculating routine. The results show the range of resistivities in this area vary between 5 and 40000 ohm-m. The aquifer appears to be defined by a sequence of layers with resistivities between 500 and 4000 ohm-m. In this pilot area three favorable sub-areas were delimited, covering about 40% of the area, where the interpreted aquifer thickness is in excess of 20 m and sometimes as great as 80 m. The depht to the top of this aquifer zone varies between 1.3 and 6.6 m in the three sub-areas. The geophysical interpretations were verified by four shallow drill holes (to 20 m). Two of these, located within the favorable sub-areas, showed dominantly sand sediments and the other two, drilled outside the favorable areas, showed much more clay and organic material, but limited amounts of fine sand. Analyses of water samples from many existing wells and of the new drill holes show that, in general, there are no problems with the quality of these shallow groundwaters. The only exceptions are several wells withing 100 m of Marajo Bay which show considerable increases in salinity during the height of the dry season, when the Bay waters also have maximum salinity. The ages and origin of the long oval belts of sand are not known with certaint, but they could be channel sands deposited by an ancient river or distributary of this deltaic region. The results of this research have outlined three large zones of good groundwater potential which will be very important for the agricultural and industrial development of this region.
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/6655455534234531
Laboratory 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.
Acesso aberto (Open Access)
Hidrogeologia da área piloto Ponta de Pedras - Ilha do Marajó
(Universidade Federal do Pará, 1979-08-14) PIUCI, Jacyro; REBOUÇAS, Aldo da Cunha; http://lattes.cnpq.br/7322958772719317; FENZL, Norbert; http://lattes.cnpq.br/6834981018643186
A shallow aquifer which is very important for the development of the Ponta de Pedras region has been found and studied. Most of this aquifer is semiconfined, excepted in some areas where he can be considered as beeing free. In various wells drilled in the western part of the area and also near Igarapé-Vilar, the aquifer could not be detected. The maximum depth of the top of the aquifer reaches 14m. The depth of the base of the aquifer and its thickness exceeds respectively 34m and 17m in the well at Mangabeira. Its recharge is principally by means of meteoric water and the infiltration rate was estimated to be 106 to 107 m3/day/km2 for the month of February 1977. The effective porosity was estimated to be between 25% and 37% permiting the calculation of a volume of stored ground-water of 250x109 liters. The average Darcy coefficient (K) of the aquifer system is approximately 200/l/day/cm2. The studied ground water has the following physical and chemical characteristics: pH always acid, between 2,4 and 6,7; electrical conductivity between 13 and 2000 μmhos/cm, the most conductive waters being from the region of the basin of the Tijucaquara River; silica with average concentration of 10,4 mg/l; total iron with very low concentration implying soft water in most of the samples; manganese with a mean concentration of 0,15 mg/l; nitrogen and phosphorous with low concentrations. Sodium and potassium showed the best correlation with seasonal precipitation. At the end of the rainy season the ground water shows extremely low concentrations of nearly all elements. During the period of infrequent rainfall and until the beginning of the rainy season, the salinity increases in some areas and this causes the water to be non-potable. The domestic use of these waters is normally limited by the following characteristics: pH too acid; total iron much over 0,3 mg/l with a maximum of 4,0 mg/l; lack of fluorides; excess of chloride in one well but generally very low contents of most chemical elements. The use of these ground waters in agriculture may be limited in some parts of the area where the pH is less than 5; the conductivity too high during the dry season and when the sodium content reaches 83% to 97% (SAR).
Acesso aberto (Open Access)
Geofísica aplicada à prospecção de água subterrânea na área do Rio Paracauari – Ilha de Marajó - Pará
(Universidade Federal do Pará, 1979-08-24) CAVALCANTI, Gerardo Majela Lima; SAUCK, William August; http://lattes.cnpq.br/6655455534234531
The Rio Paracauari pilot study area in the east-central part of Marajo Island is typical of the low, planar, natural grasslands of this deltaic region. The cattle ranches of this area suffer considerable losses during the dry seasons because the groundwater is generally brackish. A 250 Km2 study area was chosen in wich geo-electrical methods were used to search for and outline any shallow fresh-water aquifers which might be present. Fifty-three Schlumberger vertical electric sondings were made on a grid of approximately 2 by 2.5 Km, as well as 5 horizontal Wenner resistivity profiles. The VES data were initially treated with the auxiliary point method and later, groups of models were constructed using a curve-generating routine to fit the field VES curves. The geo-electric results show two types of terrain. The first with higher resistivities, reaching to 950 ohm-m, is characterized by long (10 Km) belts up to one Km wide with dominantly sand sediments beginning near surface and extending to depths on the order of 60 m. These are saturated with potable water, with the water table typically at depths of only 2 to 5 m. These aquifer zones cover less than 30% of the area. The second type of terrain occupying the rest of the area has resistivities less than 6 ohm-m and often as low as 0.5 ohm-m, and is interpreted as silts and clays with saline water. Water samples taken from the surface and from shallow wells show a range of resistivities between 1.1 and 362 ohm-m. Seven drill holes were made, to depths as great as 54m. These verified the geophysical interpretations and clearly showed the differences between the channel-fill deposits which constitute the aquifers (channel sands or point bar deposits) and the fine, organic and clay-rich sediments of the adjacent flood-plain environment. Several of the drill holes were completed as water wells and now supply potable water on two of the ranches. Although the ages of the sediments are unknown, these large channels could have been excavated during the Pleistocene sea-level minimum and later filled with coarse, medium, and fine sand as sea level rose again, diminishing the velocities of the rivers or distributaries passing through the region. There has since been a drainage reversal, with the belts underlain by channel sands now existing as slight topographic highs, which could be explained by differential compaction.
Acesso aberto (Open Access)
Estudo sedimentológico da formação Pedra de Fogo-Permiano: Bacia do Maranhão
(Universidade Federal do Pará, 1979-10-17) FARIA JUNIOR, Luis Ercílio do Carmo; TRUCKENBRODT, Werner Hermann Walter; http://lattes.cnpq.br/5463384509941553
The Pedra de Fogo Formation of the Early-Middle-Permian in the Maranhão Basin is characterized by a ciclic sedimentation with fine sandstone intercalated with siltstones, shales and carbonatic banks which have abundant sílex beds and concretions. On surface this unit is divided into three members named Basal' Silex, Middle and Upper, Trisidela. Silicified oolites, pellets, coquinas with ' fish remains, stromatolitic beds and wood remains are found in the Pedra de Fogo. Formation sediments. The lithologies indicate a shallow, restricted, marine environment ' with two transgressions phases separated by a regression phase. The lateral facies changes reflect the sedimentary dynamism and suggest that the marine environment progressed from a transitional, deltaic to shallow neritic one. The main source areas of the clastic sediments and some of the sílica are, located in the northestern to the southern parts of the Basin and derived ' from the Borborema and São Francisco Provinces rockes. The Tocantins and. Tapajós Provinces to the west and southest have supplied material also. The climate during the Pedra de Fogo sedimentation has varied from moderate to arid as a consequence of the northward South American continent slow migration. The Maranhão had tectonic stability during the Permian. The marine in cursions took place from west, through the Amazonas Basin. Besed on the cyclothemes thickness, it seems that the Pedra de Fogo sedimentation occured from the water level oscilations in the Basin, which had also motivated the transgressions and regressions phases and whose origin should be related to the climatic changes during the Permian time.
Acesso aberto (Open Access)
Métodos geofísicos aplicados ao mapeamento geológico numa área da Região Bragantina-Pará
(Universidade Federal do Pará, 1979-12-13) FERREIRA, João Batista; SAUCK, William August; http://lattes.cnpq.br/6655455534234531
The following research is about the aplication of geophysical methods in a pilot area in the Bragantina region, NE of Pará, as an auxiliary to geologic mapping. The area is covered with thick tertiary sediments and presents occurrences of industrial rocks such as limestone and granite, representing an outcrop surface smaller than 5% of area. Studies carried out by Goulart (1978) revealed that it is impossible to determine parent rock of the superficial material, of the A horizon. This makes difficult the surface geologic mapping and can lead to exaggerated extrapolation of the contacts, such as that which took place in the preliminary mapping. The geophysical methods applied in the area are: Electroresistivity and Magnetometry. Some mechanical sounding was carried out also. The results obtained contributed to a better understanding of the structural features mapped, and also made it possible to discover other important features. Two areas were defined for future detail study, with the objective to distinguish between the limestones of better and poorer quality. In reference to the granite region a new mapping of that area is suggested.
Acesso aberto (Open Access)
Equipamento eletromagnético para prospecção geofísica e modelamento reduzido
(Universidade Federal do Pará, 1979-12-13) FONSECA, Nélio Raimundo Medeiros da; VERMA, Om Prakash; http://lattes.cnpq.br/2723609019309173
In the last decade, electromagnetic methods constituted an efficient technique for prospecting of minerals. The objective of this work was to develop an equipment for quantitative electromagnetic prospecting of conducting bodies using dipole-dipole technique. The equipment can also be adopted for reduced scale model experiments. The equipment, in principle, measures the variation in the mutual electromagnetic coupling of two coils, namely the transmitting and the receiving coils. Ground will also contribute to this coupling when the coil system is used near it. This mutual impedance of the transmitter – receiver - ground system shall vary in the vicinity of an anomalous conductor which is manifested as a variation in the signal induced in the search coil. The equipment consists of two sets: a transmitter and a receiver alongwith accessories. The transmitter generates an electromagnetic field at frequencies of 520 Hz and 3090 Hz, and a reference signal for the receiver which is connected through a cable. The receiver first separates the anomalous secondary e.m. field from the uniform primary field. Then this secondary signal is decomposed into two orthogonal components, one inphase and other in quadrature with respect to the primary field. Amplitudes of these phase components can be measured directly in terms of the percentage of the primary field within a precision of 1%, using two amplitude scales. The sensibility of the receiver is 0.5 μV. Electronic circuits were rigorously tested by using precise laboratory instruments. The performance of the e.m. equipment was verified (a) by carrying out classical e.m. model experiments in the laboratory and comparing them with the published results; and (b) by taking some e. m. traverses in an area near Araci, in the State of Bahia, which has been prospected by "Rio Doce Geologia e Mineraçáo S/A-DOCEGEO". All these tests verify a highly good performance of the equipment in terms of its precision and usefulness for field work.
Acesso aberto (Open Access)
Métodos geofísicos aplicados à arqueologia no Estado do Pará
(Universidade Federal do Pará, 1979-12-13) ALVES, José Jerônimo de Alencar; LOURENÇO, José Seixas
This study is the first attempt to apply geophysical methods in research into archeological sites in Brazil. These methods were used with the objective of detecting archaeological remains in the sub-soil in two archaeological sites in the State of Pará: site PA-SA-4, from the Areão archaeological phase, and "Ilha dos Bichos" site from the Marajoara phase. In PA-SA-4, the magnetic method was employed, while at "Ilha dos Bichos" both electro-resistive and magnetic methods were used. The electro-resistive method made possible the determination of the occupied layers, since these behave like geoelectrical beds, different from those of the geological formations of the area. It also permitted the detection of compact layers of clay, planars and horizontals, of archaeological origin, located on the east side of the "Ilha dos Bichos". The magnetic method led to the detection of ancient firing places, thanks to the thermo-remnant acquired by the clay in the process of heating/cooling, and thus permitted the discovery of ancient kilns, as well as a burial urn under a thick bed of burnt clay.
Acesso aberto (Open Access)
Métodos geofísicos aplicados à prospecção de cobre na Serras de Carajás - Pará
(Universidade Federal do Pará, 1980-03-20) HOOKER, Enrique Campbell; SAUCK, William August; http://lattes.cnpq.br/6655455534234531
Through an agreement between the Federal University of Para and the Rio Doce Geologia e Mineração Company, a geophysical research was carried out in the area known as ALVO 1, MM1, Serra dos Carajás, south of Para, Brazil. The magnetic, electrical induced polarization and AFMAG methods were applied, to detect the distribution of copper in subsurface. This work was carried out both on a 9 km2 reconnaissance area (ALVO 1) and on a 0.63 km2 detail area (Corpo 2). The AFMAG method detected various conductors displaced from each other by possible faulting. The orientation of these conductors, coincides with the dominant strike of the body of schist which contains copper sulfide, associated with an iron formation. The close correlation they have with the magnetic anomaly, may imply that the AFMAG anomalies are caused, firstly by the iron formation and secondarily by the sulfide. The magnetic method detected strong anomaly over the iron formation. The displacement of the segment of the anomaly impleis faulting. This method is very important in the area due to the association of the sulfide zone with the iron formation. The electrical induced polarization/resistivity method detected anomalies with PFE, varying from 6 to 12% approximately. Several of these anomalies were confirmed by mechanical sounding and laboratory research (Rocha, 1979). It was verified that these anomalies were caused by a combined effect of the iron formation and the sulfide body. The geophysical research carried out at this pilot area turned out to be very important considering the fact that its results can be successfully extrapolated to a larger area with the same geological characteristics.