Programa de Pós-Graduação em Geologia e Geoquímica - PPGG/IG

URI Permanente desta comunidadehttps://repositorio.ufpa.br/handle/2011/2603

O Programa de Pós-Graduação em Geologia e Geoquímica (PPGG) do Instituto de Geociências (IG) da Universidade Federal do Pará (UFPA) surgiu em 1976 como uma necessidade de desmembramento do então já em pleno desenvolvimento Curso de Pós-Graduação em Ciências Geofísicas e Geológicas (CPGG), instalado ainda em 1973 nesta mesma Universidade. Foi o primeiro programa stricto sensu de Pós-Graduação (mestrado e doutorado) em Geociências em toda Amazônia Legal. Ao longo de sua existência, o PPGG tem pautado sua atuação na formação na qualificação de profissionais nos níveis de Mestrado e Doutorado, a base para formação de pesquisadores e profissionais de alto nível. Neste seu curto período de existência promoveu a formação de 499 mestres e 124 doutores, no total de 623 dissertações e teses.

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Acesso aberto (Open Access)
Avaliação da influência dos cátions Na+, Ca2+ e Mg2+ na desativação de Ca, Mg-Bentonitas
(Universidade Federal do Pará, 2015-04-28) CARMO, Andre Luiz Vilaça do; ANGÉLICA, Rômulo Simões; http://lattes.cnpq.br/7501959623721607
In Brazil there is no occurrence of sodium bentonite, because of that, companies that explore this mineral raw material using a denominated sodium activation process, which is the exchange of cations in the interlayer space by Na+. Through this process, the bentonite present considerable improvements in their properties rheologies. However, after some time, these properties decline, which has been called deactivation. Thus, the objective of this study was to evaluate the influence of cations Na+, Mg 2+ and Ca2+ in the bentonite deactivation. For this, three bentonite considered calcic, from the state of Paraíba, and a magnesian, coming from the state of Maranhão, were studied in its natural form, activated and washed. The mineralogical phases of the samples were identified by X-ray Diffraction (XRD), chemical composition by Inductively Coupled Plasma Mass Spectrometry (ICP-MS) and cations in the interlayer by Cation Exchange Capacity (CEC). The rheological properties’ study was carried out by swelling. The XRD patterns showed that the dioctahedral smectite is the dominant mineral phase. There was the improvement in swelling results of all bentonite after the sodium activation, as well as subsequent decrease in the swelling value over 95 days (deactivation). Only one of the bentonite remained activated. The swelling results of washed bentonite showed increased for approximately the first 35 days, with subsequent decrease. The chemical composition results showed that a small amount of Na+ is removed from the washed bentonite. Furthermore, these results indicate that not only Na+ influences the swelling, but also Ca2+ and Mg2+ cations.
Acesso aberto (Open Access)
Caracterização geológica da suíte ofiolítica Serra do Tapa, SE do Pará – Cinturão Araguaia
(Universidade Federal do Pará, 2015-04-30) BARROS, Luisa Dias; GORAYEB, Paulo Sérgio de Sousa; http://lattes.cnpq.br/4309934026092502
In northern Araguaia Belt (CA) along its low-grade metamorphic domain, the region known as Serra do Tapa, between the municipalities of Sapucaia and Xinguara, SE Para exposes one of the largest CA ophiolite bodies interpreted as fragment of oceanic lithosphere the Araguaia basin in Neoproterozoic. The Suite Ophiolitic Serra do Tapa (SOST), denominade in this work, is a set of elongated bodies with a length of 48 km with preferential orientation in the direction N-S. It represents a dismembered ophiolitic sequence comprising serpentinized peridotites, massive and pillow basalts, volcanossedimentary rocks, iron formation and cherts. All this set embedded through thrust zones in the metasedimentary rocks of low metamorphic grade of Formation Couto Magalhães. The serpentinized peridotites have dark or light green, coarse-grained and represent the basal portion of the stratigraphic sequence suite. Originally, the peridotites were probably the harzburgite and dunites type. The harzburgites have protogranular texture, with a marked presence of pseudomorphic textures bastite type and mesh, which result from orthopyroxene transformations; and olivine to lizardite, respectively. The dunites have mesh predominant texture, with the presence of fine chromite grains dispersed in the matrix composed of serpentine (lizardite). The volcanic unit of suite represented by massive basalt submarine flows and pillow structures. The basalts occur as homogeneous flows, massive and in the upper portions feature marked for pillow structure, and locally, breccia flow surface (hyaloclastites). The pillows have a zoning, where in the core consists of massive basalt greenish brown color, aphanitic with intersertal texture composed of crystals of plagioclase, volcanic glass and Clinopyroxene. At the edge zone are present glassy basalts of yellowish green color, aphanitics and quenching textures ultrafast as spherulites, and radial acicular crystals of plagioclase, textures type "swallowtail" and hollow sections. The hyaloclastites occur in the outer zone of the pillow and represent breccias surfaces basaltic. Finally, basalt glass is dark green color of the surface flows (interpillow zone). The volcanossedimentary interface sequence is the interaction between the basalt flows and pelitic sedimentary rocks. The tuffaceous mudstone consists of a pelitic matrix with lytic fragments of metabasalt stretched and broken. The sedimentary portion of the suite consists of iron formation and cherts and represent the chemical sedimentation records in deep-sea ocean environment, is the upper portion of this ophiolitic suite. Another important feature is the presence of sinistral strike-slip shear zones and dextral of kilometric extensions with preferential orientation NE-SW and EW. All structures truncated by normal faults of NW-SE direction. The rocks of Formation Couto Magalhães evidence of metamorphism is most obvious in slates and phyllites (sericite and chlorite formation) in serpentinized peridotites occurs generation of non-superposition serpentine pseudomorphs of pseudomorphs, the massive basalts, the metamorphic association is defined by ab + Tr act + Cl + Ep ± Stp; the paragenesis of these rocks indicate metamorphic transformation in greenschist facies low. For lithochemical studies were prioritized portions of the core of the pillow, which remained in many cases, the protected metasomatic transformations. Divergent data in some samples can be explained because they are samples closest to the edges of the pillows, which suffered intense transformation due to oceanic metamorphism. Geochemically, the basalts show subalkaline nature, tholeiitic compatible with the MORB type. Sr negative anomalies may indicate plagioclase retention during partial melting events from depleted mantle source. The ETR diagram shows slightly depleted behaviors of LREE and enriched in heavy REE and smooth Eu anomaly; and this pattern confirmed the reasons (La / Yb) N and (La / Sm) N <1 magmas also point to the N-MORB type. The evolution of the suite is on the development of oceanic Araguaia Basin with the generation of an old oceanic lithosphere to rise and perhaps upper mantle exposure, volcanism forming the deep ocean substrate and sedimentation (tuffaceous mudstone, banded iron formation and cherts). Later detachment processes of the substrate crust / mantle led to the tectonic inversion of the sequence, leading to compressional tectonic phase, which led to obduction of ophiolite bodies, generating a late thrust and transcurrent system with movement toward the Amazonia Craton, segmented the ophiolite bodies and mixing them with rocks Couto Magalhães Formation accompanied by regional metamorphism of greenschist facies low.
Acesso aberto (Open Access)
Cristaloquímica da sodalita Bayer derivada de bauxitas com alta sílica reativa de Paragominas-Pa
(Universidade Federal do Pará, 2016-05-24) MELO, Caio César Amorim de; ANGÉLICA, Rômulo Simões; http://lattes.cnpq.br/7501959623721607
In the Paragomina’s region, as well as the whole Brazilian north, gibbisitic bauxite deposits commonly shows high amount of kaolinite. The processing of this bauxites (called as High Silica Bauxites - BASR) became a challenge because in the conventional conditions of the Bayer process, the kaolinite is undesirably leached by NaOH solution, and then precipitated as sodalite. The formation of this phase brings a significant increase in process costs, both by increasing the processing time as the irreversible loss of NaOH robbed from the system to form sodalite, which is then discarded in the red mud. Given this metallurgical problem this study aimed to investigate the crystal chemistry of sodalite formed in conventional conditions of the Bayer process, so that, from these results, studies to reduce these losses of the process and facilitate the processing of BARS can be developed in the future. The materials investigated were kaolinitic gangues from 4 lithologies of an exploration well in Miltonia 3 mine (BN, BNC, BC and BCBA), as well as a kaolin from IMERYS S.A. The digestions were carried out in Teflon-lined, stainless steel autoclaves, using 1 g of solid material, 25 mL of NaOH solution and at a temperature of 150ºC in an oven. The NaOH concentration and the reaction time ranged from 2,5 to 5,0 M and 60 to 420 min, respectively. Then the solid material was characterized by XRD, DTA/TG, FTIR, SEM and ICP-OES. The results of the starting materials showed that the kaolin sample is essentially constituted by kaolinite, which has a high structural ordering degree. All the samples of kaolinitic gangue showed the same minerals: gibbsite, kaolinite, hematite, goethite and anatase. By the observation of the XRD patterns and DTA curves can be noted that the BN and BNC samples are more reactive than the others, possibly due a lower structural ordering degree and particle size. In the experiments with kaolin, it can be observed that are formed not one, but two sodalite phases, which coexist practically throughout the whole process and tending to an equilibrium phase. These two phases differs themselves by the amount and behavior of the NaOH and H2O molecules within the framework. The results of the refinments showed that these phases were: basic sodalita with cell parameter (ao) ~ 8,96 Å, which is predominant in the initial stages of the transformation, and hydrosodalite with ao ~ 8,85 Å dominant in the secondary stage (mainly in 180 min). The XRD results from kaolinitic gangues showed that in 60 min there was no full kaolinite/sodalite conversion, and the sodalite patterns in BN and BNC were more intense and well defined than BC and BCBA, confirming that these samples have more reactive kaolinites. The increase of the reaction time and NaOH concentration provided a slight increase of the structural sodalite order. It may be noted that in almost all experiments the only phase formed was basic sodalite. The exceptions were the lithologies: BCBA and BC, which hydrosodalite was formed in the highest time of reaction and NaOH concentration, thus showing that this phase is directly associated with a higher time, concentration and crystallinity of kaolinite available in the reaction medium. It can be observed that throughout the reaction, in shorter time and concentration it is not possible to achieve a balance, which leads to a constant interchange of predominant phase in the system. In the higher time and concentration experiments, a balance is virtually reached, in order that it cannot be observed separated diffraction peaks. However there is no significant increase of the structural ordering even for extreme times as 3 days of reaction. The ammonium chloride experiments showed that this reaction medium allows the formation of more crystalline phases than all others achieved in this research. However, it did not result in the diminished of the sodium consumption.
Acesso aberto (Open Access)
Desenvolvimento de processos de síntese de sodalita a partir de rejeitos de caulins da região Amazônica
(Universidade Federal do Pará, 2013-01-17) SILVA, Liliane Nogueira da; NEVES, Roberto de Freitas; http://lattes.cnpq.br/9559386620588673
In the study of the Sodalite synthesis used two wastes kaolins from two kaolin processing industries for paper coating, located in the Amazon region, operating in the region of Rio Capim (CRC) and Rio Jari (CRJ). Besides this, was also used as a source of silica and alumina to metakaolin, obtained by calcination of kaolin (MRC and MRJ, respectively). Preliminary chemical and mineralogical characterization of kaolin was performed to obtain information of its characteristics. The Sodalite synthesis was performed varying some parameters, such as starting material: kaolinite was used directly as starting material at temperatures of 80, 100, 120 and 150 °C, and, starting with metakaolinite at 95 °C. In order to observe the influence of ions OH, Cl- and CO32-, as well as Na2O/Al2O3 ratio, the syntheses were carried out varying the basic solutions, set temperature at 95 °C for the starting material MRC. Furthermore, the Na2O/Al2O3 ratio were maintained constant and temperature were varied in the reaction mixture to determine the ideal conditions for Sodalite synthesis. The starting materials and the synthesis products were identified and characterized by using XRay Diffraction (XRD) and Scanning Electron Microscopy (SEM) analysis, Thermal Methods (DTA/DTG) and Fourier Transform Infrared Spectrometry (FTIR). The method of synthesis that show best results were used as starting material metakaolin, with NaOH + Na2CO3 solution having Na2O/Al2O3 ratio of 3.89 conducted under stirring at 95 °C, atmospheric pressure and a time of 4 hours, for the two types of kaolin (CRC and CRJ). Using the MRC metakaolin, kaolin from the Rio Capim, under the above conditions was obtained by conversion of 86.5% by weight of sodalite and MRJ metakaolin, kaolin of the Rio Jari, the conversion was 73.6% in sodalite. All products were characterized as mesoporous materials, but starting from the product of metakaolin Rio Jari showed higher specific area.
Acesso aberto (Open Access)
Estudo de inclusões fluidas e química mineral do depósito aurífero do alvo Jerimum de Baixo, campo mineralizado do Cuiú-Cuiú, província aurífera do Tapajós, Pará
(Universidade Federal do Pará, 2018-03-06) OLIVEIRA, Helder Thadeu de; BORGES, Régis Munhoz Krás; http://lattes.cnpq.br/4220176741850416
The Jerimum de Baixo gold target is located in the Cuiú-Cuiú golfield, central region of the Tapajós Gold Province, Amazonian Craton. The target comprises monzogranitic rocks, essentially isotropic, that were weak to strongly hydrothermal and carriers of Fe-rich biotite. Chloritization, sericitization, sulfidation, silicification and carbonatization are the most important types of alteration. The produced chlorite is enriched in Fe of the chamosite type and was formed mainly between 280 and 315°C, whereas the white mica assumes muscovitic compositions. The mineralization is represented by quartz veinlets with low sulfide content (pyrite + pyrrhotite ± chalcopyrite ± galena ± sphalerite) in which gold occurs as free-milling particles and in more fragil and altered zones, usually associated with pyrrhotite. The petrographic and microtermometric study of fluid inclusions hosted in quartz veinlets defined aqueou-carbonic, carbonic and aqueous inclusions. The fluids with CO2 represent the probable mineralizing fluid and were generated by phase separation processes between 280 and 380°C, mainly. Further infiltration and mixing processes are indicated for the later aqueous fluids. Temperatures <400°C and the reduced character of the environment (pyrrhotite compounding the ore) point to H2S as the major ligand in the mineralizing fluid and Au (HS)-2 as the primary gold transporting complex. Phase separation, changes in pH conditions, and fluid/rock interaction were the important mechanisms for Au precipitation, which occurred at the brittle to locally brittle-ductile level of the crust (between 2 and 6 km). In general terms, Jerimum de Baixo presents similarities among the other deposits/targets previously studied in terms of hydrothermal alteration, fluid types and mineralization. The features observed in Jerimum de Baixo do not allow a classificatory framework absolutely adequate to any of the classical metalogenetic typological models. Characteristics such as type and style of hydrothermal alteration, type and low content of sulfides, types of fluids involved, estimated depth for mineralization, metallic association (e.g., S, Bi, Te), together with the good correspondence between the data collected in other deposits/targets in the Cuiú-Cuiú goldfield indicate for the Jerimum de Baixo target a gold deposit with magmatic-hydrothermal affiliation, presenting greater similarity to those deposits classified as belonging to Reduced Intrusion-Related Gold Systems (RIRGS).
Acesso aberto (Open Access)
Evolução mineralógica e geoquímica multi-elementar de perfis de solos sobre lateritos e gossans na Amazônia
(Universidade Federal do Pará, 1995-07-31) HORBE, Adriana Maria Coimbra; COSTA, Marcondes Lima da; http://lattes.cnpq.br/1639498384851302
With the aim of studying the genesis of soils developed on lateritic crusts, five profiles located in the region of Carajás (N5 and Igarapé Bahia procpects) as well as in Paragominas (Camoaí Mine) and Belém (Mosqueiro and Outeiro Beaches) municipalities all them located in Pará State, Brazil - have been selected. Based on the structures described in the profiles (N5, igarapé Bahia, Camoaí, Outeiro and Mosqueiro), it has been Possible to distinguish four differents horizons: fresh crust, partially-weathered crust, weathered crust and soil. The fresh crust is compact, vacuolar and composed of iron and aluminium oxyhydroxides. The partially-weathered crust is made up of fresh-crust relicts enclosed in yellowish or reddish clayey matrix, depending on the mineralogical composition of the fresh crust. The weathered crust is characterized by dominance of clayey matrix in relation to relicts, while the soil is composed exclusively of clayey material. The structures of the profiles show that the change from fresh crust to the overlying soil is gradual with volume expansion at the beginning of the fragmentat ion processes. This expansion is followed by the collapse of the profile as the relicts are entirely transformed into an earthy micro-aggregated material. The profiles of N5 and Igarapé Bahia prospects have been derived from a mature iron-aluminous crust, being characterized by the highest contents of kaolinite and hematite either in the crust or in the relícts. Gibbsite Al-goethite, anatasse and quartz are concentrated in the soil, which tends to be initially bauxitic, at the base of the profile, and to become kaolinite-rich toward the top. The mineralogical changes led to chemical modifications such as decrease in Fe2O3 and 8iO2 and increase in Al2O3, TiO2 and PF. The trace elements (V, Cr, Ni, R, Mo, Zr, Ga, Sc, Y, Mn, Cu and Pb besides Au in the profile of Igarapé Bahia) and REE's exhibit concentrations of 8 and Zr whereas the remaining ones tend to be progressively diluted from the crust toward the soil. The TiO2-mass balance shows that the transformation of the crust into soil took place by means of leaching of SiO2 and Fe2O3 in two profiles above mentioned, while Al2O2 underwent enrichment in the profile of N5 and leaching in the profile of igarapé Bahia. The soil formation from a mature aluminous crust in Camoaí differs from those described in the profile of Igarapé Bahia and of N5 in that it shows a decrease in gibbsite contents and an increase in kaolinite and quartz, whereas the verey low contents of ,hematite, goethite, and anatase do not present a characteristic distribution. The trace elements and the REE's, with contents much lower than those observed in the others profiles, show an increase in Zr and Mn toward the soil horizon and a dilution of the remaining ones. In the Camoaí, the transformation of the aluminous crust into soil, based on the TiO2-mass balance, took place through leaching of Al2O3 and enrichment in SiO2 and Fe2O3. In the profiles of Outeiro and Mosqueiro, deriveci from immature silicoferruginous lateritic crust the soil formation occurred by means of decreasing in hematite+goethite so that, in the resulting soil, quartz and kaolinite predominate. In consequence of this, a decrese in the Fe2O3 contents and an increase in SiO2 and Al2O3 have been observed in those profiles. The trace elements distribution presents, as in igarapé concentration of Zr and dilution of the remaining ones. Based on TiO2-mass balance, it could be noticed that the transformation of the crust in the profiles of Mosqueiro and Outeiro took place through leaching of Fe2O3, whereas SiO2 and Al2O3 underwent enrichment in the profile of Outeiro and Leaching in the one of Mosqueiro. On the basis of structures, mineralogical composition and geochemical data of the profiles, it has been possible to characterize an accentuated process of Fe loss in the iron-aluminous and in the silicoferruginous crust as well as Ai removal in the aluminous ones what led to soil generation. In the profiles derived from the iron-aluminous and the silicoferruginous crust, it has been observed substitution of hematite by Al-goethite, an intermediated segment - where there is predominance of gibbsite in the iron-aluminous profiles -- and presence of kaolinite at the top of both profiles. In every profiles, it has been reported quartz acumulation. The enrichment in quartz and the S1O2 being the latter likely come from externai sources -via vegetable-material decay - caused the neoformation of kaolinite from gibbsite in the profiles of N5, igarapé Bahia, and Camoaí. In the profiles of Mosqueiro and Outeiro the kaolinite presence in the soil is a consequence of its relative enrichment in the relation to the crust from which it has been derived. As a consequence of the mineralogical transformation, Fe has been leached from the profiles of N5, Igarapé Bahia, Mosqueiro, and Outeiro and Al from those of the Camoaí, as well as V, Cr, Mo, Ga, Sc, Cu, Pb and REErs. On the other hand, a strong enrichment in Zr and, in part, in 8 and Mn has been reported in every stud ied profiles. The transformations that caused the break down of the balance of the crusts, their desmantlement and comminution, forming relicts and a new clayey mineral phase, are consequence of organic matter influence which turns the environments conditions more acid and less oxidizing, in a process similar to that of weathering-profiles formation in humid tropical environments. The mineral and chemical difference observed between the profiles are consequence of compositional variation of the crusts which, in part, also reflect the degree of maturity of theirs. The mineralogical and geochemical characteristics of the soils in the investigated profiles allow us to correlate them to the Belterra Clay and, in consequence of this, to admit that Belterra Clay had an autochthonous origin in relation to the underlying lateritic crusts.
Acesso aberto (Open Access)
Os fragmentos de cerâmica arqueológica como fonte potencial de fertilidade dos solos TPA
(Universidade Federal do Pará, 2014-09-26) RODRIGUES, Suyanne Flavia Santos; KERN, Dirse Clara; http://lattes.cnpq.br/8351785832221386; COSTA, Marcondes Lima da; http://lattes.cnpq.br/1639498384851302
Soils of the Amazon Dark Earth (ADE) type are known for their high fertility, which contrasts with the typically poor soils found throughout most of the Amazon. The fertility of these soils appears to persist even after their intensive use for agriculture. The ADE are usually rich in sherds, important evidence linking them to the occupation of the region by prehistoric populations. Many studies have focused on the stylistic characteristics of the vessels represented by these sherds, although less attention has been paid to the chemical and mineralogical features of this material, which are important for the identification of the raw material use to produce the artifacts, provenience, technology, and in particular the origin of their relatively high P content. These high levels of P are derived from aluminum phosphates, which are generally amorphous to variscite-strengite, and have been linked to the use of the pots for the preparation of food. While the possible role of the sherds in the maintenance of the fertility of ADE has been widely discussed, no experimental data have been presented to confirm this connection. This study presents systematic evidence that the sherds contribute to the fertility of the soils. For this, sherds were obtained from three archeological sites with distinct characteristics located in different parts of the Amazon: Monte Dourado 1 (Almeirim, Pará), Jabuti (Bragança, Pará), and Da Mata (São José de Ribamar, Maranhão). Initially, 325 sherds were first described mesoscopically and then their chemical and mineralogical composition was determined by XRD, optical microscopy, TGA/DTA, FT-IR, SEM-EDS, ICP-MS and ICP-OES. Different parameters of fertility were then measured, followed by gaseous adsorption tests, and finally, P desorption assays. These data were used to identify the raw materials used in the fabrication of the vessels, details of the productive process, modifications occurring during the use of the utensils and after being discarded, with the aim of evaluating the potential contribution of these sherds to the fertility of the ADE soils. The hypothesis of contamination by nutrients from foods during the use of the vessels for the preparation of meals was confirmed by a laboratory experiment simulating cooking conditions using ceramic pots similar to the archeological artifacts, and measuring the incorporation of Ca and P during the cooking process. The results indicate that the ancient ceramicist peoples used raw materials available in the area surrounding their habitation sites. The composition of the sherds, all of which are made from a matrix of metakaolinite and quartz, and occasionally muscovite, indicating raw materials rich in kaolinite and quartz, which are fundamental to the production of ceramic artifacts. The presence of metakaolinite indicates that the pots were fired at approximately 550°C. However, the addition of different types of antiplastic contributed to chemical and mineralogical variation among sites in the overall composition of the sherds. At Da Mata, only cariapé was used, while at Monte Dourado 1, the cariapé was mixed with crushed rocks with a complex mineralogical content, and at Jabuti, shells were used in addition to cariapé. Amorphous phosphates are common to all the sites, albeit at distinct levels, with crystalline aluminum phosphates of the crandallite-goyazite type being found only at Jabuti, and Fe-Mg-Ca phosphates, segelerite, being exclusive to Monte Dourado 1. The amorphous phosphates and crandallite-goyazite were considered to be indicators of the use of the original pots (from which the sherds were derived) for the preparation of food, whereas the segelerite was interpreted as a neoformation following exposure of the fragments to the hydromorphic conditions that persist to the present day. The lowest phosphorus concentrations-1.04% of P2O5 on average- were recorded at Da Mata, and were similar to the majority of sherds studied up until now, whereas the highest concentrations (a mean of 7.75%) were recorded at Jabuti, the highest values yet reported. At Monte Dourado 1, the mean concentration was 2.23%. It seems likely that the high levels of P, Ca, and Sr are related to a diet rich in shellfish, as reflected in the diversity of shells fragments found in the sherds. The high levels of calcium recorded at Monte Dourado 1 reflect the presence of labradorite in the temper. The potential fertility of the sherds is clearly greater than that of the ADE soil when analyzed without the ceramics. It thus seems reasonable to assume that the sherds are the source of the macro- and micronutrients found in the soil. This was confirmed through desorption assays, which showed that P was desorbed at a slow rate, a characteristic which may be especially important for the persistence of fertility. This process is best described by the Freundlich model, which indicates the occurrence of interactions among the adsorbed ions. The experiment that simulated cooking conditions indicated that the Ca and P may be adsorbed into both the sides and lids of the ceramic pots, albeit with higher concentrations being accumulated in the sides. While calcium was adsorbed, no phase of this element was identified, either amorphous or crystalline, probably because the duration of the experiment was too short. By contrast, the chemical adsorption of the P did occur, and after 600 h of cooking, variscite, an aluminum phosphate, formed in the sides of the pots. Aluminum phosphates may thus form in the ceramic vessels during the cooking of food. These results indicate that the presence of aluminum phosphates in the matrix of the ceramic vessels represents a reliable indicator of their use as cooking vessels, and that the sherds of these utensils in the soil constitute a potentially important source of fertility.
Acesso aberto (Open Access)
Gênese das bauxitas nodulares do Platô Miltônia-3, Paragominas - PA
(Universidade Federal do Pará, 2017-12-12) CALADO, Waldirney Manfredi; ANGÉLICA, Rômulo Simões; http://lattes.cnpq.br/7501959623721607
There are two distinct levels of bauxites on the Miltônia-3 plateau located at the Bauxite Province of Paragominas-PA. These levels are separated by a pseudopsolitic to concretionary ferruginous laterite (FL) horizon, marking a hiatus between two distinct cycles of the current bauxite profile formation. The bauxites of the upper level (2nd cycle of formation) have nodular to concrete characteristics whereas those of the basal level (1st cycle of formation) are composed by a more physically complete concrete bauxite (CB) added by another level of a more friable bauxite with clayey portions for its base (concrete bauxite with clayey bauxite - CBCB). It was noticeable the CNB located at the upper level of gibbsite-enriched horizon with low reactive silica and iron contents, which are very similar to those found on the horizon of the main bauxite ore (CB) of the profile. In field observations, on the survey fronts and in the drill holes it was found that this CNB is a gradation of the above Nodular Bauxite (NB) horizon. This gradation is observed by the increase in the size of the bauxite nodules, where their Fe-gibbsite pseudopsolites grows up by coalescence, decreasing the diffused iron and silica contents marked by the change in color from lilac-yellow to a red-orange color, to ocher, in higher depths. It is also noticeable a decrease until the complete disappearance of the Al-ferruginous pseudopsolites, in addition to the decrease of the volume of gibsytic-kaolinite clay at this level. Based on this study using macroscopic and microscopic petrography, SEM/EDS, XRD and chemical analysis, as well as Principal Component Analysis (PCA) and descriptive statistics, two evolution model proposals were developed on the genesis of the upper level of nodular bauxites of this lateritic-bauxite deposit, considering: Model (1) - Origin from the degradation of the original bauxites (1st Cycle), related to a 2nd Lateritization Cycle which consists of the preexistence of mature bauxite (CB), overlapped by FL, which was covered by "Belterra Clay". This new nodular level (NB) occurs through the coalescence process whereby the residual aluminous phase junction occurred, resulting from the migration of Fe and Si in solution out of this level and by the migration of the neighboring levels above the clayey overburden (CAP) and below that of FL and CB, forming and concentrating large scale gibbsitepreferably and secondarily to kaolinite. With the continuous evolution of this level of NB, a maturation of the basal portion of this level is observed, forming the CNB whose nodules are interincreased, connecting locally, consuming neighboring levels above NB and levels below FL and CB, up to the total consumption of these; Model (2) - Its origin from a 2nd Lateritization Cycle, however from a later sedimentary deposition on the lateritic profile of the 1st Cycle. With the exposure of a source rock as a granitoid pluton (Cantão, Japiim, Jonasa, Ourém and Ney Peixoto of Neoproterozoic granites), gneiss (Archaean crystalline basement) or siliciclastic sediments (Itapecuru and Ipixuna Formations of the Upper Cretaceous), whose weathering degradation made it possible the generation of sediments of clayey nature preferentially kaolinite during the Paleogene until the beginning of the Oligocene. Migration of Fe, Si, Ca, Na, etc. occurred outside this level, preserving and concentrating the Al and O in situ, in addition to the residual Si. The process of coalescence allowed for the addition of the residual aluminous phase, preferentially concentrating the gibbsite and secondarily kaolinite, closing the first cycle of bauxite formation. Thereafter, there was a regional upwelling, followed by erosive processes that allowed for the exposure of this previously formed bauxite profile, under a seasonal climate, with an abundance of meteoric water and intense intercalated insolation, where the FL developed, of regional occurrence marking a hiatus between the formation cycles of these bauxites. New regional retraction movement, which allowed for the deposition of sediments of siliciclastic origin, which served as source rock for a new bauxite formation cycle during the Upper Miocene. They may be the same rocks from which physical and chemical degradation provided sediments for the 1st cycle of bauxite formation. Repeating the coalescence process of the residual aluminous phase, with the large scale development preferably of the gibbsite and secondarily kaolinite, closing the second cycle of NB and CNB formation.
Acesso aberto (Open Access)
Geologia, mineralogia e afinidades petrológicas dos granitóides neoarqueanos da porção central do Domínio Canaã dos Carajás
(Universidade Federal do Pará, 2017-10-28) OLIVEIRA, Vinícius Eduardo Silva de; OLIVEIRA, Davis Carvalho de; http://lattes.cnpq.br/0294264745783506
The central portion of the Canaã dos Carajás domain, located in the northern part of the Carajás province was originally marked by the occurrence of undifferentiated rocks belonging to the Xingu complex and Plaque suite, as well as greenstone belts, mafic rocks of the Pium diopside-norite and high K calc-alkaline leucogranites (Boa Sorte and Cruzadão granites). A semi-detailed geological mapping (1:100.0000) was carried out in the Vila União area and allowed the identification of several deformed granite bodies intrusive in the Mesoarchean units. They correspond to the most expressive unit of the studied area and are composed predominantly of monzogranites with chemical and mineralogical affinity with the Neoarchean A-type granites of the Planalto and Vila Jussara suites. The variable felsic and ferromagnesian minerals contents, as well as the different proportions between them, allowed to distinguish four major groups of granitoids: (i) biotite-hornblende monzogranites (BtHblMzG); (ii) biotite granites and leucogranites (BtLG); (iii) biotite-hornblende tonalites (BtHblTn); and quartz diorites (QD). The tectonic foliation of these rocks follows the regional E-W trend and exhibits high angles (70-85°). Well-developed core and mantle structures in quartz and feldspar crystals, as well as the presence of serrated and irregular contacts between these crystals suggest that dynamic recrystallization occurred at relatively high temperatures (> 500 °C). These rocks exhibit a wide variation in silica content (61.7 – 75.91 wt%), are metaluminous to slightly peraluminous and show affinity with A-type (high HFSE) and ferroan granites. Based on magnetic petrology studies it was possible to distinguish two groups of rocks: (1) granites containing only ilmenite with low magnetic susceptibility values (MS; <0.570 × 10-3 SI), and (2) granites with magnetite as the main iron and titanium oxide mineral and higher MS values (> 1.437 × 10-3 SI). Textural and compositional evidences indicate that magnetite and ilmenite are earlycrystallized phases and titanite has magmatic origin. Amphiboles are calcic and classified as hastingsite, whereas biotites are rich in the annite molecule. The relatively high Fe/(Fe + Mg) ratios found in the amphiboles of the BtHblMzG and BtHblTn varieties indicate that these granitoids were formed under low to moderate fO2 conditions, whereas in the BtLG the lower values of this ratio suggest more oxidizing conditions. Geothermometers point to crystallization temperatures between 830 – 930 °C in the different facies. The high total Al content in the amphibole crystals suggests crystallization at pressures between 400 and 800 MPa, indicating that these granitoids were emplaced at different crustal depths.
Acesso aberto (Open Access)
Mapeamento geoquímico e estimativa de Background em solos na região da Província Mineral de Carajás – Leste do Cráton Amazônico, Brasil
(Universidade Federal do Pará, 2018-03-09) SALOMÃO, Gabriel Negreiros; DALL’AGNOL, Roberto; http://lattes.cnpq.br/2158196443144675; ANGÉLICA, Rômulo Simões; http://lattes.cnpq.br/7501959623721607
This research is linked to the project 'Geochemical Background of the Itacaiúnas River Basin' under development by the Vale Institute of Technology Sustainable Development (ITVDS). In Brazil, geochemical surveys have been carried out mainly by the Companhia de Pesquisa de Recursos Minerais (CPRM – Brazilian geological survey), which has executed some projects focused on the region of Carajás, the largest mineral province in Brazil and in which the Itacaiúnas River basin is located. One of these projects, titled 'Evaluation of the Potential of the Strategic Mineral Resources of Brazil', carried out in the year 2012, covered the region of Canaã dos Carajás and generated a large collection of soil geochemical data. As such data were made available, the main purpose of this dissertation is to explore as much information as possible to elaborate multi-elemental geochemical maps based on interpolation techniques and to establish geochemical background values of the elements in soils of the target region of the CPRM survey. 225 soil samples, along with 32 duplicates, were collected in that project in an area of approximately 4,500 km2. The 80 mesh (0.177 mm) fraction of these samples was submitted to aqua regia digestion and 53 elements (Ag, Al, As, Au, B, Ba, Be, Bi, Ca, Cd, Ce, Co, Cr, Cs, Cu, Fe, Ga, Ge, Hf, Hg, In, K, La, Li, Mg, Mn, Mo, Na, Nb, Ni, P, Pb, Pd, Pt, Rb, Re, S, Sb, Sc, Se, Sn, Sr, Ta, Te, Th, Ti, Tl, U, V, W, Y, Zn, Zr) were analyzed by Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES) for the major and minor elements and Inductively Coupled Plasma Mass Spectrometry (ICP-MS) for the trace elements. The analytical data provided by the CPRM were initially submitted to a quality control by means of Residual Standard Deviation (RSD) calculation for each duplicate. Then, the simple substitution method was used for the values beyond the limit of detection, followed by uniand multivariate statistical analyzis, including descriptive statistical treatments, identification of outliers via Grubb test, normality tests (Lilliefors and Kolmogrov- Smirnov), correlation and cluster analysis. All statistical analyzis previously highlighted were conducted by STATISTICA® and SPSS® softwares. To determine the values of threshold and geochemical background and graphical representation were used the methods boxplot and cumulative frequency curve methods (Minitab® and Excel® software) and the iterative techniques 2 and calculated distribution function (freeware Visual Basic macro denominada VB Background®). For the construction of geochemical maps, the World Geodetic System 1984 (WGS84) coordinate system was adopted as standard. Spatial representations followed techniques of interpolation according to the kriging or inverse distance weighting (IDW) methods. 43 analyzed elements were submitted to the statistical tests, having been left aside Au, B, Ge, Na, Pd, Pt, Re, Se, Ta e Te, because they presented ≥90% of the analytical data below the limit of detection. Correlation analyzis revealed 14 moderate correlations (0.650> r ≥ 0.575) and 19 high correlations (r ≥ 0.650), generally consistent with usual geochemical associations in geological environments such as Cr-Ni, Cu-Ni and U-Th. The cluster analysis discriminated seven clusters, at a linkage distance of 0.8, with evident geogenic origin, as for example the group composed of Cr, Ni and Mg, typical of mafic-ultramafic rocks. The geochemical maps allowed to identify occurrences of several anomalies in soils, interpreted as being of geogenic origin. Thus, U, Th, La and Ce enrichment was found in soils derived from sub-alkaline neoarchean granites, for example Estrela, Serra do Rabo and Planalto granites, and Cr and Ni in soils from mafic-ultramafic rocks of Luanga and Vermelho complexes and the Cateté Suite. Elements typically associated with anthropic activities, such as P, Zn, Mn, Ba and Pb, as well as potentially toxic elements (EPT), such as Al, As, Bi, Cd, Co, Hg, Mo and Sn, did not generally exhibit, anomalous concentrations and, when this occurred, these appear to be due to geological conditions. Among the methods used to estimate the background values of the 43 evaluated elements, the iterative technique 2 was the one that presented the best result. In cases where this method could not be used, the values obtained by the calculated distribution function (As) and the boxplot representation (Hg and S) were adopted as background. The cumulative frequency curve showed to be a useful graphical technique in the identification of outliers and multiple thresholds. The 225 samples were grouped into five classes that revealed the close linkage between the background values and the geology of the region: 1) Sub-alkaline granites (39 samples); 2) Sedimentary and metasedimentary rocks (28 samples); 3) Gneisses and associated granitoids (70 samples); 4) Metamafic, intermediate and banded iron formation (BIF) (80 samples); 5) mafic-ultramafic rocks (8 samples). With the results obtained, it is concluded that, in the scale of the survey carried out, there is no conclusive evidence of contamination related to human activity, but rather strong evidence of a marked geogenic contribution in the soils of the study area.
Acesso aberto (Open Access)
Micromorfologia, mineralogia e geoquímica da bauxita nodular de Trombetas – PA
(Universidade Federal do Pará, 2018-10-18) LIMA, José Diogo de Oliveira; COSTA, Marcondes Lima da; http://lattes.cnpq.br/1639498384851302
Brazil's main bauxite deposits are concentrated in the Amazon region, specifically in the state of Pará. The three main mines are located in Trombetas, Paragominas and Juruti, and they’re responsible for 85% of Brazil's bauxite production. Even with the favorable mineral scenario in Brazil and especially in the state of Pará, there are already companies that are currently competitive in the current market, they are seeking to develop studies of the characterization and use of nodular bauxite in this type of deposit. The ore, so far, is considered as marginal, it means low-grade ore in the mineral industry. In this context, this work sought to evaluate Trombetas deposits’ nodular bauxite from their texture, mineralogical and chemical characteristics as a possible aluminum ore. In the field, seven lithographic profiles were described on the mining fronts of Bela Cruz and Monte Branco mines belonging to ‘Mineração Rio do Norte’. Then, 19 samples were collected, which were described, photographed and prepared for mineralogical and chemical analyzes. The mineralogical phases were identified by X-ray Diffraction (XRD) and Scanning Electron Microscopy coupled to the Dispersive Energy System (SEM/EDS). The textural aspects involved optical microscopy and Scanning Electron Microscopy coupled to the Dispersive Energy System (SEM/EDS). The chemical analyzes were performed by Inductively Coupled Plasma Optical Emission Spectrometer (ICP-OES), Inductively Coupled Plasma Mass Spectrometer (ICP-MS), X-ray Fluorescence (XRF), titulometry and gravimetry. The profiles investigated comprise from the base to the top the bauxite horizon (HBX) which is represented by gibbsite concretions surrounded by a clay matrix. The overlapped bauxite nodular horizon subdivided into HBNB, HBNI and HBNT, is formed by gibbsitic nodules, of fine texture, that impresses solid and porcelanate aspect and they are surrounded by a clayey matrix. The clay cover (CAR) at the top is formed by a yellow clay, corresponding to Belterra Clay. In the profiles, the fragments > 0.500 and ~0.500 mm of the HBX and HBNB, HBNI and HBNT are essentially composed of gibbsite associated with kaolinite, hematite and anatase. The dominance of gibbsite in the fragments > 0.500 and ~ 0.500 mm of the HBNB, HBNI and HBNT, presents a potential of nodular bauxite as a possible aluminum ore. However the fragments < 0.500 mm, clayey matrix of HBX and HBNB, HBNI, HBNT and CAR are mainly composed of kaolinite associated with gibbsite, hematite, quartz and anatase. The kaolinite domain in the HBNB, HBNI, HBNT fragments < 0.500 mm, makes it difficult to consider them as possible aluminum ore. As for the heavy minerals (zircon, rutile and tourmaline), no contrast was found between the horizons and the clayey cover. The chemical composition consists essentially of SiO2, Al2O3, Fe2O3 and TiO2, which reinforce the main minerals identified and as these the contents differ according to the horizons. The concentrations of the trace elements are variable, V, Cr, Ga, Se, Zr, Nb, Mo, Sn, Hf, Ta, W, Hg, Bi, Th and U are above the crustal average in all fragments, clayey matrix of HBX, HBNB, HBNT and CAR. Trace elements such as V, Cr, Ga, Mo, Hg and Bi correlate positively with Fe2O3 (hematite and goethite). While Nb, Sn, Hf, Ta, Th, U, correlate positively with zirconium (zircon) and titanium (anatase). When normalized to the chondrites, the distribution curves present parallelism between the various fragments, clayey matrix of HBX, HBNB, HBNT and CAR, with curves that exhibit Eu anomaly, as well as an enrichment of the heavy rare earth elements (HREE) in front of the light rare earths elements (LREE). The data obtained in the investigated profiles of Bela Cruz and Monte Branco mines demonstrate broad similarity to Belterra clay-type nodular lateritic-bauxite profiles found in Amazon, where the clayey matrix of the nodules resembles textural, chemical (larger elements and traces) and mineralogical (including heavy minerals) with this covering clay.
Acesso aberto (Open Access)
Microquímica e mineralogia de processos do minério de cobre de Salobo, Carajás
(Universidade Federal do Pará, 2002-03-18) CHOQUE FERNANDEZ, Oscar Jesus; COSTA, Marcondes Lima da; http://lattes.cnpq.br/1639498384851302
The Salobo deposit, located in Carajás, southeastern of Pará, is one of the largest copper reserves in Brazil. Although severa! mineralogical studies have been developed for this ore, its origin is still controversial, with severa! interpretations, such as volcanogenic copper-bearing oxide and voicanogenic massive sulfide and iron oxide (Cu-U-Au-REE). In comparison with other well-known deposits, it is a rare example of mineralization. Particular characteristics such as disseminated mineralization, fine grain and its hardness impose serious difficulties to copper concentrates production. Due to ore complexity it is difficult the metallurgical treatment, reasons why it is constantly submitted to geological and technological reevaluations. The literature on Salobo deposit is expressive but detailed works about microchemistry and technological characterization in comminution are rare or restricted to Salobo Metais S.A. company. The objectives of this work dealt with these questions. Microchemical analyses using microprobe and SEM/EDS in samples of holes and ore piles (research gallery G3) of Salobo, allowed the identification of sulfide mineralization with bornite (4%), chalcocite (2%) and chalcopyrite (0.5%), and variable proportions of molybdenite, cobaltite, safflorite, niqueline, siegenite, gold, silver, graphite, ilmenite, hematite, Te-Ag, uraninite and REE minerais. These minerais occur in schist iron formations where the deposit es found: a) magnetite and massive fayalite, eventually banded and b) banded biotite and magnetite. These groups considered as gangue (magnetite 53% and silicates 40%) contain minor amounts of gamet, amphibole, quartz, plagioclase and subordinate amounts of fluorite, greenalite, minnesotaite, stilpnomelane, apatite, monazite, allanite and occasionally siderite, goethite and malachite. Sulfides are preferentially concentrated in magnetite rich iron formations. Copper sulfides occur as crystals less than 3.0 mm and as disseminated fine grains, with fine alternated banded and/or foliated silicates, veiniets and/or long/short stringers, tiny inclusions, bornite/chalcocite and bornite/chalcopyrite mirmekitic intergrowth and bornite-chalcocite and bornite-chalcopyrite substitutions. These minerais were formed by complex processes and are characterized by compositional controls, mainly for the presence of Fe in them. Solid solutions of bomite and chalcopyrite were formed at high temperatures and gave way to those iron excesses. Atomic radios Cu/Fe of bomite (4.3-4.9) and chalcopyrite (average of 0.9) at high temperatures allowed the co-existence of bornite-chalcopyrite equilibrium and therefore of bornite/chalcopyrite. Iron contents (maximum 0.96%) in chalcocite have been incorporated at those temperatures when the structure is highly disordered. Chalcopyrite lamellaes following the { 111 } orientation in bornite as well as the bornite/chalcocite and bornite/chalcopyrite intergrowth suggest exsolution. Although those phases are associated with severa' minerais in different paragenesis, the ore features have been affected drastically by metamorphism difficulting the reconstruction of its pre-metamorphic evolution. Ore grinding produced physical changes in the grain size and according to time, long or short, of mineral comminution the pulp reologie is modified. That process originates a grain size - 270 # (53 µm), 80 % wt. passing, grounding time on 4 hours (dry) and 2 hours (humid) adapted to copper concentration. Different volumetric fractions of copper sulfides in particles were obtained through both processes: larger fraction (6 % volume) to grain sizes < 53 µm and with a prevailing fraction (7 to 15 % volume) ranging from 26.9 to 7.5 µm. Physical modification shows larger magnetite proportions than silicate ones with a clear incidence of magnetite density in the hydrocyclone classification. Mineralogically, in the comminuted products, occur the same minerals established in ROM but with chemical modifications in copper sulfides. Magnetite is the main host for sulfides and greenalite is more frequent among the silicates, fluorite being also common. Proportions of S, Fe and Cu in bornite, chalcocite and chalcopyrite are variable relative to ROM and stoichiometry, varying in function of the grain size (larger chemical variation in grain sizes of 26.9 to 7.5 pm than on the 2360 to 37µm fraction). Iron can reach up to 6.0% wt. in chalcocite. Chemical variations in S, Cu and Fe formed ternary sulfides: bornite, characterized as "complex mistures" rich in iron (Cu4.34-4.76Fe1.03-1.04S4.0) and chalcopyrite rich in Fe Cu0.93Fe1.08S2.0 (as a solid solution extension of chalcopyrite). Chalcocite oxidation and high values of Fe in its structure also contributed to the reaction of binary sulfides: djurleite and digenite Cu1.77-1.84Fe0.04-0.06S1.0. Those ternary (Cu-Fe-S) and binary (Cu-S) copper sulfides have been formed in the initial oxidation state with superficial alterations induced by temperature (25°C on) and comminution. These sulfides were formed and controlled by the phase relationships in the Cu-Fe-S system. Low copper content in sulfides leads to a slower chemical variation than there is an excess of iron. These variations favoured the appearance of oxidized surfaces on copper sulfides with different products of oxidation [M1-nS and nM(OH)2]. Chemical variations showed to be dependent on the grain size, with smaller oxidations in sizes > 53 µm and larger oxidations in sizes <53 µm, caused by a combination of surface area and ability of chalcocite to be oxidized. Iron excess mainly as highly reactive colloidal particles could have been generated by: mill material, abrasive action of particles and probable magnetite oxidation, producing chemical variation in mill atmosphere and electrochemical corrosion processes. Comminuted ore conserves the lepidoblastic textures of the silicates biotite, fayalita and greenalite and granoblastics of magnetite or bornite, chalcocite and chalcopyrite grains. Crystals of copper sulfides, liberated and mixed with high percentage of magnetite and silicates are intensively fractured and eroded and sometimes fullfilling cracks and/or fractures of greenalite. They difficult the sulfide liberation. Copper sulfide liberations increase gradually when the grain size is finer (more than 50 % in grain sizes < 29.6 µm). Only in fractions < 37 µm (Cumulative liberation yield CLY90), the copper bearing particles begin to migrate and for higher degrees of liberation though such tendency can still be insufficient for the purposes of sulfide concentration. Besides the strong metamorphic recrystallization of the schists of ore formations, its high hardness, the extremely variable grain sizes of sulfides (5 to 300 µm) and the mineralogical ore complexity (mineralogical associations, disseminations, intergrowth complexes), this microchemical investigations, in ROM and in comminution products, revealed a significant chemical variation in copper sulfides. Iron present in sulfide mineral reticules is the main contaminant to chemical modifications (Cu/Fe ratio) influencing the quality of copper concentrate in mineral processing. It has been already established that between copper sulfides and other components of pulps during grinding and flotation (water, species collectors or modifiers) occur an interaction through electrochemical mechanisms producing oxidized species, where the chemical composition of the mineral in question is very important. The technological alternative adapted to treat the copper concentrate, with basis in mineralogical and microchemical studies in run-of-mine and comminution products, seems to be the hydrometallurgy because they can take advantage the production of fine grains and to use the reground for ultrafine grains production. These can be submitted to oxidation processes of sulfides to promote copper extraction. Finally the metallic copper extraction can follow the solvent extraction/electrowinning (SX/EW) process.
Acesso aberto (Open Access)
Minerais de manganês como contaminantes do minério de ferro na mina N5W em Carajás, Pará
(Universidade Federal do Pará, 2015-09-29) COSTA, Luiz Claudio Gonçalves da; COSTA, Marcondes Lima da; http://lattes.cnpq.br/1639498384851302
Mineralogical characterization and control of manganese and silica contents in the Carajás mine iron ore is a routine task. Relatively high concentrations of manganese and silica minerals, considered ore impurities, are present in the high grade iron ore (>65% Fe) of the N5W mine. This study aimed to identify these minerals and their mode of occurrence in the iron ore from N5W, improving the mine planning and exploitation. The main manganese minerals in the iron ore are: (a) pyrolusite, bixbyite, cryptomelane, hollandite, ramsdellite and chalcophanite, all Mn oxy-hydroxides; and (b) the braunite, a silicate. These minerals were found in hydrothermal veins and veinlets, cross-cutting the primary bedding of the iron ore and subordinately forming centimetre scale lens shaped veins, interbedded in the jaspilite layers. The Mn rich veins are spatially associated with fault zones and breccia bodies showing pyrolusite, chalcophanite, braunite and bixbyite veins, subordinated lenses of cryptomelane and hollandite. The presence of pyrolusite and cryptomelane indicates weathering of the rocks. Quartz and Fe-Mn oxy-hydroxides are the main minerals filling faults and fractures in the N5W mine, where MnO grades in veins, reach up to 61,74%. The Mn minerals in the iron ore are indicative of sedimentary and hydrothermal origin. Weathering caused alteration of the primary minerals, promoting mobilization and reprecipitation of new Mn minerals together with Fe oxy-hydroxides. Typical geochemical association in the Mn rich iron ore Mn-As-Cu-Zn-Ag with positive anomalous ETR levels, whilst in the iron formation Zr-Hf-Nb-Ta-Sc-Th with ETR negative values. The rare earth elements concentrations are higher in the Mn rich zones. These zones show strong positive Ce anomalies when hollandite is present. Higher SiO2 contents are related to the presence of metric jaspilite boulders surrounded by hematite friable, in the thick saprolite zone. Finally, the Mn contaminants are diverse in origin, however hydrothermal Mn rich minerals are dominant, closely associated with the proto-iron ore. The high SiO2 contents are indicative of the base of the alteration profile, incorporating part of the proto-ores. Keywords: Mn Oxi-hydroxides; hematite; quartz; silica; contaminants, Carajás Formation.
Acesso aberto (Open Access)
Mineralizações de caráter gemológico (opala, ametista, quartzo tricolor, quartzo rutilado e com clorita) da região de São Geraldo do Araguaia (PA) - Xambioá (TO): caracterização e gênese
(Universidade Federal do Pará, 1999-06-16) COLLYER, Taylor Araújo; KOTSCHOUBEY, Basile; http://lattes.cnpq.br/0096549701457340
In the Xambioá-São Geraldo do Araguaia region, located in the northern segment of the Araguaia belt, pegmatitic and hydrothermal quartz veins with opal, amethyst, three colored quartz, and with rutile and chlorite occur. The genesis of these veins has been investigated due to their gemmological interest. The most important opal — bearing quartz vein is hosted by metasedimentary rocks of the Xambioá Formation, and presents a rough zoning in addition to a brecciated texture. The outer zone of the vein consists of milky quartz, while the inner zone is composed of onyx, jasper opal (C-T) cut by small veins of C-T opa! and A opal. High salinity fluids of H2O-0O2-NaCl and H20-KCl-NaCl systems (> 26 wt% of NaCl equiv.) have been found in the outer zone quartz, while in the intermediate zone low salinity fluids of the system H20-FeCl2-NaCl (0,88 to 3,71 wt% o NaCl equiv.) were observed. Th ranges from 232 to 310°C and from 110 to 145°C for the quartz of the outer and intermediate portions, respectively. These data, along with the opal metastability suggest that the quartz of the outer zone may be related to the regional metamorphism of Brasiliano age that affected the Araguaia belt. They also suggest a contribution of meteoric water to the formation to both the jasper opal and the C-T opal, as well as a supergenic origin to the A opal. The inner portions of these veins may have been formed by the reactivation of older fractures during the Paleozoic and/or Mesozoic. The vein with amethyst in emplaced into the granitoid body of Serra da Ametista. It is pegmatitic in nature and is composed of quartz, amethyst, microcline, oligoclase, muscovite, and biotite. Fluids of the system F120- KC1-NaCl are found in both quartz and amethyst. In quartz, the salinity of these fluids ranges from 18,95 to 20,75 wt°/.9 of NaCl equiv., and in amethyst from 12,73 to 18,00 wt% NaCl equiv. Th ranges from 190 to 248,5°C in quartz, and from 155 to 200°C in amethyst. These fluids might have had a magmatic origin and be related to the late cooling phase of the Serra da Ametista granitic body. Rb-Sr ages in pairs of minerais (muscovite-microchne and muscovite-oligoclase) range between 390 and 430 Ma. These ages are younger than the probable Brasiliano age of the vein and suggest a partial resetting of the Rb-Sr system due to subsequent tectonic reactivations. The three colored quartz occurs as zoned crystals in the inner parts of quartz veins emplaced into metarkoses and metasandstones of the Pequizeiro Formation. Inclusivas ofred rutile,pyrite and melanterite in the upper parts of the quartz crystals give them the light red to yellowish brown color. In the lower portion, the purple-yellow dual coloration is given by the presence of iron, aluminum, potassium and sodium. In the outer portion of the studied veie, the quartz presents high salinity fluids of the system H20-CaC12-NaCl (20,60 to higher than 23,18 wt°/0 of NaCl), and Th ranging from 488 to 492°C. Fluids of the systems H20- CaC12-NaCl and H20-FeC12-NaCl were identified in the lower portion of the three colored quartz crystals, and of the system H20-FeCl2-NaCl in the upper portions. The salinity of the fluids in the lower portions ranges from 13,83 to 17,34 and from 17,96 to higher than 23,18 wt% of NaCl, respectively. In the upper portions of the crystals, the salinity decreases. Th, which is higher than 485°C in the lower portions decreases to values between 272 and 305°C in the upper portions. A MEV study in the three colored quartz showed inclusions of thorite, metallic mercury in the basal portion; pyrite, cinnabar, and zircon in the intermediate portion; and pyrite, melanterite, anhydrite, and barite in the upper portion. The origin of these veins may be related to the regional magmatism in the Araguaia belt, but a possible influence of the final phases of the regional metamorphism cannot be ruled out. Contribution of meteoric water, mainly to the upper portions of the three colored quartz crystals, has also to be considered. The quartz veins with rutile and chlorite are hosted by the mica schists and quartzite of the Estrondo Group. They are composed by hyaline quartz crystals, rutile, chlorite, specular hematite, and magnetite. Fluids of the system H20-1CCI-NaCl, were identified in the quartz of the outer parts of the veie, as well as in the quartz with rutile and chlorite of the inner parts. However, the salinity of these fluids is higher in the quartz of the outer parts (18.80 to higher than 23.18 wt% of NaCl) than in the quartz with rutile and chlorite (4.34 a 5.26 wt% of NaCl). Th ranges from 293 to 345°C in the quartz of the outer zone, and from 136.54 to 198.9°C in the quartz with rutile and chlorite. The outer parts of the veie were possibly generated by fluids of magmatic and/or metamorphic origin. However, a considerai* contribution of meteoric waters is considered for the formation of the inner parts of the veins. The data suggest that the quartz veins systems are related to extensional tectonic and to hydrothermal events which took place in the late stages of structural development of the Araguaia belt, following the regional metamorphism and the consequent granitogenesis. In spite of the nature of the aqueous system, the magmatic and/or deep metamorphic fluids that generated the quartz veias show, initially, high salinity and medium to high temperature. Probably due to the increasing contribution of meteoric waters, both the salinity and temperatures (lower than 200° C) decreased. Later, tectonic reactivations during the Paleozoic and/or Mesozoic were responsible for migration and injection of silica bearing solutions, generated at depth, and by precipitation of silica as onix, jasper opal and opal C-T. More recently, opal A was formed in supergenic conditions.
Acesso aberto (Open Access)
Mineralogia e geoquímica dos perfis bauxíticos da mina Miltônia 3, região de Paragominas/PA
(Universidade Federal do Pará, 2015-10-16) PEREIRA, Carla Braga; ANGÉLICA, Rômulo Simões; http://lattes.cnpq.br/7501959623721607
The Paragominas Bauxite Province is located in eastern of Pará state and western of Maranhão state, occupying the NW portion of Grajaú Basin and the southern of Bragantina platform, with an area of approximately 50.000 km2. The important bauxite deposites from that area were originated by an intense chemistry weathering above siliciclastic rocks from Cretaceous age. This research focus on the mineralogical e geochemistry studies of bauxite profiles in the area of Bauxite mine that belongs to the Norsk Hydro Company, in Miltonia 3 mine, municipality of Paragominas, Pará state. This research aims to contribute to understanding of the origin and developing of these profiles. Were conducted two sample collections of lateritic profiles representatives of Miltonia 3 mine, following the chemistry, mineralogy and texture differences of the horizons that structures the studied profiles. We used the following methodological procedures and/or instrumental techniques: X-rays Diffraction (XRD), Scanning Electron Microscopy (SEM), petrology and chemical analysis. The lateritic profiles studied in this research were described according to their horizons structuring: Amorphous Bauxite (AB), Crystallized Amorphous Bauxite (CAB), Crystallized Bauxite (CB), Ferruginous Laterite (FL). In the profile 1, the overlying horizon to FL is described as Nodular Bauxite (NB), while in the profile 2, it is the Crystallized Nodular Bauxite (BNC). Both of these profiles are covered by unconsolidated sandy-clay horizon, with an orange red coloring, called by many authors as Belterra clay. Petrographically, the horizons show the following typical mineral of a bauxitic/lateritic profile: gibbsite, kaolinite, goethite, hematite e anatase. This paragenesis was confirmed by XRD analysis, which the mineral content varies for each horizon. Allied to the SEM analysis it is possible to describe the morphologic aspect of gibbsite and kaolinite crystals. It is noticeable the presence of three gibbsite generations, which the precocious phase is part of matrix, sometimes, associated with iron oxide-hydroxide, showing a cryptocrystalline character. The second generation comprises microcrystalline crystals that fill partially or totally pores. The latest generation is cryptocrystalline crystal found occupying totally or covering the cavity walls of cutans. The geochemical pattern of Al2O3, Fe2O3, SiO2 and TiO2 residual phases are similar in both profiles, as well as the contents of Al2O3_available e SiO2_reactive. Over the profile, the contents of SiO2 e SiO2_reactive are more expressive in the most clayey layers, and they reflect the kaolinite content. The content of Al2O3_available has the same Al2O3 behavior due to: the first is related to gibbsite, the most elevated contents are in top of AB, CAB e CB, and the last represents the most economically exploitable level. According to the order/disorder degree of this kaolinite in the soil profile, it was verified an elevation of the FWHM (Full Width at Half Maximum) results from base towards top, that showed the possibilities of: 1) kaolinite degradation with the process of developing of lateritic profile; and/or neoformations of new kaolinite generations with low crystallinity. The new data furnished during the analysis give support to understand the process that produced the mineralogical, chemistry and textural differences and similarities that exist between bauxite horizons, as well as the recovery of bauxitization process (two phases of bauxitization) that resulted in formation of Nodular Bauxite (NB) and Crystallized Nodular Bauxite horizons, leading the hypothesis of polyphasic and complex evolution of studied profile, wich culminated in the origin of bauxitic/lateritic deposits.
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)
Mineralogia, geoquímica e minerais pesados do perfil laterito-bauxítico com cobertura e sua relação com o grupo Itapecuru: lavra piloto ciríaco (Rondon do Pará)
(Universidade Federal do Pará, 2015-07-11) PANTOJA, Heliana Mendes; COSTA, Marcondes Lima da; http://lattes.cnpq.br/1639498384851302
The lateritic-bauxite profile studied in Rondon do Pará is part of the Paragominas Bauxite Province, the most important of the Brazil that hosts world-class deposits of considerable economic value. The deposit comprises six horizons: bauxitic clay at the bottom, massive bauxite, massive iron-aluminous crust, iron-aluminous crust dismantled, ferruginous spheroliths and a clay cover equivalent to the "argilas de Belterra" at the top. The sedimentary rocks of the Itapecuru Group are the probable source of the lateritic-bauxite profile and include weathered siltstone and claystone. The mineralogical composition of the three studied units (Itapecuru Group rocks, lateritic-bauxite profile and clay cover) is similar and consist to kaolinite, quartz, hematite, goethite and gibbsite, accessory minerals include anatase and heavy minerals (zircon, tourmaline, rutile, staurolite and opaque). The units differ mainly in this content variation and the absence of gibbsite and goethite in the rocks of Itapecuru Group. The chemical composition of the three units shows that Al2O3, SiO2, Fe2O3, TiO2 and LOI are the most abundant constituents, related to the major minerals. Trace elements content in the three units are heterogeneous with V, Cr, Ga, Zr, Hf and Th showing concentrations above the crustal average, these elements display good correlation with iron oxy-hydroxides. When normalized to chondrites, the three units differ by positive Ce anomaly in the Itapecuru Group rocks, but are similar in negative Eu anomaly, the depletion of LREE and enrichment of HREE. The data obtained show clear affinities between the three units, suggesting that the sediments of the Itapecuru Group are similar to those of the bedrock of lateritic-bauxite profile while their respective cover demonstrates strong relationship with the crusts and spheroliths. The structure of the lateritic-bauxite profile together with mineralogical and chemical data allow to correlate the Rondon do Pará lateritic-bauxite profile with the deposits of Paragominas and Juruti.
Acesso aberto (Open Access)
Opalas gemológicas do Piauí: gênese revelada por microtermometria e minerais associados
(Universidade Federal do Pará, 2014-04-25) MARQUES, Gisele Tavares; COSTA, Marcondes Lima da; http://lattes.cnpq.br/1639498384851302
Opals from Pedro II and Buriti dos Montes, in the Piauí State, are the most important occurrences of this gemstone in Brazil, both in terms of volume and -gemological quality that is comparable to the famous Australian opals. However, informality in the extraction and marketing of these opals, as well as the lack of information about the genesis of these deposits do not permit prospecting for new deposits, and the establishment of a certificate of origin for Piauí opals, would allow their formal participation in the international gemological market. Some authors have been studied these opals, revealing strong evidences of their hydrothermal origin, but until now, no work discussed the physico-chemical characteristics of the fluids that would have originated these opals deposits. Thus, the main objective of this work was to understand the hydrothermal system responsible for the genesis of opals from Piauí, i.e., to characterize the fluids that originated the mineralization and show its relationship with the geological context of this region. Pedro II and Buriti dos Montes counties are located in the northeastern portion of the Piauí State, at approximately 230 km east of the capital Teresina. The opal occurrences are on the basis of the Parnaíba Basin, constituting veins and veinlets in the sandstones of the Serra Grande (Buriti dos Montes) and Canindé (Pedro II) groups, which are cut by diabase sills and dikes of the Sardinha Formation. They also occur in cementing breccias and as colluvial and paleochannel deposits. Associated to opals, locally there are veins of quartz, chalcedony, barite and hematite (or goethite). In general, opals from Pedro II present play-of-color, are mostly white or bluish with a milky appearance, semitranslucent to opaque, and have solid inclusions little bit apparent. In contrast, orange opals from Buriti dos Montes do not show play-of-color, their color ranges from light yellow to brownish red, they are semitransparent to translucent, and contain a large variety of solid inclusions. The obtained data reveal that the opals from Pedro II are typically of amorphous type (opal-A), while the opals from Buriti dos Montes range between amorphous and cristobalite-tridymite (opal-CT). In the precious opals, the typical play-of-color is caused by the regular arrangement of the silica spheres that constitute them. The absence of opaline cement among the spheres reinforces the beauty of this effect. On the other hand, the orange opals do not show play-of-color, but they have greater transparency due to the small size of the spheres. The solid inclusions also produce beautiful effects in the studied opals, mainly in the orange variety that is more transparent. Besides this, the solid inclusions set reveals intrinsic characteristics to hydrothermal processes that originated the studied opals. Botryoidal, dendritic and nodular aggregates are examples of inclusions formed by fragments of the host sandstones, which were carried by the hydrothermal fluids that generated the opals. In the opals from Buriti dos Montes, the red, orange and yellow hues are produced by the partial dissolution of the Fe oxy-hydroxides inclusions. Similarly, the green color in the precious opals is related to Co-pentlandite microcrystals included in them. The set of minerals associated to opals leads to a mineralogical-geochemical signature marked by high contents of Fe and Al in opals with hematite/goethite and kaolinite inclusions, such as the considerable increase in the rare earth elements contents, in the opals that have kaolinite and apatite inclusions. Among the trace elements, Ba is the most abundant, and it probably was incorporated to hydrothermal fluid, considering that veins of barite are frequently found in this region of Parnaíba Basin. Some features such as flow structures in the opals, corrosion and partial dissolution in the hyaline quartz crystals and mineralogical inclusions, hydrothermal quartz veinlets that overgrew to detrital grains, and zoning in the quartz crystals, confirm that these opals have hydrothermal origin. The Gondwana rupture would have caused a wide fissural basic magmatism, which was the responsible for the heat supply that generated the first convective cells of hot fluids. The water contained in the sandstones certainly filled the system and enriched in silica through partial or total dissolution of the quartz grains of sandstones. This hydrothermal fluid was subsequently hosted and cooled in the fracture systems, precipitating the opal and associated minerals.
Acesso aberto (Open Access)
Organofilização de uma Mg-bentonita da bacia do Parnaíba-Sul do Maranhão e sua utilização em poli (metacrilato de metila)
(Universidade Federal do Pará, 2014-02-21) CAVALCANTE, Manoella da Silva; http://lattes.cnpq.br/7249500407405478; ANGÉLICA, Rômulo Simões; http://lattes.cnpq.br/7501959623721607
Bentonites are clays whose main constituent is a clay mineral of the smectite group, mainly montmorillonite. According to the predominant cation that occupies the interlayer space of the smectite, they can be classified as sodium-, calcium- or magnesian-bentonites. Such clays have wide industrial applications, such as: drilling fluids, pelletizing, foundry molds, among others. For some specific applications that add greater value to the final product, as in the synthesis of polymer/clay nanocomposites, it is necessary to intercalate organic ions in the interlayer of the clay mineral. In Brazil, industrial production of organoclays is small and geared towards the markets of paints, greases and polyester resins. Most companies that exploit bentonites for the traditional uses and do not produce this type of material are showing increasing interest in this new kind of application. In this context, this study aimed to evaluate the potential of the Formosa Bentonite in the production of organoclays and its application in the synthesis of polymer/clay nanocomposites. Formosa is a Mg-bentonite recently described and relatively abundant in northeastern Brazil. For this purpose, synthesis experiments were carried out by varying the concentration of two surfactants: hexadecyltrimethylammonium ions (HDTMA+) and dodecyltrimethylammonium (DTMA+), in the concentrations 0.7, 1.0 and 1.5 times the value of CEC, with reaction time of 12 hours and temperature variation of 25 ºC and 80 ºC. The Mg-bentonite was used as starting material both in natura and activated with sodium carbonate. Both the starting material and the organoclays obtained were characterized by XRD, DTA/TG and FTIR. The clays that exhibited better intercalation results were used in the proportions of 1%, 3% and 10% for further synthesis of the polymer (PMMA)/clay nanocomposites. The XRD results confirmed the intercalation of organic ions in the interlayer space of the Mg-smectite, for both in natura and activated samples. According to FTIR results, it was observed that the ratio of gauche/trans conformers decreases with the increasing of basal spacing. The results of DTA/TG confirm the thermal stability of organoclays at a maximum temperature of 200 °C, allowing the use of such material in the synthesis of polymer/clay nanocomposites obtained by the fusion process. XRD patterns confirmed the intercalation of PMMA in the interlayer space of the Mgsmectite for all nanocomposites produced. With the DSC analysis, it was possible to observe the increase in glass transition temperature for all nanocomposites in comparison with pure PMMA. Thus, it is possible to conclude that the Mg-bentonite can be intercalated with alkylammonium ions, without previous sodium activation, forming organoclays, as well as their use in the synthesis of nanocomposites. This possibility of using natural (non-activated) Mg-bentonite may represent an important difference in terms of process costs, in comparison with existing Ca-bentonites in Brazil, or even the imported, that need to be activated during beneficiation. Finally, one believes that the research should proceed with the evaluation of mechanical properties of the nanocomposites produced in this work, aiming future possibilities of application for such materials.
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.

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