Navegando por Assunto "Geologia econômica"

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Ambiente deposicional, composição mineralógica e estudo isotópico Pb-Pb das zonas sulfetadas do Alvo São Martim, Cinturão Araguaia, sul do Pará
(Universidade Federal do Pará, 2004-07-07) LIMA, Aderson David Pires de; VILLAS, Raimundo Netuno Nobre; http://lattes.cnpq.br/1406458719432983
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Aspecto tectôno-sedimentares do fanerozóico do nordeste do estado do Pará e noroeste do Maranhão, Brasil
(Universidade Federal do Pará, 1992-09-16) IGREJA, Hailton Luiz Siqueira da; FARIA JUNIOR, Luis Ercílio do Carmo; http://lattes.cnpq.br/2860327600518536
A synthesis of the tectono-sedimentary evolution of the Phanerozoic at Northeastern Pará and Northwestern Maranhão is discussed with enphasis to the Bragança-Viseu and São Luis basins. This research is based on field observations, gravity (Bouguer Anomalies), magnetic, seismic, and borehole data interpretations. Five sedimentary sequences are defined: 1) Piriá-Camiranga (Cambrian-Ordovician to Silurian), 2) Lower Itapecuru (Lower Cretaceous), 3) Upper Itapecuru (Upper Cretaceous), 4) Pirabas-Barreiras (Oligocene-Mioceneto Pliocene) and 5) Pará (Quaternarg). The regional basement is an igneous-metamorphic assemblage which outcrops in two windows. The sedimentary and structural features of the Piriá-Camiranga sequence are consistent with a tectono-sedimentary model of coastal environment with fluvio-glacial influence related to a tilted blocks system induced by strike-slip motion. This sequence represents an evolutive stage coincident to the Eo-Hercynian paroxysm (Paleozoic) which ended with the closure of the Atlantic I (first geotectonic cycle of the Gondwana). The Lower and Upper Itapecuru, as well as the Pirabas-Barreiras and Pará sequences, are related to the Equatorial Atlantic opening during the Mesozoic and Cenozoic times. They are analysed by severa), authors which reached the interpretations refered to as Models of: Fracture Zones; Anti-clockwise rotation of Africa; Intumescence and fracturing; Clockwise rotation of the South America Nate; and Wrench Tectonics. These models were experimented for the studied area. The time and environments of the sedimentary processes are related to the rift and pos-rift phases of the equatorial coastal basins, but these models were not adequate to explain the structural features. A new model is proposed to explain the origin and development of the basins taking into account a regional NE-SW extension axis and formation of the Bragança-Viseu and São Luís basins with similar polarities. The tectono-sedimentary map for the Phanerozoic of the Northeastern Pará / Northwestern Maranhão enhances the compatibility of the depositional and tectonics systems with two periods of oceanic opening of the Northern Gondwana border.
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Estudo dos fluidos hidrotermais relacionados às "brechas" mineralizadas com sulfetos de ouro da área Bahia-Carajás
(Universidade Federal do Pará, 1998-11-23) ALMADA, Maria do Carmo Oliz; VILLAS, Raimundo Netuno Nobre; http://lattes.cnpq.br/1406458719432983
The Bahia deposit is hosted by the Igarapé Bahia Group, of Archean age, which occurs in the Mineral Province of Carajás (SE of Pará). This group consists of basic metavolcanic, metapyroclastic and clastic metasedimentary rocks, in addition to banded iron formations and breccias, being cut by dikes of basic composition. All this rocky package is intensely altered by hydrothermalism that generated mineral associations compatible with the greenschist facies. The Bahia deposit is made up of the bodies Acampamento Norte, Acampamento Sul, Furo Trinta and Alemão. In the first three, mineralization is widespread and is mainly located in breccias. The latter, more recently discovered, is formed by massive sulphide lenses. The present work was based on testimonies of seven drill holes that were executed in Corpo Acampamento Sul. The breccias occur in the contact, today verticalized, between the basic metavolcanic rocks and clastic metasedimentary rocks and generally present gradational contacts with the host rocks. The clasts originate from metavolcanic rocks of basic composition and from banded iron formations, constituting angular to subangular fragments with dimensions between 1 and 3 cm most frequently. The matrix consists of chlorite, siderite, chalcopyrite, quartz, magnetite, tourmaline and calcite, with a predominance, in general, of one or two of these minerals. The matrix/clast ratio is variable and some breccias show slight matrix foliation and clast orientation. Sometimes, interspersed with breccias, massive beds of magnetite and sulfides occur. These breccias are suggested to have a phreatic origin, whose fragments were reworked and transported to deeper zones by debris currents. In breccias, mineralization also occurs in veins and pockets where sulphides join quartz and/or siderite and are more enriched in copper and gold than in host rocks. Chalcopyrite and pyrite are the main sulfides in all lithological types, but in the stratiform massive beds of magnetite and sulfides, bornite is also present. Magnetite is an abundant mineral, occurring in fragments of banded iron formation, disseminated in the matrix of breccias or in massive beds. Chloritization, carbonation, magnetization and sulfidation are the most important types of hydrothermal alteration, with silicification and tourmalinization also being recorded in a subordinate manner. Chloritization has affected almost all rocks to a greater or lesser extent, lending them a characteristic greenish tinge. Carbonation, magnetization and sulfidation are represented, respectively, by the precipitation of siderite and calcite, magnetite and chalcopyrite, pyrite and bornite. Studies on quartz crystals revealed biphasic and triphasic aqueous inclusions chemically represented by the H2O-NaCl-CaCl2 system, with variable salinity (5.3 - 41.5 % eq. NaCl). Inclusions with pure CO2 were also found, some with traces of N2. Homogenization temperatures were more frequent in the ranges of 110-140ºC for biphasic inclusions and 150-225ºC for aqueous triphasic inclusions. With the pressure correction made, the prevailing conditions for the formation of the Bahia deposit were estimated at 160-240°C and 1-2 kbar. The aqueous fluids were interpreted as seawater modified as a result of cognitive movement that made it circulate and leach metals from the volcanic sedimentary package for later deposition in the form of sulphides. On the other hand, the carbonic fluids are a probable mantle source and are responsible for the precipitation of siderite. The chlorite geothermometer proved to be inadequate to define the paleotemperatures, given the very different results obtained according to the equation and correction for Al (IV) used. The geological characteristics of the Bahia deposit favor its interpretation as a Besshi-type volcanogenic deposit, which may have incorporated, during later events, uranium and rare earths that occur in it at anomalous levels.
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Geologia e geoquímica das mineralizações supergênicas de ouro das áreas Salobo e Pojuca-Leste, Serra dos Carajás
(Universidade Federal do Pará, 1996-11-29) SILVA, Evaldo Raimundo Pinto da; KOTSCHOUBEY, Basile; http://lattes.cnpq.br/0096549701457340
In Salobo sector, the primary gold and copper mineralization occurs in two types of iron formations, both of the silicate facies: Type I composed of magnetite>50% + fayallite + grunerite and Type II constituted of magnetite<50% + biotite + grunerite + almandine, which occurs interlayered in barren metagraywacks. In iron formations gold is present as: i) microscopic (5-14m) and submicroscopic (<0,1 µm) inclusions in magnetite; ii) microscopic and submicroscopic inclusions in primary copper sulphides (mainly chalcopyrite; subordinatelly bornite and chalcosine); and iii) as rare visible gold particles in quartz-carbonate-clorite veins which cut the Type II iron formation. Magnetite is the major gold-bearing mineral at Salobo. In the veins, gold is rich in silver and copper (16,5% and 8,4%, respectively) and exhibits increasing fineness from the border to the center of the particles. In these latter, a negative correlation between silver and copper contents, and exsolution textures suggest a separation between Au-Cu and Au-Ag during gold deposition in veins. The Salobo weathering profile is truncated and developed upon a thick metagraywacke sequence with interlayered iron formations lenses. From bottom to top, the weathering profile consists of a transition zone, a saprolitic zone and a colluvium horizon. The transition zone and the saprolite exhibit textural and mineralogical variations that reflect the heterogeneous composition of the bedrock. Weathering of metagraywacke resulted in a clay-mineral rich saprolite -hidrobiotite, smectite, kaolinite- derived principally from biotite. On the other hand, the alteration of mineralized rocks resulted, from bottom to top of the profile, in a supergene sulphide zone, an oxidized zone and a ferruginous saprolite. The most important supergene sulphides are digenite and covelline, while in the oxidized zone occur minerals such as cuprite, malaquite, azurite, native copper and native silver. In the ferruginous saprolite copper is enriched in clay-minerais (smectite) and in iron oxi-hydroxides. The secundary gold mineralization at Salobo occurs only in the oxidation products of iron formations. Gold exhibits enrichment in two levels of the weathering profile: in the supergene sulphide and oxidized copper minerals zones, and in the intermediate zone of the ferruginous saprolite. In these alteration products, gold occurs as: i) tiny inclusions (7-30m) in refractory magnetite crystals and in fratures of this mineral; ii) as submicroscopic particles inclosed in martitized magnetite crystals; and iii) as submicroscopic particles adsorbed ("invisible gold") in goethite. At Pojuca-Leste the primary gold mineralization is present in quartz-tourmaline-flurite-copper sulphides veins which cut a thick quartz-biotite-schists sequence and in iron formations lenses interlayered in these rocks. Gold occurs as: i) submicroscopic inclusions in chalcopyrite of veins, schists and iron formations; ii) as submicroscopic inclusions in magnetite of iron formation; and iii) as rare microscopic inclusions in quartz of veins. In the veins gold particles shows low fineness 809). The weathering profile at Pojuca-Leste consists of a thick saprolitic horizon and a ferro-aluminous duricrust. The saprolite exhibits compositional variations related to the nature of the parent rocks. It is generally composed of kaolinite, goethite and hematite and its iron contents are higher when derived from iron formations and sulphide veins. The secundary gold mineralization at Pojuca-Leste occurs in alteration products of sulphide veins, in the ferruginous saprolite derived from iron formations and in ferro-aluminous duricrust. In these secondary products, gold is present as: i) rare particles in relict quartz-tourmaline±sulphide veins; ii) as submicroscopic inclusions in martitized cristais of magnetite; iii) as submicroscopic particles adsorbed in goethite from the veins; and as iv) submicroscopic particles adsorbed in Fe-Al oxi-hydroxides of the duricrust. The supergene concentration of gold in Salobo and Pojuca-Leste sectors, envolved principally relative enrichment, and only subordinatelly absolute enrichment. In these areal, gold enclosed in refratary cristais of magnetite and quartz, favoured a relative enrichment during alteration of the primary mineralization. On the other hand, a minar amount of gold enclosed in copper sulphides (mainly chalcopyrite) was released, mobilized and reprecipited in the sulphide oxidation zone during several phases of the lowering of water table. Such evolution resulted in individualization of several enrichment levels, which shows variable lateral extension in the weathering profile. The main factor which controlled the secondary concentration of gold in Salobo and Pojuca-Leste areas was the forro of gold occurrence in the primary ore. In these sectors, gold armoured as tiny inclusions in magnetite and quartz crystals, dificulted the supergene remobilization process and resulted in a high relative enrichment.
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Geologia e ocorrências minerais da branquianticlinal do Lontra - GO
(Universidade Federal do Pará, 1983-08-29) MACAMBIRA, Joel Buenano; KOTSCHOUBEY, Basile; http://lattes.cnpq.br/0096549701457340
Acesso aberto (Open Access)
Geologia, fluidos hidrotermais e origem do depósito cupro-aurífero Visconde, Província Mineral de Carajás.
(Universidade Federal do Pará, 2011-08-24) CRAVEIRO, Gustavo Souza; VILLAS, Raimundo Netuno Nobre; http://lattes.cnpq.br/1406458719432983
The Cu-Au Visconde deposit lies at the contact zone between the basement (>3.0Ga) and the Grão Pará Group (2.76 Ga) within the so-called Transition Domain of the Mineral Carajás Province. It is located at about 15 km east of the Cu-Au Sossego mine in the county of Canaã de Carajás, Pará state. Felsic metavolcanic rocks, probably belonging to that group, as well as granitic and mafic intrusions, dominate in the deposit and neighboring area. Subordinate ultramafic bodies occur within the mafic units. All these rocks are moderately to strongly hydrothermally altered and show varying degrees of deformation. Mafic dikes and a granitoid isotropic body, the latter probably related to the granitogenesis of 1.88 Ga, represent the last igneous activity in the area and cut the pre-existing rock package. Despite the mineralogical and textural changes, it was possible to infer a monzogranitic to granodioritic composition to the original granitoids largely based on the amounts of chess-board albite. Moreover, the scarcity of primary mafic minerals makes these granitoids similar to the Planalto Granite, which crops out approximately 7 km east of the deposit area. The mineral content and the partially preserved subophitic texture are suggestive that gabros and/or quartz diorites were potential protoliths of the mafic intrusions. On the other hand, the recognition of plagioclase, quartz and K-feldspar primary phenocrysts and the use of trace elements with limited mobility in the hydrothermal environment allowed discriminating a riodacitic composition for the protolith of the felsic volcanic rocks. Grading from ductile to brittle regimes, the hydrothermal alteration changed from early sodic-calcic assemblages, characterized by ubiquitous albitization, scapolitization or amphibolitization, to late potassic assemblages, in which the K-feldspar and Cl-biotite are the diagnostic minerals. Then the alteration restored its sodic-calcic character as indicated by albite, epidote, apatite, tourmaline and fluorite that replaced pre-existing minerals or filled open spaces. At last, it is recorded a calcic-magnesian stage during which clinochlore/Fe-clinochlore, actinolite, carbonate and subordinate talc were equilibrated. In the granitoids, albitization, epidotization and tourmalinization were the most prominent alteration processes, whereas scapolitization, biotitization, amphibolitization and magnetization were more remarkable in gabros/quartz diorites and K-feldspatization in the felsic metavolcanic rocks. The ore, whose formation began at the final stages of the potassic alteration, was essentially controlled by brittle structures. Initially represented by weak chalcopyrite, molybdenite and pyrite disseminations in the zones altered to tremoliteactinolite, scapolite, albite and magnetite, the mineralization evolved to sulfide concentrations in veins and breccias. Among the sulfides chalcopyrite, bornite, molybdenite are dominant, but pyrite and pentlandite also occur together with apatite, scapolite, actinolite, epidote, magnetite, martite, hematite, calcite, and gypsum or fluorite as the main gangue minerals. The typical metallic suite of the sulfide breccia is Fe–Cu–Ni–ETR±Au±Zn±Y±Co±Se, with ƩETR as high as 1030 ppm. Fluid inclusions trapped in quartz, scapolite, apatite and calcite crystals unraveled at least three aqueous fluids. Fluid 1, simplified by the system H2O-NaCl-CaCl2±MgCl2 and present in all host minerals, was hot (450–500ºC) and very saline (up to 58 wt% equivalent NaCl). The alteration and mineralization haloes should have resulted from the interaction of the host rocks with this fluid, which might have experienced cooling and dilution probably due to mixing with surficial waters. After the mineralization event, the deposit recorded the successive inflow of fluid 2 (H2O-NaCl-FeCl2±MgCl2, up to 30 wt % equiv. NaCl) and fluid 3 (H2O-NaCl±KCl, up to 18 wt % equiv. NaCl), both cooler than fluid 1. With a restrict circulation and preserved only in quartz and apatite crystals, fluid 2 might have been related to the intrusion of the late mafic dikes, whereas fluid 3 migration would have taken place in response to the emplacement of the alkali granite (1.88 Ga?), being trapped, similarly to fluid 1, in all host minerals, but as secondary IF. The high salinity and no evidence of boiling, coupled with the presence of Cl-rich minerals, suggest that a purely magmatic source is unlike for fluid 1. As an alternative, it is assumed a mixed source, involving the migration of magmatic or metamorphic fluids throughout carbonatic-evaporitic sequences from which Na, Ca and Cl have been largely leached. The mineralogical, chemical and microthermometric data allowed to characterize the mineralizing fluid as an aqueous solution consisting of NaCl, CaCl2, KCl, FeCl2 and MgCl2(?) that also carried P, B, F, Y, Ba, Sr, Rb and ETR, Cu, Ni and Co, besides S species. The Sossego and the Visconde deposits present similarities in terms of (1) the nature of the host rocks (felsic metavolcanics, granitoids, and mafic intrusions), (2) the types of alteration, highlighting the intense and widespread sodic-calcic metassomatism, (3) the occurrence of the major ore bodies in brecciated zones and (4) the Fe-Cu-Ni-ETR±Au±Co as the metallic signature of the ore. Regarding the main differences, the sub-economic sulfide accumulations and the smaller amounts of massive magnetitites of the Visconde deposit could be listed.
Acesso aberto (Open Access)
A jazida de wolframita de Pedra Preta, granito Musa, Amazônia Ooriental (PA): estudo dos fluidos mineralizantes e isótopos estáveis de oxigênio em veios hidrotermais
(Universidade Federal do Pará, 1995-11-14) JAVIER RIOS, Francisco; VILLAS, Raimundo Netuno Nobre; http://lattes.cnpq.br/1406458719432983
The Pedra Preta wolframite deposit contains the main known tungsten reserves of the Brazilian Amazon. It is Iocated near the western border of the 1.88Ga old Musa grafite, in the Rio Maria region, south of the Carajás Mineral Province. The mineralization occurs in a vein system thats cuts at depht the cupola of the granitic body and above it rocks of the Andorinhas Supergroup whose meta-sandstones are of archean age (2.9 Ga). At least four hydrothermal events have been identified in the Pedra Preta area which are related to severa' quartz vein generations. The first event is represented by the early EHV veins that are basically made up of quartz 1 and have been generated, prior to the emplacement of the Musa grafite, from metamorphic aquo-carbonic fluids. CH4 was the dominant carbonic phase. Fluid inclusions from the quartzite quartz grains showed H2O + CH4 with lesser amounts of CO2. The second event was associated to the Musa intrusion and involved F-poor aqueous fluids exsolved from the erystallizing magma. Once the granite was broken by hydraulic fracturing, fluids that circulated around the pluton moved towards it, mixed with the magmatic aqueous solutions and flowed through the open spaces where quartz 3 was precipitated. The late hydrothermal veins (LHV) began then to be formed. These Ca-free fluids had moderate salinity and were virtually devoid of carbonic phases. δ18O values for quartz 2 (present in the grafite) and quartz 3 (present in the LHV at greater depths) are comparable (7.6‰) indicating reequilibration with dominantly magmatic fluids. The third event was induced by the tectonic reopening of the fracture planes where the quartz 3 had been deposited. They served as escape tone for metamorphic fluids composed of different proportions of CH4, CO2 and H2O. The aqueous phase rnight have been of low salinity although containing Ca++. Temperatures varied from 230 to 400°C and pressures estimates fell in > 2,5 Kbar. Oxygen fugacity values of 10-38 to 10-37 bar indicated reducing conditions. As the metamorphic fluids entered the Pedra Preta system, they were oxidized, though, at least initially, the process had been less complete in the upper part of the deposit. Oxygen fugacities dropped to 10-27 bar by the time the wolframite began to precipitate from acidic solutions (pH 4-5) under therrnal conditions of 300-400°C and pressures > 2.5Kbar. δ18O values for quartz 3 of the LHV (9.0-9.6‰) at lower depths suggested reequilibration with fluids having more metamorphic components than those of greater depths. Soon after or partially contemporaneous with the wolfrarnite deposition, occurred a F-metasomatism brought about by a hypothetical magmatic pulse. Granitic rocks were then greisenized in the lower part of the deposit to a mineral assemblage in which topaz, fluorite and sericite are present, whereas in the upper part these minerais precipitated within the LHV as well as in the host walls. The fluids of this hydrothermal stage were aquo-carbonic, suggesting that mixing with the metamorphic solutions continued, but the carbonic phase was exclusively composed of CO2. Xco2 dropped to values below 0.01 by the time fluorite was formed. Aqueous phase was enriched in Ca++ and Na+. Temperatures did not change much from the deposition of wolframite to the deposition of topaz (300-350°C), but fell to about 250°C when fluorite started precipitating. Despite similar prevailing conditions both in the lower and higher parts of the deposit, irnportant features are recorded that differentiate these two domains. The most striking difference is the much more abundant wolframite precipitation in the upper part. Besides the structural control, the mineralization might also have been controlled by the more frequent metavolcanic lens of the Babaçu Group in the upper part, from which the W-bearing aquo-carbonic solutions leached iron for the precipitation of wolframite. The last hydrothermal event, that resulted from tectonic relaxation probably of Brasiliano age, gave origin to the so-called final veins (FHV) which constitute a net of microveinlets composed of quartz 4, chlorite, sulfides, carbonates and quartz 5. High salinity fluids (30 weigth % NaCl) with high concentration of Ca++ and Na+ acted upon the rocks at conditions of 1.5 Kbar and temperatures beiow 250°C, and may represent connate waters or even deep groundwaters. Chioritization and sulfidization were the most important processes related to this hydrothermal event which ied to the precipitation of chlorite (that replaced feldspars and micas in the host rocks or filled intergranular spaces within the veins) as well as sulfides (mainly chalcopyrite and pyrite). As the system finally died out, drusy quartz 5 was formed trapping low salinity fluids (<5 weigth % NaCl). Pressures were around 5 bar and temperatures reached no more than 100°C suggesting contribution of superficial meteoric waters.
Acesso aberto (Open Access)
Rochas encaixantes, alteração hidrotermal e caracterização dos fluídos relacionados à formação do corpo sequeirinho do depósito Cu-Au do Sossego, Região de Carajás
(Universidade Federal do Pará, 2006-09-06) ROSA, Ana Glória Noronha; VILLAS, Raimundo Netuno Nobre; http://lattes.cnpq.br/1406458719432983
The Sossego Cu-Au deposit is located at about 25 km NW of Canaã dos Carajás city (PA), southern of the Carajás transcurrent system, at the contact zone between the Archean granitic-gneisses of the basement and the Grão Pará Group rocks. This deposit is made up of five ore bodies, being Sequeirinho and Sossego the most important. The present work focused primarily on the Sequeirinho ore body, but observations have been occasionally extended of the Sossego ore body. Its main purpose was to study the hydrothermal fluids responsible for the alteration and mineralization of the Sossego deposit. Several rock types have been recognized in the deposit area: granitoids, both granular (GRA) and porphyritic (MVA), mafic volcanic (Grão Pará Group) and intrusive (GBA) rocks, biotite-rich rocks (BIX), magnetitites (MAG), ore (BSE) and dikes. These rocks are variably deformed and altered, some being essentially products of the hydrothermal alteration, namely the magnetitites and ores. The petrographic study allowed to infer that the granitic (albite + quartz +actinolite + chlorite + epidote) and mafic intrusive (scapolite + Cl-K-Fe- hastingsite ±actinolite + albite + chlorite + epidote + magnetite) had as protoliths mainly quartzdiorites and gabbros/ diorites, respectively. The BIX are mylonitized granitoids that interact with high saline fluids and are characterized by a fine banding in which light bands, composed basically of quartz and/or marialitic scapolite), alternate with black bands composed dominantly of Clbiotite, Cl-K-Fe- hastingsite and tourmaline. The MAG have magnetite contents higher than 50% and variable amounts of apatite, epidote, albite, titanite and chalcopyrite, whereas the BSE consist of chalcopyrite±siegenite + magnetite + apatite + scapolite. Felsic (quartzdiorite and riolitic/riodacitic in composition) and diabase/gabbro dikes cut the above mentioned rocks Albitization, sericitization, silicification, chloritization, epidotization, actinolitization and scapolitization, are the most important types of hydrothermal alteration, although biotitization and Fe-metasomatism also occur. The carbonation represents the final stage of the alteration. Microthermometric studies of fluid inclusions (FI) trapped in quartz, scapolite, apatite and calcite crystals from different rocks of the Sequeirinho ore body reveal aqueous fluids that may be represented, in a simplifying way, by the H2O–NaCl–CaCl2, H2O–NaCl–CaCl2–FeCl2 e H2O–NaCl–FeCl2 chemical systems. The FI show variable salinity (0.2 to 57% wt. % eq. NaCl) and homogenization temperatures that range from 100 to 480ºC. Saturated FI, corresponding to the H2O–NaCl–CaCl2, have their salinity estimated in terms of the main solutes at 15-26% NaCl and 15-23% CaCl2. FI trapped In calcite crystals show salinity between 2 and 15 wt. % eq. NaCl and the 100 to < 275ºC range as the most frequent homogenization temperature interval. The evolution of the Sossego hydrothermal system involved two primary fluids (a) H2O–NaCl–CaCl2 and (b) H2O–NaCl– FeCl2. As these fluids gradually mixed, they generated a third fluid (c) H2O–NaCl–CaCl2–FeCl2 which is interpreted to be responsible for the mineralization and associated alteration. All fluids show evidences of dilution most likely by superficial water. Fluid a is related to albitization, amphibolitization and scapolitization, whereas fluid b was the one that should have carried large amounts Fe to be later deposited as magnetitites. Fluid c is interpreted to be responsible for actinolitization, epidotization and chloritization as well as by the main stage of the mineralization. High saline fluids (>30 wt. % equiv. NaCl) are assigned to interaction with preexisting evaporite and/or exahalite layers that have been dissolved out by metamorphic processes. Magmatic aqueous fluids have also contributed to the Sossego hydrothermal system as well as meteoric waters whose influx caused strong dilution and cooling of the fluids. Comparatively to other Carajás Cu-Au deposits, the aqueous fluids related to the Sossego hydrothermal system show more similarities with those of the Archean Igarapé Salobo and Igarapé Bahia deposits, despite having a distinct typology. Most likely, these similarities arise from the fact that all three deposits are associated with metavolcanosedimentary sequences of the Itacaiunas Supergroup which resulted in part from exhalative activity and might have locally included evaporite beds. As halite was dissolved out, the resulting high saline fluids infiltrated into and were stored in the rock pores from which they might have subsequently migrated in response to thermal and/or tectonic disturbances.
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Síntese e caracterização de óxidos de manganês: transformação de estruturas em camada para estruturas em túnel
(Universidade Federal do Pará, 2007-04-24) FIGUEIRA, Bruno Apolo Miranda; SCHELLER, Thomas; http://lattes.cnpq.br/5712304485190137
This work describes the preparation, characterization e application of manganese oxides with layer structure like - birnessite with alkaline ions interlayer Na+ e K+. These structures are made of the octahedron MnO6 shared by edges and/or corners as basic building block, with oxidation states +2, +3 e +4, giving vacancies in the structure and a resulting negative charge neutralized by interlayer cations. The methods already known in literature to synthesize birnessite were: reduction (K, Na-birnessite) and sol - gel (Kbirnessite). Later, this layer structures synthesized were applied to the attainment of structures in tunnel: manganite, K-hollandite, and todorokite. From the synthetic methods, the most practical and efficient for the preparation of layer structures were chosen for study with the idea of making these compounds accessible to those interested in studying their different aspects. Some modifications were introduced into the original synthesizing route in order to adapt it to the possibilities and necessities of laboratory of geosciences, UFPA, as well as to overcome the problems which appeared during the experimental work.
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O valor econômico e estratégico das águas da Amazônia
(Universidade Federal do Pará, 2006-03-22) DUARTE, André Augusto Azevedo Montenegro; RIBEIRO, Mário Ramos; http://lattes.cnpq.br/4314158355862373; ABREU, Francisco de Assis Matos de; http://lattes.cnpq.br/9626349043103626
Water is, in itself, a natural resource that is indispensable for life, extremely important for metabolism and socioeconomic processes and vital for balancing and maintaining climatic conditions and the environment in general. The asset “water” in its ontological aspect, that is, as a substance in itself, as well as a socioeconomic entity, and the waters of Amazonia in particular, may have their ECONOMIC VALUE measured or calculated, to be expressed in monetary units, guided by the principle that these waters are a STRATEGIC ASSET. This thesis does not restrict the condition of water’s existence only to the physical liquid state of the substance, nor to the principles that the value of this asset originates or is derived from economic/financial costs of obtaining, treating, storing or distributing it, nor yet to that which is obtained under the focus of scarcity. “The Value of Non-Use” or “of the Existence” of the object of this study is the principle focus of this thesis. The Amazon region possesses the largest reserves of freshwater, tropical forest and biodiversity on the planet. The complex system resulting from this interaction, in the dynamic and functional, as well as static (stocks) aspects, is generated and its maintenance will only be possible if there is no significant alteration in the regional hydrological cycle, which is vitally important to the Earth’s climatic equilibrium, through carrying heat and humidity, and, more specifically, when it is expressed as support for productive activities in the Brazilian territory that are of great economic relevance. Thus, it is important that strategies be identified, mechanisms be created and parameters be established for managing this immense natural resource, with compensatory mechanisms and policies being presented, including the transfer of financial resources that can promote socioeconomic development for the region. The research that informed the development of this thesis has a theoretical, conceptual and multidisciplinary character, involving knowledge of geosciences (geology, meteorology, hydrology), economics, engineering, public policies, ecology and sociology, with two principal lines of thinking: hydrological and economic.