Navegando por Assunto "Itaituba (PA)"

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Acesso aberto (Open Access)
Avaliação da distribuição das concentrações de mercúrio total em sedimentos, rejeitos, solos e solos com TPA, na bacia do rio Rato-Itaituba/PA
(Universidade Federal do Pará, 1995-08-20) SOUZA, Jorge Raimundo da Trindade; RAMOS, José Francisco da Fonseca; http://lattes.cnpq.br/8189651755374537
The rio Rato located in Itaituba, SW of Pará State, is the principal mercury mining center of the region. The surveied stretch of approximatly 60 km, suffers a great environmental impact, due to gold mining activities. Two field campaigns were conducted and 161 samples were collected for analysis. Total mercury content was determined by cold vapor atomic absorption (CVAS), prior to chemical diggestion with H2SO4, HNO3 and V2O5. The mercury concentration was determined in stream sediments, mining tailings, soils and black earth archeological soils. Organic carbon and loss on ignition (LOI) were also determined to correlate with mercury data. Statistical parameters, such as minimum, maximum, average and standard deviation were used to evaluate the pollution degree of the area and also for comparison with data from other studies. Samples were distributed in seven groups according to field campaign period, type of sample and sample site. For all types of samples, the results obtained from the first field campaign were higher than those from the second campaign, indicating that mining activities are more intense during the dry season. Significant correlation between mercury concentrations and other two variables (organic carbon and LOI) was observed only in a few sample. This observation support the alleatority of the contaminations, and shows that mercury distribution depends on the type of explotation, season, granulometry and sample location. Most samples show mercury concentrations greater than the regional background, which represents a general enviromental contamination.
Acesso aberto (Open Access)
Entre o ouro e a biodiversidade: garimpos e unidades de conservação na região de Itaituba, Pará, Brasil
(Universidade Federal do Pará, 2014) BAIA JÚNIOR, Pedro Chaves; THEIJE, Marjo de; http://lattes.cnpq.br/3764097351224416; MATHIS, Armin; http://lattes.cnpq.br/8365078023155571
Examines the policies and practices of small-scale gold mining (SSGM) and protected areas (PA) performed in the region of Itaituba (Pará), and understand the impacts of the Brazilian nature conservation policy on practices developed in the small mining Amazon context. Historical and comparative methods were utilized. Documentary and bibliographical searches, semi-structured interviews with social actors involved in the issues, and data collection on websites of public agencies were conducted. The results show that the creation of a federally set of PA in the region of Itaituba, in 2006, was a response to international public opinion on the high rates of deforestation in the Amazon verified at the beginning of the century, but that resulted in direct conflict with institutions and local social actors linked to SSGM, which considered this action authoritative and impediment to regional economic development action. Despite PA have been superimposed over the 80% of areas of interest and/or gold exploration in the region of Itaituba, this conservation policy has not prevented the continuity of SSGM in the region. However, it was found that such police put into play a series of elements that increased the difficulties to regulate their activity and prospector are forcing it to remain or be directed to the illegality. The main barriers identified for the planning of mining activity in the region of Itaituba were: the physical distances between the mines and the environmental agencies, the delay in issuing environmental permits (small-scale/alluvial mining licence, for exemple), difficulties in meeting the legal requirements, and uncertainties about mining within the PA, especially National Forests. Moreover, it was found that the PA did not leave the paper, since they lack staff, infrastructure and financial resources to the minimum compliance for surveillance, education and regulation, for example, the mining activity that occurs inside. Thus, although the federal government has created the PA as an alternative to a process of sustainable development for the region, in practice these protected areas are only creating legal barriers to the continuation of an important regional productive activities without providing alternative livelihoods to users of this resource.
Acesso aberto (Open Access)
Geologia e metalogênese do depósito aurífero do Palito, Província Tapajós, Itaituba - Pa
(Universidade Federal do Pará, 2008-07-17) COSTA, Rodrigo de Melo; SANTOS, Márcio Dias; http://lattes.cnpq.br/6977793618030488
The Palito Gold Deposit lies in the Jamanxim river region, easternmost part of the Tapajós Gold Province, sonthern Pará State. The Palito deposit comprises a mineralized quartz vein system hosted by Palito and Rio Novo Paleoproterozoic granites and is controlled by a NW-SE brittleductile stike-slip shear zone which belongs to a regional structure so called Tocantinzinho Lineament. The Palito Granite crosscuts the Rio Novo Granite and is the main host rock for the gold mineralization. The Rio Novo and Palito granites are two oxidized calc-alkaline monzogranitic stocks correlated respectively to Creporizão and Tropas Suites, characterized as magmatic arc granites. The thicker lodes, of metric width, are hosted by the NW-SE main fractures, whereas thinner veins, of centimetric width, associated with the thicker lodes, make both low angle (around E-W direction) and middle to high angle (NE-SW direction) in relation to the main shear direction. Such a structural situation is compatible to the Riedel system, with parallel lodes (D), low-angle veins (R and P), middle-angle veins (gash) and high-angle veins (R’ and X). Stockwork veinlets also occur as a minor ore type. The veins are always involved by a well developed, normally brecciated, hydrothermal alteration halo. Phyllic alteration ( quartz + phengite + pyrite) and chloritization (chamosite) are the two main hydrothermal alteration types which are followed by potassic alteration (K- feldspar + biotite), carbonatization (calcite + siderite + sericite) and subordinated sufidation (pyrite + chalcopyrite + sphalerite). The gold ore, hosted by quartz veins, is always associated to iron and copper sulfides (chiefly pyrite and chalcopyrite), besides sphalerite. Pyrrhotite, bismuthinite, native bismuth and gold are minor metallic phases. Three generations of pyrite, two generation of chalcopyrite and one generation of sphalerite were recognized. Substitution of chalcopirite1 for pyrite1 and pyrite2 for chalcopirite1 are widespread, whereas sphalerite crystallization is controlled by temperature and Cu/Zn ratio of the system, that is, substitution of sphalerite for chalcopirite1 ocurrs when temperature and Cu/Zn ratio are low and, vice versa, substitution of chalcopirite1 for sphalerite occurs in higher temperature and Cu/Zn ratio conditions. The gold is always associated or included in chalcopyrite, bismuthinite and native bismuth. Late sulfide generations are represented by veinlets of pyrite3 and chalcopirite2. The main gangue minerals associated to gold ore are quartz, phengite and chlorite, besides minor carbonate, fluorite, rutile, zircon and ilmenite Three kinds of fluids were recognized in the fluid inclusion study: 1) low salinity H2O-NaCl (up to 2,0 wt.% NaCl equiv.), interpreted as meteoric water; 2) high salinity H2O-NaCl-FeCl2-MgCl2 (45-50 wt.% NaCl equiv.) interpreted as magmatic brines, 3) low salinity H2O-CO2-NaCl (1,0-1,7 wt.% NaCl equiv.), probably of magmatic origin. The temperature and pressure conditions for the Palito gold deposit formation were estimated by combination of hydrothermal chlorite geothermometry and isochores calculated from the fluid inclusion microthermometric data. P-T values for trapping of the brines range from 340 to 405oC and 2 to 4,7 kb. The magmatic brines were interpreted as the main mineralized fluid, that is, sulphur, chlorine and metals (chiefly Au and Cu) were originated and concentrated from the residual phase of the granitic magma which gave rise the Palito Granite. The brines transported the metals as chloride complexes at high temperature (over 400oC). Fluid-rock interaction and mixing between mineralized fluid and low-T and low salinity fluids (probably meteoric water) promote a raising of pH and lowering of fS2 through hydrolysis and sulfidation reactions which have triggered ore deposition at lower temperature conditions (below 400oC) in transtension sites of the shear zone. The geological and hydrothermal alteration features and the mineralizing fluid characteristics are consistent to a structurally controlled intrusion related gold deposit model for the genesis of the Palito deposit. The host granitic rocks of the gold deposit, the vein style, the hydrothermal alteration (seritization and chloritization with minor potassic alteration), the Au-Cu-Zn (Pb-Bi) metallic association and the mineralizing fluid (H2O-NaCl-FaCl2-MgCl2) are consistent to a genetic relationship between the Palito Granite and the gold deposit. The granite supplied fluids, metals and heat to move the hydrothermal system, whereas the shear zone provided the structural traps for the ore deposition.