2017-04-172017-04-172002-10-23BORGES, Régis Munhoz Krás. Greisens e Epi-sienitos potássicos associados ao granito água boa, Pitanga (AM): um estudo dos processos hidrotermais geradores de mineralizações estaníferas. Orientador: Roberto Dall'Agnol. 2002. 383 f. Tese (Doutorado em Geologia e Geoquímica) - Centro de Geociências, Universidade Federal do Pará, Belém, 2002. Disponível em: http://repositorio.ufpa.br:8080/jspui/handle/2011/8173. Acesso em:.https://repositorio.ufpa.br/handle/2011/8173Three stanniferous greisen types were characterized in the western border of Água Boa pluton, Pitinga mine (AM), associated with the rapakivi granite facies: greisen 1 (Gsl), composed mainly by quartz, topaz, brown siderophyllite and sphalerite; greisen 2 (Gs2), composed essentially by quartz, phengite and chlorite; greisen 3 (Gs3), composed of quartz, fluorite and phengite, with minor green siderophyllite. Besides these rocks, a potassic episyenite (EpSK) was identified associated with the Gs2. In spite of the compositional and petrographic differences, all of these hydrothermal rocks derived from a same protholith, a hornblende biotite aikali feldspar granite to syenogranite. The Gsl shows an inner mineralogical zoning defined by topaz or siderophyllite predominance. Along drill cores, the siderophyllite-rich zone occurs near the contact with the greisenized grafite and the topaz-rich zone is situated far from the grafite contact. The brown siderophyllite displays moderated Al contents, and its compositional changes can be explained by Fe+2 substitution for A1+3 and Li in octahedral sites, with a coupled Al+3 substitution for Si+4 in tetrahedral sites. The mineralogical zones in the Gs2 are physicaliy separated in leveis with phengite or chlorite predominance. The mica of Gs2 is a phengite, whose chemical variation is due to substitution of viAl for Fe+2, coupled with Si+4 enrichment. The calculated Li contents in phengites are lesser than those estimated in siderophyllite. The green siderophyllite from Gs3 is VIAl richer and F poorer than Gs1 brown siderophyllite, and the phengite displays two compositional types: an early Fe+2-poor aluminous phengite and a later Fe+2- F-rich one whose chemical variation is similar to that of Gs2 phengite. The chlorite from the three greisen is a Fe-rich daphnite, and its compositional range is due to VIAl substitution for R+2 cations, coupled with Si+2 enrichment. The aluminous chlorite displays higher temperature formation than ferrous one, according to the geothermeter proposed in the literature. The Pitinga greisens were formed by different processes of interaction among three main fluids: (1) low salinity, F-rich, aquo-carbonic fluid, with initial temperatures between 400° -350°C, present during Gsl and Gs3 formation; (2) low salinity aqueous fluid, with a temperature around 300°C, which during a progressive salinity increasing process, originates a moderate to high salinity residual fluid, with temperatures between 200° - 100°C, present during the Gs2 formation and silicification stage of EpSK; (3) low salinity aqueous fluid, with temperatures between 200° - 150°C, which interplayed with the others two fluids in differents grades, contributing to the formation of ali the hydrothermal rocks. The first two fluids has seemingly an orthomagmatic origin while the latter has a surface characteristic (meteoric water?). Moreover, the data suggests that the fluid responsible by the initial stage of the episyenitization process was not registered in the studied samples. These fluids were trapped in pressure conditions around 1 Kbar, representing high crustal levels conditions, similar to that of the stanniferous granites from Pitinga. Both episyenitization and greisenization processes occurred without volume changes in the granitic protholith, and the density differences of the altered rocks were caused by the mass variations along the alteration processes. The greisenization process caused a extensive loss of Na2O and K2O, while SiO2 showed a immobile behaviour in Gsl but was parcially removed in Gs2. The Al2O3 was depleted during the Gs2 formation but added in Gsl. The Fe2O3 (Fe total), Sn, S, volatiles LOl and F were the responsible by the mass increase at greisenization. In the Gsl, the chemical changes in the fiuids were caused by F activity decrease and fO2 increase during cooling. These changes also originated the differentiation between the ZT, in the inner portions of the fratures/conducts, and the ZS, nearest to surrounding gravite. The Gs3 was formed in more oxidizing conditions by F-poorer fiuids than those trapped in the ZS. The dissolution cavities generated during the episyenitization process increased the permeability of the altered rocks, providing an increase of fluid/rock ratios in the EpSK and Gs2 sites. The interaction between aqueous fluid and EpSK feldspar, during the Gs2 formation, caused a continuous salinity increase. The ZF was formed in the early stages of this interaction, at higher temperatures, while the ZC was originated by the more cold and saline, residual fluid. The latter was also trapped in the quartz filling cavities in the EpSK during the later silicification stage. In this way, the greisens and the potassic episyenites were generated from interactions among, at least, three fluids of seemingly independent origin, from a same protholith, in shallow crust conditions. The fO2, F activity and salinity variations, during the hydrothermal system cooling, and the contrast in fluid/rock ratios caused by permeability differences, were very important factors to greisen differentiation. These factors controlled greatly the fluids compositional changes, and caused the cassiterite and sulphides precipitation in the greisens and the Sn- S-enrichment during later greisenization of EpSK.Acesso AbertoQuímica mineralMineralogiaGreisensEpi-sienitos potássicosGranito Água BoaMetalogeniaHidrotermalismoCráton AmazônicoMina Pitinga - AMProvíncia Estanífera de Pitinga - AMTeseCNPQ::CIENCIAS EXATAS E DA TERRA::GEOCIENCIAS::GEOLOGIA::PETROLOGIACNPQ::CIENCIAS EXATAS E DA TERRA::GEOCIENCIAS::GEOLOGIA::GEOQUIMICA