Sn-polymetallic greisen-type deposits associated with late-stage rapakivi granites, Brazil: fluid inclusion and stable isotope characteristics

Tin-polymetallic greisen-type deposits in the Itu Rapakivi Province and Rondonia Tin Province, Brazil are associated with late-stage rapakivi fluorine-rich peraluminous alkali-feldspar granites. These granites contain topaz and/or muscovite or zinnwaldite and have geochemical characteristics comparable to the low-P sub-type topaz-bearing granites. Stockworks and veins are common in Oriente Novo (Rondonia Tin Province) and Correas (Itu Rapakivi Province) deposits, but in the Santa Barbara deposit (Rondonia Tin Province) a preserved cupola with associated bed-like greisen is predominant. The contrasting mineralization styles reflect different depths of formation, spatial relationship to tin granites, and different wall rock/fluid proportions. The deposits contain a similar rare-metal suite that includes Sri (+/-W, +/-Ta, +/-Nb), and base-metal suite (Zn-Cu-Pb) is present only in Correas deposit. The early fluid inclusions of the Correas and Oriente Novo deposits are (1) low to moderate-salinity (0-19 wt.% NaCl eq.) CO2-bearing aqueous fluids homogenizing at 245-450 degreesC, and (2) aqueous solutions with low CO2, low to moderate salinity (0-14 wt.% NaCl eq.), which homogenize between 100 and 340 T. In the Santa Barbara deposit, the early inclusions are represented by (1) low-salinity (5-12 wt.% NaCl eq.) aqueous fluids with variable CO2 contents, homogenizing at 340 to 390 T, and (2) low-salinity (0-3 wt.% NaCl eq.) aqueous fluid inclusions, which homogenize at 320380 degreesC. Cassiterite, wolframite, columbite-tantalite, scheelite, and sulfide assemblages accompany these fluids. The late fluid in the Oriente Novo and Correas deposit was a low-salinity (0-6 wt.% NaCl eq.) CO2-free aqueous solution, which homogenizes at (100-260 degreesC) and characterizes the sulfide fluorite-sericite association in the Correas deposit. The late fluid in the Santa Barbara deposit has lower salinity (0-3 wt.% NaCl eq.) and characterizes the late-barren-quartz, muscovite and kaolinite veins. Oxygen isotope thermometry coupled with fluid inclusion data suggest hydrothermal activity at 240-450 degreesC, and 1,0-2.6 kbar fluid pressure at Correas and Oriente Novo. The hydrogen isotope composition of breccia-greisen, stockwork, and vein fluids (delta(18)O quartz from 9.9parts per thousand to 10.9parts per thousand, deltaDH(2)O from 4.13parts per thousand to 6.95parts per thousand) is consistent with a fluid that was in equilibrium with granite at temperatures from 450 to 240 degreesC. In the Santa Barbara deposit, the inferred temperatures for quartz-pods and bed-like greisens are much higher (570 and 500 degreesC, respectively), and that for the cassiterite-quartz-veins is 415 degreesC. The oxygen and hydrogen isotope composition of greisen and quartz-pods fluids (delta(18)O(qtz-H2O)=5.5-6.1parts per thousand) indicate that the fluid equilibrated with the albite granite, consistent with a magmatic origin. The values for mica (delta(18)O(mica-H2O)=33-9.8parts per thousand) suggest mixing with meteoric water. Late muscovite veins (delta(18)O(qtz-H2O)=-6.4parts per thousand) and late quartz (delta(18)O(mica-H2O)=-3.8parts per thousand) indicate involvement of a meteoric fluid. Overall, the stable isotope and fluid inclusion data imply three fluid types: (1) an early orthomagmatic fluid, which equilibrated with granite; (2) a mixed orthomagmatic-meteoric fluid; and (3) a late hydrothermal meteoric fluid. The first two were responsible for cassiterite, wolframite, and minor coluChange in the redox conditions related to mixing-of magmatic and meteoric fluids favored important sulfide mineralization in the Correas deposit. (C) 2004 Elsevier B.V. All rights reserved.

First record of petrified Permian pecopterids from the Parana Basin, Brazil (Corumbatai Formation, Passa Dois Group, northeastern State of São Paulo): Morphology, anatomy and paleoecological implications

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Geologia e mineralogia de pegmatito mineralizado em estanho e metais associados (Nb, Ta, Zn, Cu, Pb), Mina Bom Futuro, Rondônia

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Litoestratigrafia da bacia do Araripe: reavaliação e propostas para revisão

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Gênese dos corpos de sulfeto maciço hidrotermal e platinóides associados no depósito de Fortaleza de Minas (MG)

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

The fortaleza de minas nickel, copper and platinoids deposit: ore types, tectonics and volcanological aspects

Pós-graduação em Geologia Regional - IGCE

Caracterização petrográfica e geoquímica das rochas encaixantes da mineralização de ouro do alvo lavra velha - Ibitiara (BA)

The Lavra Velha gold prospect is located in Ibitiara city, in the Espinhaço Setentrional physiographic domain, on the west edge of Chapada Diamantina – central part of Bahia. It is inserting on Gavião Block, a compartment of São Francisco Cráton (Almeida, 1977). The Lavra Velha gold dump is formed by an association of hydrothermal breccia lodged in acid and intermediate rocks, classifying in tonalite, granodiorite and diorite, with high alteration, cut off by a vein and venules system constituted by hydrothermal association composed by hematite, tourmaline, quarz and sericite, located in the north limit of Ibitiara granite. In the regional geological context the area is represented by Archaean rocks (Paramirim Complex) and Paleoproterozoic rocks (Ibitiara granitoid and Matinos Granite) constituted the basement, following by paleo to mesozoic pluton-vulcanic-sedimentary association of Rio dos Remédios Group, intruded by mafic rocks. It was used geochemistry and petrographic analysis compiling to field works data to characterize the rocks where the gold mineralization is inserting. Previously these rocks were classifying in volcanic rocks of Novo Horizonte Formation. Developing this monograph’s work the petrogenetic characteristics suggesting that these rocks called volcanic actually belong to Ibitiara granitoid as a portion more metamorphosed. The green schist is the predominant metamorphism in the area with low deformation, associated to high concentration of fluid circulating. The hydrothermal alteration is the process responsible for rocks modifications and strong sericitization generalize

Caracterização petrográfica das zonas de alteração hidrotermal associadas aos pegmatitos da mina Bom Futuro, Rondônia

The Bom Futuro tin deposit is located in Ariquemes, north-central state of Rondônia. Since its discovery in the late 80s, the tin deposit of Bom Futuro has been explored and considered one of the leading Brazilian producers of cassiterite, exploring it mainly in secondary deposits (placers) in the vicinity of the hill Bom Futuro. The primary mineralization occurs in the contacts between quartz veins and pegmatites with the rocks of the hill and its exploitation has been the goal of new studies in the area. These bodies occur in all rock types of the hill, leading edges of hydrothermal alteration with each rock. The focus of the study is the characterization of hydrothermal alteration through the analysis of the edges of pegmatitic veins intruded on each of the main rock types found on the hill Bom Futuro, which are: biotite gneiss, biotite amphibolite, subvolcanic breccia, topaz leucogranite, topaz leucoriolito and micro melassienito porphyry. The analysis and comparison showed familiarities between the edges of alteration encountered, and possible subdivision into three main zones: the inner zone or the vein itself, intermediate zone or transition zone and the change zone where the passage of hydrothermal features to rocks features is gradual. The cassiterite and sphalerite were found scattered in three zones, however in larger quantities in the intermediate zone, near the contact

Microbialitos da formação Codó (Aptiano Superior) às margens do rio Tocantins em São Miguel do Tocantins (TO)

The southwestern region of the São Luís-Grajaú Basin has a rare outcrop of the Codó Formation (upper Aptian) with seven outstanding microbialite bioherms along the left margin of the Tocantins river, near Imperatriz (MA). Resting on sandstones of the Grajaú Formation, the Codó Formation presents: 1) a 20 cm thick basal calcilutite with gypsite pseudomorphs and some fossil tree stems; 2) metric dark shales with carbonate nodules and thin intercalated carbonate layers, enclosing some microbial laminites; 3) a 2 cm thick upper breccia composed of microbialite fragments and other carbonate clasts, with halite hoppers on the top; 4) the carbonate bioherms, which partially overlie the extensive shales and interrupt them laterally, as well as the breccia. The bioherms in the northern part of the outcrop are thicker (<2 m) and have interbedded dark shales, whereas the southern are thinner and continuous in the vertical direction. In general, they are composed of irregular gently to strongly wavy microbial laminites, sometimes with pseudocolumnar to conical lamination. All microbialites with highest synoptic relief (<20 cm) look like columnar stromatolites on weathered lateral expositions. In plan view, the horizontal sections of these microbialites are circular to slightly elliptic, sometimes forming very small channels (N60W) filled with fine breccia. The highest bed of the northern bioherm has mixed microbial laminites and columnar stromatolites, where intercolumnar spaces were filled with microbialite clasts, fish bones, plant fragments and very small probable crustacean coprolites. Several fractures and deformation in this upper bed indicate an initial brecciation process probably caused by subaerial exposure. In microscopic scale, the lamination is smooth, diffuse, defined by subtle granulation differences of very fine granular calcite crystals within micrite, but oxide levels, dissolution surfaces or thin precipitated calcite veneers...